1. Top-Down Nanomanufacturing David T. Shaw State University of New York at Buffalo

2. Contents Process Overview Lithography –Vacuum basics –Photolithography basics –Photomasks –Exposure Tools –X-ray lithography –Immersion lithography –Nano-imprint lithography –Other techniques - Dip pen, AFM, FIB –Electron Beam lithography Thin Film Deposition Etching

3. Overview

4. How Do You Naomanufacture?

5. Top-down Fabrication for Moore’s Law of Miniaturization

6. Lithography, although imperfect, can generate complex 3-D nanostructures

7. Top-down Processing is reaching a Limit

8. Brief History of Chip Making Based on Photonic Lithographic Fabrication Photonics lithographic fab is driven by electronics 1947 - First transistor invented at Bell by Bardeen, Brattain and Shockley 1958 - First integrated circuit at Texas Instruments by Jack Kilby 1959 – Planar technology on Si substrate using SiO2 as insulation layers More than three decades of exponential miniaturization in sizes and costs based on a top-down processing Dimensions move into nanoscale range at the beginning of the 21 st century Top-down technology is facing three fundamental design limits: –Transistor scalability –Performance –Power dissipation

9. Top-down Nanostructures Top down fabrication can be likened to sculpt- ing from a block of stone. –A piece of the base material is gradually eroded until the desired shape is achieved, i.e., you start at the top of the blank piece and work your way down removing material from where it is not required. Nanotechnology techniques for top down fab- rication vary but can be split into physical and chemical fabrication techniques

10. Top-down Fabrication of Nanodots G. Capellini elat, Appl. Phys. Lett. 82, (2003) 1772-1774 Stacking Ge nano–islands on Si(001) (a) AFM image and (b) cross sectional TEM of a typical Ge/Si heterostructure.

11. Top-down Fabricating Nanowires With Alternating Diameters or Compositions (ii) Generation of PR pattern

12. Top-down Fabricating Nanowires With Alternating Compositions Preparing an array of GaAs wires with a triangular cross section from a GaAs(100) wafer patterned with mask stripes along the (011) direction and anisotropically etched in an aqueous solution, Patterning the resultant wire array (after removal of the etch mask stripes) with photoresist lines perpendicular to the orientation of the GaAs wires, Etching the GaAs wires using the photoresist as a mask to generate wires with alternating widths, or Depositing metals through the photoresist pattern to create GaAs wires with segments alternating in composition. Y. Sun et al, Small,1(11)1052(2005)

13. Combining top-down and bottom-up A lamellar-forming block copolymer on 2D surfaces chemically patterned with a square array of spots form 3D bicontinuous morphologies. K. C. Daoulas et al, PRL,96,036104(2006)

14. Integration of Top-down and Bottom-up nanomanufacturing Integrated multifunctional nano-assembly onto bio-MEM devices and lead to scalable and cost effective nanomanufacturing X. Zhang et al, Journal of Nanoparticle Research 6: 125–130, 2004.

15. Future Integrated Nano-Systems Bottom-up (sensors, memories, etc.) will be integrated with top-down nanocomponents C. Sun, X. Zhang UC Berkeley

16. Top – Down Nanomanufacturing Derived directly from the chip-making processeschip-making processes Single Silicon Crystal Growth

17. Vacuum Basics

19. Mean Free Path

20. Vacuum Circuit Liu, UCD Phy250-2, 2006

21. Pumping Speed

22. Conductance of a Straight Tube Liu, UCD Phy250-2, 2006

23. Outgassing rates for common materials (millibar-liter/sec-cm2) Common vacuum materials Construction Materials which are compatible with UHV OFHC copper, Be-Cu alloy, phosphor bronze, 304 SS, 310 series SS, 340 SS (magnetic), Teflon, MACOR (machinable glass composite), 6061 Al (essentially pure aluminum), 2024 Al (harder alloy), quartz, Pyrex (gassy), alumina (careful with glazed ceramics), molybdenum, tungsten "mu-metal" magnetic shielding (Co, Ni, Fe), polyimide (Vespel), Sn- Ag solder Construction Materials which are compatible with UHV Zn, Cd--Especially be careful of fasteners and bolts, brass, certain solders

24. Vacuum Measurements

25. PhotolithographyPhotolithography Basics

26. Photolithograpy The most important part of top down fabrication technique is nanolithography. –In this process, required material is protected by a mask and the exposed material is etched away. –Depending upon the level of resolution required for features in the final product, etching of the base material can be done chemically using acids or physically using ultraviolet light, x- rays or electron beams. This is the technique applied to the manufacture of computer chips.

27. Diminishing Lithographic Wavelengths E. Chen, Harvard

28. Optical Lithography

29. Comparison of Three Lithographic Systems

30. ContactContact and Proximity Printing

31. Mask Aligners

32. Mask Alignment

33. Contact Lithography Advantages

34. Contact Lithography Disadvantages Good contact difficult to achieve Sensitive to particular contaminants Hard to get below 2µm DUV requires quartz mask Alignment can be difficult

35. Projection Printing (Stepper)

37. Projection Lithography Advantages

38. Projection Lithography Disadvantages

39. Exposure Tools

40. Phase Shift Mask (PSM) Lithography

41. Optical Proximity Correction

42. Surface Reflections and Standing Waves

43. Phase Shift Mask (PSM)

44. Immersion Lithography

45. X-ray Lithography

46. X-Ray Lithography (XRL)

48. X-Ray Photomask

49. EUV Lithography

50. Nano-Imprint Lithography

51. Dip Pen Nanolithography

52. Focused Ion Beam Lithography

53. Electron Beam Lithography

54. Optical vs. E-Beam Lithography

55. E-Beam Lithography

56. Electron Beam Lithography

58. EBL nanostructures

59. E – beam Nanoelectromechanical (NEMS) Structures

60. Thin Film Deposition

61. Thin Film Deposition -- Sputtering High purity sputtering gas necessary –Typically 0.1mtorr – 10 mtorr Short mean free path

62. Sputter Deposition Magnetron sputtering is the most widely used method for etching and thin film deposition. Although the basic diode sputtering method (without magnetron or magnetic enhanced) is still used in some application areas, magnetron sputtering now serves over 90% of the market for sputter deposition. Magnetron sputtering can be used to coat or dry etch- ing virtually any solid materials. Ref: www.gencoa.com

63. Sputtering System A typical sputtering system consists of a vacuum chamber with substrate holders and magnetron guns, vacuum pumps and gauging, a gas supply system, power sup- plies and a computer control system. http://www.teercoatings.co.uk

64. The Magnetron A Magnetron is comprised of : A CATHODE = electron source, An ANODE = electron collector, and A combined electric & magnetic field = B X E www.gencoa.com

65. Microscopic View of Sputtering www.gencoa.com The impact of an atom or ion on a surface produces sput- tering from the surface as a result of the momentum transfer from the incoming particle. Unlike many other vapor phase techniques there is no melting of the material.

66. The Magnetron Gun A magnetron consists of a target with magnets arranged behind it to make a magnetic trap for charged particles, such as argon ions, in front of the target. Atoms are knocked out of the target surface by the ions. These sputtered atoms aren’t charged negatively or positively, so they go straight out of the magnetic trap to coat the substrate. www.teercoatings.co.uk

67. The Magnetron Plasma Confinement between a negatively biased target and closed magnetic field produces a dense plasma. High densities of ions are generated within the confined plasma, and these ions are subsequently attracted to the negatively biased target, producing sputtering at high rates. ref: www.gencoa.com

68. Target Erosion Target erosion is greatest where the magnetic field and the sub- sequent plasma density is greatest. This leads to inefficient use of target material, particularly in the case of ferromagnetic targets. www.gencoa.com

69. Sputtering Insulators For an insulator target, the ions bombarding the target will create charging, and the electric field necessary to maintain a plasma is greatly diminished. To alleviate this problem, an RF power supply is used to generate the electric field. www.gencoa.com

70. Magnetron Guns www.lesker.com

71. The Latest in UHV Sputtering A UHV, magnetron sputter source that fits through the port of a 2.75" CF flange complete with its tilt gimbals assembly. This revolutionary new design is true UHV - all ceramic to metal construction. http://www.ajaint.com

72. Vacuum Evaporation Target material is heated to melting point Atoms leave target as vapor Vacuum allows atoms to go directly to substrate

73. E-Beam Evaporation

74. Etching

75. Pattern Transfer R. B. Darling

76. Basic Etching Concepts

77. Chemical Etching R. B. Darling

78. Physical Etching R. B. Darling

79. Ion Enhanced Etching

81. Parallel Plate Etchers

82. Sputter Etching and Ion Milling

83. Positive Ion Beam Milling