Characterization of Slurry System and Suppression of Oxide Erosion in Aluminum CMP (Chemical-Mechanical Planarization)
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Lei Zhong, Jerry Yang, Karey Holland, Joost Grillaert*, Katia Devriend*, Nancy Heylen* and Marc Meuris* IPEC, 4717 E. Hilton Ave., Phoenix, AZ8503, *IMEC, Kapeldreef 75, B-3001 Leuven, Belgium
[email protected]
ABSTRACT
In this work, we investigated the dependence of the removal rate upon the oxidizer (peroxide) addition into commercially available slurries for a variety of films such as aluminum, titanium, titanium nitride and oxide. We found that the barrier layer materials were extremely sensitive to the peroxide addition while the removal rate varied only slightly for aluminum and oxide. The selectivity to titanium and titanium nitride drops from as high as 1000 to almost close to 1 as the mixture ratio (peroxide : slurry) increases. We proposed that the barrier layer be used to protect the oxide from being over-exposed and suppress the erosion eventually. This can be easily realized by dividing the process into two steps with each step being run at a specific peroxide mixture ratio. The experimental result unambiguously proved, for the first time, the effectiveness of this approach. INTRODUCTION
Peroxide is suggested by many vendors as the oxidizer for metal polish and recommended as one component of their slurry system. It is still unclear, however, what roles the peroxide plays in the polish process. The original purpose of this work is to evaluate the impact of this variable upon the process performance. The experiment result turns out to be inspiring and suggests a new approach to minimization of the oxide erosion. EXPERIMENT RESULTS AND DISCUSSION We chose a commercially available slurry, SA as an example and investigated the dependence of removal rate upon the peroxide addition. The result is shown in Fig. 1. All the data points linked with lines (solid or dotted) have been collected on the identical sheet wafers polished with the same recipe, except the slurry composition The non-uniformity is below 10% in most cases except for the barrier layer films polished without peroxide added, which indicates that the misrepresentation of removal rate which is the average of 49-point polar map, is negligible. As may be seen, the aluminum removal rate is a very weak function of the mixture ratio. This is a strong evidence that the chemicals in the slurry are capable of oxidizing aluminum so that peroxide is not indispensable for aluminum polishing at all. A closer examination shows that the removal rate drops slightly but linearly with the peroxide addition. A plausible explanation for this phenomenon is the dilution of abrasive particles. If the chemical reaction (oxidation) is fast enough, the removal rate must be mechanically dominated and roughly proportional to the availability of abrasive particles in contact with the wafer surface'. This is reasonably in agreement with our result shown in Fig. 1. Also independent of the peroxide addition is the oxide removal rate which is very low, almost two orders of magnitude lower than that of aluminum. It is worthy noting that the
115 Mat. Res. Soc. Symp. Proc. Vol.
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