JP3221214B2 - Method of forming semiconductor thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-emitting or light-receiving element, and more particularly to an LCRT (Laser Cathode- Ray).
The present invention relates to a method for forming a semiconductor thin film used in a device or a semiconductor laser device.

[0002]

2. Description of the Related Art The prior art will be described by taking as an example a method of forming a single crystal thin film for an LCRT device. Conventionally, a single crystal ingot has been manufactured by a pulling method, cut out and polished to obtain a single crystal thin film having a thickness of about 10 μm.

The process will be described below with reference to a single-crystal thin film forming process shown in FIG. In addition, (1)-of a figure
(3) is a perspective view, and (4) to (6) in the figure are cross-sectional views.

As shown in FIG. 6A, a single crystal ingot 51 is formed by a pulling method. Subsequently, FIG.
As shown in (2) above, the single crystal ingot (51)
Is cut to form a wafer 52. Then, the surface of the wafer 52 is mirror-polished.

Next, as shown in FIG. 6C, a first reflection film 53 is formed on the surface of the wafer 52 by a vapor deposition method. Then, as shown in (4) in FIG. 6, bonding the first reflecting film 53 side of the wafer 52 to the substrate 55 using an adhesive 54.

Then, as shown in FIG. 6 (5), the wafer 52 is polished by chemical mechanical polishing to form the wafer 52 into a thin film having a thickness of about 10 μm. Then, as shown in FIG. 6 (6), a second reflective film 56 is formed on the polished surface of the wafer 52 by an evaporation method.

[0007]

However, it is difficult to control the thickness of the wafer by the above method for forming a semiconductor thin film. Further, even if the mirror surface is polished by chemical mechanical polishing, crystal defects occur on the surface layer of the polished surface of the wafer. Therefore, the optical characteristics of the crystal of the wafer deteriorate. Further, since a wafer is cut out from a single crystal ingot and the wafer is formed into a thin film by mirror polishing, it is difficult to accurately control the thickness of the thin film. Further, it is difficult to form a uniform film thickness over the entire surface of the thin film. Further, it is very difficult to produce a heterostructure thin film by the above method, since different crystals cannot be formed in a joined state when forming crystals by the pulling method.

It is an object of the present invention to provide a method for forming a semiconductor thin film having excellent crystallinity and film thickness controllability.

[0009]

SUMMARY OF THE INVENTION The present invention is a method for forming a semiconductor thin film which has been made to achieve the above object. That is, in the first step, an etching stop layer is formed on a compound semiconductor substrate, and subsequently, a compound semiconductor layer is deposited on the etching stop layer by metal organic chemical vapor deposition or molecular beam epitaxy. Then, in a second step, after forming a first reflection film on the compound semiconductor layer, a third reflection film is formed.
In the step, the first reflection film side is bonded to the substrate . Then, in a fourth step, after removing the compound semiconductor substrate by etching, the etching stop layer is removed to expose the surface of the compound semiconductor layer. Further, in a fifth step, a second reflection film is formed on the surface of the compound semiconductor layer. Further, in the above method, the compound semiconductor layer may be formed in a hetero structure, and the etching stop layer may be etched.

[0010]

According to the method of forming a semiconductor thin film, no polishing is performed when the compound semiconductor layer is thinned, so that no crystal defects occur in the compound semiconductor layer. Further, an etching stopper layer is formed on the compound semiconductor substrate, and subsequently, the compound semiconductor layer is deposited on the etching stopper layer by metal organic chemical vapor deposition or molecular beam epitaxy.
Therefore, the thickness of the compound semiconductor layer is controlled at the atomic level. Also, when the compound semiconductor layer is formed in a hetero structure, the same effect as described above can be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. In the figure, (1) and (2) are shown in perspective views,
(3) to (6) are shown in sectional views. In the following description, as an example, a method of forming a zinc selenium layer of a blue material, among the methods of forming a single crystal film for a transmission type LCRT, will be specifically described.

As shown in FIG. 1A, in the first step, for example, metal organic chemical vapor deposition (hereinafter referred to as MOCVD)
Method) or molecular beam epitaxial growth method (hereinafter M
By a BE method, a gallium indium phosphide (hereinafter, GaIn) serving as an etching stop layer is formed on a gallium arsenide (hereinafter, referred to as GaAs) substrate 11 which is a compound semiconductor substrate.
P) is formed. The GaInP layer 12
Has a thickness of, for example, 20 nm and is lattice-matched to the GaAs substrate 11.

[0013] Alternatively, the etching stop layer may include, for example, aluminum gallium indium phosphide [hereinafter (Al _X G
a _1-X ) _0.5 In _0.5 P] layer. In this case, the value of X is selected in the range of X = 0 to about 0.6. The above (Al _X Ga _{1 -X} ) _0.5
When the content of aluminum in the In _0.5 P layer increases, the surface thereof is easily oxidized. Therefore, the value of X is set to 0 to 0.
Set to the range of 6.

Subsequently, for example, MOCVD or MBE
By a method, a zinc selenium (hereinafter, referred to as ZnSe) layer 13 is deposited on the GaInP layer 12 as a compound semiconductor layer.

Next, a second step shown in FIG. 1 (2) is performed. In this step, for example, the ZnS
The first reflection film 14 is formed on the e-layer 13. This first reflection film 14 is formed of a dielectric multilayer film or a metal film. As the dielectric multilayer film, a laminated film of aluminum oxide (Al ₂ O ₃ ) and silicon (Si) or titanium oxide (TiO 2)
₂ ) and silicon oxide (SiO ₂ ).
As the metal film, there is a film made of silver (Ag), gold (Au), or aluminum (Al).

Subsequently, a third step shown in FIG. 1C is performed. In this step, the first reflection film 14 side is bonded to the substrate 15 . This substrate 15 is made of, for example, a sapphire substrate. For the bonding, for example, an adhesive 16 is used. The adhesive 16 only needs to be translucent.
For example, an epoxy resin adhesive is used.

Then, a fourth step shown in FIG. 1D is performed. In this step, the GaAs substrate 11 (portion indicated by a two-dot chain line) is removed by wet etching.
In this wet etching, for example, ammonia (NH ₄ OH): hydrogen peroxide (H ₂ O ₂ ): water (H
_{2 O) = 1: 10:} 10 ( used 25 ° C.) becomes an etching solution. The composition ratio of the etching solution described above is one experimental example, and the GaAs substrate 11
May be any composition ratio as long as it is selectively removed.

When etching is performed using an etching solution having the above composition, the etching rate of GaAs is 4 μm.
m / min, and the etching rate of GaInP is 0.67.
nm / min. Therefore, the etching selectivity is 1: 6.
About 000. Therefore, the etching of the gallium arsenide substrate 11 stops accurately at the GaInP layer 12. The thickness of the GaInP layer 12 was 20 nm, but a thickness of about 10 nm is enough to stop the etching.

In place of the GaInP layer 12, (Al _x
When the Ga _1-x ) _0.5 In _0.5 P layer is used, the etching selectivity decreases by about 10% as compared with the GaInP layer as the content of aluminum (Al) increases. Has a sufficient selection ratio.

Thereafter, as shown in FIG. 1 (5), the GaInP layer 12 (portion indicated by a two-dot chain line) is removed by wet etching. For example, hydrochloric acid (HCl): acetic acid (CH ₃ COOH) =
An etching solution of 1: 4 (10 ° C.) is used. The composition ratio of the etching solution shown above is an experimental example, and ZnS
Any composition ratio may be used as long as the GaInP layer 12 is selectively removed from the e-layer 13.

When etching is performed using an etching solution having the above composition, the etching rate of GaInP becomes 2
00 nm / min. Therefore, the GaInP layer 12 is sufficiently removed by etching for about 30 seconds. Then, the surface of the ZnSe layer 13 is exposed.

Next, a fifth step shown in FIG. 1 (6) is performed. In this step, the second reflection film 17 is formed on the surface of the ZnSe layer 13 by an evaporation method. This second reflection film 17
Is formed of, for example, a dielectric multilayer film or a metal film. As the dielectric multilayer film, for example, aluminum oxide (Al ₂
There is a stacked film of O ₃ ) and silicon (Si) or a stacked film of titanium oxide (TiO ₂ ) and silicon oxide (SiO ₂ ). In addition, silver (Ag), gold (A
u) or aluminum (Al). Thus, a semiconductor thin film composed of the ZnSe layer 13 is formed.

