2. 1 Microelectronics Processing Course - J. Salzman – Fall 2006 Microelectronics Processing Lithography

3. 2 Microelectronics Processing Course - J. Salzman – Fall 2006 Photolithography Photolithography is the sequence of activities needed for transfer a pre-designed pattern to the surface of a semiconductor wafer. The pattern can be registered on a mask, or supplied directly from a computer to a scanning radiation source. Photoresist is a photo-sensitive resistant coating used to register an image on the desired surface

4. 3 Microelectronics Processing Course - J. Salzman – Fall 2006

5. 4

6. 5 Lithography Wafer printing process:  Light sources  Exposure techniques  Photoresist  Mask engineering Novel process  E-beam lithography Wafer printing process:  Light sources  Exposure techniques  Photoresist  Mask engineering Novel process  E-beam lithography

7. 6 Microelectronics Processing Course - J. Salzman – Fall 2006 The Image

8. 7 Microelectronics Processing Course - J. Salzman – Fall 2006 Light Sources: The Hg Lamp i-line (365 nm) g-line (435 nm) h-line (405 nm)

9. 8 Microelectronics Processing Course - J. Salzman – Fall 2006 Light Sources

10. 9 Microelectronics Processing Course - J. Salzman – Fall 2006 Wafer Exposure Systems

11. 10 Microelectronics Processing Course - J. Salzman – Fall 2006 Wafer Exposure Systems

12. 11 Microelectronics Processing Course - J. Salzman – Fall 2006 Optics: Basics of Diffraction

13. 12 Microelectronics Processing Course - J. Salzman – Fall 2006 Optics: Basics of Diffraction

14. 13 Microelectronics Processing Course - J. Salzman – Fall 2006 Optics: Basics of Diffraction

15. 14 Microelectronics Processing Course - J. Salzman – Fall 2006 Optics: Basics of Diffraction Assume a circular aperture of radius r 0 We define a parameter u as u=(2  / )r 0 sin  The far field radiation pattern of the aperture I(u)  I(0) (J 1 (u)/u) 2 J 1 (u) is the 1 st Bessel Function

16. 15 Microelectronics Processing Course - J. Salzman – Fall 2006 Optics: Basics of Projection Systems

17. 16 Microelectronics Processing Course - J. Salzman – Fall 2006 Optics: Basics of Projection Systems Note that the aperture (or lens) diameter determines the value of 

18. 17 Microelectronics Processing Course - J. Salzman – Fall 2006 Optics: Basics of Projection Systems

19. 18 Microelectronics Processing Course - J. Salzman – Fall 2006 Resolution Resolved imagesUnresolved images Rayleigh’s definition of resolution

20. 19 Microelectronics Processing Course - J. Salzman – Fall 2006 Numerical Aperture

21. 20 Microelectronics Processing Course - J. Salzman – Fall 2006 Inmersion Lithography

22. 21 Microelectronics Processing Course - J. Salzman – Fall 2006 NA and Depth of Focus

23. 22 Microelectronics Processing Course - J. Salzman – Fall 2006 Depth of focus In-focus Out-of-focus Source: http://emalwww.engin.umich.edu/emal/courses/SEM_lectureCW/SEM_DepthofFocus.html

24. 23 Microelectronics Processing Course - J. Salzman – Fall 2006 Example of Depth of Field problem Need a DOF larger than 

25. 24 Microelectronics Processing Course - J. Salzman – Fall 2006 Modulation Transfer Function MTF = (I MAX -I MIN )/(I MAX +I MIN ) MTF is a function of feature size!

26. 25 Microelectronics Processing Course - J. Salzman – Fall 2006 Contact and Proximity Printing (Fresnel diffraction)

27. 26 Microelectronics Processing Course - J. Salzman – Fall 2006 Contact and Proximity Printing (Fresnel diffraction)

28. 27 Microelectronics Processing Course - J. Salzman – Fall 2006 Contact and Proximity Printing (Fresnel diffraction) =365 nm

29. 28 Microelectronics Processing Course - J. Salzman – Fall 2006 Summary of Printing Systems

30. 29 Microelectronics Processing Course - J. Salzman – Fall 2006 Critical Dimension Control (Math work on the board)

31. 30 Microelectronics Processing Course - J. Salzman – Fall 2006 Photoresist (1)

