Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-03-28
2002-09-17
Allen, Stephone (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S311000, C250S227110, C250S309000, C073S618000
Reexamination Certificate
active
06452161
ABSTRACT:
The present invention relates generally to measurement instruments and more particularly to a system and apparatus for scanning and imaging a surface of a semiconductor or other type of workpiece.
BACKGROUND OF THE INVENTION
In the semiconductor industry there is a continuing trend toward higher device densities. To achieve these high densities there have been, and continue to be, efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such a high device packing density, smaller features sizes are required. This may include the width and spacing of interconnecting lines and the surface geometry such as the corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photo lithographic processes as well as high resolution inspection instruments. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which, for example, a silicon wafer is coated uniformly with a radiation-sensitive film (e.g., a photoresist), and an exposing source (such as ultraviolet light, x-rays, or an electron beam) illuminates selected areas of the film surface through an intervening master template (e.g., a mask or reticle) to generate a particular pattern. The exposed pattern on the photoresist film is then developed with a solvent called a developer which makes the exposed pattern either soluble or insoluble depending on the type of photoresist (i.e., positive or negative resist). The soluble portions of the resist are then removed, thus leaving a photoresist mask corresponding to the desired pattern on the silicon wafer for further processing.
The trend toward higher device densities in the manufacture of semiconductor devices also requires higher resolution scanning and inspection instruments for analyzing various features of semiconductor devices. A measuring apparatus is required to inspect semiconductor devices in association with manufacturing production line quality control applications as well as with product research and development. The ability to scan and/or view particular features of a semiconductor workpiece allows for adjustment of manufacturing processes and design modifications in order to produce better. products, reduce defects, etc.
The features of interest in a semiconductor device may be topographic. Conventional instruments for measuring topographic features include Scanning Probe Microscopes. One form of a Scanning Probe Microscope is an Atomic Force Microscope (AFM), which is sometimes alternatively referred to as a Scanning Force Microscope (SFM). AFMs include a sensor with a spring-like cantilever rigidly mounted at one end and having a scanning tip at a free end. AFMs may operate in contacting and noncontacting modes. In the contacting mode, the tip of an AFM is placed in low force contact with a surface of a semiconductor wafer or other workpiece of interest. The workpiece is then displaced relative to the AFM in one or more directions in a plane (e.g., the tip contacts the workpiece in a Z axis while the workpiece is displaced in the X and/or Y directions), to effect a scanning of the workpiece surface. As surface contours or other topographic features are encountered by the tip during scanning, the cantilever deflects. The cantilever deflection is then measured, whereby the topography of the workpiece may be determined.
In non-contacting operation, the tip is held a short distance, typically 5 to 500 Angstroms, from the workpiece surface, and is deflected during scanning by various forces between the workpiece and the tip. Such forces may include magnetic, electrostatic, and van der Waals forces. In both the contacting and non-contacting modes, measurements of a workpiece topography or other characteristic features are obtained through measuring the deflection of the cantilever. Deflection of the cantilever may be measured using precisely aligned optical components coupled to deflection measurement circuitry, although other techniques are sometimes employed.
Another form of Scanning Probe Microscopes is a Scanning Tunneling Microscope (STM). Where a feature of interest is non-topographic, AFMs as well as STMs may be utilized used to measure the workpiece feature. Examples of non-topographic features include the detection of variations in conductivity of a semiconductor workpiece material. An AFM can be used to scan a workpiece in the non-contacting mode during which deflections in the cantilever are caused by variations in the workpiece conductivity or other property of interest. The deflections can be measured to provide a measurement of the feature. STMs include a conductive scanning tip which is held in close proximity (within approximately 5 Angstroms) to the workpiece. At this distance, the probability density function of electrons on the tip spatially overlap the probability density function of atoms on the workpiece. Consequently, a tunneling current flows between the workpiece surface and the tip if a suitable bias voltage is applied between the tip and the workpiece. The workpiece and tip are relatively displaced horizontally (in the X and/or Y directions) while the tip is held a constant vertical distance from the workpiece surface. The variations in the current can be measured to determine the changes in the workpiece surface.
In another mode of operation, an STM can be used to measure topography. The scanner moves the tip up and down while scanning in the X and/or Y directions and sensing the tunneling current. The STM attempts to maintain the distance between the tip and the surface constant (through moving the tip vertically in response to measured current fluctuations). The movements of the tip up and down can be correlated to the surface topography profile of a workpiece.
Other features of interest in a workpiece may be visual. For example, it may be desirable to scan only specific devices in a semiconductor wafer workpiece, such as transistors, conductors, and the like. While an AFM or STM scan of the entire wafer may yield the desired topographical or other feature information, this requires a great amount of time, where in some circumstances only a localized scan is needed. In addition, tip wear is increased in situations where entire wafers are scanned only to measure small features of interest. In these circumstances, a visual image of the wafer or other workpiece may be used to locate the feature or device of interest, and a local scan may then be performed using one or more of the above methods.
Some conventional measuring instruments include an optical microscope on top of the head assembly of an AFM. However, these microscopes do not have the high resolution necessary to identify and locate the tiny devices and other features of interest in today's high device density semiconductor products. In addition, a visual image of the portion of a workpiece being scanned is unavailable to such microscopes because the cantilever and/or tip assembly of AFMs and STMs partially or completely block the view of the surface near the tip. Prior measuring devices have included optical microscopes laterally offset from the scanning location of an AFM. While the view of the optical microscope may be unobstructed, the optical microscope does not view the portion of the surface under the AMF tip. Other attempts include an AFM head for attachment directly to an optical microscope. However, the optical microscope lens head and the AFM cannot be used simultaneously to view the same portion of the workpiece surface.
SUMMARY OF THE INVENTION
A measuring system and apparatus is provided which overcomes or minimizes the problems and shortcomings of the prior art. The present invention provides a measuring apparatus used to obtain high resolution visual images of a scanned workpiece surface while scanning the surface using atomic force microscopy, scanning tunneling microscopy, or other related scanning technologies. This allows high resolution viewing of th
Choo Bryan K.
Morales Carmen L.
Singh Bhanwar
Yedur Sanjay K.
Advanced Micro Devices , Inc.
Allen Stephone
Eschweiler & Associates LLC
Glass Christopher W.
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