Oxygen Atom Kinetics in Silane-Hydrogen-Nitrous

Oxygen Atom Kinetics in Silane-Hydrogen-Nitrous Oxide Mixtures Behind Reflected Shock Waves S. Javoy1,2 , R. Mével1,2,∗ , G. Dupré1,2 Corresponding author: [email protected] 1

Institut de Combustion, Aérothermique, Réactivité et Environnement (ICARE), Centre National de la Recherche Scientifique (CNRS), Orléans 2 University of Orléans (France)

Abstract Resonance Absorption Spectroscopy has been used to study the O-atom dynamics behind reflected shock waves of highly argon diluted silane-hydrogen-nitrous oxide mixtures in the temperature range 1606-2528 K and at total pressures from 234 to 584 kPa. The absorptions at 130.5 nm of N2 O, SiH4 and Si have been taken into account to compare simulated and experimental absorption profiles. A detailed kinetic model has been also used to interpret the results and reaction pathway and sensitivity analyses have been performed to underline important elementary reactions. A comparison with the O-atom kinetic in silane-nitrous oxide and hydrogen-nitrous oxide mixtures is also proposed. keyword: Silane; Nitrous Oxide; Hydrogen; Reflected Shock Wave; Atomic Resonance Absorption Spectroscopy

1

1

Introduction

Silane is widely used in the semi-conductor manufacturing industry [1, 2, 3]. It constitutes a source of silicon for gas phase material synthesis processes. Because of silane’s high reactivity, numerous incidents occured in this industry [4]. This property also makes silane a potential additive for supersonic propulsion systems [5]. Concerning silane-nitrous oxide mixtures, some data exist in the literature. Horiguchi et al. [6] studied the flammability limits of these mixtures and found that ignition was possible from 1.90 to 87.1 mol % of silane, at room temperature and atmospheric pressure. Some kinetic studies have also been performed. Chapple-Sokol et al. [1, 2, 3], Votintsev et al. [7] and Becerra et al. [8] studied the reaction of silylene with nitrous oxide, SiH2 +N2 O=H2 SiO+N2 . Mick and Roth [9] used the Atomic Resonance Absorption Spectroscopy (ARAS) applied to Si and N atoms to examine the kinetics of silane-nitrous oxide mixtures and derived the rate constants of the Si+N2 O=SiO+N2 and Si+N2 O=SiN+NO reactions. More recently, the kinetics of O atoms have been studied by Mével et al. [10]. Although some data on silane-nitrous oxide can be found, the effect of adding hydrogen to this mixture has never been addressed. For propulsion systems, silanehydrogen-nitrous oxide mixtures can present some advantages in terms of safety compared to silane-hydrogen-oxygen mixtures since they are stable at ambient temperature and pressure conditions. Moreover, the addition of hydrogen is a well known method to limit the growth of particule in the frame of gas phase nano-particules synthesis [11, 12]. In the present study, oxygen atoms profiles in shock-heated silane-hydrogen-nitrous oxide mixtures highly diluted in argon have been studied experimentally by Atomic Resonance Absorption Spectroscopy. The absorptions by silicon atoms, silane and nitrous oxide molecules at the O-triplet emission line have been taken into account to compare simulated and experimental absorption profiles of SiH4 -H2 -N2 O-Ar mixtures. The detailed kinetic model employed for the simulations has been also used to interpret the results and to perform a comparison with the kinetics of oxygen atoms in SiH4 -N2 O and H2 -N2 O mixture. First, the materials and the methods used are described. Second, the experimental results are presented and discussed, including a comparison of the reactivity of the different systems SiH4 -N2 O, H2 -N2 O and SiH4 -H2 -N2 O.

2 2.1

Materials and methods Mixtures preparation

High purity nitrous oxide, argon and a mixture of 1 % of silane in argon from Air Liquide were employed. The partial pressure method was used to prepare the mixtures. The mixture preparation apparatus was vaccumed to less than 1.10−5 Pa with a turbo-molecular pump. The silane content was set at 5 ppmv, the hydrogen content was either 5 or 10 ppmv and the nitrous oxide content ranged from 7 to 30 ppmv at high and low temperatures, respectively. In order to check the stability of the mixtures at ambiant temperature, infrared 2

absorption spectroscopy was used. The apparatus was a Perkin Elmer Paragon 1000 Fourier Transform InfraRed spectrometer with a resolution of 5 cm−1 . The mixtures were prepared in a 15 cm long cylindrical glass cell equipped with KCl windows.

