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

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

Procedure To determine the spin speed vs. thickness, we used Shipley photoresist and spun it on with varying dwell speeds:To determine the spin speed vs. thickness, we used Shipley photoresist and spun it on with varying dwell speeds: 3000 rpm5000 rpm 3500 rpm5500 rpm 4500 rpm6000 rpm

Analysis Once the resist was spun on, we took thickness measurements with the ellipsometer and profilometerOnce 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 thicknessOn 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 regionFor 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 With the ellipsometer, we took a series of measurements across the samples as shownWith 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.) Then portrayed against theoretical data, the experimental set looks accurateThen portrayed against theoretical data, the experimental set looks accurate

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 plasmaTo 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 WSummarized in this figure are our findings on etch rate vs duration at 125 W

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

Profilometer Mishap? (cont.) Possible reasons for the error werePossible 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 The ellipsometer data shows a good agreement with the Shipley data for the thickness as a function of spin rateThe 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 speedsThe 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.) The etch depth vs. etch time displayed a linear relationship.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