As a method of forming the first and second reflection films 14 and 17, in addition to the vapor deposition method as described above,
It is also possible to use a CVD method, an MBE method, a sputtering method, an ion plating method, or the like.

In the above method for forming a semiconductor thin film, GaAs
A GaInP layer 12 is formed on a substrate 11 and then a MOC
A ZnSe layer 13 is deposited on the GaInP layer 12 by VD or MBE. Therefore, the ZnSe layer 1
3 can be accurately controlled at the atomic level.

In the fourth step, the GaAs substrate 11
Is selectively etched with respect to the GaInP layer 12,
The GaInP layer 12 is selectively etched with respect to the ZnSe layer 13. Therefore, the GaAs substrate 11 and the GaInP layer 12 are completely removed by the respective etchings. In the etching of the GaAs substrate 11, Ga
Over-etching of the InP layer 12 can be ignored, and GaIn
In the etching of the P layer 12, over-etching of the ZnSe layer 13 can be ignored. Therefore, the thickness of the ZnSe layer 13 is controlled at the atomic level.

Further, if the GaAs substrate 11 is etched after the ZnSe layer 13 is grown on the GaAs substrate 11 without forming the GaInP layer 12, if the area is sufficiently small, the flatness and the mirror surface are good. Crystal ZnS
An e-layer 13 can be obtained. However, a large area (for example, 1
When the area becomes about 1 cm × 1 cm), etching unevenness occurs, and the ZnSe layer 13 becomes a single-crystal ZnSe layer 13 having large irregularities. Therefore, as described with reference to FIG.
According to the method in which the etching is performed by providing the ZnSe layer 2, the single-crystal ZnSe layer 13 having excellent flatness and specularity even in a large area is provided.
Can be obtained.

In the above-described formation process, after the GaAs substrate 11 is removed, the GaInP layer 12 is also removed and the ZnS
An e-layer 13 is formed. This ZnSe layer 13 is formed by LCR
When used for a T target crystal, the GaInP
Layer 12 need not be completely removed. For that, GaI
As the influence of the absorption by the nP layer 12 is negligible, the G
It is necessary to form the aInP layer 12 thin.

FIG. 2 shows the relationship between the reflectance and transmittance of the GaInP layer 12 and its thickness. In the figure, the vertical axis shows the calculation results of the reflectance and the transmittance, and the horizontal axis shows the film thickness. In this case, as the first and second reflection films 14 and 17, a dielectric multilayer film composed of an aluminum oxide film and a silicon film is used.

As shown in the figure, the reflectance without the GaInP layer 12 is 77% , and the transmittance is 19% .
When the thickness of the GaInP layer 12 is increased, both the reflectance and the transmittance decrease. When the thickness becomes 20 nm, the reflectance becomes 35% and the transmittance becomes 9% . Therefore, G
As the thickness of the aInP layer 12 decreases, both the reflectance and the transmittance increase. If the film thickness is about several atomic layers, there is almost no difference from the state where the GaInP layer 12 is not formed. For example, if the GaInP layer 12 is 1
If the film thickness is not more than nm , the decrease in reflectance is suppressed to 10% or less. At this time, a decrease in transmittance is suppressed to about 1%.

In FIG. 1, the method of forming the ZnSe layer 12, which is a blue material of the transmission-type LCRT single crystal film, has been described as an example. However, zinc tellurium (ZnTe), which is a green material of the transmission-type LCRT single crystal film, has been described. The layer can also be formed by the same method as described above.

The case of forming a ZnTe layer as a second embodiment will be described with reference to FIG. As shown in FIG. 3, instead of forming a ZnSe layer (13) on the upper surface of a GaInP layer 12 deposited on a GaAs substrate 11, ZnT
An e-layer 18 is formed. The subsequent process is exactly the same as that described with reference to FIG.

When the ZnTe layer 18 is used, GaIn
If the thickness of the P layer 12 is so small that the influence of absorption can be ignored, the GaInP layer 12 may be left.

FIG. 4 shows the relationship between the reflectance and transmittance of the GaInP layer 12 and its thickness. In the figure, the vertical axis shows the calculation results of the reflectance and the transmittance, and the horizontal axis shows the film thickness.
In this case, a dielectric multilayer film made of an aluminum oxide film and a silicon film is used as the first and second reflection films.

