Abstract:
An improved apparatus ( 20 ) and method are provided for effective, high speed contact planarization of coated curable substrates such as microelectronic devices to achieve very high degrees of planarization. The apparatus ( 20 ) includes a planarizing unit ( 28 ) preferably having an optical flat flexible sheet ( 88 ) and a backup optical flat body ( 82 ), and a curing assembly ( 30 ). In operation, a substrate ( 78 ) having a planarizable coating ( 76 ) is placed within a vacuum chamber ( 26 ) beneath sheet ( 88 ) and body ( 82 ). A pressure differential is created across sheet ( 88 ) so as to deflect the sheet into contact with a central region C of the coating ( 76 ), whereupon the coating ( 76 ) is brought into full planarizing contact with sheet ( 88 ) and body ( 82 ) by means of a support ( 114 ) and vacuum chuck ( 120 ); at this point the coating ( 76 ) is cured using assembly ( 30 ). After curing, a pressure differential is established across sheet ( 88 ) for sequentially separating the sheet from the peripheral portion P of the coating, and then full separation of the sheet ( 88 ) and coating ( 76 ).

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of nonprovisional application Ser. No. 10/887,530, filed Jul. 8, 2004, which claims the benefit of provisional application Ser. No. 60/486,021 filed Jul. 10, 2003. These applications are incorporated by reference herein. 
     
    
       [0002]     This invention was made with the U.S. Government support under ATP #70NANB1H3019 awarded by the National Institute of Standards and Technology (NIST). The Government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     1. Field of the Invention  
         [0004]     The present invention is broadly concerned with the improved methods and apparatus for the contact planarization of surfaces such as those developed during the manufacture of advanced integrated circuit and other devices. More particularly, the invention is concerned with such methods and apparatus wherein a coated substrate is placed adjacent an optical flat flexible sheet, and the latter is first deflected to contact a central region of the coating, followed by full, pressurized planarizing contact between the sheet and coating; during such pressurized planarizing contact, the coating is cured. Post-curing separation of the sheet and coating preferably involves generating a pressure differential between the sheet and coating which creates a smooth edge-to-center separation.  
         [0005]     2. Description of the Prior Art  
         [0006]     Advanced integrated circuit (IC) designs are highly dependent on increasingly complex device-layering techniques to produce semiconductor devices that are more powerful, have lower profiles, and require less energy to operate. To make these qualities possible, more circuits with much finer structures must be integrated into a microchip by constructing multiple layers of interconnects and dielectrics on a semiconductor substrate in an appropriate sequence. To construct an IC, many layers containing ultra-fine structures must be patterned onto a semiconductor surface. Currently, photolithography is the predominant technique used to pattern these ultra-fine structures. This technique requires materials to be deposited and removed from the surface to construct such ultra-fine structures.  
         [0007]     Photolithography involves depositing a photosensitive material, known as a photoresist, onto a semiconductor substrate surface. An optical transparent object, known as the photomask or reticle, with pre-defined images of the structures to be built on the semiconductor surface is placed above the photoresist-coated substrate. An appropriate wavelength of light is illuminated through the optical object. The light either decomposes or cures the exposed area of the photoresist, depending on the nature of the photoresist and the process. The semiconductor surface is then developed to produce the patterned image on the substrate surface, and the device is ready for subsequent processing.  
         [0008]     Materials can be applied in a uniform thickness if the surface to be coated is entirely planar. However, if the surface is not planar, that is, it has topographic features, materials may not coat with a uniform thickness, which may greatly affect the final yield or performance of the device. A coating deposited on top of a topographic surface tends to contour the topography of the underlying surface, thus producing a non-planar surface.  
         [0009]     Fabricating one layer on top of another produces the multi-layer structure of an IC. The first layer of the structure is built on a totally planar semiconductor surface. As a result, a topographic surface is introduced onto the semiconductor substrate surface. The second layer is built on top of the topographic surface of the first structural layer. As more layers are built on the substrate, the severity of the surface topography increases. The non-planar surface is no longer suitable for constructing the next structural layer. Therefore, the topographic surface needs to be planarized, or flattened, prior to the construction of the next layer. To planarize the topographic surface, techniques such as plasma etch-back, chemical mechanical polishing (CMP), and contact planarization can be used.  
         [0010]     The plasma etch-back technique involves the deposition of a thick film to smooth the underlying topographic surface to some extent. As the thickness of the film increases, surface planarity is improved. However, a longer plasma etch time is needed to etch the thicker films.  
