Patent Publication Number: US-7223700-B2

Title: Method for fabricating fine features by jet-printing and surface treatment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of U.S. application Ser. No. 10/186,092, filed Jun. 27, 2002, now U.S. No. 6,972,261 by the same inventors and claims priority therefrom. This divisional application is being filed in response to a restriction requirement in that prior application and contains rewritten and/or additional claims to the restricted subject matter. 
    
    
     BACKGROUND 
     In recent years, the increasingly widespread use of display device alternatives to the cathode ray tube (CRT) has driven the demand for large-area electronic arrays. In particular, amorphous silicon and laser-recrystallized poly-silicon liquid crystal displays are commonly used in lap-top computers. However, fabricating such large-area arrays is expensive. A large part of the fabrication cost of the large-area arrays arises from the photolithographic process used to pattern the array. In order to avoid such photolithographic processes, direct marking techniques have been considered as an alternative to photolithography. 
     Examples of direct marking techniques used in place of photolithography include utilizing a xerographic process to deposit a toner that acts as an etch mask and using an ink-jet printhead to deposit a liquid mask. Both techniques have corresponding problems. Toner-based materials are hard to control and difficult to remove after deposition. 
     The use of ink-jetted liquids to directly write etch masks is a practical alternative to printed toner although jet printing also possesses inherent complexities. Controlling the feature sizes of printed liquid masks is difficult due to spreading of the liquid on the surface after deposition. For example, when liquid drops are deposited onto a surface, the droplet configuration is largely determined by its wetting properties. Typically, small wetting or contact angles (the angle formed by the edge of a droplet and the substrate surface) are required to obtain good adhesion to a surface but this condition allows the liquid to spread and form relatively large features. On the other hand, if the liquid does not wet the surface due to a high surface energy, a large contact angle will form allowing for the formation of small drop features. However these printed droplets may adhere poorly. Neither situation is desirable in semiconductor processing—the small contact angle droplets increase feature size while large contact angle droplets give unreliable patterning. 
     Special piezoelectric ink-jet printheads allow generation of low droplet volumes. Small printed features have been obtained using ink-jet printheads as described in W. S. Wong, et al., “Amorphous silicon thin-film transistors and arrays fabricated by jet printing” in Appl. Phys. Lett., 80, 610 (2002). In the described reference, wax etch masks patterned by ink-jet printing are used to produce feature sizes on the order of 20-40 μm with layer registration to within a few micrometers. However, even with these printheads, the small sizes of features critical to the fabrication of large-area microelectronic arrays have been difficult to achieve. In using a jet-printed feature as an etch mask, the minimum feature size was limited by the smallest droplet, typically in the range of 20 μm. 
     Thus a method of forming smaller features using inexpensive printing techniques is needed. 
     SUMMARY 
     The present invention relates generally to the field of device processing. In particular the invention relates to a method and apparatus for fabricating small features devices using materials from aqueous or non-aqueous organic solutions. 
     In the invention, a print procedure marks or prints a protective layer in a pattern on regions of a substrate that will define exposed and covered areas on the surface. Exposed substrate areas are treated to cause feature formation on the exposed regions. In one embodiment of the invention, the substrate treatment alters the surface characteristics of the exposed regions. The patterned layer is then removed and the substrate is coated such that a material of interest adheres only to the regions with the altered surface characteristics. 
     In a second embodiment, the printed protective pattern layer covers a pretreated surface. Areas of the surface unprotected by the protective pattern layer is then re-treated to remove or modify the pretreated surface. The protective pattern layer is subsequently removed and a new layer deposited to form desirable features. The new layer adheres only to the areas of the surface that were originally unprotected by the protective pattern layer. The minimum feature size of the patterned region is not critical since the feature of interest is defined by openings in the patterned region or spacing between adjacent patterned regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the invention may be more readily understood by referring to the detailed description and the accompanying drawings. 
         FIG. 1  shows one embodiment of a droplet source system used to eject a phase-change material onto a substrate. 
         FIG. 2  shows a source of acoustic waves that may be used to eject droplets in the droplet source system of  FIG. 1 . 
         FIG. 3  shows a top view of a substrate at various stages in a process to form fine features. 
         FIG. 4  is a flow chart that describes the operations used to fabricate fine features. 
         FIG. 5  shows a top view of a substrate undergoing print-dip patterning to form fine features. 
