Patent ID: 7745880

Claim:
A semiconductor device having a dielectric substrate transparent to light, the dielectric substrate having a pair of major surfaces, one of the major surfaces being a front surface having a device formation film thereon, and another of the major surfaces being a back surface, the semiconductor device comprising: a first film of a first material that reflects sensing light illuminated thereon from an external source, the first film disposed on the back surface of the dielectric substrate; a second film of a second material that reflects the sensing light, disposed on the first film, the second material differing from the first material; and a third film of a third material that reflects the sensing light, disposed on the second film, wherein the second film has a lower refractive index than the first and third films, wherein the first film comprises polysilicon, the second film comprises silicon oxide, and the third film comprises polysilicon, and wherein the first film has a thickness of substantially 42 nm, the second film has a thickness of substantially 110 nm, and the third film has a thickness of substantially 42 nm.