Patent ID: 8187481

Claim:
A process for modifying the flat upper surface of a substrate so as to suppress the reflection and scattering of electromagnetic waves from the substrate surface and thus increase transmission of the electromagnetic waves through the substrate, wherein the electromagnetic waves have known wavelengths, the process employing reactive ion etching that uses spaced electrodes, with an electrical potential applied across the electrodes, the process comprising: placing the substrate between the electrodes, where the flat upper substrate surface is directly exposed to the space between the electrodes without a mask on the substrate surface; flowing one or more gases in the space between the electrodes; applying an electrical potential across the electrodes, to create a plasma from the one or more gases, wherein the plasma attacks the substrate surface both chemically and physically, to remove material from the substrate surface; forming a polymer with the plasma, the polymer formed at random times at random locations on the flat upper substrate surface, the polymer on the surface masking the removal of substrate material at the location of the polymer; wherein the polymer persists temporarily on the flat upper substrate surface for sufficient time to temporarily mask the removal of substrate material located underneath the formed polymer; wherein the process is continued for sufficient time to fabricate a surface relief texture on the substrate surface containing surface relief structures; wherein the surface relief texture has a random distribution of structure spacing and structure depth, where the structure spacing is everywhere smaller than the shortest wavelength of the electromagnetic waves, the structure depth is no less than half the dimension of the largest wavelength of the electromagnetic waves, and the refractive index of the surface relief texture increases generally monotonically from the environment to the bulk material substrate; wherein with the electromagnetic waves incident on the substrate surface at angles in the range of from 0 to 30 degrees, the loss in transmission of the electromagnetic waves due to reflection from the surface relief texture is less than 0.5% and the loss in transmission of the electromagnetic waves due to scattering from the surface relief texture is no more than 1%.