Sputter deposited carbon tested as RIE intermediate for HSQ and its CMP reversed patterns Falco van Delft * , Eric van den Heuvel, Frank van der Kruis, Martien Maas, Francisco Gonzalez Rodriguez, Jeroen van Buul, Robert van de Laar, Ton de Win, Emile Naburgh, Frans Holthuysen Philips Research – MiPlaza, High Tech Campus 4, (WAG-01), 5656 AE Eindhoven, The Netherlands article info Article history: Received 26 September 2008 Received in revised form 7 January 2009 Accepted 8 January 2009 Available online 17 January 2009 Keywords: Glassy carbon Image reversal Electron beam lithography Hydrogen Silses Quioxane Chemical mechanical polishing Carbon-carbon neighbour ratio abstract Sputter deposited carbon has been tested as Reactive Ion Etching (RIE) intermediate, i.e. as second layer in a bi-layer resist system. E-beam written Hydrogen Silsesquioxane (HSQ) patterns or their reversed com- plementary (silicon) patterns (obtained by Chemical Mechanical Polishing (CMP)) were used as top layer. Using oxygen RIE, features smaller than 50 nm wide have been transferred into the sputtered carbon in both the forwarded and the reversed tone. After oxygen RIE of the reversed bi-layer, however, extensive surface roughness is observed. Auger spectra of our sputtered carbon show predominantly sp 2 bonds, indicating that the sputter deposited material is comparable to the glassy carbon which has been used as sputter target. The etch resistance of this sputtered carbon in many standard etch recipes outperforms Novolak and Poly Hydroxy Styrene (PHS) based resists. The etch rates can be correlated to the normalized average amount of (nearest neighbour) carbon to carbon atom bonds for a carbon atom in the resist, the carbon–carbon neighbour ratio parameter C 2 NR. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen SilsesQuioxane (HSQ) is a well known negative tone inorganic e-beam resist, featuring high resolution and high etch resistance [1–3]. Most positive tone resists with comparable resolu- tion capabilities (PMMA and its derivatives) suffer from a rather poor etch resistance. Image reversal methods using electroplating or Chemical Mechanical Polishing (CMP) have been shown to be able to reverse HSQ patterns into inorganic materials like metals, silicon, silicon oxide and silicon nitride [4]. Many well established Reactive Ion Etch (RIE) processes, however, are based on (lower res- olution) carbon built resists, e.g. Novolak and Poly Hydroxy Styrene (PHS) type resists with good etch resistance. Hence, it would be use- ful to convert the high resolution HSQ (and its reversed) patterns into a carbon built material, which can be subsequently employed in standard etch processes, while maintaining high resolution. It has been shown that the negative tone HSQ patterns can be transposed into hard baked Novolak using oxygen RIE [2], but im- age reversal attempts by CMP of hard baked Novolak covering HSQ features were not successful due to too large differences in mechanical properties between these inorganic and organic mate- rials; even Novolak, hard baked at 250 °C, appears to be too soft for CMP in combination with cross-linked HSQ. In the present paper, sputtered carbon has been tested as sec- ond layer underneath the HSQ patterns or their CMP reversed pat- terns. The etch resistance of this sputtered carbon has been compared to several typical resists in standard RIE processes. The etch rates can be correlated to the normalized average amount of (nearest neighbour) carbon to carbon atom bonds for a carbon atom in the resist, the carbon–carbon neighbour ratio parameter C 2 NR introduced in this paper. This parameter is compared to the ring- and Onishi parameters commonly used in this field [5,6]. The method described here for transferring high resolution patterns into RIE compatible sputtered carbon is not restricted to e-beam lithography, but can also be applied to e.g. Focussed Ion Beam (FIB) lithography and to the Projection Mask-Less Patterning (PMPL) system, as developed in the CHARPAN project [7]. The latter lithography system is based on hundreds of thousands of finely focussed charged particle (ion) beams, extracted from a plasma source and selected by a programmable aperture plate [8]. This mul- ti ion beam system can be used for direct 3D sputter etching [9], but also for fast pattern cross linking in HSQ [8]. Such HSQ patterns can be employed in the bi-layer methods described in this paper. 2. Experimental Silicon wafers (6 in.) were coated with a 120 nm thick carbon layer by sputter deposition from a glassy carbon target in a Leybold 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2009.01.004 Abbreviations: HSQ, Hydrogen Silsesquioxane; RIE, reactive ion etching; CMP, chemical mechanical polishing; C 2 NR, carbon–carbon neighbour ratio. * Corresponding author. Tel.: +31 40 27 43124; fax: +31 40 27 45002. E-mail address: Falco.van.Delft@philips.com (F. van Delft). Microelectronic Engineering 86 (2009) 956–960 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee