JPH02275626A - Dry etching method - Google Patents

Abstract

PURPOSE:To reduce the amount of side etching and speed up etching by coating a silicon oxide film of a mask layer on the main surface of a silicon substrate and by forming a recessed part by mixed gas etching between six fluoric sulfur and oxygen using a parallel plane type device of anode combination system. CONSTITUTION:A silicon oxide film 3 formed on a silicon substrate 1 by thermal oxidation is etched, thus forming a pattern where a recessed part formation part 4 is exposed. This substrate is placed on a lower-part electrode 12 of the parallel plane type dry etching device, a mixed reaction gas 13 between SF6 and O2 is allowed to flow into a reaction room 11, and a pressure of 53-54 Pa is retained by evacuation. Then, a high-frequency power is applied to an upper-part electrode 15 from a power supply 18 to allow a plasma 19 to be generated between itself and a lower-part electrode 12 and silicon at the recessed part forming part 5 and an active species and a reaction gas ion within plasma are allowed to react, thus eliminating silicon and forming a recessed part 2. Therefore, it is possible to reduce the amount of side etching and perform high-speed etching in the direction of depth.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dry etching method for forming a concave portion having a side wall perpendicular to the main surface from the entire surface of a single crystal silicon substrate.

(Prior Art) Conventional processing methods for forming recesses from the entire surface of a single crystal substrate include wet etching using a reactive solution, dry etching using a reactive gas, and especially reactive ion etching using a reactive gas plasma. There are two methods: (RIE).

The wet etching method is as shown in Figure 2 (18).
A mask consisting of a silicon oxide film 21 and a silicon nitride film 22 is attached to a silicon substrate l with an opening 23 so that the part to be processed is exposed, and the silicon substrate is coated with hydrofluoric acid as shown in the second opening. The recessed portion 2 is formed by etching the processed portion. On the other hand, in the dry etching method, as shown in FIG. A dry etching device is used to deep-etch the silicon to form a recess 2 as shown in the third opening.

If the recess 2 to be formed is a deep groove whose depth is larger than the area of the opening, as shown in FIG. As shown in FIG. 4(b), deep grooves 4 are formed by wet-etching the processed portion of the silicon substrate with an alkaline solution such as KOH, or with a chlorine-based etching solution. By dry etching (RIE) using a reactive gas.

[Problem to be solved by the invention]

In the wet etching method using hydrofluoric acid, etc., when depositing a mask layer on a silicon substrate, there is a certain limit to the thickness of the mask layer, so there is a limit to the etching depth, and silicon substrates with a thickness exceeding 1 m may be used. The above method is not suitable for deep etching, and the above method also has the problem that the depth of the recess after etching varies widely within the single crystal silicon substrate, resulting in a decrease in yield. The wet etching method using an alkaline solution such as KOH takes advantage of the fact that the etching rate differs depending on the plane orientation of the single crystal silicon substrate.
Deep grooves can be formed depending on the surface orientation of the substrate, and the etching rate is high. However, there are problems in that the etching rate depends on the surface orientation, so the shape of the groove may become complicated, and that deep grooves of arbitrary shapes cannot be formed in single-crystal silicon substrates with arbitrary surface orientations. Also, when forming a groove with a depth of 30irm, the groove width is 30irm.
Must be greater than 0-. Therefore, if a deep groove (trench) for LSI element isolation is formed using this method, the chip size of the LSI will increase, which is disadvantageous in terms of cost.

On the other hand, dry etching using a fluorine-based reactive gas (
In RIB), when an anodic bonding system is used, the etching speed is fast and the selectivity of the aluminum mask is very high, so it is possible to etch even silicon substrates with a thickness exceeding 1fi, and the etching is uniform within the silicon substrate. It has the advantage of good sex. However, although the amount of side etching is small compared to wet etching using hydrofluoric acid, etc., even if the etching conditions for the above method that minimize the amount of side etching are selected, the above method is originally isotropic etching, so side etching is not possible. The etching factor, which is the value obtained by dividing the etch amount by the depth, is approximately 0.
．． 55, the amount of side etching is somewhat large, which is inconvenient when forming a recess in a silicon substrate with a smaller amount of side etching, for example, when forming a recess in a silicon substrate with a complicated pattern. An etching method is required. On the other hand, if a cathode-coupled parallel plate type RIEI device is used, the etching factor can be reduced to about 0.30 in the case of dry etching using a fluorine-based reactive gas, but the etching rate is lower than that of the anodic-coupling method. Approximately 2 times the dry etching time
Moreover, there is a problem that the uniformity within the silicon substrate is rather poor. In addition, in dry etching (RIE) using a chlorine-based reactive gas in a cathode-coupled parallel plate type device, the etching progresses vertically (in the depth direction) due to the assist effect of ions. Although deep grooves can be formed with high accuracy, the maximum groove depth that can be formed is approximately 10 nm, and the etching rate is 0.2 tries/in.
Furthermore, there is a problem that the etching process is very slow and that damage remains on the etched surface due to ion bombardment.

SUMMARY OF THE INVENTION An object of the present invention is to provide an etching method capable of forming a recess from one main surface of a single crystal silicon substrate with a small amount of side etching, a small etching factor, and a high etching rate.

A further object of the present invention is to provide an etching method capable of forming deep grooves without leaving any damage on the etched surface.

[Means to solve the problem]

In order to solve the above problems, the present invention deposits a silicon oxide film on the main surface of a single crystal silicon substrate except for the area where the recess is to be formed, and performs anodic bonding parallel plate dry etching. Etching is carried out in an apparatus using a mixed gas of sulfur hexafluoride and oxygen as a reactive gas. In addition, the above method is an effective method for forming deep grooves.
Flow M5~ in the reaction chamber of parallel flat type dry etching equipment
7 ccn+ sulfur hexafluoride gas and flow! Etching is performed by simultaneously introducing 3 to 5 ccm of oxygen gas and applying high frequency power of 0.42 to 0.46 W/cm<3 >to the electrode area between both electrodes.

[Effect]

The reaction mechanism of dry etching in the present invention is as follows:
It can be considered as follows. First, SFh and 0! The respective reaction gases dissociate in the plasma, forming F radicals and 0
Radicals are generated. Next, the 0 radicals in the plasma react with the St atoms in the wet etching of the processed part,
SIO is produced as an instantaneous intermediate product. This instantaneous intermediate product SiO and F radical react, and s
ip is generated. Since this 5IF4 has a very low boiling point, it naturally turns into a gas and is exhausted outside the reaction chamber.

The side etch prevention effect of the present invention is believed to be due to the following reasons. That is, since a silicon oxide film is used as a mask material, the oxide film is thought to adhere to the sidewalls of the inner surface of the groove, resulting in a masking effect that hinders the etching reaction. Furthermore, in the dry etching reaction mechanism,
SiO, which is an instantaneous intermediate product, is also considered to have a masking effect. In particular, the mixing ratio of 08 gas is 30 to 50.
%, the proportion of the 03 gas in the total reaction gas is very large. Therefore, the intermediate product SiO is also efficiently deposited on the side walls of the deep groove, providing a masking effect, and the amount of side etching is extremely small. Etching is performed. As a result, deep grooves can be formed. On the other hand, in the depth direction, the Si
The masking effect of O or Sing is blocked, making it easier for the etch jig reaction to proceed. Also, since it is an anodic bonding method, unlike the cathodic bonding method, the etching speed is fast, and damage to the silicon substrate during etching can be minimized. . Furthermore, the density of high-frequency applied power is 0.42
~0.46W/-, which is smaller than the 2.8W/cd of conventional RIH, has a small potential gradient for accelerating ions existing in the plasma, so there is no damage caused by ion bombardment, and dry etching is reduced. Since the selection ratio is greatly improved, it becomes possible to form deep grooves with narrow depths that could not be formed conventionally.

〔Example〕

FIG. 1 (al, Q)) shows an outline of an embodiment of the present invention. As shown in FIG. Sa1-
A silicon oxide film 3 is formed on the silicon substrate l, and the silicon oxide film 3 on the portion where the recess is to be formed is removed with an etching solution such as ammonium fluoride to form a pattern in which the recess formation portion 5 is exposed.

This substrate was placed on the lower electrode stage 12 in the reaction chamber 11 of an anodic bonding type parallel plate dry etching apparatus as shown in FIG. The mixed reaction gas 13 is introduced through the gas introduction pipe 14, and the interior of the reaction chamber 11 is evacuated 16 from the bottom.
Maintain a pressure of 3 to 54 Pa and make a diameter of 15 cm inside the reaction chamber.
Matching box 17 to circular upper electrode 15 of 111
A high frequency power of 150 W is applied by the electric i*ts connected through the 150 W to generate plasma 19 between the lower mold 8i12 which is 50 mm apart, and the plasma 19 is present in the exposed silicon of the recess forming part 5 and the plasma. By causing a physicochemical reaction with active species and reactive gas ions, the silicon in the processed area is removed, and as shown in Figure 1 (bl), a 50 - A recess 2 is formed.At this time, the etching factor, which is defined as the value obtained by dividing the amount of side etching by the amount of depth etching, and is a parameter that determines the anisotropy of etching, is shown in Fig. 6 together with conventional dry etching data. The zero conditions shown are as shown in Table 1, and C is an example of the present invention.

