JP3536699B2 - Compound semiconductor vapor phase epitaxial growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for vapor-phase epitaxial growth of a compound semiconductor crystal comprising two or more heterogeneous semiconductor layers.

[0002]

2. Description of the Related Art An epitaxial wafer for various devices using a compound semiconductor exhibits its characteristics by stacking different types of epitaxial layers in multiple layers. When a heterogeneous semiconductor is continuously formed, elements are mixed near an interface between the heterogeneous semiconductors, and a so-called composition transition layer is formed. This can cause characteristic deterioration in any semiconductor device.

One of the factors for forming such a composition transition layer is incomplete gas replacement in the vapor phase epitaxial growth method. Due to the fact that different types of semiconductors are formed in the same equipment, epitaxial growth equipment has many pipes, valves, control pressure gauges, and flow meters.
Even if it is suppressed as much as possible, some gas stagnation remains in the apparatus. If the raw material of the immediately preceding growth layer remains in this portion, the gas gradually flows out of the stagnant portion at the start of the growth of the next layer, and a composition transition layer is formed at the interface between the two layers.

For this reason, when switching the normal gas, a so-called growth interruption is provided, in which a carrier gas is flowed without flowing a part or all of the raw material gas. During the growth interruption, the film formation is stopped, and the replacement of gas proceeds. This technology makes it possible to suppress the composition transition layer to one molecular layer or less.

[0005]

The above-described prior art growth interruption has an excellent effect in terms of gas replacement, but the surface after growth has been exposed to a carrier gas during the growth interruption. Since the surface exposed to the carrier gas changes, optimization is usually made by examining the time and temperature of the growth interruption.

However, particularly when hydrogen is used as a carrier gas, the growth is interrupted to cause defects on the surface and further irregularities on the surface, and after growth, it is observed as composition fluctuation at the interface. In particular, it was found that this was remarkable when the growth film before interruption was a system containing indium.

Therefore, an object of the present invention is to solve the above-mentioned problem and to prevent a composition fluctuation (composition transition layer) due to crystal defects from occurring at an interface between different types of semiconductor junctions even when a growth interruption time sufficient for gas replacement is provided. An object of the present invention is to provide a compound semiconductor vapor phase epitaxial growth method used as a growth interruption method.

[0008]

Means for Solving the Problems To achieve the above object, a compound semiconductor vapor phase epitaxial growth method of the present invention is a method for epitaxially growing a compound semiconductor crystal comprising two or more different types of semiconductor layers by a vapor phase growth method. there are, using hydrogen as a carrier gas, and a method for performing gas switching interrupt the growth layers, indicator
After the growth of the first semiconductor layer of gallium, arsenide and arsenic, before the growth of the second semiconductor layer of gallium, indium, and phosphorus , the carrier gas flowing during the interruption of the growth is made of hydrogen and an inert gas. The main gas is used (claim 1).

[0009] As the inert gas, nitrogen or a rare gas,
Or it may be used a mixed gas of nitrogen and a rare gas (請
Claims 2, 3, 4 ). The concentration of hydrogen to be mixed into the inert gas is preferably not more than 25% (claim 5). As the vapor deposition method can be used metal organic chemical vapor deposition (claim 6).

The gist of the present invention is that the carrier gas to be supplied when the growth is interrupted is changed to a composition mainly composed of an inert gas.

Conventionally, hydrogen has been used as a carrier gas. When growing using an inert gas as a carrier gas, mixing of oxygen becomes a problem particularly when aluminum is contained. However, even in systems that do not contain aluminum,
The use of hydrogen as a carrier gas has become common practice to increase purity.

However, if hydrogen is used as a carrier gas during the interruption of the growth, an element which easily combines with hydrogen in the crystal is desorbed as a hydride, or a hydride generated in an upstream portion of the reactor is mixed as an impurity. there's a possibility that. This also increases the possibility of forming crystal defects on the growth surface during growth interruption.

On the other hand, when the carrier gas is a gas mainly composed of hydrogen and an inert gas according to the present invention, it is difficult to form a compound with a constituent element of the semiconductor,
Interaction with the surface can be suppressed as compared with the case of hydrogen. At this time, the concentration of hydrogen mixed with the inert gas is 25
% Or less, a remarkable effect of improving the electron mobility of the epitaxial wafer can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described mainly with reference to examples.

