Low Temperature Silicon Oxidation with Electron Cyclotron Resonance Oxygen Plasma
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LOW TEMPERATURE SILICON OXIDATION WITH ELECTRON CYCLOTRON RESONANCE OXYGEN PLASMA K. T. SUNG AND S. W. PANG Solid State Electronics Laboratory Department of Electrical Engineering and Computer Science The University of Michigan, Ann Arbor, MI 48109-2122 ABSTRACT Silicon was oxidized at low temperature with an oxygen plasma generated by an electron cyclotron resonance (ECR) source. The ECR source utilized a multicusp magnetic field formed by permanent magnets. Microwave power at 2.45 GHz was applied to the source and rf power at 13.56 MHz was applied to the sample stage. Si oxidation was studied as a function of source distance, pressure, microwave power, and rf power. The oxide thickness increases with microwave and rf power but decreases with source distance. The oxidation rate increases with pressure up to 12 mTorr, then decreases at higher pressure. The relative emission intensities in the plasma monitored using optical emission spectroscopy showed similar dependence on the source distance and microwave power. Oxidation temperature was estimated to be 800 C) and longest time (>30 min). As a result, high quality oxide film grown at low temperature is very desirable. High temperature is needed in thermal oxidation to supply the energy required to activate the reaction. If there are another ways to supply the necessary energy, this temperature can be reduced. Plasma oxidation has been used for oxide formation at low temperature. It uses rf or microwave power to generate reactive oxygen species and oxidation 0 occurs around 300 C [3]-[9]. The quality of these plasma oxides is typically inferior to thermal oxide unless a high temperature annealing step is used to improve the oxide quality. Without the annealing step, these plasma oxides have breakdown field 1011 cm- , and interface state density -1011 cm-2eV- . In comparison, thermal oxide has breakdown field between 8-10 MV/cm, fixed charge density and interface 1 2 state density on the order of 1010 cm- eV- . Although the oxide quality improves after 0 annealing at temperature as high as 1000 C, the advantage of low temperature oxidation will be diminished. An electron cyclotron resonance (ECR) source can provide many advantages for low temperature oxidation. In this paper, the effects of source to sample distance, pressure, microwave power, and rf power on oxide growth with an ECR oxygen plasma were studied. The physical properties of the oxide films were measured using ellipsometry and X-ray photoelectron spectroscopy (XPS). The oxygen plasma was monitored by an optical multichannel analyzer (OMA). The electrical properties of the oxide films were determined by current-voltage (I-V) and capacitance-voltage (C-V) measurements. II. EXPERIMENTAL Figure 1 shows the schematic of the ECR source on top of a if-biased electrode. The
Mat. Res. Soc. Symp. Proc. Vol. 236. ©1992 Materials Research Society
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RESONANT TUNER
- SUDING SHORT MICROWAVE CAVITY
(2A5 GHz; 200-1000 W) SI SAMPLE (FACE UP) Si SAMPLE (FACE DOWN)
SUBSTRATE STAGE
rf3ýOWWATER
GLASS STACKS
COOLIN
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