Charged Particle Beam Device With Retarding Field Analyzer

• US 20090200463A1
• Filed: 06/10/2005
• Published: 08/13/2009
• Est. Priority Date: 06/11/2004
• Status: Active Grant

• Current Assignee: ICT Integrated Circuit Testing Gesellschaft Fur Halbleiterpruftechnik mbH
• Original Assignee: ICT Integrated Circuit Testing Gesellschaft Fur Halbleiterpruftechnik mbH
• Inventors: Salvesen, Carlo, Degenhardt, Ralf, Feuerbaum, Hans-Peter, Hambach, Dirk, Kögler, Walter, Munack, Harry
• Granted Patent: US 8,203,119 B2
• Time in Patent Office: Days
• US Class Current: 250/307
• CPC Class Codes: G01R 31/305 using electron beams investigating or analysing materials by measuring photoelectric effect G01N23/227
• CPC Class Codes: H01J 2237/24485 Energy spectrometers
• CPC Class Codes: H01J 2237/24585 Other variables, e.g. energy, mass, velocity, time, temperature
• CPC Class Codes: H01J 37/244 Detectors; Associated components or circuits therefor

Abstract

The invention provides a charged particle beam device to inspect or structure a specimen with a primary charged particle beam propagating along an optical axis; a beam tube element having a tube voltage; and a retarding field analyzer in the vicinity of the beam tube element to detect secondary charged particles generated by the primary charged particle beam on the specimen. According to the invention, the retarding field analyzer thereby comprises an entrance grid electrode at a second voltage; at least one filter grid electrode at a first voltage; a charged particle detector to detect the secondary charged particles; and at least one further electrode element arranged between the entrance grid electrode and the at least one filter grid electrode. The at least one further electrode element reduces the size of the stray fields regions in the retarding electric field region to improve the energy resolution of the retarding field analyzer. The improvement of the energy resolution is significant, in particular when the beam tube element is part of a high voltage beam tube.

Claims

1. A charged particle beam device to inspect a specimen with a primary charged particle beam, comprising:

a charged particle beam source configured to form the primary charged particle beam propagating within a beam tube element along an optical axis;

at least one filter grid electrode connectable to a first voltage to decelerate secondary charged particles generated by the primary charged particle beam on the specimen;

a charged particle detector positioned to detect the secondary charged particles that have passed through the at least one filter grid electrode; and

at least one further electrode element for electrically shielding the secondary charged particles from the beam tube element.

2. The charged particle beam device according to claim 1, further comprising an entrance grid electrode connectable to a second voltage for generating a retarding electric field region between the entrance grid electrode and the at least one filter grid electrode for decelerating the secondary charged particles.

3. The charged particle beam device according to claim 2, wherein the entrance grid electrode is positioned in front of the at least one filter grid electrode as viewed in a direction essentially opposite to the primary charged particle beam.

4. The charged particle beam device according to claim 2, wherein the entrance grid electrode comprises multiple openings for enabling the secondary charged particles to enter the retarding electric field region.

5. The charged particle beam device according to claim 2, wherein at least one of the entrance grid electrode, the at least one filter grid electrode, the charged particle detector, and the at least one further electrode element, are essentially coaxial to the optical axis.

6. The charged particle beam device according to claim 1, wherein the beam tube element is connectable to a tube voltage for electrically shielding the primary charged particle beam from the at least one filter grid electrode.

7. The charged particle beam device according to claim 1, wherein filter grid electrode and beam tube element are positioned with respect to each other to withstand a voltage difference between the first voltage and the tube voltage of more than 10,000 V.

8. The charged particle beam device according to claim 1, wherein the specimen is connectable with a specimen voltage, wherein, during operation, the voltage difference between the specimen voltage and the first voltage is smaller than 10 V.

9. The charged particle beam device according to claim 2, wherein the entrance grid electrode and the at least one filter grid electrode are essentially coplanar or essentially concentric to each other.

10. The charged particle beam device according to claim 2, wherein the at least one filter grid electrode, the charged particle detector, and at least one further electrode element are enclosed by a further beam tube structure comprising the entrance grid electrode, the beam tube element, and at least one further beam tube structure element.

11. The charged particle beam device according to claim 1, wherein the at least one further electrode element has an annular, cylindrical or conic shape surrounding the beam tube element.

12. The charged particle beam device according to claim 2, wherein the at least one further electrode element is a high-ohmic electrode comprising high-ohmic material with a resistance between 10⁹ Ω

cm and 10¹¹ Ω

cm.

13. The charged particle beam device according to claim 12, wherein the high-ohmic material is Murflor or a mixture of ceramics based on tin oxide, zirconium oxide, aluminum oxide, aluminum nitride, titanium nitride, or a epoxy resin based material.

