Overlay performance of an advanced X-ray stepper (XRS 200)

Stepper related contributions to the overlay budget, such as alignment accuracy and displacements during pattern replication were investigated. By improving the alignment system, a value of 70 nm (mean+3 sigma) was realized. Displacement errors induced by the stepper mechanism during pattern replication found to be in the range of 35 nm (3 sigma). This value was improved using a wafer chuck with high flatness. Summerizing the results, the total overlay contribution of the stepper (including alignment) is 75 nm (mean+3 sigma