JPS61194827A - Diffused protective film forming method - Google Patents

Abstract

PURPOSE:To accurately and readily control to etch, to improve the reliability of an element and to improve the yield by utilizing a silicon nitride film and a silicon oxide nitride film grown at a low temperature by a plasma CVD method as a diffused protective film. CONSTITUTION:A silicon nitride film 2 of 300-500Angstrom is grown by a plasma CVD method with monosilane and ammonia on a GaAsP layer 1b laminated on a GaAs layer 1a of a substrate 1, a silicon oxide nitride film 3 of 1,000-2,000Angstrom is then grown by a plasma CVD method with monosilane, ammonia and laughing gas, a resist pattern 4 is formed to expose a portion 3a. With the pattern 4 as a mask it is etched by dry etching method to form a selectively diffusing diffusion window 6 and a diffused protective film 5, and the pattern 4 is removed.

Description

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

(Prior Art) Conventionally, semiconductor elements of 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 A1203 film or a normal pressure GV film is used as a diffusion protective film.
A silicon nitride film or a silicon nitride oxide film made by the D method was used to selectively diffuse impurities by thermal diffusion.

Methods for forming insulating films such as A1203 films, silicon nitride films, and silicon nitride oxide films are described in, for example, the literature ("Semiconductor Handbook (2nd Edition)" (June 30, 1981)),
It is disclosed in Ohmsha pp2B9-291).

Further, a method for forming a silicon nitride oxide film is disclosed, for example, in a document ("Semiconductor Plasma Process" (July 10, 1980), Sangyo Tosho P, 338-349).

In the case of an Al2O3 film, since dry etching is difficult to form a diffusion window, wet etching using hot phosphoric acid is usually performed.

On the other hand, in the case of a silicon nitride film formed by the normal pressure CVN method, the growth temperature is usually set at a high temperature of 500 to BO0°C or higher in order to use the grown silicon nitride film as a diffusion protection film.

(Problems to be Solved by the Invention) However, wet etching is inferior to dry etching in controlling the etched shape of the Al2O3 film, so it is difficult to control the shape of the impurity diffusion layer region, and it is difficult to control the shape of the region of the impurity diffusion layer. This method has disadvantages in that it is not possible to achieve high density, and furthermore, there is variation in the light emitting output between each element.

In addition, wet etching has the disadvantage that the etching solution remains on the substrate surface after the etching process, which adversely affects 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 the silicon nitride film obtained by high-temperature growth as described above is ~10
Since the stress is quite large at about 9 dyn/am2, cracks are likely to occur and crystal defects are likely to occur in the underlying substrate crystal due to this stress, resulting in a disadvantage that the reliability of the obtained device is reduced.

In addition, in the case of a silicon nitride oxide film, a phenomenon occurs in which Ga (Ga in a substrate such as GaAs or GaAsP) diffuses into the silicon nitride oxide film depending on the composition of the film, and abnormal diffusion occurs in the direction of the interface. was there.

SUMMARY OF THE INVENTION In view of these conventional drawbacks, the object of the present invention is to provide a method for accurately and easily controlling 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 protection film for diffusing impurities into a semiconductor substrate, a reactive gas such as monosilane, ammonia, or A silicon nitride film is formed on this substrate using monosilane and ammonia as a first layer by plasma vapor deposition using laughing gas, and monosilane, ammonia, and laughing gas are formed as a second layer on this silicon nitride film. The invention is characterized in that a silicon nitride oxide film is formed using the silicon nitride film, and a diffusion window is formed in the silicon nitride film and the silicon nitride oxide film to form a diffusion protection film.

In carrying out this invention, it is preferable that the first layer silicon nitride film has a thickness of 300 Å to 500 λ, and the second layer silicon nitride oxide film has a thickness of 100 OA to 2000 λ.

In carrying out this invention, the flow rate ratio of monosilane and ammonia in the reaction gas was adjusted to 1 when forming the first layer of silicon nitride film.
:2 to 3, and when forming the second layer of silicon nitride oxide film, the flow rate ratio of monosilane to ammonia and the flow rate ratio of monosilane to laughing gas in the reaction gas are l:o, 2 to 0.8. is preferable.

