Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Reexamination Certificate
1998-11-20
2001-06-12
Berman, Jack (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
C250S491100, C250S441110
Reexamination Certificate
active
06246060
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to sample alignment for a scanning electron microscope and, more particularly, to apparatus for obtaining the appropriate sample alignment prior to placement of the sample in the scanning electron microscope.
During the manufacture of certain integrated circuit chips, a machine known as a photoresist stepper is utilized to define photoresist lines on the integrated circuit chip wafer. To insure that the stepper is working properly, the widths of the photoresist lines are measured to determine if they meet specifications. In order to do this, the stepper is caused to create an array of parallel lines on a wafer, the wafer is cleaved at a 90° angle to the lines to provide a cross sectional examination sample, and the sample is examined using a scanning electron microscope. To obtain proper measurements, the sample must be held in the scanning electron microscope so that the electron beam is precisely aligned parallel to the photoresist lines. If there is a misalignment, two problems are encountered. First, one edge of the image of each line will be very bright (edge blooming), making it impossible to accurately determine the positions of edges and therefore the widths of the lines. The second problem is that the apparent widths of the lines will be somewhat reduced due to being viewed at an angle. If these measurements are altered by even a small percent, the resulting product can be detrimentally affected. It would therefore be desirable to be able to accurately align a sample for examination in a scanning electron microscope.
In the past, such alignment was effected after the sample was placed in the scanning electron microscope. Present high resolution scanning electron microscopes are not capable of providing easy and accurate alignment of the sample in all angular directions. It would therefore be desirable to have apparatus and a procedure for aligning such a sample prior to its placement in the scanning electron microscope.
SUMMARY OF THE INVENTION
The present invention provides apparatus by means of which a sample can be properly aligned prior to its placement in a scanning electron microscope. The inventive apparatus includes an alignment device adapted to be installed in the scanning electron microscope in a predetermined orientation. The alignment device includes a sample holder which is adapted to hold the sample. The sample holder is mounted to a base structure for rotative movement about a rotation axis relative to the base structure. An adjuster is mounted on the base structure for movement relative thereto. The adjuster is adapted to be manipulated selectively to rotate the sample holder about the rotation axis so that the sample is properly aligned, after which the alignment device can be installed in the scanning electron microscope while holding the properly aligned sample.
In accordance with an aspect of this invention, the alignment device also includes a spring bearing against the base structure to resiliently bias the sample holder for rotative movement in a first direction about the rotation axis. The adjuster is adapted to be manipulated selectively to rotate the sample holder in a second direction about the rotation axis against the bias of the spring or to allow the spring to rotate the sample holder in the first direction.
In accordance with another aspect of this invention, the sample holder includes a projecting member, the base structure includes a first wall, and the spring is positioned between the first wall and the projecting member. The base structure includes a second wall which is substantially parallel to the first wall and on the opposite side of the projecting member from the first wall. The second wall is formed with an internally threaded bore having a central axis transversely intersecting the projecting member. The adjuster includes a threaded rod threadedly extending through the threaded bore along the central axis to engage the projecting member.
In accordance with yet another aspect of this invention, the alignment device further includes a pair of leaf spring members each secured to the base structure and the sample holder to mount the sample holder to the base structure. The pair of leaf spring members are spaced apart each on respective opposed sides of the base structure and the sample holder so that the line of force applied to the sample holder by the spring is transverse to both of the pair of leaf spring members to flex the leaf spring members and cause rotative movement of the sample holder relative to the base structure about the rotation axis parallel to both of the pair of leaf spring members.
In accordance with a further aspect of this invention, there is provided a base holder adapted to hold the alignment device in a predetermined orientation. A video camera is mounted fixedly with respect to the base holder and is positioned to capture an image of a sample held by the sample holder when the alignment device is held by the base holder. A video monitor coupled to the video camera displays an image captured by the video camera. Accordingly, an operator can manipulate the adjuster and view the image of the sample on the video monitor to properly align the sample.
In accordance with yet a further aspect of this invention, the alignment device further includes a shaft journalled for rotation on the base structure parallel to the rotation axis, and an adjustment block secured to the shaft for rotation therewith. The adjustment block includes a projection extending radially outward relative to the shaft and interposed between the spring and the adjuster. The base structure includes a rectilinear upstanding block and the shaft extends through the upstanding block. The sample holder is secured to a first end of the shaft on a first side of the upstanding block, and the adjustment block is secured to a second end of the shaft on a second side of the upstanding block.
In accordance with still a further aspect of this invention, the alignment device further includes a pair of bearing shafts mounted on the base structure parallel to the rotation axis, and a pair of bearing wheels each mounted on a respective one of the pair of bearing shafts. For each set of a bearing shaft and a bearing wheel at least one of the bearing shaft and bearing wheel of that set is journalled for rotation. The sample holder includes a holder block having a support surface shaped as a cylinder segment having a center of curvature aligned with the rotation axis, and with the support surface engaging the pair of bearing wheels.
In accordance with still another aspect of this invention, the adjuster includes an adjusting shaft journalled for rotation on the base structure parallel to the rotation axis, and a linkage connecting the adjusting shaft to the holder block so that rotation of the adjusting shaft moves the support surface on the pair of bearing wheels. The linkage includes an elongated band having its ends fixedly secured to the holder block, with the band having a central portion between its ends tightly wrapped around the adjusting shaft. Accordingly, rotation of the shaft in a first angular direction causes the holder block to rotate about the rotation axis in a second angular direction opposite to the first angular direction.
REFERENCES:
patent: 3958124 (1976-05-01), Koch et al.
patent: 4303866 (1981-12-01), Porro et al.
patent: 4447731 (1984-05-01), Kuni et al.
patent: 5149967 (1992-09-01), Otaka
patent: 5303035 (1994-04-01), Luecke et al.
Ackeret Michael A.
Bindell Jeffry B.
Bryson, III Charles E.
Plew Larry E.
Vartuli Catherine B.
Agere Systems Guardian Corp.
Berman Jack
Davis David L.
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