Patent Publication Number: US-10763151-B2

Title: Wafer carrier, method for manufacturing the same and method for carrying a wafer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/873,124, filed on Oct. 1, 2015, and entitled, “WAFER CARRIER, METHOD FOR MANUFACTURING THE SAME AND METHOD FOR CARRYING A WAFER”, which application is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate to a wafer carrier, to a method for manufacturing a wafer carrier and to a method for carrying a wafer. 
     BACKGROUND 
     There are a plurality of concepts for carrying a wafer, like (vacuum) forceps or handling substrates or in general handling means. Examples for such handling means, also referred to as wafer support system, are adhesive films, available from the company  3 M. Such wafer support systems have in common that the wafer is adhered to a foil or another substrate using an adhesive or adhesive pads. The usage of such adhesive layers typically causes adhesive residues remaining at the wafer. Additionally, such layers may cause a gassing product which could have a negative influence onto the wafer. For example, a change with regard to the adhesive properties with respect to metal layers of the semiconductor or growing properties with regard to semiconductor layers may be the result. 
     Therefore, there is a need for an improved approach. 
     SUMMARY 
     Embodiments of the invention provide a wafer carrier. The wafer carrier comprises a first foil for carrying the wafer, the first foil having a perforation, and a second foil. Furthermore, a chamber between the first and second foil is formed, wherein the first and second foils are connected to each other so as to form the chamber. The chamber is configured to be evacuated to form a vacuum in the chamber, the vacuum causes an underpressure (or low pressure or negative pressure) at the perforation so that the underpressure forms a carrying force to the wafer to be carried. 
     A further embodiment provides a method for manufacturing the wafer carrier. The method comprises the steps of providing a first foil for carrying the wafer, the first foil having a perforation; and providing a second foil and connecting the first foil and the second foil to each other so as to form a chamber between the first and the second foils. The chamber is configured to be evacuated to form a vacuum in the chamber, the vacuum causes an underpressure at the perforation so that the underpressure forms a carrying force to the wafer to be carried. 
     A further embodiment provides a method for carrying the wafer. Here, the method comprises the following steps: providing a second foil; providing a first foil for carrying the wafer, the first foil having a perforation; providing the wafer to be carried to the perforation; and connecting the first and the second foils such that an evacuated chamber is formed in between comprising a vacuum, wherein the vacuum causes an underpressure at the perforation such that the underpressure forms a carrying force to the wafer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will subsequently be discussed referring to the enclosed drawings, wherein: 
         FIG. 1 a    shows a schematic representation of a wafer carrier according to a first embodiment; 
         FIG. 1 b    shows a schematic flow chart illustrating a method for carrying a wafer according to a second embodiment; 
         FIG. 2  shows a schematic representation of a wafer carrier according to an enhanced embodiment; 
         FIG. 3 a    shows a schematic representation of a wafer attached to a wafer carrier; 
         FIG. 3 b    shows a schematic cross-section of the wafer of  FIG. 3 a    in combination with the wafer carrier during a main step of the method for carrying the wafer/during the step of fastening the wafer carrier; and 
         FIG. 4  shows a schematic flowchart illustrating the method for manufacturing the wafer carrier. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Below, embodiments of the present invention will subsequently be discussed referring to the enclosed figures, wherein identical reference numerals are provided to objects or elements having the same or similar function so that the description thereof is mutually applicable and interchangeable. 
       FIG. 1  shows a wafer carrier  10  comprising a first foil  12  and a second foil  14 . The two foils  12  and  14  are connected to each other, e.g. via their edges  13   e  such that a chamber  18  is formed in between. 
     In detail, the two foils  12  and  14 , which may have the shape of a square or a round shape, are connected to each other like a sandwich structure. For example, the two foils  12  and  14  may be connected by a rolling connection (cf. reference numeral  13   e ) surrounding the chamber  18  such that the volume within the chamber  18  is encapsulated. Consequently, the chamber  18  would be airproof with exception of the perforation  12   p.    
