Patent Publication Number: US-2021193496-A1

Title: Substrate support features and method of application

Description:
This invention relates to an assembly for applying raised features to a semiconductor substrate chuck, a method for applying a pattern of raised substrate support features onto a chuck surface, and a method for making such an assembly. 
     BACKGROUND OF THE INVENTION 
     This invention is in the field of semiconductor processing in which substrates are supported by chucks. These chucks may clamp the supported substrates during material processing using electrostatic chucking (ESC) or by vacuum clamping. The supported substrates may for example be semiconductor wafers, redistributed wafers, or panels containing die embedded in polymer material, or other substrates containing electronic circuits. The material processing applications for the invention may include vacuum or sub-atmospheric processes such as physical vapor deposition (PVD), chemical vapor deposition (CVD), ion implantation, and material removal by either reactive ion etch or physical sputtering etch. Material processing applications may also include atmospheric processing such as thermal annealing or other thermal processing, chemical mechanical polishing, etc. 
     Semiconductor substrates typically require cooling or heating during processing. This is often accomplished by providing gas to the backside of the substrate. The uniformity of heating or cooling of the substrate is an important parameter which affects processing uniformity. Thermal uniformity of substrates for chucks with backside gas provision rely on the uniformity of the gas pressure between the chuck and the substrate. 
     An example prior art chuck  100 , with a chuck face  111  on which a substrate  118  may be mounted, is shown in  FIGS. 1A and 1B . The chuck has a cooled body  110  containing a cooling-fluid manifold  116  with fluid inlet  115  and fluid outlet  117 . Gas is provided to gas manifold  114  via a gas inlet  113 , and distributed to holes  112  to provide gas to the area between the chuck face  111  and the substrate  118 . Uniform gas distribution is accomplished using radial and azimuthal channels  119  machined into the chuck face  111 . 
     An alternative prior art chuck  101  is shown in  FIGS. 2A and 2B , in which reference numerals for like components are retained where appropriate. Gas is provided to gas manifold  114  by gas inlet  113 , and distributed to one or more holes  112 . A pattern of raised embossment features  120  on chuck face  111 , which project toward the substrate  118 , allows gas to uniformly distribute in the region on the backside of the substrate  118 , i.e. the side of the substrate closest to the chuck face  111 . The chuck face  111  may be machined (for example by milling or blasting through a mask) to provide the raised embossment features  120 . Alternatively, the features  120  may be deposited on the chuck face  111  by physical vapor deposition (PVD) or by chemical vapor deposition (CVD). Alternatively, a thin capping layer of ceramic or metal containing the raised embossment features may be adhesively bonded to the chuck face  111 . The chuck face  111  may clamp the substrate  118  thereon using electrostatic or vacuum chucking. In such prior art chucks, the embossment becomes permanently integrated into the chuck face  111 . 
     Semiconductor chuck surfaces require periodic maintenance. The chuck surface may need to be cleaned of metal, polymer or other process-related contamination. Chuck embossment features  120  may become damaged during cleaning. The features may also be abraded by repeated contact with wafers or other substrates during processing. There is therefore a need to periodically replace raised embossment features on semiconductor chucks. 
     Maintenance of semiconductor chucks is often done at or near wafer fabrication facilities for reasons of cost and convenience. There is a need for the replacement of embossment features to be done in the field using low-cost materials, tooling and equipment. 
     It is an aim of the present invention to provide an assembly which allows chuck embossment features to be easily replaced without requiring expensive factory refurbishment. It is a further aim of the present invention to provide a method to apply the assembly to a chuck surface, depositing and bonding a pattern of support features to the surface. 
     In accordance with the present invention these aims are achieved by forming features and adhering these to a peel-ply layer, i.e. a layer which provides protection and reduces contamination when applied, but can be removed through peeling, which may subsequently be removed to retain the features on a chuck. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect of the present invention there is provided an assembly for applying raised features to a semiconductor substrate chuck, each feature acting to space a substrate from the chuck in use, the assembly comprising: 
     a carrier layer having first and second major sides, 
     at least one feature adhered to the first side of the carrier layer, and 
     a peel-ply layer adhered to the first side of the carrier layer such that the at least one feature is enclosed between the carrier layer and the peel-ply layer, 
     wherein the feature may be applied to a chuck by removal of the peel-ply layer and subsequently adhering the feature to the chuck. 
