Effect of Deposition Conditions on Polysilicon PNP Emitter Grain and Electrical Performance

This paper presents a study on the effect of the polysilicon emitter deposition conditions on the electrical performance and emitter film quality of a PNP transistor. An increase in the deposition temperature is seen to improve the gain of the transistor. The sheet resistance, breakdown voltage and Gummel plots were analysed to establish the mechanism for higher gain. TEM (Transmission Electron Microscopy) and XRD (X-ray Diffraction) techniques were used to characterize the emitter film, and SIMS (Secondary Ion Mass Spectrometry) analysis was done to check the dopant profile at the emitter-base junction. The improvement in gain provides a better margin from the lower specification limit provided by the customer, along with an improvement in the range of V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">be</inf> (base-to-emitter voltage) over which the transistor can be operated.