JPS6323651B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is an epitaxial crystal growth method, and is characterized in that the surface of an epitaxial crystal growth substrate is removed during the epitaxial crystal growth process.

It is no exaggeration to say that removing or selectively removing near the surface of a solid material is used in all industrial fields that handle solid materials. Its most sophisticated technology can be found in the electronic industry, especially in the field of semiconductor technology. Particularly recently, it has become necessary to create an uneven structure on the surface of a substrate prior to epitaxial crystal growth in epitaxial crystal growth for semiconductor lasers and optical circuit elements. However, in order to utilize the uneven structure itself in the operating region of the device, especially in these semiconductor lasers made from compound semiconductors, the surface with the uneven structure undergoes thermal deterioration during the substrate heating process before epitaxial growth, so conventional methods cannot be used. This will reduce the reliability of these semiconductor lasers. That is, in order to clarify the problems of the conventional method of epitaxial growth on a substrate having an uneven structure, two types of semiconductor laser manufacturing processes will be explained as examples.

Figure 1 shows a semiconductor seen from the cross section of a Fabry-Perot resonator, which was drawn by the inventor to explain the structure of the semiconductor laser device of Patent Application No. 51-6226, which is effective for horizontal transverse mode control and also for longitudinal mode control. FIG. 2 is a diagram of a laser element. To obtain the structure shown in FIG. 1, stripe-shaped grooves 2 are first formed in the n-type GaAs substrate 11, as explained in detail in the specification of the earlier patent application No. 51-6226.

In this groove, first, a window is made on the surface of the n-type GaAs substrate 11 using photoresist technology to expose the surface at approximately the position where the groove 12 will be formed, and then the photoresist is used as a mask to form a window, for example, CH ₃ OH:
Grooves 12 with a depth of approximately 1.5 μm were etched for 30 seconds with a solution of H ₃ PO ₄ :H ₂ O ₂ = 50:3:3 (volume ratio).
dig. Thereafter, the photoresist is removed from the surface of the n-type GaAs substrate 11, and after cleaning the surface of the substrate 11, it is placed in a liquid phase epitaxial (LPE) furnace, and the n-Al _0.3 Ga _0.7 As layer 13, n-GaAs active layer 14, p-Al _0.3 Ga _0.7 As layer 15, then n-
After forming the GaAs layer 16, a Zu diffusion section 17 is formed by a selective diffusion method, and electrodes 18 and 19 are formed, thereby obtaining the semiconductor laser device shown in FIG. In Fig. 1, a groove 1 is formed in a GaAs substrate 11.
The process for making 2 is performed before LPF growth and outside the LPE reactor. Therefore, the process lacks continuity, and the n-type groove 12 is made at the same time.
The GaAs substrate 11 is exposed to high temperatures in an LPE reactor prior to the LPE process, resulting in thermal deterioration of the substrate surface, and devices made from wafers made by LPE growth on this thermally degraded layer. Reliability will be low.

Another conventional example is the manufacturing process of a semiconductor laser called a so-called buried heterojunction (BH) laser. Figure 2 is a conceptual diagram of a BH laser cavity viewed from a cross section. To make this laser, first place an n-
Al _0.3 Ga _0.7 As layer 13, then n-GaAs active layer 14
A first LPE growth is performed to form a . Then LPE
The crystal is taken out from the reactor, a selective etching mask is formed using photoresist, and the active regions 2b on both sides of the stripe are removed by etching, leaving the striped active region 2a. Next, a p-Al _0.3 Ga _0.7 As layer 15 is formed on this, and then an n-Al 0.3 Ga 0.7 As layer 15 is formed.
A second LPE growth is performed to form a GaAs layer 16, a p-type diffusion region 17 is formed, and an electrode 18,
By making 19, a BH laser is made. The above is the standard manufacturing process for BH lasers. When the striped active region 2a is formed by selective etching in the manufacturing process of the BH laser explained in FIG. 2a is the second
It has the disadvantage of being exposed to high temperatures in the reactor before LPE growth, resulting in thermal deterioration. Therefore, the device life of a BH laser having such a thermally degraded active region 2a is extremely short. Many methods have been devised to create the active region 2a without thermal deterioration in the BH laser manufacturing method. Figure 3 shows an example of a BH laser obtained by a BH laser manufacturing method devised to create an active region 2a with little thermal deterioration.
FIG. 66267 is a wafer cross-sectional view showing one of the embodiments shown in No. 66267. The wafer in Figure 3 is first of n-type.
N-type Al _0.3 with uniform thickness on GaAs substrate 11
Ga _0.7 As layer 13, n-GaAs active layer 14 and p
A first LPE growth is performed to form the -Al _0.3 Ga _0.7 As layer 15p -GaAs layer 316.

