Si CH3 Bonds Research Articles

Mechanism of cyclohexene vapor curing polycarbosilane fibers

Cyclohexene vapor, instead of air, is applied to cure polycarbosilane (PCS) fibers. The cured fibers are characterized by infrared (IR), electron spin resonance (ESR), elements analysis (EA) and simulated through the HyperChemTM program for comparison. The curing process is investigated by thermoanalysis. The results indicate that the Si–H and Si–CH3 bonds in PCS are induced by cyclohexene to cleavage and form Si-central radicals. A fully developed cross-linking fibers come into being through the combination of these radicals, and the byproducts, some cyclohexyls bonded onto PCS derived from cyclohexene, introduce the variations in IR spectra, weight gain and carbon contents increase of PCS. On the basis of investigation and simulation, a likely mechanism of curing reaction is presented.

Recovery from Plasma-Process-Induced Damage in Porous Silica Low-k Films by Organosiloxane Vapor Annealing

It was demonstrated that recovery from dry etching and ashing damage in porous silica low-k films occurred by 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) vapor annealing. The increase in k-value after Ar/C5F8/O2 plasma etching was reduced from 35 to 6.5% of the initial value (k=2.25) by TMCTS vapor annealing. Leakage current also returned to the initial level. Hydrofluoric acid wet etching revealed the sidewall damaged region in a porous silica trench due to plasma processes. The TMCTS vapor annealing was found to be effective for recovery from the sidewall damage. Fourier transformed infrared absorption spectroscopy indicated that the replacement of Si–CH3 bonds in low-k films by Si–O and Si–OH bonds occurred during plasma processes. The recovery mechanism involves hydrophobic bond (–CH3) reintroduction into the film followed by stable cross-linked poly(TMCTS) network formation on pore wall surfaces by TMCTS vapor annealing.

Detecting free radicals during the hot wire chemical vapor deposition of amorphous silicon carbide films using single-source precursors

A vacuum ultraviolet single photon ionization technique has been used to probe gas-phase species important in the hot wire chemical vapor deposition (HW-CVD) of amorphous silicon carbide(a-SiC:H) films using different single-source precursors. This study focuses on monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, and 1,1-dimethyl-1-silacyclobutane, and the reactions of these precursors on tungsten and rhenium filaments between 1000 and 1950°C. Silane is also considered for comparison. Si radicals are found to be major products of hot wire decomposition for all the organosilicon precursors; CH3 is also observed. C and H radicals are expected to be produced as well but are not detected at the ionization energy used in these experiments. Within the series of methylsilanes, the reaction rate on the filament is found to decrease with increasing number of methyl groups on the precursor. We propose a model in which Si–H bonds are cleaved with lower activation barriers than Si–CH3 bonds as the molecule adsorbs onto the hot metal surface. 1,1-dimethyl-1-silacyclobutane produces Si with a lower apparent activation energy than the other molecules. Coverage-dependent reaction pathways are proposed to play a role in the temperature profile of CH3 generation. Infrared spectra of films deposited by HW-CVD show that the film composition and growth rate for the different precursors correlate with the hot wire chemistry studied by single photon ionization.

Origin of the SiCH3 Peak Position Shift in SiOC Films

SiOC films consist of the cross-linked or cross-link breakage structures depending on the variation in the flow rate ratio between O2 and bistrimethylsilylmethane due to the properties of the carbonyl group. As the results, SiOC films showed the sharp contrast in chemical shift, such as a blue and red shift. Generally, the Si–CH3 bond shows very strong bond, but the position of Si–CH3 peak in SiOC films varied depending on the bonding structure. The Si–CH3 bond at 1250 cm-1 is due to bis(trimethylsilyl)methane gas, which does not fully dissociated by substitution reaction unimolecular. On the other hand, the Si–CH3 bond at 1275 cm-1 originates from substitution reaction bimolecular inducing the reaction of nucleophilic attack of organometallic carbon.

