Abstract:
An apparatus for removing an adhesive layer from a wafer surface includes a chuck, a contact roller, a pick-up roller and a detaping tape. The chuck supports and holds a wafer that has an adhesive layer on its top surface. The contact roller rotates around a first axis and moves linearly along a direction perpendicular to the first axis over the chuck and the supported wafer. The pick-up roller rotates around a second axis, that is parallel to the first axis. The detaping tape rolls around the contact roller and the pick-up roller, and as it rolls it attaches to the adhesive layer, and then is removed together with the adhesive layer. The contact roller has a surface that has a footprint of a circle when rolled along a flat surface.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 61/348,974 filed May 27, 2010 and entitled “APPARATUS AND METHOD FOR DETAPING AN ADHESIVE LAYER FROM THE SURFACE OF ULTRA THIN WAFERS”, the contents of which are expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an apparatus and a method for detaping an adhesive layer from the surface of ultra thin wafers, and more particularly to industrial-scale detaping equipment having a specially designed roller used for detaping the adhesive layer. 
     BACKGROUND OF THE INVENTION 
     Several semiconductor wafer processes include wafer thinning steps. In some applications the wafers are thinned down to a thickness of less than 100 micrometers for the fabrication of integrated circuit (IC) devices. Thin wafers have the advantages of improved heat removal and better electrical operation of the fabricated IC devices. In one example, GaAs wafers are thinned down to 25 micrometers to fabricate power CMOS devices with improved heat removal. Wafer thinning also contributes to a reduction of the device capacitance and to an increase of its impedance, both of which result in an overall size reduction of the fabricated device. In other applications, wafer thinning is used for 3D-Integration bonding and for fabricating through wafer vias. 
     Wafer thinning is usually performed via back-grinding and/or chemical mechanical polishing (CMP). CMP involves bringing the wafer surface into contact with a hard and flat rotating horizontal platter in the presence of liquid slurry. The slurry usually contains abrasive powders, such as diamond or silicon carbide, along with chemical etchants such as ammonia, fluoride, or combinations thereof. The abrasives cause substrate thinning, while the etchants polish the substrate surface at the submicron level. The wafer is maintained in contact with the abrasives until a certain amount of substrate has been removed in order to achieve a targeted thickness. 
     For wafer thicknesses of over 200 micrometers, the wafer is usually held in place with a fixture that utilizes a vacuum chuck or some other means of mechanical attachment. However, for wafer thicknesses of less than 200 micrometers and especially for wafers of less than 100 micrometers, it becomes increasingly difficult to mechanically hold the wafers and to maintain control of the planarity and integrity of the wafers during thinning. In these cases, it is actually common for wafers to develop microfractures and to break during CMP. 
     An alternative to mechanical holding of the wafers during thinning involves attaching a first surface of the device wafer (i.e., wafer processed into a device) onto a carrier wafer and then thinning down the exposed opposite device wafer surface. The bond between the carrier wafer and the device wafer is temporary and is removed upon completion of the thinning and any other processing steps. In some temporary bonding processes, an adhesive layer is used for bonding the carrier wafer to the device wafer. After processing the device wafer, the carrier wafer is debonded and the adhesive layer that remains on the surface of the ultra thin device wafer is removed. 
     Several methods and equipment have been suggested for removing the adhesive layer from the surface of the ultra thin device wafer. However, in many cases the thinned wafers break during the removing of the adhesive layer. Accordingly, there is a need for controlled removal of the adhesive layer from the surface of ultra thin wafers in order to avoid breakage of the thinned wafers. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for removing an adhesive layer from the surface of ultra thin wafers. The apparatus includes a specially designed contact roller for attaching a detaping tape onto the adhesive layer and then removing the detaping tape together with the adhesive layer. 
