Scanning Microwave
Impedance Microscopy (sMIM)

AFM

Asylum ResearchIntroduction

Scanning Microwave Impedance Microscopy (sMIM) enables high resolution electrical characterization with Asylum
Research MFP-3D™ and Cypher S™ atomic force microscopes (AFMs). sMIM distinguishes between changes in capacitanceand resistance, allowing it to operate on a wide range of linear and non-linear materials including conductors, semiconductors,
and insulators. sMIM provides higher lateral resolution (<50 nm) and superior signal-to-noise (>10X) while operating up to80X faster and at lower power compared to competing technologies. sMIM is based on proprietary shielded AFM probes andelectronics developed by PrimeNano, Inc. and is available integrated exclusively with Asylum AFMs.

sMIM Technology and Capabilities
sMIM is a near-field technique that uses a microwave source coupled to a
proprietary shielded AFM probe. As the tip scans the sample, local sample
variations in permittivity (ε) and conductivity (σ) affect the reflected microwaves.
This is analyzed, distinguishing between changes in the measured capacitance(C) and resistance (R). A modulated bias can be applied to the sample to alsomeasure the amplitude and phase of the dC/dV and dR/dV response.
On semiconductor materials, the dC/dV signal is highly sensitive to doping,with the phase indicating dopant type and the amplitude proportional todopant concentration. On thin films, the sMIM capacitance can be related to
the film thickness and dielectric constant. More generally, sMIM is useful on awide range of nanomaterials where variations in permittivity and conductivity
might help distinguish materials that show no contrast in topography.

Common applications
l Semiconductorsl Dopant profilingl Failure analysis
l Thin films
l Ferroelectrics
l Buried chargel Graphenel Carbon nanotubes

Topography

dC/dV Amplitude

dR/dV Amplitude

DC CapacitancedC/dV Phase

dR/dV PhasesMIM images of an SRAM sample (20 µm scan size, ~400 nm tall features). These images
demonstrate the variety of data types that sMIM can measure. DC Resistance can also bemeasured, but is not present in this data set. Note that although semiconductor samples
like this one are a very common application area for sMIM, the technique is far moregeneral and can be applied to most samples to help distinguish between different materials.

Dramatically higher performance

Higher sensitivitysMIM

SMM

sMIM delivers at least 10X higher signal-to-noise comparedto scanning capacitance microscopy (SCM) and scanningmicrowave microscopy (SMM). When used for dopant
profiling, this sensitivity enables differentiation of dopant
concentrations <1014 atoms/cm3. For DC capacitancemeasurements, sMIM has demonstrated a <0.5 aF noise floor.

Higher lateral resolution
sMIM routinely achieves <50 nm lateral resolution and has
demonstrated <30 nm, all under ambient conditions. sMIM
uses proprietary shielded probes with solid metal tips forconsistent high resolution results. Note that resolution is
only a measure of the ability to resolve adjacent featuresand is not a limit on the smallest detectable feature,
which can be much smaller.

Under equivalent conditions (1 Hz line scan rate, -15 dBm source power),
the signal-to-noise of sMIM images is dramatically better than SMM.

sMIM

SMM

Faster imaging
sMIM has a much higher intrinsic bandwidth thancompeting techniques that require substantial averaging
to achieve acceptable signal-to-noise, resulting in slow line
scan rates (<1 Hz). sMIM on the Asylum Cypher S routinely
demonstrates high quality data at line scan rates >40 Hz.

Lower power
With optimized electronics and shielded probes, sMIM
provides high sensitivity at low microwave source powers.
It also measures the dC/dV response with low tip-sample
modulation voltages, limiting the perturbation of the sample.

Even scanning 80X faster (20 Hz vs. 0.25 Hz line scan rates) and at
1000X lower source power (-15 dBm vs. 15 dBm), the signal-to-noiseof sMIM images is still much better than SMM.

Simplified data interpretation
SCM and SMM are highly susceptible to crosstalk due totopography. Proprietary sMIM shielded probes dramaticallyreduce these artifacts, simplifying data interpretation.

Simple operationsMIM requires minimal sample preparation and very few
parameter adjustments. Though clean, polished samples
will produce the best data, sMIM is far more forgiving thanSCM. Parameter adjustments are few and very simple, notlike the highly sensitive and complex SCM optimization.
The hardware setup is also very straightforward, unlike
the myriad of settings present on the network analyzers
used with SMM.

