Semiconductor device and manufacturing method thereof

Abstract

Provided is a semiconductor device which allows an alignment mark used for the manufacturing of a solid-state image sensor (semiconductor device) having a back-side-illumination structure to be formed in a smaller number of steps. The semiconductor device includes a semiconductor layer having a first main surface and a second main surface opposing the first main surface, a plurality of photodiodes which are formed in the semiconductor layer and in each of which photoelectric conversion is performed, a light receiving lens disposed over the second main surface of the semiconductor layer to supply light to each of the photodiodes, and a mark for alignment formed inside the semiconductor layer. The mark for alignment is formed so as to extend from the first main surface toward the second main surface and have a protruding portion protruding from the second main surface in a direction toward where the light receiving lens is disposed.

What is claimed is: 
     
         1 . A semiconductor device, comprising:
 a semiconductor layer having a first main surface and a second main surface opposing the first main surface;   a plurality of light receiving elements which are formed in the semiconductor layer and in each of which photoelectric conversion is performed;   a light receiving lens disposed over the second main surface of the semiconductor layer to supply light to each of the light receiving elements; and   a mark for alignment formed inside the semiconductor layer,   wherein the mark for alignment extends from the first main surface toward the second main surface,   wherein the mark for alignment is formed to fill an inside of a trench portion formed in the semiconductor layer,   wherein, inside the trench portion, a first layer comprised of a conductive film or a semiconductor film and a second layer comprised of an insulating film formed inwardly of the first layer are included, and   wherein the mark for alignment is formed of the first and second layers inside the trench portion.   
     
     
         2 . A semiconductor device according to  claim 1 , further comprising:
 a transistor for inputting/outputting an electric signal to and from each of the light receiving elements,   wherein the first layer inside the trench portion is the same as a layer of the gate electrode, and   wherein the second layer is the same as a layer of an insulating layer formed so as to come in contact with the gate electrode.   
     
     
         3 . A semiconductor device according to  claim 2 ,
 wherein a width of the mark for alignment along the first and second main surfaces is not more than double a sum of respective thicknesses of the first and second layers forming the gate electrode.   
     
     
         4 . A semiconductor device according to  claim 1 ,
 wherein the semiconductor layer is made of single-crystal silicon,   wherein the first layer contains silicon or a metal material, and   wherein the second layer is a silicon oxide film or a silicon nitride film.   
     
     
         5 . A semiconductor device according to  claim 1 ,
 wherein the mark for alignment is formed only in a part of an outer peripheral portion of the semiconductor layer in planar view.