JPS6279613A - Regrowing method for compound semiconductor crystal thin film - Google Patents

Abstract

PURPOSE:To obtain a surface suitable for recrystallization by controlling etching thickness, by preliminarily forming a specific material layer and a GaAs layer which are different in their etching characteristics, and etching GaAs, and then removing the specific material layer by etching. CONSTITUTION:A mask 4 is formed to a groove on GaAs layers 7 and 9 formed on a GaAs substrate 1, where an AlAs layer 8 is inserted by the first epitaxial crystal growth. And, the upper GaAs layer 9 is etched with H2O2/NH4OH solution which does not etch AlAs, so that etching stops before the AlAs layer 8 to obtain a preliminarily designed depth of groove. Then, AlAs 10 at the part of the groove 3 is etched before regrowth with HCl which does not etch GaAs, therefore the etching surface of the GaAs layer 7 becomes flattened to enable a crystalline-easy film 6 to regrow on the groove 3. If the uppermost layer of the film 7 is GaAs or AlGaAs small in Al-mol ratio, the structure of the lower layer is permitted to be of multi-layer composition necessary for forming an element having a desirable function.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a compound semiconductor crystal that improves the quality of the regrown crystal and improves the processing accuracy in a compound semiconductor process that requires the regrowth of an epitaxial crystal. This invention relates to a method for regrowing thin films.

[Conventional technology]

Figure 2 shows how GaAs is grown by, for example, the molecular beam epitaxial method.
After trenching the epitaxial film, AlGaA
This figure shows the process of recrystallization growth of the s epitaxial film, where 1 is a GaAS substrate, 2 is a GaAs epitaxial film that has already been crystal-grown, 3 is a groove dug in the epitaxial film 2, and 4 is 'a3'. 5 is a surface layer to be removed by etching for surface cleaning before regrowth; 6 is a regrown AlGaAs mask;
It is an epitaxial film.

Next, the process will be explained. A mask 4 is formed on the GaAs film 2 on which crystals have been grown in advance, and grooves are formed by etching (Fig. 2(a), (bl)).
. Next, in order to form an epitaxial film on the groove 3, the surface of the processed film is etched to obtain a surface capable of recrystallization growth. Then, an AlGaAs film 6 is formed thereon. Chemical etching or thermal etching is usually used to expose this regrowth surface.

For simplicity, Figure 2 shows grooves formed in the GaAs film 2 and AlGa
Although the case of forming the As film 6 has been described, in general, in order to form an element having a desired function, a multilayer structure film consisting of GaAs and AlGaAs is used as the crystal-grown film 2.6.

[Problem that the invention seeks to solve]

In conventional methods, for example, the regrowth plane on a groove must be a flat and clean surface in order for successful eviaxial growth to occur, which makes it difficult to select an etchant, and it is not always possible to obtain an ideal surface. It wasn't limited. Furthermore, since the etching speed varies depending on the temperature of the etching solution, etc., it has been difficult to accurately control the depth of the grooves.

That is, even if the pattern thickness is controlled with excellent precision as in the case of molecular beam epitaxial films, the precision is lost due to processing.

This invention was made in order to solve the above-mentioned problems, and it is a compound semiconductor crystal thin film that can control the etching thickness with good reproducibility and can obtain an extremely flat surface through crystal regrowth. The purpose is to provide a regrowth method.

[Means for solving problems]

The method for regrowing a compound semiconductor crystal thin film according to the present invention is to preliminarily deposit AlA
S layer or AlGaAs layer with high Al molar ratio and GaA
A 2N film of S is formed, the GaAs layer is etched, and before regrowth, that layer is removed with an etching solution that is selective to AlAs or AlGaAs with a high Al molar ratio. It is something that grows every time.

[Effect]

In this invention, by using molecular beam epitaxial method etc., AlAs or A with a large Al molar ratio is
lGaAs are easy to grow, and they can be easily etched selectively to GaAs or AlGaAs with low Al molar ratios.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

By using molecular beam epitaxy, etc., AlAs or AIGaAs with a high Al molar ratio can be easily grown, and they can be easily etched selectively with respect to GaAs or AlGaAs with a low Al molar ratio. Soviet physics shown in Figure 3 and
Technology of Fixtures 20 161? (1
976) (Sov, Phys, Tech, Phys
.

