Microcoating goes “mini” with CCVD
By Susan English
Atlanta, GA — Combustion chemical vapor deposition (CCVD) technology was brought to national attention recently when it was featured on CNN`s November 28 broadcast of Future Watch, concluding with the startling claim that the process — which deposits high quality thin films in ambient, or open atmosphere conditions — would “do away with the need for cleanrooms.” The remark was misleading, contends Jeffery C. Moore, vice president at Atlanta-based MicroCoating Technologies, the company that invented the process.
“CNN was wrong. Even with an electronic-grade coating, you can`t have dust. But the difference is: all we really need is the clean air, and that means you can have a localized clean chamber vs. a whole clean room.” In fact, the company is currently producing its coatings in an ULPA-filtered Class 100 4 ft ¥ 3 ft clean chamber — actually more like a glovebox — at an airflow of 100 ft/min. miniumum flow constant. Combustion CVD is the vapor deposition of a film near or in a flame, which causes the precursors to chemically react, as in flame diamond deposition or silicate-based glass deposition techniques. Cost-effectiveness and flexibility are the main factors that make this an attractive technology, according to the company.
While conventional CVD requires a costly high temperature reaction furnace and vacuum chamber, as well as expensive, high vapor pressure chemicals, CCVD can be performed in ambient, using low-grade chemicals, eliminating the need for specialized environments, equipment and materials. The ability to process in ambient also means that CCVD can easily cover large or irregular surfaces, including assembled parts, difficult in a specialized environment like a vacuum chamber. Also, the process utilizes an inexpensive — and environmentally friendly — chemical solution that allows for greater command over the chemical composition of coatings, including the deposition of a broad range of multi-elemental compounds which can`t be deposited by traditional methods.
These include oxides, carbonates, sulfates, metals, chlorides, fluorides, sulfides, phosphates, borides, nitrides and carbides, as well as combinations. The result is individually tailored thin films of various advanced material at very attractive costs to users. Moore says CCVD equipment costs are generally 90 percent less than traditional CVD technologies, and chemicals are especially cheap. “The chemicals we use as our starting solution are much less expensive — up to 99 percent less expensive, or up to 1 percent of the cost.” Another commanding cost advantage, he adds, is that open atmosphere conditions make transportation of the substrate easier, enabling continuous processing. The company claims it can shorten the crucial laboratory-to-product time for customers, usually providing unstudied materials in fully characterized thin films within 10 to 90 days, depending on the required properties and chemical complexity of the material.
CCVD can be used to deposit thin films of ceramics, metals and composites onto base materials of metal, ceramic, glass or even certain plastics, such as Teflon. These thin films provide desirable surface properties to the base material, including significantly improved mechanical wear, chemical resistance and thermal protection, as well as beneficial optical, electrical, catalytic and conduction properties. Microcoating via CCVD can be applied to the manufacture of electronic devices like nonvolatile memories, multilayer thin-film capacitors, and piezoelectric sensors. It can also produce better mechanical dies, architectural glass, turbine engines, x-ray generators, and other products, such as fuel cells, production and cutting tools, mechanical dies, architectural glass, ceramic fibers, turbine engines, catalytic surfaces, and related mechanical, corrosion, optical and thermal barrier applications.
Since its founding in 1994, MicroCoating Technologies has deposited coatings for over 30 customers — mostly on a prototype basis. It has performed research for companies like 3M, Pilkington, GM, Lockheed, Alcoa, and Morton and Behr Automotive. Until recently, the company had found its chief market in corrosion protection coatings. Says Moore: “We`re working with larger companies that need coatings for corrosion protection. And those same coatings can then be used in other smaller field applications, such as pharmaceuticals, where inert surfaces are necessary for making and storing chemical compounds. In areas where a steel chamber might be needed, but would be too reactive with the media, an inert coating such as silica or platinum could be used.” These days, it is targeting the electronics industry by providing a cost-effective process for coating metal foils with electronic coatings in the manufacture of resistors, conductors and capacitors, an area of electronics which is actually higher in square footage volume of business than wafer fabrication, Moore says.”
CCVD was first performed outdoors in the inventor`s backyard. Andrew Hunt, MicroCoating Technologies` president, originally conceived of the process while working on his PhD at Georgia Institute of Technology in Atlanta. In attempting a different approach to creating thin films of ceramic materials, he was able to deposit a one-micron-thick layer of superconducting material on a crystal of magnesium oxide. A blend of powdered yttrium, barium and copper compounds was dissolved in xylene and sprayed from an artist`s airbrush. Ten percent oxygen-enriched air was used as the propellant gas, and the spray was ignited. (Flame blowoff was prevented by a small pilot light.) Later depositions were performed in a fume hood by feeding the solution through a needle bisecting a thin high-velocity air stream forming a spray that was ignited and burned. Two different solvents — ethanol and toluene — and two different metalorganic precursors — acetylacetonates (AcAc) and 2EH — were used in the first two depositions. In CCVD, the environment required for CVD to occur is provided by the flame as kinetic energy and radiation.n