Improved Emitter Resistance Through the Use of Barrier Metals
Keywords: emitter, contact, titanium, tungsten, HBT
In this paper we report the improvement of emitter series resistance for InGaP HBT transistors using barrier metals in the contact layers. To demonstrate the improvement a simple baseline process, using a thick titanium contact layer, is compared to processes using a barrier layer of either tungsten or titanium tungsten. Although each of these emitter contact schemes produces a non-alloyed ohmic contact, and does not require exposure to high process temperatures, processing above 300 °C is unavoidable in the integrated process. Trend charts show reduced emitter resistance and better uniformity over multiple lots. High resolution STEM images exhibit the absence of physically degraded interfaces. Additional data, not presented in this paper, has shown that improved emitter contacts are beneficial to the reliability of HBT power amplifiers.