Optimization of Dielectric Cap Adhesion to Ultra-Low-k Dielectrics
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Optimization of Dielectric Cap Adhesion to Ultra-Low-k Dielectrics Greg Spencer, Alfred Soyemi, Kurt Junker, Jason Vires, Michael Turner, Stuart Kirksey, David Sieloff and Narayanan Ramani Semiconductor Products Sector, Motorola, Inc. 3501 Ed Bluestein Blvd Austin, Texas 78721 ABSTRACT In this work, the adhesion of CVD dielectric caps to ULK MSQ spin-on dielectric materials with k values of 2.2 and 2.0, and a ULK CVD material with a k value of 2.7 is presented. A substantial improvement in cap adhesion to both the k2.2 ULK MSQ and the k2.7 ULK CVD material is demonstrated. The improvement is obtained using a low-k CVD glue material between the ULK dielectric and the subsequent cap material and/or by optimizing the CVD cap film deposition. Four-point bend measurement of adhesion strength is used to quantify the improvement in interface adhesion. The improvement in CVD cap adhesion is demonstrated to be strongly dependent upon both the glue layer film and the cap deposition conditions. While optimization of the CVD cap materials results in adequate adhesion for the k2.2 ULK MSQ, these improvements are demonstrated not to extend to the k2.0 ULK MSQ film. INTRODUCTION In order to meet low RC-delay requirements of future technologies, low-dielectric constant (low-k) back-end integrations are required. Future low-k integrations will likely require the use of ultra-low-k (ULK) dielectric materials with dielectric constant (k) below 2.7. The 2003 International Technology Roadmap for Semiconductors indicates k values of less than 2.7 will be required for the 90 nm technology node with a reduction to k values of less than 2.4 for the 65 nm node, and further reduction to less than 2.1 for the 45 nm node [1]. While the integration of materials with k value near 3.0 has been demonstrated [2], the integration of ULK materials poses many challenges due to low mechanical strength and high porosity of the dielectrics. In addition, ULK dielectric interface adhesion strength, both to underlying substrates and to capping materials, is known to be an issue. This current work focuses on characterizing and improving the adhesion strength of chemical vapor deposition (CVD) oxide caps to the ULK material as this is the weakest interface for the materials studied, i.e. adhesion failures during 4point bend testing consistently occur at this interface. Cap materials are required due to the relatively low mechanical strength of ULK materials, and since the cap material must provide adequate strength to act as a chemical-mechanical polish (CMP) stop, adhesion of the cap is critical to prevent delamination during polishing. While improving the adhesion of cap materials to ULK materials is critical, the need for improved adhesion must be balanced with the need for a ULK solution. Techniques to improve adhesion, such as plasma pre-treatments, while often capable of enhancing adhesion energies also can significantly degrade the ULK benefit of the materials. The goal of this study is to improve the adhesion of CVD dielectrics caps while havin
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