Diode-laser absorption spectroscopy of hydrogen halides for semiconductor plasma process diagnostics.

摘要

Hydrogen halides are widely used in semiconductor material processing. For example, HF has been applied for vapor-phase SiO₂ stripping, while HBr is a main process gas for polycrystalline silicon (poly-Si) plasma etching. This thesis aims to improve the accuracy of the spectroscopic parameters of HF and HBr transitions using near-infrared diode lasers, and to develop in situ diode-laser sensors for HBr plasma process optimization and control.; High-resolution absorption lineshapes of HF and HBr transitions in the first overtone bands have been recorded using near-infrared diode lasers. Accurate line intensities, broadening and shift coefficients, and the velocity-changing collision rates of the HF P(3) and P(6) transitions at 7618 and 7460 cm−1, respectively, were determined from Galatry and Rautian profile fits. Measured HBr line intensities for the P(2) and R(7) transitions are ∼11% and 16% higher than those listed in the HITRAN database, respectively. Hyperfine structure of the HBr P(2) transition was modeled with eight-line Gaussian profiles, based on ground-state hyperfine constants. These measurements significantly improve the accuracy of spectroscopic parameters and form the basis for HBr plasma diagnostics.; Diode-laser sensors based on high-frequency wavelength modulation spectroscopy were developed for real-time HBr plasma poly-Si etch process monitoring. A minimum detectable absorbance of 3 × 10−7/Hz 1/2 as achieved. In situ measurements were recorded in a 300-mm planar inductively coupled plasma etch reactor. The measured rotational temperature (435 ± 8 K) in the plasma was relatively independent of conditions studied. The measured HBr dissociation fraction ranged from 25%–60%, depending on the ICP power (200–1000 W), gas flow rate (25–400 sccm), and assumptions of vibrational temperature and gas composition. HBr concentration 1-cm. above the wafer surface during blank Si wafer etching varied with bias power. HBr dissociation fraction was measured before and after SF₆ plasma chamber clean with focus rings made of quartz, alumina, and silicon carbide. The results show effects of surface material/condition on the HBr plasma composition. These are the first high-resolution diode-laser absorption measurements in an HBr plasma etcher. The success of this work demonstrates the potential of diode lasers for in situ monitoring of the plasma etch process for real-time control.