Applying X-Rays in Material Analysis

Vladimir Kogan

Philips Analytical and DANNALAB

The Netherlands

X-Ray Diffraction Analysis

• Based on measuring the intensity of the x-rays diffracted by the sample at different angles

• Delivers information about the structure and composition of material at different scales

• This information is used to explain or predict the properties of a sample

Bragg's Law

= 2d sin

d

Classification of Samples

Amorphous

Polycrystalline

Monocrystalline

Bulks

Powders and Foams

Thin Films

From the monodisperse curve of HSA we have determined the average parameters of the molecule - axes of ellipsoid, suface, volume, radius of gyration etc. From the polydisperse curve (native serum) we have derived the histogram of particles distribution by average radius. DANNALAB, 2002

SAXS Analysis of Human Serum Albumin (HSA)in the Monodisperse Solution and in the Native Serum

An understanding of the structural properties of serum albumin is extremely important in the development of new human pharmaceuticals. HSA contributes to many transport and regulatory processes in the body. Distribution, free concentration and metabolism of verious pharmaceuticals can be significantly influenced depending from the binding with HSA.

XRD for Amorphous Materials

XRD for Polycrystalline Materials

• Crystallography - type and dimensions of unit cell

• Atomic structure - atom’s coordinates

• Grain’s size and shape

• Micro and macro strain

• Phase composition - presence and concentration of different phases

D-Mannitol (beta form) HOCH2(CHOH)4CH2OH

File name: org2_cap.IDF, date and time: 25/08/00 10:44:22

º2Theta10

º2Theta20

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º2Theta40

º2Theta50

º2Theta60

º2Theta70

Counts

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Si Detector for XRD Applications

• 0.07mm pitch• No cooling required• Efficiency: > 94 % for

8KeV• Maximum 4mln cps in

the complete detector• Background: < 0.1 cps

Specific of Thin Layers

Strained layerStrained layer Relaxed layerRelaxed layer

mismatchmismatch S

SL

a

aam

Substrate = aSubstrate = aSS

LayerLayer = a = aLL

ct > aL

at = aS

cct

Pseudomorphic epitaxial layers. “No” defects. Strain may be presentExample : AlGaAs/GaAs, SiGe/SiApplications: Lasers, High-frequency IC’s

Lattice mismatched epitaxial layers. Layers are partly (or fully) relaxedExample: ZnSe/GaAs, InAsSb/GaSbApplications: Blue LED’s, IR optopelectronic

Layers with large lattice mismatch and/or dissimilar crystal structuresExample: GaN/Sapphire, YBaCuO/SrTiO3, BST, PZTApplications: Blue Lasers and LED’s, High Tc Superconductors,

Ferro electrics Layers where the epitaxial relationship is weak. Highly textured.

Example: AuCo multilayers on SiApplications: Thin film media, heads

Different Types of Thin Films

XRD for Thin Films and Layers

High Resolution Diffraction

• Orientation

• Quality of Epitaxy, Lattice Mismatch

• Phase Composition

• Thickness, Density, Surface Roughness

Reflectivity Measurements

• Thickness, Density, Surface Roughness

• Lateral and Depth Correlation

• Curvature

In-plane Scattering

• Nano-layers

• Nano-structures

• In-plane properties

Typical Setup for Reflectivity Measurements

2

Divergence slit

Attenuator

Sample

Detector

Graphite monochromator

Anti-scatter slit

Beam knife

Receiving slit

The Information that can be Derived from a Reflectivity Curve

Reflectivity

XRD Study of Self-Assembled Monolayers C18H37SH on Gold

Specular Reflectivity Curve Reflectivity Map, Diffuse Scattering

Determined thickness of the layers:C18H37SH - 1.6nmAu1 - 0.6nmAu2 - 19.0nmSi > 100000nm

Determined Average Lateral Correlation Length: 2.5nm

DANNALAB, 2002

Modern High Resolution Diffractometer

monochromator Symm. Ge[220] 4 - Crystal

or Asymm.

(Perfect) epitaxial layer,stressed and textured sampleshighly textured layers

X-ray tube(line focus)

Soller slits(optional)

X-ray mirror

Divergence slit

Detector 2

Triple AxisSectionDetector 1

Optical slit

The highly parallel monochromatic beam should be used to study perfect layers

High Resolution Diffraction

Analysis of SiGe HBT Structure

The introduction of a SiGe epitaxial layer in the bipolar transistor (HBT) brings significant gains in speed, challenging GaAs in its traditional application fields. New technological step of introducing Ge requires also an accurate method for the characterization of Ge content and gradients.

Automatic simulation and refinement of a measured rocking curve helps to identify parameters of individual layers. Method delivers 1 % accuracy for composition and 3 % accuracy for SiGe thickness.

DANNALAB, 2002

High Resolution Diffraction

GaN/InGaN (Blue Laser Structure)GaN/InGaN (Blue Laser Structure)

Reciprocal Space Map

Relaxed GaInAs/GaAs (224)

SS

L

Orientation and Domain Structure

Transition in YBa2Cu3O8-x Film on SrTiO3 Substrate XRD Measurements

{304} Reciprocal Space Maps

With the increase of the thickness of the YBa2Cu3O8-x layer, the dependence of the structure from the SrTiO3 substrate is declining. This results in the appearance of the orthorhombic superconducting phase.

20nm tetragonal (nonsuperconducting) phase

100nm orthorhombic (superconducting) phase

DANNALAB, 2002

High Resolution Diffraction

Strain Fields in Boron-implanted Silicon

DANNALAB, 2002

Devices and StructuresStresses due to adhesive bonding

Different methods has been tested to make stress-free bonding of Si with steel. One of the methods (s41 and s42) delivers quality, comparable with the stress free samples (Test1 and Test2)

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2ndbatch

3rdbatch

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s11

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s21

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s31

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s41

s42

Test1

Test2

Surface Mapping by Measuring Rocking Curves

IC Chip Glued on the Ceramic Substrate

Method 1chip16

X Y Intensity( )

chip16

X Y Intensity( )

chip60

X Y Intensity( )

chip60

X Y Intensity( )

Method 2

DANNALAB, 2002

Mapping of free standing Si sensor

Sensor on Chip Assembly

Surface Mapping by Measuring Rocking Curves

Mapping of sensor bump-bonded to chip

sensor63

X Y Intensity( )

sensor63

X Y Intensity( )

Wire bonding side

DANNALAB, 2002

Roadmaps for new XRD detectors

Polycrystalline Materials

Monocrystalline Materials

• 0D, 1D and 2D• Different shapes• Very low noise• Pixel size down

to 0.05 mm• Counting speed up

to 105c/s/mm2 • Energy resolution

<250 eV

Amorphous Materials

• 0D, 1D and 2D• Flat shape• Dynamical range 107

• Counting speed up to 107c/s/mm2 useful

energy and 109 total• Energy resolution

<250 eV

• 0D, 2D• Flat shape• Dynamical range 107

• Counting speed upto the 107c/s/mm2

Conclusions

• Appearance of new technologies for x-ray detectors considered to be one of the key factors for the advances in XRD instrumentation.

• The applications of XRD actively shifting nowadays to the field of high-tech materials an devices, including advanced x-ray detectors.

• Both fields have a lot of synergy and may benefit from each other.

Special thanks toJ. Visschers, for inviting me to this conference

J. Woitok, M. Fransen, K. Bethke, R. de Vries for useful comments