Dewen Zhao

Kinematic Optimization for Chemical Mechanical Polishing Based On Statistical Analysis of Particle Trajectories

The abrasive effect of particles is one of the basic mechanical actions in chemical mechanical polishing (CMP). In this paper, numerical simulations of particle sliding trajectories are performed to examine the influence of the kinematic parameters on the polishing uniformity of typical rotary-type CMP equipment. The trajectory simulations are carried out based on the kinematic analysis. The results reveal that the speed ratio α and the period ratio kT0, which represent the coupling relationships among the three basic motions of CMP, are the two major factors affecting the trajectory distribution. Further, a trajectory density parameter is proposed to quantitatively evaluate the global uniformity of the trajectory distributions and to optimize the kinematic parameters for better uniformity. The statistical results of the trajectory density analysis reveal that the trajectory of the wafer edge is denser than that of the wafer central area. To obtain better trajectory uniformity, some particular values of α and kT0, that is, α = 1 and kT0=1, which imply that the basic motions have a special coupling relationship, should be excluded; the preferred kinematic parameter values for CMP are α = 0.91-0.93 and kT0=5-7. This paper provides a basic guide to the kinematic parameter settings of CMP.

Evolution of entrained water film thickness and dynamics of Marangoni flow in Marangoni drying

As an ultra-clean wafer drying technique, Marangoni drying has been widely applied in the integrated circuits manufacturing process. When the wafer is vertically withdrawn from a deionization water bath, Marangoni stress along the meniscus, which is induced by the organic vapour, strips off the water film entrained on the wafer surface, and the wafer drying is thereby realized. In this work, a numerical model is presented that is comprised of the film, meniscus, and bulk regions for Marangoni drying. The model combines the transfer of organic vapour from air to water and the withdrawal of the wafer from the bath. The evolution of the entrained water film thickness, the tangential velocity, and the stress at the air–water interface are quantitatively investigated. The results reveal that the thickness of the entrained water film is reduced by more than one order of magnitude compared with the wafer withdrawn process without the Marangoni effect. In addition, owing to the receding of the contact line, it is found that the capillary pressure gradient dramatically increases, which contributes to the sudden increase in the tangential velocity in the dynamic meniscus. Moreover, the tangential velocity decreases in the static meniscus adjacent to the dynamic meniscus, which results from the redistribution of the interfacial concentration of the organic species driven by the Marangoni flow.

An In Situ End-Point Detection System Using Motor Power Signal for Chemical Mechanical Planarization Process

Accurate determination of a chemical mechanical planarization (CMP) process reaching the end point is an important problem in the CMP process. In present work, the variation of the motor power signal of the polishing platen in the CMP process has been investigated, and the moving average method with 121-points moving window was used to smooth the original signal curve. Experiment results showed that the processed signal could facilitate the extraction of end-point feature for the in-situ end-point detection (EPD) system and it was relatively steady before and after the layer transition stage, which made it more reliable to detect the end point in situ. Comparing with other EPD methods, the system was less complicated, and it was easier to code for algorithm development. Finally, further analysis was performed and series of experiments provided a planarized via-revealed surface with low via dishing.