Investigation on Dissociation Process in Plasma Enhanced Chemical Vapor Deposition Using Tetraethoxysilane

Abstract

Dissociation in plasma enhanced chemical vapor deposition for SiO2 deposition using Tetraethoxysilane (TEOS) was investigated by means of mass spectrometry. First we showed basic dissociation patterns of TEOS by electron impact. It was shown that the TEOS was dissociated by electron impact at low electron energy below 7eV removing the ethyl group (C2H5). Next we presented dissociation patterns in TEOS/He plasma in order to eliminate the effect of oxidation. Finally dissociation in TEOS/O2 plasma was clarified. As the results, it was found that the oxidation plays a indispensable role for deposition of high quality SiO2 films due to the decrease in high molecular compounds with carbon (C) and hydrogen (H) although the TEOS is highly dissociated by electron impact.T. IEE Japan, Vol. 117-A, No. 8, '97

Dissociative reactions induced by electron impact and electron transport in TEOS vapor

“…Figure 5 shows the number of fragments generated in the fragmentation simulation as functions of mass number of fragments m, together with measured mass spectra reported by Ref. 13. Here, the number of fragments is normalized such that the number of Si(OC 2 H 5 ) 2 OCH 3 (m = 149) agrees with its measured intensity.…”

“…Maeda et al [13] mentioned that a TEOS molecule dissociates by electron impact at an electron energy below 7 eV, although in the fragmentation simulation fragments are generated at an initial electron energy above 10 eV. Furthermore, considering that ionization cross sections of the neutral fragments depend on their chemical structure and electron energy, the assumption that the neutral fragments generated in the simulation are fully ionized may also lead to the differences; therefore, data on ionization cross sections of the neutral fragments are needed for further investigation of the validity of the dissociative reactions and cross sections.…”

“…Furthermore, fragmentation of TEOS molecules by electron impact is simulated using the present cross section set, and then the number of fragments produced in the simulation is compared with the measured mass spectra reported by Maeda et al [13] 2. Present cross section set of TEOS vapour Table 1 shows the reactions between an electron and a TEOS molecule for elastic momentum transfer (mom), vibrational excitation (vib1, vib2), non-dissociative electronic excitation (non-diss-ex), neutral dissociation (nd1 -nd18), and ionization (i1 -i20) collisions considered in this work.…”

“…where r0 and R are respectively the radius of the filament and the cylindrical electrode, r is the distance from the filament, and is the electric potential difference between the filament and the cylindrical electrode. Since the gas pressure in the ionization chamber is generally quite low, the emitted electrons are accelerated rapidly in the vicinity of the filament, and most of them become energetic before the collision; therefore, for the sake of simplicity, the ionization chamber is assumed to comprise two infinite parallel plates P1 (z = Pa), which is almost equivalent to the experimental condition reported by Maeda et al [13] The number of fragments produced by electron collisions with TEOS molecules is counted in the simulation. Since little information on electron collision cross sections of fragments is reported as of now, collisions between an electron and fragments are not considered, and all neutral fragments produced in the simulation are assumed to be fully ionized in the ionization chamber.…”

“…In the fragmentation simulation, N is set to 2.651 × 10 11 cm −3 (0 °C, 10 −3 Pa), which is almost equivalent to the experimental condition reported by Ref. 13.…”