D. M. Shaw

Reduction of microtrenching and island formation in oxide plasma etching by employing electron beam charge neutralization

During plasma etching of oxide thin-film patterns, nonuniform charge buildup within etching features results in formation of microtrenches. Near the etch endpoint, the underlying film layer adjacent to the feature edges is exposed first, leaving an oxide island in the feature center and potentially causing underlayer damage before the endpoint is reached. Herein, a directional electron flux is added to the plasma ion flux incident on the etching substrate with the goal of minimizing microtrenching and oxide island formation. Scanning electron microscopic images of patterns etched with added electron irradiation show a reduction in microtrenching and oxide island formation as compared to patterns etched under identical conditions without electron irradiation. A computer simulation shows that the added electron irradiation reduces microtrenching by allowing more uniform ion flux to reach the feature bottom.

Radio-frequency plasma potential variations originating from capacitive coupling from the coil antenna in inductively coupled plasmas

The radio-frequency plasma potential in a stove top inductively coupled plasma source is measured by a capacitive probe. The experimental results are compared to a crude circuit model which accounts for capacitive coupling between the rf coil and the bulk plasma. The capacitive coupling model has three terms: the dielectric window capacitance, the sheath capacitance between the dielectric window and the bulk plasma, and the bulk plasma to ground sheath capacitance. The crude circuit model predictions are verified by quantitative comparison with the measured rf plasma potential in the bulk argon plasma at pressures from 1 to 20 mTorr and radio-frequency (13.56 MHz) plasma power levels from 60 to 1000 W. Finally, the measured ion energy spectrum, as determined by a retarding potential analyzer, agrees with rf plasma potential measurements over the entire range of experimental conditions.

Large area radio frequency plasma for microelectronics processing

Radio‐frequency (rf) inductively coupled planar plasma (ICP) provides a better way to generate spatially confined high density gas discharge plasmas for microelectronics processing. Commercial processing equipment using this technique is currently available, but is limited in size to 20 cm in diameter by problems with plasma uniformity and antenna dielectric window erosion. We have developed a new planar ICP antenna and dielectric window design that allows for larger dimensions (up to 50 cm in diameter) with good uniformity. The current art ICP antenna requires a thick quartz (or ceramic) plate vacuum window to separate the rf inductor and the plasma. The larger the antenna diameter the thicker the dielectric. The thick dielectric reduces inductive coupling efficiency. The large area coil and associated matching network can introduce plasma uniformity problems. Our device incorporates both the rf inductor and the dielectric window inside the vacuum chamber, allowing space for a thin layer of quartz or oth...

A Radio Frequency Driven DC Electron Beam Source

A 3 cm diameter disc shaped plasma generated electron beam source, employing ion-induced secondary electron emission from cold cathodes has been demonstrated. An inductively coupled plasma generated in 2–20 mTorr argon feedstock gas provides ions which impinge on the high secondary electron emission coefficient Al2O3 cathode. A separate 13.56 MHz radio frequency bias voltage is applied to the cathode and thereby provides the effective DC field for both ion impingement and electron beam acceleration as described herein. A differentially pumped retarding potential analyzer measures the electron beam energy spectra at a location 14 cm from the cold cathode. It is found that the maximum (negative) cathode voltage sets the maximum electron beam energy, and the electron beam current is roughly set by the inductively coupled plasma power, which corresponds to the ion flux to the cathode. A crude model relating the electron beam energy spectra to the time varying cathode sheath potential provided by the rf bias shows good agreement with measured results.

Secondary electron energy spectra emitted from radio frequency biased plasma electrodes

The ion-induced secondary electron energy spectra from a radio frequency biased (13.56 MHz) electrically insulating (Al2O3) plasma electrode surface immersed in a separately powered inductively coupled plasma are studied both experimentally and theoretically. Radio frequency (rf) electrode bias voltages of 140 and 285 V (peak to ground) are employed and the complete electron energy spectra emitted from the electrode and accelerated by the rf sheath are measured 14 cm from the rf biased electrode using a differentially pumped retarding potential analyzer. A collisionless radio frequency Child–Langmuir sheath model is used to explain the experimentally measured electron energy spectra.

