CN1222757A - Porous region removing method and semiconductor substrate manufacturing method - Google Patents

Abstract

This invention is to ensure a high planarity of an underlying layer after a porous layer is removed. A substrate to be processed is dipped in an etchant. In the first step, pores in the porous Si layer are filled with the etchant by supplying an ultrasonic wave. In the second step, supply of the ultrasonic wave is stopped, and the pore walls are thinned by the etching function. In the third step, the ultrasonic wave is supplied again to break the porous layer at once.

Description

Porous region removal method and semiconductor substrate manufacturing method

The present invention relates to a method for removing a porous region and a method for manufacturing a semiconductor substrate, and more particularly, to a method for removing a porous region from a substrate having a porous region, a method for manufacturing a semiconductor substrate using the method, and an apparatus for removing the porous region .

The following SOI substrate manufacturing method already exists. Firstly, a porous layer and a single crystal silicon layer are formed on a first substrate, the first substrate is bonded to a second substrate prepared separately, and then bonded on the porous silicon layer. The combined laminated substrate is divided into two substrates so that the single crystal silicon layer formed on the side surface of the first substrate is transferred onto the second substrate.

In this method, after the bonded laminated substrates are divided into two substrates, the residual porous silicon layer on the surface of the second substrate is removed. In removing the porous silicon, it is preferable not to impair the flatness of the underlying second substrate surface, more specifically, the film thickness uniformity of the single crystal silicon layer as the second substrate surface layer.

The present invention has been proposed in consideration of the above circumstances, and its object is to provide a method for removing a porous region capable of ensuring the flatness of an underlayer and a method for manufacturing a semiconductor substrate using the method.

According to the present invention, there is provided a method for removing a porous region from a substrate having a porous region, characterized in that it comprises the following steps: the first step, treating the porous region with an etchant while applying ultrasonic waves to the etchant; the second step, Treating the porous region with an etchant without applying ultrasonic waves to the etchant or applying ultrasonic waves weaker than the ultrasonic waves applied in the first step; and a third step of removing the residual porous region on the substrate.

In the porous region removal method, the first step includes injecting an etchant into deeper portions of the pores in the porous region.

In the porous region removal method, the second step includes thinning the pore walls of the porous region to not thicker than a predetermined thickness by etching.

In the porous region removal method, the second step includes thinning the pore walls of the porous region to a thickness capable of removing the remaining porous region at one time in the third step.

In the porous region removal method, the third step includes removing the residual porous region on the substrate with an etchant.

In the porous region removing method, the third step includes removing the residual porous region on the substrate with the etchant while applying ultrasonic waves to the etchant.

In the porous area removal method, the substrate to be treated is immersed in the same etchant to perform the treatments from the first step to the third step.

In the porous region removing method, the third step includes removing the remaining porous region on the substrate with a third treatment liquid having a higher etching rate for the porous material than the first and second treatment liquids.

In the porous area removal method, the substrate to be treated is completely immersed in an etchant to perform the treatment from the first step to the third step.

In the porous area removal method, the substrate to be treated is completely immersed in an etchant for the first and/or second treatment step.

In the porous region removal method, the third step includes removing the residual porous region on the substrate with a high-pressure fluid.

In the porous region removal method, the third step includes removing the residual porous region on the substrate by scrubbing.

In the porous region removal method, when the substrate is processed while applying ultrasonic waves to the substrate, the relative positional relationship between the substrate and the ultrasonic source is changed.

In the porous region removal method, when the substrate is processed while ultrasonic waves are applied to the etchant, the substrate is swung in the processing liquid.

In the porous region removal method, the substrate is rotated while performing substrate processing while applying ultrasonic waves to the etchant.

In the porous region removal method, when the substrate is processed while applying ultrasonic waves to the substrate, the position of at least one of the substrate and the ultrasonic wave source is changed in a direction substantially parallel to or perpendicular to the ultrasonic vibration plane.

In the porous region removal method, while treating the substrate with an etchant, the substrate is swung or rotated.

In the porous region removal method, when the substrate is treated with an etchant, the etchant is circulated to cause a flow of the etchant in the vicinity of the substrate.

In the porous area removal method, the first and second steps are performed by immersing the substrate in the same etching bath, and the first step includes operating the ultrasonic source, and the second step includes stopping the ultrasonic source.

In the porous area removal method, the substrate is immersed in the same corrosion bath for the first and second steps, and the first and second steps include continuous operation of the ultrasonic source, and the second step includes the ultrasonic source and the substrate Insert the ultrasonic shielding wrench between them.

In the porous region removal method, the substrate to be processed is mainly composed of single crystal silicon.

In the porous region removal method, the porous region is mainly composed of porous silicon.

In the porous region removal method, the porous region is obtained by anodizing a substrate composed of single crystal silicon.

In the porous area removal method, the etchant can use any of the following solutions:

(a) hydrofluoric acid;

(b) in hydrofluoric acid, at least add the mixed solution that one of ethanol or hydrogen peroxide obtains;

(c) buffered hydrofluoric acid; and

(d) A mixed solution obtained by adding at least one of ethanol or hydrogen peroxide to buffered hydrofluoric acid.

According to the present invention, there is also provided a method for manufacturing a semiconductor substrate, which is characterized in that it includes the following steps: forming a porous layer and at least one non-porous layer on the first substrate; bonding the second substrate to the first substrate removing the first substrate from the bonded laminated substrate to expose the porous layer on the surface of the second substrate; and removing the porous layer on the second substrate by the porous region removing method described above .

In the porous region removal method, the step of exposing the porous region includes grinding, polishing or etching the first substrate from the side of the lower surface of the bonded first substrate to make the porous region on the surface of the second substrate layer is exposed.

In the porous region removing method, the step of exposing the porous layer includes separating the bonded laminated substrates along the porous layer to expose the porous layer on the surface of the second substrate.

In the porous region removal method, the nonporous layer includes a single crystal silicon layer.

In the porous region removal method, the nonporous layer includes a single crystal silicon layer and a silicon oxide layer.

In the porous region removal method, the single crystal silicon layer is a layer epitaxially grown on the porous layer of the first substrate.

In the porous region removal method, the nonporous layer includes a single crystal compound semiconductor layer.

In the porous region removal method, the second substrate is mainly composed of silicon.

In the porous region removal method, the second substrate has a silicon oxide layer on its surface bonded to the first substrate.

In the porous region removal method, the second substrate includes a transparent substrate.

According to the present invention there is also provided a porous region removing apparatus for removing a porous region from a substrate having a porous region, comprising: performing a first step of treating the porous region with an etchant while applying ultrasonic waves to the etchant a device for performing the second step of treating the porous region with an etchant without applying ultrasonic waves to the etchant or applying ultrasonic waves that are weaker than the ultrasonic waves applied in the first step; and performing the third step of removing the The residual porous region of the device.

In the following detailed description in conjunction with the accompanying drawings, the purpose, features and advantages of the present invention will be more clear.