         [0011]     The deposited film is required to have a matched plasma etch rate to that of the underlying topographic layer material under specific etch parameters. Subsequently, the thick film is etched in a plasma etcher to the underneath topographic layer to improve the surface planarity. This planarization technique has been used and known to those skilled in the art.  
         [0012]     The CMP technique uses a slurry solution to mechanically polish the surface against a pad with the assistance of chemical reactions that occur between the substrate material and the slurry solution. A slurry solution containing abrasive particles and certain chemicals is dispensed on the pad surface. The topographic substrate surface is pressed against the pad. The substrate is then polished with a circular motion against the pad to remove the topography of the surface. CMP is currently used in IC fabrication. The specific requirements and processing conditions for certain materials that need to be planarized are known to those skilled in the art.  
         [0013]     Contact planarization, in theory, provides an alternative to plasma etch-back and CMP techniques to planarize topographic surfaces. the topographic surface is first deposited with a flowable planarization material. Subsequently, the surface is pressed against an optical flat surface, which allows the material to flow around the topographic structures under certain conditions. The material is then hardened by either photo-irradiation or heat to replicate the planarity of the optical flat surface onto the planarized material surface. The planarized material surface is then released from the optical flat object surface. To facilitate the separation, the optical flat object surface can be treated with a known art to lower its surface energy. This can be achieved by depositing a thin film or low surface energy material, such as a fluoropolymer or a fluorinated compound, onto the optical flat object surface. Another approach is to put a low surface energy material with comparable surface planarity, such as a disk or film, between the planarization material and optical flat object surface. Examples of low surface energy materials are Teflon® materials, fluorocarbon polymers, or the like. The planarized material surface then undergoes plasma etch to the underlying topographic layer. The planarity of the optical flat surface is transferred to the underlying topographic layer. The topographic surface is then planarized. One requirement of the planarized material is that it needs to possess a plasma etch ratio of 1 in relation to that of the underlying topographic layer material. The plasma etch parameters required to reach a 1:1 etch rate ratio are known to those skilled in the art.  
         [0014]     U.S. Pat. No. 6,048,799 to Prybyla et al. described the use of an optical flat surface in contact with a material that can be solidified by heat or ultraviolet (UV) irradiation to planarize topographical surfaces. The Prybyla patent does not provide the details associated with reducing the technology to practice. Specifically the separation of the coated wafer from the optical flat surface and the optimal range of process parameters required to perform fully automated contact planarization are not discussed.  
         [0015]     Blalock et al. (U.S. Pat. No. 6,062,133) describes method and apparatus for achieving a global planarization of a surface of a deformable layer of a wafer using a curable planarization material. A deformable material is deposited onto a substrate surface. This substrate is then placed in to the apparatus with the deformable material-coated surface facing toward and pressing against an optical flat object surface under certain press force and time. The deformable material is then cured while still in contact with the optical flat object surface. The planarity of the optical flat object surface is replicated to the coated substrate surface. Like the Prybyla et al. patent, this process and apparatus does not cover the separation of the coated wafer from the optical flat surface and the optimal range of process parameters required to perform fully automated contact planarization.  
         [0016]     In U.S. Pat. No. 6,331,488 B1, Doan et al. describes a planarization process for semiconductor substrates. This process uses an optical flat surface to press against a nonplanar insulating material-coated substrate surface onto which a deformable material is coated. The deformable material is cured while still in contact with the optical flat surface. The planarity of the optical flat surface is replicated to the planarized deformable material surface. The planarized surface then undergoes the CMP process to transfer the planarity of the planarized surface to the underlying insulating layer. This patent also fails to include the process for separating the coated wafer from the optical flat surface and the optimal range of process parameters to perform contact planarization fully automated.  
       SUMMARY OF THE INVENTION  
       [0017]     The present invention overcomes the problems outlined above and provides improved contact planarizing apparatus and corresponding methods, which are capable of quickly and efficiently planarizing various coated substrates, while achieving very high planarization ratios. Broadly speaking, the apparatus of the invention includes a support operable to engage and hold a thin flexible sheet of material (which is preferably an optically flat material fabricated from Teflon, other fluorocarbon polymers, or silicones) with an assembly operable to support and hold a substrate with the coating thereof proximal to the sheet. A differential pressure assembly is also provided to create a pressure differential across the sheet of sufficient magnitude to deflect the sheet so that the latter contacts the central region of the surface of the coating, but is spaced from the periphery thereof. The support assembly is also shiftable for moving the substrate into face-to-face planarizing contact with the sheet throughout substantially the entirety of the surface area of the coating. Finally, the apparatus includes a device for curing the coating during the course of such full planarizing contact.  
