Real-Time Prediction of Removal Rate and Friction Coefficient During Chemical Mechanical Polishing Using Motor Load Currents with a Polisher

Abstract

Herein, a method for predicting real-time removal rate and friction coefficient between the pad and substrate during chemical mechanical polishing was investigated using only the load currents of two motors of a polisher. Polishers for semiconductor devices are equipped with various sensors, enabling a real-time prediction of the removal amount. The polishers used to polish substrates are not usually equipped with sensors, and the polishing time is fine-tuned by skilled-technicians to achieve the desired substrate thickness. However, since every polisher has some motors, predicting the removal rate and friction coefficient using only the real-time data produced by these motors would be beneficial. This study attempts to predict the removal rate and friction coefficient in long-time polishing using a training dataset obtained from short-time polishing. Results showed that by performing extremely low-pressure, long-time polishing to understand the polisher characteristics and then subtracting the polisher characteristics from the motor information during long-time polishing, highly accurate predictions of the removal rate and friction coefficient within ~94% in percent match (prediction accuracy) between the experimental and predicted values can be obtained. Furthermore, slurry degradation during CMP can be monitored using this prediction method.

Proposal of Magnetic-Force-Assisted Polishing Method

“…[6][7][8][9][10] Generally, a polishing pressure of 30-100 kPa is required to perform CMP on these substrates. [11][12][13][14][15] Even for a substrate size of 1 inch, the requisite polishing load lies between 15 to 51 N. This demands a larger polishing head, which consequently complicates efforts to miniaturize the polisher. An increased size of the polishing head, when relying on the deadweight method, leads to undesirable effects: the frictional force during polishing generates a moment that can cause wobbling of the polishing head, yielding uneven results.…”