JP2569099B2 - Epitaxial growth method - Google Patents

Description

The present invention relates to a method for epitaxially growing different materials,
In particular, the present invention relates to a method for epitaxially growing a heterogeneous material having a large lattice constant difference.

[Prior Art] A so-called graphoepitaxy technique has been known as a conventional technique for epitaxially growing dissimilar materials having a large difference in lattice constant, and extremely as a method for growing a single crystal on an amorphous substrate. There is also a so-called two-step growth method in which a material having a large lattice constant difference is grown as a single crystal thin film on a single crystal substrate. The former method is described, for example, in Crystal Grouse, Vol. 63, (1
983) 527-546 (Crasal growth 63 (1983) 527)
−546), the latter method is described in, for example, the Japan Society of Applied Physics and the Subcommittee of Applied Electronic Properties, Research Report No. 415 (Friday, September 12, 1986)
Pp. 16-21). In addition,
No. 50-118976 uses a vapor phase epitaxial growth method,
It describes a method for producing a single crystal while controlling the lattice constant and the like. The prior art described above controls the lattice constant, composition, and the like by controlling the crystal temperature and the like, and is different from the one that controls the lattice constant difference by having a periodic structure in the substrate of the present invention.

[Problems to be Solved by the Invention] Among the above-mentioned conventional techniques, the grapho-epitaxial method has an advantage that it is released due to the problem caused by the lattice constant of the substrate. There is also a feature that a single crystal material can be grown on the substrate. However, since the epitaxial growth is not a method of directly reflecting the lattice constant of the substrate, the controllability of the crystal orientation is good, but the crystallinity is not good.

In addition, since heteroepitaxial growth by the so-called two-step growth method grows while partially maintaining the consistency with the lattice constant of the substrate, good crystallinity can be expected locally. However, the matching between the locally aligned epitaxial portions is insufficient. Even if the structure has a single domain structure, there are many occurrences of dislocations, and there is a practical problem.

An object of the present invention is to provide a heteroepitaxial method capable of forming a practically used heterojunction by remarkably improving the crystallinity of the heteroepitaxial layer having a large lattice constant difference.

[Means for Solving the Problems] The object of the present invention is to control crystal orientation and control of atomic arrangement over a certain area or more required for single crystallization by controlling fine periodic irregularities on a substrate surface, This can be achieved by performing periodic chemical modification or the like.

More specifically, an epitaxial growth method for growing a second crystal material having a second lattice constant on a first crystal material having a first lattice constant, wherein the epitaxial growth method comprises the steps of: A first step of forming a pattern having a periodic structure corresponding to an integer multiple of the least common multiple of the first lattice constant and the second lattice constant, and forming the pattern on the first crystal material provided with the pattern. And a second step of forming a second crystal material.

[Operation] FIGS. 1A and 1B are schematic diagrams for explaining the principle of the present invention in an easily understood manner. 1 in (a) denotes a single crystal material used as a substrate, and 2 denotes a lattice structure of a material having a different lattice constant from that of 1 epitaxially grown thereon. (B) is a continuous drawing of this, showing that the present invention provides the substrate 11 with irregularities and epitaxially grows the material 12 thereon.
It shows exactly the same thing as (a). In (a), black circles represent atoms of material 1 and open circles represent atoms of material 2. In this case, the lattice constant of material 2 is 6/5 times that of material 1. Therefore, it can be seen that dangling bonds 3 are generated every six lattices as viewed from the material 1, and the mismatch due to the lattice constant is eliminated. As described above, the interval between the concavities and convexities attached to the substrate is the least common multiple of the lattice constant of each material. As described above, since the epitaxial growth locally reflects the lattice of the substrate, and the local epitaxial portions are regularly arranged according to the period of unevenness, dislocations and the like that extend deep into the epitaxial layer occur. And an extremely good epitaxial layer can be obtained. As described above, according to the present invention, by providing a periodic structure corresponding to the least common multiple of the lattice constants of both the substrate and the material to be epitaxially grown, a very good heterojunction can be formed as described above.

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

Example 1 FIGS. 2 (a) to 2 (e) are diagrams for explaining a process outline according to an example of the present invention.

