Technology for Micro- and Nanostructures Micro- and Nanotechnology

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1 Lecture 5: Electron-Beam Lithography, Part 1 Technology for Micro- and Nanostructures Micro- and Nanotechnology Peter Unger mailto: uni-ulm.de Institute of Optoelectronics University of Ulm Copyright 2012 by Peter Unger Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 1/26 Outline of Lectures 5 and 6: E-Beam Lithography Part 1, Lecture 5 Basic Principle of Electron-Beam Lithography The Electron-Optical Column Lens Errors and Beam Size Mark Registration Field Overlay and Stitching Part 2, Lecture 6 Physics of Lenses for Electrons Scatter Effects of Electron Beams The Proximity Correction Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 2/26

2 Basic Principle of Electron-Beam Lithography Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 3/26 Basic Principle of Electron-Beam Lithography Electron Source is Demagnified onto Substrate using Electron Optics Electron Beam is Scanned by a Deflection Unit Electron Beam can be Switched On and Off Very Fast Using a Beam-Blanking Unit Substrate is Located on an Interferometrically Controlled Stage The Whole Wafer is Exposed by Stitching of Deflection Fields Writing Strategy Within a Deflection Field Raster Scan Vector Scan (Writing of Individual Shapes) Flyback (TV like) Spiral Meander (Boustrophedonic) Shaped Beam Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 4/26

3 Vector Scanning and Raster Scanning A Deflection Field is Typically Addressed by 14 bit (16 384) Resolution. Resolution 100 nm 50 nm 25 nm Deflection Field Size 1.6 mm 0.8 mm 0.4 mm Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 5/26 Writing Strategies for the Shapes The Signals for Beam Deflection to Write the Vector Shapes are Generated by a Digital Pattern Generator. Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 6/26

4 The Digital Pattern Generator The Digital Pattern Generator Mainly Consists of Programmable Counters. The Input Data for the Pattern Generator are Usually the x y Coordinates of the Lower Left and the Upper Right Corner of the Rectangle and the Exposure Frequency. At a Given Beam Current, the Exposure Frequency Determines the Exposure Dose. Output Signals of the Digital Pattern Generator. x and y Deflection Signals. Signal for the Beam-Blanking Unit. Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 7/26 The Electron-Optical Column Electron Source Beam Blanker One or Two Condensor Lenses Objective Lens Beam-Deflection Unit Electron Detectors Substrate Stage Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 8/26

5 Electron-Beam Sources Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 9/26 Comparison of Electron-Beam Sources Tungsten Tip LaB 6 Cathode Field Emitter Minimum Spot Size 5 nm 2.5 nm 1 nm Beam Current A A A Lifetime 30 h 100 h > 1000 h Operating Temp K 2000 K Room Temp. Operating Pressure < 10 5 mbar < 10 6 mbar < mbar Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 10/26

6 Focal Length of and Electron Lens For an Electron Lens, the Focal Length f is not Fixed. It can be Adjusted by the Current Through the Lens Coils. Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 11/26 Blanking Unit for the Electron Beam Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 12/26

7 Condensor and Objective Lenses Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 13/26 Basic Equations for a Thin Lens Magnification: M = S I /S O S I Size of Image, S O Size of Object Ray Equation: M = S I /S O = d I /d O d I Distance Lens to Image, d O Distance Lens to Object Basic Lens Equation: 1 f = d I d O Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 14/26

8 Condensor and Objective Lenses Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 15/26 Electron-Beam Deflection Unit Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 16/26

9 Geometry of an Electron-Optical Column Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 17/26 Lens Errors in Electron-Beam Optics Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 18/26

10 Aberation and Diffraction of an Objective Lens Resolution δ δ min Diffraction δ ~ 1/α Sum of Diffraction and Spheric Aberation Spheric Aberation δ ~ α 3 α opt Beam Divergence Angle α Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 19/26 Spot Size (Resolution) of the Electron Beam Beam Parameters U = 100 kv I = 0.1 na α = 3 mrad Objective Lens d I = 5 mm d O = 25 mm Gold Film Consisting of Small Islands on Carbon Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 20/26

11 Mark Registration by Pattern Recognition Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 21/26 Coordinate-System Transformation Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 22/26

12 Linear Deflection Errors Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 23/26 Digital Correction Unit for Deflection Errors Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 24/26

13 Control Electronics for E-Beam Lithography Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 25/26 Further Reading Henry I. Smith Submicron- and nanometer-structures technology, 2nd edition Lecture 4, Electron Optics and the TEM Lecture 5, Scanning Electron Beam Systems Lecture 14, Electron-Beam Lithography Lecture 15, Electron Scattering and Proximity Effects NanoStructures Press, 437 Peakham Road, Sudbury, MA 01776, USA 1994 Peter Unger, Technology for Micro- and Nanostructures Lecture 5: Electron-Beam Lithography, Part 1, Version of November 28, 2012 p. 26/26