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Defect Reduction in Laser Thermal Processing

Published online by Cambridge University Press:  17 March 2011

Heather Banisaukas,
Kevin S. Jones,
Somit Talwar,
Scott Falk and
Dan F. Downey
Heather Banisaukas
Affiliation:
Department of Materials Science and Engineering SWAMP Center University of Florida Gainesville, FL 32611
Kevin S. Jones
Affiliation:
Department of Materials Science and Engineering SWAMP Center University of Florida Gainesville, FL 32611
Somit Talwar
Affiliation:
Verdant Technologies San Jose, CA
Scott Falk
Affiliation:
Varian Semiconductor Equipment Associates Gloucester, MA
Dan F. Downey
Affiliation:
Varian Semiconductor Equipment Associates Gloucester, MA
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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.

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