Abstract:
A method of determining a physical characteristic of an adhesive material on a semiconductor device element using structured light is provided. The method includes the steps of: (1) applying a structured light pattern to an adhesive material on a semiconductor device element; (2) creating an image of the structured light pattern using a camera; and (3) analyzing the image of the structured light pattern to determine a physical characteristic of the adhesive material. Additional methods and systems for determining physical characteristics of semiconductor devices and elements using structured light are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 61/873,288, filed Sep. 3, 2013, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to systems and methods for measuring physical characteristics of semiconductor device elements (often in connection with bonding operations of the semiconductor elements), and more particularly, to improved systems and methods for measuring such physical characteristics using structured light. 
     BACKGROUND OF THE INVENTION 
     Semiconductor devices include various physical features or characteristics that are desirably controlled. For example, typically it is desirable that semiconductor dice are substantially flat prior to packaging (e.g., prior to die attach processes, thermo-compressive bonding processes, etc.). Also, it is typical that certain physical attributes of elements included in a semiconductor device or package be measured to ensure conformity with design criteria or specifications. 
     Specifically, in thermo-compression bonding (e.g., bonding a semiconductor device to another semiconductor device with copper pillars or similar conductive structures between the devices), physical features or characteristics of the bonding elements are desirably controlled. This is particularly true in simultaneous thermo-compression bonding of many devices. 
     Thus, it would be desirable to provide improved systems for, and methods of, measuring and/or controlling such physical characteristics. 
     SUMMARY OF THE INVENTION 
     According to an exemplary embodiment of the present invention, a method of determining a physical characteristic of an adhesive material on a semiconductor device element using structured light is provided. The method includes the steps of: (1) applying a structured light pattern to an adhesive material on a semiconductor device element; (2) creating an image of the structured light pattern using a camera; and (3) analyzing the image of the structured light pattern to determine a physical characteristic of the adhesive material. 
     According to another exemplary embodiment of the present invention, a method of determining a physical characteristic of a fillet of an adhesive material applied between elements of a semiconductor device using structured light is provided. The method includes the steps of: (1) applying a structured light pattern to an adhesive fillet between elements of a semiconductor device; (2) creating an image of the structured light pattern using a camera; and (3) analyzing the image of the structured light pattern to determine a physical characteristic of the adhesive fillet. 
     According to yet another exemplary embodiment of the present invention, a method of determining a flatness characteristic of a semiconductor device using structured light is provided. The method includes: (1) creating an image of a structured light pattern reflected by a surface of a semiconductor device using a camera; and (2) analyzing the image of the structured light pattern to determine a flatness characteristic of the semiconductor device. 
     In accordance with certain exemplary embodiments of the present invention, these and other methods (including some or all of the steps recited herein) may be performed on a thermo-compression bonding machine. 
     In accordance with certain exemplary embodiments of the present invention, the methods described herein (including methods of determining a physical characteristic of an adhesive material on a semiconductor device element, methods of determining a physical characteristic of a fillet of an adhesive material applied between elements of a semiconductor device, and methods of determining a flatness characteristic of a semiconductor device) may involve using different structured light patterns to achieve the best measurement result (e.g., a physical characteristic or a flatness characteristic as described herein). For example, the steps of creating an image of a structured light pattern using a camera, and analyzing the image of the structured light pattern to determine a characteristic, may be repeated (thereby analyzing a plurality of images) to determine the desired measurement result. 
     According to yet another exemplary embodiment of the present invention, a thermo-compression bonding system is provided. The thermo-compression bonding system includes: (1) a support structure for supporting a semiconductor device element including an adhesive material; (2) a structured light source for providing a structured light pattern on the adhesive material; and (3) a camera for creating an image of the structured light pattern on the adhesive material. 