1A to 1C are schematic diagrams illustrating a porous layer removal method according to a preferred embodiment of the present invention;

2A to 2C illustrate a manufacturing method according to a first application example of the porous layer removal method;

3A to 3F illustrate a semiconductor substrate manufacturing method according to another preferred embodiment of the present invention;

4 is a perspective view showing a first device of a wafer processing apparatus;

5 is a perspective view showing a second device of the wafer processing apparatus;

6 is a perspective view showing a third device of the wafer processing apparatus;

7A-7E illustrate the operation of the wafer processing apparatus shown in FIG. 6;

8 is a perspective view of a swing support member of the wafer processing apparatus shown in FIG. 6;

9 is a perspective view showing a fourth device of the wafer processing apparatus;

10 is a perspective view showing a fifth device of the wafer processing apparatus;

Figures 11A and 11B illustrate variations of the wafer processing apparatus shown in Figure 6 or Figure 8;

12A-12C illustrate a seventh arrangement of a wafer processing apparatus;

The present invention is applicable to the method for manufacturing SOI substrate: firstly form porous layer and monocrystalline silicon layer on the first substrate, the first substrate and the second substrate prepared independently are bonded together, then on the porous silicon layer dividing the bonded laminated liner into two substrates so that the single crystal silicon layer formed on the first substrate is transferred to the second substrate, and removing the residual porous layer on the surface of the second substrate, thereby Get the SOI structure.

A single crystal silicon substrate can be used as the first substrate. In this case, the porous layer is the porous silicon layer. On the porous silicon layer, a single crystal silicon layer can be epitaxially grown as a non-porous layer. An insulating layer such as a _SiO2 layer can be formed on the single crystal silicon layer.

In this embodiment, a porous layer and a nonporous layer are sequentially formed on a first substrate, and the first substrate is bonded to a separately prepared second substrate to form a bonded laminated substrate. After the bonded laminated substrate is separated into two substrates at the porous layer, the porous layer remaining on the second substrate is removed by, for example, wet etching.

During the etching process of the porous silicon layer, the fracture of the porous silicon layer can be accelerated by applying ultrasonic waves to the etching pool. More specifically, during the etching process, when ultrasonic waves are applied to the etching pool, specifically, to the bonded laminated substrate, the pore walls of the porous silicon layer can be broken before becoming very thin, because the pores of the porous silicon layer The time from the start to the end of the wall fracture is greatly shortened, and the etching selectivity ratio of the porous layer and the underlying second substrate (i.e., single crystal silicon substrate) is increased, therefore, the SOI thickness difference and the thickness of the second substrate surface can be reduced. The difference in size between substrates after removal of the porous layer enables to obtain a high-quality SOI substrate with a single crystal silicon layer with a very uniform film thickness.

However, if the thickness of the porous layer on the substrate to be processed varies, it will be difficult to ensure the uniformity of the film thickness of the second substrate surface layer (single crystal silicon layer) after removing the porous layer, especially in mass production, This problem can result in low yields.

This embodiment provides a method in which the surface layer (single-crystal silicon layer) of the second substrate can ensure uniformity of film thickness after removal of the porous silicon layer.

1A to 1C are diagrams explaining the principle of a porous layer removal method according to a preferred embodiment of the present invention. Wherein, reference numeral 201, the underlying substrate (second substrate); 202, the porous layer; 203, the etchant.

In FIG. 1A , etchant 203 is injected into the deepest portion of the pores of porous layer 202 . At this time, ultrasonic waves are preferably applied to the object to be processed (ie, bonded laminated substrate). When ultrasonic waves are applied, the rate at which the etchant is injected into the holes increases.

In Figure 1B, the holes are etched and enlarged. At this time, it is preferable not to apply ultrasonic waves to the object to be processed, or to reduce the intensity of ultrasonic waves. If ultrasonic waves are applied, as the pores grow, once the pore walls of adjacent pores become thinner to a certain extent, the porous layer begins to break. Since the porous layer breaks first at the thin points, the underlying substrate 201 is corroded at these points. At this time, the flatness of the substrate 201 will obviously be reduced. But without the application of ultrasound, the holes only break when they become much thinner than with ultrasound. Therefore, excessive corrosion in certain parts can be prevented at this time.

Even when ultrasonic waves are not applied to the object to be processed, corrosion proceeds not only in the horizontal direction (horizontal direction) but also in the vertical direction. However, the effect on etching at this time is negligible compared with the case of applying ultrasonic waves.

In Figure 1C, the porous layer 202 having thin pore walls is removed. Not only etching but also polishing, scrubbing or water spraying can be used in this step. In this step, the porous layer with a fragile structure caused by corrosion is removed in one go.

When etching is performed in the step of FIG. 1C, the steps from FIG. 1A to FIG. 1C can all be performed in the same etching bath. At this time, in the step shown in Figure 1B, the application of the ultrasonic wave is interrupted, and when the wall of the deepest hole in the hole of the porous layer is so thin that it can be broken immediately in the entire area, the ultrasonic wave is reapplied, and the step of Figure 1C is performed ( corrosion while applying ultrasonic waves). With this treatment, the porous layer can be removed almost simultaneously at one time, and the underlying substrate 202 over the entire area of the object to be processed is exposed. Therefore, the difference in etching can be reduced, and the lower substrate 201 can maintain high flatness.

The above porous layer removal method can be easily applied to batch processing of a large number of substrates. For each of the large quantities processed, in the step shown in FIG. 1B, when the innermost pore wall of the porous layer is thinned enough to break immediately over the entire area, the step shown in FIG. 1C is performed.

The porous layer removal method is preferably carried out when the object to be treated is fully immersed in the etchant. At this time, particles near the interface between the corrosive agent and air can be prevented from sticking to the object to be processed.

According to this porous layer removal method, the fracture of the porous layer can be accelerated by applying ultrasonic waves, and particles can also be efficiently removed from the surface of the object to be treated.

When removing the porous layer, if the relative positional relationship between the ultrasonic source (such as ultrasonic oscillator) and the processed object is changed, more specifically, the relative position of the standing wave between the substrate and the ultrasonic oscillation surface and the liquid level of the etchant can be changed. Processing is performed on the entire substrate surface. To achieve this, for example, the substrate can be rotated, swiveled, or the holder holding the substrate can be swung, or the ultrasound source can be moved.

Application examples of this porous layer removal method are described below. (first application example)

The first application example relates to a manufacturing method. 2A to 2C show the manufacturing method of this application example. In FIG. 2A, a silicon substrate 401 having a porous silicon portion 402 locally is prepared. The silicon substrate 401 can be prepared by the following methods, such as forming a photoresist film on the silicon substrate, forming a pattern on the photoresist film by lithography and anodizing the obtained structure. The photoresist film can be replaced by a patterned Si ₃ N ₄ film or wax, where wax resistant to hydrofluoric acid (fluoric acid) such as Apizoen wax (trade name) can be used.

In FIG. 2B, a non-porous layer (pattern) 403 is formed on the surface of the silicon substrate shown in FIG. 2A.

In FIG. 2C, the porous silicon portion 402 is removed, more specifically, the substrate shown in FIG. 2B is placed in an etching bath containing an etchant for porous silicon, and the etching process is performed while applying ultrasonic waves to the substrate.

When the etchant is effectively injected into the pores of the porous silicon portion 402, the application of ultrasonic waves is stopped, and the etching is continued. During this etching process, the pore walls of the porous silicon portion 402 gradually become thinner. Seen from the surface (lower part of the figure), the color of the porous silicon portion 402 gradually becomes lighter. When the pore walls are sufficiently thin, the underlying non-porous layer (pattern) 403 can be seen through the porous silicon portion 402 .

