Megasonic Irradiation Induced Chemical Reaction in the Solution for Silicon Wafer Cleaning
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3 Mat. Res. Soc. Symp. Proc. Vol. 477 01997 Materials Research Society
INTRODUCTION Ultra clean wafer surface has been confirmed to be crucial for high quality processing in Si technologies. For over a quarter of the century, the semiconductor industry has adopted RCA based cleaning [1 ][2] as substrate surface cleaning where various high concentrated chemicals are used at elevated temperatures such as 80-901C or 120--1501C, resulting in generation of excessive volumes of liquid chemical vapors and consumption of excessive volumes of liquid chemicals and ultrapure water. Due to this chemical vapor generation, it is impossible to maintain the chemical composition at the cleaning solution at the same level, resulting in very poor process accuracy and reproducibility. A progress of device miniaturization accompanies an increase in the number of process steps and masks: up to 30 to 35 due to the increase in multilevel interconnections and complexity of device structures. Thus, the number of surface wet cleaning is increased up to about 100 times for individual wafers through entire fabrications. To respond to volume production and further integration in the next generation of ULSI, we have already proposed a new type, highly effective, chemical vapor generation free and room temperature wet cleaning for Si substrates surface which is characterized by a very simplified process and very small comsumption of chemicals and ultrapure water [3][4]. Mechanisms of adsorption and desorption of contaminants on Si wafer surfaces were clarified, and total room temperature wet cleaning process was realized based on these mechanisms. The new wet cleaning method which features ozonized ultrapure water, surfactants and megasonic irradiation, perfectly cleans wafer surface with a consumption of less than I% chemicals and 5% ultrapure water compared to the conventional RCA cleaning. In this paper, chemical reaction in cleaning solution induced by megasonic irradiation is mainly discussed. OUTLINE OF UCT CLEANING PROCESS The key issue of future wet cleaning technologies should be energy saving and environmental friendliness. Therefore, the requirements for UCT cleaning process should be 1) Minimum steps number of process, 2) No chemical vapor invasion into clean environment , 3) Reduction of chemicals and UPW consumption, 4) Maximum reclamation of chemicals and UPW, 5) Total room temperature process. In order to satisfy the future trend, we proposed the UCT cleaning process as shown in figure I. The recipe is simplified to only 5 steps. In the first step, ozonized ultrapure water (0 3-UPW) is used for removal of organic and metallic contaminants from the substrate surface. Then, FPMS (Hydrofluoric acid and Hydrogen-peroxide mixture with surfactant in UPW) with megasonic irradiation is used for removal of particles and metallic contaminants. In the third step, 0 3-UPW with megasonic irradiation is used for removal of surfactant which remained on the wafer surface after FPMS treatment. The chemical oxide which is generated by ozone in ult
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