Search

As lithographic technology nodes advance beyond the 193 nm generation, the optical absorption of organic materials will require the use of thin layer imaging (TLI) techniques. Of the techniques under consideration, the use of ultra-thin resist (UTR) over a hardmask is the most desirable because of its simplicity and close similarity to standard single layer resist processes. Prior work has demonstrated that the UTR process is capable of pattern transfer to poly silicon device layers with as little as 1000 Angstrom of resist on flat wafers using 248 nm lithography. This was achieved with defect levels comparable to a conventional 5000 Angstrom resist process. In this work, we demonstrate 'proof of concept' by integrating the UTR process into the transistor gate module of a production device using 248 nm lithography. In doing so we focus on three key areas for manufacturability: inherent defectivity of UTR films, sensitivity of thin resist to topography, and quality of pattern transfer. We find that pinhole defects are of little concern in the UTR process after SEM review of defects on un-patterned UTR films. We show that the UTR process is sensitive to wafer topography, since it does not provide a completely planar surface over the underlying device features. Finally, we demonstrate that the UTR process is capable of reliable pattern transfer on a production device with defect levels comparable to the thicker baseline single layer resist process.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Resolution, R, in optical lithography is often described by the Rayleigh equation: R equals k1(lambda) /NA. Since the 0.25 um generation there has been a trend of aggressive gate length reduction for high performance devices. Leading edge logic technologies require gate CDs equal to ½to 2/3 the wavelength of the exposure system. Even with high NA steppers and scanners low k1 patterning is a requirement. Development of processes utilizing OPC and PSM technology is critical to achieving adequate process latitude and CD control. As k1 factor falls below 0.5 the image quality and contrast degrades substantially. One result of low contrast images is that the CD variation in the photomask gives rise to larger than expected printed CD changes: the so-called MEEF. The MEEF can be simply defined as the ratio of the change of the resist feature width to the change in the mask feature width, assuming constant process and illumination conditions. For a 4x mask the MEEF can be calculated.

In this paper, we evaluate the CD-uniformity performance of an advanced DUV step and scan exposure tool. Using high quality reticles CD-uniformity at semi-dense lines is shown to be less than 10nm at best focus and less than 20nm at 0.6 micrometers focus range. Isolated lines show 10nm CD-uniformity at best focus and 20nm at 0.4 micrometers focus range. Removing reticle contribution leads to a decreases of intra-field CD- uniformity up to 6nm. At 0.18 micrometers lines, 0.45 micrometers pitch we found that the Mask Error Factor (MEF) is around 1. Going to smaller feature sizes and/or defocus MEF increases rapidly. We show that proper focus control is crucial for isolated line intra-field CD-control. Horizontal and vertical lines behave very similarly at semi-dense pitch. The isolated horizontal lines show a considerably higher DOF and tighter intra-field CD-control than isolated vertical lines. We are able to show both reticle and scanner contributions are not a limiting factor for fulfilling the requirements for CD-control of state of the art microprocessors. In case of 0.15micrometers linewidth and/or smaller pitches mask eros become more critical due to a considerable increase of the MEF.

Extreme UV Lithography (EUVL) is one of the leading candidates for the next generation lithography, which will decrease critical feature size to below 100 nm within 5 years. EUVL uses 10-14 nm light as envisioned by the EUV Limited Liability Company, a consortium formed by Intel and supported by Motorola and AMD to perform R and D work at three national laboratories. Much work has already taken place, with the first prototypical cameras operational at 13.4 nm using low energy laser plasma EUV light sources to investigate issues including the source, camera, electro- mechanical and system issues, photoresists, and of course the masks. EUV lithograph masks are fundamentally different than conventional photolithographic masks as they are reflective instead of transmissive. EUV light at 13.4 nm is rapidly absorbed by most materials, thus all light transmission within the EUVL system from source to silicon wafer, including EUV reflected from the mask, is performed by multilayer mirrors in vacuum.

A laboratory extreme ultraviolet lithography tool (EUVL) has been assembled atSandia National Laboratories [1]. Its major components include a Schwarzschildcamera with 0.1 jim resolution integrated with a laser plasma source (LPS) and amagnetically levitated stage. Other subsystems are a grazing-incidence optical system to maintain focus, and a through-the-lens Moire alignment system for overlay. This exposure tool is being used to study integration issues for EUVL.Experiments have been performed to characterize the alignment system's performance. The measured sensitivity of the alignment system is 15 nm 3. 1. INTRODUCTION A laboratory extreme ultraviolet lithography tool (EUVL) has been assembled atSandia National Laboratories' . Its major components include a Schwarzschild camera with 0.1 jim resolution integrated with a laser plasma source (LPS) and a magnetically levitated stage. Other subsystems include a grazing-incidence opticalsystem to maintain focus and an alignment system for overlay. This exposure toolis being used to study integration issues for EUVL. In order to demonstrate thesuccessful integration of the system, microelectronic devices and circuits will befabricated with at least one lithography step performed with EUVL.In this paper, we will describe in detail the EUVL tool and its capabilities. We willalso report results from recent experiments performed to characterize theperformance of the visible through-the-lens (TTL) Moire alignment system.

