JP2972230B2 - Joint structure - Google Patents

Description

The present invention relates to a technology for forming a semiconductor device using electrons and holes, and more particularly to a technology for forming a device suitable for improving characteristics of an electronic device such as a diode and a transistor. Related to the joining structure.

[Conventional technology]

A typical example of the conventional bonding structure is a case where different materials are used and the lattice constants are extremely close. For example, as shown in JP-B-59-53714, this is the case of a combination of different materials of GaAs and GaAlAs. GaAs has a band gap of 1.43 eV and its lattice constant is 5.645 °. On the other hand, GaAlAs having a band gap of 2.0 eV has a lattice constant of 5.657Å,
Very close to that of GaAs, a good heterojunction can be formed. With this combination of materials, the lattice constant difference between GaAs and AlAs is small, so that a relatively arbitrary combination of bandgap materials is possible.

However, in general, a heterojunction with an arbitrary bandgap material cannot be formed due to the necessity of matching the lattice constant.

As another typical example of the related art, there is an example in which a heterojunction having a significantly different lattice constant is formed. It is a heterojunction of GaAs and Si. GaAs and Si have a mismatch of 4% in lattice constant, and it is usually difficult to grow good GaAs epitaxially on Si crystals. Recently, however, various attempts have been made with respect to the growth method, and it has become possible to grow a high-quality GaAs crystal on Si. However, in this method, although the GaAs epitaxial film itself is of good quality,
Many defects are concentrated at the bonding interface between As and Si, and at present, this interface cannot be used as a functional part of an electronic device.

As another conventional technique, it is clear that although the mismatching of the lattice constant is relatively large, if one of the materials is less than a certain film thickness, epitaxial growth can be performed so as to match the lattice constant of the substrate. Have been. Specifically, a SiGe alloy is epitaxially grown on a Si single crystal,
Although it depends on the composition ratio of SiGe, it has been reported that a heterojunction having a band gap different by about 0.1 to 0.3 eV is formed at about several hundreds to several thousand degrees (Applied Physics, Vol. 8, p. 199, 1975). (E. Kasper, H, J, Her
zog, Appl, Phys. 8 199 (1975)]. However, since a large stress is contained in the inside, the above-described conventional bonding structure may lack stability when applied to element formation or the like.

[Problems to be solved by the invention]

Among the above-mentioned prior arts, the first example has excellent characteristics, but is a very special combination in which materials having different electronic properties have little difference in lattice constant. Therefore, the composition cannot be freely changed because the heterointerface characteristics are controlled. In the second example, since the lattice constant difference is large, many defects are generated at the junction interface,
Electronic characteristics of the bonding interface are extremely deteriorated. Also, the third example shows that, despite the large lattice constant difference, it is possible to grow so that one lattice constant becomes the same as the other.
For this reason, there is a problem that a large stress generated lowers stability of bonding and device characteristics.

An object of the present invention is to solve the above-mentioned problems in the conventional joining structure.

[Means for solving the problem]

The above object is achieved by utilizing a change in band gap based on a quantum effect caused by changing dimensions of both materials to be joined. In particular, the difference in the energy gap observed in the bulk material of the same or substantially the same material between so-called lattice-matched materials having a lattice constant difference of about 0.5% or less between the two materials is about kT or less (T is (Absolute temperature), an effective hetero effect can be provided.

In the bonding structure of the present invention, the two regions to be bonded are made of a material selected from a semiconductor, an insulator, a metal, and the like having the same or a difference of less than 1/100 in composition. That is, these regions are formed of substantially the same material. Also, within 10 μm from the bonding surface, the width of the narrower bonding surface in one region is 1000 Å or less, and the width of the other region is different from this.

[Action]

FIG. 1 is a diagram showing the principle of the present invention. For simplicity, the joining as shown in FIG. Materials 1 and 2 are the same substance. For example, consider single crystal Si. Materials 1 and 2 are defect-freely connected at x = 0. It is assumed that d _1y and d _2y are sufficiently large, and a quantization effect can be obtained in the z direction. It is also assumed that the surfaces of the materials 1 and 2 have no abnormal scattering of carriers or recombination, and the surroundings are vacuum.

FIG. 1B is an energy diagram corresponding to the above-described joint structure. In this case, since d _1z > d _2z , the effective energy gap is Becomes If d _2z is sufficiently large, it becomes equal to the energy gap of the bulk Si single crystal. Effectively by reducing d _2z In order for d to become large, d _2z needs to be about 1000 ° or less.

Of course, the magnitude of this effect varies depending on the type of material, but in order for the quantum effect to be visible at about room temperature, the width in one direction of the bonding surface must be about 1000 mm or less. When used at low temperatures, the quantum effect can be detected even if it is increased.

In any case, such a junction forms a heterojunction in terms of energy level, even though 1 and 2 are made of the same material. That is, the junctions at the atomic level of 1 and 2 can be formed defect-free because they are made of the same material, and electronically operate as a heterojunction.
This hetero interface has the characteristic that the carrier is hardly scattered and defects that cause recombination are extremely rare.

Conventionally, it has been extremely difficult to predict the energy level of such a junction structure theoretically. Recently, with the development of supercomputers and the like, it has become possible to predict the electronic structure of a material based on the atomic bond structure of the material without assuming the periodicity of the arrangement of atoms.

Therefore, the present inventors set out materials 1 and 2 used in the above system.
A study was conducted to predict the electronic structure of.

Figure 2 is an example of the results has a {100} surface, Enerugigiyatsupu E _g in calculation example of the thin Si single crystal having a thickness of 11Å is about 1.6 eV (solid line).

On the other hand, in the case of a bulk Si single crystal calculated for reference (broken line), E _{g is about} 1.1 eV, which is almost the same as a conventionally known value. It is clear from this that the energy gap is increased by reducing the thickness to about 11 °. The result itself may particularly without considering the atomic bonding structure, and that E _g of the bulk Si is 1.1 eV, even understood as an effect of the increase in Enerugigiyatsupu by confinement of electrons and holes due to the thinning.

However, the results obtained from the above theoretical study show that the material gap near the joint surface also causes an increase in energy gap due to thinning. This is a fact that has not been made clear so far.

Based on this, as shown in FIGS. 3 (c) and 3 (d), a hetero effect can be exhibited even though the materials 1 and 2 are the same material. In the conventional example shown in FIGS. 1A and 1B, the energy gap can be increased by thinning the material 1 at the stage before the joining (a), but the joining is made as shown in FIG. 1B. Naturally, the properties as a heterostructure are lost. However, in the present invention, even if the same material is used as shown in FIG.
A heterojunction can be manufactured by reducing the width of the bonding surface of the above.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

(Embodiment 1) FIG. 4 is an explanatory view showing an embodiment of the present invention.

FIG. 1 shows that in the structure showing the principle of the present invention, the y direction is substantially infinite, but in this example, both the z and y directions are finite,
_2z = was d _2y = d ₂ = 20Å. d _1z and d _1y are 10 mm, which is substantially infinite. The junction was formed by the method described below.

First, a Si single crystal wafer having a {100} plane is cut into 10 mm squares, and the surface of the Si wafer is cleaned by a high-temperature heating method in a vacuum using a molecular beam epitaxy apparatus having a degree of vacuum of about 10 ^-11 Torr. . Using a electron beam source of an electron microscope, irradiate an electron beam of 20 ° φ to the portion of the Si single crystal surface where a Si column, which is to be the material 2 for growth, grows at a deposition rate of 1Å / s from the Si molecular source. the corresponding Si was irradiated by a method of decomposing the SiH _4. As a result, a length of approximately 500
It was possible to selectively epitaxially grow substantially prismatic Si of Å.

Here, the Si wafer was heated to 200 ° C., and several tens of amorphous silicon films were applied to portions other than the portions where the Si pillars 2 were formed. However, this film contains about 10 atomic% of hydrogen, has a wide energy gap, and does not prevent a situation in which a 20-degree prism is epitaxially grown on a Si wafer.

Actually, such a prism was formed two-dimensionally at 200 ° pitch, and a current value necessary for actually measuring current-voltage characteristics and the like could be obtained.

The above structure can be formed by other methods. For example, the surface of a Si single crystal was coated with a photosensitive agent for electron beams, linear exposure was performed at intervals of 40 mm by an electron beam interference exposure method, and an uneven groove-like structure with a depth of 500 mm was created by dry etching. .

It is also practically effective to cover about 10 mm of the surface with an oxide film by thermal oxidation or plasma oxidation, etc., in order to protect the uneven Si surface and keep the electrical characteristics of the surface in good condition. Was.

As described above, it was possible to form a fine structure that causes the quantum interference effect by various methods. In this way, it has been clarified that a heterojunction characteristic is exhibited electronically while the junction is made of substantially the same material.

Practically, at or near this electronic heterojunction,
It is necessary to make a -n junction, a pin junction or the like. For this purpose, when growing Si by the molecular beam epitaxy method, p-type or n-type elements, such as B and P, are vaporized or gaseously sent to the substrate at the same time, so that a desired electric power can be obtained. Characteristic can be obtained.

Embodiment 2 FIG. 5 shows an embodiment in which the technique of the present invention is applied to a transistor.

As shown in FIG. 2A, a p-type base layer 102 is formed on an n-type Si substrate 101 by ion implantation, and an n-type Si sheet 201 having a spacing of 40 ° and a thickness of 20 ° is formed on the p-type base layer 102 by the method of the present invention. Base layer 102
Epitaxial growth is performed in a manner to stand perpendicular to the surface. The height at this time was 500 mm. In order to actually operate as a transistor, extraction electrodes are provided on the emitter (E), the base (B), and the collector (C) as shown in the figure. As a result, transistor operation was confirmed. In addition, E and B
Despite's Kiyariya concentration of the respective conductivity type are comparable and approximately 10 ²⁰ cm ^-3, the current amplification factor I _C / I _B were obtained which exceeds 80 times.

This indicates that a hetero n-p junction is formed between E and B in a realistic manner as shown in FIG. 5 (b), demonstrating the effect of the present invention.

(Embodiment 3) In the embodiment of the present invention described in the embodiment 1, an electronic heterojunction is formed by using a selective growth technique or a lithography technique. By controlling, the effect of the present invention is brought out.

FIG. 6 shows a prototype of the transistor of this embodiment. First, phosphorus (P), which is an n-type impurity, was introduced into a p-type Si substrate 61 by ion implantation to form an n-type layer 62. Thereafter, a p-type layer is formed by molecular beam epitaxy and the p-type layer 63 is made porous by anodic oxidation as shown in FIG. According to this method, the upper p-type layer 63 in the figure has a large number of pores having an average of about 100 ° in about 30 minutes as shown in FIG. Quality silicon layer 63 '
Could be formed.

This was processed as shown in FIG. 3C to obtain a transistor structure. It was confirmed that the transistor formed in this manner performed a transistor operation, but formed an electronic hetero pn junction between E and B.

〔The invention's effect〕

According to the present invention, a heterojunction can be formed using the same or substantially the same material, and a high-quality junction free from distortion and defects can be formed. Accordingly, there is no restriction on the selection of materials of different materials having the same lattice constant, so that desired performance can be freely exhibited.

[Brief description of the drawings]

FIG. 1 is a perspective view and an energy band diagram of a joint for explaining the principle of the present invention, FIG. 2 is a graph showing an electronic state in a Si single crystal, and FIG. 3 is a joint for explaining a difference between the present invention and a conventional example. FIG. 4 is a perspective view and an energy band diagram of a junction according to an embodiment of the present invention. FIG. 5 is a cross-sectional view and an energy band diagram of a transistor according to an embodiment of the present invention. FIG. 21 is a cross-sectional view illustrating a step of manufacturing a transistor according to still another example of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ identification code FI H01L 29/86 H01L 29/91 H 29/861 (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 29/06 H01L 29/66-29/73

Claims (1)

(57) [Claims] In a joint structure between a first material and a second material, a difference in energy gap between the first material and the second material is less than kT (T is used). Absolute temperature), the width of the bonding surface of the bonding structure of the first material is greater than 1000 angstroms, and the width of the bonding surface of the bonding structure of the second material in one direction is
A junction structure characterized by being 1000 Å or less.