A Flexible Multilayer Resist System Using Low Temperature Plasma‐Deposited Silicon Nitride

Abstract

A three‐layer resist system which uses positive photoresists for planarizing and imaging and an intermediate layer of plasma‐deposited silicon nitride is described. The planarizing layer is 2 μm‐thick Shipley AZ® 2430. The silicon nitride transfer layer is deposited at low temperature over hard‐baked AZ 2430. Photon or electron imaging is done in a thin layer of resist spun on top of the transfer layer. The silicon nitride deposition process is described, and the properties of the resulting film are detailed. The planarizing photoresist is patterned by oxygen reactive ion etching. The vertical etch rate and the degree of isotropy are measured as a function of rf power and oxygen pressure. Controllable and reproducible undercut is achieved with this multilayer resist system. The resist profile is demonstrated to be suitable for lift‐off applications or anisotropic etching of the substrate.