As shown in the figure, the reflectance without the GaInP layer is 78% , and the transmittance is 20% . When the GaInP layer is increased, both the reflectance and the transmittance decrease, and when the film thickness becomes 20 nm, the reflectance becomes 45 %.
% , And the transmittance becomes 15% . Therefore, both the reflectance and the transmittance decrease as the thickness of the GaInP layer decreases.
If the film thickness is about several atomic layers, there is almost no difference from the state where the GaInP layer is not formed. For example, if the thickness of the GaInP layer is 3 nm or less, the decrease in reflectance is suppressed to 10% or less. Further, the decrease in transmittance is suppressed to about 1%.

Next, a method of forming a semiconductor thin film in the case where a compound semiconductor layer is formed in a hetero structure will be described with reference to FIG. In the figure, the same components as those described in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 5A, in the first step, the GaAs substrate 1 is formed by MOCVD or MBE, for example, in the same manner as described in FIG.
1 on the GaAs substrate 11 having a thickness of, for example, 20 nm.
A GaInP layer 12 lattice-matching is deposited. Alternatively, an (Al _x Ga _{1 -x} ) _0.5 In _0.5 P layer may be deposited.

Subsequently, for example, MOCVD or MBE
According to a method, zinc magnesium sulfur selenium (hereinafter referred to as ZnMgS) is formed on the GaInP layer 12 as a compound semiconductor layer.
Se) layer 21, ZnSe layer 22, and ZnMgSSe
The layers 23 are sequentially deposited. This deposition is performed continuously. Thus, the ZnMgSSe layer 21 and the ZnSe layer 22
And a ZnMgSSe layer 23 to form a compound semiconductor layer having a heterostructure (here, a double heterostructure).

Next, a second step shown in FIG. 5B is performed. In this step, the ZnMgSSe layer 2 is formed by, for example, a vapor deposition method as described with reference to FIG.
The first reflective film 14 is formed on the third reflective film 3. This first reflection film 14
Consists of the same as described above.

Thereafter, the third and fourth steps are performed in the same manner as described with reference to FIGS. 1 (3) to (5). That is, as shown in (3) of FIG. 5, the first reflection film 14 side is formed on a substrate by using, for example, an epoxy resin adhesive 16.
Paste on 15 The substrate 15 is made of a translucent material, for example, sapphire.

Then, the GaAs substrate 11 (portion indicated by a two-dot chain line) is removed by wet etching. In this wet etching, for example, ammonia (NH ₄ OH): hydrogen peroxide (H ₂ O ₂ ): water (H
_{2 O) = 1: 10:} 10 ( used 25 ° C.) becomes an etching solution. The composition ratio of this etching solution is an example, and G
The numerical value is not limited as long as the composition ratio is such that the GaAs substrate 11 is selectively removed with respect to the aInP layer 12.

In place of the GaInP layer 12, (Al _x
When the Ga _1-x ) _0.5 In _0.5 P layer is used, the etching selectivity is about 10% lower than that of the GaInP layer, but the selectivity is sufficient to stop the etching.

Then, G is obtained by wet etching.
The aInP layer 12 (portion indicated by a dashed line) is removed. For this wet etching, for example, an etching solution of hydrochloric acid (HCl): acetic acid (CH ₃ COOH) = 1: 4 (10 ° C.) is used. The composition ratio of this etchant is an example, and is not limited to the above value as long as the composition ratio is such that the GaInP layer 12 is selectively removed with respect to the ZnMgSSe layer 23.

When etching is performed using an etching solution having the above composition, the etching rate of GaInP becomes 2
00 nm / min. Therefore, the GaInP layer 12 is sufficiently removed by etching for about 30 seconds. Then, the surface of the ZnMgSSe layer 23 is exposed.

Next, a fifth step is performed in the same manner as described with reference to FIG. That is, (4) in FIG.
As shown in FIG.
The second reflection film 17 is formed on the surface of the layer 21.

As described above, a semiconductor thin film having a heterostructure composed of the ZnMgSSe layer 21, the ZnSe layer 22, and the ZnMgSSe layer 23 is formed.

