Measuring Fine Patterns
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Petit, JC: AUTHOR [+1]
In the production of semiconductor devices, the main technique used to measure line widths consists in utilizing as the threshold of a video signal, provided by an optical microscope, that is representative of the intensity of the light reflected from the surface of the wafer.
Measuring Fine Patterns
production of semiconductor devices, the main
technique used to measure line widths consists in utilizing as the
threshold of a video signal, provided by an optical microscope, that
is representative of the intensity of the light reflected from the
surface of the wafer.
reflectance profile thus obtained is shaped like a "W", the
height of which depends upon the reflectance characteristics of the
particular material employed. If the focus of the microscope is
varied, it will be found that all reflectance profiles intersect at
one point called the "isofocal point". This point is of great
significance, for if the selected measurement threshold corresponds
thereto, then the importance of focusing will become negligible and
the reliability of a given measurement will be greatest. Minimal
reliability will be obtained where the measurement threshold is equal
to the isofocal point.
measurement device commonly used to provide a reference is
the scanning electron microscope (SEM). In order to obtain a value
close to that reference, one is led to select very low thresholds (5
to 15%) which, therefore, fall short of the isofocal point.
Accordingly, known "single threshold" measurement techniques, do not
permit achieving both maximum accuracy and complete reliability.
one of the techniques commonly used is to apply a
compensation value to the result of the measurement, that is, to
apply a correction value whereby, from a given threshold, the same
value as that determined by the reference tool will be obtained.
However, this technique is somewhat unwieldy as it requires the
creation of as many modes of compensation as there are products to be
method is based upon a couple of novel principles:
(1) double thresholding, and (2) video-channel combining.
(1) DOUBLE THRESHOLDING
principle of this new type of measurement is to
perform two measurements concerning, first, the internal pattern at
isofocal point IF1, and then the external pattern at focal point IF2.
The overall pattern width can then be...