Scanning Microwave Microscopy December 15, 2010 Page 1 Agilent Technologies Agilent Technologies Scanning Microwave Microscopy (SMM Mode) Electromagnetic materials characterization at high spatial resolution

Scanning Microwave Microscopy December 15, 2010 Page 2 Overview SMM System – PNA with AFM Features and Benefits Microwave Network Analyzer Basics (VNA) System overview Calibrated capacitance & dopant density Beyond SCM, what can be done with SMM - Applications Biological samples Thin films and coatings Quantum dots/quantum structures Summary

Scanning Microwave Microscopy December 15, 2010 Page 3 Features & Benefits Provides exceptionally high spatial electrical resolution Offers highest sensitivity and dynamic range in the industry SMM facilitates –Complex impedance (resistance and reactance) –Calibrated capacitance –Calibrated dopant density –Topography measurements Works on ALL semiconductors Si, Ge, III-V and II-VI Does not require and oxide layer Operates at multiple frequencies (variable up to 18GHz)

Scanning Microwave Microscopy December 15, 2010 Page 4 What is a Vector Network Analyzer? Vector network analyzers (VNAs)… Are stimulus-response test systems Characterize forward and reverse reflection and transmission responses (S-parameters) of RF and microwave components Quantify linear magnitude and phase Are very fast for swept measurements Provide the highest level of measurement accuracy S 21 S 12 S 11 S 22 R1 R2 RF Source LO Test port 2 B A Test port 1 Phase Magnitude DUT Reflection Transmission

Scanning Microwave Microscopy December 15, 2010 Page 5 High-Frequency Device Characterization Transmitted Incident TRANSMISSION Gain / Loss S-Parameters S 21, S 12 Group Delay Transmission Coefficient Insertion Phase Reflected Incident REFLECTION SWR S-Parameters S 11, S 22 Reflection Coefficient Impedance, Admittance R+jX, G+jB Return Loss   Incident Reflected Transmitted R B A A R = B R =

Scanning Microwave Microscopy December 15, 2010 Page 6 Scanning Microwave Microscopy (SMM) Basic Idea Tip and sample form a capacitor Measuring C yields  r C =  0  r A/d Actuator Capacitance C ~ fF Capacitance bridges too slow Integration times of several seconds not practical for imaging

Scanning Microwave Microscopy December 15, 2010 Page 7 System Overview Coaxial cable Network Analyzer Network analyzer sends an incident RF signal to the tip through the diplexer RF signal is reflected from the tip and measured by the Analyzer Magnitude & phase of the ratio between the incident & reflected are calculated Apply a model to calculate the electrical properties AFM scans and moves tip to specific locations to do point probing Scanning AFM in X and Y and Z (closed loop)

Scanning Microwave Microscopy December 15, 2010 Page 8 Compatible with Agilent 5420 & 5600LS AFM/SPM 5420 AFM 5600LS AFM

Scanning Microwave Microscopy December 15, 2010 Page 9 Sub 7 nm Conductive tip development Alumina Carrier Agilent Precision Machining and Process Technologies to deliver RF/MW to the conductive tip Pt/Ir Cantilever

Scanning Microwave Microscopy December 15, 2010 Page 10 Simultaneous Imaging of Topography, Capacitance, and dC/dV

Scanning Microwave Microscopy December 15, 2010 Page 11 PNA Controls from PicoView

Scanning Microwave Microscopy December 15, 2010 Page 12 Calibration staircase sample (collaboration with National Institute of Standards and Technology, NIST) 10 micron Gold caps on SiO 2 „staircase“ on Si. AFM topography 3D view (left) and schematic overview (right). Capacitance calibration C2 C1 Transfer Function: S11 signal [dB]  capacitance [F]

Scanning Microwave Microscopy December 15, 2010 Page dB 10µm Sample: „NIST2“ staircase with goldcaps Capacitance Calibration Capacitance (amplitude) C2 C1

Scanning Microwave Microscopy December 15, 2010 Page 14 Capacitance Calibration

Scanning Microwave Microscopy December 15, 2010 Page 15 Enhancing the Sensitivity DPMM approach: Use the Flatband transfer function as AM mixer to modulate the reflected MW signal at the rate of drive frequency (<100 KHz). The AM modulation amplitude is function of the dopant density.

