Progress in placement control for ion beam stencil mask technology

摘要

A short review of the current status of IPL stencil mask development is presented in this paper. Stencil masks based on 6" Si-wafer have been fabricated with a membrane diameter of 126 mm. With a typical membrane thickness of 3μm, mechanical stability is a critical issue. The resulting placement errors have been measured using an LMS IPRO measurement tool and have been compared to Finite Element (FE) calculations simulating the fabrication process. Process-induced distortions can be predicted by FE calculations with an accuracy of up to 24 nm 3σ. In addition to large circular membranes, an alternative geometry has been considered. Masks with a quadratic membrane area of 60 x 60 mm~2 show IPDs of 3 σ= 39 nm which are about 4 times smaller than those of large circular membranes. This result agrees well with predictions of FE calculations. In order to protect the Si-mask against ion bombardment, a protective carbon layer is deposited onto the membrane, thus preventing stress changes due to ion implantation. The current status of the carbon deposition process will also be addressed briefly.