A method for calculating optimum focus and tilt for a reticle, and means to control lithography tools with this information.
Original Publication Date: 2004-Dec-16
Included in the Prior Art Database: 2004-Dec-16
A method is disclosed which describes characterization of a photolithography mask to determine its focus-related properties, and a method to supply this mask-specific information to photolithography clusters to improve printing characteristics.
A method for calculating optimum focus and tilt for a reticle, and means to control lithography tools with this information .
A method of characterizing a photolithography mask to determine its specific focus-related properties is described. In the previous state of the art, lithographers have assumed that the optimum focus setpoint for performing lithographic imaging is determined by the image type (nested, isolated; line, space), film thicknesses, and aligner aberrations. Mask-related contributions have been ignored, as the assumption has been made that by using a sufficiently flat mask substrate, mask contributions would be negligible.
Data is presented below showing that the difference in focus setpoints between reticles can be significant.
Experiments have demonstrated that the difference in focus between masks with the same image type, film stack, and aligner aberrations is significant and specific to the masks [Fig. 1]. A similar difference in the tilt across an aligner's scan slit (cross-slit tilt) [Fig. 2] and the tilt from beginning to end of aligner scan (wedge) [Fig. 3] has been established.
A method for measuring these properties for a given reticle is described.
Perform a lithographic focus matrix on a semiconductor wafer, with a series of
lithographic fields being imaged using different focus values.
Identify four or more non-collinear images...