Daniel A. Tichenor

EUV Engineering Test Stand

The Engineering Test Stand (ETS) is an EUV laboratory lithography tool. The purpose of the ETS is to demonstrate EUV full-field imaging and provide data required to support production-tool development. The ETS is configured to separate the imaging system and stages from the illumination system. Environmental conditions can be controlled independently in the two modules to maximize EUV throughput and environmental control. A source of 13.4 nm radiation is provided by a laser plasma source in which a YAG laser beam is focused onto a xenon-cluster target. A condenser system, comprised of multilayer-coated mirrors and grazing-incidence mirrors, collects the EUV radiation and directs it onto a reflecting reticle. A four-mirror, ring-field optical system, having a numerical aperture of 0.1, projects a 4x-reduction image onto the wafer plane. This design corresponds to a resolution of 70 nm at a k1 of 0.52. The ETS is designed to produce full- field images in step-and-scan mode using vacuum-compatible, one-dimension-long-travel magnetically levitated stages for both reticle and wafer. Reticle protection is incorporated into the ETS design. This paper provides a system overview of the ETS design and specifications.

Diffraction-limited soft-x-ray projection imaging using a laser plasma source

Projection imaging of 0.1-microm lines and spaces is demonstrated with a Mo/Si multilayer coated Schwarzschild objective and 14-nm illumination from a laser plasma source. This structure has been etched into a silicon wafer by using a trilevel resist and reactive ion etching. Low-contrast modulation at 0.05-microm lines and spaces is observed in polymethylmethacrylate.

System integration and performance of the EUV engineering test stand

The Engineering Test Stand (ETS) is a developmental lithography tool designed to demonstrate full-field EUV imaging and provide data for commercial-tool development. In the first phase of integration, currently in progress, the ETS is configured using a developmental projection system, while fabrication of an improved projection system proceeds in parallel. The optics in the second projection system have been fabricated to tighter specifications for improved resolution and reduced flare. The projection system is a 4-mirror, 4x-reduction, ring-field design having a numeral aperture of 0.1, which supports 70 nm resolution at a k1 of 0.52. The illuminator produces 13.4 nm radiation from a laser-produced plasma, directs the radiation onto an arc-shaped field of view, and provides an effective fill factor at the pupil plane of 0.7. The ETS is designed for full-field images in step-and-scan mode using vacuum-compatible, magnetically levitated, scanning stages. This paper describes system performance observed during the first phase of integration, including static resist images of 100 nm isolated and dense features.

First lithographic results from the extreme ultraviolet Engineering Test Stand

The extreme ultraviolet (EUV) Engineering Test Stand (ETS) is a step-and-scan lithography tool that operates at a wavelength of 13.4 nm. It has been developed to demonstrate full-field EUV imaging and acquire system learning for equipment manufacturers to develop commercial tools. The initial integration of the tool is being carried out using a developmental set of projection optics, while a second, higher-quality, projection optics is being assembled and characterized in a parallel effort. We present here the first lithographic results from the ETS, which include both static and scanned resist images of 100 nm dense and isolated features throughout the ring field of the projection optics. Accurate lithographic models have been developed and compared with the experimental results.

Sub-70 nm extreme ultraviolet lithography at the Advanced Light Source static microfield exposure station using the engineering test stand set-2 optic

Static microfield printing capabilities have recently been integrated into the extreme ultraviolet interferometer operating at the Advanced Light Source synchrotron radiation facility at Lawrence Berkeley National Laboratory. The static printing capabilities include a fully programmable scanning illumination system enabling the synthesis of arbitrary illumination coherence (pupil fill). This new exposure station has been used to lithographically characterize the static imaging performance of the Engineering Test Stand Set-2 optic. Excellent performance has been demonstrated down to the 70 nm equal line/space level with focus latitude exceeding 1 μm and dose latitude of approximately 10%. Moreover, equal line/space printing down to a resolution of 50 nm has been demonstrated using resolution-enhancing pupil fills.

Particle size measurements using an optical variable-frequency-grid technique

A fringe visibility method for sizing particles 10 microm and larger has been developed. As the image of a particle scans across a variable frequency grid, the transmitted light signal oscillates with varying visibility. The visibility goes through a null at a well-defined point where the particle diameter approximates the local grid spacing. Several optical arrangements implementing the variable frequency grid technique have been tested. Using classified alumina and pulverized coal particles we obtained good agreement between size distributions measured by this technique and those from a commercial off-line analyzer. However, our optical arrangement and signal processing techniques require further development to reduce them to practice.

Design criteria and recent developments of optical single particle counters for fossil fuel systems

Optical methods for particle size distribution measurements in practical high temperature environments are approaching feasibility and offer significant advantages over conventional sampling methods. The present paper begins by summarizing user requirements for research and on-line particle measurements in fossil fuel systems. The principles of single particle counter (SPC) design are outlined followed by a discussion of practical instrument design constraints. Three instrument design concepts currently being developed at Sandia are then discussed. An overview of these current methods and other instrument designs is presented with particular emphasis on capabilities to meet user ojectives. Validation and long term testing of these new concepts is considered to be the final important step in achieving user acceptance of in situ optical counters.

Diffraction‐limited soft x‐ray projection lithography with a laser plasma source

A laser plasma source of extreme ultraviolet and soft x‐ray radiation has been used to print diffraction‐limited features using soft x‐ray projection lithography. A spherical condenser optic, a Si/Ge transmissive mask and a Mo/Si multilayer‐coated Schwarzschild objective having 20:1 reduction ratio were employed to pattern selected single‐layer and trilevel resists. At a numerical aperture of 0.12, a 0.1‐μm line and space pattern is clearly delineated and weak modulation is observed for the analogous 0.05‐μm pattern.

Computer Analysis Of Holographic Interferograms For Nondestructive Testing

We have developed an automated technique for interferogram interpretation using a PDP-12 minicomputer, Cohu television camera and Hughes scan converter. A digitized image of the interferogram is stored on disc, and a small area is read into central memory. The fringe density in that region is estimated based on the number of peaks found in several line scans across the area under study. This calculation is repeated for successive small areas until a map of fringe density covering the entire part is compiled. If the fringe density map falls within an acceptance profile, the part is accepted. Experimental results demonstrate that this technique works well on interferograms having substantial variations in intensity and fringe contrast.

Sub-100-nm lithographic imaging with an EUV 10x microstepper

The capabilities of the EUV 10x microstepper have been substantially improved over the past year. The key enhancement was the development of a new projection optics system with reduced wavefront error, reduced flare, and increased numerical aperture. These optics and concomitant developments in EUV reticles and photoresists have enabled dramatic improvements in EUV imaging, illustrated by resolution of 70 nm dense lines and spaces (L/S). CD linearity has been demonstrated for dense L/S over the range 100 nm to 80 nm, both for the imaging layer and for subsequent pattern transfer. For a +/- 10 percent CD specification, we have demonstrated a process latitude of +/- micrometers depth of focus and 10 percent dose range for dense 100 nm L/S.