New SIMS method to characterize hydrogen in polysilicon films

A new analysis protocol for profiling the hydrogen (H) concentration depth distributions in polysilicon (poly-Si) thin films on Si oxide was developed by using secondary ion mass spectrometry (SIMS). Traditional SIMS determination of H concentrations in poly-Si films is to monitor and collect the atomic H-, but this analysis method presents some challenges for providing stable and repeatable H depth profiles, especially, for shallow profiling in thinner poly-Si films on thicker Si oxide films. In this paper, we present a thorough study of the SIMS characterization of H levels in poly-Si thin films on Si oxide. We describe an approach for the use of cluster SiH- instead of atomic H- to determine the H concentrations. The utilization of the SiH- cluster ion minimizes both H adsorption effects on the film surface regions and sample surface charging effects arising from the Si oxide layer underneath, thus enhancing the secondary ion signal stability in poly-Si films, as discussed with secondary ion energy distribution on the samples. This method differs from the conventional SIMS analysis of H in thin films and significantly improves the data quality and accuracy. Fourier transform infrared spectroscopy analysis was used to study the Si-H chemical bonding information for investigating the nature of the SIMS collected SiH- cluster ions. Both the H implant sample with no significant Si-H bonding and the poly-Si samples with high levels of H and the weak Si-H bonding exhibited strong SiH- secondary cluster ion intensities in our studies. This indicates the cluster ion signals arise from either the combination of Si and H ions through the physics formation process or weak chemically bonded Si and H.