Distribution of hydrogen in low temperature passivated amorphous silicon (a-Si:H) films from neutron reflectivity

Hydrogen plays a critical role in the passivation of dangling bonds in hydrogenated amorphous silicon (a-Si:H) to enable acceptable semiconducting characteristics during operation in devices. Low temperature processing enables fabrication of high performance transistors on flexible substrates such as plastic or stainless steel foils, but also leads to a decrease in the stability of the electronic performance. Generation of defects at the a-Si:H/insulator (hydrogenated silicon nitride, SiN:H) during electrical use due to localized heating will lead to decreased performance unless the dangling bonds are passivated in-situ by residual hydrogen. For this reason, the distribution of hydrogen within a-Si:H may be critical to understanding their aging phenomena. Here the distribution of hydrogen within both a-Si:H and SiN:H layers is probed with sub-nanometer resolution using neutron reflectivity. The hydrogen concentration within the bulk of the a-Si:H (11 ± 2 at.%) and SiN:H (18 ± 3 at.%) agree well with previous reports, but the increased resolution of the neutron measurement is able to identify an approximate three fold increase in the concentration within 2 nm of the semiconductor–insulator interface. This enhanced hydrogen content may act in the short-term as a sink to passivate any dangling bonds formed during operation.

Research Highlights
► Neutron reflectivity non-destructively quantifies the hydrogen content in amorphous silicon and silicon nitride.
► 3 fold excess of hydrogen within 2 nm of amorphous silicon/silicon nitride determined from neutron reflectivity.
► Spectroscopic ellipsometry cannot detect this thin layer of excess hydrogen.