SiC polishing requires significant investment in equipment and special tools for operation, with prices of raw materials such as silicon carbide fluctuating due to geopolitical tension between Ukraine and Russia that could interrupt supply networks.
Polishing compositions may be supplied either in one container, with liquid carrier, oxidizing agent and abrasive, or multiple containers can be supplied separately.
Abrasive
Abrasives are used to remove oxide layers from semiconductor wafer surfaces. A variety of materials exist for this task, but among these the two most frequently employed are aluminum oxide (Al2O3) and silicon carbide (SiC).
Abrasives must be hard and possess sharp edges for effectively cutting away oxide deposits, while at the same time remaining robust enough to resist fracture. Selecting an abrasive with the desired properties is vital when polishing surfaces as it determines both how much heat is produced as well as the quality of final surface finish.
To create an atomically flat surface with high MRR, abrasives must adhere to SiC wafer surfaces under specific conditions. Particles must electrostatically attach within certain slurry pH range; otherwise they could form an oxide blocking layer during oxidation that reduces MRR and further limits MRR.
Saint-Gobain Surface Conditioning ClasSiC CMP slurries utilize nano alumina abrasives to greatly increase removal rate and planarize SiC wafer surfaces, producing an outstanding surface finish and subsurface damage-free finish – perfect for the chemical mechanical planarization (CMP) process used in LED and power electronic device production. In contrast to other alumina slurries, ClasSiC CMP can even be used with FAP/semi FAP pads without impacting MRR or durability issues – unlike their counterparts.
Oxidizing Agent
Polishing silicon carbide wafers exposes them to machinery marks and subsurface damage due to lapping and grinding, leading to less visible machinery marks while increasing TTV (Total Wafer Transfer Value). Achieving high levels of surface oxidation requires expensive equipment if this process is to succeed successfully.
Oxidizing agents play an integral part of the CMP process by aiding in the reaction between pad asperities and SiC substrate. Oxidizing agents typically come from organic bases; EDA, TEA and EDTA are popular options with each offering distinct properties; for instance EDA has proven particularly successful at balancing material removal rate with surface roughness.
Apart from oxides, metal salts are also frequently employed as oxidizing agents in polishing processes, with examples including sodium sulfate, calcium nitrate and potassium nitrate being frequently chosen as agents to promote polishing processes. Which agent will best suit a given polishing task will depend upon its characteristics and requirements.
Another effective strategy for increasing oxidation is using core-shell abrasive particles. These unique particles feature hard cores with high hardness that are coated by lower hardness shells with improved chemical activity; Zhang et al. successfully implemented this strategy for 4H-SiC PCMP processes with MRR rates as low as 1 um h-1 using this approach.
Liquid Carrier
Adherence to strict quality control measures is vital in order to protect the integrity of bulk liquid cargo. Temperature and pressure monitoring, along with proper communication among shippers, carriers, terminals, and receivers is necessary in order to minimize product damage during transit.
Chemical mechanical polishing (CMP) is an integral step in fabricating high-performance silicon carbide (SiC) ICs. SiC’s unique electrical and physical properties make it suitable for high power, high frequency, and high temperature electronic devices; however, its hardness and chemical stability present unique challenges to its processing methods; traditional CMP methods often produce surface defects with poor material removal efficiency.
Electrochemical mechanical polishing (ECMP), an innovative form of chemical-mechanical polishing that utilizes composite material pads with SiC and CeO2, can dramatically enhance both quality and processing efficiency when polishing SiC substrates. By eliminating harmful chemicals and offering faster material removal rates than conventional CMP techniques, electrochemical mechanical polishing offers significant potential improvements for SiC substrate production.
Researchers have created an atomically smooth and defect-free SiC wafer by employing a slurry composed of water-dispersible oxidants including hydrogen peroxide, potassium permanganate and organic bases such as ethylenediamine and tetramethylammonium hydroxide as organic bases, plus pH buffers such as sodium tetraborate and potassium hydrogen phthalate, along with particles with various concentrations of SiC. They determined its optimal composition through orthogonal experiments aimed at measuring surface roughness and material removal rate.
Complexing Agent
Complexing agents are used to bind and stabilize metal ions, altering their chemical behavior by altering their complexing behavior. Once bound and stabilized, complexed ions become less reactive and more soluble in water or other solvents; additionally, complexing agents help prevent release of metallic ions into the environment where they could interfere with natural sorption processes and interfere with ecological safety measures. Also referred to as chelating agents, complexing agents have proven highly useful environmental safety applications for mitigating issues related to eutrophication as well as ecological concerns.
Sic polishing combines electrochemical corrosion (ECMP) with mechanical polishing to produce surfaces with extremely low surface roughness. To do this, the process involves electrically charging SiC anodes as anodes before oxidizing them using oxygen in a buffer solution; after which comes mechanical polishing using soft abrasives to produce damage-free, smooth and uniform surfaces.
However, the relatively low material removal rate of ECMP limits its application to industrial environments. To improve ECMP MRR researchers have used smaller diamond particles that achieve elastic interaction between abrasives and SiC substrate. Huang et al. has demonstrated that 4H-SiC with polyurethane/CeO2 core-shell abrasives has achieved MRR of 2.3 um h-1 and Ra of 0.449 nm, significantly outperforming conventional grinding in both MRR and surface quality achieved MRR/Ra achieved by conventional grinding methods.
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