AVS 46th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThM

Paper PS-ThM5
Competition Between Etching and Deposition in Methane/Hydrogen Plasma Interactions with the Si(100) Surface

Thursday, October 28, 1999, 9:40 am, Room 609

Session: Plasma-Surface Interactions II
Presenter: H.L. Duan, Stanford University
Authors: H.L. Duan, Stanford University
S.F. Bent, Stanford University
Correspondent: Click to Email
The addition of hydrogen to alkane-based plasmas is important in a number of applications, including diamond synthesis and compound semiconductor etching. However, the mechanisms by which hydrogen influences the plasma system are not fully understood. In this study, optical and mass spectroscopic methods have been carried out to acquire a molecular level understanding of methane/hydrogen plasma interactions with a Si (100) surface. The plasma was formed via an electron cyclotron resonance (ECR) plasma source. Multiple internal reflection Fourier transform infrared (MIR-FTIR) spectroscopy and real time in situ mass spectrometry were used to probe the time evolution of surface and gas species at the plasma surface interface. The results show that in the absence of added hydrogen, a polymer-like a-C:H film is deposited on the silicon surface with a linear growth rate. Addition of hydrogen into the plasma, depending on the methane-to-hydrogen ratio, can lead to a complete suppression of film growth; the steady-state coverage of hydrocarbon is about ten monolayers according to the FTIR results. At the same time, infrared absorption at the SiH stretching frequencies suggests a comparable coverage of silicon hydrides. These results together indicate that significant roughening of the silicon surface occurs, and suggest the possibility of etching. This conclusion is supported by preliminary mass spectrometric results indicating the presence of etch products during reaction. For the same plasma conditions, increasing the surface temperature increases the initial a-C:H film growth rate. However, even at elevated temperatures, growth can be suppressed by the addition of hydrogen. The experimental results indicate that there is a competition between etching and deposition chemistry determined by the methane-to-hydrogen ratio in the plasma. Proposed mechanisms describing this competition, and the possibility of etching of silicon by methyl species, will be discussed.