FIG. 1 shows a laminated structure of a GaInP-based epitaxial wafer to be grown according to the present invention.
This is a semi-insulating gallium arsenide (GaAs) substrate 1
An un (undoped) GaAs buffer layer 2 having a thickness of 0.5 μm is provided thereon, and a pseudomorphic (Pseudo
In a morphic state, a channel layer 3 made of un-type indium-gallium-arsenic (un-type InGaAs) having a thickness of 14 nm is provided, and a 2 nm-thick un-type GaInP is further formed thereon.
38 nm thick n-type GaInP through a spacer layer 4 of
Provided with a carrier supply layer 5 composed of a high electron mobility transistor (HEMT).

The channel layer 3 of un-type InGaAs In
As composition ratio is 15%, spacer layer 4 of carrier supply layer 5
The GaP composition ratio of the un-type GaInP is 52%, and the GaP composition ratio of the n-type GaInP of the carrier supply layer 5 is 52%.

The above gallium, indium, phosphorus (GaI)
nP) and indium gallium arsenide (InGaAs)
(A cross-sectional structure is shown in FIG. 1)
By MOVPE
Method). The growth conditions are as shown in Table 1.

[0018]

[Table 1]

The carrier gas was hydrogen gas, and the raw materials used were trimethylgallium, trimethylaluminum, trimethylindium and triethylgallium as the organic metal raw materials and arsine, phosphine and disilane as the hydride raw materials. The growth pressure is about 50 Torr and the growth temperature is 6
The temperature was set to 00 ° C. The plane orientation of the semi-insulating GaAs used for the substrate was (100).

On a semi-insulating GaAs substrate 1, an un-type Ga
As buffer layer 2, un-type InGaAs channel layer 3,
An un-type GaInP spacer layer 4 and a carrier supply layer 5 made of n-type GaInP were sequentially deposited. At that time, G
aInP spacer layer (second semiconductor layer) 4 and InGaAs
At the interface with the s channel layer 3 (first semiconductor layer), 30
The growth was interrupted for ６００600 seconds, during which the carrier gas and phosphine were flowed. Phosphine is added at l.p.m. for surface protection. 4 liters (1.4 SLM), carrier gas is 38.6S, mainly hydrogen and inert gas
LM flow was performed.

Here, in order to clarify the effect of the present invention,
(1) Only hydrogen (conventional example)
Comparison was made under three conditions: (2) a mixture of 20 SLM of nitrogen and l8.6 SLM of hydrogen (Example 1), and (3) a mixture of 30 SLM of nitrogen and 8.6 SLM of hydrogen (Example 2).

In this selective doping structure, GaInP / I
The flatness and sharpness of the composition of the nGaAs interface appear as a difference in the electrical characteristics of the two-dimensional electron gas accumulated near the interface.
Table 2 shows the results of Hall effect measurement of the epitaxial wafer (InP / InGaAs selectively doped structure) manufactured when the growth interruption time was set to 150 seconds. Here, 1 × 10 ¹² is expressed as E + 12 as a notation method of the sheet carrier concentration.
Indicated by.

[0023]

[Table 2]

As can be seen from Table 2, when only (1) hydrogen (conventional example) is used as the carrier gas, the electron mobility is 6800 cm ² / Vs, but (2) nitrogen 20SL is used.
When the mixture of M and hydrogen (18.6 SLM) was used (Example 1), the electron mobility increased to 7600 cm ² / Vs, and the mixture of (3) 30 SLM of nitrogen and 8.6 SLM of hydrogen (Example 2). In this case, the electron mobility is 10,000 cm ² /
Vs. Moreover, this increase in electron mobility is obtained with almost no increase in the sheet carrier concentration.

From this, it can be seen that by using a gas mainly containing nitrogen as the carrier gas, the electron mobility can be remarkably improved without changing the sheet carrier concentration. That is, by applying this technology to a GaInP / InGaAs pseudomorphic HEMT epitaxial wafer, a HEMT having excellent characteristics can be realized.

When the difference due to the interruption time was examined, the difference was negligible compared to the above.