Subsequently, the wafer on which the first LPE growth has been performed is taken out of the LPE reactor, a photoresist selective mask is formed on the wafer surface, and selective etching is performed until the n-GaAs active layer 14 appears except for the striped region. Next, the wafer with the photoresist removed is placed in an LPE furnace, and at least the BGaAs layer 316 and the n-GaAs active layer 14 exposed on the surface outside the stripe region are etched back to form the p-Al _0.3 Ga _0.7 As layer 31. Then, the BH structure wafer shown in Figure 3 is completed. However, even with this method, the sides of the stripe region are thermally degraded, and the sides of the exposed nAl _0.3 Ga _0.7 As layer 13 are covered with a second layer.
The disadvantage of poor conformability of the pAl _0.3 Ga _0.7 As layer 31 due to LPE growth and the extremely difficult problem of controlling etchback must be overcome.

The purpose of this invention is to improve the selective etching that clearly appeared in the fabrication of the three semiconductor laser structures.
It is possible to significantly improve the problems of discontinuities in the LPF growth process and thermal deterioration of selectively etched surfaces, and it is possible to achieve improvements in device characteristics, and it can be applied as an epitaxial crystal growth method for manufacturing many devices. The present invention provides an epitaxial growth method that includes a novel surface removal method.

The gist of this invention is to form a thin film of a different material on the entire surface or locally on the surface of a crystal substrate or a substrate that already has an epitaxial layer, and then heat treatment before epitaxial growth to form a thin film on the surface of the thin film material attachment area. The process involves reacting the materials with each other and then epitaxially growing them. In the liquid phase epitaxial method, the reaction layer is taken into an epitaxial growth solution and melted, and in the vapor phase epitaxial method, the reaction layer is removed by a gas phase reaction, and then epitaxial growth is performed.

As an example, the present invention will be explained in detail based on a specific example in which the present invention is applied to a method of manufacturing a semiconductor laser device having the structure shown in FIG.
FIG. 4 shows the important points when manufacturing the structure of the semiconductor laser device of the above-mentioned patent application No. 51-6226 by the present inventor by effectively utilizing the surface removal method of the present invention, particularly the selective removal method. It is a diagram showing the process,
Finally, a semiconductor laser device having the structure shown in FIG. 1 is obtained. Let's explain the manufacturing method step by step. First, as shown in FIG. 4a, a Zn thin film 41 is formed on an n-type GaAs substrate 11 with the (100) plane as the surface by vacuum evaporation, etc., and grooves 12 (see FIG. 1) are dug as stripe regions at positions. The Zn thin film 41 is removed using a photoresist and selective etching technique, leaving the Zn thin film 41a only on the surface. Zn thin film 4
It should be noted that the method of the present invention is not used in the step of removing 1.

In this way, the Zn thin film 41a was selectively formed.
A GaAs substrate (Fig. 4a) was prepared as a substrate crystal in an LPE growth furnace, and when the temperature rose to the crystal growth start temperature, the Zn thin film 41a on the GaAs substrate 11 came into contact.
Reacts with the GaAs surface, depending on the thickness of the Zn thin film 41.
The surface of the GaAs substrate 11 is melted.

This stage is shown in Figure 4b. GaAs substrate 11
Only the part where the Zn thin film 41a on the surface was attached,
A solution phase 42 consisting of Zn, Ga and As is formed.
When the crystal growth start temperature is 750°C, if the holding time at 750°C is longer than 20 minutes, the GaAs surface reacts with the Zn thin film 41a, as expected from the Ga-As-Zn ternary phase diagram. When the thickness of the Zn thin film is 1 μm,
The GaAs surface was approximately 2 μm thick and melted in response to the Zn thin film. After maintaining the crystal growth temperature at 750°C for 30 minutes, n-
Al _0.3 Ga _0.7 As layer 13, nGaAs active layer 14, pAl _0.3
By forming the Ga _0.7 As layer 15 and then the nGaAs layer 16, a double heterojunction laser wafer having the structure shown in FIG. A semiconductor laser device is obtained.

