E beam lithography


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E beam lithography

  1. 1. Group 2: Trần Phúc Thành. Cao Văn Phước. Tống Văn Khoa.
  2. 2.  Introduction.  Why E-beam lithography?  Schematic of e-beam lithography.  Lithography Process  Advantages and disadvantages.  Summary.  References.
  3. 3. - Electron beam lithography (often abbreviated as e-beam lithography) is the practice of emitting a beam of electrons in a patterned fashion across a surface covered with a film (called the resist), ("exposing" the resist) and of selectively removing either exposed or non-exposed regions of the resist ("developing"). - The purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. It was developed for manufacturing integrated circuits, and is also used for creating nanotechnology architectures.
  4. 4. Lower resolution systems can use thermionic sources, which are usually formed from LaB6. However, systems with higher resolution requirements need to use field electron emission sources, such as heated W/ZrO2 for lower energy spread and enhanced brightness.
  5. 5. A magnetic lens is a device for the focusing or deflection of moving charged particles, such as electrons or ions , by use of the magnetic Lorentz force. Its strength can often be varied by usage of electromagnets.
  6. 6. - Sometime we aslo use electrostatic lens however, electrostatic lenses have more aberrations and so are not used for fine focusing. -Systems of electrostatic lenses can be designed in the same way as optical lenses. -Electrostatic lenses in an electron diffraction experiment.
  7. 7.  Clean sample ◦ Remove oils, organics, etc (Acetone, IPA, ultraso nic)  Spin coating of photoresist on surface of film (positive or negative resist) substrate Deposited film Photoresist
  8. 8.  E-beam lithography and develop  Etching  (multi-step processes)  Evaporate metal contacts substrate film substrate Deposited film substrate film substrate film
  9. 9. Direct writing with narrow beam Electron projection lithography using a mask :EPL
  10. 10. oIssues: oThroughput of direct writing is very low : research tool or low pattern density manufacturing oProjection stepper (EPL) is in development stage only (primarily by Nikon). oMask making is the biggest challenge for the projection method oBack-scattering and second electron result in proximity effect –reduce resolution with dense patterns there is also the proximity effect oOperates in high vacuum (10-6 –10-10 torr) –slow and expensive
  11. 11.  Raster Scan The e-beam is swept across the entire surface, pixel by pixel Beam is turned on and off Beam is scanned across the entire surface
  12. 12.  Vector Scan ◦ The e-beam “jumps” from one patterned area to the next ◦ Adjustments to the beam can also be made relatively easily ◦ It takes longer for the beam to settle, making it more difficult to ◦ maintain accurate placing for the beam
  13. 13. 15
  14. 14. o Diffraction is not a limitation on resolution ( < 1 Å for 10-50 keV electrons) o Resolution depends on electron scattering and beam optics the size of the beam, can reach ~ 5 nm
  15. 15. 17  In EBL the resolution is not limited by diffraction  In EBL backscattering causes the electron beam to broaden and expose a large volume of resist then expected.  The proximity effect places a limit on the minimum spacing between pattern feature.
  16. 16.  • The pattern is written directly onto the  electron-sensitive resist (no mask is used)  • More precise than photolithography or X- Ray lithography  • Used to make high-resolution masks for  photolithography and X-Ray lithography  • Beats the diffraction limit of light,  minimum feature size around 5 nm
  17. 17.  Very slow. Takes over 10 hours to scan  across the entire surface of a wafer  • Very costly. One e-beam system costs  upwards of 5 to 10 MILLION dollars  • Potential problems with electron  scattering:  –Electron energy: 100eV -> very slow,  inefficient, damage the substrate  –Electron energy: 10eV -> lower  penetration depth and lower resolution
  18. 18.  S.M. Sze, Semiconductor Devices, Physics and Technology, Willey, 2002.  C.Y. Chang and S.M. Sze, Eds., ULSI Technology, McGraw-Hill, 1996.  S.M. Sze, Ed., VLSI Technology, McGraw-Hill, 1988.  Nguyễn Đức Chiến, Nguyễn Văn Hiếu, Công nghệ chế tạo mạch vi điện tử, NXB Bách khoa, 2007. 