Thin film thickness determination with a reflectometer suffers from two problems. One problem is the leakage in the Fast Fourier Transform caused by the fact that the two variables wavenumber <i>1/λ </i>and optical thickness <i>n⋅d</i> are not really independent, since the refractive index n of the film material itself depends upon the wavenumber. This causes uncertainties in the thickness determination in the order of up to 5% for highly refractive materials like semiconductors. We present a simple but effective improvement of this contribution of the leakage that reduces the uncertainty to less than 2% for highly refractive materials. <p> </p>Another problem that mainly affects thin films below about 2 μm arises if one uses measuring heads collimators or even microscope headers to obtain high lateral resolutions in the thickness determination. The use of a header introduces angles of incidence different from the default angle α = 0° in reflectometry. Then, the measured reflectance becomes polarization-dependent and the angle must be explicitly considered in the evaluation algorithm. For a microscope header however, all angles between 0° and the angle of aperture must be considered. We will present a solution that allows to reduce the work for each header on taking into account the polarization of the reflected light and a corresponding effective angle α<sub>eff</sub>.
One of the actual challenges in optics is the fabrication of micro lenses as a part of MEMS or even integrated in macroscopic systems. This task needs a completely new category of metrology devices. To fill the gap in dimensions occuring with this technologies between the milli-/micrometer technology and the nano-/subnanometer technology, it is now possible for the surface measuring instrument MicroGlider<sup>(R)</sup> from FRT GmbH to be optionally equipped with up to 17 different sensors, most of which are optical sensors. Various optical principles are under use, to meet the different needs of devices under investigation, depending on material, surface character or necessary resolution. In addition an Atomic Force Microscope (AFM) may also be added. The AFM is fixed to the instrument additionally to the standard optical topography sensor. If necessary, a spot will be selected into the available overview measurement to determine the measuring range of the AFM. The AFM is able to investigate structures down to the atomic range. The measuring instrument enables the combination of measuring ranges from 100 mm, 350 mm or 600 mm with resolutions down to the sub-nanometer range in one single instrument.
We are developing a new linewidth standard on the nanometre scale for use in the recently introduced new high-resolution optical microscopy techniques like deep ultraviolet microscopy (UVM) and confocal laser scanning microscopy (CLSM). Different types of high-resolution gratings, etched in amorphous silicon on quartz substrates, have been fabricated and evaluated using state-of-the-art UVM, CLSM, REM and AFM equipment. The produced linewidths range from about 80 nm to 2 μm. The contrast of the pattern in the UV region makes them suitable for transmission and reflection UV and laser scanning microscopy.
One of the most actual needs in metrology is the possibility to investigate aspheres. With many optical metrology tools this is just not possible in a direct way. This task needs a completely new category of metrology tools. A new approach for this application is presented. The measuring machine performs high resolution, fast and non contact measurement of lens profiles. The geometry of the lens might be spherical or aspherical. The maximum profile length is 180 degree, maximum lens height is 50 mm. The alignment of the centre of the lens is done automatically. As an option the system may be extended into a fully 3D metrology tool.