JPH02221196A - Formation of thin film of iii-v compound semiconductor - Google Patents

Abstract

PURPOSE:To improve the surface smoothness and quality of a thin film of a III-V compd. semiconductor by feeding starting material for a group V element to an Al layer formed on a crystal of a group IV element and growing the thin film on the resulting layer of a III-V compd. crystal as a buffer layer. CONSTITUTION:An Al layer is formed on a crystal 1 of a group IV element and starting material for a group V element such as AsH3 is fed to the Al layer to convert the Al layer into a layer 3 of a III-V compd. (e.g. AlAs) single crystal. A thin film 4 of a desired III-V compd. (GaAs) semiconductor is then formed on the layer 3 as a buffer layer.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention is directed to the formation of a III-V semiconductor epitaxial film of high quality and excellent surface flatness on a group III raw conductor crystal.
The present invention relates to a technique for forming a II-V compound semiconductor thin film.

(Prior art) Currently, Ga
Attempts are actively being made to form single-crystal thin films of former Group V compound semiconductors represented by As. This is because if such a thin film structure can be formed, high-performance III-V compound semiconductor devices can be fabricated on inexpensive Si substrates, and the high thermal conductivity of Si can be expected to improve the performance of optical devices. It is. Furthermore, selectively III + V on the Si substrate
This is because if a group compound semiconductor single crystal thin film can be formed, it will be possible to form a Si ultra-high integrated circuit and a III-V group compound semiconductor ultra-high-speed device or optical device on the same substrate, which is expected to lead to the development of new high-performance devices. .

However, III-V compound semiconductor crystals are
It is a polar crystal made of two types of elements, Group 1 and Group 2, whereas the Group 2 bioconductor single crystal substrate is a nonpolar crystal made of a single element. Therefore, when trying to epitaxially grow a III-V compound semiconductor single crystal thin film on a group III bioconductor single crystal substrate with a commonly used (100) plane orientation, one phase of group III and group It is only recently that it is possible to reliably obtain a so-called single-domain single-crystalline thin film in which the phase of group III and group V arrays are aligned in the front substrate plane. It was difficult until then.

A magazine was devised to solve this problem [Japanese Journal of Applied Physics (Jpn, J, Appl, Phys, ) J
This is a method called the "two-stage growth method" described in Vol. 24, No. 6 (1985), pages L391-393. That is, the temperature of the Si single crystal substrate was set to a low temperature of 450°C or less, and after depositing a fine polycrystalline or amorphous GaAs buffer layer by about 200 people, the temperature of the Si single crystal substrate was set to the normal growth temperature. 600 for the above document
This is a method of growing a GaAs single crystal thin film at .

This method has made it possible to reliably obtain single-domain single-crystal thin films. The fine polycrystalline or amorphous GaAs thin film is annealed while being heated to 600° C. to become a single crystal. The results of the above literature are MO
CVD (Metal Organic Chemistry)
cal vapor deposition) method, but has since been replaced by the MBE (Molecular Vapor Deposition) method.
It was confirmed that the two-step growth method is similarly effective in the em'Epitaxy method.

Now, in the two-step growth method, a GaAs buffer layer is first grown at a low temperature, but subsequent research has revealed that this buffer layer grows in an island shape. In order to obtain a single domain single crystal, the crystal orientations of each island do not need to initially match, but it is necessary that the islands are sufficiently small and in contact with the surrounding islands. It is thought that subsequent annealing causes rearrangement to the dominant orientation, resulting in a single domain. Also, even if no reordering occurs, 1 during GaAs growth.
It is also possible that only the negative direction remains and becomes a single domain, but even in this case, annealing at high temperature is necessary. This is because the buffer layer grown at a low temperature contains many defects, so it is necessary to anneal it to restore crystallinity while it is still thin, about 200 layers.

