Time resolved reflectivity measurements of silicon solid phase epitaxial regrowth

Solid phase epitaxial regrowth (SPE) occurs when an amorphous film in direct contact with an adjoining crystalline substrate is annealed. The regrowth velocity depends on temperature, crystallographic orientation and on the presence of impurities. The use of time resolved reflectivity (TRR) measurements to study the SPE regrowth kinetics of amorphous silicon (a-Si) is based on the higher index of refraction of a-Si at the wavelengths used (950 and 670 nm). During SPE regrowth the a-Si film thickness decreases continuously as the c/a interface moves towards the outer surface. This decreasing film thickness causes cycles of constructive and destructive interference and leads to a time dependant reflectivity. With known optical constants of the film, it is possible to convert the reflectivity vs. time to a depth of the cia interface and from that to calculate the velocity of interface movement. Samples were prepared by the deposition of electron beam evaporated Si atoms on atomically clean substrates Si(100) in an UHV equipment. The substrates were kept at a temperature of 150 degrees C during growth. The SPE crystallization caused by thermal radiation from a carefully calibrated heater was measured in a temperature range between 500 and 650 degrees C. The corresponding regrowth velocities amount to between 0.025 and 20 nm/s. From an Arrhenius-type expression we can deduce an activation energy of 2.84 +/- 0.05 eV. A rate enhancement was observed with antimony doped layers. (C) 2000 Elsevier Science S.A. All rights reserved.