Abstract:
A substrate carrier, including: a baffle having a continuous perimeter sidewall surrounding an enclosed region; and one or more standoffs attached to an inside surface of the perimeter sidewall, the one or more standoffs extending into the enclosed region and below a bottom edge of the perimeter sidewall, the one or more standoffs each having a lip located between an upper edge of the baffle and the lower edge of the baffle. Also, a method of annealing substrates using the substrate carrier.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of integrated circuit technology; more specifically, it relates to a carrier of ultra-thin substrates and a method of fabricating integrated circuits using the carrier. 
       BACKGROUND 
       [0002]    Handling ultra-thin substrates is highly problematic in a manufacturing environment, especially as product requirements drive manufacturers to produce ever thinner semiconductor chips. One problem associated with processing ultra-thin substrates is breakage. Ultra-thin substrates are extremely fragile. For example, in processes that require flowing gases in/around thin substrates breakage of the ultra-thin substrates is a continuing problem. Accordingly, there exists a need in the art to mitigate the deficiencies and limitations described hereinabove. 
       BRIEF SUMMARY 
       [0003]    A first aspect of the present invention is a substrate carrier, comprising: a baffle having a continuous perimeter sidewall surrounding an enclosed region; and one or more standoffs attached to an inside surface of the perimeter sidewall, the one or more standoffs extending into the enclosed region and below a bottom edge of the perimeter sidewall, the one or more standoffs each having a lip located between an upper edge of the baffle and the lower edge of the baffle. 
         [0004]    A second aspect of the present invention is a method, comprising: placing a lift block on a work surface; providing a substrate carrier comprising: a baffle having a continuous perimeter sidewall surrounding an enclosed region; and one or more standoffs attached to an inside surface of the perimeter sidewall, the one or more standoffs extending into the enclosed region and below a bottom edge of the perimeter sidewall, the one or more standoffs each having a lip located between an upper edge of the baffle and the lower edge of the baffle; placing the substrate carrier on the work surface over the lift block, a top surface of the lift block extending above the top edge of the perimeter sidewall relative to the surface; placing a semiconductor substrate on a substrate carrier and placing carrier plate on the top surface of the lift block; lifting the substrate carrier from the lift block; and after the lifting the substrate carrier resting on the lips of the one or more standoffs, the wafer contained within the enclosed region. 
         [0005]    These and other aspects of the invention are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
           [0007]      FIG. 1A  is a top view and  FIG. 1B  is a cross-section view thru line  1 B- 1 B of  FIG. 1A  of a substrate carrier according to embodiments of the present invention; 
           [0008]      FIG. 2  is a detailed view of  FIG. 1B ; 
           [0009]      FIG. 3  illustrates stacking substrate carriers according to embodiments of the present invention; 
           [0010]      FIG. 4A  is a top view and  FIG. 4B  is a cross-section view thru line  4 B- 4 B of  FIG. 4A  of a substrate carrier according to alternative embodiments of the present invention; 
           [0011]      FIG. 5  illustrates stacking alternative substrate carriers according to embodiments of the present invention; 
           [0012]      FIG. 6  is a cross-section of an alternative baffle that may be used in any of the substrate carriers according to embodiments of the present invention; 
           [0013]      FIG. 7  is a cross-section through a substrate carrier that incorporates a vacuum chuck according to embodiments of the present invention; and 
           [0014]      FIGS. 8A through 8E  illustrate a method of annealing ultra-thin substrates using substrate carriers according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Integrated substrates are comprised of semiconductor material (e.g., silicon), are usually circular and are often referred to as wafers. Multiple integrated circuit chips may be fabricated on a single wafer. A typical ultra-thin semiconductor wafer is about 200 mm in diameter and about 100 microns thick or less (compared to about 725 microns for a non-thinned wafer). Ultra-thin wafers of 300 mm and 450 mm diameters as well as ultra-thin wafers as thin as 40 micron thick are contemplated. These ultra-thin wafers are easily bowed and if bowed too much will fracture and break. It has been found that when placed in a process tool that flow gas over ultra-thin wafers, the edges of the ultra-thin wafers can be picked up by Bernoulli forces and the ultra-thin wafers broken. To avoid this, ultra-thin wafers are adhesively bonded to thicker handle substrates. However, if the process requires heating to about 250° C. or greater, the adhesive will break-down and the ultra-thin wafers subsequently break. 
