Plasma Processing : Materials processing


Method for Improving Plasma Processes by Controlling a Voltage Waveform

A UW-Madison researcher has now developed an improved algorithm that significantly enhances plasma etching through an automated process that modulates a voltage waveform applied to the substrate material until the optimal bombarding ion energy distribution is achieved.

To control the ion energy distribution, the inventor used a programmable waveform generator in combination with a power amplifier to tailor the waveform shape of the radio frequency (RF) bias voltage applied to the substrate during processing. The technique works by introducing a periodic bias voltage to the semiconductor substrate through a direct current (DC) blocking capacitor, which has a waveform comprised of voltage pulse peaks.

A fast Fourier Transform (FFT) of the substrate waveform is compared, one frequency at a time, with the FFT of a desired “target” waveform, to determine adjustments needed at the waveform generator. An inverse FFT then yields the waveform generator output. It is repeated until the substrate waveform converges to the targeted shape, providing a quick systematic method for producing an arbitrary distribution of ion energies at the substrate.

This iterative procedure is vital to making the system, previously done manually, fully automated. It has been verified for several target waveform shapes.

Simplified Apparatus and Methods for Producing Nanoparticles in a Dense Fluid Medium

UW-Madison resarchers have now developed a simplified design for the dense medium plasma (DMP) reactor, along with a method of using it to produce silicon, carbon and other nanoparticles. The improved DMP reactor includes a plasma reaction vessel with an internal reaction chamber into which a dense fluid medium may be introduced. An electrode assembly, consisting of two electrodes with opposing ring-shaped electrode discharge faces, is submerged in the fluid within the chamber. When an electric potential is applied, a plasma discharge zone forms between the opposing electrode discharge faces. A gas inlet port releases a cavitation gas into a zone between the electrodes, creating bubbles in the dense medium plasma. The bubbles replace the rotating electrode used to stir the fluid in the original reactor design. They promote the efficient, plasma-induced production of nanoparticles from precursors in the dense fluid medium.

System for Generating Electron Beams from a Radio-Frequency Plasma

To address these issues, UW-Madison researchers have devised an “electrode-less” electron beam system that produces electron flow from a plasma generated with radio-frequency (RF) fields in the presence of a magnetic field. The current extracted by this system exceeds that normally produced with conventional RF electron beam sources, because electrons are extracted through an “electron sheath.” In addition, the system does not consume electrode material, making long-term operation dependent only on the availability of operating gas.

Plasma Treatment within Dielectric Fluids

UW–Madison researchers have developed a method for producing a plasma discharge in liquids at low temperatures and atmospheric pressure. It shows particular promise for treating gasoline and other liquid fuels to increase combustion efficiency.

In the method, bubbles of gas or vapor are first created within a liquid through mechanical, chemical or other means. Next, the liquid is subjected to an electric field that generates micro-discharges, and thus a plasma state, within the bubbles. Unlike previous techniques aimed at treating liquids by dielectric barrier discharge (DBD) plasma processes, this method produces a very large plasma/liquid interface per unit volume of liquid. This feature is needed to treat the entire liquid volume without causing heating or other unwanted effects.

Using this process, the researchers have shown that octane can be broken down into lower molecular weight compounds of higher burning efficiency. Thus, this technology could potentially be used for in-line treating of gasoline and diesel fuels prior to fuel injection, to increase combustion efficiency and possibly reduce emissions.

Plasma-Enhanced Functionalization of Inorganic Oxide Surfaces

UW-Madison researchers have developed an efficient, two-step technique for covalently attaching epoxide functionalities to glass, silicon, quartz, and other inorganic surfaces. First, an oxide surface is exposed to a cold plasma to create hydroxyl functionalities on the surface. Next, these hydroxyl groups are reacted with epoxy group-containing molecules in the absence of plasma to form surface-bound spacer chains. Biomolecules can then be immobilized on the resulting functionalized surface by reacting the biomolecules with the spacer chains.