         [0018]     In its method aspects, the invention includes the steps of first locating a thin, flexible sheet of material in proximal spaced relationship to the surface of a planarizable coating on a substrate, and then causing the sheet to deflect so that the sheet contacts a central region of the coating surface but is spaced from the periphery thereof. Next, relative movement is effected between the substrate and sheet until the latter is in full face-to-face planarizing contact with the entirety of the surface area of the coating. In this condition, the coating is cured, usually by using UV radiation or heat. Preferably, during separation of the cured coating and the flexible sheet, a pressure differential is created across the latter to first separate the sheet from the periphery of the cured coating, followed by full separation thereof.  
         [0019]     In one embodiment, a solid planarizing body is provided having a planarizing surface which mates with the flexible sheet. Alternately, appropriate levels of air pressure and vacuum are used for manipulation of the flexible planarizing sheet without the need for a solid backup planarizing body. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a perspective view of a preferred planarizing apparatus in accordance with the invention, illustrated with a robotic arm of the apparatus supporting a resilient platen used in the preferred planarizing method, prior to insertion of the platen into the primary vacuumization chamber of the apparatus;  
         [0021]      FIG. 2  is a view similar to that of  FIG. 1 , but illustrating the apparatus during use thereof with the resilient platen inserted into the primary vacuumization chamber, the latter being closed;  
         [0022]      FIG. 3  is an exploded perspective view illustrating the operative components of the preferred planarizing apparatus;  
         [0023]      FIG. 4  is a fragmentary vertical sectional view of the planarizing apparatus, with a coated substrate therein and prior to initiation of the planarizing process;  
         [0024]      FIG. 5  is a vertical sectional view taken along line  5 - 5  of  FIG. 4  and further illustrating the configuration of the planarizing apparatus;  
         [0025]      FIG. 6  is a fragmentary vertical sectional view similar to that of  FIG. 4 , but depicting the apparatus during planarizing contact between the coated substrate and an optical flat body and sheet;  
         [0026]      FIG. 7  is a view similar to that of  FIG. 6 , but depicting the apparatus after planarization of the coated substrate;  
         [0027]      FIG. 8  is a view similar to that of  FIG. 7 , but showing the apparatus during the separation sequence between the planarized substrate coating and optical flat body and sheet;  
         [0028]      FIG. 9  is a view similar to that of  FIG. 8 , but showing the apparatus upon full separation between the planarized substrate coating and the optical flat body and sheet;  
         [0029]      FIG. 10  is a schematic illustration depicting the initial step in the planarizing process wherein the preferred optical flat sheet is deflected;  
         [0030]      FIG. 11  is another schematic illustration showing the next step in the planarizing process wherein full planarizing contact is established between the coated substrate and the optical flat body and sheet;  
         [0031]      FIG. 12  is a schematic illustration showing the initial stage of the separation sequence between the planarized substrate coating and the optical flat body and sheet;  
         [0032]      FIG. 13  is a view similar to that of  FIG. 12 , but showing the next step in the separation sequence;  
         [0033]      FIG. 14  is a schematic view similar to that of  FIG. 13  and showing the final step in the separation sequence;  
         [0034]      FIG. 15  is a schematic view similar to that of  FIG. 10 , but illustrating a method and apparatus wherein the optical flat body is eliminated, during the initial deflection of the optical flat sheet;  
         [0035]      FIG. 16  is a view similar to that if  FIG. 15 , but depicting the method and apparatus during full planarizing contact between the substrate coating and optical flat sheet;  
         [0036]      FIG. 17  is a schematic view similar to that of  FIG. 16 , but showing the initial step in the separation sequence between the planarized substrate coating and the optical flat sheet; and  
         [0037]      FIG. 18  is a schematic view similar to that of  FIG. 17 , illustrating the final step in the separation sequence. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     Embodiment of FIGS.  1 - 14   
       [0038]     Turning now to the drawings,  FIG. 1  illustrates a preferred planarization apparatus  20  in accordance with the invention. The apparatus  20  broadly includes a support flame  22 , and a planarizing assembly  24  atop the latter. The planarizing assembly  24  includes a lower vacuum chamber  26  together with an upper planarizing unit  28  and a UV light curing assembly  30 . The overall apparatus  20  is designed to efficiently contact planarize coatings applied to individual substrates, such as microelectronic, optoelectronics, photonic, optical, flat panel display, microelectromechanical systems (MEMS), biochips and sensor devices.  
