D.T. Tran

Investigation on microwave plasma diamond etching

This paper reports a Lambda Technologies, 2.45 GHz, 1.5 kW, microwave plasma-assisted etching reactor utilized to develop anisotropic and high rate etching processes on a variety of diamond substrates including polycrystalline, nanocrystalline and single substrates. This etching system consists of a 25 cm diameter discharge located inside a 30 cm microwave resonant cavity applicator. The plasma etcher also incorporates a rf bias for the substrate that operates at 13.56 MHz with induced dc bias up to 250 V.m The electron temperature Te, charge density ne and electron energy distribution function (EEDF) are measured using a single Langmuir probe (SLP). Direct comparisons are made at selected pressures for the reactor operating with and without electron cyclotron resonance (ECR) magnets.

Characterization of a Microwave Plasma Etching Reactor

Summary form only given. Plasma-assisted etching is used extensively for device fabrication processes in the semiconductor and MEMS fabrication industries. One variation of low-pressure, high-density plasma-assisted etching machines is the microwave ECR etcher. In this paper, a plasma etcher based on low pressure microwave plasmas built by Lambda Technologies is characterized for its operating properties. It is investigated at low pressures from 1 m Torr and up as it is operated both with and without ECR magnets. The 2.45 GHz microwave plasma-assisted etching reactor consists of a 25 cm diameter discharge located inside a 30 cm cavity applicator and operates in two distinct excitation modes: (1) an ECR (electron cyclotron resonance) plasma source operating at pressures of 1-10 mTorr and (2) a non-ECR, non-magnetized mode operating at higher pressures of 4 mTorr-10 Torr. The different modes of operation and the wide pressure operating region of this plasma source provide a wide range of atomic and molecular radicals and ions enabling a variety of etching recipes. Both conducting and insulating substrates can be etched because the plasma source has an independent rf bias capability for the substrate holder which facilitates controlled reactive ion etching at low pressures. Additionally, the plasma etching system includes temperature control for the substrate holder. In this paper, the operating modes and plasma behavior of ECR and non-ECR plasma discharges are investigated. The electron temperature, Te, charge density ne and electron energy distribution function (EEDF) are studied using single Langmuir probe (SLP). Direct comparisons are made at selected pressures for the reactor operating with and without ECR magnets. For example, at a pressure of 4 mTorr, the electron distribution function (EEDF) measurement results follow closer to the Maxwellian distribution without magnets and follow closer to the Druyvesteyn distribution with ECR magnets. The charge density uniformity of plasma is also investigated. At a pressure of 10 mTorr and without ECR magnets, the charge density of the plasma is as high as 5x1012 cm-3.

Diamond electron stripping foils for high energy ion beams

Summary form only given. Performance issues associated with electron stripping foils become critical for the production of accelerator ion beams at extremely high powers and high Z values. Increases in absorbed power lead to decreases in foil lifetime. Diamond stripping foils offer the potential of an improved lifetime as compared to carbon stripping elements based on graphitic carbon. This report describes fabrication, modeling, and preliminary testing observations of polycrystalline diamond electron stripping foils. Two different foil types are described. In the first, the diamond thickness is on the order of a micrometer and the foil is designed to serve as an electron stripper for heavy ions in the National Superconducting Cyclotron. In the second design, the foils are approximately 50 mum thick to absorb the entire beam energy. These foils are used to simulate power absorption levels such as may be expected in the rare isotope accelerator design. The modeling includes thermal calculations based on a beam spot of 3 mm diameter incident on a 10times10 mm foil and considers varying values of thermal conductivity and emissivity. Testing of the thick foils was performed using a 136Xe19- beam with energy of seven MeV/u

Synthesis of ultrananocrystalline diamond films by microwave plasma assisted chemical vapor deposition system

Summary form only given. Microwave plasma assisted chemical vapor deposition (MPACVD) is one of the techniques used to grow ultrananocrystalline diamond (UNCD) films in the laboratory. UNCD films are characterized as smooth films consisting of few-10s nanometer sized crystals of diamond. The exceptional properties of these films, such as high hardness and chemical inertness combined with their small crystal size and smoothness and excellent mechanical properties such as high Youngs modulus, fracture toughness and low coefficient of friction, have suggested applications as a protective, hard coating material, a material/substrate for micromechanical systems and a robust conducting coating for electrochemical electrodes. The objective of this study is to deposit both thin (less than 100 nm thick) and thick (~50 micrometer thick) UNCD films of high quality across 7.5 cm diameter substrates. In this paper we report on the development of process methods to grow UNCD films using a MPACVD system. Three different gas mixtures studied include H2:Ar:CH4, N2:Ar:CH4 and H2:He:CH4. For these three plasma discharges the process for UNCD film deposition is investigated over a wide pressure range (60-180 torr) and substrate temperature range (400-8000 C). UNCD films are grown on Si (100), p-type boron doped, substrates with thicknesses ranging from 58 nm to greater than 70 mum. The effect of various inputs such as feed gas mixture, pressure, substrate temperature and nucleation methods on growth rate, surface morphology, uniformity, and conductivity of UNCD diamond films is investigated. The highest growth rate of 1.12 mum/h was achieved at 180 torr, with gas mixtures of H2:Ar:CH4 = 4:100:2 seem and 3 kW microwave power. Film surface roughness, as low as 10 nm, was obtained as measured by AFM microscope

Local Area Materials Processing using a Microstripline-Based Miniature Microwave Discharge

Summary form only given. Miniature discharges and their potential use for local area materials processing are investigated in this study. The objective of this study is to do materials processing steps including etching, surface activation, and plasma-assisted CVD on localized areas by applying a small discharge to only the region being processed. A miniature microwave plasma discharge applicator design based on microstripline technology is applied to create a miniature stream of plasma species. The diameter of the plasma stream considered in this study ranges from 1 millimeter down to 10s microns. The miniature microwave plasma discharge is created using 2.45 GHz microwave energy inside a 1-2 mm tube with an aperture on the end. Through this aperture the plasma stream for materials processing is formed. The microwave plasma source used in this investigation has a microstripline coupling structure with the discharge created inside 1 mm and 2 mm inner diameter quartz tubes. The microwave energy couples to the discharge via the stripline. The stripline has a characteristic impedance of 50 ohms and is connected to a microwave power supply operating at 1 watt to 100 watts. The discharge tube is orientated perpendicular to the stripline conductor. The characteristics of this discharge have been measured with electron densities in the range of 1012 to over 1014 cm-3 depending on the pressure, power and feed gas composition. Two materials processing applications are investigated including etching and plasma-assisted CVD. Specifically, an argon/SF6 feed gas mixture is used to create a plasma stream with radicals for silicon etching. And, an argon/methane feed gas mixture is used to create a plasma stream for amorphous carbon deposition. A CAD-guided automated path generation system is developed to assist manufacturing micro-structures/patterns automatically using the micro plasma applicator. Based on the CAD model of a micro-structure/pattern and the model of the microwave plasma source, a path of the plasma applicator can be automatically generated. It is fed to the control system of an xyz positioning stage to generate relative motion between the substrate and the plasma applicator for either etching or plasma-assisted CVD process