Mgh Maarten Boogaarts

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

Cavity ring down absorption spectroscopy is applied for the detection of Si and SiH radicals in a remote Ar-H2-SiH4 plasma used for high rate deposition of device quality hydrogenated amorphous silicon (a-Si:H). The formation and loss mechanisms of SiH in the plasma are investigated and the relevant plasma chemistry is discussed using a simple one-dimensional model. From the rotational temperature of SiH typical gas temperatures of ∼1500 K are deduced for the plasma, whereas total ground state densities in the range of 1015–1016 m−3 for Si and 1016–1017 m−3 for SiH are observed. It is demonstrated that both Si and SiH have only a minor contribution to a-Si:H film growth of ∼0.2% and ∼2%, respectively. From the reaction mechanisms in combination with optical emission spectroscopy data, it is concluded that Si and SiH radicals initiate the formation of hydrogen deficient polysilane radicals. In this respect, Si and SiH can still have an important effect on the a-Si:H film quality under certain circumstances.

DETECTION OF CH IN AN EXPANDING ARGON/ACETYLENE PLASMA USING CAVITY RING DOWN ABSORPTION SPECTROSCOPY

Abstract Cavity ring down (CRD) absorption spectroscopy is used to measure the methylidyne (CH) radical in an Ar/C 2 H 2 plasma. The rotational spectrum of the A 2 Δ (v′=0) ← X 2 Π (v′′=0) transition around 430 nm is recorded to determine the total CH ground state density, both as a function of the current through the arc producing the low-pressure Ar plasma and as a function of the injected acetylene flow. Total ground state densities between 5×10 15 and 8×10 16 m −3 are detected. The trends show that the methylidyne radical plays a minor role in the growing mechanism of hydrogenated amorphous carbon films and is predominantly formed in the charge exchange/dissociative recombination channel starting from the C 2 H radical.

Cavity ring down detection of SiH3 in a remote SiH4 plasma and comparison with model calculations and mass spectrometry

Spatially resolved SiH3 measurements are performed by cavity ring down spectroscopy on the SiH3 A2 A1←X2 A1 transition at 217 nm in a remote Ar–H2–SiH4 plasma used for high rate deposition of hydrogenated amorphous silicon. The obtained densities of SiH3 and its axial and radial distribution in the cylindrical deposition reactor are compared with simulations by a two-dimensional axisymmetric fluid dynamics model. The model, in which only three basic chemical reactions are taken into account, shows fairly good agreement with the experimental results and the plasma and surface processes as well as transport phenomena in the plasma are discussed. Furthermore, the SiH3 density determined by cavity ring down spectroscopy is in good agreement with the SiH3 density as obtained by threshold ionization mass spectrometry.

Improvement of hydrogenated amorphous silicon properties with increasing contribution of SiH3 to film growth

From cavity ring down spectroscopy and threshold ionization mass spectrometry measurements in a remote Ar–H2–SiH4 plasma it is clearly demonstrated that the properties of hydrogenated amorphous silicon (a-Si:H) strongly improve with increasing contribution of SiH3 to film growth. The measurements corroborate the proposed dissociation reactions of SiH4 for different plasma settings and it is shown that film growth is by far dominated by SiH3 under conditions for which solar grade quality a-Si:H at deposition rates up to 10 nm/s has previously been reported.

Time-resolved cavity ring-down spectroscopic study of the gas phase and surface loss rates of Si and SiH3 plasma radicals

Abstract Time-resolved cavity ring-down spectroscopy (CRDS) has been applied to determine gas phase and surface loss rates of Si and SiH 3 radicals during plasma deposition of hydrogenated amorphous silicon. This has been done by monitoring the temporal decay of the radicals densities as initiated by a minor periodic modulation applied to a remote SiH 4 plasma. From pressure dependence, it is shown that Si is reactive with SiH 4 [(1.4±0.6)×10 −16 m −3 s −1 reaction rate constant], while SiH 3 is unreactive in the gas phase. A surface reaction probability β of 0.9 β ⩽1 and β =0.30±0.05 has been obtained for Si and SiH 3 , respectively.

