Masked ion beam resist exposure using grid support stencil masks

Submicrometer resolution ion beam resist exposure using a new type of stencil mask is described. The mask uses a grid support structure in transmission areas to remove restrictions on pattern geometry and improve stability. The image of the grid is eliminated by rocking the incident angle of the ion beam during exposure, or by special processing of the resist. We describe the mask fabrication sequence and show examples of masks that employ a 320 nm period grid structure. Patterns with a minimum feature size of less than one-half micrometer have been replicated using this type of mask with both single and multilayer resists. In addition, experiments are described which used low energy ion beams to test the ultimate resolution of stencil masks without grid support. 40 nm wide lines were printed in PMMA at a mask-to-wafer gap of 25 μm. The applicability of such masks in high resolution proximity printing systems is discussed.