High-density Microwave Plasma Research Articles

Flexible Solar Cells Using Doped Crystalline Si Film Prepared by Self-Biased Sputtering Solid Doping Source in SiCl4/H2 Microwave Plasma.

We developed an innovative approach of self-biased sputtering solid doping source process to synthesize doped crystalline Si film on flexible polyimide (PI) substrate via microwave-plasma-enhanced chemical vapor deposition (MWPECVD) using SiCl4/H2 mixture. In this process, P dopants or B dopants were introduced by sputtering the solid doping target through charged-ion bombardment in situ during high-density microwave plasma deposition. A strong correlation between the number of solid doping targets and the characteristics of doped Si films was investigated in detail. The results show that both P- and B-doped crystalline Si films possessed a dense columnar structure, and the crystallinity of these structures decreased with increasing the number of solid doping targets. The films also exhibited a high growth rate (>4.0 nm/s). Under optimal conditions, the maximum conductivity and corresponding carrier concentration were, respectively, 9.48 S/cm and 1.2 × 10(20) cm(-3) for P-doped Si film and 7.83 S/cm and 1.5 × 10(20) cm(-3) for B-doped Si film. Such high values indicate that the incorporation of dopant with high doping efficiency (around 40%) into the Si films was achieved regardless of solid doping sources used. Furthermore, a flexible crystalline Si film solar cell with substrate configuration was fabricated by using the structure of PI/Mo film/n-type Si film/i-type Si film/p-type Si film/ITO film/Al grid film. The best solar cell performance was obtained with an open-circuit voltage of 0.54 V, short-circuit current density of 19.18 mA/cm(2), fill factor of 0.65, and high energy conversion of 6.75%. According to the results of bending tests, the critical radius of curvature (RC) was 12.4 mm, and the loss of efficiency was less than 1% after the cyclic bending test for 100 cycles at RC, indicating superior flexibility and bending durability. These results represent important steps toward a low-cost approach to high-performance flexible crystalline Si film-based photovoltaic devices.

High-density microwave plasma source using negative-permeability metamaterial with tuned wave attenuation

High-density plasma generated by waves with efficient wave power consumption is suitable for various dry processes. However, when we use microwaves as power sources, the electron density in a conventional microwave plasma source is limited within the range in which the permittivity of the plasma is positive. To overcome this drawback, a negative refractive index phenomenon is applicable, in which the permittivity and permeability are both negative and microwaves can propagate even in a negative-permittivity space with high electron density. In this report, we demonstrate a promising scheme for the efficient generation of high-density plasma by propagating microwaves in a negative-permeability space, and show the experimental observation of the enhancement of plasma generation using the lower imaginary part of the permeability.

Computational modeling study of the radial line slot antenna microwave plasma source with comparisons to experiments

The radial line slot antenna plasma source is a high-density microwave plasma source comprising a high electron temperature source region within the plasma skin depth from a coupling window and low electron temperature diffusion region far from the window. The plasma is typically comprised of inert gases like argon and mixtures of halogen or fluorocarbon gases for etching. Following the experimental study of Tian et al. [J. Vac. Sci. Technol. A 24, 1421 (2006)], a two-dimensional computational model is used to describe the essential features of the source. A high density argon plasma is described using the quasi-neutral approximation and coupled to a frequency-domain electromagnetic wave solver to describe the plasma-microwave interactions in the source. The plasma is described using a multispecies plasma chemistry mechanism developed specifically for microwave excitation conditions. The plasma is nonlocal by nature with locations of peak power deposition and peak plasma density being very different. The spatial distribution of microwave power coupling depends on whether the plasma is under- or over-dense and is described well by the model. The model predicts the experimentally observed low-order diffusion mode radial plasma profiles. The trends of spatial profiles of electron density and electron temperature over a wide range of power and pressure conditions compare well with experimental results.

PLASMA TREATMENT OF CIIR RUBBER WITH IMPROVEMENT OF ADHESION AND REAL CONTACT AREA

The adhesion force between a chloride-isobutene-isoprene rubber (CIIR) and stainless steel ball was studied. To decrease the adhesion force, the CIIR rubber was treated with high-density microwave plasma employing oxygen and argon gases. The experimental results showed that the adhesion force decreases with increasing the time of oxygen and argon plasma treatments. In addition, the contact microscope measurements revealed different surface structure with two gases. The real contact area also decreased with treatment time and dramatic changes were observed after 5 min treatment of CIIR rubber. The field emission scanning electron microscope image also showed that the subsurface of CIIR rubber pattern has changed with various plasma treatments. These results imply change in the morphology of CIIR rubber surface by plasma treatment is one reason for the decrease in adhesion forces.

Fast deposition of microcrystalline Si films from SiH 2Cl 2 using a high-density microwave plasma source for Si thin-film solar cells

Fast deposition rate of 27 Å/s for microcrystalline (μc-) Si films was investigated using a high-density and low-temperature microwave plasma source with a spoke antenna of SiH 4–H 2 and SiH 2Cl 2–H 2 mixtures. The film crystallization was promoted efficiently when film was fabricated using SiH 4 with an aid of large amount of hydrogen atom, while the volume fraction of void in the film was relatively the larger of 10–20%. On the other hand, the volume fraction of amorphous silicon phase in the μc-Si films were 20–30% with no significant void fractions in films fabricated from SiH 2Cl 2, although the volume fraction of the crystalline silicon phase was 75–85%. The role of chlorine in the growth of μc-Si films is discussed in terms of the chemistry of the H and Cl terminated growing surface. The preliminary result of p–i–n Si thin-film solar cell is demonstrated using μc-Si:H:Cl films as an intrinsic layer.

Ultrafast Deposition of Crystalline Si Films Using a High Density Microwave Plasma

AbstractA multi-pressure microwave plasma source is developed and is applied for the fast deposition of crystalline silicon films. In this paper, the plasma source is diagnosed firstly. Electron density, electron temperature and discharge gas temperature of the plasmas generated in ambient air are studied using optical emission spectroscopy (OES) method. By using the high density microwave plasma source, depositions of crystalline silicon films from SiH4+He mixture at reduced pressure conditions are investigated systematically. After optimizing the film deposition conditions, highly crystallized Si films are deposited at a rate higher than 700 nm/s. We also find that the deposited films are fully crystallized and crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.

Low-temperature Oxidation of Semiconductor Surfaces by use of a Novel High-density Microwave Plasma Apparatus

This paper describes a new microwave plasma oxidation apparatus with unique features addressing the near room temperature low temperature process for forming high quality dielectrics with minimum dopant deactivation and redistribution. With this new technique the oxide growth rate was studied as a function of time, gaseous ambient, pressure, applied microwave power and silicon substrate parameters to determine crystallographic oxidation rate anisotropy and dopant concentration dependent oxidation at temperatures much below 400 {degree sign}C. Furthermore, the plasma oxide was also electrically evaluated (C-V- and I-V curves) after as grown, a post plasma anneal up to maximum temperature of 700 {degree sign}C and a post-metallization forming gas anneal. The breakdown strength improved considerably up to 7 MV/cm and the interface trap density decreased much below 10^11 states/eVcm2 so that the oxide quality is comparable to thermal oxides.

High rate synthesis of crystalline silicon films from SiH4+He using high density microwave plasma

By using a high density microwave-induced plasma source, depositions of crystalline silicon films from SiH4+He mixture are investigated systematically. Microwave power and SiH4 flow rate are used as the variable deposition parameters. Results demonstrate that film deposition rate increases with increasing both the microwave power and the SiH4 flow rate. While film crystallinity promotes with increasing the microwave power but degrades with increasing the SiH4 flow rate. After optimizing the film deposition conditions, highly crystallized Si films are deposited at a rate higher than 1000 nm/s. Promotion of the dissociation efficiency of source gases and enhancement in the diffusion length of film precursors on growing surface are suggested to be main factors responsible for the simultaneous achievements of the high deposition rate and the high film crystallinity. Mechanisms under these phenomena are discussed in detail.

Fabrication of Carbon Nanotubes by Slot-Excited Microwave Plasma-Enhanced Chemical Vapor Deposition

Carbon nanotubes (CNTs) are fabricated by adopting plasma-enhanced chemical vapor deposition (PECVD) with a planar microwave plasma source. Plasma is produced by a slot antenna at 2.45-GHz microwave injection in CH4/H2 mixture. In this study, it is shown that avoiding the exposure of the substrate to the plasma drastically improves the CNT growth. Furthermore, it is found that the CNT quality can be controlled with the optimization of one of the steps in the catalyst treatment, such as the preheating procedure; the treated catalyst is considered to be unaffected by the heating in the high-density microwave plasma treatment during the CNT growth.

Rapid treatment of polyimide film surfaces using high-density microwave plasma for enhancement of Cu layer adhesion

A high-density microwave plasma has been applied to the surface of polyimide (PI) films as a treatment to enhance the adhesion of sputter-deposited copper layers. A very short (∼5 s) exposure to Ar plasma enhanced the contact angle from 72° to ∼14°. X-ray photoelectron spectroscopy and atomic force microprobe measurements showed an increase in hydrophilic radicals (–OH, –C O) and surface roughness, respectively, following the plasma treatment. Peel strength tests of Cu layers deposited on plasma-treated polyimide films showed that the plasma treatment significantly enhanced Cu layer adhesion.

Deposition of microcrystalline silicon films at ultrafast rate by using a new microwave induced plasma source

Synthesis of microcrystalline silicon (μc-Si) film at an ultrafast deposition rate over 100nm/s is achieved from SiH4+He by using a high density microwave plasma source even without employing H2 dilution and substrate heating techniques. Systematic deposition studies show that high SiH4 flow rate and working pressure increase film deposition rate while high He flow rate decreases the rate. On the other hand, crystallinity of deposited Si film decreases with increasing SiH4 or He flow rate and working pressure. Enhancements of gas phase and surface reactions during film deposition process are responsible for the achievement of high deposition rate and high film crystallinity.

Surface Modification of Fluorocarbon Polymer Film by High Density Microwave Plasma

Surface Modification of Fluorocarbon Polymer Film by High Density Microwave Plasma

Evolution of Film Crystalline Structure During the Ultrafast Deposition of Crystalline Si Films

ABSTRACTBy using a high density microwave plasma source, an ultrafast deposition rate over 1000 nm/s has been achieved for polycrystalline silicon (poly-Si) film deposition. We find that crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Systematic study of the deposition process has been performed as a function of the deposition duration. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.

Relationship between Real Contact Area and Adhesion Force of Plasma-Treated Rubber Sheets Against Stainless-Steel Ball

The adhesion force between a chloride-isobutene-isoprene rubber (CIIR) and stainless steel ball was studied in this paper. In order to decrease the adhesion force, the CIIR rubber was treated with high-density microwave plasma employing oxygen and argon gases. The experimental results showed that the adhesion force decreases with increasing treatment time and microwave power following both oxygen and argon plasma treatments. In addition, optical measurements revealed that the real contact area between a CIIR rubber and quartz plate decreases with decreasing adhesion force. The decreasing trend of the contact area was almost similar to that of the adhesion forces. The field emission scanning electron microscope image showed that the surface roughness generally increases with treatment time and microwave power, implying that roughening of rubber surface by plasma treatment is one of the reasons for the decrease in the adhesion force.

Complex MEMS: a fully integrated TOF micro mass spectrometer

A fully integrated mass spectrometer on one chip is presented. This miniaturized mass spectrometer (MMS) is predestinated for mobile measurements, portable applications as well as continuous process monitoring. MEMS technology allows all critical structures to be fabricated by a one mask anisotropic deep silicon etch. Hence, the MMS is very cost efficient due to its mass producibility. Its small size (5 mm × 10 mm) reduces the vacuum requirements by a few orders of magnitude, so that a one stage pumping system achieves the necessary vacuum. The operation is based on electron impact ionization and a time-of-flight mass filter. The electron beam for ionization is supplied by the electron source, which operates with a high density microwave plasma. The integrated ion optics extracts and focuses the beam into the mass separator, where short ion pulses diverge based on their mass-to-charge ratio. An energy filter keeps the ion beam monochromatic before it is recorded at the detector. Mass spectra of different gas compositions measured with the MMS are presented.

