Abstract:
A process for manufacturing low-profile and flexible integrated circuits includes manufacturing an integrated circuit on a wafer having a thickness larger than the desired thickness. After the integrated circuit is manufactured the integrated circuit may be released with a portion of the wafer leaving a remainder of the bulk portion of the wafer. A second integrated circuit may be manufactured on the remainder of the wafer and the process repeated to manufacture additional integrated circuits from a single wafer. The integrated circuits may be released from the wafer by etching vias through the integrated circuit and into the wafer. The via may be used to start an etch process inside the wafer that undercuts the integrated circuit separating the integrated circuit from the wafer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application under 35 U.S.C. §371 that claims priority to PCT Application No. PCT/US2012/046205 to King Abdullah University of Science and Technology filed Jul. 11, 2012, which claims priority to U.S. Provisional Application No. 61/506,495 filed Jul. 11, 2011, both of which are specifically incorporated herein by reference without disclaimer. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to integrated circuits and more particularly relates to manufacturing integrated circuits. 
     2. Description of the Related Art 
     Conventionally, integrated circuits are manufactured on thick semiconductor wafers. Semiconductor wafers such as silicon and gallium arsenide are preferred materials for integrated circuits because of their electrical properties. Thick wafers are conventionally preferred for their ability to withstand the processing and handling required to manufacture integrated circuits on the semiconductor wafers. The thickness of the semiconductor wafers may be significantly reduced with little impact to the electronic behavior of the integrated circuit built on the wafers. In fact, manufacturing on thin wafers may be preferred over thick wafers due to lower cost of materials and the lower profile of the devices incorporating the integrated circuits manufactured on thin wafers. For example, smaller and more flexible devices may be manufactured on thin wafers. However, manufacturing integrated circuits on thin wafers presents problems with poor yield due to the fragility of the thin wafers. 
     One conventional solution for manufacturing integrated circuits on thin wafers is backgrinding the wafer as illustrated in  FIGS. 1A and 1B .  FIG. 1A  illustrates a wafer  100  having devices  102  comprising an integrated circuit. The devices  102  are manufactured according to conventional methods on the wafer  100 . After manufacturing is complete the wafer  100  is backgrinded through section  104  to reduce the thickness of the wafer  100 . Although the end product is an integrated circuit on a thin wafer, a significant amount of the wafer was destroyed during the backgrinding. Thus, the cost of the integrated circuit of  FIG. 1A  is higher than a conventional thick wafer because the same amount of material was consumed in manufacturing and the manufacturing included additional steps compared to conventional manufacturing of integrated circuits on thick wafers. 
     Another conventional solution for manufacturing integrated circuits on thin wafers is through use of a carrier wafer as illustrated in  FIGS. 2A and 2B . In  FIG. 2A  a thin wafer  202  is attached to a carrier wafer  206  through an adhesive  204 . Manufacturing of integrated circuits on the thin wafer  202  is substantially similar to conventional manufacturing on thick wafers because the carrier wafer  206  provides support for the thin wafer  202 . After devices  210  are manufactured on the thin wafer  202  the thin wafer  202  is released from the carrier wafer  206  as shown in  FIG. 2B . Although the final product is an integrated circuit manufactured on a thin wafer, the manufacturing process is more costly due to the additional materials and processing steps involved in attaching and detaching the carrier wafer. Additionally, some conventional manufacturing processes have to be adapted to prevent early dissolution of the adhesive  204 . For example, the adhesive  204  should not be exposed to high temperatures or certain chemicals. Further, additional cleaning steps may be necessary to remove residue of the adhesive  204  from the thin wafer  202 . 
     In addition to having low profiles suitable for mobile devices, thin wafers may also allow manufacturing flexible electronics. Conventional solutions for manufacturing flexible electronics involve manufacturing devices on organic substrates such as polymers or depositing semiconductor layers on polymers. However, devices manufactured on polymers may have different electrical characteristics than devices manufactured on conventional semiconductor wafers because the electronic characteristics of the polymers or the crystal structure of semiconductors deposited on polymers are different than conventional semiconductor wafers. 