     In general, in one aspect, the invention features an apparatus for removing an adhesive layer from a wafer surface. The apparatus includes a chuck, a contact roller, a pick-up roller and a detaping tape. The chuck is configured to support and hold a wafer that comprises an adhesive layer on its top surface. The contact roller comprises an elongated cylindrical body extending along a first axis passing through its center and is configured to rotate around the first axis and to move linearly along a direction perpendicular to the first axis over the chuck and the supported wafer. The pick-up roller comprises an elongated cylindrical body extending along a second axis passing through its center and is configured to rotate around the second axis. The second axis is parallel to the first axis and the pick-up roller is arranged at a first distance from the contact roller. The detaping tape is configured to roll around the contact roller and the pick-up roller. The detaping tape is also configured to attach to the adhesive layer and then to be removed together with the adhesive layer. The contact roller comprises a 360° degrees circular surface layer rolled around and attached to its outer cylindrical surface. The contact roller further comprises means for attaching the detaping tape onto the adhesive layer by rotating clock-wise around its axis and linearly moving along a first direction over the wafer and contacting the adhesive layer with the 360° degrees circular surface layer. 
     Implementations of this aspect of the invention may include one or more of the following features. The contact roller further comprises means for removing the detaping tape with the attached adhesive layer by rotating counter-clockwise around its axis and linearly moving along a second direction, opposite to the first direction, over the wafer. The contact roller further comprises means for applying pressure during the attachment of the detaping tape onto the adhesive layer. The 360° degrees circular surface layer comprises a diameter equal to the diameter of the adhesive layer. The 360° degrees circular surface layer comprises a thickness in the range of 1-2 millimeters. The apparatus further includes means for controlling the pressure applied by the contact roller and means for controlling the linear and rotational motion of the contact roller over the wafer, to ensure good contact and adhesion between the detaping tape and the adhesive layer. The applied pressure is in the range of 1-2 psi. The contact roller comprises semi-compliant materials. 
     In general, in another aspect, the invention features a method for removing an adhesive layer from a wafer surface. The method includes the following: First, providing a chuck configured to support and hold a wafer that comprises an adhesive layer on its top surface. Next, providing a contact roller comprising an elongated cylindrical body extending along a first axis passing through its center and being configured to rotate around the first axis and to move linearly along a direction perpendicular to the first axis over the chuck and the supported wafer. Next, providing a pick-up roller comprising an elongated cylindrical body extending along a second axis passing through its center and being configured to rotate around the second axis and wherein the second axis is parallel to the first axis and the pick-up roller is arranged at a first distance from the contact roller. Next, providing a detaping tape configured to roll around the contact roller and the pick-up roller. The detaping tape is configured to attach to the adhesive layer and then to be removed together with the adhesive layer. The contact roller comprises a 360° degrees circular surface layer rolled around and attached to its outer cylindrical surface. Finally, attaching the detaping tape onto the adhesive layer by rotating clock-wise around its axis and linearly moving along a first direction over the wafer and contacting the adhesive layer with the 360° degrees circular surface layer. The method further includes removing the detaping tape with the attached adhesive layer by rotating counter-clockwise around its axis and linearly moving along a second direction, opposite to the first direction, over the wafer. The method further includes applying pressure during the attaching of the detaping tape onto the adhesive layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the figures, wherein like numerals represent like parts throughout the several views: 
         FIG. 1  is an overview schematic diagram of a temporary wafer bonder and debonder system; 
         FIG. 2  is a schematic diagram of a temporary wafer bonding process and a debonding process performed in the bonder and debonder of  FIG. 1 , respectively; 
         FIG. 3  depicts a schematic cross-sectional view of the bonder of  FIG. 1  and a list of the process steps for performing the temporary wafer bonding process of  FIG. 2 ; 
         FIG. 4  depicts a schematic cross-sectional side view of the laser debonding step of  FIG. 2 ; 
         FIG. 5  depicts a schematic cross-sectional side view of the mechanical debonding step of  FIG. 2 ; 
         FIG. 6  is a schematic diagram of the detaping process of  FIG. 2 ; 
         FIG. 7  is a schematic cross-sectional side view of the thinned wafer with the applied detaping tape, according to this invention; 
         FIG. 8  is a schematic diagram of the detaper equipment according to this invention; 
         FIG. 9  is a schematic diagram of the detaper roller of the detaper equipment in  FIG. 8 ; 
         FIG. 10  depicts the beginning of the application of the detaping tape onto the adhesive layer with the equipment of  FIG. 8 ; and 
         FIG. 11  and  FIG. 12  depicts the peeling away of the detaping tape with the attached adhesive layer with the equipment of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , an improved apparatus for temporary wafer bonding  100  includes a temporary bonder  110  and a debonder  120 . Bonder  110  facilitates the temporary bonding process shown in  FIG. 2 . Debonder  120  facilitates the debonding process shown in  FIG. 2 . 
