Abstract:
A method of creating a patterned coated layer on a substrate comprises the steps of applying a pattern on the substrate by an additive process using a first material, depositing a second material by vapour deposition over the whole substrate area and mechanically removing the pattern of first material from the substrate, leaving the inverse pattern of the second material.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates to a method of patterning a substrate, in particular to a method of patterning by vapour deposition. 
       BACKGROUND OF THE INVENTION 
       [0002]    Chemical vapour deposition (CVD) and atomic layer deposition (ALD) are techniques of laying down a thin layer of material onto a substrate. 
         [0003]    Chemical vapour deposition is a chemical process used to produce high-purity, high-performance solid materials. The process is often used in the semiconductor industry to produce thin films of dielectrics and semiconductors. In a typical CVD process, the substrate is exposed to one or more volatile precursors, which react and/or decompose on the substrate surface to produce the desired deposit. 
         [0004]    Atomic Layer Deposition is a self-limiting, sequential surface chemistry that deposits conformal thin films of materials onto substrates of varying compositions. ALD is similar in chemistry to CVD except that the ALD reaction breaks the CVD reaction into two or more partial reactions, keeping the precursor materials separate during the reaction sequence. 
         [0005]    ALD can be used to deposit several types of thin films, including various ceramics, from conductors to insulators. 
         [0006]    When making components it is usually necessary to pattern the material being laid down. There are a number of ways recorded for doing this: 
         [0007]    Deposit an even layer of the material and, using a photolithographic method, etch the unwanted sections of the layer away using a suitable etch chosen so as not to damage the remainder of the device. 
         [0008]    Put down a photoresist onto the substrate and image a profile in this resist using conventional lithography methods. Optionally treat this resist and then use CVD or ALD to coat a layer over the top. Scratch the top of the coating over the resist and treat with suitable solvent to remove the resist—the solvent percolating through the scratches. The coating falls off where the resist has been dissolved. 
         [0009]    Applying a mask to the substrate, patterning the mask, using ALD or CVD to coat a layer over the patterned mask and then removing the mask mechanically (see WO 2006/111766). 
         [0010]    Using ALD and finding an inhibitor specific for the growing mechanism and printing this (see U.S. Pat. No. 7,030,001). 
         [0011]    The first methods rely on the relatively complicated procedure of photolithography. This is a multi-step process usually consisting of the steps of spin-coating the resist, baking the resist, exposing the resist, baking the resist, developing the resist, washing and then drying it. In the third method the mask is patterned after being coated onto the substrate. This may be done using a photoresist method or perhaps more conveniently by ablating the mask with a suitably tuned laser. 
         [0012]    There is a need to find a simpler way of patterning a layer of material. 
       Problem to be Solved by the Invention 
       [0013]    The invention aims to provide a method of patterning a layer of material laid down by vapour deposition such as ALD or CVD which is simpler, more convenient and more flexible than methods of the prior art. 
         [0014]    According to the present invention the pattern is applied using any suitable additive process. This method may be ink jet, flexography, offset lithography, silk screen etc. or any other additive patterning process. The ALD or CVD process is carried out to create the required thickness over the whole patterned material. The patterned layer is then peeled off, removing with it the parts of the layer of second material directly above it, thus leaving the inverse pattern of second material on the substrate. 
       SUMMARY OF THE INVENTION  
       [0015]    According to the present invention there is provided a method of creating a patterned coated layer on a substrate comprising the steps of applying a pattern on the substrate by an additive process using a first material, depositing a second material by vapour deposition over the whole substrate area and mechanically removing the pattern of first material from the substrate, leaving the inverse pattern of the second material. 
         [0016]    Preferably the second material is deposited by atomic layer deposition. 
       Advantageous Effect of the Invention 
       [0017]    The method of the present invention is simpler than the methods known in the prior art. Fewer steps are required in the process, resulting in a reduction in process and labour cost and reduction in waste due to possible errors. 
         [0018]    Compared to the prior art methods the method of the present invention is: simpler, for example, does not require as many steps; more convenient, for example, uses readily available equipment, is easier to do and is more flexible, for example, potentially allows each pattern to be completely different; allows the patterning material or the thickness of the patterning material to be varied. Furthermore, since the mask is mechanically removed no solvent wash steps are required and the surface is left free from any residual mask material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention will now be described with reference to the accompanying drawings in which: 
           [0020]      FIG. 1  is a flow chart describing the steps of an atomic layer deposition process used in the present invention; 
           [0021]      FIG. 2  is a cross sectional side view of an embodiment of a distribution manifold for atomic layer deposition that can be used in the present process; 
           [0022]      FIG. 3  is a cross sectional side view of an embodiment of the distribution of gaseous materials to a substrate that is subject to thin film deposition; and 
           [0023]      FIGS. 4A and 4B  are cross sectional views of an embodiment of the distribution of gaseous materials schematically showing the accompanying deposition operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 1  is a generalized step diagram of a process for practicing the present invention. Two reactive gases are used, a first molecular precursor and a second molecular precursor. Gases are supplied from a gas source and can be delivered to the substrate, for example, via a distribution manifold. Metering and valving apparatus for providing gaseous materials to the distribution manifold can be used. 
         [0025]    As shown in Step  1 , a continuous supply of gaseous materials for the system is provided for depositing a thin film of material on a substrate. The Steps in Sequence  15  are sequentially applied. In Step  2 , with respect to a given area of the substrate (referred to as the channel area), a first molecular precursor or reactive gaseous material is directed to flow in a first channel transversely over the channel area of the substrate and reacts therewith. In Step  3  relative movement of the substrate and the multi-channel flows in the system occurs, which sets the stage for Step  4 , in which second channel (purge) flow with inert gas occurs over the given channel area. Then, in Step  5 , relative movement of the substrate and the multi-channel flows sets the stage for Step  6 , in which the given channel area is subjected to atomic layer deposition in which a second molecular precursor now transversely flows (substantially parallel to the surface of the substrate) over the given channel area of the substrate and reacts with the previous layer on the substrate to produce (theoretically) a monolayer of a desired material. Often in such processes, a first molecular precursor is a metal-containing compound in gas form (for example, a metallic compound such as titanium tetrachloride) and the material deposited is a metal-containing compound. In such an embodiment, the second molecular precursor can be, for example, a non-metallic oxidizing compound or hydrolyzing compound, e.g. water. 
         [0026]    In Step  7 , relative movement of the substrate and the multi-channel flows then sets the stage for Step  8  in which again an inert gas is used, this time to sweep excess second molecular precursor from the given channel area from the previous Step  6 . In Step  9 , relative movement of the substrate and the multi-channels occurs again, which sets the stage for a repeat sequence, back to Step  2 . The cycle is repeated as many times as is necessary to establish a desired film or layer. The steps may be repeated with respect to a given channel area of the substrate, corresponding to the area covered by a flow channel. Meanwhile the various channels are being supplied with the necessary gaseous materials in Step  1 . Simultaneous with the sequence of box  15  in  FIG. 1 , other adjacent channel areas are being processed simultaneously, which results in multiple channel flows in parallel, as indicated in overall Step  11 . 
         [0027]    The primary purpose of the second molecular precursor is to condition the substrate surface back toward reactivity with the first molecular precursor. The second molecular precursor also provides material as a molecular gas to combine with one or more metal compounds at the surface, forming compounds such as an oxide, nitride, sulfide, etc, with the freshly deposited metal-containing precursor. 
         [0028]    The continuous ALD purge does not need to use a vacuum purge to remove a molecular precursor after applying it to the substrate. 
         [0029]    Assuming that two reactant gases, AX and BY, are used, when the reaction gas AX flow is supplied and flowed over a given substrate area, atoms of the reaction gas AX are chemically adsorbed on a substrate, resulting in a layer of A and a surface of ligand X (associative chemisorptions) (Step  2 ). Then, the remaining reaction gas AX is purged with an inert gas (Step  4 ). Then, the flow of reaction gas BY, and a chemical reaction between AX (surface) and BY (gas) occurs, resulting in a molecular layer of AB on the substrate (dissociative chemisorptions) (Step  6 ). The remaining gas BY and by-products of the reaction are purged (Step  8 ). The thickness of the thin film can be increased by repeating the process cycle (steps  2 - 9 ). 
         [0030]    Because the film can be deposited one monolayer at a time it tends to be conformal and have uniform thickness. 
         [0031]    Referring now to  FIG. 2 , there is shown a cross-sectional side view of one embodiment of a distribution manifold  10  that can be used in the present process for atomic layer deposition onto a substrate  20 . Distribution manifold  10  has a gas inlet port  14  for accepting a first gaseous material, a gas inlet port  16  for accepting a second gaseous material, and a gas inlet port  18  for accepting a third gaseous material. These gases are emitted at an output face  36  via output channels  12 , having a structural arrangement described subsequently. The arrows in  FIG. 2  refer to the diffusive transport of the gaseous material, and not the flow, received from an output channel. The flow is substantially directed out of the page of the figure. 
         [0032]    Gas inlet ports  14  and  16  are adapted to accept first and second gases that react sequentially on the substrate surface to effect ALD deposition, and gas inlet port  18  receives a purge gas that is inert with respect to the first and second gases. Distribution manifold  10  is spaced a distance D from substrate  20 , provided on a substrate support. Reciprocating motion can be provided between substrate  20  and distribution manifold  10 , either by movement of substrate  20 , by movement of distribution manifold  10 , or by movement of both substrate  20  and distribution manifold  10 . In the particular embodiment shown in  FIG. 2 , substrate  20  is moved across output face  36  in reciprocating fashion, as indicated by the arrow R and by phantom outlines to the right and left of substrate  20  in  FIG. 2 . It should be noted that reciprocating motion is not always required for thin-film deposition using distribution manifold  10 . Other types of relative motion between substrate  20  and distribution manifold  10  could also be provided, such as movement of either substrate  20  or distribution manifold  10  in one or more directions. 
