6. Photolithography
Photolithography is the transfer of patterns, circuits, device structures, etc. to a substrate or wafer using light and a mask or stencil to stop the light.
Photolithography was used extensively in the progression of microelectronics.
Today, because of the sizes involved in current computer microprocessor devices, other methods like direct patterning using electron beams are used.
Photolithography is still used for dimensions down to about 0.5um. The wavelength of UV light is um.

7. Starting material is a 100mm (4 inch) wafer of silicon - shown in an edge view

8. Wafers are cleaned first

9. Silicon Dioxide (SiO2 ) is grown on the silicon creating a dielectric or insulating layer

10. High temperature tube furnace for the formation of silicon dioxide (SiO2)

11. A conductor metal (student choice) is vacuum deposited on to the wafer

12. CVC 601-sputter deposition
Conductor vacuum deposition tools in the ECE Microelectronics Clean Room
Cooke-thermal deposition
CVC 601-sputter deposition
CHA Mark 50 e-beam deposition
Varian 3125 e-beam deposition

13. UV light sensitive material called photoresist is spin coated on to the conductor side of the wafer

14. Light sensitive material is stored in amber dropper bottles – Use 1813
Wafers are spin coated with Shipley 1813 UV sensitive photoresist spin coating produces a uniform coating
Spin speed is set here
Light sensitive material is stored in amber dropper bottles – Use 1813
A vacuum chuck holds the wafer

15. The antenna design, arrayed on a transparency sheet, is placed on top of the wafer. This transparency is called a photo mask. Production photo masks would be made on glass plates with high precision patterns.

16. The array of antenna will be cut to just larger than the wafer
The antenna pattern, arrayed and printed on a transparency paper, is used as a mask
The array of antenna will be cut to just larger than the wafer

17. Ultraviolet light is projected down on to the photoresist coated wafer

18. HTG mask aligner and UV light source The UV light source is a mercury vapor lamp at 436nm wavelength
UV light with filter surrounding it
Clear glass plates are used to make sure the transparency lays flat to the wafer
Exposure time set on timer
Wafer is held by vacuum, mask is placed on top and brought into contact with wafer

19. The wafer is developed, leaving photoresist where no UV light has penetrated the mask

20. Solitec automatic developer
Vacuum switch
Start switch

22. Conductors are etched using chemicals specific to the metal
Gold, silver, nickel, and copper etch
Chrome etch
Aluminum etch

23. After etching, the antenna pattern, in the conductor of choice, will be left on the wafer

24. In the clean room Complete one wafer first
Determine the number of complete antennas on the wafer. Partial antenna can not be counted. Record this number. It is needed for the cost analysis.
Evaluate cost – cost analysis will be next lesson
Redesign if appropriate

25. Homework Find Excel and PowerPoint programs on Mosaic
Begin learning how to use both programs
A cost analysis for your antenna design will be due shortly
Your project presentation will be done on PowerPoint