Abstract:
A method includes fabricating an image sensing element in a substrate. A plurality of inter-metal dielectric (IMD) layers are formed over the substrate. Each IMD layer includes a metal layer and a dielectric layer. A planar top surface of a top IMD layer of the plurality of IMD layers is planarized. A portion of the top IMD layer is then removed to transform a region of the planar top surface to a curved recess. A lens is formed on the top IMD layer and in the curved recess. A color filter layer is disposed over the lens and the image sensing element.

Description:
CROSS-REFERENCE 
       [0001]    The present application is a divisional of application Ser. No. 14/087,370, filed Nov. 22, 2013, which is in turn a continuation of application Ser. No. 10/939,894 filed Sep. 13, 2004, now abandoned, each of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF DISCLOSURE 
       [0002]    The present disclosure relates generally to the field of microelectronic devices and, more particularly, an image sensor including multiple lenses and method of manufacture thereof. 
       BACKGROUND 
       [0003]    Various digital imaging devices (e.g., digital cameras) use image sensors, such as charge-coupled device (“CCD”) imaging sensors and complementary metal oxide semiconductor (“CMOS”) image sensors. Such image sensors include a two dimensional array of photo receptor devices (e.g., photodiodes), each of which is capable of converting a portion of an image to an electronic signal (e.g., representing a “pixel”). Some devices (e.g., a display device) are capable of receiving one or more signals from multiple photo-receptor devices of an image sensor and forming (e.g., reconstructing) a representation of the image. 
         [0004]    A photo-receptor device stores a signal in response to intensity or brightness of light associated with an image. Thus, for an image sensor, sensitivity to light is important. 
         [0005]    Accordingly, what is needed is an image sensor with improved sensitivity to light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In the accompanying figures, in accordance with the standard practice of the industry, various features are not drawn to scale. In fact, dimensions of the various features may be shown to have increased or reduced for clarity. 
           [0007]      FIG. 1  is a block diagram of an image sensor according to the illustrative embodiment. 
           [0008]      FIGS. 2-4  are successive sectional views of a photo-receptor device according to the illustrative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    The following discussion references various embodiments, and/or examples for implementing different features of the various embodiments. Also, specific examples of components and arrangements are described for clarity, and are not intended to limit the scope this disclosure. Moreover, the following discussions repeat reference numerals and/or letters in the various examples, and such repetitions are also for clarity and does not itself indicate a relationship between the various embodiments and/or configurations discussed. Still further, references indicating formation of a first feature over or on a second feature include embodiments in which the features are formed in direct contact, and also embodiments in which one or more additional features are formed, interposing the first and second features, such that the first feature and the second feature are not in direct contact. 
         [0010]      FIG. 1  is a block diagram of an image sensor  100  according to the illustrative embodiment. In the illustrative embodiment, the image sensor  100  is a charged coupled device (“CCD”) image sensor. However in other embodiments, the image sensor  100  is another type of image sensor, such as a complementary metal oxide semiconductor (“CMOS”) image sensor. 
         [0011]    The image sensor  100  includes photo-receptor devices (e.g., photodiodes)  110 . Each of the photo-receptor devices  110  is substantially similar to one another. The photo-receptor devices  110  are organized according to a two dimensional array. As shown, the array includes N columns and M rows. Accordingly, the quantity of photo-receptor devices  110  included by the image sensor  100  is represented by a number resulting from multiplying N by M. Information (e.g., electronic signal) stored by each of the photo-receptor devices  110  is capable of representing a “pixel” of an image (e.g., an image displayed by a display device). Thus, the number resulting from multiplying N by M is also capable of representing a resolution (e.g., screen resolution) for such an image. 
         [0012]      FIG. 2  is a sectional view of a photo-receptor device (e.g., one of the photo-receptor devices  110 ), indicated generally at  200 , in an initial stage of manufacture according to the illustrative embodiment. The photo-receptor device  200  includes a sensing element  205  that reacts to light (e.g., a light beam). In one embodiment, the sensing element  205  includes a pn-junction device (e.g., a diode). The photo-receptor device  200  also includes at least one dielectric layer  210 , and one or more inter-metal-dielectric (“IMD”) layers  215 . Moreover, the photo-receptor device  200  includes a “top” (e.g., upper most) IMD layer  220 , which is one of the layers included by the IMD layers  215 . Each of the IMD layers  215  includes a metal layer  225  as shown. Also, each of the IMD layers  215  includes a dielectric layer. For example, the IMD layer  220  includes a dielectric layer  230 , which is a part of the IMD layer  220 . 
         [0013]    In the illustrative embodiment, the dielectric layer  230  includes SiO 2 . The dielectric layer  230  is formed by atomic layer deposition (“ALD”), chemical vapor deposition (“CVD”), such as plasma-enhanced CVD (“PECVD”), high density plasma CVD (“HDP-CVD”), and low pressure CVD (“LPCVD”), evaporation, or any other suitable technique. Notably, with PECVD, tetraethoxysilane (“TEOS”) is used to form the SiO 2  dielectric layer  230 . 
         [0014]    After its formation, the dielectric layer  230  is planarized. Examples of planarizing techniques include thermal flow, sacrificial resist etch-back, spin-on glass, and chemical-mechanical planarization (“CMP”). In particular, CMP is a technique for planarizing various disparate types of materials, such as dielectric and metal materials. CMP is capable of selectively removing materials from a layer (e.g., a layer of a wafer) by mechanical polishing that is assisted by one or more chemical reactions. 
         [0015]    In more detail, with conventional CMP, a wafer is mounted with its face down on a carrier. The carrier is pressed against a moving platen that includes a polishing surface (e.g., a polishing pad). While the carrier is rotated about its axis, aqueous material including abrasive elements is dripped onto the polishing pad so that the centrifugal force formed by rotating the carrier distributes the aqueous material on the polishing pad. Accordingly, via a combination of mechanical polishing and chemical reaction, CMP selectively removes a portion of a layer of the wafer. 
         [0016]      FIG. 3  is a sectional view of the of the photo-receptor device  200 , in a subsequent stage of manufacture according to the illustrative embodiment. At this stage, a curved recess  310  is formed on the dielectric layer  230 . The curved recess  310  is formed by using conventional photo-lithography and etching techniques. In one example, the curved recess is formed by patterning the dielectric layer  230  with a sequence of processes that includes: photo-resist patterning, wet etching, and photo-resist stripping. Also, the photo-resist patterning includes: photo-resist coating, “soft baking”, mask alignment, pattern exposure, photo-resist development, and “hard baking”. Moreover, wet etching is isotropic etching, and accordingly, suitable for forming the curved recess  310 . 
         [0017]    In more detail, in forming the curved recess  310 , a photo-resist layer  305  is formed over the dielectric layer  230  as shown in  FIG. 3 . After forming the photo-resist layer  305 , wet etching is performed on the dielectric layer  230 . Subsequently, the photo-resist layer  305  is removed. Although in the illustrative embodiment, the curved recess  310  is formed using photo-lithography/wet-etching, in other embodiments, the curved recess  310  is formed using one or more other suitable techniques such as maskless lithography. 
         [0018]      FIG. 4  is a sectional view of the of the photo-receptor device  200 , in a subsequent stage of manufacture according to the illustrative embodiment. At this stage of manufacture, the photo-receptor device  200  includes the dielectric layer  230 , which includes the curved recess  310 . Over the dielectric layer  230  and its curved recess  310 , a lens  405  is formed. In the illustrative embodiment, the lens  405  includes SiN, SiON, or any other suitable material. Also, examples of techniques used to form the lens  405  include ion implantation of N, sputtering, ALD, and CVD such as PECVD, LPCVD, and HDP-CVD. In one example, NH3 and HCD are used in association with LPCVD to form the lens  405  that includes SiN. As shown, the lens  405  is a convex lens. 
         [0019]    The photo-receptor device  200  also includes a spacer  410 , which is formed over the lens  405 . In the illustrative embodiment, the spacer  410  includes SiO2, polymer or any other material suitable for electrical insulation and planarization. Moreover, the photo-receptor device  200  includes a color filter layer  415  formed over the spacer  410 . In the illustrative embodiment, the color filter layer  415  includes a resin, such as a pigment-dispersed resin or polymer. A spacer  420 , which is substantially similar to the spacer  410 , is formed over the color filter layer  415  as shown in  FIG. 4 . 
         [0020]    In addition to the lens  405 , the photo-receptor device  200  includes a lens  425 . The lens  425  is substantially similar to the lens  405 . Accordingly, techniques used to form the lens  425  are substantially similar to the techniques used for forming the lens  405  as discussed above. Materials used to form lens  425  include a resin, such as a pigment-dispersed resin or polymer. The various layers between the lens  425  and the sensing element  205  are sufficiently transparent to pass light from lens  425  to the sensing element  205 . 
         [0021]    As discussed above, the photo-receptor device  200  is capable of forming (e.g., converting) a portion of an image as an electronic signal. The photo-receptor device  200  forms such electronic signal in response to light (e.g., a light beam), from an optical image, that is received through the lenses  405  and  425 , the color filter layer  415 , and the IMD layers  215 . 
         [0022]    A light beam passing from one type of medium (e.g., the lens  405 ) to another medium (e.g., the dielectric layer  230 ) is typically affected by refraction. An example of refraction can be observed when a light beam passes from air to water. An amount of refraction for a specified medium is characterized by its index of refraction. In one example, index of refraction is characterized by the following mathematical expression. 
         [0000]      n=c/v phase   
         [0023]    In the above expression, c is the speed of light and v phase  is the phase velocity. 
         [0024]    As discussed above, for the photo-receptor device  200 , light sensitivity of the image sensing element  205  is important. It has been observed that, in general, light sensitivity can be improved by receiving light from a large pixel area and focusing the light on a small image sensing element. For improving the light sensitivity of the image sensing element  205 , the photo-receptor device  200  includes the lenses  405  and  425  as discussed above. Also for improving the light sensitivity of the image sensing element  205 , an index of refraction for the lens  405  is greater than an index of refraction for the dielectric layer  230 . 
         [0025]    For example, in one version of the illustrative embodiment, the lens  405  includes SiN and the dielectric layer  230  includes SiO 2 . According to one measured value, an index of refraction for SiN is approximately 2.01 and an index of refraction for SiO 2  is 1.46. Thus, the index of refraction for the lens  405  (2.01) is greater than the index of refraction for the dielectric layer  230  (1.46). 
         [0026]    Although illustrative and alternative embodiments have been shown and described, a wide range of modification, change, and substitution is contemplated in the foregoing disclosure and, in some instances, some features of the embodiments may be employed without a corresponding use of other features. Accordingly, broad constructions of the appended claims in manners consistent with the scope of the embodiments disclosed are appropriate.