S-Wafers Project

Overview

Wafer Picture Integrated circuits (IC) and lasers are fabricated on wafers -- thin disks of silicon or gallium arsenide. Each week, thousands of wafers enter production in Lucent Technologies' Microelectronics manufacturing facilities. In most cases, the path through the fab will involve hundreds of processing steps and can take several weeks. On each wafer devices are created by the hundreds, arranged in a regular grid. The vast majority of these wafers are integrated circuits, from digital signal processors (DSP) to the latest field programmable gate arrays (FPGA). In increasing numbers, the wafers are made of gallium arsenide and the devices are semiconductor lasers used by optoelectronics components, again lasers packed densely on each wafer. While the processing of lasers and IC's is quite different, a common feature is that the object under manufacture consists of a regular array of individual devices, each device a potential product to be sold. Another commonality is the complexity of the processing to which each wafer is subjected.

Spatial Processes

Wafer Dendrogram

Historically, quality control á la Walter Shewhart consisted of simple charts tracking a single variable at a time, but effective process monitoring and quality improvement efforts in semiconductors manufacturing need to articulate the Shewhart principles of random and assignable causes in terms of spatial processes. Researchers in the Statistics and Information Analysis group, together with product, process and failure mode analysis engineers at each of the Lucent Microelectronics manufacturing sites, have extended and developed new statistical techniques for efficiently analyzing the vast amounts of data collected during the fabrication process. The S-wafers software tools embody this methodology and provide an environment for simple, but powerful, wafer visualization for the detection of defect signatures, spatial analysis of variance, parametric tests, particle scans, memory bitmap failures, and split-lot experiments. S-wafers also implements model-free yield models that directly exploit spatial patterning. These tools are based in the S language and are available on Unix workstations and personal computers (PC's).

Impact

As technology advances, engineers cannot depend on visual inspections for monitoring manufacturing processes and must increasingly rely on sophisticated data analysis and automatic statistical procedures. For the last few years this project has provided some of the next generation of data analysis techniques and software tools to Lucent Microelectronics, and our tools now serve as an analytic engine to enterprise Yield and Analysis Reporting Systems. (See the Bell Lab Technical Journal article for more details.)

Further Information

For those of you outside of Lucent Technologies, feel free to contact one of the S-wafers team members. Within the Statistics and Information Analysis department, contact Mark Hansen (new statistical methodologies), or David A. James (requests or enhancement suggestions for the S-wafers software).