Furthermore, in carrying out this invention, two plasma vapor phase epitaxes are performed.
It is preferable to carry out the process at a substrate temperature of 50 to 300°C.

(Function) With this configuration, the silicon nitride film and silicon nitride oxide film grown by the plasma CVD method can be used as the diffusion layer MI.
Since it is used as H, 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 therefore the manufacturing yield of the device is improved.

Furthermore, the internal stress of the obtained silicon nitride film and silicon nitride oxide film at room temperature is as small as ~108 dyn/cm2 or less, and the upper layer silicon nitride oxide film relieves the stress of the lower layer silicon nitride film. There is no adverse effect of stress on the 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 protection film consisting of the silicon nitride film and the silicon nitride oxide film is in good condition5, thereby increasing the reliability of the device. .

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

FIGS. 1(A) to 1(E) are diagrams showing the manufacturing process of a semiconductor element in order to explain an embodiment of the method for forming a diffusion protection film of the present invention. These Figure 1! The state of the wafer at major stages is shown in a linear manner. Further, in these figures, the same constituent components are indicated by the same reference numerals, and hatching etc. representing cross sections are partially omitted.

An example in which an n-type GaAsP/Ga+Lg substrate is used as the semiconductor substrate will be explained.

First, GaAsP is laminated on the GaAs layer 1a of the substrate 1.
A silicon nitride film 2 with a thickness of 300 to 500 λ is formed on the layer lb by a plasma CVD method using monosilane and ammonia, and then a silicon nitride oxide film 3 with a thickness of 1000 λ is formed by a plasma CVD method using monosilane, ammonia, and laughing gas. ~2
A wafer having a structure as shown in FIG. 1(A) is obtained by forming a film with a thickness of 000λ. 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, the GaAgP layer of the substrate 1! In order to remove the residual strain layer on the surface of b, the surface was organically cleaned using trichlorethylene, methanol alcohol, etc., and then H
2SO4: H2O: H2O2= 4: l:
Clean by etching for several minutes at room temperature with 1 ml of etching solution.

Next, in order to form a silicon nitride film, after setting the substrate l in the reaction chamber of the plasma CVD apparatus, a reaction gas is caused to flow.
In that case, the gas flow ratio of the reaction gas monosilane and pure ammonia is set to 1:2.0 to 1:3.0, the gas pressure in the reaction chamber is set to 0.4 to 1 Tarr, and the substrate temperature is set to 250
The low temperature is ~300℃, and the high frequency output power is 0.1
- silicon nitride I under the conditions of I W / cm2
l! Growth is performed until the film thickness of No. 2 becomes 300 to 500λ.

Next, in order to process the silicon nitride oxide film with IItI8I, the gas flow ratio of monosilane and pure ammonia was set to 1:2. Q~1:
3.0, and the gas flow rate ratio of monosilane and laughing gas is l.
: 0.2 to l:o, 8, and the gas pressure in the reaction chamber was set to 0.
4 to I Torr, the substrate temperature to a low temperature of 250 to 300°C, and the high frequency output power to 0.1 to IW/Cm.
2, the thickness of the silicon nitride oxide film 3 is 100
Growth is performed until it reaches 0 to 200 OA.

If the above is done, the result will be as shown in FIG. 1(A).

A wafer having a structure having a two-layer diffusion protection film consisting of a silicon nitride film 2 and a silicon nitride oxide film 3 is obtained.

Next, after applying a resist to the silicon nitride oxide film 31, a resist pattern 4 for etching the diffusion layer; By exposing the wafer, a wafer having a structure as shown in FIG. 1 (CB) 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, OL gas or 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 retaining film 5 having a diffusion window 6 as shown in FIG. 1(C).

Here, the thickness of the silicon nitride film is 300 to 500λ, the thickness of the silicon nitride film is 1000 to 2000λ, and the gas flow rate ratio in each step when forming these two films is as described above. The conditions were:

This is to reduce stress within the film during film formation and defects within the film (for example, pinholes), thereby preventing cracks from occurring during heat treatment.

Further, the reason for the two-layer structure consisting of silicon nitride film 2 and silicon nitride oxide 1tI3 is to suppress the spread of diffusion in the lateral direction.