14. The charged particle beam device according to claim 12, wherein the at least one high-ohmic electrode electrically connects the entrance grid electrode with the at least one filter grid electrode.

15. The charged particle beam device according to claim 12, wherein the at least one high-ohmic electrode surrounds the retarding electric field region completely within a plane normal to the optical axis.

16. The charged particle beam device according to claim 12, wherein during normal operation, the current flowing through the high-ohmic electrode from the entrance grid electrode to the at least one filter grid electrode is smaller than 1 μ

A.

17. The charged particle beam device according to claim 1, wherein the at least one further electrode element is formed of a metal conducting material.

18. The charged particle beam device according claim 2, wherein the at least one further electrode element is connectable to a third voltage which, during normal operation, is equal to the first voltage, or lies between the second voltage and the first voltage.

19. The charged particle beam device according to claim 1, wherein the at least one further electrode element comprises separate multiple further electrode elements to be connectable to different third voltages.

20. The charged particle beam device according to claim 19, wherein the multiple further electrode elements are electrically connected with each other to provide for different third voltages which are increased along a direction normal to the filter grid electrode to decelerate the secondary charged particles.

21. The charged particle beam device according to claim 19, wherein the multiple further electrode elements are electrically connected with each other to provide for different fourth voltages which are decrease along a direction normal to the filter grid electrode to accelerate the secondary charged particles towards the charged particle detector.

22. The charged particle beam device according to claim 1, wherein the at least one further electrode element comprises at least one inner further electrode element having a first radius, and an at least one outer further electrode element having a second radius which is larger than the first radius, wherein the at least one inner further electrode elements and the at least one outer further electrode elements are preferably essentially coaxial.

23. The charged particle beam device according to claim 1, wherein at least one of the at least one further electrode elements is arranged between the at least one filter grid electrode and the charged particle detector.

24. The charged particle beam device according to claim 1, wherein the charged particle beam device is a scanning electron microscope.

25. The charged particle beam device according to claim 1, wherein the charged particle beam device comprises a combined electrostatic magnetic objective lens.

26. The charged particle beam device according to claim 1, wherein the charged particle detector is arranged as an in-lens detector.

27. The charged particle beam device according to claim 13, further comprising a retarding field analyzer that comprises at least one high-ohmic electrode and at least one further electrode formed of a metal conducting material.

28. The charged particle beam device according to claim 2, wherein the at least one filter grid electrode comprises an array of openings with a pitch smaller than 60 μ

m and/or the entrance grid electrode comprises an array of openings with a pitch smaller than 200 μ

m.

76. A method of inspecting a specimen by means of a primary charged particle beam generated by a charged particle beam device according to claim 18, comprising:

providing the specimen for inspection by the primary charged particle beam;

applying a tube voltage to the beam tube element;

applying a first voltage to the at least one filter grid electrode;

directing the primary charged particle beam onto the specimen to generate secondary charged particles emitted from the specimen;

generating at least one of the third voltages of the at least one further electrode elements for electrically shielding the secondary charged particles from the beam tube element;

scanning the primary charged particle beam across a region of the specimen; and

detecting the secondary charged particles that have passed through the at least one filter grid electrode as a function of the scanning position by the primary charged particle beam.

77. The method according to claim 76, wherein the first voltage is in the range between 0 V and −

50V with respect to the voltage of the specimen.

78. The method according to claim 76, wherein the tube voltage differs by more than 8000 V from the first voltage.

79. The method according to claim 76, wherein the secondary charged particles are passed through a lens used to focus the primary charged particle.

29. A retarding field analyzer for detecting charged particles, comprising:

at least one filter grid electrode connectable to a first voltage;

an entrance grid electrode connectable to a second voltage for providing a retarding electric field region between the entrance grid electrode and the at least one filter grid electrode to decelerate the charged particles that have passed through the entrance grid electrode;

a charged particle detector positioned to detect the charged particles that have passed through the entrance grid electrode and the filter grid electrode; and

at least one further electrode element comprising high-ohmic material to provide for a high ohmic resistance between the entrance grid electrode and the at least one filter grid electrode.

30. The retarding field analyzer according to claim 29, wherein the at least one further electrode element is shaped to have a cylindrical or conical shape.

31. The retarding field analyzer according to claim 29, wherein the at least one further electrode element is a lower outer high-ohmic electrode surrounding the retarding electric field region for reducing the size of an outer stray field region of the retarding electric field region.

32. The retarding field analyzer according to claim 31, wherein the at least one high-ohmic electrode surrounds the retarding electric field region completely within at least one plane parallel with the filter grid electrode.

