Rf Substrate Bias Research Articles

1206 誘導結合プラズマリアクター内のプラズマパラメータ測定

The objective is to deepen the understanding of basic plasma properties in a high-density inductively coupled plasma (ICP) reactor. The experiment using a Langmuir probe, which is made of tungsten wire having length of 2.3 mm and diameter of 0.65 mm, is carried out to determine the characteristics of argon plasma. The axial and radial distributions of the plasma density, electron temperature, and plasma potential are measured. It was found that the electron density is in the range of 1.0×1010 to 1.0×1011 cm−3, electron temperature 4∼6 eV, and plasma potential 35∼45 V, respectively. These plasma parameters are spatially nonuniform in the axial direction; they depend on the distance between the plasma source and the measuring point. Next, etching of polycristalline silicon wafer by chlorine plasma is studied. The results obtained in this study indicate the effects of rf coil power, gas pressure, and substrate rf bias power on the distributions of the etch rate.

Etching of RuO 2 and Pt thin films with ECR/RF reactor

Ferroelectric thin films for memory and MEMS applications require noble metal or refractory metal oxide electrodes. In this paper, physical and chemical parameters during etching of RuO 2 and Pt by a dual frequency ECR/RF reactor have been investigated. The removal characteristics of blanket films and films with a patterned mask (photoresist or SiO 2 masks) were investigated as a function of gas chemistry (Ar, O 2, halogen gases), ion beam energy (ion extraction/acceleration voltages), substrate bias RF power and working pressure (from 5×10 −3 to 5×10 −1 Pa). The etch processes were characterized in terms of etch rate, selectivity, critical dimension, lateral uniformity and mask stability. High etching rate processes (up to 70 nm/min for RuO 2 and 60 nm/min for Pt with removable photoresist mask) were obtained and a micron scale patterns demonstrated. Patterning of a multilayer stack PZT/Pt/SiO 2 could be achieved with a single photolithography step.

Etching of platinum thin films with dual frequency ECR/RF reactor

Ferroelectric thin films for memory and MEMS applications require noble metal or refractory metal oxide electrodes. In this paper, physical and chemical mechanisms during platinum etching by a dual frequency ECR/RF reactor have been investigated. An ion beam was generated by means of a 50 mm diameter ECR-gun directed towards the substrate. The latter was placed on a RF powered electrode for discharging and local activation of reactive gas species. The removal characteristics of blanket platinum films and platinum films with a patterned mask (photoresist or SiO2 masks) were investigated as a function of gas chemistry (Ar, halogen gases), ion beam energy (ion extraction/acceleration voltages), substrate bias RF power and working pressure (from 5 × 10−3 Pa to 5 × 10−1Pa). The platinum etch process was characterized in terms of etch rate, selectivity, critical dimension, lateral uniformity and mask stability. A high rate etching processes (up to 100 nm/min with SiO2 mask and 25 nm/min with removable photoresist) were obtained for micron scale patterns. Patterning of a complete layer stack PZT/Pt/SiO2 could be achieved with a single photolithography step.

Modeling of the sheath and the energy distribution of ions bombarding rf-biased substrates in high density plasma reactors and comparison to experimental measurements

In plasma etching and deposition processes, the energy distribution of ions incident onto the substrate strongly affects the surface reactions and the film deposition and etching rates. The magnitude and frequency of the rf-bias power applied to the substrate electrode determines the spatiotemporal variations of the sheath potentials and hence the energy distribution of the ions impinging upon the substrate. A self-consistent dynamic model of the sheath, capable of predicting ion energy distributions impinging on a rf-biased electrode, was developed. The model consists of equations describing the charge transport in the sheath coupled to an equivalent circuit model of the sheath to predict the spatiotemporal charge and potential distributions near the surface. Experimental measurements of the energy distributions of ions impinging on a rf-biased electrostatic chuck have also been made in a high density transformer coupled plasma reactor through Ar and Ne plasmas. The predicted ion energy distributions and sheath profiles are in very good agreement with the experimental measurements.

CNxHy films obtained by ECR plasma activated CVD: the role of substrate bias (DC, RF) and some other deposition parameters in growth mechanisms

Electron cyclotron resonance (ECR) plasma activated CVD in CH4+N2 gas mixture has been used to grow thin CNxHy films on steel or Al–Si alloy. The composition, optical and mechanical properties of the films deposited at various process conditions were investigated by electron microprobe analysis (EPMA), IR spectroscopy and microhardness measurements. It was shown that the DC bias does not influence substantially the films properties and such films have a high nitrogen content (N/C∼0.6) and polymer-like structure. The RF bias changed drastically all the films properties. RF biased films had a small nitrogen content (N/C∼0.2), were rather harder 4000–7000 N/mm2 (i.e. 4–7 GPa), all the bands on the IR spectra of the films became very weak and some of them disappeared. This effect is explained by the ion bombardment influence, which may be effectively realised for dielectric CNxHy films only at RF biased substrate. Variation of RF biased CNxHy film properties is related to the destruction of their polymer-like structure under the ion bombardment and formation of a highly disordered structure of the film on the base of graphite-like clusters containing the carbon and nitrogen atoms. The tribologically best CNxHy coatings prepared by the described method of ECR plasma activated CVD were achieved under RF bias URF about −100 V and for lower ratio of N/C less than 0.2 in the films.

Deposition of ultra-thin diamond-like carbon protective coating on magnetic disks by electron cyclotron resonance plasma technique

Diamond-like carbon (DLC) films were prepared on Si and magnetic disks using an electron cyclotron resonance assisted microwave plasma chemical vapour deposition system with variable radio-frequency (rf) substrate bias. Surface morphology of disks deposited with 10 nm DLC was observed under atomic force microscopy (AFM), which revealed surfaces smoother than the uncoated disk. The root-mean-square roughness decreased with increasing substrate bias and reduced to 0.23 nm for film prepared at a bias of −150 V. Internal stress and hardness of the resulting films deposited on Si were investigated by curvature measurement and nano-indentation, respectively. Both internal stress and hardness increased with increasing ion energies. At a bias beyond −120 V, the film structure changed from diamond-like to graphite-like. There was also an improvement of scratch resistance of the DLC coatings deposited at bias >−90 V.

Dependence of growth and nanomechanical properties of ultrathin amorphous carbon films on radio frequency sputtering conditions

Ultrathin films of amorphous carbon (a-C) were deposited on Si(100) substrates by radio frequency (rf) sputtering using pure Ar as sputtering gas, rf power of 80–1000 W, and substrate bias voltage between 0 and −300 V. The films possessed a thickness of 6–95 nm, nanohardness of 12–40 GPa, and root-mean-square surface roughness of 0.15–32 nm, depending on the deposition conditions. Plasma parameters of the film growth environment were correlated to the deposition conditions to obtain insight into the phenomena responsible for changing the growth characteristics and nanomechanical properties of the a-C films. The surface binding energies of carbon atoms in the films were interpreted in terms of measured sputter etching rates due to energetic Ar ion bombardment at a kinetic energy of 850 eV. Higher etching rates were found for a-C films with higher growth rates and lower hardness. Ultrathin (10 nm) a-C films of maximum nanohardness (∼39 GPa) were synthesized at 3 mTorr working pressure, 750 W rf power, −200 V substrate bias, and 5 min deposition time. Results are presented to elucidate the effects of rf power, working pressure, and substrate bias on the quality of a-C films deposited by controlling the ion-current density, mean free path, and sheath voltages in the rf discharges. The latter are important parameters affecting the ratio of ion to atom fluxes and the intensity (power density) of ion bombardment on the growing film surface.

Assessment of as-deposited microcrystalline silicon films on polymer substrates using electron cyclotron resonance-plasma enhanced chemical vapor deposition

We have been successful in fabricating as-deposited microcrystalline silicon (μc-Si) on polyethersulfone and polyethylene terephthalate substrates and have assessed the characteristics of the Si films. We note that 13.5 MHz radio-frequency (rf) substrate bias during electron cyclotron resonance plasma deposition can be used to tailor the characteristics of these as-deposited μc-Si microcrystalline silicon films on the polymer substrates. As the rf substrate bias is applied and increased, as-deposited Si films loose their degree of crystallinity. At the same time, the activation energy of the Si film tends to be decreased and the intensity of the film photoluminescence (PL) is enhanced. Part of this increased PL intensity that is found with the addition of rf substrate bias occurs in a PL band at about 0.9 eV. This PL band in Si films may be attributed to the amorphous silicon (a-Si) materials.

