Measurement of Ultrafast Melting and Regrowth Velocities in Pulsed Laser Heated Silicon
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MEASUREmENT OF ULTRAFAST MELTING AND REGROWTH VELOCITIES IN PULSED LASER HEATED SILICON PHILIP H. BUCKSBAUM* AND JEFFREY BOKOR** *AT&T Bell Laboratories, Murray Hill, New Jersey 07974; **AT&T Bell Laboratories, Hoimoel, New Jersey 07733
ABSTRACT Direct measurements of the liquio/solid interface veiocity have been made during both melt-in and regrowth for crystaipuised (20 psec) ultraviolet lasei irradiation or line silicon. The regrowth velocity was 25 m/sec, indepen01 50 to 100 dent or laser Ifuence. Regrowtn velocities from neat aiffusion caiculations which in/sec are expected neglect unroecooiing, whereas the inclusion of an appropriate undercooling curve orings the calculation into good agreement witn the oata. Tne liquid illms produced weLe up to 40 nm truck and were tulLy amorphized on resoiiaificaion1. tiiat probe laser experiments We report tne results at melted liquid silicon films as they melt and resolidrfy with 20 laser with 15 psec psec time reso±ution. A 24d nm exciner was used as the melting source to induce a large pulse width 01 the resoliditication velocity to study the thermodynamics liquid-solid interface far from equilibrium. A much weaker 1.64 pim 15 picosecond laser pulse, produced by transient stliulateu Raman scattering of a portion of tne ultraviolet laser output, Tnis probed tne iiquia film in transmission and retiection. the depth of the related to intormation couid be directly a new iieat liquid silicon film. Comparison 01 tne data witn flow calculation provides clear evidence for uncercooling of during the interlace ouring amorphous regrowv-n and overheating melt-in. Great care was taKen to produce a spatially nomogeneous Tne 1.64 melt spot; typically, a spot size of 0.8 mm was used. laseL 1yioet pm infrared prooe puise was ueriveu from tne uit in tnaliium i pu.se by transient stimulated Raman scatteringi vapor. The infrared beam was heavily attenuated, apertured and imaged to a 100 pm spot in tne center 0t the melt spot on tne raster sample. The silicon wafers were mounted to a motorized scanner, WtliCkL moved to expose a fresin crystalline surface on yermanium pbotodiodes detected every pulse. Room temperature intrared light transmitted and reflected from tne silicon, as well as a glass surface Leriection useu tor normalizat.on. metallic liquid silicon is The attenuation constant in the imaginary part of the complex simply related to k(w), simpie refractive index n(w), wn.cn may be calcuiatea using a Tne value of K(Lu) tiius derived is in excellent Drude model. the wavelength agreement witu eliipsometry measurements in At tne probe wavelength in this experirange 0.4-1.0 Aimj2j. Once the air, metallic ment, calcuiation yields k(l.6pm)=8.4. liquid, anm solid complex indices are known, the transmission T and R can be calculated easily reflection coefficients
Kat. Res. Soc. Symp. Proc. Vol.
23 (1984) Published by Elsevier Science Publishing Co., Inc.
94
depths the are used to corroborate Reflection data The two data sets are independent, obtained from transmission. and their compar
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