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.

Generalised ERD setup

Forward scatter measured. Incident ion suppressed. Experimental cross-sections. RBS and ERD combined. Generally energy only is

measured.

Resolution limits

Detection limits:• For an optimised sample 20 ppm, up to 1000nm depth.

Comparative techniques:• SIMS, similar resolution, better depth resolution.• FTIR, measures bonds, unsure of resolution.

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 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.

ERD specra Shows surface

absorption of H

Modelling Spectrums

Guess work: • Layers.• Energy per channel.• Incident flux. • Substrate.

Experience needed:

Modelling Spectrums – RBS TiO2

Modelling Spectrums – ERD TiO2

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.