Effect of Antenna-Substrate Distance on Quality of a-Si:H During ICP CVD Using a Flat Spiral Antenna

Amorphous silicon (a-Si:H) thin films are deposited on silicon substrates by inductively coupled plasma chemical vapor deposition (ICP-CVD) using a flat spiral antenna and SiH ₄ as the precursor gas. The films are deposited at operating pressure of 20 mTorr and 50-W radio frequency (13.56 MHz) power fed to the antenna. Films are deposited by varying the distance (d _s ) between the dielectric (quartz) plate that isolates the flat spiral antenna from the chamber and the substrate location. Diagnostics of the Argon plasma generated under similar experimental conditions are performed using RF compensated Langmuir probe to get an idea about the variation in plasma parameters (plasma density, electron temperature, and plasma potential) along the axial direction (with the increase in d _s ). The deposited films are characterized for their thickness and various physical and electronic properties. It is observed that there exists a discernible dependence of the film characteristics and the coil to substrate distance (d _s ). It is also found that there is a correlation between the microstructural parameters and the optoelectronic properties as well as the electronic defect density in the films with the coil to substrate distance. An attempt has been made to correlate these observations to the plasma parameters studied by the Langmuir probe.