Abstract:
This invention relates to a mounting apparatus for mounting and supporting one structure side of a substrate, which structure side has structures thereon. The apparatus having a mounting element with a flat mounting surface for supporting the structures and a suction surface F 2  which penetrates the mounting surface solely in an outer ring surface for effecting a fluid flow which produces suctions on the substrate.

Description:
FIELD OF THE INVENTION 
     The invention relates to a mounting apparatus for mounting of a substrate, especially of a wafer, on a side of the substrate, which has structures thereon. 
     BACKGROUND OF THE INVENTION 
     Mounting apparatus are used as “chucks” in the semiconductor industry for handling of wafers in the production of electrical components in various process steps. Wafers, which are provided with individual component groups (structures), are typically referred to as product wafers. In each process step, it is important that the wafers are quickly, reliably and easily detachably fixed on the mounting apparatus so that handling of the wafers is not a disruption factor for the processing of the wafers. The fixing of product wafers, which have structures thereon, is more difficult the thinner they are and the more pronounced and higher is the topography of the components on the product wafers. Any stress in the wafer is to be avoided as much as possible so that the very expensive structures, which are present on the product wafer, are not damaged. While there are different approaches to fixing, i.e., mounting, a product wafer on the unstructured, flat side thereof, there are a host of technical problems in the fixing of a product wafer on its structured side. Thus, for example, electrostatic fixing is problematic since the electrical circuits of the structures can be destroyed by possible voltage peaks. 
     Furthermore, it is desirable to handle the electrical structures as free of contamination as possible and without impurity (for example by adhesive). 
     The object of this invention is therefore to provide a mounting apparatus for mounting and handling, as well as fixing of a substrate in which rapid, safe and careful, as well as reversible and easily controllable, mounting and fixing of the substrate are enabled. 
     This object is achieved with the features of Claim  1 . Advantageous developments of the invention are given in the dependent claims. All combinations of at least two of the features given in the specification, the claims and/or the figures also fall within the framework of the invention. At the given value ranges values which lie within the indicated limits are also to be considered disclosed and claimed in any combination. 
     SUMMARY OF THE INVENTION 
     The invention is based on the concept of developing known vacuum chucks, such that structures of the substrate are incorporated at the same time into the fluid flow which suctions the substrates such that a uniform suction action (suction pressure) as homogeneous as possible over the entire structure side of the substrate is enabled. In other words, the mounting apparatus, as claimed in the invention enables a linearly variable, homogeneous surface force on the product wafer so that the substrate can be mounted on the vacuum sample holder (mounting apparatus) with the desired surface force. Preferably, the surface force acting on the substrate can be controlled by changing the suction pressure in a linear relationship. The surface force is defined by the suction area F 2 . 
     In contrast to vacuum chucks from the prior art, according to the present invention there is no blanket pressure application along the substrate, but rather suction is applied only in the region of an outer ring surface of the mounting surface of the mounting apparatus. It has been ascertained that the configuration as claimed in the invention yields an extremely homogenous pressure distribution along the mounting surface of the mounting apparatus, especially also outside of the suction area. 
     According to one advantageous embodiment of the invention, it is provided that the outer ring surface, which is made especially as a circular ring, extends from one peripheral edge of the mounting surface in the direction toward a middle M of the mounting surface. The maximum or average ring width R of the outer ring surface is less than ½, especially ⅕, preferably less than 1/10, even more preferably less than 1/100, of a diameter D 3  of the mounting surface. The thinner the ring width R relative to the diameter D 3  (or the remaining mounting surface) and/or the farther the suction surface acting on the peripheral edge of the mounting surface or on the periphery of the substrate, the more homogeneous the pressure distribution along the (entire) mounting surface. 
     Hereinafter F i  is the i-th surface which results from the surface parameters for a round surface F i  especially from the circle diameter D i . If there is a number of j=1 . . . N bores, F i  is the sum of the areas of the F i,j  bores. 
