High Density Oxygen Plasma Research Articles

Fabrication of Micro-Pillar by plasma etching texturing of Carbon-Based thin film

Surface texturing of a carbon-based thin film is the critical technology in the development of functional surface for many kinds of sensors. This study explored the possibilities of processing the carbon film’s surface by means of plasma etching to produce micro-pillars. Circular dots with a diameter of 25 μm, 50 μm, and 100 μm were printed on a thick carbon film. A high density oxygen plasma was generated by a combination of RF and DC power in a vacuum chamber. The high density plasma was applied onto the surface of a diamond-like carbon film. The printed pattern serves as a mask-like in the lithography technique. The oxidation reaction was expected on the exposed surface, i.e. the area surrounded the dots. The results show the oxidation effectively removed the carbon on the unmasked area producing 3D circular patterns. The plasma processing, which was carried out for 2 h, was monitored and diagnosed using optical emission spectroscopy (OES). The oxidation was controlled by atomic oxygen which was the dominant species observed in the plasma. The removal (etching) rate was 9 μm/h with 91%, 98% and 99% pattern accuracy related to the larger diameter studied in this work. Observations using a Raman spectroscopy confirmed that the printed mask effectively protects the DLC from the etching process and other indirect processes.

Contact Angle Relaxation and Long-Lasting Hydrophilicity of Sputtered Anatase TiO2 Thin Films by Novel Quantitative XPS Analysis.

The contact angle relaxation of TiO2 surfaces is an important problem that must be understood, particularly for long-lasting hydrophilicity under dark conditions. The relaxation of sputtered anatase TiO2 thin films over a long time (∼22 days) in an atmospheric environment was observed using quantitative XPS analysis. A new peak was identified as H2O within a donor-acceptor complex at ∼2.57 eV above the lattice oxygen peak. This donor-acceptor complex turns out to be a key factor for long lasting hydrophilicity, and our model is presented. Adventitious carbon contamination was not the main cause of the contact angle relaxation. Instead, samples with lower amounts of donor-acceptor complexes ( IDAC/ Ibulk ≤ ∼5%) underwent contact angle relaxation over time, and samples with a high density of donor-acceptor complexes ( IDAC/ Ibulk ≥ ∼10%) showed good hydrophilicity (contact angle ≤20°) over 22 days. Larger amounts of basic Ti-OH relative to acidic OHbridge ( ITi-OH/ Ibridge ≥ 1) resulted in greater amounts of donor-acceptor complexes ( IDAC/ Ibulk ≥ ∼10%). Thus, basic Ti-OH groups interact with H2O by forming a strong electrostatic donor-acceptor complex, leading to long-lasting hydrophilicity. Indeed, TiO2 was transformed to show long lasting hydrophilicity by high-density oxygen plasma treatment by forming sufficient Ti-OH groups and H2O molecules in the donor-acceptor complexes. Contact angle relaxation is closely related to the interactions between water molecules and the TiO2 surface in the dark. It is suggested that the relaxation depends on the number of electrostatic donor-acceptor complexes. This study provides new insight by linking theoretical studies with the experimental contact angle at the TiO2 surface in an ambient environment and is the first study that provides the presented relaxation mechanism.

High density oxygen plasma ashing of CVD-diamond coating with minimum damage to WC (Co) tool substrates

High density oxygen plasma ashing of CVD-diamond coating with minimum damage to WC (Co) tool substrates

Micro-texturing into DLC/diamond coated molds and dies via high density oxygen plasma etching

Diamond-Like Carbon (DLC) and Chemical Vapor Deposition (CVD)-diamond films have been widely utilized not only as a hard protective coating for molds and dies but also as a functional substrate for bio-MEMS/NEMS. Micro-texturing into these hard coated molds and dies provides a productive tool to duplicate the original mother micro-patterns onto various work materials and to construct any tailored micro-textures for sensors and actuators. In the present paper, the high density oxygen plasma etching method is utilized to make micro-line and micro-groove patterns onto the DLC and diamond coatings. Our developing oxygen plasma etching system is introduced together with characterization on the plasma state during etching. In this quantitative plasma diagnosis, both the population of activated species and the electron and ion densities are identified through the emissive light spectroscopy and the Langmuir probe method. In addition, the on-line monitoring of the plasmas helps to describe the etching process. DLC coated WC (Co) specimen is first employed to describe the etching mechanism by the present method. Chemical Vapor Deposition (CVD) diamond coated WC (Co) is also employed to demonstrate the reliable capacity of the present high density oxygen plasma etching. This oxygen plasma etching performance is discussed by comparison of the etching rates.

Motion-Controlled Precise Stamping for Microtexturing onto Aluminum Sheet

Mass production of heat radiation devices requires for fine stamping of micro-textured patterns in the order of micro-meters in dimension onto the sheet product. In this duplication of micro-textured patterns, an original mother micro-pattern in the convex type has to be transferred onto the metallic sheet in the concave type with sufficient accuracy. The authors have proposed a micro texturing of original micro patterns onto the DLC coated mother die-and mold-unit. Once this unit is inserted and fixed in the stiff cassette die-set, the CNC-controlled stamping system works well for progressive stamping process to duplicate the original micro-patterns onto aluminum sheet. In the present paper, two kinds of motion in the stamper were designed to investigate the effect of loading and unloading sequences on the geometric accuracy in micro-texturing. Both the macroscopic and microscopic plastic deformations were described by SEM observation. First, high density oxygen plasma etching method was introduced to explain how to fabricate the micro-textured DLC-die unit. The constant-load motion control was employed as a normal motion in CNC-stamping to describe the microscopic metal flow by piercing the DLC micro-punch into the aluminum sheet. Deep micro-cavities with 3.5x3.5x3 μm3were successfully formed by application of high pressure in stamping. The pulse-wise motion control was further used to improve the geometric accuracy in the present duplication of original micro-texturing pattern onto the aluminum sheet. Owing to the incremental loading in this motion control, the micro-friction was significantly reduced to activate the microscopic metal flow in formation of micro-cavities.

Recycling of DLC-Coated Tools for Dry Machining of Aluminum Alloys via Oxygen Plasma Ashing

DLC coated tools have been widely utilized in the dry milling and cutting of aluminum alloy parts and components for automotive industries and cellular phone makers. Most of these tools are inevitably exchanged with new ones to preserve high quality of machined products. Then, the used DLC coating must be removed or ashed away before grinding and polishing. Complete removal of used DLC coating plays a key to make DLC-recoating onto the ashed surface of tools for their reuse. High density oxygen plasma ashing provides a solution to make perfect ashing of DLC coating together with metallic interlayers before recoating. In the present paper, this plasma system with quantitative diagnosis instrumentation is first stated to describe the effect of processing conditions on the ashing behavior. Two types of end-milling tools were prepared to prove that the whole DLC-coating should be completely removed with fast rate. This ashed tool substrate was ground and DLC-recoated to demonstrate that the reused tools have the same machinability in dry as the original virgin tools through dry milling experiments.

Complete ashing of used DLC coating for reuse of the end-milling tools

Abstract Diamond like carbon (DLC) coated tools have been widely utilized in the dry milling and cutting of aluminum alloy parts and components. Since the DLC film deteriorates during milling operations by reduction of the film thickness or adhesive wear, it must be removed or ashed away before grinding, polishing and recoating not only to preserve high quality of the machined products but also to reduce the production cost. In the present paper, high density oxygen plasma ashing was applied for the complete removal of the used DLC coating together with the chromium interlayers without damaging the tool substrate materials. DLC-coated end-milling tools were prepared to prove that the whole DLC coating could be completely removed at a faster rate than by conventional approaches.

Micro-Texturing onto Amorphous Carbon Materials as a Mold-Die for Micro-Forming

Among various kinds of carbon materials, two types of amorphous carbon were employed as a mold-die material for micro-forming. Diamond like carbon (DLC) has sufficient strength and toughness as a protective coating onto the steel and WC (Co) substrates. Glassy carbon is a solid material which also has high strength even at the elevated temperature under inert gas atmosphere. These two materials are selected to fabricate the micro-textured mold-die as a mother tool to duplicate this micro-textured pattern onto the metallic and polymer sheets via table-top CNC micro-forming systems. High density oxygen-plasma etching and pico-second laser machining were developed to make micro-texturing onto the above two mold-die materials. In the former, micro-groove and micro-grid patterns were formed on the DLC coating; table-top CNC stamping system with CNC-feeder and cropper was used to duplicate these patterns onto the aluminum sheets in dry and at the room temperature. In the latter, micro-wedge patterns were imprinted onto the glassy carbon substrate; table-top CNC mold-stamping system with heating equipment was utilized for duplication of these patterns onto thermoplastic polymer sheets above the glass transition temperature. Formation of micro-textures onto these amorphous carbon materials provides us a new tool to fabricate the micro-patterned parts and devices in mass production via cold and hot stamping processes.

Oxygen plasma etching of diamond-like carbon coated mold-die for micro-texturing

Diamond-like carbon (DLC) coating via PVD/CVD on the SKD11 substrate was employed to make micro-texturing by using high density oxygen plasma etching. Original pattern by metal chromium was first line-drawn on the surface of DLC coating; then, it was subjected to oxygen plasma etching. Even without any hazardous etchants such as CF4, high etching rate was attained only by using oxygen gas; i.e. 5μm/H. Plasma diagnosis by spectroscopy proved that this etching process should be controlled by activated oxygen atom flux of {O, O*}. Direct chemical reaction by C (in DLC)+O→CO, or, C (in DLC)+O*→CO, drove this etching process. Detection of CO peaks in the wave length range from 200 to 300nm also proved that this oxygen plasma etching should be advanced by chemical reactions. This etching behavior was insensitive to line width (WG) and pitch width (PG) for 2μm<WG<100μm and 5μm<PG<100μm. Scanning electron microscope and laser-profilometer were also used to make precise measurement on the etched profiles.

New oxygen radical source using selective sputtering of oxygen atoms for high rate deposition of TiO2 films

We have developed a new oxygen radical source based on the reactive sputtering phenomena of a titanium target for high rate deposition of TiO2 films. In this oxygen radical source, oxygen radicals are mainly produced by two mechanisms: selective sputter-emission of oxygen atoms from the target surface covered with a titanium oxide layer, and production of high-density oxygen plasma in the space near the magnetron-sputtering cathode. Compared with molecular oxygen ions, the amount of atomic oxygen radicals increased significantly with an increase in discharge current so that atomic oxygen radicals were mainly produced by this radical source. It should be noted that oxygen atoms were selectively sputtered from the target surface, and titanium atoms sputter-emitted from the target cathode were negligibly small. The amount of oxygen radicals supplied from this radical source increased linearly with increasing discharge current, and oxygen radicals of 1 × 1015 atoms/s/cm2 were supplied to the substrate surface at a discharge current of 1.2 A. We conclude that our newly developed oxygen radical source can be a good tool to achieve high rate deposition and to control the structure of TiO2 films for many industrial design applications.

A ground-based radio frequency inductively coupled plasma apparatus for atomic oxygen simulation in low Earth orbit

A radio frequency (rf) inductively coupled plasma apparatus has been developed to simulate the atomic oxygen environment encountered in low Earth orbit (LEO). Basing on the novel design, the apparatus can achieve stable, long lasting operation, pure and high density oxygen plasma beam. Furthermore, the effective atomic oxygen flux can be regulated. The equivalent effective atomic oxygen flux may reach (2.289-2.984) x 10(16) at.cm(2) s at an oxygen pressure of 1.5 Pa and rf power of 400 W. The equivalent atomic oxygen flux is about 100 times than that in the LEO environment. The mass loss measured from the polyimide sample changes linearly with the exposure time, while the density of the eroded holes becomes smaller. The erosion mechanism of the polymeric materials by atomic oxygen is complex and involves initial reactions at the gas-surface interface as well as steady-state material removal.

