Optimization of the chemical mechanical polishing process for premetal dielectrics

Since a premetal dielectric (PMD) is used in the first level of interconnec ts, tight control of the critical dimension of the subsequent first-level c ontact is essential. The thickness nonuniformity due to PMD chemical mechan ical 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 pressu re/high speed CMP process for PMD. Using a polishing pressure of only 2.5 p si, we improve the within die nonuniformity by 20-30%. To meet the throughp ut requirement, we can achieve a very high polish rate (>5000 Angstrom/min) by using high rotational speeds. Second, we describe an integrated noncont act clean to achieve low post-CMP defect counts and metallic contaminations . Cleaning phosphosilicate glass (PSG) is generally more difficult than und oped oxides. Because PSG is softer than an undoped oxide, it usually has mo re microscratches. Because phosphorous acts as a gettering center for metal lic impurities, PSG can have high metallic contamination after post-CMP cle an. HF immersion can greatly reduce the metallic contamination, but it enla rges the microscratches, leading to a large number of detectable defects. M echanisms for the removal of slurry residue, microscratches, and metallic c ontamination are discussed in this paper. (C) 2000 The Electrochemical Soci ety. S0013-4651(99)03-037-5. All rights reserved.