Linkage of test data with front-end metrology
10/01/1998
Linkage of test data with front-end metrology
With chipmakers striving to boost profits through improved fab productivity and yield enhancement analysis, much effort is being devoted to developing systems for collection and analysis of process data. One of the missing links, at least from an open standard point of view, is some software framework that can unite back-end test and yield data with information from front-end metrology tools.
By linking probe yield data to metrology information from the front end, a chipmaker could in theory track the effects of process variations and defects on final yield and device speed. And many equipment and service companies are eager to sell the necessary hardware and software.
With this in mind, the SEMI trade association is in the very early stages of gearing up its standards development process to approve a framework. One complication is that front-end metrology giant KLA-Tencor is one of the
companies offering yield management products, and the closest thing to a de facto standard is that company`s proprietary Results File data format. While KLA officials say they are willing to explore the possibility of adopting this as an open standard, they raise concerns about how such a change would affect their future business.
Joe Savarese, VP of business development at Electroglas, which is seeking new opportunities in yield management in addition to its traditional prober business, began conversations on a standard with SEMI officials during SEMICON West. "SEMI has to get involved in software standards," says Savarese, who was also active in developing chip traceability standards, that will be published this fall. "The KLA format is very proprietary, and I think (SEMI) will see the need for more openness. There`s so much pressure from customers."
Several years ago, Electroglas and several other firms formed a Yield Management Alliance with an eye toward offering combined solutions, but a lack of SEMI sponsorship for the software effort was an issue, says Savarese. "Now we`re trying to shift and work through SEMI, make that a standard, and invite KLA in. We`ve got to get to the correct people at KLA, and do an overview of what SEMI has now."
SEMI is setting up a task force to write a SNARF - a Standards New Activity Request Form, a document outlining the scope of activity for a proposed new standards committee. "That form is used by the next higher level of committee to ensure that there is no overlap....we`re in the very early stages of task force formation," says SEMI staffer Heidi Hoffman. She notes that SEMI hopes to find a company from the chipmaking community to join Electroglas in spearheading the effort. Interested parties can contact Alana Hall at 650/940-6974.
Glyn Davies, director of marketing for KLA-Tencor`s Yield Management Software division, comments, "In a state-of-the-art fab now, they have superb tracking - they can track from wafer through packaging. The difficulty is in tying bin data to defect data. Testers put out different types of files, and they`re often customized. There is no strong standard for data from the test floor." A great deal of value could be obtained, he notes, by tying this data to work-in-process tracking information from the front end.
The KLA-Tencor file format is a step toward this, says Davies; KLA-Tencor has a policy of licensing the format for a nominal fee and has granted over 25 licenses to date, to equipment and service suppliers as well as customers, who use the format in their data handling. While the company does look at competitive situations when granting licenses, Davies said licenses have been granted to competitors and that "fundamentally, we have not denied any licenses to the KLA Results File."
The most significant issue seen by KLA-Tencor is possible modifications to the file format, says Davies. "As soon as you have a standard, you should have a committee to approve modifications," he notes. "The transition from KLA to a committee is something we`d have to look at." Davies states that KLA-Tencor is eager to participate in standards efforts, and says his firm would look at alternate formats. However, he notes, "there would probably be a lot of pushback from customers. That`s what they tell me - that as soon as they have an infrastructure, they don`t want to go back and do it again. It`s unlikely they would let us go to something different." - P.N.D.