JP2522036B2 - Deep etching method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a deep etching method for forming a recess having a side wall perpendicular to a main surface of a single crystal silicon substrate.

[Conventional technology]

Conventional processing methods for forming a recess from the main surface of a single crystal substrate include wet etching using hydrofluoric acid and CF ₄ , SF ₆
There are two types of methods such as dry etching using a reactive gas such as. The wet etching method is shown in Fig. 2 (a).
As shown in FIG. 2, a mask made of a silicon oxide film 21 and a silicon nitride film 22 is deposited on the silicon substrate 1 so that the processed portion is exposed, and as shown in FIG. The portion to be processed is etched to form the recess 2. On the other hand, in the dry etching method, as shown in FIG. 3A, a mask 3 made of aluminum is applied to a silicon substrate 1 in the same manner as in the wet etching method, and an anodic-bonding or cathode-bonding parallel plate is used. With a mold dry etching apparatus, silicon is deeply etched to form a recess 2 as shown in FIG. 3 (b).

[Problems to be Solved by the Invention]

In the conventional wet etching, when a mask layer is deposited on a silicon substrate, the thickness of the mask layer is limited to a certain extent, which causes a limit to the etching depth.
The above method is not suitable for deeply etching a silicon substrate exceeding 1 mm. Further, the above method has a problem that the depth of the recessed portion after the etching largely varies within the single crystal silicon substrate, and thus the yield is reduced.

On the other hand, in dry etching using a fluorine-based reaction gas, when an anodic bonding type device is used, the etching rate is fast and the selectivity of the aluminum mask is very large, so etching is performed even on silicon substrates with a thickness of more than 1 mm. It is possible and has the advantage of good uniformity within the silicon substrate. However, although the side etching amount is smaller than that of wet etching, even if the etching condition that minimizes the side etching amount is selected by the above method, since the above method is originally isotropic etching, the side etching amount is reduced by the depth etching. The etching factor, which is the value obtained by dividing the amount, is 0.55, and the side etch amount is slightly large. Therefore, it is inconvenient when it is desired to form a recess in the silicon substrate with a smaller side etch amount, for example, when a recess is formed in a silicon substrate having a complicated pattern, and a more anisotropic etching method is required. .
On the other hand, if a parallel plate type dry etching apparatus of the cathode coupling method is used, in the case of dry etching using a fluorine-based reaction gas, the etching factor can be reduced to about 0.30, but the etching rate is higher than that of the anodic coupling method. Compared with the dry etching of 1), it becomes 1/25, and there is a problem that the uniformity in the silicon substrate is a little poor.

An object of the present invention is to provide a deep etching method which has a small side etching amount, a small etching factor, and a high etching rate.

[Means for solving the problem]

In order to achieve the above-mentioned object, according to the present invention, in a parallel plate type dry etching apparatus of an anodic coupling type, deep etching is performed using a mixed gas of sulfur hexafluoride and oxygen as a reaction gas. A method of depositing an aluminum film on a main surface of a single-crystal silicon substrate in which a recess is to be formed, except for a portion where a recess is to be formed, and a photoresist film on the film, the reaction gas and the The reaction product with the photoresist is attached to the side surface of the recess and etching is performed.

[Action]

The aluminum film does not react to the active species and reactive gas ions present in the plasma generated in the reaction tank of the anodic bonding type dry etching apparatus, but the resist film does.
This produces a reaction product. This reaction product adheres not only to the bottom surface but also to the side surface of the concave portion generated by the physicochemical reaction of active species and reactive gas ions with the single crystal silicon substrate, and also serves as a mask for etching. However, active species and reaction gases hit the reaction products attached to the bottom surface more vertically than to the reaction products attached to the side surfaces, so that the attached reaction products are removed in a relatively short time. Etching of the bottom surface proceeds.
The progress of etching on the side surface where the adhered reaction product remains as a mask is small, and therefore the wraparound under the aluminum mask is reduced, and the side etch amount is reduced.
Deep etching is possible at a high etching rate of the anodic coupling method.

〔Example〕

FIGS. 1 (a) and 1 (b) show an outline of one embodiment of the present invention. For example, as shown in FIG.
m of the silicon substrate 1 is coated with an aluminum thin film 3 having a thickness of 4 μm by a sputtering method or the like, and a photoprocess resist thin film 4 is deposited thereon with a thickness of 2 to 3 μm. After removing the resist thin film 4 on the silicon substrate 1 where the concave portion is to be formed, the exposed aluminum thin film 3 is removed by an etching solution using a phosphoric nitric acid solution or the like, and the remaining resist thin film 4 on the aluminum mask is peeled off. The exposed pattern of the recess forming portion 5 is formed without leaving it. This substrate is used as the lower electrode stage 12 in the reaction chamber 11 of the parallel plate type dry etching apparatus of the anode coupling type as shown in FIG.
The reaction gas 13 containing SF ₆ and O ₂ mixed in a ratio of 7: 3 is introduced into the reaction chamber 11 through the gas introduction pipe 9, and the inside of the reaction chamber 11 is evacuated to 0.4 Torr by vacuum evacuation 16 from the lower part. While maintaining the pressure, a high-frequency power of 150 W (0.85 W / cm ² ) is applied between the lower electrode in the reaction chamber and the upper electrode 14 50 mm apart by the power supply 18 connected to the upper electrode through the matching box 17. Then, plasma 19 is generated between both electrodes. Then, the exposed silicon in the recess forming portion 5 and the active species or reactive gas ions existing in the plasma are caused to physically react with each other to remove the silicon in the recess forming portion, as shown in FIG. 1 (b). As shown in FIG. 3, a recess 2 having a depth of 20 μm is formed at a predetermined portion of the silicon substrate 1. At this time, the etching factor, which is defined as a value obtained by dividing the side etching amount by the depth etching amount and is a parameter for knowing the anisotropy of etching, together with the data of the dry etching when only the conventional aluminum mask is used, Shown in the figure. line
Reference numeral 51 is an embodiment of the present invention, and line 52 is a conventional example. Fifth
From the figure, the etching factor of the present invention is 0.266 to 0.556, which is smaller than the etching factor of 0.517 to 0.576 of dry etching when dry etching is performed by the anodic bonding method using only the conventional aluminum mask, that is, the present invention is the side etch amount. It can be seen that even less etching can be performed. Further, the etching rate of the present invention is 4.7
The etching rate of the present invention is extremely high, which is 25 times or more than the etching rate of 0.2 μm / min in the dry etching of the cathode coupling method which is conventionally capable of anisotropic etching at μm / min. .

〔The invention's effect〕

According to the present invention, the etching rate is high, but isotropic etching is performed, so that it is considered to be unsuitable for deep etching with a small amount of side etching on a single crystal silicon substrate. By using an etching device and leaving the photoresist film as it is when patterning the aluminum mask, which has been used in the past,
The active species and reactive gas ions existing in the plasma react with the resist film in the peripheral portion to generate a reaction product. This reaction product adheres to the bottom surface and side surface of the recess formed by etching, and the one adhered to the side surface serves as a mask for etching, but the one adhered to the bottom surface is mechanically affected by the violently colliding active species and reaction gas. , And only the etching proceeds to the bottom surface. For this reason, the side etching amount of the silicon substrate is very small, and the etching rate is 25
The recess can be formed at a speed twice or more. Further, according to the present invention, since the resist thin film that has been peeled off at the end of the conventional pattern formation is left, one resist peeling step at the time of patterning can be omitted, and the productivity is improved. Therefore, according to the present invention, it is possible to form a recess even in a single crystal silicon substrate having a complicated pattern shape, which is not possible due to a large amount of side etching by the conventional dry etching or the yield cannot be increased. Become. Further, as described above, since the etching rate of the present invention is much higher than the etching rate of the cathode-coupled dry etching apparatus which is conventionally capable of anisotropic etching, high productivity is secured. To be done. Further, it is considered that the etching in the dry etching apparatus of the cathode coupling type, which is conventionally capable of anisotropic etching, may be anisotropic due to the assist effect of the ions existing in the plasma. There is a drawback in that the processed surface of the recess on the silicon substrate to be etched is impacted by the ions, and damage remains on the processed surface, which adversely affects the silicon substrate. However, in the case of the present invention, it is considered that the active species in plasma is the main component of the etching reaction in the etching by the anodic bonding type dry etching apparatus, and there is an advantage that the recessed surface of the silicon substrate is not so damaged. is there.

[Brief description of drawings]

1 (a) and 1 (b) are cross-sectional views sequentially showing steps of one embodiment of the present invention, FIGS. 2 (a) and 2 (b) are cross-sectional views sequentially showing steps by wet etching, and FIG. a), (b)
Is a cross-sectional view sequentially showing the steps of the conventional dry etching, FIG. 4 is a cross-sectional view of a parallel plate type dry etching apparatus by an anodic coupling method used for implementing the present invention, and FIG. 5 is an etching effect of the present invention on an etching factor. It is a diagram shown in relation to the depth. 1: Silicon substrate, 2: Recess, 3: Aluminum thin film, 4: Resist thin film.

Claims (1)

(57) [Claims] 1. A deep etching method in which a parallel plate type dry etching apparatus of an anodic coupling method is used to perform etching using a mixed gas of sulfur hexafluoride and oxygen as a reaction gas, in which a recess is to be formed. An aluminum film is deposited on the main surface of the single crystal silicon substrate except a portion where a concave portion is formed, and a photoresist film is further deposited on the film, and a reaction product of the reaction gas and the photoresist is deposited on the concave portion. The deep etching method is characterized in that etching is performed by adhering to the side surface of the.