Photoresist patterning experiments on the EUVL Engineering Test Stand using two masks with different types of architecture indicate that etched-multilayer binary masks can provide larger process latitude than standard patterned absorber masks. The trends observed in the experimental data are confirmed by rigorous electromagnetic simulations taking into account the mask structure, the imaging optics characteristics and the illumination conditions.
For logic design, Chrome-less Phase Shift Mask is one of the possible solutions for defining small geometry with low MEF (mask enhancement factor) for the 65nm node. There have been lots of dedicated studies on the PCO (Phase Chrome Off-axis) mask technology and several design approaches have been proposed including grating background, chrome patches (or chrome shield) for applying PCO on line/space and contact pattern. In this paper, we studied the feasibility of grating design for line and contact pattern. The design of the grating pattern was provided from the EM simulation software (TEMPEST) and the aerial image simulation software. AIMS measurements with high NA annular illumination were done. Resist images were taken on designed pattern in different focus. Simulations, AIMS are compared to verify the consistency of the process with wafer printed performance.
The impact of wafer and reticle anti-reflection coatings (ARCs) on the aerial image of ArF lithography scanners is measured using contrast curves and critical dimension (CD) analysis. The importance of a good ARC layer on the wafer appears to be greater than that of the reticle-ARC. In fact, for state-of-the-art lithography scanners, the influence of the reticle-ARC is practically undetectable. Numerical simulations are used to understand the relative contributions of the lens, the wafer and the reticle to the overall loss of contrast associated with non-optimized ARCs.
The integration of 193nm Lithography is close to full production for the 90nm node technology. With the potential of emerging 193nm lithographic resolution down to 65nm, the quality of 193nm reticles including binary, EAPSM and AAPSM must be outstanding so that low K1 factor reticles may be used in production. One area of concern in the IC industry is haze contamination on the mask once the reticle has been exposed to ArF radiation. In this study, haze was found outside of the pellicle and on the quartz side of the mask. Standard through-pell inspections will typically miss the contamination, yet its severity can ultimately affect mask transmission. For this reason, DuPont Photomasks and Cypress joined forces to quickly decipher how it develops. In this investigation, tests were devised which altered conditions such as mask environment, exposure, traditional and advanced cleaning chemistry. This paper describes the relationship between surface and environmental photochemical reactions, the resultant growth, analysis, and how it is controlled.
Spin spray and bath immersion systems are still the competing technologies for mask process. The preference for one or the other is largely dependent on factor such as performance, size, throughput, and cost. This paper focuses on the process optimization of the immersion bath technology in relation to the performance such as particulate soft defects, EAPSM optical parameter change, and antireflective layer reflectivity.
Extreme Ultraviolet Lithography (EUVL) is the leading candidate for manufacturing integrated circuits beyond the 45-nm technology node. The masks for EUVL are reflective and significantly different from current transmission masks for deep UV lithography. Many authors have demonstrated the patterning of EUVL masks using different types of absorber stacks that were deposited on top of the multilayer reflector. More recently, a new approach based on the etching of the multilayer reflector in order to define the mask pattern was proposed . Using rigorous electro-magnetic simulations, it was shown that this subtractive approach could provide better process latitude, less H-V bias and smaller image-placement errors compared to the traditional masks based on the additive method. Even though the mask processing shows interesting challenges, this approach might offer immediate advantages over the more traditional patterning technique using the absorber stack, beyond those predicted for lithography imaging. These include the possibility to use optical inspection in transmission mode, which can provide the high-contrast images that are essential for high-sensitivity detection of small defects.
In this paper, we present the first results on the patterning of EUVL masks using the direct etching the EUVL multilayer reflector (Mo/Si type) to produce EUV binary masks. In particular, we show how the process parameters can be adjusted to control the pattern sidewall angle. We also present an analysis of the influence of this sidewall angle on lithography imaging, based on lithography simulations. Finally, we show results from the optical inspection of these etched-multilayer binary masks (EMBM).
A method based on UV in air environment to improve the stability of the material of the photoreticles throughout cleans repeated over is suggested in this work. A typical aggressive clean was performed on two different Embedded Shifter materials, 193nm Molybdenum-Silicon-Oxy-Nitride (MoSiON) and 193nm Multilayer Silicon Nitride-Titanium Nitride (SiN-TiN). The variation of phase and transmission of each reticle is reported with the number of cleans. Given the appropriate exposure the phase and the transmission of the treated materials were significantly improved. All treated EAPSMs could stand cleans repeated over.
Photomask resist strip processes have traditionally used the sulfuric-peroxide-mix, known as SPM, or Piranha. This paper details a recent investigation into the utilization of solvent-based resist strip solutions applied to photomask resist stripping. Studies of two commercially available solvents are documented in this report: one formulated for positive resist stripping [Chem A, which contains a primary amine, glycol and is semi-aqueous], and another rated for 'hard-to-remove' positive resist stripping [Chem B, which contains glycol ethers, organic cyclics -- all proprietary]. Resist types, such as IP3600, and most Chemically Amplified Resists (CAR) will strip easily with any of the chemicals mentioned, however, other adverse effects may deter one from using them. The screening process employed in this study monitors effects of processing on EAPSM phase and transmission, AR layer reflectivity changes and surface ionic analytical comparisons. Chem A and B will show similarly low phase and transmission shifts at higher temperature and longer process times, while reflectivity data shows lower level changes associated with the use of Chem A (favorable). As for surface ionic contamination: on F and Cl contaminated surfaces, Chem A shows favorable results. Overall Chem A seems to be the appropriate choice for more thorough investigation in a production mask-making environment.
Contact patterning for the 65nm device generation will be an exceedingly difficult task. The 2001 SIA roadmap lists the targeted contact size as 90nm with +/-10% CD control requirements of +/-9nm. Defectivity levels must also be below one failure per billion contacts for acceptable device yield. Difficulties in contact patterning are driven by the low depth of focus of isolated contacts and/or the high mask error (MEF) for dense contact arrays (in combination with expected reticle CD errors). Traditional contact lithography methods are not able to mitigate both these difficulties simultaneously. Inlaid metal trench patterning for the 65nm generation has similar lithographic difficulties though not to the extreme degree as seen with contacts. This study included the use of multiple, high transmission, 193nm attenuated phase shifting mask varieties to meet the difficult challenges of 65nm contact and trench lithography. Numerous illumination schemes, mask biasing, optical proximity correction (OPC), mask manufacturing techniques, and mask blank substrate materials were investigated. The analysis criteria included depth of focus, exposure latitude and MEF through pitch, reticle inspection, reticle manufacturability, and cost of ownership. The investigation determined that certain high transmission reticle schemes are strong contenders for 65nm generation contact and trench patterning. However, a number of strong interactions between illumination, OPC, and reticle manufacturing issues need to be considered.
Semiconductor manufacturers are increasingly focusing on contact and via layers as the most difficult lithography pattern. Focus and exposure latitude, MEF, as well as iso-dense bias are challenges for contact patterning. This situation is only expected to worsen for the 65nm device generation where the 2001 SIA roadmap update lists the contact size as 90-100nm in 2004-2005. Thus, new contact pattern techniques with novel manufacturability are required. One possible avenue to meet these stringent process control requirements is the use of tri-tone high transmission attenuated phase shifting masks (tri-tone AttPSM) for the 65nm generation.
Multilayered SiN/TiN (9%-18%) EAPSM materials to manufacture advanced reticles were used in this investigation. Extensive study during the photomask processing (Front End and Back End) to access any issues related to the making of High %T tri-tone product types was performed.
Finally, the 2 prototype reticles were evaluated on a 193nm scanner (0.75NA) with various illumination settings to generate imaging to support the 65nm node technology generation.
ArF lithography that is expected the candidate for next generation optical lithography and attenuated Phase Shift Mask (att-PSM) will be adapted for 0.12micrometers design-rule and beyond. For the next-generation lithography, the most important requirement for mask process is enough resolution and good pattern fidelity to generate various critical patterns, of which sizes are below 0.5micrometers main pattern including OPC patterns. In this paper we describe in terms of blank mask properties, mask making process and wafer performance of ArF attenuated Phase Shift Mask (att-OSM) using TiN/Si3N4(abbreviated as TiN/SiN) multi-layer for Next Generation Lithography (NGL). In view point of material, we have evaluated for the applicability of TiN/SiN multi-layer to ArF lithography as compared with non- stoichiometric MoSiON-based single-layer structure. In mask making process, we used Chemically Amplified Resist (CAR) process characteristics and Dry etching system for improvement of enough resolution and pattern fidelity. Also we have investigated wafer performance for ArF att-PSM in terms of process windows as compared with BIM (Binary Intensity Mask) in 120nm D/R real cell pattern and 100nm L/S(Line and Space)D/R pattern, respectively.
Improving microprocessor speed, design and density are mainly determined by the minimum feature size that can be imaged on the wafer . On the other hand, the latter is limited by the optics, the lithographic wavelength and the process used. Phase shift photomasks were introduced to extend the usefulness of any optical lithographic generation [2,3]. As smaller feature sizes are required by the IC industry, the use of phase shift masks is expected to increase for a specific stepper generation.
Optical lithography is one of the key enabling technologies in semiconductor microcircuit fabrication. As the demand for devices with higher performance and speed continue, the need for patterning circuits with finer features is driving optical microlithography to shorter and shorter wavelengths (248 nm yields 193 nm yields 157 nm). This is because the resolution with traditional Cr masks, that either block or pass light for imaging, is limited by optical diffraction. At any wavelength, however, phase-shift masks can enhance resolution beyond the wavelength-imposed diffraction limit. Phase-shift masks work by employing destructive optical interference to enhance contrast. This paper discusses a novel, systematic materials approach--optical superlattices- -to design embedded attenuating phase-shift masks, the most versatile and common type phase-shift mask, for any optical wavelength. These superlattices are comprised of alternating, ultrathin (< 10 nm) layers of an optically transparent compound multilayered with an optically absorbing one, e.g., Si3N4 and TiN. Film structure, optical properties, etching, chemical stability, and radiation durability are discussed.