Silanic hydrogen

FIG. 8. (a) The total and partial pressures p and (b) the partial pressure ratio of silane and hydrogen in a silane-hydrogen mixture, at different flow ratios The total flow rate is 30 seem. (Adapted from E. A. G. Hamers. Ph.D. Thesis. Universiteit Utrecht. Utrecht, the Netherlands. 1998. with permission.)... 

This section treats the plasma physics and plasma chemistry of the typical silane-hydrogen RF discharge, with occasional examples that employ a somewhat higher excitation frequency. Electrical characterization of the discharge is followed by an analysis of the silane chemistry. An appropriate set of gas phase species is presented, which are then used in the modeling of the plasma. A comparison is made between modeling results and experimental work in ASTER. Extension to 2D modeling is presented as well. 

In a silane-hydrogen discharge the feedstock gases SiHa and H2 take part in all the processes that occur. A large number of reactions have been proposed (see e.g. Kushner [190]). Nienhuis et al. [191] have performed a sensitivity analysis in their self-consistent fluid model, from which a minimum set of reactions have been extracted for a typical low-pressure RF discharge. Tables II and III list these reactions. They will be used in the plasma models described in subsequent sections. The review articles on silane chemistry by Perrin et al. [192] and on hydrogen by Phelps [193] and Tawara et al. [194] have been used. The electron collision data are compiled in Figure 13 [189]. 

Nienhuis et al. [189, 191] have developed a self-consistent fluid model that describes the electron kinetics, the silane-hydrogen chemistry, and the deposition... 

The ID fluid discharge model has been applied to the ASTER deposition system (see Section 1.2.4). The deposition reactor has an inner volume of 10 1 and an inner diameter of 20 cm. The upper electrode is grounded (see Fig. 4a), and the powered electrode is located 2.7 cm lower. Other typical silane-hydrogen discharge parameters are summarized in Table IV. 

Pressure variation. In Figure 17 are shown the effects of total pressure on the relative pressures (i.e., the ratio of the partial pressure to the total pressure) of silane, hydrogen, and disilane (Fig. 17a) and on the deposition rate (Fig. 17b). The RF frequency is 50 MHz, and the plasma power is 5 W. The relative pressure of hydrogen slowly increases, and the relative pressure of silane slowly decreases, both in model as well as in experiment. This is caused by an increase in silane depletion at higher total pressures, which results from a higher power dissipation... 

As a first attempt to modify the code to be able to run simulations on SiH4-H2 discharges, a hybrid PlC/MC-fluid code was developed [264, 265]. It turned out in the simulations of the silane-hydrogen discharge that the PIC/MC method is computationally too expensive to allow for extensive parameter scans. The hybrid code combines the PIC/MC method and the fluid method. The electrons in the discharge were handled by the fluid method, and the ions by the PIC/MC method. In this way a large gain in computational effort is achieved, whereas kinetic information of the ions is still obtained. 

Simulation of RF Discharges in Silane-Hydrogen Mixtures with the Hybrid Model... 

In order to relate material properties with plasma properties, several plasma diagnostic techniques are used. The main techniques for the characterization of silane-hydrogen deposition plasmas are optical spectroscopy, electrostatic probes, mass spectrometry, and ellipsometry [117, 286]. Optical emission spectroscopy (OES) is a noninvasive technique and has been developed for identification of Si, SiH, Si+, and species in the plasma. Active spectroscopy, such as laser induced fluorescence (LIF), also allows for the detection of radicals in the plasma. Mass spectrometry enables the study of ion and radical chemistry in the discharge, either ex situ or in situ. The Langmuir probe technique is simple and very suitable for measuring plasma characteristics in nonreactive plasmas. In case of silane plasma it can be used, but it is difficult. Ellipsometry is used to follow the deposition process in situ. 

The partial pressures of the stable neutral molecules in the discharge (silane, hydrogen, disilane, trisilane) can be measured by a quadrupole mass spectrometer (QMS). The QMS usually is mounted in a differentially pumped chamber, which is connected to the reactor via a small extraction port [286]. In the ASTER system a QMS is mounted on the reactor that is used for intrinsic material deposition. The QMS background pressure (after proper bake-out) is between 10 and 10 mbar. The controllable diameter in the extraction port is adjusted so that during discharge operation the background pressure never exceeds 10"" mbar. 

Sheath Properties of an Argon-Silane and Two Silane-Hydrogen Discharges"... 

The increase in the deposition rate rj (Fig. 63d) corresponds to the increase in the ion flux (Fig. 63c) the fraction of arriving ions per deposited atom, / ,, is constant at about 0.25. Such observations have also been reported by Heintze and Zedlitz [236], who furthermore suggested that the deposition rate may well be controlled by tbe ion flux. The kinetic ion energy per deposited atom, max, is also constant and amounts to about 5 eV. As was shown in Section 1.6.2.3, the material quality as reflected in the refractive index 2 eV (Fig. 63e) and the microstructure parameter R (Fig. 63f) is good 2 cv is around 4.25, and R is low (<0.1). The depletion of the silane stays constant at a value of 4.0 0.4 seem in this frequency range. The partial pressures of silane, hydrogen, disilane (1.3 x 10 - mbar), and trisilane (2 x 10 mbar) in the plasma are also independent of frequency. Similar... 

Another alternative for conversion of diols to alkenes is the use of the Barton radical fragmentation conditions (see Section 5.5) with a silane hydrogen atom donor.299... 

Multifunctional poly(dimethylsiloxane) (PDMS) networks were prepared via the addition of a silane hydrogen on poly(methyl-hydrogensiloxanes) (PMHS) to vinyl terminated linear PDMS... 

Since they have both a vacant low-energy orbital and a lone pair, silylenes might behave either as electron pair donors or acceptors. There is scant evidence for silylenes reacting as Lewis bases, but complexes of silylenes acting as Lewis acids are now well-established these complexes can also be described as silaylides, R2>Si —B+262. Trinquier has calculated that even SiLL should form a weak complex with 112S i , in which a silane hydrogen binds to the p-orbital of the silylene263. 

Fig. 2.5. Diagram showing the typical deposition conditions for microcrystalline silicon and a-Si H films deposited from silane/hydrogen mixtures at different rf power.

The method is also applicable to siloxanes containing silanic hydrogen. The gas chromatography of siloxanes associated with chlorosilanes and methyl chlorosilanes has been discussed404. 

Many reactions are known for which addition of silane is accompanied by the elimination of a small molecule (H2, hydrocarbon, a different silane, hydrogen halide). Examples of such reactions are shown in equations 6-10 (Cp = r/5-C5Me5)18"22. Generally these reactions can be viewed as proceeding through successive oxidative addition and reductive elimination steps (or vice versa). 

Polymers that contain Si—H groups show the usual reactivity of the silane hydrogen, e.g., addition of olefins with H2PtClg catalysis. Chloromethylation of phenylmethyl-polysilane takes place ... 

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