Photolithography is used in the manufacturing of integrated circuitry to form device feature patterns onto a substrate. Generally, this involves projecting an image of a reticle onto photosensitive material received over a substrate. One type of photolithography is scanning photolithography. In such, electromagnetic radiation is passed through an exposure slit which is scanned at a predetermined rate across a reticle and which is imaged onto the photosensitive substrate. The reticle and photosensitive substrate move synchronously with each other at different rates in opposite directions such that an exposure field on the substrate is scanned.
Critical dimension (CD) is the dimension of the smallest geometrical features (i.e., width of interconnect line, contacts, trenches, etc.) which can be formed during semiconductor device/circuit manufacturing using given technology. Using photolithography, it is desirable that CD be consistent throughout the exposure field, and correspondingly across the entirety of the substrate being patterned. However, CD variation within an exposure field can occur in all types of photolithographic processing, including in scanning photolithography.
For example, FIG. 1 graphically depicts CD variation of a partial area of a scanned exposure field of a substrate relative to x and y axes defining that partial area. CD variation is evident in FIG. 1 from the differently shaded regions. If CD were constant throughout the depicted area, only a single uniform shading would be shown.
CD variation may be caused by a number of factors taken alone or in combination. For example, the reticle may not be fabricated as precisely as desired, wherein feature sizes in the reticle undesirably vary. FIG. 2 diagrammatically depicts one such example in the patterning of a substrate 10 using a reticle 12. Substrate 10 is shown as comprising a base substrate 14 having a photosensitive material 16, such as photoresist, formed thereover. Reticle 12 comprises an alternating array of blocks 20 and line openings 18 there-across. In this example, it was desired that reticle 12 be fabricated such that each line opening 18 and each block width be equal to the CD. However as shown, some of the blocks at the left in the figure are larger than the other blocks, thereby decreasing the width of the line spaces between such blocks with immediately adjacent blocks. Electromagnetic radiation 17 is used to ultimately transfer the pattern of reticle 12 to photosensitive material 16, thereby transferring the CD variation in reticle 12 onto substrate 10.
CD variation can also occur where a reticle is perfectly fabricated, or at least fabricated to within acceptable CD tolerances. For example, optical artifacts may be introduced by the scanning lithography equipment itself which results in CD variation at two or more different locations within an exposure field. Further, CD variation in a reticle may combine with CD variation due to any optical artifact and compound the variation.
Accordingly, need remains for improved methods in scanning photolithography equipment which enables reduction of CD variation within an exposure field. While the invention was primarily motivated in addressing these issues, it is no way so limited, with the invention only being limited by the accompanying claims appropriately interpreted in accordance with the doctrine of equivalence.