A Study on Ultra-Deep X-ray Lithography Technique with Highly-Sensitive SU-8 Resist
|關鍵字:||微機電;厚膜光阻;X光深刻術;同步輻射;高深寬比;毫米波源;LIGA;SU-8;DXL;X-ray;high aspect ratio;mm-wave|
研究結果亦發現，以X光深刻SU-8光阻時其頂部劑量必須小於200 J/cm3，方能獲致優異的光刻品質，因此曝光時必須施加適當的濾片以調變頂部劑量。此外，當高能量的X光穿透光阻時往往會引發螢光的產生進而影響光刻的精度。此時可藉由增加光阻內的氧含量，應用氧淬火(oxygen quench)效應抑制螢光所引發的光阻聚合反應，進而提昇X光深刻的精準度。
This study investigates the feasibility of using SU-8 as a highly sensitive X-ray resist. An ultra-deep X-ray lithography (UDXL) technique will be developed to give a high- efficiency and high-precision micromachining process. This technique will be used to fabricate a deep (~1.5mm) and precise (＜2μm) resonant cavity of an mm-wave power supply in the future. Via chemical amplification mechanism, the SU-8 resist revealed very high sensitivity under X-ray irradiating. The result showed that its sensitivity is about 160 times higher than that of the traditional PMMA resist; meanwhile, the lithographic surface quality (Ra~12nm) is as good as that of PMMA. The epoxy-based SU-8 resist also has higher adhesion strength, chemical stability and stress-corrosion resistance than that of PMMA. In addition, due to the high contrast and sensitivity behaviors of the SU-8 resist, the corresponding mask absorber can be thinner and the mask membrane can be thicker. As a result, the fabrication process of the X-ray mask will be much simpler and easier than ever before. The results showed that the maximum dosage of the SU-8 resist must be lower than 200 J/cm3 to achieve an excellent lithographic quality. This can be done applying a proper filter to control the dose distribution in the resist. The results also indicated that high-energy X-ray will induce fluorescence, which will activate unwanted cross-linking reaction in the resist and then give very poor pattern definition. This problem is successively resolved in this study by increasing the oxygen concentration in the resist to “quench” the cross linking reaction under the masked area. Based on the established capability in this study, a 1.5mm thick SU-8 resist was exposed by synchrotron-radiating X-ray. The results showed that the DXL SU-8 technique could provide excellent pattern-transfer quality with high precision (~1μm) and high accuracy (＜3μm). The sidewall is quite perpendicular to the substrate with an inclined angle of only about 0.06°. The micromachining quality of the DXL SU-8 technique can fulfill the severe demands both in depth and precision of the mm-wave microcavity.