     SUMMARY OF THE INVENTION 
     A method for manufacturing is presented. In one embodiment, the method includes manufacturing an integrated circuit on at least a portion of a surface of a wafer. The method also includes etching at least one via into the wafer. The method further includes releasing at least the portion of the wafer having the manufactured integrated circuit from a bulk portion of the wafer. 
     Another method for manufacturing is presented. In one embodiment, the method includes manufacturing a first integrated circuit on a wafer. The method also includes releasing a first thickness of the wafer including the first integrated circuit from the wafer. The method further includes manufacturing a second integrated circuit on the wafer. The method also includes releasing a second thickness of the wafer including the second integrated circuit from the wafer. 
     The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. 
     The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. 
     The term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment “substantially” refers to ranges within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5% of what is specified. 
     The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”) and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes” or “contains” one or more steps or elements possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes” or “contains” one or more features possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed. 
     Other features and associated advantages will become apparent with reference to the following detailed description of specific embodiments in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. 
         FIGS. 1A and 1B  are block diagrams illustrating manufacturing integrated circuits on thin wafers using a conventional backgrinding method. 
         FIGS. 2A and 2B  are block diagrams illustrating manufacturing integrated circuits on thin wafers using a conventional carrier wafer method. 
         FIGS. 3A-3F  are block diagrams illustrating an exemplary manufacturing process for manufacturing low-profile integrated circuits according to one embodiment of the disclosure. 
         FIG. 4  is a flow chart illustrating an exemplary manufacturing process for manufacturing low-profile integrated circuits according to one embodiment of the disclosure. 
         FIGS. 5A-5D  are block diagrams illustrating an exemplary manufacturing process for manufacturing multiple low-profile integrated circuits from a single wafer according to one embodiment of the disclosure. 
         FIG. 6  is a flow chart illustrating an exemplary manufacturing process for manufacturing multiple low-profile integrated circuits from a single wafer according to one embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various features and advantageous details are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well known starting materials, processing techniques, components, and equipment are omitted so as not to unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and/or rearrangements within the spirit and/or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure. 
     A method of manufacturing low-profile integrated circuits on conventional semiconductor wafers is presented that results in a reduced waste of materials, reduced impact on other manufacturing processes, and reduced cost. Manufacturing of an integrated circuit may be performed on a wafer according to conventional or other processes. The wafer may have a sufficient thickness to withstand the manufacturing processes. After the integrated circuit is manufactured on the wafer a top portion of the thickness of the wafer, including the integrated circuit, may be released from the wafer. According to one embodiment, the top portion of the wafer may be released through an undercut technique. The released top portion of the wafer is an integrated circuit having a low-profile. The low-profile integrated circuit may be used, for example, to create mobile devices or another device having a small form factor. The low-profile integrated circuit may also be used in flexible electronics. The remaining portion of the wafer may be recycled and another integrated circuit manufactured on the top of the remaining portion of the wafer. This integrated circuit may be released from the wafer and the process of additional manufacturing integrated circuits may continue on the wafer. 
       FIGS. 3A-3F  are block diagrams illustrating an exemplary manufacturing process for manufacturing low-profile integrated circuits according to one embodiment of the disclosure. The block diagrams of  FIGS. 3A-3F  will be described with reference to  FIG. 4 , which is a flow chart illustrating an exemplary manufacturing process for manufacturing low-profile integrated circuits according to one embodiment of the disclosure. A method  400  for manufacturing a low-profile integrated circuit beings at block  402  with manufacturing an integrated circuit on a wafer.  FIG. 3A  is a block diagram illustrating a wafer  300  after manufacturing an integrated circuit having devices  302 . According to one embodiment, the wafer  300  may be a silicon wafer having a crystal orientation of &lt;100&gt;. However, the wafer  300  may be other materials such as gallium arsenide. According to one embodiment, the wafer  300  may be a conventional thickness wafer. However, the wafer  300  may be any wafer having a thickness greater than the desired thickness of the integrated circuit. 
