Single-layer and bilayer resist processes for EUV-type integrations

Abstract

The high absorption of extreme ultraviolet (EUV) radiation by all materials necessitates the use of thin photoresist films with thicknesses less than 200 nm for EUV lithography to ensure good imaging. Thinning the resist thickness below 150 nm or even 100 nm may produce benefits such as increased sensitivity, larger process latitude, and increased resolution. However, these potential benefits as well as the required need for thin resists come at the expense of reduced etch resistance. EUV lithography will require the use of some type of thin imaging technique such as top-surface imaging, bilayer resists, or single layer resists with hardmasks in order to achieve the necessary etch resistance. In this paper, we discuss results that demonstrate the feasibility of using thin resist approaches for fabricating working devices. We have successfully fabricated working 130-nm-node SRAMs using a single layer 248 nm ultrathin resist (< 150-nm-thick) with a hardmask for both gate and contact layers on the same wafer. This result represents the first demonstration of working devices fabricated using ultrathin resists on multiple device layers. We also present initial patterning experiments using a 193 nm bilayer resist for brightfield applications such as the gate layer, and compare imaging performance to that of a 193 nm single layer resist. The advantages and disadvantages of the single layer and bilayer approaches are discussed.