On the other hand, attempts have recently been made to directly grow a single crystal film at low temperatures by alternately supplying a group III raw material and a group raw material. For example, magazines [Applied Physics Letters (Appl, Phys, Lett,
) J Vol. 53 No. 24 (1988) No. 2435-
III in high vacuum as described on page 2437.
MEE (Migr
A thick single-domain single-crystalline film was obtained by directly growing a single-crystalline film of approximately 400 layers at a low temperature using the cation Enhanced 9itaxy method, and then by MBE growth at the same temperature. In this case, it is thought that only the dominant orientation remains during growth, forming a single domain.

(Problems to be Solved by the Invention) Let us consider the above-mentioned problems of the prior art in the epitaxial growth method of III-V group compound semiconductor thin films.

From the viewpoint of device applications of semiconductor thin films, it is important to improve crystal quality and surface flatness in addition to single domain formation. In order to obtain a flat surface, the smaller and denser the islands are, the better in island growth. Furthermore, layered growth is most desirable. Furthermore, a grown layer on a 5i (100) substrate usually contains far more dislocations, stacking faults, etc. than expected from the lattice mismatch between the substrate and the grown layer. Since most of these are thought to be generated between the islands, layered growth is desirable in order to improve crystal quality.

In the case of the two-step growth method, when the growth temperature of the buffer layer is low, the size of the islands tends to be small and the density becomes high.

However, if the temperature is too low, the film will have extremely poor crystal quality, including many twins and stacking faults, and will even become amorphous, making it extremely difficult to achieve layered growth. Moreover, in reality, it is necessary to perform annealing to recover crystallinity before the film thickness is sufficient. However, even though we have grown a flat buffer layer at low temperatures, if we anneal too much, large irregularities will occur on the surface due to solid-phase growth, and if we do not anneal insufficiently, the crystal quality will not improve sufficiently. There was a problem.

On the other hand, in the method of alternately supplying the H1 group raw material and the V group raw material, since the crystallinity is relatively good from the initial stage of growth, there is no need to anneal the film while the film is thin, unlike the two-step growth method. Therefore, a sufficiently thick single-crystal film can be grown at a low temperature first, and then annealing can be performed to improve crystallinity if necessary, and there is no need to worry about large irregularities occurring on the surface. However, even with this method, the initial stage of growth is still island-like growth, and there is a problem in that layered growth cannot be realized and fundamental improvements in crystallinity and flatness cannot be expected.

Furthermore, a 5i (100) plane, which facilitates crystal growth, is usually used as a substrate, but in this case, dislocations generated at the interface between the substrate and the growth layer easily extend to the upper layer and become threading dislocations. A common problem was that in order to obtain this, it was necessary to grow a thick film of several μm or more.

The purpose of the present invention is to overcome the drawbacks of the prior art, and
High quality III- conductor crystal with excellent surface flatness
III + V forming a group V semiconductor epitaxial film
The purpose of the present invention is to provide a technology for forming thin films of group compound semiconductors.

(Means for Solving the Problems) The present invention provides a method for forming a thin film of a III-V compound single-conductor conductor on a group (III) crystal, including a step of forming a thin Al layer on the group (III) crystal, and a step of forming a thin Al layer on the group (III) crystal. a step of supplying a V group raw material on top and converting the Al layer into a III-V group compound single crystal having Al as a group III constituent element; It forms a semiconductor thin film. In another method, a step of supplying an organic volatile compound containing Al on the Group III crystal to form a thin Al layer, and supplying a Group V element or a volatile compound of a Group V element on the Al layer, After the step of converting the Al layer into an ILV group compound single crystal layer in which the group III constituent element is Al, a desired III-V group compound semiconductor single crystal thin film is formed.

Furthermore, it is more effective to use the (111) plane as the plane orientation of the group II crystal.

Further, it is preferable to form the Al layer at 4006C or less.

As the Al raw material, it is preferable to use an organometallic compound in which Al and a halogen element are combined from the viewpoint of selectivity.

Furthermore, in the early stage of growth of the former group V compound semiconductor thin film, it is preferable to alternately supply the group III raw material group raw materials from the viewpoint of lowering the growth temperature.

