Specific Process Knowledge/Wafer and sample drying/Critical Point Dryer: Difference between revisions

The critical point dryer is used to dry fragile structures that may be damaged in a normal drying procedure. Fragile structures may be thin membranes, or free hanging structures like cantilevers and grippers.  

In the critical point dryer, these structures are dried in CO<math>_2</math>. In the drying process, the sample is first put into Isopropanol, and loaded into the machine. In the process itself, the isopropanol is exchanged for liquid CO<math>_2</math>. When there is only CO<math>_2</math> in the machine, the pressure and temperature in the chamber is raised, above the so called “critical point”. In this way, there is never a liquid/gas interface, but instead the liquid is turned into a mixture of equal parts of gas and liquid. Because of this, the problem with surface tension, which destroys the fragile structures through capillary forces, is avoided.