         FIG. 6  is a flowchart that describes one method of forming an amorphous semiconductor thin-film transistor using one embodiment of the invention. 
         FIG. 7  shows a side view of the formation of an amorphous semiconductor thin-film transistor at various stages of fabrication. 
         FIG. 8  is a flowchart that describes one method of forming a polymeric semiconductor thin film transistor. 
         FIG. 9  is a top view of a semiconductor substrate at various stages of forming a dip-coated polymeric semiconductor. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description a method and system of forming fine-feature devices on a substrate using printed patterns will be described. The system will create a pattern, typically using a printer to controllably eject individual droplets to form a patterned protective layer or coating over regions of the substrate to define the outline of a feature. Regions that were not at one time covered by protective layer will be subject to deposition (or removal) of materials used to form various features. Thus feature size will not be limited by droplet size, but instead by how closely droplets can be positioned together without combining to form a single droplet. A system to tightly control the boundaries of the droplet and minimize possible coalescence of juxtaposed droplets will also be described. 
       FIG. 1  shows a system  100  including a heat source  104  that heats a reservoir  108  of typically phase-change material to a temperature that is sufficient to maintain the material in a liquid state. In one embodiment of the invention, the temperature of the reservoir is maintained above 100 degree centigrade and in some embodiments, at temperatures above 140 degrees centigrade, a temperature sufficient to liquify most phase change organics. 
     The phase-change material may be an organic media that melts at low temperatures. Other desirable characteristics of the phase-change material include that the patterning material is non-reactive with organic and inorganic materials used in typical semiconductor materials processing, and that the phase change material has a high selectivity to etchants. An alternate embodiment of the invention may also include a material suspended in a liquid. When liquid suspension is used, the substrate material is maintained above the boiling point of the liquid, and after deposition of the patterning material, the liquid carrier evaporates upon contact with the substrate surface. When evaporation is used, the phase change process is directed from liquid to vapor, rather than from liquid to solid. 
     An additional desirable characteristic of the phase-change patterning material is that the resulting pattern should be robust enough to withstand wet-chemical or dry etching processes. When a dry etching process is used, phase change patterning materials with low-vapor pressures may be used. Wax is an example of a phase-change material with the previously described characteristics. Kemamide 180-based waxes from Xerox Corporation of Stamford Conn. is one example of a suitable wax for use as a phase-change patterning material. 
     A plurality of droplet sources such as droplet source  112  receives the liquid phase-change marking material from reservoir  108  and outputs droplets  116  for deposition on a substrate  120 . The substrate is typically a thin film of semiconductor material or a thin-film metal such as aluminum. The substrate is maintained at a temperature such that the droplet cools rapidly after deposition. In some embodiments of the invention, a wetting agent, typically a dielectric material such as silicon dioxide, SiO 2  or silicon nitride, Si 3 N 4  may be included on the surface to enhance wetting thereby assuring that sufficient wetting occurs to form a good contact between the pattern and the substrate. The temperature of the system is maintained such that the cooling rate is sufficient to control the behavior of the droplet after contacting substrate  120  despite the enhanced wetting properties of the surface to be etched. 
     When increased coalescence between adjacent droplets is required, the substrate temperature can be increased to increase droplet spreading and thereby increase coalescence. When printing lines of Kemamide-based wax from an acoustic ink-jet printer, it has been found that increasing the substrate temperature from 30 degrees to 40 degrees centigrade improves the print quality of the pattern. In the case of Kemamide-based waxes, it has been found that excellent results are achieved when the surface is maintained at 40 degrees centigrade, which is about 20 degrees centigrade below the freezing point of the wax. At 40 degrees centigrade, the temperature of the substrate is still low enough that the droplet rapidly “freezes” upon contacting substrate  120 . 
     In order to minimize the possibility of partial midair freezing of droplets in space  121  between droplet source  112  and substrate  120 , an electric field  122  may be applied to accelerate the droplet from droplet source  112  to substrate  120 . The electric field may be generated by applying a voltage, typically between one to three kilovolts between droplet source  112  and an electrode or platen  122  under substrate  120 . The electric field minimizes droplet transit time through space  121  and allows substrate surface temperature to be the primary factor controlling the phase change operation. Moreover, the increased droplet velocity in space  121  improves the directionality of the droplet allowing for improved straight-line features. 
     After a droplet of marking material is deposited on substrate  120 , the relative positions of the substrate and the droplet source are adjusted to reposition the droplet source over a second position to be patterned. The repositioning operation may be achieved either by moving droplet source  112  or by moving substrate  120 . In the illustrated embodiment, a control circuit  124  moves droplet source  112  in a predetermined pattern over substrate  120 . A driver circuit  128  provides energy to droplet source  112  causing ejection of droplets when droplet source  112  is positioned over a region of substrate  120  to be patterned. By coordinating the movement of droplet source  112  with the timing of droplet source outputs, a pattern can be “printed” on the substrate. 
     As each drop is printed, a feedback system may be used to assure droplets of proper size. An imaging system, such as camera  122 , may be used to monitor droplet size. When smaller features are to be printed, or the droplet size otherwise reduced, a temperature control circuit  123  lowers the temperature of a surface of substrate  120 . The lower temperature increases the quench rate resulting in rapid solidification of the phase change patterning material upon contact with substrate  120 . When larger droplets are needed, usually for merging droplets in larger features, temperature control circuit  123  raises the temperature of substrate  120 . In one embodiment of the invention, temperature control circuit  123  includes a heating element thermally coupled to substrate  120  such that ambient heating of media around the substrate is minimized. 
     In one embodiment of the invention, the phase change material is a solid at temperatures below approximately 60 degrees centigrade. In such embodiments, it may be unnecessary to cool the substrate below room temperature because as previously described, a sufficiently small droplet cools rapidly when a 20 degree temperature differential is maintained between the freezing point of the phase change material and the substrate temperature. In such cases, the temperature control circuit may merely be a sensor and a heater that raises the substrate slightly above room temperature when larger feature sizes are to be printed. 
     In order to control and align the movement of droplet source  112 , printed alignment marks, such as mark  113 , patterned from a previous patterned layer may be used to coordinate the next overlying layer. An image processing system such as the previously described camera may be used to capture the orientation of the previous patterned layer. A processing system then adjusts the position of the overlying pattern layer by altering the pattern image file before actual printing of the pattern layer. In this way, the substrate remains fixed and mechanical movement of the substrate holder is unnecessary. Instead positioning adjustment are accomplished in software and translated to movements of droplet source  112 . 
     Each droplet source may be implemented using a variety of technologies including traditional ink-jet technology. An alternative technology well suited for generating extremely small droplet sizes is the use of sound waves to cause ejection of droplets of patterning material as done in acoustic ink printing systems.  FIG. 2  shows one embodiment of an acoustic droplet source  200  implemented using acoustic ink printing technology. 
     In  FIG. 2 , a source of acoustic waves such as piezo electric driver  204  generates acoustic waves  208  in a pool  212  of phase change patterning material. Acoustic lens  216  focuses the acoustic waves such that a droplet of phase change patterning material is ejected from the surface of pool  212 . The droplet is deposited on substrate  120  of  FIG. 1 . 
       FIG. 3  shows a top view of a substrate at various stages in a process to form fine features and  FIG. 4  is a flow, chart that describes the operations used to fabricate the fine features. As used herein, fine features are defined as features that have either a width or length typically less than 50 micrometers. Initially a substrate  300  is provided as described in block  404 . Examples of typical substrate surfaces include a thin film surface such as an epitaxial layer supported by glass or a polymer such as poly(ethyleneterephthalate). When thin film transistors are being formed, common substrate materials include gold or silicon oxide. Typically, the substrate is easily wettable by polar liquids such that the contact angle of the liquids on the substrate form small contact angles, typically less than 90 degrees. Hydrophilic wettable surface allows liquid droplets to be quickly absorbed into the substrate. 
     A printing apparatus such as the printing apparatus of  FIG. 1  ejects droplets of a protective material in a pattern over the substrate in block  408  resulting in a patterned protective layer  304  over substrate  300 . The protective material may be made of a variety of materials, typically materials that solidify reasonably soon after contact to minimize absorption into the substrate. The protective material may be deposited using a variety of techniques. One method of deposition is described in filed patent application Ser. No. 09/838,685 entitled “APPARATUS FOR PRINTING ETCH MASKS USING PHASE-CHANGE MATERIALS” and Ser. No. 09/838,684 entitled “METHOD FOR PRINTING ETCH MASKS USING PHASE-CHANGE MATERIALS” which are hereby incorporated by reference. The rapidly solidifying protective material may be made from a number of different compounds. One example of a suitable protective material is the previously described wax compound such as Kemamide 180-based wax from Xerox Corporation of Stamford Conn. 