32. 31 Microelectronics Processing Course - J. Salzman – Fall 2006 Photoresist (2)

33. 32 Microelectronics Processing Course - J. Salzman – Fall 2006 Photoresist (3) Novolac

34. 33 Microelectronics Processing Course - J. Salzman – Fall 2006 PAC Changed due to illumination

35. 34 Microelectronics Processing Course - J. Salzman – Fall 2006 (h ) H2OH2O soluble on basic solution

36. 35 Microelectronics Processing Course - J. Salzman – Fall 2006 Deep UV Resists

37. 36 Microelectronics Processing Course - J. Salzman – Fall 2006 Deep UV Resists

38. 37 Microelectronics Processing Course - J. Salzman – Fall 2006 Basic Properties of Resists Contrast:

39. 38 Microelectronics Processing Course - J. Salzman – Fall 2006 Basic Properties of Resists

40. 39 Microelectronics Processing Course - J. Salzman – Fall 2006 Non-ideal Exposure

41. 40 Microelectronics Processing Course - J. Salzman – Fall 2006 Critical MTF (CMTF) CMTF is the minimal MTF value of the optical system that results in a fully resolved pattern in the photoresist

42. 41 Microelectronics Processing Course - J. Salzman – Fall 2006 Other issues in Photoresist Exposure

43. 42 Microelectronics Processing Course - J. Salzman – Fall 2006 Other issues in Photoresist Exposure

44. 43 Microelectronics Processing Course - J. Salzman – Fall 2006 Spin-on photoresist Thickness of PR t=KS( /ω 2 R 2 ) 1/3 t = thickness K = constant S= fraction of solids υ= viscosity ω= angular velocity R = radius

45. 44 Microelectronics Processing Course - J. Salzman – Fall 2006 Other issues in Photoresist Exposure Constructive interference Destructive interference

46. 45 Microelectronics Processing Course - J. Salzman – Fall 2006 Mask Engineering

47. 46 Microelectronics Processing Course - J. Salzman – Fall 2006 Mask Engineering: OPC Mask Printed Desired With OPC

48. 47 Microelectronics Processing Course - J. Salzman – Fall 2006 Mask Engineering: Phase shifting

49. 48 Microelectronics Processing Course - J. Salzman – Fall 2006 Optical lithography - Steps required for a pattern transfer (7) Photoresist removal

50. 49 Microelectronics Processing Course - J. Salzman – Fall 2006 Flow chart of a typical resist process Substrate cleaning Plasma de-scum Post exposure treatment Strip Spin coat Pre-bake Develop Expose Post bake Etch * Steps in dashed (pink) lines are not always used HMDS 90 0 C 140 0 C

51. 50 Microelectronics Processing Course - J. Salzman – Fall 2006 Equipment (1)

52. 51 Microelectronics Processing Course - J. Salzman – Fall 2006 Equipment (2)

53. 52 Microelectronics Processing Course - J. Salzman – Fall 2006 Equipment (3)

54. 53 Microelectronics Processing Course - J. Salzman – Fall 2006 Step-and-scan system

55. 54 Microelectronics Processing Course - J. Salzman – Fall 2006 Modeling

56. 55 Microelectronics Processing Course - J. Salzman – Fall 2006 A generic Projection System

57. 56 Microelectronics Processing Course - J. Salzman – Fall 2006

58. 57 Microelectronics Processing Course - J. Salzman – Fall 2006

59. 58 Microelectronics Processing Course - J. Salzman – Fall 2006 Example: Rectangular slit

60. 59 Microelectronics Processing Course - J. Salzman – Fall 2006

61. 60 Microelectronics Processing Course - J. Salzman – Fall 2006

62. 61 Microelectronics Processing Course - J. Salzman – Fall 2006 Summary of Modeling

63. 62 Microelectronics Processing Course - J. Salzman – Fall 2006

64. 63 Microelectronics Processing Course - J. Salzman – Fall 2006

65. 64 Microelectronics Processing Course - J. Salzman – Fall 2006

66. 65 Microelectronics Processing Course - J. Salzman – Fall 2006 Idealized photolithographic system

67. 66 Microelectronics Processing Course - J. Salzman – Fall 2006 Light diffraction Source: http://library.thinkquest.org/16468/quan-a3.htm O X