33. The retarding field analyzer according to claim 31, further comprising at least one further electrode formed of a conducting material, preferably a metal, for reducing the size of the outer stray field region of the retarding electric field region.

34. The retarding field analyzer according to claim 29, further comprising an upper outer high-ohmic electrode surrounding an accelerating electric field region between the at least one filter grid electrode and the charged particle detector for defining the equipotential lines of the accelerating electric field region.

35. The retarding field analyzer according to claim 31, wherein at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode is formed as a jacket laterally surrounding said retarding electric field region or said accelerating electric field region.

36. The retarding field analyzer according to claim 31, wherein at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode consists of high-ohmic material having a resistivity between 10⁹ Ω

cm and 10¹¹ Ω

cm.

37. The retarding field analyzer according to claim 31, wherein at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode consists of Murflor or a mixture of ceramics based on tin oxide, zirconium oxide, aluminum oxide, aluminum nitride, titanium nitride, or a epoxy resin based material.

38. The retarding field analyzer according to claim 31, wherein a wall of at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode has a thickness of at least 500 μ

m.

39. The retarding field analyzer according to claim 31, wherein the resistivity of the material of at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode varies by less than 5%.

40. The retarding field analyzer according to claim 31, wherein at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode has an n-fold rotational symmetry with respect a symmetry axis and a fully rotational symmetry with respect to said symmetry axis.

41. The retarding field analyzer according to claim 31, wherein at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode is essentially cylindrically or conically shaped.

42. The retarding field analyzer according to claim 31, wherein at least one of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode are aligned with respect to the same symmetry axis.

43. The retarding field analyzer according to claim 31, wherein the cross sections of the lower outer high-ohmic electrode and an upper outer high-ohmic electrode are the same within at least respective one plane orthogonal to said symmetry axis.

44. The retarding field analyzer according to claim 31, wherein the cross section of an upper outer high-ohmic electrode within a plane orthogonal to the symmetry axis is varied along said symmetry axis in order to direct the charged particles towards the charged particle detector.

45. The retarding field analyzer according to claim 31, wherein the thickness of a wall of an upper outer high-ohmic electrode is varied in an axial direction to focus the charged particles that have passed the filter grid electrode onto the charged particle detector.

46. The retarding field analyzer according to claim 31, further comprising an electrically shielding housing short-circuited with the entrance grid electrode for shielding the surrounding of the retarding field analyzer from the fields of the retarding electric field region.

47. The retarding field analyzer according to claim 46, wherein the electrically shielding housing encloses at least one of the filter grid electrode, the charged particle detector, the lower outer high-ohmic electrode, and an upper outer high-ohmic electrode to more than 90% of the full solid angle as seen from the center of the filter grid electrode.

48. The retarding field analyzer according to claim 46, wherein the electrically shielding housing is comprised of at least two of an outer shield, a detector shield and said entrance grid electrode.

49. The retarding field analyzer according to claim 46, wherein the electrically shielding housing is shaped and positioned to shield a primary charged particle beam from the electric field generated by the retarding field analyzer wherein the charged particles are secondary charged particles generated by the primary charged particle beam.

50. The retarding field analyzer according to claim 29, wherein the entrance grid electrode has only one opening for maximizing the detection efficiency of the charged particles.

51. The retarding field analyzer according to claim 29, wherein the at least one filter grid electrode comprises an array of openings with a pitch smaller than 60 μ

m and/or the entrance grid electrode comprises an array of openings with a pitch smaller than 200 μ

m.

52. The retarding field analyzer according to claim 31, wherein at least two of the entrance grid electrode, the at least one filter grid electrode, the charged particle detector, the lower outer high-ohmic electrode, and an upper outer high-ohmic electrode are coaxially aligned with respect to a common symmetry axis.

53. The retarding field analyzer according to claim 29, wherein the entrance grid electrode and the at least one filter grid electrode are coplanar with respect to each other.

63. A charged particle beam device to inspect or structure a specimen with a primary charged particle beam, comprising:

a charged particle beam source to form the primary charged particle beam propagating along an optical axis;

at least one retarding field analyzer according to claim 29 to detect secondary charged particles generated by the primary charged particle beam on the specimen.

64. The charged particle beam device according to claim 63, further comprising a beam tube element biasable with a tube voltage to shield the primary charged particle beam from interference by the at least one retarding field analyzer.

65. The charged particle beam device according to claim 64, wherein a wall of the beam tube element has a beam tube opening for receiving said at least one retarding field analyzer for enabling detection of secondary charged particles within said beam tube element.

66. The charged particle beam device according to claim 65, wherein said beam tube opening is located off-axis on one side of said beam tube element.