Properties of High-Performance Porous SiOC Low-k Film Fabricated Using Electron-Beam Curing

In this paper, we describe the effect of electron-beam (EB) curing on ultra-low-k dielectric porous SiOC material (k=2.2) and the application of this technology to the 90-nm-node Cu/low-k multilevel damascene process. A significant improvement of dielectric porous SiOC films with EB curing has been demonstrated. The mechanical and adhesion strength of these films were increased by a factor of 1.5–1.6 without degrading the film's k. This result can be explained by the reconstruction of a Si–O random network structure from cage Si–O bonds and Si–CH3 bonds through EB curing. Additionally, the EB curing of spin-on dielectric (SOD) porous low-k films contributes to a decrease in their curing temperature and a decrease in their curing time. Under optimum EB curing conditions, no degradation of transistor performance was revealed. The excellent adhesion strength obtained by EB curing, has contributed to the success of multilevel damascene integration. On the basis of our findings, this EB curing technology can be applied in devices of 65-nm-node and higher.

Double-layered Structure of Surface Modification of Low-k Dielectrics Induced by He Plasma

AbstractSurface modification of a p-SiOC film induced by Helium (He) plasma was investigated using various measurements. Differential Fourier transform infrared absorption (FT-IR) spectra and the etch-depth measurements with the immersion in the mixed hydrofluoric acid (HF) indicate that the almost all of Si-CH3 bonds are broken in the modification layer, resulting in carbon-depletion, an SiO2-like composition. The x-ray photoelectron spectroscopy (XPS) measurements at different take-off angles reveal that the modified surface forms a double-layered structure, a thin carbon-rich top layer (about 1 nm thick) on a thick carbon-depletion layer (about 20 nm thick) with the irradiation of He plasma over 300 W. Atomic force microscopy (AFM) observations show that the modified surface is the smoothest in the case of the carbon-depletion surface.

Swelling and modification of silicone surface by F2 laser irradiation

The surface of silicone rubber swelled and was modified by 157-nm F2 laser irradiation at a laser fluence less than the ablation threshold. The irradiated surface swelled to a height of approximately 3 μm. Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy showed that the irradiated surface was modified to SiO2. 193-nm ArF laser irradiation of the silicone rubber induced the surface to swell, but not to modify to SiO2. The IR peaks of end groups of silicone were observed in the FT-IR spectra of the surface. From these results, it is concluded that the main chains (Si-O) of silicone were photodissociated and generation of low molecular weight silicones caused the swelling. In addition, it was observed that methane and carbon dioxide were released from silicone rubber when each laser beam irradiated it. These gases were generated by photodissociation of the side chains (Si-CH3) of silicone. An F2 laser beam can photodissociate the Si-CH3 bonds and the Si-O bonds of silicone and O2 effectively even at a laser fluence less than the ablation threshold, resulting in the modification to SiO2 and the swelling.

Photochemical Modification of Silicone Films Using F2 Laser for Selective Chemical Etching

Silicone ([SiO(CH3)2]n) films were photochemically modified into SiO2 by irradiation with a 157 nm F2 laser. The dissociation of Si–CH3 bonds of silicone simply depended on the photon number of the F2 laser. The quantum yield of the modification was estimated to be approximately 1×10-2. Mechanisms of oxidation and O–H production in the modified films were clarified. The depth of the modification was not limited by the absorption coefficient of silicone because SiO2 of the modified films is transparent for the F2 laser. A fine pattern of the 1.5-µm-thick silicone films could be fabricated by immersing the modified samples in 0.2 wt% hydrogen fluoride solution.

