Plastic and nonmetallic article shaping or treating: processes – Laser ablative shaping or piercing
Utility Patent
1997-10-08
2001-01-02
Fiorilla, Christopher A. (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Laser ablative shaping or piercing
C264S430000, C264S482000
Utility Patent
active
06168744
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to materials and to methods and apparatus for processing materials. In another aspect, the present invention relates to diamonds and diamond related materials, and to methods and apparatus for processing diamonds and diamond related materials. In even another aspect, the present invention relates to polished and/or planarized diamonds and to methods and apparatus of polishing and/or planarizing diamonds. In still another aspect, the present invention relates to polished and/or planarized substrates, and to methods and apparatus for laser polishing and/or planarizing substrates. In yet another aspect, the present invention relates to polished and/or planarized diamond materials, and to methods and apparatus for polishing and planarizing diamond materials utilizing at least two wavelengths of laser light.
2. Description of the Related Art
As the best thermal conductor known, diamond is the ultimate choice as a substrate material for the fabrication of denser, smaller and faster electronic packages. Prior art efforts have focused on designing manufacturing transparent technologies for post-synthesis processing (polishing, planarization, metallization, die attach) of diamond substrates.
Diamond, while it could be very useful for many electronics applications, presents extreme processing problems.
Chemical vapor deposited (CVD) diamond is attractive due to its high thermal conductivity, high electrical resistivity, low coefficient of thermal expansion, and extreme hardness. Now, as free-standing CVD diamond substrates are readily available in different sizes at reasonable cost, the consideration of diamond for commercial applications is viable.
State-of-the-art CVD-diamond technology produces CVD diamond films that are non-uniform in crystal orientation, chemical quality, grain size and thickness across the diamond surface. Large surface roughness (2-30 microns) and non-uniformity across the surface often limit the usefulness of diamond films for thermal management and numerous other applications. Particularly for MCM applications, the roughness affects heat spreading efficiency due to insufficient contact between the attached devices and the diamond substrate. Roughness also introduces discontinuities and reliability problems for the electrical interconnections. These issues must be addressed by polishing and planarizing CVD-diamond films. Various conventional and non-conventional agents (diamond grit abrasion, chemicals, ion beam, photons, hot metal, filling) have been used for trimming, polishing and planarizing diamond substrates.
Particularly, there are many approaches to polishing diamond films discussed in the literature, including hot metal polishing, diamond grit abrasion, chemical polishing, and ion beam irradiation polishing.
In conventional mechanical polishing diamond impregnated metal polishing wheels are used to grind the surface of the diamond. This is a very slow process and as of yet is unlikely to be practical or economical.
Chemical-mechanical polishing of diamond utilizes an iron wheel, and a technique based on the chemical reaction between diamond and a heated iron wheel. The diamond sample is polished with an iron wheel maintained at a temperature of about 600° C. in the presence of atomic hydrogen. The sharp tips of the diamond film are polished by the local conversion of the diamond into graphite and the diffusion of the graphite into the hot iron. The atomic hydrogen serves to remove the carbon from the iron and prevents saturation of the iron by carbon. A variation of this process involves the use of compacted manganese powder placed in contact with the rough diamond to achieve surface planarization.
Unfortunately, these techniques can be time consuming, expensive, and contaminate the surface.
Another technique discussed in the literature utilizes high energy pulsed lasers for the smoothening of the diamond surface. Depending upon the wavelength utilized the diamond may undergo heating, sublimation, band-gap photon reaction, graphitization followed by sublimation, and the like.
Lasers offer a quick and inexpensive method to trim/polish selected small or large areas at high speeds without significant chemical contamination of the surface. Sufficiently powerful and rapid lasers can process thick diamond substrates in a matter of seconds. This can occur in air without the need for a vacuum or special chemical environment, further reducing the cost, making this a robust and manufacturing transparent process.
However, even the laser techniques are in need of improvements.
The following articles and patents relate to processing of diamonds.
“Excimer laser etching and polishing of diamond Films”, A. Blatter et al., J. Electrochem. Soc., 91 (1991) 352, discloses the use of a KrF excimer laser to cause surface modification and etching of diamond films.
“Excimer-laser etching of diamond and hard carbon films by direct writing and optical projection”, M. Rothschild et al., J. Vac. Sci. Technol., January/February 1986, discloses the use of laser-induced microchemical etching as an alternative to ion-etching. It further discloses that the ArF laser, at a wavelength of 193 nm, is particularly suitable for interaction with diamond, since its photon energy of 6.4 eV at this wavelength is higher than the band-gap of diamond (5.4 eV), making diamond highly absorptive at 193 nm. Still further disclosed is that lasers operating at longer wavelengths, such as the KrF laser operating at 248 nm, interact with diamond via absorption by impurities.
“Smoothening of diamond films with an ArF laser”, U. Bogli et al., Diamond and Related Materials, 1 (1992) 782-788, discloses homogeneous large-area smoothening of diamond films using an ArF excimer laser at 193 nm.
“Excimer laser processing of diamond films”, S. M. Pimenov et al., discloses the use of a KrF excimer laser operating at 248 nm wavelength for etching and smoothening of polycrystalline diamond films. It further discloses that “laser smoothing in a scanning mode is thought to be an effective method in the first stage of [diamond film] surface treatment, followed by hot metal polishing or by a conventional abrasive technique at the final stage of [diamond film] surface polishing.
“Laser processing of diamond and diamond-like films”, V. P. Ageev et al., Materials & Manufacturing Processes, 8(1), 1-8 (1993), discloses the use of XeCl or KrF excimer lasers at wavelengths of 308 nm and 248 nm, respectively, for etching, patterning and writing on diamond films.
“Modelling of self-limiting laser ablation of rough surfaces: application to the polishing of diamond films”, V. N. Tokarev et al., Diamond and Related Materials 4 (1995) 169-176, discloses a theoretical model for the interaction of excimer laser radiation with rough polycrystalline diamond films. Further disclosed is a self-limiting laser ablation technique which allows faceted films to be smoothed without wasteful ablation of the bulk. Experiments were carried out utilizing an XeCl excimer laser for self-limiting laser ablation.
“Fine patterning of diamond films by laser-assisted chemical etching in oxygen”, V. G. Ral'chenko et al., Diamond and Related Materials 4 (1995) 893-896, discloses the use of a low power continuous wave Ar+ laser for etching of diamond films.
U.S. Pat. No. 5,458,827, issued Oct. 17, 1995 to Holly, discloses a method of polishing and shaping diamond and other superhard material surfaces. The method generally includes diffusion smoothing of the diamond surface with hot reactive metals. The method includes shaping the smoothed diamond surface by laser ablation using a pulsed laser beam from a UV excimer KrF laser operating at &lgr;=247 nm or a Q-switched pulsed YAG laser, operating at its second or fourth harmonic wavelength. Finally, the method includes ion-beam assisted polishing of the ablated diamond surface to an optical smoothness.
U.S. Pat. No. 5,490,963, issued Feb. 13, 1996, to Fleischer et al., discloses a process for s
Brown William D.
Malshe Ajay P.
Ozkan Arzu M.
Board of Trustees University of Arkansas
Fiorilla Christopher A.
Gilbreth J. M.(Mark)
Gilbreth Mary A.
Gilbreth & Assoc. P.C.
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