Optics: measuring and testing – Standard – Surface standard
Reexamination Certificate
2001-09-24
2003-11-11
Adams, Russell (Department: 2857)
Optics: measuring and testing
Standard
Surface standard
C356S243100, C438S014000
Reexamination Certificate
active
06646737
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to submicron dimensional calibration standards and methods of manufacture and use. Certain embodiments relate to calibration standards having a traceably measured submicron lateral dimension that may be smaller than lateral dimensions of features which may be formed with current lithography equipment.
2. Description of the Related Art
As the dimensions of semiconductor devices continue to shrink with advances in semiconductor materials and fabrication processes, monitoring and controlling semiconductor fabrication processes by lateral dimensional metrology has become increasingly important in the successful fabrication of advanced semiconductor devices. Currently available systems which may be used for lateral dimensional metrology may include systems configured to perform a technique such as optical, electron beam, ion beam, atomic force, and scanning probe microscopy. In addition, lateral dimensional metrology systems may also include systems configured to perform an electrical metrology technique. For example, an electrical metrology technique may involve measuring resistance of a feature of a known material and determining a cross-sectional area and/or a linewidth of the feature from the measured resistance.
A calibration standard may be used to calibrate lateral dimensional metrology systems as described above. A calibration standard may include features such as lines and/or spaces having a certified lateral dimension. Currently available linewidth calibration standards may have a lateral dimension artifact of approximately 500 nm to approximately 30,000 nm. For example, such calibrations standards may typically be formed by semiconductor fabrication processes such as lithography and etch. Such lithography and etch processes may produce features having a lateral dimension of greater than approximately 180 nm. As such, a minimum lateral dimension of calibration standards formed by current lithography and etch processes may be limited by a performance capability of such processes and systems. In this manner, lateral dimensional metrology equipment may be calibrated at a minimum lateral dimension which may be substantially greater than a lateral dimension of features formed by advanced semiconductor fabrication processes. Lateral dimensional metrology equipment, therefore, may have limited usefulness for monitoring and controlling advanced semiconductor fabrication processes.
Several calibration methods for lateral dimensional metrology equipment, however, have been developed for use with currently available calibration standards to expand the usefulness of lateral dimensional metrology equipment for advanced processing applications. Examples of methods for expanding the usefulness of lateral dimensional metrology equipment for advanced semiconductor fabrication process applications are illustrated in U.S. Pat. Nos. 5,914,784 to Ausschnitt et al., 5,969,273 to Archie et al., and 6,128,089 to Ausschnitt et al., and are incorporated by reference as if fully set forth herein. Such methods, however, may include indirectly determining a location of an edge of a feature. Therefore, lateral dimensional calibration and measurement using such methods may be subject to substantial inaccuracy.
An example of a calibration standard may include conductive features formed on a insulating layer. For example, a silicon dioxide insulating layer may be formed below the surface of a monocrystalline silicon substrate using an implantation process which may be commonly referred to as “Separation by the Implantation of Oxygen,” or “SIMOX.” The insulating layer may be annealed to form an amorphous layer of insulating silicon dioxide within the monocrystalline silicon substrate. The monocrystalline silicon layer above the insulating layer may have a defined crystal structure. In addition, the monocrystalline silicon layer above the insulating layer may be patterned using standard photolithography and etch techniques. In this manner, the monocrystalline silicon layer may be etched along a plane of the crystal structure to form silicon features having substantially planar sidewalls. Linewidth and line spacing of the silicon features may be measured using transmissive electron microscopy measurements and electrical measurements. Linewidth and line spacing of the silicon features may also be measured using “atomic lattice counting” techniques such as scanning probe microscopy (“SPM”) because etching the monocrystalline layer along crystal planes may form a very accurate structure. Examples of such calibration standards are illustrated in U.S. Pat. Nos. 5,684,301 to Cresswell et al. and 5,920,067 to Cresswell et al., and are incorporated by reference as if fully set forth herein.
Such currently available calibration standards, however, may include opaque conductive features formed by standard lithography and etch techniques. In this manner, a lateral dimension of the opaque conductive features may be greater than or equal to a minimum lateral dimension of a feature that may be produced by currently available processes and systems. For example, opaque conductive features of such calibration standards may have a minimum lateral dimension of approximately 500 nm.
Another currently available calibration standard may include at least one pair of different structures such as a line and trench. Examples of such calibration standards are illustrated in U.S. Pat. Nos. 5,534,359 to Bartha et al., 5,665,905 to Bartha et al., and 5,960,255 to Bartha et al., and are incorporated by reference as if fully set forth herein. Such calibration standards may be used to calibrate an ultra-fine tip such as a tip which may be used for AFM or SPM. Calibration may include determining a width of the tip. A width of the tip may be determined by profiling a pair of different structures with the tip. For example, calibration of the tip may include measuring a width of a line by profiling the line with the tip. In addition, calibration of the tip may include measuring a width of a trench of the same pair of structures by profiling the trench with the tip. If the pair of structures have substantially equal lateral dimensions, then the measured widths of the line and the trench may be subtracted, and the resulting value may be divided by two to determine the exact diameter or width of the tip.
Once the exact diameter or width of the tip has been determined, the tip may be used to measure features and layers of additional samples. Therefore, it is very important that the calibration standard have at least one pair of different structures such as a line and a space which have exactly the same width. In addition, it is very important that two measurements are carried out with different structures of the same pair of structures to assure accurate calibration and subsequent accurate measurement. In this manner, knowledge of the exact dimensions of the features of the calibration standard is not necessary to calibrate the tip. Therefore, lateral dimensions of the features of the calibration standard may not be traceably measured. Traceable measurements may include measurements performed in a manner traceable to the National Institute of Standard and Technology (“NIST”). As such, the calibration standard may not be certified and may not be used to calibrate additional measurement systems such as optical microscopes, scanning electron microscopes, focused ion beam microscopes, and electrical metrology systems.
Accordingly, it would be advantageous to develop a calibration standard including at least one feature having a lateral dimension of less than approximately 500 nm which may be traceably measured, accurately certified, and relevant to a semiconductor fabrication process being monitored and controlled by a lateral dimensional metrology system calibrated with the calibration standard.
SUMMARY OF THE INVENTION
An embodiment of the invention relates to a calibration standard which may be used to calibrate lateral dimensional measurement systems. The later
Laird Ellen
Scheer Bradley W.
Smith Ian
Tortonese Marco
Adams Russell
Conley & Rose, P.C.
Dalakis Michael
KLA-Tencor Technologies
Mewherter Ann Marie
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