Study of deep X-ray lithography behaviour for microstructures

The aim of this study is to investigate how the exposure dosage and developing temperature affect the developing rate for microstructures, with and without ultrasonic stirring, when the photoresist is exposed to X-ray radiation. Two experiments, “thick photoresist with low aspect ratio microstructure” (TPLARM) and “thick photoresist with high aspect ratio microstructure” (TPHARM) were conducted in this study. The TPLARM experiment was performed in order to investigate the relationship between exposure dosage and developing rate under ultrasonic agitation during the developing process. X-rays with an incident dose of 3500 mAmin/cm passed through the beryllium (Be) window and fell directly onto three graphite membranes of different thicknesses to expose a 3-mm thick PMMA substrate. PMMAs exposed to the X-rays were then placed into beakers filled with GG developer in two separate 28 and 36 °C isothermal baths for developing for 400 min. The TPHARM experiment was performed in order to study the effects of a high aspect ratio on developing rate using a Au microstructure as the absorber (15 μm in thickness; gap of 10 μm). This absorber was transferred onto a 3-mm thick PMMA substrate to form a conformal mask. The incident X-ray, at a dose of 800 mAmin/cm, passed through the Be window and directly exposed the PMMA substrate; the PMMA exposed to the X-ray was then immersed in a beaker filled with GG developer in a 28 °C isothermal bath for developing. The relationship between developing depth and time was then measured without the use of ultrasonic agitation stirring.