TSOM: R&D 100 Award Winner TSOM Method for Nanoelectronics Dimensional Metrology Ravikiran Attota Nanoscale Metrology Group Physical Measurement Laboratory National Institute of Standards and Technology Gaithersburg, USA *TSOM is pronounced as “tee -som ” ; A latest presentation on TSOM can be found here. Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Contents What is TSOM ? Method to construct TSOM images Characteristics of TSOM images Applications 2 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
TSOM: Through-focus Scanning Optical Microscopy TSOM transforms conventional optical microscopes into three-dimensional metrology tools with nanometer scale measurement sensitivity Not an image resolution enhancement method 3 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
TSOM: Through-focus Scanning Optical Microscopy Analysis in lateral and vertical directions as large as over 50 m. Requirement for defining the "Best Focus" is eliminated. 4 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
How does TSOM achieve this? • By using a set of through-focus images instead of one “best focus” image • Going beyond edge-based imaging • Using the image as a signal/dataset 5 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Requires a TSOM Image 6 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Animation showing the TSOM image construction method using a conventional optical microscope 2D optical Schematic Optical intensity Optical images at showing through- profiles extracted Constructed TSOM Microscope different focus scanning of from the optical image using the through-focus optical intensities the target images positions Digital camera Motor for focusing Color scale represents the optical intensity Computer Computer algorithms process acquires multiple the acquired digital images digital images of and produce the TSOM targets images 7 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Simulation Differential TSOM images are distinct for different dimensional variations Isolated Si line on Si substrate; = 546 nm; LW = 40 nm; LH = 100 nm Linewidth Line height LW40-LW41 LH100-LH101 Isolated line Line width and height Sidewall angle LW40LH100-LW41LH101 SW89-SW90 LW=Linewidth; LH=Line height; SW=Sidewall angle 8 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Differential images appear similar for small Simulation changes in the same dimension Difference = 2 nm Difference = 4 nm LW100-LW102 LW100-LW104 difference Linewidth MSD= 10 x10 -6 MSD= 35 x10 -6 LH100-LH102 LH100-LH104 Line Height difference MSD= 11 x10 -6 MSD= 37 x10 -6 Linewidth difference = 2 nm 2 2 (TSOM Image1 – (TSOM Image1 – TSOM Image2 ) TSOM Image2 ) 9 MSD MSD = Total number of pixels Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Characteristics of TSOM images: Summary • TSOM images change with target (assumed to be unique). • Differential TSOM images • Highlight nanometer scale dimensional differences using a conventional optical microscope. • Appear distinct for different dimensional change (breaks the correlation between parameters, e.g., height and width, in the optical signal). • Are additive. • Appear qualitatively similar for a change in the same dimension. • Integrated optical intensity of differential TSOM image indicates the magnitude of the dimensional difference. • TSOM images are (assumed to be) unique. • Robust to optical aberrations and illumination variations. • Good quantitative agreement between measurement and simulation is not established yet. • Trends observed in simulations generally match measurements. 10 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Two Applications Evaluate Determine differences in dimensions dimensions of a target • Requires a library of either Accurate simulations • Requires two targets or Measurements • Simulation is not necessary but useful • Requires good agreement between measurement and simulation • TSOM images are assumed to be unique 11 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Some Example applications of the TSOM method Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Experiment Simulation to Experiment comparison Line gratings Simulation Experiment (a) (b) Linewidth = 152 nm, Line height = 230 nm, Pitch = 601 nm, Wavelength = 546 nm, Si line on Si substrate. 13 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Experiment Simulation to Experiment comparison Differential TSOM images for 3 nm difference in the line width Simulation Experiment 14 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Experiment Experimental line width determination using simulated library Determining the dimension using Experimental TSOM image the library matching method MSD MSD TSOM Matched target line width : 153 nm AFM measured line width: 145 nm 15 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Size determination of nanodots (nanoparticles, quantum dots) using experimental library Experiment SEM image of 121 nm nanodot Experimentally created library. MSIx10 -6 MSIx10 -6 Experimental TSOM image of SEM measured size = 103 nm 121 nm nanodot = 546 nm. TSOM measured size = 106 nm Si nanodot on Si substrate. 16 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Experiment Experimental defect analysis of four types of 10 nm defects in dense gratings Pitch = 270 nm, Linewidth = 100 nm, = 546 nm Every 10 th line Every 10 th line Every 5 th line Every 5 th line smaller by 10 nm larger by 10 nm smaller by 10 nm larger by 10 nm 6 (d) (a) (b) (c) Through Focus Distance, m 5 4 3 2 1 0 0 2.5 5.0 0 2.5 5.0 0 2.5 5.0 0 2.5 5.0 Distance, m 17 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Simulation Defect analysis: Random structure Detected 25 nm defect that is 25 nm tall, (one fourth the height of the features) 25 nm Defect Cross section X-Z plane X-Z plane Defect Defect Y-Z plane Y-Z plane (XZ-plane reversed) Defect size: 25 nm, Defect height = 25 nm; Linewidth of the features= 100 nm, Line height =100 nm Wavelength = 365 nm, Si features on Si substrate 18 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
3D Metrology Simulation High aspect ratio through silicon via (TSV) dimensional analysis TSV Diameter = 5 m, Depth = 25 m, = 546 nm 5.0 m 25.0 m 20 nm change in 20 nm change in the depth the diameter 19 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Photo mask application: Simulation Transmission microscope Optimization of Illumination NA to obtain maximum sensitivity Photo mask Chrome Simulated TSOM image Quartz target Chi Square, x10 -6 Chi Square, x10 -6 Dimension Dimension Diff. Diff. INA INA MSD MSD (nm) (nm) UP UP TE TE TM TM Line width Line width 2 2 0.1 0.1 9.5 9.5 15.7 15.7 6.6 6.6 Line width Line width 2 2 0.6 0.6 2.0 2.0 2.9 2.9 1.5 1.5 Line height Line height 2 2 0.1 0.1 4.3 4.3 4.0 4.0 5.8 5.8 Line height Line height 2 2 0.6 0.6 0.6 0.6 1.0 1.0 0.5 0.5 For line width measurements select low INA and TE polarization For line height measurements select low INA and TM polarization Line width = 120 nm, Line height = 100 nm, Wavelength = 365 nm, UP=Unpolarized, TE=TE polarized, TM=TM polarized, 20 MSD=Mean Square Difference Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Experiment Thin film metrology Simulation Intensity normalized TSOM images at the edge of thin films for different film thickness 1 nm 2 nm 3 nm Film Thickness Area of analysis Calibration curve to measure films of unknown thickness 21 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Simulations Overlay Targets for Double Patterning Experiment First process -4 -2 0 2 4 Second process OL=0 nm OL=2 nm Mean Square Difference Measured TSOM Image Determination of the overlay value using the target 22 Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
Simulation Monitoring/Measuring Nanoscale Movements for MEMS/NEMS Devices Fixed frame Fixed frame Moving part Moving part A simplified schematic of a MEMS device (fabricated at NIST) containing inner 20 mx20 m 20 m 20 m 20 m 20 m movable part and the outer fixed frame. Every 30 m 30 m time the device is powered the inner part moves 10 nm to the right side relative to the outer frame. Calibration Curve 30 m 30 m Mean Intensity difference as a function of movement Differential TSOM image showing 10 nm movement of the inner part MD 23 Wavelength = 546 nm Ravikiran Attota, Frontiers of Metrology, Grenoble, May 24 2011
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