IN-SITU ELECTRO-CHEMICAL RESIDUE SENSOR AND PROCESS MODEL APPLICATION IN RINSING AND DRYING OF NANO-STRUCTURES

Abstract

Typical surface preparation consists of exposure to cleaning chemical to remove contaminants followed by rinsing with ultra-pure water which is followed by drying. Large quantities of water, various chemicals, and energy are used during rinsing and drying processes. Currently there is no in-situ metrology available to determine the cleanliness of micro- and nano-structures as these processes are taking place. This is a major technology gap and leads to over use of resources and adversely affects the throughput.Surface preparation of patterned wafers by batch processing becomes a major challenge as semiconductor fabrication moves deeper in submicron technology nodes. Many fabs have already employed single wafer tools. The main roadblock for single-wafer tools is their lower throughput. This obstacle is eased by introduction of multi chamber tools. To reduce cycle time and resource utilization during rinse and dry processes without sacrificing surface cleanliness and throughput, in-situ metrology is developed and used to compare typical single wafer spinning tools with immersion tools for rinsing of patterned wafers. This novel metrology technology includes both hardware for an in-situ measurement and software for process data analysis. Successful incorporation of this metrology will eliminate dependency on external analysis techniques such as Inductively Coupled Mass Spectroscopy (ICPMS), Scanning Electron Microscope (SEM), and Tunneling Electron Microscope (TEM), and will lead to fast response time.In this study the electro-chemical residue sensor (ECRS) was incorporated in a lab scale single-wafer spinning and single- wafer immersion tool. The ECRS was used to monitor dynamics of rinsing of various cleans such as ammonium peroxide mixture (APM), hydrochloric peroxide mixture (HPM), and sulfuric peroxide mixture (SPM). It was observed that different cleaning chemicals impact the subsequent rinse not only through adsorption and desorption but also through surface charge. The results are analyzed by using a comprehensive process model which takes into account various transport mechanisms such as adsorption, desorption, diffusion, convection, and surface charge. This novel metrology can be used at very low concentration with very high accuracy. It is used to study the effect of the key process parameters such as flow rate, spin rate, temperature, and chemical concentration.