Using an Innovative Polishing Process to Fabricate Ultra-High Uniformity of Polymer Surface

Commonly used in forming high aspect ratio structures, thick-layer polymers generally differ in surface uniformity due to relatively higher viscosity. This problem would become even worse along with the increase of substrate diameter. Non-uniform coated photoresist surface would cause bonding failure and dimensional error in advanced three-dimensional packaging and WLP (wafer level packaging). Using traditional CMP (chemical mechanical polishing) to polish such a huge height deviation is time-consuming, high-cost and low-efficiency. This paper aims to provide an innovative polishing mechanism that is particularly suitable to polish wider height deviation in microstructures. Predominately in mechanical polishing force entails it surpassing CMP in MRR (material removal rate) by 300 times. The final experimental result indicates that the polishing rate could reach as fast as 20 um/min. Most importantly, the whole uniformity after polishing could be sharply decreased from 105plusmn3 mum (uniformity: 2.8%) to 95plusmn1 mum (uniformity: 1%). This proposed polishing mechanism could assist sticky polymers in precisely getting better uniformity so as to enhance packaging accuracy, reliability and yield.