Process Steps for High Quality Si-Based Epitaxial Growth at Low Temperature via RPCVD

Abstract

The key process steps for growing high-quality Si-based epitaxial films via reduced pressure chemical vapor deposition (RPCVD) are investigated herein. The quality of the epitaxial films is largely affected by the following steps in the epitaxy process: ex-situ cleaning, in-situ bake, and loading conditions such as the temperature and gaseous environment. With respect to ex-situ cleaning, dry cleaning is found to be more effective than wet cleaning in 1:200 dilute hydrofluoric acid (DHF), while wet cleaning in 1:30 DHF is the least effective. However, the best results of all are obtained via a combination of wet and dry cleaning. With respect to in-situ hydrogen bake in the presence of H2 gas, the level of impurities is gradually decreased as the temperature increases from 700 °C to a maximum of 850 °C, at which no peaks of O and F are observed. Further, the addition of a hydrogen chloride (HCl) bake step after the H2 bake results in effective in-situ bake even at temperatures as low as 700 °C. In addition, the effects of temperature and environment (vacuum or gas) at the time of loading the wafers into the process chamber are compared. Better quality epitaxial films are obtained when the samples are loaded into the process chamber at low temperature in a gaseous environment. These results indicate that the epitaxial conditions must be carefully tuned and controlled in order to achieve high-quality epitaxial growth.

Fabrication of Crystalline Si Thin Films for Photovoltaics

“…Because a clean Si substrate surface favors the growth of high-quality epitaxial Si, various wafer treatment methods have been developed to improve the epitaxial layer quality. For example, wafer surface cleaning methods such as HF-based wet cleaning, [93,94] plasma-based dry cleaning with SiF 4 , [95,96] Ar, [97] H 2 , [98,99] and combined wet and dry cleaning [100] have been studied. Many techniques have been developed to prepare c-Si thin films by epitaxial methods.…”

“…In recent years, many kinds of epitaxial growth techniques have been developed. For example, ultrahigh vacuum low pressure chemical vapor deposition (UHVLPCVD) at high temperatures in the range of 700-960 °C, [118][119][120] reduced pressure chemical vapor deposition (RPCVD) at temperatures below 700 °C, [100] pulsed DC magnetron sputtering deposition [121] at substrate temperature TTV: Total thickness variation.…”

“…In recent years, many kinds of epitaxial growth techniques have been developed. For example, ultrahigh vacuum low pressure chemical vapor deposition (UHVLPCVD) at high temperatures in the range of 700–960 °C, [ 118–120 ] reduced pressure chemical vapor deposition (RPCVD) at temperatures below 700 °C, [ 100 ] pulsed DC magnetron sputtering deposition [ 121 ] at substrate temperature below 500 °C [ 122 ] (see Figure 12f,g), high‐vacuum electron cyclotron resonance plasma deposition epitaxy with temperatures in the range of 450–525 °C, [ 123 ] ion beam epitaxy using temperatures of above 300 °C, [ 124–127 ] electron cyclotron resonance plasma CVD (ECR‐CVD) using temperatures as low as 285 °C, [ 128 ] laser‐enhanced chemical vapor deposition at temperatures as low as 250 °C [ 129 ] and plasma‐enhanced chemical vapor deposition (PECVD) (see Figure 12b,c) using temperatures in the range of 700 °C and down to 150 °C. [ 44,79,95,109,130–132 ] It should be emphasized that PECVD is the only technique that has allowed to produce thick c‐Si films at low temperatures.…”