         [0039]     In more detail, the support frame  22  includes a base  32  with four upstanding, rigid support legs  34  secured thereto. A base plate  36  is affixed to the upper ends of the legs  34 , and has a pair of opposed tubular guides  38  and a further pair of laterally spaced apart, forward tubular guides  40 . A conventional robotic arm assembly  42  is also secured to base plate  36  via coupler  44 . The assembly  42  has a pivotally mounted arm  46  terminating in a pair of opposed, arcuate support segments  48 . The base plate  36  also supports superposed piston and cylinder assemblies  50 ,  134 . Finally, a dual piston and cylinder assembly  52  is secured to the underside of base plate  36  with the piston rods  54  thereof extending upwardly through the forward guides  40  for purposes which will be explained.  
         [0040]     The vacuum chamber  26  includes an annular, upstanding outer chamber wall  56  presenting a lower surface  58  resting atop plate  36  and secured thereto by peripheral clamps  37 ; a circular O-ring  60  (see  FIG. 5 ) serves to effect a vacuum seal between the wall  56  and base plate  36 . The wall  56  is equipped with an elongated, transverse entryway  62  adjacent the upper margin thereof, leading to the interior of the chamber  26 . The upper margin of the wall  56  is of stepped configuration in section, and is equipped with a sealing O-ring  64 . The chamber  26  also has a door  66  designed to selectively cover entryway in order to permit establishment of a vacuum condition within the chamber, and allow for insertion and removal of substrates. In particular, the door  66  includes a pneumatic actuator  68 , coupler  70  and arcuate segment  72  which conforms to the shape of sidewall  56 . A peripheral gasket  74  (see  FIG. 5 ) is provided on the inner face of segment  72  for sealing purposes. As best seen in  FIGS. 1, 2  and  5 , the door  66  is supported for selective vertical shifting movement by the piston rods  54 , so that upon actuation of the assembly  57 , the door  66  is moved from the  FIG. 1  position to the  FIG. 2  position, thereby sealing entryway  62 . Door  66  moves vertically upon actuation of assembly  52 , then horizontally upon actuation of assembly  68 . Alternately, when the assembly  52  is actuated to lower the door  66 , the entryway  62  is open (see  FIG. 1 ).  
         [0041]     The planarizing unit  28  includes the components operable for contact planarizing a coating  76  on one surface of a substrate  78  (see  FIG. 10 ). The unit  28  operates in conjunction with the vacuum chamber  26  to effect this planarization. Broadly speaking, the planarizing unit  28  includes an optical flat assembly  80  made up of a UV-transparent optical flat block or body  82  presenting a lower optically flat surface  84 , as well as a thin, flexible sheet  86  of optically flat material, the latter being supported by a sheet support  88 ; and a support assembly  90  beneath the assembly  88  and operable to support and hold the substrate  78  with coating  76  proximal to sheet  86 .  
         [0042]     In greater detail, the body  82  is of circular configuration, having an upper, radially enlarged section  92  and a depending section  94  terminating in optical flat surface  84 . The body  82  is supported within a complemental annular head  96  which also has a threaded port  98  and a sealing ring  99 . A retainer ring  100  having a pair of outwardly projecting, opposed ears  102  is positioned atop body  82  and is connected to head  96  via screws  104 , thereby securing the body  82  in place. The sheet support  88  includes a pair of opposed upper and lower clamping rings  106 ,  108  which receive and support the sheet  86 . In detail (see  FIG. 5 ), the upper ring  106  includes an annular, depending rib  110  whereas the second or lower ring  108  has a mating groove  112  which receives rib  110 . The sheet support  88  and sheet  86  are positioned within the stepped upper margin of wall  56 , with the lower ring  108  in engagement with sealing O-ring  64 .  
         [0043]     Considering  FIG. 5  for example, it will be appreciated that the chamber  26  communicates with one face of the sheet  88  whereas wall  56  defines the chamber  26  which is adjacent to and communicates with the lower face of sheet  88 . However, another chamber  113  is created between the inner surface of head  96  and body  82  below O-ring  99 . The port  98  is in communication with this chamber  113  as shown.  
