INVESTIGATION OF PARTICLE GENERATION DURING THE LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION OF BOROPHOSPHOSILICATE GLASS-FILMS

A particle beam mass spectrometer (PBMS) was used to monitor particle generation during the deposition of borophosphosilicate glass (BPSG) f ilms in a Lam Research Corporation DSM (TM) 9800 low-pressure chemical vapor deposition reactor. The precursors used were tetraethylorthosil icate (TEOS), triethylborate (TEB), phosphine, and oxygen. Typical pro cess pressures ranged from 1-3 Torr, while the process temperatures va ried from 775-825 degrees C. The PBMS monitored the flow in the reacto r exhaust line, and under typical process conditions detected a high c oncentration of fine particles (similar to 10(5)/cm(3)) whenever TEOS was flowing into the reactor, indicating that the particles are formed by a gas-phase nucleation process initiated by the decomposition of T EOS. The median particle diameter was determined to be about 0.2 mu m. It is not known whether the particle generation occurred within the r eactor or in the cooler (similar to 350 degrees) exhaust line. Fourier transform infrared, energy-dispersive X-ray, and inductively coupled plasma analysis showed that the particles had a composition largely si milar to that of BPSG films, suggesting that the particles could have formed within the reactor. However, wafer scanner measurements after d eposition detected very few added particles. This lack of adverse effe ct could imply that the particle generation occurred downstream of the reactor chamber, or that if it did occur within the reactor, the part icles were prevented from depositing due to thermophoresis. PBMS measu rements also showed the existence of a threshold for process pressure and for TEOS flow rate below which no particle formation was detected. A similar threshold was not observed for film formation.