(Function) One reason for the island-like growth of GaAs on a Si single crystal substrate is the large difference in lattice constant between Si crystal and GaAs crystal, and the large difference of 4% in growth on the (100) plane. This is thought to be due to the difference. However, as explained in the magazine "Applied Physics" Vol. 57, No. 11 (1988), pp. 1754-1759, ME
Even if Ga and As are alternately supplied at 150° C. using the E method, island-like growth occurs from the very early stage of one molecular layer of GaAs or less. Moreover, although the first one atomic layer is two-dimensionally attached to the entire surface, as soon as the second atomic layer is attached, it changes to an island shape and the surface coverage decreases. Furthermore, even when GaP is grown on a Si single crystal substrate, which should have a sufficiently small lattice constant difference of 0.37%, island-like growth occurs (Journal of Applied Physics (J, Appl, Phys, )).
J Vol. 64 No. 9 (1988) No. 4526-45
page 30).

Therefore, the reason for island-like growth in the growth of III-V compound semiconductor crystals on the parent crystal substrate is not simply due to the stress caused by the difference in lattice constants, but rather the surface group III atoms and III It is thought that the chemical bonding state between group or V group atoms, and furthermore the chemical bonding state between group III and V atoms, is deeply involved.

Based on these considerations, the first Al
A raw material containing Al is supplied to form an Al layer of several atoms to several tens of atoms, and this Al layer is formed by forming an Al layer containing Al in which the group III constituent element is Al.
After converting into a II-V group compound single crystal layer, the desired II
This is a method of forming an IV group compound semiconductor thin film.

The 5i-Al bond is extremely strong and difficult to break compared to the 5i-Ga, 5i-As, etc. bonds, so the Al layer formed on the Si single crystal substrate is flat and continuous from the beginning of its growth. It becomes a membrane. However, in order to suppress the alloying reaction between Si and Al, it is desirable to form this Al layer at a low temperature of 400° C. or lower. In this respect, low-temperature growth is possible when an organic volatile compound is used as the Al raw material. Subsequently, a group V element or a volatile compound of a group V element, such as As
When a volatile compound of is supplied, As generated by decomposition diffuses through the thin Al layer and reaches the interface with the Si substrate, and AlAs crystals grow epitaxially from the interface. As a result, the Al layer is converted into a continuous film of several tens of thin flat AlAs single crystals. Furthermore, using this AlAs film as a buffer layer, a desired III-V original crystal thin film is then grown, but at this time it is necessary to set the growth temperature high to improve crystal quality. However, since the bonds of Al and -As are stronger than the bonds of other III-V bx compounds such as Ga-As, large irregularities do not occur on the surface of the AlAs layer by solid phase growth. Furthermore, at least until a sufficient thickness is obtained, volatile compounds of group III elements and V
By alternately supplying a group element or a volatile compound of a group V element, the growth temperature can be kept low. Therefore, a high quality III with excellent surface flatness can be grown on a group III bioconductor single crystal substrate. - A method for forming a III+V group compound semiconductor thin film for forming a V group semiconductor epitaxial film can be realized.

Furthermore, another invention for specifying the (111) plane as the plane orientation of the group II crystal was obtained based on the following considerations. When the (100) plane is used as a group III crystal, dislocations existing on the (111) plane called 60° dislocations occur at the interface between the crystal and the growth layer and easily extend to the upper layer to form threading dislocations. be. The fact that dislocations on the (111) plane are more easily introduced than other dislocations is also common when the (111) plane is used as a group II crystal. Therefore, if the (ILL) plane is used as a substrate, dislocations generated at the interface between the substrate and the growth layer are easily bent into the (111) plane parallel to the substrate, and therefore are unlikely to become threading dislocations. In addition, since the (111) plane consists of two atomic layer steps, even if a polar semiconductor is grown on it, it becomes a single domain, and there is essentially no problem of anti-phase domain formation. Therefore, using the (111) plane as the group III crystal, we first form a thin Al layer at a low temperature, convert this Al layer into a IIIeV original crystal layer, and then form the desired III-V group compound semiconductor thin film. By recommending III e V, which has a thin film thickness and sufficiently high quality.
A method for forming a III-V compound semiconductor thin film for forming a group III-V compound semiconductor epitaxial film can be realized.