Effects of High-Density Oxygen Plasma Posttreatment on Field Emission Properties of Carbon Nanotube Field-Emission Displays

The effects of oxygen plasma posttreatment (PPT) on the morphology and field emission properties of carbon nanotube (CNT) arrays grown on silicon substrates are proposed and experimental results are reported. Oxygen PPT led to an enhancement in the emission properties of CNTs, which showed an increase in total emission current density and a decrease in turn-on field after plasma treatment. Scanning electron microscopy (SEM) images showed reduced densities of the CNTs, which resulted in a decrease of the screening effect in the electric field. Raman spectra showed an increase in the number of defects which served as field-emission sites when the plasma power or treatment time with the plasma increased. Transmission electron microscopy (TEM) images were used to identify the quality of the nanotubes, so that we could clearly find evidences of improvement in the field emission properties after plasma treatment. The measurement of electrical characteristics revealed improved field emission properties under proper plasma conditions. The turn-on field decreased from 4.8 to 2.5 V/µm, and the emission current density increased from 78.7 µA/cm2 to 18 mA/cm2 at an applied field of 5.5 V/µm.

Application of polyimide sacrificial layers for the manufacturing of uncooled double-cantilever microbolometers

ABSTRACTIn this paper, a low-temperature surface micromachining module with two sacrificial layers of polyimide is developed for the manufacturing of double-cantilever microbolometer focal plane arrays. The use of spin-on polyimide allows an all-dry final release step overcoming stiction problems often encountered in wet sacrificial etching processes. For the patterning of the polyimide, a plasma-enhanced chemical vapor deposited silicon oxide is employed as a mask layer. Anisotropic etching of both the mask film and the polyimide layer is accomplished by reactive ion etching. After patterning structural layers, sacrificial etching of the polyimide is conducted using an isotropic dry etch process in high-density oxygen plasma.

Comparison of silicon dioxide layers grown from three polymethylsiloxane precursors in a high-density oxygen plasma

We have compared the elemental composition, growth rates, and hardness of silicon dioxide layers grown from hexamethyldisiloxane (HMDSO), octamethylcyclotetrasiloxane (OMCTS), and tetramethylcyclotetrasiloxane (TMCTS) in a high-density electron cyclotron resonance oxygen plasma. Hard colorless coatings could be grown from each precursor; coating composition, growth rates, and hardness depended strongly on the ratio of oxygen to precursor flow. At the highest O2/precursor flow ratios (4:1 for HMDSO and 8:1 for OMCTS and TMCTS), the coatings were SiO2-like with oxygen-to-silicon ratios close to 2:1 and carbon percentages as low as 12% for HMDSO, 3.4% for OMCTS, and 1.4% for TMCTS. Growth rates were 0.7–1.1 μm/min, initially increasing with the O2/precursor flow ratio; final coating thicknesses after 5 min were 3.5 μm to 5.5 μm. Coating hardness values generally increased with increasing O2/precursor flow ratio, attaining 6 GPa, 7.4 GPa, and 8.7 GPa for HMDSO, OMCTS, and TMCTS, respectively.

Ge-doped SiO 2 thin films produced by helicon activated reactive evaporation

Ge-doped SiO 2 thin films for optical waveguide application were produced at low temperature by using an improved helicon plasma assisted reactive evaporation technique. Pure Si and Ge materials were simultaneously evaporated from two separated crucibles by using e-beams into high-density oxygen plasma to form the oxide films on a substrate. The film density was enhanced by supplying an r.f. bias to the substrate. Nearly H-free Ge-doped SiO 2 thin films with very high atomic density (∼0.66×10 23 cm −3), good adhesion and very low surface roughness were produced. The influence of deposition conditions, mainly the helicon r.f. power and substrate bias, on the properties of the films was studied by using surface profilometer, ellipsometer, atomic force microscope, Rutherford backscattering spectrometry, Fourier transform infrared spectrometry, and field emission scanning electron microscope.

Polyimide sacrificial layer and novel materials for post-processing surface micromachining

We present a low-temperature post-processing module, utilizing polyimide as a sacrificial layer and novel materials such as PECVD SiC and metals (sputtered aluminium and titanium) as structural layers. The use of spin-on polyimide allows an all-dry final release step overcoming stiction problems often encountered in wet sacrificial etching processes. The spinning and curing procedure has been tailored to the specific needs of the IC-compatible post-process module. For the patterning of the polyimide, thin films of aluminium, PECVD silicon oxide or silicon carbide are employed as a mask layer. Anisotropic etching of the mask film and of the polyimide layer is accomplished by RIE. After patterning the structural layer, sacrificial etching of the polyimide is done using an isotropic dry etch process in high-density oxygen plasma. An underetch rate of 4 μm min−1 is achieved. Compatibility with different structural materials is tested and test structures are designed and realized in a fully post-processing surface micromachining module.

