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Photoresist Characterization

Photoresist Characterization

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Photoresist Characterization

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  1. Photoresist Characterization Spin Speed vs. Thickness Nate Hamm, Steve Kelly, Brian MacFarland, John Yarbrough, Jeff Flint

  2. Introduction • Photolithography is an important procedure in semiconductor processing • For our processes in the lab, having the proper thickness coating is essential • This is controlled by the spin speed on the spin coater

  3. Procedure • To determine the spin speed vs. thickness, we used Shipley 1813+ photoresist and spun it on with varying dwell speeds: 3000 rpm 5000 rpm 3500 rpm 5500 rpm 4500 rpm 6000 rpm

  4. Analysis • Once the resist was spun on, we took thickness measurements with the ellipsometer and profilometer • On the ellipsometer we used two angle measurements to obtain the correct thickness • For the profilometer we first put a glass slide over part of the resist and used the RIE to etch the exposed region

  5. Thickness vs. Spin Speed • With the ellipsometer, we took a series of measurements across the samples as shown • This demonstrates the resist uniformity across the sample vs. spin rate

  6. Thickness vs. Spin Speed (cont.) • Then portrayed against theoretical data, the experimental set looks accurate

  7. Etch rate on RIE • To make measurements on the profilometer, we placed a slide over part of the photoresist and etched away the exposed portion with an oxygen plasma • Summarized in this figure are our findings on etch rate vs duration at 125 W

  8. Profilometer Mishap? • The data we gathered from the profilometer is not close to the theoretical set

  9. Profilometer Mishap? (cont.) • Possible reasons for the error were • Outside of optimal spin range • Uneven coating of the wafer by the photoresist • User error interpreting the data obtained by the profilometer • RIE etching process • Gnomes?

  10. Conclusions • The ellipsometer data shows a good agreement with the Shipley data for the thickness as a function of spin rate • The thickness was shown to be inversely proportional to the square root of the spin rate • The profilometer data did not agree well with either the ellipsometer data or the Shipley data, especially at low spin speeds • This may have been a result of uneven coating of the wafer by the photoresist or outside the optimal range

  11. Conclusions (cont.) • The etch depth vs. etch time displayed a linear relationship. • From this we found the etch rate for an oxygen plasma in the reactive ion etcher at 125 W to be 37.90Å/sec