     Referring to  FIG. 2 , temporary bond process  80   a  includes the following steps. First, a surface of the device wafer  20  is coated with an adhesive layer  23  ( 82 ). In one example, adhesive layer  23  is a UV curable adhesive LC3200™, manufactured by 3M Company, MN, USA. The adhesive coated device wafer is then flipped ( 84 ). Next, a light-absorbing release layer  33  is spin-coated on a surface  30   a  of the carrier wafer  30  ( 86 ). In one example, light absorbing release layer  33  is a LC4000, manufactured by 3M Company, MN, USA. Next, the flipped device wafer  20  is aligned with the carrier wafer so that the surface  20   a  of the device wafer with the adhesive layer  23  is opposite to the surface  30   a  of the carrier wafer  30  with the light absorbing release layer  33 . The two surfaces  20   a  and  30   a  are brought into contact and the adhesive layer  23  is cured with UV light ( 87 ). The two wafers are bonded ( 88 ) in temporary bonder  410 , shown in  FIG. 3 . The bond is a temporary bond between the light absorbing release layer  33  and the adhesive layer  23  and is formed under vacuum of 0.1 mbar and low applied bond force. 
     Referring to  FIG. 3 , the carrier wafer  30  with the laser absorbing release layer LTHC layer  33  is placed on the top chuck  412  and held in place by holding pins  413 . Next, the device wafer  20  is placed on the bottom chuck  414  with the adhesive layer  23  facing up. Next, the wafers  20 ,  30  are aligned, the chamber is evacuated, and the top chuck  412  with the carrier wafer  30  is dropped onto the device wafer  20 . A low force is applied for the formation of the bond between the release layer  33  and the adhesive layer  23 . Next, the bonded wafer stack  10  is unloaded and the adhesive is cured with UV light. 
     Referring back to  FIG. 2 , the debond process  80   b  includes the following steps. The bonded wafer stack  10  is mounted onto a dicing frame  25  ( 56 ) and the carrier wafer  30  is illuminated with a YAG laser beam, as shown in  FIG. 4 . The laser beam causes the separation of the wafer stack along the release layer  33  ( 57 ) and the separated carrier wafer  30  is mechanically lifted away from the device wafer  20  ( 58 ) by pushing edge  31  away, as shown in  FIG. 5 . The laser debonding process is a low stress process that utilizes no chemicals and is carried out at room temperature. The mechanical debonding process utilizes very low force. After separation the carrier is recycled, cleaned and reused again. The mechanical debonding operation is described in co-pending application Ser. No. 12/761,014 entitled “Apparatus for mechanically debonding temporary bonded semiconductor wafers” the contents of which are incorporated herein by reference. The adhesive layer  23  is then peeled away from the device wafer surface  20   a  ( 59 ) and the thinned device wafer  20  remains supported by the dicing frame  25 . 
