ERDA, for measurement of hydrogen in PV applications -- DERF 06/08 -- Presented by: Andrew Thomson Supervisor: Dr Keith McIntosh

Introduction Specialised form of ion beam analysis. Understand the role of H in passivation. Measuring SC dielectric coatings and silicon—dielectric interfaces, after various treatments. Overview:

Really what is ERD – fancy RBS Measurement of backscattered particle energy. Gives energy count and yield. Knowing “R cross-sections” give quantative measurement. Ernest Rutherford was born on August 30, 1871, in Nelson, New Zealand, the fourth child and second son in a family of seven sons and five daughters. His father James Rutherford, a Scottish wheelwright, emigrated to New Zealand with Ernest's grandfather and the whole family in 1842. His mother, née Martha Thompson, was an English schoolteacher, who, with her widowed mother, also went to live there in 1855. Rutherford married Mary Newton, only daughter of Arthur and Mary de Renzy Newton, in 1900. Their only child, Eileen, married the physicist R.H. Fowler. Rutherford's chief recreations were golf and motoring. He died in Cambridge on October 19, 1937. His ashes were buried in the nave of Westminster Abbey, just west of Sir Isaac Newton's tomb and by that of Lord Kelvin. Fifth level

Generalised ERD setup Forward scatter measured. Incident ion suppressed. Experimental cross-sections. RBS and ERD combined. Generally energy only is measured. Forward scatter uses as opposed to RBS, we’re measuring “sputtered” light ions not the energy of recoiling incident ion’s. To removed background noise of incident ion suppressed. Often with a foil but also… The foil has a much lower stopping power for low mass H ions. The foils almost completely filter any other ions that incident the detector. High energies >0.3 MeV RBS and ERD are almost always combined as the information can be combined to give a more completed picture of the sample being measured. ERD setup corresponds to a setup of theta being less than 90 degrees. There are various ranges of optimum angles for different setups

Resolution limits Detection limits: Comparative techniques: For an optimised sample 20 ppm, up to 1000nm depth. Comparative techniques: SIMS, similar resolution, better depth resolution. FTIR, measures bonds, unsure of resolution. Referenece:

The physics of ERD – descriptively Single atomic layer Multiple layers add spread Increased variance. Straggle lowers energy. Measured spectrum convolution of input spectrum with straggling function. The effect of straggling, single atomic layer, gaussian energy spread. I deal situation we’d measure a single atomic layer. Measuring real samples we have in effect a convoluton of single layer signal with the straggling function. The straggle is very easily modelled, by straggle introduced by the foil, detector, and increased stopping power of increased layers.

The physics of ERD – descriptively Example of an ideal RBS spectrum: Generalised two part dielectric on a substrate. Example of an actual silicon substrate.

Setup at ANSTO – Lucas Heights

Setup at ANSTO – Lucas Heights 3 MeV tandem accelerator with a He ion source So far we have used an incident power of 1.8 MeV. Mylar foil RBS: Θ = 170 °, β = 60 °, α = 70 °. ERD: Θ = 30 °, β = 80 °, α = 70 °.

RBS and ERD measurements RB Spectra of a TiO2 dielectric layer on. RB spectra detector only measures recoil of the incident He ions ERD spectra is fitered and is mostly showing H ions supttered from the sample, however at low energies there is a contribution of the incident ions. ERD specra Shows surface absorption of H

Modelling Spectrums Guess work: Experience needed: Layers. Energy per channel. Incident flux. Substrate. Experience needed: At the moment it seems that fitting is fairly abitary. With a few more decent runs I should be able to understand and calibrate better.

Modelling Spectrums – RBS TiO2

Modelling Spectrums – ERD TiO2 Stopping power much greater, lower channel peak corresponds to high energy He recoiled off Si Ti and O atoms

PECVD vs. TiO2 PECVD Optimised TiO2

Plans for PV applications of ERDA Hydrogen characterisation: Basic PV processing steps. PV dielectrics. Hydrogenated TiO2 Degradation processes. Other applications: Boron, and phos profiles. Densification of TiO2. Look at the resultant hydrogen conc, from PV type processes, for eg: diffusion, RCA, HF dip, oxidation, FG anneal, Alneal.