Defect Reduction in Laser Thermal Processing
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Defect Reduction in Laser Thermal Processing Heather Banisaukas1, Kevin S. Jones1, Somit Talwar2, Scott Falk3, Dan F. Downey3 1 Department of Materials Science and Engineering SWAMP Center University of Florida Gainesville, FL 32611 2 Verdant Technologies San Jose, CA 3 Varian Semiconductor Equipment Associates Gloucester, MA 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 1x1015/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. INTRODUCTION The further scaling of device dimensions prompts an investigation into alternate implantation and annealing techniques for the formation of ultra-shallow highly doped junctions. Shallow junction formation is currently limited by inadequate dopant activation by conventional ion implantation and rapid thermal annealing. Laser thermal processing (LTP), which involves melting and recrystallization of an implantation
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induced amorphous layer, has shown promising results in creating low resistance ultra shallow junctions [1]. However, as previously reported [2], there is a high density of stacking faults and microtwins after LTP processing. During LTP, the power is set such that only the amorphous layer melts and thus, the recrystallization process originates at the amorphous/crystalline interface. Therefore, a better understanding of the effect of the amorphous/crystalline interface morphology on the formation of extended defects is needed. Two approaches to alter the amorphous/crystalline interface morphology and thus possibly reduce the density of extended defects that form upon melt recrystallization are to use a low temperature pre-annealing process or to vary the implant
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