     Following the debonding operation the UV curable adhesive layer  23  is removed via a detaping process  150 . Referring to  FIG. 6 , a detaping tape  155  is applied on top of the exposed adhesive layer  23 . In one example, detaping tape  155  is tape  3305  manufactured by 3M Company. Tape  3305  is a transparent polyester film tape with an aggressive rubber adhesive specifically designed for the removal of silicon backgrinding tape. The detaping tape  155  is pressed onto and attached to the adhesive layer  23  and when the tape  155  is peeled away the adhesive layer  23  is also peeled away from the surface  20   a  of the device wafer  20 . Chemical cleaning may be used to remove any remaining adhesive residue from the device wafer surface  20   a . However, the adhesive residue levels on the device wafer  20  after the removal of the adhesive layer  23  with the detaping process  150  are minimal and usually no post-peel cleaning is required. Removal of the adhesive layer with the detaping process creates very little stress to the thinned wafer and is compatible with low-k dielectrics. 
     One of the problems with the detaping process involves the interference of the detaping tape  155  with the components surrounding the device wafer  20 . In one example, the detaping tape  155  may stick to the frame  25  or to the frame tape  25   a  in the area  26  between the frame  25  and the device wafer  20 . This interference of the detaping tape  155  with the components surrounding the device wafer  20  may cause breakage of the thin device wafer  20  and may prevent the removal of the adhesive layer  23 . In order to avoid this interference between the detaping tape  155  and the components surrounding the device wafer  20  provisions need to be taken to ensure that the detaping tape  155  is only applied and attached to the top surface of the adhesive layer  23  and only in the area above the device wafer  20 , as shown in  FIG. 7   
     Referring to  FIG. 8 , detaper  300  includes a support table  301 , a vacuum chuck  305 , a roller  310  that rolls around axis  303  and moves back and forth above the top surface of table  301  along directions  302   a ,  302   b , a moving stage  306  supporting and moving roller  310  back and for the along direction  302 , a pick-up roller  320  and detaping tape  315 . The device wafer  20  supported by the frame  25  is placed on top of the vacuum chuck  305  and the vacuum chuck  305  is then moved up in the direction  307   a  so that the top surface of the device wafer  20  is brought into contact with the roller  310 . Next, the detaping tape  315  is applied and pressed on the adhesive layer  23  that is attached to the top surface  20   a  of the device wafer  20  by rolling the tape  315  around roller  310  and around pick-up roller  320  while moving stage  306  along direction  302   a . Roller  310  applies pressure on the top surface  20   a  of the device wafer  20  and causes high instant adhesion of the taper  315  to the adhesive layer  23 . The outer cylindrical surface  311  of roller  310  has a 360° degrees circular surface layer  312  rolled around it, as shown in  FIG. 9 . Surface layer  312  has a footprint of a circle when rolled along a flat surface. Circular surface layer  312  is dimensioned to ensured contact of the tape  315  only with the adhesive layer  23  on the top surface  20   a  of the device wafer  20  and no contact with the surrounding components, as shown in  FIG. 10  and  FIG. 11 . Circular surface layer  312  is also dimensioned to ensured application of pressure by the roller  310  only on the area of tape  315  immediately above the top surface  20   a  of the device wafer  20  and no pressure onto the surrounding components. In one example, circular surface layer  312  has a diameter equal to the diameter of the device wafer  20  (50-300 millimeters) and a thickness of the order of 1-2 millimeters. The pressure applied by the roller  310  and the speed of the translational motion along direction  302   a  and of the rotational motion around axis  301  are controlled to ensure good contact and adhesion between the tape  315  and the adhesive layer  23 . In one example, the pressure applied by the roller is of the order of 1-2 psi and the time it takes for the traversing of the roller  310  is of the order of 15-30 seconds. 
     After the tape  315  is applied and adhered to the adhesive layer  23  on the top surface  20   a  of the device wafer  20 , the direction of the roller stage  306  translation is reversed to  302   b  and the tape  315  with the attached adhesive layer  23  is peeled away from the top surface  20   a  of the device wafer  20  and is rolled onto the pick-up roller  320 , as shown in  FIG. 12 . Finally, after the adhesive layer  23  is peeled away from the top surface  20   a  of the device wafer  20 , the vacuum chuck  305  is moved down along  307   b  and the device wafer supported on the frame  25  is unloaded. Roller  310  is made of semi-compliant metallic or ceramic materials. 
     Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.