JP2010141068A - Method of manufacturing epitaxial wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce defocus failures in a region for applying an edge shot in a device exposure process generated owing to the thickness distribution of an epitaxial layer in a thick epitaxial wafer. <P>SOLUTION: In an improvement of a method of manufacturing an epitaxial wafer, on a susceptor rotating in a horizontal state provided in a chamber, a plurality of semiconductor wafers with orientation flats or notches are positioned at a fixed distance from the center of the susceptor. They are horizontally mounted in such a manner that the interval of the adjacent wafers becomes an equal interval. While the susceptor is rotated, a source gas is supplied into the chamber in such a manner as to flow in a horizontal direction. An epitaxial layer is each formed on the surface of a plurality of the mounted wafers at the thickness of 20 μm or greater. A plurality of wafers are each mounted on the susceptor in such a manner that the flat edge of the orientation flat or the notch of the wafer are positioned at an angle of ±45° to the radial direction from the center of the susceptor. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an epitaxial wafer on which a thick epitaxial layer is formed.

  In the device exposure process, if the distance between the wafer surface and the light source varies depending on the location, the focus at the time of exposure does not match, and a part where the pattern is not formed as designed is formed. Such a symptom is called poor defocus.

  In order to reduce the defocus failure, the stepper (exposure apparatus) performs a leveling mechanism that corrects the local surface inclination so that each exposure target surface is perpendicular to the optical axis for each exposure shot. (For example, refer to Patent Document 1). This leveling mechanism tilts the wafer stage on which the wafer is placed in accordance with the wafer thickness distribution (inclination of the surface shape) for each exposure shot so that the variation in the distance between the wafer surface and the light source is minimized. By performing various operations, it is possible to prevent the occurrence of a defocus failure.

Further, on the wafer side to be used, flatness that satisfies the design rule of each product type is required in order to solve the problem that causes the occurrence of the defocusing failure and the decrease in the product yield.
Japanese Patent No. 3211810 (paragraph [0002] of the specification)

  Among the epitaxial wafers, a so-called “thick epi” type in which a thick epitaxial layer is formed on a silicon wafer, the epitaxial layer formed by epitaxial growth rather than the flatness of the silicon wafer as a base material. Since the thickness variation becomes larger, the flatness of the entire epitaxial wafer is largely governed by the thickness distribution of the epitaxial layer. In order to obtain a high-thickness epitaxial wafer, the thickness of the epitaxial layer Distribution adjustment is important.

  Conventionally, when manufacturing a thick epi wafer, an epitaxial apparatus called a mini-batch furnace has a box-shaped chamber and a structure in which a source gas flows in a horizontal direction in the chamber and can epitaxially grow a plurality of wafers simultaneously. Was sometimes used. In such a mini-batch furnace, a plurality of wafers are placed at equal intervals on a susceptor installed in the chamber, the inside of the chamber is heated, and the susceptor is rotated in a horizontal state while being horizontally placed in the chamber. By supplying the source gas so as to flow, a plurality of wafers can be epitaxially grown simultaneously.

  And when thickness distribution is observed about the thickness epiwafer manufactured using this mini batch furnace, for example, many cases which become thickness distribution as shown in FIG. 4 are seen. The thin line drawn in the wafer of FIG. 4 is a contour line, and shows a change in the thickness of the entire wafer surface.

  In this thickness distribution, there are a region where the change in thickness is gentle and a region where the change in thickness is abrupt. In particular, when the orientation flat of the wafer is placed on the lower side, among the areas surrounded by thick frames located at the four corners of the wafer, the thickness changes in the vicinity of the outer periphery including the upper right and lower right thick frames. It can be confirmed that a large number of sharp regions occur.

  As described above, the change in thickness differs depending on the region in the wafer surface. The source gas is supplied so as to flow in the horizontal direction in the chamber. It is presumed that this is caused by uneven growth within the wafer surface due to the influence of uneven flow.

  On the other hand, when correcting the local surface tilt using the leveling mechanism with the stepper during the device exposure process, the stage tilt is set while calculating the wafer thickness distribution (surface shape tilt), and the exposure target The inclination of the surface is corrected. However, in the stepper, there is a region where the stage tilt calculation cannot be performed in the corresponding exposure shot region, and in this region, the stage tilt is set based on the calculated stage tilt value in the adjacent shot region. This shot is called an edge shot.

