JP2845464B2 - Compound semiconductor growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for growing a compound semiconductor on a substrate made of a material having a different lattice constant, wherein the epitaxial layer of the compound semiconductor having a flat growth surface and excellent crystallinity of the grown layer has a different lattice constant. The purpose of the present invention is to provide a method for growing a compound semiconductor that can be grown on a substrate.
A first preparation step of supplying As in the form of molecules or hydrides to form an As layer of about 1 atomic layer, and then supplying Al in the form of molecules or organometallic gas to form an Al layer of about 1 atomic layer III-V having a lattice constant different from that of the base crystal and within ± 5% of the lattice constant of AlAs.
And a growth step of growing a group III compound semiconductor.

The present invention relates to epitaxial crystal growth, and more particularly to a method for growing a compound semiconductor on a substrate made of a material having a different lattice constant.

In recent years, with the progress of compound semiconductor devices, there has been a demand for a crystal material having a larger diameter, a lower price, and a crystal structure realizing new functions. Therefore, a technique for growing a heteroepitaxial crystal in which the lattice constants of the substrate and the growth layer are different from each other is required. A typical example is GaAs on a Si substrate.
This is generally called GaAs on Si. However, in order to produce such a heteroepitaxial crystal, it is necessary to take special measures in the early stage of growth in order to overcome the difference in lattice constant.

[Prior Art] The following mainly describes an example of epitaxial growth of GaAs on a Si substrate.

As a conventional technique for epitaxially growing GaAs on a Si substrate, there is a technique called two-step growth in which MOCVD or MBE is improved. For example, a method published by Akiyama et al. In the Japanese Journal of Applied Physics (M.Akiy
ama et al., Jpn. J. Appl. Phys. 23 (1984) L843) is as follows.

As shown in FIG. 2A, first, the substrate temperature is set to a temperature lower than a normal single crystal growth temperature (600 to 850 ° C.), for example, 40 ° C.
Keep at 0-450 ° C, and use thin amorphous or polycrystalline Ga
As buffer layer 23 is grown. The thickness is, for example, about 10 nm. At this stage, the buffer layer 23 is in an amorphous phase or a polycrystalline phase and is not an epitaxial growth layer.

Next, the substrate temperature is raised to a normal single crystal growth temperature, for example, around 700 ° C. Then, as shown in FIG. 2 (B), the buffer layer having an amorphous phase or a polycrystalline phase was obtained.
Solid phase growth proceeds within 23, and changes into an epitaxial single crystal phase.

After the buffer layer 23 is single-crystallized, as shown in FIG. 2C, the GaAs epitaxial layer 25 having a required thickness is formed thereon.
Grow.

It is known that when an attempt is made to grow a GaAs layer directly on a Si substrate, an island-like growth occurs in which oil repels water, and it is difficult to grow a flat surface. In the two-stage growth described above, a flat growth surface is realized by first growing a buffer layer of an amorphous phase or a polycrystalline phase.

However, even if two-step growth is used, it is not easy to produce high-quality crystals because the first growth layer is not a single crystal, high-density dislocations occur, and the flattening of the growth layer surface deteriorates. Or

[Problems to be Solved by the Invention] As a crystal for an electronic device, a crystal layer having a flat surface and excellent crystallinity is desirable. If the surface is not flat, problems are likely to occur in the processing process. If the crystallinity is poor, the carrier life is reduced, and it is difficult to sufficiently bring out the original performance of the material, and the life and reliability of the device are also likely to be reduced.

As described above, the growth layer obtained by the conventional heteroepitaxial crystal growth technique is not always sufficient in terms of the flatness of the growth surface and the crystallinity of the growth layer.

Therefore, the characteristics of a device using this crystal as a material cannot be improved, and there has been a problem that a light emitting device has a short lifetime.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compound semiconductor growth method capable of growing a compound semiconductor epitaxial layer having a flat growth surface and excellent growth layer crystallinity on substrates having different lattice constants.

