Abstract:
A method and apparatus for improved metal oxide chemical vapor deposition on a substrate surface where the application boundary layer is reduced and where the uniformity of the application boundary layer is greatly enhanced in a reactor. Primary and secondary sonic or other disturbance sources are introduced to the interior chamber or an oscillating chuck is incorporated to influence the boundary layer thickness and uniformity.

Description:
CROSS REFERENCES TO CO-PENDING APPLICATIONS 
     This application is a division, of application Ser. No. 09/272,036, filed Mar. 18, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is for a chemical vapor deposition (CVD), and more particularly, pertains to a method and apparatus for metal oxide chemical vapor deposition (MOCVD) upon a substrate surface. 
     2. Description of the Prior Art 
     Several difficulties in prior art metal oxide chemical vapor deposition have been found to be prevalent in the deposition of metal oxide chemical vapors upon a substrate, such as utilized for micro-chip manufacturing or other purposes. Difficulties encountered during deposition are created in the most by (a) undesirable topology on the substrate surface, (b) non-uniform heating of the substrate, and (c) by a non-uniform gas boundary layer along and about the substrate. 
     The first problem in MOCVD is related to undesirable and inherent substrate topology where at low pressures, such as 1 Torr, MOCVD best takes place, the different vapor components necessary to thermally decompose on a wafer surface in perfect stoichiometry for a particularly useful compound must arrive at the wafer surface at the correct ratio. If the wafer substrate surface were always flat, this ratio could be achieved by simply altering the relative mixture of the vapors, i.e., 10/90 percent to 11/89 percent. However, in most useful cases in integrated circuit construction, inherent uneven topology is usually present, i.e., 0.50 micron high plateaus with 0.25 micron spaces. In this case, each vapor component must arrive not only at the top of the topology features at the correct ratio, but must also arrive at the bottom of the topology features at the same ratio. If the deposition ratio is not maintained, then the composition of the complex metal oxide will be non-uniform and will not be useful. Since a gas boundary layer is usually present for a chemical vapor deposition (CVD) reactor with flowing gases of about 0.80 cm at 760 Torr, for example, for an 8 inch wafer bl=2/3L(v/UL){circumflex over ( )} 0.50, each vapor component must replenish the boundary layer. Furthermore, different depths within the boundary layer must get the same ratio of vapors in order to allow uniform compositions to form from thermal decomposition. Generally, different metal containing Metalorganic vapors diffuse at different speeds, as to most gases in general. The basic problem with the current art and prior art is that on uneven topography, uniform compound electrical and crystalline control is difficult, at best. Since the use of the dozens of new complex metal oxides will become prevalent, it is important to develop production methods to deposit the compounds that have been studied in planar applications. 
     The solution to the uneven topology problem, such as presented by the present invention, is to artificially reduce the boundary layer to significantly smaller and uniform thickness, such as in microns. The boundary layer thickness can be significantly reduced and the boundary layer uniformity can be enhanced and stabilized by any one method or combinations of methods including the use of an externally generated periodically disturbed gas motion in the form of a pressure wave, or by moving or oscillating the wafer itself, or by changing the pressure of the injected gas, any or all in the range of Hz through kilo Hz. With reference to reducing boundary layer thickness, Appendix A is attached. Eg. bl=(v/pi.fr.d) where v=viscosity, pi is 3.14, etc., fr=frequency, and d=density of the gas. Appendix A is a spreadsheet relating to various fluids and gases over an 8 inch wafer with no disturbance, and with either 40,000 Hz for water and 10 Hz for the N2 and Argon, where the change in boundary layer (bl) is orders of magnitude. 
     If the boundary layer is made small, then the compound variation due to differential diffusion lengths will also be small, thereby offering a solution for the problem of two and three chemical component MOCVD. An additional benefit is the speeding up of the deposition rate since most MOCVD reactions are limited by the delivery to the surface through a thick boundary layer. 
     The second and third prior art problems in MOCVD are the creation of uniform heating and a uniform gas boundary layer of any thickness. Improved uniformity of the gas layer boundary is accomplished in the present invention in part or wholly as previously described. Usually, a prior art rotating wafer in a downflow creates a uniform boundary layer, independent of scale. The speed of rotation controls, to a certain extent, the thickness. Physical rotation is limited by a vacuum rotating seal and particle problems in prior art devices. Rotation is also helpful or necessary in creating uniform lamp heating and is the subject of several existing patents, such as in Applied Materials, etc. If a prior art stationary platen is used to heat the wafer uniformly, then the gas boundary layer will be non-uniform from the center to the edge with the center being thicker and the edge being a thinner boundary layer or the gradient will either increase or decrease from left to right accordingly. The preferred embodiment of the present invention provides for crossflow longitudinally and laterally along the substrate structure. If prior art rotation is used to make the boundary layer uniform, then a rotating vacuum seal is necessary, and lamp heating is necessary which is inherently non-uniform due to re-radiation differences at the edges of the wafer where radiation emits from all sides instead of just one side. Usually prior art multiple heat zones and multiple pyrometer feedback zones are used to compensate for non-uniformities. As well as gas delivery uniformity, temperature drives the reaction, so temperature uniformity is critical. The present invention eliminates the need for pyrometry since it is non-rotating and allows the use of contacting thermocouples imbedded in the heated stage. Multiple heat zones are eliminated since a large mass-conducting heated static chuck is used. 