         [0016]      FIG. 1A  is a top view and  FIG. 1B  is a cross-section view thru line  1 B- 1 B of  FIG. 1A  of a substrate carrier according to embodiments of the present invention. In  FIGS. 1A and 1B , a substrate carrier  100  comprises a baffle  105  having a continuous perimeter side wall, three identical and equally spaced standoffs  110 A,  110 B and  110 C attached to the inside sidewall of baffle  105 , a non-attached carrier plate  115  resting on standoffs  110 A,  110 B and  110 C and optional handles  120 A and  120 B attached to the outside sidewall of baffle  105 . In the example of  FIGS. 1A and 1B , baffle  105  is a thin-walled cylinder. Handles  120 A and  120 B and standoffs  110 A,  110 B and  110 C may be attached to baffle  105  by screws or rivets or may be welded to baffle  105 . Standoffs  110 A,  110 B and  110 C only extend part way from the inside of baffle  105  toward the geometric center of baffle  105 . Carrier plate  115  is required with ultra-thin substrates that are defined as substrates that are flexible to the extent that they will sag in their middles under their own weight when only supported by their edges. Light and stiff substrates do not require a standoff plate. A stiff and light substrate is defined as a substrate that can be easily moved by a gas flow passing directly across the surface of the substrate but does not sag in the middle when supported only by its edges. A Styrofoam plate is an example of a light and stiff substrate. An ultra-thin substrate  125  (i.e., a substrate having a thickness of 100 microns or less), which is an example of a flexible substrate, is illustrated resting on (not bonded) or otherwise attached to carrier plate  115 . In one example, ultra-thin substrate  125  is an ultra-thin semiconductor wafer having a diameter between about 100 mm and about 450 mm and a thickness of between about 100 microns and about 40 microns. Carrier plate  115  may be fabricated from glass, metal, ceramic or a non-thinned semiconductor wafer. Carrier plate  115  may be a solid disk, a disk having perforations or a wire mesh disk. It is advantageous that carrier plate  115  have a flat surface for the substrate to rest on. Materials for baffle  105  and standoffs  110 A,  110 B and  110 C include stainless steel, aluminum or other metals. While three standoffs  110 A,  110 B and  110 C are illustrated, there may be N-standoffs, where N is an integer of three or more. 
         [0017]      FIG. 2  is a detailed view of  FIG. 1B . In  FIG. 2 , standoff  110 A includes a lip region  130  and a sloped region  135  positioned within baffle  105 . Carrier  115  rests on lip region  130  and is separated from sloped region by a distance “A.” An edge of substrate  125  is separated from an edge of carrier  115  by a distance “B.” Thus the diameter of carrier is equal to the diameter of substrate  125  plus two times the value of “B.” Baffle  105  has a height “C” above lip  130 . In one example, for a 200 mm diameter substrate “A” is about 2 mm, “B” is about 6 mm and carrier  115  has a diameter of about 212 mm. In one example, “C” is selected so gas flowing across the top of baffle  105  will not pick up substrate  125  by Bernoulli forces. In one example, for a 200 mm diameter semiconductor wafer “C” is at least 25 mm. 
         [0018]      FIG. 3  illustrates stacking substrate carriers according to embodiments of the present invention. In  FIG. 3 , four substrate carriers  140  are stacked on a surface  145 . Substrate carriers  140  are similar to substrate carrier  100  of  FIGS. 1A and 1B  except standoffs  110 A,  110 B and  110 C of  FIGS. 1A and 1B  are replaced with standoffs  150 A,  150 B and  150 C respectively (only standoffs  150 A are illustrated in  FIG. 3 ). The difference between standoffs  110 A,  110 B and  110 C and standoffs  150 A,  150 B and  150 C is standoffs  150 A,  150 B and  150 C include notches  151  that will engage the bottom regions of baffles  105 . 
