JPH08316145A - Method for forming semiconductor thin film - Google Patents

Abstract

PURPOSE: To obtain the semiconductor thin film having the excellent crystalline property by hetero-epitaxial growth by forming thin a buffer layer, which comprises one kind or plural kinds of chalcogenide and comprises the compound having a layer crystal structure, on a substrate comprising the different kind of a semiconductor from a semiconductor constituting the thin film. CONSTITUTION: A molecular-beam epitaxy device is used, and metal Ga and Se are evaporated by a Knudsen cell. Then, a GaSe buffer layer 2 is formed on an Si substrate 1. This GaSe layer 2 has the layer crystal structure and comprises a plurality of unit layers 21. All three bonding parts of Se at the upper part and the lower part of each unit layer 21 are bonded to Ga atoms. Therefore, there is no dangling bond. There is no common bonding between the surface of the Si substrate 1 and the neighboring GaSe unit layer 21 and between the mutual unit layers 21 of GaSe. They are bonded with very weak van der Waals force.

Description

Detailed Description of the Invention

[0001]

The present invention is used in a method for forming a semiconductor thin film by heteroepitaxial growth.

[0002]

2. Description of the Related Art Thin film formation, especially semiconductor thin film formation,
It has an important position as one of the device manufacturing technologies. For example, GaAs thin film is a semiconductor laser or HEMT.
It has been put to practical use in devices such as (high electron mobility transistors), and GaAs thin films have been extensively studied as short-wavelength light emitting materials by taking advantage of their wide bandgap characteristics. One of the restrictions in forming such a semiconductor thin film is that the degree of freedom of the substrate on which the thin film is grown is low. The substrate material that has been put to practical use for GaAs is GaAs single crystal, but this is about 10 times more expensive than the Si single crystal in the same area. In the case of semiconductor lasers and HEMTs, the element area is very small, so this cost has little effect, but it is a major obstacle when trying to fabricate highly integrated LSIs and the like.

The reason for this restriction is considered to be that a strong bond is generated between the substrate material and the thin film material, and the thin film being formed is strongly influenced by the substrate material through this bond. Therefore, although it is possible to form a film with the same material as the substrate and a crystal structure and a lattice constant close to each other, the film formation when the substrate and the thin film are different materials results in a large defect density, generation of surface roughness, and residue. Various problems such as warpage of the substrate due to thermal stress occur.

As a measure against these problems, a method of using an amorphous layer of a thin film material as a buffer layer has been adopted. For example, when GaAs is deposited on Si, amorphous GaAs is used as a buffer layer, and when GaN is deposited on sapphire, amorphous GaN is used as a buffer layer. In this method, the amorphous layer is provided in the middle to weaken the bonding force between the substrate material and the thin film material.

[0005]

However, the thin film formed on the amorphous film has poor crystallinity, and as a result, there is a drawback that a large defect density and surface roughness remain. Thus, there are two conflicting issues. The first is that the bond between the substrate material and the thin film material is very weak, and
Secondly, when a buffer layer is used to weaken the bond, the crystallinity of the thin film material / buffer material / substrate material is increased. In particular, regarding the second point, it is necessary to have an epitaxial property such that the crystal orientation of the substrate material matches the crystal orientation of the thin film material. In addition, the use of sapphire as a substrate has a drawback that the electrode cannot be removed from the lower part of the film because the substrate is insulating.

An object of the present invention is to solve the above two problems at the same time and to provide a method for forming a semiconductor thin film having good crystallinity by heteroepitaxial growth using a substrate which can be selected in a wide range. .

[0007]

In order to achieve the above object, a method for forming a semiconductor thin film according to the present invention is a method of forming a thin film of a semiconductor having a crystal structure in which atoms are arranged in a regular tetrahedron. Has a crystal structure having a regular tetrahedral arrangement, but a buffer layer made of a compound having a layered crystal structure made of one or more kinds of chalcogenide is formed on a substrate made of a semiconductor different from the semiconductor forming the thin film. Shall be formed through. Before forming the buffer layer, it is effective to perform a treatment for terminating the dangling bonds on the surface of the substrate. Even if the semiconductor constituting the thin film or the substrate is composed of one or more elements of Group IV elements of the periodic table, II
One or more of Group I elements and one or more of Group V elements, one or more of Group II elements of the Periodic Table and one or more of Group VI elements Good. One kind or plural kinds of chalcogenides forming the buffer layer may be a compound of Ga and an element of S, Se, and Te. Or Sn, Mo,
A compound of an element of Ta, Nb, and Hf and an element of S, Se, and Te is preferable.

