KrF excimer laser crystallization of silicon thin films

Abstract

A KrF excimer laser operating at 249 nm has been employed to crystallize silicon thin films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) and by RF magnetron sputtering on Corning glass and SiO2. All films display a substantial improvement in crystallinity after ELC with the optimum laser fluence for as-deposited ECR films being higher than for sputtered films. This is probably related to the presence of Si−Hx bonds in the former. A pronounced bimodality in the Raman spectra of some amorphous, as-deposited ECR samples has been observed after laser crystallization where, in addition to the peak at 520cm−1, a strong peak at 509cm−1 is also present. Such behavior has not been reported previously to our knowledge in ELC silicon films. Interestingly, the XRD spectra of these samples do not exhibit any peaks suggesting the films are composed of nano-grain material. The dehydrogenation of ECR films by ELC has been demonstrated to be substantial, the hydrogen content typically decreasing from ∼30 at % in an as-deposited film to ∼10 at % after a single low fluence laser shot. Raman spectroscopy has shown that the film bonding changes from predominantly Si−H2 to Si−H after ELC. Electrical resistivity measurements of phosphorus-doped films show a controllable and repeatable change with laser fluence. The results in this paper show that it is possible to crystallize and controllably change the electrical characteristics of ECR PECVD produced silicon thin films by ELC.