Mask CD control (CDC) with ultrafast laser for improving mask CDU using AIMS as the CD metrology data source

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CD uniformity control by ultrafast laser system writing inside the bulk of photomasks has previously been shown to be an effective method for local CD Control (CDC) [1], Intra-field CD variations correction has been implemented effectively in mask-shops and fabs based on CDC SEM [2, 3] and OCD as the CD data source. Using wafer CD data allows correction of all wafer field CD contributors at once, but does not allow correcting for mask CD signature alone. In case of a mask shop attempting to improve CDU of the mask regardless of a particular exposure tool, it is a better practice to use mask CD data by itself as the CD data source. We propose using an aerial imaging system AIMS 45-193i as the mask CD data source for the CDC process. In this study we created a programmed CD mask (65nm dense L/S) with relatively large CD errors. The programmed CD mask was then measured by AIMS 45-193i (AIMS45) which defined the CDU map of the programmed CD mask. The CDU data from AIMS 45-193i was then used by Pixer CDC101 to correct the CDU and bring it back to a flat almost ideal CDU. Results 1. AIMS 45-193i managed to map the full mask CDU with a resolution of 0.5 nm. 2. The CDC101 managed to correct the CDU based on the AIMS 45-193i data from Range 5nm and 3S 4nm down to Range 45-193i and CDC101 alone, without any wafer CD data, the mask CDU can be improved >70% and mask contribution to wafer CDU can be brought down to <1.0 nm 3S.