Precision Fabrication of Nanostructures by Optimal Mixed H2/H Control of Microcontact Next Generation Lithography Systems

Stanford University, Stanford CA

Investigators

Abstract

0000541 Kailath A number of different so-called NGL (next generation lithography) techniques are currently begin explored for continuation of the so-far incredibly successful optical lithography techniques, which can take the PI's to devices with 70 nm critical dimensions, one of the more interesting classes of NGL techniques, called microcontact or soft lithography, has demonstrated exceptional patterning fidelity in even the fabrication of 10 nm feature sizes and working integrated devices. Microcontact lithography methods involve a 1:1 conformal mask or template, brought into direct contact with the surface of the substrate with several different approaches for completing the printing process subsequent to contact, including physical, chemical, and photonic means. Recently, a novel microcontact NCL strategy utilizing permeable membrane materials (PMM) has been developed in the PI's Stanford semiconductor manufacturing group. In this approach, pattern transfer is achieved by molecular transport of reactive species through a permeable porous template to form a spatially selective etch-resistant mask on the substrate surface. At the dimensions envisaged for microcontact NGL techniques, extremely precise positioning and alignment of mask and substrate will be needed during the entire printing trajectory including extension, hold, and retraction. The PI's propose to develop an optimal multivariable control system for this purpose, with their recently developed PMM system as a specific test vehicle. Preliminary explorations have led them to focus on a dual servo 6-axis piezeo-driven nanopositioning flexure stage along with real-time mask-substrate gap detection and laser interferometry for positioning and alignment. Overall, the fine-stage system will employ six piezoactuators and nineteen high resolution positioning detectors. Although the control laws will be developed and demonstrated on their PMM technology and a related near-field direct write patterning system, the strategy will be generally applicable to other microcontact NCL techniques that employ flexure positioning methods. Some details on their proposed approach follow. First, a state-space model of the flexure stage will be identified using recent advances in the so-called subspace methods developed by Cho and Kailath at Stanford. In the planned approach, frequency domain data will be generated and a linear time invariant model will be computed. Subspace identification techniques offer a non-iterative method to generate multivariable state-space models. For their application which has considerable redundancy in the sensor set, the subspace approach to model identification is useful since, by employing results from displacement structure theory, fast algorithms can be obtained. They also plan to investigate the use of the subspace identification output to determine a minimal set of detectors and actuators to control the unit. Using the identified model, they will design an optimal mixed H2/H controller. The H2/H control objective is applicable to this project because of the need to optimize the positioning speed for an increase in throughput while guarding against worst-case crashes of the mask to the substrate surface. Both stochastic and bandlimited disturbances due to vibrations, as well as internal effects such as nonlinear beam bending moments, hysteresis, and variable initial conditions and topography effects, enter the plant and must be compensated along the desired positioning trajectory. In brief, this proposal envisages the extension and application of recent control design theories to design a very high performance nanopositioning control system. A specific new so-called PMM technology will be the testbed for the development. However the techniques are relevant to several microcontact technologies; they should also be useful for specific applications such as fabrication on curved surfaces, and for manufacturing MEMS (microelectro- mechanical systems), microsynthetic and microfluidic systems. ***