Investigating the role of hydrogen in silicon deposition using an energy-resolved mass spectrometer and a Langmuir probe in an Ar/H _2 radio frequency magnetron discharge

摘要

The plasma parameters and ion energy distributions (IED) of the dominant species in an Ar-H _2 discharge are investigated with an energy resolved mass spectrometer and a Langmuir probe. The plasmas are generated in a conventional magnetron chamber powered at 150 W, 13.56 MHz at hydrogen flow rates ranging from 0 to 25 sccm with a fixed argon gas flow rate of 15 sccm. Various H _n ~+, SiH _n ~+, SiH _n fragments (with n 1, 2, 3) together with Ar ~+ and ArH ~+ species are detected in the discharge. The most important species for the film deposition is SiH _n (with n 0, 1, 2). H fragments affect the hydrogen content in the material. The flux of Ar ~+ decreases and the flux of ArH ~+ increases when the hydrogen flow rate is increased; however, both fluxes saturate at hydrogen flow rates above 15 sccm. Electron density, n e, electron energy, T _e, and ion density, n _i, are estimated from the Langmuir probe data. T _e is below 1.2 eV at hydrogen flow rates below 8 sccm, and about 2 eV at flow rates above 8 sccm. n _e and n _i decrease with increased hydrogen flow but the ratio of n _i to n _e increases. The formation of H ~+ ions with energies above 36 eV and electrons with energies greater than 2 eV contributes to the decrease in hydrogen content at hydrogen flow rates above 8 sccm. Analysis of the IEDs indicates an inter-dependence of the species and their contribution to the thin film growth and properties.