As the size of structures of advanced integrated circuits has decreased, manufacturers are turning to a micro-lithography technique called immersion lithography, because of its improved resolution capability. In immersion lithography, an immersion fluid is placed between the optical lens and a photoresist layer. The immersion fluid provides considerably higher depth-of-focus than conventional photoirradiation in air, therefore facilitating the use of high-numerical-aperture optical designs, which enable enhanced resolution during photoresist patterning. However, there are two problems associated with immersion lithography. The first problem is that in many photoresist systems, components of the photoresist leach out into the immersion fluid and/or the immersion fluid penetrates into the photoresist thus degrading performance. The second problem is that trace contaminants present in the immersion fluid can leach into the photoresist layer and ultimately contaminate various structures in the integrated circuits, degrading yield and/or reliability. Therefore, there is a need for a method to prevent interaction between photoresist layers and immersion fluid in an immersion lithography system and to prevent or reduce contaminants in the immersion fluid from contaminating the integrated circuit being fabricated.
USPTO Backgrounds
USPTO Backgrounds