2.2

Shock-tube and optical arrangement

The shock tube used in the present study has been described in previous papers [13, 14, 15]. Briefly, the apparatus was a 78 mm internal diameter stainless-steel pressure-driven shock tube with a 5.5-m-long driven section and a 3.5-m-long driver section. A turbomolecular pump evacuated the test section to less than 2.10−4 Pa, and the typical leak-plus-outgassing rate was of the order of 2.10−6 Pa/s or less. Helium was used as driver gas, and the shock wave was initiated by the bursting of a double diaphragm. The shock wave velocity was measured by piezoelectric pressure gauges mounted flush to the inner wall. Thermodynamic conditions behind the incident and reflected shock waves were computed from the experimental incident shock velocity using the SHOCK routine [16]. The optical detection technique for measuring O atom concentration was an emission line absorption method. A microwave-excited discharge lamp that contained a flowing mixture of 1 % O2 in He maintained at a pressure of 1.4 kPa was used as light source. This lamp consisted of a 2.45-GHz microwave generator operating at 100 W power level. A vacuum ultraviolet (UV) monochromator was used to isolate the O triplet wavelength, and a solar blind photomultiplier was used to convert vacuum UV photons. The operating conditions were chosen to minimize noise and reflected power without significant loss of signal strength. The absorption measurements were made behind a reflected shock front through two thin MgF2 windows located at 10 mm from the end wall. Because the emission line shape is not known in detail, it was required to perform a calibration to link the O atom concentration to the absorption [17]. It was obtained from nitrous oxide pyrolysis experiments, which constitute the classical procedure for O atom ARAS calibration [18, 19]. Mixtures containing 2.9-29.3 ppmv of N2 O in Ar were shock-heated in the temperature range 1900-3750 K and for pressure between 170 and 310 kPa in order to obtain steadystate O concentrations. The uncertainty on the O atom mole fraction in the initial mixture is of ±1.5% or less, and the uncertainties on the reflected shock temperature and pressure are no more than ±1%. The resulting uncertainty on the O atom density behind reflected shock wave is of the order of ±5%. From the calibration, a modified Lambert-Beer law was obtained. This kind of law is often used in ARAS studies [18, 20] since it allows to extend the range of measurable concentration. It is described by the following relationship: AO = 1 − exp −3.38.10−10 ` [O]0.625

(1)

where AO is the absorption by O atoms, ` is the length of the optical path (7.8 cm) and [O] is the O atoms concentration (atom cm−3 ).

3

The Lambert-Beer law coefficients were found independent of temperature over the experimental range 1900-3740 K and were assumed to be constant over the total experimental temperature range 1606-2528 K. Our optical set-up allowed the measurement of O atom concentration from 1.1013 to 1.1014 atom cm−3 . Although the absorption coefficients of molecular species at resonance wavelengths are, in general, very much smaller than those of atoms, under certain conditions, their contribution to the absorption signal is not negligible. In the present study, the absorption of N2 O and SiH4 exerted an appreciable influence on the absorption profiles. In the same way, from some silane pyrolysis experiments at high temperatures, it was found that silicon atoms absorb at the O-triplet emission line. To take into account the contribution of the absorption by Si, SiH4 and N2 O to the total absorption monitored during the experiments with SiH4 -H2 -N2 O-Ar mixtures, the absorption cross sections of these species, determinate previously [10, 15], have been used. Finally, the total absorption Atot could be expressed by the following expression: Atot = 1 − exp(−2.56.10−17 ` [N2 O] − 6.91.10−17 ` [SiH4 ] −5.62.10−17 ` [Si] − 3.38.10−10 ` [O]0.625 )

2.3

(2)

Chemical kinetic scheme

The detailed kinetic model used was described previously in [10]. Briefly, the H2 -N2 O sub-set was taken from [15, 21]. Three modifications were brought to this sub-set: (i) the rate coefficient for the O+H2 =OH+H rate was that from [13], (ii) the reaction rate for the NO+N=>N2 +O reaction was that from [22], (iii) the N+OH=NO+H reaction was added and taken from [9]. The silane pyrolysis sub-set was that of Petersen and Crofton [23]. The reactions for the Si-H-O system were taken from the studies of Miller et al. [24], Babushok et al. [25], Zachariah and Tsang [26] and Mick [18]. The interactions between Si and SiH2 and the NyOx species came from [8, 9, 20]. The complete mechanism was composed of 448 elementary reactions and 92 chemical species. The thermodynamic data are taken from [21] for the H2 -N2 O system species, from [23] for silicon hydride species and from [24] for other silicon containing species. It is worth noting that none of the rate coefficients were adjusted. The modeling of the experimental results was performed by using the SENKIN code [27] of the CHEMKIN II package [28]. The constant volume reactor type has been chosen. First order sensitivity analysis and reaction pathway analysis were performed using this code.

3

Results and discussions

This section is devoted to the presentation and the discussion of the experimental results. First, the results about the stability of the mixtures at ambiant conditions 4

are shown. Second, the experimental and the calculated oxygen atoms absorption profils obtained in reflected shock heated SiH4 -H2 -N2 O-Ar mixtures are presented. Third, a comparison of the kinetics of O atoms in H2 -N2 O-Ar, SiH4 -H2 -N2 O-Ar and SiH4 -N2 O-Ar mixtures is made.

3.1

Stability of the mixtures

Although some studies [6] report that silane-nitrous oxide mixtures are stable at ambient temperature and atmospheric pressure, this feature was checked in the present study. Infrared absorption was used to investigate the possible evolution of SiH4 -N2 O-Ar mixtures. The presence of hydrogen was neglected since both H2 -N2 O [29] and SiH4 -H2 [18] mixtures are stable. Moreover, hydrogen can not be observed by infrared spectroscopy. Figure 1 presents an exemple of the results obtained for a rich SiH4 -N2 O-Ar mixture (equivalence ratio: Φ=2.62). The silane infrared spectrum is characterised by strong absorption bands centered around 900 and 2200 cm−1 . These two bands are attributed to the H-Si-H angle deformation and to the Si-H bond stretching, respectively [30]. The nitrous oxide infrared spectrum is characterised by strong absorption bands centered around 1200 and 2300 cm−1 . These two bands are attributed to the N-O bond stretching and to the N-N bond stretching, respectively [31]. Figure 1 clearly shows that there is no evolution of the spectrum and thus that silane-nitrous oxide mixtures are stable at ambient conditions of temperature and pressure. By extension, silane-hydrogen-nitrous oxide mixtures can also be considered as stable in these conditions.

3.2

Experimental and modeling results

The oxygen atom profils in silane-hydrogen-nitrous oxide-argon mixtures have been monitored by atomic resonance absorption spectroscopy over the temperature range 1606-2528 K and at pressure between 234 and 584 kPa. Because of the timedependant contributions of SiH4 , Si and N2 O to the absorption signal, it was preferred to present absorption profiles rather than concentration profiles. Figure 2 to Figure 5 show typical results obtained at different temperatures and pressures. At low and intermediate temperatures and low pressure (Figure 2 and Figure 3, respectively) a relatively slow increase followed by a plateau is observed. At intermediate temperature and high pressure, Figure 4, a fast increase followed by a fast decrease of the absorption signal can be seen. At high temperature and low pressure, Figure 5, a fast increase followed by a rather slow decrease is observed. Figure 2 to Figure 5 also compare the predictions of the developed kinetic scheme with the experimental absorption profiles. In order to take into account the timedependant absorption of SiH4 , Si and N2 O at 130.5 nm, simulated absorption profiles were calculated using Equation 2. It can be seen that the agreement between the experimental and the calculated absorption profiles is very satisfactory. For the 25 experiments performed in the present study, a good agreement was observed. Sensitivity and reaction pathway analysis showed that, for all the conditions studied, the kinetics of oxygen atoms is dominated by the N2 O(+M)=N2 +O(+M) and 5