The demand for smaller critical dimensions in advanced computer chips has driven projection lithography to shorter wavelengths. Deep ultraviolet systems, operating at 248 nm, are commercially available and 193 nm lithography is under development. This paper describes a research and development program to extend this trend to extreme ultraviolet (EUV) wavelengths, in the range of 11 nm to 14 nm. Research and development activities are concentrated in four major areas: (1) aspheric reflectors required in an advanced EUV camera, (2) surface- imaging resists having the required resolution and sensitivity, (3) defect-free reflecting substrates required for mask fabrication, and (4) a compact source of EUV radiation. Each of these issues is discussed and efforts to address them are described. An intermediate EUVL laboratory tool, currently under construction, will also be described. This system uses a 10x reduction Schwarzschild camera and a magnetically levitated wafer stage driven by a digital feedback controller. This system represents the first attempt at integrating all major subsystems into an EUVL laboratory tool, suitable for use in device fabrication experiments.

This paper reports results from a study of defect printability for extreme ultraviolet lithographic masks (EUVL). Imaging experiments were preformed with an EUVL mask containing programmed defects. The mask contained defects of different sizes and locations with respect to the absorber patterns. Since an EUVL mask consists of absorber layer patterned above a multilayer-coated substrate, both substrate defects, located below the reflective coating, and absorber defects, located above the reflective coating, were included on the programmed defect mask. The absorber layer was patterned using a process previously described by Tennant et al. Imaging was performed using a 10X Schwarzschild camera operating at 13.4 nm with a numerical aperture of 0.08, corresponding to a Rayleigh resolution of 0.1 micrometers . This system has an effective exposure field of 0.4 mm diameter. Both positive-tone and negative-tone resists were used. Measurements of the defect-induced linewidth variations on the printed resist lines were performed with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Results show that substrate defects are more printable compared to defects of the same sizes located above the reflective coating. In addition, defects located in the center of a clear region in lines-and- space pattern are more printable compared to those located nearer to the absorber lines.

Defect densities in coatings deposited by planar magnetron sputtering were measured with a Tencor Surfscan 6200 laser particle detector. The measurements were performed on two sets of coatings - one deposited in a research chamber at the Center for X-ray Optics (CXRO) at Lawrence Berkeley Laboratories, the other deposited in a MTI Sypherline used for metal deposition in a class 1 cleanroom at the Microelectronics Development Laboratory (MDL) at Sandia National Laboratories. For coatings deposited in the research chamber, as much as 90% of the defects counted were particulates deposited during venting of the chamber. As a result, these defects were located on the surface of the coatings and were removable by ultrasonic clean in de-ionized water. Of the remaining defects on these coatings, as much as 75% of them were generated from inside the chamber during the coating process. The average number of defects in 30 bilayers of Mo/Si was 20 cm-2 for defects of sizes ≥ 0.5 µm latex-sphere-equivalent (LSE) diameter. For coatings deposited in a clean chamber located in a class 1 cleanroom, the density of ≥ 0.5 µm LSE diameter defects in a 1000 Å thick Si film was 0.2 cm-2. This is two orders of magnitude fewer defects compared with coatings deposited in a research chamber. For ≥ 0.14 µm LSE diameter defects, defect density was 7 cm-2. Defect density also increased with increased film thickness.

A study was conducted to explore the manufacturability of ultrathin resist by focusing on two key issues, defects and etch resistance. Defects in ultrathin resist were characterized by optical inspection and scanning electron microscopy reviews. A number of representative defect types in the ultrathin resist/hardmask process were identified. With process optimization, defect density in ultrathin resist was reduced to levels that are comparable to that of a baseline 0.5 μm thick resist process on nontopographic wafers. Etch resistance sufficient for patterning metal–oxide–semiconductor transistor gate film stacks was demonstrated for a 100–150 nm thick resist layer.

One of the most critical emerging challenges in lithography is achieving rapid and accurate alignment. The problem is exacerbated by wafer and stage distortions. Thus, an effective learning process is needed to rapidly acquire the best possible positional information from an array of marks across the wafer. An algorithm based on a neural network model of global alignment was presented [A. A. Ghazanfarian et al., Proc. SPIE 3051, 629 (1997); J. Vac. Sci. Technol. B 15, 2146 (1997)], which incorporated both wafer and stage distortion. Yet in almost all cases, the stepper machines are precalibrated and the stage distortion is well controlled. Therefore, the aforementioned methods need to be revisited to specifically address the wafer distortion problem. In this article, we propose a new global alignment algorithm based on array processing techniques [J. Rissanen et al., Automatica 14, 465 (1978); M. Wax et al., IEEE Trans. Acoust., Speech, Signal Process], which exploits the structure of the overlay data fro...

Extreme ultraviolet lithography (EUVL) is a candidate for high‐volume production of integrated circuits with 0.1 μm design rules. As a reduction imaging technique with robust mask substrates, EUVL reduces the mask contribution to the critical dimension (CD) error budget. However, the ability to manufacture EUVL mask blanks that are free of printable defects remains an important challenge. Electromagnetic simulations and imaging experiments have suggested that defects in the substrates and reflective coatings, in particular, may be highly printable and difficult to detect. A defect printability study using programmed defects was performed in order to determine the printing behavior of mask defects of different sizes and locations with respect to absorber features. Imaging was performed using a 10× Schwarzschild camera operating at 13.4 nm with a numerical aperture of 0.08, corresponding to a Rayleigh resolution of 0.1 μm. This system has an effective exposure field of 0.4 mm diam. Measurements of the defec...

We report experimental and theoretical studies of the resist sidewall angles produced using extreme ultraviolet lithography at exposure wavelengths of 37.5, 13.9, and 6.8 nm. We show that high resist absorption in this wavelength region leads to a significant degradation in pattern sidewall angle. Because steep resist profiles are needed in semiconductor manufacturing to ensure adequate linewidth control it seems unlikely that a single‐layer resist process can be used in extreme ultraviolet lithography except at the shortest wavelength.