Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2002-05-29
2004-05-11
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S198100, C359S201100, C359S202100, C359S223100, C250S201200, C250S206100, C356S498000, C356S614000, C369S044110, C369S112010, C369S044370
Reexamination Certificate
active
06735005
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a Cartesian scanning system and, in particular, it concerns optical non-contact scanning devices for determining the physical condition of a specimen.
One of the problems encountered in relation to Cartesian scanning systems is the frequent velocity reversals required at the end of each swath. Such reversals use large quantities of energy and introduce vibrations and mechanical distortion into the system. In order to reduce these problems the scanning head needs to be very small and lightweight.
The above problems are compounded in relation to a wafer inspection system where a high degree of accuracy is required. By way of introduction, semiconductor wafers are produced by a complicated multi-step process and involve sub-micron range technologies. Technologies in the sub-micron range are very delicate and error or malfunction needs to be detected as soon as possible. Effective inspection of wafers is therefore required. Automated devices for inspection have been developed since the 1970's including precision stage positioning systems and auto-focus systems. Further developments in the Art included the introduction of automatic inspection machines, which analyze inspected wafers and determine a defect location automatically. The future generation of wafers, which will require a scanning resolution of less than 0.1 microns, cannot be scanned using current available mechanical structures as they are not rigid enough to provide the required accuracy at the required throughput. Therefore, designing a wafer inspection system for the sub 0.1 micron range places the repeatability and accuracy tolerances of the inspection system to the 10 nanometer range. Working at the nanometer range, most mechanical systems are “rubber like” due to the limited rigidity of the structures at this resolution. Therefore, designing and manufacturing mechanical structures that conform to such high demands is expensive and the resulting systems are bulky and difficult to maintain. High resolution can be achieved by scanning a flat specimen at a low speed, by keeping the scanning head stationary and mechanically floating above a moving specimen.
Of most relevance to the present invention is U.S. Pat. No. 5,530,579, a polygon scanner. The polygon scanner allows scanning a surface with a minimal number of moving parts. However, a shortcoming of the polygon scanner is the requirement to vary the distance between the specimen and the camera, leading to a distortion of the image at high resolutions. A further shortcoming of the polygon scanner is the inherent change of angle of reflectance in the system. This shortcoming is correctable using a special correcting lens but this also leads to image distortion and increased cost.
Also of relevance to the present invention is U.S. Pat. No. 5,432,622 to Johnston et al. relating to a high resolution scanning apparatus. However, the Johnston et al. patent does not produce high throughput.
There is therefore a need for a high throughput scanning system that operates at a resolution in the nanometer range.
SUMMARY OF THE INVENTION
The present invention is a Cartesian scanning system and method of operation thereof.
According to the teachings of the present invention there is provided, a Cartesian scanning system for scanning a surface of a sample comprising: (a) a light source assembly configured to produce at least one collimated beam of light; (b) a light sensing system; (c) a stage configured for mounting the sample thereon; (d) a linear track having a direction of elongation wherein: (i) the linear track and the stage are configured to move relative to each other in a direction substantially perpendicular to the direction of elongation; and (ii) the light source and the light sensing system are mounted in fixed spatial relation to the linear track; and (e) a scanning head including a reflecting system wherein: (i) the reflecting system is configured to direct the collimated beam of light onto the surface and to direct a beam of light reflected from the surface to the light sensing system; and (ii) the scanning head is slidably associated with the linear track so as to be moveable in a direction parallel to the direction of elongation.
According to a further feature of the present invention, there is also provided a beam splitter configured to enable a beam of light being transmitted by the light source and a beam of light being received by the light sensing system to share substantially a same path between the surface and the beam splitter.
According to a further feature of the present invention the beam splitter is a polarizing beam splitter.
According to a further feature of the present invention the light source is configured to produce a plurality of light beams that are collimated.
According to a further feature of the present invention the scanning head further includes an objective lens disposed between the reflecting system and the surface and wherein the objective lens is configured to focus a light beam onto the surface.
According to a further feature of the present invention, there is also provided at least one bearing disposed between the scanning head and the linear track.
According to a further feature of the present invention: (a) the stage is configured to move in a direction substantially perpendicular to the direction of elongation; and (b) the linear track is configured to be stationary.
According to a further feature of the present invention, there is also provided a position determination system configured to determine a position of the scanning head in relation to an X-position on an X-axis and a Y-position on a Y-axis, the X-axis and the Y-axis being defined in relation to the stage, the X-axis being parallel to the direction of elongation of the linear track and the Y-axis being orthogonal to the X-axis, the position determination system including: (a) a first reflecting element mechanically connected to the scanning head; (b) a first optical displacement measurement device configured to measure the distance between the first optical displacement measurement device and the first reflecting element to determine the X-position wherein the first reflecting element faces the first optical displacement measurement device; (c) a second reflecting element mechanically connected to the scanning head; (d) a third reflecting element mechanically connected to the stage wherein the third reflecting element is substantially parallel to the direction of elongation of the linear track; (e) a second optical displacement measurement device configured to measure the distance from the second optical displacement measurement device to the third reflecting element via the second reflecting element wherein the second reflecting element is positioned to enable a light beam to be transmitted between the second optical displacement measurement device and the third reflecting element; and (f) a feedback system configured to determine the Y-position of the scanning head from an output of the first optical displacement measurement device and an output of the second optical displacement measurement device.
According to a further feature of the present invention, there is also provided a scan displacement correction system configured to perform a real-time correction for a position of the scanning head, the position of the scanning head being defined in relation to an X-position on an X-axis and a Y-position on a Y-axis, the X-axis and the Y-axis being defined in relation to the stage, the X-axis being parallel to the direction of elongation of the linear track and the Y-axis being orthogonal to the X-axis, the scan displacement correction system including: (a) a control system configured to determine a real-time correction command from the X-position of the scanning head and the Y-position of the scanning head; and (b) a deflection apparatus disposed between the light source and the scanning head, the deflection apparatus being configured to deflect parallel to the Y-axis a position of a light bea
Karin Jacob
Shtein Amnon
Friedman Mark M.
Phan James
Tokyo Seimitso (Israel) Ltd.
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