Inspection method and apparatus using charged particle beam
Inspection method and apparatus using a charged particle beam for the inspection of defects on an unfinished semiconductor wafer in the manufacturing process of a semiconductor device, a uniform charge across the wafer is attained by performing ultraviolet irradiation and voltage application to a charge control electrode in a coordinated manner.
1. An inspection method using a charged particle beam apparatus having an electrode for applying an electrical potential to a substrate on which a circuit pattern is formed, comprising the steps of:
charging the electrode to a negative potential relative to the substrate;
irradiating ultraviolet light onto an area on the surface of the substrate;
charging the area on the surface of the substrate negative by drawing back photoelectrons emitted from the area and making the photoelectrons adhere to the area;
scanning the area with the electron beam and detecting the signals of the secondary electrons emitted from the area;
forming an image of the area based on the signals of the detected secondary electrons; and
inspecting the circuit pattern based on the formed image.
2. The inspection method of claim 1 , further comprising the step of:
charging the electrode to a positive potential relative to the wafer when scanning the negatively charged area with a primary charged particle beam.
3. The inspection method of claim 1 , further comprising the step of:
detecting defects in the pattern by comparing the image with a standard image.
4. The inspection method of claim 1 , further comprising the steps of:
comparing an image of first area with an image of second area and determining a difference therebetween; and
judging defects of the circuit pattern from the results of the determination.
5. The inspection method of claim 1 , further comprising the steps of:
acquiring an image corresponding to coordinates of a defect obtained by an appearance inspection apparatus, based on information on the coordinates,
acquiring information on the shape, voltage contrast, and unevenness of the image, and
classifying the information.
6. The inspection method of claim 1 , further comprising the processes of:
measuring an optionally selected portion of the circuit pattern based on the image.
7. The inspection method of claim 1 , wherein the charged particle beam is an electron beam.
8. The inspection method of claim 1 , further comprising the steps of:
forming an image from signals of the detected secondary electrons;
extracting from the image a contrast profile of the pattern;
assessing a strength of contrast from the contrast profile;
judging from the strength of contrast whether to charge the area negatively again through the process of negative charging.
9. An inspection method using a charged particle beam apparatus having an electrode for applying an electrical potential to a substrate on which a circuit pattern is formed, comprising the steps of:
irradiating ultraviolet light onto an area on the surface of the substrate, applying a potential to the electrode while alternating the polarity of the potential, and decreasing an absolute value of the applied potential.
10. The inspection method of claim 9 , wherein,
the potential of the electrode is controlled so that the photoelectrons or secondary electrons are drawn back to the area to get the area charged to a desired potential.
11. An inspection apparatus comprising:
a sample stage to load an inspection sample on which a circuit pattern is formed;
an electron beam acceleration energy-controlling unit for irradiating a primary charged particle beam onto the inspection sample;
an ultraviolet irradiation device for irradiating ultraviolet light onto the inspection sample;
a control unit for varying a retarding voltage of means for retarding the primary charged particle beam;
a charge control electrode for getting secondary electrons or photoelectrons emitted from the inspection sample to adhere to the inspection sample;
a detection unit for detecting the secondary electrons emitted from the inspection sample; and
a monitoring unit for displaying an image based on signals from the detection unit.
12. The inspection apparatus of claim 11 , further comprising:
a comparison operation circuit for forming an image based on the signals from the detection unit and comparing the image for inspection with an image of another same circuit pattern; and
an arithmetic circuit for identifying defects on the circuit pattern of the inspection sample based on the results of comparison by the comparison operation circuit.
13. The inspection apparatus of claim 11 , further comprising:
a computing unit for forming an image based on the signals from the detection unit and classifying the image into defect varieties.
14. The inspection apparatus of claim 11 , further comprising:
a computing apparatus for measuring the length of the circuit pattern from the image.
15. The inspection apparatus of claim 11 , further comprising:
a control means for ultraviolet irradiation device, a power source for applying a predetermined voltage onto the charge control electrode and a power control unit,
wherein
when performing a charge control of the inspection sample, the control means for the ultraviolet irradiation device directs the ultraviolet irradiation device to irradiate, and the power control unit applies a positive or negative voltage to the charge control electrode, and
when acquiring the secondary electron image of the inspection sample, the control means for the ultraviolet irradiation device directs the ultraviolet irradiation device to cease irradiation, and the power control unit applies a positive voltage to the charge control electrode.