April 23rd, 2019
Chemical mechanical planarization (CMP) is an innovative technique used to level and polish substrates and layered devices for outstanding degrees of planarity. CMP polishing has emerged as a crucial method of preparing and finishing electronic wafers: smoothing the substrate topography by gently removing surface materials. This is achieved through a combination of chemical reactions and application of “gentle” abrasive forces.
Outlining CMP Polishing
CMP polishing is an adaptation of abrasive lapping, in which two surfaces are rubbed together with an intermediate abrasive such as alumina (Al2O3). The primary difference between mechanical lapping and CMP polishing is the chemical interactivity of the slurry with the substrate. In its simplest form; CMP polishing introduces chemically active particles or chemical oxidizers to the process which react with the uppermost layers of the wafer and/or form a soft patina that is easily removed through particle abrasion.
Challenges facing modern CMP polishing include stricter defectivity requirements, variable surface and surrounding chemistries; abrasive nanoparticle size, morphology, and functionality; novel substrate materials; requirements for angstrom-scale levels of uniformity. Holistic performance of CMP polishing is the only way to ensure the success of electronic wafers and eventual end-products.
Performing CMP Polishing
In a typical CMP polishing process, the wafer is mounted on a carrier via surface tension or back pressure then pressed against a rotating platen with a compliant polishing pad. The abrasive particles, chemical accelerants, and oxidizers are dispersed through the interface between these two surfaces as a singular chemical slurry. Rates of material removal are controlled by the relative velocity and pressure of the platen, the chemical activity between the wafer and the slurry, and the physiochemical nature of the abrasive particles at work in the CMP polishing slurry.
Provided each of these factors is optimized, CMP polishing can guarantee efficient material removal for highly-planarized, defect-free electronic wafers that are epi-ready.
As an example, Saint-Gobain Surface Conditioning has developed a specialized range of alumina-based slurries for silicon carbide (SiC) wafer planarization and polishing. Monocrystalline SiC is of increasing interest in micro- and printed electronics manufacturing, facilitating the design of high power microcircuits with exceptional levels of efficiency and outstanding thermal performance. Yet the complex microstructure and high hardness of the material has proven difficult for epitaxial electronics manufacturing, as achieving a suitably planarized, epi-ready surface can be challenging.
The ClasSiCTM CMP polishing range from Saint-Gobain utilizes new nano-abrasive particles and highly efficient oxidizers to enhance material removal rates and improve planarization for SiC electronic wafers. Despite comparatively aggressive material removal performance (>2μ/hr), these CMP polishing slurries have a very low scratch potential and defectivity, limiting sub-surface damage for SiC electronic wafers.
In CMP polishing of electronic wafers, it is vital to consider the unique mechanical properties of the substrate and utilize a specialized slurry that enhances your end-product qualities.
CMP Polishing with Saint-Gobain Surface Conditioning
Saint-Gobain Surface Conditioning is one of the world’s leading authorities in CMP polishing for electronic wafers and functional surfaces. We offer the ClasSiCTM range for SiC electronic wafer planarization and have also developed unique solutions for CMP polishing of aluminum nitride (AlN), gallium nitride (GaN), sapphire (Al2O3), silicon (Si), and silicon nitride (SiNx).