Photochemical Moisture Proof Coating on Nonlinear Optical Crystal by ArF Excimer Laser

ABSTRACTSilicone oil was photo-chemically oxidized to change into SiO2 on the crystal by using an ArF excimer laser; the protective moistureproof film has been developed for a nonlinear optical crystal that is deliquescent.The nonlinear optical crystals such as CsLiB6O10 (CLBO) and KH2PO4 (KDP) are deliquescent, which causes their surfaces to be cloudy by absorbing moisture in the air. We, therefore, demonstrated the growth of the SiO 2 film directly on the crystal so as to be moistureproof.Firstly, dimethylsiloxane silicone oil (-O-Si(CH3)2-O-)n was poured on the substrate and coated by a spinner for making the silicone oil thin layer. Then, the ArF excimer laser was vertically irradiated on the sample in oxygen atmosphere. The O atom on the substrate surface was photo-excited by the laser to generate a high active O atom. At the same time, the Si-CH3 bond of the silicone oil was photo-dissociated and the dangling bond of Si was linked with the active O atom to form a SiO 2 film on the crystal surface.In short, the film formed by the new technology can be used as a protective coating, which has the moisture resistance and the UV permeability, for a nonlinear optical crystal.

Properties of low-k SiCOH films prepared by plasma-enhanced chemical vapor deposition using trimethylsilane

The properties of low-k SiCOH film deposited by plasma-enhanced chemical vapor deposition using trimethylsilane are reported here. The deposition process was performed at different temperatures from 200 to 400°C. The influence of deposition temperature on the films were characterized using Fourier transform infrared spectroscopy (FTIR) to understand its impact on the studied properties. The films were annealed at ∼450°C in an inert ambient after deposition in all the cases. The deposition rate decreases with increase in deposition temperature. The refractive index of the films increases as a function of deposition temperature. From FTIR spectra, OH-related bonds were not detected in films even when deposited at 200°C. The Si–CH3 bonds were detected in all the films and decreased monotonically from 200 to 400°C. All deposition conditions studied resulted in films with dielectric constant less than 3, the lowest being ∼2.7 when deposited at 200°C. All films exhibited good thermal stability.

Effects of NH3 Plasma Treatment on Methyl Silsequioxane for Copper Multi-Level Interconnect

We have tried to modify the surface of methylsilsequioxane (MSQ) by NH3 plasma treatment. As a result, the mechanical hardness of the surface of MSQ increases from 0.242 to 0.419 GPa as the NH3 plasma treatment temperature is increased from 150 to 350°C, which is important for chemo-mechanical polishing process. The dielectric constant (k) and surface energy are also fairly improved by the NH3 plasma treatment because the NH3 plasma breaks Si–O and Si–CH3 bonds, resulting in lower k, and then nitrogen atoms reduce the imperfect dangling bonds, forming Si–N bonds. However, the NH3 plasma treatment at 350°C raises the k value of the MSQ since more nitridation occurs at the higher temperature for long time. The leakage current density of Cu/MSQ/Si can be reduced as low as 7 orders of magnitude after the NH3 plasma treatment.

Low Dielectric Constant 3MS α-SiC:H as Cu Diffusion Barrier Layer in Cu Dual Damascene Process

The primary candidate for the barrier/etch stop layer in damascene process is silicon nitride. However, silicon nitride has a high dielectric constant. To reduce the effective dielectric constant in the copper damascene structure, silicon carbide, which is prepared by plasma enhanced chemical vapor deposition (PECVD) using 3 methyl silane source (Z3MS), is studied for the dielectric copper diffusion barrier. The dielectric constant of PECVD α-SiC:H is varied from 4.0 to 7.0 and the fourier transform infrared (FTIR) spectra peak intensity ratio of Si–CH3 bond to Si–C is also examined. The reduction in dielectric constant of α-SiC:H using 3MS gas seems to be related to the decreased density upon incorporation of Si–CH3 groups. The value of capacitance with α-SiC is 8–10% lower than that with PECVD SiN. The leakage current with α-SiC:H barrier is lower by 1 order of magnitude than that with PECVD SiN barrier.

Oxidation study of plasma-enhanced chemical vapor deposited and rf sputtered hydrogenated amorphous silicon carbide films

An oxidation study of plasma-enhanced chemical vapor deposited (PECVD) and rf sputtered hydrogenated amorphous silicon carbide (a-Si1−xCx:H) films was carried out using the infrared (IR) and electron spin resonance (ESR) techniques. a-Si1−xCx:H films with x=0.3, 0.5, and 0.8 were prepared with the PECVD method and significant oxide growth can only be obtained in a-Si0.2C0.8:H film. IR results showed that Si–CH3 bonds provide the necessary porous structure for oxide growth. The oxide quality was found to be poor when compared to oxide obtained from pure silicon. Annealing in nitrogen enhances the porosity of the PECVD films and results in faster oxide growth. For sputtered films, oxide growth can only be observed in film containing Si–CH3 bonds. We are not able to separate the contributions of the Si–H, Si–C, Si–CH3, and the Si dangling bonds to the oxide growth for the PECVD and rf sputtered films.

Low-k Si–O–C–H composite films prepared by plasma-enhanced chemical vapor deposition using bis-trimethylsilylmethane precursor

Low-k Si–O–C–H composite films were prepared using bis-trimethylsilylmethane as a precursor and oxygen in a rf plasma reactor. The growth rate of the Si–O–C–H composite film followed a second-order exponential decay function. This behavior could be explained by the formation of nanosized voids due to Si–CH3 and OH-related bonds included in the film. OH-related bonds were detected in films deposited at 30 °C, but could not be observed for the films deposited above 60 °C. In contrast, Si–CH3 bonds were also detected at 30 °C, but decreased monotonically up to 210 °C and were absent of higher temperatures. After postannealing the film deposited at 30 °C, the Si–CH3 bonds were unchanged, but the OH-related bonds were easily removed. This film showed a low dielectric constant of 2.44 and leakage current density of 4.4×10−7 A/cm2 at 1 MV/cm.

Infrared Spectroscopic Study of the Formation of Reactive Silica by Pyrolysis in Vacuo of a Trimethylsiloxylated Sample

The pyrolysis of a trimethylsiloxylated silica (TMS-silica) in vacuo up to 750 °C gives a “reactive silica” with surface species and properties similar to those previously reported by degassing a methoxylated silica above 600 °C. Both surface silanes absorbing around 2290 cm-1 and very stable Si-C⋮CH groups appear. A dissociative chemisorption of water on the reactive silica at 25 °C, leading to both SiH and SiOH groups, involves silylene centers (SiO)2Si: with a bicoordinated silicon atom. A concentration of about 0.13 sorption centers nm-2 is estimated, which is a value higher than on pyrolyzed ex-methoxylated silica. The SiH stretching range in the infrared spectra of TMS-silica displays a larger variety of intermediate SiH sites, at increasing temperatures, than for a methoxylated silica. In addition, the pyrolysis of TMS-silica creates intermediate aliphatic species absorbing at 2975 and 2986 cm-1, correlated to the intensity decrease of the νaCH3 band of the TMS group at 2964 cm-1. Similar intermediate components, assigned to Si(CH3)2 and SiCH3 groups, were observed by oxidation of TMS-silica in air, although at much lower temperatures than in vacuo. A SiCH3 bond is thus attributed to the previously unidentified species which absorbs at 2983 cm-1 during the last stages of the pyrolysis of a methoxylated silica.

Thermal Evolution of Hybrid Sol-Gel Silica Coatings: A Structural Analysis

The sol-gel method has been increasingly used to prepare organic-inorganic hybrid coatings with both glass and polymeric properties by including alkylalkoxides with one or more non-hydrolizable groups in the precursor alkoxide solution. When using MTES and TEOS precursors, it was found that the increase in Si–CH3 bond concentration in the coating augments the critical thickness, and strongly affects other properties. The final methyl content depends on both the composition of the precursor solution and the thermal treatment for densification. But little is known about the effect of this organic group on the hybrid structure and microstructure of the coatings. In this work, the effect of methyl content on the film structure and the evolution of porosity are analysed by using ellipsometry and infrared spectroscopy. A theoretical correction of the refractive index of the film and a description of the thermal evolution of the coating structure are also proposed.

