Publication
We have used powder blasting as a technique to structure brittle materials like glass using an erosion resistant mask. The study of the erosion rate shows that the erosion of glass is maximum at a normal incidence of the powder beam while the erosion rate of metals and elastomers is minimum. A metallic contact mask is very resistant, easy to use, but its resolution as defined by its manufacturing process (laser ablation) is limited. The resolution of the mask depends on the thickness of the metal piece. However due to the stress generated by the powder blasting technnique, the metal mask used must have an important thickness (about 0,5 mm), which limits the resolution (50 μm). The photolithographic masking method we developed allows to increase the resolution. We have demonstrated that the erosion resistance of Polydimethylsiloxane (PDMS), an elastomer very frequently used in microsystems realisation is excellent, and that the use of a photosensitve epoxy resist like SU8 allows to define high-resolution structures. The replication quality is good as the majority of structures defined in PDMS have the same size compared to the features defined by the SU8. In our process, the SU8 is patterned into a mould structure that is filled with PDMS. The SU8, has a similar erosion behavior as glass and is quickly removed by powder blasting. The resolution of the process determined by the particle size ; we have used particles with 10 μm diameter to explore the ultimate limits of powder blasting. The study of the etching by powder blasting shows that the etching rate changes with the width of the channel and the etching time. Furthermore, dimensions of channels or hole structures change during powder blasting, they are increased by the underetching effect. This underetching depends on the depth of the channels and can induce changes in resolution.The erosion mask resistance is function of the thickness of the mask, of the etching time and of the applied pressure. We typically have chosen a PDMS mask thickness of 50 μm. When the applied pressure of the powder jet increases, the PDMS erosion is more important. When an energetic particle impacts on the PDMS, the glass underneath the mask can be damaged and the resolution of the structures is decreased. Experimentally, this PDMS/SU8 mask is resistant and efficient for an applied pressure up to 200 kPa and for a glass erosion depth of 300 μm for large channels. The minimum feature size is 20 μm, but this depends also on the shape ; for example triangular holes are only well defined for a minimum dimension of 60 μm.