When the concentration of hydrogen mixed with the inert gas was examined, about 50% was obtained in the case of the first and second embodiments.
When the hydrogen concentration was 23%, the characteristics were not sufficient. At 23%, a remarkable effect was obtained. In order to sufficiently improve the electron mobility, the hydrogen concentration is preferably set to 25% or less.

Although only nitrogen is dealt with in Examples 1 and 2, it is well known that noble gases such as argon and helium do not react with the above compound semiconductors, and it is clear that they can be used as a substitute gas for nitrogen. It is.

<Other Embodiments and Modifications> The growth method of the present invention is directed to the GaInP / InGaAs-based
Instead of the P spacer layer 4 and the carrier supply layer 5, A
spacer layer 4 of lGaAs (AlAs mixed crystal ratio 0.28)
The same applies to the case where a selective doping structure using the carrier supply layer 5 is formed. Table 3 shows the results of Hall effect measurement of the epitaxial wafer having the AlGaAs / InGaAs selective doping structure, which was obtained in the same manner as described above.

[0030]

[Table 3]

As can be seen from Table 3, when only (1) hydrogen (conventional example) is used as the carrier gas, the electron mobility is 20,000 cm ² / Vs, and (2) nitrogen 20SL is used.
The electron mobility is also 1600 cm ² / Vs when a mixture of M and hydrogen (18.6 SLM) is used (comparative example). However, when a mixture of nitrogen (30 SLM) and hydrogen (8.6 SLM) is used in (3) (Example 3). Has an increased electron mobility of 24000 cm ² / Vs. Therefore, the growth method of the present invention
This is also effective for the case of an As / InGaAs-based wafer.

[0032]

As described above, according to the present invention,
Since the carrier gas flowing at the time of the growth interruption is changed to a composition mainly composed of an inert gas, that is, a gas mainly composed of an inert gas with hydrogen as a slave, even if the carrier interruption gas has a sufficient growth interruption time for gas replacement, the carrier gas is not changed. It is difficult to form a compound with a constituent element of a semiconductor, suppresses interaction with the surface more than in the case of hydrogen, and eliminates the occurrence of composition fluctuation due to crystal defects at the interface between different types of semiconductor junctions. Can be.

Therefore, this technique can be applied to, for example, GaInP / I
By applying the present invention to an nGaAs-based pseudomorphic HEMT epitaxial wafer, it is possible to prevent a crystal defect from being formed on a growth surface during a growth interruption, and to realize a HEMT having excellent characteristics with increased mobility as compared with the related art. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of an epitaxial wafer to be grown by applying the growth method of the present invention.

[Explanation of symbols]

1 Semi-insulating GaAs substrate 2 un-type GaAs buffer layer 3 un-type InGaAs channel layer 4 un-type GaInP spacer layer 5 n-type GaInP carrier supply layer

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/205 C30B 29/40 502

Claims (6)

(57) [Claims] 1. A method for epitaxially growing a compound semiconductor crystal comprising two or more heterogeneous semiconductor layers by vapor phase epitaxy, wherein hydrogen is used as a carrier gas, and growth is interrupted between layers to switch the gas. The method comprises the steps of: growing a first semiconductor layer of indium gallium arsenide; and growing a second semiconductor layer of gallium indium phosphorus .
A compound semiconductor vapor phase epitaxial growth method, characterized in that a gas mainly composed of hydrogen and an inert gas is used as a carrier gas flowing during the growth interruption before growing the semiconductor layer. 2. The compound semiconductor vapor phase epitaxial growth method according to claim 1 , wherein nitrogen is used as said inert gas. 3. The compound semiconductor vapor phase epitaxial growth method according to claim 1 , wherein a rare gas is used as said inert gas. 4. The compound semiconductor vapor phase epitaxial growth method according to claim 1 , wherein a mixed gas of nitrogen and a rare gas is used as said inert gas. 5. The method according to claim 1, wherein the concentration of hydrogen mixed with said inert gas is 2
5. The method according to claim 1 , wherein the content is 5% or less.
4 compound semiconductor vapor phase epitaxial growth method according. 6. A claim which comprises using a metal organic chemical vapor deposition as the vapor deposition method 1, 2, 3, 4 or 5
The compound semiconductor vapor phase epitaxial growth method according to the above.