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Characterization of a Silicon Wafer after the Removal of Photoresist Layer Using Two Lasers of Different Wavelengths
Akira USAMI Hideki FUJIWARA Takahisa NAKAI Kazunori MATSUKI Tsutomu TAKEUCHI Takao WADA
IEICE TRANSACTIONS on Electronics
Publication Date: 1992/09/25
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Silicon Devices and Materials)
lifetime, SRMI, impedance mismatching, R-SRMI,
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A laser/microwave method using two lasers of different wavelengths for carrier excitation is proposed to evaluate Si surfaces. These constitute a He-Ne laser (wavelength=633 nm, penetration depth=3 µm) and a YAG laser (wavelength=1060 nm, penetration depth=500 µm). Using a microwave probe, the amount of excited carriers can be detected. The carrier concentration is mainly dependent on the condition of the surface when carriers are excited by the He-Ne laser, as well as on the condition of the bulk region when carriers are excited by the YAG laser. Microwave intensities detected under the He-Ne and the YAG lasers illumination are referred to as the surface-recombination-velocity-related microwave intensity (SRMI) and the bulk-related microwave intensity (BRMI), respectively. The difference between SRMI and BRMI is called relateve SRMI (R-SRMI), and is closely related to the condition of the surface and surface active region. We evaluate the surfaces of the samples after plasma and wet etching to remove the photoresist layer. And we evaluate the surfaces of the samples after heat or HF treatment which is done to recover the damage introduced by plasma etching. It was found that the R-SRMI method is better suited to surface evaluation than conventional lifetime measurements.