Methods for Thinning Silicon Chips,

We describe the results obtained using three different techniques for thinning silicon chips. We have found that 3 in. diameter silicon wafers can be reliably thinned to thicknesses of under 20 microns by means of a non-selective etch. This technique is also suitable for chemically polishing silicon wafers. Selective anodisation appears to be capable of thinning chips incorporating an epitaxial layer to five microns or less, but this is more complicated since electrical contact must be made with the sample. A selective HNA etch has been investigated which is supposed to selectively dissolve heavily doped silicon, but the results have not been consistent. Methods for handling thin silicon layers and a technique for encapsulating silicon samples for electrochemical measurements and etching are also described. Great Britain