O+H2 =OH+H reactions. This feature is illustrated in Figure 2, Figure 3 and Figure 5 by multiplying the rate constants of these reactions by a factor of 2 and 0.5. The N2 O(+M)=N2 +O(+M) reaction controls the initial increase of the oxygen atom concentration whereas the O+H2 =OH+H reaction dominates the consumption of O atoms. As underlined in Baulch et al. review [22], the rate constants of these two reactions have been extensively studied. The kinetic parameters used in the present study come from two recent investigations performed in our laboratory using the ARAS technique [13, 15]. These rate constants are in good agreement with the recommandations of Baulch and are known within 30 %, assuring an accurate prediction of the O-atom concentrations in SiH4 -H2 -N2 O-Ar mixtures. The O+OH=O2 +H reaction contributes significantly to the consumption of O atoms whatever are the temperature and the pressure. Its sensitivity trends to increase with the temperature increase. The rate constant of this reaction is one of the most well known of the litterature for the H2 -O2 sytem. The other important kinetic pathes are the reactions between silicon atoms and nitrous oxide: Si+N2 O=SiO+N2 and Si+N2 O=SiN+NO, especially the first one. The sensitivity of the Si+N2 O=SiO+N2 reaction reaches a maximum at intermediate temperatures and high pressure. The effect of multiplying the rate constant of this reaction by a factor of 2 and 0.5 is illustrated in Figure 4. It can be seen that the calculated profiles are only slightly modified although the normalised sensivity coeffcient of the Si+N2 O=SiO+N2 reaction is significant. At low temperature, the sensitivity coefficient of the Si+N2 O=SiO+N2 reaction is low but it can be noted that the contribution of this reaction to the nitrous oxide consumption is significant, from 30 %, at low temperatures, to 20 %, at high temperatures. The reactions between silicon atoms and nitrous oxide have been studied by Takashara et al. [32], Swearengen et al. [33] and Husain and Norris [34] but these invesgations are limited to temperatures below 350 K and do not discriminate between the different possible reaction pathes. Consequently, the only rate constants available at high temperature are those from Mick and Roth [9] who used the ARAS technique applied to Si and N atoms. They found that the formation of SiO+N2 is the preferred path compared to the formation of SiN+NO, in good agreement with the thermodynamics since the formation of SiO+N2 is ten times more exothermic than the formation of SiN+NO. The uncertainties associated with the kinetic parameters of these reactions is of 50 %.

3.3

Comparison between H2 -N2 O-Ar, SiH4 -H2 -N2 O-Ar and SiH4 -N2 O-Ar mixtures

A comparison between the kinetics of O atoms in SiH4 -N2 O-Ar, H2 -N2 O-Ar and SiH4 -H2 -N2 O-Ar mixtures has been carried out by using the kinetic model developed previously [10, 15, 29], which reproduces accurately oxygen atom profiles for all these mixtures. Figure 6 presents the O-atom profiles calculated at different temperatures and pressures for mixtures highly diluted in argon containing constant molar fractions of N2 O (XN 2O was varied only with temperature) but with (i) 10ppmv SiH4 , (ii) 10ppmv H2 or (iii) 5ppmv SiH4 and 5 ppmv H2 . At given 6

temperature, the shape of the curves is the same one, whatever the mixture: first, O atoms are more or less quickly generated (depending on the temperature) and second, a more or less fast decrease of the O concentration can be observed (depending on the temperature too). On the other hand, the O concentration ranges differ significantly in the three mixtures: O concentrations are higher with H2 , than with mixtures containing H2 and SiH4 that are themselves higher than with only SiH4 . However it can be noted that the variations decrease as the temperature increases. This might be due to additional pathways that involve silicon containing species and that consume either N2 O or O atoms. In order to investigate this feature, the rates of consumption of nitrous oxide and of oxygen atom have been calculated. Figure 7 and Figure 8 show the results of this analysis. For H2 -N2 O-Ar mixtures, nitrous oxide is almost entirely consumed by the N2 O(+M)=N2 +O(+M) reaction. For silane containing mixtures, although this reaction represents the dominant pathway for the consumption of N2 O, the Si+N2 O=Products reactions also contribute significantly. The importance of these reactions decreases as the temperature increases whereas that of the nitrous oxide decomposition increases. For the three mixtures, the consumption of oxygen atoms is distributed between the two following reactions: O+H2 =OH+H and O+OH=H+O2 . The importance of the O+OH=H+O2 reaction is lower for silane based mixtures because the consumption of OH radicals is mainly driven by the Si+OH=SiO+H reaction, especially at high temperature. Although oxygen atom profiles are not very sensitive to the value, within a factor of 2, of the Si+N2 O=SiO+N2 reaction rate constant, it can be noted that the exclusion of the Si+N2 O=Products reactions from the kinetic scheme involves a shift of the calculated oxygen atom profiles outside the confidence intervalle associated with the experimental measurement. The effect of the reactions between silicon atoms and nitrous oxide is to limit the formation of O atoms by the N2 O decomposition. This feature explains the differences between the oxygen mole fractions calculated in SiH4 -N2 O-Ar, SiH4 -H2 -N2 O-Ar and H2 -N2 O-Ar mixtures. As the temperature increases, the nitrous oxide decomposition rate increases and the influence of the Si+N2 O=Products reactions decreases. This lower influence involves a reduction of the differences between the O atom profiles in the different mixtures. At high temperature, the fast removal of nitrous oxide induces an increase of the influence of the Si+OH=SiO+H reaction. It might be advanced that this reaction would modify significantly the chemistry of OH radicals in silane based mixtures compared to mixtures without silane. However, this particular point is beyond the scope of the present study and a specific validation of the present kinetic scheme against experimental OH radical profiles is necessary.

