Yasuto Kakemura

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.

Evaluation of Strain in Si-on-Insulator Substrate Induced by Si3N4 Capping Film

Strain introduced to Si-on-insulator (SOI) substrates by Si3N4 capping film was evaluated by UV-Raman spectroscopy. The induced strain became larger with increasing Si3N4 film thickness. SOI substrates originally had tensile strain and the Si3N4 cap shifted the strain toward the compressive direction. The induced strain was larger in thinner SOI substrates with the same thickness of the Si3N4 capping film. In the SOI substrates with patterned Si3N4 film, the strain was in different directions between the regions with and without Si3N4 film; i.e., if the strain was compressive in the region beneath the Si3N4 film, it was tensile beneath the space between the Si3N4 lines. We also evaluated substrates after Si3N4 patterning with a high spatial resolution of 200 nm, and observed strain enhancement near the pattern edge on both sides.

Evaluation of SOI substrates with local or global strain by means ofin-plane XRD measurement

The SOI substrates with local or global strain were evacuated by in-plane XRD (X-ray diffraction) measurement. SOI substrates with local strain, i.e. SOI substrate with SiN capping layer, had good crystal quality with sharp XRD spectra; however the strain was very small. On the contrary, SOI with global strain such as SGOI and SSOI had large strain, but the crystal qualities were very poor showing significantly wide and occasionally multiple peaks in XRD spectra.