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

Abstract

Single crystalline silicon wafers whose surfaces were machined by diamond grinding were irradiated by a nanosecond-pulsed Nd:YAG laser. Changes in the subsurface crystallinity and surface topography were investigated by transmission electron microscopy and atomic force microscopy. It was found that the grinding process gave rise to amorphous layers, dislocations and micro cracks. However, all of this damage could be eliminated by a single laser pulse of suitable energy density, which also led to a remarkable amount of smoothing of the wafer surface. When excessively high energy densities were used, tiny particles were found to form on the wafer surface. It is speculated that these particles are produced by the recondensation of silicon boiled away from the wafer surface during the laser pulse. The temperature rise during laser irradiation was estimated using a simplified model. The results obtained in this study suggest that nanosecond-pulsed laser irradiation may be an effective approach for processing grinding-damaged silicon wafers.

Characterization of microparticles and oxide layers generated by laser irradiation of diamond-machined silicon wafers

“…The machined samples were then irradiated with a Nd:YAG laser (QuikLaze-50, New Wave Research, Inc., Fremont, US). Details regarding the laser can be found in [6] and [7]. Single pulses with a pulse width of 3-4 ns were used.…”

“…Two laser pulse energies were used, 4.16 and 5.76 μJ, which gave energy intensities of 1.04 and 1.44 J cm −2 , respectively. Microparticles should be generated on wafer surfaces under these conditions [7]. After laser irradiation, the surface topographies of the samples were examined by atomic force microscopy (AFM; Veeco, Nanoscope IIIa).…”

“…The calculation in [7] revealed that the wafer surface temperature increases with increasing laser energy density. When the laser energy density is 0.96 J cm −2 , the wafer surface temperature is 3028 • C, which is higher than the boiling point of silicon (2878 • C) [12].…”

“…Particle generation can be prevented using a lower laser energy density (<0.96 J cm −2 ) [7]. When this is done, silicon melts without boiling so that the subsurface damage is removed without forming unwanted particles.…”

Thermal Damage Characterization of Silicon Wafer Subjected to CW Laser Beam

“…기존의 레이저와 실리콘 웨이퍼간의 상호작용에 대한 연구는 주요 단파장 (10~12) 또는 가시광 (13,14) 대 역의 레이저 빔에 대해 수행되었으며 근적외선 대 역의 레이저 빔에 실리콘의 손상에 대한 연구는 실리콘의 낮은 흡수 계수로 인해 제한되었다. (15,16) 그러나 광학적 물성인 흡수 계수는 온도에 의존적 인 물성으로, 근적외선 파장에 대한 흡수계수는 온도가 증가하게 되면 급격히 증가한다.…”