Wafer measurement apparatus and operating method thereof
A wafer measurement apparatus includes an electronic-optical system configured to irradiate a wafer with an electron beam and acquire a raw signal by detecting electrons emitted by the wafer, and an image processing device configured to convert the raw signal acquired by the electronic-optical system into image data. The electronic-optical system includes a detector configured to acquire the raw signal. The detector calibrates a gain offset using a difference in electron emission yields of different materials.
1 . A wafer measurement apparatus, comprising:
an electronic-optical system configured to irradiate a wafer with an electron beam and acquire a raw signal by detecting electrons emitted by the wafer; and
an image processing device configured to convert the raw signal acquired by the electronic-optical system into image data,
wherein the electronic-optical system comprises a detector configured to acquire the raw signal, and
the detector calibrates a gain offset using a difference in electron emission yields of different materials.
2 . The wafer measurement apparatus of claim 1 , wherein the detector receives gray levels by acquiring electrons emitted by a test sample having the different materials, and
the gain offset is calibrated using each of the gray levels of the different materials.
3 . The wafer measurement apparatus of claim 2 , wherein the different materials comprise carbon (C), aluminum (Al), copper (Cu), or tungsten (W).
4 . The wafer measurement apparatus of claim 2 , wherein each of the gray levels is calibrated by comparing each of the gray levels with a reference gray level.
5 . The wafer measurement apparatus of claim 1 , wherein the electronic-optical irradiates the wafer with the electron beam after the detector calibrates the gain offset, and acquires the raw signal emitted by the wafer.
6 . The wafer measurement apparatus of claim 1 , wherein the electronic-optical system detects a gray level of the different materials, compares the detected gray levels with a reference gray level, and transmits a delta value of a difference between the gray levels according to a comparison result to the image processing device.
7 . The wafer measurement apparatus of claim 6 , wherein the image processing device additionally calibrates a gray level of the raw signal measured in a subsequent measurement using the delta value.
8 . The wafer measurement apparatus of claim 1 , wherein the image processing device converts the raw signal into an 8-bit image signal.
9 . The wafer measurement apparatus of claim 1 , wherein the electronic-optical system comprises:
a stage configured to support the wafer and having a test sample having the different materials;
an electron gun configured to generate the electron beam;
a lens system configured to control a direction and a width of the electron beam; and
an energy filter configured to filter the electrons emitted by the wafer.
10 . The wafer measurement apparatus of claim 1 , wherein the image processing device detects a defect pattern by storing the raw signal, converting the raw signal into an image, and comparing the converted image with a design image of a pattern.
11 . An operating method of a wafer measurement apparatus, the method comprising:
loading a wafer onto a stage;
moving an electron beam to a test sample comprising a plurality of materials;
controlling a gain offset of a detector using a gray level of a test detection signal emitted by the test sample;
moving the electron beam to an image acquisition position after controlling the gain offset of the detector; and
acquiring an image using a detection signal emitted at the image acquisition position, wherein the gain offset is controlled based on a difference in electron emission yields of the plurality of materials.
12 . The operating method of claim 11 , wherein controlling the gain offset comprises:
acquiring the gray level of the test detection signal;
comparing the gray level with a reference gray level; and
calibrating the gain offset according to the comparison result.
13 . The operating method of claim 12 , further comprising:
outputting a delta value corresponding to the comparison result to an image processing device.
14 . The operating method of claim 13 , further comprising:
post-calibrating a gray level of a raw signal subsequently acquired using the delta value in the image processing device.
15 . The operating method of claim 11 , wherein the acquiring the image comprises:
acquiring a raw signal corresponding to the detection signal from the detector; and
converting the raw signal into a converted image in an image processing device.
16 . An operating method of a wafer measurement apparatus, the method comprising:
acquiring a sample signal emitted by a test sample;
determining whether detection calibration of a detector is to be performed using the sample signal;
adjusting a gain offset of the detector when the detection calibration is to be performed;
post-calibrating a gray level of a raw signal acquired at a predetermined position of a wafer when the detection calibration is not to be performed; and
converting the raw signal into an 8-bit image using the calibrated gray level, wherein the gain offset is adjusted based on a difference in electron emission yields of different materials.
17 . The operating method of claim 16 , wherein determining whether detection calibration of the detector is to be performed comprises:
comparing a gray level of the sample signal with a reference gray level.
18 . The operating method of claim 16 , wherein post-calibrating the gray level comprises:
receiving a delta value corresponding to a difference between a gray level corresponding to the test sample from the detector and a reference gray level; and
storing the received delta value.
19 . The operating method of claim 18 , wherein post-calibrating the gray level further comprises:
calibrating the gray level of the raw signal using the stored delta value.
20 . The operating method of claim 16 , further comprises:
acquiring the raw signal at the predetermined position of the wafer.