PATENT DOCUMENT

Publication Number: US-9053952-B2
Application Number: US-201213631769-A
Country: US
Kind Code: B2

Title: Silicon shaping

Abstract:
One embodiment for forming a shaped substrate for an electronic device can form a shaped perimeter to define the substrate shape on the surface of a substrate. The shaped perimeter can extend at least part way into the substrate. A subsequent thinning process can remove substrate material and expose the shaped perimeter effectively forming shaped dies from the substrate.

Claims:
What is claimed is: 
     
       1. A method for forming a shaped die from a substrate, the substrate including at least one circuit element, the method comprising:
 forming a trench partially extending through a thickness of the substrate, the trench defining a first edge of the shaped die and a second edge the shaped die opposite the first edge, wherein a terminal end of the trench includes an elongated cavity that chamfers the second edge; 
 attaching a handle to the substrate; 
 thinning the substrate such that the trench extends all the way through the thickness of the substrate; and 
 separating the shaped die from a remaining portion of the substrate by removing the handle. 
 
     
     
       2. The method of  claim 1 , wherein forming the trench involves direct ion reactive etching of the substrate. 
     
     
       3. The method of  claim 1 , wherein forming the trench involves defining a perimeter of the shaped die, the perimeter including a curved corner. 
     
     
       4. The method of  claim 1 , wherein forming the trench involves chamfering the first edge of the shaped die. 
     
     
       5. The method of  claim 1 , wherein the trench defines a perimeter of each of a plurality of shaped dies on the substrate. 
     
     
       6. The method of  claim 1 , further comprising, prior to separating the shaped die, forming a second trench that intersects the trench. 
     
     
       7. The method of  claim 1 , wherein the thinning is performed by back-grinding the substrate. 
     
     
       8. A method of forming a shaped die from a substrate, the shaped die configured to support an integrated circuit, the method comprising:
 etching a trench partially through the substrate, the trench defining a first edge of the shaped die and a second edge of the shaped die opposite the first edge, wherein the etching forms a first chamfer along the first edge and a second chamfer along the second edge; 
 coupling a handle to the shaped die; and 
 thinning the substrate such that the trench extends through an entire thickness of the substrate; and 
 separating the shaped die from the handle. 
 
     
     
       9. The method of  claim 8 , wherein etching the trench includes defining a perimeter of the shaped die, wherein the perimeter includes a rounded corner. 
     
     
       10. The method of  claim 8 , wherein etching the trench includes defining a perimeter of the shaped die, wherein the perimeter includes a cut out area configured to accommodate a component within an electronic device. 
     
     
       11. The method of  claim 8 , wherein etching the trench includes defining a perimeter of the shaped die, wherein the perimeter has an annular shape. 
     
     
       12. The method of  claim 11 , wherein the annular shape includes an opening for accommodating a feature of an electronic device. 
     
     
       13. The method of  claim 8 , wherein forming the trench involves direct ion reactive etching of the substrate. 
     
     
       14. The method of  claim 8 , wherein a second shaped die is formed from the substrate, the method further comprising:
 etching a second trench adjacent the trench, the second trench defining a first edge of the second shaped die and a second edge of the second shaped die opposite the first edge of the second shaped die, wherein etching the second trench chamfers the first edge and the second edge of the second shaped die. 
 
     
     
       15. The method of  claim 8 , wherein a plurality of shaped dies are formed from the substrate, wherein each of the plurality of shaped dies is defined by a corresponding trench. 
     
     
       16. The method of  claim 8 , wherein a second shaped die is formed from the substrate, wherein etching the trench defines a first edge of the second shaped die and a second edge of the second shaped die opposite the first edge, wherein etching the trench chamfers the first edge and the second edge of the second shaped die. 
     
     
       17. The method of  claim 8 , wherein prior to separating the shaped die, forming a second trench that intersects the trench.