As shown in FIG. 1A, a PMMA (poly-methyl methacrylate) 5 having a thickness of 0.5
It was spin-coated to a thickness of μm and prebaked at 170 ° C. for 20 minutes. A pattern was drawn by a drawing apparatus using a variable rectangular beam type electron beam 6 with an acceleration voltage of 30 kV (FIG. (B)). The amount of electron beam irradiation is 300 μC / cm ² . Next, IPA as a developer
(Isopropyl alcohol) and static development for 3 minutes to obtain a 0.19 μm line and space pattern (FIG. (C)). Using the obtained pattern as a mask, dry etching was performed for about 10 minutes in a 50 mTorr CBrF ₃ plasma to form an uneven pattern (0.05 step) on the Si surface.
μm). Thereafter, the wafer was washed with acetone to remove PMMA, thereby obtaining the structure shown in FIG. As a result, there is a step of 0.05 μm on the Si surface, and the line and space of 0.19 μm is equivalent to the Si lattice spacing (5.431Å)
14 of the least common multiple (135.8Å) with the lattice spacing of (5.653Å)
The interval is doubled. Also, when forming the above-mentioned line and space, the effectiveness of the present invention does not change even if any technique other than electron beam drawing is used.

Normal molecular beam deposition (MB) is performed on the obtained Si substrate (Fig. (D)).
F) method or vapor phase growth by thermal decomposition of organic metal (MOCVD)
A GaAs layer was grown by using the method (FIG. 4E).

A typical growth sequence is as follows. That is,
First, heat treatment is performed at 900 ° C. to clean the Si substrate surface. Next, 400-450 ° C for MOCVD and 150-400 for MBE
An amorphous GaAs layer having a thickness of about 20 nm is deposited on a Si substrate at a low temperature of ° C. After that, the growth was suspended and the substrate temperature was increased to 700
Raise the temperature to 750 ° C. and perform the second growth with a thickness of 300 nm.
When the substrate temperature rises, the amorphous GaAs layer becomes single crystal, and the GaAs layer grown on it becomes single crystal. Although this is a typical sequence of the two-step growth method, a method of introducing a system superlattice at the interface between GaAs and Si may be used instead of the two-step growth method.

Observation of the GaAs crystal thus formed using an electron microscope revealed that GaAs contained about 10 ⁶ / cm ² lattice defects. This value is the normal smooth Si
Lattice defects remaining in GaAs formed on the substrate surface (10 ⁷
Unit / cm ² ), which is about one digit lower than that of the present invention, that is, the effectiveness of the present invention can be understood.

Example 2 Next, the period of the irregularities on the Si surface was reduced to 0.054 μm, that is, Si and G
The results when the distance is four times the least common multiple of the lattice spacing of aAs is shown below.

In the present embodiment, first, OFPR-800
(Manufactured by Tokyo Ohka) is spin-coated to a thickness of 0.4 μm, and prebaked at 180 ° C. for 10 minutes. Spin-coat PMMA (poly-methyl methacrylate) to a thickness of 0.15 μm on the upper surface,
Pre-bake at ℃ 20 minutes. Then, a pattern is drawn by using a variable rectangular beam type electron beam drawing apparatus with an acceleration voltage of 30 kV. Here, the electron beam irradiation amount is 300 μC / cm ² . Using IPA (isopropyl alcohol) as a developer,
A static development was performed for 1 minute to obtain a 0.054 μm line and space pattern. Then, SOG (Spin-on-Glass) thickness of 0.2 μm is spin-coated to flatten the pattern steps. Next, dry etching is performed for 20 minutes in a 100 mTorr CHF ₃ plasma, and the SOG is etched back until the PMMA surface is exposed.
Then, PMMA and OFPR-800 are anisotropically etched by reactive ion etching in a 10 Torr O ₂ plasma. Here, the portion where SOG remains, that is, the portion where PMMA has been removed by electron beam lithography remains during etching. Thereafter, the Si surface was processed by dry etching in 50 mTorr CBrF ₃ plasma. Thereafter, the wafer was washed with acetone to remove OFPR-800. As a result, a pattern of 0.054 μm line and space irregularities (step difference 0.05 μm) was obtained on the Si surface. Here, a pattern obtained by inverting the PMMA pattern obtained by electron beam lithography is obtained.

The above steps are substantially the same as the steps described in [Example 1], and can be formed by a method usually used in an electron beam drawing process. Further, even if the above-mentioned line and space is formed by using a method other than electron beam drawing, the effectiveness of the present invention described below does not change.