In this state, the remaining porous silicon portion is removed. In order to remove the porous silicon portion, for example, 1) etching can be performed by reapplying ultrasonic waves, or 2) etching can be performed using an etchant that corrodes silicon quickly.

If the remaining structure is rigid, a water jet can be used to remove the porous silicon portion.

If the entire silicon substrate 401 is made of porous silicon, only the non-porous layer formed on the substrate will be left, and, as mentioned above, when making the pattern of the non-porous layer 403, it is possible to form a Various structures in beam shape. (second application example)

The second application example relates to a method of manufacturing a semiconductor substrate. 3A to 3F show a semiconductor substrate manufacturing method of this application example. In FIG. 3A, a first single-crystal silicon substrate 501 is prepared, and a porous silicon layer 502 is formed on one surface thereof. In FIG. 3B , at least one non-porous layer 503 is formed on the porous silicon layer 502 . As the non-porous layer 503, a single crystal silicon layer, a polycrystalline silicon layer, an amorphous silicon layer, a metal layer, a compound semiconductor layer, or a superconducting layer may be used. As the non-porous layer 503, a layer including a device structure such as MOSFET can be formed. Preferably, a SiO ₂ layer 504 is formed on the surface to complete the first substrate. The _SiO2 layer 504 is useful because when the first substrate is bonded to the second substrate 505, the interface state of the bonding surface can be separated from the active layer.

Next, as shown in FIG. 3D , the first substrate shown in FIG. 3C is brought into contact with the second substrate 505 prepared for separation through the SiO ₂ layer 504 at room temperature. Thereafter, anodic bonding, pressure, heat treatment (if necessary), or a combination thereof are performed to tightly bond the substrates.

When forming a single crystal silicon layer on the non-porous layer 503, it is preferable to bond the first substrate and the second substrate 505 after forming an _SiO2 layer 504 on the surface of the single crystal silicon layer by, for example, thermal oxidation.

As the first substrate, a silicon substrate, a substrate obtained by forming a SiO ₂ layer on a silicon substrate, and transparent substrates including quartz glass, quartz, and sapphire substrates are suitable. Any other substrate may also be used as long as the second substrate 505 has a sufficiently flat surface for bonding.

FIG. 3D shows a state where the first substrate and the second substrate are bonded through the SiO ₂ layer 504 . If the non-porous layer 503 or the second substrate does not contain silicon, it is not necessary to form the SiO ₂ layer 504 .

At the time of bonding, an insulating sheet may be sandwiched between the first substrate and the second substrate.

In FIG. 3E , the first substrate 501 is removed from the second substrate at the porous silicon layer 502 . To remove the first substrate, the first substrate is removed by grinding, polishing, or etching, or the bonded laminated substrate is separated into the first substrate and the second substrate at the porous silicon layer 502 .

In FIG. 3F, the remaining porous silicon layer 502 on the surface of the second substrate is removed. More specifically, the second substrate portion was placed in an etching bath containing a porous silicon etchant, and the etching process was performed while ultrasonic waves were applied to the substrate.

When the etchant is effectively put into the pores of the porous silicon portion 402, the application of ultrasonic waves is stopped, and the etching is continued. During this etching process, the pore walls of the porous silicon layer 502 gradually become thinner. Seen from the surface, the color of the porous silicon layer 502 gradually becomes lighter. When the pore wall is thin enough, the underlying non-porous layer (such as a single crystal silicon layer) 503 can be seen through the porous silicon layer 502 .

The remaining porous silicon layer 502 is removed in this state. In order to remove the porous silicon layer, for example, 1) ultrasonic waves can be applied again for etching, 2) etching is performed with an etchant that corrodes silicon quickly, 3) the porous silicon layer 502 is removed with a jet of water, 4) the porous silicon layer 502 is removed by polishing, or 5 ) to wear off.

FIG. 3F schematically shows a semiconductor substrate (SOI substrate) obtained by the above method. A non-porous layer (such as a single crystal silicon layer) 503 with a flat surface and uniform film thickness is formed on a second substrate 505 through an insulating layer (such as a SiO ₂ layer) 504 . According to this method, a high-quality large-area semiconductor substrate can be manufactured.

When an insulating substrate is used as the second substrate 505, the semiconductor substrate obtained by the above-described manufacturing method is very useful for forming an insulating electronic device.

When the bonded laminated substrate shown in Figure 3D was separated at the porous silicon layer 502, after the porous silicon layer 502 remaining on the surface of the second substrate 501 was removed, the first substrate could also be reused, if necessary. Smooth surface treatment.

Selected examples of wafer processing equipment suitable for removing the porous layer will be listed below. (the first unit of processing equipment)

Figure 4 is a schematic setup diagram of a wafer processing apparatus suitable for removing a porous layer.

In the wafer processing apparatus 100, members that may come into contact with the processing liquid are preferably composed of quartz glass or plastic depending on their use. As plastics, fluorinated plastics, vinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PBT) or polyether ether ketone (PEEK) can be used. As fluorinated plastics, PVDF, PFA or PTFE are suitable.

The wafer processing apparatus 100 includes a wafer processing tank 110, an overflow tank 120, an ultrasonic tank 130, and a wafer rotation mechanism (111 to 119) that supports a wafer 140 while rotating.

Before processing a wafer, a processing liquid (etchant) is injected into the wafer processing bath 110 . An overflow tank 120 is arranged around the upper part of the wafer processing tank 110 for temporarily storing the processing liquid overflowing from the wafer processing tank 110 . The treatment temporarily stored in the overflow tank 120 is discharged from the bottom of the overflow tank 120 into the circulator 121 through the drain pipe 121a. The circulator 121 filters the discharged processing liquid to remove particles and sends the processing liquid to the bottom of the wafer processing pool 110 through the liquid inlet pipe 121b. With this arrangement, particles in the wafer processing bath 110 can be effectively removed.

The depth of the wafer processing bath 110 is preferably such that the wafer 140 is completely submerged. With this arrangement, particles in the air or near the liquid surface can be prevented from adhering to the wafer 140 .

An ultrasonic bath 130 is located below the wafer processing bath 110 . In the ultrasound cell 130 , an adjustment mechanism 132 supports an ultrasound source 131 . Like the mechanism for adjusting the relative positional relationship between the ultrasonic source 131 and the wafer processing pool 110, the adjusting mechanism 132 has a mechanism for adjusting the vertical position and the horizontal position of the ultrasonic source 131. By this mechanism, ultrasonic waves can be satisfactorily applied to wafer processing. pool 110 , and more specifically, to wafer 140 . Preferably, the ultrasonic source 131 has the function of adjusting the frequency and intensity of the generated ultrasonic waves. With this setup, the ultrasound provided is more optimized. By adding a function of optimally supplying ultrasonic waves to the wafer 140, ultrasonic waves can be supplied to various types of wafers one by one. The ultrasonic pool 130 is filled with an ultrasonic propagation medium (such as water), so the ultrasonic wave can be transmitted to the wafer processing pool 110 through the ultrasonic propagation medium.

The wafer processing apparatus 100 has a control section for on/off controlling the ultrasonic source 131, by which the removal process of the porous layer can be controlled.

