Investigation Of Process Time-Delay On Polyimide With Different Thicknesses For Photolithography Process
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Date
2011-06
Authors
Ang, Karen Huei Ling
Journal Title
Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
Polyimides (PI), particularly photosensitive polyimide (PSPI) has wide applications in semiconductor industries due to their good thermal, mechanical and chemical properties. During photolithography process, there might be time delays from coat to expose and from expose to develop. The time delay could change the profile of the structures and residues of precursor might leave on the film. In Infineon technologies, those wafers are scrapped if time delay exceeded 5 hours and every scrapped cost RM37500. As such, a study is carried out to investigate the effect of time delay in photolithography process to the cured polyimide film. Based on the results, a guideline is established and unnecessary wafer scrapped can be prevented. Meanwhile, it also eases the production and reduce work force. Two types of polyamic ester (PAE) precursors that give different thicknesses involved in this study. Optical microscope, profilometer, Fourier Transform Infrared (FTIR) spectroscopy and cross-sectional scanning electron microscope (SEM) is used to characterize and investigate the polyimide. Based on the results, the time delay did not significantly changed the final thickness of polyimide. There are no significant defects or residues remained. However, degree of imidization for some of the samples are affected. There are unreacted PAE and anhydride left on the film of 11 and 16 μm thick samples. This is caused by NMP, which is highly miscible with water, easily evaporates and absorbed moistures from the environment. The PAE can reverse to polyamic acid (PAA) and subsequently become anhydride.
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Keywords
Effect of time delay in photolithography process , to the cured polyimide film