This paper deals with the characteristics of circular shaped polysilicon pressure sensor diaphragms operating in the non-tactile mode. Using a phase shifting interferometer the main characteristics of diaphragms were investigated under applied pressure with respect to sensitivity, initial deflection and cavity height. Diaphragms with a thickness of 1 μm and a diameter of 96 μm were investigated in an intended pressure range of applied pressure of about 700 – 2000 hPa. Process parameters with major impact on performance and yield limitations were identified. These include the variance in diaphragm sensitivity and the impact of the variance of the sacrificial oxide layer defining the diaphragm cavity height on the contact pressure point. The sensitivity of these diaphragms including the variance was found to be - 19.8 ± 1.3 nm per 100 hPa. The impact of variance in the cavity height on the contact pressure point was found to be about 3.7 ± 0.5 hPa per nm. Summarizing both impacts a maximum variation of the contact pressure point of more than 450 hPa is possible to occur considering a nominal deflection of 300 nm. By optimizing the process of diaphragm deposition the variance in the sensitivity of the diaphragm was decreased by a factor of 2. A semi – empirical formula was evaluated that describes the deflection including initial deflection due to intrinsic stress and the process variations. A validation to the experimental obtained deflection lines showed a good agreement with deviations of less than 2 % for radial ranges of maximum deflection.
Since micro- and nanostructures for photon management are of increasing importance in novel high-efficiency solar cell
concepts, structuring techniques with up-scaling potential play a key role in their realization. Interference lithography
and nanoimprint processes are presented as technologies for origination and replication of fine-tailored photonic
structures on large areas.
At first, these structure origination and replication technologies are presented in detail: With the interference pattern of
two or more coherent waves, a wide variety of structures with feature sizes ranging from 100 nm to 100 μm can be
generated in photoresist by interference lithography. Examples are linear gratings, crossed gratings, hexagonal structures,
three dimensional photonic crystals or surface-relief diffusers. The strength of this technology is that homogeneous
structures can be originated on areas of up to 1.2 x 1.2 m2.
The structures in photoresist, the so-called master structures, can serve as an etching mask for a pattern transfer, as a
template for infiltration with different materials or they can be replicated via electroplating and subsequent replication
processes. Especially in combination with replication steps, the industrially feasible production of elaborate structures is
possible. As a particularly interesting process, nanoimprint lithography (NIL) is described in detail. As a way towards
industrial production, a roller NIL tool is presented.
After the description of the basic technologies, three application examples for solar cells are presented with details about
the design of the structures, the structuring processes, sample characterization and evaluation: (1) honeycomb structures
for the front side texturization of multicrystalline silicon wafer solar cells, (2) diffractive rear side gratings for absorption
enhancement in the spectral region near the band gap of silicon, and (3) plasmonic metal nanoparticle arrays
manufactured by combined imprint and lift off processes.