68. 67 Microelectronics Processing Course - J. Salzman – Fall 2006 Diffraction Long and narrow aperture Rectangular aperture

69. 68 Microelectronics Processing Course - J. Salzman – Fall 2006 Multiple slits Source: http://hyperphysics.phy-astr.gsu.edu/

70. 69 Microelectronics Processing Course - J. Salzman – Fall 2006 Airy’s disc Circular aperture Source: http://hyperphysics.phy-astr.gsu.edu/

71. 70 Microelectronics Processing Course - J. Salzman – Fall 2006 Far field Fraunhofer diffraction and optical intensity patterns of a rectangular aperture

72. 71 Microelectronics Processing Course - J. Salzman – Fall 2006 Fresnel diffraction Inteference

73. 72 Microelectronics Processing Course - J. Salzman – Fall 2006 Uneven topography Thinner area: overexposed Thicker area: underexposed

74. 73 Microelectronics Processing Course - J. Salzman – Fall 2006 Depth of focus (DOF) DOF=

75. 74 Microelectronics Processing Course - J. Salzman – Fall 2006 Standing wave effect (1)

76. 75 Microelectronics Processing Course - J. Salzman – Fall 2006 Standing wave effect (2) Constructive interference Destructive interference

77. 76 Microelectronics Processing Course - J. Salzman – Fall 2006 Mask engineering: Optical proximity correction (OPC)

78. 77 Microelectronics Processing Course - J. Salzman – Fall 2006 Mask engineering: correction by phase shifting Phase shift masks (PSMs)

79. 78 Microelectronics Processing Course - J. Salzman – Fall 2006

80. 79 Microelectronics Processing Course - J. Salzman – Fall 2006 Electron scattering limits resolution Higher energy electrons have larger back-scattering range

81. 80 Microelectronics Processing Course - J. Salzman – Fall 2006 Schematic of the IBM EL-4 column for e-beam lithography Schematic of column for shaped-beam lithography. On the right, the dashed ray trace corresponds to the source, and the solid trace to the shaped spot.

82. 81 Microelectronics Processing Course - J. Salzman – Fall 2006

83. 82 Microelectronics Processing Course - J. Salzman – Fall 2006 A commercial electron beam lithography tool

84. 83 Microelectronics Processing Course - J. Salzman – Fall 2006 E-beam resists

85. 84 Microelectronics Processing Course - J. Salzman – Fall 2006 X-ray as a light source for lithography AM FM Cell phone, PCS Microwave X-ray

86. 85 Microelectronics Processing Course - J. Salzman – Fall 2006 X-ray: a point source

87. 86 Microelectronics Processing Course - J. Salzman – Fall 2006 Deep X-ray Lithography (DXRL) What is SR (Synchrotron Radiation)? Shield Wall Storage Ring Synchrotron radiation is an electromagnetic radiation (light) emitted from electrons (positrons) moving with relativistic velocities on macroscopic circular orbits.

88. 87 Microelectronics Processing Course - J. Salzman – Fall 2006 Synchrotron radiation source

89. 88 Microelectronics Processing Course - J. Salzman – Fall 2006 The LIGA Technology Comparison : SR & Other Sources SR is the most intense light source in the VUV and in the X-ray region. SR Bending Magnet Sun (6000° C) Light Bulb 10 7 10 8 10 9 10 10 11 10 12 Brightness Wavelength (10 -10 m) 10 4 10 3 10 2 10 1 10 0 10 -1 X-ray

90. 89 Microelectronics Processing Course - J. Salzman – Fall 2006 The LIGA Technology Synchrotron Light Generation 6.5cm 0.4cm XRLM3 Continuous electromagnetic spectrum from the infrared to the hard x-rays

91. 90 Microelectronics Processing Course - J. Salzman – Fall 2006 XRLM3 Beamline at CAMD X-ray Exposure Station with SR Source Circumference of the ring52 m Maximum Energy(E) 1.3 / 1.5 GeV Current(I) 300 / 150 mA Radius of dipole magnets(r o ) 2.928 m Characteristic energy(E C ) 1.7 / 2.6 keV Power(Energy loss per turn) 1.0 W /mrad-100 mA Lifetime > 8 hours

92. 91 Microelectronics Processing Course - J. Salzman – Fall 2006 Principle setup of proximity x-ray lithography