Investigation of Nickel on Silicon Thin Films with XRD

One of the most commonly used structural analysis techniques to characterize thin films/layers and coatings is X-ray diffraction. The demand for the analysis of thin films and coatings has been growing both in research and industrial laboratories, owing to the development of a large variety of applied materials. Such materials are, for instance, used in photovoltaic collectors for green energy harvesting, vice versa as materials for generating light in Lasers and LEDs, or as materials for advanced optical applications.

It is possible to characterize the crystallographic structure of multi-functional inorganic and hybrid organic-inorganic thin films (nanometer scale) by GIXRD (Grazing Incidence XRD). This is essential as optical and electronic properties are greatly influenced by the structure of compounds. In GIXRD, a fixed gracing angle (~0.5° – 2° Ω) is used to exclusively measure not the substrate, but the layer.

Another parameter to design thin film materials for several applications is the thickness of certain layers. X-ray reflectometry (XRR) is a standard method used for determining the thickness of thin layers. It is based on the interference between X-rays reflected on different layers in the material.

Instrument

Thermo Scientific™ ARL™ EQUINOX Series signify a range of XRD instruments from simple, user-friendly bench-top systems for routine analysis to more sophisticated floor-standing, high-performance, research grade systems.

Thermo Scientific™ ARL™ EQUINOX 100 makes use of a custom designed 15 W Co or 50 W Cu high-brilliance micro-focus tube with mirror optics. No external water chiller is required to operate this instrument. The thin film attachment offers computer-controlled ω and z movement for alignment and measurement of samples (cf. Figure 1). This benchtop instrument is transportable between laboratories or into the field without the need for any special infrastructure.

The ARL EQUINOX 100 (Figure 2) provides more rapid data collection in comparison to other diffractometers owing to its unique curved position sensitive detector (CPS) that measures all diffraction peaks in real time and simultaneously, and is hence suitable for fast screening of thin film samples using GIXRD.

Figure 1. Thin Film Attachment.

Figure 2. ARL EQUINOX 100 diffraction system.

Experiment

The measurement of Ni on Si substrate sample (1 layer, 306.9 Å thickness; AXO) was carried out using an ARL EQUINOX 100 (CuKα radiation: 1.541874 Å) after careful alignment of z and ω. Data processing and evaluation was achieved using SYMPHONIX (data processing), MAUD (XRR data refinement), and MATCH! equipped with the COD database (qualitative phase analysis).

Results

The GIXRD was used to investigate the crystallographic structure of the Ni layer. The XRD pattern was later compared with a database (COD) which clearly allows assigning the common Ni structure type (space group Fm3m, a = 3.5238 Å) following 1 minute of measurement time (cf. Figure 3).

Figure 3. GIXRD pattern (20 - 90°2θ grazing angle 0.5°).

In order to refine the XRR data, a model containing the Si substrate, a buffer layer, and the final Ni layer compared to air was arranged and in the concluding step, all parameters were refined independently. The model yields an adequate fit (cf. Figure 4 and Table 1).

Figure 4. XRR pattern (black; 0 - 4°2θ) with fit (red); Intensities in logarithmic scale.

Table 1. Results of XRR refinement.

The deviation between refined and given thickness is 5%, which is acceptable for a benchtop system.

Conclusion

With the help of the ARL EQUINOX 100, a full GIXRD scan was acquired within a measurement time of 1 minute, making it possible to differentiate between various types of structures or amorphous / crystalline character of the sample. Sample alignment is an uncomplicated procedure and does not require an advanced operator.

Even XRR measurements are possible, thanks to the almost parallel beam generated by the X-ray mirror optics of the ARL EQUINOX 100. The evaluation of the measurement makes it possible to determine layer thicknesses with a reasonable precision.

The ARL EQUINOX 100 coupled with the thin layer attachment is a user-friendly system for basic thin film / coating investigations in industrial as well as academic research. It allows rapid and convenient QC/QA procedures, even for traditional operators.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers.

For more information on this source, please visit Thermo Fisher Scientific - Elemental Analyzers.