Extending optical lithography with immersion

Abstract

As the semiconductor industry looks to the future to extend manufacturing beyond 100nm, ASML have developed a new implementation of an old optical method for lithography. Immersion lithography can support the aggressive industry roadmap and offers the ability to manufacture semiconductor devices at a low k1.In order to make immersion lithography a production worthy technology a number of challenges have to be overcome. This paper provides the results of our feasibility study on immersion lithography. We show through experimental and theoretical evaluation that we can overcome the critical concerns related to immersion lithography. We show results from liquid containment tests focussing on its effects on the scan speed of the system and the formation of microbubbles in the fluid. We present fluid-to-resist compatibility tests on resolution, using a custom-built interference setup. Ultimate resolution is tested using a home build 2 beam interference setup. ASML built a prototype full field scanning exposure system based on the dual stage TWINSCAN TM platform. It features a full field 0.75 NA refractive projection lens. We present experimental data on imaging and overlay.keywords: immersion lithography, high NA, TWINSCAN, bath, shower 1.INTRODUCTIONFor more than 25 years the semiconductor industry has predicted the end of optical lithography. Recent developments, however, show us that optical lithography is more alive than ever before. Immersion lithography has emerged as the potential technology for extending optical lithography. Immersion lithography makes use of fluids with refractive indexes that are greater than 1.0 (the refractive index of air) to enable the use of lenses that have Numerical Apertures (NAs) larger than 1.0. Immersion, in principle, is not a new technique. Its viability for microlithography, however, has become a practical consideration because of advances made in lens manufacturing technology, especially a-spherical surface figuring. For 193-nm lithography, water proves to be a suitable immersion fluid. The refractive index for water is 1.43, which makes lens NAs above 1.2 feasible. Immersion offers the potential to extend conventional optical lithography to the 45-nm node and even potentially to the 32-nm node. The main challenges for deployment of immersion are in the design of the exposure tool. Early work done by International Sematech shows that existing photo resists can be compatibility with immersion. However, further work is required in this area.In this paper we discuss the achievements of both exposure tool design and the interaction between existing photoresists and immersion fluids. Section 2 provides the results of our feasibility study on immersion lithography. Section 3 shows the results of our prototype TWINSCAN TM immersion scanner, and finally section 4 summarizes the conclusions of this paper.

Polarization effects in immersion lithography

“…From these plots a ~1.6-1.7X improvement in available DOF is evident. These simulations confirm experimental results recently presented in [10]. …”

Fabrication of 3D Metamaterial Resonators Using Self‐Aligned Membrane Projection Lithography

“…[ 3 ] Fabrication of composite materials with designed constituent elements of sub-micrometer size typically requires cutting edge lithography techniques such as immersion lithography, [ 4 ] nanoimprint lithography, [ 5 ] or e-beam lithography. [ 6 ] While these techniques are capable of printing features with the requisite lateral dimensions, they are all planar patterning approaches, and hence offer limited options for creation of 3D structures, or structures with out-of-plane components.…”

Investigation of polarization effects on new mask materials

“…As a result, topography effects have a significant influence on the diffraction properties of reticles 1 . This will become even more severe with the emergence of immersion lithography extending imaging to the sub-50nm regime [2][3][4][5][6] . The intensity distribution of the diffracted light is substantially different from the case of an infinitely thin mask, which is often referred to as the Kirchhoff-approximation.…”