     According to yet another exemplary embodiment of the present invention, a thermo-compression bonding system is provided. The thermo-compression bonding system includes: (1) a support structure for supporting a semiconductor device; (2) a structured light source for providing a structured light pattern; and (3) a camera for indirectly viewing the structured light pattern using a reflective surface of the semiconductor device, the camera generating an image of the structured light pattern. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
         FIG. 1  is a block diagram view of elements of a thermo-compression bonding machine in accordance with an exemplary embodiment of the present invention; 
         FIGS. 2A-2B  are top views of an structured light patterns projected onto an adhesive material in accordance with an exemplary embodiment of the present invention; 
         FIG. 3  is a three dimensional representation of an adhesive material generated in accordance with an exemplary embodiment of the present invention; 
         FIG. 4A  is a block diagram side view of an adhesive material fillet to be imaged in accordance with an exemplary embodiment of the present invention; 
         FIG. 4B  is a three dimensional representation of an adhesive material fillet generated in accordance with an exemplary embodiment of the present invention; 
         FIG. 5  is a block diagram view of imaging elements, which may be used in connection with a thermo-compression bonding machine, in accordance with an exemplary embodiment of the present invention; 
         FIG. 6  is a block diagram view of elements of a thermo-compression bonding machine in accordance with an exemplary embodiment of the present invention; 
         FIGS. 7A-7C  are a series of images of a structured light patterns reflected from surfaces of semiconductor devices in accordance with an exemplary embodiment of the present invention; and 
         FIG. 8  is another block diagram view of elements of a thermo-compression bonding machine in accordance with an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As used herein, the term “structured light” is intended to be defined as is known to those skilled in the art, and specifically refers to light including a projection (e.g., a pattern, such as pixels with different gray levels in a grid or horizontal bar configuration) applied to a surface to be imaged. 
     In accordance with certain exemplary embodiments of the present invention, systems and methods for measuring (e.g., profiling, characterizing, etc.) elements of semiconductor devices using structured light are provided. Exemplary elements of semiconductor devices being measured include adhesive material between elements of the semiconductor device, a fillet of adhesive material between elements of the semiconductor device, and semiconductor device surfaces. 
     Adhesive material elements measured may include, for example, curable liquid materials such as epoxy, non-conductive paste, etc. Such adhesive materials may be applied between elements bonded together during thermo-compression bonding. More specifically, a first element of a semiconductor device, with conductive regions, may be provided on a support structure. An adhesive material may then be applied to this first element. Then, a second element (which may be semiconductor die or other device including conductive pillars or the like) is thereto-compressively bonded to the first element. This bonding may include, for example, heat and bond force. The adhesive material may be measured to determine, for example, a volume of the material (such as a 3D volume of the material), a distribution of the material (e.g., the pattern of the material), etc. 
     Aspects of the present invention may also be used to measure a fillet of adhesive material between such first and second elements. The fillet is the portion of the adhesive material that is exposed between the two elements (See, e.g.,  FIG. 4A ). The fillet may be measured to determine, for example, a height of the fillet (reference number  410  in  FIG. 4A ), a length of the fillet (reference number  412  in  FIG. 4A ), a volume (e.g., a 3D volume of the fillet), amongst other quantities. 
     Aspects of the present invention may also be used to measure semiconductor device flatness characteristics. As will be appreciated by those skilled in the art, it is typically desirable that semiconductor devices (e.g., semiconductor die to be thereto-compressively bonded to another semiconductor element) are substantially flat and/or planar. The present invention may be used to determine if such devices are within a predetermined flatness specification (e.g., tolerance). 
     Aspects of the present invention may also be used to measure for semiconductor device crack characteristics including the size and location of such cracks. 
     As used herein, the term “semiconductor device” is intended to refer to any type of semiconductor device element including but not limited to bare semiconductor die, packaged semiconductor die, partially packaged semiconductor die, a region of a substrate to which a die will be bonded, a semiconductor wafer (or a portion thereof) including a plurality of semiconductor die, etc. Elements of a semiconductor device may include a semiconductor die, a substrate for supporting a semiconductor die, etc. 