4

Conclusion

In the present study, the kinetics of oxygen atoms in silane-hydrogen-ntirous oxideargon mixtures behind reflected shock waves have been investigated, in the range T5 =1606-2528 K and P5 =234-584 kPa, using atomic resonance absorption spectroscopy. A chemical kinetic model has been developed and validated against the present data. Sensitivity and reaction pathway analyses have shown that the kinetics

7

of O atoms were mainly controlled by the N2 O(+M)=N2 +O(+M) and O+H2 =OH+H reactions. The comparison of the oxygen atom profiles in SiH4 -N2 O-Ar, SiH4 -H2 N2 O-Ar and H2 -N2 O-Ar mixtures has demonstated the implication of the Si+N2 O=Products reactions. Acknowledgement ´ This work was partly supported by the French ”Ministère de l’Education Nationale, de l’Enseignement Supérieur et de la Recherche”. The authors acknowledge Gaëlle Fourny (University of Orléans) for her help in the preliminary modeling study.

8

References [1] J. Chapple-Sokol, C. Giunta, R. Gordon, A kinetics study of the atmospheric pressure cvd reaction of silane and nitrous oxide., Journal of the Electrochemical Society 136 (10) (1989) 2993–3003. [2] J. Chapple-Sokol, C. Giunta, R. Gordon, Kinetics of silicon oxide thin film deposition from silane and disilane with nitrous oxide., Proceedings of the Materials Research Society Symposium 105 (1988) 127–132. [3] C. Giunta, J. Chapple-Sokol, R. Gordon, Kinetic modeling of the chemical vapor deposition of silicon dioxide from silane or disilane and nitrous oxide., Journal of the Electrochemical Society 137 (10) (1990) 3237–3253. [4] T. Roigelstad, J. Mosovsky, J. Valdes, C. Lichtenwalner, Silane safety in amorphous silicon and silicon nitride operations, Tech. Rep. 94062405A-ENG, SEMATECH Technology Transfer (1994). [5] V. Golovitchev, C. Bruno, Numerical study of the ignition of silane/hydrogen mixtures., Journal of Propulsion and Power 15 (1) (1998) 92–96. [6] S. Horiguchi, Y. Urano, K. Tokuhashi, S. Kondo, Explosion hazard of silanenitrogen oxides gas mixture., Koatsu Gasu 26 (11) (1989) 840–847. [7] V. Votintsev, I. Zaslonko, V. Mikheev, V. Smirnov, Mechanism and kinetics of silane decomposition in shock waves., Kinetics and Catalysis 27 (8) (1987) 972–976. [8] R. Becerra, H. Frey, B. Mason, R. Walsh, Absolute rate constant and temperature dependence for the reaction of silylene with nitrous oxide., Chemical Physics Letters 185 (1991) 415–420. [9] H. Mick, P. Roth, High-temperature kinetics of si + n2 o., Journal of Physical Chemistry 98 (1994) 5310–5313. [10] R. Mével, S. Javoy, G. Dupré, A chemical kinetic study of the oxidation of silane by nitrous oxide, nitric oxide and oxygen, Proceedings of The Combustion Institute, In press. [11] M. Swihart, S. Girshick, Thermochemistry and kinetics of silicon hydride cluster formation during thermal decomposition of silane, Journal of Physical Chemistry B 103 (1999) 64–76. [12] M. Frenklach, L. Ting, H. Wang, M. Rabinowitz, Silicon particle formation in pyrolysis of silane and disilane, Israel Journal of Chemistry 36 (1996) 293–303. [13] S. Javoy, V. Naudet, S. Abid, C. Paillard, Rate constant for the reaction of O with H2 at high temperature by resonance absorption measurements of O atoms, International Journal of Chemical Kinetics 32 (2000) 686–695.

