1. Microfabrication Nathaniel J. C. Libatique, Ph.D. nlibatique@gmail.com

2. Sze, Semiconductor Devices, John Wiley and Sons Process Steps Start with polished wafers of chosen  and crystal orientation Films: epitaxial, thermal oxides, polysilicon, dielectrics, metals Doping: via diffusion or ion implantation Lithography: shadow masked or projection Etching: Wet and Dry Sequential Mask Transfer Stepper Iteration

3. Sze, Semiconductor Devices, John Wiley and Sons Wafer  Die  Device

4. Ingredients Clean Rooms Exposure Techniques Masks Photoresist Pattern Transfer Etching

5. Clean Room Technology Sze, Semiconductor Devices, John Wiley and Sons 1.Pinholes 2.Constriction of I 3.Short ckt Epitaxy: Dislocations Gate Oxide: Low V b Rule of Thumb: particles greater than 1/10 of L min is disruptive. L min = 5  m requires < 0.5 micron dust particles

6. Clean Room Technology Dust count should be four orders of magnitude lower than ordinary room air. Class 100: 100 particles (half micron or greater) per cubic foot = 3500 particles per cubic meter If we expose a 125 mm wafer for 1 minute to a laminar flow air stream at 30 m/min, how many dust particles will land on the wafer in a class 10 clean room? Sze, Semiconductor Devices, John Wiley and Sons

7. Particle Emission Sze, Semiconductor Devices, John Wiley and Sons

8. Clean Room Classes

9. Keep critical areas very small Keep critical areas very small Separate working areas Separate working areas Slight overpressure in white areas Slight overpressure in white areas Laminar flow boxes in poor air quality areas Laminar flow boxes in poor air quality areas Design

10. Comb Structure White area for wafer and chip processing

11. Ball Room Structure “HEPA filter” = high efficiency particulate air filter, Ceiling to floor laminar flows, Perforations in floor Ceiling Floor

12. Exposure Sze, Semiconductor Devices, John Wiley and Sons

13. Goals Resolution Resolution Registration Registration Throughput Throughput  Yield and cost, complexity- function, power dissipation, speed

14. Shadow Printing l m ~ ( g) 1/2 l m ~ ( g) 1/2 the gap g includes the resist layer the gap g includes the resist layer = 0.4 um, g = 50 um, 4 um = 0.4 um, g = 50 um, 4 um = 0.25 um, g = 15 um, 2 um = 0.25 um, g = 15 um, 2 um Dust dimensions > g can damage the mask! Dust dimensions > g can damage the mask!

15. Projection Printing Avoids mask damage Avoids mask damage To increase resolution  image a small portion at a time To increase resolution  image a small portion at a time Large masks followed by 10:1 demag or Large masks followed by 10:1 demag or 1:1 masks 1:1 masks Tradeoff: defect free masks vs. simpler optics Tradeoff: defect free masks vs. simpler optics

16. Annular Field Scan Sze, Semiconductor Devices, John Wiley and Sons

17. Small-Field Raster Scan Sze, Semiconductor Devices, John Wiley and Sons

18. Reduction Step and Repeat Sze, Semiconductor Devices, John Wiley and Sons

19. 1:1 Step and Repeat Sze, Semiconductor Devices, John Wiley and Sons

20. Resolution and DOF

21. http://en.wikipedia.org/wiki/F-number f/# = f/D f/32 f/5 D f

22. D f 

23. CAD used to generate mask artwork Secondary chip sites for process evaluation as well as for alignment- registration Mask defect density is a concern in mask fabrication

24. Yield vs Defect Density Semicon’s Dirty Secret Y ~ e -DA for one mask level For multiple mask levels: Y ~ e -NDA

25. Photolithography

26. Response Curve Vertical axis: % Remaining after exposure and development Vertical axis: % Remaining after exposure and development Horizontal Axis: Exposure Horizontal Axis: Exposure Solubility increases with exposure for a positive resist ETET Completely soluble. Measure of sensitivity for +ve resist 100% E1E1

27. Negative resist – cross linked polymers insoluble Positive resist – exposed areas become soluble E T = threshold energy, E 1 drawn from tangent at E T (+ve) Finite Solubility

28. Post-Etch

29. gamma = solubility with incremental energy increase, contrast ratio, sharpness

30. Negative resists: lower exposure times due to higher sensitivity  high throughput Negative resists: lower exposure times due to higher sensitivity  high throughput Positive resists: does not swell significantly unlike negative resists  high resolution Positive resists: does not swell significantly unlike negative resists  high resolution CRM Grovenor, Microelectronic Materials

31. Sites http://jas.eng.buffalo.edu/education/fab/NM OS/nmos.html http://jas.eng.buffalo.edu/education/fab/NM OS/nmos.html http://jas.eng.buffalo.edu/education/fab/NM OS/nmos.html http://jas.eng.buffalo.edu/education/fab/NM OS/nmos.html http://www.ecse.rpi.edu/~schubert/Course- ECSE-6290 http://www.ecse.rpi.edu/~schubert/Course- ECSE-6290 http://www.ecse.rpi.edu/~schubert/Course- ECSE-6290 http://www.ecse.rpi.edu/~schubert/Course- ECSE-6290 http://www.nikon.com/about/technology/core /optical_u/evanescent_e/index.htm http://www.nikon.com/about/technology/core /optical_u/evanescent_e/index.htm http://www.nikon.com/about/technology/core /optical_u/evanescent_e/index.htm http://www.nikon.com/about/technology/core /optical_u/evanescent_e/index.htm