Defect Quantity Optimization Method For Advanced Immersion Lithography Process

In the manufacturing progress of IC, lithographic process is a very important part. As the prediction of Moore’s law, the size of device becomes smaller and smaller. Meanwhile, scanner as the pattern printing tool grows more and more precise with the development of modern technology. Immersion era of lithographic has come, we use pure water instead of traditional air, with the help of water refraction property, we can push our process to65nm and even smaller.New immersion process gives a possibility of aggressive patterning; it also brings us some strange defect types which are different from ’dry’ process. These new defect types are called water mark, bubble, micro bridge, etc. in this paper, I studied the defect generation principle. Air bubbles are caused by hardware movement and those chemicals we use for immersion process. Water mark defect is generated by remaining water droplet on wafer surface, which decreases resist sensitivity and makes resist under exposure. Under exposure patterns, then, becomes water mark defects. Micro bridges are also a kind of under exposure pattern, but, it’s caused by micro bubble or particle, or the resist leaching into top coating instead of losing resist sensitivity.all the above are the main reasons for defectivity in immersion lithographic process. I introduce some optimized method to improve process defect, such as choosing better top coating material, optimizing scanning loop, decreasing particle quantity from its source, optimizing rinse process and regular machine maintenance, etc. Through my study, I figure out the best common method for all the different resist, with the help of which the fewest defects could be generated. Finally, for each certain resist, I individually fine tune parameters for them, so as to meet the critical requirement of modern lithographic immersion process.With the help of these multiple methods, I make the defect quantity of PDM less than60ea. Moreover, I make the defect quantity of product less than10ea. Machine performance achieves company’s guide line, and it makes stable contributions to yield improvement.