Abstract:
Methods are provided for fabricating field emitters by using laser-induced re-crystallization. A substrate is first provided on which a silicon-containing layer is formed. A plurality of extrusive tips are thereafter formed to be extruded from the surface of the silicon-containing layer by using laser-induced re-crystallization. The methods of the laser-induced re-crystallization include a step of subjecting the overall or partial silicon-containing layer to an energy source, either unpatterned or patterned.

Description:
BACKGROUND OF THE INVENTION 
   The present invention generally relates to semiconductor manufacturing process and, more particularly, relates to a method for manufacturing field emitters by means of laser-induced re-crystallization. 
   In recent years, field emitters have been developed and widely used in electronic applications such as field emission displays (FEDs), backlight units, field emission transistors and field emission diodes. When subjected to a suitable electrical field, electrons are emitted from the field emitters and impinge on phosphors coated on the back of a transparent cover plate to produce an image or light. Such a cathodoluminescent process is known as one of the most efficient methods for generating light. Typically, the field emitters can be implemented by means of an array of micro-tips or carbon nano-tubes. 
   In the early development for field emitters, a so-called spindt tip process for forming metal micro-tips was utilized. In such a process, a silicon wafer is first oxidized to produce a thick silicon oxide layer and then a metallic gate layer is deposited on top of the oxide. The metallic gate layer is then patterned to form gate openings, while subsequent etching of the silicon oxide underneath the openings undercuts the gate and creates a well. A sacrificial material layer such as nickel is deposited to prevent deposition of nickel into the emitter well. Molybdenum is then deposited at normal incidence such that a cone with a sharp point grows inside the cavity until the opening closes thereabove. An emitter cone is left when the sacrificial layer of nickel is removed. 
   In an alternate design, silicon micro-tip emitters can be formed by first conducting thermal oxidation on silicon and then followed by patterning the oxide and selectively etching to form silicon micro-tips. 
   However, a major disadvantage of the micro-tip emitter is the complicated processing steps that must be used to fabricate the device. For instance, the formation of the various layers in the device, and specifically the formation of the micro-tips, requires a thin film deposition technique followed by a photolithographic and etching process. As a result, numerous process steps must be performed in order to define and fabricate the various structural features. The film deposition processes, photolithographic processes and etching processes involved greatly increase the manufacturing cost thereof. 
   BRIEF SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a method for fabricating filed emitters by using a laser-induced re-crystallization technique that does not have the drawbacks or shortcomings of the conventional method. 
   It is another object of the present invention to provide a method for fabricating field emitters by using a laser-induced crystallization technique that is simple and cost-effective. 
   The present invention is directed to a method for fabricating field emitters that obviates the problems resulting from the limitations and disadvantages of the prior art. 
   In accordance with an embodiment of the present invention, there is provided a method for fabricating field emitters, including the steps of (a) providing a substrate; (b) forming a silicon-containing layer over the substrate; and (c) forming a plurality of extrusive tips extruded from the surface of the silicon-containing layer by subjecting the silicon-containing layer to an energy source. 
   Also in accordance with the present invention, there is provided a method for fabricating field emitters, including the steps of: (a) providing a substrate; (b) forming a silicon-containing layer over the substrate; and (c) forming a plurality of extrusive tips extruded from the surface of the silicon-containing layer by subjecting the silicon-containing layer to a patterned energy source. 
   Further in accordance with the present invention, there is provided a method for fabricating field emitters, including the steps of: (a) providing a substrate; (b) forming a first conductive layer over the substrate; (c) forming a silicon-containing layer over the first conductive layer; (d) sequentially forming an insulative layer and a second conductive layer over the silicon-containing layer; (e) patterning the second conductive layer and the insulative layer to expose the silicon-containing layer; and (f) forming a plurality of extrusive tips extruded from the surface of the exposed silicon-containing layer by subjecting the exposed silicon-containing layer to an energy source. 
