by Carmine Sileno, Product Manager, Semiconductor Industry, and Dr. Diego Calvo Ruiz, Sales and Business Development Manager, Meister Abrasives
Figure 1. Representative picture of UF6-ground SiC wafer.
The key role of silicon (Si) in the semiconductor industry over recent decades has hugely broadened its applications. Although the wide modern portfolio of Si also includes power devices, current demands for higher power ratings, faster switching frequencies and elevated operating temperatures recently led the industry towards silicon carbide (SiC). The breakdown field strength of SiC is 10 times that of Si because of its higher bandgap, and the thermal conductivity is three times greater. These properties have enabled SiC’s use in efficient switching at high voltages and frequencies, and have driven the industry’s change from Si to SiC. Thus, today, one can already find large SiC manufacturing lines ready to upscale its production capabilities.
A high-quality finished surface is essential for mass production of novel power SiC-based semiconductor devices. As device manufacturers search for ways to increase productivity, they look to reduce both the number and the duration of grinding and polishing steps. State-of-the-art SiC wafers are pre-processed via several cycles of lapping or mechanical diamond polishing followed by Chemical Mechanical Polishing (CMP), processes that entail many steps and high machining costs because of their slow material removal rates. To reduce consumable costs, grinding with a consolidated diamond abrasive technology is currently considered the preferred alternative to lapping.
Figure 2. Comparison of standard lapping processes vs Meister course and ultra-fine grinding technologies.
Meister’s innovative SiC Ultra Fine 6 (UF6) grinding wheel technology can help prime wafer and device manufacturers shorten wafer preparation steps to the minimum. The ultra-smooth surface profile achieved with this method enable manufacturers to avoid diamond slurry costs, reduce CMP cost tremendously and drastically increase throughput. Furthermore, the highly porous open structure of the unique bond technology enables manufacturers to use low-force grinding processes that improve wafer geometry (TTV, bow and warp) and decrease surface roughness even further.
Despite the well-known hardness, stiffness and strength of monocrystalline SiC, Meister has developed ultra-fine grinding technologies that assure sub-nm average surface roughness (Ra) and sub-µm Total Thickness Variation (TTV) values on 4″, 6″ and 8″ SiC wafers. The novel technology, based on a fixed Meister Abrasives bond-grit formulation, targets best-in-class, low-cost and high-quality finished SiC wafer surfaces. Grinding wheels manufactured with this formula can accomplish ultra-smooth SiC (Ra = 0.5 nm and TTV < 1 µm) surfaces because of their unique bonding structure and tailored grit size. Additionally, SiC wafers ground with these wheels exhibit reduced crystal damage, mirror-like surface and improved wafer geometry while maintaining low grinding forces and wheel wear.
Meister’s 70-year history includes extensive experience designing and manufacturing customized grinding wheels in Switzerland. The company’s highly process-individualized solutions respond directly to customer and market needs, and the company’s integral involvement with customers means that it constantly solicits active feedback during the development of each customized solution. Additionally, Meister has established a state-of-the-art in-house test center that enables it to ensure each solution responds directly to customer needs. Customers can provide dummy SiC wafers or other sample materials, and Meister can refine its approach in the test center. Hence, customers can take advantage of Meister’s wide portfolio and boost their production throughput in a short period of time with Swiss precision.
