ECE6450L7-Optical Lithography

ECE6450L7-Optical Lithography - Lecture 7 Lithography and...

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ECE 6450 - Dr. Alan Doolittle Georgia Tech Lecture 7 Lithography and Pattern Transfer Reading: Chapter 7
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ECE 6450 - Dr. Alan Doolittle Georgia Tech Used for Pattern transfer into oxides, metals, semiconductors. 3 types of Photoresists (PR): 1.) Positive : PR pattern is same as mask. On exposure to light, light degrades the polymers (described in more detail later) resulting in the photoresist being more soluble in developers. The PR can be removed in inexpensive solvents such as acetone. 2.) Negative : PR pattern is the inverse of the mask. On exposure to light, light polymerizes the rubbers in the photoresist to strengthen it’s resistance to dissolution in the developer. The resist has to be removed in special stripping chemicals. These resists tend to be extremely moisture sensitive. 3.) Combination : Same photoresist can be used for both negative and positive pattern transfer. Can be removed in inexpensive solvents. Lithography and Photoresists Mask Pattern Pattern transferred to the Photoresist on the wafer Positive PR Light Negative PR Light
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ECE 6450 - Dr. Alan Doolittle Georgia Tech Photoresists are used in a process typical of this process: Dehydration Bake, Apply Adhesion Promoter, Apply Resist, Soft bake, Exposure with Mask, Post Exposure Bake, Develop, Optional Processing. For example: 1.) Dehydration in an oven at ~120 degrees C for as long as 30 minutes 2.) Spin coat (verbally explain) adhesion promoter such as hexamethyldisilane (HMDS) 3.) Spin coat resist 4.) Soft bake to partially solidify PR (85-95 degrees C for 1 to 30 minutes depending on the resist) 5.) Expose to few hundred mJoules/cm 2 of high energy light 6.) (Optional) Hard bake, removes more solvent (~110-150 C) 7.) Develop: weak regions of PR dissolved 8.) Additional Hard bake or chemical treatment to harden PR for aggressive processes such as Ion implantation or Plasma etching Lithography and Photoresists More details at the Gt microelectronics teaching lab web page: http://www.ece.gatech.edu/research/labs/vc/
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ECE 6450 - Dr. Alan Doolittle Georgia Tech 1.) Etching Processes: open windows in oxides for diffusion, masks for ion implantation, etching, metal contact to the semiconductor, or interconnect. 2.) Lift off Processes: Metalization (more common in III-V). Uses of Lithography: Wafer Metal, Oxide, etc… Photoresist Wafer Metal, Oxide, etc… Wafer Wafer Spin PR Lithography Etch Layer using PR as Mask Remove PR Wafer Photoresist Wafer Wafer Metal Wafer Metal Spin PR Lithography Evaporate Metal Lift Off excess metal with PR
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ECE 6450 - Dr. Alan Doolittle Georgia Tech 1.) Resolution : How small of features can you make.
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This note was uploaded on 08/23/2011 for the course ECE 6450 taught by Professor Doolittle during the Fall '10 term at University of Florida.

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ECE6450L7-Optical Lithography - Lecture 7 Lithography and...

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