Time‐resolved reflectivity technique: improvement and applications

Abstract

A new method for determination of the reflectivity of Si in different phase transitions during pulsed laser irradiation is presented in this paper. This method is applied on TRR spectra of crystalline silicon (c-Si) in a medium of oxygen and amorphous hydrogenated silicon (a-Si : H). Time resolved reflectivity (TRR) measurements on silicon has been made during pulsed XeCl excimer laser irradiation (308 nm, 28nm FWHM) in a medium of oxygen. The samples were irradiated in the energy density range 400−100mJ/cm2. The reflectivity was measured with a probe He-Ne laser (632.8 nm). Depending on the energy density of the excimer pulse, heating, melting and resolidification of the surface were monitored by TRR spectra. From these measurements we were able to determine the melting threshold energy density for c-Si, depending on the energy densities, time of melting and maximum reflectivity have been measured. TRR spectra of a sample with 3μm thick a-Si layer for first shot of measurements were calibrated. A series of a-Si : H samples of the same thickness (0.34 μm) irradiated with a constant energy density 450mJ/cm2 and the three consecutive TRR spectra of the irradiated samples were calibrated

In situprobing of pulsed laser melting and laser-induced periodic surface structures formation by dynamic reflectivity

“…When the fluence is around 700 mJ cm −2 (curves 2 in figures 2(a) and (b) and curves 3, 4 in figure 2(c)), a significant reflectivity increase is observed due to the presence of silicon liquid phase. In this case, a melting threshold of ~700 mJ cm −2 was determined, which is very similar to the experiment in [51].…”

In situ time-resolved optical measurements of a-Si thin films during excimer laser crystallization

“…Time-resolved optical inspections [3][4][5][6][7][8] at the film surface have been extensively employed to monitor the laser-induced melting and rapid solidification processes in semiconductors such as Si and Ge thin films. The physical meaning of optical spectra obtained by time-resolved optical reflection and transmission (TRORT) measurements have not been interpreted satisfactorily up to now even though this technique is quite simple in principle, inexpensive, reliability, and process stability.…”