Apparatus for detecting defects in patterns
First Claim
1. An apparatus for detecting defects in patterns, particularly defects in chip patterns of photomasks for use in manufacturing semiconductor integrated circuits comprisingoptically scanning means including first and second lens systems each of which projects a scanning light spot onto a respective one of two identical portions of two patterns to be compared with each other and for scanning simultaneously said portions in a two dimensional scanning mode to produce first and second picture signals corresponding to said two identical pattern portions, respectively;
- delay means for delaying at least one of said first and second picture signals for a delay time which is varied as a function of a position on the two dimensional scanning plane so as to decrease a relative deviation of the picture signals mainly due to a difference in distortion and/or magnification between the first and second lens systems; and
means for receiving output picture signals from said delay means and forming a difference between these picture signals to produce a defect signal.
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Abstract
An apparatus for detecting defects in patterns, particularly defects in chip patterns of photomasks for use in manufacturing semiconductor integrated circuits comprising optically scanning means for scanning in a raster scan mode identical portions of the two patterns to be compared with each other by means of a pair of lens systems to produce a pair of picture signals each corresponding to a respective one of the scanned pattern portions and a defect signal producing means for receiving said pair of picture signals and producing a defect signal as a difference between the two picture signals. A variable delay circuit is provided between the optically scanning means and defect signal producing means to correct or compensate for deviations in the two picture signals due to differences in optical characteristics between the two lens system such as distortion and magnification. The variable delay circuit delays the picture signals for a delay time which is varied as a function of a position on the raster.
24 Citations
22 Claims
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1. An apparatus for detecting defects in patterns, particularly defects in chip patterns of photomasks for use in manufacturing semiconductor integrated circuits comprising
optically scanning means including first and second lens systems each of which projects a scanning light spot onto a respective one of two identical portions of two patterns to be compared with each other and for scanning simultaneously said portions in a two dimensional scanning mode to produce first and second picture signals corresponding to said two identical pattern portions, respectively; -
delay means for delaying at least one of said first and second picture signals for a delay time which is varied as a function of a position on the two dimensional scanning plane so as to decrease a relative deviation of the picture signals mainly due to a difference in distortion and/or magnification between the first and second lens systems; and means for receiving output picture signals from said delay means and forming a difference between these picture signals to produce a defect signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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Specification