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.
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.
In active triangulation systems, one side of the triangulation triangle is made up of a spatial light structure of well-known shape and location, causing a pattern on the surface of the target object. The other
side of the triangle is embodied by ray bundles, imaging this pattern onto a position sensor. Because nearly all surfaces show scattering characteristics between specular and diffuse reflection, the corresponding image-forming wavefronts are not of uniform amplitude, and so the irradiance of the imaging pupil is also nonuniform. If the imaging is done by an aberrated system, this can cause deviations from the image as predicted by geometric optics. An estimate of deviations resulting from defocusing by treating the imaging process in terms of scalar diffraction theory, using a linear model for nonuniform pupil irradiance is given.
Conference Committee Involvement (1)
Advances in Metrology for X-Ray and EUV Optics
2 August 2005 | San Diego, California, United States