Highly selective dry etching of alternating phase-shift mask (PSM) structures for extreme ultraviolet lithography (EUVL) using inductively coupled plasmas (ICP) H.Y. Jung a , Y.R. Park a , H.J. Lee a , N.-E. Lee a, ⁎, C.Y. Jeong b , Jinho Ahn b a School of Advanced Materials Science & Engineering, Center for Advanced Plasma Surface Technology, Sungkyunkwan University, 300 Chunchun-dong, Suwon, Kyunggi-do 440-746, South Korea b Department of Materials Science & Engineering, Hanyang University, Seoul, 133-792, South Korea abstract article info Available online 4 February 2009 Keywords: Extreme ultraviolet lithography (EUVL) mask Alternating phase-shift mask (PSM) Inductively coupled plasma (ICP) Plasma etching Extreme ultraviolet lithography (EUVL) is the most promising candidate for next generation lithography due to its feature size of 32 nm or below. We investigated the etching properties of materials in an alternating, phase-shift mask (PSM) structure for EUVL, including a Ru top capping layer, Mo–Si multilayer (ML) and Ni etch stop layer (ESL), by varying the Cl 2 /O 2 and Cl 2 /Ar gas flow ratios, and the dc self-bias voltage (V dc ) in inductively coupled plasma (ICP). The Ru layer could be etched effectively in Cl 2 /O 2 plasmas and Mo–Si ML could be etched with an infinitely high etch selectivity over Ni ESL in Cl 2 /Ar plasmas, even with increasing overetch time. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The increasing miniaturization trend of nano-scale silicon de- vices requires new lithography technologies, of which extreme ultraviolet lithography (EUVL) using a wavelength of 13.5 nm is the most promising candidate due to its ability to adopt current litho- graphy equipment without requiring major changes [1]. One of the critical technologies in EUVL is the fabrication of reflective EUVL masks. The EUVL mask typically consists of a mirror layer reflecting the extreme ultraviolet (EUV) lights and an absorber stack absorbing the EUV lights selectively. Several advanced types of EUVL masks such as the etched binary mask, refilled multilayer (ML) binary mask, etched attenuated phase-shift mask (PSM), embedded attenuated PSM and alternating PSM have been developed for improved performance [2,3]. PSM is one of the mask structures capable of improving the resolution using destructive and constructive interference of lights with different phases from each other [4–7]. A schematic diagram of the proposed, alternating PSM structure is shown in Fig 1 . The stacked structure of alternating PSM has two groups of Mo–Si ML. By removing some bi-layers, 180° phase shift can be obtained between the near field reflected from the etched region and that from the un-etched region [8,9]. One pair of Mo–Si ML consists of a 2.8-nm-thick Mo layer and a 4.15-nm-thick Si layer. The top Mo–Si ML is capped with a 2-nm-thick Ru layer to prevent oxidation [10]. Ni, Si and Ru layers exist between the two Mo–Si ML groups. The Ni layer acts as the etch stop layer (ESL) during etching of Mo–Si ML, while both the bottom and top Ru layers act as the capping layer. Mo–Si ML should be etched using the same etch conditions for the Mo and Si layers. Mo can be effectively etched in chlorine-based plasmas [11–15] with the formation of volatile by-products such as MoCl 3 and MoCl 5 with boiling points of 100 °C and 268 °C, respectively [15]. Si can also be etched in chlorine-based plasmas with the formation of SiCl x by-product [16,17]. In contrast to the etch characteristics of Mo–Si ML, Ni has often been used as an etch mask in chlorine plasmas due to its high etch durability [17]. The dry etching of Ru layer using Cl 2 /O 2 plasma has been reported [18–22]. In this study, we investigated the etching characteristics of the mask materials for fabricating ML-etched, alternating PSM with a large depth of focus, a high contrast, no line width variation and reduced image placement error [23]. We focused on the etching characteristics of Mo–Si ML and Ni ESL because the thickness of Ni ESL is only 3 nm in the alternating, PSM-stacked structure. The etching experiments for each layer (Ru and Mo–Si ML) and for the stacked structure of Ru/Mo–Si ML/ Ni ESL were performed using Cl 2 -based, inductively coupled plasma (ICP) by varying the gas flow ratio and etching time. An infinitely high etch selectivity of Mo–Si ML to Ni ESL and a precise etch stop on Ni ESL were achieved under certain process conditions. 2. Experiments This experimental investigation on the top Ru capping layer and Mo–Si ML etching was performed with a modified commercial ICP etcher. The ICP etcher had a 3.5-turn, spiral copper coil on the top of the chamber, which was separated by a 1-cm-thick quartz window, and a turbo pump backed by a dry/booster combo pump. The etcher was capable of etching 8-inch diameter wafers. Radio frequency (RF) power (13.56 MHz) was applied to the top electrode coil and to the substrate holder to induce the plasma and a dc self-bias voltage (V dc ) to the wafer, respectively. Thin Solid Films 517 (2009) 3938–3941 ⁎ Corresponding author. E-mail address: nelee@skku.edu (N.-E. Lee). 0040-6090/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2009.01.119 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf