Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrophotometer
Reexamination Certificate
2001-11-13
2004-12-28
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrophotometer
C356S630000, C356S632000, C356S635000
Reexamination Certificate
active
06836324
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of measurement techniques and relates to a method and a system for measuring the parameters of patterned structures.
BACKGROUND OF THE INVENTION
Techniques for thickness measurements of patterned structures have been developed. The term “patterned structure” used herein signifies a structure formed with regions having different optical properties with respect to an incident radiation. More particularly, a patterned structure represents a grid having one or more cycles, each cycle being formed of at least two different locally adjacent stacks. Each stack is comprised of layers having different optical properties.
Production of integrated circuits on semiconductor wafers requires maintaining tight control over the dimensions of small structures. Certain measuring techniques enable the local dimensions of a wafer to be measured with relatively high resolution, but at he expense of discontinued use of the wafer in production. For example, inspection using a scanning electron microscope gives measurements of the parameters of a patterned structure, but at the expense of cleaving it and thus excluding it from continued processing. Mass production of patterned structures such as wafers requires a non-destructive process for controlling thin film parameters in a manner enabling the local measurements to be performed.
One kind of the conventional techniques for measuring thickness of thin films is disclosed in U.S. Pat. No. 4,999,014. The technique is based on the use of small spot size and large numerical aperture for measurements on small areas. Unfortunately, in the case of a very small structure, this approach suffers from a common drawback associated, on the one hand, with the use of a small spot-size and, on the other hand, owing to the large numerical aperture, with the collection of high diffraction orders. The term “small spot-size” signifies the spot diameter similar in size to the line or space width of the measured structure, i.e. a single grid cycle. This leads to various problems, which are difficult to solve. Indeed, not all the stacks' layers are in the focus of an optical system used for collecting reflected light, the optical system being bully and complicated. Detected signals are sensitive to small details of a grid profile and to small deviations in the spot placement. Diffraction effects, which depend significantly on the gird profile and topography and therefore are difficult to model, have to be included in calculations.
Another example of the conventional techniques of the kind specified is disclosed in U.S. Pat. No. 5,361,137 and relates to a method and an apparatus for measuring the submicron linewidths of a patterned structure. The measurements are performed on a so-called “test pattern” in the form of a diffraction grating, which is placed in a test area of the wafer. Here, as in most conventional systems, a monochromatic incident light is employed and diffraction patters are produced and analyzed. However, a large number of test areas are used and also information on multiple parameters cannot be obtained.
According to some conventional techniques, for example that disclosed in U.S. Pat. No. 5,087,121, portions with and without trenches are separately illuminated with broadband light, the reflection spectrum is measured and corresponding results are compared to each other with the result being the height or depth of a structure. However, it is often the case that the structure under inspection is such that the different portions cannot be separately imaged. This is owing to an unavoidable limitation associated with the diameter of a beam of incident radiation striking the structure.
The above approach utilizes frequency filtering to enable separation of interference signals from different layers. This is not feasible for layers of small thickness and small thickness difference because of a limited number of reflection oscillations.
Yet another example of the conventional technique for implementing depth measurements is disclosed in U.S. Pat. No. 5,702,956. The method is based on the use of a test site that represents a patterned structure similar to that of the wafer (circuit site), but taken in an enlarged scale. The test site is in the form of a plurality of test areas each located in the space between two locally adjacent circuit areas. The test areas are designed so as to be large enough to have a trench depth measured by an in-line measuring tool. The measurements are performed by comparing the parameters of different test areas assuming that the process is independent of feature size. For many processes in the field such as etching and photoresist development; this assumption is incorrect and this method is therefor inapplicable.
SUMMARY OF THE INVENTION
It is a major object of the present invention to overcome the above listed and other disadvantages of the conventional techniques and provide a novel method and system for non-destructive, non-contact measurements of the parameters of patterned structures.
It is a further object of the invention to provide such a method and system that enables the relatively small amount of information representative of the structure's conditions to be obtained and successfully processed for carrying out the measurements, even of very complicated structures.
According to one aspect of the present invention, there is provided a method for me at least one desired parameter of a patterned structure, which represents a grid hating at least one cycle formed of at least two metal-containing regions spaced by substantially transparent regions with respect to incident light thereby defining a waveguide, the structure having a plurality of features defined by a certain process of its manufacturing, the method comprising the steps of:
(a) providing an optical model, which is based on at least some of said features of the structure, on relation between a wavelength range of the incident light to be used for measurements and a space size between the two metal-containing regions in the gird cycle, and a s depth of said meta, and is capable of determining theoretical data representative of photometric intensities of light components of different wavelengths specularly reflected from the sure and of calculating said at least one desired parameter of the structure;
(b) locating a measurement area for applying thereto spectrophotometric measurements, wherein said measurement area is a grid cycles containing area;
(c) applying the spectrophotometric measurements to said measurement area by illuminating it with incident light of a preset substantially wide wavelength range, detecting light component substantially specularly reflected from the measurement area, and obtaining measured data representative of photometric intensities of each wavelength with said wavelength range;
(d) analyzing the measured data and the theoretical data and optimizing said optical model until said theoretical data satisfies a predetermined condition; and
(e) upon detecting that the predetermined condition is satisfied, calculating said at least one parameter of the structure.
Thus, the present invention utilizes the features of a patterned structure, whose parameters are to be measured, which are defined by manufacturing steps of a certain technological process completed prior to the measurements, and a relation between the wavelength range of incident light used for measurements and a space size between the two metal-containing regions in the grid cycle, and a in depth of the metal. Actual design-rule features can often be found in the structure in sets (e.g. read lines in memories). The term “design-rule features” signifies a predetermined set of the allowed pattern dimensions used throughout the wafer. Hence, information regarding the desired predetermined can be obtained using super-micron tools such as a large spot focused on a set of lines.
The present invention, as distinct from the conventional approach, utilizes a spectrophotometer that receives reflected it substantially from zero-ord
Machavariani Vladimir
Scheiner David
Font Frank G.
Greer Burns & Crain Ltd.
Nova Measuring Instruments Ltd.
Punnoose Roy M.
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