Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
2003-03-31
2004-08-17
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C118S7230ER, C156S345430, C204S298080
Reexamination Certificate
active
06777880
ABSTRACT:
RELATED APPLICATION
This application is a divisional of application Ser. No. 09/676,366, filed Sep. 29, 2000, now U.S. Pat. No. 6,616,987 which is a continuation of PCT/EP99/02241, filed Apr. 4, 1999, which claims benefits from German Patent Application No. 198 14 871.2, filed Apr. 2, 1998, incorporated herein by reference.
FIELD OF THE INVENTION
This invention relates to a procedure and device for the specific manipulation and/or deposition of microscopic particles in high-frequency plasma.
BACKGROUND
As is generally known, formation of high-frequency plasma in the respective reaction gas is a suitable means for achieving the desired degradation reactions or the like for processing or degradation procedures such as plasma etching, or chemical vapor deposition (CVD). To optimize CVD applications, e.g., for separating amorphous, hydrogenated silicon (a-Si:H) for photovoltaic devices, thin-film transistors, flat-screen displays or color detectors in imaging systems, there are numerous studies on how the properties of deposited layers depend on plasma parameters, e.g., the types of reaction gas, HF voltage or gas pressure. It has been shown that microscopic particles (so-called “particles”) can form in the plasma and have a disruptive or facilitative effect on the layer properties, depending on the application.
For example, in “Appl. Phys. Lett.”, Vol. 69, 1996, pp. 1705 forward, D. M. Tanenbaum et al. describe the formation of particles in plasma during a-Si:H deposition as follows: Negative ions are formed in the silane reaction gas as the result of electron bombardment, and react in the plasma with radicals and cations. This produces growing particles, which have a negative charge, as the electron velocities are significantly higher in comparison to the cation velocities. Due to the formation of space charge regions near the electrodes, these particles, which can grow to &mgr;m dimension sizes, to not get to the substrate, which generally is secured to one of the electrodes. D. M. Tanenbaum et al. showed that, despite the space charge zone, particles ranging from roughly 2 to 14 nm in size reach the substrate during plasma discharge and, once there, can trigger disruptions in the layer properties.
In the “14
th
European Photovoltaic Solar Energy Conference” (Barcelona 1997), Paper No. P5A.20, P. Roca i Cabarrocas et al. describe a significant improvement in charge carrier transport in a-Si:H layers by embedding particles. The particles arise under specific pressure conditions in the reaction gas, and are identified by characteristic, so-called “hydrogen evolution” measurements in the layer. The layers containing the particles exhibit a considerable increase in dark conductance and photoconductivity in comparison to amorphous layers. In addition, a considerable improvement was achieved in the stability of photoelectric properties under illumination.
One general problem in the previous studies on the effects of particles in CVD deposited layers is that a means for the targeted and reproducible handling of particles occurring irregularly in the reaction gas has thus far not been available. A particular problem in this case is that the particles can arise within roughly 1 second at the usual plasma frequencies of about 14 MHz.
Additional aspects of particle formation are illustrated below making reference to a conventional device according to FIG.
13
.
In a plasma state, e.g., generated by a glow or gas discharge, a gas encompasses particles of varying charge, e.g., positively or negatively charged ions, electrons and radicals, but also neutral atoms. If microscopic particles (up to several 10 &mgr;m in size), e.g., dust particles, form or exist in the plasma, these take on an electrical charge. The charge can reach several hundred thousand electron charges depending on the particle size and plasma conditions (type of gas, plasma density, temperature, pressure, etc.).
In the known device shown in
FIG. 13
, two flat discharge electrodes
11
and
12
are arranged one atop the other in a reactor (vessel walls not shown) with a carrier gas. The lower circular or disk-shaped HF electrode
11
is actuated with an alternating voltage, while the upper, annular counter-electrode
12
is grounded, for example. The electrode distance measures roughly 2 cm. A control circuit
13
is set up to connect the HF generator
14
with the HF electrode
11
and actuate the grounding and separation circuit
15
of the counter-electrode
12
. The high-frequency energy can be injected with a frequency of 13.56 MHz and a power of roughly 5 W, for example. The carrier gas is formed by inert gases or reactive gases at a pressure of approx. 0.01-2 mbar.
A state of equilibrium preferably sets in among the particles, in which the gravitational force G acting on the particles is balanced with an electrical field strength E, to which the particles are exposed as the result of a space charge near the HF electrode
11
as a function of their charge. Also known is the formation of plasma crystalline states of particle configurations, but this is limited to particles with characteristic dimensions exceeding 20 nm, since the respectively carried charge is so low for smaller particles that thermal fluctuations have a stronger influence on the particles than the Coulomb interactions required for the plasma crystals, so that a uniform structure cannot be formed. In addition, formation of plasma crystals was previously limited to particles introduced into the reaction space from outside, e.g. dust particles. Therefore, a targeted handling of nanocrystalline particles, in particular with characteristic sizes of a few to several 10 nm, could not be derived from the manipulation of particles arranged in a plasmacrystalline manner.
However, in view of the known influence of structural or photoelectric properties of deposited layers resulting from built-in nanocrystalline particles, there is a strong interest in being able to control particle incorporation, in particular with regard to the type, size, number and position of the particles.
The manipulation of particles in a plasmacrystalline state is known from PCT patent application WO 98/44766 being published after the priority date of the present patent application. In JP 04-103769, a Laser-CVD-procedure is described.
Thus, it would be advantageous to provide a method for the specific manipulation or separation (deposition) of particles in or from plasmas, in particular, for influencing the particles themselves or modifying a substrate surface or a layer, and a device for implementing the procedure.
SUMMARY OF THE INVENTION
When exposed to a sufficiently energetic irradiation, which triggers in particular a discharging or reversing the charge of the particles, or exerts a light pressure, particles that arise internally in the reaction space with an ignited plasma, or are provided to the reaction space from outside (externally) and initially have a negative charge, are moved to an altered target position from an initial position corresponding to the force equilibrium of the negatively charged particles. The particles can have sizes ranging from several nanometers to roughly 100 &mgr;m. The energetic irradiation can encompass laser radiation to trigger a discharge, a UV laser or electron irradiation for reversing particle charge via secondary electron emission, or light irradiation to generate a light pressure. The target position of the particles can be a range with altered plasma conditions, or a substrate on which the particles are applied alone or simultaneously with layer formation via plasma deposition.
The nanoparticles exhibit a substantially non-uniform spatial distribution in the plasma. This means that the nanoparticles are randomly distributed relative to each other, at statistically distributed locations. To this end, the conditions in the reaction space, in particular the plasma conditions, e.g., the ratio of electrons to ions in the plasma, are adjusted depending on the particles in such a way that the particles possess such a high energy that substantiall
Konopka Uwe
Morfill Gregor
Stuffler Timo
Thomas Hubertus
Alemu Ephrem
Max-Planck-Gesellschaft zur Forderung der Wissenschaften e.V.
Piper Rudnick LLP
Wong Don
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