The study for close correlation of mask and wafer to optimize wafer field CD uniformity

As device pattern size is shrinking to below 65nm on wafer, the small amount of CD variation on wafer field determine the wafer yield. Most of the wafer field CD variations come from mask CD variations across mask field. By correction of dose and transmittance on mask using wafer field CD variation, wafer CD uniformity can be extremely enhanced. To get fine correction of wafer field CD uniformity, we have developed various methods to get close correlation of mask and wafer field CD uniformity by SEM, scatterometry and area CD methods. Especially, area CD from CD-SEM and optical CD measurement tools are developed to represent each area of masks. By optimizing measurement methods, repeatability and correlation of CD uniformity between masks and wafers are enhanced to get more than 0.7 of correlation between mask and wafer. And these give us the correction method to compensate field CD variation of maskCD on wafer. More than mask CD uniformity requirement on 65nm tech of DRAM memory device has been achieved.