Polishing an Emerging Technology

Electronic News, August 13, 2001 by Jeff Chappell

Newcomers vie for spot in chemical mechanical planarization market

For a technology that chip engineers would have scoffed at in the dark ages of semiconductor technology, chemical mechanical planarization (CMP), or wafer polishing, is poised to become an important technology as copper, low-k and high-k dielectric films move from R&D labs to production fabs.

The irony of CMP is that at one time, as critical defects became more of an issue as line widths shrunk, the idea of removing excess material deposited on a wafer by grinding it with chemical abrasives and abrasive pads seemed anathema.

But with copper chips now rolling off of fab lines, the era of CMP is here. But if this summer's Semicon West trade show is any indication, just who will be the major players of this market once the copper dust settles and the process becomes mature or exactly what type of polishing technology will be dominant are both yet to be determined.

The list of players in the CMP market has some large and well-established names among its suppliers, including Applied Materials, Lam Research, Ebara and SpeedFam-IPEC. This year's Semicon West witnessed a number of CMP-related announcements from tool vendors and materials suppliers. One of the more notable, perhaps, is that of Nikon Corp.

Tokyo-based Nikon, at least inside the semiconductor biz, is a name associated with steppers and scanners and metrology equipment, as opposed to CMP. But the company said on Nov. 15 of last year that it planned to leverage its lens-polishing technology for use in wafer polishing and combine it with CMP technology developed by partner Okamoto Machine Tool Works Ltd., a toolmaker based in Kanagawa, Japan.

Nikon's announcement at the time produced predictable skepticism on the part of its more established competitors. Before it teamed up with Nikon, Okamoto had tried unsuccessfully to break into the CMP tool market. Seemingly undaunted, Nikon officially unveiled its CMP tool, the NPS2301, at Semicon West.

The NPS2301 uses pads smaller than the wafer being polished and utilizes a wafer data profile to target specific areas on a wafer in order to control polishing uniformity across the wafer surface, explained Akira Miyaji, a member of the executive staff of Nikon's CMP department. "We believe that this analytical technique is very effective ... Our system is more capable of doing advanced process control," he said.

The smaller pad sizes -- 150mm for 200mm wafers and 200mm for 300mm as opposed to conventional 600mm pads -- allow the NPS2301 to polish at a high rate of speed but with low pressure, which will make the technology ideal for copper/low-k applications, according to Nikon. It also uses less slurry, the company said. The tool also has an auto exchange system to change pads automatically in less than a minute, Miyaji said.

According to Nikon, the NPS2301 can polish copper with dishing of less than 50nm, while its variation between wafers is typically 1.04 percent sigma. Its 200mm version is currently under evaluation and has a throughput of approximately 50 wafers per hour. It's 300mm version, which it expects to introduce this fall, will have a throughput of 40 or more wafers per hour, the company said.

While Nikon's entry into the world of polishing still resembles conventional CMP, Milipitas, Calif.-based start-up NuTool Inc., which is taking a decidedly different approach, said at Semicon West that it is continuing to make headway in the marketplace.

"We've really gone fast track down the line to qualify the tool for production," said Homayoun Talieh, NuTool's chief operating officer.

NuTool unveiled its electrochemical mechanical deposition (ECMD) tool and technology at Semicon Japan last December, when it also announced that it had enlisted no less than Tokyo Electron Ltd. for assistance with sales and support.

In NuTool's ECMD process, as the tool deposits a copper layer, a pad is in physical contact with the wafer and this, coupled with NuTool's process chemistry, allows differential copper growth rate between copper deposited on the wafer surface and copper deposited in a feature, according to the company. The rate, pressure and the mechanical path of the pad can all be controlled via software, eliminating the common problems of polishing copper, such as dishing and erosion, according to NuTool.

Since Semicon Japan, the company has begun to see interest from more conservative customers. "The downturn is helping us quite a bit. Now the customers have time to sit down and think about the future," Talieh said. He added that the company recently shipped a tool to Taiwan for qualification. He expects to make announcements about completed production qualifications for ECMD tools this fall.