Whether you are manufacturing RFICs for cell phone modules on III-V wafers or DSPs on a silicon-based technology, predicting final product performance and reliability requires s-parameter measurements at the wafer level to complement the DC data. This is only practical when calibration and deembedding of the s-parameters is automated, along with probe cleaning. Cost of consumables and overall cost of test must also be comparable to the traditional DC process monitor operation. The ideal case is to have a single test operation collect the DC and s-parameter data.
RF Process Monitoring – Who Needs It?
Almost without exception, semiconductor device manufacturers use DC data for statistical process control of their manufacturing operations. They have traditionally taken s-parameter data only in device modeling laboratories due to the complex nature of the measurements and associated cost. RF parameters are extracted from the s-parameter data and included in the simulation models used by design engineers during product development. RF parameters for modeling and DC data for production was a working paradigm until product performance approached the gigahertz range. Process control for gigahertz devices requires RF parameter sampling to meet the Known Good Die goals of RFICs for cell phone modules, guarantee the frequency performance of DSP chip level interconnect, and monitor gate dielectrics with complex material properties. As device performance improves to meet the demands of the wireless market, component manufacturers are struggling to improve test coverage without unacceptable increases in test cost. Several leading manufacturers have attempted to migrate the RF parametric measurement capability from their device modeling labs to manufacturing operations with little success and high levels of frustration.