     Here, the chamber  18  is illustrated as a chamber being filled with a gas, like air. In the case of evacuating the chamber  18 , an underpressure at the perforation  12   p  is caused, wherein the wafer  16  is attached to the first foil  12  in a manner such that the perforation  12   p  is completely covered, a carrying force F c  to the wafer  16  is generated due to the underpressure. Vice versa, this means that the wafer  16  may be carried by generating a vacuum within the chamber  18 . Due to the fact that the wafer  16  covers the perforated portion  12   p , the chamber  18  is sealed. This results in the situation that the vacuum is maintained when the wafer  16  is attached to the first foil  12 . Thus, the wafer remains attached to the wafer carrier  10 . This enables that the wafer  16  may be carried using wafer carrier  10  for several hours or days, wherein the following sequence of steps is used for the “attaching procedure”, which will be discussed with respect to  FIG. 1   b.    
       FIG. 1 b    shows a flowchart of the method  100  comprising the four basic  102 ,  104 ,  106  and  108 . The first step  102  is to provide the second foil  14 , wherein the second step  104  is to provide the first foil  12  having the perforation  12   p . These two foils  14  and  12  are provided on top of each, wherein at this point both are not connected. After that, the third step  106  is performed, namely providing the wafer  16  to the first foil or, in more detail, to the perforation  12   p . Starting from this point, the chamber  18  between the two foils  14  and  12  is filled with gas, wherein the perforation  12   p  is sealed by the wafer  12 . 
     Now, two steps belonging together may be performed in parallel or in series, as illustrated by the step  108 . During the step  108  the chamber  18  is created (cf. step  108   a ) in order to generate an underpressure at the perforation  12   p  holding the wafer  16  using the carrying force. In order to maintain the vacuum within the chamber  18  after performing the method  100 , the two foils  12  and  14  are connected to each other, e.g. using welding, such that the chamber  18  is encapsulated (cf. step  108   b ). 
     Due to the maintaining of the vacuum inside the chamber  18  the shown carrier  10  enables to carry a wafer for a long period, e.g. five hours or five days or even one or two weeks without the usage of adhesive means. Further advantages are that a wafer carried by a first carrier  10  may be switched to a second carrier easily, since releasing the wafer just comprises the step of removing the vacuum within the chamber and not to release an adhesive connection. 
     With respect to the above described method  100  it should be noted that the two steps  108   a  and  108   b  may be performed in parallel or in series or in a mixed manner, e.g. connecting the two foils  12  and  14  with the exception of a smaller portion, evacuating the chamber via the small portion and closing the small portion after the evacuation. 
     With respect to the two above embodiments regarding the wafer carrier and the method for carrying the wafer, it should be noted that these are the basic implementation, wherein improvements, e.g. with respect to the chamber or with respect to the question how to evacuate the chamber, are feasible.  FIG. 2  shows an implementation of the wafer carrier enabling these advantages. 
       FIG. 2  shows a wafer carrier  10 ′ comprising a first perforated foil  12 , also referred to as perforated inlet air foil  12 , the second foil  14 , also referred to as extraction foil  14 , and means  25  for structurally supporting the carrier  10 ′. The means  25  may comprise a grid or a porous plate being arranged between the first foil  12  and the second foil  14 , i.e. in the chamber  18  formed between the two foils. Due to the fact that the grid  25  or the porous plate  25  are permeable to air, it forms a volume (for a gas) enabling that the chamber  18  or, to be exact, the volume ( 18 ) can be evacuated. 
     Just for the sake of completeness, it should be noted that the first foil  12  also has the perforation portion  12   p  by which the wafer  16 , e.g. a silicon wafer, is carried using the force F c . Additionally, here the second foil  14  has a perforation within the edge area marked by the reference numeral  14   p . In case of evacuating the chamber  18  the evacuation may be performed via the perforation  14   p , as will be discussed with respect to  FIG. 3 . 
     The wafer carrier  10 ′ has the advantage that the carrier  10 ′ has an improved stability and good stiffness, such that a carried wafer  16  may be processed easily. For example, the carrier  10 ′ may be used for carrying a wafer  16  during further manufacturing processes like a thinning process using a CMP-machine. Another advantage is that also a broken wafer  16  or fragment of a wafer  16  may be carried due to the increased carrying surface defined by the perforated area  12   p.    
