JPH0496320A - Method of growing thin film semiconductor crystal - Google Patents

Abstract

PURPOSE:To stop propagation of high-density dislocation occurring in a III-V compound semiconductor thin film layer in the middle of growth and make it possible to make a III-V compound semiconductor thin film having a low- dislocation-density surface by forming a super lattice layer, which consists of two sorts of III-V compound semiconductor thin films formed alternately, or a structure, which includes lattice deformation, in the intermediate section of the III-V compound semiconductor thin film layer at a low substrate temperature. CONSTITUTION:When a super lattice layer 3 is introduced in a compound semiconductor thin film layer 2, sufficient deformation to bend dislocation in the lower part of the compound semiconductor thin film layer 2 can be included in the super lattice layer 3, with occurrence of mis-fit dislocation in the upper interface of the super lattice layer 3 suppressed, by forming the super lattice layer 3 at 400 deg.C or lower. Hence almost all the propagation of dislocation in the lower section of the semiconductor thin film layer 2 can be prevented with the super lattice layer 3 and a low-dislocation-density surface layer (the upper part of the semiconductor thin film layer 2) can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for depositing a high quality III-V compound semiconductor thin film layer onto a single crystal substrate such as Si or GaAys.

[Prior art] 111-V group compound semiconductors are used as materials for optical devices such as semiconductor lasers and light emitting diodes, and as materials for transistors that can operate at ultra-high speeds. Among them, its importance has been increasing in recent years1. It's coming.

Focusing on GaAs and Al2GaAs, which are the most important materials among these III-V compound semiconductor materials, the various devices described above are made of 10μ
High quality GaAs, At! It is formed in a thin layer of GaAs.

Although these devices have overwhelmingly superior characteristics compared to those using Si, in terms of the electronic device sector of the semiconductor industry, the share of these materials is far behind Si, which is the mainstream. It's only a small amount in comparison. The reasons for this can be summarized into the following three points.

(i) The substrate material (G, aAs) is expensive.

(if) The mechanical strength of the substrate material (GaAs) is low.

(iii) The crystal quality of the substrate material (GaAs) is insufficient compared to Si.

The same situation applies to other III-V compound semiconductor materials such as InPs InGaAs.

Regarding the above problems, it is overwhelmingly cheaper than III-V compound semiconductors, has higher crystallographic perfection,
Using Si as the substrate, which also has excellent mechanical strength,
On top of that, thin GaAs (or III-V such as InP)
group compound semiconductor layer) and convert it into a new III-
A method for using it as a group V compound semiconductor has been proposed, and much research has been conducted so far.

However, for example, if we talk only about the growth of GaAs on a Si substrate, there are differences between the two in terms of lattice constant, coefficient of thermal expansion, and crystal structure (mainly the polarity of covalently bonded crystal or ionic bonded crystal). There is a big difference. For this reason, epitaxially grown III-V compound semiconductors have many misfit dislocations due to lattice mismatch, threading dislocations caused by strain caused by cooling from the growth temperature, and other causes, and their crystallographic quality is poor. Extremely low.

For this reason, even if various devices are made using GaAs grown on a Si substrate, its characteristics are low, and at present, when talking about III-V compound semiconductor substrates such as GaAs, compared to Si substrates, The dislocation density of the substrate itself is still high, which leads to threading dislocations in the thin film layer.
The current situation of deteriorating the crystallinity of the epitaxial layer cannot be overlooked.

Various methods have been studied to reduce dislocation density, but the most effective methods include association and annihilation of dislocations through heat treatment, and prevention of upward propagation of dislocations by introducing a superlattice layer. It is. Here, the superlattice layer refers to a multilayer epitaxially grown layer in which each layer has a small thickness of about 100A. In addition, when the thickness of each layer is relatively thick, up to several hundred, it is called an alternating layer.

By the way, the best result achieved so far by the above method was to grow GaAs of about 4 μm on a Si substrate, and the dislocation density was 1 to 2 x 10'/cm.
It is. This value is approximately 10 times higher than that of a normal GaAs substrate.
00 times, and it is almost impossible to use it for practical purposes in producing devices that take advantage of the original characteristics of III-V compound semiconductors.

If a dislocation-free GaAs thin film can be grown on Si, the share of III-V compound semiconductors in the semiconductor market can be expected to increase dramatically, and its effects include saving scarce resources such as As. □This would be significant, but for the reasons mentioned above, this technology has not yet been realized.

