An Exploration of the Copper CMP Removal Mechanism
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PETER RENTELN, TON NINH Advanced Products Research and Development Laboratory (APRDL), Motorola, 3501 Ed Bluestein Blvd., Austin, Texas 78721
ABSTRACT Copper CMP is emerging as the next generation process technology enabling feature size reduction to .15gm and beyond[ I]. We propose a copper removal mechanism in the context of a slurry consisting of an oxidizer and an abrasive. The body of evidence suggests that we are polishing in an oxidation complex rate limited regime. We observed low removal rate of copper in the absence of either oxidizer or abrasive, but rate was still dependent on CMP parameters and strongly tied to temperature. Any proposed mechanism must explain the observed dependence of rate on CMP aggressiveness and the role of each of the components. For the slurry used in this work we propose that an increase in temperature resulting from an increase in CMP intensity drives the kinetics of the oxidation reaction, and that the removal process can be classified as temperature-activated, abrasion assisted dissolution.
INTRODUCTION There is an increasing body of literature on the copper CMP process[2-8], approaching the issue both from a phenomenological and a fundamental point of view. To be sustained, any
model in which a removal mechanism is advanced must be either supported by all - or at least not contradicted by any - available observations. These observations generally include CMP rate and nonplanarity (dishing) effects as a function of CMP parameters such as speed and pressure, or as a function of slurry components such as oxidizers, abrasives and etchants. One model[9,10], for example, offers that the observation of low removal rate when polishing with abrasive only is due to the effect of redeposition of copper, which reduces the net removal rate. In this work we advance a model and evidence for it which explains removal as a function of oxidation of the copper surface and the corresponding creation of a soluble solid oxidation complex. While the model does not expressly disallow redeposition to occur, it is not required to explain low removal rate. The essence of the model is that friction caused by the interaction of the wafer and the pad heat the slurry to an elevated temperature without the addition of any intentional introduction of heat (the role of friction in oxide CMP has been investigated, e.g. ref. 11). And that while room temperature slurry may show no etch rate, when activated by temperature the slurry becomes an aggressive oxidizer/etcher (an investigation carried out simultaneously to this work reveals similar effects [12]). It is under these conditions that copper CMP proceeds at acceptable removal rates. This phenomenon also may affect dishing, although that topic is outside the scope of this work.
155 Mat. Res. Soc. Symp. Proc. Vol. 566 ©2000 Materials Research Society
EXPERIMENTAL Temperature and Rate Unpatterned electroplated copper wafers were polished using an IPEC 472 polisher equipped with an IR temperature sensor which measures pad surface temperature. The copper
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