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

(Example 1) Equipped with a subchamber capable of thermally cleaning the substrate at 900 to 1000°C under high vacuum, diethyl gallium chloride (DEGaCl) was used as the group III organometallic raw material,
Low-pressure MOCVD that can supply diethylaluminium chloride (DEAlCI), trimethyl gallium (TMG), and arsine (AsH3) gas as a group III raw material.
Using the apparatus, GaAs was grown on a Si single crystal substrate.

The GaAs growth method is the atomic layer epitaxial growth method (ALE method) in which DEGaCl and AsH3 are alternately supplied.
was used. This method involves alternately supplying DEGaCl and AsH3 regardless of the raw material gas partial pressure, supply time, or growth temperature.
This method allows growth of GaAs monolayer units per cycle.

As a Si substrate, (100)4°off to <01
1> and (111) planes, and in order to simultaneously examine the possibility of selective growth during growth, a 5i02 mask portion was provided on a part of the substrate surface. The thoroughly cleaned substrate was introduced into the reaction tube, H2 was flowed as a carrier gas at 91/min, and the pressure inside the reaction tube was 100 Torr.
The Si substrate on the carbon susceptor was heated to 350° C. by high-frequency heating. After that, first figure 1(a)
DEAl at a partial pressure of 5X10-2 torr as shown in
By supplying CI for 30 to 60 seconds, 10 to 2
0 Al layer 2 was deposited.

After that, supply AsH3 with a partial pressure of 1 torr.
The temperature of the i-substrate 1 was raised to 450° C. and held for 30 seconds. During this time, the Al layer 2 deposited at 330°C is shown in Figure 1 (b).
), it is converted into an AlAs layer 3. Then A
Stop the supply of sH3, and after 0.5 seconds, 0'tor
DEGaCl at a partial pressure of r was supplied for 1 second. Thereafter, there was a period of 0.5 seconds during which no raw material was supplied, and then AsH3 at a partial pressure of 1 torr was supplied for 1 second.

By repeating this 3 second operation 1000 times, Figure 1 (
As shown in C), a GaAs layer 4 was grown on a Si substrate 1 using an AlAs layer 3 as a buffer layer. We also performed growth at a temperature higher than 450°C, and in this case, the initial growth rate was 45°C.
Alternate supply of 0°C''cDEGac1 and AsH3 was repeated 70 times, and then the temperature was raised to a predetermined temperature, and alternate supply was continued for the remaining 930 times.

For comparison, the Al layer was not deposited, that is, the Al layer was not deposited.
An experiment was also conducted in which GaAs was grown without using an As buffer layer. In this case, after introducing the substrate into the reaction tube, the temperature was immediately raised to a predetermined temperature, and alternate supply of DEGaCl and AsH3 was repeated 1000 times.

Figure 2 shows GaAs per cycle versus growth temperature.
Figure 2(a) shows the thickness of the grown film of 5i (100
) 4°off<011>i substrate, and FIG. 2(b) shows the case of growth on a 5i (111) substrate.

In the case of growth through the AlAs buffer layer, growth in monolayer units was obtained on the side substrates, and the film thickness distribution within the substrate plane was extremely uniform and the surface was mirror-finished.

On the other hand, when the film was grown without an AlAs buffer layer, the growth was smaller than a monomolecular layer, and the film thickness was not uniform and the morphology was also poor.