Density functional theory applied to the calculation of dielectric constant of low-k materials

Abstract The interest of low-k dielectric materials to reduce capacitance in multilevel metal interconnects of integrated circuits is well known in the semiconductor industry. The use of these materials (especially hydrogen silsesquioxane (HSQ) and methyl silsesquioxane (MSQ): intermetal dielectric applications in the back end of line fabrication) leads to a reduction of the dielectric constant from k≅4 in a traditional intermetal dielectric material of silicon dioxide to a value of ≅2.5–3. The physical difference between HSQ or MSQ and a-SiO2 is the presence of Si–H bonds (for HSQ) or Si–CH3 bonds (for MSQ) and the density of the material. A theoretical calculation of bond polarizability (Si–H or Si–CH3) associated to experimental values of electric dipole densities can lead, using the Clausius-Mossotti relationship, to the calculation of the dielectric constant. After validation of the calculation methods both on simulation and experimental values, it is shown that for a constant density, the difference between the materials could be due to the bond polarizability and furthermore that this difference accounts, in part, for the value of dielectric constant. Consequently, even if densification remains the main parameter explaining low-k values, the polarizability of building units of these materials is not negligible.

Structural Investigation of the First Stages of Pyrolysis of Si-C-O Preceramic Polymers Containing Si–H Bonds

The polymer-to-glass transformation in the Si-C-O system usually involves cross-linking reactions at the C sites, which transform for example ≡Si–\(\underline {\text{C}} \)H3 sites into \(\underline {\text{C}} \)(Si)4 sites, leading to the formation of a silicon oxycarbide network. Identification of the various C sites that form during pyrolysis under inert atmosphere is rather difficult from 13C MAS-NMR spectra, due to strong overlap of resonance lines, which prevents an accurate determination of the chemical shift values. This paper reports on the use of a spectral editing technique called Inversion Recovery Cross Polarization (IRCP), which, when combined with Cross Polarization (CP) technique, allows us to identify and quantify the formation of Si-\(\underline {\text{C}} \)H2-Si bridges during the early stages of the pyrolytic transformation of a polysiloxane containing Si–CH3 and Si–H groups. Several Si-C-O systems characterized by the same initial number of Si–CH3 bonds but with increasing number of Si–H bonds, have been investigated by MAS-NMR as well as thermogravimetric analysis coupled with mass spectrometry (TG/MS). The Si—H bonds play clearly an active role in the insertion of C atoms within the silica network.

Low Dielectric Constant Insulator Formed by Downstream Plasma CVD at Room Temperature Using TMS/O2

We present an insulator with a dielectric constant lower than 3.0, thermal stability up to 500° C and good gap-filling characteristics. This insulator was formed by downstream plasma chemical vapor deposition (CVD) at room temperature using tetra-methylsilane (TMS)/O2 gases. It contained a large amount of water in the as-deposited state. Annealing at 350° C resulted in a decrease in the water content of the insulator, and the insulator did not absorb water after the annealing. The film is constructed from Si–O and Si–CH3 bonds, which produce a low dielectric constant and high thermal stability.

Structure of Spherical Porous Silica Particles Derived from Tetramethoxysilane and Methyltrimethoxysilane

Spherical porous silica particles were synthesized by the sol-gel process from tetramethoxysilane and methyltrimethoxysilane in W/O emulsion. The difference in structure change by calcination is remarkable between air and nitrogen atmospheres. By calcination of the particles under N2 gas atmosphere their pore structures can be maintained up to 1000°C. This is due to the fact that Si-CH3 bond remains at high temperature. The 29Si MAS NMR spectra revealed that the intensity of T3 structural unit, whose origin is Si-C bonding, increased with an increase in methyltrimethoxysilane in a starting solution.