[0008]

The chalcogen element compound having a layered crystal structure composed of a plurality of unit layers, that is, a chalcogenide, has no bond in the direction between the unit layers and is bonded only by the Van der Waals force. Since the van der Waals force is very weak, even if there is a mismatch in the interatomic distance between different semiconductors that compose the thin film and the substrate and also have a crystal structure in which the atoms have a tetrahedral arrangement, the substrate material and the thin film material The bond with and is completely cut off at the buffer layer portion made of this chalcogenide. This solves the first problem.
The chalcogenide of the buffer layer has a strong cohesive force in the lateral direction and has good crystallinity, so that it is compensated by the buffer layer so that the crystal orientation of the laminated thin film material matches that of the thin film material. . This solves the second problem. Terminating the dangling bond on the substrate surface before forming the buffer layer means that the bond between the substrate surface and the unit layer of the buffer layer adjacent to the substrate surface also depends on the Van der Waals force, and the above-mentioned buffer layer Improve the effect more. Ga, S, and S are chalcogenides having a layered crystal structure used for the buffer layer.
e, a compound with any of Te, Sn, Mo, Ta, N
Examples thereof include compounds of b or Hf and S, Se or Te.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. Example 1: The substrate of silicon (Si) substrate (111) surface, after the substrate was boiled in _{HCl-H 2 O 2 -H 2} O solution was treated with 2% HF solution. As a result,
As shown in, a bond on the surface of the Si substrate 1 is a hydrogen atom.
The structure is terminated with (H), and there is no dangling bond that is an unbonded hand. Next, using a molecular beam epitaxy (MBE) device, the metals Ga and Se are evaporated in a Knudsen cell, and GaSe is deposited on the Si substrate 1.
The buffer layer 2 was formed. The GaSe layer 2 has a layered crystal structure as shown in FIG. 1 when viewed directly from the side and as shown in FIG. 2 when viewed three-dimensionally, and is composed of a plurality of unit layers 21, and three Se layers are provided above and below each unit layer 21. Since all the bonds are bonded to Ga atoms, there is no dangling bond. As shown in FIG. 1, the surface of the Si substrate 1 and the adjacent GaS
There is no covalent bond between the e unit layer 21 and each of the GaSe unit layers 21, and they are bonded by a very weak Van der Waals force. The distance between Se atoms on the surface of this GaSe layer 2 is 0.376 nm, and the S on the (111) surface of the Si substrate 1 is S.
There is a mismatch of about 2% compared to the i-atomic distance of 0.384 nm. Despite this relatively large mismatch, G with the a-axis aligned with the [111] -axis direction of Si of the substrate 1
Epitaxial buffer layer 2 made of aSe
That high energy electron diffraction (RHEE
D) It confirmed using the apparatus.

After the buffer layer 2 is formed to a thickness of about 10 nm, the Se molecular beam of the MBE device is switched to the As molecular beam to continuously form a GaAs thin film 3 having a thickness of 1000 nm as shown in FIG. Filmed As a result, the in-plane [11
1] GaA whose axis is parallel to the a-axis of GaSe in the buffer layer 2
The s (111) orientation film 3 was obtained. Ga of the GaAs layer 3
The interatomic distance is 0.399 nm, and S of the buffer layer 2
It was found that an epitaxial film was obtained even though there was a mismatch of 6% as compared with the e interatomic distance of 0.376 nm. As a result, G with in-plane crystallographic orientation
aAs (111) / GeSe (0001) / Si (11
The laminate of 1) could be produced. When the surface roughness of the uppermost GaAs thin film 3 was measured by an atomic force microscope, it was 5n.
It was found that the unevenness was within m, and the electrical characteristics were sufficient to withstand device application.