Description:
FIELD OF THE DESCRIBED EMBODIMENTS 
     The described embodiments relate generally to integrated circuits and more particularly to integrated circuits with shaped substrates. 
     BACKGROUND 
     Integrated circuits have long become a mainstay of many electronic designs. Many items such as processors, memories, custom electronic designs including application specific integrated circuits (ASICs), field programmable gate arrays and sensors use integrated circuit device technology to manufacture these items. Integrated circuit technologies can produce devices en masse, typically on a substrate commonly referred to as a wafer. Individual devices can be separated from the wafer to form dies that include the device. Dies commonly have a square or rectangular shape. This shape is largely an artifact of the sawing technique that is used to separate individual dies from an original substrate. 
     Often, the initial substrate can be too thick for a particular application. To address substrate thickness, the substrate can be subsequently thinned as one of the final manufacturing steps. Thinned substrates can be very thin, often 200 microns or less. Consequently, the thinned substrate can be more fragile than regular substrate. Furthermore, the square or rectangular shapes of the dies can exacerbate substrate damage, particularly when the substrates are handled after manufacture, but before installation into a device or product. Sharp corners of the die can be prone to damage and can incur fractures to the substrate and can contribute to device failures. 
     Therefore, what is desired is a way to easily produce thinned integrated circuit substrates without sharp corners to help reduce fractures and damage that can occur on the substrate. 
     SUMMARY OF THE DESCRIBED EMBODIMENTS 
     This paper describes various embodiments that relate to shaped substrates that can be used for integrate circuits or sensors. In one embodiment, a method for forming a shaped integrated circuit can include the steps of receiving a substrate, forming a curvilinear trench that can partially extend into the substrate and define a shape of the shaped substrate and attaching a handle to the received substrate. Next, the substrate can be thinned until the formed trenches are exposed and individual dies are formed. The handle can be removed and the individual dies are released. 
     In another embodiment, an integrated circuit substrate can include multiple integrated circuit areas and a curvilinear trench formed around each integrated circuit area where the trench only projects part way through the substrate. 
     In yet another embodiment, computer code for forming a shaped substrate can include code for receiving an integrated circuit substrate, computer code for forming a curvilinear trench that defines a die area and computer code for thinning the received substrate. 
     Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The described embodiments and the advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings. These drawings in no way limit any changes in form and detail that may be made to the described embodiments by one skilled in the art without departing from the spirit and scope of the described embodiments. 
         FIG. 1  is a simplified prior art diagram of a substrate for forming integrated circuits. 
         FIG. 2  is a simplified diagram of shaped dies disposed on a substrate in accordance with one embodiment described in the specification. 
         FIG. 3  is an illustration of cross section A-A shown in  FIG. 2 . 
         FIG. 4  is an illustration of the cross section A-A after a handle object is attached to the substrate. 
         FIG. 5  is an illustration of the cross section A-A showing a thinned substrate. 
         FIG. 6A  is an illustration of the cross section A-A showing a released die after handle is removed. 
         FIG. 6B  shows a possible top view of die in  FIG. 6A . 
         FIG. 7A  shows a cross section of a substrate with a shaped perimeter that can include additional shaping features. 
         FIG. 7B  shows a cross section of the substrate in  FIG. 7A  after the substrate has been thinned. 
         FIG. 8  is a cross sectional view of a substrate showing another embodiment of a shaped substrate. 
         FIGS. 9A and 9B  can show other curvilinear shapes that can be used for a shaped substrate. 
         FIGS. 10A and 10B  illustrate another embodiment of a shaped substrate. 
         FIG. 11  is an example of a shaped substrate system. 
         FIG. 12  is a flow chart of method steps for forming a shaped substrate in accordance with one embodiment described in the specification. 
         FIG. 13  is a block diagram of an electronic device suitable for controlling some of the processes in the described embodiment 
     
    
    
