Linewidth measurement method and apparatus
AssigneeBell Telephone Laboratories, Incorporated
InventorsJohn David Cuthbert, David Farnham Munro
Life of this patent
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Abstract
Very rapid and accurate linewidth measurements in selected subregions of an LSI mask or wafer are made by means of a low-cost apparatus. The apparatus embodies the recognition that an accurate linewidth determination can be made for any particular feature among a variety of features in a repeated array by a calibrated and normalized measurement of the average light transmission or reflection of a subregion that includes the feature. In turn, the measurement is automatically converted to a linewidth reading by analog computing circuitry.
Claims6
A method for measuring linewidths in selected subregions of a microminiature element, such subregion including features exhibiting two contrasting optical properties, said element also including at least two reference subregions each exhibiting uniformly a different one of said two optical properties, said method comprising the steps of
- directing light from a source at each of said reference subregions,
- generating normalized reference signals derived from light obtained directly from said source and from light that impinged upon said reference subregions,
- directing light from said source at a selected subregion,
- generating a normalized subregion signal derived from light obtained directly from said source and from light that impinged upon said selected subregion,
- processing said normalized reference signals and said normalized subregion signal to generate a signal representative of one of said optical properties of said selected subregion,
- and processing said last-mentioned signal in accordance with a predetermined relationship to generate a signal representative of a specific linewidth in said selected subregion.
A method of determining mask linewidth for any particular feature among a variety of features in a repeated LSI mask array by measuring the average light transmission of any specified subregion of the mask that includes said feature, said method comprising the steps of
- measuring the normalized light transmission S of a specified subregion of said mask,
- measuring the normalized light transmission B of a nominally opaque subregion of said mask,
- measuring the normalized light transmission C of a nominally transparent subregion of said mask,
- calculating the actual light transmission T of said specified subregion in accordance with the relationship T = (S-B/C-B)
- and in an analog computing circuit automatically converting said value of T to an actual determination of linewidth in accordance with the relationship w = k.sub.1 T + k.sub.2, where w is the linewidth and k.sub.1 and k.sub.2 are predetermined constants respectively associated with a particular feature in each different specified subregion.
Apparatus for measuring linewidths in selected subregions of a microminiature element, each subregion including features exhibiting two contrasting optical properties, said element also including at least two reference subregions each exhibiting uniformly a different one of said two optical properties, said apparatus comprising
- means including a source for directing light at each of said reference subregions and at a selected subregion to be measured,
- means responsive to light obtained directly from said source and from light that impinged upon said reference and selected subregions for generating normalized reference and subregions signals,
- means for processing said normalized signals to generate a signal representative of one of said optical properties of said selected subregion,
- and means for processing said last-mentioned signal in accordance with a predetermined relationship to generate a signal directly representative of a specified linewidth in said selected subregion.
Apparatus for determining mask linewith for any particular feature among a variety of features in a repeated LSI mask array by measuring the average light transmission of any specified subregion of the mask that includes said feature, said apparatus comprising
- means for measuring the normalized light transmission S of a specified subregion of said mask,
- means for measuring the normalized light transmission B of a nominally opaque subregion of said mask,
- means for measuring the normalized light transmission C of a nominally transparent subregion of said mask,
- means for calculating the actual light transmission T of said specified subregion in accordance with the relationship T = (S-B/C-B).
- and means for automatically converting said value of T to an actual determination of linewidth in accordance with the relationship w.sub.x = k.sub.1 T + k.sub.2, where w.sub.x is the linewidth and k.sub.1 and k.sub.2 are predetermined constants respectively associated with a particular feature in each different specified subregion.
Dependencies are inferred from the claim text.