JPH04271114A - Defect reduction method of compound semiconductor - Google Patents

Abstract

PURPOSE:To reduce defects like dislocation existing in compound semiconductor formed on a semiconductor substrate by epitaxial growth. CONSTITUTION:A semiconductor wafer 10 formed by epitaxially growing compound semiconductor 16 on a semiconductor substrate 12 is irradiated with laser light, and a boundary part 14 is locally heated. Thereby the temperature of the boundary part 14 is set higher than that of the compound semiconductor 16, which is kept at a temperature capable of crystal rearrangement wherein defects can be moved. After that, the heating with laser light is interrupted, and the temperature of the semiconductor wafer 10 is wholly decreased. Since the temperature of the boundary part 14 in which crystal defects are generated by lattice mismatch and the like at the time of decreasing the temperature is higher than the temperature of the compound semiconductor 16 because of local heating, the temperature fall is slow, and crystal of the compound semiconductor 16 is fixed in advance. Hence crystal defects generated in the boundary part 14 is prevented from spreading over the compound semiconductor 16.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing defects such as dislocations existing in a compound semiconductor formed on a semiconductor substrate by epitaxial growth.

0002

[Prior art and its problems] A semiconductor wafer in which a compound semiconductor is epitaxially grown on a semiconductor substrate such as Si,
It is widely used in OEICs (optoelectronic integrated circuits), solar cells, light emitting diodes, semiconductor lasers, etc. In such semiconductor wafers, if the lattice constant or thermal expansion coefficient differs between the semiconductor substrate and the compound semiconductor layered thereon, crystal defects such as dislocations may form in the compound due to lattice mismatch or thermal strain when the temperature is lowered after epitaxial growth. There is a problem in that a large number of these occur in semiconductors.

The present invention was made against the background of the above circumstances, and its purpose is to reduce internal defects such as dislocations existing in semiconductor wafers.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a semiconductor wafer in which a compound semiconductor having a lattice constant or thermal expansion coefficient different from that of the semiconductor substrate is epitaxially grown, and a laser beam is applied to the semiconductor wafer. irradiate,
By locally heating only the boundary portion between the semiconductor substrate and the compound semiconductor, the temperature of the boundary portion is relatively higher than the temperature of the compound semiconductor, and the temperature of the compound semiconductor is a temperature at which the crystals can be rearranged. The method is characterized in that the local heating by the laser beam is stopped and the temperature of the semiconductor wafer is lowered.

[0005]

[Operation and Effects of the Invention] In other words, defects in an epitaxially grown compound semiconductor are caused by lattice mismatch and thermal strain when dislocations in the crystal freeze when the temperature drops after epitaxial growth. Many crystal defects that occur near the boundary with the substrate spread into the compound semiconductor, so to prevent this, the temperature at the boundary where crystal defects occur is made higher than the temperature of the compound semiconductor. It is sufficient to first fix the crystal of the compound semiconductor by lowering the temperature while the semiconductor wafer is in a state of The temperature of the compound semiconductor is made relatively higher than that of the semiconductor, and the temperature of the compound semiconductor is set to a temperature that allows crystal rearrangement, and then local heating by laser light is stopped and the temperature of the semiconductor wafer is lowered. It is. As a result, when the semiconductor wafer cools down, the crystals of the compound semiconductor are fixed before the boundary area, and even if crystal defects are subsequently generated at the boundary area due to lattice mismatch, the crystal defects will spread to the compound semiconductor. This reduces defects within the compound semiconductor.

Here, a method of locally heating only the boundary area between a semiconductor substrate and a compound semiconductor using a laser beam is to use a laser beam whose optical energy is transmitted through either the semiconductor substrate or the compound semiconductor and absorbed by the other. Just use it,
Specifically, laser light having a light energy intermediate between the band gap energies of both semiconductors is irradiated from the one with the larger band gap energy. Note that an intermediate layer may be formed between the semiconductor substrate and the compound semiconductor, and light energy may be absorbed in the intermediate layer.

[0007] Furthermore, the laser beam irradiation is performed while the semiconductor wafer is kept at a low temperature such as room temperature, and the temperature is raised to a temperature at which the compound semiconductor crystals can be rearranged by thermal conduction of local heating at the boundary. However, when the temperature of a semiconductor wafer containing a compound semiconductor is still maintained at a temperature that allows crystal rearrangement, such as when the temperature is lowered after epitaxial growth, laser light is irradiated to reduce the temperature of the boundary part to that of the compound. There is no problem in making the temperature relatively higher than the temperature of the semiconductor.

