A modified molecular beam instrument for the imaging of radicals interacting with surfaces during plasma processing

Abstract

Dissociative chemisorption of CH 4 on a cesiated Pt (111) A new instrument employing molecular beam techniques and laser induced fluorescence ͑LIF͒ for measuring the reactivity of gas phase radicals at the surface of a depositing film has been designed and characterized. The instrument uses an inductively coupled plasma source to create a molecular beam containing essentially all plasma species. A tunable excimer pumped dye laser is used to excite a single species in this complex molecular beam. LIF signals are imaged onto a gated, intensified charge coupled device ͑ICCD͒ to provide spatial resolution. ICCD images depict the fluorescence from molecules both in the molecular beam and scattering from the surface of a depositing film. Data collected with and without a substrate in the path of the molecular beam provide information about the surface reactivity of the species of interest. Here, we report the first measurements using the third generation imaging of radicals interacting with surfaces apparatus. We have measured the surface reactivity of SiH molecules formed in a 100% SiH 4 plasma during deposition of an amorphous hydrogenated silicon film. On a 300 K Si ͑100͒ substrate, the reactivity of SiH is near unity. The substrate temperature dependence ͑300-673 K͒ of the reactivity is also reported. In addition, reactivity measurements for OH molecules formed in a water plasma are presented. In contrast to the SiH molecule, the reactivity of OH radicals is 0.55Ϯ0.05 on the surface of a Si ͑100͒ substrate.

On the importance of ions and ion-molecule reactions to plasma-surface interface reactions

“…To extract the surface reactivity of the radicals, the numerical simulations described previously are used to model the cross sectional data [17,21]. Briefly, the spatial distribution of the radical number density along the laser beam is calculated for radicals in the molecular beam and for those scattered at the surface based on the known geometry of the experiment.…”

“…The IRIS apparatus has been described in detail previously [17]. In a typical IRIS experiment, an inductivelycoupled plasma (13.56 MHz) is created in a glass reactor, and the plasma is expanded into a doubledifferentially pumped high-vacuum chamber.…”

“…Characterization of gas-phase plasma species and gas-surface interactions during plasma processing can be achieved with our Imaging of Radicals Interacting with Surfaces (IRIS) technique [17]. This method combines molecular beam and plasma technologies with spatially-resolved laser-induced fluorescence (LIF) to measure radical-surface interactions.…”

From Carbon Nanostructures to New Photoluminescence Sources: An Overview of New Perspectives and Emerging Applications of Low‐Pressure PECVD

“…Experiments using space-and time-resolved, laser-induced fluorescence (LIF) and absolute calibration techniques [48,49] have established that CF and CF 2 radicals are produced essentially at the surfaces, and that the actual film precursors are oligomers of the C x F y (CF 2 ) n type formed in gas-phase polymerization reactions of the relatively abundant CF 2 radicals. The production of CF 2 at the surface of the forming FC films, and the low sticking probability of the radical, were also observed by Fisher and co-workers, [50] who conducted detailed experiments on various plasma precursors using the "imaging of radicals interacting with surfaces" (IRIS) technique, [51] which combines molecular beams and LIF imaging methods. The enhancement in CF 2 production through ion bombardment has also been investigated by this group.…”

Cavity ring down study of the densities and kinetics of Si and SiH in a remote Ar-H2-SiH4 plasma

“…27 For SiH sϭ␤ϭϳ0.95 44,45 and for Si it is generally assumed that sϭ␤ϭϳ1 on the basis of its hydrogen deficiency. 1,46 We note that the uncertainty in the density but also the uncertainty in the other parameters in Eq.…”