     According to further embodiments, the means  25  for structurally supporting the wafer carrier may be formed by a so-called substrate carrier  25 . According to a first embodiment, the substrate carrier  25  comprises a substrate-supporting region for supporting a substrate; wherein a first portion of the substrate-supporting region comprises a pore network of at least partially interconnected pores; wherein a second portion of the substrate-supporting region surrounds the first portion and comprises a sealing member for providing a contact sealing; at least one evacuation port for creating a vacuum in the pore network, such that a substrate received over the substrate-supporting region is adhered by suction; and at least one valve configured to control a connection between the pore network and the at least one evacuation port, such that a vacuum can be maintained in the pore network; wherein the pore network comprises a first pore characteristic in a first region and a second pore characteristic in a second region different from the first pore characteristic. 
     According to an optional embodiment, the carrier substrate  25  may comprise an evacuation line structure coupling the pore network with the at least one evacuation port and comprising at least one of: an evacuation line at least partially extending into the pore network, an evacuation line at least partially surrounding the pore network. 
     Additionally, the substrate may comprise a recess; and a porous carrier  25  comprising the first portion, wherein the porous carrier  25  is disposed in the recess. The porous carrier  25  may be detachably received in the recess. For example, the substrate carrier  25  may comprise a carrier  25  plate in which the recess is formed. Optionally, the porous carrier  25  physically contacts a bottom of the recess opposite to the substrate supporting region. 
     According to a further embodiment, the first pore characteristic is greater than the second pore characteristic in at least one of: a spatial pore-density, a spatial pore-size and/or a porosity. 
     According to further embodiments, a pore network comprises a gradient in a pore characteristic, wherein the gradient is in a direction from the second region to the first region. Alternatively or additionally, the substrate-supporting region may comprise a further pore network of at least partially interconnected pores, wherein the pore network and the further pore network are spatially separated from each other. 
     According to a further embodiment, the first portion comprises at least one of the following materials: a metal, a ceramic, a glass and/or a polymer. 
     Below, the evacuation of the wafer carrier  10 ′ will be described with respect to  FIGS. 3 a    and  3   b.    
       FIG. 3 a    shows the wafer carrier  100 ′ in a three-dimensional view. As can be seen, the wafer carrier  10 ′ comprises the foil cover  12 + 14  and the structural supporting means  25  enclosed in the foil cover  12 + 14 . The structural support means  25  has a smaller diameter than the foil cover  12 + 14  comprising the first foil  12  and the second foil  14 . Furthermore, the porous plate  25  has preferably, but not necessary, a reduced diameter when compared to the diameter of the wafer  16 , i.e. 145 mm for a 150 mm wafer or 290 mm for a 300 mm wafer. Additionally, it should be noted that the first foil  12  is preferably as large as the second foil  14  in order to simplify the connection process of the two foils  12  and  14  as will be discussed with respect to  FIG. 3   b.    
       FIG. 3 b    shows a cross section through the wafer carrier  10 ′. The layer of the cross section is illustrated in  FIG. 3 a    by the arrow A. As can be seen in  FIG. 3 b   , the two foils  12  and  14  form a sandwich, wherein the support means  25  is arranged in between. The two foils  12  and  14  are directly in contact with each other at the edge region marked by the reference numeral  12 _ 14 _ e , in which the welding is performed. 
     Furthermore, the layer stack comprising the layers  12 ,  25  and  14  is held by an apparatus performing the evacuation and the welding. In detail, the second foil  14  is provided to a plate of the apparatus marked by the reference numeral  30 . After providing the second foil  14 , the plate  25  as well as the foil  12  is provided to the second foil  14  before the wafer  16  is provided to the foil  12  within the perforated area  12   p.    
     According to embodiments, the plate  30  may comprise a ring-shaped nozzle  30   n . This nozzle  30   n  is arranged within the edge region of the plate  30 . Due to the nozzle  30   n , the plate  30   o  has a cavity into which the wafer carrier  10 ′ can be inlaid such that lateral displacement of the wafer carrier  10 ′ can be avoided during the process of evacuating same and/or welding same. Within a portion of the nozzle  30   n , a small channel  30   c  is arranged via which the chamber  18  (comprising the grid or porous plate  25 ) can be evacuated, as illustrated by the arrow marked by the reference numeral  32 . Due to the evacuation of the chamber  18 , the wafer  16  is pulled against and/or attached to the foil  12   p  by the force F c  (cf. arrow marked by F c , resulting from an under pressure at the perforation  12   p ). Here, the extraction of the air from the chamber  18  may be performed via the entire edge region  12 _ 14 _ e  or via a small portion of same. 
