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Method to Predict TDDB Defects in Copper Interconnects

IP.com Disclosure Number: IPCOM000238190D
Publication Date: 2014-Aug-07
Document File: 3 page(s) / 77K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to use a dual rate voltage breakdown (Vbd) method to determine if defects, such as residual metal material that can cause time dependent dielectric breakdown (TDDB) failure when voltage is applied, between copper (Cu) interconnect lines.

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Method to Predict TDDB Defects in Copper Interconnects

The traditional use of copper (Cu) interconnects is to employ a dielectric cap layer, such as a silicon nitride (Si3N4) or silicon carbide (SiC) layer. The purpose of this layer is to prevent Cu from diffusing into the surrounding dielectric material. Due to the poor adhesion between Cu and the dielectric cap layer, this interface acts as a fast diffusion path, leading to electromigration failure by void formation in the Cu lines. The use of a metal cap layer instead of the dielectric cap layer improves the adhesion at this interface and therefore improves the electromigration performance of the Cu lines. The metal cap can be a cobalt (Co) or ruthenium (Ru) layer.

Even though the deposition of these metal cap layers is intended to be selective and should only deposit on the Cu lines and not in the dielectric regions, this is often not the case. As a result, it is possible for residual metal cap material to be present on the surface of the dielectric material in the region between the Cu lines. This presents reliability concerns since the residual metal cap material could lead to time dependent dielectric breakdown (TDDB) failure when a voltage is applied between the Cu lines.

The typical way to evaluate the TDDB behavior is to stress different samples at different voltage conditions, which allows the tester to determine the TDDB lifetime as well as the voltage acceleration value. If the lifetime is low or the voltage acceleration value is low, then the TDDB performance is considered poor and the process must be improved. Although these are high voltage conditions, the TDDB stress may take several days to complete, which may not be practical in terms...