Single-Wafer vs. Batch Wet Surface Preparation in BEOL: a Comparison of Polymer Cleans using Inorganic Chemicals in Flash Memory Production

In this paper a specific case study comparing a batch and a single-wafer process using inorganic chemicals to remove post-etch residue (polymer) on flash device wafers is presented. The adoption of polymer cleans using dilute sulfuric-peroxide-HF (DSP⁺) mixture on a single-wafer SEZ spin processor was reported earlier and has resulted in a significant cost reduction and marked yield improvement at Spansion Fab 25. Initially, the process was introduced for all metal layers and contact layers 2 through 6. Contact 1, however, was performed on a spray batch tool using a sulfuric-per oxide mixture (SPM) followed by an ammonium-peroxide mixture (APM). As part of their continued desire to use single-wafer tools and to diminish the number and quantity of chemicals used in the fab, the effectiveness of the DSP ⁺ process on contact 1 was investigated. The results of this investigation are presented here. Detailed wafer metrology and electrical characterization and yield data are discussed