PARTICLE-BEAM MASS-SPECTROMETER MEASUREMENTS OF PARTICLE FORMATION DURING LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION OF POLYSILICON AND SIO2-FILMS

We have recently built a particle beam mass spectrometer (PBMS) for me asuring ultrafine particle size distributions (0.005-0.25 mu m) at low pressures (>100 mTorr). The PBMS is being used to study nucleation an d growth in low pressure chemical vapor deposition processes relevant to the production of semiconductor devices. In this article, the funct ion and performance of the PBMS is summarized, and results of measurem ents made while depositing polysilicon and silicon dioxide films in tu be furnaces are discussed. Measurements made during deposition of poly silicon films showed that there was a critical reactor pressure below which particles were not present; this critical pressure varied in pro portion to the residence time in the reactor, and was insensitive to r eactor temperature. Above the critical pressure, however, the concentr ation of particles produced was sensitive to reactor temperature. The average particle size was in the 0.003-0.03-mu m-diam range, with conc entrations of similar to 10(4) cm(-3). In contrast, particles produced during the deposition of oxide films in a low-temperature oxide (LTO) furnace were considerably larger (0.1-0.3 mu m) and were present at l ower concentrations (similar to 10(3) cm(-3)). These differences sugge st that the chemical mechanisms of particle formation and growth in th e two systems are quite different. Simultaneous measurements of partic le accumulation on witness wafers during the LTO experiments showed a reasonable correlation with PBMS data, thereby illustrating the releva nce of PBMS measurements to device fabrication. (C) 1996 American Vacu um Society.