AB LO A/D Source Probetip Sample Scanner Coupler Wave- guide Agilent PNA AFM Agilent DPMM LF AC Bias LF Demodulator dC/dV Module Imaging Dopant Density December 15, 2010 Page 16 Scanning Microwave Microscopy

December 15, 2010 Page 17 Dopant Density calibration with IMEC Standard Si Wafer Deposit Layers with Various Doping Levels Cleave or polish from top to expose the layers Density (/cm³) Depth [µm] Resistivity [Ωcm] Spec sheet IMEC calibration sample edge bulk

Scanning Microwave Microscopy December 15, 2010 Page 18 Dopant Density calibration with IMEC Standard dC/dV Amplitude bulk edge

Scanning Microwave Microscopy December 15, 2010 Page 19 Images of an SDRAM Very high sensitivity Can see semiconductor, insulators and conductors Can be calibrated Can also get inductance and reactance Topography Capacitance dC/dV Images of SDRAM chip acquired with SMM Mode. The underneath n-type (bright) and p-type doped structure clearly indentified in both capacitance and dC/dV Images (W.Han)

Scanning Microwave Microscopy December 15, 2010 Page 20 SMM Images of SRAM Chip Topography (A and C) and dC/dV (B and D) images of SRAM. C and D are zoomed scans on one of the transistors in the n well marked in the blue square in A / B. A very fine line feature of 10 to 20 nm in width can be seen in the dC/dV image, as pointed in D, indicating high resolution capability of the scanning microwave microscope.

Scanning Microwave Microscopy December 15, 2010 Page 21 Simultaneous Images of SRAM Chip Simultaneous topography (A), capacitance (B), and dC/dV (C) images of an SARM chip. Alternating lightly doped p and n wells are clearly identified in both capacitance and dC/dV images. Five of the six transistors in a unit cell are marked in B and C.

Scanning Microwave Microscopy December 15, 2010 Page 22 Dopant on SiGe Topography (left) capacitance (middle) and dC/dV (right) images of a dpoed SiGe device acquired with Scanning Microwave Microscopy (SMM). Both capacitance and dC/dV images showed dopant structure not seen topography.

Scanning Microwave Microscopy December 15, 2010 Page 23 InGaP/GaAs Transistor Topography (left) and impedance (right) images of a cross section of a InGaP/GaAs hetrrojunction bipolar transistor. Different regions from the emitter to the subcollector with different dopant levels were clearly resolved in the impedance image. (W. Han sample courtesy of T. Low)

Scanning Microwave Microscopy December 15, 2010 Page 24 Semiconductor Failure Analysis Optical image of a small section of the tested SRAM chip. The failed bit contains an n-type FET (the 48th on that row) with an abnormal Vt. Four sets (A, B, C, and D) of scanning microwave microscopy images on the failed SRAM chip. Each set contains topography (top), dC/dV (middle), and VNA amplitude (bottom) images acquired simultaneously. The red squares outlined the failed 48th n-type FET, the blue squares are normal n FETs on the same row.

Scanning Microwave Microscopy December 15, 2010 Page 25 Bacteria Cells Topography (left) and impedance (right) images of dried bacteria cells. (W. Han, Sample courtesy of N Hansmeier, T. Chau, R.Ros and S. Lindsay at ASU)

Scanning Microwave Microscopy December 15, 2010 Page 26 Summary Characterization of electromagnetic materials at High spatial resolution Offers highest sensitivity and dynamic range in the industry Complex impedance Sidewall diffusion –Calibrated capacitance – unique –Calibrated dopant density – unique Works on ALL semiconductors Si, Ge, III-V and II-VI Does not require and oxide layer Operates at multiple frequencies (variable up to 18GHz)

Scanning Microwave Microscopy December 15, 2010 Page 27 Back-up Slides Scanning Microwave Microscopy

December 15, 2010 Page 28

Scanning Microwave Microscopy December 15, 2010 Page 29 Scanning only qualitative poor sensitivity limited Atoms/cm3 No Conductors/Insulators

Scanning Microwave Microscopy December 15, 2010 Page 30 Lightwave Analogy to RF Energy RF Incident Reflected Transmitted Lightwave DUT

Scanning Microwave Microscopy December 15, 2010 Page 31 Standard Vector Network Analyzer as a reflectometer Highly resistive load High SNR Low Resolution Low resistive load High SNR Low Resolution Load close to 50 Ohms Low SNR High Resolution Figure 1: reflection coefficient vs.. impedance A B LO A/D Source Probe Very small capacitor High SNR Low Resolution

Scanning Microwave Microscopy December 15, 2010 Page 32 Simplified Single Frequency Solution A B LO A/D Source Half wave length Coaxial resonator 50 Ohm Probe