The wafer 140 is supported at a position substantially perpendicular to the bottom surface of the wafer processing tank 110 by four wafer rotating rods 111, each of which has a groove 111a for inserting the wafer 140 therein. The wafer rotation rod 110 has a function of supporting the wafer 140 when rotating, and constitutes a part of the substrate rotation mechanism. Each wafer rotation lever 111 is pivotally supported by opposing two lever support members 118 so that the wafer rotation levers 111 rotate in the same direction by receiving a driving torque generated by the motor 119 . Preferably, the diameter of each wafer rotating rod 111 should be small enough not to hinder the propagation of ultrasonic waves.

The number of wafer rotating rods 111 is preferably as small as possible. In order to ensure that the wafer 140 gets the desired friction, preferably, two wafer rotation rods 111 for limiting the rotation direction of the wafer 140 (ie, the X-axis direction) and two wafer rotation rods 111 for supporting the wafer 140 from below are provided. When two wafer rotation rods are arranged at proper intervals under the wafer, the driving torque can be efficiently transmitted to the substrate with the oriented platen. If only one wafer rotating rod 111 is set under the wafer, the orientation plate is just above the wafer rotating rod 111, and the wafer rotating rod 111 cannot rotate the wafer.

Usually, a standing wave is formed between the bottom of the wafer processing tank 110 and the liquid surface, that is, ultrasonic waves with high-intensity parts and low-intensity parts. However, since the wafer processing apparatus 100 processes the wafer 140 while rotating it, processing unevenness due to standing waves can be reduced.

In the wafer processing apparatus 100 , the bottom of the wafer processing apparatus 100 and the surrounding parts of the wafer 140 have as few parts as possible, and thus ultrasonic waves can be efficiently and uniformly supplied to the wafer 140 . Also, in such an apparatus, since the process liquid can freely flow around the wafer 140, the wafer is processed uniformly and processing defects can be prevented. (Wafer processing equipment second unit)

Fig. 5 schematically shows an arrangement of a wafer processing apparatus suitable for removing a porous layer.

In the wafer processing apparatus 10, components that may come into contact with the processing liquid are preferably made of quartz glass or plastic depending on their use. As plastics, fluorinated plastics, vinyl chloride, polyethylene, polypropylene, polyethylene terephthalate (PBT) or polyetheretherketone (PEEK) can be used. As fluorinated plastics, PVDF, PFA or PTFE are suitable.

The wafer processing apparatus 10 includes: a wafer processing tank 11 and a clamp driving mechanism 31 for swinging the wafer clamp 21 in the wafer processing tank 11 . Preferably, the wafer processing apparatus 10 has an ultrasonic bath 61 .

Before processing a wafer, a processing solution (etchant) is injected into the wafer processing pool 11 . The wafer processing tank 11 has a four-sided overflow tank 12 . The processing liquid is injected from the bottom of the wafer processing pool 11 through a circulator 71 having a filter. The processing liquid overflowing from the wafer processing tank 11 is stored in the four-rim overflow tank 12 and discharged from the bottom of the four-rim overflow tank 12 into the circulator 71 . In this wafer processing apparatus 10, the chuck driving mechanism 31 swings the wafer chuck 21 while agitating the processing liquid. Therefore, the circulation system provided with the four-edge overflow pool 12 is very useful for keeping the liquid level of the treatment liquid constant.

As the wafer holder 21, an industrially available product can be used. Preferably, the wafer holder 21 is made of quartz glass or plastic. As plastic, fluorinated plastics, vinyl chloride, polyethylene, polypropylene, PBT or PEEK can be used. As fluorinated plastics, PVDF, PFA or PTFE are suitable.

The chuck driving mechanism 31 has a pair of gripping portions 31a for gripping the wafer chuck 21 . The wafer holder 21 is held by the two holding portions 31 a and immersed in the wafer processing bath 11 . Desired processing can be performed on the wafer 40 while the wafer holder 21 is swung in the wafer processing bath 11 . The clamp driving mechanism 31 can transfer the wafer clamp 21 clamping the wafer 40 processed in the previous step to the wafer processing pool 11 or to the next step. Furthermore, the chuck driving mechanism 31 is also a part of the wafer processing apparatus 10 .

In the present embodiment, the clamping portion 31a clamps the wafer clamp 21 so that the wafer 40 is indirectly clamped. However, instead of the holding portion 31a, the wafer 40 may be directly held by, for example, a chuck pad. The clamping direction of the wafer 40 is not limited to the direction perpendicular to the bottom surface of the wafer processing tank 11 , and may also be parallel to the bottom surface.

The ultrasonic pool 61 has an ultrasonic source 51 and is filled with an ultrasonic propagation medium (such as water). The ultrasonic source 51 is fixed on an adjustment mechanism 62 for adjusting the vertical and/or horizontal position of the ultrasonic source 51 . When the positional relationship between the ultrasonic source 51 and the wafer processing bath 11 is adjusted by the adjustment mechanism 62, the ultrasonic waves supplied to the wafer processing bath 11, more specifically, to the wafer 40 can be optimized. Preferably, the ultrasonic source 51 has the function of adjusting the frequency and intensity of the generated ultrasonic waves. The supply of ultrasound can be further optimized by means of this arrangement. By adding a function of optimizing the supply of ultrasonic waves to the wafer 40, ultrasonic waves can be supplied to various types of wafers one by one.

The wafer processing apparatus 10 has a control section for ON/OFF control of the ultrasonic source 51 . The removal process of the porous layer can be controlled by the control section. (The third device of the wafer processing equipment)

Figure 6 is a schematic setup diagram of a wafer processing apparatus suitable for removing a porous layer. 7A to 7E show operations of the wafer processing equipment shown in FIG. 6 . FIG. 8 is a perspective view of a swing support member in the wafer processing apparatus shown in FIG. 6. FIG.

In order to improve the efficiency with which the chuck drive mechanism 31 swings the wafer 40, the wafer processing tank 11 preferably has a swing support member 13 on its bottom surface. When the wafer holder 21 moved, the swing support member 13 was in contact with the side of the wafer 40 clamped by the wafer holder 21, and the wafer 40 was rolled and moved up and down by frictional force. The swing support member 13 helped to improve the surface uniformity of the processed wafer .

It is also effective if a drive mechanism is used to move the swing support member 13 vertically (Y-axis direction) and/or horizontally (X-axis direction). In this case, the swing support member 13 moves by itself to rotate the wafer 40 and move the wafer 40 up and down within the wafer holder 21 . Therefore, the range in which the wafer chuck 21 is moved by the chuck driving mechanism 31 is small, in other words, the wafer processing tank 11 becomes compact.

The ultrasonic pool 61 has an ultrasonic source 51 and is filled with an ultrasonic propagation medium (such as water). The ultrasonic source 51 is fixed on the adjustment mechanism 62 to adjust the vertical and/or horizontal position of the ultrasonic source 51. When the relative position between the ultrasonic source 51 and the wafer processing pool 11 is adjusted with the adjustment mechanism 62, the supply to the wafer processing pool can be optimized. 11, more specifically the ultrasound of the wafer 40. Preferably, the ultrasonic source 51 has the function of adjusting the frequency and intensity of the generated ultrasonic waves. With this arrangement, the supply of ultrasound can be further optimized. By adding a function of optimizing the supply of ultrasonic waves to the wafer 40, it is possible to supply ultrasonic waves to multiple crystals one by one.

The wafer processing apparatus 10 has a control section that performs ON/OFF control of the ultrasonic source 51 . The removal process of the porous layer can be controlled by this control section.

