JPH08245291A - Method for growing iii-v compound semiconductor crystal - Google Patents

Abstract

PURPOSE: To provide a method for growing a DI-V compd. semiconductor crystal by which the thickness of a layer in which carbon has been doped at a high concn. can be controlled on an atomic layer level and highly uniform growth can be carried out even on a substrate of a large diameter. CONSTITUTION: When a III-V compd. semiconductor crystal is grown by an organometallic vapor growth method, organometallic stock of a group III metal and organometallic stock of a group V metal are alternately fed and carbon is doped. If necessary, hydride of a group V metal is fed between the feeds of the stocks or added to the latter stock and fed, the amt. of the hydride fed and the feeding time are regulated and the amt. of carbon doped is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal organic chemical vapor deposition method for III-V compound semiconductor crystals.

[0002]

2. Description of the Related Art Metal Organic Chemical Vapor Deposition Method (OMVPE Method)
Has excellent film thickness control, and has been used for producing a substrate for a heterojunction device using a compound semiconductor. Among the heterojunction devices, HBT (heterojunction bipolar transistor) is actively developed because it operates at a very high speed. The structure of HBT is as follows: n-GaAs collector, p-AlGaAs base and n-AlGaAs
It consists of an emitter. The HBT characteristics are higher as the hole concentration of the base layer is higher and the thickness of the base layer is thinner. Further, by grading the Al composition in the base layer from the emitter side to the collector side, higher speed operation becomes possible.

Conventionally, Zn has been used as a p-type dopant in the OMVPE method, but since the diffusion coefficient of Zn is large, it diffuses from the base region to the emitter region during growth to obtain a sharp pn junction. There was a problem that I could not do it. In addition, doping of Mg, which has a diffusion coefficient five orders of magnitude smaller than that of Zn, has been studied, but since the Mg raw material is likely to be adsorbed by the pipe or the reaction tube, the steep doping
It is difficult to form a profile. Therefore, recently, carbon doping has been studied. For example, it has been proposed to perform carbon doping of 2 × 10 ¹⁹ cm ⁻³ using TMGa as a group III source material and TMAs as a group V source material at a growth pressure of 76 Torr (Appl. Phys. Lett. Vol.
53, No. 14, p. 1317-1319: TF Kuech et al.).

The present inventors have used a Group V organometallic raw material,
2.5 × 1 by OMVPE method by growing under reduced pressure
It was reported that carbon doping with a high concentration of 0 ²⁰ cm ^-3 is possible (Inst. Phys. Conf. Ser. No 112: Cha.
pter 3, Paper presented at Int. Symp. GaAs and Rela
ted Compounds, Jersey, 1990). In addition, when TMGa as a group III source and TMAs as a group V source were simultaneously flown to perform carbon-doped GaAs vapor phase growth by the OMVPE method, it was proposed to add AsH ₃ to control the carbon doping amount. (Japanese Patent Laid-Open No. 2-3516).

On the other hand, regarding the thickness of the base layer, 100
It is necessary to accurately control the thickness of nm or less, and it is also required that the uniformity within the substrate surface is high. Conventional OMV
In the PE method, since the growth rate of the crystal thin film is basically determined by the supply rate of the group III raw material to the substrate surface, accurate control of the raw material supply amount is necessary to accurately control the thickness of the base layer. However, control at the atomic layer level is difficult. Moreover, since the uniformity of the thickness in the plane of the substrate depends on the gas flow,
It is also difficult to ensure uniformity on a large-diameter substrate.

Thus, a high-performance HBT has been realized.
As a base layer, 10²⁰cm ^-3High concentration dose
Ping and uniform atomic layer level thickness below 100 nm
OM using conventional Group V organometallics is required because
Growth of the carbon-doped layer by the VPE method is not sufficient.
Was. Further, in the case of a tilted base layer, A within 100 nm
l It is necessary to change the composition in a predetermined profile.
Was.

[0007]

Therefore, according to the present invention,
Growth of III-V group compound semiconductor crystal capable of solving the above problems and controlling a layer doped with high concentration of carbon at a thickness of atomic layer level and capable of performing highly uniform growth even on a large-diameter substrate. It is intended to provide a method.

[0008]

The present invention provides (1) a metal-organic vapor phase epitaxy method for III-V compound semiconductor crystals, comprising:
Carbon is doped by alternately supplying Group I organometallic raw materials and Group V organometallic raw materials III-
Method for growing V group compound semiconductor crystal, (2) Between supply of group III organometallic raw material and supply of group V organometallic raw material, and /
Alternatively, a Group V hydride is supplied between the supply of the Group V organometallic raw material and the supply of the Group III organometallic raw material, and the carbon doping amount is controlled by adjusting the supply amount and supply time. The method for growing a III-V compound semiconductor crystal according to the above (1), and (3) adding a group V hydride to a group V organometallic raw material and supplying the raw material to adjust the amount of the group V hydride added. (1) characterized by controlling the carbon doping amount by
The method for growing a III-V compound semiconductor crystal described above.