20 1617 (1976)) with boiling HCl. According to the Al molar ratio dependence characteristic of the tGal-Air As etching rate, it is found that when HCI is used, AlGaAs having an Al molar ratio of about 0.4 or more is selectively etched.

Also Journal of Applied Fixtures 4
4 4172 (1973) (J, App
According to Phys. 44.4172 (1973)), if a H202/NH40H solution is used, GaAs can be
It can be seen that etching can be performed selectively with respect to GaAs. The present invention takes advantage of this fact.

FIG. 1 shows a process in which an AlGaAs epitaxial film is recrystallized after grooves are formed in a GaAs epitaxial film according to an embodiment of the present invention. The lower GaAs layer formed by growth, 8 is the thin AlAs layer, 9 is the upper G
aAs layer, 3 a groove, 4 a mask for cutting the groove 3, 10
is the AlAs removed before regrowth, and 6 is the regrown AlGaAs layer.

Next, the present regrowth method will be explained.

As shown in FIG. 1(a), a mask 4 is placed on a GaAs substrate 1 to form a groove by inserting an AlAs layer 8 through the first epitaxial crystal growth to form a GaAs layer 7.9. The upper GaAs layer 9 is formed by H202/N
Etch with H40H solution. This etching solution is Al
Since As does not etch, even if the etching time becomes long, it stops at the AlAs layer 8. Therefore, a groove with a pre-designed depth is obtained. That is, an etching thickness with good reproducibility can be obtained. Next, before regrowth, Al in the tI3 part is
Etch As1O with HCI. GaAs is MCI
Since the etched surface of the lower GaAs layer 7 is not etched, the etched surface of the lower GaAs layer 7 becomes extremely flat.

Therefore, the film 6 regrown on the groove 3 has extremely good crystallinity.

By placing the AlAs layer 8 in a predetermined position in advance as described above, a groove of the designed depth can be formed and an extremely flat regrowth surface can be obtained.

If this method is used in the molecular beam epitaxial method where the film thickness can be precisely controlled, grooves can be processed without losing the precision, and a high-quality recrystallized film can be obtained.

In the above embodiment, the case where regrowth is performed on grooved GaAs is explained, but the uppermost layer of the film 7 formed in the first growth is made of GaAs or AlGaA with a small Al molar ratio.
s, the underlying structure may be a multilayer structure necessary to form an element having a desired function. Further, the structure of the regrown film 6 is arbitrary.

Furthermore, this method can be used not only for groove processing, but also when a flat surface is required for regrowth, such as when crystal growth is interrupted and the necessary processes are performed, and then regrowth is performed. can.

Furthermore, the present invention can be applied to a process that requires regrowth two or more times, in which case an AlAs layer may be inserted in the growth before each growth.

More generally, any structure or structure can be used as long as the film 9 formed in the initial growth can be selectively etched with respect to the film 8 below it, and the film 8 can be etched selectively with respect to the film 7 below it. It can be any material.

〔Effect of the invention〕

As described above, according to the present invention, in the method for regrowing a compound semiconductor crystal thin film, 11. Taking advantage of the difference in etching properties from lGaAs, the latter film was inserted in a predetermined position during the first epitaxial crystal growth, allowing for highly accurate processing and subsequent regrowth of high-quality crystals. This has the effect of making it possible.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a process of recrystallizing an AlGaAs epitaxial film after grooves are formed in a GaAs epitaxial film according to an embodiment of the present invention, and FIG. 2 is a diagram showing a process in which a similar process is performed using a conventional method. Diagrams showing the process,
FIG. 3 is a diagram showing the dependence of the Al-Ga+□As etching rate on the Al molar ratio X using boiling HCl. l is a GaAs substrate, 2 is a GaAsC pitaxial film, 3
are grooves dug in the epitaxial film, 4 is a mask, 5 is the surface layer removed by etching, 6 is the regrown epitaxial film, 7 is the lower Ga/1. s layer, 8 is an AlAs layer, 9 is an upper GaAs layer, and 10 is an AlAs portion to be removed. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) On the surface to be regrown, an AlAs layer or a two-layer film of an AlGaAs layer with a high Al molar ratio and a GaAs layer is formed in the first epitaxial crystal growth, and after etching the GaAs layer, the next step is performed. A method for regrowing a compound semiconductor epitaxial crystal thin film, which comprises removing the AlAs layer or the AlGaAs layer with a high Al molar ratio by selective etching before crystal growth.