     The deposited pattern includes openings  308  in the protective layer that define features to be fabricated. The minimum dimensions of the openings in the protective layer  304  defines the resolution of the features to be fabricated. 
     After deposition of the pattern, a surface treatment is applied to the exposed portions of the substrate (portions of the substrate not covered by the pattern), including the openings, as described in block  412  of  FIG. 4 . In one embodiment of the surface treatment, the exposed regions of the substrate are exposed to a binder, a surfactant or other chemical treatment to differentiate the exposed surface of the substrate from the patterned areas. One method of differentiation is that the chemical treatment changes the wettability of the substrate, thus when a positive protective pattern was formed, if the substrate was originally hydrophilic, exposed regions will be hydrophobic. In alternate embodiments, an originally hydrophobic substrate may be converted to a hydrophilic substrate in the exposed regions. 
     After surface treatment, the protective layer pattern may be removed as described in block  416 . Removal of the pattern may be done by a variety of techniques including using organic solvents such as tetrahydrofuran (THF). After removal of the pattern, the substrate is coated with a material of interest that preferentially adheres to formerly patterned or unpatterned areas depending on the surface treatment as described in block  420 . A negative of the printed pattern is formed when the material of interest preferentially adheres to previously unpatterned areas. A positive of the printed pattern is formed when the material of interest adheres to the previously patterned areas. Negative patterns allow the formation of small features, for example, a fine line feature, having a feature size smaller than the minimum spot size of an ink jetted wax droplet can be created between adjacent lines in a printed pattern. 
     In an alternate embodiment of the invention, the surface treatment may involve directly depositing a material of interest over the patterned substrate. For example, a thin-film layer  312  may be formed to adhere to unpatterned or exposed portions of the substrate. Such a thin-film layer may be deposited using printing techniques, conventional deposition or coating processes. When a solution of a material in a polar solvent is used, the protective pattern acts as a nonwetting surface to prevent coverage of protected regions, allowing coverage only of the wettable substrate exposed in the openings of the protective layer. One example of a conductive polymer in an aqueous mixture is Baytron P manufactured by Bayer Corporation (Pittsburgh, Pa.) which may be coated onto the surface using a spin-on application. Alternative methods of exposure to a polar solution may include either through printing or by dipping in a bath solution. After application of the thin film, the protective pattern may be removed leaving the thin film covering only areas that were formerly openings in the protective layer. 
     The above operations may be repeated in various combinations to eventually form a multilayered semiconductor structure. The materials used to form a thin-film layer  312  are not necessarily dissolved in an aqueous solution. In certain instances, the hydrophobicity of the patterning material prevents sufficient wetting of the exposed regions. In such cases, solvents may be used to assist in wetting the exposed regions or alternatively, surfactants may be added to aqueous solutions to improve the wetting characteristics. In an alternate embodiment, both the patterned and exposed areas may be coated simultaneously followed by a lift-off process that removes the wax and defines the exposed regions. 
       FIG. 5  shows a series of top views of a substrate undergoing print-dip pattering to form fine features. The print-dip patterning shown in  FIG. 5  is a specific example of the general methods shown in  FIGS. 3 and 4  and described in the accompanying text. In particular, the method described in  FIG. 5  shows one method of achieving a hydrophobic substrate through a thin film coating and a plasma cleaning surface treatment to achieve a hydrophilic unpatterned region and a hydrophobic patterned region. 
     In the first structure  500  of  FIG. 5 , a hydrophilic substrate is coated with a thin film such as a thin polymeric film or a monolayer. An example of a typical coating material is octadecyltricholorosilane, otherwise known as OTS. Another example of a coating layer is organic trichlorosilane. Other organic compounds, typically tricyclines, may also be used as a coating layer. In order to maintain uniformity across the coating surface and minimize processing time, the layer is typically kept thin, less than 10 nanometers thick. Thicker coating can also be used if deposition time is not a factor in the overall fabrication process. The coated substrate presents a hydrophobic surface as shown in the image of the coated substrate  504 . 
     A protective pattern  512  is printed over the coated substrate to result in printed patterned surface  508 . The pattern is typically a wax mask, such as Kemimide-based wax. Although a typical width of each printed line  516  may be 50 micrometers, the spacing  520  between adjacent lines may be controlled down to 5 micrometers. In one implementation, a Tektronix Piezoelectric printhead with an x-y translation stage having a resolution of 100 nm was used to deposit the pattern. 
     The hydrophobic coating is removed in regions unprotected by the protective pattern resulting in structure  524 . A process such as plasma treatment or a chemical oxidant may be used to remove the hydrophobic coating. Removal of the hydrophobic coating exposes the underlying hydrophillic substrate in regions  528  unprotected by pattern  512 . Subsequently, pattern  512  itself is removed. Removal of pattern  512  results in structure  532  where the formerly patterned regions  536  are hydrophobic and the unpatterned regions  540  are hydrophillic. 
     Finally, a material of interest may be deposited over structure  532  such that the material of interest adheres only to the unpatterned regions  540  yielding the structure  544 . Such a deposition may occur by dip coating structure  532  in a solution containing the material of interest, such as a polymeric organic or colloidal inorganic semiconductors and polymeric organic or colloidal inorganic conductors. 
     The described methods allows for overlays of subsequent layers to form devices having features sizes less than 5 micrometers using printed patterns. The spacing between printed dots, rather than the printed dots themselves define the feature size making possible the formation of relatively small features even using larger dot sizes. However, the use of larger dots does not alleviate the need for tight control over print dot boundaries. One method of tightly controlling print dot boundaries is to print using a phase change material and carefully controlling the temperature of the substrate upon which the phase change material is deposited. The temperature is maintained such that as the droplet source deposits droplets of phase-change patterning material onto the surface of the substrate, the droplets remain in a liquid state for only a very brief period of time. As previously described, this can be achieved by maintaining the temperature of the substrate below the freezing point of the phase change patterning material. 
     One application of the described patterning and surface treatment procedure is to form fine features for fabricating an amorphous silicon thin-film transistor (TFT).  FIG. 6  is a flow chart showing typical operations to form an example TFT while  FIG. 7  shows cross sectional views of the TFT at various stages in the fabrication process. In block  604 , a conductive layer  704  such as silver, gold or palladium that subsequently forms the bottom gate electrode of the TFT is deposited onto a transparent substrate  708  such as glass or quartz. 
     In block  608 , a first patterned protective layer is printed over the conductive layer. The protective layer is typically a wax  712  that is deposited using an ink jet printing process. The spacing  716  between adjacent masked regions defines a fine feature to be fabricated 
     In block  612 , a surface treatment is applied to the TFT structure. Typical surface treatments include exposure of the surface to OTS or a self-assembled monolayer. The self-assembled monolayer  720  forms a mask layer for the gate electrode. Although palladium and gold are typically associated with monolayer formation, more conventional gate electrode metals such as chromium may also be used with a compatible self-assembled monolayer. 
     In block  616 , the printed protective layer is removed leaving the surface treatment, typically a self assembled monolayer, as the masking element. Regions of transparent substrate unprotected by the surface treatment are etched in block  620  leaving behind only a gate electrode  724  remaining over the substrate  708  as shown in  FIG. 7 . After formation of the gate electrode, a thin film transistor stack  726  is formed over the gate electrode  724 . In block  624 , a bottom dielectric layer  728 , such as silicon nitride or silicon dioxide, is deposited over the gate electrode. An amorphous silicon layer  732  is deposited over bottom dielectric layer  728  in block  628 . Finally, in block  632 , a top dielectric layer  736 , such as silicon nitride or silicon dioxide, is deposited over amorphous silicon layer  732  to complete the thin-film transistor stack. Typical thickness of gate electrode, bottom dielectric, amorphous silicon, and top dielectric layers are 100 nm, 300 nm, 50 nm, and 200 nm, respectively. The described patterning process may be repeated on subsequently deposited layers, composed of bottom dielectric, semiconductor, and top dielectric layer over entire substrate surface to form multiple TFTs. 
     A second feature etch mask  740  (called the island mask) is deposited over the top dielectric layer in block  636  to form the transistor active-area stack also called the island structure. Dielectric and semiconductor stack are etched in block  640  and the printed pattern is removed to define the island features and device active areas. A photosensitive mask layer, such as positive photoresist  740 , is then deposited over the substrate surface in block  644 . In block  648 , the mask layer is defined by exposing the photoresist  740  to ultraviolet light through the backside of transparent substrate  708 . The opaque bottom gate electrode  724  serves as a mask for the ultraviolet light reaching the photoresist. Thus mask features are automatically self-aligned to bottom gate electrodes  724  forming a self-aligned source/drain region over the island area. 
