The Nikon eReview

Nikon scan-field i-line steppers have been an extremely successful product line with more than 350 systems installed worldwide. The newest generation systems in the SF series, the NSR-SF150 and SF155 incorporate Skyhook Technology, where the lens module is suspended from a rigid frame using the Skyhook mounting system as shown below. The Skyhook design eliminates the influence of ground and stage vibration on the lens and associated metrology. A side (lateral) airflow system protects the lens against environmental thermal disturbances while increased spacing optimizes temperature control, together improving lens stability. Further, SF150/SF155 lens positioning is controlled using sophisticated noncontact actuators.

In the NSR-SF150 and SF155 systems the lens module is suspended from the stepper main body using the Skyhook Technology mounting system.

Skyhook Technology eliminates the need for a moveable reticle stage or reticle interferometry system. Instead, the reticle is aligned and then fixed on the lens column, making it easy to tune out external vibration effects, and eliminate this potential source of variability. Reticle loading offsets are corrected using the new lightweight wafer stage with enhanced positioning control and six degrees of freedom for wafer fine stage control, optimizing overlay accuracy. Data from multiple SF150 systems have demonstrated stepping 3 sigma ≤ 8 nm (standard specification = 15 nm). The SF155 also features newly developed heat countermeasures that further enhance chamber temperature stability. Together, these improvements enable the SF150/SF155 to deliver overlay accuracy well below 25 nm, easily satisfying the requirements for sub or non critical layers. At the LithoVision symposium in February, David Godfrey, Nikon Precision Associate Staff Engineer, presented data from five SF150 systems with overlay accuracy consistently below 15 nm 3 sigma.

Using Skyhook Technology, overlay accuracy easily satisfies the requirements for i-line applications, consistently delivering performance below 15 nm 3 sigma.

While Skyhook Technology coupled with the new high-accuracy stage design ensures optimal system performance and stability, the SF150 and SF155 systems also provide excellent cost of ownership for i-line applications. The SF150 delivers more than 180 wafers per hour (50% higher throughput than the previous generation SF140 system), and the SF155 further minimizes stage settling time to boost throughput to 200 wafers per hour on a cost-effective platform. In addition, existing SF150 systems can be upgraded to the SF155 configuration in the field to realize these significant throughput gains.

While the SF150 enabled a 50% increase in throughput compared to the SF140, the SF155 includes further design optimization to deliver 200 wafers per hour. Existing SF150 systems can be upgraded in the field to the SF155 configuration.

The NSR-SF150/SF155 i-line steppers successfully pair Skyhook Technology with a cutting-edge stage design to deliver optimized performance and stability for sub or noncritical applications, (Standard resolution ≤ 280 nm) with excellent cost of ownership.

Skyhook Technology Eliminates Vibration and Optimizes Stepper Stability