[Problems to be Solved by the Invention] In the growth of III-V group compound semiconductors on Si single crystal substrates, the introduction of a superlattice layer as described above is known as an effective method for reducing dislocation density.

FIG. 4 shows, as an example, G grown on a Si substrate 1.
This is a schematic cross-sectional view showing how dislocations 4 propagate when a superlattice layer 3 consisting of an InGaAs thin film 3a and a GaAs thin film 3b is formed in the aAs thin film layer 2.

Due to the strain in the superlattice layer 3 and the interaction with misfit dislocations 6 formed at the interface of the superlattice layer 3, most of the dislocations 4 are bent in a direction parallel to the substrate 1 surface, and upward propagation is blocked. be done. The bending 5 of the dislocations 4 is thought to occur due to the strain in the superlattice layer 3 or the interaction with the misfit dislocations 6 at the interface of the superlattice layer 3. There is a limit to lowering the dislocation density of layer 2, and the dislocation density cannot be lowered sufficiently.

The reason is that crystal growth of III-V compound semiconductors such as GaAs usually requires a substrate temperature of at least 600°C! -1 At these temperatures 1. When the thickness of the molecular layers constituting the strained superlattice layer exceeds the critical film thickness, misfit dislocations easily occur.1-1 Misfit dislocations are generated at the J interface of the superlattice layer 3 in order to alleviate the lattice strain. This is because misfit dislocations generate new dislocations 4 penetrating toward the surface due to interaction or the like. Although it is possible to suppress the occurrence of such misfit dislocations by appropriately selecting the thickness of the thin film of the superlattice layer 3 and the components of the superlattice layer 3, it is possible to suppress the occurrence of such misfit dislocations. 3 becomes smaller, bending 5 of dislocations is less likely to occur, and the proportion of dislocations 4 penetrating through the superlattice layer 3, 5, and further propagating to the surface of the thin film layer 2 increases.

The purpose of the present invention is to provide an I
When forming an IN-V group compound semiconductor, III-
The high-density dislocations generated in the group V compound semiconductor thin film layer are stopped mid-propagation, and the surface is formed with a low-dislocation-density III-
The purpose of the present invention is to provide a technology that enables the production of Group V compound semiconductor thin films.

[Means and effects for solving the problems] In order to solve the above problems, the present invention has the following configuration.

That is, in the thin film semiconductor crystal growth method according to the present invention, IIN-V group compound semiconductor and J-
In growing and forming films of these mixed crystals, two different types of III-V compound semiconductor thin films are alternately laminated in the middle part of this semiconductor thin film layer, which is called an alternating layer or a superlattice layer. The structure containing lattice strain was heated to 400℃.
It is characterized by being formed at a low substrate temperature of:

The method of the present invention will be explained in detail below with reference to the drawings.

The present invention is based on the previously published Japanese Patent Application Laid-open No. 2-22262.
1. The technique described in Japanese Patent Application Laid-open No. 2-222628 (1999) can be easily achieved by applying 8. This is a method to obtain a thin film on a substrate by growing crystals of 1. This provides the advantage that it is possible to significantly reduce the substrate temperature.

When this alternate supply growth method is applied to the present invention, as shown in FIG.
By alternately supplying the group original layer 2B, the III-V compound semiconductor is crystallized fi=8, and the III-V compound semiconductor thin film layer 2 is obtained.

By using such a growth method to grow a superlattice layer formed in a semiconductor thin film layer, a superlattice J! 1! The present invention's claim that the formation of (or alternating layers) is performed at a low temperature (400° C. or lower) becomes possible. By forming the superlattice layer (J-take alternating layer) in the middle part of the semiconductor thin film layer under such low temperature conditions, the critical film thickness can be reached.1. However, a strained superlattice layer or alternating layers can be obtained without generating misfit dislocations, and as a result, a semiconductor thin film layer with no surface strain can be obtained on a carved crystal substrate.

FIG. 2 is a cross-sectional view schematically showing the state of dislocation propagation in the semiconductor thin film layer 2 when the superlattice layer 3 is introduced into the compound semiconductor thin film layer 2 at a low temperature according to the present invention. . Forming the superlattice layer 3 at a temperature of 400° C. or less suppresses the occurrence of misfit dislocations at the upper interface of the superlattice layer 3 while allowing the formation of the superlattice layer 3 in the lower compound semiconductor thin film layer 2. Since it is possible to contain enough strain to bend dislocations, the superlattice layer 3 can completely prevent the propagation of dislocations in the semiconductor thin film layer 2 below, and the surface layer with a low dislocation density can be completely blocked. (Upper semiconductor thin film layer 2) is obtained.

