1. Introduction

With the remarkable progress of thin filmtechnology comes a need for diversification of theapplications necessary to characterize crystalmaterials that range from Silicon to III-V compoundsemiconductors.

To further improve the performance of electronicdevices, it has become important to control filmthickness, preferred orientation, composition, andperfection of these crystals as well as epitaxiallygrown crystals.

Various thin film materials, such as magnetic andsemiconductor thin films, require proper evaluation of the in-plane preferred orientation and the surfacestructure. The ATX-G uses the in-plane diffractionmethod designed for grazing incidence Diffractionclose to the total reflection angle. Direct measurement of the surface structure is thereby possible and resultsshow an excellent signal to noise ratio.

2. Features• A high-precision 3-axis thin film goniometer has

recently been developed to enable in-planemeasurement. The counter can scan over a 1/4sphere while keeping the Xray beam at the grazingangle on the sample.

• Different incident optical systems can be set up byselectively combining a multilayer mirror withseveral 4-crystal monochromators.

• Rigaku rotating anode generators, coupled with amultilayer mirror, produce a powerful X-ray source capable of measuring extremely thin films.

• A variety of multifunctional measurement modessupport the thin film evaluation, inclu-ding therocking curve measurement, reflec-tivitymeasurement and in-plane measurement.

53 The Rigaku Journal

The Rigaku Journal

Vol. 16/ number 1/ 1999

Product Information

Advanced Thin film X-ray system-Grazingincidence in-plane diffractometer.

ATX-G

4. ATX-G Optical System and Goniometer

The in-plane diffraction measurement is per-formed by rotating the counter arm upward along thesample surface by the 2θχ-axis.Since this axis ismounted on the 2θ section of a highprecision ω/2θ

goniometer, the conventional 2θ scan in thehorizontal plane can also be made.It is possible toconduct measurement of broad reciprocal latticespace while maintaining the grazing incidenceconditions.

Vol. 16 No. 1 1999 54

Fig. 1 Multi-layer Mirror Section

A system using a multi-layer mirror is growing morepopular as a new optical system with high pefor-mance for analyzing various thin film materials. Thisoptical system makes the X-ray source 6 to 10 timesmore efficient than the conventional system.

Method Content of evaluation

Rocking curve

Mixed crystal composition ratio,lattice distortion, epitaxial layerthickness, superiattice periodicity structure evaluation

Reciprocal lattice mapmeasurement

Separation between latticedistortion and mosaicity, obliquesuper-lattice periodicity

Reflectivitymeasurement

Film thickness measurement,

roughness, density

In-plane diffractionIn-plane crystal structureevaluation

Topography Lattice defect photography

Pole figure, Thin filmdiffraction

Phase analysis, preferredorientation, distortion, residualstress

3.List of Applications

Fig. 2 ATX-G Optical system

55 The Rigaku Journal

Fig. 4

2. Crystal structure analysis of ultrathin (5nm) film deposited on glass substrate

Check was made to see whether or not ultrathin (5nm) film deposited on a glass substrate iscrystallized or not.Very small angle incident X-ray diffraction made it possible to detect Bi2Te3 peak, whichcannot be seen by ordinary X-ray diffraction. This peak is hidden by halo caused by glasssubstrate in the case of the latter diffraction.

Fig. 3

5. Examples of Thin Film Measurement Data

Vol. 16 No. 1 1999 56

Fig. 6 ATX-simulation

6. CrystalGuide Reciprocal Lattice Guide Software

3. Detection of a crystal structure change in the direction of depth after formation of titanium silicide.

Ti thin film was sputtered on silicon substrate and was annealed in nitrogen at 650°C. The resultantsample was analyzed.

CrystaIGuide is a new measurement softwarepackage specifically developed for the ATX.It is apowerful aid for the operator who must performcomplicated measurements.The software containsmany functions such as reciprocal lattice simulationof a crystal, automatic peak search, programmedmeasurement and so forth.

Features• There is no need for complicated angular calcula-

tions.The operator simply enters the sample name,and the reciprocal lattice points of that sampleappears on the CRT screen. Clicking with themouse allows visual selection of the reflection.

• The crystal orientation can be determined byautomatic measurement. Once the determination ismade, the chosen reflection is measured bydesignating the Miller Indices.

• Unattended measurements can be set up to runcontinuously for extended periods of time by theuse of batch measurement software.

Reverse Lattice Simulation• For a crystal whose structure is already known,

certain information (e.g. crystal name, directionnormal to the sample plane, and X-ray incidencedirection) may be entered beforehand. Thesoftware will then simulate the reciprocal latticepoints of that crystal.

• The reciprocal lattice points displayed hererepresent the Bragg reflection on the diffractingplane. This diffracting plane can be selected byrotating the χ and θ axes with the mouse. Clickingon the optional reciprocal lattice point on a planewith the mouse displays the Ewald sphere thatsatisfies the diffraction condition, scatter vector,

the incoming/outgoing X-rays, and the 4-axisangle.

• When the reciprocal lattice point is specified, thereciprocal lattice mapping measurement allows thedesignation of its measurement region with themouse. Positioning the goniometer at a 4-axis angle indicated by the reciprocal lattice point is alsoachieved through mouse control and manualmeasurement.

• The combination of 4-axis angles that satisfy theBragg condition can also be designated with themouse according to the grazing incidencecondition.

• Each reciprocal lattice point is represented byvarying the color intensity proportion to themagnitude of the structure factor.The crystal layerdifferences are represented by various shapes. Inthis way, distinction of reciprocal lattice pointsbetween multilayer films and the difference in thereflection intensity is clear.

• In multilayer films like an epitaxial thin film,reciprocal lattice points consisting of multiplelayers (n layer) are shown simultaneously over-lapped on the diffracting plane. This makes it pos-sible to evaluate the crystal structure given therelative crystal orientation between multilayerfilms.

Auto Peak Search• By using the auto mode in the crystal orientation

measurement, crystal orientation is automaticallydetermined from a particular reflection positionmeasured based on the crystal information.

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Fig. 7 Crystal orientation measurement

• In the manual mode more specific measurementparameters can be set, such as measuring conditions and sorting of measured reflections.

• The auto peak search easily handles samples whosecrystal orientation is not known at all.For examplethe direction normal to the sample plane.

• Once the crystal orientation is determined, allreflections can be estimated by the Miller indices.

• Lattice constant refinement is made from themeasured reflection positions.

• Lattice constants are calculated from the measuredreflection positions. This is effective for those

crystals whose lattice constants are unknown, suchas an epitaxial film.

Programmed Measurement• ·The programmed measurement allows an operator

to conduct continuous measurement by combiningoptional measurements. Once a condition file is setup by identifying the measuring condition for eachindividual measurement, these measurements maybe incorporated into the programmed measure-ment.

• It is also possible to conduct measurement byvarying the measurement position in the sampleplane by combining the area map measurementwith each individual measurement.

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Figure. 8 Programmed Measurement

(5. Examples of Thin Film Measurement Data Fig. 3, 4 and 5: By courtesy of Mr. Shin-ya Matsuno of AsahiChemical Industry Co., Ltd)