Agilent Technologies Scanning Microwave Microscopy (SMM) Expanding Impedance Measurements to the Nanoscale: Coupling the Power of Scanning Probe Microscopy with the PNA Presented by: Craig Wall PhD Product Manager Agilent AFM, Nanomeasurements Division
Outline Introduction Principle Instrument setup Experiments Summary Page 2
Introduction Available SPM-based techniques to probe materials electric properties: Scanning near-field microwave microscopy (SNMM) Scanning capacitance microscopy (SCM) Scanning spreading resistance microscopy (SSRM) Electrostatic force microscopy (EFM) Current-sensing (or conductive) AFM (CSAFM) Kelvin force microscopy (KFM) More Scanning Probe Microscopy, edited by S. Kalinin and A. Gruverman, Springer, New York, 2007. Vector network analyzer + AFM impedance capacitance dopant density more (SMM) Page 3
AFM Basic Configuration Z Y X AFM tip monitors surface Closed loop scanner (xyz) or stage Scan with tip or with sample Video access Page 4
AFM Imaging Modes Contact Mode AFM (1986) Dynamic in x and y Tip is in contact or near contact with the surface Small vertical force, but the probe dragged over the surface exerting lateral force. Weakly bound or soft samples move easily. Lower lateral resolution. AC Mode AFM (1993) Dynamic in x, y, and z Intermittent contact. Soft surfaces are stiffened by viscoelastic response. Impact is predominately vertical, therefore large vertical force, but no lateral force. Higher lateral resolution. Page 5
incident Principle transmitted complex reflection coefficient Γ = Z Z L L + Z Z REFLECTION 0 0 reflected Optical analogy incident Reflected Incident = A R SWR S-Parameters Return Loss Impedance, S 11, S 22 Reflection Admittance Coefficient R+jX, Γ, ρ G+jB transmitted reflected Microwave transmission Page 6
Schematic Source Half wave length Coaxial resonator 50 Ohm Probe Page 7
Instrument setup AFM professional network analyzer For dc/dv measurements, a low-frequency modulation is added to the microwave. Demodulated signal is detected by an ac mode controller with built-in digital lock-in amplifiers. Page 8
Agilent 5400 Based SMM Page 9
Agilent 5400 Based SMM Load Diplexer RF to PNA Scanner head With Conductive Tip Page 10
Scanner assembly, cantilever Cantilever holder Pt/Ir cantilever Scanner assembly Al substrate Page 11
Agilent Performance Vector Network Analyzer PNA Signal Conditioning Conductive tip Agilent 5400 SPM Instrument Agilent Precision Machining and Process Technologies to deliver RF/MW to the conductive tip Page 12
PNA Controls from PicoView Agilent General Audience Page 13
Experiments frequency sweep Agilent General Audience Page 14
DRAM Agilent General Audience Page 15
SMM image of SRAM A topography B capacitance C dc/dv Schematic of 6-FET unit cell of SRAM Agilent General Audience Page 16
1 st Eigen/10kHz SiGe Kelvin Force Microscopy of Semiconductor Surfaces Topography Phase Surface Potential 0 0 0 2.5 2.5 2.5 5 5 5 7.5 7.5 7.5 10 10 10 12.5 12.5 12.5 15 15 15 17.5 17.5 17.5 20 20 20 22.5 22.5 22.5 SRAM µm 0 5 10 15 20 25 30 µm 0 5 10 15 20 25 30 µm 0 5 10 15 20 25 30 35 35 35 40 40 40 45 45 45 50 50 50 Surface Potential Surface Potential Surface Potential 40 μm 40 μm 25 μm (70kHz/10kHz) (70kHz/425kHz) (425kHz/70kHz) Agilent General Audience Page 17
Images of an SDRAM Very high sensitivity Can see semiconductor, insulators and conductors Can be calibrated Can also get inductance and reactance Agilent General Audience Page 18
SMM image of SRAM Topography dc/dv Zoomed scans of a transistor. Line feature of 10 20 nm in width can be seen in the dc/dv image Agilent General Audience Page 19
Carriers at 0V bias in SRAM Page 20
Sample 1 Optical images of sample 1. The failed 48 th transistor is marked with a blue circle. Agilent General Audience Page 21
Sample 1 Topography (top), dopant concentration (middle), and capacitance (bottom) images of scans across FETs 43 46 (right) and FETs 45 48 (left). Dopant density images (middle) clearly show a difference on the 48 th FET from all others (43 47). The missing dark area (p dopant) indicates a problem in the channel of the 48 th FET. Agilent General Audience Page 22
Sample 1 Topography (top), dopant concentration (middle), and capacitance (bottom) images of scans across FETs 47 50 (right) and FETs 49 52 (left). Like the last slide, dopant concentration images also show a noticeable difference on the 48 th FET from all others. Capacitance image of the 48 th FET appears some difference from others as well. The result here is consistent with the observation obtained on July 10. Agilent General Audience Page 23
SiGe device Topography Capacitance dc/dv Page 24
InGaP/GaAs heterojunction bipolar transistor Topography 1 4 7 Impedance 1 4 7 Different regions from the emitter-side contact layer (7 and 8) to the subcollector layer (1) with different doping levels were clearly resolved in the impedance image. (Sample courtesy of T. Low) Page 25
Biological sample Bacteria cells of geobacter sulfurreducens Topography Impedance Sample courtesy of N. Hansmeier, T. Chau, R. Ros, and S. Lindsay at Arizona State University. Page 26
Summary A new technique, which integrates AFM with a professional network analyzer, has been developed. scanning microwave microscopy Mapping impedance, capacitance, dielectric constants, etc. SNMM Measuring two-dimensional dopant density of semiconductors. SCM High sensitivity with resolution ultimately limited by the probe. Metals, semiconductors, dielectric materials, ferroelectric materials, insulators, and even biological samples. Page 27
Agilent Technologies = Innovation in Measurements We are presenting a state of the art AFM/SMM microscope to enable material measurements at the Nanoscale + = Coaxial cable Coaxial Resonator Sample The MW diplexer Ground/Shield Sample scanning AFM in X and Y and Z (closed loop) Network Analyzer Page 28