Direct measurement of the melt depth of silicon during laser irradiation

Abstract

We have studied the change in morphology of laser irradiated silicon wafers by annihilating the oxygen thermal donors and the oxidation-induced stacking faults in order to verify the melting of the near-surface regions. The laser beam used was of 1.06 μm with a diameter of 40 μm, generated from a Q-switched neodymium:yttrium aluminum garnet (Nd:YAG) laser with a 150-ns pulse width and at a repetition rate of 12 kHz. Laser beam irradiation above about 6 J/cm2 annihilated both thermal donors and stacking faults, giving evidence of melting and suggesting that the annihilation of the thermal donors and of the stacking faults can be useful in studying the surface morphology in laser/electron beam irradiation.

Complete Restoration of the Subsurface Damages in Single-Crystalline Silicon by Laser Irradiation

“…The mechanism of the lattice structure reconstruction during laser irradiation is still unknown and under further investigation. Previous studies on laser annealing have found that the crystallization of amorphous silicon thin films results from the sudden melting of silicon due to the high energy of laser irradiation and subsequent epitaxial regrowth during cooling [11][12][13][14][15]. Although there are differences in wafer subsurface structures and laser irradiation conditions between laser annealing and the present work, similar mechanisms might have occurred in the present work.…”

“…Laser irradiation, from a few decades ago, has been used as a surface processing method for silicon. One of the widespread laser processing techniques is laser annealing [11][12][13][14][15][16][17][18][19][20][21][22][23]. After selected dopant impurities have been implanted into silicon wafers as energetic ions, the disordered silicon surfaces can be restored to crystalline perfection by laser.…”

“…After selected dopant impurities have been implanted into silicon wafers as energetic ions, the disordered silicon surfaces can be restored to crystalline perfection by laser. It has been demonstrated that laser can crystallize sputtered, ion-implanted, vapor-deposited or hydrogenated amorphous silicon thin films on substrates of glass, sapphire and silicon [11][12][13][14][15][16][17][18][19][20][21][22][23]. These crystalline silicon thin films have important applications in solar cells, transistors, flat panel display drivers, and so on.…”

Recovery of microstructure and surface topography of grinding-damaged silicon wafers by nanosecond-pulsed laser irradiation

“…It is presumed that the recovery of the subsurface structure may be the result of sudden melting of the surface layer and subsequent epitaxial regrowth during cooling [8]. A similar phenomenon has been confirmed in conventional laser annealing processes [ [10][11][12][13][14]. Since amorphous silicon has a much higher light absorption coefficient than crystalline silicon, there is likely to be sufficient absorption of laser energy in the near-surface layer to form a thin liquid silicon film.…”

“…This epitaxial regrowth mechanism is different from that involved in the laser annealing of silicon layers on substrates such as glass and sapphire, where no lattice-matched crystal seed exists. The melting of silicon has been confirmed in the conventional laser annealing process by measuring the timeresolved optical reflectivity [13] or by detecting the presence/absence of oxygen thermal donors and oxidationinduced stacking faults [14]. In this work, it was difficult for the authors to directly detect the melting phenomenon.…”