Optics: measuring and testing – By dispersed light spectroscopy – Utilizing a spectrometer
Reexamination Certificate
2000-03-13
2001-02-20
Kim, Robert (Department: 2877)
Optics: measuring and testing
By dispersed light spectroscopy
Utilizing a spectrometer
C356S329000, C356S035500
Reexamination Certificate
active
06191855
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method for characterizing a sample composed of one or more thin films through the use of electromagnetic radiation to generate and detect stress or strain pulses. The grain size in the sample is determined from measurements of the propagation characteristics of the strain pulses in the sample.
BACKGROUND OF THE INVENTION
Currently, in the semiconductor industry there is a great interest in the characterization of thin films. Integrated circuits are made up a large number of thin films deposited onto a semiconductor substrate, such as silicon. The thin films include metals to make connections between the transistors making up the chip, and dielectric films to provide insulation between the metal layers (see: S. A. Campbell, The Science and Engineering of Microelectronic Fabrication, Oxford University Press, (1996)). The metal films (interconnects) are typically arranged as a series of patterned layers. At the present time there may be 4 or 5 layers of interconnects. It is likely that as more complex integrated circuits are developed which will require a greater number of interconnections the number of layers will increase. Metals of current interest include, for example, aluminum, copper, titanium and suicides. Insulating films include, for example, oxide glasses of various compositions and polymers.
A metal film will contain crystal grains with a distribution of sizes and orientations. The range of sizes may be narrow or broad, and a distribution of grain sizes may have a maximum at some size and then decrease monotonically as the size increases or decreases. Alternatively, there may be a bi-modal distribution so that there is a high concentration of grains in two different ranges of size. The grain size affects the mechanical and electrical properties of a metal film. Consequently, in the semiconductor industry there is a strong interest in finding techniques that can monitor the grain size in metal films.
In the semiconductor device fabrication industry, it is important that a method for grain size determination be non-destructive, be able to measure the grain size within a small area of film, and give results in a short period of time. Current techniques for the determination of grain size include; measurement of the width of the peaks in intensity of diffracted X-rays, electron microscopy and atomic force and scanning tunneling microscopy. These techniques cannot meet the combined requirements listed above.
OBJECTS OF THE INVENTION
It is a first object of the invention to provide a method for the determination of grain size in films through the use of an optical metrology technique employing a short optical pulse to generate a mechanical strain pulse and a second optical pulse to detect the propagation of the strain pulse. From the measured characteristics of the detected strain pulse the grain size is determined.
It is a further object of the invention to provide a means for the determination of both the grain size and information about the distribution of grain orientations.
SUMMARY OF THE INVENTION
In accordance with a method of the present invention, a method for the determination of grain size in a thin film sample is provided. The method comprises the steps of measuring a first change in optical response and a second change in the optical response of the thin film, comparing the first and second changes to find the attenuation of a propagating disturbance in the film, and associating the attenuation of the disturbance to the grain size of the film. The second change in optical response is time delayed from the first change in optical response.
In accordance with a first embodiment of the present invention, a metal film grain size measuring system is provided. The measuring system comprises a stage holding a substrate having the metal film, means for applying a non-destructive optical pump pulse and a non-destructive optical probe pulse to the metal film, means for detecting changes in the probe pulse, means for defining the detected changes in the probe pulse and means for relating the changes in the probe pulse to the grain size of the metal film. The substrate has the metal film disposed on a first side thereof. The pump pulse and probe pulse are applied to a free surface of the thin film. The probe pulse is temporally delayed from the pump pulse. The means for detecting detect changes in the probe pulse reflected from the metal film. The detecting means detect the change in the probe pulse as a function of time. The means for defining define the detected changes in the probe pulse as a function of frequency. The means for relating relate the changes in the probe pulse defined as a function of frequency to a grain size of the metal film.
In accordance with a second method of the present invention, a method for determining the grain size in a sample is provided. The method comprises the steps of measuring a first change in optical response of the sample, comparing the first change in optical response to a calculated ideal optical response to determine the attenuation of a propagating disturbance in the sample and relating the attenuation of the propagating disturbance in the sample to the grain size of the sample.
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Brown University Research Foundation
Kim Robert
Ohlandt Greeley Ruggiero & Perle L.L.P.
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