20 March 2018 Hot spot variability and lithography process window investigation by CDU improvement using CDC technique
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Abstract
Within the current paper, we will concentrate on the well-known CDC technique from Carl Zeiss to improve the CD distribution of the wafer by improving the reticle CDU and its impact on hotspots and Litho process window. The CDC technique uses an ultra-short pulse laser technology, which generates a micro-level Shade-In-Element (also known as "Pixels") into the mask quartz bulk material. These scatter centers are able to selectively attenuate certain areas of the reticle in higher resolution compared to other methods and thus improve the CD uniformity.

In a first section, we compare the CDC technique with scanner dose correction schemes. It becomes obvious, that the CDC technique has unique advantages with respect to spatial resolution and intra-field flexibility over scanner correction schemes, however, due to the scanner flexibility across wafer both methods are rather complementary than competing. In a second section we show that a reference feature based correction scheme can be used to improve the CDU of a full chip with multiple different features that have different MEEF and dose sensitivities. In detail we will discuss the impact of forward scattering light originated by the CDC pixels on the illumination source and the related proximity signature. We will show that the impact on proximity is small compared to the CDU benefit of the CDC technique.

Finally we show to which extend the reduced variability across reticle will result in a better common electrical process window of a whole chip design on the whole reticle field on wafer. Finally we will discuss electrical verification results between masks with purposely made bad CDU that got repaired by the CDC technique versus inherently good “golden” masks on a complex logic device. No yield difference is observed between the repaired bad masks and the masks with good CDU.
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Thomas Thamm, Bernd Geh, Marija Djordjevic Kaufmann, Rolf Seltmann, Alla Bitensky, Martin Sczyrba, Aravind Narayana Samy, "Hot spot variability and lithography process window investigation by CDU improvement using CDC technique", Proc. SPIE 10587, Optical Microlithography XXXI, 105870F (20 March 2018); doi: 10.1117/12.2297382; https://doi.org/10.1117/12.2297382
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