   Still further in accordance with the present invention, there is provided a method for fabricating field emitters, including the steps of: (a) providing a substrate; (b) forming a silicon-containing layer over the substrate; (c) patterning the silicon-containing layer to form a plurality of silicon-containing islands; and (d) forming a plurality of extrusive tips extruded from the surface of the silicon-containing islands by subjecting the silicon-containing islands to an energy source. 
   Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The features and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
   The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the present invention and together with the description, serve to explain the principles of the invention. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Reference will now be made in detail to the present embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same or analogous reference numbers are used throughout the drawings to refer to the same or like parts. 
     In the drawings: 
       FIGS. 1A  thru  1 D are schematic diagrams showing the formation of extrusive tips after a silicon layer is subjected to a laser beam and then crystallized. 
       FIG. 2  is an SEM diagram of extrusive tips formed by laser-induced crystallization in accordance with the present invention. 
       FIGS. 3A and 3B  are schematic diagrams showing processing steps for fabricating a triode device according to one preferred embodiment of the present invention in cross-sectional views. 
       FIGS. 4A and 4B  are schematic diagrams showing processing steps for fabricating a triode device according to another preferred embodiment of the present invention in cross-sectional views. 
       FIGS. 5A and 5B  are schematic diagrams showing processing steps for fabricating a triode device according to further preferred embodiment of the present invention in cross-sectional views. 
       FIGS. 6A and 6B  are schematic diagrams showing processing steps for fabricating a triode device according to further another preferred embodiment of the present invention in cross-sectional views. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1A  thru  1 D, schematic diagrams for explaining the formation of extrusive tips after a silicon-containing layer is subjected to laser beam and then crystallized are illustrated. In  FIG. 1A , a silicon-containing layer  11  is deposited on or over a substrate  10 , which can be one of several types of substrates. For example, substrate  10  can be one of a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate, and the like. Preferably, the silicon-containing layer  11  is an amorphous silicon layer or a polycrystalline silicon layer. The silicon-containing layer  11  can be doped with n-type or p-type impurities. Preferably, the silicon-containing layer  11  has a thickness in the range between about 200 Å and about 8000 Å. The silicon-containing layer  11  is then exposed to an energy source (not shown in  FIGS. 1A  thru  1 D) and melted to become a liquid  14 . Preferably, the energy source can be a laser beam, such as Nd:YAG laser, carbon dioxide (CO 2 ) laser, argon (Ar) laser, excimer laser or the like. At time t 0  in  FIG. 1A , the liquid  14  cools down such that some portions  12 A and  12 B nucleate to become crystallized. The solid portions  12 A and  12 B are generally known as grains to those ordinarily skilled in the art. The grains  12 A and  12 B gradually extend from liquid-solid interface (see time t 1  in  FIG. 1B ), and the liquid portion  14  gradually extrudes from the surface (see time t 2  in  FIG. 1C ) because the density of liquid silicon (D LS ) is greater than that of solid silicon (D SS ). Note that the gap between solid portions  12 A and  12 B becomes smaller as time progresses. At time t 3  in  FIG. 1D , the gap between the solid portions  12 A and  12 B is closed to form a grain boundary  18 . At time t 3 , the liquid  14  is vanished. However, an extrusive tip  16  is formed in the vicinity of grain boundary  18  and extruded from the surface of the silicon-containing layer  11 . 
   Referring to  FIG. 2 , a Scanning Electron Microscope (SEM) diagram of extrusive tips formed by laser-induced crystallization in accordance with the present invention is illustrated.  FIG. 2  shows that the silicon-containing layer  11  of  FIG. 1D , after being subjected to the energy source, produces many extrusive tips  16  which can serve as field emitters in the application of field emission displays, backlight units, field emission transistors or field emission diodes. 
