Inspection equipment

Patent metadata

Field	Value
Publication number	US-9460891-B2
Application number	US-201614993470-A
Country	US
Kind code	B2
Filing date	Jan 12, 2016
Priority date	Jan 13, 2015
Publication date	Oct 4, 2016
Grant date	Oct 4, 2016

Abstract

Inspection equipment frequency transforms a mirror electron image with respect to position coordinates, calculates a value of a frequency plane origin or a value at a vicinity of the frequency plane origin as a first measurement value, and calculates a second measurement value by totalizing values of image intensities in a certain area, the image intensities having been obtained through normalization by the origin value or origin-vicinity value and the frequency transform. The inspection equipment automatically controls the voltage of a wafer holder based on the first and second measurement values.

First claim

What is claimed is:

1. Inspection equipment, comprising:
an irradiation optical system to irradiate an area including a field of view on a wafer with an electron beam emitted from an electron source;
a voltage application unit to apply a controlled negative voltage to the wafer or a wafer holder holding the wafer;
a mirror-electron imaging optical system to capture a mirror electron image by, with the voltage applied to the wafer or the wafer holder, having an image formed by electrons reflected from the wafer;
a calculation unit that frequency-transforms the mirror electron image with respect to position coordinates and calculates a value of a frequency plane origin or a value at a vicinity of the frequency plane origin as a first measurement value and that also calculates a second measurement value by totalizing values of image intensities in a certain area the image intensities having been obtained through normalization by the origin value or origin-vicinity value and the frequency transform;
a control unit that, based on the first measurement value and the second measurement value, outputs to the voltage application unit a signal to control the voltage applied by the voltage application unit; and
a defect detection unit that detects a defect of the wafer using the mirror electron image obtained at the voltage controlled by the control unit.

2. The inspection equipment according to claim 1 ,
wherein, when the second measurement value decreases exceeding a predetermined range relative to a predetermined second setting value whereas the first measurement value is in a predetermined range relative to a predetermined first setting value, the control unit outputs a signal for decreasing an absolute value of the voltage to the voltage application unit.

3. The inspection equipment according to claim 2 , wherein, when the first measurement value decreases exceeding a predetermined range relative to a predetermined first setting value, the control unit outputs a signal for increasing an absolute value of the voltage to the voltage application unit.

4. The inspection equipment according to claim 3
wherein, in frequency-transforming the mirror electron image, the calculation unit, taking into account also a frequency range not attributable to any defect of the wafer, totalizes values of intensities normalized by the origin value or origin-vicinity value.

5. The inspection equipment ac cording to claim 1 ,
wherein the frequency transform is performed using a fast Fourier transform algorithm.

6. Inspection equipment, comprising:
an irradiation optical system to irradiate an area including a field of view on a wafer with an electron beam emitted from an electron source;
a voltage application unit to apply a controlled voltage to the wafer or a wafer holder holding the wafer;
a mirror-electron imaging optical system to capture a mirror electron image by, with the voltage applied to the wafer or the wafer holder, having an image formed by electrons reflected from the wafer;
a calculation unit that makes an absorbed current from the water or a sum of intensity values of a whole of the mirror electron image a first measurement value and that frequency-transforms, with respect to position coordinates, a whole or part of the mirror electron image normalized by the first measurement value and calculates a second measurement value by totalizing value of transformed image intensities in a certain area;
a control unit that, based on the first measurement value and the second measurement value, outputs to the voltage application unit a signal to control the voltage applied by the voltage application unit; and
a detection unit that detects a defect of the wafer using the mirror electron image obtained at the voltage controlled by the control unit.

7. The inspection equipment according to claim 6 ,
wherein, when the second measurement value decreases exceeding a predetermined range relative to a predetermined second setting value whereas the first measurement value is in a predetermined range relative to a predetermined first setting value, the control unit outputs a signal for decreasing an absolute value of the voltage to the voltage application unit.

8. The inspection equipment according to claim 7 ,
wherein, when the first measurement value decreases exceeding a predetermined range relative to a predetermined first setting value, the control unit outputs a signal for increasing an absolute value of the voltage to the voltage application unit.

9. The inspection equipment according to claim 8 ,
wherein, in frequency-transforming the mirror electron image, the calculation unit, taking into account also a frequency range not attributable to any defect of the wafer, totalizes values of intensities normalized by the origin value or origin-vicinity value.

10. The inspection equipment according to claim 6 ,
wherein the frequency transform is performed using a fast Fourier transform algorithm.

11. The inspection equipment according to claim 1 ,
wherein, when the defect detection unit indicates presence of a defect during inspection operation or when a predetermined location is being imaged, the voltage applied by the voltage application unit is not changed.

12. The inspection equipment according to claim 1 , further comprising an input unit through which a user inputs an optional number of wafers or an optional amount of time as a setting so as to have the applied voltage updated every time the optional number of wafers have been inspected or every time the optional amount of time has elapsed.

13. The inspection equipment according to claim 1 , further comprising monitoring means to monitor a current value of an irradiating electron beam,
wherein the first measurement value is normalized by the monitored current value of the electron beam.

14. The inspection equipment according to claim 1 ,
wherein, when the second measurement value increases exceeding a predetermined range relative to a predetermined second setting value, the control unit outputs a wafer defect indication signal to the detection unit or to a display unit to display an indication of whether the wafer has a defect.

15. The inspection equipment according to claim 14 , wherein, for a mirror electron image of a coordinate location to which the wafer defect indication signal corresponds, a defect type is determined.

Assignees

• Hitachi High Tech Corp

Inventors

• Hasegawa Masaki

Classifications

• H01J37/265

  Controlling the tube; circuit arrangements adapted to a particular application not otherwise provided, e.g. bright-field-dark-field illumination · CPC title

• H01J37/263

  Contrast, resolution or power of penetration · CPC title

• H01J37/29 Primary

  Reflection microscopes · CPC title

• H01J2237/24592

  Inspection and quality control of devices · CPC title

• H01J2237/223

  Fourier techniques · CPC title