A New Phase in Imaging Finding the odd atom by Jason Han and Michael Kemeny

Hitchhiker’s Guide to Our Presentation Aims and Introduction to Phase Imaging Semiconductors Quantum theory Transmission Electron Microscope Phase Extraction using TEM Data Preparation and Errors The Results Jason Michael

Semiconductors and Phase Imaging Project partially funded by Semiconductor industry is highly interested in viewing dopant profiles at extremely high resolutions for: device evaluation control of production process Current techniques that allow this heavily involve Phase Imaging

Phase Retrieval and Holography Standard Sine Waveform

Phase Retrieval and Holography Phase can be found by electron holography / interferometry - Special technical requirements - Limited field of view - Phase retrieval using Transmission Electron Microscopy is much more flexible -Easily extends to many other areas including biological TEM

Transmission Electron Microscope Biofilter TEM

Semiconductors Silicon is typically used for chips and semiconductor devices Impurities are deposited in extremely small concentrations

Semiconductors - Semiconductors have a band structure -The introduction of dopants adds extra energy levels into gap

CMOS and Field-Effect Transistors Complementary Metal-Oxide Semiconductor Metal-Oxide-Semiconductor Field-Effect Transistor Source Drain Distribution of dopants in a transistor gate Used in Microprocessors, SRAM and other digital logic circuits. CMOS devices use much less power than other devices Terminals in Field-Effect Transistor are called gate, source and drain Typically made from SiO2

Wave Particle Duality of Electrons - Bohr’s Principle of Complementarity: an electron may behave as a particle or a wave in different circumstances, but never as both simultaneously The de Broglie equation (1923) assigns a wavelength to an electron

Rayleigh Criterion - The Rayleigh criterion shows that resolution is proportional to wavelength - Visible light has a wavelength of 400 – 700 nm.

An Overview of the TEM

Using the TEM Top right : Sample holder Above : Michael studying sample Left : Viewing Hole - Vacuum leaks may occur during insertion of specimen holder.

Aberrations and alignments - Diffraction patterns (Kikuchi lines) can be used to ensure sample is correctly aligned - The GIF filters out non-elastic electrons Above : Diffraction Pattern Top Right : Tim fiddling with knobs Right : Fluorescent Screen

What does phase represent? Normal TEM Imaging (Amplitude based) shows: - Mass-Thickness contrast - Diffraction contrast Phase contrast highlights: - Magnetic fields - Electrostatic fields - Topography Doping changes internal electric fields Electrostatic potentials can be viewed by Phase Imaging

Extracting the Phase Under focus Sample Objective Lens Focal Plane In Focus Over focus

Extracting the Phase Transport of Intensity Equation: Probability current is conserved between planes Phase map (thickness profile)

- Beam instability during data acquisition Cleaning up the mess MgO Crystal Underfocus In Focus Overfocus Phase Map High Band Pass Filtered Image FFT Masking - Alignment - Beam instability during data acquisition

The Results Silicon based transistor – source and drain region

The Results Section of Junction in Silicon Transistor

The Results Phosphorus Dopants

Comparing and Evaluating Phase image showing contrast in doped regions (A.C. Twitchett and P.A. Midgley) Phase image of transistors revealing souce and drain areas. (W.D. Rau et al.) Holographically reconstructed phase image of cross section of a field effect transistor. (H. Lichte) Our results of cross-section transistor phase image.

Conclusions and Consequences Semiconductors are doped with extremely small impurities and are used to make many modern electronic components Production needs control of accurate doping to nanometre scales Phase retrieval methods in Transmission Electron Microscopy is a promising technique to analyse semiconductor devices and help with accurate production The area still needs much more development, including resolving errors to do with contrast and Fourier transforms Combine or confirm results with other techniques such as off-axis electron holography Current research for Intel may result in such possibilities as correcting chip malfunctions, more efficient doping and consequently the next generation of semiconductor devices

Acknowledgements Lichte H. The Royal Society (March 2002), Electron Interference : Mystery and Reality, 360, 897 – 920. McMahon P.J., Barone-Nugent E.D., Allman B.E., Journal of Microscopy (June 2002) Quantitative phase-amplitude microscopy II: Differential interference contrast imaging for biological TEM. pp. 204 - 208 Nagayama K. and Danev R., Asia/Pacific Microscopy and Analysis (July 2003) Image Enhancement with Phase Plates in Electron-Phase Microscopy. MacCartney M.R. et al. Applied Physics Letters (April 2002), Quantitative analysis of one-deminesional dopant profile by electron holography 80:17 3213 – 3215 Rau W.D., Schwander P., Ourmazd A.,Phys. Stat. Sol. (March 2000) Two-Dimensional mapping of pn Junctions by Electron Holography 213 - 222 http://universe-review.ca We would like to thank Tim Petersen and Vicki Keast for all their input!