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 0 0 REFLECTION Reflected Incident = A R reflected Optical analogy incident SWR S-Parameters S 11, S 22 Reflection Coefficient Γ, ρ transmitted Return Loss Impedance, Admittance R+jX, G+jB reflected Microwave transmission Page 6
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 7
Agilent 5400 Based SMM Page 8
Agilent 5400 Based SMM Load Diplexer RF to PNA Scanner head With Conductive Tip Page 9
Scanner assembly, cantilever Cantilever holder Pt/Ir cantilever Scanner assembly Al substrate Page 10
Experiments frequency sweep Page 11
DRAM Page 12
SMM image of SRAM A topography B capacitance C dc/dv Schematic of 6-FET unit cell of SRAM Page 13
KFM of SDRAM 0 0 5 10 15 20 25 30 35 40 45 50 55 60 µm µm 0 5 10 15 20 25 30 35 40 45 50 55 60 µm 0 V 2.4 5 0.55 5 2.3 2.2 10 0.5 10 2.1 2 15 0.45 15 1.9 1.8 20 0.4 20 1.7 1.6 25 0.35 25 1.5 1.4 30 0.3 30 1.3 1.2 35 0.25 35 1.1 1 40 0.2 40 0.9 0.8 0.7 45 0.15 45 0.6 0.5 50 0.1 50 0.4 0.3 55 0.05 55 0.2 0.1 60 µm 0 60 µm 0 Topography Surface Potential Page 14
Images of an SDRAM Very high sensitivity Can see semiconductor, insulators and conductors Can be calibrated Can also get inductance and reactance Page 15
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 Page 16
Carriers at 0V bias in SRAM Page 17
SiGe device Topography Capacitance dc/dv Page 18
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 19
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 20
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 21
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 Sample scanning AFM in X and Y and Z (closed loop) The MW diplexer Ground/Shield Network Analyzer Page 22