Addition Of SiF4 Research Articles

Activation of Strong Boron-Fluorine and Silicon-Fluorine σ-Bonds: Theoretical Understanding and Prediction

The oxidative addition of BF3 to a platinum(0) bis(phosphine) complex [Pt(PMe3)2] (1) was investigated by density functional calculations. Both the cis and trans pathways for the oxidative addition of BF3 to 1 are endergonic (ΔG°=26.8 and 35.7 kcal mol(-1), respectively) and require large Gibbs activation energies (ΔG°(≠)=56.3 and 38.9 kcal mol(-1), respectively). A second borane plays crucial roles in accelerating the activation; the trans oxidative addition of BF3 to 1 in the presence of a second BF3 molecule occurs with ΔG°(≠) and ΔG° values of 10.1 and -4.7 kcal mol(-1), respectively. ΔG°(≠) becomes very small and ΔG° becomes negative. A charge transfer (CT), F→BF3, occurs from the dissociating fluoride to the second non-coordinated BF3. This CT interaction stabilizes both the transition state and the product. The B-F σ-bond cleavage of BF2Ar(F) (Ar(F)=3,5-bis(trifluoromethyl)phenyl) and the B-Cl σ-bond cleavage of BCl3 by 1 are accelerated by the participation of the second borane. The calculations predict that trans oxidative addition of SiF4 to 1 easily occurs in the presence of a second SiF4 molecule via the formation of a hypervalent Si species.

Epitaxial growth of graphene on SiC by Si selective etching using SiF4 in an inert ambient

Epitaxial graphene growth on SiC by Si selective etching using tetrafluorosilane (SiF4) is introduced, where SiF4 in Ar ambient selectively etches Si from the SiC surface at temperatures 1400 °C or above, leaving the C as graphene. Raman spectra of SiC treated in Ar for 60 min at 300 Torr did not show a graphene G-peak. However, with the addition of SiF4, a clear G-peak was observed for the surface treated for only 1 min, demonstrating faster Si removal using SiF4. Si selective etching of SiC is explained by the Gibbs free energy, where Si removal is more favorable compared to C removal by SiF4.

Low Damage Cryogenic Etching of Porous Organosilicate Low-k Materials Using SF6/O2/SiF4

Low temperature plasma etching of porous organosilicate low-k films is studied, in an ICP chamber with cryo-cooled substrate holder, using Fluorine-based plasma discharges. It is demonstrated that plasma-induced damage is significantly reduced when the base temperature is below a threshold Tc that depends on pore size of low-k materials. For T < Tc, almost no carbon depletion is observed and the k-value degradation is negligible. It is shown that protection occurs mainly through the condensation of the etch by-products and their ability to seal the open pores against radical diffusion. By addition of SiF4 and O2 into the gas discharge, plasma-induced damage is further reduced, as a result of SiOxFy deposition. Vertical trench profiles are obtained in patterned structures, using an inorganic hard mask. The damage reduction mechanism is discussed and a protection model is proposed.

Fluorine‐Mediated Crystallization of Silicon in Plasma‐Enhanced CVD

Fluorine mediated crystal silicon thin films in plasma‐enhanced chemical vapor deposition were grown using a Si2H6 and SiF4 gas mixture without an intentional hydrogen dilution. The crystal growth took place at the temperatures above 400°C, and both crystallinity and growth rate were increased with an addition of SiF4. Optical emission spectroscopy reveals that addition of SiF4 changes the major precursor from SiH3 to SiHnFm (n+m≤3), and provides an abundant atomic fluorine ambient. These results indicate that contribution of atomic hydrogen is not indispensable for the crystallization, and atomic fluorine can be an alternative to atomic hydrogen.

Addition of SiF4 to standard SiH4+H2 plasma: an effective way to reduce oxygen contamination in μc‐Si:H films

AbstractThe effect of adding of silicon tetrafluoride (SiF4) to silane (SiH4) hydrogen gas mixture on the properties of highly crystallized microcrystalline silicon (μc‐Si:H) films was studied. We found that the addition of a small amount of SiF4, with a ratio to SiH4 not exceeding 1/10, has almost no effect on deposition rate and does not affect the structure of the μc‐Si:H films, but strongly reduces oxygen incorporation into the films. Reduction of oxygen content to values below 1019 cm‐3 results in intrinsic character of the films with ratio of photo to dark conductivity about 103 in whole studied range of deposition temperatures from 175 to 250 °C in contrast to films, deposited without SiF4 addition, which show strong decrease of photosensitivity with increase of deposition temperature above 200 °C (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effects of Addition of SiF4 During Growth of Nanocrystalline Silicon Films Deposited at 100°C by Plasma-Enhanced Chemical Vapor Deposition

