Coating processes – Direct application of electrical – magnetic – wave – or... – Electromagnetic or particulate radiation utilized
Reexamination Certificate
2002-05-10
2004-10-19
Beck, Shrive P. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electromagnetic or particulate radiation utilized
C427S595000, C427S554000, C427S555000
Reexamination Certificate
active
06805918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a laser transfer method for the deposition of a rheological fluid or system onto a substrate.
2. Description of the Prior Art
A direct-write process is a technique which allows the creation of a pattern and the transfer of material simultaneously onto a given surface or substrate. To be most useful, it does not require any masks or pre-existing form and is usually done under ambient temperature and pressure conditions. Direct-write technologies have been developed in response to a need in the electronics industry for a means to rapidly prototype passive circuit elements on various substrates, especially in the mesoscopic regime, that is, electronic devices that straddle the size range between conventional microelectronics (sub-micron-range) and traditional surface mount components (10+ mm-range). (Direct-writing may also be accomplished in the sub-micron range using electron beams or focused ion beams, but these techniques, because of their small scale and vacuum requirements, are not appropriate for large-scale rapid prototyping.) Direct-writing allows for circuits to be prototyped without iterations in photolithographic mask design and allows the rapid evaluation of the performance of circuits too difficult to accurately model. Further, direct-writing allows for the size of printed circuit boards and other structures to be reduced by allowing passive circuit elements to be conformally incorporated into the structure. Direct-writing can be controlled with CAD/CAM programs, thereby allowing electronic circuits to be fabricated by machinery operated by unskilled personnel or allowing designers to move quickly from a design to a working prototype. Mesoscopic direct-write technologies have the potential to enable new capabilities to produce next generation applications in the mesoscopic regime. Other applications of direct-write technologies in microelectronic fabrication include forming ohmic contacts, forming interconnects for circuit and photolithographic mask repair, device restructuring and customization, design and fault correction.
Currently known direct-write technologies for adding materials to a substrate include ink jet printing, Micropen, laser induced forward transfer (LIFT), laser chemical vapor deposition (LCVD), laser particle guidance (Optomec, Inc.), and laser engineered nano-shaping (LENS). Currently known direct-write technologies for removing material from a substrate include laser machining, laser trimming, and laser drilling.
The direct-writing techniques of ink jet printing, screen-printing, and Micropen are wet techniques, that is, the material to be deposited is combined with a solvent or binder and is applied onto a substrate. In the case of ink jet printing, inks with very low viscosity are required so that they can be forced through nozzles via mechanical or thermal forces. In the case of screen-printing and Micropen, inks with relatively high viscosities are required so as to minimize their spreading once applied to the substrate. The solvent or binder must later be removed by a drying or curing process, which limits the flexibility and capability of these approaches. In all these techniques, only inks within a narrow range of viscosity can be used and therefore the choices of materials or formulations that can be transferred are rather limited.
In the direct-writing technique known as “laser induced forward transfer” (LIFT), a pulsed laser beam is directed through a laser-transparent target substrate to strike a film of material coated on the opposite side of the target substrate. The laser vaporizes the film material as it absorbs the laser radiation and, due to the transfer of momentum, the material is removed from the target substrate and is redeposited on a receiving substrate that is placed in proximity to the target substrate. Laser induced forward transfer is typically used to transfer opaque thin films, typically metals, from a pre-coated laser transparent support, typically glass, SiO
2
, Al
2
O
3
, SrTiO
3
, etc., to the receiving substrate. Various methods of laser-induced forward transfer are described in, for example, the following U.S. patents and publications incorporated herein by reference: U.S. Pat. No. 4,752,455 to Mayer, U.S. Pat. No. 4,895,735 to Cook, U.S. Pat. No. 5,725,706 to Thoma et al., U.S. Pat. No. 5,292,559 to Joyce, Jr. et al., U.S. Pat. No. 5,492,861 to Opower, U.S. Pat. No. 5,725,914 to Opower, U.S. Pat. No. 5,736,464 to Opower, U.S. Pat. No. 4,970,196 to Kim et al., U.S. Pat. No. 5,173,441 to Yu et al., and Bohandy et al., “Metal Deposition from a Supported Metal Film Using an Excimer Laser, J. Appl. Phys. 60 (4) Aug. 15, 1986, pp 1538-1539. Because the film material is vaporized by the action of the laser, laser induced forward transfer is inherently a pyrolytic technique used to deposit simple one-component materials and typically cannot be used to deposit complex crystalline, multi-component materials as they tend to decompose when vaporized and may become amorphous upon condensation. Moreover, because the material to be transferred is vaporized, it becomes more reactive and can more easily become degraded, oxidized, or contaminated. The method is not well suited for the transfer of organic materials, since many organic materials are fragile, thermally labile, and can be irreversibly damaged during deposition. Moreover, functional groups on an organic polymer can be irreversibly damaged by direct exposure to laser energy. Other disadvantages of the laser induced forward transfer technique include poor uniformity, morphology, adhesion, and resolution. Further, because of the high temperatures involved in the process, there is a danger of ablation or sputtering of the support, which can cause the incorporation of impurities in the material that is deposited onto the receiving substrate. Another disadvantage of laser induced forward transfer is that it typically requires that the coating of the material to be transferred be a thin coating, generally less than 1 &mgr;m thick. Because of this requirement, it is very time-consuming to transfer large amounts of material. Finally, LIFT was not designed originally for the transfer of rheological systems. The art of applying a solid coating to the target substrate was already well established in the field and a rheological coating as described in this invention would have added extra complexity to its manufacture, use, and storage.
In a simple variation of laser induced forward transfer, the target substrate is coated with several layers of materials. The outermost layer, that is, the layer closest to the receiving substrate, consists of the material to be deposited and the innermost layer consists of a material that absorbs laser energy and becomes vaporized, causing the outermost layer to be propelled against the receiving substrate. Variations of this technique are described in, for example, the following U.S. patents and publications incorporated herein by reference: U.S. Pat. No. 5,171,650 to Ellis et al., U.S. Pat. No. 5,256,506 to Ellis et al., U.S. Pat. No. 4,987,006 to Williams et al., U.S. Pat. No. 5,156,938 to Foley et al. and Tolbert et al., “Laser Ablation Transfer Imaging Using Picosecond Optical pulses: Ultra-High Speed, Lower Threshold and High Resolution” Journal of Imaging Science and Technology, Vol.37, No.5, Sept./Oct. 1993 pp.485-489. A disadvantage of this method is that, because of the multiple layers, it is difficult or impossible to achieve the high degree of homogeneity of deposited material on the receiving substrate required, for example, in the construction of electronic devices, sensing devices or passivation coatings. In addition, the multiple layers tend to leave residues that may contaminate the transferred material or degrade its properties.
The direct-write technique called laser chemical vapor deposition (LCVD) utilizes a laser beam focused on the surface of a substrate to induce localized chemical reactions. Usually the surface of the substrat
Auyeung Raymond C. Y.
Chrisey Douglas B.
Fitz-Gerald James M.
Modi Rohit
Pique Alberto
Beck Shrive P.
Fuller Eric B.
Grunkemeyer Joseph T.
Karasek John J.
The United States of America as represented by the Secretary of
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