Volume 118, number 4 CHEMKAL PHYSICS LETTERS 2 August 1985 DETECTION OF SIF RADICALS WITH M-IKTIPHOTON IONIZATION SPE-OSCOPY C.S. BULCEY ’ and Jeffrey W. HUDGENS Chemrcol Kmellu Diukoq Cemer for Chemical Physicr, Narronal Bureau o/ Skmdar& Garrhersburg. MD 20899. USA and Combumon and Fuels Branch ‘, ChemEtty Dluiuon, Naval R-earth Loborarory. Warhrngron, DC 20375, USA Received 1 April 1985; III fiial form 1 May 1985 We rep011 Lhe resonance enhanced mullipholon ionization spectrum of SIF between 430 and 492 run SIF radicals absorbed al least Lhrec photons lo generate the observed m/r 47 SiF ions Two-pholon absorption bands from C”‘Z* + X 2JI, and C’21TI, c X 21T, witions were observed An intense band from sequential one-photon lransitions from the X 211,,( u”= 0) s!ale Through the A’Z+( u’= 0) and C”22+((u’= 1) states was observed_ 1. Introduction This paper demonstrates sensitive. resonance en- hanced multiphoton ionization (REhWI) detection of silicon monofluoride radicals, SiF. This radical is of interest to the semiconductor industry since it is one of the products observed during chemical etching reac- tions at silicon surfaces [ 1,2] _ In this study the reso- nances that enhance the laser-induced ionization cross sections arise from twc+photon transitions from the C’ 21Tr + X ‘Il, bands and from sequential one-photon absorption steps involvmg (0,O) A 2Z+ + X 2111,,2 and (1 ,O) C” 2x+ f A 2ZZ+ transitions. 2. Experimental These expenrnents were conducted in the laser ion- ization mass spectrometer described in previous pub- lications [3-6]_ Briefly, it consists of a quadrupole mass spectrometer, a flow reactor [5-71 which pro- duced the desired free radical, a computer data acqulsi- tion system, and a Nd :YAG-pumped dye laser. In the flow reactor fluorine atoms were produced from F2 m ’ NRCjNRL PosldocLoral Associate, 1983-64 ’ Experimental work performed at NRL. a microwave discharge and mixed downstream with SiH,. The product radicals effused through a small orifice mto the mass spectrometer ion source where they were irradiated with the focused (focal length = 38 mm) dye laser output. The laser generated ions were mass selected, amplified, recorded, and signal averaged with the computer. The Nd:YAG-pumped dye laser produced pulses of = 10 ns duration with a fkhrn bandwidth of EO.8 cm-l_ Dyes used in these experiments and their pulse ener@es were coumarin 440 (43046 run; 1.2-2.7 mJ), coumarin 460 (446468.5 run; 2.8-4.7 rnJ) and coumti 480 (468.5-493 run; 2.2-4.7 ITLT) in methanol solvent_ 3. ResuIis and analysis 3.1. Generation of SiF mdfcals This study began as a search for the spectrum of SiH, m which we attempted to generate SiH, by reac- ting fluorine atoms with SiH4_ No m/z 3 1 signals attrit utable to SiHg were observed over the spectral range of this study (430-490 run). At somewhat higher F2 to SiH, flow rate ratios than stoichiometric for S&I, production, strongm/z 47 signals were observed. These, 444