Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Patent
1989-10-20
1993-06-15
Robinson, Ellis P.
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
428156, 428172, 428219, 428409, 428688, 148DIG84, 437247, 437248, 437939, 437949, B32B 1302
Patent
active
052196321
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to compound semiconductor single crystals and wafers for improving the homogeneity of the device properties when used as substrates and a method for producing the compound semiconductor single crystals and wafers and, more particularly, the invention relates to a heat treatment method for single crystals after growing of the single crystals.
BACKGROUND TECHNIQUE
Various methods for producing compound semiconductor single crystals are well known. For example, a seed crystal is immersed in a melted solution of the crystal and then the seed crystal is pulled up to grow the single crystal from the seed crystal. As an alternative method, the melted solution is gradually solidified to grow the single crystals. Particularly, GaAs single crystals are produced in an industrial scale by the Liquid Encapsulated Czochralski Method (LEC Method) which belongs to the former method, and by the Gradient Freeze Method (GF Method), Horizontal Bridgeman Method (HB Method), and the Vertical Bridgeman Method (VB Method), which belongs to the later method.
Although these single crystal growth methods each are a little different from each other, crystals are grown in a basically similar process such that the temperature gradient between the crystal and the melted solution is generated to gradually solidify the melted solution. In the process, the interface between the liquid and the solid where the crystal is grown is kept at the melting point, but the part of the crystal already grown is kept at the lower temperature than the melting point. Accordingly, these single crystal producing methods can not avoid the production of inhomogeneous single crystals.
Conventionally, the compound semiconductor single crystals produced by these producing methods have been used as various optoelectric devices such as light emitting diodes, laser diodes, and photo-detectors; and various substrates for high speed devices such as FET (Field Effect Transistor). Further the compound semiconductor single crystals have been expected to be used as substrates for OEIC (Optoelectronic Integrated Circuit) on the same substrate of which optoelectric devices and FETs are fabricated.
As disclosed above, however, these single crystal producing methods can not essentially avoid the production of the single crystals with inhomogeneous properties. Thus the devices employing the single crystals produced by these methods would remarkebly scatter in their properties depending on the single crystal wafer used in the devices. Particularly in the production for discrete high frequency FETs and digital ICs, this scattering in the crystal property would cause a decrease the yield rate of the products. This fact has been realized as one of the reasons why the compound semiconductor device has not been broadly used.
This scattering would be caused by various factors, for example dislocations generated in the crystal. In order to eleminate the dislocations some impurities such as In have been doped in the crystal.
In addition to the above method, Rumsby provided the method for annealing the single crystal ingot at a high temperature to decrease the scattering in the crystal property. Thereafter various inventions relative to this ingot-annealing method have been provided; for example, Japanese Patent Application Laid-Open Publication No. 62-21699 and No. 62-21800.
Conventionally, the ingot-annealing has been carried out at temperatures 138.degree. C. lower than the melting point. If the crystal ingot is subjected to the annealing at high temperatures than the above level, many defects would be generated in the annealed ingot. In detail, even if the whole of the ingot is heated at an uniform temperature during the annealing process, the ingot can not be uniformly cooled and thus thermal stress would be generated in the crystal by the cooling process after the annealing process. This thermal stress would cause an increase in the dislocation density which is generally called as EPD (Etch Pit Density) in the ingot, or slip lines
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Improved Uniformity of LEC Undoped Gallium Arsenide Produced by High Temperature Annealing, D. Rumsby et al., Cambridge Instruments Limited, Cambridge, England, GaAs IC Symposium, pp. 34-37, 1983.
Etching Characteristics of (001) Semi-Insulating GaAs Wafers, Y. Okada, Japanese Journal of Applied Physics, vol. 22, No. 3, Mar. 1983, pp. 413-417.
Kano Gaku
Oda Osamu
Shimakura Haruhito
Yamamoto Hiromasa
Ahmad Nasser
Robinson Ellis P.
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