Photostructured glass

One exception is the special types of photostructurable glass. For the construction of microreactors, the borosilicate types of glass as well as fused silica are the most important ingredients. 

Figure2.15 Examples of structures in photostructuring glass, (a) long hole, (b) columns and (c) interlocking channels.(With friendly permission of the Technical University of llmenau, Faculty of Mechanical Engineering, Department of Inorganic-Nonmetallic Materials).

The roughness of the finished surface is Rz 2-4 pm. Surfaces treated by lapping and microabrasion are similar. In contrast to what happens to photostructured glass, only the areas without a mask are processed the covered parts of the wafer surface remain virtually intact. Figure 2.20 shows various examples of one-sided and doublesided structuring. 

Albrecht, A., Frank, T., and Harnisch, A. (1998) Glass relief structuring system using fine linear scanner to irradiate photostructurable glass , German Patent DE1984675112. 

Fig. 1. 39. Scanning electron micrograph [220] of the photostructurable glass FS 21, which was developed by Bruntsch [75] at the TU llmenau...

Fig. 1.41. SEM micrograph of partially crystallised areas in the photostructurable glass FS 21 after UV exposure and tempering for Ih at 590°C. The LMS crystals where dissolved in 2.5% HF [446]...

Tailoring the Thermal Expansion Coefficients of Photostructurable Glasses... 

Just like the commercially available photostructurable glasses, FS 21 also has an intense Ce +-absorption band with a maximum between... 

Table 1.9. Compositions (mass %) of photostructurable glasses with different thermal expansion coefficients [128]. The numbers correspond to the compositions shown in the simplified phase diagram in Fig. 1.44...

The mechanical properties of photostructurable glasses allow the fabrication of spring-like mechanical sensor devices, because of their linear stress-strain behaviour (see also Sect. 11.1.1). However, for such applications it is necessary to detect the distortion of these devices. Real microstructured glass springs or other microstructured glass components could be used... 

The standard structuring process is based on photolithography and consists of three main steps UV exposure, thermal treatment and acid etching. A schematic of the process is shown in Fig. 9.1. The following discussion focuses on the photostructurable glass FS21 developed at the Technische Universitat Ilmenau. 

For photostructuring, a polished sheet of a photostructurable glass is required. The substrates are prepared by grinding and polishing processes... 

Alternatively laser-structured stainless steel foils or even machined thin brass sheets can be used to photostructure glasses. However, such masks offer lower precision. The precision of structures in laser-structured stainless steel foils is around 20 pm, whereas that of machined thin brass sheets is not better than 50 pm. Such masks offer only a limited variety of structures. No freely standing structures are possible, because these masks do not possess a mask blank. However, the main advantage of these masks is their low cost. These masks are therefore a cost effective alternative to manufacture simple structures. 

Fig. 9.7. A step profile between partially crystallised and glassy areas of thermally treated samples of the photostructurable glass Fotoform the matrix is crystallised. The hills are rounded because of the surface tension causing the formation of giass lenses [477]...

Fig. 9.8. Comparison of the temperature-time regimes for the thermal treatment of various photostructurable glasses [366]...

A microstructured photostructurable glass can again be exposed to a second, unmasked UV treatment. The partial crystallisation of lithium metasilicate takes place during the second thermal treatment similarly to the first... 

The influence of the composition of a photostructurable glass in the partially crystallised state on the etching behaviour was investigated by Hinz... 

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