Radio Frequency Power Dependence of Defect Density at Hydrogenated Amorphous Silicon Interface
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RADIO FREQUENCY POWER DEPENDENCE OF DEFECT DENSITY AT HYDROGENATED AMORPHOUS SILICON INTERFACE HISANORI IHARA, TAKEO SAKAKUBO AND HIDETOSHI NOZAKI Research and Development Center, Toshiba Corporation, Toshiba-cho, Saiwai-ku, Kawasaki, 210, Japan
1, Komukai,
ABSTRACT A hydrogenated amorphous silicon (a-Si:H) interface fabrication technology for the plasma CVD method , which can produce low interface defect density, is presented. The relation between the interface defect density and radio frequency (RF) power was investigated. As a result, the difference between the interface defect density and the bulk defect density decreased with increasing the RF power. A high RF power (25 W) a-Si:H buffer layer 5 nm thick was deposited on the interface before depositing low RF power (5 W) a-Si:H layer with a low bulk defect density. It has been found that the ideal defect density distribution, which shows the uniform distribution with the very low defect density (4.2xlO cm') from the i/i interface to the bulk, can be accomplished by 5 nm buffer layer.
INTRODUCTION We have investigated the hydrogenated amorphous silicon (a-Si:H) layered interface (i/i interface) between intrinsic aSi:H (i-a-Si:H) layers. Through the comparative investigation between mercury-sensitized photo-CVD method and plasma CVD method, we have already found that, 1) the mercury-sensitized photo-CVD method scarcely generates defect density at the i/i interface, and that, 2) the plasma CVD method generates defect density at the i/i interface, in spite of depositing a-Si:H at low radio frequency (RF) power(l]. However plasma CVD method is utilized most generally among many kinds of a-Si:H deposition methods[2-6]. Therefore, a-Si:H deposition technology, which does not generate any defect density at the interface, is desired in the plasma CVD method. We investigated RF power dependence of defect density at the i/i interface. As a result, it has been found that the difference (&Dif) between the interface defect density and the bulk defect density decreases with increasing the RF power. Therefore, an experiment was carried out in which a high RF power a-Si:H layer was deposited as a buffer layer on the i/i interface before depositing the low RF power a-Si:H layer with low bulk defect density. It has been found *that 5 nm high RF power a-Si:H buffer layer can remarkably decrease the interface defect density and produce the uniform defect density distribution from the i/i interface to the bulk. SAMPLE PREPARATION The sample structure, Fig.
1.
It
is
used in this study,
the a-Si:H i-p diode structure.
is
illustrated in
The i/i
Mat. Res. Soc. Symp. Proc. Vol. 237. @1992 Materials Research Society
interface
638
ITOELECTME• p TYPELAYER
I/P MENACE
Table I Plasma CVD a-Si:H deposition conditions
PLANAi TYa-S i:HLAYER
S
sm
i /i INTWACE 2 FLO RATE
(scem)
SUBSTRATE TEMPERATURE (C) PRUSSUE (Torr)
i TYKEa-St:H LAE
75 2 0 0 0. 4
Ti/I INTERFAcE
E TI ELECTRO
Fig.1 a-Si i-p diode diagram was located intentionally in the middle of the i-a-Si:H layer 2 ja
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