In place of the ZnMgSSe layer 21, Zn
An MgTe layer is formed, and ZnTe layer 22 is used instead of ZnSe layer 22.
A layer is formed and ZnMgTe is used instead of ZnMgSSe23.
It is also possible to form layers. In this case as well, a heterostructure semiconductor thin film including a ZnMgTe layer, a ZnTe layer, and a ZnMgTe layer is formed in the same manner as described above.

In the above method for forming a semiconductor thin film, GaAs
A GaInP layer 12 is formed on a substrate 11 and then a MOC
A heterostructure ZnMgSSe layer 21, a ZnSe layer 22, and a ZnMgSSe layer 23 are deposited on the GaInP layer 12 by the VD method or the MBE method. Therefore, Z
nMgSSe layer 21, ZnSe layer 22, and ZnMgS
Each film thickness of the Se layer 23 can be accurately controlled on an atomic level.

In the fourth step, the GaAs substrate 11
Is selectively etched with respect to the GaInP layer 12,
The GaInP layer 12 is selectively etched with respect to the ZnMgSSe layer 21. Therefore, the GaAs substrate 11
And GaInP layer 12 are completely removed by each etching. When the GaAs substrate 11 is etched, over-etching of the GaInP layer 12 can be neglected.
Over-etching of the SSe layer 21 can be ignored. Therefore, the ZnMgSSe layer 21, ZnSe layer 22, and Z
Each film thickness of the nMgSSe layer 23 can be controlled at the atomic level.

[0049]

As described above, according to the present invention,
Since an etching stop layer is formed between the compound semiconductor substrate and the compound semiconductor layer and the compound semiconductor substrate and the etching stop layer are sequentially removed by etching, there is no need to perform polishing for generating crystal defects. Therefore, it is possible to form a thin film of a compound semiconductor layer having excellent quality without crystal defects. Further, since the compound semiconductor layer is deposited on the etching stopper layer by the metal organic chemical vapor deposition method or the molecular beam epitaxial growth method, the thickness of the compound semiconductor layer can be controlled at the atomic level. Therefore, the compound semiconductor layer can be formed with an accurate thickness. Therefore, the optical characteristics of the compound semiconductor layer can be improved. Further, even when the compound semiconductor layer is formed in a hetero structure, the same effect as described above can be obtained.

[Brief description of the drawings]

FIG. 1 is a process chart of a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between reflectance and transmittance and film thickness.

FIG. 3 is an explanatory diagram of a second embodiment.

FIG. 4 is a diagram showing the relationship between reflectance and transmittance and film thickness.

FIG. 5 is a process chart of forming a semiconductor thin film having a hetero structure.

FIG. 6 is a diagram showing a forming process of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 GaAs substrate 12 GaInP layer 13 ZnSe layer 14 1st reflective film 15 substrate 17 2nd reflective film

Continuation of the front page (72) Inventor Jun Toda 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Kenji Funato 6-35, Kita-Shinagawa-ku, Shinagawa-ku, Tokyo Sony Stock In-company (56) References JP-A-6-204621 (JP, A) JP-A-4-311079 (JP, A) JP-A-4-72608 (JP, A) JP-A-5-335690 (JP, A) JP-A-3-222488 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/205 H01L 21/02 H01L 21/203 H01S 3/23

Claims (2)

(57) [Claims] A first step of forming an etch stop layer on a compound semiconductor substrate and subsequently forming a compound semiconductor layer on said etch stop layer by metal organic chemical vapor deposition or molecular beam epitaxy; A second step of forming a first reflective film on the compound semiconductor layer, a third step of bonding a substrate to the first reflective film side, and after removing the compound semiconductor substrate by etching, the etching stop layer Removing a surface of the compound semiconductor layer by exposing a second reflection film, and forming a second reflective film on the surface of the compound semiconductor layer.
A method of forming a semiconductor thin film. 2. The method for forming a semiconductor thin film according to claim 1, wherein said first step includes forming an etching stop layer on a compound semiconductor substrate, followed by a metal organic chemical vapor deposition method or a molecular beam epitaxial growth method. Forming a compound semiconductor layer having a heterostructure on the etching stop layer, and thereafter performing the second and subsequent steps.