Abstract:
Integrated circuits, the key components in thousands of electronic and computer products, are generally built layer by layer on a silicon substrate. One common technique for forming layers is called chemical-vapor deposition (CVD.) Conventional CVD systems not only form layers that have non-uniform thickness, but also have large chambers that make the CVD process wasteful and slow. Accordingly, the inventor devised new CVD systems, methods, and apparatuses. One exemplary CVD system includes an outer chamber, a substrate holder, and a unique gas-distribution fixture. The fixture includes a gas-distribution surface having holes for dispensing a gas and a gas-confinement member that engages or cooperates with the substrate holder to form an inner chamber within the outer chamber. The inner chamber has a smaller volume than the outer chamber, which not only facilitates depositions of more uniform thickness, but also saves gas and speeds up the deposition process.

Description:
[0001]     This application is a Divisional of U.S. application Ser. No. 09/797,324, filed Mar. 1, 2001 which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention concerns methods of making integrated circuits, particularly layer-formation, such as chemical-vapor deposition.  
       BACKGROUND OF THE INVENTION  
       [0003]     Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators generally build these circuits layer by layer, using techniques, such as deposition, doping, masking, and etching, to form thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.  
         [0004]     One common technique for forming layers in an integrated circuit is called chemical vapor deposition. Chemical vapor deposition generally entails placing a substrate in a reaction chamber, heating the substrate to prescribed temperatures, and introducing one or more gases, known as precursor gases, into the chamber to begin a deposition cycle. The precursor gases enter the chamber through a gas-distribution fixture, such as a gas ring or a showerhead, one or more centimeters above the substrate, and descend toward the heated substrate. The gases react with each other and/or the heated substrate, blanketing its surface with a layer of material. An exhaust system then pumps gaseous by-products or leftovers from the reaction out of the chamber through a separate outlet to complete the deposition cycle.  
         [0005]     Conventional chemical-vapor-deposition (CVD) systems suffer from at least two problems. First, conventional CVD systems generally form layers that include microscopic hills and valleys and thus have non-uniform thickness. In the past, fabricators have been able to overcome these hills and valleys through use of post-deposition planarization or other compensation techniques. However, escalating demands for greater circuit density, for thinner layers, and for larger substrates make it increasingly difficult, if not completely impractical, to overcome the non-uniform thickness of conventional CVD layers.  
         [0006]     Second, some conventional CVD systems are also inefficient and time consuming. One significant factor affecting both CVD efficiency and duration is the size of conventional reaction chambers, which are generally made large to allow a loading mechanism to insert and extract the substrate. Large chambers generally require more gases to be introduced to achieve desired gas concentrations. However, much of this gas is not only unnecessary based on the amount of material deposited, but is typically treated as waste. Moreover, large chambers also take longer to fill up or pump out, prolonging deposition cycles and thus slowing fabrication of integrated circuits.  
         [0007]     Accordingly, there is a need for better systems and methods of chemical-vapor deposition.  
       SUMMARY OF THE INVENTION  
       [0008]     To address these and other problems, the present inventor devised new systems, methods, and apparatuses for chemical-vapor deposition. One exemplary chemical-vapor deposition system includes an outer chamber, a substrate holder, and a unique gas-distribution fixture. The fixture includes a gas-distribution surface having holes for dispensing a gas and a gas-confinement member that forms a wall around the holes. In operation, the gas-confinement member engages, or otherwise cooperates with the substrate holder to form an inner chamber within the outer chamber.  
         [0009]     The inner chamber has a smaller volume than the outer chamber and thus consumes less gas during the deposition process than would the outer chamber used alone. Also, the smaller chamber volume allows the exhaust system to pump the chamber more quickly, thus increasing the rate of the CVD process. In addition, the exemplary showerhead is made of a material, like silicon, which can be easily passivated to reduce reaction with reactive gases, thus reducing chemical-vapor buildup in the showerhead. Also, the exemplary showerhead includes a configuration of holes that permits uniform gas flow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a side view of an exemplary deposition reactor according to the invention;  
         [0011]      FIG. 2  is a top view of an exemplary gas-distribution fixture according to the invention;  
         [0012]      FIG. 3  is a flowchart showing an exemplary method according to the invention; and  
         [0013]      FIG. 4  is a diagram of an exemplary deposition system  400  incorporating a set of four deposition stations similar in structure and function to system  100  of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     The following detailed description, which references and incorporates  FIGS. 1-4 , describes and illustrates specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to make and use the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.  
         [0015]      FIG. 1  shows an exemplary chemical-vapor-deposition system  100  which incorporates teachings of the present invention. In particular, system  100  includes a chamber  110 , a wafer holder  120 , a gas-distribution fixture  130 , a gas supply system  140 , and exhaust pump  150 , and a exhaust pump  160 .  
