Carbon-rich Film Research Articles

Plasma/reactor walls interactions in advanced gate etching processes

Wafer-to-wafer reproducibility is a major challenge in gate etching processes. Periodic dry cleaning of the reactor in F-based chemistry between wafers is the most common strategy to ensure process repeatability. However X-ray Photoelectron Spectroscopy analysis of the chamber walls show that this cleaning procedure leaves AlF x species on the reactor walls, eventually resulting in process drifts and formation of particles. We have thus investigated a new cleaning/conditioning strategy of plasma etching reactors, in which the chamber walls are coated by a carbon-rich film between each wafer, allowing stable processing conditions and highly anisotropic etching profile to be achieved in advanced gate stacks. Finally, we present a new method (based on the detection of Cl 2 by laser absorption) to characterize the reactor walls conditions that could prevent process drifts.

Substrate temperature effects on 193 nm photoresist deformation and self-aligned contact hole etching performances

The authors managed to accomplish an etching condition for a self-aligned contact (SAC) structure patterned with the 193nm lithography. With lowering the substrate temperature from the previous SAC etching condition optimized for the 248nm lithography, they could minimize the 193nm photoresist deformation. The low-temperature setting is found to form relatively thicker, more uniform, and more carbon-rich fluorocarbon polymer film on the photoresist top and sidewall, which effectively prevents the ion-enhanced selective volatilization of carbonyl groups of the 193nm photoresist [Ling et al. J. Vac. Sci. Technol. B 22, 2594 (2004)]. Along the contact hole, the transmission electron microscope-energy dispersive x-ray spectrometry and field emission-Auger analyses were performed for the two temperature settings. At the low-temperature setting, relatively thinner fluorocarbon film with high fluorine content is observed within the contact hole, which is consistent with the observed etching phenomena of both the decrease in the etching selectivity of SiO2 to Si3N4 and the increase in the etching open strength within the SAC narrow slit. They could maintain the proper Si3N4 etching selectivity even at the low temperature with utilizing a part of the increased etching open strength endowed by decreasing the substrate temperature. They propose a model consistently describing most of all the SAC etching phenomena and surface analysis results observed in this work. The model separates the fluorocarbon radicals into the two groups, the carbon- and fluorine-abundant ones and considers the carbon-abundant radicals much stickier.

Friction and wear scar analysis of carbon nanofiber-reinforced polymeric composite coatings on alumina/aluminum composite

Alumina/aluminum based composites with excellent physical and mechanical properties offer great potential for lightweight, wear resistant, and high temperature applications. The objective of the present research was to investigate a suitable coating material to provide a low coefficient of friction (COF) during sliding contact. The friction behavior of carbon nanofiber-reinforced aerospace polymer coatings prepared by the spin coating technique were investigated. Polymethylmethacrylate (PMMA), bis A polycarbonate, and two biphenyl endcapped poly(arylene ether phosphine oxide) compositions, namely BPETPP-E and 6FETPP-E, were used as the matrices. Pin-on-disc experiments were performed between 440C stainless steel balls and disc samples of coated alumina/aluminum interpenetrating phase composites at 0.2 m/s sliding velocity, in air, at room temperature under 0.25 and 0.74 N normal load. In all cases, formation of a lubricious carbon layer and its transfer to the steel counterface was observed to result in lower COF (∼0.2–0.3). Higher levels of fiber content (40 and 60 wt.% fibers) contributed to a faster formation of this layer. Wear scar analysis showed the dual roles of the carbon nanofibers, serving as solid lubricants and as reinforcement in the coatings. The amount of debris generated and the coverage of the lubricious carbon-rich film on the scar surface was dependent on the matrix material used. Adherent and uniform coverage of a lubricious carbon-rich film at the wear contact with the least amount of debris fragments was obtained only for composite coatings using BPETPP-E and 6FETPP-E matrices.

New C–F interatomic potential for molecular dynamics simulation of fluorocarbon film formation

A new interatomic potential of fluorocarbon systems has been developed. This potential is based on Brenner’s reactive empirical bond-order potential [D. W. Brenner, Phys. Rev. B 42, 9458 (1990)] for hydrocarbon systems which is a variation of Tersoff potential [J. Tersoff, Phys. Rev. Lett. 56, 632 (1986)]. A set of empirical correction functions was determined so as to reproduce the accurate atomization energies of many types of fluorocarbon molecules. To check the transferability of Tersoff–Brenner potential to ion sputtering problems, molecular dynamics simulations were conducted. We thereby studied carbon sputtering by argon ions for the first time and obtained reasonable sputtering yield compared with experimental data. The fluorocarbon film formation on an amorphous carbon surface exposed to CFx+ (x=1,2,3) bombardments was also simulated with the new C–F potential. (The ion energy was 100 eV.) CF+ impacts continued to grow carbon-rich fluorocarbon film, but CF2+ ions formed a fluorocarbon film that was then etched down. And CF3+ ion impacts turned the deposition into etching more rapidly than CF2+. The composition of etching products changed according to the state of fluorocarbon films, and this change should be included in boundary conditions of macrolevel simulations.