7A to 7E are used to explain the wafer swing method. In these figures, arrows indicate the moving direction of the wafer holder 21 . Fig. 7A shows the state when the wafer is about to start swinging. When an instruction to start the swinging action is given, as shown in FIG. 7B, the clamp swing mechanism 31 presses down the clamping portion 31a under the control of the microcomputer. The side surface of the wafer 40 is in contact with the swing support member 13 during this pressing. The wafer 40 is supported by the swing support member 13 at the lower portion.

When the swing support member 13 comes into contact with the wafer 40, some particles are generated regardless of the amount. To prevent this, the end portion of the swing support member 13 is preferably processed into a circular shape as shown in FIG. 8 to be in smooth contact with the wafer 40 .

Since the swing support member 13 only needs to support the swing of the wafer 40, its shape may not hinder the propagation of ultrasonic waves, such as a thin plate shape. With this arrangement, ultrasonic waves can be uniformly supplied to the wafer 40, and the wafer 40 can be uniformly processed.

In the wafer processing apparatus 10, the wafer 40 is processed while changing the relative position of the wafer 40 and the swing support member 13, that is, the relative position of the wafer 40 and the wafer processing tank 11. Therefore, the slight unevenness of the ultrasonic waves caused by the oscillating support member 13 is not a problem.

When the pressing amount of the wafer chuck 21 is large to a certain extent, the contact pressure between the wafer 40 and the swing support member 13 increases. Thereby, slippage between the swing support member 13 and the wafer 40 can be eliminated to prevent erroneous operation. If the pressing amount is small, the weight of the wafer 40 falls more on the wafer holder 21 than on the end of the swing support member 13 . If the swing support member 13 has the shape employed in the present embodiment, after the wafer 40 and the swing support member 13 come into contact, the pressing amount is preferably set to about 30 mm.

When the operation of pressing the wafer chuck 21 ends, as shown in FIG. 7C, the chuck driving mechanism 31 moves the gripping portion 31a to the right (X-axis positive direction) under the control of the microcomputer. When rotating clockwise, the wafer 40 moves substantially horizontally to the right (in the positive direction of the X axis) in the wafer processing pool 11 . The pressing amount of the holding portion 31 a must be set within a range in which the holding portion 31 a does not collide with the lower opening portion of the wafer holder 21 .

When the movement of the wafer clamp 21 to the right (in the positive direction of the X axis) is completed, as shown in FIG. 7D , the clamp driving mechanism 31 moves up the clamping portion 31a under the control of the microcomputer. The movement of the holding portion 31a is preferably set within a range where the wafer 40 does not come close to the liquid level of the processing liquid. If the wafer 40 is close to the liquid level 41 , the particles will stick to the surface of the wafer 40 .

After the upward movement of the wafer clamp 21 ends, the clamp driving mechanism 31 moves the clamping part 31a to the left (in the negative direction of the X axis) under the control of the microcomputer, as shown in FIG. 7E , and then returns to the initial state ( FIG. 7A ).

By repeating the above operations (FIG. 7A→7B→7C→7D→7E), the wafer 40 can be properly rocked and uniformly processed.

According to the wafer processing apparatus 10, the ultrasonic waves acting on the wafer 40 can be optimized by oscillating the wafer 40 in the region where the ultrasonic supply is optimized by adjusting the ultrasonic bath 61.

It is well known that a standing wave of ultrasonic waves has nodes and anti-nodes at predetermined intervals. Therefore, it is difficult to uniformize the ultrasonic waves in the wafer processing bath 11 .

In this wafer processing apparatus 10, however, since the chuck drive mechanism 31 swings the wafer 40, the wafer 40 can be uniformly processed despite uneven intensity distribution of ultrasonic waves. Even if the wafer 40 is simply moved in a horizontal direction, a vertical direction, or an oblique direction, the wafer 40 can be uniformly processed. When the wafer 40 is also wobbled in the axial direction (Z-axis direction), processing unevenness between wafers caused by the high-intensity portion of the ultrasonic wave on the horizontal plane can also be corrected.

Since the wafer processing apparatus 10 has the swing supporting member 13, the swing amount of the wafer 40 can be effectively increased. The fixed position of the swing support member 13 is not limited to the bottom of the wafer processing pool 11 . As long as the swing support member 13 can contact all wafers 40 in the wafer holder 21, the swing support member 13 can be fixed on the inner wall of the wafer processing tank 11 or on the clamp drive mechanism 31 (at this time, it is necessary to change the clamping portion 31a and swing The mechanism of the relative position between the support members 13).

Also, according to the wafer processing apparatus 10, since there is no driving mechanism in the wafer processing tank 11, there are no particles generated by the action of the driving mechanism. (Fourth device of wafer processing equipment)

Fig. 9 schematically shows an arrangement of a wafer processing apparatus suitable for removing a porous layer.

In the wafer processing equipment 300, the wafer 40 is clamped at a position substantially parallel to the bottom surface of the wafer processing tank 11 (that is, substantially parallel to the vibration plane of the ultrasonic wave), and is completely immersed in the processing liquid (etchant) of the wafer processing tank 11. In this state, the wafer is swung by the wafer moving mechanism 80 to achieve uniform processing of the wafer 40 and prevent particle contamination.

The wafer moving mechanism 80 holds the wafer 40 with the arm 81 and swings the wafer 40 in the wafer processing tank 11 . Preferably, the wafer 40 is rocked in a direction crossing the ultrasonic vibration plane (ie, the vertical direction) and in a direction parallel to the ultrasonic vibration plane (ie, the horizontal direction).

Also in the wafer processing apparatus 300, preferably, the wafer 40 is completely immersed in the processing liquid for processing. In this case, it is possible to prevent particles from adhering to the wafer 40 near the interface between the processing liquid and the gas.

According to the wafer processing apparatus 300, by swinging the wafer 40 in the wafer processing pool 11, uniform processing thereof can be achieved. (fifth device of wafer processing equipment)

Fig. 10 schematically shows an arrangement of a wafer processing apparatus suitable for removing a porous layer. In the second to fourth devices of the wafer processing apparatus, the wafer is processed while being oscillated. In contrast, in the wafer processing apparatus 500, the flow rate of the processing liquid (etchant) is increased instead of the wafer being swung.

In the wafer processing apparatus 500 , a support portion 73 for supporting the wafer holder 21 is provided at a lower portion of the wafer processing pool 11 . The treatment liquid supplied by the circulator 71 is ejected at a high speed from the nozzle 72 below the support portion 73 . The supporting portion 73 has a plurality of opening portions through which the treatment liquid ejected from the nozzle 72 moves upward.

When the processing liquid is circulated at a high speed, the wafer 40 can be uniformly processed.

It is also effective to install the above-mentioned circulation mechanism (71-73) in the wafer processing apparatus 10 shown in FIG. (The sixth device of the wafer processing equipment)

In the above-mentioned wafer processing equipment, the supply or non-supply of ultrasonic waves is realized by controlling the ultrasonic source through a switch. In addition, a mechanism for shielding ultrasonic waves may be inserted between the ultrasonic wave source and the wafer if necessary.

Modifications of the wafer processing apparatus of FIG. 5 or 6 are described below. 11A and 11B show modifications of the wafer processing apparatus shown in FIG. 5 or 6 . In Figures 11A and 11B, the overflow tank and circulator are omitted.

