Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-05-25
2001-04-24
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S225000, C356S389000
Reexamination Certificate
active
06222199
ABSTRACT:
CROSS REFERENCE TO COPENDING APPLICATION
Cross Reference is made to application Ser. No. 09/160,017, Filed Sep. 24, 1998, of John L. Freeouf, titled HIGH PHOTON ENERGY RANGE REFLECTED LIGHT CHARACTERIZATION OF SOLIDS, assigned to the assignee of this application, and incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to highly sensitive metrology involving ellipsometry in the accurate measurement of layers, such as the gate dielectric of a semiconductor device, that are of the order of less than 10 Angstroms in thickness and in particular to the achievement of accuracy in that thickness range.
BACKGROUND OF THE INVENTION AND RELATION TO THE PRIOR ART
Major efforts in the art are currently being directed to a form of ellipsometry in which the light is incident to and reflected from a sample under study at angles with respect to that sample. Changes in polarization of a reference polarized light resulting from variations of the angles, and changes in light both in and out of the plane of incidence are the measured quantities. In ellipsometry, one determines the amplitude and polarization of the reflected beam as a function of the polarization, wavelength and angle of incidence of the incident beam, as well as of the deviation of the measured direction. This deviation being defined in the two directions of “within” and “perpendicular to”, the plane of incidence.
While the principles are useful in many types of characterization measurements, each situation in which the principles are applied will involve a number of considerations that are unique to that situation.
In order to establish a perspective in the application of the technology; the semiconductor industry is used as an illustration for the reasons that the technology is quite amenable to such considerations as the dimensions being small, that the characterization of the material under study usually be non-destructive and that there be an ability to make monitoring determinations in real time. In the semiconductor industry the principles of ellipsometry have been extensively applied to the types of material characterizations needed to meet the ever decreasing dimensions encountered in devices and in their fabrication.
The present technology has been yielding satisfactory results where the dimensions under study are above ten of nanometers(nm) but it is becoming increasingly difficult to get the accuracy needed. Current expectations in the semiconductor device technologies are toward electrode dimensions such as gate widths of the order of 0.25 micrometers in the year 1998, progressively becoming narrower to about 0.1 micrometers by the year 2007. Dielectric thicknesses must shrink to meet the electrode dimensions for a gain in performance to be realized. The dielectric thickness must therefore shrink from about 4.0 nanometers(nm) in the year 1998 to about 1.5 nm in the year 2007. Further such dimensions will probably be made up of several thinner layers. Metrology is a necessary corrollary to achieving these technologies. It is necessary to be able to measure a dimension in order to be able to properly control it. The thicknesses and tolerances predicted to be necessary in the coming technology cannot be properly measured and characterized with current technologies.
SUMMARY OF THE INVENTION
Improvements in accuracy and sensitivity of metrology for material dimensions of the order of less than 10 nanometers are achieved through the providing of specular ellipsometric characterization such as BiDirectional Ellipsometry(BDE) in a totally controlled ambient between the light source and the detector, in which, a precise 2.75 through 9.0 eV photon energy range continuum of light is employed. The specular ellipsometric precise energy range light is interdependently particularly effective together with, in the signal analysis, of the taking into consideration the effect of noise in the development of the ellipsometric parameter values and in the resulting data. In the invention the precise photon energy range operates to sharpen the identifiability of the change parameters imparted into the reflected light in the ellipsometry while minimizing absorption and signal definiteness masking; and the taking into consideration of noise in the signal analysis involves providing a simulated noise spectrum of comparison with the least squares fitting algorithm-derived parameters of the sample to help determine the quality of the minimum and the reliability of the inferred parameters of the sample.
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Interface Studies Inc.
Le Que T.
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