         [0044]     The support assembly  90  within chamber  26  includes an arcuate, generally C-shaped ring-like body  114  which is sized to support the substrate  76 . The body  114  is selectively moveable through the medium of two pneumatic piston and cylinder assemblies  116  each having the rod  118  thereof coupled to the underside of body  114 . As illustrated in  FIG. 5 , each assembly  116  is secured to the upper face of base plate  36 .  
         [0045]     In addition, the assembly  90  includes a circular vacuum chuck  120  which includes an upper, ringed vacuum surface  122  and a central, hollow vacuumizing screw  124  communicating with surface  122 . The chuck  120  is supported on a bored block  126  which receives the lower end of screw  124 . Block  126  includes an L-shaped vacuum passageway  128  terminating in a fitting  130 . A flexible pneumatic hose  132  is secured to fitting  130  and passes through base plate  36  as shown for connection to a vacuum source (not shown). The block  126  and chuck  120  are vertically moveable within chamber  26  by means of piston and cylinder assembly  134 , operably secured to the lower end of block  126  through coupler  127 . Reciprocation of the block  126  and chuck  120  is guided by a pair of spaced, upright rods  136  secured to base plate  36 . As best shown in  FIG. 4 , the block  126  has laterally extending sections  138  each equipped with a slide bushing  140  to ensure smooth up and down reciprocation of the block  126 .  
         [0046]     In the preferred practice of the invention, use is made of a resilient platen  142  which is of circular configuration and is adapted to overlie surface  122  of chuck  120 . The platen  142  includes a lowermost bottom plate  144  having a depending peripheral lip  146 , together with an upper resilient pad  148 . As best seen in  FIG. 5 , the platen  142  is sized to complementally fit on the surface  122  of chuck  120 .  
         [0047]     A threaded port  150  is provided through base plate  36 . A vacuum pump (not shown) is operably coupled with the port  150  and with hose  132  for purposes to be described. In addition, another pneumatic hose (not shown) is secured to port  98  provided in head  96  for alternate drawing of a vacuum and injection of positive pressure air.  
         [0048]     In order to permit opening of apparatus  20 , upper planarizing unit  28 , UV light carrying assembly  30 , and the stricture carried thereby, are selectively vertically shiftable; this permits changeout of the sheet support  88 . To this end, a pair of elongated, vertically oriented rods  152  are provided which are coupled to the ears  102  of retainer  100  via fasteners  154 ; the rods  152  extend downwardly through the corresponding guides  38  to a point beneath piston and cylinder assembly  50 . A crossbar  156  extends between and interconnects the rods  152  at their lower ends. A piston rod  158  forming a part of assembly  50  is secured to crossbar  156 . The assembly  50  may be selectively actuated for raising and lowering of the retainer  100 . The open and closed positions of the apparatus  20  are shown in  FIGS. 1 and 2 , respectively.  
         [0049]     The light curing assembly  30  is positioned above retainer  100  and includes a spacer  160  affixed to retainer  100  by screws  162 . Finally, a UV light box  164  is connected to the spacer  160 . The light box  164  has a selectively operable UV light source which directs UV light downwardly through optical flat body  82  and sheet  86  as will be described.  
         [0050]     The overall apparatus  20  is also provided with conventional control circuitry for monitoring and controlling the planarizing operations. Such control circuitry includes a vacuum sensor, pressure sensor and a gas supply (not shown) secured in threaded port  166  (see  FIG. 5 ) of base plate  36 , various other position and condition sensors, and programmable microprocessor controllers. This equipment and the use/programming thereof is well within the skill of the art.  
         [0000]     Operation  
         [0051]     The planarizing operation of apparatus  20  will now be described. It will be first assumed that the apparatus is in the  FIG. 1  position thereof, i.e., the assembly  50  has been actuated to open apparatus  20  so that head  96  and the structure carried thereby is spaced above chamber  26 . Also, the support  114  and chuck  120  are in their lowered positions. In this orientation of apparatus  20 , a sheet support assembly  88  carrying flexible sheet  86  is positioned atop chamber wall  56  with ring  108  engaging seal  64 . The assembly  50  is then actuated to lower head  96  until the underside thereof carrying seal  97  comes into direct engagement with the upper ring support  106 . Next, a fresh substrate  78  having a coating  76  thereon is placed upon C-shaped body  114 , with the coating  76  facing upwardly. The arm assembly  42  is then actuated to rotate arm  46  so that the support segments  48  carrying platen  142  enter chamber  26  through entryway  62 . The platen is thus placed upon the surface  122  of vacuum chuck  120 .  
