Periodic sub-wavelength electron beam lithography defined photonic crystals for mode control in semiconductor lasers

Surface structure lasers possess lithographically defined patterns, such as gratings and waveguides, on the wafer surface and are usually fabricated without semiconductor regrowth. Optical surface structures typically require sub-micron to nano-scale accuracy in fabrication. For surface structures with more complex geometries, electron beam lithography offers the necessary flexibility, control, and accuracy in fabrication. However, a challenge with electron beam lithography is the patterning of large (~1 mm by 1 mm) areas while maintaining the fabrication accuracy. In this work, we demonstrate two electron beam lithography techniques in a process for the fabrication of surface structure lasers with large areas that require sub-micron to nanometer accuracy. The first technique uses proximity effect correction to fabricate two-dimensional surface gratings each consisting of approximately one million 100 nm diameter circles over an 800 μm by 160 μm area. The second part of the process uses overlay lithography with an alignment accuracy better than 45 nm over a 1 mm by 3.2 mm area to planarize waveguide array lasers.