JPH05226319A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve patterning precision by selectively eliminating a first insulating layer by wet etching wherein a second pattern film is used as a mask. CONSTITUTION:A resist film is formed on a silicon oxide film 13. By development after selective exposure, the resist film is left in the region where a compound semiconductor substratum 11 turning to an active layer is to be left, and a resist pattern film 14 is formed. Said resist pattern film 14 is used as a mask, the silicon oxide film 13 is selectively eliminated by dry etching wherein mixed gas of CHF3/H2 is used, and a second pattern film 13a is formed. A silicon nitride film 12 is selectively eliminated by wet etching wherein the second pattern film 13a is used as a mask, and a first pattern film 12a is formed. Thereby the patterning precision of the first pattern film can be improved.

Description

Detailed Description of the Invention

(Table of contents) -Industrial application field-Conventional technology (Fig. 3) -Problem to be solved by the invention (Fig. 4) -Means for solving the problem-Action-Examples (Fig. 1, Fig. 1) 2) ・ Effect of invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more specifically, it is formed of an insulating film by selectively etching and removing the insulating film on a semiconductor substrate using an etching resistant film. The present invention relates to a semiconductor device manufacturing method for forming a pattern.

[0003]

2. Description of the Related Art There are wet etching methods and dry etching methods as an etching method. In the wet etching method, the boundary condition of diffusion of the reaction medium in the etching solution is in-plane due to slight variations in the temperature conditions of the etching solution. However, since there is a considerable variation, etching unevenness is likely to occur and accurate pattern formation cannot be performed. Therefore, dry etching has been frequently used in response to the recent demand for finer patterns of semiconductor devices.

However, in the case of dry etching, etching products are produced and adhere to the surface of the object to be etched. This deposit is often not removable until the final step of the semiconductor manufacturing process, which may adversely affect the characteristics and reliability of the semiconductor device.

Therefore, in order to form an accurate pattern without adversely affecting the characteristics and reliability of the semiconductor device,
The wet etching method and the dry etching method are used together.

FIGS. 3A to 3C are cross-sectional views for explaining a conventional pattern forming method using both a wet etching method and a dry etching method. For example, an active region layer of a semiconductor laser is formed. The case of forming a mask pattern for mesa etching the compound semiconductor substrate will be described below.

First, the insulating film 2 is formed on the compound semiconductor substrate 1 composed of the substrate 21, the clad layer 22, the active layer 23, and the clad layer 24, and then the resist film is formed. Then, the resist pattern film 3 is left in the region where the compound semiconductor substrate 1 should be left (FIG. 3A).

Next, using the resist pattern film 3 as a mask, the insulating film 2 is first etched by dry etching. At this time, in order to prevent the reaction product of the etching from directly adhering to the compound semiconductor substrate 1,
The thin insulating film 2a is left (see FIG. 3).
(B)).

Next, after removing the resist pattern film 3 by ashing or the like, the remaining thin insulating film 2a is removed by wet etching to form a pattern film 2b (FIG. 3C).

After that, the compound semiconductor substrate 1 is selectively wet-etched by using the pattern film 2b as a mask to form the convex portion 1a including the active layer 23a, thereby forming the active region layer of the laser diode (FIG. 3 (d). )).

[0011]

By the way, when the insulating film 2 is dry-etched to leave the thin insulating film 2a (FIG. 3B), it is difficult to control the thickness of the remaining insulating film 2a. In some cases, the insulating film 2a may be removed before the end, and the surface of the compound semiconductor substrate 1 is exposed to etching gas particles to cause the introduction of crystal defects, or the reaction product of the compound semiconductor substrate 1 is attached. There's a problem. To avoid this, as shown in FIG. 4A, if the insulating film 2c is left thick, the side etching amount in the next wet etching becomes large and the accuracy of the formed pattern film 2d deteriorates ( There is a problem as shown in FIG.

The present invention has been made in view of the problems of the prior art, improves the patterning accuracy while preventing the surface of the semiconductor substrate from being exposed to etching gas particles and reaction products, and An object of the present invention is to provide a method for manufacturing a semiconductor device capable of preventing contamination of other substances such as resist.

