Abstract:
A semiconductor device including a semiconductor substrate having a photosensor formed therein; a first layer overlying the substrate, the first layer includes a portion having a generally concave shaped surface being the negative shaped of a micro-lens to be formed there over; a second layer overlying the first layer, the second layer including a generally convex shaped portion vertically aligned with and mating with the generally concave shaped surface, the generally convex shaped portion being constructed and arranged to define a micro-lens positioned to cause parallel light passing through the micro-lens to converge on and strike the photosensor.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to semiconductor devices, and in particular to semiconductor devices including a micro-lens, and methods of making the same.  
       BACKGROUND OF THE INVENTION  
       [0002]     In advanced image sensor devices, a micro-lens is usually used to collect and focus light on a sensor. However, typical prior micro-lenses have a number of disadvantages. The overall height from the silicon surface of the semiconductor to the top layer, formed by a color filter process, is typically very large. This large height or distance might decrease the function of the micro-lens. Some micro-lenses are made from a positive photoresist. However, this positive photoresist has reliability issues in that the photoresist materials may yellow and are not capable of resisting high temperatures.  
         [0003]      FIG. 1  illustrates a sectional view of a prior art semiconductor device  10  including a micro-lens  12 . The semiconductor device includes a silicon-based substrate  30  in which a sensor  28  is formed such as a photodiode. An inter-metal dielectric layer  26 , such as silicon dioxide, is provided over the silicon-based substrate  30 . A silicon dioxide passivation layer  24  is provided over the inter-metal dielectric layer  26 . A silicon nitride layer  22  is provided over the silicon dioxide passivation layer  24  and a planarization layer  20  is provided over the silicon nitride layer  22 . A color filter layer  18  is provided over the planarization layer  20  and a micro-spacer  16  is provided over the color filter layer  18 . The micro-lens  12  is formed over the color filter layer  18 . The micro-lens  12  includes a convex shaped upper surface  14  which causes parallel light rays  2  to converge on and strike the sensor  28 .  
         [0004]     Abramovich, United States Patent Application Publication No. 2001/0010952A1, published Aug. 2, 2001, discloses a method of producing a color CMOS image sensor. Disclosed is a color image sensor that is formed on an n-type semiconductor substrate, having a p-well layer. An array of photodiodes and charged transfer regions are formed in a p-well layer, and are covered by silicon oxide or nitride film. A poly-silicon electrode is located over charged transfer regions such that it is surrounded by film. A photo-shielding metal layer is formed over the electrode, and a surface protective coating and a passivation layer are formed over the metal layer. The color filter layer is formed on the passivation layer, and an intermediate transfer film is formed over the color filter layer. A micro-lens for focusing light beams is formed from silicon dioxide or a resin material on intermediate transparent film. In the operation, light beams are focused by the micro-lens through the color filter layer such that they converge on the focal axis of the micro-lens to strike the photodiode, wherein photo energy from the light beams frees electrons in the photodiode. When a select voltage is applied to the poly-silicon electrode, these freed electrons generate a current in the charge transfer region. A sensor circuit associated with a color sensor then determines the amount of light received by the photodiode by measuring the amount of current generated in the charge transfer region. A dielectric layer may be provided and is etched to form the micro-lens. This may be accomplished using reactive-ion etching. The etching process is controlled such that a portion of the dielectric layer remains over the passivation layer. A silicon nitride layer may also be deposited and etched to form a micro-lens. Disclosed also is the process of depositing a photoresist portion and subsequently etching the photoresist layer to form a micro-lens.  
         [0005]     Hsiao, et al., U.S. Pat. No. 6,417,022, issued Jul. 9, 2002, discloses a process of forming a multiplicity of micro-lenses for the color filters. A photodiode is first formed in the surface of a substrate, which also includes a series of metal connectors covered by a layer of passivation that forms an irregular upper surface. The irregular upper surface is then planarized to deposit a layer of dielectric material over the passivation layer. After the planarization step has been performed, a subsequent step is carried out to form a color filter layer providing red, green and blue color elements. As a final step, a micro-lens spacer is applied and followed by a step, which produces a micro-lens. Disclosed is a method in which a micro-lens material is patterned into at least three separate embryos performing three separate micro-lenses of long focal length. Each of the micro-lens embryos may be divided into nine discreet regions of different sizes. After the embryos are patterned by standard photolithographic methods, the embryos are reflown in a reflow process at a temperature of about 160 degrees Celsius, forming a micro-lens.  
