Fabrication of Organic Thin Films for Copper Diffusion Barrier Layers using Molecular Layer Deposition
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Fabrication of Organic Thin Films for Copper Diffusion Barrier Layers using Molecular Layer Deposition Paul W. Loscutoff,1 Scott B. Clendenning,2 and Stacey F. Bent1 1 Department of Chemical Engineering, Stanford University, 381 North South Mall, Stanford, CA 94305, U.S.A. 2 Intel Corporation, RA3-252, 2513 NW 229th Ave., Hillsboro, OR 97124, U.S.A. ABSTRACT Device scaling predicts that copper barrier layers of under 3 nm in thickness will soon be needed in back-end processing for integrated circuits, motivating the development of new barrier layer materials. In this work, nanoscale organic thin films for use as possible copper diffusion barrier layers are deposited by molecular layer deposition (MLD) utilizing a series of selflimiting reactions of organic molecules. MLD can be used to tailor film properties to optimize desirable barrier properties, including density, copper surface adhesion, thermal stability, and low copper diffusion. Three systems are examined as copper diffusion barriers, a polyurea film deposited by the reaction of 1,4-phenylene diisocyanate (PDIC) and ethylenediamine (ED), a polyurea film with a sulfide-modified backbone, and a polythiourea films using a modified coupling chemistry. Following deposition of the MLD films, copper is sputter deposited. The copper diffusion barrier properties of the film are tested through adhesion and annealing tests, including 4-point bend testing and TEM imaging to examine the level of copper penetration. The promise and challenges of MLD-formed organic copper diffusion barriers will be discussed. INTRODUCTION For over 40 years, the scaling of semiconductor devices has followed Moore’s Law, with a doubling of transistor counts every 2 years. This aggressive scaling leads to a continual need for new processes and materials to meet next generation requirements. While much attention is given to the scaling of the front-end transistor dimensions, the back-end interconnect scaling is equally severe. The requirements on copper diffusion barriers at the 22 nm node and beyond are stringent, as the barrier thickness is projected to be 1 nm by 2021 [1] with conformal, smooth, pin-hole free films. The current TaN barriers have not been shown to be effective at thicknesses
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