[0008]

[Example] Fig. 1 is a diagram illustrating the structure of a semiconductor wafer 10 manufactured by applying the method of the present invention.
A GaAs layer 14 with a thickness of about 0.5 μm is provided as an intermediate layer on the Si substrate 12 with a thickness of about 500 μm, and a GaP layer 16 with a thickness of about 2 μm is further provided on the GaAs layer 14. . The GaAs layer 14 and the GaP layer 16 are formed by metal organic chemical vapor deposition (MOCVD).
l Organic Chemical Vapor
This is epitaxially grown on the Si substrate 12 using the Si substrate 12 deposition method.
corresponds to a semiconductor substrate, and the GaP layer 16 corresponds to a compound semiconductor. Further, the GaAs layer 14 corresponds to the boundary portion between them. Note that these semiconductors Si, GaAs, Ga
The lattice constant (Å), thermal expansion coefficient (°C-1), and band gap energy Eg (eV) of P are shown in Table 1, and Si and GaP have different lattice constants and thermal expansion coefficients. .

[0009]

The epitaxial growth of the GaAs layer 14 and the GaP layer 16 will be explained in detail with reference to the time chart shown in FIG.
Clean the surface by baking at a moderately high temperature. Next, after lowering the heating temperature to about 450° C., a GaAs layer 14 is epitaxially grown on the Si substrate 12 by a two-step growth method. In the two-step growth, GaAs raw material gas is first introduced into the reactor at a low temperature of about 450°C to grow the crystal, and then the temperature is raised to about 750°C to grow GaAs again.
In this method, a raw material gas of s is introduced to cause crystal growth. The introduction time of GaAs raw material gas at high temperature is determined by the amount of G to be formed.
It is determined according to the film thickness of the aAs layer 14, so that S
A GaAs layer 14 with a thickness of about 0.5 μm is formed on the i-substrate 12.
is formed. Subsequently, the heating temperature is raised to about 850° C. and a GaP raw material gas is introduced into the reactor, thereby forming a GaP layer 16 of about 2 μm on the GaAs layer 14.
grown epitaxially. The introduction time of the GaP raw material gas in this case is also determined according to the thickness of the GaP layer 16 to be formed, and thereby a semiconductor wafer 10 in which the GaAs layer 14 and the GaP layer 16 are epitaxially grown on the Si substrate 12 is obtained. It will be done.

Thereafter, the semiconductor wafer 10 is subjected to a defect reduction process according to the defect reduction method of the present invention. That is, after the semiconductor wafer 10 is taken out from the reactor of the MOCVD apparatus, the entire surface of the semiconductor wafer 10 is continuously irradiated with ruby laser light from the GaP layer 16 side, and at the same time, the front and back surfaces of the semiconductor wafer 10 are irradiated with a fan. After cooling with air and continuing this for about 2 hours, irradiation of ruby laser light is stopped while cooling with air by the fan is continued, and the temperature of the semiconductor wafer 10 is lowered to room temperature. The optical energy of ruby laser light is approximately 1.79
eV, the ruby laser light passes through the GaP layer 16 whose band gap energy Eg is larger than that,
It is absorbed by the GaAs layer 14 whose band gap energy Eg is smaller than 1.79 eV. For this reason, the Ga
Only the As layer 14 and the vicinity of the GaAs/GaP interface are locally heated, and the heat is conducted to the GaP layer 16 with a predetermined temperature gradient. The laser output at this time is Ga
Most of the P layer 16 is at about 400 to 500°C, that is, G
The temperature is set so that the aP crystal can be rearranged and crystal defects such as dislocations can move, and in this example, the temperature is set at 500 m.
It is W. In addition, the locally heated GaAs layer 14 and the vicinity of the GaAs/GaP interface reach a temperature sufficiently higher than that of the GaP layer 16, and the laser beam irradiation is stopped after 2 hours. is lowered in temperature with a predetermined temperature difference.

[0012] In this way, the GaP layer 16 has a thickness of 400 to 500
When the temperature is raised to about .degree. C., the GaP layer 16 is annealed and internal defects such as dislocations are reduced. Furthermore, when the temperature subsequently decreases, since the GaP layer 16 is at a lower temperature than the GaAs layer 14, the crystals of the GaP layer 16 are frozen first, and then the GaAs layer 14 and the crystals near the GaAs/GaP interface are frozen. Therefore, even if crystal defects such as dislocations occur in the GaAs layer 14 or near the GaAs/GaP interface due to differences in lattice constants and thermal expansion coefficients, they will not occur in the GaP layer 16.
The crystal defects in the GaP layer 16 are kept well reduced by the annealing.

