Edward F. Gleason

Growth of fluorocarbon polymer thin films with high CF2 fractions and low dangling bond concentrations by thermal chemical vapor deposition

Thermal chemical vapor deposition was used to deposit fluorocarbon films with chemical resemblance to bulk polytetrafluoroethylene. X‐ray photoelectron spectroscopy revealed that the films deposited from thermal decomposition of hexafluoropropylene oxide had fluorine to carbon ratios of 2.0 and CF2 fractions of 90% along with 10% of CF3 and CF moieties. Electron spin resonance results found the dangling bond density to be 1.2×1018 spins/cm3, low compared to conventional plasma polymerized films. Low dangling bond densities were achieved by using a clean source of CF2 in the absence of plasma source.

FLEXIBLE FLUOROCARBON WIRE COATINGS BY PULSED PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION

A method to coat thin wires, 25 μm in diameter, with fluorocarbon material that is flexible and conformal has been achieved using pulsed plasma enhanced chemical vapor deposition (PECVD). This process enables the chemical composition of the films to be tailored in order to achieve similar stoichiometry and chemical composition to bulk polytetrafluoroethylene [PTFE, (CF2)n, Teflon™]. The deposited film had a F/C ratio of 1.9 and a CF2 fraction of 65%. In comparison, a film deposited under continuously applied power had a F/C ratio of only 1.6 and a CF2 fraction of 32% and was found to form brittle wire coatings. The flexibility of the pulsed PECVD film was consistent with its connectivity number of 2.1 corresponding to an underconstrained, flexible material. In addition, the connectivity number for the brittle film was 2.5, consistent with an overconstrained brittle network.

Pulsed plasma-enhanced chemical vapor deposition from hexafluoropropylene oxide: Film composition study

Films deposited using pulsed plasma-enhanced chemical vapor deposition (PECVD) from hexafluoropropylene oxide (HFPO) were investigated by X-ray photoelectron spectroscopy (XPS). As compared to continuous rf PECVD, pulsed excitation increases the CF2 fraction in the film. Film composition was determined as a function of plasma processing conditions including on-time, off-time, pressure, flow rate, substrate temperature, electrode spacing, substrate potential, and input power. Varying the on–off pulsing cycle resulted in compositional control of the deposited films. At a low duty cycle [ton/(ton + toff)], up to 70% CF2 could be incorporated into the film. The input gas, HFPO, may facilitate greater CF2 incorporation into the films as this gas thermally decomposes into a difluorocarbene. Both absolute on-time and off-time, rather than simply duty cycle, are important parameters for determining film composition. A simple model was developed to describe the experimentally determined variation %CF2 as a function of substrate temperature and off-time. This model accounts for changes in film composition due to plasma-surface modification and differences in gas-phase chemistry. The model suggests that surface modification by the plasma is the dominant factor only for long on-times or for low deposition rates. However, the gas-phase concentration of CF2 relative to other film-forming species is typically the controlling factor under conditions which achieve the high %CF2 in the film. The gas-phase composition will depend on both abslute on-time and off-time, rather than simply on the duty cycle.

Molecular Design of Fluorocarbon Film Architecture by Pulsed Plasma Enhanced and Pyrolytic Chemical Vapor Deposition

Pulsed plasma enhanced chemical vapor deposition (pulsed PECVD) and pyrolytic chemical vapor deposition (pyrolyric CVD) of fluorocarbon films from hexafluoropropylene oxide (HFPO) have demonstrated the ability to molecularly design film architecture. Film structures ranging from highly amorphous crosslinked matrices to linear perfluoroalkyl chain crystallites can be established by reducing the modulation frequency of plasma discharge in plasma activated deposition and by eventually shifting mechanistically from an electrically activated to a thermally activated process. X-ray photoelectron spectroscopy (XPS) showed CF2 content increasing from 39–65 mol%. Fourier transform infrared spectroscopy (FTIR) showed an increasing resolution between the symmetric and asymmetric CF2 stretches, and a reduction in the intensity of the amorphous PTFE and CF3 bands. High-resolution solid-state 19F nuclear magnetic resonance spectroscopy (NMR) revealed an increasing CF2CF2CF2 character, with the pyrolytic CVD film much like bulk poly(tetrafluoroethylene) (PTFE). X-ray diffraction (XRD) patterns evidenced an increase in crystallinity, with the pyrolytic CVD film showing a characteristic peak at 2θ = 18° representing the (100) plane of the hexagonal structure of crystalline PTFE above 19°C.

A novel metal-insulator-metal structure for field-programmable devices

A metal-insulator-metal (MIM) capacitor structure has been developed for use in field-programmable gate arrays (FPGAs) as a voltage-programmable link (VPL). The structure relies on a combination of a refractory metal and aluminum as the lower electrode, and either a similar combination or aluminum alone as the top electrode. The insulator is prepared by means of plasma-enhanced chemical vapor deposition (PECVD). It comprises a sandwich of nearly stoichiometric silicon dioxide interposed between two like layers of silicon-rich silicon nitride. The structure has displayed characteristics desirable for use in emerging FPGA technology, including high density, low on-resistance, reduced capacitance, and low programming voltage. >

A flat-aluminum based voltage-programmable link for field-programmable devices

A new metal-insulator-metal (MIM) structure has been developed for use in field-programmable gate arrays (FPGAs) as a voltage-programmable link (VPL). The present capacitor structure relies on aluminum metallization; hence, it should be amenable to immediate application. The addition of minute amounts of titanium or molybdenum has been found to suppress hillock formation. The insulator, prepared by means of plasma-enhanced chemical vapor deposition (PECVD), comprises a sandwich of a nearly stoichiometric silicon dioxide interposed between two like layers of silicon-rich silicon nitride. This MIM structure has displayed characteristics desirable for use in the emerging FPGA technology including high density, very low on-resistance, reduced capacitance, low programming voltage, and the potential for further scaling to the sub-micron regime. >

High density metal cross-point laser linking

Laser-programmed inter-level metal connections have been developed as a means of achieving high-density linking for additive redundancy in restructurable logic and in wafer scale integration. The authors report on the successful linking of 8*8 cross-points of aluminium alloy lines separated by SiN/sub x/ insulation. Both processing and linking issues are addressed. The processing issues are extensions of the problems associated with any reliable two-level metal process with the added concerns of making structures for laser linking. The linking issues involve aiming a laser and forming a link with minimum peripheral damage to either the connecting metal lines or the underlying oxide and silicon.<<ETX>>

The Effects of Silicon Source Gas on PECVD SiO 2 Properties

Silicon dioxide was plasma-deposited at 300C using either the reaction of silane and nitrous oxide or the reaction of tetraethylorthosilicate with oxygen. The structural and electronic properties of films produced by both reactions were studied as functions of post-deposition heat treatments. The former reaction produced films which were more dense and less conductive than the latter. A model was developed to determine the amount and location of charge in the deposited films. The charge was found to be dependent on the reaction and the post-deposition anneal.