Polysilicon thin films fabricated by solid phase crystallization using reformed crystallization annealing technique


Özmen Ö. T. , Karaman M., Turan R.

THIN SOLID FILMS, cilt.551, ss.181-187, 2014 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 551
  • Basım Tarihi: 2014
  • Doi Numarası: 10.1016/j.tsf.2013.11.098
  • Dergi Adı: THIN SOLID FILMS
  • Sayfa Sayıları: ss.181-187

Özet

In this work, a reformed crystallization annealing technique is presented for the solid phase crystallization (SPC) of amorphous silicon (a-Si) on SiNx-coated quartz substrate. This technique includes a two-step annealing process which consists of a low-temperature (475 degrees C) classical furnace annealing for nucleation of Si and a high-temperature (900 degrees C) grain growth process of polycrystalline silicon (poly-Si) during thermal annealing in classical tube furnace. The aim of this reformed two-step annealing technique is reducing the long (up to 48 h) crystallization annealing duration of single step annealing at low temperatures (similar to 600 degrees C) while maintaining the film quality, as low-temperature single step annealing, by using reformed technique. Continuous p-type poly-Si film was formed on quartz substrate thanks to exodiffusion of boron, which was deposited prior to a-Si, through Si film by thermal annealing. The stress and degree of crystallinity of the p-type poly-Si were studied by the micro-Raman Spectroscopy. The crystallization fraction value of 95% was deduced for annealed samples at 900 degrees C, independent from crystallization technique. On the other hand, the Raman analysis points out that compressive stress was induced by increasing the annealing duration at 900 degrees C. X-ray diffraction (XRD) analysis reveals that the preferred crystallite orientation of the films, independent from crystallization temperature and substrates, is < 111 >. Additionally, the average crystallite size calculated from XRD patterns increases from 69 angstrom to 165 angstrom by using reformed two-step annealing instead of single step annealing at 900 degrees C for 90 min. The exodiffusion of boron into the silicon film was deduced from secondary ion mass spectrometry (SIMS) analysis and the p(+)/p graded boron profile was obtained, which may result higher carrier diffusion length and longer carrier life time. Finally, the annealing duration dramatically decrease to 9 h by using reformed two-step annealing technique instead of conventional single step annealing at 600 degrees C. The results show that reformed SPC annealing technique has major advantages by combining the lower annealing duration and high crystal quality. (C) 2013 Elsevier B. V. All rights reserved.