Low-reflectivity back-illuminated image sensor
An image sensor for short-wavelength light includes a semiconductor membrane, circuit elements formed on a first surface of the semiconductor membrane, and a boron-coated, textured surface on a second surface of the semiconductor membrane. The textured surface comprises pseudo-random, periodic, and/or random distribution of upright pyramids, inverted pyramids, and/or nanocones. The textured surface reduces the reflection of incident light across wide bands in the DUV and VUV regimes, thus increasing the amount of light absorbed and improving the efficiency of the image sensor. Reflectance may be further reduced by applying an antireflective coating on the textured surface. The image sensor may be a two-dimensional area sensor, or a one-dimensional array sensor. and incorporated in an inspection system.
1 . An image sensor comprising:
a semiconductor membrane comprising an epitaxial layer, wherein the epitaxial layer includes a first surface and a second textured surface opposite of the first surface, wherein the second textured surface comprises a distribution of nanocones configured to reduce reflection of DUV and VUV light, wherein at least some of the nanocones have heights between 350 nm and 1000 nm and radii of their bases between 80 nm and 160 nm;
one or more circuit elements formed on the first surface of the epitaxial layer; and
a boron layer disposed on the distribution of nanocones of the second textured surface of the epitaxial layer, wherein the boron layer conforms to and seals the distribution of nanocones and seals the second textured surface of the epitaxial layer.
2 . The image sensor of claim 1 , wherein the image sensor is configured to sense at least one of deep ultraviolet (DUV) radiation or vacuum ultraviolet (VUV) radiation.
3 . The image sensor of claim 1 , wherein the boron layer comprises a boron composition of 75% or greater.
4 . The image sensor of claim 1 , wherein the distribution of nanocones of the second textured surface comprises a pseudo-random distribution of nanocones.
5 . The image sensor of claim 1 , wherein the distribution of nanocones of the second textured surface comprises a periodic distribution of nanocones.
6 . The image sensor of claim 1 , wherein the distribution nanocones of the second textured surface comprises a random distribution of nanocones.
7 . The image sensor of claim 1 , wherein the boron layer is between 2 nm and 20 nm thick.
8 . The image sensor of claim 1 , wherein the boron layer comprises less than 10% oxygen near an interface between the boron layer and the epitaxial layer.
9 . The image sensor of claim 1 , further comprising: an anti-reflection coating disposed on the boron layer.
10 . The image sensor of claim 9 , wherein the anti-reflection coating comprises at least one of magnesium fluoride, hafnium oxide, strontium tetraborate, silicon dioxide, silicon nitride, titanium dioxide, or aluminum oxide.
11 . The image sensor of claim 1 , wherein the epitaxial layer is greater than 10 μm in thickness.
12 . The image sensor of claim 11 , further comprising a doped layer formed in the second textured surface of the epitaxial layer and adjacent to the boron layer.
13 . The image sensor of claim 1 , further comprising: a support wafer attached to the one or more circuit elements.
14 . The image sensor of claim 1 , further comprising: a protective layer formed on the one or more circuit elements.
15 . The image sensor of claim 1 , wherein the image sensor is incorporated within at least one of a one of a charge-coupled device (CCD) and a CMOS device.
16 . The image sensor of claim 1 , wherein the second textured surface comprises a distribution of at least one of inverted pyramids, and wherein the bases of 80% or more of the at least one of the inverted pyramids have linear dimensions between 150nm and 300nm.
17 . The image sensor of claim 1 , wherein 80% or more of the nanocones have heights between 350 nm and 1000 nm, and 80% or more of the nanocones have radii of their bases between 80 nm and 160 nm.