| Summary: | 博士 === 國立成功大學 === 機械工程學系碩博士班 === 96 === Chemical mechanical planarization (CMP) has played an enabling role in producing near-perfect planarity of interconnection and metal layers in ultra-large scale integrated (ULSI) devices. During CMP, a rotating wafer is pressed against a rotating pad, while a slurry is dragged into the pad–wafer interface. For stable and high performance of CMP, it is important to ensure uniform slurry flow at the pad–wafer interface, hence necessitating the use of grooved pads that help discharge debris and prevent subsequent particle loading effects. Furthermore, due to stress concentration, the interfacial contact stress near the wafer edge generally is much higher than that near the wafer center, resulting in spatially non-uniform material removal rate (MRR) and hence imperfect planarity of the wafer surface. In order to alleviate this problem, the use of multi-zone wafer back pressure profiles has been proposed.
In the first part of this thesis, taking into account the dependence of local MRR on the slurry’s chemical activity, we examine the effects of pad groove design and various process parameters on the spatial average and non-uniformity of MRR. The numerical results indicate that the presence of pad grooves generally decreases the slurry impurity concentration, and increases the contact stress on the pad–wafer interface, so that the local MRR is increased. However, as a grooved pad has less contact area for effective interaction with the wafer surface, the average MRR may or may not be increased, depending upon the specific values of process parameters.
In the second part of this thesis, for flat pads, we calculate the interfacial contact stress and slurry pressure distributions on the wafer surface produced by a multi-zone (i.e., piecewise constant) wafer-back pressure profile. In particular, the possibility of using a multi-zone wafer-back pressure profile to improve the contact stress and MRR uniformity is examined, by studying a particular case with realistic parameter settings. Our numerical results show that using a two-zone wafer-back pressure profile with “optimized” zonal sizes and pressures can increase the “usable” wafer surface area (within which the average contact stress non-uniformity is below 0.1%) by as much as 12%. Using an “optimized” three-zone wafer-back pressure profile, however, does not much further increase the usable wafer surface area. So, one may simply employ a wafer carrier that provides a two-zone wafer-back pressure profile, and use the theoretical model and numerical procedures devised in this thesis to estimate the “optimal” zonal sizes and pressures.
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