9

[14] S. Javoy, V. V. Naudet, S. Abid, C. Paillard, Elementary reaction kinetics studies of interest in H2 supersonic combustion chemistry, Experimental Thermal and Fluid Science 27 (4) (2003) 371–377. [15] S. Javoy, R. Mével, C.-E. Paillard, A study of N2 O decomposition rate constant at high temperature: Application to the reduction of nitrous oxide by hydrogen, International Journal of Chemical Kinetics 41 (5) (2009) 357–375. [16] R. Mitchell, R. Kee, Shock: a general purpose computer code for predicting chemical kinetic behavior behind incident and reflected shocks, Tech. Rep. 828205, Sandia National Laboratories (1982). [17] V. Naudet, S. Javoy, C.-E. Paillard, A high temperature chemical kinetics study of the reaction: Oh+ar =h+o+ar by atomic resonance absorption spectrophotometry, Combustion Science and Technology 164 (2001) 113–128. [18] H.-J. Mick, Untersuchungen zur kinetic elementarer reaktionen in silanereaktionssystemen basierend auf atom- und molek¨ ulspektroskopischen messungen, Ph.D. thesis, University of Duisburg (1995). [19] K. Takahashi, A. Giesen, P. Roth, High temperature reaction of sn(3 p0 ) atoms with o2 based on sn and o-concentration measurements., Physical Chemistry Chemical Physics 3 (2001) 4296–4300. [20] H. Mick, H. Matsui, P. Roth, High-temperature kinetics of si atom oxidation by no based on si, n, and o atom measurements., Journal of Physical Chemistry 97 (1993) 6839–6842. [21] R. Mével, S. Javoy, F. Lafosse, N. Chaumeix, G. Dupré, C.-E. Paillard, Hydrogen-nitrous oxide delay time: shock tube experimental study and kinetic modelling, Proceedings of The Combustion Institute 32 (2009) 359–366. [22] D. L. Baulch, C. T. Bowman, C. J. Cobos, R. A. Cox, T. Just, J. A. Kerr, M. J. Pilling, D. Stocker, J. Troe, W. Tsang, R. W. Walker, J. Warnatz, Evaluated kinetic data for combustion modeling: supplement II, Journal of Physical and Chemical Reference Data 34 (2005) 757–1397. [23] E. Petersen, M. Crofton, Measurements of high-temperature silane pyrolysis using sih4 ir emission and sih2 laser absorption., Journal of Physical Chemistry A 107 (2003) 10988–10995. [24] T. Miller, M. Wooldridge, J. Bozzelli, Computational modelling of the sih3 + o2 reaction and silane combustion., Combustion and Flame 137 (2004) 73–92. [25] V. Babushok, W. Tsang, D. Burgess, M. Zachariah, Numerical study of low- and high-temperature silane combustion., Proceedings of The Combustion Institute 27 (1998) 2431–2439. [26] M. Zachariah, W. Tsang, Theoretical calculation of thermochemistry, energetics, and kinetics of high-temperature six hy oz reactions., Journal of Physical Chemistry 99 (1995) 5308–5318. 10

