New intense bands in the nonlinear absorption and multiphoton dissociation spectra of monosilane in the 11-μm emission range of an isotopic¹³C¹⁶O₂laser

Collision-Free Infrared Multiphoton Dissociation of Silane

“…The lower curve of Figure 4 shows the fluence dependence of the dissociation yield using the NH 3 laser in multi-line mode. One can see that the threshold fluence using this laser source is on the order of 4 J/cm 2 , which is 25 times lower than that of Dzhidzhoev et al 8 The data of Table 1 also shows that if we use individual lines of our tunable NH 3 laser below 870 cm -1 , the dissociation yield drops by 1-2 orders of magnitude. The frequency dependence of the dissociation yield that we observe is consistent with that determined by Dzhidzhoev et al, 8 where the maximum IRMPD efficiency is observed with a 13 CO 2 laser 895 cm -1 .…”

“…The detection of vibronically "cold" fragments suggests an IRMPD fluence threshold below 17 J/cm 2 when using the 10P(36) line of CO 2 laser, which is significantly lower than previous measurements. 8 When irradiated by all lines from a pulsed NH 3 laser, which emits 95% of its energy below 868 cm -1 , silane exhibits a threshold fluence for IRMPD of ∼4 J/cm 2 . This value drops to less than 2 J/cm 2 when the molecules are first preexcited to the first Si-H stretch overtone.…”

“…In one early report, 3 no collisionfree MPD of silane was observed using CO 2 laser pulses with fluence in excess of 150 J/cm 2 . In another study, 8 IRMPD of silane at a pressure of 1 Torr was successfully achieved using 100 ns pulses from 12 CO 2 and 13 CO 2 lasers with energy fluence above 100 J/cm 2 . It is well-known that to achieve efficient IRMPD of molecules, the frequency of the dissociating laser has to be shifted to the low-frequency side of the fundamental band of the pumped vibrational mode.…”

“…Using a 13 CO 2 laser, which emits frequencies to the red side of the Q-branch of ν 4 , leads to a 10-fold increase in dissociation yield as compared to a 12 CO 2 laser. 8 Unfortunately, the tuning range of the 13 CO 2 laser is limited on the red side to about 880 cm -1 , and it is not clear if this is the optimum for the IRMPD process. We employ in the present work a simple, efficient, optically pumped NH 3 laser with a tuning range down to 780 cm -1 .…”

“…Silane, SiH 4 , is widely used in the semiconductor industry for deposition of silicon films, since it allows the production of SiH x ( x = 0−3) fragments in a well-controlled, chemically clean environment . Dissociation of silane is thus a primary step in many silicon deposition processes, and a number of studies have been devoted to CO 2 laser infrared multiphoton dissociation (IRMPD) of this molecule. − These studies suggest that collisions, and hence relatively high pressures, are necessary for efficient multiphoton pumping of SiH 4 to the dissociation threshold. Despite the fact that it might be key for developing a laser driven molecular beam epitaxy technique, there is little known about collision-free IRMPD of silane.…”