         [0016]     More particularly, chamber  110  includes respective top and bottom plates  112  and  114  and a sidewall  116 . In the exemplary embodiment, chamber  110  is a cylindrical structure formed of stainless steel or glass. However, other embodiments use different structures and materials. Bottom plate  114  includes an opening  114 . 1 . Extending through opening  114 . 1  is a stem portion  122  of wafer holder  120 .  
         [0017]     Wafer holder  120  also includes a support platform  124 , one or more heating elements  126 , and one or more temperature sensors  128 . Support platform  124  supports one or more substrates, wafers, or integrated-circuit assemblies  200 . Substrate  200  has an exemplary width or diameter of about 30 centimeters and an exemplary thickness in the range of 850-1000 microns. (The term “substrate,” as used herein, encompasses a semiconductor wafer as well as structures having one or more insulative, conductive, or semiconductive layers and materials. Thus, for example, the term embraces silicon-on-insulator, silicon-on-sapphire, and other advanced structures.) Heating elements  126  and temperature sensors  128  are used for heating substrates  200  to a desired temperature. Holder  120  is coupled to a power supply and temperature control circuitry (both of which are not shown.) In the exemplary embodiment, wafer holder  120  is rotatable either manually or automatically and raises via manual or automatic lever mechanism (not shown). Above wafer holder  120  and substrate  200  is gas-distribution fixture  130 .  
         [0018]     Fixture  130  includes a gas-distribution member  132 , a surface-projection (or gas-confinement) member  134 , and a gas inlet  136 . Gas inlet  132  couples to gas-supply, gas-distribution channels  134 , and a gas inlet  136 . In the exemplary embodiment, fixture  130  has two operating positions  138 . 1  and  138 . 2  relative support platform  124 . Fixture  130  takes operating position  138 . 1 , before and after depositions and operating position  138 . 2  during depositions.  
         [0019]     Gas-distribution member  132  includes gas-distribution holes, or orifices,  132 . 1  and gas-distribution channels  132 . 2 . Holes  132 . 1  define a gas-distribution surface  132 . 3 . In the exemplary embodiment, holes  132 . 1  are substantially circular with a common diameter in the range of 15-20 microns; gas-distribution channels  132 . 2  have a common width in the range of 20-45 microns; and surface  132 . 3  is substantially planar and parallel to support platform  124  of wafer holder  120 . However, other embodiments use other surface forms as well as shapes and sizes of holes and channels. The distribution and size of holes may also affect deposition thickness and thus might be used to assist thickness control. Holes  132 . 1  are coupled through gas-distribution channels  132 . 2  to gas inlet  136 .  
         [0020]     Surface-projection member  134  projects or extends from surface  132 . 3  toward support platform  124 , defining a fixture cavity  134 . 1 . The exemplary embodiment forms surface-projection member  134  from stainless steel as a uniform annular or circular wall or collar that projects perpendicularly from surface  132  to define a right-cylindrical cavity. However, other embodiments form member  134  to project at other angles relative surface  132 . 3 . For example, some form the projection at an acute or obtuse angle, such as 45 or 135 degrees, and others form the projection to peripherally define an oval, ellipse, triangle, square, or any desirable regular or irregular polygon. Thus, the present invention encompasses a wide variety of projection shapes and configurations, indeed any projection shape that facilitates definition of an effective cavity or gas-confinement volume in cooperation with wafer holder  120  and/or substrate  200 .  
         [0021]      FIG. 2 , a plan view, shows further details of the exemplary embodiment of gas-distribution fixture  130 . In particular, the plan view shows not only exemplary circular peripheries of gas-distribution member  132  and surface-projection member  134 , but also an exemplary distribution pattern for holes  132 . 1  and an exemplary orthogonal arrangement of gas-distribution channels  132 . 2 . Other embodiments, however, use other hole distribution patterns and channel arrangements. For example, some embodiments include random or concentric hole patterns and various channel geometries, including concentric circles, rectangles, or other regular or irregular concentric polygons. Some embodiments may also dedicate various subsets of channels and corresponding holes to different gases.  
         [0022]     Gas-distribution member  132  can be made in a number of ways. One exemplary method entails providing two wafers of materials, such as silicon or other passivatable, inert, or non-reactive material. One wafer is patterned and etched, for example, using conventional photolithographic or micro-electro-mechanical systems (MEMS) technology, to form a pattern holes, and the other wafer is patterned and etched to include a complementary or corresponding pattern of gas-distribution channels. (MEMS refers to the technologies of making structures and devices with micrometer dimensions.) Dry-etching techniques produce small openings and channels, while wet etching produces larger openings and channels. For further details, see, for example, M. Engelhardt, “Modern Application of Plasma Etching and Patterning in Silicon Process Technology,” Contrib. Plasma Physics, vol. 39, no. 5, pp. 473-478 (1999).  
