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Yield issues, defects mount in 28nm node

Posted: 08 Nov 2011 ?? ?Print Version ?Bookmark and Share

Keywords:foundry? 28nm process? chip manufacturing?

According to market analysts including Gartner Inc., foundry chip manufacturing is running into a lot of issues in the 28nm node. This is despite the forecast that the segment will grow faster than the rest of the chip market.

In particular, foundries are struggling with the introduction of 32nm/28nm high-K metal gate (HKMG) CMOS, said Bob Johnson, research VP at Gartner. "[Making] bulk silicon HKMG at 28nm is hard. All foundries are having yield issues and defect density issues right now." Richard Wallace, president and CEO of KLA-Tencor Corp., gave the same message saying that foundries are investing in tools for 28nm and running into challenges with yield.

There is also reducing demand at 28nm as customers push out projects because of global economic uncertainty, Johnson added. And those designs that are going ahead are taking longer to qualify because of the customers' tightening engineering budgets, he noted.

This does not fit with some of the bullish comments that have come from Taiwan Semiconductor Manufacturing Co. Ltd (TSMC). Earlier this year, TSMC was claiming that its design starts at 28nm were times that they were at the equivalent stage in the roll out of the 40nm manufacturing processes. However, at that time, TSMC was aiming for 20 percent annual growth in 2011. For the first nine months of the year, TSMC's sales are 4.2 percent up on the equivalent sales last year. TSMC is still set to outgrow the overall chip market this year, but only by a few percentage points.

Johnson said that the foundries were taking the push out in demand at 28nm as an opportunity to try and effect yield improvements. "In 2012, total 28nm HKMG shipments will not exceed 200,000 300mm wafers; or less than four percent of foundries' revenue. Shipments won't start until next year and it's coming slower than people had previously thought."

Foundry Shipment

A forecast of foundry shipments by technology node shows that 32/28nm will take a time to get on to the same ramp curve as 45/40nm. Source; Gartner

When asked for specific problems Johnson said that Globalfoundries had experienced yield issues with its 32nm SOI process. They had serviced customer Advanced Micro Devices Inc. but only by running more wafers. Intel introduced HKMG earlier than the foundries and has moved on to ramping 22nn manufacturing. Johnson said the rest of the semiconductor industry is running about a node behind Intel.

Wallace compared the move to 28nm with the move to the 40/45nm node, when chip manufacturing yields 'hit a speed bump.' He said a similar phenomenon was taking place at the 28nm node, which caught many of KLA's customers "because they thought they had it dialled in." Wallace noted that there is a range of yields at 28nm, depending on the fab line. He said yield issues at the 28nm node are related to shrink and that KLA is benefiting from the trend with orders for wafer inspection and metrology equipment.

Steve Newberry, CEO of Lam Research Corp., said foundries have been bringing 28nm capacity online to the tune of roughly 40,000-50,000 wafer starts per month by the end of the year. But, whether all of this 28nm capacity is fully qualified and fully required is "an open question."

Newberry added that foundries are caught in a bind because they are concerned that customers are feeding them overly optimistic projections about the need for 28nm capacity and that it's quite possible the actual demand for 28nm might be lower than the capacity they are putting into place.

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