Facsimile and static presentation processing – Facsimile – Picture signal generator
Reexamination Certificate
1998-06-26
2003-01-14
Grant, II, Jerome (Department: 2624)
Facsimile and static presentation processing
Facsimile
Picture signal generator
C382S194000
Reexamination Certificate
active
06507417
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates in general to visual inspection apparatus and, in particular, to image detection technology for use with such apparatus. More particularly but not limited to, the invention relates to image pickup devices for use in detecting a two-dimensional (2D) image of an object to be sensed through the main scanning (H scanning) and subsidiary scanning (V scanning) operations.
One typical approach to detection of a 2D image using a linear image sensor is to read image data out of the linear image sensor while simultaneously permitting a projection image of an object being sensed on the image formation plane to move in a direction perpendicular to the linear image sensor, wherein the internal scanning (H-scanning) gets started every time the projected object image moves a distance corresponding to a single pixel (V-scanning). This H-scan distance may be the size of one pixel in the V direction.
For detection of a movement amount (V-scanning) of the object image in this case, a scale for use in detecting the coordinate system of a workpiece mount table is employable, by way of example.
Currently available scale and its associative detection scheme for detecting the movement amount or coordinates (position) of an object being sensed may include a variety of types of techniques based on various principles, such as the transmitted light detection scheme, diffraction light interference scheme and the like. In any one of these approaches, a graduation detection signal is of a sinusoidal waveform having two phases—phase “A” and phase “B”—with the phase difference of 90°, the sine-wave signal being wave-shaped into a pulse signal for use as a coordinate signal.
In addition, in order to obtain a higher degree of resolution than the graduation of scale, a certain scheme is widely employed which employs a divider circuit for dividing the period of a graduation detection signal into several tens of segments or more.
The term “scale resolution” as will be used in the description below refers to the resulting degree of resolution after execution of the period division processing, rather than the resolution of the scale per se.
It is also noted that the term “scale detection pulse” as used herein refers to a pulse signal obtainable after execution of the division processing in cases where the period is divided.
Conventionally, setup of a pixel size along the movement (in the V direction) of the object to be sensed is such that the scale detection pulse is such that the scale detection pulse is frequency-divided at a predefined frequency division ratio to provide an internal scan start signal of a linear image sensor used. This is because the linear image sensor is internally scanned at equal distances or intervals each equivalent to the pixel size.
Note that one prior known technique for variable control of the accumulation time length in order to control the detection sensitivity of a linear image sensor is disclosed in JP-A-62-225081.
Another technique is disclosed in JP-A-6-133209, which is to deal with CCD shift clocks independently of each other at the upper and lower ends of a known time delay and integration (TDI) image sensor in the case where an image within a pickup view filed is different in movement speed or rate between the upper and lower ends, thereby equalizing them to respective image movement rate values.
SUMMARY OF THE INVENTION
In visual inspection apparatus for use in inspecting the quality of a workpiece under manufacture including a semiconductor wafer or membrane, where comparative inspection is carried out with respect to repetitive patterns, it is desirable that two images under comparison be sensed or picked up in a way such that the pattern period or cycle is an integer multiple of the pixel size to thereby ensure that the resultant pattern-to-pixel positional relation is kept constant in any events.
More specifically, as shown in
FIG. 5
, when comparing patterns
51
a
and
51
b
to each other, it is desirable to compare image information items detected at pixels
61
and
62
that are identical to each other in pattern-to-pixel positional relation; to this end, the distance of such comparative patterns may be an integer multiple of the pixel size. Unless the comparative pattern distance is an integer multiple of the pixel size, detection might be done at a position such as a pixel
63
with respect to the pattern
51
b,
for example. In such a case, the resultant image information could contain some errors even when no differences are present in the patterns per se, which would result in correct comparison result being no longer expectable.
Conventionally, in an image pickup device of the type which detects a 2D image by use of a linear image sensor while moving (V scanning) an object to be sensed, the pixel size in the V direction is set by starting the internal scanning of such linear image sensor every time an object being sensed moves or travels a fixed distance, i.e. one pixel size.
In cases where a detection pulse of an object V-coordinate detection scale is utilized as the internal scan start signal of the linear image sensor, the unit of a minimal variable amount of such image sensor scan start signal is the resolution obtainable from the scale (either the resolution of graduation or a resolution as divided therefrom by signal processing), which is a digital value.
Accordingly, when a given distance segment L is divided by a pixel number M, the minimal variable amount relative to a distance corresponding to M pixels might be equal to the “M multiplication of the scale resolution,” which results in difficulty in any precise adjustment. In other words, when the distance L=K·lu (where K is a given integer, and lu is the scale resolution), the pixel number capable of equally dividing the distance L is limited only to those divisors of the integer K.
For example, suppose that a given distance L=525 lu is to be divided into fifty pixels. If the pixel size=10 lu, then the result is (52 pixels+reminder 5 lu). In this respect, when the pixel size is enlarged or expanded by a minimal variable amount 1 lu obtaining the value 11 lu, the resultant pixel number is equal to (47 pixels+reminder 8 lu). Obviously, this value is far less than the target value of fifty pixels, which in turn makes it impossible to set at the desired pixel number.
In the case of such image pickup device using a TDI image sensor, it is the basic condition for guaranteeing achievement of normal operations of the TDI image sensor to let the distance on an object plane, which distance corresponds to the total TDI stage number, be exactly an integer times the pixel size in order to ensure that a packet of accumulated or “integrated” charge carriers at one TDI stage is sequentially transferred to its neighboring TDI stage in synchronism with movement of an image formed on the photosensitive surface of the TDI image sensor.
Unfortunately, as in the case described previously, presence of the limitation to the coordinate detection resolution can make it difficult, in many cases, to divide the distance on the object plane corresponding to the TDI stage number into the TDI stage number. In addition, the more the TDI stage number, the higher the required pixel size setup accuracy. For example, consider that the TDI stage number is ninety six (96). If the pixel size is increased or decreased by the scale resolution 1 lu which is the minimum variable amount, then the resulting minimum increase/decrease amount in the distance corresponding to such 96 pixels is 96 lu, which makes it impossible, or at least greatly difficult, to provide the intended fine or precise adjustability.
It is therefore an object of the present invention to provide an inspection apparatus for performing visual inspection of an object to be sensed by detecting a 2D image through the main and sub-scanning operations, which apparatus is capable of dividing a desired distance segment along the sub-scanning direction into a desired pixel number.
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Maeda Shunji
Makihira Hiroshi
Nakayama Yasuhiko
Oka Kenji
Yoshida Minoru
Antonelli Terry Stout & Kraus LLP
Grant II Jerome
Hitachi , Ltd.
Worku Negussie
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