Plasma Parameter and Film Quality in the ECR-Plasma-CVD
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PLASMA PARAMETER AND FILM qUALITY IN THE ECR-PLASMA-CVD Y. Nakayama, M. Kondoh, K. Hitsuishi and T. Kawamura of Engineering, College Engineering, Electrical Prefecture, Mozu-Umemachi, Sakai, Osaka 591, Japan
University
of
Osaka
ABSTRACT New DC bias method for the electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) is demonstrated, where the highly photosensitive a-Si:H film of the device grade is deposited on the dielectric substrate. The measurement of plasma parameters using a probe technique indicates that the impinging of ion H' on the growing surface is the key to the high quality a-Si:H film and this DC bias method controls the film properties by the ion density rather than the ion energy.
INTRODUCTION Recently, an electron cyclotron resonance (ECR) plasma has been studied to be used for the chemical vapor deposition (CVD) of thin films such as hydrogenated amorphous silicon (a-Si:H) and its based alloys at low temperature. In this process, the exposure of the film growing surface to the stream of charged particles enables one to decrease the process temperature lower than that of the plasma CVD using a glow discharge. However, the stream of charged particles extracted from the ECR plasma by a divergent magnetic field is insufficient for obtaining device grade films. In order to overcome this for a-Si:H films, a DC bias method[l-3] has been studied on the basis of the concept that the attack of ions on the growing surface is important, where a DC bias voltage is applied to the substrate. However, this method restricts the substrate to the electrical conductive material, and the detailed relation between film quality and plasma parameters have been scarcely reported. In this paper, we demonstrate new DC bias method which is applicable to the deposition of the dielectric as well as the conductive films both on the conductive and on the dielectric substrates and investigate the key to the high quality film of a-SJ,:H in terms of the plasma parameters.
EXPERIMENTS An ECR-plasma-CVD system used was a divergent magnetic type illustrated in Fig.l. A reactor consisted of an ECR room maintaining a hydrogen plasma and a CVD room where a source gas of SiH4 was fed. A 2 grounded mesh electrode with 1.6xl.6mm squares consisting of stainless steal wires of 0.3mm in diameter was set at a window separating two rooms and an opposite electrode of an aluminum (Al) plate attached to the substrate holder was llcm away from the window. A glass substrate (Corning 7059) was set on the Al electrode to which a DC bias voltage Vb was applied during the deposition. A small piece of crystalline Si wafer was also set on the glass substrate, where the electrical isolation of Si wafer from the Al electrode is essential. The frequency of microwave was 2.45GHz and the magnetic flux density of 875Gauss satisfying the ECR condition was established at a position above the window by 12cm. A source gas of SiH4 was fed as a horizontal flow toward the center from several orifices of imm in diameter on a ring of 15cm in di
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