Then, Ga was deposited on the Si substrate by using the same method as in [Example 1].
As crystals were grown. When these samples were evaluated by electron microscope observation, the lattice defects remaining in GaAs were 10 ³
Pcs / cm ² . That is, 0.
GaAs formed on it by narrowing from 19μm to 0.054μm
It can be seen that lattice defects in s decrease.

The horizontal axis represents the distance (d) of one cycle of the irregularities on the Si substrate surface, and
FIG. 3 shows the results of sorting the lattice defect densities remaining in GaAs on the vertical axis. For the straight line (31), d is 0.054 μm, 0.135 μm
m, 0.189 μm, that is, 4 times, 10 times, 16 times the least common multiple (0.0135 μm) of the lattice spacing between GaAs and Si, respectively.
It is the result at the time of double. It can be seen that the lattice defect density is significantly reduced with the decrease of d.

On the other hand, the straight line (32) in FIG. 3 shows that d is 0.061 μm and 0.088 μm.
m, 0.155μ. That is, d is 4.5 times, 6.5 times, 11.5 times the least common multiple (0.0135 μm) of the lattice spacing between GaAs and Si.
Doubled. As can be seen from this figure, d is 0.0135 μm
Even if there is a deviation from an integral multiple of about 50% to about 50%, the lattice defect density in GaAs is reduced by forming a period of irregularities on the Si surface.

In the above-described embodiment, the unevenness of the Si surface portion was constituted by a line and space, that is, the distance ratio between the concave portion and the convex portion was 1: 1. If one period (d) of the concavo-convex structure is within an integral multiple of the least common multiple of the Si lattice and the GaAs lattice (0.0135 μm) or a deviation of 50% thereof, even if the ratio between the concave part and the convex part is not 1: 1. good. FIG. 4 is one embodiment which also shows this. Figure (a)
Is a ratio of the concave portion to the convex portion constituting d of 1: 1, and FIG.
FIG. 3C shows a 3: 1 structure. The same experiment as in Examples (1) and (2) was performed using these samples. However, it has been confirmed that a GaAs layer having substantially the same degree of crystallinity is formed on a Si substrate in the samples having the structures shown in FIGS.

In the embodiment shown in FIGS. 2 to 4, the description has been given only of the structure having a concave-convex cross section. It is clear from the description of FIG. 1 that the effectiveness of the present invention is also effective for structures other than the concavo-convex type. Actually, the same experiment as in FIGS. 2 to 4 was performed using a Si substrate having a sawtooth-shaped → cross-sectional periodic structure or a sinusoidal → cross-sectional periodic structure as shown in FIG.
In these examples, it was confirmed that the present invention was effective.

Incidentally, the periodic cause of the Si substrate surface for controlling the crystal growth of GaAs does not need to be geometrical irregularities on the Si surface, but may be the presence of an insulating film or a substance having a different chemical composition.

5 (a) and 5 (b) show a structure corresponding to FIG. 2 (e) formed by a method other than the unevenness of the Si surface. That is, in FIG. 5A, the periodic structure 51 on the Si surface for controlling the crystal growth of GaAs is formed of an insulating film such as an oxide film or a nitride film. Reference numeral 52 in FIG. 5B is formed by implanting a substance such as F, O, or C using a focused ion beam to change the chemical properties near the Si surface. When GaAs is grown using these samples by the same method as in the embodiment (1) or (2), a GaAs layer having substantially the same crystallinity as the embodiment (1) or (2) is grown on the Si surface. Was confirmed.

[Embodiment 3] In the above embodiments, for simplicity of explanation, the explanation has been made using a linear pattern arranged in parallel on the Si surface. The present invention is effective even if there are two or more types of these patterns and they are orthogonal or intersect at an arbitrary angle. FIG. 6 is a diagram for explaining these embodiments.

That is, FIG. 6 (a) shows a Si substrate having a plane orientation inclined at both positions of (100) or several degrees from (100). 6 (b) and 6 (c) are enlarged views of a part thereof. That is, in (b), the protrusion (62) and the recess (63) on the surface of the Si substrate are [11].
0] direction. In (c), the concave and convex portions on the Si surface are arranged in the [110] and [10] directions, that is, the linear patterns are perpendicular to each other.

