Method of measuring the performance of a scanning electron microscope
First Claim
1. A method of determining the imaging quality of a scanning electron microscope used for measuring sizes of device features configured in a substrate layer during manufacture of devices, the method comprising the steps of:
- providing porous silicon surface areas;
scanning the surface areas by means of the scanning electron microscope;
analyzing the images taken by the scanning electron microscope by means of a Fast Fourier Transform technique to obtain an indication of the resolution of the scanning electron microscope, characterized in that the step of scanning the surface areas and the step of obtaining the resolution, respectively, comprise;
taking images of a number of surface structures having different average pore sizes;
calculating the Fourier spectrum of each of these images, and determining the resolution of the scanning electron microscope by extrapolating the resolution belonging to a signal to noise ratio of zero from the width, the signal amplitude and the noise offset of the Fourier spectrum of all of said images.
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Abstract
The performance of a scanning electron microscope (SEM) (10) is determined by scanning, with this SEM, porous silicon surface areas (PSF, PSC) each having a different average pore size, calculating the Fourier transform spectra (Fc) of the images of the surface areas and extrapolating the resolution (R) at a zero signal-to-noise ratio (SNR) from the width (W(1/e)), the signal amplitude (Sa) and the noise offset (NL) of the spectra. A test sample provided with the different surface areas is obtained by anodizing a silicon substrate (Su) at a constant electric current, while continuously decreasing the substrate area exposed to the etching electrolyte (El).
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Citations
16 Claims
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1. A method of determining the imaging quality of a scanning electron microscope used for measuring sizes of device features configured in a substrate layer during manufacture of devices, the method comprising the steps of:
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providing porous silicon surface areas;
scanning the surface areas by means of the scanning electron microscope;
analyzing the images taken by the scanning electron microscope by means of a Fast Fourier Transform technique to obtain an indication of the resolution of the scanning electron microscope, characterized in that the step of scanning the surface areas and the step of obtaining the resolution, respectively, comprise;
taking images of a number of surface structures having different average pore sizes;
calculating the Fourier spectrum of each of these images, and determining the resolution of the scanning electron microscope by extrapolating the resolution belonging to a signal to noise ratio of zero from the width, the signal amplitude and the noise offset of the Fourier spectrum of all of said images. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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- 15. A scanning electron microscope comprising a scanning electron unit, an object holder for holding an object to be examined by the microscope and a signal processing unit provided with a program to analyze data supplied by the scanning unit, characterized in that a small portion of the object holder surface facing the scanning device is permanently provided with a test sample in the form of a small porous silicon surface, the average pore size of which increases continuously in the scanning direction of the scanning unit, and in that the processing unit is provided with an additional program to analyze the data supplied by the scanning unit during scanning of the test sample.
Specification