Charge Utilization Efficiency and Side Reactions in the Electrochemical Mechanical Polishing of 4H-SiC (0001)

Abstract

Slurryless electrochemical mechanical polishing (ECMP) is very effective in the polishing of silicon carbide (SiC) wafers. To achieve a high material removal rate (MRR) of SiC wafer using ECMP with low electrical energy loss, charge utilization efficiency in the anodic oxidation of the SiC surface was investigated and the underlying mechanism was clarified by modeling the anodic oxidation system of SiC in 1 wt% NaCl aqueous solution. The charge utilization efficiency in the anodic oxidation of SiC was found to be constant when the current density was less than 20 mA/cm2 and significantly decreased when the current density was greater than 30 mA/cm2, resulting in a significant reduction in the MRR. Modeling of the anodic oxidation system indicates that the charge utilization efficiency depended on the potential applied on the SiC surface: the oxidation of SiC occupied the dominant position in the anodizing system when the potential is lower than 25 V vs Ag|AgCl, charge utilization efficiency greatly decreased when the applied potential was greater than 25 V owing to the occurrence of oxidations of the H2O and Cl-. This research provides both a theoretical and practical foundation for using ECMP to polish SiC wafers.

Piezocatalysis for Chemical–Mechanical Polishing of SiC: Dual Roles of t‐BaTiO3 as a Piezocatalyst and an Abrasive

“…[8,9b] After pizeo-MCP for 60 min (Figure 5a,b), a new weak peak was observed at 102.1 eV in Si 2p spectrum, and the binding energy much matched with that of Si─O in SiO 2 . These changes in energy spectra were similar to that of RS-SiC oxidized by anodic processes reported by Yang et al [8] It was interesting that although the two processes had similar changes of energy spectra, the polishing effect of piezo-CMP was rather different from that of the reported anodic oxidation CMP toward RS-SiC. The former could present an ultra-smooth surface of RS-SiC, as shown in Figure 3e, while the latter only offered a rough surface with oxide protrusion, as reported by Yang et al [8] This divergence was possibly dependent on the expected selectivity of catalytic oxidation of piezo-CMP.…”

“…These changes in energy spectra were similar to that of RS-SiC oxidized by anodic processes reported by Yang et al [8] It was interesting that although the two processes had similar changes of energy spectra, the polishing effect of piezo-CMP was rather different from that of the reported anodic oxidation CMP toward RS-SiC. The former could present an ultra-smooth surface of RS-SiC, as shown in Figure 3e, while the latter only offered a rough surface with oxide protrusion, as reported by Yang et al [8] This divergence was possibly dependent on the expected selectivity of catalytic oxidation of piezo-CMP. That is, piezo-CMP possibly preferentially oxidized these protuberances of SiC surface, leading to the formation of a local softer oxide layer to be easily mechanically polished, [32] because these protuberances were subjected to greater stress than other parts from polishing pad, experienced a stronger piezocatalytic oxidation effect according to the relationship between the piezocatalytic effect and pressure as indicated in the Equation (3).…”

“…These likely originated from the natural oxidation of the functional groups of Si─C and the C─C bonds of its adhesive and sintering. [ 8,9b ] After pizeo‐MCP for 60 min (Figure 5a,b), a new weak peak was observed at 102.1 eV in Si 2p spectrum, and the binding energy much matched with that of Si─O in SiO 2 . These changes in energy spectra were similar to that of RS‐SiC oxidized by anodic processes reported by Yang et al.…”

“…[36] However, on bubble was observed when additional H 2 O 2 was introduced in the polishing system using SiO 2 as an abrasive. This fact indicated that H 2 O 2 decomposition of H 2 O 2 was mainly via reaction (8).…”

“…[ 3,7 ] However, its inherent high hardness (Moh's hardness 9.2) and chemical inertness bring many challenges to traditional polishing techniques. [ 8 ] For example, the mechanical polishing method can introduce scratches and subsurface damage to surface of SiC. Thus, in the 1980s, IBM first introduced the chemical mechanical polishing (CMP) technology and it has been extensively utilized to generate ultra‐smooth and low‐damage surfaces of semiconductor wafers presently.…”