Evaluating pHEMT Process Improvements Using Wafer Level RF Tests
Keywords: RF test, pHEMT, process improvement, harmonics, IMD
To increase production capacity, improve the performance of existing processes, and to introduce new, more advanced process technologies, processes must be evaluated using electrical tests. PCM’s are used to evaluate the active transistor and passive device characteristics produced by the wafer process. DC testing of circuit designs is used to evaluate the success of the design, the success of the wafer processing, and the interaction of the design with the process. While good PCM and DC circuit test results are necessary, they are not sufficient to guarantee acceptable RF performance for products used in high performance RF applications such as cell phones. Consequently, RF testing is utilized to assure good RF performance. RF testing is performed at the package level. The time required to move product from wafer fab completion through package assembly delays feedback to the wafer fab process engineer. Adding wafer level RF tests provides quicker feedback and reduces the time required to complete a cycle of learning. This paper discusses the RF wafer probe tests used to evaluate the continuous improvements in Skyworks’ pHEMT wafer process.