JPH03284837A - Manufacture of semiconductor substrate - Google Patents

Abstract

PURPOSE:To avoid defects such as dislocations caused by lattice mismatching created at the time of the growth of a GaAs layer and reduce the dislocation density of a GaAs growth substrate which is made to grow on an Si substrate by a method wherein, after an AlAs layer is made to grow at a low temperature, the GaAs layer is made to grow on the AlAs layer at a specific temperature at which the lattice constant agrees with the lattice constant of GaAs bulk. CONSTITUTION:If an AlAs layer is made to grow on an Si substrate at a low temperature (t1), the lattice constant of the low temperature growth AlAs layer on the Si substrate agrees with the lattice constant of AlAs bulk at the temperature (t1) (point P). If the temperature is elevated after that, the lattice constant of the low temperature growth AlAs layer on the Si substrate agrees with the lattice constant of GaAs bulk at a temperature (t2) (point K). If a GaAs layer is made to grow at the temperature (t2), the GaAs layer can be made to grow with the values of the lattice constants of the AlAs layer and the GaAs layer along the direction parallel with the Si substrate agreeing with each other. With this constitution, introduction of dislocations into the growth layer at the time of the growth of the GaAs layer can be avoided and, a dislocation density can be reduced compared to the dislocation density of a growth substrate made by a conventional GaAs low temperature growth method.

Description

[Detailed description of the invention] Ll upper Ω gori upper! The present invention relates to a method for manufacturing a semiconductor substrate, and more particularly to a method for manufacturing a semiconductor substrate having a GaAs growth layer on a Si substrate.

Compound semiconductors such as GaAs have various characteristics that cannot be realized with Si, and there is a great demand for optical or high-speed devices. On the other hand, compared to Si substrates, GaAs substrates have the disadvantages of being small, brittle, having low thermal conductivity, and being extremely expensive.

Therefore, if a GaAs layer can be grown on the 31 substrate, it will be possible to realize a device that has the advantages of Si while taking advantage of the advantages of GaAs. However, the lattice constant of Si at room temperature is a,, = 5.4309, and the lattice constant of GaAs is a, QaAs = 5.6533, so there is a difference of about 4% in lattice constant between GaAs and Si. However, it was difficult to grow a single-crystal GaAs thin film directly on the 81 substrate under the same growth conditions as for the GaAs substrate.

However, using the MOCVD (metal-organic pyrolysis vapor phase growth) method or the MBE (molecular beam eviaxial growth) method, as shown in Figure 2, approximately 1.
After heat-treating and cleaning the surface of the 31 substrate at 000°C, it is heated to a thickness of about 200 mm at a low temperature of about 450°C for the MOCVD method and 400°C for the MBE method.
Grow aAs. After the growth is stopped, the substrate temperature is raised, and a second growth is performed at a high temperature of 600 to 750°C to form a GaAs layer of several micrometers.
A stepwise growth method has been used to successfully form a GaAs layer on a Si substrate by alleviating the lattice mismatch caused by the difference in lattice constants.

When GaAs is grown on a Si substrate as described above, the lattice constant of GaAs in the grown layer is
s, and also differs in the direction parallel to and perpendicular to the 31 substrate. This is because when the growth substrate is cooled to room temperature, the entire substrate shrinks, but since GaAs and 51 have different coefficients of thermal expansion, thin GaAs
This is because the layer is pulled by the Si substrate, elongating in a direction parallel to the substrate and contracting in a direction perpendicular to the substrate.

Figure 3 shows the lattice constant-temperature curve of GaAs when the low-temperature growth temperature is 450°C.
The lattice constant of GaAs in the direction perpendicular to the Si substrate on the 31 substrate is expressed by 111-, and the lattice constant of the GaAs bulk is expressed by .

As shown in Figure 3, at a low temperature growth temperature of 450°C, the value of the lattice constant of GaAs in the direction parallel to the Si substrate, the value of the lattice constant of GaAs in the direction perpendicular to the Si substrate, and the lattice of GaAs bulk. Constant values match.

In the conventional semiconductor substrate manufacturing method described above, the coefficient of thermal expansion of the Si substrate and the GaAs layer in the direction parallel to the Si substrate is such that the lattice constant of the GaAs layer in the direction parallel to the Si substrate is 31. Since it corresponds to the expansion and contraction of the board, o8□=07y=
2.6XlO-'deg-', while GaAs
The bulk thermal expansion coefficient is aaaag=6.5Xlo-'
It is deg-.

Therefore, when a GaAs layer is grown on a Si substrate at a high temperature (650°C), the lattice constant of the GaAs layer in the direction parallel to the 31 substrate is a77=5.
The lattice constant of 6727.6aAs bulk is a:
5.6772, resulting in a mismatch. If there is a difference in lattice constant in this way, during the growth of the GaAs layer,
Defects such as dislocations due to lattice mismatch are likely to occur, and the dislocation density is about LX 10'/cm", resulting in G
There was a problem of reducing the crystallinity of the aAs layer.

The present invention was invented in view of these problems, and includes three
By reducing the dislocation density of the GaAs layer grown on one substrate,
It is an object of the present invention to provide a method for manufacturing a semiconductor substrate in which the crystallinity of a GaAs layer is improved.

In order to accomplish the above-mentioned object, the method for manufacturing a semiconductor substrate according to the present invention involves growing AlAs on a Si substrate at a low temperature, and then changing the lattice constant of the AlAs layer to that of the QaAs bulk. G on top of the AlAs layer at a temperature consistent with the lattice constant.
It is characterized by growing aAs.