From Table 1 and Figure 6, the etching factor of the present invention is 0.20, which is 0.11 smaller than the etching factor of 0.31 in the cathode-coupled dry etching, which is conventionally thought to be capable of anisotropic etching. It can be seen that the present invention further reduces the amount of side etching. FIG. 7 shows the etching speed in comparison with the conventional cathode bonding method. The etching speed in one embodiment of the present invention is 4.7 m/min, which is higher than that in the conventional cathode bonding dry etching method. It can be seen that the etching speed of the present invention is more than 25 times higher than the etching speed of 0.2 m/min, which is extremely high.

Furthermore, in this embodiment, the recess 2 in the silicon substrate 1
The depth non-uniformity is less than 5%.

8(al) and (b) show a deep groove forming process in another embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. The thickness of the silicon oxide film 3 was 500 tna.The single crystal silicon substrate 1 on which the pattern of the silicon oxide film 3 was formed was placed in the lower part of the reaction chamber II of a cathode-coupled parallel plate dry etching apparatus as shown in FIG. Place it on the electrode stage 12, adjust the distance between the parallel plate electrodes 12.15 to 45 to 55 m, and set the flow rate to 5.
5-6.5 ccm SF & gas and flow rate 3.5-4.5
ccm of 08 gas is simultaneously flowed into the reaction chamber 11, and the pressure inside the reaction chamber is maintained at a pressure of 26 to 27 Pa.
During the period of 2.15, high frequency power within the range of 0.42 to 0.46 W/cm3 is applied to generate plasma 19 to remove silicon from the workpiece area, as shown in Figure 8 (bl). A deep groove 4 having a groove width of 5-1 and a depth of 30 .mu. is formed in the substrate 1.If such a deep groove is used as an LSI element isolation trench, the chip size can be reduced.

〔Effect of the invention〕

According to the present invention, an anodic bonding type parallel plate dryer, which has a fast etching speed but is isotropic etching, was thought to be unsuitable for deep etching of single crystal silicon substrates without side etching. By using an etching device and forming a silicon oxide film that protects the side walls of the recess formed by partially volatilizing the mask material during etching, the amount of side etching on the silicon substrate can be extremely small and the etching speed can be reduced compared to conventional etching. Concave portions can be formed at a speed more than 25 times faster than when a cathode-coupled dry etching device is used, and the non-uniformity of the depth of the concave portions in the silicon substrate is 5% or less.

In other words, according to the present invention, it is possible to form recesses even in single crystal silicon substrates with complex pattern shapes, which was impossible or did not improve yield due to the large amount of side etching using conventional dry etching. It is also possible to form narrow deep grooves.

Further, since an anodic bonding type dry etching device is used, the etching speed is very high, so high productivity is ensured. Furthermore, it is thought that etching using a cathode-coupled dry etching device, which is conventionally thought to be capable of anisotropic etching, may result in anisotropy due to the assisting effect of ions existing in the plasma. The etched surface of the recessed portions of the silicon substrate is bombarded by the ions, leaving damage on the etched surface, which has a disadvantage in that it has an adverse effect on the silicon substrate. However, in the case of the present invention, when etching is performed using an anodic bonding dry etching apparatus, the active species in the plasma are thought to be the main cause of the etching reaction, and the etching is almost a chemical reaction. The advantage is that it does not leave much damage.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the steps of an embodiment of the present invention in the order of (al and Cbl), FIG. 2 is a cross-sectional view showing the steps of wet etching in the order of +a+ and (bl), and FIG. FIG. 4 is a cross-sectional view showing the process of dry etching in order of fat and RBL, FIG. Schematic diagram of a parallel plate type dry etching device using an anodic bonding method used for
FIG. 7 is a graph showing the effect of the present invention on etching factor, FIG. 7 is a graph showing the effect of the present invention on etching speed, and FIG. 8 is a diagram showing the process of deep groove machining in another embodiment of the present invention (a). FIG. 1: Silicon substrate, 2: Concave portion, 3: Oxide film, Figure 1, Figure 2, Figure 5, Figure 3, Figure 4, Figure 6

Claims (2)

[Claims] (1) A silicon oxide film is deposited on the main surface of the single crystal silicon substrate where the recess is to be formed, except for the area where the recess is to be formed;
A dry etching method characterized by etching using a mixed gas of sulfur hexafluoride and oxygen as a reactive gas in an anodic bonding parallel plate type dry etching apparatus. (2) Sulfur hexafluoride gas with a flow rate of 5 to 7 ccm and oxygen gas with a flow rate of 3 to 5 ccm are simultaneously introduced into the reaction chamber of a parallel plate type dry etching apparatus, and between the two electrodes 0.42 to 2. The dry etching method according to claim 1, wherein the etching is performed by applying a high frequency power of 0.46 W/cm^3.