     In accordance with a second aspect of the present invention there is provided a method for applying raised features to a semiconductor substrate chuck, each feature acting to space a substrate from the chuck in use, the method comprising the steps of: 
     i) providing the assembly of the first aspect, 
     ii) removing the peel-ply layer, and 
     iii) adhering the feature to the chuck. 
     In accordance with a third aspect of the present invention there is provided a method of making the assembly of the first aspect, comprising the steps of: 
     bonding together a peel-ply layer, an adhesive layer and a polymeric embossment layer to form a multi-layer structure, 
     removing portions of the embossment layer and adhesive layer to create at least one feature bonded to the peel-ply layer, and 
     adhering a carrier layer onto the peel-ply layer to enclose the at least one feature therebetween. 
     Other specific aspects and features of the present invention are set out in the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the accompanying drawings (not to scale), in which: 
         FIGS. 1A and 1B  respectively show schematic plan and section views of a prior art chuck with backside gas distributed by channels; 
         FIGS. 2A and 2B  respectively show schematic plan and section views of a prior art chuck with backside gas distributed by integrated embossment features; 
         FIGS. 3A to 3D  are schematic section views of an assembly for depositing support features on a chuck, shown at initial and intermediate fabrication steps, in accordance with an embodiment of the present invention; 
         FIGS. 4A and 4B  are schematic section and plan views of a portion of the assembly for depositing support features on a chuck at an intermediate fabrication step; 
         FIGS. 5A and 5B  schematically show, in plan and section views respectively, an assembly for depositing features onto a chuck following fabrication; 
         FIG. 6  is a schematic section view of a chuck, an applicator assembly for depositing support features on the chuck and fabrication tooling; and 
         FIG. 7  is a schematic section view of a chuck with deposited features supporting a substrate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
       FIG. 3A  schematically shows in section an initial structure for depositing support features on a chuck at an initial fabrication step. Three bonded layers are shown at this fabrication step, namely embossment layer  212 , which is bonded to a smooth-surfaced peel-ply supportive polymer layer  210  (hereafter “peel-ply layer  210 ”) by an adhesive layer  211 , here a pressure sensitive adhesive layer. 
     The embossment layer  212  may consist of polymer material such as polyetheretherketone (PEEK) or polyimide for example, with a thickness in the range from 5-100 um, and preferably between 10-30 um. The peel-ply layer  210  may comprise a woven fabric, nylon or other synthetic polymer material. The thickness of peel-ply layer  210  may be in the range 0.1-1.0 mm. The adhesive layer  211  may be constituted as an adhesive pad material which may be fabricated from a variety of polymers including acrylic acid esters, polyurethanes and silicones for example, and should have a bond strength greater than 10 lb/inch (1750 N/m) and flow at a temperature above 150° C. 
       FIG. 3B  schematically shows, in an expanded sectional view, the assembly at a second fabrication step, following laser cutting of the embossment layer  212  and adhesive layer  211  to remove portions thereof so as to leave a plurality of small supporting features  213 . These supporting features  213  may for example be of rectangular, circular or of other shapes when viewed from above (i.e. towards the peel-ply layer  210 ). The supporting features  213  may have width and length (dimensions parallel to the peel-ply layer  210 ) or diameters of between 0.25-3 mm. 
       FIGS. 3C and 3D  schematically show, in plan and expanded sectional views respectively, additional details of the assembly for the second fabrication step. The laser cutting of embossment layer  212  and adhesive layer  211  is controlled to form a feature in the form of a raised-edge rim  217  around the perimeter of peel-ply layer  210 . This raised-edge rim  217  defines a continuous border surrounding all other features, such as supporting features  213 , when applied to a chuck. In addition, the laser cutting is controlled to form other features in the form of a plurality of raised rings  220 , each of which defines a closed shape surrounding no other features when applied to a chuck. Both the raised-edge rim  217  and raised rings  220  project outwardly from peel-ply layer  210 . The raised-edge rim  217  and raised rings  220  may have width in the range of 0.5-5.0 mm, and may preferably be less than 3 mm. For round substrates, the outer diameter of raised-edge rim  217  should match the diameter of substrate  118 . For substrates of other shapes, the outer edge of raised-edge rim  217  should be coincident with the edge of substrate  118 . The raised rings  220  are used to isolate holes (such as  112 , see  FIGS. 1, 2 ) on chucks to prevent gas leakage. 