  As shown in FIG. 4, when the orientation flat of the wafer is arranged on the lower side, the areas indicated by thick frames located at the four corners of the wafer are areas that overlap with the area where the edge shot is performed. The areas indicated by the bold frames on the upper right side and the lower right side are areas where the change in epi thickness is abrupt, so the thickness gradient difference between the adjacent shot areas is large. When the exposure process is performed with the wafer stage tilted, the stage is not properly tilted, so that there is a problem in that the focus is not adjusted during exposure and a defocus failure occurs.

  When such a defocus failure occurs, the portion in that region becomes a defective chip, which causes a reduction in product yield.

  It is an object of the present invention to reduce the defocus failure in a region where an edge shot is performed in a device exposure process, which has occurred due to the thickness distribution of an epitaxial layer, in a thick epitaxial wafer. It is to provide a manufacturing method.

  In the invention according to claim 1, as shown in FIG. 1, a plurality of orientation flat or notched semiconductor wafers are positioned at a certain distance from the susceptor center on a susceptor that rotates in a horizontal state provided in a chamber. Further, the wafers are placed horizontally so that the intervals between adjacent wafers are equal, and the raw material gas is supplied so as to flow horizontally in the chamber while rotating the susceptor. And an epitaxial wafer manufacturing method for forming an epitaxial layer with a thickness of 20 μm or more. The characteristic configuration is that a plurality of wafers are mounted on the susceptor so that the flat edge or notch of the orientation flat of the wafer is positioned at an angle of ± 45 degrees with respect to the radial direction from the susceptor center. .

  In the invention according to claim 1, when epitaxially growing at a thickness of 20 μm or more, a plurality of wafers such that the flat edge or notch of the orientation flat of the wafer is positioned at an angle of ± 45 degrees with respect to the radial direction from the susceptor center. Each of the wafers is placed on the susceptor, thereby shifting the position where the region where the epi-thickness change that has occurred when the thick epi-wafer is manufactured by the conventional method is formed is formed.

  In the thick epi-wafer obtained by this method, the region where the epi-thickness change is abrupt and the region where the edge shot is performed by the stepper during the device exposure process do not overlap.

  Therefore, by using the epitaxial wafer obtained by this method, the region subjected to the edge shot during the device exposure process corresponds to a region where the change in thickness is gentle, and as a result, it is possible to reduce defocusing defects. it can.

  In the epitaxial wafer manufacturing method of the present invention, a plurality of wafers are positioned at a specific angle so that an area where the epi-thickness change is abrupt and an area where an edge shot is performed by a stepper during a device exposure process do not overlap. In this way, each is placed on a susceptor and epitaxially grown.

  In the thick epi wafer obtained by this method, the region where the epi thickness change is abrupt and the region where the edge shot is performed by the stepper during the device exposure process do not overlap, and the region where the edge shot is performed during the device exposure step is Since the change in thickness corresponds to a gentle area, it is possible to reduce defocusing failure as a result.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

  The present invention is a method for manufacturing a thick epitaxial wafer in which a thick epitaxial layer is simultaneously formed on the surface of a plurality of silicon wafers by epitaxial growth.

  Here, “thick epi” refers to an epitaxial layer having a thickness of 20 to 200 μm. In consideration of practical aspects such as the size of the epitaxial growth apparatus, the silicon wafer serving as the substrate for forming the epitaxial layer preferably has a diameter of 5 to 8 inches (125 to 200 mm). A silicon wafer having an orientation flat or a notch is used. Furthermore, it is preferable to use a silicon wafer having a crystal orientation of (100).

The epitaxial apparatus used in the manufacturing method of the present invention is an apparatus called a mini batch furnace capable of epitaxially growing a plurality of wafers simultaneously. This epitaxial apparatus includes a box-shaped chamber, a susceptor capable of mounting a plurality of wafers, source gas supply means for supplying source gas into the chamber, carrier gas supply means for supplying carrier gas into the chamber, and A heating means for heating the inside of the chamber is provided. The shape of the susceptor is a disk shape and is installed in the chamber so as to rotate in a horizontal state. The susceptor is provided with a recess at a position where the wafer is placed so that a plurality of wafers are located at a certain distance from the center of the susceptor and the intervals between adjacent wafers are equal. Currently available mini-batch furnaces include eight 6-inch wafers and five 8-inch wafers. Further, the source gas is supplied from the source gas supply means into the chamber, and the carrier gas is supplied from the carrier gas supply means into the chamber. Examples of the source gas include SiH ₂ Cl ₂ , SiHCl ₃ , SiH _{4, and} SiCl ₄ , and examples of the carrier gas include H ₂ . The orientations of the supply ports of the source gas supply means and the carrier gas supply means are fixed so that the supplied source gas and carrier gas flow horizontally in the chamber. Furthermore, the heating means has a configuration capable of heating the inside of the chamber to 1000 to 1200 ° C.

  The manufacturing method of the present invention will be described using the epitaxial apparatus having the above-described configuration.

  First, a plurality of wafers with orientation flats are placed horizontally on a recess provided in the susceptor on a susceptor provided in the chamber.

  In the present invention, as shown in FIG. 1, a plurality of wafers are placed on the susceptor so that the flat edge of the orientation flat of the wafer is positioned at an angle of ± 45 degrees with respect to the radial direction from the susceptor center. Place. In addition, when using a wafer having a notch, a plurality of wafers are mounted on the susceptor so that the tangent of the wafer outer peripheral edge at the notch portion of the wafer is positioned at an angle of ± 45 degrees with respect to the radial direction from the susceptor center. Put. In this way, by placing all the wafers at a fixed angle with respect to the radial direction from the susceptor center, the epitaxy that occurred when thick epiwafers were produced by the conventional method was used. The position where the region where the change in thickness is abrupt was formed can be shifted. Further, it is preferable to place the wafer with the orientation flat or notch of the wafer positioned on the leeward side with respect to the rotation direction of the susceptor, because the orientation flat or notch does not disturb the flow of the raw material and the carrier gas.

  Next, the inside of the chamber is heated to a temperature range of 1000 to 1200 ° C. suitable for epitaxial growth. Next, the susceptor on which the wafer is placed is rotated in a horizontal state clockwise at a speed of 3 to 40 rpm. In this state, the source gas and the carrier gas are supplied at a constant ratio so as to flow in the horizontal direction in the chamber, and an epitaxial layer is formed on the surface of the wafer until a predetermined film thickness is obtained. The supply ratio of the source gas and the carrier gas is preferably 12:88 to 30:70.

  As described above, in the thick epitaxial wafer obtained by the manufacturing method of the present invention, on the susceptor during epitaxial growth, the region where the epi-thickness change is abrupt and the region where the edge shot is performed by the stepper during the device exposure process do not overlap. Since the angle of the wafer to be mounted on the device is positioned at a specific angle, the edge shot area during the device exposure process corresponds to an area where the change in thickness is gentle. Can be reduced.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
First, eight silicon wafers having a diameter of 6 inches (about 150 mm) and an orientation flat having a crystal orientation of (100) were prepared.

  In addition, an epitaxial apparatus capable of simultaneously epitaxially growing a plurality of wafers was prepared. The epitaxial apparatus includes a chamber, a susceptor for mounting a plurality of wafers, a source gas supply unit for supplying source gas into the chamber, a carrier gas supply unit for supplying carrier gas into the chamber, and a heating unit for heating the chamber. Is provided. The susceptor has a disk shape and is installed in the chamber so as to rotate in a horizontal state. Also, the size of the 6-inch wafer is such that eight wafers can be placed, the eight wafers are located at a certain distance from the center of the susceptor, and the wafers adjacent to each other are equally spaced. A dent is provided at the mounting position. Further, the orientations of the supply ports of the source gas supply means and the carrier gas supply means are fixed so that the supplied source gas and carrier gas flow horizontally in the chamber.

  Next, as shown in FIG. 1, eight wafers prepared so that the flat edge of the orientation flat was positioned at an angle of ± 45 degrees with respect to the radial direction from the center of the susceptor were placed on the susceptor.