Both silicon nitride 1lI2 and silicon nitride oxide $3 thus formed can be dry-etched, are high-quality films with no pinholes, and have an internal stress of ~10
Since it is about 8 dyn/cm2, which is less than about 1710 dyn/cm2 of the silicon nitride film conventionally used as a diffusion protection film, the influence on the underlying substrate is small.

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 p-type impurity (for example, zinc or other impurity) in this case is diffused into the GaAsP layer 1b of the substrate 1 through this diffusion window 6 by a suitable thermal diffusion method, such as a sealed tube thermal diffusion method, and this layer lb A p-type diffusion layer 7 is formed therein. Since this diffusion layer is a p-type semiconductor layer, it forms a pn junction with the n-type substrate l. Diffusion conditions in this case can be appropriately set as required. Subsequently, an insulating film 8 is formed on the entire surface of the diffusion protection film 5 by an appropriate method, for example, a CVD method.
Subsequently, a groove 9 for forming a p-side electrode is etched to a depth reaching the diffusion layer 7 from the surface of the insulator J1!8 to obtain a wafer structure as shown in FIG. 1(D).

Next, an AM main electrode is deposited as the p-side electrode lO, which is one electrode, and Au-Ge-old, etc. is deposited on the opposite surface of the substrate 1 as the n-side electrode 11, which is the other electrode. Alloyed (Figure 1(E)).

In the above-described embodiments, a GaAs-based semiconductor element is used as the substrate, but the substrate is not limited to this. For example, an InP-based, Si-based, or other semiconductor element may be used, and the element structure may also be changed. It is not limited to the structure described above.

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 in the designed shape, and the cross-sectional shape of the region of the diffusion layer obtained by diffusion of impurities into the underlying layer through the diffusion window, especially thermal diffusion, can be improved. It 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 ~108 dyn/cm2 or less, and the upper silicon nitride oxide film relaxes the northern part of the lower silicon nitride film. In addition to obtaining a high-quality diffusion layer without holes, this structure has an internal stress that is about one-seventh or less of that of conventional diffusion protection films, which prevents cracks from forming or crystallizing. The occurrence of defects is significantly reduced.

Therefore, the region of the diffusion layer obtained by diffusion is in a good quality state, and therefore 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.

Further, according to the present invention, since the dry etching process is a circular process, there is no possibility that the etching solution remains on the substrate as in the case of wet etching, and therefore, the etching process has no adverse effect on the subsequent manufacturing process of semiconductor devices. As a result, the manufacturing yield of the device is significantly improved compared to the conventional method. The diffusion layer N1 film obtained in this way is
The use is not limited to the above-mentioned heat diffusion;
Of course, it can also be used when using ion implantation.

Since the present 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 the drawing]

FIGS. 1(A) to 1(E) provide an explanation of the method for forming a diffusion protection film of the present invention. It is a process diagram showing the manufacturing process of a semiconductor element. 1... Semiconductor substrate (GaAsP/GaAs substrate) l
a・-GaAs layer, lb・-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 1
1...Other electrode. Figure 1 2! 1 [and Otori E November ruled line

Claims (4)

[Claims] (1) When forming a diffusion protection film for diffusing impurities on a semiconductor substrate, a first layer is formed on the substrate by plasma vapor deposition using monosilane, ammonia, or laughing gas as a reactive gas system. A silicon nitride film is formed using monosilane and ammonia, a silicon nitride oxide film is formed as a second layer on the silicon nitride film using monosilane, ammonia, and laughing gas, and the silicon nitride film and the silicon nitride oxide A method for forming a diffusion protective film, characterized in that the diffusion protective film is formed by opening a diffusion window in the film. (2) The thickness of the first layer silicon nitride film is 300 Å to 50 Å.
0 Å, and the thickness of the second layer silicon nitride oxide film is 1000 Å to 20 Å.
The method for forming a diffusion protective film according to claim 1, wherein the diffusion protective film has a thickness of 00 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 1:2 to 3, and when forming the silicon nitride oxide film as the second layer, The method for forming a diffusion protective film according to claim 2, characterized in that the flow ratio of monosilane to ammonia and the flow ratio of monosilane to laughing gas in the reaction gas are set to 1:0.2 to 0.8. . (4) The method for forming a diffusion protective film according to claim 3, wherein the plasma vapor phase growth is performed at a substrate temperature of 250 to 300°C.