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Method of Making Synthetic Diamond Film

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Method of Making Synthetic Diamond Film Europaisches Patentamt European Patent Office © Publication number: 0 597 445 A2 Office europeen des brevets EUROPEAN PATENT APPLICATION © Application number: 93118150.7 int. Ci.5; C23C 16/00, C23C 16/26 @ Date of filing: 09.11.93 ® Priority: 10.11.92 US 973994 32 Cornell Street Arlington, MA 02174(US) @ Date of publication of application: Inventor: Frey, Robert M. 18.05.94 Bulletin 94/20 77 Santa Isabel Nr.2-14 Laguna Vista, Texas 78578(US) © Designated Contracting States: DE FR GB 0 Representative: Diehl, Hermann, Dr. © Applicant: NORTON COMPANY Dipl.-Phys. et al 1 New Bond Street DIEHL, GLASER, HILTL & PARTNER Worcester, MA 01615-0008(US) Patentanwalte Fluggenstrasse 13 @ Inventor: Simpson, Matthew D-80639 Munchen (DE) © Method of making synthetic diamond film. © The invention describes a method for making a free-standing synthetic diamond film of desired thickness, comprising the steps of: no SELECT TARGET providing a substrate; X THICKNESS OF DIAMOND selecting a target thickness of diamond to be TO BE PRODUCED produced, said target thickness being in the range 200 urn to 1000 urn; finishing a surface of the substrate to a rough- 1 20 finish surface of ness, RA that is a function of the target thickness, substrate to prescribed said roughness being determined from ra Roughness 0.38t/600 urn ^ Ra = 0.50 urn 200 urn < t ^ 600 urn 0.38 urn ^ Ra = 0.50 urn 600 urn < t < 1000 1 30, urn DEPOSIT INTERLAYER where t is the target thickness; said the inter- CM depositing an interlayer on substrate, layer having a thickness in the range 1 to 20 urn; depositing synthetic diamond on said interlayer, by I40. DEPOSIT SYNTHETIC DIAMOND chemical vapor deposition, to about the target thick- BY CVD TO ABOUT THE ness; and TARGET THICKNESS cooling said synthetic diamond to effect the release Oi thereof. 1 50 RELEASE DIAMOND FROM SUBSTRATE BY COOLING FIG. I Rank Xerox (UK) Business Services (3. 10/3.09/3.3.4) 1 EP 0 597 445 A2 2 This invention relates to a method of making released from the substrate after the desired thick- synthetic diamond film. ness of synthetic diamond film has been deposited, Diamond has a number of properties which such as by chemical vapor deposition. The dia- make it attractive for use in various applications. mond is deposited at a relatively high temperature Among these properties are extreme hardness and 5 and, as the diamond (as well as the titanium nitride excellent transmissivity of certain radiation. Dia- interlayer and substrate below) cools after comple- mond is also an extraordinary heat conductor, ther- tion of the diamond deposition, the diamond should mally stable, and an electrical insulator. However, be released from the substrate, preferably in one natural diamond is prohibitively expensive for ap- piece. However, problems have been found to oc- plications which require any substantial size and is io cur in the procedure. One of these problems is difficult to form into certain shapes. premature flaking off of the diamond and/or its In recent years, a number of techniques have underlayer during deposition or premature release been developed for synthesizing diamond and for of the diamond before deposition is complete. A depositing synthetic diamond on surfaces of var- further problem is cracking of the diamond upon its ious shapes to obtain a diamond film or coating. 75 release from the substrate. These techniques include so-called high-pressure It is therefore the object of the present inven- high-temperature ("HPHT") methods and chemical tion to a method for making a free standing syn- vapor deposition ("CVD") methods. The CVD thetic diamond film of desired thickness which methods include plasma deposition techniques avoids the above mentioned drawbacks of the prior wherein, for example, plasmas of a hydrocarbon 20 art. This object is solved by the method according and hydrogen are obtained using electrical arcing. to independent claim 1 . Further advantageous fea- The resultant plasma can be focused and acceler- tures, aspects and details of the invention are evi- ated toward a substrate using focusing and accel- dent from the dependent claims, the description, erating magnets. Reference can be made, for ex- the examples and the drawings. The claims are to ample, to U.S. Patent Application Serial No. 25 understood as a first non-limiting approach to de- 773,465, assigned to the same assignee as the fine the invention in general terms. present Application, for description of an example The invention specifically refers to generally of a type of plasma jet deposition that can be improve the fabrication of free-standing synthetic utilized to deposit synthetic diamond on a sub- diamond by chemical vapor deposition process. strate. 30 Applicant has discovered that for obtainment of Synthetic diamond film can be deposited as a relatively thick free standing diamond films having permanent coating on a substrate, such as on the a thickness in the range 200 to 1000 urn, the wear surface of a tool or as an environmentally roughness of the substrate surface, beneath the protective coating. Such films are generally consid- thin interlayer upon which the diamond is to be ered to be relatively thin films. Alternatively, a 35 deposited by CVD, should be closely controlled in synthetic diamond film that is generally considered order to maximize the efficacy of the diamond a thick film, can be deposited on a substrate and deposition and release process. In particular, the then removed, preferably intact as a single "free substrate surface roughness must not only be standing" piece, for use in applications such as smooth enough to permit release of the diamond heat sinks, optical windows, and in tools. However, 40 after deposition of a desired diamond thickness is the obtainment of such thick films, especially of complete, but also rough enough to prevent pre- relatively large area, has proven troublesome. In mature lift-off of the diamond or flaking-off of dia- addition to the difficulty of depositing quality syn- mond during the deposition process. thetic diamond of substantial thickness, there is the In accordance with an embodiment of the in- problem of removing the diamond intact from the 45 vention, there is set forth a method for making a substrate. The substrate material will generally free-standing synthetic diamond film of desired have a different coefficient of expansion than the thickness, comprising the following steps: providing diamond, as well as a different molecular and a substrate; selecting a target thickness of diamond chemical structure. The adherence and growth of to be produced, said target thickness being in the the diamond film, as well as its release, will de- 50 range 200 urn to 1000 urn; finishing a surface of pend, inter alia, on the materials used, surface the substrate to a roughness, RA, that is a function preparation, and deposition parameters. of the target thickness, said roughness being deter- Titanium nitride and other materials have been mined from used as a coating for a substrate, such as molyb- 0.38t/600 urn ^ Ra = 0.50 urn 200 urn < t denum, upon which synthetic diamond is to be 55 ^ 600 urn deposited. Titanium nitride adheres reasonably well 0.38 urn ^ Ra = 0.50 urn 600 urn < t < to molybdenum. Diamond can be deposited over a 1000 urn thin layer of the titanium nitride and then, ideally, where t is the target thickness; depositing an inter- 2 3 EP 0 597 445 A2 4 layer on the substrate, the interlayer having a thick- 0.38 urn ^ Ra = 0.50 urn 600 urn < t < ness in the range 1 to 20 urn; depositing synthetic 1000 urn diamond on said interlayer, by chemical vapor de- where t is the target thickness. position, to about the target thickness; and cooling A relatively thin interlayer, preferably in the the synthetic diamond to effect the release thereof. 5 range 1 to 20 urn, is then deposited on the finished In a disclosed embodiment hereof, the step of substrate surface (block 130), such as by physical providing a substrate comprises providing a molyb- vapor deposition ("PVD"). The interlayer, which denum substrate, and said step of depositing an may if desired comprise several sublayers, should interlayer comprises depositing a layer of titanium not bond strongly to diamond. A strong chemical nitride. In this embodiment, step of depositing an io bond will promote adhesion and ultimately prevent interlayer also preferably comprises depositing an removal of the diamond from the substrate in one interlayer having a thickness in the range 3 to 5 piece. The layer should be thick enough to prevent urn. chemical bonding of the diamond to the underlying As seen from the above indicated relationship substrate, and thin enough to maintain the neces- between target diamond thickness and surface 15 sary degree of roughness of the coated substrate roughness, for target thicknesses between 200 and surface to permit a degree of mechanical bonding 600 urn the minimum acceptable surface rough- that deters premature release. For titanium nitride, ness increases with increasing target diamond a preferred interlayer hereof, the layer will have a thickness. This results in reducing instances of the thickness in the range about 3 to 5 urn. Examples types of failure that were first described above. 20 of other interlayer materials that can be utilized Further features and advantages of the inven- herein are titanium carbide, hafnium nitride, zirco- tion will become more readily apparent from the nium nitride, aluminum nitride, and aluminum ox- following detailed description when taken in con- ide. Mixtures and compounds of these materials junction with the accompanying drawings. can also be utilized. Fig. 1 is an operational flow diagram of the 25 Synthetic diamond is then deposited, by steps of an embodiment of the method of the chemical vapor deposition, to about the target invention.
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