The Effects of Hardness Variation on a CMP Model of Copper thin Films
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1157-E08-06
THE EFFECTS OF HARDNESS VARIATION ON CHEMICAL MECHANICAL POLISHING OF COPPER THIN FILMS J.Bonivel 1,2, Y. Williams1 , S. Blitz 2, A.Kumar 1 1 University of South Florida 4202 E. Fowler Ave Tampa, FL 33620 2 Carnegie Mellon University 5000 Forbes Ave, Pittsburgh, PA 15213 ABSTRACT With the rapid change of materials systems and decreased feature size, thin film microstructure and mechanical properties have become critical parameters for microelectronics reliability. An example of a major driver of this new technology is the data storage community who is pushing for 1 Terabit/square inch on its magnetic disk hard drives. This requires inherent knowledge of the mechanical properties of materials and in depth understanding of the tribological phenomena involved in the manufacturing process. Chemical mechanical polishing (CMP) is a semi-conductor manufacturing process used to remove or planarize ultra-thin metallic, dielectric, or barrier films (copper) on silicon wafers. The material removal rate (MRR), which ultimately effects the surface topography, corresponding to CMP is given by the standard Preston Equation, which contains the load applied, the velocity of the pad, the Preston coefficient which includes chemical dependencies, and the hardness of the material. Typically the hardness, a bulk material constant, is taken as a constant throughout the wafer and thereby included in the Preston coefficient. Through metallurgy studies, on the micro and nano scale, it has been proven that the hardness is dependent upon grain size and orientation. This research served to first relate the crystallographic orientation to a specific hardness value and secondly use the hardness variation in the previously developed particle augmented mixed-lubrication (PAML) model to simulate the surface topography and MRR during CMP. Recent test and results show that currently there is no empirical formula to relate the crystallographic orientation and thereby a critically resolved shear stress (CRSS) to a specific hardness value. The second part of this investigation utilized the variation in hardness values from the initial study and incorporated these results into the PAML numerical model that incorporates all the physics of chemical mechanical polishing (CMP). Incorporation of the variation of hardness resulted in a surface topography with a difference in roughness (Ra) from the bulk constant hardness value of 60 nm. The material removal rate (MRR) of the process differs by 2.17 µm3/s.
1. INTRODUCTION Wear is the phenomenon of material removal from a surface due to interaction with a mating surface, either through micro fracture, chemical dissolution, or melting the contacting surface. In the case of plastic contact between hard and sharp material and a relatively softer material the hard material penetrates the softer one causing fracture; this fracture can lead to micro-cutting and ultimately material removal. Chemical mechanical polishing (CMP) is a semi-conductor manufacturing process used to remove or planarize ultra-thin
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