An optimization of tungsten plug chemical mechanical polishing (CMP) using different consumables

Abstract

The continuous shrinkage of integrated circuit devices provides the advantage of having more electrical functions on the smaller chips. However, it has posed severe challenges to the manufacturing of these products. In patterning steps, the depth of focus becomes small, due to the nature of patterning small features and is aggravated by the presence of step height differences in the exposure field. When the aspect ratio of holes increases, aluminum, which has been the choice of metal to fill holes, no longer effectively fills small holes. On some occasions, discontinuous aluminum exists in the holes, resulting from poor step coverage. Tungsten (W), on the other hand, can satisfactorily fill small holes by chemical vapor deposition and thus fills a need to replace aluminum as an electrical connector plug for layers separated by this plug. Chemical mechanical polish (CMP) has been used recently to planarize substrates and improve the depth of focus, as in the case of hole patterning. It is also used to prepare the metal plug effectively. CMP processing involves various parameters, such as machine configuration, slurry chemistry and formulation, polishing pad configuration, pad hardness, etc. Although the mechanism is not fully understood, these parameters are known to significantly influence the degree of planarization, contamination, defects, etc. In this paper we explore the effects of consumables used in the W-CMP process on the control of several problems, such as recessed plug, dishing and oxide erosion, etc. Based on our findings, we implement a two-step W-CMP process to improve the qualities of the polished wafers. The first step involves a proper combination of slurry and pad to polish most of the bulk tungsten with a high polish rate. The second step uses the same pad, slurry and a proprietary additive to slowly polish the remaining tungsten. In this way, we are able to obtain a workable W-CMP process. © 2001 Kluwer Academic Publishers