The Raman Diagnostics and Process Physics of Laser - Surface Modifications.

Raman microprobe spectroscopy is used to analyze laser surface processing, including cw laser heating of Si microstructures, melting of c-Si and c-Ge, and chemical etching of c-Si and copper films. In the investigation of steady-state laser heating of silicon disk microstructures on fused silica and sapphire substrates, the Raman frequency shift and lineshape are compared to simulated Raman spectra. These simulations utilize temperature profiles calculated by a finite element analysis of the heat flow equation. The inhomogeneity of the temperature profiles strongly affects the energy shifts and linewidths of the Raman spectra. Polarization Raman microprobe spectroscopy is used to study laser-induced melting in c-Si and c-Ge. At their respective melting points, the Raman shifts of solid Si and Ge are 481.7 and 281.4 cm^{ -1}, and the linewidths are 24.3 and 14.1 cm ^{-1}. Optical-phonon coupling both to two and to three phonons is used to explain the temperature dependence of the Raman linewidth. Thermal expansion and coupling to two phonons are important in determining anharmonic corrections to the Raman energy shift, while coupling to three phonons is relatively less important. The real-time Raman spectrum is also used to probe the progress of silicon flow during melting and the trench depth during laser-assisted etching. The reactions of copper films on glass with chlorine are studied at room temperature and during laser heating. Raman scattering is used to follow the transformation of the copper film in situ to the copper chlorides, CuCl and CuCl _2. The thin film product formed at ambient temperature without laser heating is shown to be CuCl, while the deposit-like line produced during scanning laser heating is mostly CuCl_2. Post -processing profilometry is used to measure the etching rate for different laser powers, laser scan speeds and chlorine pressures. A model was developed that successfully describes laser etching at low chlorine pressures, high laser powers, and fast laser scan speeds. In other regimes a thick copper chloride layer forms during the reaction of the copper film with chlorine, which inhibits the laser etching.