Film deposition mechanisms were investigated in capacitively-coupled plasmas of fluorocarbon (C4F8, C3F6 and C5F8) gases. In a C5F8 plasma, slightly fluorine-rich film was obtained and the deposition rate was twice as large as those in C4F8 and C3F6 plasmas. In order to understand such a different behavior in the film deposition, densities of the gas-phase species were measured by infrared laser absorption spectroscopy (IRLAS). Densities of smaller mass radicals such as CF, CF, and CF, were on the order of 10(10), 10(12) and 10(11) cm(-3), respectively, in every source gas but had no direct correlation with the deposition tendency. Stable molecules such as CF4 and C2F6 were also produced in every gas, but the quantities were smallest in a C5F8 plasma. This indicates that polymerization reactions in the gas phase and on the surface were suppressed in producing the stable species in C4F8 and C3F6 plasmas. The presence of high-mass and less-stable species in the gas phase in a C5F8 plasma was suggested to be responsible for the deposition of polymers with a higher rate and larger fluorine content.