  Then, the inside of the chamber is heated to 1000 to 1200 ° C., and the susceptor on which the wafer is placed is rotated in a horizontal state clockwise at a speed of 8 rpm, and the raw material gas flows in the horizontal direction in that state. Trichlorosilane and hydrogen were supplied at a rate of 30 slm and 150 slm, respectively, and an epitaxial layer was formed on the surface of the wafer so as to have a thickness of 100 μm, thereby obtaining a thick epiwafer.

<Comparative Example 1>
Epitaxial growth is performed in the same manner as in Example 1 except that eight wafers prepared so that the flat edge of the orientation flat is positioned at an angle of 0 degrees with respect to the radial direction from the susceptor center are placed on the susceptor. Thus, a thick epi wafer was obtained.

<Comparison test 1>
When one of the thick epitaxial wafers obtained in Example 1 and Comparative Example 1 is used and arranged so that the flat edge of the orientation flat is positioned below, the wafer is centered on the upper right side (as a clock). Edge shot at 1 o'clock), lower right (5 o'clock including flat edge corner), upper left (11 o'clock) and lower left (7 o'clock including flat edge) The thickness of the epitaxial layer up to the region to be subjected to is measured by FTIR (Fourier transform infrared spectroscopy). The results are shown in FIGS. 2 and 3, respectively.

  As is clear from FIG. 3, the thickness of the epitaxial wafer of Comparative Example 1 is almost the desired thickness at a distance from the wafer center to 60 mm, but the thickness on the upper right side and the lower right side exceeds 60 mm. Increases sharply, and the difference in thickness gradient between the adjacent shot regions increases in the region where the edge shot is performed. The region width at the position where the thickness suddenly increases is ± 30 minutes as a watch. When such wafers are used for device manufacturing, when edge shots are performed during the device exposure process, the thickness gradient difference between adjacent shot regions is large, and as a result, the probability of defocusing failure occurring in the edge shot regions Is estimated to be high.

  On the other hand, as apparent from FIG. 2, in the thick epi-wafer of Example 1, no extreme change in thickness occurred from the wafer center to the region where the edge shot was performed. When such a wafer is used for device manufacturing, even when an edge shot is performed during the device exposure process, the difference in thickness gradient from the adjacent shot region is small, so the occurrence of defocus defects in the region where the edge shot is performed is reduced. Inferred.

  For the remaining thick epitaxial wafers obtained in Example 1 and Comparative Example 1, the thickness of the epitaxial layer was similarly measured by FTIR measurement, and the same tendency as the results shown in FIGS. It was observed.

  Moreover, when the epitaxial layer was formed using the silicon wafer which has a notch similarly to Example 1 and Comparative Example 1 and the thickness epiwafer was obtained and the thickness of the epitaxial layer of these thick epiwafers was measured by FTIR, Example The same tendency as the thick epiwafers of No. 1 and Comparative Example 1 was observed. From this result, it was found that the manufacturing method of the present invention is effective not only for a wafer having an orientation flat but also for a wafer having a notch.

  From the above, it was confirmed that the manufacturing method of the present invention is effective in reducing the defocus failure at the edge shot in the device exposure process in the thick epi wafer.

The figure which shows the state which mounted the wafer on the susceptor when carrying out the epitaxial growth of the several wafer by the method of this invention. FIG. 3 is a diagram showing the thickness of the epitaxial layer from the center of the wafer to the region where the edge shot is performed in the first embodiment. The figure which shows the thickness of the epitaxial layer from the wafer center in the comparative example 1 to the area | region which performs an edge shot. The figure which shows the wafer thickness in-plane distribution when making it epitaxially grow on several wafers with the conventional method.

Explanation of symbols

11 Wafer 11a Orientation Flat 12 Susceptor

Claims (1)

A plurality of orientation flat or notched semiconductor wafers are positioned at a certain distance from the susceptor center on a susceptor that rotates in a horizontal state provided in a chamber, and the intervals between adjacent wafers are equal. Place the source gas so that it flows horizontally into the chamber while rotating the susceptor while rotating the susceptor, and deposit epitaxial layers with a thickness of 20 μm or more on the surfaces of the plurality of wafers placed above, respectively. In the manufacturing method of the epitaxial wafer to be formed,
The plurality of wafers are mounted on the susceptor so that the flat edge or notch of the orientation flat of the wafer is positioned at an angle of ± 45 degrees with respect to a radial direction from the susceptor center. Epitaxial wafer manufacturing method.

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