     Advantageously, the fluid flow is formed by a flow channel which has the following sections: 
     in the mounting element a host of suction channels which are comprised of through holes and which end in the suction area F 2 , 
     a fluid chamber which is connected to the suction channels on their channel ends opposite the suction area F 2  and 
     at least one pressure connection which is provided on the fluid chamber for connection of a controllable aspiration apparatus. 
     The fluid chamber  6  is used here especially as a buffer and at the same time as a distributor for uniform suction along the suction area F 2  so that advantageously only a single pressure connection and a single pump are required to operate the mounting apparatus. 
     To the extent the suction area F 2  is adjustable, by at least partially closing a part of the suction channels, the mounting apparatus can be used for different product substrates with different structures/dimensions (especially the height H of the structures is relevant). The suction channels can be closed, preferably individually, by triggerable valves on/in the suction channels. Alternatively, it is conceivable to provide a rotating disk with openings in the region of the suction channels (corresponding to the outer ring surface) on the end of the suction channels which is facing away from the suction area F 2 . In this way the suction channels can be adjusted continuously from fully open to fully closed by rotating the rotary disk. In this way all suction channels can be continuously adjusted at the same time. 
     It is also advantageous if the fluid chamber is formed by a fluid chamber element which is sealed to the mounting element, and by the mounting element. Thus the fluid chamber can be easily produced, for example, by milling of a trough shape into the fluid chamber element. The trough shape encompasses encompasses a round cylinder-shaped recess a round cylinder-shaped recess with a diameter which is larger than the maximum distance between the suction channels on their ends facing the fluid chamber. The fluid chamber element is thus comprised of a ring-shaped peripheral wall and an upper wall which border the fluid chamber. The fluid chamber element is sealed to the mounting element by connecting elements, such as screws. The seal is preferably a circular ring-shaped seal with a diameter which is larger than the diameter of the fluid chamber on the periphery of the fluid chamber between the fluid chamber element and the mounting element. 
     In another advantageous embodiment of the invention, it is provided that the flow channel in the region of the fluid chamber has a flow cross section of at least the same size, which is especially at least 5 times, preferably 10 times, even more preferably at least 20 times larger than the suction area F 2  and/or of the flow cross section F 1  of the pressure connection. The fluid chamber is thus used at the same time as a buffer and collecting space for the fluid which is flowing in from the suction channels. 
     It is furthermore advantageously provided that the suction area F 2  is chosen, or can be adjusted, such that it corresponds essentially to an inflow surface Z of a ring gap which has been formed between the mounting surface and the substrate which is mounted on the mounting surface. The ring gap has a height H which is defined by the height of the structures of the substrate. The ring gap runs on the periphery of the mounting surface (or on the periphery of the substrate) and is in the shape of a circular cylinder, wherein the inflow surface Z can be at least roughly computed from the periphery of the substrate or of the mounting surface and the height H. 
     According to another advantageous embodiment, it is provided that the mounting surface is provided on a projection of the mounting element whose contour is chosen such that it corresponds essentially to the surface contour of the substrates which are to be processed, especially with a diameter D 3  of the mounting surface between 200 mm and 450 mm, preferable exactly 200 mm or 300 mm or 450 mm. This feature more sharply defines the inflow surface Z since it corresponds to the more or less common outer contour between the mounting surface and the substrate surface which has the contours. 
     To the extent the mounting surface, especially the projection, is coated with an elastic layer, the structures which are present on the substrate are on the one hand mounted carefully on the mounting surface and on the other contamination (for example with metal shavings) is avoided. 
     The suction is further homogenized by a first group of especially at least 10, preferably at least 50, even more preferably at least 100, suction channels on a common first circle on the outer ring surface, the suction channels lying especially equidistantly to one another. This is because a uniform fluid flow, especially between the mounting surface and the substrate as far as to the middle M of the mounting surface, is effected by a concentric arrangement of the suction channels to the middle M of the suction surface or rotationally symmetrically to the mounting element. 