[0013]

The above-mentioned problems are as follows. Firstly, the first insulator layer on the semiconductor substrate, and the etching rate against the etching gas is larger than that of the first insulator layer. A second insulator layer having a small etching rate with respect to the step of forming an etching resistant film, patterning the etching resistant film, and using the patterned etching resistant film to form the second insulating layer. Selectively removing the insulating layer by dry etching to form a second pattern film made of the second insulating layer, and removing the remaining etching resistant film, and then performing the second etching. Forming a first pattern film by selectively removing the first insulator layer by wet etching using the pattern film as a mask. It is achieved I, the second, and said etch-resistant film is a resist film 1
According to a third aspect of the present invention, there is provided a method for manufacturing a semiconductor device, and thirdly, at least one of the first insulator layer and the second insulator layer comprises a plurality of insulator layers. According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device according to the first or second aspect of the present invention. Fourthly, the semiconductor substrate is a compound semiconductor substrate, and after the step of forming the first pattern film, This is achieved by the method for manufacturing a semiconductor device according to the first, second or third invention, characterized in that the compound semiconductor substrate is selectively etched using the first pattern film as a mask.

[0014]

[Operation] According to the method for manufacturing a semiconductor device of the present invention, the second insulating layer is selectively removed by dry etching using the etching resistant film to form the second pattern film. Then, the first insulating layer is selectively removed by wet etching using the second pattern film as a mask. That is, since the dry etching is performed so as to leave the first insulator layer, it is possible to prevent the surface of the semiconductor substrate from being exposed to the reaction products and etching gas particles. At this time, the upper second insulating layer has a higher etching rate with respect to the etching gas as compared with the lower first insulating layer. Therefore, when the second insulating layer is dry-etched, the controllability is improved. Therefore, it is possible to prevent the first insulator layer from being accidentally removed.

Further, since the etching resistant film is removed while the first insulating layer is left on the semiconductor substrate after the second insulating layer is selectively removed by dry etching, the etching resistance is particularly high. When a resist film is used as the film, it is possible to prevent contamination of other substances such as resist.

Further, the upper second insulating layer is the lower first insulating layer.
The etching rate with respect to the etching gas is higher and the etching rate with respect to the etching solution is lower than that of the insulating layer. Therefore, when the second insulating layer is dry-etched, the remaining film thickness of the lower first insulating layer can be easily adjusted, and when the first insulating layer is wet-etched, Since the lateral etching of the second insulator layer can be reduced, it is possible to improve the patterning accuracy of the finally formed first pattern film.

Therefore, in the case of selectively etching a semiconductor substrate, particularly a compound semiconductor substrate which is often subjected to mesa etching such as formation of an active region layer in a semiconductor laser, using the first pattern film as a mask, the active region layer with high accuracy is obtained. Etc. can be formed.

[0018]

Embodiments of the present invention will now be described with reference to the drawings. 1 (a)-(d), FIG. 2 (e),
(F) is a cross-sectional view illustrating a pattern forming method according to an embodiment of the present invention, which uses a wet etching method and a dry etching method together, and mesa-etches a compound semiconductor substrate to form an active region layer of a semiconductor laser. A case of forming a mask pattern for the following will be described.

First, a compound semiconductor substrate (semiconductor substrate) 1
A silicon nitride film (first insulator layer) 12 having a film thickness of about 500Å and a silicon oxide film (second insulator layer) 13 having a film thickness of about 2000Å are formed on the substrate 1 (FIG. 1A). The compound semiconductor substrate 11 is composed of a substrate 21 made of n-type InP / a cladding layer 22 made of n-type InP / non-doped InGa.
An active layer 23 made of AsP / a clad layer 24 made of p-type InP are sequentially laminated.

