A study of the process time effect to photosensitive polyimides

Polyimides are used extensively in the semiconductor industry as passivation layers, interlayers and dielectrics because of their excellent properties. These properties include thermal stability, superior chemical resistance, high mechanical strength and low dielectric constant. Most polyimide used in the semiconductor industry is the negative-type photosensitive polyimide due to its direct patternability. The purpose of this paper is to study the effect of process time delay during the polyamic ester formation to the final imidized polyimide. Post Coat Delay (PCD) is the delay time after coating before undergoing exposing while Post Expose Delay (PED) is the delay time after exposing before undergoing development. Samples of imide coated on bare wafers with after cure thickness of 6 Em are used. The image from Microscope inspection shows that the sample that is processed immediately is different from those other samples. The results of the after cure thickness of polyimides show that all the samples are within specification limit. Fourier Transform Infra Red (FTIR) is used to check for the chemical bonding. All the samples are fully imidized without peaks indicating the existence of PAE precursor. The imidization rate is lower as the delay time increase for both PCD and PED. Further investigation need to be done to verified the results.