When the LPE growth solution for forming the n-Al _0.3 Ga _0.7 As layer 13 comes into contact with the n-type GaAs substrate 11, the solution layer 42 melts into the LPE growth solution. At this time, the solution phase 42
The Zn inside is taken into the LPE growth solution, but the taken in Zn easily scatters from the LPE growth solution, and the segregation coefficient of Zn into the LPE crystal is small, so even if Zn gets into the LPE growth solution, n-type Al _0.3 Ga _0.7
It is easy to grow an As layer.

In the semiconductor laser device shown in FIG. 1 obtained by the method of the present invention, a solution phase 42 containing Ga, Zn, and As is applied to the surface of the n-type GaAs substrate 11, which will become the stripe region, before crystal growth. GaAs located under the stripe region prior to LPE growth.
The board will not deteriorate due to heat.

Therefore, the reliability of the semiconductor laser device manufactured in this way and having the structure shown in FIG. 1 is high. In addition, this invention enables the creation of fine patterns that cannot be obtained using the etchback method normally used in LPE growth, that is, the method of melting the crystal surface with a pre-prepared melt and then performing LPE growth.
It can be made before LPE growth, making it possible to realize devices with complex structures. This will be specifically explained with reference to the case where a semiconductor laser device having the structure shown in FIG. 1 is obtained. The structure shown in Figure 1 can be obtained by using the usual etch-back technique, for example, by first contacting the substrate with an unsaturated n-Al _0.3 Ga _0.7 As layer growth solution with the same width as the groove to be formed. Only the predetermined groove portions are etched back, and then a saturated n-Al _0.3 Ga _0.7 As layer growth solution is brought into contact with the entire surface of the substrate to perform LPE growth. In this case, the width of the groove is 10 μm, and it is extremely difficult to place the solution within a width of 10 μm due to the influence of the surface tension of the solution, making it almost impossible to control the etchback. However, according to the present invention, as shown in the examples, a thin film is formed on the substrate in advance,
By reacting this thin film with the substrate and then removing the reaction layer, a semiconductor laser device having the structure shown in FIG. 1 can be easily obtained.

Next, an example in which the method of the present invention is applied to the manufacture of the BH laser shown in FIG. 2 will be described. Fifth
The figure is a cross-sectional view of a wafer showing important steps in which the surface removal method of the present invention is introduced into the BH laser manufacturing process. FIG. 5a shows an n-type GaAs substrate 11 grown on an n-type GaAs substrate 11 by the first LPE growth as explained in FIG.
- Al _0.3 Ga _0.7 As layer 13 and then n-GaAs active layer 14 are grown by LPE, and then Zn thin film 51 is grown by n-GaAs.
Only the portion corresponding to the active region 2a that is formed on the surface of the active layer 14 and then becomes a striped oscillation region
5 is a diagram showing a stage in which the Zn thin film 51 is removed using a photoresist technique and a selective etching technique. FIG. The wafer shown in FIG.
A solution phase 52 is formed by melting the n-GaAs active layer 14 only at the part where Zn 1 is attached (when the Zn thin film layer is thick, in addition to the n-GaAs active layer 14, the n-Al _0.3 Ga _0.7 As layer 13 underneath is also melted). The state shown in FIG. 5b is reached. If the thickness of the nGaAs active layer 14 is about 0.2 μm,
By depositing 100 Å of Zn, a reaction layer sufficient to easily remove the nGaAs active layer 2b (see FIG. 2) is obtained.

Thereafter, when the crystal in the state shown in FIG. 5b is brought into contact with the LPE solution in which the pAl _0.3 Ga _0.7 As layer 15 is grown, the solution phase 52 is mixed with the LPE solution. Next, by slow cooling, a p-Al _0.3 Ga _0.7 As layer 15 grows. Furthermore, a z-GaAs layer 1 is formed on this p-Al _0.3 Ga _0.7 As layer 15.
By growing 6, LPE wafer for BE laser is completed. (Fig. 5c) The BH laser thus completed is the second LPE.
During growth, Ga except for the stripe active layer 2a,
Due to the presence of a solution phase consisting of Zn and As,
Even during high-temperature heating, the growth from the first LPE growth layer
Since the amount of evaporation of As is suppressed, the first LPE growth layer is not thermally degraded.

Therefore, the BH laser made in this way has extremely high reliability.