   Referring to  FIGS. 3A and 3B , processing steps for fabricating a triode device according to one preferred embodiment of the present invention in cross-sectional views are illustrated schematically. As shown in  FIG. 3A , a cathode electrode layer  31  and a silicon-containing layer  33  are sequentially deposited on or over a bottom substrate  30 . As noted above, the bottom substrate  30  can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate or the like. Preferably, the silicon-containing layer  33  is an amorphous silicon layer or a polycrystalline silicon layer, which is doped with n-type or p-type impurities and has a thickness ranging between about 200 Å and about 8000 Å. The whole of the silicon-containing layer  33  is then exposed to an energy source  32  and melted to become liquid. Preferably, the energy source can be a laser beam, such as Nd:YAG laser, carbon dioxide (CO 2 ) laser, argon (Ar) laser, excimer laser or the like. After it is melted and crystallized, the silicon-containing layer  33  has a plurality of extrusive tips  310  extruded from the surface of the silicon-containing layer  33 . 
   Next, an insulative layer  34  and a gate electrode layer  35  are sequentially deposited on or over the silicon-containing layer  33  as shown in  FIG. 3B . The insulative layer  34  and the gate electrode layer  35  are etched and patterned to form openings  300  exposing portions of the silicon-containing layer  33  by etch and photolithography processes. Moreover, an anode electrode layer  37  and a phosphor layer  38  are sequentially formed to overlay a top substrate  36  that can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate or the like. The top substrate  36  and the bottom substrate  30  are spaced apart by a predetermined distance and mounted together to form a complete triode device as shown in  FIG. 3B . Such device of a triode structure utilizes the extrusive tips  310  of the silicon-containing layer  33  as field emitters. When a voltage difference is applied between a cathode electrode layer  31  and a gate electrode layer  35 , electrons  39  are extracted from the cathode electrode layer  31  and accelerated toward the phosphor layer  38 . 
   Referring to  FIGS. 4A and 4B , processing steps for fabricating a triode device according to another preferred embodiment of the present invention in cross-sectional views are illustrated schematically. As shown in  FIG. 4A , a cathode electrode layer  41  and a silicon-containing layer  43  are sequentially deposited on or over a bottom substrate  40 , which can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate or the like. Preferably, the silicon-containing layer  43  is an amorphous silicon layer or a polycrystalline silicon layer, which is doped with n-type or p-type impurities. The silicon-containing layer  43  preferably has a thickness in the range between about 200 Å and about 8000 Å. In this embodiment, portions of the silicon-containing layer  43  are then exposed to a patterned energy source  42  and melted to become liquid at predetermined positions. Preferably, the energy source  42 , such as a laser beam, passes through an optical grating or a raster so as to generate the patterned energy source  42 . The energy source  42  can be one of Nd:YAG laser, carbon dioxide (CO 2 ) laser, argon (Ar) laser and excimer laser. After being melted and crystallized, the silicon-containing layer  43  has a plurality of extrusive tips  410  extruded from the surface of the silicon-containing layer  43 . 
   Next, an insulative layer  44  and a gate electrode layer  45  are sequentially deposited on or over the silicon-containing layer  43  as shown in  FIG. 4B . The insulative layer  44  and the gate electrode layer  45  are etched and patterned to form openings  400  exposing the extrusive tips  410  of the silicon-containing layer  43  by means of etch and photolithography processes. Moreover, an anode electrode layer  47  and a phosphor layer  48  are sequentially formed to overlay a top substrate  46  that can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate or the like. The top substrate  46  and the bottom substrate  40  are spaced apart by a predetermined distance and mounted together to form a complete triode device as shown in  FIG. 4B . Such device of a triode structure utilizes the extrusive tips  410  of the silicon-containing layer  43  as field emitters. When a voltage difference is applied between a cathode electrode layer  41  and a gate electrode layer  45 , electrons  49  are extracted from the cathode electrode layer  41  and accelerated toward the phosphor layer  48 . 
