TSMC increases R&D spend as 40nm yield issues emerge
Foundry TSMC has admitted problems with yields on its 40nm process have proven tougher to crack than expected and has increased R&D spend to handle the current issues and plan for the later move to dual 28nm processes.
In a conference call primarily to discuss TSMC’s second-quarter financial results, Mark Liu, senior vice president of TSMC’s advanced technology business, claimed that after inspecting failed devices, process engineers had since the first quarter of the year found problems that had lain unidentified until then. He added that average yield has roughly doubled within the past three months since the primary causes of failure emerged.
Liu cited the two materials changes, including the use of silicon germanium to strain the silicon layers, and a move to immersion lithography contributed to problems with defects, making it a tougher step than the shift to 65nm which only involved a change in lithography. “So we encountered major issues,” he said.
Liu explained the major problem with yield lay in the stress layers produced by adding different amounts of silicon germanium.
Several senior R&D directors – two experts on process modules and one on integration – were drafted in to work on the problem during the past quarter. Morris Chang, TSMC chairman and CEO, added later that R&D spend has been increased to put more effort into work on advanced processes.
“If we had not increased our R&D resources, that kind of help would have been very difficult to come by,” Chang claimed.
“We studied in further detail the fundamental module design and we have made improvements since,” said Liu. “We have made a major improvement in 40nm yield in the last quarter.”
Liu claimed, adding that the foundry is attempting to ramp-up yield through the summer. “We have several activities in place to move the yield forward. We expect the defect density reduction will continue through September.”
Chang admitted that the yield problems reduced the profitability of the 40nm process. “The profitability is not nearly as good as that on 65nm or the other nodes. But we do expect that when the yields improve along the experience curve that we have seen for every other node in the past then I think 40nm profitability will be going up to the standard that we expect.”