Method and apparatus for compensating for astigmatism in electron beam devices

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.

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.

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.

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.