Defect classification using a logical equation for high stage classification
View Patent ↗With little efforts, to estimate the appropriateness of automatic defect classification, and to make classification criteria settable with a guarantee for the better classification performance, defects unknown with their classification classes are classified based on two different classification criteria. Also, defects differed in classification results are collected, and each thereto, a defect classification class is provided by using a manual. Then, the defects provided with the classification classes are divided into two types of groups: one is a setting group for the classification criteria; and the other is an evaluation group. Based on the classification criteria that is so set as to classify the defects included in the setting group with the maximum performance, the classification performance of a case where classification is applied to defects included in the evaluation group is calculated, and the appropriateness of thus set classification criteria is evaluated.
1. A computer-readable medium for defect classification having sets of instructions stored thereon which, when executed by a machine, cause the machine to:
create a classification criteria using teaching data whose defect classification class is known;
classify defects, whose defect classification class is known by using the classification criteria created at the step of creating;
derive a classification performance of the classification criteria from a result of the step of classifying defects; and
correct the classification criteria created by the step of creating based on the classification performance derived by the step of deriving,
wherein in the step of creating the classification criteria, the classification criteria is set by using a classification unit having a hierarchy structure including a higher stage classifier which includes intermediate classes and a lower stage classifier which includes plural classifiers each belonging to one of the intermediate classes and provides a final classification result, and the higher stage classifier includes a logical equation using a feature amount of the defect and a threshold and said higher stage classifier is so determined that the classification performance of the lower stage classifier derived at the step of deriving is of a greater degree than other classifiers when estimating changes of the classification accuracy ratio of the lower layer by changing the logical equation of the higher stage classifier, wherein the higher stage classifier is configured to classify the defects into the intermediate classes by using a first feature amount, and the lower stage classifier is configured to classify the defect which classified into the intermediate classes into the final classification result, by using a second feature amount which is different from the first feature amount.
2. The computer-readable medium according to claim 1 , wherein in the step of deriving the classification performance of the classification criteria, the classification performance is derived based on an accuracy ratio for the data known with the classification class that is derived in the step of classifying the data known with the defect classification class based on the classification criteria.
3. An apparatus for classifying defects comprising:
classification criteria creating unit which creates a classification criteria using teaching data whose defect classification class is known;
classifying unit which classifies defects by using the classification criteria created by the classification criteria creating unit;
classification performance deriving unit which derives a classification performance of the classification criteria from a result of the classifying unit classifying defects whose defect classification class is known; and
classification criteria correcting unit which corrects the classification criteria based on the classification performance outputted from the classification performance deriving unit,
wherein said classification criteria creating unit creates a set of classifiers having a hierarchy structure including a higher stage classifier which includes intermediate classes and a lower stage classifier which includes plural classifiers each belonging to one of the intermediate classes and provides a final classification result, and the higher stage classifier includes a logical equation using a feature amount of the defect and a threshold and said higher stage classifier is so determined that the classification performance of the lower stage classifier derived at the step of deriving is of a greater degree than other classifiers when estimating changes of the classification accuracy ratio of the lower layer by changing the logical equation of the higher stage classifier, wherein the higher stage classifier is configured to classify the defects into the intermediate classes by using a first feature amount, and the lower stage classifier is configured to classify the defect which classified into the intermediate classes into the final classification result, by using a second feature amount which is different from the first feature amount.
4. An apparatus for classifying defects according to the claim 3 , further comprising a display unit which displays an image of the classification criteria corrected by the classification criteria correcting unit together with an image of a defect classified by the classifying unit using the classification criteria corrected by the classification criteria correcting unit.