Figure 1 shows the lattice constant-temperature curves of GaAs and AlAs.
s Bulk lattice constant □ and low temperature growth A on 81 substrate
The lattice constants of the AlAs layer in the direction parallel to the Si substrate when the lAs layer is grown are expressed as 1111, respectively.

The thermal expansion coefficient of GaAs bulk is OaaAs=6.5Xl
O-'deg-', while the thermal expansion coefficient of the AlAs bulk is a A, A,: 5.2X10-6deg-'
Therefore, the lattice constants of GaAs bulk and AlAs bulk when the temperature is t [℃] are aoaAi=5.6533(146,5X10-' t
)aAIA$=5.6605fl+5.2XlO-6t
).

First, when the AlAs layer is grown at a low temperature on the 81 substrate at a temperature t, the lattice constant of the low temperature grown AlAs layer on the 31 substrate is
It corresponds to the lattice constant of the AlAs bulk at the temperature t1 (
P point).

When the temperature is subsequently increased, the AlAs layer is thin, so it expands in the direction parallel to the Si substrate at the same rate as the expansion of the Si substrate, and follows the broken line, which is the lattice constant curve of the AlAs layer in the direction parallel to the S1 substrate. It turns out. Then, the lattice constant of the low temperature grown AlAs layer on the 81 substrate matches the lattice constant of the GaAs bulk at temperature t2 (point K).

Therefore, if j+ and jz are respectively suitable temperatures for the two-step growth method, by growing GaAs at the growth temperature t2, the lattice constant of the A I As layer in the direction parallel to the Si substrate and the lattice constant of the GaAs layer can be changed. A GaAs layer can be grown at a value that matches the lattice constant, and lattice matching can be achieved.

When an AlAs layer is grown on a 31 substrate at 450°C, the lattice constant of the AlAs layer in the direction parallel to the substrate is azz
It is expressed by the equation a+As=5.6671(1+2.6XlO-6t), and the temperature at the point where the curve expressed by the above equation intersects the lattice constant curve of the GaAs bulk is t2=630.
℃. This is the temperature at which GaAs can grow.

Note that by changing the low-temperature growth temperature, GaA
It is possible to increase or decrease the growth temperature of s.

Therefore, as in the method described above, after growing AlAs on a 31 substrate at a low temperature, the lattice constant of the AlAs layer becomes GaAs.
At a temperature consistent with the bulk lattice constant, the AlA
By growing GaAs on top of the s-layer, GaAs
During the growth of s, the introduction of dislocations into the grown layer is prevented, and the dislocation density is lowered compared to the growth substrate of the conventional GaAs low-temperature growth method.

A method for manufacturing a semiconductor substrate using a two-step growth method according to the present invention will be described below.

First, 81 substrate (p-type or p-type,
After cleaning the (100) surface (2° off in the [011] direction) by heat treatment for several minutes, a low-temperature AlAs film with a thickness of approximately 200 nm was deposited at a temperature of 450 °C using the MOCVD method.
Grow layers. After the growth is temporarily interrupted, the substrate temperature is raised to 630° C. and a 3 μm thick GaAs layer is formed.

The dislocation density of the semiconductor substrate thus obtained and the threshold current value when a semiconductor laser was manufactured using the semiconductor substrate were compared with those of a conventional example, and are shown in Table 1.

In the conventional example for comparison, a low-temperature grown GaAs layer with a thickness of about 200 layers was formed at a temperature of 450 degrees Celsius, and then a GaAs layer of about 630 layers thick was formed at a temperature of 450 degrees Celsius.
A 3 μm thick GaAs layer was formed at °C.

As is clear from this result, according to the above-mentioned example, in order to grow a GaAs layer on a Si substrate, the AlAs layer and the GaAs layer grown thereon are formed by forming the AlAs layer at a low temperature. By forming a GaAs thin film on a 31 substrate using a two-step growth method in which a GaAs layer is formed at high temperature after matching the lattice constant between By manufacturing a semiconductor device using a substrate manufactured in this manner, device characteristics can be improved.

Effects of the Invention As is clear from the above explanation, in the method for manufacturing a semiconductor substrate according to the present invention, after AlAs is grown on an 81 substrate at a low temperature, the lattice constant of the AlAs layer matches the lattice constant of the GaAs bulk. Since GaAs is grown on the AlAs layer at a certain temperature, the occurrence of defects such as dislocations due to lattice mismatch during the growth of the GaAs layer is prevented, and the dislocation density of the GaAs growth substrate grown on the Si substrate is reduced. can be reduced, and the crystallinity of the GaAs layer can be improved. Therefore, if a semiconductor element is manufactured using a semiconductor substrate formed using this manufacturing method, the characteristics of the semiconductor element can be improved.

[Brief explanation of the drawing]

Figure 1 shows the growth of a Ga layer when an AlAs layer is grown at t1°C to explain the method of manufacturing a semiconductor substrate according to the present invention.
As bulk, AlAs bulk and low temperature growth layer 81
The lattice constant-temperature curve of the AlAs layer on the substrate. Figure 2 shows the growth temperature profile for explaining the conventional method. Figure 3 shows the growth temperature profile of the GaAs layer formed on the Si substrate in the direction parallel to the substrate. , in the vertical direction and the lattice constant-temperature curve of the GaAs bulk.

Claims (1)

[Claims] (1) A semiconductor substrate characterized in that after AlAs is grown on a Si substrate at a low temperature, GaAs is grown on the AlAs layer at a temperature where the lattice constant of the AlAs layer matches the lattice constant of the GaAs bulk. manufacturing method.