Defect Reduction in Laser Thermal Processing

Abstract

Laser thermal processing (LTP) of Si involves laser melting a preamorphized layer in order to activate dopants and create a low resistivity contact. Defects are often observed to form during the recrystallization of the molten layer. This work focuses on varying the implant conditions and the pre-LTP annealing conditions in an effort to reduce these defect concentrations. The effect of very low temperature anneals (VLTA) and varying dose rates on the amorphous/crystalline interface roughness prior to LTP and the defect density after LTP have been investigated. The amorphous layer was created by a 10 keV 1×1015/cm2 Si+ implant. VLTA were conducted in a nitrogen gas furnace at temperatures between 400°C and 450°C for times between 5 minutes and 60 minutes. These anneals were chosen to minimize recrystallization of the amorphous layer by solid phase epitaxial regrowth. Variation in the dose rate from 0.06 mA/cm2 to 0.48 mA/cm2 was achieved by changing the beam current in the ion implanter. High-resolution crosssectional transmission electron microscopy (HR-XTEM) was used to analyze the effect of the VLTA or dose rate on the amorphous/crystalline interface. Results show that the 400°C 60 minute VLTA or the 0.48 mA/cm2 dose rate reduced the roughness of the amorphous/crystalline interface from over 45Å to around 15Å. This reduction in amorphous/crystalline interface roughness prior to laser thermal processing results in a reduction in LTP recrystallization defects by as much as an order of magnitude.

Optimisation of Junctions formed by Solid Phase Epitaxial Regrowth for sub-70nm CMOS

“…There are various other approaches that may affect the number of end of range defects that have been researched elsewhere. Among these are wafer temperature during implant [24], beam current dynamic annealing [25], pre-annealing [12], amorphising species, dose and energy, or the use of co-implants to create vacancies for the excess interstitials. For normal device processing there may be operational or device issues with implementing all of these apart from preannealing.…”

Varying implant dose rate for defect reduction in laser thermal processing

“…During LTP, the power is set such that only the amorphous layer melts and thus, the recrystallization process originates at the amorphous/crystalline (a/c) interface. Therefore, previous work has focused on the effect of the a/c interface morphology on the formation of extended defects [3]. Earlier studies investigated very low temperature anneals (VLTA) as a method of altering the implantation induced a/c interface [3].…”

“…Therefore, previous work has focused on the effect of the a/c interface morphology on the formation of extended defects [3]. Earlier studies investigated very low temperature anneals (VLTA) as a method of altering the implantation induced a/c interface [3]. Results showed that a 4008C 60 min VLTA reduced the a/c interface roughness.…”