Confirming the layer structure of an organic FET device

Importance of the Topic

Understanding the layer structure of organic field effect transistors (FETs) is critical for optimizing device performance and reliability. Precise knowledge of composition and thickness in each layer guides material selection and process control, especially as organic and organometallic semiconductors gain traction in flexible electronics.

Objectives and Study Overview

This study demonstrates a depth profiling approach to confirm the structure of a copper phthalocyanine (CuPc)–based organic FET on SiO2/Si. The key aims are to preserve chemical information in the soft organic layer while profiling through both organic and inorganic regions using a single dual‐mode ion source.

Methodology and Instrumentation

A Thermo Scientific Nexsa Surface Analysis System equipped with a MAGCIS dual‐mode ion source was used. Profiling proceeded in two stages:

• Cluster Ion Mode: 4 keV Ar clusters (~2000 atoms) to gently sputter the CuPc layer without subsurface damage.
• Monatomic Ion Mode: Ar+ ions to etch through the SiO2 insulation and into the Si substrate.

This combined approach yields a continuous depth profile from the device surface to the silicon bulk.

Main Results and Discussion

Initial C 1s spectra of the device surface showed additional hydrocarbon contamination at 285 eV compared to a reference CuPc sample. After removing ~6 nm with Ar cluster sputtering, the cleaned spectrum closely matched the reference, confirming pure CuPc in the organic semiconductor layer. Quantitative analysis revealed atomic concentrations in agreement with expected stoichiometry (C ~78 at% observed vs 78 at% expected; N 19.5 at% both observed and expected; Cu 1.9 at% observed vs 2.4 at% expected).

By switching to monatomic ions, the SiO2 layer and underlying Si substrate were profiled with proper stoichiometry, demonstrating the source’s versatility and the integrity of chemical state information across the entire stack.

Benefits and Practical Applications

• Damage-free profiling of soft organic layers preserves chemical state data.
• Single ion source capable of both cluster and monatomic sputtering simplifies analysis workflows.
• Enables detailed failure analysis and interfacial studies in organic electronic devices.

Future Trends and Applications

As polymer and organometallic semiconductors evolve, demand for nondestructive depth profiling will grow. Advances may include larger cluster sizes for deeper organic etching, combined multimodal analysis, and integration with complementary techniques such as TOF-SIMS for enhanced molecular information.

Conclusion

The MAGCIS dual‐mode source on the Nexsa system offers a robust solution for confirming multilayer structures in organic FETs. Gentle cluster sputtering preserves the chemistry of soft layers, while monatomic etching completes profiles into inorganic substrates using a single instrument.