is used to generally deposit a 50 nm thick teflon like polymer layer on the side walls or on the etching base of the silicon substrate during the following etching step the side walls of the structure to be etched in remain protected by the polymer applied during the deposition step as positively charged cations are accelerated toward the silicon substrate by means of the electric prestress and fall nearly vertically onto the substrate surface the repetitive alternation of the etch and deposition steps results in an anisotropic etching at rates of between 2 to 20 u03bcm min depending on the recipe and machine this process is particularly useful in etching high aspect ratio holes at high etching rate and these are eminently suitable for use in the present invention in particular holes 20 may be formed by dry plasma etching each hole 20 may have a dimension 38 of between about 25 microns and about 100 microns and the holes 20 may be a distance 40 apart of between about 100 microns to 1 mm stated another way the holes 20 can cover between about 0 05 and about 5 of the surface area of the supporting substrate 18 any size hole 20 and spacing of holes 20 however is envisioned so long as the holes 20 can be used to separate the wafer 16 and the supporting substrate 18 for example so that a liquid e g a loosening agent such as acid and.