     DETAILED DESCRIPTION OF SELECTED EMBODIMENTS 
     Representative applications of methods and apparatus according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
     In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments. 
     Substrates used for integrated circuits, sensors and similar devices can often be thinned to fulfill one or more physical requirements for a final application. The thinned substrate based devices can be relatively more fragile compared to their non-thinned counterparts. For example, thinned substrates can be more easily chipped, cracked or fractured compared to regular substrates. 
     Devices based on thinned substrates are typically formed en masse on a wafer. The devices are typically separated with a sawing operation that creates square or rectangular dies. Unfortunately, the relatively sharp corners that are a result of the sawing operation can be subject to damage as the thinned substrate is handled. Cracks and fractures can originate from the corners and can damage the device and adversely affect device yield. 
     One approach to improve the robustness of thin substrate based devices can address the final shape of the thin substrate. In one embodiment, a shaped perimeter can be formed on the substrate prior to a thinning operation where the shaped perimeter can be used to define the final shape of the resulting device. The shaped perimeter can include rounded corners that can improve the robustness of the thinned device. 
       FIG. 1  is a simplified prior art diagram of a substrate  100  for forming integrated circuits. In one embodiment, the substrate  100  can be silicon. In other embodiments, the substrate can be gallium arsenide or any other technically feasible material. Integrated circuits can be formed on the substrate and located within integrated circuit areas that can later be separated from the substrate  100  to form dies  102 . Dies are often separated from the substrate  100  with a saw such that the resultant dies  102  are rectilinear in shape. These dies  102  can include sharp corners as shown in  FIG. 1 . Sharp corners can allow relatively more stress to be subjected to the die  102  during handling and allow stress induced failures to occur, thereby limiting part yields. 
     One approach to reducing stress induced failures on a die seeks to replace traditionally sawn dies that include sharp corners with shaped dies that can include rounded corners. In one embodiment, dies can be shaped by forming a shaped perimeter around the die. The perimeter can take the form of a trench that extends partially through the substrate  100 . After forming the shaped perimeter, a handle can be affixed to the substrate and the substrate can subsequently be thinned. In one embodiment, the shaped perimeter features can be exposed by the thinning and the outline of the dies can take the form of the shaped perimeter. After the thinning step, the handle can be removed and the dies can be separated and can undergo further processing for packaging or bond wire fixture, for example. 
       FIG. 2  is a simplified diagram  200  of shaped dies disposed on a substrate in accordance with one embodiment described in the specification. The outline of the substrate has been omitted from  FIG. 2  to simplify the illustration. Each die  202  can include a shaped perimeter  204 . In one embodiment, the shaped perimeter  204  can be formed with trenches that can extend at least partially into the substrate. As shown, each die can be associated with a shaped perimeter  204 . The shaped perimeter  204  can used to define die edges and can separate the dies  202  from the substrate, particularly when the shaped perimeter  204  is formed with a trench. Furthermore, the shaped perimeter can allow rounded edges to be formed on the dies  202  that can reduce stress induced failures on dies.  FIGS. 2  though  FIGS. 6A-6B  can show the shaped substrate at different intermediate steps of formation. 
       FIG. 3  is an illustration  300  of cross section A-A shown in  FIG. 2 . The die  202  is shown disposed between shaped perimeters  204 . The shaped perimeter  204  is shown in the figure as trenches partially extending through substrate  302 . In one embodiment, the shaped perimeter  204  can be formed with deep ion reaction etch (DRIE) techniques. DRIE techniques can provide very high aspect ratio features such as this relatively tall and relatively narrow shaped perimeter  204  feature as shown. 
       FIG. 4  is an illustration  400  of the cross section A-A after a handle object is attached to the substrate  302 . Subsequent thinning of the substrate can require that a handle  404  be attached to substrate  302 . The handle  404  can provide stability as well as a means to support the substrate  302  during the thinning process. In one embodiment, the handle  404  can be formed from a borosilicate glass. In another embodiment, the handle can be formed from silicon, or gallium arsenide. Any technically feasible material can be used for the handle  404  provided the handle  404  includes a thermal coefficient of expansion relatively similar to that of the substrate  302  and can withstand processing steps along with substrate  302 . Adhesive  402  can be used to bond handle  404  to substrate  302 . Any technically feasible adhesive can be used. In one embodiment an ultra violet releasable adhesive can be used, particularly when the handle  404  is formed from a transparent or translucent material such as glass or borosilicate glass. 
       FIG. 5  is an illustration of the cross section A-A showing a thinned substrate  502 . In one embodiment, the substrate  302  in  FIG. 4  can be ground to form thinned substrate  502  and expose the shaped perimeter  204  features. As shown, handle  404  can remain be attached to thinned substrate  502  with adhesive  402 . The thinned substrate  502  shows the dies  202  separated from each other. The shaped perimeter  204  can become the shaped outline of the die  202 . In one embodiment, the shape of the perimeter  204  is not constrained to linear or rectilinear shapes, but can be relatively arbitrary. In one embodiment, the shaped perimeter  204  can be a curvilinear shape and can include round corners. 
