Via wave guide with curved light concentrator for image sensing devices

A method for fabricating a via wave guide in a CMOS image sensor (CIS), the method comprising:

• forming a sensing element in a substrate;
• forming a metallization layer over the sensing element, wherein the metallization layer includes a plurality of insulation layers and a plurality of metal lines disposed in the insulation layers, and having an upper surface;
• dry etching the metallization layer through a mask opening to define a first, relatively narrow hole through the upper surface of the metallization layer, the first hole extending a first, relatively short distance between the upper surface and the sensing element;
• and
• wet etching the metallization layer through the mask opening to define an light concentrator of the via wave guide, the light concentrator having a first, relatively wide opening located adjacent to the upper surface and a tapered surface extending between the upper opening and a lower end,
• wherein defining the light concentrator comprises forming a parabolic surface.

A method for fabricating a via wave guide in a CMOS image sensor (CIS), the method comprising:

• forming a sensing element in a substrate;
• forming a metallization layer over the sensing element, wherein the metallization layer includes a plurality of insulation layers and a plurality of metal lines disposed in the insulation layers, and having an upper surface;
• dry etching the metallization layer through a mask opening to define a first, relatively narrow hole through the upper surface of the metallization layer, the first hole extending a first, relatively short distance between the upper surface and the sensing element;
• and
• wet etching the metallization layer through the mask opening to define an light concentrator of the via wave guide, the light concentrator having a first, relatively wide opening located adjacent to the upper surface and a tapered surface extending between the upper opening and a lower end;
• dry etching the metallization layer through the mask opening to define an lower section of the via wave guide such that a peripheral surface of the lower section has a substantially uniform cross section extending from the lower end of the light concentrator toward the sensing element;
• forming a mirror coating on the curved surface of the light concentrator.