Efficient Production of O- by Dissociative Attachment of Slow Electrons to Highly Excited Metastable Oxygen Molecules

In this paper, the mechanism for efficient production of O- in the afterglow of a low-pressure and high-density oxygen plasma has been described. We proposed a new production process, the dissociative attachment of slow electrons to highly excited metastable oxygen molecules O2 (A3 Σu+, A'3Δu, c1Σu-). The electron attachment frequency has been obtained from the experimental results, and was significantly high for the electron temperature of less than 2 eV. The cross section, σDA, for this process was evaluated by a quantum mechanical approach. σDA at 0.1 eV was larger by two-orders of magnitude than the peak value at 6.7 eV for the ground state O2 (X3Σg+). The enhancement of the electron attachment frequency at low temperature can be explained by dissociative attachment of slow electrons to O2 (A3Σu+, A'3Δu, c1Σu-).

Response surface study of resist etching in high density oxygen plasma and interactions of O2 plasma with NiFe, Cu, Ta, and Al2O3

Etching of a photosensitive polymer in high density oxygen plasma was studied. The polymer is a commonly used insulation material in a magnetic recording head. A quantitative relationship between etch rate and inductive power, bias power, and pressure was established by using the response surface method. Etch rate was found to increase with both inductive power and bias power, and a maximum etch rate was found at about 5 mTorr pressure. The effect of exposing the commonly used materials in magnetic recording heads such as NiFe (81/19 wt %), Cu, Ta, and Al2O3 to high density oxygen plasma was also investigated. Electron spectroscopy for chemical analysis and Rutherford backscattering spectroscopy were used to characterize the plasma-exposed samples. It was found that exposure to high-density oxygen plasma caused rapid oxidation of Cu, segregation and oxidation of Fe at the surface of NiFe, relatively slight oxidation of Ta, and no change in the physical thickness or the composition of Al2O3.

Low dielectric constant, fluorine-doped SiO2 for intermetal dielectric

Shrinking device geometry has produced a need for lower dielectric constant materials for intermetal dielectric to reduce circuit RC time constants and intertrace ‘‘cross-talk’’ capacitance and reduce power consumption at high frequency. One such material is F-doped SiO2. This study utilized an electron cyclotron resonance high-density oxygen plasma source to produce SiO2 from a mixture of SiH4 and SiF4, O2, and Ar. The total silicon gas flow was held constant and the ratio of SiH4 to SiF4 was varied from 0% to 100%. The fluorine content was measured using nuclear resonance analysis (NRA) with the reaction 19F(p,αγ)16O. A comparison of the NRA data and the ratio of the Fourier transform infrared Si–F absorbance near 934 cm−1 to the Si–O peak near 1080 cm−1 gives a proportionality constant of 144. The refractive index and dielectric constant were determined as a function of fluorine content. The dielectric constant decreased linearly from 4.0 at zero F to 3.55 at 10.5 at. % F and the refractive index decreased from 1.474 to 1.417. Film stress, thermal stability, moisture absorption, and electrical breakdown were also measured. Film stress decreased from 150 to 70 MPa compressive as the F content increased.

Effect of oxygen plasma annealing on superconducting properties of Bi2(Sr,Ca)3Cu2Ox and YBa2Cu3O7−δ thin films

Thin films of the Bi2(Sr,Ca)3Cu2Ox and YBa2Cu3O7−δ system were annealed at 400 °C in a high-density oxygen plasma and its effect on superconducting properties was investigated. After being annealed in the oxygen plasma, their superconducting transition temperatures decreased by about 10 K and 2 K, respectively, and the c-axis lattice constants of these films were also found to decrease as a result of the annealing in the oxygen plasma. These results suggest that excessive oxygen incorporated into the films by the annealing in the oxygen plasma caused the excessive hole carriers, which deteriorated the superconducting transition temperatures of these films.