Photolithography Terms and Definitions Page

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2. Description and Purpose
   1. Definitions for different lithography terms and other cleanroom jargon.
3. Definitions
   1. Photoresist
      1. A light sensitive material that can be used to form a patterned coating on a surface.
   2. Positive Resist
      1. A photoresist that becomes soluble to developer after exposure. Unexposed portions remain insoluble.
   3. Negative Resist
      1. A photoresist that becomes insoluble to developer after exposure. The unexposed portions are soluble.
   4. Dry Film Photoresist
      1. A photoresist that comes as a uniform thickness, semi-solid film on a polyester substrate and is applied through lamination, instead of being in a liquid form.
   5. Exposure
      1. Process of subjecting photoresist to intense light, or something else such as an electron beam, to create a desired pattern by chemically altering portions of it.
   6. Development
      1. After photoresist is exposed a chemical known as a developer is used to remove portions of the photoresist from the substrate.
   7. Etching
      1. The use of a liquid (wet) or plasma (dry) chemical agent to remove the uppermost layer(s) of the substrate in areas not protected by photoresist.
   8. Photolithography
      1. Pattern definition method which uses UV radiation to expose the resist; the most common lithography technique in semiconductor manufacturing. Advantages: exposes entire surface simultaneously, exact control over shape and size - Disadvantages: requires flat substrate, requires a mask
   9. Contact Lithography
      1. Form of photolithography in which the image to be developed is obtained by illumination of a photomask in direct contact with the photoresist coated substrate; Achieves higher resolution, but can damage both the mask and substrate.
   10. Proximity Lithograpy
       1. Similar to contact lithography, but a small gap is introduced between the mask and the substrate; Has lower resolution due to this gap and diffraction, but used more than contact lithography because it is not as damaging to mask and substrate.
   11. Projection Lithography
       1. Achieves higher resolution by projecting the pattern to be developed onto the substrate through a lens system. Highly used for IC production.
   12. Stepper
       1. A machine that uses projection lithography and a 'step-and-repeat' method to expose one small grid area of a wafer at a time and then moves on to the next until the entire wafer has been exposed.
   13. Electron beam lithography (e-beam)
       1. A beam of electrons scans across the surface of the resist exposing some areas and not others in a patterned fashion. Advantages: maskless, diffraction limit of light not a problem - Disadvantages: long exposure time, not good for high-volume production
   14. I-line
       1. Photolithography using 365 nm wavelength UV radiation for exposure.
   15. H-line
       1. Photolighography using 405 nm wavelength UV radiation for exposure.
   16. G-line
       1. Photolithography using 436 nm wavelength UV radiation for exposure.
   17. Absorption Coefficient
       1. Defines depth of penetration of a given medium with the light of a given wavelength; decreases as the wavelength shortens.
   18. HMDS
       1. A chemical compound often used as an adhesion promoter for photoresist. Full name is hexamethyldisilazane.
   19. MEMS
       1. Acronym for Microelectromechanical Systems. They are very small mechanical devices driven by electricity.