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Photoresist Characterization. Spin Speed vs. Thickness Nate Hamm, Steve Kelly, Brian MacFarland, John Yarbrough, Jeff Flint. Introduction. Photolithography is an important procedure in semiconductor processing For our processes in the lab, having the proper thickness coating is essential

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Photoresist characterization

Photoresist Characterization

Spin Speed vs. Thickness

Nate Hamm, Steve Kelly, Brian MacFarland, John Yarbrough, Jeff Flint


Introduction
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


Procedure
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


Analysis
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


Thickness vs spin speed
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


Thickness vs spin speed cont
Thickness vs. Spin Speed (cont.)

  • Then portrayed against theoretical data, the experimental set looks accurate


Etch rate on rie
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


Profilometer mishap
Profilometer Mishap?

  • The data we gathered from the profilometer is not close to the theoretical set


Profilometer mishap cont
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?


Conclusions
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


Conclusions cont
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


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