Performance results of a new generation of 300-mm lithography systems

Abstract

ASML's recently announced TWINSCAN™ lithography platform is specifically designed to meet the specific needs of handling and processing 300 mm substrates. This new platform, already supporting a family of Step & Scan lithography systems for I-line and 248 nm DUV, is designed to further support optical lithography at its limits with systems for 193 nm and 157 nm. The conflicting requirements associated with higher productivity on one side, and more extensive metrology on the other, have led to the development of a platform with two independent wafer stages operating in parallel. The hardware associated with exposure, and the hardware and sub-systems required for metrology, are located in two separate positions. While a wafer is exposed on one stage, wafer unload/load and measurements of the horizontal and vertical wafer maps are done in parallel on the second stage. After the two processes are completed, where the exposure sequence typically is the longest, the two stages are swapped. The process is continued on the second stage, while the first stage unloads the exposed wafer and starts the process again. This system has an innovative design. It consists of a Metrology Frame that holds the projection lens and all measurement systems, and which is fully de-coupled from the force frame holding the stage actuators. To further suppress vibrations resulting from stage movements, a 'balance mass' principle is adopted. This principle uses an opposite movement of the balance mass to cancel out the acceleration forces caused by the high 300mm stage mass, and the speed and acceleration associated with high productivity. Long-term stability and alignment accuracy support the required stringent overlay performance. Dual wafer stage design requires careful characterization of the influence of stage-to-stage performance differences and calibration methods. Performance results of this new system indicate that dynamic performance of the stages is as expected and tracking errors for stage movement are negligible, demonstrating the benefits of balance masses. Crosstalk between the two independent wafer stages does not influence imaging and overlay performance. With two wafer stages, a wafer map can be generated prior to exposure. The wafer coordinates in the wafer plane are determined by means of the ATHENA™ alignment system with two colors and seven diffraction orders. To control focus, the position of the wafer surface is measured with a new level sensor system that maps the entire wafer surface. The wafer coordinate system is aligned to the aerial image at the exposure position by a proprietary alignment method, based on the actinic exposure light under actual illumination and NA settings. The first system based on dual wafer stage technology on the TWINSCAN platform is the AT:750 Step & Scan system, which is equipped with a Zeiss Starlith™750 248 nm DUV lens with a variable NA up to 0.7. When combined with the offaxis and multi-pole illumination capabilities of the AERIAL II illuminator, the system is capable of supporting lea...

Adaptive Feedforward for a Wafer Stage in a Lithographic Tool

“…When estimating multiple feedforward parameters , and , the stability proof remains intact if the process transfer function is given by (1). With and according to (15), and because .…”

“…Here, the motor body is indicated by , the stage itself by , the total mass . In a single direction the relation between a force acting on the motor body and the stage position equals (1) with the stiffness and the damping. Since is generally very small, (1) is approximated by (2) which, with a position reference , would require a feedforward force of (3)…”

“…The exposure itself takes place in a scanning fashion, in which both the wafer on which the IC pattern is exposed, and the reticle holding the original pattern, move at constant velocity through an illuminated slit, as shown in Fig. 1 and described in [1]. The position of the exposed image on the wafer needs to align accurately with previous layers, with a maximum error of about 3 nm.…”

Model-Based ILC with a Modified Q-Filter for Complex Motion Systems: Practical Considerations and Experimental Verification on a Wafer Stage

“…In order to reduce the overhead time created by wafer exchange, thereby improving throughput, two wafer stages are used during wafer scanning. While the first stage performs overhead activities such as wafer unload/load, horizontal alignment, and measurement of the surface topography, the second one exposes the previously measured wafer [29]. When both stages are finished with their tasks, the stages are swapped and a new cycle begins.…”

Online-Offline Optimized Motion Profile for High-Dynamic Positioning of Ultraprecision Dual Stage

“…To improve throughput of lithography, there are always two wafer stages constituting the dual-stage system [2]. The two wafer stages work at the same time, one for preprocessing and the other for exposure.…”