Laser Induced Bulk Defects in Single Crystal Silicon Below the Melting/Vaporization Thresholds
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TASER INDUCED BULK- DEFECTS IN SINGCLE CRYSTAL SILICON BELOW rTH MELTING/ VAPORIZATION THRESHOLDS Donald L. Parker Institue for Solid State Electronics, Department of Electrical Engineering, Texas A&M University, College Station, TX 77843-3128 ABSTRACT Highly focused Q-switched Nd:VDr fundamental (1.05 micron wavelength IR) and second harmonic (0.53 micron wavelencth green) laser nulses have been shonm to produce bulk defects in single crystal silicon at peak ocwer densities below the vaporization threshold for the IR and below the melting threshold for the green. The defects decrease the encess rinoritv carrier lifetime as measured by junction leakage, junction step recovery, the MOS CV method, bioolar transistor current qain, and pn junction photocurrent. Green pulses have no effect on the thermal oxide dielectric strength or on junction breakdow.m voltage at power densities up to the melting threshold. IR pulses begin to lower the junction breakdown voltage below the vaporization threshold and oxide dielectric strength is drastically lowered at or slightly below this threshold. The defect density decreases exponentially into the crystal with effective ranges of 0.7 micron and 1.7 -microns for the green and IR respectively. IR absorption is very nonlinear near the vaporization peak power density threshold. The defects are a point type; are unchanged by a subsequent 4001C anneal; and are completely removed by an 800 0C anneal. The results suggest some detrimental effects of laser processing of silicon intergrated circuits as well as some new potential applications. .7TIODUCION Laser beam processino research and production applications in the microelectronics industry have been steadily increasinc during the past decade. Laser link blowing for the repairs of VLSI circuits by substituting redundant circuit elements is currently underqoina widespread expansion and the trend seems destined to continue. Furthermore many new potential production applications of laser beams are being developed. This naner concerns a phenomena of laser beam interaction with single crystal silicon which has not received 'idesoread attention in the literature of the field: [1-31 the production of bulk crystal defects at peak power densities which produce no visable change in the material. The phenomena could produce detrimental ef-fects in some production applications and the phenomena itself has scme potential for specific production applications. EXPERIMENTAL The existance and location of the laser produced crystal defects is presumed to correlate with changes in the excess minority carrier lifetime in the semiconductor before and after laser scanning. 'The lifetime may be measured by a variety of electrical tests on devices including pn junction diodes, MOS1capacitors and bipolar transistors. The devices were scanned durina or after fabrication in scuare or rectanqular patterns in a serpenMat. Res. Soc. Symp.
Proc. Vol.
23 (1984) QElsevier Science Publishing Co., Inc.
360
of the IR at these peak power densities is very unstable due
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