Riding the wave of CMP
04/01/2008
CMP is rapidly becoming one of the most important and widespread fab processes enabling the continuation of device shrinks. Overall, the total number of CMP operations is expected to grow ~67% from ~0.9 billion unit operations in 2007 to ~1.5 billion in 2011.
CMP is impacting both frontend-of-line processing as well backend-of-line processing. On the frontend, CMP is critical in enabling the implementation of new metal gate structures as well as in shallow trench isolation (STI) processing. On the backend, it is one of the key enablers for the increasing number of interconnect layers, especially for copper metallization with more fragile porous low-k dielectrics.
CMP applications that will experience strong growth include direct STI and tungsten polishing, both of which are expected to grow by almost 50% from 2007 to 2011. Direct STI applications typically use high selectivity slurries with ceria abrasives and unique chemical packages to planarize the oxide film, while completely stopping on a nitride film, which is subsequently removed with a phosphoric acid treatment.
Tungsten seems to be in a similar position as PVD–it is the application that is always prognosticated to have only one more generation, but never seems to go away. This is true in CMP as well, as the number of tungsten polishes will continue to grow with the strong anticipated ramp of 45nm half pitch DRAM and NAND flash devices that will rely on tungsten as key to interconnect fabrication.
However, copper and barrier polishing applications will be the major driver for future CMP growth. Linx Consulting estimates that the number of CMP polishes for copper and barrier will grow by 87% from 2007 to 2011. Much of this growth will be driven by increasing the average number of copper interconnect levels in advanced logic devices from 6 to 7 metal layers today to perhaps a dozen in 2011.
On top of this growth in logic devices will also be growth in memory applications incorporating copper interconnects. Micron’s implementation of copper wiring in 2007 for DRAM was only the beginning. Both Samsung and Hynix are anticipated to be in high-volume manufacturing of copper this year at the 55nm and 50nm half pitch, respectively. Also, by 2011, most NOR flash will have copper interconnects and a significant portion of NAND flash will also have some copper wiring in high volume manufacturing.
The largest shifts expected over the next several years will involve structural changes in the industry related to the growth of memory. Memory applications accounted for about 20% of all CMP steps in 2007. This figure is anticipated to increase to about one-third of all CMP operations by 2011 and after this will only accelerate: More than 80% of the wafer starts for 45 half pitch production in 2011 will be for memory applications. Based on requirements to fit the memory business model, many changes will come with this shift. Key among these requirements will be:
- Lower cost, high-productivity processes.
- Processes that can be rapidly ramped at the newer, multiple hundred thousand wafer start/month “mega fabs.”
- Processes with enough latitude that they can be readily applied between mixed product (mostly NAND and DRAM) production, as these mega-fabs will likely swing back and forth from DRAM to NAND to meet immediate demand.
All participants in the value chain will be required to invest to meet the attendant requirements. First, there will be the investment required to ensure sufficient manufacturing capacity for the process tools, consumables, and related services necessary for the growth in CMP, especially with the rapid ramp-up of the mega-fabs. Second, there will be investments and enhancements in collaborative efforts to develop manufacturing-ready solutions, and such emerging technical requirements as CMP of advanced logic devices utilizing third-generation low-k dielectric materials.
Finally, careful investments in customer relationships will be required. Combined with collaborative centers such as IMEC and Albany Nanotech, suppliers can mitigate development risk by targeted key development alliances.
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Michael Corbett, managing partner, Linx Consulting
Contact Michael Corbett at Linx Consulting, ph 973/698-2331, e-mail [email protected].