Mask Registration Metrology Systems
The LMS IPRO6 mask registration metrology tool is designed to accurately verify pattern placement performance of reticles for the 1X nm node. It offers comprehensive characterization of reticle pattern placement error, which is a direct contributor to intra-field wafer overlay error. As several papers indicate1, due to different mask registration performance of targets and on-device features, it will be mandatory to characterize the reticle contribution to intra-field wafer overlay on on-device patterns. KLA-Tencor’s new proprietary model-based metrology algorithm allows the LMS IPRO6 mask metrology system to accurately measure placement error for on-device pattern features, and thus characterize real mask contribution to intra-field overlay.
Based on the industry-proven IPRO platform, the LMS IPRO6 mask registration metrology system achieves its industry-leading performance by incorporating several new or improved features:
Mask OQC: When a mask is shipped, many IC fabs now require that densely sampled registration data - not just a 3-sigma value - are provided along with the mask. A single number is no longer sufficient to characterize a mask, given the tight wafer overlay specifications driven by 1X nm challenging lithography technologies. Likewise, an under-sampled mask can harbor an unrecognized pattern registration excursion—which can result in a major yield hit for the IC fab. Sufficient sampling however requires accurately measuring on-device patterns inside the active array. LMS IPRO6 is the only mask registration tool based on the model-based measurement algorithm, which enables highly accurate measurements of any feature.
The LMS IPRO6 mask metrology system delivers the complete set of tools needed for a mask manufacturer to provide a registration characterized mask to the fab on schedule—and allows both the mask shop and fab to have confidence that the mask registration is good.
Mask writer qualification and monitoring: Today’s mask writers are able to incorporate sub-nm pattern placement corrections. In order to take advantage of this capability, pattern placement error must be measured accurately with high sampling frequency. LMS IPRO6 supplies the automation performance, high throughput, and analytical software needed to fully characterize reticle pattern placement error. Based on these data the performance of the mask writer can be verified and adjustments performed if required, so that fewer problems are discovered at outgoing quality control (OQC).
Mask process development and monitoring: LMS IPRO6 is the only mask registration metrology system to offer flexible, automated on-device metrology, industry-leading performance, and the ability to take through-pellicle measurements. In order to envision and correct pattern dependent registration error, the LMS IPRO6 provides accurate measurement capability on actual on-device features.
Furthermore, the LMS IPRO6 is the only DUV illumination-based registration tool which enables measurement on resist masks in order to separate e-beam error from process deviations.
Wafer patterning control: As part of the 5DTM Patterning Control Solution, LMS IPRO6 reticle data can be directly uploaded to the industry standard K-T Analyzer software to assess the mask’s contribution to wafer overlay error. Thus, on-device data can be fed forward to the wafer fab’s lithography module and used for optimized scanner corrections that can improve intra-field wafer overlay yield.