TOKYO -- Nikon Corp., the largest supplier of steppers, is entering the market for chemical mechanical planarization equipment with a technology that literally turns the CMP process upside down. Applying a technique used in lens polishing, Nikon designed its CMP system so that the surface to be polished faces upward rather than downward, as in conventional CMP.

The shift to finer semiconductor fabrication processes (below 0.13 micron) and to new technologies such as low-k dielectric materials and copper wiring demands smoother planar wafer surfaces, said Yosuke Takahashi, assistant chief officer at Nikon's business development center, who oversees Nikon's CMP business. "Present CMP equipment does not necessarily satisfy users' requirements," he said.

Nikon thus saw an opportunity to leverage its strong position in steppers and in lens-polishing technology to address the CMP equipment market, he said.

Applied Materials Inc. and Ebara Corp. are the two major CMP suppliers. But supplier rankings in the CMP market shift frequently, Takahashi said. "This means that users are not fully satisfied with existing CMP equipment and may be more likely to give a newcomer a chance."

"These days, users tend to request CMP performance as a part of a total process," said Takashi Ogawa, principal analyst with the Dataquest division of Gartner Group Japan K.K. "In this sense, equipment suppliers like Applied Materials have an advantage. It may be difficult to enter the CMP market with CMP equipment alone.

"But Nikon has strong polishing technology that has been fostered in lens polishing. Its success will depend on how well the company can make full use of its technology in the CMP arena," Ogawa said.

Inverted polishing

Conventional CMP systems hold wafers face down and rub them on a polishing pad. Nikon's system polishes wafers with the polishing pad held over the wafers, as in lens polishing. Takahashi claimed the inverted setup has several advantages.

For a 200-mm wafer, the polishing-pad diameter is about 150 mm. The pad rotates at about 800 rpm maximum, and the wafer chuck table rotates at about 400 rpm, whereas in conventional systems the table rotates at 50 to 60 rpm. The high rotating speed allows the same polishing rate to be achieved at a lower pressure, of 100 to 200 g, compared with the 300 g typical for conventional systems. The reduction in pressure makes for more even polishing.

A smaller-diameter polishing head is held over the wafer, and the wafer surface covered by the head can vary: Sometimes the full head is within the diameter of the wafer, while at other times only part of the head is used. Although achieving precise control of the head tilt was a challenge, the Nikon team pursued the configuration because it "allows partial polishing, which is another merit," said Osamu Shimoda, general manager for CMP promotion at Nikon.

Nikon used the index table technologies of Okamoto Machine Tool Works Ltd. to hold (chuck) wafers. The table holds four wafer cassettes. Takahashi said the technology allows wafers to be positioned with high precision and to be conveyed at high speed. With the index table system, a wafer is held on the same wafer chuck throughout the polishing processes to assure a high level of consistency, since polishing conditions may vary slightly from table to table.

Polishing the wafers face up also simplifies inspection of the process to determine when polishing should be stopped. Conventional systems provide access to detect the polishing level via a hole bored through the polishing table.

Another claimed advantage is the lowered cost for expendables, such as slurry. In conventional systems, slurry is dribbled onto a polishing pad apart from the wafers. The imprecise procedure is wasteful, Takahashi said. In Nikon's system, slurry is directly supplied through the polishing head to the space between the wafers and the polishing pad, he said, ensuring that "100 percent of the slurry is used for polishing."

According to Nikon's measurements, a conventional system consumes slurry at a rate of about 150 milliliters per second, whereas Nikon's system consumes 36 ml/s.

The smaller polishing pad -- 150 mm in diameter for 200-mm wafers and 200 mm in diameter for 300-mm wafers -- is another cost-reduction factor. Conventional pad diameters are about 600 mm.

Shipment of Nikon's CMP system is slated to begin in next spring, first mainly to Japanese clients. Exports are expected to being roughly a year later.

In the first year, Nikon expects to log about 3 billion yen ($28 million) in sales of the CMP equipment. By 2005, sales are expected to be about $280 million.