Trends and technologies for CMP in hard-disk drives
About 40 fellow techno-geeks attended a Sept. 15 meeting of the NCCAVS CMP Users Group at SEMI headquarters in San Jose, CA, with an agenda comprising seven topics for a combination of technical, technical marketing, and marketing presentations, all with the theme of chemical mechanical planarization (CMP) for the hard-disk drive (HDD) industry. The group will post proceedings and presentations in the coming weeks.
Opening the meeting with a HDD market overview was John Kim of Trend Focus. Growth in the HDD sector has dropped from 15% CAGR in 1998-2007 to 10% for 2008-2014, with seasonal stability provided by strong markets in the BRIC region (Brazil, Russia, India, China), he said. By 2014, the majority of drives will be in the 1Tb-2Tb range. At the same time, solid-state drives (SSD) will comprise 5%-6% of the market, even though the upper size will still be in the range of 128Gb. The consumer appetite for larger and larger drives has shown no evidence yet of an upper limit.
Western Digital's Sungpyo Jung talked about consumables challenges in magnetic head CMP. Production uses 150mm AlTiC substrates, a wafer size not actively supported by all equipment manufacturers. Slurries use alumina abrasive with different chemistries to planarize features of Al2O3, magnetics (NiFe, CoNoFe, CoFe), metals (Au, Cu, CoPt, Ta, Ti, Cr, Ru, etc.), and photoresist. Performance metrics are familiar to semiconductor CMP engineers, but their rank importance is different for HDD. Within-wafer uniformity improvement is a key unmet need.
Kristan Bhatten of Dionex introduced a new-generation ion chromatography tool with a 0.4mm capillary and 0.4µL sample injection volume. The tool is expected to be useful for characterizing substrate surface contamination down to ppt levels, but specific data sets to showcase the tool for HDD and semiconductor CMP are still being developed.
Haijing Peng of KLA-Tencor showed a non-contact eddy current alternative to a four-point probe for measuring sheet resistance and polishing rates. The non-contact characteristic makes it possible to monitor processes on product wafer, eliminating the expense and throughput overhead of monitor wafers.
Sarah Okada of Strasbaugh gave an overview of the company's STB P300 polisher, touted as a customized solution for GMR polishing needs. The platform supports all substrate sizes from 125mm to 300mm. One GMR-unique feature is an option for rapid grinding of thick Al2O3 with 800 or 1200 grit abrasive as a rapid removal step before polishing the final 1-2µm.
Vamsi Velidandla of Zeta Instruments described a new 3D imaging and metrology microscope that builds up topographical images with 70nm vertical resolution using a broadband white-light LED source. Sample scans of polishing pads and pad conditioners showed a level of detail superior to other methods I've seen. The data sets included a black felt carrier pad, which is often impossible to measure by other optical methods because the reflection intensity is so low.
Denise Hunter of Cabot Microelectronics wrapped up the meeting with a description of their mixed abrasive slurry for HDD substrates. The NiP plated platters are typically smoothed in a two-step process: alumina abrasive coarse polishing followed by silica abrasive final polish. The irregularly shaped alumina particles can leave embedded fragments in the NiP grain boundaries, resulting in defects on the platter. The HDD mixed abrasive slurry combines alumina with much smaller colloidal silica abrasive. The silica is thought to envelop the alumina particles and decrease the incidence of fragmentation. Removal rate of the mixed abrasive slurry is ~10% lower than alumina slurry, but defect levels are significantly improved—to the extent that several HDD fabs are qualifying the new material for volume production. — Michael A. Fury Ph.D, senior technology analyst, Techcet Group