[27] A. Lutz, R. Kee, A. Miller, Senkin : a fortran program for predicting homogeneous gas phase chemical kinetics with sensitivity analysis, Tech. Rep. Sand87-8248, Sandia International Laboratories (1992). [28] R. Kee, F. Rupley, J. Miller, Chemkin ii : A fortran chemical kinetics package for the analysis of gas phase chemical kinetics, Tech. Rep. Sand89-8009B, Sandia International Laboratories (1993). [29] R. Mével, Etude de mécanismes cinétiques et des propriétés explosives des mélanges hydrogène-protoxyde d’azote et silane-protoxyde d’azote. Application a` la sécurité industrielle, Ph.D. thesis, Université d’Orléans (2009). [30] T. Shimanouchi, Tables of Molecular Vibrational Frequencies Consolidated, National Bureau of Standards, 1972. [31] S. Kudoh, K. Onoda, M. Takayanagi, M. Nakata, N2 O clusters in a supersonic jet studied by matrix-isolation infrared spectroscopy and density functional theory calculation, Journal of Molecular Structure 524 (2000) 61-68. [32] A. Takahara, A. Tezaki, H. Matsui, Production of sio and si(3 p) atom in the reaction of silane with o(1 d), Journal of Physical Chemistry A 103 (1999) 11315– 11320. [33] P. Swearengen, S. Davis, T. Niemczyk, Reaction rate studies of atomic germanium (3 p0,10 ) and silicon (3 pj ) with various oxidizers., Chemical Physics Letters 55 (1978) 274–279. [34] D. Husain, P. Norris, Kinetic study of ground state silicon atoms, si[3p2 (3 pj)], by atomic absorption spectroscopy., Journal of Chemical Society, Faraday Transactions 2 74 (1978) 93–105.

11

Figure captions 1

2

3

4

5

6

7

8

Evolution of the infrared absorption spectrum of silane-nitrous oxideargon mixtures. Φ = 2.62 ; XAr = 0.994 ; T = 295 K ; P = 106.6 kPa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Example of experimental and calculated absorption profiles obtained at 1606 K and 297 kPa for a SiH4 -H2 -N2 O-Ar mixture. XSiH4 = 5 ppmv ; XH2 = 9.9 ppmv ; XN 2O = 32.4 ppmv . . . . . . . . . . . . Example of experimental and calculated absorption profiles obtained at 1903 K and 272 kPa for a SiH4 -H2 -N2 O-Ar mixture. XSiH4 = 4.9 ppmv ; XH2 = 5 ppmv ; XN 2O = 20.7 ppmv . . . . . . . . . . . . . Example of experimental and calculated absorption profiles obtained at 2189 K and 464 kPa for a SiH4 -H2 -N2 O-Ar mixture. XSiH4 = 5 ppmv ; XH2 = 5 ppmv ; XN 2O = 6.6 ppmv . . . . . . . . . . . . . . Example of experimental and calculated absorption profiles obtained at 2528 K and 234 kPa for a SiH4 -H2 -N2 O-Ar mixture. XSiH4 = 5 ppmv ; XH2 = 5 ppmv ; XN 2O = 12.5 ppmv . . . . . . . . . . . . . Comparison of simulated O atom profiles for SiH4 -N2 O-Ar, SiH4 -H2 N2 O-Ar and H2 -N2 O-Ar mixtures. Plain lines: H2 -N2 O-Ar (10 ppmv H2 ), Dashed lines: SiH4 -H2 -N2 O-Ar (5 ppmv H2 and 5 ppmv SiH4 ), Dashed-doted lines: SiH4 -N2 O-Ar (10 ppmv SiH4 ). At T5 = 1800 K and P5 = 507 kPa: XN 2O = 30 ppmv, at T5 = 2200 K and P5 = 355 kPa: XN 2O = 20 ppmv, at T5 = 2500 K and P5 = 253 kPa: XN 2O = 10 ppmv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Evolution of the importance of N2 O consumption pathways as a function of temperature for SiH4 -N2 O-Ar, SiH4 -H2 -N2 O-Ar and H2 -N2 OAr mixtures. Conditions: (i) H2 -N2 O-Ar (10 ppmv H2 ), (ii) SiH4 -H2 N2 O-Ar (5 ppmv H2 and 5 ppmv SiH4 ), (iii) SiH4 -N2 O-Ar (10 ppmv SiH4 ). At T5 = 1800 K and P5 = 507 kPa: XN 2O = 30 ppmv, at T5 = 2200 K and P5 = 355 kPa: XN 2O = 20 ppmv, at T5 = 2500 K and P5 = 253 kPa: XN 2O = 10 ppmv . . . . . . . . . . . . . . . . . . . Evolution of the importance of O consumption pathways as a function of temperature for SiH4 -N2 O-Ar, SiH4 -H2 -N2 O-Ar and H2 -N2 O-Ar mixtures. Conditions: (i) H2 -N2 O-Ar (10 ppmv H2 ), (ii) SiH4 -H2 N2 O-Ar (5 ppmv H2 and 5 ppmv SiH4 ), (iii) SiH4 -N2 O-Ar (10 ppmv SiH4 ). At T5 = 1800 K and P5 = 507 kPa: XN 2O = 30 ppmv, at T5 = 2200 K and P5 = 355 kPa: XN 2O = 20 ppmv, at T5 = 2500 K and P5 = 253 kPa: XN 2O = 10 ppmv . . . . . . . . . . . . . . . . . . .

