반도체 공정용 Ni-Cr-Mo계 합금의 전해연마에서전해액 조성이 표면 품질에 미치는 영향
Effect of Electrolyte Composition on Surface Finish during Electropolishing of Ni-Cr-Mo Alloys for Semiconductor Processing
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This study investigated how electrolyte composition affects surface roughness during the electropolishing of Ni-Cr-Mo alloys. Mixtures of phosphoric acid, sulfuric acid, and water in ratios ranging from 6:3:1 to 8:1:1 were tested at 50 oC and 3.5 V for 20 minutes. The 7:2:1 ratio produced the lowest surface rough- ness, meeting semiconductor specifications. Surface observations revealed uniform dissolution with min- imal bubble traces. An inverse correlation between weight loss and conductivity with Ra suggested that smoothness is governed by uniform, rather than excessive, dissolution. ICP-OES analysis identified nickel and chromium as the primary elements dissolving from the alloy, contributing to surface leveling, while molybdenum enhanced corrosion resistance. Conversely, significant amounts of iron were detected, which were attributed to contamination from the experimental jig rather than from the alloy's primary dissolu- tion. Copper was also found to originate from counter-electrode dissolution. These results indicate that bath contamination from the fixtures (jig and electrode) is a critical process variable. Overall, the 7:2:1 electrolyte effectively balanced the viscous film-forming properties of phosphoric acid with the ionic con- ductivity of sulfuric acid, facilitating stable electrochemical dissolution and achieving a defect-free finish.
Abstract
This study investigated how electrolyte composition affects surface roughness during the electropolishing of Ni-Cr-Mo alloys. Mixtures of phosphoric acid, sulfuric acid, and water in ratios ranging from 6:3:1 to 8:1:1 were tested at 50 oC and 3.5 V for 20 minutes. The 7:2:1 ratio produced the lowest surface rough- ness, meeting semiconductor specifications. Surface observations revealed uniform dissolution with min- imal bubble traces. An inverse correlation between weight loss and conductivity with Ra suggested that smoothness is governed by uniform, rather than excessive, dissolution. ICP-OES analysis identified nickel and chromium as the primary elements dissolving from the alloy, contributing to surface leveling, while molybdenum enhanced corrosion resistance. Conversely, significant amounts of iron were detected, which were attributed to contamination from the experimental jig rather than from the alloy's primary dissolu- tion. Copper was also found to originate from counter-electrode dissolution. These results indicate that bath contamination from the fixtures (jig and electrode) is a critical process variable. Overall, the 7:2:1 electrolyte effectively balanced the viscous film-forming properties of phosphoric acid with the ionic con- ductivity of sulfuric acid, facilitating stable electrochemical dissolution and achieving a defect-free finish.