Next, FIG. 3 is a diagram showing X-ray diffraction intensity versus growth temperature. When grown through an AlAs buffer layer, A
The X-ray diffraction intensity on the side substrate is about 2 to 10 times stronger than when grown without an IAs buffer layer,
It can be seen that the crystallinity is significantly improved. 5 more
When grown on an i(111) substrate, 5i(100
) The X-ray diffraction intensity is several to several tens of times stronger than when grown on a 4°off<011> substrate. Therefore, Si(11
1) It can be seen that by growing on a substrate via an AlAs buffer layer, a GaAs film with good crystallinity can be grown despite the extremely thin film thickness of 300 OA in this case.

Furthermore, when grown under any of the above conditions, 5i02
No precipitation of AlAs or GaAs was observed in the masked portion, allowing selective growth.

Although a pressure reducing device is used as the MOCVD device in the above, a normal pressure device may also be used.

Furthermore, in the method of forming the Al layer, DEAlCI was used as a raw material gas, and by using this raw material gas, a flat continuous thin film can be formed selectively and uniformly at a low temperature with extremely high reproducibility. Therefore, this method is considered to be the most suitable method to be applied to the present invention. However, basically, it is sufficient if a flat continuous thin film can be formed with low heat resistance, and for example, DMAAlC1 or the like in which the alkyl group is changed from ethyl group to methyl group may be used as the raw material gas.

Further, triisobutylaluminum (TIBA) or dimethylaluminum hydride (DMALH) may be used as the source gas, but in this case selective growth is possible only under very limited conditions.

Further, although the growth of GaAs using DEGaCl and AsH3 has been described as an example of a method for growing a desired group III e V compound semiconductor, the group III and group V raw materials may basically be used as long as they can be supplied as gases. For example, growth of GaP using DEGaCl and PH3, InP using DMInCl and PH3, and even DEGaCl + DMInC.
The present invention can also be applied to the growth of mixed crystals such as the growth of InGaAs by alternately supplying l and AsH3. Further, the group III organic metal raw material may be TMG, TEG, TMIn, etc., which do not have a bond with chlorine, but in this case, selective growth is difficult or possible only under very limited conditions. Furthermore, as a group III raw material, GaCl3
Alternatively, the V group hydride raw material may be replaced with a V group organic metal raw material such as TEAs or a V group element such as As metal.

(Example 2) Using Si substrates with (100)4°off<011> and (111) planes, DE was first performed at 450°C via an AlAs buffer layer using the same equipment and the same procedure as in Example 1.
GaCl and AsH3 were alternately supplied, and in this case, this cycle was repeated 500 times to grow a GaAs layer of about 150 OA. After that, the substrate temperature was raised to 600°C, and the TM
G by the normal MOCVD method that simultaneously supplies G and AsH3.
AAs was grown to a thickness of 2 μm. For comparison, an experiment was also conducted in which growth was performed without using an AlAs buffer layer, but under the same conditions.

All grown films are single-domain single crystals,
Compared to Example 1, since the film thickness is much thicker, threading dislocations are also reduced, and the crystallinity is greatly improved as a whole. However, Al
While the surface of the GaAs film grown through the As buffer layer was mirror-like on the side substrate, considerably large irregularities were observed on the surface of the GaAs film grown without the AlAs buffer layer. Furthermore, the X-ray diffraction intensity is stronger when grown through the AlAs buffer layer than when grown without it, and the crystallinity is significantly improved.1. Also 5i (111
) When grown on a substrate, 5i(100)4°of
Exactly the same trends as in Example 1 were obtained, including a much stronger X-ray diffraction intensity and better crystallinity than when grown on an f<011> substrate.

In the above embodiments, the III-V group compound semiconductor thin film was formed on the Si substrate, but the thin film may be formed, for example, on a Si crystal formed on the III-V group compound substrate. In addition, as a group II material other than Si, for example, 5iG
The effect of the invention was confirmed for e, Ge, etc. in the same way as the above method. Furthermore, the method for growing the Al layer and III-V group compound semiconductor thin film is not limited to chemical vapor deposition, but may also be molecular beam growth.

(Effects of the Invention) Since the present invention is configured as described above, it produces the effects described below.