Plasma-Enhanced Functionalization of Carbon-Containing Substrates

UW-Madison researchers have developed an efficient, dry plasma technique for functionalizing surfaces that holds several advantages over traditional wet chemical approaches. The technique involves two steps. First, a carbon containing substrate is exposed to an inert plasma (e.g., argon or hydrogen) that generates reactive active sites, such as free radicals or ions, on the surface of the substrate. Next, the surface is exposed to volatile compounds in the absence of plasma. The compounds react with the active sites to produce surface-bound spacer chain molecules containing one or more functional groups. These functional groups, in turn, can react with molecules of DNA or protein.

Method of Treating Surfaces to Create Extremely Hard Carbon Films

UW-Madison researchers have developed a new method of producing extremely hard carbon films at room temperature and under low pressure. The method involves exposing an organic polymer on a surface to a sulfur hexafluoride-containing plasma. The researchers have shown this treatment converts pre-deposited, poly-acrylic thin layers on surfaces into carbon films with hardness values greater than nine. For comparison, diamond-like coatings have a hardness of 10.

Method for Disinfecting Liquids in a Dense Fluid Plasma Reactor

UW–Madison researchers have developed an efficient new method for disinfecting liquids, especially water, by using a dense medium plasma (DMP). Water is placed inside a DMP reaction vessel and vigorously stirred between two electrodes. Multiple spark discharges between the electrodes then produce reactive plasma species, including electrons, ions and free radicals, which inactivate any bacteria, fungi or other microbes present in the water. In a second sterilization method, which can be applied alone or in conjunction with the first, the plasma reactor is used to generate antimicrobial colloidal nanoparticles, especially silver nanoparticles, which interact with microbial cells and deactivate them.

Device and Method for Plasma Modification of Materials at Atmospheric Pressure

UW-Madison researchers have developed a novel plasma generator that operates at atmospheric pressure and is designed to modify inorganic and organic substrates with large surface areas. The plasma reactor is composed of a flat-bed, multi-cylinder array, with each point in the array housing a recess that contains a pair of plasma-generating electrodes. When these multiple plasma sources discharge together, they create a plasma over the entire array surface, making the system ideal for treating two-dimensional materials of large size.

Method and Apparatus for Producing Colloidal Nanoparticles in a Dense Medium Plasma

UW-Madison researchers have developed a method for producing a colloidal dispersion of nanoparticles of at least one conductive material in a dense fluid medium. The dense fluid medium is a liquid at the operating conditions of a plasma reactor. Specifically, the nanoparticles of the conductive materials can be produced by generating a plasma reaction between two electrodes made of the desired conductive material, which are immersed within the dense fluid medium. Preferred materials for the electrodes include carbon, copper, silver, gold and platinum. The electrodes may also be made of different materials to produce colloidal suspensions with more than one conducting material.

Method and Apparatus for Etching and Deposition Using Microplasmas

UW-Madison researchers have developed a method for generating and using spatially localized microplasmas operating in parallel with one another to add or remove material over large substrate areas. This means that a plasma can be developed in a specific region, which is tailored to the treatment requirements of that region.

Process for Intercalation of Spacer Molecules between Substrates and Active Biomolecules

UW–Madison researchers have developed a method of functionalizing the surface of a wide variety of substrates so that spacer molecules are attached. The substrates are exposed to a cold plasma ignited in dichlorosilane, silicon tetrachloride or hexachlorodisilane gas to implant silicon-chlorine functionalities in the substrate surface. The plasma implanted surface functionalities then are utilized to initiate second stage gas phase derivatization reactions to form linker molecules attached to the substrate. Active biomolecules such as enzymes are bound to the exposed linker molecules to bind the bioactive molecules to the substrate while allowing freedom of movement and conformation of the bound molecule comparable to that of the free molecule.

Control of Ion Energy Distribution during Plasma-Assisted Etching of Semiconductor Substrates

UW-Madison researchers have developed a novel means for controlling IEDF and ion energy at the substrate surface during plasma-assisted etching of semiconductor materials. The method applies a periodic bias voltage consisting of a short voltage spike and a longer, slow voltage ramp down, resulting in a narrow IEDF that is centered at a specific ion energy. Both the magnitude of the ion flux peak and the ion energy at which the peak is centered may be selected for varying applications. These parameters may also be changed during processing to accommodate the requirements of different processing stages.