Example 2 A GaSe buffer layer and a GaAs thin film were laminated in the same manner as in Example 1 except that the HF treatment for terminating the bond on the surface of the Si substrate was not performed. Also in this case, GaAs (11
1) / GaSe (0001) / Si (111) structure was obtained.

Example 3 A (111) -oriented GaAs substrate was used, Se vapor was jetted onto the surface of this substrate to terminate dangling bonds on the surface, and then GaSe was removed in the same manner as in Examples 1 and 2. A film was formed to a thickness of 10 nm. Subsequently, Si was vapor-deposited to a film thickness of 1000 nm, and an epitaxial film in which the [111 axis] of GaAs, the a axis of GaSe, and the [111 axis] of Si were parallel to each other was obtained. As a result, Si (111) / G with in-plane crystallographic orientation
The aSe (0001) / GaAs (111) structure was produced. The surface roughness of the surface of the uppermost Si thin film was measured by an atomic force microscope, and it was found that the surface roughness was within 2 nm and the electrical characteristics were sufficient for device application.

Example 4 A Si (111) substrate was treated with HCl--
A substrate that had been boiled with an H ₂ O ₂ —H ₂ O solution and then treated with a 2% HF solution was used. On this surface, a film of GaSe having a thickness of about 10 nm was formed in the same manner as in Examples 1 to 3, and the Ga molecular beam and the Zn molecular beam were continuously switched to form ZnS.
When the e film was formed to a film thickness of 100 nm with an MBE apparatus, an epitaxial film in which the [111] axis of ZnSe, the a axis of GaSe, and the [111] axis of Si were parallel to each other was obtained. As a result, ZnSe (111) with crystallographic directions aligned in the plane
A / GaSe (0001) / Si (111) structure was produced. As a result of measuring the surface roughness of the uppermost ZnSe film by an atomic force microscope, it was found that the surface roughness was within 6 nm, and the electrical characteristics were sufficient for device application.

Example 5: A Si (111) substrate was treated with HCl--
After boiling with H ₂ O ₂ -H ₂ O solution was used after treated with 2% HF solution. GaSe was formed into a film having a thickness of about 10 nm on the surface terminating the bond in the same manner as in Examples 1 to 4, and the Se molecular beam was switched to the N radical molecular beam to continuously produce 1000 nm in the same MBE apparatus. A GaN film having a thickness of 1 was formed. This gives GaN (000
An epitaxial film having an orientation of 1) / GaSe (0001) / Si (111) was obtained.

As a result of RHEED analysis, a
It was found that the axis was rotated 30 ° from the GaSe a-axis. FIG. 4 shows the positional relationship of the arrangement of atoms in the (0001) plane of GaSe and GaN when the a-axis is rotated by 30 °. □ shows the atomic arrangement of Se of GaSe seen from above, and the dotted line is the a-axis of GaSe. ● is GaN G
It is an atom of a or N, and the solid line indicates the a-axis of GaN. The lattice constant mismatch in this case is about 2
However, if the a-axis of GaN and the a-axis of GaSe are parallel to each other without such rotation of 30 °, the mismatch of the lattice constant becomes about 18%. It is considered that the reason why this atomic arrangement occurs is that the surfaces bonded by Van der Waals force easily rotate. Furthermore, as a result of measuring the surface roughness of the uppermost GaN surface by an atomic force microscope, it was found that the surface roughness was within 10 nm, and the electrical characteristics were sufficient to withstand device application. all right.

Conventionally, the c-face of sapphire is usually used as a substrate for GaN film formation, but there is a drawback that the electrode cannot be removed from the lower part of the film because this substrate is insulating. This problem can be solved by forming a film on a semiconductor substrate as in this embodiment. This leads to simplification of the device process, and has a great application advantage. Example 6: GaAs of (111) plane is used for the substrate, and Se vapor is jetted to the surface to terminate the dangling bond on the surface. In the same manner as in Examples 1 to 5, about 10 n is obtained.
A GaSe film having a thickness of m was formed. Next, in the same manner as in Example 5, a GaN film was continuously formed by switching the Se molecular beam with the N radical molecular beam in the same MBE apparatus.
GaN (0001) / GaSe (0001) / GaAs
An epitaxial film having a compoundability of (111) was obtained. As a result of RHEED analysis, in this film as well as in Example 5, the a-axis of the uppermost GaN thin film was a of the buffer layer GaSe.
It was found that the mismatch was reduced by rotating 30 ° from the axis.

