The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 13, 2003
Filed:
Mar. 01, 1999
Dirk M. Knotter, Eindhoven, NL;
Antonius A. M. Van De Vorst, Eindhoven, NL;
Koninklijke Philips Electronics N.V., Eindhoven, NL;
Abstract
A method of reducing the thickness t of a layer of material on a substrate when the substrate is exposed to an etchant for a span of time sufficient to reduce t to a value t , at which point exposure to the etchant is interrupted, includes the thickness to being determined using monitoring means which, at any given instant, allow determination of the depth &Dgr;t of material which has been etched away. The method further includes the monitoring means being 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 Am in m corresponding to a decrease &Dgr;d in d, in turn corresponding to a decrease &Dgr;t in t. The resonant frequency f is monitored so as to identify the increase &Dgr;f in f corresponding to a decrease &Dgr;m in m, in turn corresponding to a decrease &Dgr;t in t, and exposure of both the substrate and the crystal to the etchant is interrupted upon attainment of a frequency f =f+&Dgr;f corresponding to the desired value t =t−&Dgr;t.