Here, sMIM demonstrates a feature in the SRAM sample thatmeasures 30.5 nm in width.

Shielded Probe

Unshielded Probe

Capacitance images of an etched silicon sample with 40 nm highsquare pillars. The entire sample is silicon, so the capacitance on
top of the pillars should be the same as the surrounding area. Usinga shielded probe this is what we observe, with only small artifacts
at the step edges. Using an unshielded probe, however, we see avery large capacitance difference between the top of the pillars andthe surrounding lower level. Exclusive PrimeNano shielded sMIM
probes localize the capacitance measurement to the tip compared
to unshielded probes where the entire cantilever contributes to themeasurement.

New, unique capabilities

Compatible with most sample types
sMIM operates on almost any material, including
conductors, semiconductors, and insulators. It does
not require an oxide layer. SCM is limited to non-linear
semiconductor materials.

Measure C and R simultaneouslysMIM can measure both capacitance and resistancesimultaneously. There’s no need to switch modes
or probe holders and try to find the same area ofthe sample. This additional information assists inunderstanding complex microelectronic structures.

DC capacitance image ofoxidized Al dots on a SiO2substrate, 15 µm scan.

Detect buried structures
sMIM is sensitive to sub-surface features, readily
imaging detailed sample features even underinsulating or dielectric films >100 nm thick.

SiO2 pattern on Si imaged undera 100 nm Al2 O3 film, 5 µm scan.

Exclusive technology enables
superior sMIM performance
Shielded probes
PrimeNano’s patented sMIM probes are fully shielded
all the way to the tip to improve sensitivity andresolution and reduce topography crosstalk. The tips
are solid metal, eliminating inconsistent results that
occur due to wear of metal-coated tips.

PrimeNano
ScanWave™ sMIM
Technology

Optimized electronics
PrimeNano’s sMIM electronics have been designed
to do exactly one thing very well – sMIM. They were
purpose-built for this application and the impedance
carefully matched to optimize performance at 3 GHz.
General purpose network analyzers are not optimized
for scanning microwave measurements.

Asylum Research AFMs
Asylum Research, the technology leader in AFM,
builds the world’s highest performance AFMs. sMIM
benefits from numerous features, including sample
scanning, low-noise lock-in amplifiers, low-noise /high resolution scanners, and the fast scanningcapability of the Cypher S AFM.

Dopant profiling

Failure analysis

sMIM enables high sensitivity dopant profiling in the range of1014 to 1020 atoms/cm3. Below, the DC capacitance image ofa dopant staircase sample demonstrates sensitivity better than
0.5x1015 atoms/cm3.

sMIM is a powerful tool for semiconductor failure analysis.
The ability to image all materials in the device, including
metals and dielectrics, provides a more complete view andassists in navigating to the region of interest. The highsensitivity of sMIM gives it the potential to find challenging
defects. Below, an apparent defect was found in an SRAM
device, an unexpected dopant variation revealed in thephase channel of the dC/dV measurement.

dC/dV phase image of an SRAM device. The region
circled shows a possible failure, 2.5 µm scan.

Specifications
Compatibility: sMIM is available integrated exclusively with the Asylum Research MFP-3D and Cypher S AFMs
Measurement capabilities: DC capacitance, DC resistance, dC/dV (amplitude and phase), dR/dV (amplitude and phase)
Microwave source: 3 GHz at -45 to -15 dBm power
Lateral resolution: <50 nm typical, <30 nm has been demonstrated
Noise floor (capacitance): 0.5 aF
Dynamic range (dopant level): 1014 to 1020 atoms/cm3Probes: Fully shielded, hardened solid metal tip probes (patented)

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The foregoing datasheet is copyrighted by Oxford Instruments Asylum Research, Inc. Oxford Instruments Asylum Research, Inc. does
not intend the datasheet or any part thereof to form part of any order or contract or regarded as a representation relating to theproducts or service concerned, but it may, with acknowledgement to Oxford Instruments Asylum Research, Inc., be used, applied orreproduced for any purpose. Oxford Instruments Asylum Research, Inc. reserves the right to alter, without notice the specification,
design or conditions of supply of any product or service. Application Note 31 – 6/2014.

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