JPH0147003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming a diffusion protective film used for forming a diffusion layer by diffusing impurities into a compound semiconductor substrate containing Ga.

(Prior Art) Semiconductor elements having various structures have been manufactured by forming a diffusion layer on a semiconductor substrate. When forming this diffusion layer, for example, in the case of a planar type light emitting device or a high density light emitting device, an Al ₂ O ₃ film, a silicon nitride film made by atmospheric pressure CVD method, or a nitride oxide film is used as a diffusion protective film. A silicon film was used to selectively diffuse impurities through thermal diffusion.

Methods for forming insulating films such as these Al ₂ O ₃ films, silicon nitride films, and silicon nitride oxide films are described, for example, in the document "Semiconductor Handbook (2nd Edition)" (June 1981).
30th), Ohmsha pp289-291).

Furthermore, the method for forming a silicon nitride oxide film is described in, for example, the literature (``Semiconductor Plasma Process'' (July 1982).
(Japanese), Sangyo Tosho P.336-349).

In the case of Al ₂ O ₃ films, dry etching is difficult to form a diffusion window, so wet etching using hot phosphoric acid is usually performed.

On the other hand, in the case of silicon nitride film made by atmospheric pressure CVD method,
In order to grow the silicon nitride film and use it as a diffusion protection film, the growth temperature was usually set at a high temperature of 500 to 600°C or higher.

(Problems to be Solved by the Invention) However, wet etching is inferior to dry etching in controlling the etched shape of the Al ₂ O ₃ film, so it is difficult to control the shape of the impurity diffusion layer region. This method has disadvantages in that it is not possible to achieve a high density of devices, and furthermore, there is variation in the light emitting output between the devices.

In addition, in wet etching, after the etching process,
Since the etching solution remains on the substrate surface, it has an adverse effect on the next process, resulting in a reduction in manufacturing yield.

On the other hand, in the case of a silicon nitride film, the internal stress at room temperature of a silicon nitride film obtained by high-temperature growth as described above is quite large, approximately 10 ⁹ dyn/cm ² .
There are disadvantages in that cracks occur and crystal defects are likely to occur in the underlying substrate crystal due to this stress, thereby reducing the reliability of the obtained device.

In addition, in the case of a silicon nitride oxide film, the composition of this film causes a phenomenon in which Ga (Ga in a substrate such as GaAs or GaAsP) diffuses into the silicon nitride oxide film, resulting in abnormal diffusion in the direction of the interface. It was hot.

In view of these conventional drawbacks, the object of the present invention is to provide a method that allows precise and easy control of the etching shape.
It is an object of the present invention to provide a method for forming a diffusion protective film that improves the reliability of an element and also improves manufacturing yield.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, when forming a diffusion protective film for diffusing impurities particularly into a compound semiconductor substrate containing Ga, a reactive gas is used. A silicon nitride film is formed using monosilane and ammonia as a first layer on this substrate by plasma vapor phase epitaxy using monosilane, ammonia, and laughing gas, and a second layer of monosilane and ammonia is formed on this silicon nitride film. The present invention is characterized in that a silicon nitride oxide film is formed using nitrogen gas and laughing gas, and a diffusion window is formed in the silicon nitride film and the silicon nitride oxide film to form a diffusion protective film.

In carrying out this invention, it is preferable that the first layer of silicon nitride film has a thickness of 300 Å to 500 Å, and the second layer of silicon nitride oxide film has a thickness of 1000 Å to 2000 Å.

In carrying out this invention, the flow rate ratio of monosilane and ammonia in the reaction gas is set to 1:2 to 3 when forming the first layer of silicon nitride film, and when forming the second layer of silicon nitride oxide film. It is preferable that the flow ratio of monosilane to ammonia and the flow ratio of monosilane to laughing gas in the reaction gas be 1:0.2 to 0.8.

Further, in carrying out the present invention, it is preferable to carry out plasma vapor phase growth at a substrate temperature of 250 to 300°C.

(Function) With this configuration, plasma
Since the silicon nitride film and silicon nitride oxide film grown by the CVD method are used as the diffusion protection film, dry etching can be performed and the etched shape can be controlled extremely accurately and easily.

Furthermore, since dry etching can be used to form the diffusion window, there is no problem of residual etching solution as in the prior art, and the manufacturing yield of the device is therefore improved.

Furthermore, the internal stress of the obtained silicon nitride film and silicon nitride oxide film at room temperature is as small as ~10 ⁸ dyn/cm ² or less, and the upper silicon nitride oxide film relieves the stress of the lower silicon nitride film. Therefore, stress does not have an adverse effect on the substrate crystal.

Further, according to the present invention, since the lower silicon nitride film prevents Ga from diffusing into the upper silicon nitride oxide film, abnormal lateral diffusion in the case of selective diffusion can be significantly reduced.

