# US 4,392,054 A · Method and apparatus for compensating for astigmatism in electron beam devices > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,392,054 A - Document ID: US4392054A - Status: Granted - Kind: A - Application number: 06/254,523 - Filed: 1981-04-15 - Granted: 1983-07-05 - Earliest claimed: 1980-04-16 - Assignees: Kabushiki Kaisha Nichidenshi Technics - Inventors: Takeshi Sato; Shunichi Suzaki - Web page: https://patentgrep.com/patent/US4392054A ## CPC - H01J 37/153: Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators - H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H) ## Abstract In a scanning electron microscope, astigmatism in an electron lens system is compensated for by an XY type stigmator equipped with two quadrupole lenses and their manually controlled direct current supplies. During the operation of astigmatism compensation, the supplemental current components are added stepwise to the output currents of said direct current supplies in synchronism with beam scanning in the microscope, so that the scanning image displayed in the microscope is divided into areas where astigmatism compensation is different. The operator of the microscope may accord the most sharp divided area with the center area of the scanning image by adjusting said direct current supplies, so that the output values of the direct current supplies become oprimum for astigmatism compensation. ## Claims ### Claim 1 A method for compensating astigmatism in an electron beam device comprising means for generating an electron beam, means including a lens system for focussing the electron beam on a specimen, means for deflecting the beam to cause it to scan over the specimen and means for detecting a signal generated by the interaction of the beam and the specimen surface, an image display means in synchronism with said scanning deflecting system to which the detected signal is applied, and an XY type stigmator equipped with two quadrupole lenses positioned in said lens system for compensating astigmatism, said method comprising: (a) a step for supplying periodically stepwise changed currents to at least one of said two quadrupole lenses in synchronism with said scanning deflecting means so that different areas on the image of said display means are differently corrected for astigmastism, (b) a step for visually identifying the area on the image of the said displaying means that is best corrected for astigmatism, and (c) a step for constantly applying direct currents corresponding to those applied for the image area best corrected for astigmatism in the preceding step to said two quadrupole lenses. ### Claim 2 A method for compensating astigmatism in an electron beam device comprising means for generating an electron beam, means including a lens system for focussing the electron beam on a specimen, means for deflecting the beam to cause it to scan over the specimen and means for detecting a signal generated by the interaction of the beam and the specimen surface, an image display means in synchronism with said scanning deflecting system to which the detected signal is applied, and an XY type stigmator equipped with two quadrupole lenses positioned in said lens system for compensating astigmatism, said method comprising: (a) a step for supplying periodically stepwise changed currents to at least one of said two quadrupole lenses in synchronism with said scanning deflecting means so that different areas on the image of said display means are differently corrected for astigmatism, (b) a step for simultaneously shifting the total values of stepwise changed currents so that the area best corrected for astigmatism is located at the center of said display means, and (c) a step for constantly applying direct currents corresponding to those applied to the area at the center of the display means in the preceding step to said two quadrupole lenses. ### Claim 3 An electron beam device comprising: (a) a lens system for focussing the electron beam on a specimen; (b) a scanning means equipped with first and second deflecting coils and first and second scanning power supplies for scanning the electron beam in a two dimensional raster over the specimen, (c) means for detecting a signal generated by interaction of the beam and specimen surface, (d) an image display means synchronized with said scanning means and supplied with the signal detected from the specimen as a brightness modulation signal for displaying the scanning image of the specimen, (e) an XY type stigmator equipped with two quadrupole lenses for compensating astigmatism in said focussing lens system, being characterized by (f) a means for automatically stepwise changing the values of currents applied to said two quadrupole lenses, (g) a means for controlling the changing means (f) in synchronism with said first scanning power supply and/or said second scanning power supply to provide at least three steps per scan in at least one direction, (h) a means controllable by an operator visually observing the area of best correction for astigmatism upon the image display for simultaneously shifting the total values of the stepwise changed currents applied to said two quadrupole lenses so that the area best corrected for astigmatism is displayed on the screen of the image display means, and (i) means for constantly applying the direct currents corresponding to those applied for the best corrected image area on the image display means to said two quadrupole lenses. ### Claim 4 An electron beam device comprising: (a) a lens system for focussing the electron beam on a specimen, (b) a