     According to another aspect of this invention the distance between the suction channels is smaller than 1 mm, especially smaller than 500 μm, preferably smaller than 250 μm, even more preferably smaller than 150 μm. 
     It is especially advantageous if there is a second group of at least 10, preferably at least 20 suction channels, offset to the suction channels of the first group, on a common second circle with a smaller radius than the first circle on the outer ring surface, concentrically to the middle M and/or equidistantly to one another. In this way, on the outer ring surface more suction channels can be accommodated. The more suction channels there are, the smaller they can be made and the more uniformly and more carefully suction of the substrate takes place. At the same time, arranging at least two groups on the outer ring surface yields higher stability of the mounting element. The number of suction channels is consequently limited upward only by the minimum diameter of the suction channels and the dimensions of the mounting element. The offset bores are thus a replacement for a slot which would act disadvantageously on the mechanical stability of the wafer on the edge. 
     According to another aspect of this invention the inflow surface Z is conceivable by changing, especially controlling, the diameter D 2i  of each suction channel. 
     To the extent method features have been disclosed, they are to be considered and claimed as disclosed as the method as claimed in the invention. 
     Other advantages, features and details of the invention will become apparent from the following description of preferred exemplary embodiments and using the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 a    shows a plan view of a mounting apparatus as claimed in the invention from underneath with a cutting line A-A, 
         FIG. 1 b    shows a cross sectional view according to cutting line A-A from  FIG. 1   a,    
         FIG. 2 a    shows a view according to  FIG. 1 b    with a structured substrate which is mounted on the mounting apparatus, 
         FIG. 2 b    shows a detailed view from  FIG. 2 a    and 
         FIG. 2 c    shows a detailed view from  FIG. 2   a.    
         FIG. 3  shows a contour plot view of the pressure distribution of the surface  3   o , computed with a fluid simulation program 
         FIG. 4  shows an enlargement of the contour plot view of the pressure distribution of the surface  3   o , computed with a fluid simulation program. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The same components or components with the same action are identified with the same reference numbers in the figures. 
       FIG. 1 a    shows a mounting apparatus  1  which consists of a fluid chamber element  2  and a mounting element  3 . The fluid chamber element  2  consists of a ring-shaped peripheral wall  2   w  which is formed by out-milling a circular cylinder and an upper wall  2   o  which covers the ring-shaped peripheral wall  2   w . The upper wall  2   o  also forms the bottom of the milled-out cylinder. To facilitate fixing of the mounting element  3  on the fluid chamber element  2 , in the production of the fluid chamber element  2  internal threads  4   i  are cut into the peripheral wall  2   w . The internal threads  4   i  are distributed on the periphery of the peripheral wall  2   w  equidistantly to one another. In the production of the fluid chamber element  2 , at least one seal groove  2   n  is provided on the connecting surface between the fluid chamber element  2  and the mounting element  3 . In the production of the fluid chamber element  2 , a pressure connection  13  is provided in the upper wall  2   o . A connection element  9  is sealed (or can be sealed) to the pressure connection  13 . The connection element is used to connect an intake pipe  14  which is connected to a pump  16 . In the intake pipe  14  there can be one or more measurement apparatus  15  for pressure measurement. The pressure can also be measured in the pump  16  and/or at another position in the flow channel. 
     The pressure connection  13  has a flow cross section F 1 , defined by a bore with a diameter D 1 . The pressure connection  13  is part of a flow channel which runs through the mounting apparatus  1 . The pressure connection  13  (and thus the flow channel) leads to a fluid chamber  6  which is formed by the upper wall  2   o  and the peripheral wall  2   w  and an attachment side  3   b  of the mounting element  3 . 
     The mounting element  3  has essentially a cylinder shape with an outer periphery which corresponds to the fluid chamber element  2 , especially to the peripheral wall  2   w  so that the mounting element  3  can be sealed with its especially planar attachment side  3   b  on one contact surface to the fluid chamber element  2 . For this purpose there are screw receivers  4   a  which are arranged corresponding to the internal threads  4   i  for accommodating connecting elements  4  which are made as screws. The mounting element  3  can be fixed by the connecting elements  4  on the fluid chamber element  2  on their common contact surface, a seal  5  being made as a ring seal in the seal groove  2   n  and optionally a corresponding seal groove  3   n  of the mounting element  4  for sealing the fluid chamber  6  relative to the environment. 
     The fluid chamber  6  forms another section of the flow channel. Proceeding from the fluid chamber  6 , the flow channel is divided or branched in another section of the flow channel which is formed by a plurality of suction channels  7  which are provided in the mounting element  3 . 
     The suction channels  7  are made as through bores which run especially parallel to one another and whose ends  7   e  all communicate with the fluid chamber  6 . The opposite ends of the suction channels  7  terminate in the region of one outer ring surface  8  of a mounting surface  3   o  for mounting of a substrate  10 . The mounting surface  3   o  is provided on a projection  3   e  which is made as a circular ring with a diameter D 3  and an obliquely running shoulder  3   a . The diameter D 3  corresponds essentially to the diameter of the substrate  10 . 
     A first group of suction channels  7  is located on a circle and within the outer ring surface  8 , while a second group of suction channels  7  is located on a second circle which is located farther inside and likewise within the outer ring surface  8 . Thus, as many suction channels  7  as possible with a diameter D 2  as small as possible are accommodated as near as possible to one peripheral edge U of the mounting surface  3   o . Due to the thickness of the mounting element  3  a support section of the mounting surface  3   o  provided within the outer ring surface  8  remains stable. In the support section there are no suction channels  7  and the support section and the entire mounting surface  3   o  are made flat. 
     The surface of the mounting element  3  can be at least partially coated with a coating  12  of soft material especially in the region of the mounting surface  3   o . Preferably it is a polymer, preferably an elastomer. The coating  12  is used to protect sensitive structures  11  provided on the substrate  10  and to prevent contamination of the substrate  10  which is made as a product substrate. 
     The suction channels  7 , which are produced by drilling, are arranged concentrically relative to a middle M of the rotationally symmetrical mounting element  3 . 
     A ring width R of the outer ring surface  8  is made as small as possible and is located as far as possible on the peripheral edge U. Ring width R is between 1 mm and 50 mm, preferably between 1 mm and 10 mm. The diameter D 3  is between 200 mm and 450 mm, preferably exactly 200 mm, 300 mm or 450 mm. 
     By continuously exposing the fluid chamber  6  to a negative pressure via the pressure connection  13  and the pump  16 , a suction action arises on a suction area F 2  which is formed by the sum of the flow cross sections of the suction channels  7  on the mounting surface  3   o . In this way the substrate  10  with its structure side  10   s  can be sucked onto the mounting surface  3   o  and fixed. Although there are suction channels  7  only on the outer ring surface  8  (circular ring), the area is also evacuated or negatively pressurized which is penetrated by structures  11 , which lies within the outer ring surface  8  and between the mounting surface  3   o  and the substrate  10 , and which is surprisingly homogeneous. The homogeneous pressure distribution is most easily explained by the statistical multiparticle system in this region being understood as a large canonical ensemble. An ensemble is a set of replicas of a statistical multiparticle system which differ in their microstates but have equivalent macrostates. A large canonical ensemble is an ensemble which is subject to fluctuations of particles and energy. Although the embodiment as claimed in the invention continuously sucks particles on the edge, some particles always find the path into the interior region, likewise particles will also leave this region again. Therefore an absolute vacuum or even only a high vacuum will never be attainable. Still the number of particles can on average be kept constant with constant starts and boundary conditions. Since there are no potentials which make the statistical distribution function locally dependent (aside from gravitation potential whose effects on the distribution function are negligible for the short height of the examined region) the pressure distribution must likewise be a homogeneous function of the site. Thus the substrate  10  with the structures  11  is fixed very uniformly on the mounting surface  3   o . The force acting on the substrate  10  is defined by controlling the negative pressure on the pump  16  and by means of the flow cross sections of the individual sections of the flow channel. 
