Deposition and Characterization of 3-Aminopropyltrimethoxysilane Monolayer Diffusion Barrier for Copper Metallization
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ctronics industry has moved toward copper instead of using aluminum as a preferred material for the conductive traces and interconnects because of its high electrical conductivity and electromigration resistance.[1] One problem that can occur in the use of copper is its tendency to diffuse into adjoining SiO2 layers and related low dielectric materials under electrical bias and annealing during the device operation, which can result in short circuits with neighboring traces and interconnects resulting into the failure of device.[1,2] Thus, copper-containing structures are generally surrounded by diffusion barriers to prevent such diffusion. Typically Ta/TaN, Ta-Si-N, W-Si-N, W-B-N, and Ta-W-N serve as barrier layers.[3,4] These barrier layers with thicknesses less than 10 nm are known not to have enough barrier ability when deposited by conventional methods.[1,2,6] But as the technology is shrinking, there is a need for ultra-thin barrier layers. Barriers with thicknesses less than 5 nm are needed in future devices to fully realize the advantage of Cu interconnects.[1,6] So new materials are always the point of interaction.
Materials like organosilanes can be deposited in the form of self-assembled monolayer (SAMs) making a sandwich structure of Cu/SAM/SiO2 and can be affective diffusion barriers. SAMs have thickness in the order of 1 to 3 nm.[3] The thickness of SAM is not the only advantage; it is compatible with standard microfabrication techniques also.[1] The process of self-assembly is easier and does not require the complicated instruments as compared to the other diffusion barriers. In this article, we presented an approach of depositing SAM using 3-aminopropyltrimethoxysilane (APTMS) as precursor molecule and evaluated the properties of APTMS SAM as diffusion barrier for copper metallization. APTMS is a novel material as it is not used widely to work as a barrier layer. Several research groups have worked in the area of depositing organosilanes based SAM layers for diffusion barrier applications, but to the best of the authors’ knowledge, APTMS is not explored much as a diffusion barrier for copper metallization.[1,2,7-10] An easy and clear approach is presented to deposit the monolayer on SiO2/Si substrate, and the diffusion barrier property against copper diffusion is studied.
II. SUMIT SHARMA, SUMITA RANI, Research Fellows, MUKESH KUMAR, Assistant Professor, and DINESH KUMAR, Professor, are with the Electronic Science Department, Kurukshetra Unversity, Kurukshetra, Haryana 136119, India. Contact e-mail: [email protected] Manuscript submitted July 17, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
MATERIALS AND METHODS
A. Sample Preparation p-type Si(100) samples were used for the deposition of films. Samples were cleaned using standard wafer cleaning method i.e. Radio Corporation of America (RCA) cleaning method and 65-nm-thick SiO2 was
thermally grown over these samples. The backside oxide layer was removed using HF while covering the front side with photoresist. The SiO2 layer was cleaned using a H2O2
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