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Controlling the Type of Bonded Hydrogen Sites in Glow Discharge Amorphous Silicon Films

IP.com Disclosure Number: IPCOM000088158D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 4 page(s) / 37K

Publishing Venue

IBM

Related People

Brodsky, MH: AUTHOR

Abstract

Recently, the silane glow-discharge method has been used to make amorphous Si (a-Si) films that are doped [1]. Such films are useful for solar cells [7]. A problem in making a-Si this way is that hydrogen from the silane starting gas remains in the final a-Si film. The present method controls a plasma glow discharge to provide knowledge in advance as to whether a-Si has hydrogen predominately in SiH(2) and SiH(3) groups or predominately in SiH groups isolated for other SiH groups.

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Controlling the Type of Bonded Hydrogen Sites in Glow Discharge Amorphous Silicon Films

Recently, the silane glow-discharge method has been used to make amorphous Si (a-Si) films that are doped [1]. Such films are useful for solar cells
[7]. A problem in making a-Si this way is that hydrogen from the silane starting gas remains in the final a-Si film. The present method controls a plasma glow discharge to provide knowledge in advance as to whether a-Si has hydrogen predominately in SiH(2) and SiH(3) groups or predominately in SiH groups isolated for other SiH groups.

Glow-discharge methods have wide applications. Relevant examples are semiconductor physics for the deposition of doped amorphous Si and Ge films [1] and polymer chemistry for the synthesis of organic films [2]. This article addresses an apparent paradox referred to as the glow-discharge decomposition [1,3,4] process. Chemists refer to similar methods as plasma polymerization [2,5]. Recently, plasma chemists categorized plasma conditions leading to different types of incomplete polymerization [5] which may be partial decomposition. In semiconductor physics certain results indicate compound formation [6] and polymerization.

In glow-discharge decomposition of silane with the aim of producing amorphous Si (a-Si) films, generally, bonded hydrogen is incorporated in films. The amount and location of the hydrogen were measured by techniques including infrared and Raman spectroscopies, nuclear reactions involving protons, wet chemical and microprobe analyses, and mass spectroscopy of thermally evolved gases. Fig. 1 shows a portion of the infrared transmission spectra for two films of a-Si prepared under different conditions of silane pressure and flow rate in an inductively coupled radio frequency (RF) glow- discharge apparatus. The apparatus is similar in all essential aspects to that described in [1]. The important feature in Fig. 1 is that the absorption band characteristic of the silicon hydrogen stretching mode lies at a higher frequency for the film deposited at the higher silane pressure.

Fig. 1 shows Si-H stretching band optical absorption coefficients vs. wave- number W for two a-Si films grown at room temperature in glow-discharge plasmas of silane. The dashed curve with its peak near 2000 cm/-1/ is for a film grown at a pressure of 0.07 torr, while the solid curve with its Peak near 2090 cm/-1/ is for a film grown at 0.8 torr. The films were grown on sapphire substrates and the infrared transmission data was normalized to the background interference fringe pattern. Pressure was determined by a Pirani gauge calibrated for air and may be as much as a factor of two too high in each case.

The results indicate a change in the number of hydrogen atoms bonded to a given silicon atom. Higher pressure deposition with a higher frequency absorption band gives hydrogen in predominantly SiH(2) and SiH(3) groupings, while lower pressure deposition with its lower frequency absorp...