An atomically controlled Si film formation process at low temperatures using atmospheric-pressure VHF plasma

Abstract

To grow epitaxial Si films with atomic- and electronic-level perfection, a high-temperature chemical vapor deposition (CVD) process (>1000 °C) has been generally employed. To reduce the growth temperature below 600 °C but keeping a high deposition rate, other energy sources than thermal heating are required. Atmospheric pressure plasma CVD (AP-PCVD) is considered to be suitable for fabricating high-quality films at high deposition rates due both to the high radical density and to the low ion bombardment against the film surface, because the collision frequency among ions and neutral atoms is high. The present study focuses on the low-temperature growth of epitaxial Si, and experimentally demonstrates that AP-PCVD is capable of growing epitaxial Si films with high perfection applicable for semiconductor devices. It is found that the pre-growth cleaning of the Si surface by H(2) AP plasma is effective to grow high-purity Si films, and that the exposure of a film-growing surface to AP plasma during growth is important to form particle-free and defect-free Si films. From the experimental results and the first-principles molecular dynamics simulations of surface atomic reactions, it can be mentioned that both H atoms in the AP plasma and high-density He atoms having thermal kinetic energy contribute to the reduction of growth temperature by supplying considerable energy to the surface.

Low-Temperature Epitaxial Growth by Quiescent Plasma-Enhanced Chemical Vapor Deposition at Atmospheric Pressure

“…The reduction in high-energy particles has opened a new approach to plasma processing, that is, atmospheric pressure (AP) plasma-enhanced chemical vapor deposition (PECVD), which enables thin-film deposition without plasmainduced damage. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The enhancement of the gas-phase reaction is usually inappropriate in thin-film processing, because it implies the ambient generation of solid particles during film deposition. Therefore, in AP chemical vapor deposition, precursor molecules are highly diluted by inert gas molecules, where the apparent mass transfer rate is similar to that at low pressure even at a higher total pressure.…”

“…19 In addition, hydrogen incorporation exponentially increases the deposition rate, 17 which is somewhat inconsistent with the Si etching effect of hydrogen plasma. 20,21 Yasutake et al proposed that the physical mechanism underlying rapid deposition in AP PECVD is a heating effect due to energetic atomic hydrogen impinging on the deposition surface, 7 which causes the abstraction of Si-H bonds and subsequent adsorption of Si radicals. The tradeoff between Si-H bond abstraction and the Si etching effect may be controlled by controlling the density of atomic hydrogen, as has been shown in several experiments.…”

“…For the fraction η of the substrate Si surface without Si-H bonds during AP PECVD, the time derivative of η is proportional to the atomic hydrogen concentration in a hydrogen heating model. 7 Under given plasma conditions, increasing the carrier gas flow enhances the surface heating because more hydrogen is available. In addition, an increase in precursor radicals, for example, SiH 3 , results in stacking faults caused by surface Si-H bond generation, and thus the failure of epitaxial growth.…”