Preparation of Low-Reflectivity Amorphous Silicon Using DC Magnetron Sputtering

Abstract

The optical properties of dc magnetron-sputtered amorphous Si (a-Si) films grown under different Ar pressures (1.5≤P _Ar≤12 mTorr) and substrate-target distances (5≤l _s-t≤30 cm) were investigated. The reflectivity was found to decrease with increasing P _Ar and l _s-t, or equivalently with decreasing film density, and was 0.22 at λ=436 nm for the film with the lowest density. The absorption coefficient for this lowest reflectivity film was larger than 1×10⁵ cm^-1 at λ=436 nm. These optical properties meet the requirements for anti-reflective coatings in photolithography. Low-reflectivity a-Si could be obtained under deposition conditions for which P _Ar·l _s-t was larger than 150 mTorr·cm. The low density and low reflectivity were found to be due to a self-shadowing effect and thermalization of sputtered Si atoms.