     According to the present invention, it has been found to be optimum if the cross sectional area F 1  of the pressure connection  13  corresponds roughly to the sum of the cross sectional areas of the suction channels  7 , therefore roughly the suction area F 2 . The ratio of the areas F 1  to F 2  is especially between 1 to 10 and 10 to 1, preferably between 2 to 7 and 7 to 2, more preferably between 3 to 5 and 5 to 3, most preferably between 4 to 5 and 5 to 4. 
     The suction area F 2  is moreover advantageously chosen such that it corresponds roughly to an inflow surface Z which is formed by a ring gap  17  between the peripheral edge U of the mounting surface  3   o  and the substrate  10  due to the height of the structures  11  during suction. The inflow surface Z corresponds to the periphery of the ring gap  17  multiplied by the height H of the ring gap  17 , a ratio of the suction area F 2  to the inflow surface Z being between 4 to 5 and 5 to 4. 
     As long as the substrate  10  is to be held on the mounting apparatus  1 , the pump  16  must provide for a continuous fluid flow along the flow channel. It is provided by the above described flow cross section of the flow channel as claimed in the invention that the amount of gas which flows through the suction channels  7  per unit of time is equal to the amount of gas which leaves the fluid chamber  6  through the pressure connection  13  or the connection element  9 . 
     The topographical structures  11  keep the substrate  10  (wafer) separated at a distance H (corresponds to height H of the ring gap  17 ) from the projection  3   e , specifically the mounting surface  3   o . The space between the substrate and the mounting surface  3   o  at the start of the suction process is automatically lowered to a certain pressure level somewhat above the suction pressure on the suction area F 2  and subsequently remains constant for further continuous pressurization of the fluid chamber  6 . At this instant there is an especially steady-state pressure distribution along the flow profile from the inflow surface Z to the pump  16 . 
     Thus, as claimed in the invention, how large the surface force acting on the substrate  10  on the mounting surface  3   o  is can be controlled by the suction performance, especially the volumetric flow or any other easily accessible and measurable physical quantity, of the pump  16 , by changing the suction performance, a preferably linear change of the surface force taking place. According to another embodiment of the invention it is provided that the elastic coating  12  is elastic such that the structures  11  penetrate at least partially, especially at least by one third of the height H, preferably by half of the height H, even more preferably by three fourths of the height H, into the elastic coating  12 . In this way the height H′ of the ring gap  17  is reduced so that the inflow surface Z′ becomes correspondingly smaller. This could result in a reinforcing effect. A smaller inflow surface Z′ at the same volumetric flow would mean a higher force and thus would press the wafer farther into the coating  12 ; this in turn would result in a reduction of the inflow surface Z′. 
     According to another advantageous embodiment of the invention, especially in combination with the embodiment described in the preceding paragraph, it is conceivable as claimed in the invention to make the suction channels  7  at least partially sealable. In this way there would be a dynamic matching possibility for the inflow surface Z′. 
     REFERENCE NUMBER LIST 
     
         
           1  mounting apparatus 
           2  fluid chamber element 
           2   w  peripheral wall 
           2   o  upper wall 
           2   n  seal groove 
           3  mounting element 
           3   o  mounting surface 
           3   e  projection 
           3   b  attachment side 
           3   n  seal groove 
           4  connecting elements 
           4   i  internal thread 
           4   a  screw receiver 
           5  seal 
           6  fluid chamber 
           7  suction channel 
           7   e  ends 
           8  outer ring surface 
           9  connection element 
           10  substrate 
           10   s  structure side 
           11  structures 
           12  coating 
           13  pressure connection 
           14  intake pipe 
           15  measurement apparatus 
           16  pump 
           17  ring gap 
         F 1  flow cross section 
         F 2  suction surface 
         U peripheral wall 
         M middle 
         R ring width 
         D 1  diameter 
         D 2  diameter 
         D 3  diameter 
         Z inflow surface 
         H height