光刻机结构及工作原理.ppt

* * * * * In the left illustration, the reticle feature is smaller than can be resolved with coherent illumination. As a result of the feature being smaller than the resolution limit of the lens, the first order diffraction angle has increased and all first order information is now outside the perimeter of the entrance pupil. Imaging of this feature cannot occur. Sigma, as an illumination term, refers to the amount of decollimation applied to the illumination (which takes place in the beam shaping optics, discussed previously). The quantity “sigma” is the ratio of pupil fill; that is, the fraction of the entrance pupil which is filled by zeroth order information. (If half the entrance pupil is filled with zeroth order information, then sigma = 0.5) Therefore, decollimation of the illumination equates with higher sigma, and conversely collimation of the illumination equates with lower sigma. In the notes of the previous slide, we proposed making sigma larger. This involves decollimation of the illumination or, in other words, making the light less coherent. High sigma thus results in the right illustration, where the center of each order is still in exactly the same place with respect to the entrance pupil, but now because sigma is high, some first order information is captured by the lens, and assuming the process is engineered to cope with the reduction in contrast, the feature will be imaged. (Contrast was discussed in slides 29 30, where the ratio of first order to zero order information was shown to define contrast of the aerial image.) The Scanning Electron Microscope photos (often referred to as micrographs) of 120- and 110-nanometer lines in the slide illustrate what is possible with proper application of annular illumination. The drawing shows how, with sufficiently decollimated illumination and annular settings chosen to minimize attenuation of 1st order information, features well below the resolution limit of the lens can still be resolved. This