Abstract:
A system of changing lensing effect of microlenses on a substrate, by forming indentations in the substrate, which effect the microlenses, by either carrying out a lensing effect, or by changing the shape of the eventual microlens.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the U.S. Provisional Application No. 60/204,618 filed May 16, 2000. 
    
    
     BACKGROUND 
     Image sensors often suffer a trade-off between the size of the image sensor and the number of items that can be placed on the image sensor. For example, larger sensor parts may be used to acquire more light, or to allow more control structure to be placed on the sensor substrate. It is often desirable to maximize the amount of circuitry that can be placed on a sensor. 
     Microlenses may often be placed on image sensor pixels. A conventional sensor may have the structure shown in FIG. 1. A planarization layer  100  covers the pixels  105 , which may be image sensor pixels. Each microlens  110  is separated from an adjacent microlens  120  by a gap  112 . The gap needs to have a specified size, e.g. one “design rule” wide. The presence of the gap may reduce the effective fill factor of the image sensor. These gaps between the lenses may be necessary to shape the lenses into their lens-like shape during the lens fabrication process. However, these gaps may lose certain real estate on the image sensor, and hence may affect the “fill factor”. 
     SUMMARY 
     The present application teaches a way of forming spacing elements between gaps between lenses in an image sensor device. By doing this, the spacing between elements may be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other aspects of the invention will be described in detail with reference to the accompanying drawings, wherein: 
     FIG. 1 shows conventional micro lenses, with a gap therebetween; 
     FIG. 2 shows a specific view of the microlenses of the present specification; 
     FIG. 3 shows an effective view of the micro lenses of the present specification; 
     FIG. 4 shows a view with troughs between microlenses, relative to the pixels; 
     FIG. 5 shows a second embodiment with alleys between square microlenses; 
     FIG. 6 shows a top view of the re-forming of the microlens; and 
     FIG. 7 shows the changing of the lens height based on width. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 shows an embodiment. The FIG. 2 view shows a cross-section across the image sensor with microlenses formed thereon. The surface on which the microlenses are formed is referred to herein as a planarization layer  200 . 
     The planarization layer is first etched to form a gap area  202  which will end up being between two adjacent microlenses. The gap area is shaped in a way that provides it with a lensing effect. 
     The planarization layer is formed over the circuitry of the image sensor to even out the height of the top surface. The top surface of the planarization layer is usually flat. Here, instead, the top surface  204  is partially flat, but only in the area where the mircrolenses will be formed. The top surface forms a dip area  202  between those microlenses. The flat areas  204  are formed with microlenses  206  covering the flat area. As conventional, the bottom surfaces  208  of the microlenses abut against the flat surface  204 . 
     In the embodiment shown in FIG. 2, the flat area  204  is substantially the same size as the bottom surface of the micro lens  206 . The flat bottom surface of the microlens  206  forms a continuous surface with the portion of the substrate  212  to the center line  214  of the gap. Accordingly, the system effectively forms larger sized microlenses, at least part of which is formed from substrate material, as shown in FIG.  3 . Each microlens, such as  300 , has a continuous portion which includes the microlens portion, and the substrate portion  212  on both sides of the microlens portions. This avoids the necessity for gaps between the microlenses, thereby forming a higher fill factor. 
     The areas between the microlenses are “troughs”, i.e., indentations in the substrate. The troughs may be of any desired shape that can cause a lensing effect for incoming light. That desired shape is preferably slightly curved, but can be of any shape that causes a lensing effect for light. 
     The troughs between the microlens may be flat and substantially triangular shaped, or may be in substantially the shape of the intersection of two spheres. The first sphere part would be  212 , with the second sphere part being a continuation of the spherical shape from the other adjacent microlens. 
     The troughs are shown in more detail in FIG.  4 . Trough  400  has a lowest portion which is preferably aligned with edges between the image sensor pixels  402 , which are also covered by color filters  404 . Accordingly, the troughs between the microlenses may act to deflect light from regions between the pixels, into one of the pixel areas. 
     Another embodiment shown in FIG. 5 is intended for use with a square outer shaped microlens. These square microlenses often have the same problems noted above of lower fill factors and relatively poor optical qualities. In a conventional square-footprint microlens, the surface profile after formation is somewhat pyramid shaped. The inventor believes that this pyramid shape is due to the way that the microlenses are formed. The microlens is formed by starting with a square microlens, then melting and reflowing. As the microlens melt re-flow cools, the free energy in the surface tension is reduced. This may tend to form non-regular structures. Such a structure profile does not necessarily make a good lens. 
     The present embodiment changes the surface profile by making the microlens more close to spherical. The system described herein uses indentations in the surface on which the microlenses are formed. These indentations are referred to as “alleys”. The alleys are formed between the square footprint microlenses. 
     FIG. 5 shows an embodiment. The FIG. 5 system shows the top before melting. A square footprint microlens  500  is surrounded at four edges by alleys  502 ,  504 ,  506 ,  500 . The alleys are indentations in the substrate on which the lenses are formed. The microlenses are heated to form liquid microlenses. The alleys alter the free energy state of these liquid lenses microlenses, and cause the resulting surface profile to become closer to spherical. In fact, for a system formed by four alleys around a square microlens, the resulting microlens, after melting and cooling, becomes a biaxial octagon. 
     The alleys are formed along an axis as shown in FIG.  6 . The alleys  504 ,  508  are formed along axis  1 . The alleys  506 ,  502  are formed along axis  2 . The alleys adjust the surface height of the microlenses as shown in the graph of FIG.  7 . During the melt, the areas of the lens such as  600 , which are nearest the alleys, are drawn at least slightly towards the alleys. Accordingly, the area  600  is drawn towards the alleys  506 , thereby making that area more close to spherical. 
     While the above has been described using four alleys, one surrounding each microlens, it should be understood that more alleys could be used, and that the alleys need not be symmetrical. An asymmetrical system may be used, for example, where the optical effect of part of the microlens is more important than the effect of some other part of the microlens. 
     In addition, the same ideas can be used for other shaped microlenses including round microlenses in order to alter the shape of the microlenses. 
     All such modifications are intended to be encompassed within the following claims, into which: