Matthew Goeckner

Model of energetic electron transport in magnetron discharges

A particle model of energetic electron transport in sputtering magnetron discharges is presented. The model assumes time‐independent magnetic and electric fields and supposes that scattering by neutral atoms is the dominant transport mechanism. Without scattering, we find that some orbits are confined indefinitely. Using the differential cross sections for elastic, excitation, and ionization collisions in argon, we perform a Monte Carlo simulation of the electrons emitted by ion bombardment of a planar magnetron cathode to predict the spatial distribution of ionization. We find good agreement with experimental measurements of the radial profile of ion flux to the cathode and of the axial profile of optical emission.

Observation of two‐temperature electrons in a sputtering magnetron plasma

We experimentally find that there are hot and cold electron components present in a sputtering magnetron plasma. The density of the hot component is greatest in the magnetic trap and decreases with the distance from the cathode. The cold electron density is negligible inside the trap and is approximately constant outside. The largest cold electron density is nearly as great as the hot electron density inside the magnetic trap.

Monte Carlo simulation of ions in a magnetron plasma

A simulation of ion dynamics in a planar magnetron discharge is performed using separate three-dimensional Monte Carlo codes for the electrons and ions. First, to predict the ionization sites, the orbits of energetic electrons are simulated for prescribed DC electric and magnetic fields, subject to collision with neutrals at random intervals. In the second code the predicted sites are used as the starting positions of ion trajectories. The ion trajectories are followed taking into account collisions with neutrals, turbulent electric fields, and the DC field. The authors report results for ion impact on the cathode and substrate anode surfaces (energy, angle, and spatial distribution) and ion parameters in the plasma (density, drift velocity, random energy, and transit time). To test these results they compare them to several previously reported experiments, and in most cases find good agreement. These simulation methods not only are useful for gaining an understanding of the magnetron plasma operation, but may also aid in designing magnetrons. >

Plasma doping for shallow junctions

In this article we review the characteristics of ultrashallow junctions produced by plasma doping (PLAD). PLAD is one of the alternate doping techniques being developed for sub-0.18 μm devices. Here, we describe results from a wide range of experiments aimed at the production of ultrashallow junctions. For the results shown here, a BF3 plasma was used to provide the dopant ions that were implanted into 150 and 200 mm Si substrates using wafer biases ranging from −0.14 to −5.0 kV. The ultrashallow junctions formed with this technique have been examined with both secondary ion mass spectrometry and electrical profiling techniques. Good sheet resistance uniformity, charging performance, structural quality, and photoresist integrity have been obtained. When PLAD is used in the production of sub-0.2 μm gate length p-metal–oxide–semiconductor field effect transistors, one finds subthreshold swing, off-state leakage, and hot-carrier reliability that are similar to beamline-implanted ones. In addition, higher dri...

Laser-induced fluorescence characterization of a multidipole filament plasma

A multidipole filament discharge was characterized using sub‐Doppler laser‐induced fluorescence (LIF). The ion temperature was found to be Ti=0.028±0.007 eV, measured in the center of an argon discharge. This stands in contrast to the much higher ion temperatures, 0.2<Ti<0.5 eV, reported by researchers using gridded electrostatic energy analyzers. The discrepancy is attributed to the energy resolution of the detectors, with the LIF providing more accurate measurements. In another result, the metastable excited‐state ion density was found to scale linearly with the electron density and the discharge current under most conditions. This experiment also demonstrates that LIF can be used for basic plasma physics research in multidipole discharges.

A source of hyperthermal neutrals for materials processing

In this letter, we describe a unique method of producing hyperthermal neutrals for material processing. The hyperthermal neutrals are produced by accelerating ions across a sheath from a plasma onto a surface. On impact, the ions are neutralized and reflected with ∼50% of their incident energy. These neutrals then bounce off of additional surfaces prior to impacting the target. This unique multiple bounce system was developed for the following reasons: to reduce contamination from sputtered surface material, improve beam uniformity, and reduce UV radiation in the beam path. As a test of this method, we built a prototype beam source and used it to ash photoresist at rates up to 0.022 μm/min. These rates are consistent with a predicted neutral beam flux, 2×1014 cm−2 s−1. In addition, a simple model is used to indicate that this method is capable of producing economically acceptable ash rates. Comparisons with other neutral-beam production methods are made.

Deposition and patterning of diamondlike carbon as antiwear nanoimprint templates

In this work, antiwear nanoimprint templates were made by depositing and patterning diamondlike carbon (DLC) films on Si and quartz. A capacitively coupled plasma enhanced chemical vapor deposition (PECVD) system was configured to deposit 100nm–1μm thick DLC films on Si and quartz substrates. These films were characterized with Raman spectroscopy, electron energy loss spectroscopy, atomic force microscopy, nanoindentation, contact angle measurements, and optical transmission measurements. The rf power and pressure of the PECVD process were varied to obtain uniform coating of DLC films with smooth surface (∼0.2nm rms), low surface energy (∼40mJ∕m2), and high hardness (∼22GPa). The resulting films’ wear resistance is more than three times better than quartz. The DLC films were patterned by nanoimprint lithography using polymethylmethacrylate (PMMA) followed by CF4 plasma etch. Thermal nanoimprint tests with DLC templates were performed in PMMA. Atomic force microscopy measurements indicated excellent patter...

Electron velocity distribution functions in a sputtering magnetron discharge for the E×B direction

The electron velocity distribution function is measured for the E×B (azimuthal) direction in a cylindrically symmetric, planar, sputtering magnetron discharge as a function of height above the cathode. Near the cathode, the distribution function is approximately a warm Maxwellian (Te≈2 eV) shifted in the E×B direction, indicating a strong azimuthal drift. Farther above the cathode, the distribution function is characterized by a cold (Te≈0.5 eV), Maxwellian bulk with energetic, asymmetric tails.

Measurements of the presheath in an electron cyclotron resonance etching device

The first direct measurement of a collisional Bohm presheath from plasma potential measurements is given. By measuring the presheath thickness in front of a grounded wafer stage, a determination of the collision mean free path for ions in an electron cyclotron resonance etching tool has been made. Presheaths were measured in N2 and CF4 plasma using an emissive probe. The presheath thickness in N2 was found to be linearly dependent on the mean free path. Measurements of CF4 plasmas, for which the collision cross sections are unknown, have shown results similar to those found for nitrogen. This result has enabled an extrapolation to be made of the effective cross section for collisions in plasmas created from CF4.

Collisional sheath dynamics

Using a collisional fluid model, we investigate the dynamics of the collisional sheath following the application of a large, negative, finite‐rise‐time, voltage pulse to a planar target. For a moderate amount of collisionallity, we find that the ion impact energy decreases significantly, while the sheath width and ion flux (i.e., the ion current) are not greatly reduced. The theory shows fair agreement with experimental measurements.