     At block  404  a protective layer is deposited on the wafer  300 .  FIG. 3B  is a block diagram illustrating the wafer  300  after a protective layer  310  is deposited on the wafer  300 . The protective layer  310  may be, for example, a conformally deposited layer of silicon oxide (SiO x ) or silicon nitride (SiN x ). The protective layer  310  may be deposited by chemical vapor deposition (CVD), physical vapor deposition (PVD) such as sputtering, atomic layer deposition (ALD), and/or electrodeposition. The protective layer  310  may also include multiple materials. For example, the protective layer  310  may include a layer of silicon oxide and a layer of silicon nitride. The protective layer  310  may be used as a hard mask for later etching processes. Thus, the material for the protective layer  310  may be selected according to the material of the wafer  300  and the etching process to obtain a desired etching ratio of the protective layer  310  to the wafer  300 . 
     At block  406  at least one via is etched into the wafer.  FIG. 3C  is a block diagram illustrating the wafer  300  after vias  320  are etched into the wafer  300 . The vias  320  may be created by first patterning the protective layer  310  and then performing a deep reactive ion etch (DRIE) of the wafer  300  using the patterned protective layer  310  as a hard mask. According to one embodiment, a photoresist layer (not shown) is used to pattern the protective layer  310 . Any photoresist remaining after patterning the protective layer may also be used as a mask for patterning the vias  320 . The depth of the vias  320  may be selected based, in part, on the desired thickness for the released portion of the wafer  300 . According to one embodiment the vias  320  are designed to extend through a region of the wafer  300  between the devices  302 . According to another embodiment, the vias  320  may be designed around the integrated circuit having the devices  302 . For example, the vias  320  may form a pattern around the edges of the integrated circuit made up by the devices  302 . According to one embodiment, the vias  320  may be formed with only one additional photomask. Additionally, the vias  320  may form a pattern in the center of the integrated circuit made up by the devices  302 . In this embodiment, the layout of the devices  302  may remain substantially the same as when manufactured with other processes. 
     At block  408  a barrier layer is deposited in the at least one via.  FIG. 3D  is a block diagram illustrating the wafer  300  after a barrier layer  330  is deposited in the vias  320 . The barrier layer  320  may be silicon dioxide. According to one embodiment, the barrier layer  320  is grown by thermally oxidizing the wafer  300 . The barrier layer  320  may also be deposited through other techniques such as CVD, PVD, ALD, and/or electrodeposition. 
     At block  410  the barrier layer is removed from a bottom surface of the at least one via.  FIG. 3E  is a block diagram illustrating the wafer  300  after the barrier layer  330  is removed from a bottom surface of the vias  320 . According to one embodiment, a highly directional etch, such as reactive ion etching (RIE) at low pressure and high energy may be used for removing the barrier layer  330  from the bottom surface of the vias  320 . After the barrier layer  330  is removed from the bottom surface of the vias  320  the bulk potion of the wafer  300  is exposed. 
     At block  412  a portion of the wafer having the integrated circuit is released from the wafer.  FIG. 3F  is a block diagram illustrating the wafer  300  after etching the wafer  300  through the vias  320 . An isotropic etch of the wafer  300  through the bottom surface of the vias  320  after removing the barrier layer  330  results in etching of the wafer  300  in all directions at a substantially similar rate. After a period of time, the etching starting from the bottom surface of at each of the vias  320  intersects causing a top portion  300   a  of the wafer  300  to detach from a bottom portion  300   b . According to one embodiment, isotropic etching is performed with xenon difluoride (XeF 2 ). According to another embodiment, a wet isotropic etch may be performed. According to yet another embodiment, the wafer  300  may include a boron doped buried region (not shown), which may act as an etch stop during etching of the wafer  300 . Although isotropic etching is described with reference to the embodiment of  FIG. 3F , anisotropic etching may be used in other embodiments. According to one embodiment, an anisotropic etch of the wafer  300  may be performed. For example, if the wafer  300  is silicon with a &lt;111&gt; crystal orientation then a potassium hydroxide (KOH) etch may be used. 
