Greg P. Hughes

Attenuated phase-shifting photomasks fabricated from Cr-based embedded shifter blanks

I-line (365 nm) and G-line (436 nm) attenuated phase shifting photomasks have been developed using single layer Cr-based photoblanks. The absorber layer has a composition gradient that allows the desired transmission to be tuned while maintaining control over reflectivity and phase shift. These photoblanks are manufactured in existing facilities, and masks are processed much like conventional opaque Cr-based materials. They can be inspected and repaired on current equipment with slight modifications. Printing has been demonstrated on current generation steppers. Deep UV extendability of these materials is also being studied, with a 5% Deep UV (248 nm) single layer photoblank chemistry already demonstrated.

Issues associated with the commercialization of phase-shift masks

Issues associated with the commercialization of phase shift masks are discussed. Design layouts incorporating multiphase transitions and voting are presented along with methods of mask fabrication. Issues associated with mask inspection and repair are discussed, along with data on actual reticles produced using the prescribed method of manufacture. Cost of reticles in relation to potential wafer processing gains are compared along with problems associated with the increased complexity of the mask making process.

Advanced mask metrology enabling characterization of imprint lithography templates

Lithography costs for IC production at resolutions of 65-nm and beyond have grown exponentially for each technology node and show no sign of slowing. Step and Flash Imprint Lithography (S-FIL), developed at the University of Texas (UT) uniquely offers IC manufacturers the potential for lower cost of ownership, because S-FIL does not require expensive optics, advanced illumination sources or chemically amplified resists (CAR). The SIA’s addition of Imprint Lithography to the International Technology Roadmap for Semiconductors (ITRS) in 2003, indicates the promise to become a preferred technology and has some compelling advantages over traditional 4X optical lithography. Advanced 90nm binary & phase shift mask processes have been altered using thin Cr (15-nm) & thin e-beam resist (<150nm) resulting in sub 100-nm geometries necessary for S-FIL, and have become the baseline for template manufacture. Commercial production of advanced 1X templates requires CD metrology capability beyond the equipment typically used in 4X mask making. Full commercialization of Imprint Lithography requires not only the ability to generate a 1X template but also a metrology solution that can characterize critical dimension (CD) parameters of the template. Previous published work on S-FIL has focused mainly on high resolution templates produced on 100keV Gaussian pattern generators (PG), and has shown that resolution is only limited by the template. This work demonstrates that an advanced commercial photomask facility can fabricate templates with sub-100 nm critical dimensions, and that the CDs can be characterized using a commercially available CD-SEM metrology tool. CD metrology repeatability of 0.7nm 3σ was established on a quartz only template with a 6025 form factor.

Detection of 60° phase defects on alternating PSMs

In this paper we present results of an algorithm that has been developed which is sensitive to phase defects of 60 degrees on i-line alternating PSMs. This algorithm consists of microcode and software, which can be loaded into existing inspection hardware. The algorithm works in die-to-die inspection mode and uses both transmitted and reflected light images to maximize sensitivity. Isolated phase defects as well as phase defects close to chrome edges were inspected. In addition, the algorithm is able to detect missing and mis-aligned shifter edges. A programmed phase defect test plate was developed to characterize defect detection sensitivity. Detection of 60 degrees defects smaller than 0.75 micrometers has been demonstrated with this algorithm. Defect sensitivity characterization and actual production plate effect results are shown. Finally, recent results showing the application of the algorithm to the inspection of Deep-UV multiphase reticles using a shorter inspection wavelength are presented.

Chromium-based attenuated embedded shifter preproduction

Attenuated embedded phase shifting photomask technology can improve lithography performance for both g-line and i-line steppers. Emphasis at i-line is shifting from development to production as lithographers integrate phase shifting masks into their processes. This paper describes pilot production of i-line and g-line, Cr-based, attenuated embedded phase shifter photoblanks and photomasks.

Design and fabrication of highly complex topographic nano-imprint template for dual Damascene full 3-D imprinting

At SPIE Microlithography 2005, the concept of direct imprinting of dielectric material for dual damascene processing and its benefits was introduced 1. Manufacturing a nano-imprint template with multi-tier 3-D structures presents a unique set of challenges. The main issues are patterning two different mask layers with good overlay and etch depth control into the quartz at each step on the same substrate. This work describes the tools and processes used to build these types of structures in a commercial photomask shop. The results of using a template with two levels of patterning to imprint dual damascene 3-D structures will also be presented.

Aberration determination in early 157-nm exposure system

Aberrations, aberrations, here there everywhere but how do we collect useful data that can be incorporated into our simulators? Over the past year there have no less than 18 papers published in the literature discussing how to measure aberrations to answering the question if Zernikes are really enough. The ability to accurately measure a Zernike coefficient in a timely cost effective manner can be priceless to device manufacturers. Exposure tool and lens manufacturers are reluctant to provide this information for a host of reasons, however, device manufacturers can use this data to better utilize each tool depending on the level and the type of semiconductors they produce. Dirksen et al. first discussed the ring test as an effective method of determining lens aberrations in a step and repeat system, later in a scanning system. The method is based on two elements; the linear response to the ring test to aberrations and the use of multiple imaging conditions. The authors have been working to further enhance the capability on the test on the first small field 157 nm exposure system at International SEMATECH. This data was generated and analyzed through previously discussed methods for Z5 through Z25 and correlated back to PMI data. Since no 157nm interferemetric systems exist the lens system PMI data was collected at 248nm. Correlation studies have isolated the possible existence of birefringence in the lens systems via the 3-foil aberration which was not seen at 248nm. Imaging experiments have been conducted for various geometrys and structures for critical dimensions ranging from 0.13micrometers down to 0.10micrometers with binary and 0.07micrometers with alternating phase shift mask. The authors will review the results of these experiments and the correlation to imaging data and PMI data.

Optical superlattices as phase-shift masks for microlithography

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.

Manufacturing of ArF chromeless hard shifter for 65-nm technology

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.

Advanced 193 tri-tone EAPSM (9%-18%) for 65 nm node

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.