Tribological, Thermal and Kinetic Characterization of Dielectric and Metal Chemical Mechanical Planarization Processes

Abstract

This dissertation presents a series of studies that describe the impacts of, among other things, temperature and kinematics on inter-level dielectric (ILD) and metal chemical mechanical planarization (CMP) processes. The performance of CMP is often evaluated in terms of removal rate, uniformity, planarization length, step height, defects and resulting topography such as erosion and dishing. The assessment of these parameters is significantly dependent on the selection of tool and consumable set (polishing pad or slurry type), as well as the kinematics involved in the process. Variations in pressure, sliding velocity, temperature and slurry flow rate are just a few of the dynamic inputs that can affect polishing performance. The studies presented in this dissertation focus on some of these external parameters and how they influence the mechanisms involved with the CMP process and their overall outcome on performance.Studies presented in this dissertation include topics such as the effects wafer-ring configurations and wafer geometries on the applied wafer pressure distribution across a wafer surface. In addition to this, another study related to understanding applied wafer pressure investigated the estimation of the effective (envelop) pressure for patterned shallow trench isolation (STI) wafers during CMP. When considering the regularity of issues such as changing wafer geometries and wafer feature patterns, these two studies provided significant insight on the potential issues that could arise during CMP when dealing with such events, as well as potential solutions for controlling such events.Another study in this dissertation investigated the effects of polishing pad type on dielectric CMP performance. Polishing pads varied in thickness and grooving, and tests were done to characterize the tribological and thermal behavior of the pads under a wide range of p × V and slurry flow rate conditions. Of key importance in this study was observing any combined effects between changes in platen set point temperature and pad type on ILD removal rate.The greatest contribution to this dissertation involved studies related to the role of temperature in CMP. These studies implemented variable platen set point temperatures to further understand the thermal effects on parameters such as removal rate and coefficient of friction (COF). As a result of these studies, a new removal rate model based on flash heating was developed to describe observed non-linear trends in removal rate. The application of this model has shown great utility in removal rate prediction when compared to prior models.