Characterisation of low-stress LPCVD silicon nitride in high frequency BJT's with self-aligned metallization

In the self-aligned metallization process, a metal base contact is self-aligned to the emitter by using free-standing silicon nitride spacers directly on the silicon. Low-stress silicon nitride (SiN/sub x/) is electrically characterized for use as a spacer material in this process. A comparison is also made to stoichiometric Si/sub 3/N/sub 4/ for which mechanical stress related problems can in some cases reduce the device yield. Overall good device characteristics and yield are obtained with the SiN/sub x/ spacers.