JP2712505B2 - Vapor phase epitaxy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention mainly relates to gas phase heteroepitaxial growth of semiconductor materials, and aims at suppressing dislocations caused by a difference in lattice constant from propagating to a growth layer. In the process of rapidly raising and lowering the substrate temperature, which is performed to turn the dislocations generated in the substrate into those that do not propagate in the growth direction, the substrate is spatially separated from the susceptor and cooled, and the temperature is raised by contacting the susceptor It is configured to include processing.

Since the temperature falls independently of the susceptor having a large heat capacity, the temperature decreasing speed is increased, and the effect of the non-propagation treatment of dislocations is enhanced.

[Industrial applications]

The present invention generally relates to a vapor phase growth process for epitaxially growing a compound semiconductor such as GaAs on a Si substrate, and particularly to a process for preventing dislocations caused by lattice constant mismatch from propagating into a growth layer. Things.

In recent years, an integrated circuit is formed on a semiconductor material such as GaAs, and a single crystal wafer with few crystal defects is required as a substrate for the purpose. In order to reduce defects in the element formation region, it is conceivable to use an epitaxial growth layer.However, in consideration of economy, a material such as Si that can obtain a defect-free single crystal at relatively low cost is used as the base crystal. It is desirable to form an integrated circuit by epitaxially growing a defect-free or low-defect GaAs layer. Further, in terms of mechanical strength, Si is superior to GaAs as a base substrate.

However, since the lattice constant of Si is 5.431 ° and that of GaAs is 5.653 °, if GaAs is epitaxially grown on a Si substrate by a commonly used two-step growth method,
Since the difference of about 4% causes misfit dislocation, a low defect growth layer cannot be obtained.

One method for dealing with such lattice mismatch is to interpose a strained superlattice. This is a method in which two layers having different lattice constants each consisting of several atomic layers are alternately stacked, and the strain is absorbed therein to make the final epitaxial growth layer low in defect and low in stress. Although it is a method, it is currently impractical in terms of cost.

[Conventional technology]

Misfit dislocations are unavoidable in heteroepitaxial growth of GaAs / Si.However, as a processing method that does not propagate this into the growth layer, the epitaxial growth must be stopped once, subjected to thermal shock, and then epitaxially grown again. Has been proposed. This is intended to suppress the subsequent propagation to the epitaxial layer by moving the dislocations by the stress of thermal shock, connecting the dislocations or changing the directions.

FIG. 2 shows an example of the temperature history by this processing. For example, if the growth temperature is 700 ° C., the G
aAs layer is grown (growth A part)
After the temperature is rapidly increased and decreased by ten to several tens of times within the temperature range described above, epitaxial growth is performed again at 700 ° C. (growth B portion) to grow an element formation layer.

At the growth temperature, the GaAs / Si heterojunction does not generate stress because the crystal strain is absorbed in the form of dislocations. However, since the two have different thermal expansion coefficients, as shown in FIG. In GaAs, a compressive stress occurs in GaAs, and a tensile stress occurs below the growth temperature. By repeatedly applying the positive and negative strains, dislocations extending from the heterojunction plane can be combined into a loop shape, or dislocation lines can be changed so that they do not extend to the growth method.

The reason why the temperature is maintained at a high temperature in the repetition of the above temperature rise / fall is to move the dislocation during this period since the dislocation movement speed is higher as the temperature is higher.

[Problems to be solved by the invention]

In the above process, the faster the substrate temperature is raised or lowered, the better the thermal shock is applied. However, in normal high-frequency heating, the substrate is placed on a susceptor such as a graphite block, and even when the high-frequency current is stopped, the heat capacity of the susceptor is large. It is difficult to make it strong enough.

[Means for solving the problem]

In the process of heteroepitaxial growth included in the present invention, in the process of rapidly raising and lowering the substrate temperature, which is performed to convert dislocations generated in the initial growth layer to those that do not propagate in the growth direction, the substrate is moved from the susceptor to the space. The process is performed at least once, usually several times or more, in which the temperature is lowered in a state in which the flow of heat by conduction is eliminated, and the temperature is lowered by contacting the susceptor after the temperature of the substrate is lowered.