     In the present invention, the new boundary layer created by the periodical disturbance gas motion stabilizes the boundary layer thickness and reduces the usual thick boundary layer to a mere fraction, and gas delivery and temperature uniformity are achieved utilizing simple reactor construction. The vapors or gases are sent into the reactor with associated pressure waves, transmitted pressure waves from a transducer, a vibrating or oscillating wafer chuck, or other suitable device. 
     SUMMARY OF THE INVENTION 
     The invention discloses and provides a method and apparatus for metal oxide chemical vapor deposition on a substrate surface providing a crossflow and a downflow reactor. The preferred embodiment of the present invention includes a crossflow reactor having a centrally located oscillatible static chuck for grasping a substrate. A gas inlet in the one end of the crossflow reactor is plumbed to a primary disturbance source which generates periodic disturbances in wave form. Generated periodic disturbances are transferred through a sealed chamber and bellows arrangement to influence boundary layer delivery of metal oxide chemical vapor to the substrate surface. The boundary layer is minimized by the periodic disturbances to provide for greatly reduced and desirable boundary layer thickness. The boundary layer uniformity is also enhanced by the generated periodic disturbance. Additional disturbance can also be provided by oscillating the static chuck to reduce boundary layer thickness and to favorably influence the boundary layer uniformity. The chuck also provides a uniformly heated surface which enhances the thermal boundary layer uniformity. An alternate disturbance source is also provided to generate periodic disturbances to the interior of the crossflow reactor by use of a transducer. 
     The preferred embodiment of this invention is the crossflow reactor since (1) the crossflow reactor limits the volume of gas required, and (2) the crossflow reactor provides an even heating from wafer to opposite surface to produce uniform thermal gradients. 
     One significant aspect and feature of the present invention is the reduction of boundary layer thickness to provide for improved deposition on and about the uneven topology surfaces of a substrate. 
     Another significant aspect and feature of the present invention is improved uniformity of the boundary layer to provide for improved deposition on and about the uneven topology surfaces of a substrate. 
     A further significant aspect and feature of the present invention is the use of primary and alternate disturbance sources either singularly or in unison to reduce boundary layer thickness and to provide for uniformity of the boundary layer. 
     An additional significant aspect and feature of the present invention is the use of an oscillatible chuck to reduce boundary layer thickness and to provide for uniformity of the boundary layer. 
     Still another significant aspect and feature of the present invention is the use of an evenly heated chuck. 
     Yet another significant aspect and feature of the present invention is the use of a downflow reactor. 
     Still another significant aspect and feature of the present invention is the use of a crossflow reactor. 
     Having thus described embodiments and significant aspects and features of the present invention, it is the principal object of the present invention to provide a method and apparatus for metal oxide chemical vapor deposition on a substrate surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein: 
     FIG. 1 illustrates the method and a downflow reactor apparatus for metal oxide chemical vapor deposition on a substrate surface; and, 
     FIG. 2, the preferred embodiment, illustrates the method and a crossflow reactor apparatus for metal oxide chemical vapor deposition on one or more substrate surfaces. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates the method and apparatus for Metal Oxide Chemical Vapor Deposition on a substrate surface. A downflow reactor  10  apparatus is incorporated and utilized for Metal Oxide Chemical Vapor Deposition (MOCVD) upon the upper surface of a substrate  12  positioned central to the downflow reactor  10 . The downflow reactor  10  is a cold wall vacuum reactor having a surrounding vessel wall  14  about and to which related structure and devices are attached or extend therefrom. A gas inlet  16  for receiving a gas from the Mass Flow Controller (MFC) is located at the upper region of the downflow reactor  10 . Opposing the gas inlet  16  and located at the lower region of the downflow reactor  10  is a gas outlet  18  to which a metering valve  20  for control of the transitting gases through the vessel  14  is attached. A static chuck  22 , which is utilized to secure the substrate  12 , is centrally located within the surrounding vessel wall  14 . The static chuck  22  of large and sufficient mass is resistively heated and can be vibrated or oscillated at a low frequency either vertically or horizontally, or in the alternative can be vibrated or oscillated at a low frequency simultaneously both vertically and horizontally to assist in control of reduced boundary layer thickness and to contribute to boundary layer uniformity control. The relatively large mass of the static chuck  22  is conducive to appropriate uniform and even temperature distribution across the static chuck  22  to enhance boundary layer control. A plurality of thermocouples  24   a - 24   n  and a suitable resistance heater  25  are embedded