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) films in a Lam Research Corporation DSM™ 9800 low-pressure chemical vapor deposition reactor. The precursors used were tetraethylorthosilicate (TEOS), triethylborate (TEB), phosphine, and oxygen. Typical process pressures ranged from 1-3 Torr, while the process temperatures varied from 775-825°C. The PBMS monitored the flow in the reactor exhaust line, and under typical process conditions detected a high concentration of fine particles (∼10⁵/cm³) whenever TEOS was flowing into the reactor, indicating that the particles are formed by a gas-phase nucleation process initiated by the decomposition of TEOS. The median particle diameter was determined to be about 0.2 μm. It is not known whether the particle generation occurred within the reactor or in the cooler (∼350°C) exhaust line. Fourier transform infrared, energy-dispersive X-ray, and inductively coupled plasma analysis showed that the particles had a composition largely similar to that of BPSG films, suggesting that the particles could have formed within the reactor. However, wafer scanner measurements after deposition detected very few added particles. This lack of adverse effect could imply that the particle generation occurred downstream of the reactor chamber, or that if it did occur within the reactor, the particles were prevented from depositing due to thermophoresis. PBMS measurements 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.