Optics: measuring and testing – By light interference – Spectroscopy
Reexamination Certificate
2000-11-27
2002-06-25
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
Spectroscopy
C356S450000, C356S453000
Reexamination Certificate
active
06411388
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates, in general, to non-linear spectroscopy systems and, in particular, to a system and method for simultaneously measuring the amplitude and phase of second harmonic radiation over a broad spectral range without laser tuning.
BACKGROUND OF THE INVENTION
The continual demand for enhanced integrated circuit performance has resulted in numerous advancements in semiconductor processes. One example of such advancement is a considerable scaling down of semiconductor process feature sizes. While such scaling has improved certain performance aspects, it has also created a number of challenges in areas such as fine feature measurement and characterization during production. Spectroscopy systems and techniques are widely used to provide detail measurement and characterization in such applications.
Spectroscopy systems are commonly used to non-invasively measure the properties or states of a semiconductor surface or sub-surface interface by analyzing light reflected therefrom. A typical objective of spectroscopy is the measurement of phase shift in the light reflected from the material under examination. Spectroscopy systems generally fall within one of two categories: linear spectroscopy or non-linear spectroscopy. Linear spectroscopy systems and non-linear spectroscopy systems typically differ in their ability to detect and characterize phenomena and material properties of particular interest; and are therefore generally employed in different applications.
Linear spectroscopy systems are typically characterized by operation involving a single wavelength of light. Linear systems typically use lamps (e.g. incandescent or arc lamps) as a light source; and typically examine a sheath-like area around the surface of interest. Conventionally, linear systems are employed to measure bulk properties of some material, such as film thickness or a varying chemical composition. For example, in a typical semiconductor processing application, a linear system would measure thickness and composition of a epitaxial growth film.
In comparison, non-linear spectroscopy systems are typically characterized by operation involving varying wavelengths of light. Typically, a high intensity light source, such as a laser, is used. Non-linear systems possess unique diagnostic capabilities due, in part, to a high surface specificity and sensitivity. This means that the reflection point from the item under examination is confined to one or two atomic layers in the immediate area of a surface or sub-surface interface.
This comparison is illustrated with reference now to
FIGS. 1
a
and
1
b
.
FIG. 1
a
provides a representative illustration of a linear spectroscopy system, specifically a spectroscopic ellipsometer
100
. In ellipsometer
100
, light
101
emitted from source
102
(typically an incoherent white light source such as a Xenon arc lamp) is filtered through a polarizing element
104
, and directed by focusing element
106
(typically a lens) at a target sample
108
(e.g. SiGe) within processing unit
110
(e.g. a Chemical Vapor Deposition chamber). Light
101
is reflected from sample
108
through a second element
106
, passing through analyzer element
110
(e.g. a polarization analyzer) to detector
114
; where data such as the amplitude of the reflected light is evaluated.
FIG. 1
b
provides a representative illustration of a second harmonic (SH), non-linear spectroscopy system
150
. In system
150
, light
152
emitted from source
154
(typically a laser), with frequency
156
of &ohgr; is filtered through polarizing element
158
, and directed by focusing element
160
(typically a lens) at a target sample
162
(e.g. SiGe) within processing unit
164
(e.g. a Chemical Vapor Deposition chamber). Light
152
is non-linearly reflected from sample
162
through a second element
160
, passing through analyzer element
166
(e.g. a polarization analyzer) to detector
168
; detecting light at twice the incident frequency (2&ohgr;)
170
created by the non-linear reflection. Detector
168
evaluates data such as the amplitude of the reflected light.
Thus, the spectra of the reflected light is used to measure material properties. System
100
detects light at the same optical frequency as the incident light reflected from the sample. System
150
detects light at twice the incident frequency created by non-linear reflection. System
100
measurement therefore characterizes bulk properties of a sample, such as thickness and average composition of an epitaxial film; while system
150
measurement characterizes properties of the interface or surface of the film, such as surface composition, interface dc electric fields, and atomic and molecular adsorption, which can used to evaluate growth chemistry and rates. This information is of particular interest in semiconductor processing.
For semiconductor processing applications, spectroscopy system users are typically interested in characterizing the interface between a growing film and its substrate; for purposes such as detecting the presence of contamination or improper bonding, or measuring material strain. As previously presented, linear reflected light is insensitive to such phenomenon; compelling users to either employ non-linear systems or other alternative methods of measurement and characterization.
This presents a dilemma, however, because spectroscopy users need systems that are compact, inexpensive, simple to use. Conventional linear systems often possess these characteristics, making them a viable choice for use in high volume commercial production. Previously, non-linear spectroscopy systems have not been commercially viable, and thus limited to research and academic applications, because nobody has been able to produce them in a compact, simple to use, or inexpensive manner. Therefore, conventional commercial spectroscopy systems are typically linear in nature. For example, linear systems such as spectroscopic ellipsometers are widely used in the semiconductor industry.
Further, conventional non-linear systems are difficult to use in certain spectroscopic modes; particularly in sampling different wavelengths of second-harmonic (SH) reflected light. To examine varying wavelengths of SH reflected light, conventional systems require a manual tuning process. This results in a serial mode of data acquisition (i.e. sampling one wavelength at a time); which decreases the speed and efficiency of such systems, and increases their complexity of use. Additionally, conventional non-linear systems typically are limited in phase shift measurement; again requiring serial mode data acquisition and complex, time-consuming movement of system apparatus.
SUMMARY OF THE INVENTION
From the foregoing, it is recognized that a need has arisen for commercially viable non-linear spectroscopy systems and methods. Further, a need has arisen for a non-linear spectroscopy system, providing simultaneous measurement of both amplitude and phase of second harmonic radiation over a broad spectral range without requiring superfluous system tuning or apparatus adjustment; and further providing parallel mode data acquisition, acquiring multiple wavelengths simultaneously, and increasing system speed and efficiency while overcoming the aforementioned limitations of conventional methods.
In the present invention, a frequency domain interferometric second harmonic (FDISH) spectroscopy system is provided for use in high volume commercial applications, such as semiconductor processing; providing non-linear (i.e. second harmonic) spectroscopy systems having unique diagnostic potential due (at least in part) to unusually high surface specificity and sensitivity; providing real time measurement during processing, parallel mode data acquisition, and a unique method of acquiring phase shift information in second harmonic radiation.
In one embodiment of the present invention, a method of spectroscopically analyzing amplitude and phase information of a particular sample comprises providing a femtosecond laser source positioned in an ang
Downer Michael W.
Wilson Philip T.
Board of Regents , The University of Texas System
Flores Edwin S.
Gardere Wynne & Sewell LLP
Natividad Phil
Turner Samuel A.
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