No abstract

2inch 6H-SiC (0001) wafers were sliced from the ingot grown by a conventional physical vapor transport (PVT) method using an abrasive multi-wire saw. While sliced SiC wafers lapped by a slurry with 1~9㎛ diamond particles had a mean height (Ra) value of 40nm, wafers after the final mechanical polishing using the slurry of 0.1㎛ diamond particles exhibited Ra of 4Å. In this study, we focused on investigation into the effect of the slurry type of chemical mechanical polishing (CMP) on the material removal rate of SiC materials and the change in surface roughness by adding abrasives and oxidizer to conventional KOH-based colloidal silica slurry. The nano-sized diamond slurry (average grain size of 25nm) added in KOH-based colloidal silica slurry resulted in a material removal rate (MRR) of 0.07mg/hr and the Ra of 1.811Å. The addition of oxidizer (NaOCl) in the nano-size diamond and KOH based colloidal silica slurry was proven to improve the CMP characteristics for SiC wafer, having a MRR of 0.3mg/hr and Ra of 1.087Å.

Brush cleaning can trigger both mechanical and chemical reaction to efficiently remove the adsorbed particles on the wafer. However, the removal mechanism of nanosized particles by brush cleaning is far from clear because no direct experimental data, such as the friction and contact force of the interface between brush and wafer surface, are available to back up the theoretical models in the literature. In this paper, we set up a monitoring system to measure the friction force of the interface between brush and wafer surface during brush cleaning to investigate the effect of the brush nodule structure having different nodule heights and nodule gaps on particle removal efficiency. To confirm the mechanical effect of the brush nodule structure, an oxide wafer contaminated with Polystyrene latex (PSL) particles (mean diameter: 300 nm) was cleaned with each PVA brush having different brush nodule structures using de-ionized water (DIW). The silica particle (mean diameter: 22 nm) and chemical solution (NH4OH, 0.1 wt%) were also used to investigate the chemical-aided particle removal. The remaining particles were measured with a Surfscan 6420 (KLA Tencor) and the friction force monitoring was conducted by using a Cleaner812-L (G&P Technology). The results indicated that a higher brush nodule height produced lower friction force, resulting in lower particle removal efficiency. When the nodule gap became smaller, the contact area between brush nodule and wafer surface became larger, resulting in higher particle removal efficiency. However, the experimental results using silica particles and 0.1 wt% of NH4OH showed different trends under each condition. The particle removal mechanism with silica particle and NH4OH was also verified by measuring the zeta potential between the particle and wafer.

We investigated the effects of hydrogen addition to the growth process of SiC single crystal using sublimation physical vapor transport (PVT) techniques. Hydrogen was periodically added to an inert gas for the growth ambient during the SiC bulk growth. Grown 2”-SiC single crystals were proven to be the polytype of 6H-SiC and carrier concentration levels of about 1017/cm3 was determined from Hall measurements. As compared to the characteristics of SiC crystal grown without using hydrogen addition, the SiC crystal grown with periodically modulated hydrogen addition definitely exhibited lower carrier concentration and lower micropipe density as well as reduced growth rate.

A sublimation epitaxial method, referred to as the Closed Space Technique (CST) was adopted to produce thick SiC epitaxial layers for power device applications. We aimed to systematically investigate the dependence of SiC epilayer quality and growth rate during the sublimation growth using the CST method on various process parameters such as the growth temperature and working pressure. The etched surface of a SiC epitaxial layer grown with low growth rate (30 μm/h) exhibited a low etch pit density (EPD) of ~2000 /cm2 and a low micropipe density (MPD) of 2 /cm2. The etched surface of a SiC epitaxial layer grown with a high growth rate (above 100 μm/h) contained a high EPD of ~3500 /cm2 and a high MPD of ~500 /cm2, which indicates that high growth rate aids the formation of dislocations and micropipes in the epitaxial layer.