Next, a resist film is formed on the silicon oxide film 13. Subsequently, after the selective exposure, the resist film is left in a region where the compound semiconductor substrate to be developed to be the active layer should be left, and the resist pattern film 14 is formed. Then, using the resist pattern film 14 as a mask, CHF ₃ / H
_The silicon oxide film 13 is selectively removed by dry etching with a mixed gas of 2 to form a second pattern film 13a. At this time, the underlying silicon nitride film 12 is hardly etched due to the selectivity of the CHF ₃ / H ₂ mixed gas (FIG. 1B). This can prevent the reaction product of the etching from directly adhering to the compound semiconductor substrate 11, and also prevent the surface of the compound semiconductor substrate 11 from being exposed to the plasma particles of the mixed gas. ..

Next, the remaining resist pattern film 14 is removed by ashing using a stripping solution or oxygen gas (FIG. 1 (c)). At this time, the resist pattern film 1 with the silicon nitride film 12 left on the compound semiconductor substrate 11 is left.
Since 4 is removed, contamination of other substances such as resist can be prevented.

Next, using the second pattern film 13a as a mask, the silicon nitride film is selectively removed by wet etching using a hydrofluoric acid-based aqueous mixed solution to form a first pattern film 12a. (Fig. 1
(D)).

Next, the compound semiconductor substrate 11 is selected by wet etching using a bromine-based etching solution to a depth of about 1 μm which reaches the clad layer 26 below the active layer 27 using the first pattern film 12a as a mask. Portion 11a including the active layer 27a serving as the active region layer, which is etched as
Are formed (FIG. 2E).

After that, the laser diode is completed through a normal process (FIG. 2 (f)). In the figure, reference numeral 29 denotes a buried layer made of p-type InP formed on the side of the convex portion 11a, and 30 denotes a side portion of the convex portion 11a formed on the buried layer 29 made of p-type InP. A buried layer made of n-type InP, 31 a p-type InP clad layer formed by covering the clad layer 28a and the buried layer 30 above the active layer 27a, 32 a contact layer made of p-type InGaAsP, and 33 a It is an electrode on the contact layer 32.

In the above embodiment, the silicon nitride film 1 is used.
The hydrofluoric acid-based etching liquid is used as the second etching liquid, and the phosphoric acid-based etching liquid is not used in order to prevent the underlying compound semiconductor substrate 11 from being etched. Further, the hydrofluoric acid-based etching solution is also known as an etching solution for a silicon oxide film, but an etching selection ratio with a silicon nitride film can be secured by appropriately adjusting the composition. Needless to say, phosphoric acid can be used as the etching solution for the silicon nitride film if the base is a silicon substrate.

As described above, according to the embodiment of the present invention,
When the silicon oxide film 13 is selectively removed by dry etching (FIG. 1B), since the dry etching is performed so that the silicon nitride film 12 remains, the surface of the compound semiconductor substrate 11 is exposed to etching gas particles. Can be prevented. At this time, since the upper silicon oxide film 13 has a higher etching rate with respect to the etching gas than the lower silicon nitride film 12, the controllability is improved when the silicon oxide film 13 is dry-etched, and the silicon nitride film is erroneously mistaken. It is possible to prevent 12 from being removed.

The compound semiconductor substrate 11 is formed after the silicon oxide film 13 is selectively removed by dry etching.
Since the resist pattern film 14 is removed with the silicon nitride film 12 left on it (FIG. 1C), it is possible to prevent contamination of other substances such as resist.

Further, the upper silicon oxide film 13 has a higher etching rate with respect to the etching gas and a lower etching rate with respect to the etching solution than the lower silicon nitride film 12. Therefore, the silicon oxide film 13
When dry etching (FIG. 1B), the remaining film thickness of the silicon nitride film 12 can be easily adjusted, and when the silicon nitride film 12 is wet-etched (FIG. 1D), silicon is used. Since the lateral etching of the oxide film 13 can be reduced as much as possible, the patterning accuracy of the finally formed first pattern film 12a can be improved.