According to the method described in claim 1, an Al layer is formed on the group (1) crystal and a group V element is supplied to form a group III-V crystal layer continuous with the group (2) crystal. This In
+ Since the III-V group compound semiconductor thin film is grown using the V group crystal layer as a buffer layer, it is possible to form a high quality III-V group compound semiconductor thin film with excellent surface flatness.

If an organic volatile compound is used as the Al raw material and a volatile compound is used as the V group element raw material as in claim 2, A
The growth of the L layer can be performed at low temperatures, and the III layer is continuous to the Dlc crystal.
-V group crystals are easily obtained, so reproducibility is good <III
- A group V compound semiconductor thin film can be formed.

According to the method of claim 3, the plane orientation of the group III crystal is (1
11) III-V7 with fewer threading dislocations because it uses a plane
An IN compound semiconductor thin film can be formed.

When the formation temperature of the Al layer is set to 400° C. or lower as in claim 4, alloying of Si and Al is suppressed, so that a continuous film with a flat surface can be reliably obtained.

When an organometallic compound in which Al and a halogen are bonded is used as a raw material for Al as claimed in claim 5, II.
A method for forming an I e V group compound semiconductor thin film can be realized.

As described in claim 6, if a group III raw material and a group V raw material are used when forming a group III-V compound semiconductor thin film, the growth temperature can be lowered, so that a thin film of high quality can be obtained more reliably.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a crystal growth process according to an embodiment of the present invention, and FIG. 2 is a diagram showing the growth film thickness of GaAs per cycle with respect to growth temperature in the same embodiment. Figure (a) shows 5i(100)4°off<01
1> When grown on a substrate, and FIG. 2(b) shows that 5i (
111) When grown on a substrate, FIG. 3 is a diagram showing the X-ray diffraction intensity versus growth temperature in the same example. 1-8i substrate, 2-Al layer, 3-AlAs layer, 4-Ga
As layer.

Claims (6)

[Claims] (1) A method for forming a III-V compound semiconductor thin film on a group IV crystal, which includes the steps of forming a thin Al layer on the group IV crystal, and supplying a group V raw material onto the Al layer. a step of converting the Al layer into a group III-V compound single crystal layer in which the group III constituent element is Al; and a step of forming a desired group III-V compound semiconductor thin film on the group III-V compound single crystal layer. A method for forming a III-V compound semiconductor thin film, the method comprising: (2) A method for forming a III-V compound semiconductor thin film on a group IV crystal, including the step of forming a thin Al layer by supplying an organic volatile compound containing Al on the group IV crystal; a step of converting the Al layer into a single crystal layer of a III-V compound having Al as a group III constituent element by supplying a group V element or a volatile compound of a group V element onto the layer; Desired III− on the compound single crystal layer
1. A method for forming a III-V compound semiconductor thin film, comprising the steps of: forming a group V compound semiconductor thin film. (3) In a method of forming a III-V compound semiconductor single crystal thin film on a group IV crystal, the (111) plane is used as the plane orientation of the group IV single crystal substrate, and the A
A thin A by supplying an organic volatile compound containing l
The above A
A step of converting the L layer into a III-V group compound single crystal layer whose group III constituent element is Al, and a step of forming a desired III-V group compound semiconductor thin film on the III-V group compound single crystal layer. 1. A method for forming a III-V compound semiconductor thin film, the method comprising: (4) The method for forming a III-V compound semiconductor thin film according to claim 1, 2 or 3, wherein the Al layer is formed at a low temperature of 400°C or lower. (5) III according to claim 2, 3 or 4, characterized in that the organic volatile compound containing Al is an organometallic compound having at least one bond between Al and a halogen element.
- A method for forming a group V compound semiconductor thin film. (6) The whole or at least an initial part of the formation of the desired Group III-V compound semiconductor single crystal thin film is performed by alternating between a volatile compound of a Group III element and a Group V element or a volatile compound of a Group V element. 6. The method of forming a III-V compound semiconductor thin film according to claim 2, 3, 4 or 5, characterized in that the method is based on a supplying method.