       FIG. 1  illustrates elements of a thermo-compression bonding machine  100 . Many elements have been omitted from  FIG. 1  (and other machines illustrated herein) for clarity such as, for example, a bond head assembly, a material handling system, etc. Machine  100  includes a structured light source  102  (e.g., shown as, but not limited to, digital fringe projector  102 ). Light source  102  includes grating  104  or other structure (such as a DLP chip in a digital fringe projector embodiment). Light  108  transmitted from source  102  is structured light that includes a structured light pattern imposed on the light, for example, using grate  104 .  FIG. 1  also illustrates support structure  110  which supports element  112 . Element  112  may be, for example, a semiconductor device to which an adhesive material (e.g., an epoxy material, a non-conductive paste, etc.—applied to the semiconductor device as a curable liquid) has been applied. The adhesive material includes a diffusive surface  114 . When structured light  108  is received by diffusive surface  114 , at least a portion of the resultant diffused light pattern  116  is imaged within field of view  120  of camera  118 . The image generated by camera  118  may be used to measure a physical characteristic of the adhesive material (included in elements  112 ,  114 ) such as a volume or volume distribution. While element  112  is described as an adhesive material, other types of elements are contemplated such as substrates having a diffusive surface (or an at least partially diffusive surface). 
       FIGS. 2A-2B  illustrate two top view images  216   a ,  216   b  of adhesive material samples as applied to respective semiconductor devices. As illustrated, the adhesive material has a conventional “star” shaped or “burst” pattern. In  FIG. 2A , the center portion  260   a  of the adhesive material sample is not very clear. In  FIG. 2B , the image had been processed (e.g., using image processing hardware and/or software which may be included on a thermo-compression bonding machine) such that a clearer image is provided as in  FIG. 2B . In  FIG. 2B , the center portion  260   b  is much clearer than in  FIG. 2A , and the structured light pattern (and the variation among the structured light lines in the pattern) is more visible. Using such an image, image processing hardware and/or software may be used to determine the desired physical characteristic which may be a simple characteristic (e.g., a number such as a volume) or a more complex physical characteristic such as a topographical map or representation.  FIG. 3  illustrates an example of such a map  360 . 
     The exemplary structured light imaging approach illustrated in  FIG. 1  may be used to measure more than just a physical characteristic of an adhesive material such as shown in  FIGS. 2A-2B . In another example, the light may be used to image (and thereby measure) a physical characteristic of an adhesive fillet.  FIG. 4A  illustrates a portion of semiconductor device  400  including a first semiconductor element  402  (e.g., a die or substrate), an adhesive layer  404  disposed on element  402 , and a second semiconductor element  406  disposed on the adhesive layer  406 . Fillet  408  (which is part of adhesive material  404 ) extends past an edge of element  406 . It may be desirable to measure a physical characteristic of fillet  408  for example, height  410 , length  412 , or curvature “c”. It may be useful to know such a characteristic in order to be confident that the adhesive material has not extended into areas where it should not extend. Of course, a more complex physical characteristic such as a topographical map or representation may be measured.  FIG. 4B  illustrates an example of such a map. 
     The physical characteristic of a fillet measured according to the present invention may include measuring the characteristic around the entire perimeter along which the fillet extends. For example, if a fillet extends around an entire edge of a semiconductor device, this entire fillet may be measured. 
     In the images generated according to the present invention (e.g., using cameras, structured light, etc.)—various imaging complications may arise. One such complication relates to hot spots which may render the image less clear.  FIG. 5  illustrates a configuration that may be useful to reduce such hot spots. More specifically, light source  576  (e.g., an LED or other source) is transmitted through polarizer  1 , and into projection element  502  (e.g., including a grating or the like to generate a structured light image). The structured light  508  is diffused off of test sample  578  (e.g., adhesive material on a semiconductor device, etc.). A diffused image  520  is transmitted through polarizer  2  and is received by camera  518 . The use of polarizers may be useful in reducing the effect of hot spots. 
     Certain exemplary embodiments of the present invention may be used to measure other physical characteristics of semiconductor devices such as flatness characteristics, crack propagation, amongst others.  FIG. 6  illustrates an exemplary thermo-compression bonding machine  600  (with many elements omitted for clarity) including a structured light source  602  (e.g., shown as, but not limited to, digital fringe projector  102 ). Light source  602  includes grating  604  or other structure (such as a DLP chip in a digital fringe projector embodiment). Light  608  transmitted from source  602  is structured light that includes a structured light pattern imposed on the light, for example, using grate  604 . Structured light  608  is received by a diffuser screen  630   a .  FIG. 6  also illustrates support structure  610  which supports element  612 . Element  612  may be, for example, a semiconductor device such as a semiconductor die or other element having a reflective (or at least partially reflective) upper surface  644 . Camera  648  images an area within field of view  640  including reflective surface  644  of element  612 . This reflection allows camera to image the structured light pattern seen by (and possibly distorted by) element  612 . As will be appreciated by those skilled in the art, this type of configuration allows for imaging of a virtual image as shown by reference number  630   b . As recited above, the image generated by camera  648  may be used to measure a physical characteristic of the element  612  such as a a flatness characteristic and/or a crack propagation characteristic.  FIG. 7A-7C  are exemplary images of structured light distorted by various semiconductor devices using the technique illustrated in  FIG. 6 . 
     In certain exemplary embodiments of the present invention, it may be desirable to image both a diffusive surface characteristic (e.g., an adhesive material characteristic) and a reflective surface characteristic (e.g., a flatness characteristic).  FIG. 8  illustrates elements of a thermo-compression bonding machine  800 . Many elements have been omitted for clarity. Machine  800  includes a structured light source  802  (e.g., shown as, but not limited to, digital fringe projector  802 ). Light source  802  includes grating  804  or other structure (such as a DLP chip in a digital fringe projector embodiment). Light  808  transmitted from source  802  is structured light that includes a structured light pattern imposed on the light, for example, using grate  804 .  FIG. 8  also illustrates support structure  810  which supports element  812 . Element  812  may be, for example, a semiconductor device including a diffusive surface  814  (e.g., an adhesive material) and a reflective surface  844  (e.g., a die surface). Structured light  808  is received by switching diffusive screen  850  (illustrated as, but not limited to, a liquid crystal diffuser screen). When it is desired to image the reflective surface  844 , screen  850  may be operated in a diffusive mode, allowing camera  848  to generate an image as described above with respect to  FIG. 6 , and thereby allowing a physical characteristic (e.g., a flatness characteristic, a crack propagation characteristic, etc.) to be measured. When it is desired to image diffusive surface  814 , screen  850  may be operated in a transparent mode, allowing camera  818  to generate an image as described above with respect to  FIG. 1 , and thereby allowing a physical characteristic (e.g., a volume, a volume distribution, etc.) to be measured. 
     Although the present invention has been described primarily with respect to imaging using structured lights, it is not limited thereto. Certain aspects of the present invention have applicability to use with other forms and/or configurations of light. 
     Although the present invention has primarily been described in connection with thermo-compressive bonding machines and processes (e.g., thermo-compressively bonding a first semiconductor device element to another semiconductor device element), it is not limited thereto. For example, the teaching of the present invention have application in conventional die attach systems and methods of using the same. 
     In certain exemplary embodiments of the present invention described herein, closed loop processes (or feedback driven processes) are described. For example, if a given physical characteristic (e.g., adhesive material volume or distribution) is measured and is not within a predetermined specification (e.g., tolerance), then an aspect of the dispensing process (e.g., the volume of adhesive dispensed, the rate of material dispensed, the temperature of the material dispensed, amongst others) may be adjusted in a closed loop manner. However, it is also within the scope of the present invention to adjust other aspects of the thermo-compression bonding process to in order to achieve the desired physical characteristic specification. Such thermo-compression bonding process aspects that may be adjusted include, for example, bonding temperature, bonding temperature profile, bond force, bonding time, etc. 
     Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.