in the static chuck  22  for monitoring and control of the static chuck  22  temperature. A chamber  26  is located at and attached to the gas inlet  16  at the upper region of the downflow reactor  10 . An isolation bellows  28  is located in the chamber  26 . An inlet  30  is attached to the chamber  26  to receive a disturbance input from a primary disturbance source  32 . The primary disturbance source  32  introduces periodic disturbances to the downflow reactor  10  through the inlet  30 , the chamber  26 , the isolation bellows  28  and the gas inlet  16 . The periodic disturbances  29  emanating from the primary disturbance source  32  can be provided by, but not limited to, devices such as a pneumatic oscillator which provide a sinusoidal disturbance. One or more transducers  33  and alternate disturbance sources  34  are attached to the vessel wall  14  to provide additional periodic disturbance either acting as an additional single unit for imparting a disturbance to the downflow reactor  10  or acting in concert with the primary disturbance source  32  to impart multiple or reinforced disturbances to the downflow reactor  10 . Both the primary and the alternate disturbance sources  32  and  34  respectively can include but are not limited to a pneumatic oscillator, a speaker, a piezo or other electromagnetic device, a bellows with a pneumatic source, a pneumatic oscillator or other device which generates an appropriate disturbance. 
     FIG. 2, the preferred embodiment, illustrates the method and apparatus for Metal Oxide Chemical Vapor Deposition on a substrate surface. A horizontally aligned crossflow reactor  40  apparatus is incorporated and utilized for Metal Oxide Chemical Vapor Deposition (MOCVD) upon the upper surface of a substrate  42  positioned central to the crossflow reactor  40 . The crossflow reactor  40  is a cold wall vacuum reactor having a surrounding vessel wall  60  about and to which related structure and devices are attached or extend therefrom. A gas inlet  46  for receiving a gas from the Mass Flow Controller (MFC) is located at one end of the crossflow reactor  40 . Opposing the gas inlet  46  and located at the opposing end of the crossflow reactor  40  is a gas outlet  48  to which a metering valve  50  for control of the transitting gases through the vessel  44  is attached. A static chuck  52 , which is utilized to secure the substrate  42 , s centrally located and extends through the surrounding vessel wall  44 . At least one or more wafers are flush to the surface of the crossflow reactor  40  to reduce gas flow while having good laminar flow. The static chuck  52  of large and sufficient mass is resistively heated and can be vibrated or oscillated vertically or horizontally, or in the alternative can be vibrated or oscillated simultaneously both vertically and horizontally to assist in control of reduced boundary layer thickness and to contribute to boundary layer uniformity control. The relatively large mass of the static chuck  52  is conducive to appropriate uniform and even temperature distribution and to having an even reaction across the static chuck  52  to enhance boundary layer control. One or more thermocouples  54   a - 54   n  and a resistance heater  55  are embedded in the static chuck  52  for monitoring and control of the static chuck  52  temperature. One or more transducers  56  and primary disturbance sources  58 , preferably in a location opposite to the gas inlet  46 , are attached to the end or other suitable site on the vessel wall  44  to provide periodic disturbance acting to impart a disturbance to the crossflow reactor  40 . The periodic disturbances  60  emanating from the primary disturbance source  58  can be provided by, but not limited to, devices such as a pneumatic oscillator which provide a sinusoidal disturbance. With respect to an alternate disturbance source  62 , a chamber  64  is located at and attached to the gas inlet  46  at the end of the crossflow reactor  40 . An isolation bellows  66  is located in the chamber  64 . An inlet  68  is attached to the chamber  64  to receive a disturbance input from the alternate disturbance source  62 . The alternate disturbance source  62  introduces periodic disturbances to the crossflow reactor  40  through the inlet  68 , the chamber  64 , the isolation bellows  66  and the gas inlet  46 . Both the primary and the alternate disturbance sources  58  and  62 , respectively, and the additional transducer  70  can include but are not limited to a pneumatic oscillator, a speaker, a piezo or other electromagnetic device, a bellows with a pneumatic source, a pneumatic oscillator or other device which generates an appropriate disturbance. 
     In use, the primary disturbance source  58  and transducer  56  can be used as a stand device for introduction of periodic disturbance, but in the alternative can incorporate the additional and simultaneous use of the transducer  70  located on the vessel wall  44 . In a similar fashion, the alternate disturbance source  62 , including the delivery components, can be used as a stand-alone device for introduction of periodic disturbances, but in the alternative can incorporate the additional and simultaneous use of the transducer  70  located on the vessel wall  44 . Other combinations incorporating the use of one or more disturbance sources, transducers and the like are also included in the scope of the invention. 
     Any suitable reactor can be utilized such as crossflow or downflow or even an atmospheric pressure reactor that uses gas and boundary layer technology. Any reactor that depends on a uniform and thin boundary layer can include CVD, MOCVD, MBE, LPE and VPE. 
     Various modifications can be made to the present invention without departing from the apparent scope hereof. 
     Method and Apparatus for Metal Oxide Chemical Vapor Deposition on a Substrate Surface 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 PARTS LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 downflow reactor 
               
