Takanori Kido

Frictional and removal rate studies of silicon dioxide and silicon nitride CMP using novel cerium dioxide abrasive slurries

Novel slurries containing cerium dioxide particles as the abrasives were used for silicon dioxide and silicon nitride CMP in this study. Real-time frictional force was measured during polishing. Slurries with varying ceria abrasive concentrations achieved different friction forces during the silicon dioxide and silicon nitride polishing. The effects of the ceria abrasive concentration on the silicon dioxide and silicon nitride removal rates were also investigated. The silicon dioxide removal rates exhibited non-Prestonian behavior, which was attributed to the additives used in the slurries. Being specially formulated for shallow trench isolation (STI) applications, these novel slurries achieved high oxide-to-nitride removal rate selectivities.

Micro-structural analysis of local damage introduced in subsurface regions of 4H-SiC wafers during chemo-mechanical polishing

The surface morphology and lattice defect structures in the subsurface regions of 4H-SiC wafers introduced during chemo-mechanical polishing (CMP) were studied by scanning electron microscopy and transmission electron microscopy. It is known that local damage consisting of high-density lattice defects is introduced in the wafers during the current CMP, however, optical microscopy showed that the surface was very flat and clean without any presence of surface defects. Specifically, this study focused on the detailed analysis of such lattice defect structures. The high-density lattice defects locally introduced in the subsurface regions consisted of nano-scale surface scratches, high-density basal-plane dislocation loops, Shockley-type stacking faults, and Y-shaped defects. Two types of dislocation loops were introduced near the scratches that were selected for further study: nearly perfect basal-plane dislocations, which were accompanied by narrow stacking faults, and apparent partial basal-plane dislocati...

Microstructural Analysis of Damaged Layer Introduced during Chemo-Mechanical Polishing

Damaged layers, which are introduced during chemo-mechanical polishing (CMP) underneath the 4°off-cut 4H-SiC wafer surface and cause surface defects formations after epitaxial films growth, are investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM observations show presence of small scratches on wafer surfaces after CMP process. The widths of such scratches are submicron meters, thus it is hard to detect them by optical microscopy. TEM observations show that high-density regions of dislocation loops exist below scratches and the widths of such dislocation loops are much wider than the morphological width. Details of the dislocation structure are also analyzed. It is shown that the high-density dislocation loops cause local surface roughening on the surface of the epitaxial film.

A Novel Grinding Technique for 4H-SiC Single-Crystal Wafers Using Tribo-Catalytic Abrasives

Diamond abrasives are generally used to machine silicon carbide (SiC) single crystals because of the high hardness of those crystals. Although Chemo-Mechanical Polishing (CMP) employs abrasives softer than the SiC single crystals together with oxidizing agents in order to avoid mechanical damage to the surface of SiC single-crystal wafers, none has reported so far the use of abrasive wheels other than diamond for grinding large SiC single-crystal wafers. The current study revealed that a novel grinding technique using non-diamond abrasives such as ceria (CeO2) can efficiently machine large SiC single-crystal wafers of 100 mm in diameter due hypothetically to the nature of newly named tribo-catalytic abrasives, and is promising to minimize the surface damage prior to the final CMP step.