Thermochemical Properties of Halides and Halohydrides of Silicon and Carbon

Abstract

Atomization energies, enthalpies of formation, entropies as well as heat capacities of the SiH n X m and CH n X m systems, with X being F, Cl and Br, have been studied using quantum chemical calculations. The Gaussian-4 theory (G4) and Weizman-1 theory as modified by Barnes et al. 2009 (W1RO) have been applied in the calculations of the electronic, zero point and thermal energies. The effects of low-lying electronically excited states due to spin orbit coupling were included for all atoms and diatomic species by mean of the electronic partition functions derived from the experimental or computational energy splittings. The atomization energies, enthalpies of formation, entropies and heat capacities derived from both methods were observed to be reliable. The thermochemical properties in the temperature range of 298-2500 K are provided in the form of 7-coefficient NASA polynomials. © The Author Silicon carbide (SiC) is an attractive material for power electronics. The characteristics of having wide bandgap, high thermal conductivity, high blocking voltage and switching frequencies have made it superior for applications at high temperatures, frequencies and voltages.1 To this end, it is vital to achieve high material quality as well as manufacturing process reliability and efficiency. In chemical vapor deposition (CVD), a widely used fabrication method for SiC layers, this means suppressing the formation of Si clusters and parasitic depositions which are known to introduce defects and degrade the growing layers, along with shortening the lifetime of reactor components. 2-4Halogenated gases have been utilized to reduce the cluster formation by breaking the Si-Si bonds in the clusters and forming the stronger Si-halogen bonds and consequently introduce a new parameter into the process, namely the halogen/Si ratio. This ratio has shown impacts on not only the cluster formation and parasitic growth, but also on the growth rates as well as defect formations. 4,5 In complex processes such as CVD, computational modeling has become essential in research as well as process development and design. Modeling accuracy and correctness depend crucially on the quality of the kinetics and thermochemistry data input. Thermochemistry data of some halides and halohydrides of Si and C are provided in databases, 6-8 review, 9 as well as experimental [10][11][12][13][14][15][16] and theoretical studies.17-32 Nevertheless, inconsistency derived from various means of achieving data along with many data mismatches have rendered it far from complete. Here we present thermochemical properties from quantum chemical calculations of a complete set of halides and halohydrides of Si and C, namely SiX n H m and CX n H m with X = F, Cl and Br, and n+m ≤4, covering the temperature range of 298-2500 K. The study range accommodates applications such as CVD process, surface etching of semiconductors, combustion, as well as fundamental studies. The quantum chemistry composite methods of Gaussian-4 theory (G4) 33 are utilized and compared to the Weizmann...

Silicon Chemistry in Fluorinated Chemical Vapor Deposition of Silicon Carbide

“…The whole package was then placed in a quartz tube. SiC substrates of 4H Si-face 4° off-cut in the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) direction, 16×16 mm 2 in size, were placed at certain positions along the center line of the susceptor bottom. For the experiments, the temperatures were 1600 °C and 1650 °C, the pressure was 100 mbar and the carrier gas flow was 25 standard l/min (SLM) as well as 37.5 SLM where explicitly written.…”

“…Here, we have allowed in total 153 different species to form, with their thermochemical properties taken from recent and updated literature sources. The set of allowed species include hydrocarbons and silicon hydrides with up to five carbon or silicon atoms, organosilicon species with one and two silicon atoms and up to four carbon atoms, pure carbon and silicon molecules from C to C 6 and Si to Si 6 , and all Si x C y where 2 ≤ x + y ≤ 6, as well as the complete sets of the SiH n F m and CH n F m molecules ( n + m ≤ 4) . No condensed phases were allowed to form, a common approach for probing the gas-phase composition before it reaches the substrate, but the larger Si and Si–C molecules (such as Si 6 or Si 5 C) could be thought of as embryos to solid particles in the gas.…”

Refining the thermochemical properties of CF, SiF, and their cations by combining photoelectron spectroscopy, quantum chemical calculations, and the Active Thermochemical Tables approach

“…In fact, while in the case of CF and CF + the situation is relatively benign, there being available thermochemical values for CF that arguably appear reliable, things are veritably more complicated in the case of SiF and SiF + . Namely, the values for the enthalpy of formation of SiF available from the literature 24,25,29,69,71,77–88 encompass a spectacularly wide range, differing on the extremes by more than 16 kcal mol −1 , as demonstrated in Table 3. In principle, one might venture assuming that the values reported from the three most accurate electronic structure approaches 71,81,82 are likely the most reliable.…”

“…In fact, while in the case of CF and CF + the situation is relatively benign, there being available thermochemical values for CF that arguably appear reliable, things are veritably more complicated in the case of SiF and SiF + . Namely, the values for the enthalpy of formation of SiF available from the literature 24,25,29,69,71,[77][78][79][80][81][82][83][84][85][86][87][88] encompass a spectacularly wide range, differing on the extremes by more than 16 kcal mol À1 , Fig. 6 Energies of the lowest vibrational levels of the electronic ground state of SiF + with respect to its v + = 0 level as a function of…”

A Quantum Chemical Exploration of SiC Chemical Vapor Deposition

“…For this to be reliable it is important to include all important species including the short-lived radicals where thermodynamic properties are usually not available in the commonly used databases. Quantum chemical calculations such as ab initio, DFT and their composites are great tools to derive such properties, especially for short-lived species which are hard to measure experimentally [55][56][57] .…”