Hydrophobic and wear-resistible surface coating of carbon steel using linear microwave plasma with TE-TEM mode power coupling

A linear microwave plasma source has been prepared for hydrophobic and wear-resistible surface coating of carbon steel. Hydrophobic wear-resistible properties are essential for adhesive film cutting tools. Microwave power was coupled to plasma through TE₁₀-TEM mode converter. Compared with RF capacitively couple plasmas which have long been used for hydrophobic surface treatment, microwave plasma can provide wider process windows, independent ion energy controllability and faster processing rate. In this study, Ar/CH₄/CF₄ and their mixture was used for surface treatment. Stable and uniform 45cm-long plasma could be obtained in a pressure range of 100 ~ 500 mTorr with microwave power of 500 W. 13.56 MHz RF power was independently applied to substrate electrode for bias voltage control. After Ar plasma treatment for surface cleaning, Ar/CH₄ and Ar/CH₄/CF₄ plasma enhanced deposition process has been performed. CH₄ was chosen to achieve wear-resistibility and improve tribological properties by forming a-C:H diamond-like carbon layer. Additional CF₄ incorporation allowed us to enhance hydrophobicity of the surface layer. Optimized deposition condition was investigated as a function of microwave power, gas pressure, gas flow rate and bias power. The nominal deposition rate was 124Å/min at Ar:CH₄ = 25:50 sccm, 300 mTorr with microwave power of 300W. After CF₄ plasma incorporation, hydrophobicity was drastically improved. The contact angle was changed from 57 degree to 120 degree.