Application of electron beam lithography to produce corrugated surface for DFB lasers

For long wavelength single node DFB type laser devices it Is required to rrugate the surface of InP substrate in the form of lines (Grating) with spatial period In sub-half micron ng. Electron beam lithography (E2L) can be used to make such high resolutlon lines first in the resist and then these lines can be transferred to the substrate by suitable dry or wet etching process. In delineating such closely spaced lines In the resist which Is coated on a relatively high average atctnic number substrate ( At.No.32), the well known proximity exposure (PE) effect associated with EBL requires cxrrection • The paper discusses arid gives the simulation results which depict the effect of PE on the width and spacing of lines. A comparison Is made between the lines on the lower At.No. substrate Si, and high At.No. InP substrate. A proximity exposure compensation (PEC) scheme based on dose variation technique is found to provide just adequate correction to PE effect. The experimental results on the delineation of lines before and after correction show good agreement with the simulated results within experimental limitations.