MULTI-MODE ION SOURCE continued
The key to minimizing damage to a polymer system during depth profiling is to reduce the energy going into the surface.
Figure 2 – C1s spectrum after cluster ion etching. Table 1 – Quantification of MAGCIS-cleaned CuPc
Figure 1 – Schematic of copper phthalocyanine (CuPc) organic FET.
(hundreds of nanometer or micrometer scales). For an organic or organometallic-based material, such as copper phthalocyanine (CuPc), which is used in the device investigated in this example, a monatomic ion beam will irrevocably damage the surface chemistry. MAGCIS uses gas clusters to address this problem and preserve the delicate chemistry during analysis. The device consists of the organic layer; beneath the CuPc is another layer of SiO2
. This is removed much more slowly by cluster ions,
and thus the possibility to switch to the monatomic mode of MAGCIS means that the entire device can be analyzed in one experiment.
The Thermo Scientific K-Alpha+ XPS instrument, fitted with the MAGCIS
isolation layer into the silicon substrate. The two profiles were combined to produce a single depth profile through the entire stack.
AMERICAN LABORATORY
cluster ion source, was used to acquire depth profiles from the CuPc FET (see Figure 1). The organometallic layer was profiled using a 4-keV argon cluster ion beam with an average cluster size of 2000. This results in each atom of the cluster having an energy of 2 eV, which is low enough to pre- vent chemical damage from occurring. Once the CuPC layer was removed, the source was switched to monatomic ion generation to profile through the SiO2
14
The initial stage of the profile shows the removal of hydrocarbon con- tamination from the surface of the device. It is very common for a few nanometers of adventitious carbon contamination to be present at the surface, which typically accumulates from exposure to the atmosphere; in fact, another key application of the MAGCIS source is the ability to easily remove contamination from samples without damaging the un- derlying material of interest. Comparison spectra from Figure 2 show that the acquired C1s spectrum looks identical to the reference spectrum of CuPc, indicating that the layer chemistry is as expected, and that the ion beam is not modifying the surface. The measured composition of the layer confirms it to be CuPC, as displayed in Table 1. To show how the XPS data reflects the sample chemistry, the spectrum was deconvoluted by peak fitting. The red peak in Figure 2 corresponds to the six-membered ring carbon atoms, while the blue peak reflects the carbon atoms bonded to nitrogen in the five-membered rings; green peaks arise from a complex set of loss features due to the aromatic ring systems. Preservation of these
MARCH 2016
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