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CN-121978149-A - Automatic calibration method for electron beam quantity detection equipment

CN121978149ACN 121978149 ACN121978149 ACN 121978149ACN-121978149-A

Abstract

The invention discloses an automatic calibration method of electron beam quantity detection equipment, which is based on image recognition and calibration closed loop, mutually verifies and evaluates, realizes one-key high-precision automatic calibration through a preset software flow and algorithm, and meets the requirements of use scenes of different electron beam machines.

Inventors

  • SHI XINYAO
  • LIU KUI
  • DING ZHENGYONG
  • ZHAO YAN

Assignees

  • 苏州矽视科技有限公司

Dates

Publication Date
20260505
Application Date
20251208

Claims (9)

  1. 1. An automatic calibration method for electron beam quantity detection equipment is characterized in that: step 1, switching to an OM mode, transmitting a product, identifying two points on the same line by an image, and transmitting a sheet for correction; step 2, re-inputting a product with patterns, respectively moving two points on the same line to the center by image recognition, and performing OM coordinate system calibration and OM center calibration; step 3, searching edges of three points with sizes based on product sizes and image recognition, moving the edges to the center of an image, and calculating an origin of a product coordinate system; step 4, based on image recognition, moving the electric diaphragm in the X and Y directions under a set step length, and searching the spot position to find the coordinate positions of the standard sample and the Faraday cup calibration; Step 5, switching to an SEM mode, closing other power supplies to drive, moving out an electric iris diaphragm, reserving three electromagnetic lenses and swinging coil currents, checking the mechanical centering of the electromagnetic lenses and a detector based on image light spots, centering the maximum light spots, and simultaneously concentrically zooming and changing brightness and darkness; Step 6, inserting an electric iris diaphragm, searching the position of the diaphragm, centering a small Kong Guangban, and checking the central position of a beam spot and a brightness distribution histogram through image recognition; step 7, beam calibration; step 8, carrying out a detector brightness and contrast algorithm, optimizing detector gain and signal proportion distribution, adjusting sampling parameters, and searching optimal image parameters through image resolution and pixel distribution histograms; Step 9, under a small visual field, alternately executing by focusing, astigmatism eliminating and magnetic deflection algorithm, and searching the parameter at the time of the clearest image quality; Step 10, under a large visual field, deflecting the signal which leaks through the central hole of the lower detector to the upper detector for supplementary collection by dynamically adjusting the proportion parameters of the detectors, combining the signals of the upper detector and the lower detector, identifying the shadows of the detectors through images, and selecting a proper electromagnetic field deflection direction until the uniformity of SEM images is consistent, and the distribution histogram of pixels is close to normal distribution; Step 11, after the automatic neutralization optimization of the SEM image is completed, correcting the OM-SEM coordinate difference based on the OM and SEM images of the same pattern through image feature recognition at the standard sample position; step 12, performing pixel size calibration at the characteristic pattern, generating calibration coefficients of the images X and Y in two directions by shifting the images, performing deflection system orthogonality correction, and storing configuration; step 13, selecting Z Level positions with different heights, and automatically calibrating the height-focusing and image scaling coefficients based on the patterns on the product.
  2. 2. The method according to claim 1, further comprising the step of verifying the repeatability and stability of the measurement of the quantity on the product to generate a complete set of calibration reports.
  3. 3. The method for automatically calibrating an electron beam measuring apparatus according to claim 1, wherein said step 4 comprises: The electric diaphragm automatic calibration is used for verifying the mechanical centering of a primary condenser coil, a secondary condenser coil and an objective lens coil through a large aperture APT1, then switching to a small aperture APT2, automatically searching for centering a light spot, changing the concentric brightness of an image when swinging the primary condenser coil, centering the image when swinging the secondary condenser coil 6 without offset, zooming the image concentrically when swinging the objective lens coil, performing beam current calibration after the image judgment is passed, fitting a beam current Ip and a primary condenser coil current curve, then evaluating deflection gain, linearity and orthogonality after focusing, astigmatism, magnetic deflection centering and automatic brightness contrast, then selecting Z Level positions with different heights, and automatically calibrating height-focusing and image zooming coefficients based on patterns on products.
  4. 4. The method for automatically calibrating an electron beam measuring apparatus according to claim 1, wherein in the step 5, three electromagnetic lenses, namely, a first-stage condenser coil, a second-stage condenser coil and an objective lens coil, are used for switching an electron beam shutter and an electron gun valve in a switching mode, and setting currents of the first-stage condenser coil to obtain a CL1-Ip curve; brightness contrast, focus, astigmatism, magnetic deflection centering, and automatic pixel size calibration were then performed using SEM image algorithms.
  5. 5. The method for automatically calibrating an electron beam amount detecting apparatus according to claim 4, wherein: The SEM image algorithm comprises: z Level height automatic linkage calibration, recorded data information is X and Y coordinates, Z Leve height, focus current OLFine and current pixel size P, (X,Y,Z,OLFine,P) Two different pattern position information are recorded again, (X0,Y0,Z0,OLFine0,P0)&(X1,Y1,Z1,OLFine1,P1) Focusing auto-tracking: The focusing factor kf= (OLFine 1-OLFine 0)/(Z1-Z0), OLfine =kf (Z-z0) + OLfine 0=kf+z+ (OLfine 0-kf×z0) =kf×z+bf (slope and intercept), Pixel size auto-tracking: pixel size coefficient kp= (P1-P0)/(Z1-Z0), P=kp (Z-Z0) +p0=kp+z+ (P0-Kp Z0) =kp+bp (slope and intercept).
  6. 6. The method according to claim 1, wherein the step 7 of calibrating the beam current comprises checking the central position and the histogram of the brightness distribution of the beam spot, ensuring concentric brightness variation of the image when swinging the first-stage condenser coil, no offset of the image when swinging the second-stage condenser coil, and concentric zooming of the image when swinging the objective coil.
  7. 7. The method for automatically calibrating an electron beam measuring apparatus according to any one of claims 1 to 6, wherein the current of the current first-stage condenser coil is moved to a Faraday cup sample stage coordinate position, a current beam value is read in real time, then the current position is moved left and right to find a maximum beam position, and the maximum beam position is stored as Faraday cup coordinates, then the current value of the first-stage condenser coil is changed step by step according to a configuration file, the beam value is recorded, a calibration curve is drawn and stored, and the corresponding first-stage condenser coil current is issued based on the current of the current amount measuring set.
  8. 8. The method according to claim 1, wherein the step 12 of correcting the deflection system in the step of shifting the image comprises: The method comprises the steps of scanning voltage 2Vscan of a field angle, reserved voltage 2Voffset of electron beam offset, direct current offset voltage 2Vdc and a nonlinear voltage range, wherein the maximum linear range comprises field scanning voltage, electron beam offset voltage and direct current offset voltage, pixel size is determined by the intensity of deflection excitation signals, linearity is judged through fitting by establishing a corresponding relation between deflection gain and pixel size, and the linearity is judged through interpolation and reverse inquiry, the electron beam is offset to different positions through reserved scanning offset voltage Voffset, moving distance is calculated through image recognition, X and Y direction pixel sizes are calculated respectively, proportion and angle are compared, and orthogonality is estimated.
  9. 9. A computer-readable medium, on which a computer program is stored, characterized in that the program, when being executed by a processor, carries out the steps of the method according to any one of claims 1-8.