12

. 13

. 14

. 15

. 16

. 17

. 18

. 19

. 20

t = 0 m in

T ran sm iss io n (A .U .)

N -O stretch in g

N -N s tre tc h in g

S i-H s tretch in g

H -S i-H d efo rm a tio n

t = 63 m in

t = 1 19 m in P = 1 06 .6 kP a X A r = 0 .9 94 T = 295 K Φ = 2 .62 3000

2000

1000

W a v e n u m b er (cm -1 ) Figure 1

13

80

2 x k N 2 O (+ M )= N 2 + O (+ M )

A b so rp tio n (% )

60

40 0 .5 x k N 2 O (+ M )= N 2 + O (+ M ) X N O = 32 .4 p p m v 2 X S iH = 5 p p m v

20

4

X H 2 = 9 .9 p p m v P 5 = 2 9 7 kP a T 5 = 1 6 06 K

0 0

400

800 T im e (µs ) Figure 2

14

1200

1600

100 2 x k N 2 O (+ M )= N 2 + O (+ M )


80

60 0 .5 x k N 2 O (+ M )= N 2 + O (+ M )

40 X N 2 O = 20 .7 p p m v X S iH 4 = 4.9 p p m v XH2 = 5 ppm v

20

P5 = 272 kPa T 5 = 1 90 3 K

0 0

400


15

1200

1600

80

0 .5 x k S i+ N 2 O = S iO + N 2

X N O = 6 .6 p p m v 2 X S iH = 5 p p m v 4

XH = 5 ppm v 2

P 5 = 46 4 kP a


60

T5 = 2189 K

40

20 2 x k S i+ N 2 O = S iO + N 2

0 0

400


16

1200

1600

80 0 .5 x k O + H 2 = O H + H


60

40 2 x k O + H 2= O H + H X N 2 O = 12 .5 p p m v X S iH 4 = 5 p p m v XH = 5 ppm v 2 P 5 = 23 4 k P a

20

T 5 = 252 8 K

0 0

400

800 T im e (µs )

Figure 5

17

1200

[O] (atom/cm3)

3E+014

2E+014

1E+014

P5 = 507 kPa T5 = 1800 K 0 0

400

800

1200

1600

2000

2E+014

P5 = 355 kPa T5 = 2200 K

[O] (atom/cm3)

1 .6 E + 0 1 4

1 .2 E + 0 1 4

8E+013

4E+013

0 0

400

800

1200

[O] (atom/cm3)

8E+013

P5 = 253 kPa T5 = 2500 K

6E+013

SiH4-H2-N2O-Ar SiH4-N2O-Ar H2-N2O-Ar

4E+013

2E+013

0 0

400

800

time (µs)

Figure 6

18

1200

20

40

1800

19

Figure 7 2200 Temperature (K)

0 2500

H 2 -N 2 O mixture

SiH 4 -H 2 -N 2 O mixture

SiH 4 -N 2 O mixture

H 2 -N 2 O mixture



H 2 -N 2 O mixture



Contribution to N2O consumption (%)

Contribution of Si+N2O=Products

Contribution of N2O(+M)=N2+O(+M)

Contribution of other reactions

100

80

60

Contribution to O consumption (%)

80

60

1800

20

Figure 8 2200 Temperature (K)

40

20

0 2500

H 2 -N 2 O mixture



H 2 -N 2 O mixture



H 2 -N 2 O mixture



Contribution of O+OH=H+O2

Contribution of O+H2=OH+H

Contribution of other reactions

100