By using a new crystal growth system, it is intended to improve the quality, eg, dislocation density, of a compound semiconductor epitaxial layer on a substrate having a different lattice constant such as GaAs on Si.

[Means for Solving the Problems] According to the present invention: (1) Instead of directly growing a target compound semiconductor on a substrate, AlAs is first grown.

(2) In the growth of AlAs, the first layer has As and the second layer has
A growth raw material is supplied to the substrate so as to apply Al by approximately one atomic layer at a time.

 1 (A) to 1 (D) show explanatory diagrams of the principle of the present invention.

In FIG. 1 (A), an As layer 3 is grown by about one atomic layer on a base crystal 1 made of either Si or Ge. In this step, the surface of base crystal 1 is almost hidden.

Next, as shown in FIG. 1B, an Al layer 5 is grown on the As layer 3 by about one atomic layer.

Next, as shown in FIG. 1C, a buffer layer 7 of AlAs or a target III-V compound semiconductor to be grown is grown on the Al layer 5. Here, the target group III-V compound semiconductor is a group III-V compound semiconductor having a lattice mismatch within ± 5% of the lattice constant of AlAs, and includes a mixed crystal.
When the target group III-V compound semiconductor does not contain As, it is preferable to grow As one atomic layer at the beginning of the buffer layer growth.

Further, it is preferable to repeat a cycle of growing the As atomic layer and growing the Al atomic layer a plurality of times.

Thereafter, as shown in FIG.
A layer 9 of a group V compound semiconductor is grown to a required thickness.

When doping with an impurity is desired, for example, an impurity element may be added simultaneously with the growth.

Further, the intended group III-V compound semiconductor includes a mixed crystal of group III-V compound semiconductor.

[Function] First, an AlAs molecular layer is grown on a base crystal having a different lattice constant, and thereafter, the deviation of the lattice constant with respect to AlAs is within 5%.
By growing a group III-V compound semiconductor, the effects of lattice irregularities are reduced.

Further, when growing a crystal of a III-V compound semiconductor on a heterogeneous substance, island-like growth is generally likely to occur. In particular,
When the underlying crystal is a single element semiconductor such as Si or Ge, only nonpolar covalent bonds are formed in the substrate, and an ionic III-V compound semiconductor layer is uniformly grown thereon. Is difficult. When first growing an atomic layer of As on the base crystal and then growing an atomic layer of Al, it is easy to obtain a very excellent surface coverage. As a result, island-like growth hardly occurs, and an epitaxial layer having a flat surface is easily grown thereon.

It is preferable to appropriately provide the buffer layer 7 according to the degree of lattice irregularity between the base crystal and the growth layer.

Unlike the conventional two-step growth, a single crystal phase III-V compound semiconductor layer can be directly grown on a base substrate.

Example An example in which a GaAs epitaxial layer is grown on a Si substrate will be described with reference to FIGS. 3 (A) to 3 (H).

First, as shown in FIG. 3 (A), an Si substrate 11 is prepared as a base crystal, on which a (100) plane or a plane inclined within 10 degrees from the (100) plane is exposed.

All of the crystal growth was performed in the gas phase using an apparatus capable of atomic layer growth (ALE) and metal organic chemical vapor deposition (MOCVD). The source gas used was such that the As atom was arsine (As
H ₃ : diluted to 10% with hydrogen), Ga atoms are trimethylgallium (TMG), and Al atoms are trimethylaluminum (TMA).

The monoatomic layer is grown by, for example, selectively flowing a single group V element source gas onto the heated substrate 11, replacing the inside of the reaction tube with hydrogen after stopping, and then flowing another group III element source gas. The cycle of replacing the inside of the reaction tube with hydrogen was repeated.

 The procedure of crystal growth will be described in more detail below.

(1) The Si substrate 11 as shown in FIG. 3 (A) is housed in a growth apparatus capable of selectively performing atomic layer growth (ALE) and metal organic chemical vapor deposition (MOCVD), and is placed in a hydrogen gas stream. 20 minutes, about 10
Heat at 00 ° C. Thus, the surface of the Si substrate 11 is cleaned. After cleaning, the substrate temperature is lowered to 500 ° C.

