1. 1 AlCl 3 -induced crystallization of amorphous silicon thin films 指導教授 : 管 鴻 (Hon Kuan) 老師 學生 : 李宗育 (Tsung-Yu Li)

2. 2 Outline Introduction Experimental Results and discussion Conclusions References

3. 3 Introduction Polycrystalline Si (poly-Si) thin films are generally fabricated by crystallizing amorphous Si (a-Si) thin films because these can render larger grains compared to directly deposited poly-Si films [1,2]. But it generally takes tens of hours to crystallize a-Si films even at 600 ℃. One of the methods to enhance the solid-phase crystallization is to deposit metal film or metal particles on a-Si films [3–11]. However, the metals are incorporated into Si films during crystallization and most of them exist as deep-level impurities in Si and act as recombination centers. An exception is Al, which exists as a shallow acceptor in single crystal Si. Thus, using Al metal- induced crystallization can significantly relieve the contamination from the metal. It is called specially as aluminum-induced crystallization (AIC). In this study, they report the utilization of AlCl 3 vapor for AIC, instead of Al metal film. Al was supplied in the form of vapor from the AlCl 3 during the a-Si deposition. A-Si films with Al metal under layer were also prepared for comparison.

4. 4 Experimental The a-Si films were deposited by plasma-enhanced chemical vapor deposition (PECVD) at 300 ℃ on Si wafers and 7059 Corning glasses using the mixture of SiH 4 (1 sccm), Ar (10 sccm) and SiH 4 (1 sccm), Ar(10sccm), AlCl 3 vapor (AlCl 3 sublimates at 178 ℃ ), respectively. The a-Si films were also deposited on substrates with evaporating Al layers using SiH 4 (1 sccm) and Ar (10 sccm) at the same temperature for 30 min. The vapor pressure in the reactor chamber is 10 Pa and that of the AlCl 3 is from 0.1 to 1 Pa. When there are only SiH 4 and Ar in the reactor chamber, the a-Si growth layer is 380 nm. And when the AlCl 3 vapor was added in, the a-Si growth layers are 500,575 and 473 nm, for the pressure of AlCl 3 0.1, 0.2 and 1.0 Pa separately, which indicate that the velocity of the a-Si layer growth is dependent on the partial pressure of the AlCl 3 vapor.

5. 5 Results and discussion Fig.1. XRD patterns of the samples after annealing in dry nitrogen ambient for 5 h at 540 ℃. (a) a- Si/Al/glass; (b1), (b2), (b3) a-Si/glass with AlCl 3 vapor during a-Si films deposition, the vapor pressure of the AlCl3 were 1.0, 0.2 and 0.1 Pa,respectively, and (c) a-Si/glass without AlCl 3 vapor during the a-Si film deposition.

6. 6 Results and discussion Fig. 2. (a) Typical and (b) three-dimensional AFM images of the annealed Si film deposited with AlCl 3 vapor.

7. 7 Results and discussion Fig. 3. Depth profile of the XPS spectra showing the qualitative concentration variations of Al, O, Cl and Si for the samples (a), (b1), (b2), and (b3) in Fig. 1.

8. 8 Conclusions The crystallization of a-Si was able to be enhanced by using AlCl 3 vapor. Al was supplied in the forms of vapor from AlCl 3 during the deposition of the a-Si film. Crystallization was enhanced with the effect of AlCl 3 so that the crystallization was completed in 5 h at 540 ℃. The surface of the poly-Si film induced by AlCl 3 was even smoother than that of nanocrystal- line Si films prepared by PECVD techniques, while the surface roughening was inevitable with Al metal layer. And the grain size was much larger than that of the AIC poly-Si films.

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