       FIGS. 4A and 4B  schematically show, in expanded sectional and expanded plan view respectively, an assembly for depositing supporting features  213  onto a chuck in a third fabrication step. A carrier layer  215 , with an adhesive backing  214  adhered directly onto the lower surface of the carrier layer  215 , is aligned and placed onto the upper surface of the assembly shown in  FIG. 3 . The peel-ply layer  210  and carrier layer  215  are pressed together with sufficient pressure to securely enclose and adhere the supporting features  213  to the carrier layer  215 . The carrier layer  215  is made from a polymer, which may for example comprise a woven fabric, nylon or other synthetic material. The carrier layer  215  thickness may be between 0.1-1.0 mm. 
       FIGS. 5A and 5B  schematically show, in plan and section views respectively, an applicator assembly  200  for depositing features onto a chuck at the completion of its fabrication, after the final fabrication step in which plurality of alignment holes  216  have been laser cut in the carrier layer  215 . The peel-ply layer  210  has been manually removed, for example by insertion of a small tool between the peel-ply and carrier layers. The smooth surface of the peel-ply layer  210  facilitates its removal. In addition, the adhesive backing layer  214  and adhesive layer  211  are chosen so that at room temperature, the adhesion between the carrier layer  215  and the embossment layer  212  exceeds the adhesion between the peel-ply layer  210  and the embossment layer  212 . It should be noted that in  FIG. 5B  the carrier layer  215  is shown as being smooth, unlike the view in  FIG. 4A . This difference is simply due to the difference in scale between the two figures. 
       FIG. 6  schematically shows, in sectional view, a chuck  230 , the assembly  200  for depositing raised features on the chuck  230 , and alignment pins  218  which have been inserted into and interface with the alignment holes  216  in the assembly  200  for properly positioning the assembly with respect to the chuck  230 . Chuck  230  has previously been cleaned of any raised features, for example as previously adhered using a similar assembly. Heated tooling  219  is used to press the assembly  200  against the chuck  230  to activate the adhesive layer  211 , bonding the raised supporting features  213 , the raised rings  220  and the raised-edge rim  217  to chuck  230 . Practitioners skilled in the art will understand that other methods can be used for applying pressure and heat in order to adhesively bond the assembly  200  to the chuck  230 . The chuck is then cooled, and after cooling the carrier layer  215  can be removed by mechanical peeling, leaving raised features  213  bonded to the chuck  230 . 
       FIG. 7  schematically shows, in sectional view, the chuck  230  after processing with the assembly  200 , and ready for use in a semiconductor process. Components  113 ,  115 ,  116 ,  117  are all as previously described with reference to  FIGS. 1 and 2 . The raised supporting features  213 , raised rings  220  and raised-edge rim  217  are shown in contact with the substrate  118 . Gas supplied through the holes  112  is uniformly distributed between a chuck face  231  and the backside of substrate  118 . The backside gas pressure is maintained through the seal with the substrate  118  provided by the raised-edge rim  217 . 
     The above-described embodiment is exemplary only, and other possibilities and alternatives within the scope of the invention will be apparent to those skilled in the art. 
     REFERENCE NUMERALS USED 
     
         
         
           
               100 ,  101 ,  230 —Chuck 
               110 —Cooled body 
               111 —Chuck face 
               112 —Holes 
               113 —Gas inlet 
               114 —Gas manifold 
               115 —Fluid inlet 
               116 —Cooling-fluid manifold 
               117 —Fluid outlet 
               118 —Substrate 
               119 —Channels 
               120 —Embossment features 
               200 —Assembly 
               210 —Peel-ply supportive polymer layer 
               211 —Adhesive layer 
               212 —Embossment layer 
               213 —Supporting features 
               214 —Adhesive backing 
               215 —Carrier layer 
               216 —Alignment holes 
               217 —Raised-edge rim 
               218 —Alignment pins 
               219 —Heated tooling 
               220 —Raised rings