References cited in this section

1. B. Gorowitz, T.B. Gorczyca, and R.J. Saia, in Solid State Technology, Vol 28 (No. 6), 1985, p 197

9. A.C. Adams, Solid State Technology, in Vol 26 (No. 4), 1983, p 135; also in VLSI Technology, S. Sze, Ed., McGraw-Hill, 1983, Chapter 3

13. R. Reif and W. Kern, Plasma Enhanced Chemical Vapor Deposition, Thin Film Processes II, Academic Press, Inc., 1991

21. E.R. van de Ven, I.-W. Connick, and A.S. Harrus, in Proceedings of the Seventh International IEEE MultiLevel Interconnection Conference (Santa Clara, CA), Institute of Electrical and Electronics Engineers, June 1990, p 194

26. A.K. Sinha, in Solid State Technol, Vol 23 (No. 4), 1980, p 133

27. J.L. Vossen, in J. Electrochem. Soc., Vol 126, 1979, p 319

28. S.J. Fijita, N.S. Zhon, H. Toyoshima, T. Ohishi, and A. Sasaki, in IEDM Tech. Digest, Vol 84, 1984, p 630

29. W. Kern and R.S. Rosler, in J. Vac. Sci. Technol., Vol 14 (No. 5), Sept/Oct 1977, p 1082

30. A.C. Adams, in Reduced Temperature Processing for VLSI, R. Reif and G.R. Srinivasan, Ed., The Electrochemical Society, 1986, p 111

31. A.C. Adams and C D. Capio, in J. Electrochem. Soc., Vol 128, 1981, p 423

32. I T. Emesh, G. D'Asti, J.S. Mercier, and P. Leung, in J. Electrochem. Soc., Vol 136, 1989, p 3404

33. E.P.G.T. van den Ven, in Solid State Technol, Vol 24 (No. 4), 1981, p 167

34. J R. Hollahan, in J. Electrochem. Soc., Vol 126, 1979, p 930

35. A C. Adams, F.B. Alexander, C.D. Capio, and T.E. Smith, in J. Electrochem. Soc., Vol 128, 1981, p 1545

36. A.C. Adams, in Reduced Temperature Processing for VLSI, R. Reif and G.R. Srinivasan, Ed., The Electrochemical Society, 1986, p 111

37. V.S. Nguyen, S. Burton, and P. Pan, in J. Electrochem. Soc., Vol 131, 1984, p 2349 PECVD of Amorphous and Polycrystalline Silicon Films

Amorphous Silicon Films. The PECVD process is extensively used to deposit amorphous silicon films. Amorphous hydrogenated silicon (a-Si:H) films are deposited by the PECVD process by the decomposition of monosilane, disilane, or chlorosilane in a glow discharge plasma at temperatures in the range of 200 to 300 °C (390 to 570 °F) (Ref 38). The amorphous-to-polycrystalline transition temperature is sensitive to reactor design and deposition conditions and has to be controlled carefully. The a-Si:H films have important applications in the fabrication of solar cells (Ref 39), as photoreceptors in photolithography, and in Vidicon-type photoconductive image tubes (Ref 40).

Polycrystalline Silicon Films. Polycrystalline silicon is used as the gate electrode in metal-oxide semiconductor devices and as the emitter in bipolar devices. It is also used as interconnect material in ICs. In commercial manufacturing of ICs, polycrystalline silicon is deposited by thermally driven LPCVD at 625 °C (1150 °F). The PECVD process is rarely used for polycrystalline silicon film deposition, because deposited polycrystalline silicon films are intrinsic and have very high resistivity. Most applications in the microelectronic industry require the polycrystalline films to be highly conductive, which is achieved by doping the films after deposition. The number of processing steps can be reduced if the films are doped in situ. Application of PECVD for in-situ doping of polycrystalline silicon films is being explored. Thickness, uniformity, and deposition rates are very much affected when relatively high concentrations of dopant species are introduced in the LPCVD reactor during film growth. When PECVD is used to dope the polycrystalline silicon films in situ, the conductivity of these films can be modulated by six orders of magnitude for both p-type (by adding diborane) and n-type (by adding arsine) (Ref 41).

In other applications of polycrystalline silicon films, for example in the fabrication of thin-film transistors, PECVD is very desirable. Thin-film transistors are being explored for use in flat-panel displays and require much lower deposition temperatures, which can be achieved by PECVD. In addition, the growth rate of PECVD polycrystalline silicon films is less sensitive to the deposition temperature (Ref 4), as shown in Fig. 4, and so uniform film deposition requires less stringent control of the wafer temperature.

200 100

20 10 5

Deposition temperature, cC BOO 700 eoo

0 0

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