Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1998-05-19
2001-02-13
Mehta, Bhavesh (Department: 2721)
Image analysis
Applications
Manufacturing or product inspection
C382S147000, C348S126000
Reexamination Certificate
active
06188785
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pattern inspecting apparatus and a pattern inspecting method for inspecting a minute or fine pattern of a semiconductor memory such as a DRAM having memory cells formed in an array shape on a wafer and a mask to be used for manufacturing the wafer.
2. Prior Art
There has been disclosed a conventional minute or a fine pattern inspecting apparatus in, for example, Japanese Patent Application Laid-open No. 61-200415.
FIG. 1
is a block diagram for showing the conventional minute pattern inspecting apparatus similar to the apparatus disclosed in the publication. In
FIG. 1
, a reference numeral
410
denotes an image processing and a system control unit,
412
an image memory,
413
an image processing auxiliary unit,
414
an auxiliary image memory,
415
an image display circuit,
416
a display,
417
a stage control circuit,
421
a light source,
423
a CCD image sensor,
441
an XY stage,
445
a specimen to be inspected,
451
an irradiation beam,
452
a reflected beam, and
453
an image signal.
In this example, a general optical beam is used instead of an electron beam source for the light source. Referring to
FIG. 1
, this apparatus includes the image processing and system control unit
410
, the light source
421
as a beam irradiating unit for generating an image, the CCD image sensor
423
as a detector, the image memory
412
for storing the image signal
453
by having an input of this image signal, the image processing auxiliary unit
413
, the auxiliary image memory
414
for storing a normal inspection pattern, the image display circuit
415
, the display
416
for displaying a result of an inspection, the XY stage
441
for moving the specimen to be inspected
445
, and the stage control circuit
417
for controlling the XY stage.
An inspection of a minute pattern by this apparatus is performed in the following manner. The irradiation beam
451
is irradiated onto the specimen to be inspected
445
on the XY stage
441
from the light source
421
for generating an image. The reflected beam
452
having image information such as a surface shape or the like of the specimen to be inspected
445
is detected by the CCD image sensor
423
. The image signal
453
obtained from the CCD image sensor
423
is stored in the image memory
412
. The image processing and system control unit
410
extracts a defect on the specimen to be inspected
445
by comparing image information obtained through the image processing auxiliary unit
413
and normal inspection pattern data prepared separately and called from the auxiliary image memory
414
.
The image processing and system control unit
410
further calculates a position of a defect based on the above information and information of a stage position obtained from the stage control circuit
417
, and displays on the display
416
a position of the defect on the specimen to be inspected
445
through the image display circuit
415
.
The conventional minute or fine pattern inspecting apparatus shown in
FIG. 1
has the following problems.
At First, at the time of comparing the inspection data pattern with the pattern obtained from the specimen to be inspected, it is necessary to match an image position for recognizing the pattern, taking a relatively long time for the calculation. Further, for carrying out a pattern recognition in high accuracy, it is necessary to move the stage in high accuracy. As a result, the apparatus tends to be larger in size, making it relatively difficult to perform a rapid move of the stage. Moreover, as the comparison operation is carried out in one image frame unit, a large amount of memories are required, leading to a large-size apparatus.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a pattern inspecting apparatus and an inspecting method therefor capable of increasing a processing speed, simplifying a configuration of the apparatus and miniaturizing the apparatus.
A pattern inspecting apparatus according to the present invention is an apparatus for performing an appearance inspection of a minute defect in a large number of repeated patterns of the same shape within individual chips formed on an LSI wafer. This apparatus includes a moving stage for loading a specimen to be inspected, which can be moved for positioning said specimen to be inspected, a stage control unit for driving the moving stage and outputting positional information, a light source for irradiating an irradiation beam to be projected to the specimen to be inspected, a microscopic optical system for collecting reflected beams by irradiating an irradiation beam to the specimen to be inspected, a CMOS image sensor chip incorporating a one-dimensional photodiode array for receiving a reflected beam, an analog-to-digital conversion circuit for converting a received image signal into a digital signal, a memory circuit for storing a converted image signal, and a processing circuit for processing an image signal for detecting a defect, a display unit for displaying a result of an inspection, and a system control unit for controlling each unit.
A method for inspecting a pattern according to the present invention is a method for performing an appearance inspection of a minute or fine defect in a large number of repeated patterns of the same shape within individual chips formed on an LSI wafer. This method includes the steps of moving a specimen to be inspected to a predetermined position, projecting an irradiation beam to minute pattern elements with repeated same patterns formed on the specimen to be inspected, receiving a reflected beam by light receiving elements laid out in one dimension and converting the received beam into an analog signal string, converting the analog signal string obtained into a digital signal string and storing it as an original digital signal string, cyclically displacing the stored original digital signal string into one-cycle and two-cycle displaced signal strings of repeated cycles of patterns respectively and storing them, algebraically processing the stored one-cycle displaced digital signal string and two-cycle displaced digital signal string and the stored original digital string to extract a defect image, and generating and displaying defect information of the specimen to be inspected from the defect image obtained and positional information of the minute pattern elements inspected.
According to the present invention, in an apparatus for performing an appearance inspection of a minute defect in a large number of repeated patterns of the same shape within individual chips formed on an LSI wafer, the use of a CMOS image sensor chip incorporating a one-dimensional CMOS photodiode array, an analog-to-digital conversion circuit, a memory circuit and a processing circuit makes it possible to provide a compact minute pattern inspecting apparatus which avoids the need for matching a normal inspection pattern with an image, shortens the calculation time and requires no large amount of memories.
According to the present invention, it is possible to extract a defect image without using a normal inspection pattern by the method including the steps of holding in a memory circuit an image signal of a large number of patterns of the same shape on an LSI wafer obtained by an image sensor, cyclically displacing this image signal into one-cycle and two-cycle displaced signals of repeated patterns respectively by using a processing circuit, and by carrying out an algebraic processing to the original image signal and the cyclically displaced signals by a defect detection algorithm.
The minute pattern inspecting apparatus and the method of the present invention have a characteristic in that a defect image is extracted by obtaining an image with the use of a CMOS image sensor chip, holding in a memory circuit an image signal of minute patterns consisting of minute pattern elements formed repeatedly on a specimen inspected within the chip, cyclically displacing this image signal into one-cycle and two-cy
Nakamura Toyokazu
Tsai Benjamin
Mehta Bhavesh
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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