67. The charged particle beam device according to claim 64, further comprising moving means for repeatedly moving said at least one retarding field analyzer towards the beam tube element and away from the beam tube element.

68. The charged particle beam device according to claim 64, further comprising rotation means for repeatedly rotating said at least one retarding field analyzer within said beam tube element.

69. The charged particle beam device according to claim 68, wherein said rotation takes place with respect to an axis normal to the direction of the optical axis.

70. The charged particle beam device according to claim 63, wherein the charged particle beam device is a scanning electron microscope.

71. The charged particle beam device according to claim 63, wherein the charged particle beam device comprises a combined electrostatic magnetic objective lens for focusing the primary charged particle beam.

72. The charged particle beam device according to claim 71, wherein the charged particle detector is arranged as an in-lens detector for detecting secondary charged particles that have passed through the focusing lens.

73. The charged particle beam device according to claim 63, wherein the at least one filter grid electrode comprises an array of openings with a pitch smaller than 30 μ

m.

54. A retarding field analyzer for detecting charged particles, comprising:

at least one filter grid electrode connectable to a first voltage;

an entrance grid electrode connectable to a second voltage for providing a retarding electric field region between the entrance grid electrode and the at least one filter grid electrode to decelerate the charged particles that have passed through the entrance grid electrode;

a charged particle detector to detect charged particles that have passed through the entrance grid electrode and the filter grid electrode; and

at least one further electrode element connectable to a third voltage for adjusting the electric field in the retarding electric field region between the entrance grid electrode and the at least one filter grid electrode.

55. The retarding field analyzer according to claim 54, wherein the at least one further electrode element comprises separate multiple further electrode elements to be connectable to different third voltages.

56. The retarding field analyzer according to claim 55, wherein the multiple further electrode elements are electrically connected with each other to form a voltage divider to provide for different third voltages between the entrance grid electrode and the at least one filter grid electrode.

57. The retarding field analyzer according to claim 54, wherein the at least one filter grid electrode and entrance grid electrode are positioned with respect to each other to withstand a voltage difference of more than 10000 V.

58. The retarding field analyzer according to claim 54, wherein the at least one further electrode elements are ring electrodes having a ring shape.

59. The retarding field analyzer according to claim 54, wherein at least two of the entrance grid electrode, the at least one filter grid electrode, the charged particle detector, and the at least one further electrode element are essentially coaxial to each other.

61. The retarding field analyzer according to claim 54, further comprising a further beam tube structure connectable to the second voltage that encloses the at least one filter grid electrode, the charged particle detector and the at least one further electrode element.

62. The retarding field analyzer according to claim 54, wherein the entrance grid electrode has one opening or multiple openings for enabling the charged particles to enter the retarding electric field region.

60. The retarding field analyzer according to aim 54, wherein the at least one further electrode element comprises at least one further inner electrode element having a first radius, and at least one further outer electrode element having a second radius, wherein the second radius is larger than the first radius.

74. A charged particle beam device to inspect or structure a specimen with a primary charged particle beam, comprising:

a charged particle beam source to form the primary charged particle beam within a beam tube element propagating along an optical axis; and

a retarding field analyzer to detect secondary charged particles generated by the primary charged particle beam on the specimen, comprising;

at least one filter grid electrode surrounding the beam tube element, the at least one filter grid electrode being biasable with a first voltage to decelerate the secondary charged particles;

an entrance grid electrode surrounding the beam tube element to shield the primary charged particle beam from interference by the first voltage;

a charged particle detector positioned to detect the secondary charged particles that have passed through the at least one filter grid electrode; and

at least one ring electrode surrounding the beam tube element for electrically shielding the secondary charged particles from the beam tube element and for reducing the size of stray field regions within a retarding electric field region.

75. A charged particle beam device to inspect or structure a specimen with a primary charged particle beam, comprising:

a charged particle beam source to form the primary charged particle beam propagating along an optical axis;

a beam tube element biasable with a tube voltage to electrically shield the primary charged particle beam; and

a retarding field analyzer to detect secondary charged particles generated by the primary charged particle beam on the specimen, comprising;

at least one filter grid electrode surrounding the beam tube element, the at least one filter grid electrode being biasable with a first voltage to decelerate the secondary charged particles;

an entrance grid electrode surrounding the beam tube element, the entrance grid electrode being biasable with the tube voltage to shield the primary charged particle beam from interference by the first voltage;

a charged particle detector to detect the secondary charged particles that have passed through the at least one filter grid electrode; and

at least one high-ohmic electrode which encircles the beam tube element, the at least one high-ohmic electrode comprising high-ohmic material to provide for a high ohmic resistance between the entrance grid electrode and the at least one filter grid electrode.