     A second conductive layer, such as: gold/titanium-tungsten or palladium/titanium-tungsten tri-layers are deposited in block  652  to form a source/drain metal contact  744 . The typical thickness of the source/drain contact metal is 100-200 nm; while a typical thickness of the adhesive layer (titanium/tungston) is 5-10 nm. A second pattern layer  748  is printed over second conductive layer  744 . In one embodiment of the invention, the pattern layer  748  is printed such that fine features are defined by the openings in pattern layer  748 . The second conductive surface is treated with a surface treatment such as OTS or a self-assembled monolayer in block  656 . In block  660 , the second pattern layer  478  is removed leaving behind the surface treatment that defines the fine features. The second conductive layer is then etched with the surface treatment acting as a mask to create fine features in block  664 . Other source/drain contact metals, such as aluminum, chromium, aluminum/titanium-tungsten tri-layers or chromium/titanium-tungsten tri-layers can be used with the appropriate self assembled monolayer to complete the final structure. 
     Another specific application of using the described patterning and surface treatment procedure is to form a polymeric-semiconductor thin-film transistor.  FIG. 8  is a flow chart showing the operations used to form such a transistor.  FIG. 9  shows top views of the polymeric-semiconductor thin-film transistor (TFT) at various stages in fabrication where the drain, source and gate of the TFT are formed. In block  804 , a conductive layer  904  such as gold or palladium is deposited onto a substrate, such as silicon, glass, quartz, or a polymeric-based flexible material. A patterned etch mask. Layer  908  is printed over the conductive layer to define bottom gate electrode features in block  808 . The masked surface is etched in block  812  using either a wet or dry etchant to remove conductive layers exposed by the printed mask leaving exposed substrate  912 . After etching, the printed etch mask is removed in block  816  revealing conducting gate  920 . 
     A dielectric layer, such as silicon nitride or silicon dioxide (typical thickness between 200-300 nm) is deposited over the entire substrate surface in block  824 . Alternative dielectric materials include spin-on glass, polyamide, or benzocyclobutene. Source and drain contacts are formed by depositing a second conductive layer  924  of  FIG. 9 , typically gold or palladium, over the dielectric layer in block  828 . The typical thickness of the source/drain contact metal is between 100-200 nm. To define the source/drain contact features, a second pattern layer  928  is printed over the second conductive source/drain contact layer in block  832 . In block  836 , this second conductive layer is etched to define the source/drain contact features  936 ,  940  as shown in structure  942  of  FIG. 9 . In block  840 , the second pattern layer is removed leaving defined source/drain contact features  936 ,  940 . 
     In block  848 , a mask layer  944  is printed to cover the active regions of the polymeric TFT to be formed. The substrate is coated with a surface treatment layer  948  of  FIG. 9  such as OTS or a self-assembled monolayer in block  852 . The printed mask layer removed in block  856 . Areas that were subject to the surface treatment layer  948  are hydrophobic while previously masked surfaces  952  that were not subject to the surface treatment are hydrophilic. A Polymeric semiconductor  956  that serves as the active region is deposited onto the surface treated substrate. One method of depositing the polymeric semiconductor onto the surface treated substrate is by dip coating the entire substrate as described in block  860 . The polymeric semiconductor  956  that serves as the active material adheres to the hydrophilic regions and dewets off hydrophobic areas. The final structure that results is a polymeric semiconductor thin-film transistor. 
     The described methods can use wax as the patterned layer and etch mask material. Registration of overlying layers is accomplished by alignment marks on the processed surface. Alignment may be performed visually using a camera and substrate-stage controller. In addition, the application of the polymeric semiconductor or any liquid-based material can be applied by various methods such as jet printing, spin coating, “doctor blading”, or other methods of large-area coating known to those of skill in the art. 
     It should be understood that the foregoing description is intended to be illustrative of the invention. Variations and modification of the descriptions provided herein will present themselves to those skilled in the art. For example, the description has identified examples of phase-change materials, as well as different methods of causing a droplet to be ejected from a fluid reservoir. Examples of devices fabricated, such as a thin-film transistor, have been described. However, other methods, other phase-change materials may also be used. Other devices may also be fabricated using the methods described herein. Accordingly, the present description should not be read as limiting the scope of the invention except as described in the claims that follow.