A modification of the wafer processing apparatus is provided with protective doors 91 and 92 between the ultrasonic source 51 and the bottom surface of the wafer processing pool 11 for shielding ultrasonic waves, if necessary. As shown in FIG. 11A, in order to transmit ultrasonic waves to the wafer processing pool 11, a driving section (not shown) opens the protective doors 91 and 92. In order to shield the ultrasonic waves from entering the wafer processing pool 11, as shown in FIG. 11B, the driving part (not shown) closes the protection doors 91 and 92. As the material of the protection doors 91 and 92, a material that hardly transmits ultrasonic waves such as PFA or PTFE is suitable. (Seventh device for wafer processing setup)

12A to 12C schematically show the apparatus of a wafer processing apparatus suitable for removing the porous layer, FIG. 12A is a front view, FIG. 12B is a side view, and FIG. 12C is a plan view.

In the wafer processing apparatus 700 , a fluid jet 701 such as water is sprayed from a spray nozzle 700 to remove the porous layer of the wafer 40 .

In the example shown in FIGS. 12A to 12C , when the spray fluid of the spray nozzle 700 is perpendicular to the wafer 400, the spray nozzle 700 scans in the positive axis direction, thereby removing the porous layer 40a on the entire surface.

Examples of the above-mentioned porous layer removal method are described below. (Example 1)

A film of a material resistant to HF corrosion was formed on the surface of a single crystal silicon substrate, and the film was patterned for forming a mask with openings. The single crystal silicon substrate exposed at the opening portion was anodized in HF solution to form a porous layer. A 50 µm thick porous layer was formed on a single crystal silicon substrate by this process. Then, remove the mask. Instead of forming a mask on the single crystal silicon substrate, the single crystal silicon substrate may be placed on a jig so that the HF solution only touches the region where the porous layer is to be formed and anodized.

The obtained substrate was placed in the wafer processing apparatus 100 shown in FIG. 4 . A mixed solution (etchant) of hydrofluoric acid, hydrogen peroxide and pure water has been preliminarily injected into the wafer processing tank 110 of the wafer processing equipment 100 shown in FIG. 4 . In the wafer processing apparatus 100, the substrate was rotated for two hours while ultrasonic waves of approximately 1 MHz were applied to inject etchant into the pores of the porous silicon layer.

Then the ultrasonic wave source 131 was stopped, and the substrate was kept in the wafer processing bath 110 for 1 hour, by which the pore walls of the porous silicon layer were thinned.

Then, the porous silicon layer was completely removed using the apparatus shown in Figs. 12A to 12C. As a result, a groove portion with a depth of 50 µm was formed on the substrate.

Using the apparatus shown in Fig. 5, 6, or 9 also obtains a structure identical to that described above. (Example 2)

A film of a material resistant to HF corrosion was formed on the surface of a single crystal silicon substrate, and the film was patterned for forming a mask with openings. The single crystal silicon substrate exposed at the opening portion was anodized in HF solution to form a porous layer up to the lower surface. Then, remove the mask. It is also possible not to form a mask on the single crystal silicon substrate, but to place the single crystal silicon substrate on a jig so that the HF solution only touches the area where the porous layer is to be formed and anodized.

Then, a single-crystal Si layer was formed to a thickness of 1 m on the surface of the substrate by epitaxial growth as the resultant structure.

The resulting substrate was placed in a wafer processing apparatus 100 shown in FIG. 4 . A mixed solution (etchant) of hydrofluoric acid, hydrogen peroxide and pure water has been preliminarily injected into the wafer processing tank 110 of the wafer processing equipment 100 shown in FIG. 4 . In the wafer processing apparatus 100, the substrate was rotated for about 6 hours while ultrasonic waves of approximately 0.25 MHz were applied to inject etchant into the pores of the porous silicon layer.

Then the ultrasonic source 131 was stopped, and the substrate was kept in the wafer processing bath 110 for 2 hours, by which the pore walls of the porous silicon layer were thinned.

The ultrasonic source 131 was restarted for five minutes to completely remove the porous silicon layer, and as a result, a single-crystal silicon film including an epitaxial layer (single-crystal silicon layer) was formed on the porous silicon layer. The thickness of the epitaxial layer is substantially the same over the entire surface.

As shown in FIG. 2C, by partially removing the epitaxial layer (single crystal silicon layer) in advance, a cantilever beam structure of single crystal silicon can be formed.

The same structure as described above can also be obtained by using the apparatus shown in Fig. 5, 6, or 9. (Example 3)

Prepare the first single crystal silicon substrate. The surface layer is anodized in HF solution to form a porous silicon layer, and the anodization conditions are as follows:

Current density: 7 (mA/cm ² )

Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH=1:1:1

Time: 11(min)

Porous silicon layer thickness: 12 (μm)

The substrate was oxidized at 400°C for 1 h in an oxygen atmosphere. The inner wall of each hole passing through this oxidized porous silicon layer is covered with a thermally oxidized film. On the porous silicon layer, a single crystal silicon layer was epitaxially grown to a thickness of 0.30 m by CVD (Chemical Vapor Deposition). The growth conditions were as follows:

Source gas: SiH ₂ Cl ₂ /H ₂

Air velocity: 0.5/180(l/min)

Air pressure: 80 (Torr)

Temperature: 950(℃)

Growth rate: 0.3(μm/min)

Then, a SiO ₂ layer with a thickness of 200 nm was formed on the epitaxial silicon layer by thermal oxidation.

The surface of the _SiO2 layer of the first substrate was bonded to the surface of another separately prepared substrate (second substrate).

The first substrate side is removed by grinding, polishing or etching to expose the porous silicon layer on the entire plane of the second substrate.

The second substrate is placed in the wafer processing apparatus 100 shown in FIG. 4 . The wafer processing tank 110 of the wafer processing equipment 100 shown in FIG. 4 has been pre-filled with a mixed solution (etchant) of hydrofluoric acid, hydrogen peroxide and pure water. In the wafer processing apparatus 100, the substrate was rotated for 1.5 hours while ultrasonic waves of approximately 0.25 MHz were applied to inject etchant into the pores of the porous silicon layer.

Then the ultrasonic wave source 131 was stopped, and the substrate was kept in the wafer processing bath 110 for 1 hour, by which the pore walls of the porous silicon layer were thinned.

Restart the ultrasonic source 131 for five minutes to completely remove the porous silicon layer. At this time, as shown in FIG. 10, when the etchant circulates properly, the surface uniformity of the processed substrate can be improved.

Ultrasonic waves are applied to the etchant of the porous silicon layer, and the substrate is rotated while circulating the etchant to inject the etchant into the pores of the porous layer on the substrate. Then, the application of ultrasonic waves is stopped, and the substrate is held for a suitable period of time. Through this treatment, the pores of the porous silicon layer over the entire surface area of each substrate can be sufficiently thinned. By applying ultrasonic waves again in this state, the residual porous silicon layer can be removed uniformly and immediately over the entire area of each substrate.

The same results as described above can be obtained with the apparatus shown in Fig. 5, 6 or 9.

The residual porous silicon layer can be removed with high quality even if the application of ultrasonic waves is not applied again after stopping the application, but by any of the following methods:

(1) The obtained structure was immersed in a mixed solution of hydrofluoric acid, nitric acid and pure water for about 5 seconds to remove the porous layer.

(2) The porous silicon layer is removed by polishing.

(3) Remove the porous silicon layer by scrubbing.

