The Extraction Of Dielectric Functions Using an Ex-Situ Spectroscopic Ellipsometry Multisample Analysis Approach
Jennifer Rittenhouse
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07/28/2021
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After Fabricating 22 nanoscale thin films divided between two techniques, optical constants were extracted in this study.
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- [00:00:01.890]Hello, my name is Jennifer Rittenhouse,
- [00:00:04.150]and I'm a Physics Major attending Millersville University.
- [00:00:07.620]In this presentation, I will be discussing the extraction
- [00:00:10.390]of Dielectric Functions using an Ex-situ
- [00:00:12.750]Spectroscopic Ellipsometry Multi-sample Analysis Approach.
- [00:00:17.820]The means of how a material is deposited
- [00:00:20.070]when fabricating a thin film
- [00:00:21.730]can drastically alter its optical properties.
- [00:00:24.740]Deposition conditions and techniques alter how light
- [00:00:28.180]and energy interact with those material
- [00:00:31.560]that's being described by its optical constants
- [00:00:34.010]and bioelectric function, respectively.
- [00:00:36.830]By understanding and exploiting these method,
- [00:00:39.460]we can enhance the materials of our technologies
- [00:00:42.210]to make up our everyday life from optical switches,
- [00:00:45.460]chemical gas sensors, electrochromic smart windows,
- [00:00:48.810]and improve solar panels, to name a few examples.
- [00:00:55.080]Using two separate deposition techniques,
- [00:00:57.390]we fabricated 22 individuals thin films
- [00:01:00.380]divided between two separate experiments.
- [00:01:03.010]The thin films were measured
- [00:01:04.300]with the spectroscopic ellipsometer
- [00:01:06.490]in order to perform a multisample analysis.
- [00:01:09.520]The analysis was fitted to a model
- [00:01:11.790]and these optical constants
- [00:01:13.390]were compared with prior research literature.
- [00:01:17.660]For the first sample set,
- [00:01:18.880]we deposited Polymethyl methacrylate (PMMA),
- [00:01:22.190]onto silicon wafers using a deposition technique
- [00:01:25.290]called sol-gel spin coating.
- [00:01:27.420]Sol-gel spin coating is a deposition method,
- [00:01:29.920]where a centrifugal force spreads the material uniformly
- [00:01:33.350]across the substrate.
- [00:01:35.080]In our study, we pipetted four sets of PMMA solutions
- [00:01:38.770]with different density, and changed their rotation speed
- [00:01:42.560]in increments of 500 RPMs per sample.
- [00:01:49.580]For the second sample set, we used a magnetron sputterer.
- [00:01:53.193]A nanofabrication device,
- [00:01:54.790]where an ionized gas in a pressurized vacuumed chamber,
- [00:01:59.530]collides with negatively charged target material,
- [00:02:03.470]and then, sputters off onto a rotating substrate.
- [00:02:11.340]After collecting our samples, we measured our initial data
- [00:02:14.450]with the spectroscopic ellipsometer.
- [00:02:17.040]Spectroscopic ellipsometry or SE,
- [00:02:19.670]utilizes changes in polarized light
- [00:02:21.860]as it reflects off of sample,
- [00:02:23.810]which in turn measures its thicknesses
- [00:02:26.380]and optical constants.
- [00:02:32.660]Multi Sample Analysis, as the names suggests,
- [00:02:35.280]uses multiple samples, analyzing them simultaneously.
- [00:02:39.850]This approach allows one
- [00:02:41.390]to determine the thicknesses of samples
- [00:02:43.240]which might be difficult to normally resolve
- [00:02:45.810]because of how thin they are.
- [00:02:47.930]It is important to note that the samples must be
- [00:02:50.340]of different thicknesses, and that one can assume
- [00:02:53.040]that same dielectric function
- [00:02:54.650]for all the samples.
- [00:02:57.440]Upon analysis and systematic study of different model,
- [00:03:00.960]it was determined that the sample sets of PMMA,
- [00:03:03.940]most closely matched a Cauchy relation model.
- [00:03:07.080]We compared four different optical constant plots
- [00:03:10.050]with different densities
- [00:03:11.300]to that of available literature PMMA,
- [00:03:14.070]and found that 1.5 milligrams per milliliter density,
- [00:03:17.590]PMMA solution was comparable to the literature,
- [00:03:20.270]as shown in this graph.
- [00:03:23.580]Further analysis showed a relationship
- [00:03:25.750]between density and rotations per minute,
- [00:03:28.360]and the thickness of film in nanometer.
- [00:03:30.890]Atomic Force Microscopy was also performed
- [00:03:33.330]to examine the morphology of the sample.
- [00:03:39.730]Silicon Dioxide Film with varying deposition times
- [00:03:42.460]were measured with ellipsometry,
- [00:03:44.260]and their optical constants were successfully modeled.
- [00:03:47.090]Scanning electron microscope images
- [00:03:48.930]were also taken to examine surface
- [00:03:50.840]and roughness features.
- [00:03:53.100]The optical constants were also measured
- [00:03:55.090]for measuring the ellipsometric data
- [00:03:56.840]from silicon on top of silicon substrates.
- [00:04:01.030]In conclusion, we successfully fabricated PMMA thin films
- [00:04:05.160]using sol-gel spin-coating technique.
- [00:04:07.900]Using a magnetron sputterer device,
- [00:04:10.370]we fabricated thin films
- [00:04:12.070]of silicon dioxide and silicon, respectively.
- [00:04:15.570]As a systematic case study,
- [00:04:17.510]we performed PMMA thin-film depositions
- [00:04:20.120]of different densities
- [00:04:21.170]and extracted their optical constants.
- [00:04:24.150]We found that the change in density
- [00:04:25.770]results in the change of refractive index
- [00:04:28.090]as well as the thickness of PMMA thin films
- [00:04:30.300]for the same rotation speed.
- [00:04:32.400]By using spectroscopic ellipsometry data based
- [00:04:35.030]multisample analysis, we achieved the extraction
- [00:04:37.930]of optical constants together with thin film thicknesses.
- [00:04:41.980]Using scanning electron microscopy
- [00:04:44.220]and atomic force microscopy techniques,
- [00:04:46.470]we investigated the morphology
- [00:04:48.100]of fabricated thin films.
- [00:04:52.250]I would like to pay special acknowledgement
- [00:04:54.720]to the Schubert laboratory team,
- [00:04:57.220]who I worked alongside this summer
- [00:04:59.010]at UNL Research Laboratories,
- [00:05:01.420]with special emphasis on Ufuk Kilic,
- [00:05:04.440]who helped me to be able to understand
- [00:05:06.900]and operate the various machines that we use
- [00:05:09.280]for the fabrication techniques.
- [00:05:13.890]This is my poster.
- [00:05:15.150]I would also like to acknowledge, Dr. Adnan Adawi,
- [00:05:17.690]as well as Dr. Beilin Ma,
- [00:05:19.420]who wrote letters of recommendation,
- [00:05:21.250]as well as the National Science Foundation
- [00:05:23.300]for which I would not be here otherwise.
- [00:05:25.695]Thank you for your attention.
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