Intrinsic crystalline-to-amorphous transition above 400°C in plasma-deposited Si thin films

Abstract

There has been long debate concerning why microcrystalline Si formation is disrupted at a deposition temperature above around 400°C: is it due to the loss of surface hydrogen coverage or to the incorporation of oxygen impurities? The authors reduced the atmospheric concentration of such impurities as O, C, and N in this work by using an ultraclean plasma deposition apparatus and demonstrate that microcrystalline Si films showed improved crystallinity at a deposition temperature of 350°C, resulting in a mobility of 5. As the deposition temperature was raised to 450°C, however, the Raman spectrum shows an amorphous structure of the film under such clean conditions. According to secondary ion mass spectrometry, the O, C, and N concentrations in this film were as low as 1017, 1016, and 1017cm−3, respectively, demonstrating that the crystalline-to-amorphous transition around 400°C should be intrinsic under the present conditions and may be correlated with thermal hydrogen desorption on a film-growing surface.