Abstract:
Temperatures in microelectronic integrated circuit packages and components may be measured in situ using carbon nanotube networks. An array of carbon nanotubes strung between upstanding structures may be used to measure local temperature. Because of the carbon nanotubes, a highly accurate temperature measurement may be achieved. In some cases, the carbon nanotubes and the upstanding structures may be secured to a substrate that is subsequently attached to a microelectronic package.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 11/477,267, filed on Jun. 29, 2006. 
     
    
     BACKGROUND 
       [0002]    This relates generally to measuring temperature in connection with microelectronic packages and components. 
         [0003]    The effects of temperature on microelectronic packages and components may be various. Many packaging processes involve the application of elevated temperatures. These elevated temperatures may adversely affect components, including the integrated circuit chip within the package. In addition, the packages may be exposed to various other temperature effects which may have an impact on the packaged components. Also, the integrated circuits themselves can be exposed to various temperature conditions. 
         [0004]    It is known how to integrate integrated circuit temperature sensors within an overall integrated circuit. Temperature readings can be obtained from serpentine, integrated temperature sensors. However, the accuracy of these measurements may, in some cases, be limited. Moreover, the temperature sensors may take up a relatively significant percentage of the overall available integrated circuit space. Also, in some cases, the places at which such temperature sensors can be formed are limited. Namely, there are generally limited to areas of sufficient size that can receive such an integrated element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a greatly enlarged, partial, cross-sectional view of one embodiment of the present invention; 
           [0006]      FIG. 2  is a greatly enlarged, cross-sectional view of the embodiment shown in  FIG. 1  after further processing; 
           [0007]      FIG. 3  is a top plan view of the embodiment of  FIG. 2  in position on an integrated circuit or other microelectronic package component; 
           [0008]      FIG. 4  is an enlarged, cross-sectional view of a package in accordance with one embodiment of the present invention; 
           [0009]      FIG. 5  is an enlarged, cross-sectional view of a package in accordance with another embodiment of the present invention; 
           [0010]      FIG. 6  is an enlarged, cross-sectional view of an integrated circuit in accordance with one embodiment of the present invention; 
           [0011]      FIG. 7  is an enlarged, cross-sectional view of still another embodiment of the present invention using two spaced metallic lines; and 
           [0012]      FIG. 8  is a system depiction in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIG. 1 , in accordance with some embodiments of the present invention, a temperature sensor  10  may be formed on an integrated circuit substrate  12 . A plurality of metallic structures  16  may be formed which extend upwardly from the substrate  12 . The structures  16  may be made of a material suitable for the growth of bridge-like carbon nanotubes  18 . Those carbon nanotubes  18  may act as temperature sensors. Namely, the conductivity of those nanotubes is a function of temperature. By measuring the conductivity of the nanotubes, by passing current through them, one can determine the local temperature. 
         [0014]    In some embodiments of the present invention, a large number of upstanding structures  16  may be formed. They may be formed in regular arrays, in some embodiments, using well known techniques. The arrays may be composed of an inner pillar  14  which may be a non-metallic material and a metallic coating that forms the upstanding structure  16 . 
         [0015]    Carbon nanotubes  18  may bridge between adjacent structures  16 . Thus, a plurality of carbon nanotubes  18  may be randomly arranged in a generally horizontal configuration transverse to the upstanding structures  16 . 
         [0016]    In some embodiments of the present invention, the structures  16  may be formed directly on the substrate  12 . The structures  16  may include the pillars  14 , in one embodiment of the present invention, covered by a metal catalyst to form the metallic structure  16 . Suitable metal catalysts include iron, cobalt, and nickel. As an example, the structure  16  may be of a height of about a micron. 
         [0017]    The structures may be formed, for example, by glancing angled deposition methods. By controlling the substrate  12  rotational motion, including both its angle and velocity, the structure  16  height can be controlled. Although different metal catalysts may be utilized to form the structures  16 , nickel may be preferred because it may offer lower contact resistance with the nanotubes  18  to be formed subsequently. 
         [0018]    In some embodiments of the present invention, some number of the upstanding structures  16  on the substrate  12  may be used to make a separable unit  20 , shown in  FIG. 2 . The separable unit  20  may be formed of a portion of the substrate  12  whose thickness has been reduced so that the substrate thickness does not adversely affect the temperature measurements. Thus, the substrate  12  may be reduced in size and thickness to form the unit  20  with some lesser number of upstanding structures  16  formed thereon. 
         [0019]    The carbon nanotubes  18 , shown in  FIG. 1 , may be grown so as to bridge between structures  16 . This is particularly useful when large arrays of structures  16  are provided in regular rows and columns. In one embodiment, gas phase chemical vapor deposition may be used to grow the carbon nanotubes. In one embodiment of the present invention, methane may be used as a source for carbon for the growth of carbon nanotubes. As a result, nanotubes may extend from one upstanding structure to another. Argon gas may be supplied during the deposition of the carbon nanotubes to reduce oxidation. A pressure of about 500 Torr and a furnace temperature in a range including, but not limited to, 800 to 950 degrees Celsius in the methane environment may be utilized in one embodiment. 
         [0020]    Advantageously, adjacent structures  16  are spaced reasonably proximately so that the carbon nanotubes ( FIG. 3 ) of a given length may span across them. 
         [0021]    The structures  16  may be formed, in one embodiment, by depositing a catalyst over the pillar  14 , preformed on the substrate  12 . For example, the pillars  14  may be silicon or silicon dioxide pillars. The pillars may be formed, for example, by growing or depositing the pillar material, masking, and etching to form the pillars in the desired arrangement. In some embodiments, at least two of the pillars may be aligned with a crystallographic plane of the substrate  12  in an embodiment where the substrate is a crystalline semiconductor. 
         [0022]    During catalyst film deposition, the substrate  12  may be tilted twice about +/−45 degrees to spread the catalyst over the pillars  14  to form the structures  16 . The carbon nanotubes  18  later form on the tops and sidewalls of the pillars  14  where the catalyst is present. The catalyst may not completely cover the pillars in some cases. 
         [0023]    In some embodiments, an array of pillars (not shown) may be grown, but only some of the pillars may be activated with the catalyst. For example, only two pillars may be activated with catalyst so carbon nanotubes bridge only the two catalyst activated pillars. The selective activation may be accomplished using masks or selective catalyst deposition. While cylindrically shaped structures  16  are depicted, other shapes may also be used. 
         [0024]    Generally, the nanotubes  18  grow generally or roughly horizontally from the top to the bottom along the structures  16 . The nanotubes span like bridges over the substrate  12 . 
         [0025]    In some embodiments, the substrate  12  ( FIG. 1 ) may subsequently be thinned down to form the unit  20  ( FIG. 2 ) so that its own thickness does not contribute to changes in the temperature of the die whose temperature is being measured. A thinned down unit  20  may then be glued onto any polymeric or ceramic surface. 
         [0026]    Referring to  FIG. 3 , the nanotubes  18  may then be electrically coupled to an external temperature sensor (not shown) using metal lines  30 . Particularly, the unit  20  may be adhesively secured to a structure  32  whose temperature is to be measured. Then, metal lines  30  may be deposited or otherwise formed to the structures  16 . The metal lines  30  may then connect each side of the array of carbon nanotubes  18  to a suitable pad (not shown) to which a temperature sensing circuit may be attached. The metal lines  30  and the pads may be printed using conventional processes such as screen printing or plating. 
         [0027]    In other embodiments, the nanotubes may be prepared on a substrate using a tall pillar pattern such as one which uses staples secured to a substrate. By “tall,” it is intended to refer to structures  16  having a height on the order of (but not limited to) 0.7 centimeters. Subsequently, the nanotubes are grown and metallizations are completed. Other structures  16  may be also be utilized to grow bridge-like carbon nanotubes, including telephone pole and soccer goal oriented office staples. Literally, upstanding office staples may be utilized by securing them to silicon wafers using an appropriate adhesive such as carbon tape. The staples may have their points upstanding (“telephone poles”) or inverted (“soccer goal”) and extending into the substrate. 
         [0028]    Then, carbon nanotubes may be grown using chemical vapor deposition in a furnace at 1373 degrees Kelvin under about 100 m Torr vacuum. To 0.02 g/ml solution of ferrocene and 10 ml of hexane, two volume percent thiophene is added. The hexane may act as a source of carbon and the ferrocene acts as a catalyst for gas diffusion formation of carbon nanotubes. The solution may be heated to 150° C. and then introduced into a horizontal quartz tube furnace at an average rate of 0.1 mls. per minute for ten minutes. Other process parameters may also be used. 
         [0029]    Thiophene is known to promote the formation of single walled carbon nanotubes in a hydrogen gas atmosphere, whereas multi-walled carbon nanotubes are found to grow predominantly in the absence of a hydrogen gas atmosphere. Single walled carbon nanotubes or multi-walled carbon nanotubes can be used by controlling the nanotubes growth conditions by controlling the hydrogen gas concentration in the furnace (no hydrogen gas atmosphere giving multi-walled carbon nanotubes, whereas hydrogen gas atmosphere may promote the single walled carbon nanotube growth). 
         [0030]    Although the recipe and numbers recited above are recommended to grow carbon nanotubes, the growth conditions are not limited to this recipe or these numbers, but, rather, is inclusive of them. In some temperature sensing applications, multi-walled carbon nanotubes may be advantageous. 
         [0031]    Referring to  FIG. 4 , in accordance with one embodiment of the present invention, temperatures associated with surface mount techniques may be measured by growing carbon nanotubes across second level interconnects, such as solder ball or surface mount pads  26   a . The pads  26   a  may mount solder balls  34 . The solder balls  34  may couple the package  37  to an external printed circuit board (not shown) such as a motherboard. 
         [0032]    The carbon nanotubes  18  may be grown so as to span between sufficiently adjacent pads  26   a . In some cases, only some of the pads  26   a  may be used for the temperature measurement and other pads may have no such function, but, instead, function conventionally as second level interconnects. In some cases, the pads  26   a  may be otherwise electrically non-functional and may only be used for temperature measurement purposes. 
         [0033]    The pads  26   a  may be formed on a suitable substrate  36 , over which is mounted the integrated circuit die  40 . A housing  38  may cover the die  40  and be secured to the substrate  36 . First level interconnects  44  may be positioned between the die  40  and the substrate  36 . 
         [0034]    Referring to  FIG. 5 , basically the same package is shown. However, in this case, the carbon nanotubes  18  are grown between first level interconnects  44 , instead of between second level interconnects, as depicted in  FIG. 4 . In this way, carbon nanotubes  18  can be selectively grown between appropriately spaced elements to make temperature measurements for first and/or second level interconnects. 
         [0035]    In some cases, the length of the carbon nanotubes may be different for different applications in order to span the necessary space. For example, in some cases, it may be desirable to have carbon nanotubes on the order of 1 micron to span between metal lines on a die, 10 to 50 microns to span between adjacent surface mount pads, and all the way up to 1 millimeter for adjacent solder bumps. 
         [0036]    Generally, different techniques may be utilized to form the carbon nanotubes in different applications. In one embodiment, some interconnects, such as the solder ball pads  26 , may be masked and other interconnects, such as the solder balls  26   a , may not be masked so that the carbon nanotubes form only between the exposed pads  26   a . As another example, a unit  20  may be laminated into position between adjacent pads  26   a  to achieve a comparable effect. As still another possibility, nanotubes in a solvent solution may be dispensed as a liquid at selected locations at room temperature and allowed to dry. As still another option, electrodeposition may be utilized. 
         [0037]    For the first level interconnects, it may be desirable to use the electrodeposition or liquid deposition techniques to avoid exposing the substrate or die  40  to excessive temperatures that may be required in some carbon nanotube fabrication processes. 
         [0038]    In some embodiments, it may be desirable for the first level interconnects, from the silicon to the substrate, to connect to second level interconnects that are actually active (non-temperature sensing) interconnects, even though the first level interconnects with the carbon nanotubes between them may be electrically non-functional for their normal interconnect (non-temperature sensing) purposes. Thus, the first level interconnects with the carbon nanotubes connected to them may be only functional for sensing temperature, but may be connected to second level interconnects that are effective, but are effective really only to convey the signals to and from the carbon nanotubes of the first level interconnects. Similarly, the second level interconnects with carbon nanotubes may be functional only for purposes of providing signals to and from the carbon nanotubes for purposes of making temperature measurements and perform no other interconnection function, in some embodiments. 
         [0039]    In some embodiments, the nanotubes may be highly accurate temperature indicators. Because they have anisotropic characteristics in the length dimension and have very small dimensions transversely to length dimensions, high temperature resolutions may be obtained with carbon nanotubes. Carbon nanotubes may tend to be atomically relatively perfect and chemically stable and, therefore, may be more reliable as sensors than metallic structures of similar dimensions. In addition, temperatures in hard to reach locations may be measured in some cases. 
         [0040]    Referring to  FIG. 6 , the units  20  may be secured to opposite sides of an integrated circuit die  40  in another embodiment. In one embodiment, a unit  20  may be secured to the front side  42  of the die  40  and, in another embodiment, a unit  20  may be secured to the back side  44  of the die  40 , as shown. In some cases, temperature sensing units  20  may be provided on both die sides, together with suitable metallizations to an external temperature sensor. The suitable metallizations may be provided to a current source which provides current to the carbon nanotubes in the units  20  and measures the resulting current therefrom to determine temperature in accordance with known principles. 
         [0041]    Referring to  FIG. 7 , in accordance with another embodiment of the present invention, spaced metal lines  26  may be bridged by carbon nanotubes  18 . The carbon nanotubes  18  may span an intermediate underlying trench  24  and a substrate  22 . The metal lines  26  may be dummy metal lines for temperature purposes only or, in some cases, could be actual metal lines. Where the lines  26  are actual metal lines, these metal lines may be subsequently used for carrying signals, for example, by first destroying the carbon nanotubes  18  after having used them, if desired, for temperature measurements. Alternatively, the lines  26  may couple to a temperature sensor that uses the varying resistance of the nanotubes to develop a temperature indication. 
         [0042]    Finally, referring to  FIG. 8 , in accordance with some embodiments of the present invention, the integrated circuits or packaged devices with the integrated temperature sensors may be incorporated into a system including a processor  10 . The processor  10  may be coupled by a bus  38  to a dynamic random access memory  40  and an input/output device  42 . While a simple architecture is shown, many other embodiments may be possible. 
         [0043]    References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application. 
         [0044]    While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.