     The top portion  300   a  of the wafer  300  may be further processed to create an electronic device. For example, the top portion  300   a  may be packaged. Because the top portion  300   a  has a low-profile the integrated circuit comprising the devices  200  may be suitable for small form factor devices such as mobile phones. Additionally, the integrated circuit may be employed in flexible electronics. Because the low-profile integrated circuit was manufactured from a conventional thickness wafer little to no alteration of the manufacturing process for the integrated circuit may be necessary. Instead, in the conventional manufacturing processes for thin wafers well-understood manufacturing processes are adapted to account for thin wafers or carrier wafer adhesives. 
     The exemplary manufacturing process described above for low-profile integrated circuits also allows recycling of the wafer materials. For example, after the top portion  303   a  is removed from the wafer  300 , the bottom portion  303   b  may be used for manufacturing additional integrated circuits. According to one embodiment, additional circuits may be manufactured on the bottom portion  303   b  and packaged as another electronic device. A polishing step may be performed to remove roughness from the wafer  300  after each portion of the wafer  300  is released. For example, the bottom portion  303   b  may be polished before additional integrated circuits are manufactured on the bottom portion  303   b . According to another embodiment, additional circuits may be manufactured on the bottom portion  303   b  and released from the wafer  300  similar to the top portion  303   a.    
       FIGS. 5A-5D  are block diagrams illustrating an exemplary manufacturing process for manufacturing multiple low-profile integrated circuits from a single wafer according to one embodiment of the disclosure. The block diagrams of  FIGS. 5A-5D  will be described with reference to  FIG. 6 , which is a flow chart illustrating an exemplary manufacturing process for manufacturing multiple low-profile integrated circuits from a single wafer according to one embodiment of the disclosure. A method  600  begins at block  602  with manufacturing a first integrated circuit on a wafer.  FIG. 5A  is a block diagram illustrating a first integrated circuit  510  having devices  502  manufactured on a wafer  500 . 
     At block  604  a first thickness of the wafer is released from the wafer such that the first integrated circuit  510  and devices  502  are separated from the wafer  500 .  FIG. 5B  is a block diagram illustrating a first thickness  500   a  of the wafer  500 , including the first integrated circuit  510 , released from the wafer  500 . The first thickness  500   a  may be released through patterning vias and etching the wafer  500  as described above with reference to  FIGS. 3A-3F  and  4 . 
     At block  606  the wafer may be polished to improve electrical properties and yield of manufactured devices on the remaining portion of the wafer  500 . 
     At block  608  a second integrated circuit is manufactured on the wafer.  FIG. 5C  is a block diagram illustrating a second integrated circuit  520  having devices  512  manufactured on the wafer  500 . The second integrated circuit  520  may be the same circuit as the first integrated circuit  510  or a different circuit. 
     At block  610  a second thickness of the wafer is released from the wafer such that the second integrated circuit is separated from the wafer.  FIG. 5D  is a block diagram illustrating a second thickness  500   b  of the wafer  500 , including the second integrated circuit  520 , released from the wafer  500 . The release may be performed through a method as described above with reference to  FIGS. 3A-3F  and  4 . 
     The method  600  may continue by manufacturing additional integrated circuits from the wafer and releasing the additional integrated circuits from the wafer. The method  600  may continue until the wafer is depleted and there is insufficient wafer remaining to manufacture additional integrated circuits. According to one embodiment, the released first integrated circuit and second integrated circuit may be packaged together in a stacked integrated circuit. 
     The exemplary methods described above for manufacturing low-profile electronic devices and flexible electronics devices may be used in implantable biomedical devices, renewable energy devices, biomimic-robotic devices, and/or flexible displays. The low-profile device manufacturing process allows construction of devices with little to no modification of manufacturing processes to accommodate for thin wafers. Additionally, the exemplary processes reduce wasted materials by allowing for multiple integrated circuits to be manufactured from a single wafer. 
     The schematic flow chart diagrams of  FIGS. 4 and 6  are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of one embodiment of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown. 
     All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the apparatus and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. In addition, modifications may be made to the disclosed apparatus and components may be eliminated or substituted for the components described herein where the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.