Mass spectra measured by a fully integrated MEMS mass spectrometer

Breakthrough measurements of a single chip mass spectrometer are presented. This planar integrated micro-mass spectrometer (PIMMS) is dedicated for mobile measurements, portable applications as well as for continuous process monitoring. The waferbased fabrication in MEMS technology allows a very cost-efficient mass production. All critical structures are fabricated by a one mask anisotropic deep silicon etch, avoiding alignment difficulties. The small size ( 5 mm × 10 mm) reduces the vacuum requirements by several orders of magnitude, thus a one stage pumping system can provide the necessary vacuum. The operation is based on electron impact ionization and a synchronous ion shield mass filter. The electron beam for ionization is supplied by a source, that extracts electrons from a high density microwave plasma. The integrated ion optics extract and focus the beam into the mass separator, where time variant electric fields separate the ions according to their mass-to-charge ratio. An energy filter ensures that the ion beam is monochromatic before it is finally recorded at the detector. The accomplished experiments prove the concept of the fully integrated mass spectrometer on a chip. Mass spectra of different gas compositions measured with the PIMMS are presented.

Mechanism of Oxidation of Si Surfaces Exposed to O2/Ar Microwave-Excited Plasma

Plasma oxidation of 200-mm-diameter Si wafer surface at low temperature (400 °C) with use of high-density microwave plasma in O2/Ar gas was investigated. Dependence of the time-averaged oxidation rate on the percentage O2 showed a maximum value of 0.95 nm/min at a few % O2 in Ar. However, the measured O radical density was considerably low in this condition, and hence the O radical is not considered to be a key species in the plasma oxidation. A good correlation was found between the oxidation rate and the electron density; the oxidation rate averaged for 10 min discharge is proportional to the square root of the electron density measured near the Si wafer. The experimental results are basically explained by the Jorgensen-Mott model: in a presence of electron flux from plasma, the O2 molecule adsorbed on SiO2 surface is dissociated into negative ions which are transported to the SiO2–Si interface.

Effect of substrate bias on high-rate synthesis of microcrystalline silicon films using a high-density microwave SiH4/H2 plasma

In this paper, we demonstrate the effect of dc substrate bias on high-rate deposition of microcrystalline silicon (μc-Si) films by using a high-density microwave plasma source. Film depositions are performed at a high silane concentration of 67% (deposition rate of ∼ 60 Å s−1) with a low substrate temperature of 250 °C. The μc-Si films deposited under appropriate negative dc substrate bias exhibit improved film crystallinity, mass density and reduced defect density along with thinner amorphous silicon incubation layer at the initial growth stage. These can be attributed to the beneficial effect of moderate ion bombardment as well as the less contribution of harmful short-lifetime radicals to film growth.

High rate growth highly crystallized microcrystalline silicon films using SiH 4/H 2 high-density microwave plasma

The plasma parameter for fast deposition of highly crystallized microcrystalline silicon (μc-Si) films with low defect density is presented using the high-density and low-temperature microwave plasma (MWP) of a SiH 4–H 2 mixture. A very high deposition rate of ∼ 65 Å/s has been achieved at SiH 4 concentration of 67% diluted in H 2 with high Raman crystallinity I c / I α > 3 and low defect density of 1–2 × 10 16 cm − 3 by adjusting the plasma condition. Contrary to the conventional rf plasma, the defect density of the μc-Si films strongly depend on substrate temperature T s and it increased with increasing T s despite T s below 300 °C, suggesting that the real surface temperature at the growing surface was higher than the monitored value. The sufficient supply of deposition precursors such as SiH 3 at the growth surface under an appropriate ion bombardment was effective for the fast deposition of highly crystallized μc-Si films as well as the suppression of the incubation and transition layers at the initial growth stage.

Characterisation of high-quality thick single-crystal diamond grown by CVD with a low nitrogen addition

Single-crystal homoepitaxial diamond has been grown by chemical vapour deposition using a high-density microwave plasma. It has been shown that the growth rate can be increased by factors of up to 2.5 by adding small concentrations (2 to 10 ppm) of nitrogen to the gas phase. Free-standing specimens up to 1.7 mm thick have been characterised using optical absorption, cathodoluminescence, photoluminescence and Raman spectroscopies, and by electron paramagnetic resonance. These techniques all demonstrate that the colourless type IIa material is of excellent quality with total defect concentrations not exceeding 200 ppb, and is ideally suited for optical and electronic applications.