Copper Interconnect on GaAs pHEMT by Evaporation Process

Gold (Au) has remained the metal of choice for forming interconnects in the compound semiconductor industry. However, the prices of precious metals have risen steadily in the last two years driving the wafer cost up with it. Most development work being done on a Cu metal scheme suitable for compound semiconductor focuses on electroplating adopted from the matured Silicon processes. Recently Skyworks has successfully developed an evaporated Cu process; replacing Au in Metal 1 of our pHEMT process. In addition to lower wafer cost, evaporated Cu offers other technical advantages such as lower resistivity and reduced likelihood of spitting at high deposition rates. We will discuss the challenges in the development work. A comparison of DC and RF test parameters between wafers that have Au and Cu interconnects as well as reliability data will be presented