Structural properties of nanocrystalline silicon (nc-Si) films, deposited at 100°C using SiF4/SiH4/H2 by plasma-enhanced chemical vapor deposition, were investigated by changing the SiF4 flow rate, [SiF4]. At a certain low [SiF4] value (=[SiF4]S), both the crystallinity and the grain size had minimum values. The Raman peak shifts corresponded well with a change in stress, and films with [SiF4]S were suggested to be free from random stress in the local Si–Si networks. The photoluminescence spectra had the highest intensity and the highest peak energy at [SiF4]S. It was proposed that nc-Si films with high [SiF4] have microvoid-like grain boundaries with high densities of Si–F and SiH2 bonds, exhibiting an increase in crystallinity and susceptibility to O contamination after deposition. These results were interpreted in terms of the change in the etch rates by H and F radicals, depending on deposition temperature.

Structure of Polycrystalline Silicon Films by Glow-Discharge Decomposition using SiH4/H2/SiF4 at Low Temperature

ABSTRACTFor poly-Si films prepared by a plasma-enhanced chemical vapor deposition, we examined the changes in the local structure caused by adding H2 and/or SiF4 in the SiH4 feed gases and by changing supplied rf power values. The conditions of low rf power supply, low H2 addition, and SiF4 addition allow formation of films with microcrystalline or nanocrystalline structures. In addition, the H2 or SiF4 addition was found to be effective in promotive growth of &lt;111&gt; or &lt;110&gt; grains, respectively. In such low crystallized films, it was suggested that high-angle boundary would be formed, leading to a decrease in the density of SiH2 and Si dangling bonds, and to an increase in g values.

Fluorinated Silicon Nitride Film Deposited at Low Temperatures from SiH4-SiF4-NH3

ABSTRACTThe effect of SiF4 addition on the deposition characteristics and film property has been studied for the improvement of long term stability of the SiNx:F film in TFT applications. During the deposition with SiF4 addition, atomic hydrogen species in the gas phase significantly decreased. A detailed bonding configuration of fluorine and hydrogen was investigated by XPS and FT-IR. Optical band gap increases with the increment of fluorine concentration in the film. High compressible stress turned to low tensile stress with increasing SiF4 flow rate. The breakdown strength and barrier height for the conduction of trapped electron were improved by SiF4 addition even in Si-rich SiNx:H films due to the stable Si-F bond formation.

Effects of the Addition of SiF4 to the SiH4 Feed Gas for Depositing Polycrystalline Silicon Films at Low Temperature

Polycrystalline silicon films with a strong (110) texture were prepared on a corning 7059 glass substrate at 400° C by a plasma-enhanced chemical vapor deposition method using a mixture of gases with different SiF4 flow rates ( [SiF4] = 0–0.5 sccm) under a fixed SiH4 flow rate ( [SiH4] = 1 or 0.15 sccm). The effects of the addition of SiF4 to SiH4 on the structural properties of the films were studied by Raman scattering, X-ray diffraction (XRD), atomic force microscopy and stress measurements. For [SiH4] = 1 sccm, the crystallinity and the (110) XRD grain size monotonically increased with increasing [SiF4], and their respective maxima reach 90% and 900 Å. In contrast, for [SiH4] = 0.15 sccm, both the crystallinity and the grain size decreased with [ SiF4]. Mechanisms causing the change in crystallinity are discussed, and it was suggested that an improvement in the crystallinity, due to the addition of SiF4, is likely to be caused by the effect of a change in the surface morphology of the substrates along with the effect of in situ chemical cleaning. On the other hand, both the effect of in situ chemical etching on the growing surface and the effect of a change in the capability for surface migration of adsorbates may provide a minor contribution in determining the crystallinity.

Effect of fluorine chemistry in the remote plasma enhanced chemical vapor deposition of silicon films from Si2H6-SiF4-H2

SiF4 was added into Si2H6-H2 to deposit polycrystalline silicon films at low temperatures around 400°C in a remote plasma enhanced chemical vapor deposition reactor. It was found out that the fluorine chemistry obtained from SiF4 addition had an influence on the chemical composition, crystallinity, and silicon dangling bond density of the film. The fluorine chemistry reduced the amount of hydrogen and oxygen incorporated into the film and also suppressed the formation of powders in the gas phase, which helped the crystallization at low temperatures. Effect of SiF4 concentration as well as the deposition temperature was also significant.

Selective reactive ion etching of InGaAs and InP over InAlAs in SiCl4/SiF4/HBr plasmas

A new selective reactive ion etching (RIE) process has been developed for etching InGaAs and InP over InAlAs using a mixture of SiCl4/SiF4/HBr gases. Optical emission spectroscopic (OES) investigation showed that the dominant emitting species in the plasma are HBr+, Br, and Br2, with weaker emission from SiBr and SiHBr. Using a flow rate of SiCl4/HBr of 6/15 SCCM, a pressure of 100 mTorr, and with a dc bias of 180 V, the etch rates of InGaAs and AlInAs can be as high as 200 nm/min at room temperature with good surface morphology. The formation of bromosilanes or chlorosilanes of the form (SiHxBry, SiHxCly) in the plasma is believed to be responsible for the etching In-containing compounds through the formation of indiumbromosilanes and indiumchlorosilanes. The selectivity of etching InGaAs and InP over InAlAs is obtained by the addition of SiF4 to the mixture of SiCl4/HBr, which is thought to be due to the formation of an etch stop layer of AlF3 on the AlInAs layer. Using a flow rate ratio of SiCl4/SiF4/HBr of 5/6/25 SCCM, a dc bias of ≤70 V, and a pressure of 100 mTorr, the selectivity was extraordinary high for this material system a minimum of (600:1). The etching was stopped on a 5-nm-thick AlInAs layer for at least 60 min. These values of selectivity are an order of magnitude higher than the reported values in the literature. Moreover, this RIE process (SiCl4/SiF4/HBr) etches silicon nitride, and NiCr very slowly. Structures in InP have been etched as deep as 6 μm with very little erosion to the mask which was a very thin layer (100 nm thick) of either Si3N4 or NiCr. The dry etch damage was evaluated using Hall effect measurements made on a high electron mobility transistors material structure. This structure had a 7 nm InGaAs capping layer. Etching the 7 nm cap layer had very little effect on the value of the sheet carrier concentration and the mobility even after 7 min of continuous bombardment of the active layers by selective etching of the 7 nm capping layer.

New chemistry for selective reactive ion etching of InGaAs and InP over InAlAs in SiCl4/SiF4/HBr plasmas

A selective reactive ion etching process which etches InP and InGaAs, but not InAlAs, using a mixture of SiCl4/SiF4/HBr gases has been developed. Optical emission spectroscopy shows that the dominant emitting species in the plasma are HBr+, Br, and Br2, with a weaker emission from SiBr and SiHBr. We believe that the bromosilanes or chlorosilanes of the form (SiHxBry,SiHxCly) are responsible for the etching of these In-containing compounds by the formation of indium bromosilanes and indium chlorosilanes. Using a flow rate ratio of SiCl4/HBr of 7/15 sccm, a pressure of 100 mTorr and with dc bias of 80 V, an etch rate of InGaAs and InAlAs as high as 100 nm/min at room temperature was achieved with good surface morphology. The addition of SiF4 suppresses the etching of InAlAs and the selectivity obtained can be changed by varying the proportion of SiF4. At a flow rate ratio (SiCl4:SiF4:HBr) of 5/6/20 sccm, dc bias of ≤70 V and a pressure of 150 mTorr, the selectivity obtained is extraordinarily high (≳600:1) for this material system.

In Situ Ellipsometric Monitoring of the Growth of Polycrystalline Silicon Thin Films by RF Plasma Chemical Vapor Deposition

Polycrystalline silicon thin films have been deposited by RF plasma-enhanced chemical vapor deposition (CVD) using SiF4, SiH4 and H2 gases at a substrate temperature of 300° C. Growth of the films has been monitored by spectroscopic ellipsometry, and time resolved film compositions have been investigated. The film deposited with SiH4 diluted by H2 at a power level of 500 mW/cm2 showed crystal fraction of 50%, and it increased up to 80% with addition of SiF4, although the deposition rate decreased and the surface roughness was enhanced. These results suggest that preferential etching of amorphous tissue brings about the increase of crystalline fraction. Crystallization of the film was verified by transmission electron microscopy along with the decrease in hydrogen content shown by the infrared absorption spectrum.

Material Characterization of Low-Temperature Silicon Epitaxial Growth on Patterned Oxidized Wafers by ULPCVD From SiH4/SiF4/H2

ABSTRACTLow temperature silicon selective epitaxial growth on patterned oxidized wafers is becoming crucial to ultra large scale integration (ULSI) technologies. Low temperature processes can reduce dopant redistribution via solid state diffusion so that a sharp transition region can be obtained. This paper presents material characterization of epitaxial films grown on patterned oxidized wafers by ultralow pressure chemical vapor deposition (ULPCVD) from SiH4/SiF4/H2 (≤ 10 mTorr), in which SiF4 was used to explore its capability for selective epitaxial growth. The deposition temperature is 800°C. The effects of the SiF4 addition to SiH4/H2 are discussed. Defects in epitaxial layers resulting from a high composition of the SiF4 during deposition were characterized. Results of in–situ surface cleaning using a SiF4/H2 plasma are also presented.