In addition to the above examples, the buffer layer is not limited to GaSe but may be formed of gallium chalcogenide using chalcogen elements S and Te other than Se.
A film of the same quality as the heteroepitaxial film of the above example was obtained. When MoS ₂ was used for the buffer layer and the same substrate material and upper thin film material combination as in Examples 1 to 6 were used to form a film, a heteroepitaxial film of the same quality was obtained. The structure of this MoS ₂ is shown in FIG. G
Similar to aSe, the layers are weakly coupled by Van der Waals force, and it is considered that the same effect is obtained. Furthermore, not only MoSe ₂ but also metallic elements such as Sn and T
a, Nb, Hf and S, Se of diatomic chalcogen element,
It was found that any of the metal chalcogenides having a layered crystal structure composed of Te is suitable as the buffer layer.

[0018]

According to the present invention, chalcogenide, which has a strong binding force in the lateral direction of the layer, but is bound by a very weak van der Waals force in the longitudinal direction, is used as a material for the buffer layer. As a result, the bonding force between the semiconductor material of the thin film and the semiconductor material of the substrate was weakened, the deterioration of the characteristics of the semiconductor thin film due to the mismatch of the crystal structures of both materials could be prevented, and the surface irregularities were also reduced. In addition, since the semiconductor material can be used for the substrate, it becomes easy to extract the current or voltage from the lower portion of the thin film by forming the electrode on the substrate.

[Brief description of drawings]

1 is a Ga deposited on a Si substrate in Example 1. FIG.
Side view schematically showing the Se buffer layer

2 is a perspective view showing a crystal structure of a GaSe unit layer in Example 1. FIG.

FIG. 3 is a sectional view of a heteroepitaxial film structure according to Example 1.

FIG. 4 is a sectional view schematically showing a GaN thin film deposited on a GaSe buffer layer in Example 5.

FIG. 5 is a perspective view showing the crystal structure of MoS ₂ used in another embodiment of the present invention.

[Explanation of symbols]

 1 Si substrate 2 GaSe buffer layer 21 GaSe unit layer 3 GaAs thin film

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroshi Kimura 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 inside Fuji Electric Co., Ltd.

Claims (7)

[Claims] 1. A thin film made of a semiconductor having a crystal structure in which atoms have a regular tetrahedral arrangement, and a semiconductor having a crystal structure in which atoms also have a regular tetrahedron arrangement, but different from the semiconductor forming the thin film. Forming a semiconductor thin film via a buffer layer made of a compound having one or more kinds of chalcogenide and having a layered crystal structure on the substrate. 2. The method for forming a semiconductor thin film according to claim 1, wherein a treatment for terminating dangling bonds on the surface of the substrate is performed before forming the buffer layer. 3. The semiconductor constituting the thin film or the substrate is made of one or more of Group IV elements of the periodic table.
Alternatively, the method for forming a semiconductor thin film according to the item 2. 4. The semiconductor according to claim 1, wherein the semiconductor constituting the thin film or the substrate comprises one or more kinds of Group III elements and one or more kinds of Group V elements of the periodic table. Thin film forming method. 5. The semiconductor according to claim 1, wherein the semiconductor constituting the thin film or the substrate comprises one or more kinds of Group II elements and one or more kinds of Group VI elements of the periodic table. Thin film forming method. 6. The film formation of a semiconductor thin film according to claim 1, wherein the chalcogenide or chalcogenides constituting the buffer layer is a compound of gallium and an element selected from sulfur, selenium and tellurium. Method. 7. The chalcogenide of one or more kinds which constitutes the buffer layer is a compound of an element selected from tin, molybdenum, thallium, niobium and hafnium and an element selected from sulfur, selenium and tellurium. A method for forming a semiconductor thin film as described above.