         [0006]     Hsaio, et al., U.S. Pat. No. 6,582,988, issued Jun. 24, 2003, discloses a method of making a micro-lens including providing a silicon substrate having a plurality of CMOS devices. A non-photosensitive planarization layer is deposited over the substrate. A color filter layer is placed over the top of the planarization layer with individual red/green/blue (RGB) sub-section pixel areas. A negative type photo-resistant material is utilized for the planarization/passivation layer formed directly over the color filter layer. One material disclosed as suitable for that application is a novolac/acrylic matrix supplied as CT-3050L by Fuji-Olin Corporation. A positive type photo-sensitive material is applied over the planarization/passivation layer. One embodiment disclosed as suitable for the positive type photo-sensitive material is a mixture of melamine resin and generic novolac based resin. Thereafter, a plasma etch step is utilized with oxygen plasma to etch through exposed regions of the planarization layer to define the micro-lens array. After the plasma etch step, the micro-lens array undergoes a hard bake reflow operation to produce the micro-lens.  
         [0007]     The present invention provides alternatives to the prior art.  
       SUMMARY OF THE INVENTION  
       [0008]     One embodiment of the invention includes a method of making a semiconductor device comprising a micro-lens comprising: 
        providing a semiconductor device comprising a substrate having a plurality of sensors formed therein;     forming a first protrusion containing layer on the semiconductor device, wherein the first protrusion containing layer comprises spaced apart protrusion portions;     forming a first layer over the first protrusion containing layer so that the first layer comprises spaced apart crest portions aligned with the protrusion portions of the first protrusion containing layer, and wherein a concave shaped surface is provided between spaced apart crest portions of the first layer;     forming a second layer over the first layer, and wherein the second layer comprises spaced apart convex shaped portions, each convex shaped portion aligned with and mating with one of the convex shaped surfaces of the first layer.        
 
         [0013]     Another embodiment of the invention includes a method of forming a semiconductor device comprising a micro-lens comprising: 
        forming a top metallization layer, comprising a plurality of spaced apart protrusions, over a semiconductor device comprising a plurality of sensors formed in a silicon based substrate;     forming a first layer over the top metallization layer comprising high density plasma silicon oxide deposition, wherein the first layer comprises concave shaped surface portions;     forming a second layer over the first layer comprising plasma enhanced chemical vapor silicon nitride deposition;     chemical mechanical planarizing the second layer; wherein the second layer comprises convex-shaped portions each defining a micro-lens; forming a color filter over the planarized second layer;     forming a color filter over the planarized second layer.        
 
         [0019]     Another embodiment of the invention includes a method of making a semiconductor device comprising: 
        forming a first pre-protrusion containing layer over a semiconductor device comprising a plurality of sensors formed in a silicon-based substrate, the forming of the first layer comprising high density plasma chemical vapor silicon oxide deposition;     etching portions of the first pre-protrusion containing layer to form a first protrusion containing layer comprising spaced apart protrusion portions;     depositing a first layer over the first protrusion containing layer comprising high-density plasma chemical vapor oxide deposition so that the first layer comprises spaced apart crest portions and a concave shaped portion extended between adjacent spaced apart crest portions;     depositing a second layer over the first layer, the depositing of a second layer comprising plasma enhanced chemical vapor silicon nitride deposition;     chemical mechanical planarizing the second layer, wherein the second layer comprises a convex-shaped portion aligned with the concave-shaped portion; forming a color filter over the planarized second layer.        
 
         [0025]     Another embodiment of the invention includes a semiconductor device comprising: 
        a semiconductor substrate comprising a photosensor forming therein; a first layer overlying the substrate, the first layer comprising a portion comprising a generally concave shaped surface being the negative shaped of a micro-lens to be formed there over;     a second layer overlying the first layer, the second layer comprising a generally convex shaped portion vertically aligned with and mating with the generally concave shaped surface, the generally convex shaped portion being constructed and arranged to define a micro-lens positioned to cause parallel light passing through the micro-lens to converge on and strike the photo sensor.        
 
         [0028]     These and other embodiments of the present invention will become apparent from the following brief description of the drawings, detailed description of exemplary embodiments, and appended claims and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  illustrates a prior art semiconductor device including a micro-lens.  