[Example] Shown in Figure 1! -Alternate supply (Japanese Patent Application Laid-Open No. 62-222628
), a GaAs thin film layer is grown on a 51 substrate using a III-V group compound semiconductor from a group III raw material and a group II raw material.
Examples 1 to 1 will be described in which a superlattice layer consisting of a thin film is introduced.

Normally, crystal growth of 111-V group a compound semiconductors such as GaAs requires a substrate temperature of at least 600°C as described above, whereas this growth method is almost impossible with normal crystal growth methods. Crystal growth becomes possible at a low temperature of about 300°C.

FIG. 3 shows S
In the GaAs thin film layer 2 grown on the i-substrate l by alternately supplying Ga and As molecular beams, Ga.

I grown by alternating supply of In and As molecular beams
n01Ga0. This diagram schematically shows the introduction of a superlattice layer 3 composed of an As thin film 3a and a GaAs thin film 3b grown by alternately supplying Ga and As molecular beams. This figure 3 shows substantially the same contents as the above-mentioned figure 2, but the difference is that figure 2 emphasizes the effect of suppressing dislocation propagation without particularly limiting the material. On the other hand, this FIG. 3 directly shows the embodiment itself. Moreover, In, Ga, As thin film 3a and Ga
The thickness of each As thin film 3b was 100A, and the period was 10 periods.

The results of cross-sectional observation of the obtained semiconductor thin film layer using a transmission electron microscope show that most dislocations are bent at the lower interface of the superlattice layer 3 and are bent at the upper part of the superlattice layer 3 as seen in high-temperature growth. No misfit dislocations at the interface were observed.

These effects were observed not only in GaAs but also in other III-V group compound semiconductor materials, and were also observed in cases where single crystal substrates other than Si, such as GaAs, were used.

The superlattice layer 3 grown at a low temperature as described above is extremely effective in preventing the propagation of dislocations in the III-V compound semiconductor thin film layer 2 and obtaining a surface of the epitaxial layer (semiconductor thin film layer 2) with a low dislocation density. was confirmed.

In order to achieve such low-temperature growth, it is important to reduce the substrate temperature during growth by using an alternate supply method of raw materials.

The embodiment described above is one embodiment of the present invention, and it is clear that the present invention has various other modifications, and the embodiment described above is not intended to limit the present invention in any way.

[Effects of the Invention] As explained above, in a thin film semiconductor crystal growth technique for growing a III-V compound semiconductor on a single crystal substrate such as Si or GaAs, dislocations occurring in a III-V compound semiconductor thin film layer can be avoided. Since the propagation of can be inhibited by the superlattice layer grown at a low temperature in the middle portion of the semiconductor thin film layer, a III-V compound semiconductor thin film layer with a low dislocation density on the surface can be easily produced.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing how a III-V compound semiconductor is grown on a substrate by alternately supplying Group III raw materials and Group II raw materials, and Figure 2 is a schematic diagram showing how a III-V compound semiconductor is grown on a single crystal substrate according to the method of the present invention. A schematic diagram showing the state of dislocation propagation when a superlattice layer is formed in the middle part of a III-V group compound semiconductor thin film layer. In a GaAs thin film layer grown on
A schematic diagram showing how a superlattice layer composed of an As thin film and a GaAs thin film is introduced. FIG. 3 is a schematic diagram showing dislocation propagation when a superlattice layer consisting of a GaAs thin film and a GaAs thin film is formed. l...Si single crystal substrate, 2...GaAs thin film layer, 3...-In,, Ga,, As thin film and GaAs
A superlattice layer composed of a thin film, 3a...In, ,Ga,,As thin film, 3b...
・GaAs thin film.

Claims (1)

[Scope of Claims] A thin film semiconductor crystal growth method for obtaining a III-V compound semiconductor thin film layer by growing a III-V compound semiconductor and a mixed crystal thereof on a semiconductor single crystal substrate, comprising: A structure containing lattice strain called a superlattice layer or alternating layer, in which two different types of III-V group compound semiconductor thin films are alternately laminated in the middle part of the compound semiconductor thin film layer, is created at a low substrate temperature of 400°C or less. A thin film semiconductor crystal growth method characterized by forming.