Comparison between poly emitter bipolar characteristics with and without native oxide layers under various processes

The effect of the interfacial native oxide layer between polycrystalline and single-crystal Si was investigated in the submicron-rule bipolar and BiCMOS processes. It was found that the native oxide increases the current gain, but significantly degrades bipolar transistor performance. Bipolar transistors without the oxide layer, fabricated by different methods, were investigated. Without the layer, low emitter resistance and small current gain variation were achieved for a low-temperature process. The current gain reduction due to the lack of the oxide layer does not degrade the cutoff frequency. Improved performance for structures without native oxide was confirmed with ECL (emitter-coupled logic) ring oscillators