(4) Scan the substrate with a jet of water at a pressure of eg 100kg/cm ³ to remove the porous silicon layer.

In the step of removing the porous silicon layer, the single crystal silicon layer serves as an etching stopper so that the porous silicon layer is selectively etched and completely removed.

The etching speed of non-porous silicon single crystal in the above etchant is very slow. The selective ratio of the etching speed of the non-porous silicon single crystal to the etching speed of the porous layer is ≥10 ⁵ . The corrosion amount of the non-porous layer (about tens of angstroms) is allowed in practical applications.

Through the above treatment, an SOI substrate having a 0.2 µm thick single crystal silicon layer on a silicon oxide film was formed. The thickness of the obtained monocrystalline silicon layer was measured at 100 points over the entire surface, and the thickness was 201 nm ± 4 nm.

The obtained structure was heat-treated: the temperature was kept at 1100° C. for 1 hour in hydrogen, and then the surface roughness was measured with an atomic force microscope. The average area roughness is about 0.2 nm for a 5 μm square area. This is almost the same as a silicon wafer in industry.

Cross-sectional observation with a transmission electron microscope showed that no new crystal defects were formed in the single-crystal silicon layer, and satisfactory crystallinity was maintained.

Even if the oxide film (SiO ₂ ) is formed not on the surface of the epitaxial layer but on the surface of the second substrate or all of these surfaces, the same results as above can be obtained.

Satisfactory results can be obtained even if a transparent substrate such as quartz glass is used as the second substrate. However, in this case, due to the difference in thermal expansion coefficient between the quartz glass and the single crystal silicon layer, a slit will be formed on the single crystal silicon layer, and the temperature of the heat treatment in hydrogen is reduced from 1100°C to ≤1000°C. (Example 4)

The second substrate is subjected to two-step anodization in HF solution to form two porous layers, and the conditions of anodization are as follows: <the first step of anodization>

Current density: 7 (mA/cm ² )

Anodizing solution: HF: H ₂ O: C ₂ H ₅ OH=1:1:1

Time: 5(min)

Porous silicon layer thickness: 5.5 (μm) <Second step anodizing treatment>

Current density: 30 (mA/cm ² )

Anodizing solution: HF:H ₂ O:C ₂ H ₅ H=1:1:1

Time: 110(sec)

Porous silicon layer thickness: 3 (μm)

The substrate was oxidized at 400°C for 1 hour in an oxygen atmosphere. The inner wall of each hole passing through this oxidized porous silicon layer is covered with a thermally oxidized film. A single crystal silicon layer with a thickness of 0.15 µm was grown on the porous silicon layer by CVD (Chemical Vapor Deposition). The growth conditions were as follows:

Source gas: SiH ₂ Cl ₂ /H ₂

Air velocity: 0.5/180(l/min)

Air pressure: 80 (Torr)

Temperature: 950(℃)

Growth rate: 0.3(μm/min)

Then, a SiO ₂ layer with a thickness of 100 nm was formed on the epitaxial silicon layer by thermal oxidation.

The surface of the _SiO2 layer of the first substrate was bonded to the surface of another separately prepared substrate (second substrate).

The bonded laminated substrate was divided into two substrates along the porous silicon layer formed at a current density of 30 mA/cm ( ^second -step anodization treatment), and the porous silicon layer was exposed on the side of the second substrate. on the entire surface. To separate bonded laminated substrates, the substrates may be mechanically stretched, twisted, compressed, wedged along the bonded edges, oxidized from the end faces for peeling, thermally stressed, ultrasonic waves are applied, or applied to the bonded laminated substrates. Edge water jets, etc.

The second substrate is placed in the wafer processing apparatus 100 shown in FIG. 4 . The wafer processing tank 110 of the wafer processing equipment 100 shown in FIG. 4 has been previously filled with a mixed solution (etchant) of hydrofluoric acid, hydrogen peroxide and pure water. In the wafer processing apparatus 100, the substrate was rotated for 1.5 hours while ultrasonic waves of approximately 0.25 MHz were applied to inject etchant into the pores of the porous silicon layer.

Then the ultrasonic wave source 131 was stopped, and the substrate was kept in the wafer processing bath 110 for 1 hour, by which the pore walls of the porous silicon layer were thinned.

Restart the ultrasonic source 131 for five minutes to completely remove the porous silicon layer. At this time, as shown in FIG. 10, when the etchant circulates properly, the surface uniformity of the processed substrate can be improved.

Ultrasonic waves are applied to the etchant of the porous silicon layer, and the substrate is rotated while circulating the etchant to inject the etchant into the pores of the porous layer on the substrate. Then, the application of ultrasonic waves is stopped, and the substrate is held for a suitable period of time. Through this treatment, the pores of the porous silicon layer over the entire surface area of each substrate can be sufficiently thinned. By applying ultrasonic waves again in this state, the residual porous silicon layer can be removed uniformly and immediately over the entire area of each substrate.

The same results as described above can be obtained with the apparatus shown in Fig. 5, 6 or 9.

The residual porous silicon layer can be removed with high quality even if the application of ultrasonic waves is not applied again after stopping the application, but by any of the following methods:

(1) The obtained structure was immersed in a mixed solution of hydrofluoric acid, nitric acid and pure water for about 5 seconds to remove the porous layer.

(2) The porous silicon layer is removed by polishing.

(3) Remove the porous silicon layer by scrubbing.

(4) Scan the substrate with a jet of water at a pressure of eg 100kg/cm ³ to remove the porous silicon layer.

In the step of removing the porous silicon layer, the single crystal silicon layer serves as an etching stopper so that the porous silicon layer is selectively etched and completely removed.

The etching speed of non-porous silicon single crystal in the above etchant is very slow. The selective ratio of the etching speed of the non-porous silicon single crystal to the etching speed of the porous layer is ≥10 ⁵ . In practical applications, the corrosion amount of the non-porous layer (about tens of angstroms) is acceptable.

Through the above treatment, an SOI substrate having a 0.2 µm thick single crystal silicon layer on a silicon oxide film was formed. The thickness of the obtained monocrystalline silicon layer was measured at 100 points over the entire surface, and the thickness was 201 nm ± 4 nm.

Heat treatment of the obtained structure: heat preservation at 1100° C. for 1 hour in hydrogen, and then measure the surface roughness with an atomic force microscope. The average area roughness is about 0.2 nm for a 5 μm square area. These levels are the same as industrial silicon wafers.

Cross-sectional observation with a transmission electron microscope showed that no new crystal defects were formed in the single-crystal silicon layer, and satisfactory crystallinity was maintained.

Even if the oxide film (SiO ₂ ) is formed not on the surface of the epitaxial layer but on the surface of the second substrate or all of these surfaces, the same results as above can be obtained.

Satisfactory results can be obtained even if a transparent substrate such as quartz glass is used as the second substrate. However, in this case, due to the difference in thermal expansion coefficient between the quartz glass and the single crystal silicon layer, a slit will be formed on the single crystal silicon layer, and the temperature of the heat treatment in hydrogen is reduced from 1100°C to ≤1000°C.

When the porous silicon layer left on the side of the first substrate is selectively etched and subjected to surface treatment such as hydrogen annealing or surface polishing, the substrate can be recycled as the first or second substrate.

Even a porous layer formed by anodization having a single-layer structure can obtain the same results as described above.