         [0019]      FIG. 4A  is a top view and  FIG. 4B  is a cross-section view thru line  4 B- 4 B of  FIG. 4A  of a substrate carrier according to alternative embodiments of the present invention. In  FIGS. 4A and 4B , a substrate carrier  200  comprises a cylindrical baffle  205 , an annular ring shaped standoff  210  attached to the inside sidewall of baffle  205 , a non-attached carrier plate  215  resting on standoff  210  and optional handles  220 A and  220 B attached to the outside sidewall of baffle  205 . Ultra-thin substrate  125  is illustrated resting on (not bonded or otherwise attached to carrier plate  215 . Carrier plate  215  may be fabricated from glass, metal, ceramic or a non-thinned semiconductor wafer. Materials for baffle  205  and standoff  210  include stainless steel and aluminum 
         [0020]      FIG. 5  illustrates stacking alternative substrate carriers according to embodiments of the present invention. In  FIG. 5 , four substrate carriers  225  are stacked on surface  145 . Substrate carriers  225  are similar to substrate carrier  200  of  FIGS. 4A and 4B  except baffle  210  of  FIGS. 4A and 4B  is replaced with baffle  230  and standoff  210  of  FIGS. 3A and 3B  is replaced with standoff  235 . The difference between standoff  210  and standoff  235  is standoff  235  includes a circular notch  236  that will engage the bottom regions of baffles  230 . Baffles  230  are illustrated with a small number of optional perforations  240  that allow ambient atmosphere to fill the volume between the top surface of a lower substrate  125  and a bottom surface of a higher standoff plate. In one example, perforations  240  account for less than about 10% of the surface areas of baffles  230 . 
         [0021]      FIG. 6  is a cross-section of an alternative baffle that may be used in any of the substrate carriers according to embodiments of the present invention. In  FIG. 6 , a baffle  250  includes a large number of circular perforations  255  that allow a reduced gas flow over substrate  125  (see  FIGS. 1A and 1B  or  4 A and  4 B) such that the Bernoulli effect is reduced so substrate  125  cannot be lifted by the gas flow. In one example, perforations  255  account for between about 25% and about 75% of the surface area of baffle  250 . 
         [0022]      FIG. 7  is a cross-section through a substrate carrier that incorporates a vacuum chuck according to embodiments of the present invention. In  FIG. 7 , a substrate carrier  300  comprises a cylindrical baffle  305 , three identical and equally spaced standoffs  310 A,  310 B and  310 C (only standoff  310 A is illustrated) similarly to standoffs  110 A,  110 B and  110 C of  FIG. 1A  that are attached to the inside sidewall of baffle  305 , a vacuum chuck  315  that serves as a wafer carrier resting on or attached to standoffs  310 A,  310 B and  310 C and optional handles  320 A and  320 B attached to the outside sidewall of baffle  305 . Vacuum chuck  315  may be fabricated from sintered aluminum or any porous metal or ceramic material. In  FIG. 7 , vacuum chuck  315  includes a porous core  330  surrounded on the sides and bottom with a no permeable liner  335 . A vacuum line  340  connects to core  330 . Materials for baffle  305  and standoffs  310 A,  310 B and  310 C include stainless steel and aluminum. 
         [0023]      FIGS. 8A through 8E  illustrate a method of annealing ultra-thin substrates using substrate carriers according to embodiments of the present invention. In  FIG. 8A , a lift block  400  is provided and a substrate carrier  405  is lowered over lift block  400 . In  FIG. 8B , with both lift block  400  and carrier  405  resting on the same surface, the top surface of the lift block  400  is raised above substrate carrier  405 . A substrate  125  resting on but not bonded or otherwise attached to a carrier  410  is lowered onto lift block  400 .  FIG. 8C  illustrates the substrate/carrier combination  125 / 410  resting on lifting block  400 . In  FIG. 8D , substrate carrier  405  is lifted off lifting block  400  and the substrate/carrier combination  125 / 410  (dashed line) is captured by substrate carrier  405  similar to the position of substrate  125  and carrier  115  of  FIG. 1B . Carrier  405  represents any of the carrier embodiments described supra. In  FIG. 8E , a series of substrate/carrier combination  125 / 410  have been stacked in an annealing oven  415 . In one example, substrates  125  are ultra-thin semiconductor substrates having a thickness of 100 microns or less and containing integrated circuit chips that are to be annealed at temperatures of greater than about 250° C. Annealing oven  415  includes a gas input port  420  and a gas output port  425 , a shelf  430 , a heater  435  and a temperature sensor  440 . In one example, substrates  125  are ultra-thin semiconductor substrates containing integrated circuit chips that are to be annealed at temperatures of greater than about 250° C. and the annealing gas is nitrogen or a nitrogen/hydrogen mixture. For stiff and light substrates, the substrate carrier  410  may be eliminated. 
         [0024]    Though the present invention has been described using semiconductor substrates which are circular and a circular substrate carrier, substrate carriers of the embodiments of the present invention may be used for any ultra-thin substrate, such as glass, plastic, metal or ceramic substrates and are not limited to being circular, but may be n-sided (with n being an integer equal to or greater than 3) and/or shaped to conform to the circumference of the substrate. 
         [0025]    The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.