Optimization of the Chemical Mechanical Polishing Process for Premetal Dielectrics

Abstract

Since a premetal dielectric (PMD) is used in the first level of interconnects, tight control of the critical dimension of the subsequent first‐level contact is essential. The thickness nonuniformity due to PMD chemical mechanical polishing (CMP) can consume most of the depth‐of‐focus budget for the deep UV lithographic process. In this paper, we first describe a low pressure/high speed CMP process for PMD. Using a polishing pressure of only 2.5 psi, we improve the within die nonuniformity by 20–30%. To meet the throughput requirement, we can achieve a very high polish rate (>5000 Å/min) by using high rotational speeds. Second, we describe an integrated noncontact clean to achieve low post‐CMP defect counts and metallic contaminations. Cleaning phosphosilicate glass (PSG) is generally more difficult than undoped oxides. Because PSG is softer than an undoped oxide, it usually has more microscratches. Because phosphorous acts as a gettering center for metallic impurities, PSG can have high metallic contamination after post‐CMP clean. HF immersion can greatly reduce the metallic contamination, but it enlarges the microscratches, leading to a large number of detectable defects. Mechanisms for the removal of slurry residue, microscratches, and metallic contamination are discussed in this paper. © 2000 The Electrochemical Society. All rights reserved.