(Operation)

As a result of the adoption of the above means, dislocations generated in the first growth layer are formed in a loop or turned in the direction efficiently, and the effect of the repetitive treatment of temperature rise and fall is enhanced. I have.

The higher the temperature rise / fall rate, the better. Therefore, if the substrate temperature is reduced by eliminating the heat conduction from the susceptor having a large heat capacity as in the present invention, the temperature fall rate is increased, and the effect of the non-propagation treatment of dislocations is enhanced. .

〔Example〕

FIG. 1 is a schematic view showing a configuration of a vapor phase growth apparatus used for carrying out the present invention. In the figure, 1 is a reaction tube, 2 is a growth chamber for adjusting the flow of a source gas to grow uniformly, 3 is a susceptor made of a graphite block, 4 is a substrate for epitaxial growth, and 4 is a susceptor mounted on a tray 5. Placed on top. The graphite fork 6 is used to carry the tray on which the substrate is placed from the downstream side of the reaction tube to the susceptor, and is moved to the downstream side of the tube during the epitaxial growth. Reference numeral 7 denotes an RF coil for heating the susceptor. Further, the raw materials for GaAs epitaxial growth are AsH ₃ and TMG using H ₂ as a carrier gas. Hereinafter, the processing of the present invention will be described with reference to FIG. 1 and FIG.

During the epitaxial growth period indicated by the growth A in the temperature history curve of FIG. 2, the substrate crystal is placed on the susceptor with the tray 5 interposed therebetween as shown in FIG. 1A, and is heated by heat conduction from the susceptor. I have. In this process, 1-2 μm Ga
After growing the AS layer, the supply of TMG among the source gases is stopped, and the amount of AsH ₃ is reduced to a level sufficient to suppress the thermal decomposition of GaAs, and the substrate temperature is raised to 900 ° C. for 2 to 3 minutes. Hold.

Next, the high-frequency current is stopped, and the fork is operated to lift the substrate from the susceptor as shown in FIG. A high-frequency current is supplied at the same time as the temperature of the substrate drops to a predetermined temperature, and the substrate is brought into contact with the susceptor by operating a fork, thereby rapidly heating the substrate. FIG. 1 (c) is a plan view of FIG. 1 (b) as viewed from above. In this operation, the substrate is handled while being placed on the tray and heated by heat conduction through the tray, so it is necessary to consider the heat conduction of the tray. But there is no particular problem.

After the substrate temperature is repeatedly raised and lowered by more than ten times by the above operation, the substrate temperature is returned to 700 ° C., the supply of the source gas is increased, and the epitaxial growth shown as growth B in FIG. 2 is performed.

A distance of about 10 mm for lifting the substrate from the susceptor is sufficiently effective. In addition, in the operation of epitaxial growth, lifting a substrate, carrying it on a susceptor, lowering the substrate, and placing the substrate on the susceptor is a normal operation, and the operation of the present invention can be performed without any trouble by a fork moving and holding mechanism.

〔The invention's effect〕

As in the processing of the above embodiment, in the present invention, the rate of temperature rise and fall for applying a thermal shock is increased, so that the effect of dislocation movement is great, and the dislocation generated in the first epitaxial growth layer is Propagation to the growth layer is effectively suppressed. As a result, the compound semiconductor layer having a low defect density can be epitaxially grown by the vapor phase growth method of the present invention.

[Brief description of the drawings]

 FIG. 1 is a schematic diagram showing an apparatus used for carrying out the present invention, FIG. 2 is a diagram showing a heat treatment history for suppressing dislocation propagation, and FIG. In the figure, 1 is a reaction tube, 2 is a growth chamber, 3 is a susceptor, 4 is a substrate, 5 is a tray, 6 is a fork, and 7 is an RF coil.

Claims (1)

(57) [Claims] In a process for supplying a vapor-phase raw material to the surface of a single crystal substrate and epitaxially growing a single crystal having a lattice constant different from that of the substrate crystal, the crystal growth period and the next crystal growth period are separated. Substrate,
A step of cooling the substrate while preventing heat conduction from a susceptor used for heating the substrate, and then heating the substrate by heat conduction from the susceptor at least once. .