Trimethylgallium (TMGa), trimethylaluminum (TMAl), etc. can be used as the group III organic metal raw material used in the present invention, and trimethylarsenic (TMAs), trimethylarsenic (TMAs), etc. can be used as the group V organic metal raw material.
Triethyl arsenic (TEAs) etc. can be used,
Group V hydrides include arsine (AsH ₃ ), tertiary butyl arsine [(C ₄ H ₇ ) AsH ₂ = TBA
s] Triethylgallium (TEGa), triethylaluminum (TEAl) and the like can be used.

[0010]

[Operation] Using TMGa and TMAs as raw materials, GaA
The procedure for growing s is as follows. TMGa is introduced into the growth chamber to adsorb one atomic layer on the substrate surface. Excess TMGa in the growth chamber is purged. The TMAs are introduced into the growth chamber and reacted with the Ga compound adsorbed on the substrate surface to grow only one molecular layer of GaAs. Purge TMAs in the growth chamber.

When TMGa is adsorbed on the substrate in a single layer in the step (1), it becomes a Ga compound in which one or two methyl groups are bonded to Ga, and the Ga compound is not adsorbed on it. When TMAs is introduced and GaAs grows as a monolayer in the step of, the C of the methyl group that has been bonded to Ga is taken into the crystal and becomes an acceptor. Since As is not adsorbed on the As layer, TMAs is purged in the step of
Repeat steps from. Thus, in order to grow crystals by adsorbing and reacting one atomic layer of Ga and As,
It becomes possible to control the film thickness in atomic layer units.

Usually, in a growth method called an atomic layer epitaxial method or a molecular layer epitaxial method, arsine (AsH ₃ ) is introduced. In this case, a hydrogen atom formed by decomposition of arsine is bonded to a methyl group of TMGa. It is thought that most of the carbon is not incorporated into the crystal. However, in the present invention, since a Group V organometallic raw material that does not generate hydrogen atoms is used, most of the carbon is incorporated into the crystal, so high-concentration carbon doping is possible.

Since the above GaAs growth rate does not depend on the amount of the group III raw material supplied to the substrate surface by the gas flow, it enables an extremely uniform layer thickness even on a large-diameter substrate. In the above GaAs growth, TEAs can be used instead of TMAs to perform the same growth. Also, using TMAl instead of TMGa, AlA
s can be similarly grown.

In carbon doping of the OMVPE method using a group V organic metal, the doping amount of carbon can be controlled by changing the growth temperature. Even in the present invention, it is possible to control the doping amount by the growth temperature to some extent. This is because the higher the growth temperature is, the more the methyl group bonded to Ga adsorbed on the substrate is thermally decomposed, and the carbon uptake is reduced.

However, if the growth temperature is too low or too high, the growth of each atomic layer cannot be maintained. That is, when the temperature is low, the growth reaction becomes difficult to occur, and when the temperature is high, the thermal decomposition of TMGa proceeds, and Ga is deposited on the substrate surface. Therefore, a method of controlling the doping amount other than the growth temperature is required.

By the way, when a Group V hydride such as arsine is supplied after adsorbing a Group III organometallic raw material on the substrate surface, the methyl group or ethyl group of the Group III organometallic raw material adsorbed on the substrate surface is converted from arsine. It reacts with the generated hydrogen atoms to form methane or ethane, which is released from the substrate surface, so that carbon uptake is suppressed.

Therefore, in the present invention, the doping amount of carbon is controlled by adjusting the supply amount and / or supply time of the group V hydride such as arsine. The supply of the group V hydride may be performed between the supply of the group III organic metal raw material and the supply of the group V organic metal raw material, or may be added to the group V organic metal raw material and supplied.

According to the present invention, the doping amount of carbon into the III-V compound semiconductor crystal is 5 × 10 ¹⁶ to 1 × 10 ²¹ c.
It is possible to control in the range of m ⁻³ , and in order to secure the doping amount, the supply amount of the group V hydride is III
A range of 0 to 200% of the supply amount of the group organometallic raw material is suitable.

[0019]

【Example】

(Example 1) A semi-insulating GaAs substrate was placed in a reaction tube, the pressure in the tube was kept at 10 Torr, and the substrate was heated to 700 ° C and cleaned in advance with TMAs flowing, and then the substrate temperature was raised to 450 ° C. Lowered the supply of TMAs. The carrier gas hydrogen is always 500 scc.
supplied in m.

Next, TMGa was introduced at 6 sccm for 5 seconds and then purged with hydrogen for 10 seconds.
It was introduced at 0 sccm for 5 seconds and then purged with hydrogen for 10 seconds. After repeating this operation for 500 cycles, TMAs
The substrate temperature was returned to room temperature while flowing, and the growth was completed. The thickness of the grown crystal was 1400Å, which was in agreement with the value obtained when one molecular layer (2.83Å) was grown per cycle, and it was confirmed that the growth was one molecular layer epitaxial. When the carbon concentration was measured by SIMS measurement, high concentration doping of 1 × 10 ²¹ cm ⁻³ was confirmed. In addition, when the substrate temperature was changed to 350 ° C. and 550 ° C. and other conditions were the same as those described above, only 0.5 molecular layer was grown at 350 ° C.
At ° C. It became thick with 1.5 molecular layers.

Example 2 A semi-insulating GaAs substrate was placed in a reaction tube, the pressure in the tube was kept at 10 Torr, and the substrate was heated to 700 ° C. in a state where TEAs was flowed in advance and cleaned. TEA down to 550 ° C
The supply of s was stopped. The carrier gas hydrogen is always 5
Supplied at 00 sccm.

Next, TMAl was introduced at 8 sccm for 5 seconds and then purged with hydrogen for 10 seconds.
It was introduced at 00 sccm for 5 seconds and then purged with hydrogen for 10 seconds. After repeating this operation for 500 cycles, TEA
The growth was completed by returning the substrate temperature to room temperature with s flowing. The thickness of the grown crystal was 1400Å, which was in agreement with the value obtained when one molecular layer (2.83Å) was grown per cycle, and it was confirmed that the growth was one molecular layer epitaxial. When the carbon concentration was measured by SIMS measurement, high-concentration doping of 3 × 10 ²¹ cm ⁻³ was confirmed. When the substrate temperature was changed to 350 ° C. and 650 ° C. and the other conditions were the same as above, only 0.4 molecular layer was grown at 350 ° C.
At ° C. It became thick with 1.4 molecular layers.

(Third Embodiment) In the first embodiment, TMGa is used.
50 sccm of hydrogen containing 1% arsine was supplied for 1 second between the supply of TMAs and TMAs. The gas supply procedure is as follows. TMGa (6 sccm) supplied for 5 seconds Hydrogen (500 sccm) purge for 10 seconds 1% arsine-containing hydrogen (50 sccm) supplied for 1 second Hydrogen (500 sccm) purge for 10 seconds TMAa (50 sccm) supplied for 5 seconds Hydrogen (500 sccm) purge 10 seconds 1% arsine-containing hydrogen (50 sccm) was supplied for 1 second Hydrogen (500 sccm) purging for 10 seconds The above operation was repeated 500 cycles to give a crystal thickness of 140
It became 0 Å, and it was confirmed that the growth was one molecular layer epitaxial. When the carbon concentration was measured by SIMS, it was 2 × 10 ²⁰ cm ⁻³ , and it was confirmed that carbon doping could be controlled by supplying arsine.

(Example 4) In Example 2, TMAl
And TEAs are supplied, and at the same time as TEAs, TBAs are set to 10
Supplied at 0 sccm. The gas supply procedure is as follows. Supply TMAl (8 sccm) for 5 seconds Hydrogen (500 sccm) purge for 10 seconds TEAa (100 sccm) and TBAs (100 sc)
cm) for 5 seconds Hydrogen (500 sccm) purge for 10 seconds The above operation was repeated 500 cycles to obtain a crystal thickness of 140
It became 0 Å, and it was confirmed that the growth was one molecular layer epitaxial. When the carbon concentration was measured by SIMS, it was 5 × 10 ²⁰ cm ⁻³ , and TB
It was confirmed that the carbon doping can be controlled by supplying As.

When the epitaxial layer thickness of the 3-inch diameter substrate obtained by the conventional method was measured, there was a variation of 5 to 10%, but in the above examples, all were within the measurement error range of 1% or less. .

[0026]

As described above, according to the present invention, by supplying the group III organic metal raw material and the group V organic metal raw material alternately onto the substrate, the layer doped with carbon at a high concentration can be formed at the atomic layer level. It has become possible to grow an epitaxial layer having high uniformity even on a large-diameter substrate. Further, the doping amount of carbon can be controlled in a wide range by supplying the Group V hydride between the supply of the Group III organic metal raw material and the Group V organic metal raw material or by adding it to the Group V organic metal raw material. Became possible.

Claims (3)

[Claims] 1. A metal-organic vapor phase epitaxy method for a III-V group compound semiconductor crystal, wherein carbon is doped by alternately supplying a group III organic metal raw material and a group V organic metal raw material. Method for growing group V compound semiconductor crystal. 2. A group V organic metal raw material supply to a group V organic metal raw material supply and / or a group V organic metal raw material supply to a group III organic metal raw material supply. The method for growing a III-V compound semiconductor crystal according to claim 1, wherein hydride is supplied, and the carbon doping amount is controlled by adjusting the supply amount and the supply time. 3. The II according to claim 1, wherein a group V hydride is added to a group V organometallic raw material and supplied, and the amount of the group V hydride supplied is adjusted to control the carbon doping amount.
Method for growing group IV compound semiconductor crystal.