   Referring to  FIGS. 5A and 5B , processing steps for fabricating a triode device according to a further preferred embodiment of the present invention in cross-sectional views are illustrated schematically. As shown in  FIG. 5A , a cathode electrode layer  51  and a silicon-containing layer  53  are sequentially deposited on or over a bottom substrate  50  that can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate or the like. Preferably, the silicon-containing layer  53  is an amorphous silicon layer or a polycrystalline silicon layer, which is doped with n-type or p-type impurities and has a thickness in the range between about 200 Å and about 8000 Å. Next, an insulative layer  54  and a gate electrode layer  55  are sequentially deposited on or over the silicon-containing layer  53 . The insulative layer  54  and the gate electrode layer  55  are etched and patterned to form openings  500  exposing portions of the silicon-containing layer  53  by means of etch and photolithography processes. In this embodiment, the exposed portions of the silicon-containing layer  53  are then subjected to an energy source  52  by the masking of the patterned gate electrode layer  55 , and melted to become liquid at predetermined positions. Preferably, an energy source  52 , such as Nd:YAG laser, carbon dioxide (CO 2 ) laser, argon (Ar) laser or excimer laser, passes through the openings  500  and melt the exposing portions of the silicon-containing layer  53 . After being melted and crystallized, the silicon-containing layer  53  is has a plurality of extrusive tips  510  extruded from the surface of the silicon-containing layer  53 . 
   Moreover, an anode electrode layer  57  and a phosphor layer  58  are sequentially formed to overlay a top substrate  56  that can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate or the like. The top substrate  56  and the bottom substrate  50  are spaced apart by a predetermined distance and mounted together to form a complete triode device as shown in  FIG. 5B . Such device of a triode structure utilizes the extrusive tips  510  of the silicon-containing layer  53  as field emitters. When a voltage difference is applied between a cathode electrode layer  51  and a gate electrode layer  55 , electrons  59  are extracted from the cathode electrode layer  51  and accelerated toward the phosphor layer  58 . 
   Referring to  FIGS. 6A and 6B , processing steps for fabricating a triode device according to another preferred embodiment of the present invention in cross-sectional views are illustrated schematically. As shown in  FIG. 6A , a cathode electrode layer  61  and a silicon-containing layer  63  are sequentially deposited on or over a bottom substrate  60  that can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate or the like. Preferably, the silicon-containing layer  63  is an amorphous silicon layer or a polycrystalline silicon layer, which is doped with n-type or p-type impurities and has a thickness in the range between about 200 Å and about 8000 Å. Next, the silicon-containing layer  63  is etched and patterned to form silicon-containing islands  63 A and  63 B by means of etch and photolithography processes. In this embodiment, the silicon-containing islands  63 A and  63 B are then subjected to an energy source  62  and melted to become liquid. Preferably, the energy source  62  is a laser beam, such as Nd:YAG laser, carbon dioxide (CO 2 ) laser, argon (Ar) laser or excimer laser. After being melted and crystallized, the silicon-containing layer  63  has a plurality of extrusive tips  610  extruded from the surface of the silicon-containing layer  63 . 
   An insulative layer  64  and a gate electrode layer  65  are sequentially deposited on or over the silicon-containing layer  63  as shown in  FIG. 6B . The insulative layer  64  and the gate electrode layer  65  are etched and patterned to form openings  600  exposing the extrusive tips  610  of the silicon-containing layer  63 A and  63 B by means of etch and photolithography processes. Moreover, an anode electrode layer  67  and a phosphor layer  68  are sequentially formed to overlay a top substrate  66  that can be a silicon substrate, glass substrate, quartz substrate, sapphire substrate, plastic substrate or the like. The top substrate  66  and the bottom substrate  60  are spaced apart by a predetermined distance and mounted together to form a complete triode device as shown in  FIG. 6B . Such device of a triode structure utilizes the extrusive tips  610  of the silicon-containing layer  63  as field emitters. When a voltage difference is applied between a cathode electrode layer  61  and a gate electrode layer  65 , electrons  69  are extracted from the cathode electrode layer  61  and accelerated toward the phosphor layer  68 . 
   The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents. 
   Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.