| 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. |