Characterization and Optical Investigation of Diamondlike Carbon Prepared by Electron Cyclotron Resonance Plasma

Diamondlike carbon (DLC) films have been prepared on radio-frequency (rf) biased substrates maintained at low temperature (∼60 °C) using electron cyclotron resonance CH4 –Ar plasma. The structures of the resultant films were characterized by Fourier transform infrared (FTIR), Raman, and ultraviolet/visible (UV/VIS) spectrometry. The studies revealed that the deposited structures were DLC films with sp3/sp2 bond hybridization, extremely high hardness (>3000 kgf/mm2), and high electrical resistivity (up to 1014 Ω cm). The DLC films deposited on colorless (transparent) polymer plastics were examined to determine visible light transparencies and optical bandgaps. The results indicate that electron cyclotron resonance (ECR) plasma processing with low negative rf bias, low deposition temperature, and suitable CH4/Ar gas composition can form optically visible light transparent and hard protective DLC films on polymer plastic surfaces.

Characterization and optical properties of diamondlike carbon prepared by electron cyclotron resonance plasma

Diamondlike carbon (DLC) films have been prepared on radio-frequency (rf) biased substrates maintained at low temperature using electron cyclotron resonance CH4–Ar plasma. The effects of negative rf bias and reactant gas composition on the bonding structure, hardness, and resistivity of the films were systematically investigated. DLC films deposited on PMMA (polymethyl methacrylate) were examined by optical methods to determine the absorption coefficients and the optical band gap. It was found that DLC films synthesized at bias voltage of 2(80–100) V and FCH4/FAr of 0.075–0.086 exhibit extreme hardness of more than 3000 kgf mm−2, high electrical resistivity up to 1014 Ω cm, band gap larger than 2.5 eV, and excellent optical transparency. The results indicate that ECR CH4–Ar plasma with low negative rf bias and suitable CH4/Ar gas ratio can process optically transparent and hard protective DLC films on PMMA plastics.

RF-bias effect on structural and magnetic properties in CoCrPt/Cr/sub 75/Ti/sub 25//CoTi trilayer type longitudinal recording media

The effects of an rf substrate bias on the structural and magnetic properties of the CoCrPt/Cr/sub 75/Ti/sub 25//CoTi trilayer type longitudinal recording media deposited on glass substrate have been studied. It was found that the coercivity of 30 nm thick CoCrPt films deposited on Cr/sub 75/Ti/sub 25//CoTi underlayer was 4000 Oe by substrate bias of 100 W rf, which is 800 Oe increase than the non-biased case. X-ray diffraction indicated that the rf-bias to substrate improved the Co (101~0) and (112~0) plane textures of the CoCrPt magnetic layer. From RES analyses, Pt content of the CoCrPt magnetic layer increased with rf-bias power. In addition to the Pt increase, better lattice matching between the CoCrPt magnetic layer and the Cr/sub 75/Ti/sub 25//CoTi underlayer was obtained through the expansion of the lattice parameter, a and c of Co in the CoCrPt with the substrate bias. These two factors are thought to be the origin of the coercivity increase.

Oblique-incidence anisotropy in very thin Ni-Fe films

A study was made on the magnetic anisotropy in very thin Ni-Fe films of 10 nm or less sputtered at oblique-incidence. The anisotropy field H/sub k/'s of Ni-Fe films induced on Ta films by oblique-incidence was different from that on Al/sub 2/O/sub 3/ films and was reduced with an application of the RF substrate bias while the films were being formed. Hk's, at oblique-incidence, were dependent on the film structure. The difference in the chain structure of Ni-Fe films is considered to be the cause of difference in H/sub k/.

Diagnostic technique for measuring plasma parameters near surfaces in radio frequency discharges

A plasma diagnostic technique for measuring the electron density, electron temperature, and ion current near a surface in radio frequency (rf) discharges is proposed. The sensor uses a small wire probe to determine the plasma potential and a small metal electrode to measure the current and voltage profiles. The values of current, sheath voltage, and time derivative of sheath voltage at three distinct points during the rf cycle are used in conjunction with an analytical sheath model to determine the plasma parameters. The technique is demonstrated by implementing the diagnostic in a computer model of an inductively coupled plasma reactor which has an rf biased substrate. Although any three disjoint sets of measurements can ideally be used, a sensitivity analysis is used to show that certain sets may be more suitable in experimental systems where noise is present.

Evaluation of the ion bombardment energy for growing diamondlike carbon films in an electron cyclotron resonance plasma enhanced chemical vapor deposition

The amorphous hydrogenated carbon (a-C:H) films were deposited on (100) silicon substrates using a divergent Ar+CH4 electron cyclotron resonance plasma. During the deposition sequence, the rf bias was applied to the substrate to increase the ion bombardment energy. The results of the microhardness test and the Raman spectroscopy revealed that these films showed abrupt changes in the mechanical properties and in the bonding characteristics from polymerlike to diamondlike when the rf substrate bias (Vsub) was increased to −40 V. Such changes were attributed to the structural and compositional modifications of the growing film by the bombarding ions. In addition, the results of the plasma diagnostics and calculation showed that the required ion energy for growing a hard diamondlike carbon film was about 65 eV or higher. The bombardment by high energetic ions caused the a-C:H film to have diamondlike properties with a strong three-dimensional carbon network by dislodging hydrogen atoms from CH3 radicals on the growing surface, as was identified by Fourier transform infrared spectroscopy.

Characteristics of amorphous and polycrystalline silicon films deposited at 120 °C by electron cyclotron resonance plasma-enhanced chemical vapor deposition

Amorphous and polycrystalline silicon (poly-Si) films, deposited by an electron cyclotron resonance plasma-enhanced chemical vapor deposition system at 120 °C, have been investigated. All films have been grown with either hydrogen or argon dilution. Using the films with the hydrogen dilution, the effect of rf (13.56 MHz) substrate bias has also been studied. Analysis with x-ray diffraction shows that films grown with Ar dilution and no rf bias do not show any crystallinity while the corresponding films deposited with H2 dilution and no rf bias contain a significant amount of the crystalline phase. With only a 3:1 H2 to silane ratio, highly crystallized films can be grown at 120 °C. In the presence of rf (13.56 MHz) substrate bias, there is a decrease of crystallinity in films. It has been found from cross-sectional transmission electron microscopy that films deposited without rf bias develop a very uniform columnar structure whereas films made with rf bias develop a closely packed, continuous but more amorphous structure. It is found that these changes caused by rf bias affect the photoluminescence intensity.

Optical investigations of the microstructure of hydrogenated amorphous carbon films

The electronic and vibrational properties of hydrogenated amorphous carbon (a-C:H) films deposited by a dual electron cyclotron resonance-radio frequency (ECR-RF) plasma technique from methane at different negative RF substrate bias voltages have been investigated by several complementary optical methods covering a wide spectral range (0.06 to 30 eV). The results as a whole are interpreted in terms of local C/C and C/H bonding configurations and their effects on the electronic states introduced by the π-bonded clusters.

The influence of deposition conditions on the growth and mechanical properties of CN xH y films obtained by ECR plasma-activated CVD

The effects of the main deposition parameters: (1) microwave power ( P w); (2) nitrogen content in a CH 4-N 2 gas mixture (%N 2): and (3) RF-substrate bias ( U F) on the growth rate V g, nitrogen concentration N:C, microhardness H, friction coefficient K and wear resistance of CN xH y, films, deposited by ECR plasma-enhanced CVD, are reported. The plots of V g versus U F a and N:C versus U F h have peaks at certain values of U F. The maximal values of N:C and V g of about 0.2 and 1.2 nm s 1, respectively, for CN xH y films were obtained. The microhardness of the film increased with the increase of parameter J∼ U F × (%N 2), while the influence of nitrogen concentration in the film on its microhardness and tribological properties was not revealed. The microhardness derived from nanoindentation measurements was in the range 3700–7000 N mm 2 depending on deposition conditions; the friction coefficient was 0.08–0.4 depending on measuring technique (scratch test or ball-on-disk test) and deposition parameters. Ball-on-disk tests revealed relativly high wear resistance of the best samples at a 5 N normal load. An increase of the load to 20 N noticeably resulted in an increase in the wear. The main factor which greatly influenced CN xH y film properties and the growth mechanisms was the ion bombardment of the film during the growth process.

