Epitaxy and device behaviour of collector-up SiGeHBTs with a partial p-type collector

A detailed experimental study has been made of the issues related to base d opant activation and mesa isolation in collector-up SiGe HBTs. It is conclu ded that to avoid excessive emitter-base diode leakage: (i) the metallurgic emitter-base junction should be moved away from the trenched p(+) base dop ing peak, and (ii) the base contact implant should not be placed in the hig h n-doped emitter substrate. Both recommendations can be followed by applyi ng an implanted pedestal emitter. To furthermore avoid TED, the base contac t implantation is activated by laser annealing. To achieve a good quality c ollector-base diode, a p(-)nn(+) collector profile is introduced. As a resu lt, the transistor profile is a stack of several doped Si and SiGe layers. This stack is grown by A-P/LPCVD dichlorosilane based epitaxy, which was op timised to suppress autodoping and to achieve sharp transitions. Hence the 1150 degreesC prebake was performed at low pressure and high flow, and foll owed by a 10 nm undoped Si deposition at 700 degreesC. Moreover, 5 nm undop ed Si layers were inserted for dopant decoupling. The effect of the p(-) la yer in the collector on the device behaviour was analysed by device simulat ions. It was found that this p(-) layer does not significantly affect the D C and high-frequency performance of the device. (C) 2001 Elsevier Science L td. All rights reserved.