scanning means equipped with first and second deflecting coils and first and second scanning power supplies for scanning the electron beam in a two dimensional raster over the specimen, (c) means for detecting a signal generated by interaction of the beam and specimen surface, (d) an image display means synchronized with said scanning means and supplied with the signal detected from the specimen as a brightness modulation signal for displaying the scanning image of the specimen, (e) an XY type stigmator equipped with two quadrupole lenses and manually and independently adjustable d.c. power supplied for compensating astigmatism in said focussing lens system, being characterized by (f) a means controllable by an operator visually observing the area of best correction for astigmatism upon the image display for automatically changing direct currents supplied to said two quadrupole lenses by periodically adding at least two supplemental current components, and (g) a means for controlling the changing means in synchronism with said first scanning power supply and/or said second scanning power supply. ### Claim 5 (depends on 4) An electron beam device according to claim 4, in which said control means (g) controls the changing means (f) so that each stepwise change of the currents applied to the two quadrupole lenses is of the same polarity. ### Claim 6 (depends on 4) An electron beam device according to claim 4, in which said control means (g) controls the changing means (f) so that the stepwise changes of the currents applied to said two quadrupole lenses are repeatedly carried out during one sweep of the output signal of one of the scanning power supplies. ### Claim 7 (depends on 4) An electron beam device according to claim 4, in which said changing means (f) generates negative, zero and positive supplemental current components added to the output currents of said d.c. power supplies. ### Claim 8 (depends on 4) An electron beam device according to claim 4, further comprising means for controlling magnification and in which said changing means (f) changes the step magnitude in the stepwise currents according to the condition of said magnification control means. ### Claim 9 An electron beam device comprising: (a) a lens system for focussing the electron beam on a specimen, (b) a scanning means equipped with first and second deflecting coils and their first and second scanning power supplies for scanning the electron beam in a two dimensional raster over the specimen, (c) means for detecting a signal generated by interaction of the beam and specimen surface, (d) an image display means being synchronized with said scanning means and supplied with a signal detected from the specimen as a brightness modulation signal for displaying the scanning image of the specimen, (e) an XY type stigmator equipped with two quadrupole lenses for compensating astigmatism in said focussing lens system, being characterized by (f) a means controllable by an operator visually observing the area of best correction for astigmatism upon the image display for automatically stepwise changing the values of currents applied to said two quadrupole lenses, (g) a control means for controlling the changing means (f) in synchronism with said horizontal scanning power supply and/or said vertical scanning power supply to provide at least three steps per scan in at least one direction, (h) a signal generating means for generating brightness modulation signals to the image display means (d) in synchronism with said control means (g) so that lines are displayed on the screen of said image display means between areas of different astigmatism correction, (i) an adjusting means for simultaneously shifting the total values of the stepwise changed currents applied to said two quadrupole lenses so that the image area best corrected for astigmatism is displayed on the screen of the image display means, and (j) a means for constantly applying the direct currents corresponding to those applied for the best corrected image area on the image display means to said two quadrupole lenses. ### Claim 10 An electron beam device comprising: (a) a lens system for focussing the electron beam on a specimen, (b) a scanning means equipped with first and second deflecting coils and their first and second scanning power supplies for scanning the electron beam in a two dimensional raster over the specimen, (c) means for detecting a signal generated by interaction of the beam and specimen surface, (d) an image display means being synchronized with said scanning means and supplied with a signal detected from the specimen as a brightness modulation signal for displaying the scanning image of the specimen, (e) an XY type stigmator equipped with two quadrupole lenses and manually and independently adjustable d.c. power supplies for compensating astigmatism in said focussing lens system, being characterized by (f) a means controllable by an operator visually observing the area of best correction for astigmatism upon the image display for automatically changing direct currents supplied to said two quadrupole lenses by periodically adding at least two supplemental current components, (g) a means for controlling the changing means in synchronism with said first scanning power supply and/or said second scanning power supply, and (h) a signal generating means for generating brightness modulation signals to the image display means in synchronism with said control means so that lines are displayed on the screen of said image display means between areas of different astigmatism correction.