CMP conference: Its not just for ILD anymore

05/01/1997

CMP conference: It`s not just for ILD anymore

The second annual Chemical-Mechanical Polish for ULSI Multilevel Interconnection Conference (CMP-MIC), held in February in Santa Clara, CA, gave attendees an overview of current manufacturing challenges as well as future planarization requirements.

The biggest challenge in oxide CMP is no longer interlevel dielectric planarization. Half of the dielectric presentations were for shallow trench isolation (STI) oxide processing. STI will come online this year, as fabs migrate to the 0.25-?m process generation, and will require oxide CMP instead of the unmanageable sacrificial etch-back scheme.

The two greatest challenges in STI planarization are selectivity to nitride and final surface roughness. Standard oxide slurries have been able to achieve only 5:1 selectivity. Rodel, in association with IMEC, presented a proprietary slurry that suppresses nearly 98% of nitride etching for greater than 200:1 selectivity.

OnTrak compared its linear (belt-sander) process to the traditional rotating platen. The linear process left approximately 500 ? of oxide thickness variation across a 15 ? 15 mm die, which is claimed to be four times less than the best results obtainable with a rotary polisher.

Tungsten CMP is being investigated to reduce plug damage caused by W etch-back (WEB). A team from Mosel Vitelic stated that the RIE WEB process is the single largest source of defects in the entire back end, and showed that oxide slurry buffing with CMP improved final DRAM yield by 3%.

Copper and low-k dielectrics will undoubtedly be in regular use by the 0.18-?m generation. Copper processing conditions were studied by Clarkson University and Rodel. Blanket copper and oxide films were polished to determine removal rates and selectivities. Both acidic and alkaline slurries were capable of achieving 100:1 selectivity to oxide.

Low-k dielectrics based on long-chain molecules seem to exhibit extreme process control problems. The extent of cross-linking and crystallinity, and the distribution of molecular weights all influence the chemical resistance and mechanical properties of a given polymer dielectric. Researchers at Cabot Corp. in Aurora, IL, investigated the performance of slurries on Schumacher`s poly(arylene) ether (PAE-2) films. Within a defined set of film deposition conditions, the CMP removal rate varied from 300 to 2000 ?/min. - E.K.