Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2001-05-04
2002-04-23
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559400, C250S208100
Reexamination Certificate
active
06376854
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of inspecting a pattern and an apparatus thereof, in which a defect or a candidate for a defect is inspected by obtaining an image indicating physical properties of objects such as a semiconductor wafer, a TFT, and a photo mask with the use of an electron beam or a light beam, and by then comparing the image with an image obtained differently. More particularly, the present invention relates to a method of inspecting a pattern and an apparatus thereof, in which a microscopic defect or a candidate for a microscopic defect is inspected.
Concerning an inspection for recognizing a defect of a pattern, known as a prior art technology 1, as disclosed in Japanese Laid-Open Patent Publication No. 57-196377, is as follows. First, a pattern of an object to be inspected, such as a semiconductor including a pattern with a repetition, is detected, and the pattern detected is stored. Then, position alignment is performed in a pixel or picture element unit between the detected pattern and a pattern stored in advance. Finally, a defect is recognized by extracting a mismatch between the two patterns over which the position alignment has been made. Also, known as a prior art technology 2, as disclosed in Japanese Laid-Open Patent Publication No. 3-177040, is a technique which makes it possible to improve, of a problem of a mismatch between the both images in a normal part, a portion of the problem that is attributed to a missing of a position at which the both images are to be detected. Namely, described in the prior art technology 2 is the following technique. First, a pattern of an object is detected as an image signal. Then, position alignment is performed in a pixel unit between the image signal of the detected pattern and an image signal of the pattern stored in advance or an image signal of the pattern detected differently. Still then, with one pixel or less of accuracy, additional position alignment is further made between the image signals over which the position alignment has been made in the pixel unit. Finally, a defect of the pattern is recognized by extracting and comparing errors of the image signals of the two patterns over which the additional position alignment has been made with one pixel or less of accuracy.
Between the two images to be compared, even in the normal part, there exists differences such as an infinitesimal difference in pattern configuration, a difference in a gradation or tone value, a distortion of the pattern, and a shift of the position, which are attributed to the object to be inspected and an image detecting system. Namely, the mismatch in the normal part is classified into a mismatch due to the object to be inspected and a mismatch due to the image detecting system. The mismatch due to the object to be inspected is caused by a subtle difference in repetition patterns produced through a wafer manufacturing process such as an exposure, a developing and an etching. This, on the detected images, appears as the infinitesimal difference in pattern configuration and the difference in the gradation value. The mismatch due to the image detecting system is caused by variations in illuminating light quantity, an oscillation of a stage, a variety of electrical noises, and a missing of the position at which the both images are to be detected. These, on the detected images, appear as a difference in a gradation value of partial images, the distortion of the pattern, and the position shift of the images.
In the above-mentioned prior art technology 1, there existed the following problem. Since the above-described factors cause the mismatch to occur even in the normal part, if every mismatched portion is judged to be a defect, it turns out that there occurs a lot of false information. If, in order to prevent this, a criterion for the defect judgement is lowered, it becomes impossible to detect a microscopic defect.
Also, in the above-mentioned prior art technology 2, of the infinitesimal difference in the pattern configuration, the difference in the gradation value, the distortion of the pattern, and the position shift, which are attributed to the object to be inspected and the image detecting system, there existed an effect of reducing an influence of the position shift between the images. The other differences, however, were not taken into consideration.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide, in order to solve the above-mentioned problems accompanied by the prior arts, a method of inspecting a pattern and an apparatus thereof, which make it possible to further reduce the number of false information caused by a mismatch due to an object to be inspected and an image detecting system, and to detect a more microscopic defect or a candidate for a more microscopic defect.
It is another object of the present invention to provide, when a pattern formed on an object to be inspected is inspected by means of an electron microscope, a method of inspecting the pattern and an apparatus thereof, which make it possible to further reduce the number of false information caused by a mismatch due to the object to be inspected and an image detecting system, and to detect a more microscopic defect or a candidate for a more microscopic defect.
It is still another object of the present invention to provide a method of inspecting a pattern and an apparatus thereof, which make it possible to obtain an image signal having a stable gradation value (a value of light and shade) from an inspection through an electron microscope of a pattern formed on an object to be inspected, and to stably detect a more microscopic defect or a candidate for a more microscopic defect.
In order to attain the above-described object, the present invention is characterized by the configuration described below, when a defect or a candidate for a defect of an object to be inspected is detected by comparing a first two-dimensional image, on each pixel of which a gradation value is a sampling value of a physical quantity at each point in one area to be inspected on the object to be inspected, with a second two-dimensional image, on each pixel of which a gradation value is a sampling value at each point in the other area which is supposed to have the same physical quantity as the above-mentioned physical quantity.
Namely, the present invention is characterized by comprising the steps of performing position alignment between the first two-dimensional image and the second two-dimensional image in a pixel unit, calculating one pixel or less of position shift quantity of corresponding portions between the first two-dimensional image f
1
(x, y) and the second two-dimensional image g
1
(x, y) over which the position alignment has been made in the pixel unit, determining for each pixel sub(x, y), i.e. a distance (difference) between a partial image (an image in a smaller area) in the first two-dimensional image and a partial image (an image in a smaller area) in the second two-dimensional image which have the one pixel or less of position shift quantity, determining for each pixel an allowable range (threshold values thH(x, y) and thL(x, y) at an upper limit and a lower limit, respectively) of the distance (difference) from the one pixel or less of position shift quantity determined and gradation values of the first two-dimensional image and the second two-dimensional image, checking whether or not the above-described distance (difference) between the partial images falls within the above-described allowable range for each pixel, and judging a pixel, on which the distance between the partial images is within the allowable range, to be an non-defective candidate and a pixel, on which the distance between the partial images is beyond the allowable range, to be a defective candidate.
Also, the present invention is characterized by comprising the steps of performing position alignment between the first two-dimensional image and the second two-dimensional image in a pixel unit, calculating one pixel or less of position shift quan
Doi Hideaki
Hiroi Takashi
Kuni Asahiro
Maeda Shunji
Ninomiya Takanori
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Le Que T.
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