         [0052]     Next, the door  66  is closed by operation of the piston and cylinder assembly  52  to extend the rods  54  and operation of pneumatic actuator assembly  68  respectively until gasket  74  comes into circumscribing and sealing relationship with the wall structure about entryway  62 , thus establishing a closed chamber  26 . A vacuum is then drawn through hose  132  (normally from about 685 to 750 torr) in order to hold the platen  142  in place on the chuck  120 . At this point a vacuum is drawn within chamber  26  through port  150 , and through port  98  of head  96 , sufficient to create a pressure differential across sheet  86  sufficient to deflect the sheet sufficient to deflect the sheet towards region C of substrate coating  76  while the sheet remains spaced from the peripheral region P thereof. Generally, with the preferred apparatus  20 , a vacuum of from about 685 to 750 torr is drawn through port  150 , whereas a lesser vacuum of from about 635 to 710 torr is drawn through port  98 .  
         [0053]     In the next step, the assembly  134  is actuated so as to move chuck  120  carrying platen  142  into the position of  FIGS. 6 and 11 , i.e., in the planarizing position where the coating  76  is fully in contact with sheet  86 , the latter fully engaged with the surface  84  of body  82 . In order to establish the appropriate planarizing contact, the chuck  120  should exert a pressure of from about 1 to 90 lb/square inch against the substrate  78 . Next, the vacuum, drawn through port  150  and chamber  26  is relieved, and the latter is allowed to return to atmospheric pressure, to release the sheet  86  from its deflected condition.  
         [0054]     During such movement of the chuck  120  to the frill planarizing position, any entrained air bubbles between the sheet  86  and surface  84  and/or platen  142  are eliminated. Moreover, the sequential movement toward the full planarizing position, involving the initial defection of sheet  86  followed by movement of the chuck  120 , has been found to materially expedite the planarizing operation while giving superior end products.  
         [0055]     The light assembly  30  is then actuated to cure the coating  76  during the above-described planarizing contact. The wave length of UV light selected for this purpose, and the duration of the light-on condition, is dictated by the nature of the coating to be cured, and these parameters are within the skill of the art.  
         [0056]     Once the coating  76  is properly cured and planarized, the apparatus  20  is operated to detach the substrate  78  and coating  76  from sheet  86  and to permit retrieval of the cured substrate and insertion of a fresh coated substrate. In particular, in the next step depicted in  FIG. 7 , the piston and cylinder assemblies  116  are actuated to move the support  114  to come into contact with the substrate  178  to secure it while the platen  142  is removed. Next, the piston and cylinder assembly  134  is actuated to withdraw chuck  120  and platen  142  from the substrate  78 , the vacuum drawn through hose  132  is relieved. The door  66  is then opened and robotic arm assembly  42  is used to retrieve platen  142 . The door  66  is then moved back to its chamber-closing position relative to entryway  62 , so that the apparatus assumes the  FIG. 7  position. Next, the assembly  134  is again actuated to elevate chuck  120  until the vacuum surface  122  thereof comes into direct contact with the substrate  78 . This orientation is shown in  FIG. 8 . Next the piston and cylinder assemblies  116  are actuated to move the support  114  to its lower position away from substrate  78 . At this point, the vacuum is drawn through hose  132 . An appropriate pressure differential is created across sheet  86  by directing positive pressure air through port  98  of head  96 . Normally, a vacuum of from about 685 to 750 torr is drawn through hose  132 , while air at a positive pressure of from about 0.5 to 50 psi is directed through port  98 . As best seen in  FIG. 12 , this combination creates a situation where the sheet  86  is cleanly drawn away from surface  84  of body  82  while the sheet remains adhered to coating  76  of substrate  78 .  
         [0057]     The next step is depicted in  FIG. 13 , where it will be seen that a pressure differential is created across sheet  86  sufficient to separate the sheet  86  from the coating  78  at the peripheral region P, while maintaining such contact at the central region C. This is accomplished by slightly shifting the chuck  120  downwardly, while maintaining the vacuum through hose  132  with a corresponding positive pressure delivered through port  98 .  