         [0033]    The cross-sectional view of  FIG. 3  shows gas flows emitted over a portion of front face  36  of distribution manifold  10 . In this particular arrangement, each output channel  12  is in gaseous flow communication with one of gas inlet ports  14 ,  16  or  18  seen in  FIG. 2 . Each output channel  12  delivers typically a first reactant gaseous material O, or a second reactant gaseous material M, or a third inert gaseous material I. 
         [0034]      FIG. 3  shows a relatively basic or simple arrangement of gases. It is possible that a plurality of non-metal deposition precursors (like material O) or a plurality of metal-containing precursor materials (like material M) may be delivered sequentially at various ports in a thin-film single deposition. Alternately, a mixture of reactant gases, for example, a mixture of metal precursor materials or a mixture of metal and non-metal precursors may be applied at a single output channel when making complex thin film materials, for example, having alternate layers of metals or having lesser amounts of dopants admixed in a metal oxide material. The critical requirement is that an inert stream labeled I should separate any reactant channels in which the gases are likely to react with each other. First and second reactant gaseous materials O and M react with each other to effect ALD deposition, but neither reactant gaseous material O nor M reacts with inert gaseous material I. 
         [0035]    The cross-sectional views of  FIGS. 4A and 4B  show, in simplified schematic form, the ALD coating operation performed as substrate  20  passes along output face  36  of distribution manifold  10  when delivering reactant gaseous materials O and M. In  FIG. 4A , the surface of substrate  20  first receives an oxidizing material from output channels  12  designated as delivering first reactant gaseous material O. The surface of the substrate now contains a partially reacted form of material O, which is susceptible to reaction with material M. Then, as substrate  20  passes into the path of the metal compound of second reactant gaseous material M, the reaction with M takes place, forming a metallic oxide or some other thin film material that can be formed from two reactant gaseous materials. 
         [0036]    As  FIGS. 4A and 4B  show, inert gaseous material I is provided in every alternate output channel  12 , between the flows of first and second reactant gaseous materials O and M. Sequential output channels  12  are adjacent, that is, share a common boundary, formed by partitions  22  in the embodiments shown. Here, output channels  12  are defined and separated from each other by partitions  22  that extend perpendicular to the surface of substrate  20 . 
         [0037]    Notably, there are no vacuum channels interspersed between the output channels  12 , that is, no vacuum channels on either side of a channel delivering gaseous materials to draw the gaseous materials around the partitions. This advantageous, compact arrangement is possible because of the innovative gas flow that is used. Unlike gas delivery arrays of earlier processes that apply substantially vertical (that is, perpendicular) gas flows against the substrate and should then draw off spent gases in the Opposite vertical direction, distribution manifold  10  directs a gas flow (preferably substantially laminar in one embodiment) along the surface for each reactant and inert gas and handles spent gases and reaction by-products in a different manner. The gas flow used in the present invention is directed along and generally parallel to the plane of the substrate surface. In other words, the flow of gases is substantially transverse to the plane of a substrate rather than perpendicular to the substrate being treated. 
         [0038]    The above described method and apparatus are one example of a vapour deposition process that can by used in the present invention. The invention works equally well using chemical vapour depositions. 
         [0039]    In the example ALD/CVD coating was carried out using apparatus similar to that described above. Either titanium dioxide or alumina was coated. For titanium dioxide, titanium tetrachloride was in one bubbler and water in the other. For alumina, a 1M solution of trimethylaluminium in heptane was in one bubbler and water in the other. 
         [0040]    For both oxides, the flow rate of the carrier gas through the bubblers was 50 ml/min. The flow rate of diluting carrier gas was 300 ml/min for the water reactant and 150 ml/min for the titanium tetrachloride or trimethylaluminium. The flow rate of the inert separator gas was 21/min. Nitrogen was used for the carrier gas in all instances. A calibration was run to determine the thickness versus number of substrate oscillations for both oxides. 
       EXAMPLE 
       [0041]    A small piece of tape, acting as a mask, was stuck to a 63×63×1 mm piece of borosilicate glass which was coated with GH17R (Nippon Gohsei) 10% polyvinylalcohol, PVA, using a gravure roller using a 150 micron bar. The thickness of the PVA layer not masked was estimated to be about 15 microns. The tape was removed to leave a hole in the PVA coating creating a simple pattern. The entire substrate was coated with a layer of titanium dioxide about 100 nm thick. The edge of the PVA coating was found and peeled off, removing the titanium dioxide coating which was on top of the PVA layer. The thicknesses of the titanium dioxide remaining on the glass were determined by ellipsometer. It was found that there was no titanium dioxide where there had previously been PVA and a layer thickness of 101 nm where there had been none. 
         [0042]    It will be understood that the material used for the first layer need not be PVA, as in the above example. Any suitable film forming polymer with low adhesion to the substrate may be used. Similarly the second material is not limited to those used in the example described above. The second material may be any metal, metal oxide, metal nitride, metal sulphide, metal oxysulphide or metal oxynitride. 
         [0043]    The invention has been described in detail with reference to preferred embodiments thereof. It will be understood by those skilled in the art that variations and modifications can be effected within the scope of the invention.