         [0023]     The two wafers are then bonded together with the holes and channels in appropriate alignment using known wafer-bonding techniques. See, for example, G. Krauter et al., “Room Temperature Silicon Wafer Bonding with Ultra-Thin Polymer Films,” Advanced Materials, vol. 9, no. 5, pp. 417-420 (1997); C. E. Hunt et al., “Direct Bonding of Micromachined Silicon Wafers for Laser Diode Heat Exchanger Applications,” J. Micromech. Microeng, vol. 1, pp. 152-156 (1991); Zucker, O. et al., “Applications of oxygen plasma processing to silicon direct bonding,” Sensors and Actuators, A. Physical, vol. 36, no. 3, pp. 227-231 (1993), which are all incorporated herein by reference. See also, copending and co-assigned U.S. patent application Ser. No. 09/189,276 (dockets 303.534US1 and 97-1468) entitled “Low Temperature Silicon Wafer Bond Process with Bulk Material Bond Strength,” which was filed Nov. 10, 1998 and which is also incorporated herein by reference. The resulting bonded structure is then passivated using thermal oxidation for example.  
         [0024]     For an alternative fixture structure and manufacturing method that can be combined with those of the exemplary embodiment, see U.S. Pat. No. 5,595,606, entitled “Shower Head and Film Forming Apparatus Using Same, which is incorporated herein by reference. In particular, one embodiment based on this patent adds a projection or gas-confinement member to the reported showerhead structure.  
         [0025]      FIG. 1  also shows that gas inlet  136  couples gas-distribution fixture  130  to gas-supply system  140 . Gas-supply system  140  includes a gas line  142 , gas sources  144  and  145 , and mass-flow controllers  146  and  147 . Gas line or conduit  142 , which includes a flexible portion  142 . 1 , passes through an opening  116 . 1  in chamber sidewall  116  to connect with gas inlet  136 . Gas source  144  is coupled via mass-flow controller  146  to gas line  142 , and gas source  147  is coupled via mass-flow controller  147  to gas line  142 . The exemplary embodiment provides computer-controlled thermal or pressure-based mass-flow controllers; however, the invention is not limited to any particular number or type of mass-flow controller, nor to any particular number or set of gas sources.  
         [0026]     System  100  also includes vacuum pumps  150  and  160 . Vacuum pump  150  is coupled to gas-distribution fixture  130  via a mass-flow controller  152  and gas line  142 . And, vacuum pump  160  is coupled to the interior of chamber  110  via a line  162  and an opening  114 . 2  in chamber bottom plate  114 . In the exemplary embodiment, vacuum pump  160  has a greater capacity than vacuum pump  150 .  
         [0027]     In general operation, system  100  functions, via manual or automatic control, to move gas-distribution fixture  130  from operating position  138 . 1  to position  138 . 2 , to introduce reactant gases through fixture  130  onto substrate  200 , and to deposit desired matter through chemical-vapor deposition onto the substrate. After the desired matter is deposited, pump  150  evacuates gases through fixture  130 .  
         [0028]     More particularly,  FIG. 3  shows a flowchart  300  which illustrates an exemplary method of operating system  100 . Flowchart  300  includes process blocks  202 - 216 .  
         [0029]     The exemplary method begins at block  302  with insertion of substrate  300  onto wafer holder  120 . Execution then proceeds to block  304 .  
         [0030]     Block  304  establishes desired temperature and pressure conditions within chamber  110 . In the exemplary embodiment, this entails operating heating element  126  to heat substrate  200  to a desired temperature, and operating vacuum pump  160  to establish a desired pressure. Temperature and pressure are selected based on a number of factors, including composition of the substrate and reactant gases, as well as the desired reaction. After establishing these deposition conditions, execution continues at block  306 .  
         [0031]     In block  306 , the system forms or closes an inner chamber around substrate  200 , or more precisely a portion of substrate  200  targeted for deposition. In the exemplary embodiment, this entails using a lever or other actuation mechanism (not shown) to move gas-distribution fixture  130  from position  138 . 1  to position  138 . 2  or to move wafer holder  120  from position  138 . 2  to  138 . 1 . In either case, this movement places gas-distribution surface  132 . 3  one-to-five millimeters from an upper most surface of substrate  200 . In this exemplary position, a lower-most surface of surface-projection member  134  contacts the upper surface of support platform  124 , with the inner chamber bounded by gas-distribution surface  132 . 3 , surface-projection member  134 , and the upper surface of support platform  124 .  