X-ray photoelectron spectroscopy analyses of metal stacks etched in Cl2/BCl3 high density plasmas

We have used x-ray photoelectron spectroscopy to determine the chemical elements present on the tops, sidewalls, and bottoms of submicron metal features etched in a high density inductively coupled plasma source using Cl2/BCl3 gas mixtures. X-ray photoelectron spectroscopy analyses have shown that aluminum oxide is deposited on all the surfaces of the features exposed to the plasma due to erosion of the alumina liner located in the source region. A chlorine rich carbon film is formed on the sidewalls and at the bottom of the aluminum features during the etching process. At the bottom of the features, chlorine species must diffuse through the carbon layer to etch aluminum whereas spontaneous reactions between chlorine and aluminum are blocked on the sides of the features. On the sidewalls of the features, aluminum oxide species coming from the sputtering of the alumina liner are embedded in the carbon rich film as it grows. This sidewall passivation film enhances anisotropic etching by providing a thin protective layer against spontaneous etching reaction of chlorine with aluminum.

Evaluation of CF2 Radical as a Precursor for Fluorocarbon Film Formation in Highly Selective SiO2 Etching Process Using Radical Injection Technique

A radical injection technique (RIT) was developed to evaluate CF2 radical as a precursor for fluorocarbon film formation in a highly selective SiO2 etching process. Using RIT, the CF2 radical was successfully injected into electron cyclotron resonance (ECR) downstream plasmas employing Ar and H2/Ar mixtures. The fluorocarbon films formed on the Si surfaces exposed to ECR downstream plasmas were investigated using X-ray photoelectron spectroscopy. The deposition rate of fluorocarbon films was measured by varying microwave power in the Ar and H2/Ar ECR plasmas while keeping CF2 radical density constant using RIT. From the experimental results, it was found that the CF2 radical was the important precursor for fluorocarbon film formation only with the assistance of the surface activation due to the plasma exposure and that H atoms and CF2 radicals in the plasma played an important role in the formation of carbon-rich fluorocarbon film resulting in highly selective SiO2 etching. Furthermore, the highly selective SiO2 etching was demonstrated using the H2/Ar ECR downstream plasma with CF2 radical injection.

Highly Selective SiO2/Si Etching and Related Kinetics in Time-Modulated Helicon Wave Plasma

Highly selective SiO2/Si etching has been achieved by using time-modulated helicon wave plasma (HWP) employing C4F8/H2 mixture. Time modulation of less than 5 µ s. effectively controlled the electron energy, suppressing redissociation of HF. The selectivity window for H2 concentration was widened by synchronizing the phase of 100 kHz self-bias to the phase of 100 kHz time-modulated HWP. This is performed by extension of the polymer point to higher H2 concentration due to bombardment of more ions. Measurements of AMS of radicals and XPS of polymer formed on the Si surface suggest that CF1 radicals contribute to the polymer formation and produce carbon-rich film in the presence of hydrogen in the case of the pulse discharge in which electron energy is controlled and dissociation is suppressed. Measurement of CF1/F ratio also supported this conclusion.

Study of radiation damage and contamination by magnetized inductively coupled plasma etching

Radiation damage and contamination on the silicon surfaces etched by magnetized inductively coupled C4F8 plasmas were investigated. X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, spectroscopic ellipsometry, and transmission electron microscopy were used to characterize contamination and high resolution transmission electron microscopy, and I–V characteristics of Schottky diodes fabricated on the etched and/or annealed silicon surface were used to evaluate radiation damage. As the magnetic field applied to the inductively coupled plasmas increased from 0 to 12 G, the thickness of the residue layer formed on the silicon surface increased with the increase of SiO2 etch rate and selectivity. XPS analysis showed that the composition of the residue layer changed from fluorine rich to carbon rich film by changing the carbon binding state from C–CFx to C–C. Dense defects distributed about 40 Å deep from the etched silicon surface were found for the 0 G condition and thicker but less dense defects were observed for higher magnetic field conditions. The electrical damage estimated from the I–V characteristics of Schottky diodes was reduced with increasing applied magnetic field strength.

