Scanning Microwave Microscopy

December 15, 2010Page 1

Agilent Technologies

Scanning Microwave Microscopy (SMM Mode) Electromagnetic materials characterization at high spatial resolution

Scanning Microwave Microscopy

December 15, 2010Page 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

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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

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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

S21

S12

S11 S22

R1 R2

RF Source

LO

Test port 2

BA

Test port 1

Phase

Magnitude

DUT

Reflection

Transmission

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High-Frequency Device Characterization

TransmittedIncident

TRANSMISSION

Gain / Loss

S-ParametersS21, S12

GroupDelay

TransmissionCoefficient

Insertion

Phase

ReflectedIncident

REFLECTION

SWR

S-ParametersS11, S22 ReflectionCoefficien

t

Impedance, Admittance R+jX

, G+jB

ReturnLoss

, G r,T t

Incident

Reflected

TransmittedRB

A

A

R=

B

R=

Scanning Microwave Microscopy

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Scanning Microwave Microscopy (SMM) Basic Idea

Tip and sample form a capacitor

Measuring C yields er

C = e0 er A/d

Actuator

Capacitance

C ~ fF

Capacitance bridges too slow

Integration times of several seconds not practical for imaging

Scanning Microwave Microscopy

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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

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Compatible with Agilent 5420 & 5600LS AFM/SPM

5420 AFM 5600LS AFM

Scanning Microwave Microscopy

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Sub 7 nm Conductive tip development

Alumina CarrierAgilent Precision Machining and ProcessTechnologies to deliver RF/MW to the conductive tip

Pt/Ir Cantilever

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Simultaneous Imaging of Topography, Capacitance, and dC/dV

Scanning Microwave Microscopy

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PNA Controls from PicoView

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Calibration staircase sample (collaboration with National Institute of Standards

and Technology, NIST)

10 micronSILICON

SILICONOXIDE

METAL

TOP VIEW

SIDE VIEW

60 mm

50mm

20

0 n

m

Gold caps on SiO2 „staircase“ on Si.AFM topography 3D view (left) and schematic overview (right).

Capacitance calibration

SILICON

SILICONOXIDE

METAL

TOP VIEW

SIDE VIEW

60 mm

50mm

20

0 n

m

C2

C1

2*

1

CAd

signal

Transfer Function: S11 signal [dB] capacitance [F]

Scanning Microwave Microscopy

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0

8

16

4

12

dB

10µm

Sample: „NIST2“ staircase with goldcaps

Capacitance Calibration

Capacitance (amplitude)

SILICON

SILICONOXIDE

METAL

TOP VIEW

SIDE VIEW

60 mm

50mm

20

0 n

m

C2

C1

Scanning Microwave Microscopy

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Capacitance Calibration

2*

1

CAd

signal

Scanning Microwave Microscopy

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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.

0

011 ZZ

ZZS

L

L

k

A B

LO LO

A/D A/D

Source

Probetip

Sample

Sca

nne

r

Coupler Coupler Wave-guide

Agilent PNA AFM

Agilent DPMM

LF AC Bias

LFDemodulator

dC/dV Module

Imaging Dopant Density

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Scanning Microwave Microscopy

Scanning Microwave Microscopy

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Dopant Density calibration with IMEC Standard

Si Wafer

DepositLayers withVarious DopingLevels

Cleave or polish from top to expose the layers

Den

sity (/cm

³)

Depth [µm] 30 20 10 0

101

4 101

7 102

0

1

000

1

0

.00

1

Res

isti

vity

[Ωcm

] 6

5

4

3

1

7

8

2

Spec sheet IMEC calibration sample

edge

bulk

Scanning Microwave Microscopy

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Dopant Density calibration with IMEC Standard dC/dV Amplitudebulk edge

1 2 3 4 5 6 7 8

Scanning Microwave Microscopy

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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

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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

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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

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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

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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

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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

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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

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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

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Back-up Slides

Scanning Microwave Microscopy

Scanning Microwave Microscopy

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Scanning Microwave Microscopy

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• Scanning only• qualitative• poor sensitivity• limited 1015-1020 Atoms/cm3• No Conductors/Insulators

Scanning Microwave Microscopy

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Lightwave Analogy to RF Energy

RF

Incident

Reflected

Transmitted

Lightwave

DUT

Scanning Microwave Microscopy

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Standard Vector Network Analyzeras a reflectometer

Highly resistive load High SNRLow Resolution

Low resistive loadHigh SNRLow Resolution

Load close to 50 OhmsLow SNRHigh Resolution Figure 1: reflection

coefficient vs.. impedance

0

011 ZZ

ZZS

L

L

A BLO LO

A/D A/D

Source

Probe

Very small capacitor High SNRLow Resolution

Scanning Microwave Microscopy

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Simplified Single Frequency Solution

A B

LO LO

A/D A/D

Source

Half wave lengthCoaxial resonator

50 Ohm

Probe

freq (500.0MHz to 3.000GHz)

S(1

,1)

1.910E90.001 / -90.076

m1

m1freq=S(1,1)=0.001 / -90.076impedance = Z0 * (1.000 - j0.003)

1.910GHz

1.0 1.5 2.0 2.50.5 3.0

-40

-20

-60

0

freq, GHz

dB

(S(1

,1))

1.910G-57.55

m2

m2freq=dB(S(1,1))=-57.550

1.910GHz