Tatsuo Nishita

Characterization of Strain for High-Performance Metal-Oxide-Semiconductor Field-Effect-Transistor

Strain evaluation in a small area is required because the extremely short channel length in state-of-the-art metal–oxide–semiconductor field-effect transistors (MOSFETs) leads to a narrow and shallow channel region. The strain in this limited area strongly affects the device performance owing to carrier mobility modification. We used UV–Raman spectroscopy with a quasi-line-shape excitation source and a two-dimensional charge-coupled-device detector in order to evaluate the strain distribution in Si or Si-on-insulator (SOI) substrates with a patterned SiNx film. As results, the strain was concentrated at the SiNx/Si interface and SiNx film pattern edge. A large tensile (compressive) strain was induced by the SiNx film with inner tensile (compressive) stress in the space region that corresponds to a channel region of the n- or p-MOSFETs. We assume that these large strains in the space region are the origin of the mobility enhancement in n- or p-MOSFETs. Furthermore, in addition to the size effect of channel length, we confirmed that the strain could be controlled by changing SiNx film thickness, film stress, and the substrate (SOI or bulk-Si). The quantitative evaluation of strain by means of simulation is also discussed.

Study of Strain Induction for Metal–Oxide–Semiconductor Field-Effect Transistors using Transparent Dummy Gates and Stress Liners

Strain induction was studied on a sample that had a dummy gate tetraethyl orthosilicate–silicon dioxide (TEOS–SiO2) and SiN film by UV-Raman spectroscopy with high spatial and high wave-number resolution. The UV laser penetrated through the dummy gate that was transparent to UV light, which enabled us to evaluate strain in the channel of the metal–oxide–semiconductor field-effect transistor (MOSFET) model. Furthermore, we compared stress profiles obtained by finite element (FE) calculations with those obtained by UV-Raman measurements. There was a difference between the stress profiles in the line-and-space pattern sample and in the dummy-gate sample; large compressive (tensile) strains were concentrated at the channel edges in the dummy-gate sample with the compressive (tensile) stress liner, although both tensile and compressive strains existed at the channel edge in the line-and-space pattern sample. The results from UV-Raman spectroscopy were consistent with those obtained by the FE calculation.

Study of Charge Trap Sites in SiN Films by Hard X-ray Photoelectron Spectroscopy

Hard X-ray photoelectron spectroscopy (HAX-PES) was performed at SPring-8, and has enabled us to study the bulk properties of SiN films deposited by microwave plasma-enhanced chemical vapor deposition and deeply buried SiN/SiO2 interfaces, owing to the large inelastic mean free path of a photoelectron with a high kinetic energy. The defect states in the SiN films were examined by HAX-PES in order to verify the charge-trapping mechanism in a silicon–oxide–nitride–oxide–silicon flash memory device. X-ray reflectometry (XRR) was also performed at SPring-8. There is a complementary relationship between photoelectron spectroscopy and XRR. This methodology is proposed in this paper as a powerful tool for examining material properties. The detailed depth profile analysis of the chemical states in the SiN films obtained by angle-resolved HAX-PES also helped us to examine the charge-trapping mechanism.

HAX-PES Study of SiN Film for Charge Storage Layer in High Performance SONOS Type Flash Memory Cell

1 School of Science and Technology, Meiji University 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571, Japan Phone: +81-44-934-7324 E-mail: d_kose@isc.meiji.ac.jp 2 TOKYO ELECTRON AT LTD 1-8 Fuso-cho, Amagasaki, Hyogo, 660-0891, Japan 3 Japan Synchrotron Radiation Research Institute (JASRI) 1-1-1 Koto, Saya-cho, Sayo-gun, Hyogo, 679-5198, Japan 4 Research Fellow of the Japan Society for the Promotion of Science 8 Ichiban-cho, Chiyoda-ku, Tokyo, 102-8472, Japan