Incidentally, using the semiconductor wafer 10 of this embodiment subjected to the defect reduction treatment by laser irradiation and a conventional semiconductor wafer not subjected to the defect reduction treatment, an etching solution containing a mixture of hydrofluoric acid and nitric acid was used. When the surface of the GaP layer 16 was etched and the density of etch pits caused by defects was investigated, the density of etch pits caused by defects was found to be 3 x 107 (pits/cm2) in the product of this example, while it was 7 x 107 (pits/cm2) in the conventional product.
crystal defects/cm2), and the number of crystal defects was reduced to less than half. Figure 3 is an optical microscope photograph showing the crystal structure of the etched surface of the product of this example, and Figure 4 is an optical microscope photograph showing the crystal structure of the etched surface of the conventional product. It can be seen that it has been reduced by half.

Although one embodiment of the present invention has been described above in detail with reference to the drawings, the present invention can also be implemented in other embodiments.

For example, in the embodiment described above, the Si substrate 12 is used as the semiconductor substrate, but it is also possible to use a semiconductor substrate made of a compound semiconductor. As for the compound semiconductor epitaxially grown on the semiconductor substrate, a III-V compound semiconductor other than GaP or other compound semiconductors can be used. The type of laser light to be used and the conditions for irradiation of the laser light are determined as appropriate depending on the type of semiconductor. For example, in the case of a semiconductor wafer that is simply epitaxial growth of GaAs on a Si substrate, the light energy is approximately 1.16 eV. A YAG laser or the like is preferably used.

Furthermore, in the embodiment described above, the temperature of the GaP layer 16 is raised to a temperature at which crystal rearrangement is possible by irradiation with a laser beam, but the GaAs layer 14 can be GaP layer 1
The temperature may be set higher than 6, and then the laser beam irradiation may be stopped and the temperature may be lowered while there is a temperature difference between them. Laser light irradiation does not necessarily have to be continuous, and pulse irradiation may be performed at predetermined time intervals.

Furthermore, in the above embodiment, the case where a compound semiconductor is epitaxially grown by a metal organic chemical vapor deposition method using an MOCVD apparatus has been described, but other epitaxial growth apparatuses such as those using a molecular beam epitaxy method can also be used. . The temperature conditions and the like when epitaxially growing a compound semiconductor can also be changed as appropriate.

Further, in the above embodiment, GaA is used as the intermediate layer.
Although the s-layer 14 is provided, the GaP layer 16 can be epitaxially grown directly on the Si substrate 12 by omitting the GaAs layer 14, or the GaP layer 16 can be epitaxially grown directly on the Si substrate 12, or InGa having a small band gap energy Eg can be used instead of the GaAs layer 14.
As or the like can also be provided as an intermediate layer.

Further, in the above embodiment, only one GaP layer 16 is provided, but the present invention can also be applied to a semiconductor wafer having a plurality of compound semiconductor layers constituting a heterostructure or the like.

Furthermore, in the embodiment described above, the front and back surfaces of the semiconductor wafer 10 are air-cooled by a fan to increase the temperature difference between the GaAs layer 14 and the GaP layer 16, but air cooling by a fan is not always necessary. It's not something.

Although no other examples are given, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram illustrating an example of a semiconductor wafer that has been subjected to defect reduction processing according to the present invention.

FIG. 2 is a time chart showing the temperature history during the formation of an epitaxial layer of the semiconductor wafer in FIG. 1;

FIG. 3 is an optical micrograph showing the crystal structure of the etched surface of the semiconductor wafer in FIG. 1;

FIG. 4 is an optical micrograph showing the crystal structure of the etched surface of a semiconductor wafer that was not subjected to the defect reduction treatment according to the present invention.

[Explanation of symbols]

10: Semiconductor wafer 12: Si substrate (semiconductor substrate) 14: GaAs layer (boundary part) 16: GaP layer (compound semiconductor)

Claims (1)

[Claims] 1. A semiconductor wafer in which a compound semiconductor having a lattice constant or thermal expansion coefficient different from that of the semiconductor substrate is epitaxially grown is irradiated with a laser beam, and only the boundary portion between the semiconductor substrate and the compound semiconductor is locally grown. By heating, the temperature of the boundary portion is made relatively higher than the temperature of the compound semiconductor and the temperature of the compound semiconductor becomes a temperature at which the crystals can be rearranged, and then local heating by the laser beam is performed. 1. A method for reducing defects in compound semiconductors, which comprises stopping the process and cooling the semiconductor wafer.