Hybrid DHF and N-2 jet spray cleaning for silicon nitride and metal layer DRAM patterns

Abstract

Cleaning different layers during dynamic random-access memory (DRAM) pattern making is critical to the removal of particles. Physical cleaning techniques such as deionized water (DIW) with N-2 spray and hybrid cleaning using an ammonia and hydrogen peroxide mixture (APM) with N-2 spray have been employed. However, with the continuing shrinkage of device structures for the next generation technology nodes existing cleaning systems could be problematic. DIW spray-based physical cleaning could cause pattern damage, whereas an APM-based hybrid system presents the threats of low particle removal efficiency (PRE) for silicon nitride (SiN) surfaces and corrosion of metal layers. In this study, a hybrid DHF spray-cleaning process based on dilute hydrofluoric acid (DHF) and N-2 was tested on a 40 nm scale DRAM pattern, and its cleaning performance on different patterns of SIN and metal layers such as TiN and tungsten (W) was analyzed. In optimized conditions, a PRE of > 90% was achieved using DHF spray cleaning. The dominant mechanism responsible for the higher PRE on SiN and metal layers was found to be slight surface etching. However, surface roughness did not change even after treatment with a DHF spray. Based on these observations, a DHF and N-2 jet spray system could be a promising method for particle removal from SiN and metal films during DRAM pattern-making.