论文研究-Control technique of Sapphire roughness in CMP processing.p...
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Control technique of Sapphire roughness in CMP
processing
1
Liu Yuling, Tan Baimei, Niu Xinhuan, Zhao Haitao
Institute of Microelectronics Hebei University of Technology,Tianjin(300130)
E-mail:bmtan@hebut.edu.cn
Abstract
Sapphire is the main substrate for the third generation semiconductor materials-GaN. The surface
quality directly affects device performance. In this paper, chemical mechanical polishing (CMP) of
sapphire substrate is studied, several factors which influence the CMP quality are analyzed, and the
mechanism of CMP model is discussed. Small size (20~30nm) and low dispersion silica sol is used
as abrasive, which can avoid scratches caused by abrasive granules with uneven diameter. The
complex surfactant of the slurry can reduce the surface tension and accelerate the mass transfer of
the reactant and reaction product effectively, which can accelerate the reaction and lead to better
concave-convex selectivity and low roughness. We also find that the mass transfer is related with
the temperature, the higher the temperature, the faster the transmission speed. So the removal rate is
higher. By controlling the polishing temperature, the roughness can reach 0.2nm and the perfect
sapphire surface is achieved.
Keywords: Chemical mechanical polishing (CMP), Sapphire, Roughness, Control
1. Introduction
The sapphire has the same optical characteristic and mechanical performance as the
natural gem
[1]
. It has fine thermal characteristic, good electrical specification, stable chemical
property and strong anticorrosion. It has good diaphanous performance and can transmit
infrared ray easily. It is hard to grind and stable ever at high temperature, and its melting point
is 2030℃
[2,3]
. So it is widely used as window and reflector of laser device and the epitaxial
substrate of semiconductor silicon. Because sapphire belongs to hexagonal crystal system the
same with GaN, it is the main substrate for the third generation semiconductor materials-GaN.
Along with the rapid development of the photoelectricity technology, the sapphire has already
become one of the most important substrate materials of the photoelectricity device.
Because sapphire is very hard and brittle, which hardness degree is Morse 9 levels, it is
extremely difficult to mechanical treatment. The mirror surface processing technology is more
complex. But with the light emitter diode and the laser rapid development, the requirement for
sapphire performance is more and more critical and this sets a higher request to the surface
technology.
At present, it is believed that Chemic-Mechanical Polishing is the only best method for the
crystal surface planarization
[4,5]
. Through precise polishing process, the smooth and scatheless
surface can be obtained. By using low hardness polish pad, the low roughness can be gotten.
But when the diameter of substrate is increasing, low hardness pad will result in the declining
of surface planarization and removal rate, which can not be satisfied to the need of the further
development of microelectronic. This study selects SiO2 hydrosols made by ourselves with
small size (20～30nm) and low decentralization as abrasive particles, and also adds complex
non-ionic surfactant into slurry
[6]
. After CMP process, it is proved that complex non-ionic
surfactant can reduce the surface tension and enhancing concave-convex selectivity, which can
effectively reduce roughness
[7]
.
1
Support by Specialized Research Fund for the Doctoral Program of Higher Education of
China(No.20050080007)
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