(2) As shown in FIG. 3 (B), arsine as an As source is supplied for about 10 seconds, and then the supply of arsine is stopped and hydrogen is supplied for about 10 seconds. As a result, about one atomic layer of the As layer 13 is formed.
Grows, and the arsine or As in the reaction tube is purged.

(3) Next, as shown in FIG. 3 (C), TM as an Al source
A is supplied for about 7 seconds, then the supply of TMA is stopped, and hydrogen is supplied for about 10 seconds. Thereby, the Al layer 15 grows, and TMA or Al in the reaction tube is purged.

Incidentally, the Al atomic layer 15 on the As atomic layer 13 is shown in FIG.
As schematically shown in FIG. 3, the in-plane density is about twice that of the underlying As layer. Therefore, it is considered that excellent surface coverage is achieved.

(4) A next As layer is grown on the double-density Al atomic layer in the same process as in FIG. 3 (B). Then, it is considered that Al atoms freely move up and down in at least one layer, and therefore it is considered that Al is supplied from the lower double density Al layer 15 upward as AlAs is bonded. That is, the original Al layer 15
Becomes the original density, and As layer 13-2, Al layer 15-2, As
Layer 13-3 grows. That is, FIGS. 3 (C) and (E)
The two molecular layers grow in one cycle of the two steps.

(5) Further, by the same process as in FIG.
As shown in FIG. 3F, when TMA is supplied to grow an Al layer, an Al layer 15-3 having twice the surface density grows.

(6) In this way, the As atomic layer and the Al atomic layer
After growing for 50 cycles, an AlAs buffer layer 17 as shown in FIG. 3C is grown.

Wherein the reaction tube pressure 20 torr, the flow rate is AsH ₃ 480scc
m, the flow rate of hydrogen is adjusted so that TMG is 40 sccm and the total flow rate is 2 slm.

Such atomic layer epitaxy is described in, for example, Ozeki et al. (M. Ozeki et al., Extended Abstracts of
the 19th Conf.on Solid State Devices and Material
s, Tokyo, 1987, p. 475).

(7) Next, the temperature is raised to 650 ° C., and GaAs is grown by MOCVD as shown in FIG. Here, the pressure inside the reaction tube is 20 torr, and the flow rate is 2 scc for TMG.
m, AsH ₃ is 40 sccm. When the thickness of the growth layer 19 by MOCVD reaches a value required for the device (for example, 3 μm), the growth is stopped.

The epitaxially grown layer thus obtained exhibited excellent crystallinity. The dislocation density, which was 10 ⁸ / cm ^{2 in the} conventional two-stage growth, was reduced to 10 ⁶ / cm ^{2 in} the case of the sample of this example. In addition, the flatness of the surface was greatly improved.

FIG. 4 shows another embodiment of the present invention. In the above embodiment, 100 molecular layers of AlAs are first grown, but after growing two molecular layers of AlAs, the process may shift to atomic layer epitaxy of GaAs. In FIG. 4, reference numeral 11 denotes a (100) plane Si substrate,
When an As atomic layer, an Al atomic layer, and an As atomic layer are grown thereon, the AlAs 2 molecular layer 14 and one more As atomic layer grow as described above. After that, the Ga atomic layer and the As atomic layer are alternately grown on this As atomic layer, so that the Ga atomic layer grows.
As a buffer layer 16 is obtained. After growing a certain amount of the buffer layer 16 in the atomic layer, the temperature is increased and the thickness of G required for MOCVD is increased.
The aAs layer 19 is grown. The method of growing GaAs and AlAs while controlling them in the atomic layer order is not limited to the atomic layer epitaxy described above. Any method capable of growing a target atomic layer may be used, for example, migration enhanced epitaxy (Y.Ho.)
rikoshi et al .: Jpn.J.Appl.Phys. 25 (1986) L868) and M
A flow-modulated epitaxy modified from OCVD
ated epitaxy) (N.Kobayashi et al .: Jpn.J.Appl.Phy
s. 25 (1986) L513) and similar growth can be achieved. In addition, it can be carried out in principle using an ordinary MOCVD or MBE apparatus. The difference between these growth methods is completeness with respect to single atomic layer growth, and in this regard, atomic layer epitaxy is the best at the current state of the art, and is preferred for crystal growth.

