Low cost X-ray lithographic mask based on microsputtered lead film on Transparencies

• Published in: ECTI-CON2010: The 2010 ECTI International Confernce on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology pp. 772 - 775
• Main Authors: Wisitsora-at, A, Mongpraneet, S, Phatthanakun, R, Chomnawang, N, Patthanasettakul, V, Tuantranont, A
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.05.2010
• Subjects: Costs; Gold; Lead; Resists; Sputtering; Steel; Substrates; Testing; Thick films; X-ray lithography
• ISBN: 9781424456062; 1424456061

In this work, a low-cost X-ray micromask is developed by sputtering lead (Pb) film on Transparencies (Mylar) sheet substrate and the X-ray mask is experimented for patterning SU-8 negative photoresist on stainless steel substrate. Pb layer is sputtered on the substrate through Ni-electroplated microshadow masks with varying thicknesses from 8 to 19 μm. Sputtering is a suitable process for Pb thick film deposition due to its high sputtering yield. The tested pattern is 100 μm-wide microchannels, which is designed for microfluidic chip fabrication. Next, 150-350 μm thick SU-8 photoresist is spun on the stainless substrate. The Pb mask is then used for X-ray lithography by X-ray source produced by synchrotron radiation at Siam photon laboratory, Thailand. X-ray exposure is conducted with different X-ray doses and intensity. According to the experimental results, the lead film thickness of more than 10 μm is the required to block the X-ray for 200 μm thick SU-8 photoresist that requires X-ray dose of 4,200 mJ/cm 3 produced at beam line current of 70 mA. This is almost twice of the thickness required for the gold absorbing layer, which is about 6 μm. Although Pb requires higher thickness than gold does, the proposed Pb based X-ray mask will be much more practical for commercial applications than gold X-ray mask due to much lower material cost and simpler fabrication process.