Gas-Phase Chemical Cleaning of Silicon Surfaces.
Abstract
Wafer fabrication is a critical and frequently encountered step in the microfabrication of integrated circuits. Efforts to replace conventional wet chemical processes (e.g., the RCA clean) with alternatives employing gaseous reagents are motivated by the stringent chemical purity requirements of ultra-large-scale integration (ULSI), the industry-wide trend towards dry processing, and strict environmental discharge regulations. These new cleaning processes seek to utilize reactive neutral species, such as ozone, atomic oxygen and atomic hydrogen, to effect the removal of organic, native-oxide, and metallic microcontamination. Ultraviolet (UV) photo-oxidation processes (e.g., UV/air and UV/ozone), which employ ozone, atomic oxygen and hydroxyl radical to remove organic contaminants and grow a thin oxide layer, and hydrogen plasma cleaning, which employs atomic hydrogen to remove organics and native oxide and yield a hydrogen -terminated surface, were investigated. The primary experimental techniques were infrared multiple internal reflection spectroscopy (MIRS), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). MIRS evidenced that UV/air photo-oxidation of Pentadecanoic acid films is first-order in CH_{rm x} (x = 2 and 3) concentration. The activation energies for cyclohexane photo-oxidation and Si surface oxidation, at 100 mTorr are both very small ~2 -3 kcal mol^{-1}. Characterization by MIRS of hydrogen plasma treated Si surfaces evidences the formation of hydrogen-decorated sub-surface defects; infrared bands are observed corresponding to monohydride, dihydride and trihydride configurations. The substrate temperature during hydrogen plasma treatment and the substrate phosphorous-doping level have strong effects on defect formation. In addition, the in situ photochemical production of ozone was modeled using the kinetics of elementary steps as reported in the atmospheric chemistry literature. In a prelude to on-going research on removal of metallic microcontamination, Cu deposition from hydrofluoric acid solutions onto Si wafers was investigated by using glancing-angle X-ray absorption fine structure (XAFS) spectroscopy.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT.......204B
- Keywords:
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- Engineering: Chemical; Engineering: Materials Science; Physics: Fluid and Plasma