         [0030]      FIG. 2A  illustrates a method according to one embodiment of the present invention including providing a first protrusion containing layer over a substrate, wherein the first protrusion containing layer includes a plurality of protrusion portions.  
         [0031]      FIG. 2B  illustrates a method according to one embodiment of the present invention including providing a first layer over the first protrusion containing layer of  FIG. 2A , wherein the first layer includes a plurality of concave shaped portions.  
         [0032]      FIG. 2C  illustrates a method according to one embodiment of the present invention including providing a second layer over the first layer of  FIG. 2B , wherein the second layer includes a plurality of convex shaped portions, each convex shaped portion aligned with one of the concave shaped portions of the first layer.  
         [0033]      FIG. 2D  illustrates a method according to one embodiment of the present invention including providing a third layer over the planarized second layer of  FIG. 2C , wherein the third layer includes color filter portions, each colored filter portion aligned with a sensor formed in the substrate.  
         [0034]      FIG. 2E  illustrates a method according to one embodiment of the present invention including applying an oxide layer over the third layer and etching down to a contact pad on the semiconductor device.  
         [0035]      FIG. 3  is a plan view showing the pattern of the first protrusion containing layer overlying the substrate according to one embodiment of the present invention.  
         [0036]      FIG. 4A  illustrates a method according to one embodiment of the invention including providing a pre-protrusion containing layer over a substrate.  
         [0037]      FIG. 4B  illustrates a method according to one embodiment of the present invention including forming protrusion and trough portions in the pre-protrusion containing layer of  FIG. 4A  to provide a first protrusion containing layer.  
         [0038]      FIG. 4C  illustrates a method according to one embodiment of the invention including providing a first layer over the first protrusion containing layer of  FIG. 4B , and wherein the first layer includes a plurality of concave shaped portions, each concave shaped portion extending between adjacent spaced apart protrusion portions of the first protrusion containing layer.  
         [0039]      FIG. 4D  illustrates a method according to one embodiment of the invention including providing a second layer over the first layer and wherein the second layer includes a plurality of convex shaped portions, each convex shaped portion aligned with a concave shaped portion of the first layer.  
         [0040]      FIG. 4E  illustrates a method according to one embodiment present invention including providing a third layer over the planarized second layer of  FIG. 4D , wherein the third layer includes color filter portions, each color filter portion aligned with a sensor formed in the substrate. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0041]     Referring now to  FIG. 2A , one embodiment of the present invention includes a method including providing a semiconductor device  10  which includes at least one inter-metal dielectric layer  26  onto which a first protrusion containing layer  32  is formed. The first layer  32  includes a plurality of spaced apart protrusion portions  34 , each protrusion portion  34  including a summit. In one embodiment, the first protrusion containing layer  32  may include a top metallization layer which may comprise a metal such as, but not limited to, aluminum or copper and alloys thereof. A trough  36  may be provided between two of the spaced apart protrusion portions  34 . In one embodiment the trough  36  is provided by an opening extending all the way down to the inter-metal dielectric layer  26 . The first protrusion containing layer  32  may also include other structures such as a bond pad  38 . As will be appreciated from  FIG. 2A , alternatively, an additional passivation layer  56  may be formed over the first protrusion containing layer  32 . The passivation layer  56  may include silicon dioxide.  
         [0042]     Referring now to  FIG. 2B , one embodiment of the present invention includes a method of forming a first layer  40  over the first protrusion containing layer  32 . The first layer  40  also includes crest (or summit) portions  43  which are vertically aligned with the protrusion portions  34  of the first protrusion containing layer  32 . A trough  41  is formed between spaced apart adjacent crest portions  43  of the first layer  40 . The first layer  40  includes a convex shaped surface  42  extending between spaced apart adjacent protrusion portions  43 . In one embodiment, the first layer  40  may comprise a dielectric such as silicon dioxide. In one embodiment, the first layer  40  comprises silicon dioxide deposited by high-density plasma oxide chemical vapor deposition.  
         [0043]     Referring now to  FIG. 2C , in one embodiment of the invention a second layer  44  is formed over the first layer  40 . The second layer  44  includes convex shaped portion  46  aligned and mated with the concave shaped surface  42  of the first layer  40 . After the second layer  44  has been deposited, the second layer  44  may be planarized, for example using chemical mechanical planarization. In one embodiment, the second layer may be silicon nitride and may be deposited by a variety of methods including plasma enhanced chemical vapor nitride deposition. The semiconductor device  10  may be etched to form an opening down to the bottom pad  38 , if present.  
         [0044]     Referring now to  FIG. 2D , another embodiment for the invention includes providing a color filter layer  48  over the second layer  44 . The color filter layer  48  may include individual color sections such as a red filter, green filter, and blue filter  50 ,  52 , and  54 . Each color filter section  50 ,  52 , and  54  is aligned with one of the sensors  28  formed in the silicon- based substrate  30 .  
         [0045]     As shown in  FIG. 2E , one embodiment of the invention includes providing an upper passivation layer  58  such as that provide by low temperature silicon dioxide deposition process, and etching away portions of the semiconductor device  10  to provide an opening  60  down to the bottom pad  38 . It will be appreciated from FIGS.  2 C-E, that the convex shaped portion  42  of the second layer of  44  provides a micro-lens that will causes parallel light rays passing through one of the color filter sections  50 ,  52 ,  54 , and through the convex shaped portion  42  to converge on and strike one of the sensors  28  formed in the silicon-based substrate  30 . In one embodiment of the invention, the use of a second layer  44  including silicon nitride produces a micro-lens which is not subject to the yellowing problem that prior art micro-lenses made from different materials such as photoresist materials are subject to.  
         [0046]      FIG. 3  is a plan view of a portion of a semiconductor device  10  according to the present invention illustrating the pattern of the first protrusion containing layer  32  including a plurality of spaced apart protrusion portions  34  separated by a trough portion  36 .  
         [0047]     FIGS.  4 A-E illustrates an alternative embodiment that does not require a top metallization layer to include spaced apart protrusion portions. Referring now to  FIG. 4A , in one embodiment of the invention, a semiconductor device  10  is formed wherein a first pre-protrusion containing layer  32 ′ is provided over an inter-metal dielectric layer  26 , and over a bond pad  38 , if present. However, in this case the first pre-protrusion containing layer  32 ′ may include silicon dioxide that may be deposited, for example by high-density plasma chemical vapor oxide deposition.  
         [0048]     Referring now to  FIG. 4B , a plurality of spaced apart trough portions  36  are formed in the first pre-protrusion containing layer  32 ′, for example using photolithographic and etching techniques known to those skilled in the art. The resulting first protrusion containing layer  32  includes spaced apart protrusion portions  34 .  
         [0049]     Referring now to  FIG. 4C , a first layer  40  may be deposited over the first protrusion containing layer  32  so that the first layer  40  includes spaced apart crest portions  43  each aligned with one of the protrusion portions  34  of the first protrusion containing layer  32 . In one embodiment, the first layer  40  includes silicon dioxide that may be deposited by any of a variety of methods including high-density plasma chemical vapor oxide deposition. As will be appreciated from  FIG. 4C , the first layer  40  includes a concave shaped portion  42  extending between spaced apart adjacent crest portions  43 .  
         [0050]     Referring now to  FIG. 4D , in one embodiment of the invention, a second layer  44  may be deposited over the first layer  40  and thereafter may be planarized by, for example, chemical mechanical planarization. In one embodiment, the second layer  44  may include silicon nitride, and may be deposited by any of a variety of methods including plasma enhanced chemical vapor silicon nitride deposition. As shown in  FIG. 4D , it will be appreciated that the second layer  44  includes convex shaped portions  46  aligned with and mated with the concave shaped portions  42  of the first layer  40 . The semiconductor  10  may be edged to form an opening  60  down to the bottom pad  38  if present.  
         [0051]     Referring now to  FIG. 4E , again, a color filter layer  48  may be deposited with an adhesion layer  200  over the planarized second layer  44  and the color filter layer  48  may include individual color filter segments  50 ,  52 ,  54  corresponding to a red filter, green filter, and blue filter respectively. Thereafter, a top layer  58  may be deposited over the color filter layer  48 . The top layer  58  may include low temperature silicon oxide, and the semiconductor device  10  may be etched to form an opening  60  down to the bond pad  38 , if present.  
         [0052]     When the terms “overlying”, “overlie”, “over” and the like terms are used herein regarding the position of one component of the invention with respect to another component of the invention, such shall mean that the first component may be in direct contact with the second component or that additional components such as under bump metallurgies, seed layers and the like may be interposed between the first component and the second component.  
         [0053]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.