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Photolithography

Photolithography. PEOPLE Program. How is Lithography Related to Computers?. Computer chips are made using photolithography Instead of drawing with a sharp tip, it uses light to transfer a tiny pattern from a photomask to a light-sensitive chemical. Packaging.

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Photolithography

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  1. Photolithography PEOPLE Program

  2. How is Lithography Related to Computers? • Computer chips are made using photolithography • Instead of drawing with a sharp tip, it uses light to transfer a tiny pattern from a photomask to a light-sensitive chemical Packaging Central Processing Unit (CPU)

  3. How is Lithography Related to Computers? Apple II An early personal computer Apple MacBook Air Modern laptop computer weighing only 3 pounds! ENIAC (Electronic Numerical Integrator and Computer) First general-purpose electronic computer 65 years… and many advances in photolithography!

  4. Photolithography • Role of the Resist: Light exposure changes solubility and allows mask formation • Applications: Making tiny, detailed stuff! For example, microelectronics, microfluidics, MEMS, bioanalytics, sensing, and many more • Main Benefit: High throughput! Geissler, et al. Adv. Mater.2004, 16, 1249-1269

  5. Exposure of Photosensitive Material to Light • What do you think “photosensitive” means?

  6. Exposure of Photosensitive Material to Light • What do you think “photosensitive” means? Faded Paint • Photosensitive materials react when exposed to light. • Examples: Suntan

  7. Transferring the Pattern: Make a Mask! Substrate that will “receive” the pattern Mask that controls the passage of light Silicon wafer Transparency with desired pattern

  8. Silicon Wafer Transferring the Pattern to the Silicon Wafer 1. Coat silicon wafer with photoresist Photoresist Mask 2. Tightly place mask on top 3. Expose to UV light Silicon wafer 4. Develop and Rinse ? Depends on the type of photoresist

  9. What it mean if something can dissolve?What does it mean if something can’t dissolve?

  10. What could be some examples of things that can dissolve in H2O?What could be some examples of things that cannot dissolve in H2O?

  11. Our definition Dissolve: A solid loses its structure and becomes dispersed into a liquid.* • Examples: • Table salt (NaCl) dissolves in water. • Sand (SiO2) does not dissolve in water. • Gasoline does not dissolve in water. • A breath-strip dissolves in your saliva. *Dissolving can take other forms, as well. For example a gas can dissolve into another gas, or a gas can dissolve into a liquid.

  12. Positive vs. Negative Photoresist • Positive Photoresist:Exposed areas become able to dissolve in the developer (so the exposed portion is dissolved by the developer) • Negative Photoresist:Exposed areas become not able to be dissolved in the developer (so the unexposed portion is dissolved by the developer) • We will use S-1813, a common positive photoresist

  13. Positive vs. Negative Photoresist 3. Expose to UV light POSITIVE Photoresist NEGATIVE Photoresist 4. Develop and rinse 4. Develop and rinse 5. Etch patterns into wafer 5. Etch patterns into wafer 6. Remove residual photoresist 6. Remove residual photoresist

  14. Positive vs. Negative Photoresist 3. Expose to UV light POSITIVE Photoresist NEGATIVE Photoresist 4. Develop and rinse 4. Develop and rinse 5. Etch patterns into wafer 5. Etch patterns into wafer Positive vs Negative Painting 6. Remove residual photoresist 6. Remove residual photoresist

  15. Make sure you get it! Fill in the blanks: In a _____ photoresist, _____ light reacts with the photoresist to make it unable to be dissolved, so it is rinsed away by the _____. 3. Expose to UV light POSITIVE Photoresist NEGATIVE Photoresist 4. Develop and rinse 4. Develop and rinse 5. Etch patterns into wafer 5. Etch patterns into wafer 6. Remove residual photoresist 6. Remove residual photoresist

  16. Review! What is cross-linking? Do you think that a substance that has a lot of cross-links would be more easily or less easily dissolved? Why do you think so?

  17. Bucky masks have been created for you Glass slides have been primed and coated S1813 photoresist You will be performing photolithography using these masks PEOPLE Program 2016 Your Name Today’s Activity: Photolithography Your Mask:

  18. UV Light  Resist Mask  2) Soft bake 1) Spin coat 3) Alignment and Exposure 5) Develop 4) Post-exposure bake 6) Hard bake 7) Inspect Today’s Activity: Photolithography

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