ZTY

The New Texas Instruments Method for Analyzing Yield Loss Based on the Critical Wafer Yield Zones

Nick Atchison
Texas Instruments
Santa Cruz, California, USA / ??????
Texas Instruments
Tustin, California, USA / Ron Ross
Texas Instruments
Santa Cruz, California, USA

ABSTRACT

The wafer fabrication process can produce both global problems that uniformly reduce the wafer probe yields and regionally distinct problems that reduce the yield of specific regions of the wafer. The manual method to detect regional yield loss consists of engineers reviewing wafer probe yield maps and parametric wafer maps. At the Texas Instruments Santa Cruz FAB, programs to automate the review of wafer maps have been formulated, tested and put into production with very gratifying results.

This paper will discuss an overview of these automated methods to locate and monitor the severity of low yielding wafer regions. Wafer regional yield trend graphs will be explained and the comparative interpretation of yield trend changes will be discussed. Finally the methods used to correlate the regional yield changes to specific units of process equipment at specific process steps will be briefly explained.

The continual introduction of new processes into a single wafer manufacturing environment creates a dynamic situation that makes computerized wafer zone yield analysis very desirable.

New processes are brought on line with expectation to ramp yields by at least 3% to 6% a month. The most critical process problems have to be found and corrected as soon as possible if maximum yield is to be achieved. To do this, the yield of the wafers shall be analyzed zone by zone to remove the blurring of results caused by averaging wafer data.

Because of the volumes of parametric test, wafer probe, and defect analysis date, the manual analysis of data by wafer zone is impractical. The use of Artificial Intelligence programs capable of “Machine Learning” is required if the volumes of data gathered are to be reduced to a meaningful form.

To simply divide the wafer up into zones will not produce the same results as dividing the wafer up into zones that correspond to regions that are damaged by particular recurring process problems. Also, to increase the usefulness of the zone analysis, the analysis must be refined to determine which process equipment units are contributing to the zone yield loss, and yield improvement efforts must be focused on the areas causing the greatest loss.