Impurities can be added during atomic layer growth. For example, Si may be added to the Al layer to make it n-type, or Si may be added to the As layer to make it p-type.

The growth of the growth layer is not limited to MOCVD, and various methods of liquid phase and gas phase can be used.

By the way, GaAs on Si has been described as an example, but other underlying crystals and grown crystals can also be used. In particular, when the underlying crystal is a single element semiconductor such as Si or Ge, the effect of preventing island growth and growing an epitaxial layer having a flat surface is great. The most characteristic point of the present invention is that an Al atomic layer having an area density about twice as large as that of an Al atomic layer is grown on the As atomic layer, and is continuously grown thereon.

When GaAs is grown, AlAs is a material that lattice-matches almost with GaAs, and Si has a lattice constant smaller than about 4% GaAs. On the other hand, InP has a lattice constant larger than about 4% GaAs.

When InP is grown on Si, two or more AlAs molecular layers are formed on a Si substrate, GaAs is grown to a thickness of, for example, 1 μm, and InP is grown to a predetermined thickness.

Although the effect is lower than in the case of a single element semiconductor substrate, GaP, GaAs, In _x Ga _{1 -x} As (X ≦ 0.02) or the like can be used as a base crystal. The growth layer has good compatibility with the AlAs molecular layer, and has a zinc-blende type crystal structure having a lattice mismatch with AlAs of 5% or less (including mixed crystals).
Can grow.

[Effects of the Invention] As described above, according to the present invention, a single crystal can be grown from the beginning with respect to the growth of a heteroepitaxial crystal in which the substrate and the growth layer have different lattice constants.

Therefore, there is an effect of improving the quality of the growth layer, which greatly contributes to the improvement of the performance of a device using the material.

[Brief description of the drawings]

1 (A) to 1 (D) are explanatory views of the principle of the present invention, each showing a cross-sectional view of a crystal, and FIGS. 2 (A) to 2 (C) are diagrams showing a conventional two-stage Si growth.
3 (A) to 3 (H) are cross-sectional views illustrating the growth of GaAs on Si.
FIG. 4 is a sectional view for explaining GaAs growth on Si according to another embodiment of the present invention. In the figure, 1... Underlying crystal 3... As layer 5... Al layer 7... AlAs or target buffer layer 9... Target layer 11... Si substrate 13. 13-i ... As layer in buffer layer 15-i ... Al layer in buffer layer 17 ... Buffer layer 19 ... Epitaxial growth layer 14 ... AlAs2 molecular layer 16 ... GaAs buffer layer 21 ... Si substrate 23 …… GaAs buffer layer 25 …… GaAs single crystal

────────────────────────────────────────────────── (5) References JP-A-1-296672 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/203 H01L 21/205 C30B 23 / 00-25/00 C30B 29/00

Claims (3)

(57) [Claims] An underlayer crystal made of one of Si and Ge (1)
A first preparation step in which As is supplied in the form of molecules or hydrides to form an As layer (3) of about one atomic layer, and then Al is supplied in the form of molecules or organometallic gas to form an Al layer A second preparation step of forming about one atomic layer of (5), and thereafter, a III-V compound semiconductor having a lattice mismatch different from that of the base crystal and within ± 5% of the lattice constant of AlAs (9) A growing step of growing a compound semiconductor. 2. Following the second preparation step, As is further supplied in the form of a molecule or a hydride to form a bimolecular AlAs layer with Al adhering to stoichiometry or more on the underlying crystal. 2. The method for growing a compound semiconductor according to claim 1, comprising a step. 3. The compound semiconductor growth method according to claim 1, wherein the pair of the first preparation step and the second preparation step is one preparation cycle, and after performing a plurality of preparation cycles, the method proceeds to the growth step.