Quantitative two-photon laser-induced fluorescence measurements of atomic hydrogen densities, temperatures, and velocities in an expanding thermal plasma

We report on quantitative, spatially resolved density, temperature, and velocity measurements on ground-state atomic hydrogen in an expanding thermal Ar–H plasma using two-photon excitation laser-induced fluorescence (LIF). The method’s diagnostic value for application in this plasma is assessed by identifying and evaluating the possibly disturbing factors on the interpretation of the LIF signal in terms of density, temperature, and velocity. In order to obtain quantitative density numbers, the LIF setup is calibrated for H measurements using two different methods. A commonly applied calibration method, in which the LIF signal from a, by titration, known amount of H generated by a flow-tube reactor is used as a reference, is compared to a rather new calibration method, in which the H density in the plasma jet is derived from a measurement of the two-photon LIF signal generated from krypton at a well-known pressure, using a known Kr to H detection sensitivity ratio. The two methods yield nearly the same re...

Cavity ring down detection of SiH3 on the broadband à 2A1′ ←X 2A1 transition in a remote Ar–H2–SiH4 plasma

Abstract Here we report on the use of the cavity ring down (CRD) technique for the detection of the silyl radical SiH 3 on the broadband A 2 A 1 ′ ← X 2 A 1 transition around 215 nm. SiH 3 has been detected in a remote Ar–H 2 –SiH 4 plasma during hydrogenated amorphous silicon (a-Si:H) thin film growth. The measurements demonstrate the capability of CRD to measure small broadband absorptions in the deep UV in the hostile environment of a deposition plasma. The SiH 3 absorption shows an expected dependence on the SiH 4 precursor flow and correlates well with the a-Si:H growth rate. The observed absorptions correspond with SiH 3 densities in the range 2–13 × 10 18 m −3 , which is at least two orders of magnitude above the estimated SiH 3 detection limit.

Plasma chemistry of an expanding Ar/C2H2 plasma used for fast deposition of a-C:H

Mass spectrometric measurements in combination with Langmuir probe measurements reveal that the plasma chemistry of an expanding Ar/C2H2 is dominated by argon-ion-induced dissociation of the precursor gas. Under high arc current conditions complete depletion of acetylene is observed, indicating an efficient consumption of the injected acetylene. A clear correlation between the ion fluence emanating from the arc determined from modeling the mass spectrometry results and Langmuir probe measurements is observed. First measurements by means of cavity ring down and optical emission spectroscopy of the products of the dissociation of acetylene indicate that the dominant dissociation channel is C2H and H.

Relation between growth precursors and film properties for plasma deposition of a-Si:H at rates up to 100 Å/s

From investigations on the SiH3 and SiH radical density and the surface reaction probability in a remote Ar-H2-SiH4 plasma, it is unambiguously demonstrated that the a-Si:H film quality improves significantly with increasing contribution of SiH3 and decreasing contribution of very reactive (poly)silane radicals. Device quality a-Si:H is obtained at deposition rates up to 100 A/s for conditions where film growth is governed by SiH3 (contribution ~90%) and where SiH has only a minor contribution (~2%). Furthermore, for SiH3 dominated film growth the effect of the deposition rate on the a-Si:H film properties with respect to the substrate temperature is discussed.

Transport of neutral atomic hydrogen in a supersonic plasma jet

ABSTRACT: In a supersonically expanding plasma jet created by a cascaded arc from an Ar‐H2 mixture, spatially resolved densities, temperatures, and velocities of ground state atomic hydrogen are obtained by applying two‐photon excitation laser induced fluorescence. The axial velocity profile of H indicates a strong coupling between Ar and H atoms and it can be fully described in terms of a supersonic expansion model. However, whereas H atoms temperature profiles along the jet centerline clearly reveal the presence of a normal shock front, the atomic hydrogen density profiles do not. From the absence of a density jump across the normal shock front, it is conclude that the atomic hydrogen flux in the axial direction is not conserved. There are several indications that the coupling between H and Ar atoms is lost in the course of the expansion and that hydrogen atoms can escape the supersonic domain by a scattering process due to their large mean free path.