Therefore, the compound semiconductor substrate 11 can be selectively etched by using the first pattern film 12a as a mask to form an accurate active region layer. In the above embodiment, the silicon oxide film 13 is used as the upper second insulating layer and the silicon nitride film 12 is used as the lower first insulating layer, but the reverse configuration is also possible. At this time, it is necessary to properly select the etching gas and the etching solution. In addition, the second insulating layer has a higher etching rate with respect to the etching gas and a lower etching rate with respect to the etching solution as compared with the first insulating layer. Combinations can also be used.

Although the first and second insulating layers are applied to the case where the insulating film is composed of a single layer, respectively, of the upper second insulating layer and the lower first insulating layer, It is also applicable to the case where at least one of them is a plurality of layers, for example, the second insulating layer is an insulating film composed of a two-layer film such as SOG (spin on glass) film / silicon oxide film.

Further, although the present invention is applied to the method for producing a semiconductor laser, it can be applied to the method for producing other semiconductor devices.

[0032]

As described above, according to the method of manufacturing a semiconductor device of the present invention, since the dry etching is performed so that the first insulating layer remains, the surface of the semiconductor substrate is exposed to the dry etching gas particles. Can be prevented. At this time, the etching rate of the upper second insulating layer against the etching gas is higher than that of the lower first insulating layer. Therefore, when the second insulating layer is dry-etched, controllability is improved. It is possible to prevent the erroneous removal of the first insulator layer.

Further, since the etching resistant film is removed while leaving the first insulating layer on the semiconductor substrate, when a resist film is used as the etching resistant film, contamination of other substances such as resist is caused. Can be prevented.

Further, the upper second insulator layer is the lower first insulator layer.
The etching rate with respect to the etching gas is higher and the etching rate with respect to the etching solution is lower than that of the insulating layer. Therefore, the remaining film thickness of the first insulator layer can be easily adjusted, and the lateral etching of the second insulator layer can be reduced, so that the first pattern film finally formed. The patterning accuracy of can be improved.

Therefore, when selectively etching a semiconductor substrate, particularly a compound semiconductor layer which is often subjected to mesa etching such as formation of an active region layer in a semiconductor laser, using the first pattern film as a mask, the active region layer with high accuracy is obtained. Can be formed.

[Brief description of drawings]

FIG. 1 is a sectional view (No. 1) for explaining a method for manufacturing a semiconductor laser including a pattern forming method according to an embodiment of the present invention.
Is.

FIG. 2 is a cross-sectional view (No. 2) for explaining the method for manufacturing the semiconductor laser including the pattern forming method according to the embodiment of the present invention.
Is.

FIG. 3 is a cross-sectional view illustrating a method for manufacturing a semiconductor laser including a conventional pattern forming method.

FIG. 4 is a cross-sectional view illustrating a problem of a conventional example.

[Explanation of symbols]

 11 compound semiconductor substrate (semiconductor substrate), 11a convex portion, 12 silicon nitride film (first insulating layer), 12a first pattern film, 13 silicon oxide film (second insulating layer), 13a second Pattern film, 14 resist pattern film (etching resistant film), 25 substrate, 26, 26a, 28, 28a clad layer, 27, 27a active layer, 29, 30 buried layer, 31 clad layer, 32 contact layer, 33 electrode.

Claims (3)

[Claims] 1. A first insulator layer on a semiconductor substrate, and a second insulator layer having a high etching rate for an etching gas and a low etching rate for an etching solution as compared with the first insulator layer. A step of sequentially forming an etching resistant film, a step of patterning the etching resistant film, and a step of selectively removing the second insulating layer by dry etching using the patterned etching resistant film. Then, a step of forming a second pattern film composed of the second insulator layer, and a step of selectively removing the first insulator layer by wet etching using the second pattern film as a mask 1. A method of manufacturing a semiconductor device, which comprises the step of forming a pattern film. 2. The method of manufacturing a semiconductor device according to claim 1, wherein at least one of the first insulator layer and the second insulator layer is composed of a plurality of insulator layers. 3. The semiconductor substrate is a compound semiconductor substrate, and after the step of forming the first pattern film, the compound semiconductor substrate is selectively etched using the first pattern film as a mask. The method for manufacturing a semiconductor device according to claim 1 or 2.