The method for manufacturing a semiconductor laser device and BH laser having the structures shown in FIGS. 1 and 2 has been described above as an example to which the surface removal method of the present invention is applied. In the above embodiments, a thin film of Zn, which is a different material, is formed on the surface of a crystal substrate or a substrate that already has an epitaxial layer, and the thin film and the surface of the substrate are reacted in the next LPE crystal growth process.
Later, we demonstrated a new liquid phase epitaxial method in which this reaction layer was melted in a solution for LPE crystal growth. According to the present invention, the problem of thermal deterioration of substrate crystals can be significantly improved, and highly reliable devices can be easily manufactured. In the examples, GaAs or AlxGa ₁ -xAs material is used for the crystal substrate of the present invention, Zn is used as the thin film material, and GaAs or AlxGa 1 -xAs material is used for the crystal substrate of the present invention.
The epitaxial growth of AlGaAs is shown.
However, it is clear that the method of the present invention is not limited to substrate materials and thin film materials.

If the thin film material is undesirable as an impurity in the liquid phase epitaxial layer, cover the substrate with another solution similar to the epitaxial solution not used for liquid phase epitaxial growth in advance to dissolve the layer that reacts with the thin film; This dissolving solution may be removed and a liquid phase epitaxial solution may be placed on the substrate for growth. In addition, in the example, the state after the reaction of the thin film material and the material whose surface is to be removed was heated to a high temperature showed a liquid phase, but this reaction layer is not limited to a liquid phase, but can also be in a solid phase. The same effect can be obtained. In an example where the reaction layer is a solid phase, Ni is used instead of Zn. Ni reacts with GaAs to form NiAs.
Since the reaction between GaAs and Ni proceeds as a solid phase reaction, an extremely uniform reaction layer can be obtained, which is convenient for applying the present invention. To apply the present invention to the AlGaAs surface, if Al is used as a thin film-like dissimilar material,
The same effects as in this example using a Zn thin film on GaAs can be obtained. Furthermore, in the above embodiments, two types of semiconductor lasers were manufactured using the LPE growth method, but when vapor phase epitaxial growth is used, the reaction phase is gas-etched and then vapor phase epitaxial growth is performed. Just do it. In the case of vapor phase growth, for example, if an In thin film is formed on GaAs and heated to about 500°C, the In melts the GaAs surface.
Next, by flowing HCl gas, the molten components are easily etched away, exposing the clean GaAs surface. At a heating temperature of 500° C., etching of the GaAs surface by HCl does not normally proceed, but by using the method of the present invention, vapor phase etching proceeds easily and good epitaxial growth is achieved.

As described above, the epitaxial method of the present invention enables selective surface removal in an epitaxial reactor prior to epitaxial growth, and during epitaxial growth using a compound semiconductor material as a substrate, surface removal during heating of the substrate before growth is possible. It is useful as an epitaxial growth method in many fields since it can significantly reduce the problem of thermal deterioration. It goes without saying that it is particularly suitable for manufacturing optical devices using - group compounds by epitaxial growth.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of a double hetero semiconductor laser seen from the hexagonal plane, which can be manufactured by effectively utilizing the present invention, and Figure 3 is a conventional manufacturing method for the semiconductor laser shown in Figure 2. The cross-sectional views of the wafer, Figures 4 and 5, drawn to explain the
FIG. 3 is a wafer cross-sectional view showing a manufacturing process of a heterostructure wafer when the present invention is applied to form the double heterostructure semiconductor laser shown in FIGS. 11 is n-type GaAs substrate, 13 is n-type Al _0.3 Ga _0.7
As layer, 14 is n-type GaAs active layer, 15 and 31
is a p-type Al _0.3 Ga _0.7 As layer, 16 is an n-type GaAs layer 17
and 18 is an electrode metal, 12 is a striped groove formed in the GaAs substrate 11, 2a is a striped n-GaAs active layer to be embedded, 2b is an nGaAs active layer outside the stripe area to be removed, 316
is a p-GaAs layer, 41 and 51 are Zn thin films, 42
and 52 indicate a solution phase which is a reaction layer generated by reacting with the Zn thin film 41 or 51, respectively.

Claims (1)

[Claims] 1. A method for growing a compound semiconductor epitaxial crystal on a crystal surface of a compound semiconductor substrate, in which a first material layer having a composition or constituent element different from that of the material constituting the substrate crystal is formed on the entire or part of the surface of the substrate crystal. forming a reaction layer by heating in an epitaxial growth furnace to cause the substrate crystal to react with the material layer formed on its surface; and contacting the substrate crystal with a liquid phase epitaxial growth solution to form a reaction layer. A second step in which the reaction layer is removed and epitaxial crystal growth layers are successively formed on the surface.
An epitaxial crystal growth method comprising the steps of: