New mask format for low-energy electron-beam proximity projection lithography

Abstract

In order to solve the various problems associated with a LEEPL mask as originally demonstrated in the form of single-membrane diamond mask, we propose a new mask format termed COSMOS (complementary stencil mask on strut-supports). The COSMOS has small-area membranes with strut reinforcement and is somewhat similar to the masks used for other types of electron projection lithography (EPL). However, the exposure strategy is completely different from the other EPLs; a complete pattern image can be transcribed by overlaying complementary portions of a mask pattern via multiple exposures. The inter-membrane and intra-membrane distortions of image placement have been computed by the finite element method (FEM) simulation. It is concluded that the global distortion induced by the inversion of gravity can be corrected for by mask writing, and the intra-membrane distortion, induced by both the gravitational flexure of a membrane and the pattern density distribution, can be neglected with the membrane intrinsic stress of approximately 5 MPa.

BEOL process technology based on proximity electron lithography: demonstration of the via-chain yield comparable with ArF lithography

“…In that case, finite-element analysis showed that in-plane distortion of mask patterns due to the intrinsic stress of the membrane exceeds the tolerable limit. 7 Since the marks for metrological measurement to determine the distortion cannot be located within the device area to be exposed, it is extremely difficult to correct the global placement error. 8 Considering these serious problems above as well as the availability of defect-free masks, the COSMOS supplied from Toppan Printing, Ltd. was adapted for this work.…”

Experimental analysis of image placement accuracy of single-membrane masks for LEEPL

“…One is a stencil mask with a single-membrane 4,5 and the other is a complementary stencil mask on strut-supports. 6 Both have merits and demerits. One inherent advantage of the single-membrane mask is to avoid the pattern stitching that is necessary in the case of complementary stencil masks.…”