         [0058]     The final removal step involves a further shifting of chuck  120  away from body  82 . The drawing of the vacuum through port  98  ensures that the sheet  86  moves back into full planarizing contact with the surface  84  of body  82 , so that the apparatus  20  is ready to begin the planarization process again.  
       Embodiment of FIGS.  15 - 18   
       [0059]     The apparatus  20  in preferred forms includes the use of the solid planarized body  82  with lower planarizing surface  84 . However, the invention is not so limited. That is, the same improved operational characteristics can be achieved using positive air pressure and vacuum alone, without a solid planarizing body. In  FIG. 15-18  this apparatus and method are shown in schematic format. A flexible planarizing sheet  88   a  is provided with adjacent stationary support  114   a  and chuck  120   a . As shown, the chuck  120   a  holds a substrate  78   a  having a coating  76   a  to be planarized.  
         [0060]     In the first step of the planarizing operation depicted in  FIG. 15 , a pressure differential is created to bow the central region C towards the coating  76   a  and substrate  78   a . The central region C of the sheet  88   a  comes into contact with the corresponding region of the coating, as described in connection with the first embodiment. At this point positive pressure air indicated by arrows  168  is directed against the upper face of sheet  88   a , while (optionally) a vacuum may be drawn though chuck  120   a . Next, the chuck  120   a  is moved to the full planarizing position, and additional positive pressure air is directed against the upper face of sheet  88   a . This ensures the desired full planarizing contact between the sheet  88   a  and coating  76   a . Of course, during such contact the coating  76   a  is cured, typically by application of UV radiation or heat.  
         [0061]      FIG. 17  illustrates the first step in the detachment of sheet  88   a  from the now-cured coating  76   a . This involves creation of a differential pressure across the sheet  88   a , by application of positive pressure air above the sheet  88   a  and/or drawing a vacuum below sheet  88   a . In either instance the central region of the sheet  88   a  remains in contact with the coating  76   a  at central region C, whereas the peripheral region P of the coating is spaced from the sheet. In the final step ( FIG. 18 ), a negative pressure is drawn against the face of sheet  88   a  remote from the coating  76   a  thereby fully separating the sheet  88   a  from coating  76   a , and thereby positioning the apparatus for the next planarizing operation.  
       EXAMPLE I  
       [0062]     In this example, a trench wafer having a photocurable material was planarized using apparatus  20 . In particular, a silicon wafer having trench structures about 1 μm was used as the substrate. The featured density of the wafer ranged from about 4-96%. A photocurable material was prepared by thoroughly mixing 20 grams of epoxy (D.E.R. 354LV, Dow Chemical Co.), 80 grams of propylene glycol monomethyl ether (PGME, Aldrich Chemical Co.), and 1.2 grams of Sarcat KI-85 (Sartomer Chemical) in a yellow-lighted laboratory. The material was then filtered using a 0.2 μm filter and stored in a clean brown bottle. A film of the photocurable planarization material less than 0.5 μm thickness was spin-coated onto the silicon trench wafer.  
         [0063]     During processing, the closed apparatus chamber was evacuated to less than 20 torr for about 30 seconds to remove residual solvent. During planarization, the substrate was pressed against the Teflon optical flat surface using a force of about 68 psi for 300 seconds. During this time, UV light was used to cure the coating. After UV exposure, the chamber was pressurized to atmospheric, the substrate was separated from the optical flat surface, and the substrate was removed from the chamber.  
         [0064]     As a comparison, another similar trench wafer was coated with the same material under identical conditions. This reference product was cured in the same manner, except that there was no press step used. The comparative wafers were characterized using a Tencor Alphastep Profilometer. A surface topography of about 250 Å was measured across the structure produce in accordance with the invention. The reference wafer exhibited a measured surface topography of about 7000 Å. The planarization film thickness within different feature-density areas of the pressure-planarized wafer was measured using a scanning electron microscope. Film thicknesses over feature-density areas, representing a maximum of about 40% difference feature density, were measured. Film thicknesses on top of the structures, not over the trenches, in two feature-density areas were about 0.45 μm, with a thickness difference of about 0.012 μm (120 Å).  