       FIG. 6A  is an illustration of the cross section A-A of substrate  600  showing a released die  602  after handle  404  is removed. In one embodiment, handle  404  can be released from dies  602  as described above in  FIG. 4 .  FIG. 6B  shows a possible top view of die  602 . The outline of  602  can be the shaped perimeter  204 . 
       FIG. 7A  shows a cross section of a substrate  302  with a shaped perimeter  204  that can include additional shaping features. In one embodiment, an upper portion of the shaped perimeter  204  can receive chamfers  706 . Chamfers  706  introduced on the upper surface of the substrate  302  can remove sharp corners that will be exposed when die  702  is singulated in later steps. In one embodiment, chamfers  706  can be formed by any technically feasible means such as DRIE. Similarly, elongated chambers or cavities  704  can be formed on the bottom of the shaped perimeter  204 . These cavities  704  can also form chamfers that are exposed when the substrate  302  is thinned.  FIG. 7B  shows a cross section of the substrate in  FIG. 7A  after the substrate  302  has been thinned. Die  702  can include chamfers  706  on a first surface and chamfers  710  on a second surface. The chamfers  710  on the second surface can be the portion of the cavity  704  that was not removed by the thinning of substrate  302 . 
       FIG. 8  is a cross sectional view  800  of a substrate showing another embodiment of a shaped substrate. In this embodiment, the process described by  FIG. 3  and  FIG. 4  can be used to form shaped perimeters  204  and to bond handle  404  to the substrate  302 . The shaped perimeters  204  can be extended beyond the amount shown in  FIG. 4  by forming additional shaped perimeters  802  on a surface opposed to the initial surface receiving the shaped perimeters  204 . In one embodiment, additional shaped perimeters  802  can be substantially similar to shaped perimeter  204  and can intersect and connect with shaped perimeters  204 . In this fashion, a complete trench can be formed that extends from a first side of the substrate  302  to a second side of the substrate  302 . In one embodiment, the additional shaped perimeters  802  can be formed with DRIE. Subsequent processing steps can include substrate  302  thinning and handle  404  removal as describe above. 
       FIGS. 9A and 9B  can show other curvilinear shapes that can be used for a shaped substrate. Shaped substrates can include shapes that can be arbitrarily complex and can include cut-outs and curves that can enable the shaped substrate to fit more easily within a fixture, a machine or a product.  FIG. 9A  shows a C shaped die  902  having outer perimeter  904  formed on a substrate. The large cut-out area  908  can allow the C shaped die  902  to fit around standoffs, screws, mounting points or other features that may otherwise make the positioning of the C shaped die  902  relatively more difficult. Although such die shapes may not be efficient in terms of die utilization, the design may not be die usage constrained. For example, in some embodiments, inefficient utilization of die area can be an acceptable tradeoff for mounting ease. C shaped die  902  can also include a chamfered corner  906  as shown with a dotted line. The chamfered corner  906  can also reduce sharp corners.  FIG. 9B  shows yet another embodiment of a shaped substrate. In this embodiment, the die  910  can be shaped like an annular ring. In this embodiment, circular perimeters  912  and  914  can define the die shape  910 . This embodiment may be useful for positioning within a product that can include a mounting screw or feature in the center of die  910 . 
       FIGS. 10A and 10B  illustrate another embodiment  1000  of a shaped substrate. In this embodiment, the shaped perimeters  204  shown in  FIG. 2  have been combined between adjacent dies  1002 . Thus, a shaped perimeter  1004  can be shared between two or more dies  1002 . In one embodiment, the shared shaped perimeter  1004  can offer an advantage with respect to die usage efficiency by requiring less substrate area to be used for shaped perimeters  1004 .  FIG. 10B  shows cross section B-B for  FIG. 10A . The shared shaped perimeter  1004  is more clearly shown surrounding die  1005 . Although not shown here, the steps described in  FIG. 3-FIG .  8  can be applied to this embodiment as well. For example, chamfered shaped perimeters as describe in  FIG. 7A  can be added to shaped perimeter  1004 . 
       FIG. 11  is an example of a shaped substrate system  1100 . In this example, shaped substrate  1104  can be used in conjunction with other electrical components  1106  on a printed circuit board  1102 . In one embodiment, the shaped substrate  1104  can enable advantageous placement of electrical components  1106  such that trace length may be improved between electrical components  1106  and shaped substrate  1104 . 
       FIG. 12  is a flow chart of method steps for forming a shaped substrate in accordance with one embodiment described in the specification. The method can begin in step  1202  where the substrate is received. In step  1204 , perimeters can be formed on the substrate. In one embodiment, the perimeters can be curvilinear shapes that can partially extend into the substrate. In step  1206 , a handle can be attached to the substrate to increase substrate stability and ease handling in subsequent steps. In step  1208 , the substrate can be thinned. In one embodiment, the substrate can be thinned by back grinding. In step  1210  the handle can be removed and individual dies can be formed and the method can end. In some embodiments, an optional step  1209  can be included to form additional perimeters shapes on a second side of the substrate. 