On the other hand, FIG. 6D shows a Si substrate having a (111) plane orientation or a plane orientation inclined several degrees from (111). In (e)
Convex portions and concave portions formed on the Si surface are arranged in parallel only in the [10] direction, whereas in (f), they are [10]
And [01] direction, that is, two types of patterns intersect at 120 °. Also, as shown in (g), these linear patterns are represented by [10] and [0], respectively.
Patterns formed parallel to the [1] and [10] directions and crossing each other may form an equilateral triangle. An experiment of the same type as in FIGS. 2 to 4 was performed using an Si substrate formed by intersecting linear uneven patterns in this manner.
Also in these examples, it was confirmed that the present invention was effective and a good quality GaAs crystal was formed. By forming a pattern along the crystal orientation in this manner, lattice defects can be further reduced. In addition, it has become clear that it is more effective to form the patterned crystal while maintaining the symmetry thereof, which is even more effective.

In the present embodiment, the pattern has been described by taking a parallel straight line as an example, but the pattern is not limited to this. For example, in FIG. 6 (b), the straight lines 62 and 63 may be dots at appropriate intervals. Also, in FIG. 6 (c), projections or holes may be arranged in a point-like manner only at the intersection of the orthogonal straight lines. Further, projections or holes may be arranged at the middle of the intersections instead of the intersections. In any case, the point of the present invention is to provide some periodic structure as described in these examples.

In the above embodiments, the GaAs / Si structure has been described as an example. However, it goes without saying that the method of the present invention is effective even when applied to other heterostructure semiconductors. In fact, the method of the present invention is applied to GaP / Si, SiC / Si, AIP / Si, GaP / Ge, GaAs.
It has been confirmed that this method is also effective when applied to a range of hetero materials such as / Ge, Si _x Ge _y C _z / Si (x + y + z = 1).

Example 4 As an example, an example of application to Ge _0.5 Si _0.5 / Si heteroepitaxy will be described. According to the findings of the present inventors, Ge
_The lattice constant of _0.5 Si _0.5 differs from that of Si by about 2%. When the film thickness exceeds 100 °, dislocations are formed in the Si _0.5 Ge _0.5 film in order to reduce strain. On the Si substrate, irregularities having a depth of 0.05 μm were formed at intervals of line and space of 0.054 μm in the same manner as in Example 2, and a Si _0.5 Ge _0.5 film having a thickness of 500 μm was formed thereon by MBE.
Å formed. The formation condition is base vacuum degree 2 × 10 ^-11 T
Orr, a growth degree of 5 × 10 ⁻⁷ Torr, a substrate temperature of 550 ° C., a Ge cell temperature of 1200 ° C., and a Si source generated a molecular beam by electron beam heating. Observation of the formed film with a transmission electron microscope revealed that no dislocation was introduced even though the strain was relaxed. This indicates that the unevenness formed on the Si substrate very effectively solves the problem caused by the lattice constant difference in heteroepitaxy.

[Effects of the Invention] According to the present invention, there is an effect that two kinds of crystal layers having a large difference in lattice constant can be joined with extremely few various defects caused by lattice mismatch such as dislocation.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the present invention, and FIGS. 2 to 6 are explanatory diagrams of an embodiment of the present invention. 1 ... substrate material, 2 ... growth material, 3 ... tangling bond, 4 ... substrate material, 7 ... growth material, 51 ... insulating film, 52 ... ion implantation region.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masakazu Ishino 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory of Hitachi, Ltd. (72) Inventor Toshiyuki Yoshimura 1-280 Higashi-Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. (56) References JP-A-62-224946 (JP, A) JP-A-63-98120 (JP, A)

Claims (5)

(57) [Claims] 1. An epitaxial growth method for growing a second crystal material having a second lattice constant on a first crystal material having a first lattice constant, the method comprising: A first step of forming a pattern having a periodic structure corresponding to a substantially integral multiple of the least common multiple of the first lattice constant and the second lattice constant; and providing the pattern and forming the pattern on the first crystal material. A second step of forming a second crystalline material. 2. A method according to claim 1, wherein the period of the pattern is from a value corresponding to an integral multiple of the least common multiple of the lattice constant to ± 50% of a value corresponding to the least common multiple. Epitaxial growth method with a period changed within. 3. The epitaxial growth method according to claim 1, wherein said pattern is formed along a crystal axis of said first crystal material. 4. The epitaxial growth method according to claim 1, wherein said pattern has periodic irregularities. 5. The epitaxial growth method according to claim 1, wherein the pattern is a pattern formed by a periodic chemical modification or a material different from the first crystal material. Method.