A pinhole camera was used to evaluate source geometry of the GCA6700 g-line stepper. To create the camera, a photomask with various pinhole sizes was placed in the stepper, in close proximity to a wafer to generate an image. The images were evaluated to determine the shape and observe the radial intensity of the source. The variation across the source was evaluated because varying intensity across the wafer results and contributes to changes in critical dimension. Dose was varied in order to show how an illumination source might be characterized. As dose increased, the pinhole image became larger. Stacking the images could be used to create a three dimensional image of the source. Additionally, source images were used to verify the numerical aperture of the condenser lens of the illumination system.
"Evaluation of Source Geometry Using a Pinhole Camera,"
Journal of the Microelectronic Engineering Conference: Vol. 11
, Article 1.
Available at: http://scholarworks.rit.edu/ritamec/vol11/iss1/1