         [0032]     Other embodiments define in the inner chamber in other ways. For example, some embodiments include a surface-projection member on support platform  124  of wafer holder  120  to define a cavity analogous in structure and/or function to cavity  134 . 1 . In these embodiments, the surface-projection member takes the form of a vertical or slanted or curved wall, that extends from support platform  124  and completely around substrate  200 , and the gas-distribution fixture omits a surface-projection member. However, some embodiments include one or more surface-projection members on the gas-distribution fixture and the on the support platform, with the projection members on the fixture mating, engaging, or otherwise cooperating with those on the support platform to define a substantially or effectively closed chamber. In other words, the inner chamber need not be completely closed, but only sufficiently closed to facilitate a desired deposition.  
         [0033]     After forming the inner chamber, the exemplary method continues at block  308 . Block  308  entails introducing one or more reactant or precursor gases into the separate chamber. To this end, the exemplary embodiment operates one or more mass-flow controllers, such as controllers  146  and  147 , to transfer gases in controlled quantities and temporal sequences from gas sources, such as sources  144  and  147 , through gas line  142  and fixture  130  into the separate chamber.  
         [0034]     Notably, the inner chamber is smaller in volume than chamber  100  and thus requires less gas and less fill time to achieve desired chemical concentrations (assuming all other factors equal.) More precisely, the exemplary embodiment provides an inner chamber with an empty volume in the range of 70 to 350 cubic centimeters, based on a 1-to-5 millimeter inner-chamber height and a fixture with a 30-centimeter diameter. Additionally, the number and arrangement of holes in the fixture as well as the placement of the holes close to the substrate, for example within five millimeters of the substrate, promote normal gas incidence and uniform distribution of gases over the targeted portion of substrate  200 .  
         [0035]     Block  310  entails allowing the gases to react with each other and/or the heated substrate to deposit a layer of material on targeted portions of the substrate. It is expected that the resulting layer will exhibit a highly uniform thickness across the entire substrate because of the more uniform gas distribution.  
         [0036]     Next, as block  312  shows, the exemplary method entails evacuating gaseous waste or by-products produced during the deposition. To this end, the exemplary embodiment, activates vacuum pump  160  to pump gaseous waste from the inner chamber through gas-distribution fixture  130 . In some embodiments, pumps  150  and  160  are operated concurrently to establish initial pressure conditions and to evacuate the inner and outer chambers after deposition.  
         [0037]     In block  314 , the system opens the separate chamber. In the exemplary embodiment, this entails automatically or manually moving gas-distribution fixture  130  to position  138 . 1 . Other embodiments, however, move the wafer holder or both the fixture and the wafer holder. Still other embodiments may use multipart collar or gas-confinement members which are moved laterally relative the wafer holder or gas-distribution fixture to open and close an inner chamber.  
         [0038]     In block  316 , substrate  200  is unloaded from chamber  110 . Some embodiments remove the substrate manually, and others remove it using an automated wafer transport system.  
         [0039]      FIG. 4  shows a conceptual representation of another exemplary chemical-vapor-deposition system  400  incorporating teachings of the present invention. System  400  includes a rectangular outer chamber  410  which encloses four deposition stations  420 ,  422 ,  424 , and  426 , loaded with respective substrates  200 ,  202 ,  204 , and  206 . Although the figure omits numerous components for clarity, each deposition station is structurally and operationally analogous to system  100  in  FIG. 1 . In the exemplary embodiment, two or more of the stations are operated in parallel. Additionally, other embodiments of this multi-station system arrange the stations in a cross formation, with each station confronting a respective lateral face of the chamber. Still other embodiments use different outer chamber geometries, for example cylindrical or spherical.  
       CONCLUSION  
       [0040]     In furtherance of the art, the inventor has presented new systems, methods, and apparatuses for chemical-vapor deposition. One exemplary system includes an outer chamber, a substrate holder, and a unique gas-distribution fixture. The fixture includes a gas-distribution surface having holes for dispensing a gas and a gas-confinement member that engages, or otherwise cooperates with the substrate holder to form an inner chamber within the outer chamber.  
         [0041]     Notably, the inner chamber not only consumes less gas during deposition to reduce deposition waste and cost, but also facilitates rapid filling and evacuation to reduce deposition cycle times (with all other factors being equal.) The inner chamber also places the gas-distribution fixture within several millimeters of a substrate on the substrate holder, promoting normal gas incidence across the chamber and thus uniform deposition thickness.  
         [0042]     The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the invention, is defined only by the following claims and their equivalents.