               
                 12 
                 substrate 
               
               
                 14 
                 vessel wall 
               
               
                 16 
                 gas inlet 
               
               
                 18 
                 gas outlet 
               
               
                 20 
                 metering value 
               
               
                 22 
                 static chuck 
               
               
                 24a-n 
                 thermocouples 
               
               
                 25 
                 resistance heater 
               
               
                 26 
                 chamber 
               
               
                 28 
                 isolation bellows 
               
               
                 29 
                 periodic disturbances 
               
               
                 30 
                 inlet 
               
               
                 32 
                 primary disturbance source 
               
               
                 33 
                 transducer 
               
               
                 34 
                 alternate disturbance source 
               
               
                 40 
                 crossflow reactor 
               
               
                 42 
                 substrate 
               
               
                 44 
                 vessel wall 
               
               
                 46 
                 gas inlet 
               
               
                 48 
                 gas outlet 
               
               
                 50 
                 metering valve 
               
               
                 52 
                 static chuck 
               
               
                 54a-n 
                 thermocouples 
               
               
                 55 
                 resistance heater 
               
               
                 56 
                 transducer 
               
               
                 58 
                 primary disturbance 
               
               
                 60 
                 periodic disturbances 
               
               
                 62 
                 alternate disturbance source 
               
               
                 64 
                 chamber 
               
               
                 66 
                 isolation bellows 
               
               
                 68 
                 inlet 
               
               
                 70 
                 transducer