Challenges and Rewards of Low-Abrasive Copper CMP: Evaluation and Integration for Single-Damascene Cu/Low-k Interconnect
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Challenges and Rewards of Low-Abrasive Copper CMP: Evaluation and Integration for Single-Damascene Cu/Low-k Interconnects for the 90nm Node Christopher L. Borst, Stanley M. Smith, Mona Eissa Texas Instruments Incorporated Kilby Center 13560 North Central Expressway Dallas, TX 75243 U.S.A. email: [email protected]
ABSTRACT Low-abrasive content slurries for copper (Cu) chemical-mechanical planarization (CMP) have been developed to achieve removal rate and removal uniformity comparable to conventional slurries. They can improve post-CMP defectivity, improve topography and allow operation at lower polish pressures that are more compatible with the low-dielectric constant (low-k) materials required for current and future high-performance interconnects. Integration of these slurries into a yielding product with 9-level Cu/low-k metallization requires fundamental learning and process characterization. This paper discusses the some of the challenges encountered during development, integration, and qualification of a low-abrasive Cu CMP process for Texas Instruments (TI) Incorporated's 90 nm technology node with copper/organosilicate interconnect. As abrasive content is reduced, the slurry chemistry must play a larger role in CMP removal. A more aggressive reactive chemical formulation requires an effective inhibitive component to keep Cu static etch rate low. As a result, wafer-scale process and consumable interactions, die-scale planarization efficiency, and feature-scale removal rates each become more sensitive to process changes. Pressure and temperature have larger effects on removal rate/profile than conventional slurries, and complete clearing of Cu puddled over underlying topography becomes more difficult. Successful integration of these slurries, however, can achieve excellent results in dishing and erosion topography, Cu thickness uniformity, and Cu loss in small features such as vias and landing pads. Low-abrasive content solutions are also more stable and easy to handle in slurry distribution vessels and lines, have lower scratch and residue defectivity, and have greatly extended margin for overpolish. As lowabrasive content Cu slurry options continue to evolve to become manufacturable solutions, their benefits far outweigh the costs and challenges encountered in their successful integration. INTRODUCTION For many unit processes, integration at the 90 nm node has been compounded by a wide array of tool, material, and consumable options. Copper (Cu) chemical-mechanical planarization (CMP) is no exception. Decisions made at the 90 nm node include selection of low-dielectric constant (low-k) materials, CMP slurries and pads, and post-CMP clean approaches. Of these changes, one of the most crucial for advanced interconnect is the selection of a Cu slurry with improved performance over prior-node slurries. In recent years, several Cu CMP slurry alternatives have emerged on the market, with options in abrasive type, size, and concentration, as well as pH and inhibitor chemistry1. Selection of a slurry candidate
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