Developing an analytic methodology to accurately predict probing depth in integrated circuit structures

Abstract

This work designs an analytic methodology for applying the probe-before-bump procedure to predict probing depth and proposes feasible probing design parameters to avoid excessive probing of the bump pad. Two kinds of multi-level wafers were used to implement the probing experiment, with a single touch down, and an overdrive of 70 µm, 100 µm, 130 µm, and 150 µm by using a vertical probe card. The Young’s modulus and hardness of the two multilevel structures are measured on which the first bump pads are produced by sputtering aluminum onto the SiO₂, while the second bump pads are produced by sputtering aluminum onto the copper, creating a pad metal of approximately 1-µm thickness by using the nanoindenter. The test results indicate that the Young’s modulus of the thin film material exceeds that of bulk material by 20–30 GPa. The difference between analytic and experimental probing depth ranges from 2.3% to 8.9%, revealing that the proposed novel analytic model is extremely accurate. Engineers or researchers can use the analytic methodology to accurately predict probing depth and acquire probing parameters that are accurate, cost effective, and efficient, thus eliminating the need to use focused ion beam (FIB) or other measurement instruments to determine the probing depth.