Udo Dinger

Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology

In this paper, the metrology and fabrication concepts at Carl Zeiss will be reviewed. The present status in the fabrication of specific EUVL mirrors will be reported as well.

Progress of the EUVL alpha tool

After the successful completion of the European program EUCLIDES in which core competence for Extreme UltraViolet Lithography (EUVL) technology was generated, ASML (system integration), Carl Zeiss (optics), and their partners have entered the next phase of the program: design and realization of an exposure tool called the alpha tool ((alpha) -tool). This tool should be completed in 2003, and will demonstrate 50-nm-node compliant imaging using full- field all-reflective four-times reducing optics, as well as high performance vacuum scanning wafer- and reticle stages. IN this paper we present the status of the project, as well as highlight the progress in the optics development and optics contamination mitigation efforts.

Fabrication and metrology of diffraction limited soft x-ray optics for the EUV microlithography

EUVL, i.e. microlithography at 13nm is one of the most likely technologies to satisfy the requirements for the 45nm-node and below of the IC-manufacturing roadmap. The development of the first step and scan machines meeting production requirements of field size and resolution is in progress. A key component of these machines will be a diffraction limited, off-axis mirror system with aspherical surfaces. The optical surfaces of these mirrors have to be fabricated and measured with unprecedented accuracy. In recent years, technology development at Carl Zeiss SMT AG was focussed on the on-axis aspheres of the NA=0.30 micro exposure tool (MET). Presently this technology is transferred to the surfaces of a NA=0.25 off-axis, large field system The current status of the fabrication and metrology of both on-axis and off-axis mirrors will be reviewed.

Manufacturing of Wolter-I mirror segments with slumped glass

In our ongoing studies of high precision glass slumping we have successfully formed the first Wolter-I X-ray mirror segments with parabola and hyperbola in one piece. It could be demonstrated that the excellent surface roughness of the 0.55 mm thick display glass chosen is conserved during the slumping process. The influence of several parameters of the process, such as maximum temperature, heating and cooling rates etc. have to be measured and controlled with adequate metrology. Currently, we are optimizing the process to reduce the figure errors down to 1 micrometer what will be the starting point for further, final figure error corrections. We point out that metrology plays an important role in achieving a high precision optics, i.e. an angular resolution of a few arcsec. In this paper we report on the results of our studies and discuss them in the context of the requirements for future X-ray telescopes with large apertures.

EUV microlithography: a challenge for optical metrology

EUVL (extreme ultraviolet lithography), utilizing an actinic wavelength of about 13 nm , appears to be the most promising technology approach to reach the 30 nm node. Calling for diffraction limited imaging performance, EUV demand unprecedented requirements for figure metrology and fabrication technology. This paper gives an overview over problems rising from the interferometric measurement of aspheric EUV mirrors.

EUV Imaging - an aerial image study

This work discusses the imaging properties of EUVL systems on the basis of an aerial image study in resist. A process window analysis for the lithographic structures which are driving the ITRS roadmap is presented. Here we cover the 45 nm and 32 nm node. In a first step we focus on the contribution of wavefront aberrations and flare effects to the imaging performance. In a second step we investigate the process latitude for different generic pattern of the above mentioned nodes. It becomes clear that EUVL tools are a very good choice for the printing of contact holes. Dense and semi-dense lines can be easily printed too, using a conventional illumination setting. From our current perspective, isolated features on bright field reticles are the most challenging structures for EUV imaging due to the flare impact on contrast and process latitude. Related to flare we discuss our progress in mirror surface manufacturing to reduce the overall flare level.

Wave-front correction methods for extreme-ultraviolet multilayer reflectors

In this theoretical study we show that by removing or depositing additional multilayer (ML) periods of a thin-film interference coating, distortions in the reflected wave front induced by surface figure errors can be corrected. At lambda = 13.4 nm in the extreme-ultraviolet region the removal or deposition of a single period of the standard two-component molybdenum-silicon (Mo/Si) ML interference coating induces an effective phase change of magnitude 0.043pi with respect to an identical optical thickness in vacuum. The magnitude of this wave-front shift can be enhanced with multicomponent MLs optimized for phase change on reflection. We briefly discuss the contributions of the shift in the effective reflection surface of the ML on the phase change. We also predict the feasibility of novel phase-shifting mask for subwavelength imaging applications.

An Optical Test And Alignment Method For The XMM Mirror Module

XMM is a highly nested (58 individual shells) Wolter-I type X-ray telescope with a focal length of 7.5 m. The specified resolution (HEW) is 30 (goal 20) arcsec. In order to qualify single mirror shells and align and assemble the whole mirror module in a reasonable time it is inevitable to apply fast test and strongly converging alignment procedures. By means of two scanning laser beams intra- and extrafocal images of two mirror shells will be registered on a CCD-camera coupled to an image processing PC. One of the mirrors is already glued and serves as a reference while the second one has to be aligned yet. From the data axial and lateral focus positions as well as focus dimensions are calculated. A feed back loop then activates a set of actuators coupled to the mirror to be aligned. In an iterative way the alignment status of this mirror will be optimized. Finally, this mirror is cemented under optical control. First results from a basic test setup with only one mirror will be presented.

Recent results on manufacturing of segmented x-ray mirrors with slumped glass

Future X-ray missions are aiming at large mirror collecting areas of the order of several square meters. This is obtained with mirror assemblies composed of a large number of segments. The angular resolution of each one must be measured separately down to 1 arcsec. The mass limits imposed by the launchers require low weight and high stiffness materials. In this context we have focused our recent studies on the manufacturing of thin glass mirror segments. These mirrors are made from sheet glass which can be shaped in a high-precision slumping process to e.g. a Wolter-I figure. The excellent surface roughness of the sheet glass chosen is conserved during the slumping process and the final figure corrections with non-contacting tools. The influence of several parameters of the process, such as glass and mould material, heating and cooling, has been measured and controlled with adequate metrology. In this paper we describe our current efforts which are aiming at the production of a Wolter-I scaled demonstration model - preferentially with parabola and hyperbola in one piece - made of thin sheet glass.

Substrate material aspects of optics manufacturing for high-intensity synchrotron beamlines

Proven bulk materials for mirrors with high surface qualities are classical optical glass, quartz, and low thermal expansion materials like ZERODURR. New requirements for mirrors with high heat load capabilities have established the need for different bulk materials. Metals, silicon and silicon carbide (SiC) are presently the favorite materials for the manufacturing of optical components for high brilliance synchrotron beam lines. This paper discusses properties of different types of material under manufacturing and applicational aspects.