     The apparatus further comprises a welding entity  30   w  which can be pressed against the two foils  12  and  14  from the upper side, i.e. from the side opposite to the plate  30 . The welding entity  30   w  is arranged within the edge region  12 _ 14 _ e . The welding entity  30   w  may, for example, be configured to perform plastics welding. This welding is performed by the step of pressing the ring-shaped welding entity  30   w  against the two foils  12  and  14  (cf. arrow  34 ) in the edge region  12 _ 14 _ e , wherein the ring-shaped welding entity  30   w  puts energy into the edge region  12 _ 14 _ e , e.g. pressure energy, thermal energy (using a resistor heater), inductive energy or ultrasonic energy. Preferably the thermal heating and the pressing is performed simultaneously such that the material of the two foils  12  and  14  form a conjunction or connection. Expressed in other words, this means that the welding entity  30   w  is configured to perform ultrasonic welding, inductive welding, thermic welding, friction welding process or another welding type enabling to connect the two foils  12  and  14  within the edge region  12 _ 14 _ e , wherein the other welding type may be selected in dependency on the materials of the two foils  12  and  14 . 
     Alternatively, the connection of the foils  12  and  14  may be made by a gluing process which comprises the substep of arranging an adhesive (glue) between the two foils  12  and  14 . 
     After evacuating the chamber  18  and connecting the two foils  12  and  14 , the vacuum and thus the force F c  is maintained. Due to the force F c , the wafer can be carried and the wafer carrier  10 ′ together with the wafer  16  can be removed from the apparatus  30 , wherein the means  25  for structurally supporting the wafer carrier  10 ′ improve the handling due to the increased stiffness of the entity. Now, the wafer  16  may be processed, e.g. by using thinning technologies or other semiconductor technologies. After processing, the wafer  16  may be removed from the carrier  10 ′ by opening the chamber  18 , e.g. in such a manner that the second foil  14  is cut. As a consequence of the opening of the chamber  18 , the force F c  does not affect the wafer  16  anymore. Vice versa, this means that the wafer carrier  10  or  10 ′ is designed as product for one-time usage. 
     According to further embodiments, the second foil  14  is perforated within the edge region  12 _ 14 _ e  so that the chamber  18  can be evacuated via this perforation and does not have to be evacuated via a channel formed between the two foils  12  and  14 , as illustrated by the embodiment of  FIG. 3   b.    
     According to an alternative embodiment, the two foils  12  and  14  are not connected to each other via welding, but using a zip, wherein a first portion of the zip is formed or integrated into the foil  12  and the second portion of the zip is integrated into the second foil  14 . With respect to the above embodiments, it should be noted that the perforation  12   p  is preferably smaller than the wafer to be carried, i.e. has a diameter of 280 mm in the case of carrying a 300 mm wafer or 140 mm in the case of carrying a 150 mm wafer. Furthermore, it should be noted that the two foils  12  and  14  are preferably larger than the wafer, i.e. 320 mm or 160 mm depending on the wafer size. Other wafer and wafer carrier size combinations are possible. 
     Another embodiment provides a method for manufacturing a wafer carrier which will be illustrated with respect to  FIG. 4 . 
       FIG. 4  shows a flowchart illustrating the method  200  for manufacturing a wafer carrier. The method comprises the first step  104 , the second step  102  and a third step  206 . The steps  102  and  104  are equal to the steps of the method  100 , as discussed with respect to  FIG. 1 b   . The step  206  refers to the step of connecting the first and the second foils so as to form a chamber between the first and the second foil. Here, the two foils are connected in a manner such that the chamber  18  can be evacuated afterwards. Optionally, the method may comprise a step of integrating the above discussed grid or porous wafer into the chamber  18 . 
     Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of a corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of the method steps also represent a description of a corresponding block or item of a feature of a corresponding apparatus. Some or all of the method steps may be executed by (or using) a hardware apparatus. 
     The above described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is therefore the intent be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein.