The Interaction of Ultra-Pure Water and Photoresist in 193nm Immersion Lithography

The proposed paper investigates the effects of ultra-pure water on DUV photoresist used in 193 nm immersion lithography. Microlithography is the key technology that is pacing Moore’s Law. With critical transistor features reaching the 45nm device node, the development for new techniques in optical lithography are well underway. Large investments have been made into the Next Generation Lithography (NGL) technology development such as VUV (vacuum ultraviolet) and EUV (extreme ultraviolet) projection lithography. However, an extension of optical imaging at 193 nm deep ultraviolet (DUV) to immersion lithography at the same wavelength offers considerable potential for it to be used as a next step in production, postponing the introduction of EUVL

Preparation of RIT for 157-nm Lithography

This project investigated the feasibility of 157-nm Vacuum UltraViolet (VUV) Lithography and its’ possible utilization as a future source to extend the capabilities of optical lithography. In addition, this project undertook the initialization of VUV lithography here at JUT by the conversion of a 193-nm ArF excimer laser to a 157-nm F2 excimer laser source. The investigation of the completed body of work on 157-nm lithography led to the conclusion that this technology is viable and may represent the last frontier with respect to optical lithography. The excimer laser at RIT was successfully retrofitted for 157-nm operation and exhibited RIT’s first excitation at this wavelength on May 11, 1998

Phase-Shift Mask Issues for 193 nm Lithography

As feature sizes below 0.25 micron are pursued, it becomes apparent that there will be few lithographic technologies capable of such resolution. Of these, deep-UV lithography at 193 urn is being investigated, which may prevail over X-ray lithography in terms of manufacturability. Furthermore, through the use of image enhancement techniques such as phase-shift masking, 193 rim lithography may dominate for feature resolution below 0.20 micron. This paper presents results from investigations into phase-shift mask issues for 193 nm excimer laser lithography. A small field refractive projection system for operation at the 193 .3 nm wavelength of a spectrally narrowed ArF excimer laser has been constructed for lithographic research. The small field, 20X system operates with a variable objective lens numerical aperture from 0.30 to 0.60, variable partial coherence, and control over illumination fill. Through the use of attenuated and alternating phase-shifting techniques resolution can be pushed to the 0.2 micron range with depth of focus as large as 2 microns. Problems do arise, though, as these techniques are applied to such short wavelengths of an excimer laser. Sensitivities to shifter deviations and resist interaction increase. Shifter etch influences on fused silica surface characteristics need to be addressed. Transmission effects of attenuating materials becomes increasingly important. Resist imaging and simulation results presented will shed some light on the potential of phase-shift masking for 193 nm lithography, along with inherent difficulties

Al2O3 hosted attenuated phase shift mask materials for 157 nm

The Semiconductor Industry Association Roadmap 2003 has put 157 nm optical lithography as the next generation lithography wavelength for the node of 70 nm integrated circuits and below. The small departure from 193 nm puts more challenge on imaging tools and processes. One of the crucial areas is the exploration of thin film optical materials for mask coatings at vacuum ultraviolet (VUV) wavelength. Attenuated Phase Shift Mask (APSM) is one of the optical enhancement technologies pushing critical dimension of lithography to diffraction limits. As no existing single material satisfies those demanding requirements of APSM, non-stoichiometric composite materials will be explored to keep optical lithography from demise. In this case, the individual dielectric response of those constituents must be combined in an effective model to reproduce composite film dielectric response. The relationships between thin film microstructure and optical properties are extremely useful for the development and characterization of thin films. Effective Media Approximation (EMA) theory will bridge thin film composition and/or microstructure to optical properties. APSM can improve both resolution and depth of focus with complexity in fabrication. It has become an attractive candidate to replace those of multilevel mask processes such as aligning, rim, or sub-resolution schemes. The APSM should have transmission between 4% and 15% with a π phase shift [1]. Also the thin film must be feasible to pattern. This thesis worked on several potential AI2O3 hosted composite materials. By carefully combining the absorbing and non-absorbing components based on the database of RIT lithography research group for optical properties of various materials, the optical properties of the composite thin film can be tailored to achieve the desired requirements by adjusting the deposition conditions, which include reactive gas partial pressure, power and time. Four promising AI2O3 hosted composite materials were proposed and two of them were fabricated and tested with satisfactory results. An image reversal lift-off process was adapted and modified for patterning of the APSM film. The lift-off process was able to pattern the APSM film with 2 microns critical dimension. AI2O3 hosted oxide non-stoichiometric composite materials satisfy all the APSM film requirements and can be patterned by lift-off process with reasonable critical dimension. Table: Left Column: Criteria, Right Column: Target Range. Left Column: Transmission at 157 nm, Right Column: 4-15%. Left Column: Transmission at 193 nm, Right Column: below 50%. Left Column: Reflectance at 157nm, Right Column: Below 15%. Left Column: Phase Shift at 157 nm, Right Column: 180 degree. Left Column: Critical dimension of patterned film, Right Column: 2 micons. Table 0.1 APSM film requirements

Optical lithography

Optical lithography is a photon-based technique comprised of projecting an image into a photosensitive emulsion (photoresist) coated onto a substrate such as a silicon wafer. It is the most widely used lithography process in the high volume manufacturing of nano-electronics by the semiconductor industry. Optical lithography’s ubiquitous use is a direct result of its highly parallel nature allowing vast amounts of information to be transferred very rapidly. For example, a modern leading edge lithography tool produces 150-300-mm patterned wafers per hour with 40-nm two-dimensional pattern resolution, yielding a pixel throughput of approximately 1.8T pixels/s. Continual advances in optical lithography capabilities have enabled the computing revolution over the past 50 years

High-Q photonic crystal nanocavities on 300 mm SOI substrate fabricated with 193 nm immersion lithography

On-chip 1-D photonic crystal nanocavities were designed and fabricated in a 300 mm silicon-on-insulator wafer using a CMOS-compatible process with 193 nm immersion lithography and silicon oxide planarization. High quality factors up to 10(5) were achieved. By changing geometrical parameters of the cavities, we also demonstrated a wide range of wavelength tunability for the cavity mode, a low insertion loss and excellent agreement with simulation results. These on-chip nanocavities with high quality factors and low modal volume, fabricated through a high-resolution and high-volume CMOS compatible platform open up new opportunities for the photonic integration community

Characterization of PECVD Silicon Nitride Photonic Components at 532 and 900 nm Wavelength

Low temperature PECVD silicon nitride photonic waveguides have been fabricated by both electron beam lithography and 200 mm DUV lithography. Propagation losses and bend losses were both measured at 532 and 900 nm wavelength, revealing sub 1dB/cm propagation losses for cladded waveguides at both wavelengths for single mode operation. Without cladding, propagation losses were measured to be in the 1-3 dB range for 532 nm and remain below 1 dB/cm for 900 nm for single mode waveguides. Bend losses were measured for 532 nm and were well below 0.1 dB per 90 degree bend for radii larger than 10 mu m

Study of Air Bubble Induced Light Scattering Effect On Image Quality in 193 nm Immersion Lithography

As an emerging technique, immersion lithography offers the capability of reducing critical dimensions by increasing numerical aperture (NA) due to the higher refractive indices of immersion liquids than that of air. Among the candidates for immersion liquids, water appears to be an excellent choice due to its high transparency at a wavelength of 193 nm, as well as its immediate availability and low processing cost. However, in the process of forming a water fluid layer between the resist and lens surfaces, air bubbles are often created due to the high surface tension of water. The presence of air bubbles in the immersion layer will degrade the image quality because of the inhomogeneity induced light scattering in the optical path. Therefore, it is essential to understand the air bubble induced light scattering effect on image quality. Analysis by geometrical optics indicates that the total reflection of light causes the enhancement of scattering in the region where the scattering angle is less than the critical scattering angle, which is 92 degrees at 193 nm. Based on Mie theory, numerical evaluation of scattering due to air bubbles, polystyrene spheres and PMMA spheres was conducted for TE, TM or unpolarized incident light. Comparison of the scattering patterns shows that the polystyrene spheres and air bubbles resemble each other with respect to scattering properties. Hence polystyrene spheres are used to mimic air bubbles in studies of lithographic imaging of “bubbles” in immersion water. In direct interference lithography, it is found that polystyrene spheres (2 μm in diameter) 0.3 mm away from the resist surface would not image, while for interferometric lithography at 0.5NA, this distance is estimated to be 1.3 mm. Surprisingly, polystyrene spheres in diameter of 0.5 μm (which is 5 times larger than the interferometric line-width) will not image. It is proposed that “bubbles” are repelled from contact with the resist film by surface tension. The scatter of exposure light can be characterized as “flare”. This work shows that microbubbles are not a technical barrier to immersion lithography