       FIG. 13  is a block diagram of an electronic device suitable for controlling some of the processes in the described embodiment. Electronic device  1300  can illustrate circuitry of a representative computing device. Electronic device  1300  can include a processor  1302  that pertains to a microprocessor or controller for controlling the overall operation of electronic device  1300 . Electronic device  1300  can include instruction data pertaining to manufacturing instructions in a file system  1304  and a cache  1306 . File system  1304  can be a storage disk or a plurality of disks. In some embodiments, file system  1304  can be flash memory, semiconductor (solid state) memory or the like. The file system  1304  can typically provide high capacity storage capability for the electronic device  1300 . However, since the access time to the file system  1304  can be relatively slow (especially if file system  1304  includes a mechanical disk drive), the electronic device  1300  can also include cache  1306 . The cache  1306  can include, for example, Random-Access Memory (RAM) provided by semiconductor memory. The relative access time to the cache  1306  can substantially shorter than for the file system  1304 . However, cache  1306  may not have the large storage capacity of file system  1304 . Further, file system  1304 , when active, can consume more power than cache  1306 . Power consumption often can be a concern when the electronic device  1300  is a portable device that is powered by battery  1324 . The electronic device  1300  can also include a RAM  1320  and a Read-Only Memory (ROM)  1322 . The ROM  1322  can store programs, utilities or processes to be executed in a non-volatile manner. The RAM  1320  can provide volatile data storage, such as for cache  1306   
     Electronic device  1300  can also include user input device  1308  that allows a user of the electronic device  1300  to interact with the electronic device  1300 . For example, user input device  1308  can take a variety of forms, such as a button, keypad, dial, touch screen, audio input interface, visual/image capture input interface, input in the form of sensor data, etc. Still further, electronic device  1300  can include a display  1310  (screen display) that can be controlled by processor  1302  to display information to the user. Data bus  1316  can facilitate data transfer between at least file system  1304 , cache  1306 , processor  1302 , and controller  1313 . Controller  1313  can be used to interface with and control different manufacturing equipment through equipment control bus  1314 . For example, control bus  1314  can be used to control a computer numerical control (CNC) mill, a press, an injection molding machine or other such equipment. For example, processor  1302 , upon a certain manufacturing event occurring, can supply instructions to control manufacturing equipment through controller  1313  and control bus  1314 . Such instructions can be stored in file system  1304 , RAM  1320 , ROM  1322  or cache  1306 . 
     Electronic device  1300  can also include a network/bus interface  1311  that couples to data link  1312 . Data link  1312  can allow electronic device  1300  to couple to a host computer or to accessory devices. The data link  1312  can be provided over a wired connection or a wireless connection. In the case of a wireless connection, network/bus interface  1311  can include a wireless transceiver. Sensor  1326  can take the form of circuitry for detecting any number of stimuli. For example, sensor  1326  can include any number of sensors for monitoring a manufacturing operation such as for example a Hall Effect sensor responsive to external magnetic field, an audio sensor, a light sensor such as a photometer, computer vision sensor to detect clarity, a temperature sensor to monitor a molding process and so on. 
     The various aspects, embodiments, implementations or features of the described embodiments can be used separately or in any combination. Various aspects of the described embodiments can be implemented by software, hardware or a combination of hardware and software. The described embodiments can also be embodied as computer readable code on a computer readable medium for controlling manufacturing operations or as computer readable code on a computer readable medium for controlling a manufacturing line. The computer readable medium is any data storage device that can store data which can thereafter be read by a computer system. Examples of the computer readable medium include read-only memory, random-access memory, CD-ROMs, HDDs, DVDs, magnetic tape, and optical data storage devices. The computer readable medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20120928
Publication Date: 20150609
Grant Date: 20150609
Priority Date: 20120928
Inventors: ARNOLD SHAWN X.
LAST MATTHEW E.
Assignee: APPLE INC
CPC Classifications: [{"code": "H10D84/038", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2221/68381", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/6834", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68327", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68318", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/6835", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/78", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/6836", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2221/68381", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/6834", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68327", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68318", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/6835", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/78", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D62/117", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10D62/117", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L21/6836", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2221/68327", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L29/0657", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L2221/68381", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L21/6835", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/78", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L21/822", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2221/6834", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2221/68318", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 50384390