Tribological characteristics of DLC films and duplex plasma nitriding/DLC coating treatments

An innovative approach to improving tribological behavior of surfaces and meeting long-term durability requirements of engineering devices is to design and develop novel systems incorporating multilayers and/or duplex diffusion/plasma coating treatments. In the present work, the wear and friction characteristics of diamond-like carbon (DLC) films and composite surface layers were studied by conducting pin-on-disc experiments. M 50 steel and Ti-6A1-4V alloy were used as substrate materials. The composite layers consisted of a N-diffusion zone obtained by ion nitriding, followed by a 500 Å vapor-deposited Si bond layer and a 0.4 µm DLC film. The purpose of the bond layer was to enhance adhesion between the substrate and the DLC films. An ion-beam method was used for the deposition of the DLC films. The pin-on-disc results showed that for both materials the DLC coating produced a reduction in the coefficient of friction of about one order of magnitude. The reduction in the coefficient of friction was found to be consistent with the formation of a carbon-rich transfer film on the contact surfaces. Wear scar profiling and weight loss calculations showed that the wear resistance of the DLC-coated materials was dramatically improved. Comparisons between duplex N-diffusion layer/DLC coating and single DLC coating on Ti-6A1-4V alloy substrates showed that the duplex treatments possessed a significantly higher wear resistance. Nitriding was found to cause substrate hardening that reduces subsurface deformation, thus improving coating support and extending considerably DLC film lifetime.

High rate and highly selective SiO2 etching employing inductively coupled plasma and discussion on reaction kinetics

High rate and highly selective SiO2/Si etching employing a C4F8+H2 mixture was achieved in the diffusive region of an inductively coupled plasma where electrons in its diffusive region were not so energetic. It was considered that hydrogen fluoride formed by hydrogen introduced to scavenge fluorine (F) radicals was not dissociated in the region and was exhausted outside. The carbon-rich film was deposited selectively on the Si surface, thereby providing high selectivity. The thick film, in particular, deposited selectively onto the bottom of holes below 1 μm and exposure of C4F8+30% H2 for as-etched holes at floating potential showed that polymer films conformed to the inner surfaces of holes. Hence, this selective deposition was ascribed to the accumulation of the resputtered polymer on the bottom films. Appearance mass spectroscopy measurements of fluorocarbon radicals for some discharge conditions showed that the CF1 radical played a major role in the polymer film deposition, while the CF2 radical might not contribute to the polymer deposition and a sticking probability of the CF1 radical was reduced considerably in the presence of hydrogen. A simulated etching experiment using a capillary plate mask made it clear that the carbon-rich polymer film was deposited on the Si bottom surface in the presence of hydrogen at a high CF1/CF2 radical density ratio. Accordingly, CF1 radicals whose surface loss is suppressed in the presence of hydrogen were likely to arrive at a deep bottom surface, forming a carbon-rich polymer by scavenging fluorine from CF1 radicals with hydrogen.

Measurement of Fluorocarbon Radicals Generated from C4F8/H2 Inductively Coupled Plasma: Study on SiO2 Selective Etching Kinetics

The kinetics of highly selective SiO2 etching were studied on the basis of appearance mass spectroscopy (AMS) measurement of fluorocarbon radicals generated from C4F8/H2 inductlvely coupled plasma (ICP). Results obtained by varying of H2 concentration in C4F8, total pressure and RF power implied that CF1 radical played a major role in the polymer film deposition. In particular, radical measurements carried out by varying the length of a quartz tube which was set in front of an inlet of radicals effusing into AMS revealed that CF2 radical might not contribute to the polymer deposition and that the sticking probability of CF1 radical was reduced considerably in the presence of hydrogen. It was also observed that in etching using a capillary plate as a high-aspect-ratio mask, the carbon-rich polymer film is deposited on the Si bottom surface in the presence of hydrogen at high CF1/CF2 radical density ratio. Accordingly, CF1 radicals whose surface loss is suppressed in the presence of hydrogen are likely to arrive at deep the bottom surface, forming the carbon-rich polymer by reaction of hydrogen with fluorine from CF1 radicals.

Microloading Effect in Highly Selective SiO2 Contact Hole Etching Employing Inductively Coupled Plasma

The highly selective SiO2 etching achieved in the downstream region of the inductively coupled plasma (ICP) employing C4F8+H2 was studied regarding polymer film deposition characteristics. Polymer deposition into as-etched 0.5 µ m holes at floating potential showed an overhang feature with C4F8 alone and a conformal one with C4F8+30%H2. When as-etched 0.5 µ m holes were subjected to C4F8+30%H2 plasma, the film thickness on bottom surfaces increased rapidly with increasing self-bias voltages. This result demonstrated that high selectivity in holes less than 0.8 µ m was achieved by deposition of resputtered film on the side wall onto the bottom. To analyze the bottom Si surface in deep holes, a simulated experiment was also performed using a capillary plate with 10 µ mφ (aspect ratio 40); the Si surface masked by the plate was exposed to plasma, then the Si surface was measured by X-ray photoemission spectroscopy (XPS). Etching occurred on the Si surface covered by the fluorine-rich polymer in C4F8 alone, and carbon-rich film was deposited on the Si surface with addition of 30%H2. The latter explains the origin of high selectivity.