Description

Automatic calibration method for electron beam quantity detection equipment Technical Field The invention belongs to the technical field of high-end manufacturing, and particularly relates to an automatic calibration method of electron beam quantity detection equipment. Background Electron beam quantity detection equipment is an essential metering and detection tool for high-end manufacturing, especially for semiconductor chip manufacturing. The high-precision instrument is used for quantitatively measuring the microscopic morphology, size, composition and electrical property of a sample and checking defects by using a focused electron beam as a probe to scan the surface of the sample and detecting various signals (such as secondary electrons, back scattered electrons and the like) generated by the interaction of electrons and the sample. The core working principle is based on Scanning Electron Microscope (SEM) technology, and on the basis, higher-level functions are developed. In a vacuum environment, an electron gun (typically thermal field emission or schottky emission) emits electrons. The emitted electrons are focused into a very fine electron probe (beam spot diameter can reach nanometer level) through a series of electromagnetic lenses. The electron beam is then controlled by a scanning coil to perform a raster scan over the sample surface. When the high energy electron beam impinges on the sample surface, various signals are excited. The detector receives the signals, converts the signals into electric signals, amplifies the electric signals and synchronizes the electric signals with the position signals of the scanning system, and finally forms a high-resolution gray level image on a computer screen. The electron beam quantity detection device is a foundation stone for supporting the binary Cheng Fazhan and improving the yield. In the research and development stage, the method is used for new technology, development of new materials and characteristic characterization. In the mass production stage, the process control can be performed, the CD and the overlay accuracy can be monitored in real time, and the process parameters can be adjusted in time. When the yield is problematic, the electron beam is a "final tool" for physical failure analysis, which can be used to locate and classify specific defects, and can also be used to detect potential electrical defects. Conventional electron beam quantity detection device calibration methods typically appear as a set of steps performed serially and sequentially, but are essentially a multi-step, multi-parameter iterative and coupling process. Conventional procedures include beam centering, astigmatic correction, focus correction, field distortion correction, beam intensity calibration, etc. However, this single step series suffers from the following serious problems, which are also the main bottlenecks of the current calibration techniques: Parameter coupling problems. Parameters in electron optical systems are highly coupled. For example, adjusting the scan field distortion (a deflection parameter) may slightly affect the beam spot shape (a lens parameter), thereby destroying the previously completed focus and astigmatism correction. In a serial flow, the subsequent operation may disable the calibration effect of the previous step. The global optimal solution is lacking. Serial calibration is like a "blind image", where each step only seeks the best (local optimum) of the current single parameter, but there is no guarantee that the whole system is in the best state (global optimum) when all parameters are combined together. And the efficiency is low. Because of the parameter coupling, multiple rounds of repeated calibration may be required to obtain a marginally usable result, which is time consuming. Relying on operator experience. When the automatic flow cannot achieve the satisfactory effect, the manual fine adjustment is extremely dependent on intuition and experience of a senior engineer, and the repeatability and standardization degree are low. Disclosure of Invention Aiming at the defects of the prior art, the invention aims to provide an automatic calibration method of electron beam quantity detection equipment. In order to achieve the aim of the invention, the technical scheme adopted by the invention comprises an automatic calibration method of electron beam quantity detection equipment, Step 1, starting calibration, switching to an OM mode, transmitting products, identifying two points on the same line by images, carrying out slice transmission correction according to a sequence aligner, establishing an accurate sample coordinate system, providing an accurate and uniform space reference for all subsequent electron beam calibration steps, eliminating systematic errors caused by sample placement deviation and stage motion errors, and being a basis for realizing high-precision and repeatable calibration. Step 2, re-inputting a product with pattern