ELECTRON-BEAM INDUCED MODIFICATION OF GAAS-SURFACES FOR MASKLESS THERMAL CL-2 ETCHING

We have investigated how exposure to an electron beam can modify the surface of a GaAs epitaxial layer, causing the irradiated areas to later show a variable reaction to Cl2 gas at elevated temperatures. In the work presented here, electron beam exposure and thermal Cl2 etching are performed sequentially in two separate vacuum systems. The reaction to Cl2 at elevated temperatures is moderated by the electron beam dose. Below a critical dose we observe that the areas which have been exposed to the electron beam begin etching much sooner than the nonexposed areas. Above the critical dose, a masking effect takes place so that the irradiated areas become more resistant to etching by Cl2 than the unexposed areas. Both positive and negative lithographic patterns can thus be produced in adjacent areas with high contrast. These effects are attributed to changes in a native oxide only a few monolayers thick. The electron beam exposure forms a latent image which is not found in our experiments to be altered or healed by exposure to the atmosphere. The process presents possibilities for maskless patterning and simplification for in situ processing, possibly removing the need for the e-beam system to be directly connected to the growth chamber. Its use would eliminate the difficult sample transfer mechanics permiting separate high resolution e-beam writing machines to be used for pattern generation.