Ferrite Core Effects in a 13.56 MHz Inductively Coupled Plasma

We investigate the effects of adding a ferrite core to the rf coil in a cylindrical inductively coupled plasma, thereby increasing the mutual inductance between the rf coil and the plasma at 13.56 MHz. This could reduce resistive power loss, Pcoil(loss)=Icoil2Rcoil, in the copper coil because of lower required rf drive current to ignite and sustain a plasma. The air core transformer circuit model of Piejak et al.. is modified to account for the effects of the ferrite core on the rf circuit. Specifically, circuit elements accounting for core power losses and the new primary inductance created by the addition of the core are included. The plasma electron density created by inductive drive, with and without the core was the same at the same total rf power. Any energy savings in the copper coils are offset by the large core losses at 13.56 MHz due to hysteresis and eddy currents.

Photo-Deposition of Hydrogenated Amorphous Silicon on Downstream Substrates Using an Upstream Windowless Hydrogen Lamp

An upstream 19 cm diameter disc-shaped hydrogen plasma has been used to deposit hydrogenated amorphous silicon films on 7.5 cm diameter wafers placed 10 cm downstream with 10 percent thickness variation. The disk plasma may offer an alternative to radio frequency excitation and this study is the first in that direction. The films have an optical band gap of 1.75 eV and an optimum photosensitivity of 2?105. The total hydrogen content was 20 at.%. There is one SiH bond for every 20 Si-H bonds. A 42 cm diameter hydrogen disk plasma has also been constructed and characterized as regards uniformity of optical emission.

Arsine and hydride generation for MOCVD film growth

A simple detector has been developed using a quartz microbalance to qualitatively measure the flux of atomic hydrogen in a hydrogen beam. We have used the monitor to measure the flux of atomic hydrogen produced by two sources, a hot tungsten filament and a microwave plasma. The atomic hydrogen flux data is then compared to arsenic hydride generation from our in‐situ arsenic hydride MOCVD source, where a strong correlation is found.

Gallium arsenide homoepitaxy employing in‐situ generated arsine radicals

Removed from the deposition region, an upstream hydrogen microwave plasma generates arsenic hydrides by etching the surface of solid arsenic. The hydrides are transported to the deposition region and mixed with trimethylgallium to achieve low temperature (350–400 °C) and low pressure (750 mTorr) homoepitaxial GaAs films. Low precursor V/III ratios are used to achieve homoepitaxial films with high levels of carbon dopants (1019 to mid 1020 cm−3). No active or afterglow plasma exists in the growth region. The observed homoepitaxial growth activation energies of 54 kcal/mole and 66 kcal/mole for films deposited with V/III ratios of 1/1 and 1/4, respectively, are in the range of those reported for the heterogeneous decomposition of trimethylgallium in the absence of arsine. The majority carriers are holes and have hole concentrations which correlate to the carbon doping, as determined by room temperature Hall effect measurements and secondary ion mass spectroscopy. Carrier mobility versus carbon concentration...

Secondary electron energy profiles as a diagnotic tool for RF plasma sheaths

Summary form only given, as follows. Ion-induced secondary electron energy profiles from a radio frequency biased (13.56 MHz) electrically insulating (Al/sub 2/O/sub 3/) electrode placed adjacent to an inductively coupled plasma (ICP) discharge are studied both experimentally and theoretically. Plasma feedstock gases include Ar, He, H/sub 2/, and N/sub 2/ over the pressure range of 2-20 m Torr. Radio frequency electrode bias voltages of 140, 285, and 425 V (peak to ground) are employed and the complete electron energy spectrum is measured 14 cm from the RF biased electrode using a differentially pumped retarding potential analyzer. The experimental measurements are compared to a collisionless Child-Langmuir RF sheath model, indicating that this technique is a useful in-situ diagnostic method to check the validity of RF sheath theories.