In situ synchrotron based x-ray fluorescence and scattering measurements during atomic layer deposition: Initial growth of HfO2 on Si and Ge substrates

Abstract

The initial growth of HfO 2 was studied by means of synchrotron based in situ x-ray fluorescence ͑XRF͒ and grazing incidence small angle x-ray scattering ͑GISAXS͒. HfO 2 was deposited by atomic layer deposition ͑ALD͒ using tetrakis͑ethylmethylamino͒hafnium and H 2 O on both oxidized and H-terminated Si and Ge surfaces. XRF quantifies the amount of deposited material during each ALD cycle and shows an inhibition period on H-terminated substrates. No inhibition period is observed on oxidized substrates. The evolution of film roughness was monitored using GISAXS. A correlation is found between the inhibition period and the onset of surface roughness.

Mobile setup for synchrotron based in situ characterization during thermal and plasma-enhanced atomic layer deposition

“…The high sensitivity of the synchrotronbased XRF technique is illustrated by the fact that one single ALD cycle resulted in a clear fluorescence signal, implying submonolayer sensitivity. 13,14 In Figure 5(b), the integrated Ru Lα intensity is plotted against the number of deposition cycles for the thermal ALD process on Si-H and SiO 2 , and for the plasma-enhanced ALD process on SiO 2 . Because the XRF intensity is proportional to the amount of Ru on the surface, the obtained growth curves provide direct information about the difference in deposition rate with process conditions and substrate nature.…”

“…In situ XRF has proven an easy-to-implement and valuable tool to monitor ALD growth at the synchrotron. 10,11,13,14,29 It provides direct information about the amount of material deposited per ALD cycle, on planar substrates as well as on more complex 3D surfaces. In situ XAS during ALD allows probing the local atomic environment and provides information such as the level of oxidation, coordination numbers, and bond lengths.…”

“…To enable such synchrotron based experiments, a dedicated ALD setup is required that is preferably mobile so that it can be used at different beamline end stations (enabling different x-ray based characterization techniques), preferably at different synchrotron user facilities. In recent years, "in situ" setups have been developed at the National Synchrotron Light Source (NSLS I) at Brookhaven National Lab (by temporarily transforming a multi-purpose UHV chamber at beamline X21 into an ALD reactor), 10,24 at the Pohang Light Source (PLS), 14 at the Advanced Photon Source (APS) at Argonne National Laboratory, 21 at Stanford Synchrotron Radiation Lightsource (SSRL), 20 and at SOLEIL, 19,22 while "in vacuo" setups have been developed at BESSY II 25,26 and at SSRL, 27,28 mainly targeting XPS.…”

“…In recent years, several groups have explored extending this concept of using light to study ALD growth towards the x-ray part of the electromagnetic spectrum. 8,[10][11][12][13][14][15][16][17][18][19][20][21][22][23] Indeed, when an ALD reactor is equipped with x-ray transparent windows (e.g., beryllium, graphite, or kapton), then the film can be (intermittently) exposed to x-rays during growth, and a wide range of x-ray based thin film characterization techniques can be used for in situ characterization, as recently reviewed by Devloo-Casier et al 17 Since ALD is typically used for nanocoatings with a thickness of 0.1 to several tens of nanometers, while xrays typically penetrate several micrometers deep into most materials, it is challenging to obtain a sufficient signal to noise ratio for x-ray based characterization techniques, in particular when targeting acquisition rates of 1-60 s in order not to interfere too much with the standard exposure cycle of the ALD process. Therefore, while lab-based x-ray sources are used routinely for ex situ analysis of, e.g., the crystallinity of ALD grown films, the in situ studies typically require the high photon flux that can only be offered by synchrotron based sources.…”

In situ synchrotron based x-ray techniques as monitoring tools for atomic layer deposition

“…This has already been shown in a study of the initial growth of HfO 2 on Si and Ge substrates. 29 Second, in the case of, for example, metal ALD, where islands of material are being formed during the initial stages of growth, GISAXS allows for the analysis of the size, shape, and interparticle spacing. This can be very important in, e.g., the determination of particle size and dispersion for catalyst preparation by ALD.…”