| 摘要 |
A method of reducing the thickness t of a layer of material on a substrate, whereby the substrate is exposed to an etchant for a span of time sufficient to reduce t to a value t?0?, at which point exposure to the etchant is interrupted, whereby: the thickness t?0? is determined using monitoring means which, at any given instant, allow determination of the depth DELTA t of material which has been etched away; the monitoring means are embodied as a resonant crystal whose resonant frequency f at any given instant is a function of the mass m of the crystal at that instant; the crystal is coated with a layer of reference material of thickness d, which material can be etched using the same etchant as for the material on the substrate; the crystal is exposed to the etchant simultaneously with the substrate, thus causing m to decrease as reference material is etched away, a decrease DELTA m in m corresponding to a decrease DELTA d in d, in turn corresponding to a decrease DELTA t in t; the resonant frequency f is monitored so as to identify the increase DELTA f in f corresponding to a decrease DELTA m in m, in turn corresponding to a decrease DELTA t in t; exposure of both the substrate and the crystal to the etchant is interrupted upon attainment of a frequency f?0? = f + DELTA f corresponding to the desired value t?0? = t - DELTA t. In a particular example, the substrate is a semiconductor device, the material on the substrate is silicon oxide and the etchant is aqueous hydrogen fluoride. |
