Pattern Dependent Modeling for CMP Optimization and Control
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regions across the chip is a key concern. In addition, the remaining local step height (or height differences in the oxide over patterned features and between patterned features) may also be of concern, although such local step heights are typically small compared to the global nonplanarity across the chip resulting from pattern density dependent planarization. In shallow trench isolation (STI), one is typically concerned about dishing within oxide features resulting from over-polish, as well as the erosion of supporting nitride and in some cases the details of the corner rounding near active areas. In metal polishing (such as in copper damascene), one is concerned also with dishing into metal lines, as well as the erosion of supporting oxide or dielectric spaces in arrays between lines. In this paper, we begin by reviewing previous work on characterization and modeling of oxide CMP pattern dependencies. In Section II, we review the density-dependent oxide CMP model, as well as the important determination of "effective density" based upon a planarization length or planarization response function determination. In Section III, we also review a recent advance in oxide modeling, through which a step height dependent model (proposed elsewhere) has been integrated with the effective density model to produce an integrated time-evolution model for improved accuracy in step height and down area polish prediction. In Section IV we present
example applications of the oxide characterization and modeling methodology. These include, first, some comments on the importance of such effects in the design and optimization of the CMP process, and second, an example in which pattern dependent models are integrated with a run by 197 Mat. Res. Soc. Symp. Proc. Vol. 566 ©2000 Materials Research Society
run feedback control scheme to enable pattern dependent oxide control. As a third example, the application of oxide CMP modeling to STI process issues is discussed. In Section V we further generalize the modeling approach to enable application to pattern dependent issues in copper CMP. In particular, we contribute a concise "removal rate diagram" concept that helps to identify the key step height and material dependencies in copper CMP modeling. Finally, a summary is presented in Section VI.
Oxide CMP Global Nonplanarity
ShallowTrench Isolation
Copper CMP
Nitride Erosion
Oxide
1
OxdErosion • Cosphper
Rounding
I
Metal lines
Local Step Height
Silicon
Figure 1.Pattern-dependencies of concern in typical CMP process steps. II. REVIEW: OXIDE CMP DENSITY DEPENDENT MODELING In previous work, the fundamental problem we have examined in oxide modeling is the global non-planarity within the die resulting from pattern dependent planarization, as shown in Fig. 2 [1,2]. The goal of our approach has been to achieve efficient chip-level modeling of the oxide thickness across arbitrary product die patterns [3]. The approach has been simplified analytic modeling, in which the removal rate at any location is inversely proportional to the effe
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