As mentioned above, the region of the diffusion layer obtained by performing impurity thermal diffusion through the two-layer diffusion protective film consisting of the silicon nitride film and the silicon nitride oxide film is in good condition, thus improving the reliability of the device. It increases.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1A to 1E are diagrams showing the manufacturing process of a semiconductor element to explain an embodiment of the method for forming a diffusion protection film of the present invention. These figures schematically show the state of the wafer at major stages. Further, in these figures, the same components are shown with the same reference numerals, and hatching etc. representing cross sections are partially omitted.

An example using an n-type GaAsP/GaAs substrate as the semiconductor substrate will be explained.

First, it was laminated on the GaAs layer 1a of the substrate 1.
A silicon nitride film 2 of 300 to 500 Å is formed on the GaAsP layer 1b by plasma CVD using monosilane and ammonia, and then a silicon nitride oxide film is formed by plasma CVD using monosilane, ammonia, and laughing gas. Figure 1A
A wafer having the structure shown in is obtained. The formation of the silicon nitride film 2 and the silicon nitride oxide film 3 are performed sequentially, for example, as follows.

During this film formation, in order to remove the residual strain layer on the surface of the GaAsP layer 1b of the substrate 1, the surface was organically cleaned using trichloroethylene, methanol alcohol, etc., and then H ₂ SO ₄ :H ₂ O:H ₂ O ₂ = 4:
Clean by etching with a 1:1 etching solution for several minutes at room temperature.

Next, to form a silicon nitride film, plasma
After setting the substrate 1 in the reaction chamber of the CVD device,
Flow the reaction gas. In that case, the gas flow ratio of the reaction gas monosilane and pure ammonia should be 1:2.0~
1:3.0, and the gas pressure in the reaction chamber was 0.4 to 1 Torr.
The silicon nitride film 2 is grown to a thickness of 300 to 500 Å under conditions of a low substrate temperature of 250 to 300° C. and a high frequency output power of 0.1 to 1 W/cm ² .

Next, in order to form a silicon nitride oxide film, the gas flow ratio of monosilane and pure ammonia was adjusted to 1:2.0 to 1:2.0.
1:3.0, the gas flow ratio of monosilane and laughing gas was 1:0.2 to 1:0.8, and the gas pressure in the reaction chamber was
The film thickness of the silicon nitride oxide film 3 is 1000 to 1000 m under the conditions of 0.4 to 1 Torr, low substrate temperature of 250 to 300°C, and high frequency output power of 0.1 to 1 W/ ^cm2 .
Growth is performed until the thickness reaches 2000 Å.

By doing the above, a wafer having a structure as shown in FIG. 1A having a two-layer diffusion protection film consisting of a silicon nitride film 2 and a silicon nitride oxide film 3 can be obtained.

Next, after applying a resist on the silicon nitride oxide film 3, a resist pattern 4 for etching the diffusion protection film into a desired pattern is formed on this resist using photolithography technology, and a portion of the silicon nitride oxide film is etched. If 3a is exposed, Figure 1B
A wafer with a structure like this is obtained.

Next, using this resist pattern 4 as a mask, the exposed portion 3a of the silicon nitride oxide film is first etched by a dry etching method using, for example, CF ₄ gas and other suitable reactive gas. A portion of the silicon nitride film 2 exposed from the lower layer is continuously etched.

As a result, a diffusion window 6 for selective diffusion is formed in the silicon nitride oxide film 3 and the silicon nitride film 2, and a diffusion protection film 5 is formed. Thereafter, the remaining resist pattern 4 is removed to obtain a diffusion protective film 5 having a diffusion window 6 as shown in FIG. 1C.

Here, the thickness of the silicon nitride film is set to 300 to 500 Å,
The reason why the thickness of the silicon nitride oxide film was set to 1000 to 2000 Å and the gas flow rate ratio in each step when forming these two films was set to the conditions described above was to reduce inner film stress during film formation. This is to reduce defects in the film (for example, pinholes) and thereby prevent cracks from occurring during heat treatment.

Further, the reason for the two-layer structure consisting of the silicon nitride film 2 and the silicon nitride oxide film 3 is to suppress the spread of diffusion in the lateral direction.

Both the silicon nitride film 2 and the silicon nitride oxide film 3 formed in this way can be dry-etched and are high-quality films that do not generate pinholes.
The internal stress is also about 10 ⁸ dyn/cm ² , about 1/10 or less of the silicon nitride film conventionally used as a diffusion protection film, so the effect on the underlying substrate is reduced.

Next, the next step for forming a semiconductor element using the diffusion protection film 5 formed by the method of the present invention will be explained.

First, a suitable thermal diffusion method, such as a sealed tube thermal diffusion method,
In this case, p-type impurities (for example, zinc or other impurities) are introduced into the substrate 1 through the diffusion window 6.
It diffuses into the GaAsP layer 1b, forming a p-type diffusion layer 7 in this layer 1b. Since this diffusion layer is a p-type semiconductor layer, it forms a pn junction with the n-type substrate 1. Diffusion conditions in this case can be appropriately set as required. Subsequently, on the entire surface of the diffusion protection film 5,
An insulating film 8 is formed by an appropriate method, for example, a CVD method, and then a groove 9 for forming a p-side electrode is etched to a depth reaching from the surface of this insulating film 8 to the diffusion layer 7. A wafer structure as shown in FIG. 1D is obtained.