Correlation of boron and nitrogen contents with the flux of energetic Ar+ ions at the substrate during the deposition of BN coatings by RF magnetron sputtering

Thin films of BN x O y have been deposited by RF magnetron sputtering from a BN target in Ar plasma (1 Pa) at different substrate RF bias conditions. The possibility of obtaining high-quality BN coatings at a target–substrate distance greater than the mean free path of B and N atoms has been investigated. The discharge characteristics have been measured by means of an electrostatic probe of the Langmuir type. The flux and energy of the Ar + ions have been determined and correlated to the net contents of boron and nitrogen as measured by means of the N(d,p) and 11 B(p,α) nuclear reactions. The results deduced by XRD, FTIR and nanohardness measurements show that under the experimental conditions used, the flux of Ar + ions at the substrates is insufficient to promote the formation of crystalline BN films.

Analysis of the etching of silicon in an inductively coupled chlorine plasma using laser thermal desorption

The etching of silicon by a chlorine inductively coupled plasma (ICP) was studied using laser desorption laser-induced fluorescence (LD-LIF) analysis to determine the surface coverage of chlorine during steady-state etching. Laser interferometry was used to measure etch rates, and optical emission actinometry and Langmuir probe analysis were used to characterize the plasma. The ICP operated in the dim mode for radio frequency (rf) powers ≲ 350 W and in the bright mode for higher powers. Under typical operating conditions in the ICP bright mode, the ion density was about 4× 1011/cm3, the electron temperature was 2.8 eV, and about 90% of the Cl2 was dissociated. The chlorine surface coverage in the dim and bright modes was ∼2.0× that with chlorine flow and the plasma off, and increased slowly with power. This coverage ratio monotonically increased from ∼1.6× to 2.5× that with the plasma off as the ion energy was increased from 16 to 116 eV by increasing the rf substrate bias voltage during bright mode operation. Since roughly equivalent adlayer chlorine contents were measured by LD-LIF under high ion current/fast etch conditions (ICP bright mode), and low ion current/slow etch conditions [ICP dim mode and reactive ion etching mode (substrate stage powered and no ICP power)], both the adlayer chlorine content and the etch rate seem be controlled by the ion current to the wafer.

Characterization of amorphous hydrogenated carbon nitride films prepared by plasma-enhanced chemical vapor deposition using a helical resonator discharge

Amorphous hydrogenated carbon nitride thin films (a-CNx:H) have been prepared by plasma-enhanced chemical vapor deposition of N2 and CH4 gases using a helical resonator discharge. The structural and optical properties of the deposited a-CNx:H films have been systematically studied as a function of the substrate temperature and radio frequency (rf) substrate bias. The chemical structure and elemental composition of the a-CNx:H films were characterized by Fourier transform infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The optical properties of the films were evaluated using transmission ultraviolet–visible spectroscopy. The morphology of the films was investigated by scanning electron microscopy and atomic force microscopy. The FT-IR and XPS studies demonstrate the presence of carbon–nitrogen bonds with hydrogenated components in the films. The film composition ratio N/C was found to vary from 0.127 to 0.213 depending on the deposition conditions. The Raman spectra, showing the G and D bands, indicate that the a-CNx:H films have a graphitic structure. It can be found that the optical band-gap Eg of a-CNx:H films is associated with graphitic clusters, while the decrease in Eg is correlated with an increase in the size and number of graphitic clusters. Combining the results of Raman and optical measurements, it can be concluded that a progressive graphitization of the films occurs with increasing the substrate temperature and rf substrate bias power, corresponding to bias voltage.