Flexible microdischarge arrays: Metal/polymer devices

Journal of Applied Physics

Giapis

2002

119

Extending the principle of operation of hollow cathode microdischarges to a tube geometry has allowed the formation of stable, high-pressure plasma microjets in a variety of gases including Ar, He, and H 2 . Direct current discharges are ignited between stainless steel capillary tubes (d ϭ178 m) which are operated as the cathode and a metal grid or plate that serves as the anode. Argon plasma microjets can be sustained in ambient air with plasma voltages as low as 260 V for cathode-anode gaps of 0.5 mm. At larger operating voltage, this gap can be extended up to several millimeters. Using a heated molybdenum substrate as the anode, plasma microjets in CH 4 /H 2 mixtures have been used to deposit diamond crystals and polycrystalline films. Micro-Raman spectroscopy of these films shows mainly sp 3 carbon content with slight shifting of the diamond peak due to internal stresses. Optical emission spectroscopy of the discharges used in the diamond growth experiments confirms the presence of atomic hydrogen and CH radicals.

Section: A Characteristics Of the Hollow Cathode Plasma Microjet Sourcementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hollow cathode sustained plasma microjets: Characterization and application to diamond deposition

Journal of Applied Physics

Giapis

2002

119

“…Our initial efforts were therefore focused on fabricating and testing multiple hole and line patterns in metal-dielectric-metal structures. Devices were constructed from thin copper foils (100 µm thick, 99.995% pure) which were spin-coated with polyimide films as described in [11]. These materials were chosen for degradation resistance when exposed to fluorocarbon chemistry, as well as for their flexibility.…”

Section: Silicon Etching Using Patterned Micro-dischargesmentioning

confidence: 99%

High-pressure micro-discharges in etching and deposition applications

J. Phys. D: Appl. Phys.

Giapis²

2003

High-pressure micro-discharges are promising sources of light, ions, and radicals and offer some advantages in materials processing applications as compared to other more conventional discharges. We review here results from etching experiments using stencil masks where the discharge is formed only in the pattern cutout. The mask consists of a thin metal-dielectric structure and is pressed against a Si wafer, which becomes part of the electric circuit. Pattern transfer takes place, albeit the profile shape appears to be limited by the expansion of the plasma into the etched hole at long etch times. We also review experiments on using micro-discharges as sources of radicals for materials deposition applications. In the latter case, the micro-discharges form in metal capillary tubes permitting incorporation of gas flow and a short reaction zone that can be controlled to favour production of specific radicals. We demonstrate these concepts by using CH 4 /H 2 chemistry for diamond deposition on a heated Mo substrate. Good quality micro-and nano-diamond crystals could be produced.

“…Since discharges can be formed in structures as small as 50 m, 8 wafers could be etched directly thus eliminating the need for a lithographic step. Furthermore, the ability to form microdischarges in flexible structures 9 could allow the patterning of curved surfaces such as cylinders and spheres. While the length scales over which these plasmas are formed may not be small enough for microelectronic applications, this patterning technique could assist in the fabrication of microelectromechanical systems where dimensions are often on the order of 10-500 m.…”

mentioning

confidence: 99%

“…Two-layer structures, which act as the stencil mask, were made from copper foils ͑100 m thick, 99.995% pure͒ spin coated with polyimide films as described in the literature. 9 These materials were chosen for their flexibility and degradation resistance when exposed to fluorine. Holes and slots were drilled or cut out mechanically in the twolayer structure to produce a desired pattern.…”

mentioning

confidence: 99%

Maskless etching of silicon using patterned microdischarges

Applied Physics Letters

Giapis

2001

Microdischarges in flexible copper-polyimide structures with hole diameters of 200 m have been used as stencil masks to pattern bare silicon in CF 4 /Ar chemistry. The discharges were operated at 20 Torr using the substrate as the cathode, achieving etch rates greater than 7 m/min. Optical emission spectroscopy provides evidence of excited fluorine atoms. The etch profiles show a peculiar shape attributed to plasma expansion into the etched void. Forming discharges in multiple hole and line shapes permits direct pattern transfer in silicon and could be an alternative to ultrasonic milling and laser drilling. © 2001 American Institute of Physics. ͓DOI: 10.1063/1.1388867͔Microdischarges have gained recent attention for several characteristics such as high-pressure operation and intense UV radiation.1-3 Optical studies in neon discharges have shown the presence of excited ionic states that lie more than 50 eV above the ground state.4 Furthermore, excimer formation in these discharges suggests a relatively large concentration of high-energy electrons.5-7 Such electrons should assist in the production of reactive radicals at high pressures, rendering microdischarges suitable for materials processing. While the use of these plasmas as light sources has been studied, to our knowledge, their potential as a reactive source has not yet been explored.A materials application of microdischarges that takes advantage of their size would be maskless pattern transfer. Since discharges can be formed in structures as small as 50 m, 8 wafers could be etched directly thus eliminating the need for a lithographic step. Furthermore, the ability to form microdischarges in flexible structures 9 could allow the patterning of curved surfaces such as cylinders and spheres. While the length scales over which these plasmas are formed may not be small enough for microelectronic applications, this patterning technique could assist in the fabrication of microelectromechanical systems where dimensions are often on the order of 10-500 m. 10This letter reports the operation of microdischarges in CF 4 /Ar gas mixtures and examines their use in patterning silicon. Two-layer structures, which act as the stencil mask, were made from copper foils ͑100 m thick, 99.995% pure͒ spin coated with polyimide films as described in the literature.9 These materials were chosen for their flexibility and degradation resistance when exposed to fluorine. Holes and slots were drilled or cut out mechanically in the twolayer structure to produce a desired pattern. Either a drilled copper foil or, in the case of etch experiments, a blanket n-type Si͑100͒ wafer was pressed against the mask. A schematic of the latter structure is shown in Fig. 1. The assembly was then placed in a reactor chamber and was pumped to 1 ϫ10 Ϫ6 Torr. Silicon wafers were cleaned prior to etching by dipping in a dilute HF solution ͑1-5 % in H 2 O͒ for 1 min and rinsing in deionized water. Microdischarges operated in direct curent mode are typically formed at 20 Torr with inflow of 75 sccm Ar and 25...