+Analysis of Anomalous Film Growth when Yttrium Oxide Thin Films are Exposed to 7.2eV Light

Alison WellsDr. David D. AllredDevon MortensonKristal Chamberlain

+Background

Group members took some samples to Berkeley for measurements using the Advanced Light Source.

When they got back needed to put it in the plasma cleaner. Why? Because there is a sort of “gunk”

composed mainly of hydrocarbons deposited on samples.

Problem: the plasma cleaner was broken.

Solution: Use the excimer (VUV) lamp instead.

+Background Continued

After approximately 5 minutes under the VUV lamp, the sample became visibly thicker.

Use ellipsometry measurements to determine if this is true.

The Mystery

+Ellipsometry Measurements: Y2O3Before cleaning: 24.94

nmAfter 5 min VUV: 31.061

nmGenerated and Experimental

Photon Energy (eV)1.0 2.0 3.0 4.0 5.0 6.0 7.0

Y in

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0 si_jaw 1 mm1 sio2_jaw 2.000 nm2 ema y2o3/30% void 24.733 nm3 polycarb 0.000 nm4 srough 0.500 nm

Generated and Experimental

Photon Energy (eV)1.0 2.0 3.0 4.0 5.0 6.0

Y in

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300Model Fit Exp Y -E 70°Exp Y -E 72°Exp Y -E 74°Exp Y -E 76°Exp Y -E 78°Exp Y -E 80°Model Fit Exp D-E 70°Exp D-E 72°Exp D-E 74°Exp D-E 76°Exp D-E 78°Exp D-E 80°

0 si_jaw 1 mm1 sio2_jaw 1.800 nm2 y2o3 constants based on 091130b on si 31.061 nm3 srough 0.500 nm

+In Search for an AnswerBig question is: What’s going on here?

+First Theories

First thought: the yttrium is not fully oxidized. Too thick

Is it possible that the VUV lamp is actually depositing material onto the sample? Not possible that more Y2O3 is being added to film.

Subject a blank silicon substrate to same VUV treatment and look for film deposition. No growth

+First Set of Conclusions

Oxidation of Silicon Substrate Thickness decreases in furnace

Only other option is that what is already on the film is somehow being altered.

It doesn’t seem likely that the VUV lamp is depositing material onto our film.

+Second theories and Tests (cont.)Necessity of VUV Interaction with Sample

+Second theories and Tests (cont.)Necessity of an ozone

+

Look at Neighboring OxideWhat would happen to a scandium oxide when exposed to same VUV treatment.

New Theories

+Comparing Oxides

May be slightly hydroscopic

Reactively Sputtered sample

Insoluble in water

Natural oxidation vs. reactive sputtering

Y2O3 Sc2O3

Water in the voids

+Ellipsometry Measurements: Natural Oxidized Sc2O3

Before VUV: 22.842 nm After 40 min: 23.310 nm

+Ellipsometry Measurements: Reactively Sputtered Sc2O3

Before Cleaning: 12.528 nm After 5 min VUV: 13.218 nm

+Ellipsometry Measurements: Reactively Sputtered Sc2O3

After 10 min VUV: 14.406 nm After 20 min VUV: 15.524 nm

+Ellipsometry Measurements: Reactively Sputtered Sc2O3

After 40 min VUV: 17.902 nm After 70 min VUV: 17.203 nm

+The Mystery Continues

Thicker Films

Use XPS to look at oxygen to metal ration

Observe other oxides

Deposit Silicon cap over samples

Future Work

+

Thank YouBrigham Young University Physics DepartmentDr. David D. AllredBYU Thin Film Optics Research Group