Method for fabricating GaN substrate

Details Method for fabricating GaN substrate Method for fabricating GaN substrate

1999-09-21

2001-04-03

Pham, Long (Department: 2823)

Semiconductor device manufacturing: process

Chemical etching

Combined with the removal of material by nonchemical means

C438S689000, C438S690000, C438S692000, C438S693000, C438S799000

Reexamination Certificate

active

06211089

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a method for fabricating GaN substrates and, more particularly, to the minimization of defects in GaN substrates, along with the method.
2. Description of the Prior Art
Recently, blue light elements utilizing GaN, such as light emitting diodes (LEDs) and laser diodes (LDs), have been one subject of great interest for many researchers and are now in a mature commercialization phase. As a consequence, such light elements find numerous applications in large size, color flat panel displays, signal lamps, interior lamps, high density light sources, high definition printing systems, optical communication, etc.
The substrates useful in the blue light elements are made of bulk GaN which is obtained by hydride vapor phase epitaxy. This technique is evaluated as being useful in minimizing the defects caused by the thermal expansion difference and lattice mismatch between substrates and thin films deposited thereon.
In order to produce thin films of high quality, these substrates should provide suitable surfaces. However, there remains a need for an improved polishing or pretreatment process that is adapted to accomplish sufficiently flat surfaces.
Using a diamond slurry, plate, or paste, alone, for example, a polishing process is conventionally conducted on bulk GaN substrates. The polished surfaces of the GaN substrates, however, do not show desired surface roughness because there exists a great difference in hardness between the diamond used and the bulk GaN. With expectations to solve this problem, sufficiently small sizes of diamond particles were used to polish GaN substrates, but could not yet bring about sufficiently reduced surface roughness in the GaN substrates.
The resulting surface roughness leads subsequent thin films to three-dimensional growth, making it impossible to obtain thin films of high quality. Upon the mechanical polishing with diamond particles, in addition, there are formed damaged layers whose defects are, in their entirety, transferred to subsequent thin films so that the thin films of high quality cannot be achieved which are as low in defect density as desirable. Consequently, devices of high properties cannot be fabricated by such conventional techniques.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and to provide a method for fabricating a smoothly surfaced GaN substrate on which thin films of high quality can be deposited.
In one aspect, the present invention provide a method for fabricating a smoothly surfaced GaN substrate, comprising the steps of: providing a raw GaN substrate; polishing the raw GaN substrate with diamond slurries; polishing the GaN substrate with carbide compound plates; etching damaged layers of the polished GaN substrate, the damaged layers being caused by the mechanical polishing; and thermally treating the etched GaN substrate.


REFERENCES:
patent: 3643331 (1972-02-01), Futterer et al.
patent: 3844858 (1974-10-01), Bean
patent: 5268070 (1993-12-01), Nagayama et al.
patent: 5913712 (1999-06-01), Molinar
patent: 5993542 (1999-11-01), Yanashima et al.

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