Friction and wear performance of ion-beam-deposited diamond-like carbon films on steel substrates

In this study, we investigated the friction and wear performance of ion-beam-deposited diamond-like carbon (DLC) films (1.5 μm thick) on AISI 440C steel substrates. Furthermore, we performed a series of long-duration wear tests under 5, 10 and 20 N loads to assess the load-bearing capacity and durability limits of these films under each load. Tests were performed on a ball-on-disk machine in open air at room temperature, about 22 ± 1 °C, and humidity, about 30% ± 5%. For the test conditions explored, we found that (1) the steady state friction coefficients of pairs without a DLC film were in the range 0.7–0.9 and the average wear rates of 440C balls (9.55 mm in diameter) sliding against uncoated 440C disks were on the order of 10 −5 mm 3 N −1 m −1, depending on contact load; (2) DLC films reduced the steady state friction coefficients of test pairs by factors of 6–8, and the wear rates of pins by factors of 500–2000; (3) the wear of disks coated with a DLC film was virtually unmeasurable whereas the wear of uncoated disks was quite substantial; (4) the DLC films were able to endure the range of loads, 5–20 N, without delamination, and to last over 1 000 000 cycles before wearing out. During long-duration wear tests, the friction coefficients were initially on the order of 0.15, but decreased to some low values of 0.05–0.07 after sliding for 15–25 km, depending on the load, and remained low until wearing out. This low friction regime was correlated with the formation of a carbon-rich transfer film on the wear scar of 440C balls. Microlaser Raman spectroscopy and scanning electron microscopy were used to examine the structure and chemistry of worn surfaces and to elucidate the wear- and friction-reducing mechanisms of the DLC film.

X-ray photoemission spectroscopy characterization of silicon surfaces after CF4/H2 magnetron ion etching: Comparisons to reactive ion etching

Silicon surfaces subjected to CF4/H2 magnetron ion etching (MIE) have been characterized by x-ray photoemission spectroscopy. Low-power-density (0.274 W/cm2) 25-mTorr MIE plasmas cause fluorocarbon films on Si which are characterized by C–CFx, CF, CF2, and CF3 groups. Graphitic carbon and silicon carbon type bonding can also be observed at the film/silicon interface. Thicker films are formed in hydrogen-rich CF4/H2 etching gas mixtures. Carbonaceous films with significant chemical differences are produced under high-power/low-pressure MIE operating conditions (1 W/cm2 at 4 mTorr). These films are characterized primarily by C–C/C–H type carbon and a very low intensity of highly fluorinated carbon groups. The carbon/fluorine ratio is 0.8 for the films formed in a pure CF4 magnetron discharge at a power density of 0.27 W/cm2, similar to that of films formed in a conventional reactive ion etch plasma, whereas it is 2.2 for the films formed at a power density of 1 W/cm2. The carbonaceous film formed during high-power MIE does not have a dominant role in determining the silicon etching behavior in contrast to fluorocarbon films formed under low-power MIE conditions which suppress the Si etch rate. This explains the lack of SiO2/Si etch selectivity observed under high-power MIE conditions using CF4/H2 in contrast to low-power magnetron ion etching where SiO2/Si etch selectivity is achieved. The formation of carbon-rich film in high-power MIE can qualitatively be explained by a large flux of highly dissociated CF4 derived plasma species to the silicon surface under high-power magnetron ion etching conditions and a Si substrate temperature difference of more than 100 °C between high-power MIE (>200 °C) and low-power MIE (near 100 °C or less) processing.

Characteristics of Al maskless patterning using focused ion beams

Maskless patterning of Al films has been performed by focused ion beam implantation and etching by phosphoric acid. The effects of ion implantation on the etching properties were investigated by ion implantations with various broad ion beams in different background atmospheres. It was found that implanted regions became etch-resistant for implantations at doses higher than 5 × 10 15 cm 2 and at a vacuum pressure around 7 × 10 −5 Torr. By using this effect, maskless patterning of 500 nm-thick Al films can be achieved by more than 3 orders of magnitude lower dose than patterning by physical sputter etching. From Auger electron spectroscopy measurements, it was found that the implantation effect is related to the formation of about 1–2 nm-thick carbon-rich film.