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Lithographic process steps used in today's integrated circuit production require tight control of critical dimensions (CD). With new design rules dropping to 32 nm and emerging double patterning processes, parameters that were of secondary importance in previous technology generations have now become determining for the overall CD budget in the wafer fab. One of these key parameters is the intra-field mask CD uniformity (CDU) error, which is considered to consume an increasing portion of the overall CD budget for IC fabrication process. Consequently, it has become necessary to monitor and characterize CDU in both the maskshop and the wafer fab. Here, we describe the introduction of a new application for CDU monitoring into the mask making process at Samsung. The IntenCD TM application, developed by Applied Materials, is implemented on an aerial mask inspection tool. It uses transmission inspection data, which contains information about CD variation over the mask, to create a dense yet accurate CDU map of the whole mask. This CDU map is generated in parallel to the normal defect inspection run, thus adding minimal overhead to the regular inspection time. We present experimental data showing examples of mask induced CD variations from various sources such as geometry, transmission and phase variations. We show how these small variations were captured by IntenCD TM and demonstrate a high level of correlation between CD SEM analysis and IntenCD TM mapping of mask CDU. Finally, we suggest a scheme for integrating the IntenCD TM application as part of mask qualification procedure at maskshops. |
