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Effect of Copper Surface Condition on Passivation Characteristics for Applications to Area Selective Atomic Layer Deposition

Su Min Hwang (University of Texas at Dallas); Harrison Kim‚ Jin-Hyun Kim (The University of Texas at Dallas); Yong Chan Jung (University of Texas at Dallas); Luis Fabian Pena‚ Kui Tan‚ Jean-Francois Veyan (The University of Texas at Dallas); Dan Alvarez‚ Jeffrey Spiegelman (RASIRC); Kashish Sharma‚ Paul Lemaire‚ Dennis Hausmann (Lam Research Corp.); Jiyoung Kim (University of Texas at Dallas)

Recently‚ area-selective atomic layer deposition (AS-ALD) by locally passivating the copper surface has garnered attention by reducing the number of processing steps as well as by alleviating key challenges associated with lithography and layer alignment at the sub-5 nm node.1–3 However‚ despite the enormous scientific effort in recent years‚ lack of surface science during cleaning and passivation of Cu surfaces impede the development of AS-ALD. Specifically‚ the effect of the copper surface on the quality of passivation materials‚ such as self-assembled monolayers (SAMs) has been rarely reported.

Herein‚ electroplated Cu films were treated using glacial acetic acid (CH3COOH) and anhydrous N2H4‚ respectively.4 After cleaning‚ the Cu samples were immersed in a 1 mM solution of octadecanethiols (ODTs) in ethanol for 20 h. To elucidate the surface chemistry and stability of ODTs‚ the passivated Cu samples were loaded into an in-situ reflectance absorption infrared spectroscopy (RAIRS) system equipped with an ALD chamber‚ then ALD of AlOx process was performed using TMA and H2O at 120 oC. During surface cleaning‚ CH3COOH removes surface adventitious contaminants (e.g.‚ –CHx‚ –CO3‚ and –OH)‚ and most importantly‚ reduces the surface oxide (Cu2O) to metallic copper by forming copper acetate as an intermediate material. In the ex-situ XPS and RAIRS‚ the SAMs on the CH3COOH-treated Cu sample gives poor selectivity of ALD-AlOx compared to the SAMs on the as-is Cu and N2H4-treated Cu‚ respectively. It implies that the residual copper acetate on the surface can affect the chemisorption of ODTs during passivation‚ eventually attributing a relatively lower surface coverage‚ poor thermal stability of ODTs‚ and poor selectivity during ALD process. To circumvent the issue‚ the effect of post-treatment after surface cleaning with CH3COOH was investigated. Vacuum treatment of the sample under the UHV condition (~10-8 Torr) can partially reduce the copper acetate by forming -CHx and -OH species. However‚ a post-annealing at 75 oC effectively removes the copper acetate and residual contaminants on the surface‚ which can improve not only ODTs quality in the passivation process but also the increase of nucleation delay during the consecutive ALD process. The detailed experimental results will be presented.

The authors acknowledge Lam Research Foundation for the partial financial support and Rasirc Inc. for providing the Brute N2H4 as well as their partial support.

1 N.F.W. Thissen et al.‚ 2D Mater. 4‚ (2017)

2 L.F. Pena et al.‚ ACS Appl. Mater. Interfaces 10‚ 38610 (2018)

3 M. He et al.‚ J. Electrochem. Soc. 160‚ D3040 (2013)

4 S.M. Hwang et al.‚ ECS Trans. 92‚ 265 (2019)

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Area Selective ALD
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