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Use of a sacrificial Ruthenium hard mask for Cu Back End of Line (BEOL) interconnect structures

IP.com Disclosure Number: IPCOM000204628D
Publication Date: 2011-Mar-07
Document File: 1 page(s) / 23K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to use a sacrificial Ruthenium hardmask for Cu Back End of Line (BEOL) interconnect structures. This helps control dielectric/Cu-line thickness across a wafer. The invention uses a Ruthenium (Ru)-based metal hardmask which is deposited on top of the Ultra-Low K (ULK) dielectric stack. The hardmask permits finer control of the ULK thickness remaining underneath.

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Use of a sacrificial Ruthenium hard mask for Cu Back End of Line (BEOL) interconnect structures

22nm node requires line height control (for resistance and capacitance control) across pattern densities and across the wafer. For example, for the ULK/OMCTS/OMOX (OMCTS refers to octamethylcyclotetrasiloxane, and OMOXis bilayer hardmask of OMCTS and silicon dioxide) integration scheme, chemical-mechanical planarization (CMP) is used to remove ~350A of OMCTS in addition to ~300A of Ultra-Low K (ULK). The thickness of the OMOX layer incoming to CMP varies depending on pattern density. Due to the need to remove such large thicknesses of dielectric materials, with roughly similar polish rates, it is difficult to control the remaining dielectric/Cu-line thickness. This affects line Rs control deleteriously. Additionally, dielectric hardmask thickness variation across pattern densities incoming to liner deposition can affect liner thickness on sidewalls.

The disclosed invention is a solution which uses a Ruthenium (Ru)-based metal hardmask which is deposited on top of the ULK dielectric stack. The Ru-based layer is of the order of 100A. The hardmask acts a thin, but effective, stop for Etch and for CMP. Stopping on the metal hardmask as an intermediate step during CMP permits finer control of the ULK thickness remaining underneath. This hardmask also provides the advantage of reducing dielectric loss that is required for integrated builds (by reducing flare/undercut); hen...