JPS6052572B2 - Wafer for semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structure of a wafer for a semiconductor device having a compound semiconductor crystal layer.

Generally, in compound semiconductor devices, a wafer in which a compound semiconductor crystal layer has a homo-epitaxial structure is used.

Such a wafer has a multilayer structure in which compound semiconductor single crystal layers serving as a buffer layer, an active layer, an electrode layer, etc. are epitaxially grown on a compound semiconductor single crystal layer substrate. By the way, the compound semiconductor single crystal layer substrate is quite expensive and accounts for most of the wafer cost.

Further, such a substrate is manufactured by, for example, the Bort-Cron method or the Czochralski method, but there is also the problem that it is difficult to obtain a large-area substrate like a silicon single crystal substrate. Therefore, if you want to reduce the wafer cost and obtain a large-area wafer, you can use a cheap and large-area single-crystal substrate such as a silicon single-crystal substrate. When a compound semiconductor single crystal layer is directly grown epitaxially, it has few crystal defects, has a mirror surface, and has a high enough height to fabricate semiconductor devices due to the difference in crystal structure or lattice constant between silicon and compound semiconductor. It is difficult to obtain a compound semiconductor single crystal layer of high quality.

The present invention makes it possible to obtain a wafer in which a high-quality compound semiconductor single crystal layer is epitaxially grown on a silicon single crystal, which is inexpensive and easily obtained in a large area, as a substrate. will be explained in detail.

FIG. 1 is a side sectional view of a main part showing a basic embodiment of the present invention. In the figure, 1 is a silicon single crystal substrate, 2 is an aluminum oxide (to A12, ie, sapphire) single crystal layer, and 3
is a compound semiconductor single crystal layer.

The method for manufacturing this wafer is as follows.

(1) An aluminum oxide single crystal layer 2 is formed on a silicon single crystal substrate 1 by applying a vapor phase growth method. To carry out this vapor phase growth method, the following two reaction systems are usually considered. That is, (a) alkyl derivative -C02-H2 system, (
mouth) A1C13-C02-H2 system. However, the reaction system (a) is dangerous to handle, and
The drawback is that the reaction temperature is too low. (mouth) reaction system is A1
Since C13 has strong hygroscopicity, it absorbs water (H2O) during the growth reaction.
) is mixed in, and a silicon dioxide film is formed on the surface of the silicon single crystal substrate 1 at the initial stage of the reaction, making it difficult to obtain the aluminum oxide single crystal layer 2. Therefore, in the present invention, the reaction temperature is appropriately high, simultaneous growth on multiple substrates is possible, and although the oxide substance (aluminum oxide) is grown in a vapor phase, the surface of the silicon single crystal substrate 1 is made of silicon dioxide. As a reaction system that can prevent the formation of a film, an A1-HCl-CO2-H2 (or N2) system is used.

In that case, the growth reaction formula is as follows. ---The growth material in this case is 5N (99.999 [%])
and 4N (99.99 [%]) HCl.

Further, the silicon single crystal substrate 1 is placed on a support made of Carbo 7, and heated by high frequency to raise the temperature. The temperature of the silicon single crystal substrate, that is, the crystal growth temperature of sapphire, is set to 1100 to 120.
When CfC is used, an aluminum oxide single crystal layer (sapphire) 2 can be epitaxially grown on a silicon single crystal substrate. Especially when the crystal growth temperature is 1160'C, high quality γ-sapphire can be obtained. On the other hand, in a crystal growth temperature range other than the above-mentioned crystal growth temperature range of 1100 to 1200'C, a single crystal of high quality α-sapphire can be epitaxially grown at 1080C when α-sapphire or a mixed crystal layer of α and γ-sapphire is formed. I can do it. {2) A compound semiconductor single crystal layer 3 is epitaxially grown on the aluminum oxide single crystal layer 2 by applying a vapor phase growth method that utilizes thermal decomposition of an alkyl compound.

When the compound semiconductor is gallium arsenide (GaAs),
To carry out this vapor phase growth method, the following steps are required. Usually, the following three reaction systems can be achieved.

That is, {a) trityl gallium (TMG: (CH3)
(3Ga) and arsine (AsH3), (1) triethylgallium ((C2Yl6)3Ga) and As oxide, and (3) diethylgallium chloride ((C2H5)2GaC1) and AsH3. In the present invention, the THG-AsH3 system is employed, and the silicon single crystal substrate 1 having the aluminum oxide single crystal layer 2 is heated and heated in the same manner as in the step (1). The molar ratio of raw materials is XAs2H, /XTMG=1
By setting the growth temperature to 700 to 740 [° C.], it was possible to grow a GaAs single crystal of high quality and having a mirror surface.

Note that to make a GaAs single crystal n-type, hydrogen sulfide (H2S) or hydrogen selenide (H2Se) is used as a dopant, and to make it p-type, dibutylzinc ((C4He)2Zn) or sulfide is used as a dopant. Methyl zinc (
It is preferable to use C2H5)2Zn.

As described above, in the present invention, by interposing the epitaxially grown aluminum oxide single crystal layer 2, a high-quality silicon substrate 1 is formed on the silicon single crystal substrate 1, which can be easily obtained at low cost and with a large area.・Compound semiconductors (e.g. Ga
As) Although the single crystal layer 3 could be grown epitaxially, it is possible to further improve the quality of the compound semiconductor single crystal layer based on this technique.

That is, for example, as seen in FIG.
A single crystal layer 2″ is grown, and a GaAs single crystal layer 3 is grown on top of it.
By epitaxially growing the GaAs single crystal layer 3'', the surface of the GaAs single crystal layer 3'' can be made to have extremely few defects and a good mirror surface.

In general, aluminum oxide single crystal refers to α-A]203 single crystal, and crystal growth of compound semiconductors onto this α-Al2O3 single crystal substrate is known.

The crystal properties of compound semiconductors on such α-,Al2O3 single crystal plates are not necessarily good; for example, G
a-A compared to a GaAs crystal grown on an As substrate.
GaAs crystals formed into 12O3 single crystals have problems such as extremely low mobility, a tendency to abnormal growth, and the inability to obtain mirror-like crystal surfaces. However, the compound semiconductor crystal on the γ-Al2O3 single crystal substrate is of sufficient quality to be used in the manufacture of semiconductor devices.

When epitaxially growing a GaA>single crystal layer on an aluminum oxide single crystal layer, aluminum oxide
The reason why γ-Al2O3 gives better results than l2O3 is that, for example, there are almost no building blocks, pyramid-like abnormal growths, cracks, etc., it has a mirror surface, and the thickness is uniform. A GaAs single crystal layer can be obtained.

Therefore, in order to perform the growth according to the present invention, it is preferable to epitaxially grow a γ-Al2O3 single crystal layer 2'' on the silicon single crystal substrate 1, and then grow Ga and As. When growing a GaA>single crystal layer on an aluminum single crystal layer, aluminum oxide is α-Al2
The reason why abnormal growth is less likely to occur with γ-Al2O3 than with O3 is that α-A]203 has a hexagonal crystal structure, whereas γ-AI2O3 has a cubic spinel structure like Ga and As. Therefore, it is thought that defects caused by lattice mismatch are less likely to occur. In addition, in the example shown in FIG.
By using a silicon single crystal substrate 1 whose crystal plane is shifted by several degrees, for example 2 to 5 degrees, from the low index plane, the rate of abnormal growth occurring in the GaAs single crystal layer 3'' can be further reduced. It decreases rapidly.Now, for example, GaAs-M
When manufacturing a semiconductor device with a planar structure such as an ES-FET, an insulating or semi-insulating substrate is used.

Therefore, the wafer shown in FIG. 1 or 2 can be used, but in order to obtain better effects, it is better to use a wafer having the structure shown in FIG. 3. In FIG. 3, 1 is a silicon single-crystal substrate, 2 is an aluminum oxide single-crystal layer, 4 is a semi-insulating GaAs single-crystal layer (buffer layer), 5 is an n-type GaAs single-crystal layer (active layer), 6 is n+
Type GaAs (or GaAlAs) single crystal layer (electrode layer)
There is.

The buffer layer, semi-insulating constant ρAAl, single crystal layer 4 contains chromium (Cr), iron (Fe), manganese (M
It is possible to perform epitaxial growth by doping with an impurity that creates a deep impurity level in the semiconductor, such as Tl) or oxygen (0). NSρAAs single crystal layer 5 which is an active layer
An n+ type GaAs single crystal layer 6 serving as an electrode layer is grown thereon, or if it is a pn junction type, GaAlAs is grown.

M manufactured using the wafer thus obtained
The ES-FET is a MES-FET that uses a structure in which the active layer is grown homo-epitaxially on a conventional wafer, that is, a semi-insulating GaAs substrate, in terms of output, gain, width, and Fma8. We were able to obtain similar characteristics both statically and dynamically.

Although the above description relates to a wafer suitable for manufacturing MES-FETs, important devices using compound semiconductors include microwave semiconductor devices such as Gunn diodes, varactors, and mixer diodes. When hybridizing devices, it is preferable to use a wafer as shown in FIG. That is, in the illustrated wafer, an n+ type GaAs single crystal layer 7 is grown as an electrode layer on an aluminum oxide single crystal layer 2, and a planar NyfJaAs single crystal layer 5 is grown as an active layer thereon. It can be used for manufacturing type semiconductor devices. Note that the impurity concentration in the n+ type GaAs single crystal layer 7 is normally set to 5×10 18 [d−3] or more. As can be seen from the above description, according to the present invention, a high-quality aluminum oxide single crystal layer is formed on a silicon single crystal substrate, which is cheaper than a GaAs single crystal substrate and can easily be obtained with a large area. A wafer having a compound semiconductor single crystal layer formed thereon is obtained, and by using this wafer, compound semiconductor devices can be manufactured at extremely low cost.

[Brief explanation of the drawing]

1 to 4 are side sectional views of main parts of different embodiments according to the present invention. In the figure, 1 is a silicon single crystal substrate, 2 is an aluminum oxide single crystal layer, and 3 is a compound semiconductor single crystal layer.

Claims (1)

[Claims] 1 γ-type aluminum oxide (γ-Al_2O_3) grown epitaxially on a silicon single crystal substrate
) A wafer for a semiconductor device comprising a single crystal layer and a compound semiconductor single crystal layer.