CMP Process for Phase Change Materials

摘要

Due to its multiple bit operation, scalability, and very fast switching speed [1-3] phase change memory (PCM) technology is a leading candidate for next generation nonvolatile memory devices. Ge_2Sb_2Te_5 (GST) is a promising material for this technology, but can be susceptible to damage during etch processing, especially in high density PCM integration [2, 4]. Alternative process integration schemes using chemical mechanical planarization (CMP) of GST material are currently being considered in PCM device process development, as CMP technology offers excellent surface finish and topography control.rnThe first challenge for a GST CMP process is defectivity control. As shown in Table 1, the GST alloy is considerably softer and also more fragile than Cu metal [5, 6]. As a result, it is more difficult to planarize GST without scratching the surface [7] or causing film delamination in localized areas. Another challenge is controlling the polish rate. Since the CMP process involves both chemical reactions and mechanical interaction, the physical and chemical properties of GST simultaneously influence the CMP process. The GST alloy is a ternary 1V-V-VI compounds with electro-negativity values on the Pauling scale for Ge, Sb,and Te of 2.01, 2.05 and 2.1, respectively [8]. They will therefore have dissimilar chemical reactions toward an oxidizing agent with potentially different removal rates [7].rnApplied Materials has demonstrated a manufacturable CMP baseline process for GST that addresses the above issues by optimizing the consumable set and process conditions. The process was first tuned to minimize scratches. Next, an electrochemical