Berliner Glas is a privately owned, mid-sized manufacturer of precision opto-mechanics in Germany. One
specialty of Berliner Glas is the design and production of high performance vacuum and electrostatic wafer
chucks. Driven by the need of lithography and inspection for smaller overlay values, we pursue the production
of an ideally flat wafer chuck. An ideally flat wafer chuck holds a wafer with a completely flat backside and
without lateral distortion within the wafer surface.
Key parameters in influencing the wafer chucks effective flatness are thermal performance and thermal
management, roughness of the surface, choice of materials and the contact area between wafer and wafer
chuck. In this presentation we would like to focus on the contact area. Usually this is decreased as much as
possible to avoid sticking effects and the chance of trapped particles between the chuck surface and the
backside of the wafer. This can be realized with a pin structure on the chuck surface. Making the pins smaller
and moving pins further apart from each other makes the contact area ever smaller but also adds new
challenges to achieve a flat and undistorted wafer on the chuck. We would like to address methods of
designing and evaluating such a pin structure.
This involves not only the capability to simulate the ideal pattern of pins on the chuck’s surface, for which we
will present 2D and 3D simulation results. As well, we would like to share first results of our functional models.
Finally, measurement capability has to be ensured, which means improving and further development of
Fizeau flatness test interferometers.
Berliner Glas KGaA is specialized on the manufacturing of high performance wafer and reticle chucks. Electrostatic
chucks (ESC) are especially used in vacuum environments e.g. during lithographic processing, coating and etching. The
main task of the chuck is to provide a well defined positioning and thermal stabilization of the wafer or reticle. Typical
wafer materials are semiconductors like silicon and in some special cases dielectrics like magnesia, alumina or glass.
For a functional characterization of the ESC clamps Berliner Glas has developed a measurement method to determine the
clamp pressure with a Fizeau interferometer. The setup utilizes the local bending of clamped wafers to determine the
effective clamp pressure.
The clamp pressure is measured in the range of 20...500 mbar. This new method allows for a lateral resolution of the
clamp pressure measurement. It can be calibrated by various methods. Direct computation of the clamp pressure based
on the bending height or comparative measurements with vacuum chucking by the same chuck gives evidence for the quantitative results. Transient clamp pressure variation can be measured with a resolution of 2 mbar. The results can be used to qualify and optimize ESC´s and even for a local correction of the clamp force.
The efficient manufacturing of light-weighted mirror substrates is an important technology for the optical industry. The presentation deals with the prerequisites for the production of such substrates with respect to material properties, as well as manufacturing technology. Different materials are being presented with special emphasis on low- and zero thermal expansion materials. Their material properties of importance for the production of light weighted mirror substrates are
being compared. Further more possible light weighting strategies are compared regarding light weighting success, manufacturing effort, necessary manufacturing technology and therefore price impact. For the successful implementation of these manufacturing processes a demonstrator part is shown including the flatness results achieved.
Microstructures on glass surfaces achieved an increasing relevance in industry and research during the last years. They are used to add various optical and/or mechanical functionalities to surfaces of glass components. Important mechanical functionalities are e.g. the anti-sticking behaviour of nanostructures or the generation of micro cavities. Reduced reflectivity and the addition of diffractive optical power with negative dispersion are examples of relevant optical functionalities which can be supplemented. The authors evaluated theoretically and experimentally different promising technologies for generating such structures. Especially there was tested the compression moulding replication process, the deep drawing of glass, etching and sandblasting. All these methods are able to generate microstructures and show characteristic advantages and disadvantages. Ion beam etching allows the smallest structures but is relatively expensive. Furthermore, the ion beam etching can be used for a large variety of materials. Sandblasting is a very effective way of generating deep structures, but is limited in feature size. Wet chemical etching is suitable for small structures but not able to achieve high aspect ratios in glass. The deep drawing of glass presents a very cost efficient way for generating microstructures in volume production. Here the disadvantage is the limited feature size and aspect ratio that can be generated. Utilizing its different advantages, applications are developed by the authors for all three technologies. These are applications to be used in sensors, displays and in the semiconductor industry.