The effect of laser thermal processing ͑LTP͒ on implantation-induced defect evolution and transient enhanced diffusion ͑TED͒ of boron was investigated. A 270-Å-thick amorphous layer formed by 10 keV Si ϩ implantation was melted and regrown using a 20 ns ultraviolet laser pulse. Transmission electron microscopy revealed that recrystallization of the amorphous layer following LTP results in a high concentration of stacking faults and microtwins in the regrown region. Also, the end-of-range loop evolution during subsequent 750°C furnace annealing, is different in a LTP sample compared to a control sample. Secondary ion mass spectroscopy of a boron marker layer 6000 Å below the surface showed that LTP alone produced no enhanced diffusion. However, during subsequent furnace annealing, the boron layer in the LTP sample experienced just as much TED as in the control sample which was only implanted and furnace annealed. These results imply that laser melting and recrystallization of an implantation-induced amorphous layer does not measurably reduce the excess interstitials released from the end-of-range implant damage. © 1999 American Institute of Physics. ͓S0003-6951͑99͒00149-7͔Continued scaling of the transistor to sub-100 nm dimensions requires the formation of ultrashallow highly doped abrupt junctions for contact formation. A box-shaped, high dopant concentration profile could ideally meet such a requirement. 1 Ion implantation and conventional rapid thermal annealing inevitably lead to less than ideal Gaussian or exponential dopant profile. Also, the interaction between implantation induced point defects and dopant atoms during annealing can considerably broaden the profile shape through transient enhanced diffusion ͑TED͒. One proposed method for circumventing some of these problems is the use of laser annealing. 2 Various approaches proposed include: melting and regrowing crystalline silicon in the presence of a dopant ͑the PGILD process͒ or preamorphization of the surface by implantation followed by a dopant implant into the amorphous material and finally laser melting only the amorphous material ͓also called laser thermal processing ͑LTP͔͒. 2-4 The advantage of the second method is that lower temperatures can be used because amorphous Si melts at a temperature 300°C lower than crystalline Si. This is important because it allows thickness of the melted region to be controlled by the preamorphization.One question that remains is does LTP have an advantage in the transient enhanced diffusion reduced from the implant. It is well known that after implantation induced amorphization of Si, there exists a highly damaged region in the crystalline material just beyond the amorphous/ crystalline interface. 5 This layer, referred to as the end-ofrange ͑EOR͒ damage region, is known to contain a large supersaturation of interstitials. During annealing these interstitials are released and flow both toward the surface and into the bulk, resulting in TED of the common dopants ͑e.g., B, As, P͒. 6 This TED has the undesirable effe...

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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