Fabrication of polyimide x-ray masks with high dimensional stability

Abstract

Articles you may be interested inFabrication of high resolution x-ray masks using diamond membrane for second generation x-ray lithography A new polyimide membrane for xray masks

High-aspect-ratio microstructures for magnetoelectronic applications

“…Although the stability problem associated with thin polyimide membranes was thought of as an issue by some workers 18 , a large number of submicron and nanoscale structures have been successfully fabricated with high dimensional stability using this membrane 16,17,19,21 . Since very small variations of feature sizes (less than submicron) 16,17,19,21 were observed with the use of thin polyimide membranes (<2µm) in a number of investigations, it was expected that by using thicker (25 µm that is ten to twenty times thicker than the most membranes formed on a spinner) membrane these dimensional variations would be even smaller, which is well qualified in this investigation. This selection accompanied by the usage of low stress sulfite gold baths (<20 MPa) 31 minimized both in-plane and out-of-plane distortions caused by gold electroplating.…”

“…Unlike most polyimide mask fabrications in the literature where a very thin polyimide layer (typically less than 2 µm) was spun on silicon wafers [15][16][17][18][19][20][21] , an approach that used a commercially available 25-µm polyimide film (Fralock, Canoga Park, CA) was adopted in this work. We followed the procedure described in Staler et al 22 with some modifications.…”

“…Fig.2(b) shows 10-µm wide loops and lines on the first mask for the aligned exposure. For aligned x-ray exposures, a number of materials, such as boron-doped silicon 23,24 , silicon nitride 11,23 , silicon carbide [23][24][25][26] , diamond [23][24][25]27 , and polyimide [15][16][17][18][19][20][21] , have been utilized as membranes. While stiff materials offer better mechanical support and thus less mask distortion, their membranes must be thin enough (typically less than 1 µm) to transmit sufficient visible light.…”

“…This selection accompanied by the usage of low stress sulfite gold baths (<20 MPa) 31 minimized both in-plane and out-of-plane distortions caused by gold electroplating. In an detailed investigation, most serious source causing the distortion of the polyimide membrane was identified as the nonuniformity of the silicon back etching rate at elevated temperatures (>100 o C) 21 . The approach utilized in this work did not involve the silicon etch step, thus minimizing the possible mask distortion resulting from this source.…”