In the above examples, as the epitaxial growth method for forming the single crystal silicon layer on the porous silicon layer, not only the CVD method but also the MBE, sputtering or liquid phase growth method can be used. A single crystal compound semiconductor layer GaAs or InP can also be epitaxially grown on the porous silicon layer. In this case, GaAs on silicon or GaAs on glass (quartz) in high-frequency devices can be fabricated or a substrate suitable for OEIC.

As an etchant for selectively etching the porous silicon layer, a mixed solution of 49% hydrofluoric acid and 30% hydrogen peroxide is suitable. Then, the following etchant can also be used. Selective etching is easy due to the large surface area of the porous silicon layer.

(a) Hydrofluoric acid

(b) A mixed solution obtained by adding at least one of ethanol or hydrogen peroxide to hydrofluoric acid.

(c) Buffered hydrofluoric acid

(d) A mixed solution obtained by adding at least one of ethanol or hydrogen peroxide to buffered hydrofluoric acid

(e) Mixed solution of hydrofluoric acid, nitric acid and acetic acid

In the above example, the ultrasonic source is stopped to realize the stopping of the use of ultrasonic waves, however, it is also effective to use a protective door, as shown in FIGS. 11A and 11B .

According to the invention, the flatness of the layer below the porous region can be maintained.

The present invention is not limited to the above-described embodiments, and various changes and modifications can be made within the spirit and scope thereof. Therefore to convey the scope of the present invention to the public, the following claims are made.

Claims (35)

1. A porous region removal method for removing a porous region from a substrate having a porous region, comprising the steps of: In the first step, treating the porous region with an etchant while applying ultrasonic waves to the etchant; a second step, treating the porous region with an etchant without applying ultrasonic waves to the etchant or applying ultrasonic waves weaker than those applied in the first step; and In the third step, the residual porous area on the substrate is removed. 2. The method of claim 1, characterized in that: The first step involves injecting an etchant into the deeper portion of the pores in the porous zone. 3. The method according to claim 1 or 2, characterized in that: Said second step includes thinning the pore walls of the porous region to no thicker than a predetermined thickness by etching. 4. The method of claim 3, characterized in that: The second step includes thinning the pore walls of the porous region to a thickness capable of removing the residual porous region at one time in the third step. 5. The method according to any one of claims 1 to 4, characterized in that: The third step includes removing residual porous regions on the substrate with an etchant. 6. The method of claim 5, characterized in that: The third step includes removing the residual porous region on the substrate with an etchant while applying ultrasonic waves to the etchant. 7. The method according to claim 5 or 6, characterized in that: The substrate to be treated is immersed in the same etchant for the treatment from the first step to the third step. 8. The method according to claim 5 or 6, characterized in that: The third step includes removing the residual porous region on the substrate with a third treatment solution having a higher etching rate for the porous material than the first and second treatment solutions. 9. The method according to any one of claims 5-8, characterized in that: The substrate to be treated is completely immersed in the etchant for the treatment from the first step to the third step. 10. The method according to any one of claims 1 to 4, characterized in that: The substrate to be treated is completely immersed in the etchant for the first and/or second step. 11. The method according to any one of claims 1 to 4, characterized in that: The third step includes removing residual porous regions on the substrate with a high pressure fluid. 12. The method according to any one of claims 1 to 4, characterized in that: The third step involves scrubbing to remove residual porous regions on the substrate. 13. The method according to any one of claims 1-12, characterized in that: When substrate processing is performed while applying ultrasonic waves to the substrate, the relative positional relationship between the substrate and the ultrasonic source is changed. 14. The method of claim 13, wherein: When substrate processing is performed while applying ultrasonic waves to an etchant, the substrate is swung in the processing liquid. 15. The method of claim 13, wherein: When performing substrate processing while applying ultrasonic waves to an etchant, the substrate is rotated. 16. The method of claim 13, wherein: When substrate processing is performed while applying ultrasonic waves to the substrate, the position of at least one of the substrate and the ultrasonic wave source changes in a direction substantially parallel to or perpendicular to the ultrasonic vibration plane. 17. The method according to any one of claims 1-12, characterized in that: When treating a substrate with an etchant, the substrate is swung or rotated. 18. The method according to any one of claims 1-12, characterized in that: When treating a substrate with an etchant, the etchant is circulated to cause a flow of the etchant in the vicinity of the substrate. 19. The method according to any one of claims 1-18, characterized in that: Submerge the substrate in the same corrosion pool for the first and second steps, and the first step includes making the ultrasonic source work, and the second step includes stopping the ultrasonic source. 20. The method according to any one of claims 1-18, characterized in that: Submerge the substrate in the same corrosion pool for the first and second steps, and the first and second steps include continuous operation of the ultrasonic source, and the second step includes inserting an ultrasonic shielding plate between the ultrasonic source and the substrate. twenty one. The method according to any one of claims 1-20, characterized in that: The substrate to be processed consists mainly of single crystal silicon. twenty two. The method according to any one of claims 1-20, characterized in that: The porous region is mainly composed of porous silicon. twenty three. The method of claim 22, wherein: The porous region is obtained by anodizing a substrate composed of single crystal silicon. twenty four. The method according to any one of claims 1-23, characterized in that: The etchant can use any of the following solutions: (a) hydrofluoric acid; (b) in hydrofluoric acid, at least add the mixed solution that one of ethanol or hydrogen peroxide obtains; (c) buffered hydrofluoric acid; and (d) A mixed solution obtained by adding at least one of ethanol or hydrogen peroxide to buffered hydrofluoric acid. 25． A method of manufacturing a semiconductor substrate, characterized in that it comprises the following steps: forming a porous layer and at least one non-porous layer on the first substrate; bonding the second substrate to the non-porous layer side of the first substrate; removing the first substrate from the bonded laminate substrate to expose the porous layer on the surface of the second substrate; and The porous layer on the second substrate is removed by the method described in any one of claims 1-24. 26． The method of claim 25, wherein: The step of exposing the porous region includes grinding, polishing or etching the first substrate from the side of the lower surface of the bonded first substrate to expose the porous layer on the surface of the second substrate. 27． The method of claim 25, wherein: The step of exposing the porous layer includes separating the bonded laminated substrates along the porous layer to expose the porous layer on the surface of the second substrate. 28． The method according to any one of claims 25-27, characterized in that: The non-porous layer includes a single crystal silicon layer. 29． The method according to any one of claims 25-27, characterized in that: The non-porous layer includes a single crystal silicon layer and a silicon oxide layer. 30． The method according to claim 28 or 29, characterized in that: The single crystal silicon layer is a layer epitaxially grown on the porous layer of the first substrate. 31． The method according to any one of claims 25-27, characterized in that: The non-porous layer includes a single crystal compound semiconductor layer. 32． The method according to any one of claims 25-31, characterized in that: The second substrate consists essentially of silicon. 33． The method according to any one of claims 25-32, characterized in that: The second substrate has a silicon oxide layer on its surface bonded to the first substrate. 34． The method according to any one of claims 25-31, characterized in that: The second substrate includes a transparent substrate. 35． A porous region removal apparatus for removing a porous region from a substrate having a porous region comprising: means for performing the first step of treating the porous region with the etchant while applying ultrasonic waves to the etchant; means for performing the second step of treating the porous region with the etchant without applying ultrasonic waves to the etchant or with ultrasonic waves that are weaker than those applied in the first step; and A third step is performed to remove the residual porous region of the device on the substrate.

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