       EXAMPLE II  
       [0065]     In this example a thermocurable material was applied to a silicon wafer. The wafer was prepared by first coating it with a silicon dioxide film having a thickness of about 1 μm. A pattern containing vias of 0.2 to 1 μm in diameter and having various feature density areas was patterned into the silicon dioxide film. The depth of the vias was about 1 μm. A thermocurable material was prepared as set forth in Example I, except that 1.0 grams of Nacure® Super XC-A  230  catalyst (King Industries) was used in lieu of the Sarcat product. The material was spin-coated to a thickness of about 0.2 μm onto the silicon via wafer.  
         [0066]     The coated wafer was transferred to the apparatus  20  which, after sealing, was evacuated to less than about 20 torr for about 180 seconds to remove residual solvent. The coated substrate was pressed against the optical flat surface using a force of 68 psi for 60 seconds. During this time a pulsing UV/infrared heating light was illuminated through the optical flat surface to cure the planarization material (120 seconds at a curing temperature of at least about 130° C.). After curing, the chamber was vented to atmospheric, the substrate stage was lowered, the chamber door was opened, and the substrate was removed for characterization.  
         [0067]     The planarized via wafer surface was characterized with a Tencor Alphastep profilometer. A surface topography over planarized structures of less than 100 Å and less than about 300 Å across adjacent feature density areas was measured. The planarization film thickness over structures in different feature-density areas was measured using a scanning electron microscope. Two feature-density areas were measured. Film thickness on top of the structures in an area having about 0.3 μm diameter vias with a pitch of about 0.5 μm was measured. Film thickness was also measured on top of the structures in an area having about 0.3 μm-vias with a pitch of about 1.75 μm. The film thickness measured were about 0.19 μm and 0.21 μm, respectively.  
       EXAMPLE III  
       [0068]     In this example, photocurable planarization material consisting of 5 grams of Novolac epoxy resin (D.E.R.™ 354LV, The Dow Chemical Company), 5 grams oft-butyl glycidyl ether (Aldrich), and 0.6 grams of 500% triarylsulfonium hexafluorophosphate (a photo acid generator) solution (Aldrich) was formulated and mixed thoroughly. The solvent used in the photo acid generator solution was a reactive solvent. The material was filtered with 0.2 μm filter.  
         [0069]     A 1.7 μm thick layer of the planarization material was coated onto a 6-inch silicon wafer surface that had been treated with an adhesion promoter APX-K1 (Brewer Science, Inc.) using the vendor&#39;s recommended process. A standard edge bead removal process was conducted that removed about 5 mm of edge bead.  
         [0070]     The substrate was placed within the apparatus  20  as described in previous examples, and pressed against the optical flat surface using a pressure of 68 psi for 30 seconds. During this contact, a continuous UV light from a mercury-xenon lamp was illuminated through the optical flat surface for 10 seconds to cure the planarization material. The pressure was then released and the wafer was removed from the apparatus. A Dektak 8 (Veeco Metrology Group) was used to characterize the planarized surface roughness and the degree of planarization. A step height of approximately 200 Å was found on the 1 μm tall portions of the original substrate structures. A degree of planarization of about 98% was achieved, and no voids were found in the planarized material.  
       EXAMPLE IV  
       [0071]     In this example, a curable material was planarized using air pressure in lieu of the optical flat body  82 . The photocurable material and wafers of Example I were used. The coated substrate was placed in the apparatus  20 , and the chamber was evacuated to less than 20 torr for about 30 seconds for residual solvent removal. The substrate was then pressed against the optical flat sheet. After such contact, air pressure was applied to the opposite side of the film at a pressure of about 20 psi for 300 seconds. While the surface was thus maintained in contact with the optical flat film, UV light was illuminated through the film for 10 seconds to cure the planarization material. After planarization, the pressure within the chamber was relieved to atmospheric, and the substrate was separated from the film and removed for characterization.  
         [0072]     A reference wafer was prepared in the same fashion, except that it was not subjected to the air pressure pressing step. The wafer surface produced according to the invention, and the reference surface were characterized using a Tencor Alphastep Profilometer. A surface topography of about 350 Å was measured across the structures and across adjacent feature density areas in the substrate produce din accordance with the invention. Planarization film thickness within different feature-density areas was measured using a scanning electron microscope. Film thicknesses over feature-density areas, representing a maximum of about 40% difference over feature-density, were measured. Film thicknesses on top of the structures, not over the trenches, into feature-density areas were about 0.45 μm with a thickness difference of about 0.014 μm (140 Å). The reference wafer exhibited a surface topography of about 7000 Å across the topographic structures.