Next, as one electrode, the p-side electrode 10,
At the same time, an Al electrode is vapor-deposited, and Au-Ge is deposited on the opposite surface of the substrate 1 as the other electrode, the n-side electrode 11.
-Ni or the like is deposited to form an alloy (Fig. 1E).

In the above-mentioned embodiments, a GaAs-based semiconductor element was used as the substrate, but the substrate is not limited to this. For example, it may be an InP-based or other semiconductor element, and the element structure may also be the same as the above-mentioned structure. It is not limited to those of. Furthermore, the conductivity types may be any combination of conductivity types that is compatible with the semiconductor element.

(Effects of the Invention) As is clear from the above description, according to the present invention, a silicon nitride film and a silicon nitride oxide film grown at low temperatures by plasma CVD are used as a diffusion protective film. Dry etching can be performed. Therefore, etching control becomes accurate and easy, and the diffusion window can be formed into the designed shape, and the diffusion of impurities into the underlying layer through the diffusion window, especially in the region of the diffusion layer obtained by thermal diffusion, is prevented. The cross-sectional shape will also be accurate and beautiful. Therefore, for example, it is possible to increase the density of the light emitting elements than in the past, and it is also possible to significantly reduce the variation in light emission output between the elements than in the past.

Furthermore, the internal stress of these silicon nitride films and silicon nitride oxide films at room temperature is as small as ~10 ⁸ dyn/cm ² or less, and the upper silicon nitride oxide film relieves the stress of the lower silicon nitride film. In addition to obtaining a high-quality diffusion protection film with no pinholes, this structure has an internal stress that is approximately one-tenth or less of that of conventional diffusion protection films, which prevents the occurrence of cracks or crystal defects. decreases significantly.
Therefore, the region of the diffusion layer obtained by diffusion is in a good quality state, and thus the reliability of the device is significantly improved compared to the conventional one.

Further, according to the present invention, since the lower silicon nitride film prevents Ga from diffusing into the upper silicon nitride oxide film, abnormal lateral diffusion in the case of selective diffusion can be significantly reduced.

Furthermore, according to the present invention, since dry etching is possible, the etching solution does not remain on the substrate unlike in the case of wet etching. As a result, the manufacturing yield of the device is significantly improved compared to the conventional method.
The use of the diffusion protection film thus obtained is not limited to the above-mentioned thermal diffusion, but can also be used by ion implantation.

Since this invention has the above-mentioned advantages,
It is suitable for application to the manufacture of planar semiconductor devices, particularly semiconductor light emitting devices and high density light emitting devices.

[Brief explanation of drawings]

FIGS. 1A to 1E are process diagrams illustrating the manufacturing process of a semiconductor device to explain the method for forming a diffusion protection film of the present invention. 1...Semiconductor substrate (GaAsP/GaAs substrate), 1a
...GaAs layer, 1b...GaAsP layer, 2...silicon nitride film,
3...Silicon nitride oxide film, 3a...Part of silicon nitride oxide film, 4...Resist pattern, 5...Diffusion protection film,
6... Diffusion window, 7... Diffusion layer, 8... Insulating film, 9... Groove,
10...One electrode, 11...The other electrode.

Claims (1)

[Claims] In forming a diffusion protection film for diffusing impurities on a compound semiconductor substrate containing 1 Ga, the above method is performed by plasma vapor deposition using monosilane, ammonia, or laughing gas as a reactive gas system. forming a silicon nitride film on the substrate as a first layer using monosilane and ammonia; forming a silicon nitride oxide film as a second layer on the silicon nitride film using monosilane, ammonia, and laughing gas; A method for forming a diffusion protective film, comprising forming a diffusion protective film by opening a diffusion window in a silicon nitride film and the silicon nitride oxide film. 2 The thickness of the first layer silicon nitride film is 300 Å to 500 Å.
Å, and the thickness of the silicon nitride oxide film of the second layer is 1000 Å ~
2. The method for forming a diffusion protection film according to claim 1, wherein the thickness is 2000 Å. 3. When forming the silicon nitride film as the first layer, the flow rate ratio of monosilane and ammonia in the reaction gas is set to 1:2 to 3, and when forming the silicon nitride oxide film as the second layer, the flow rate ratio of monosilane and ammonia in the reaction gas is The flow rate ratio of monosilane and ammonia and the flow rate ratio of monosilane and laughing gas inside are 1:0.2 to 0.8.
A method for forming a diffusion protective film according to claim 2, characterized in that: 4. The diffusion protection film forming method according to claim 3, wherein the plasma vapor phase growth is performed at a substrate temperature of 250 to 300°C.