Evaluation of Silicon Nitride Film Formed by Atomic Layer Deposition on the Silicon Substrate with Trench Structure Using Angle-Resolved Hard X-ray Photoelectron Spectroscopy

Abstract

1. Introduction As a packing density in the large-scale integration (LSI) becomes higher, the devices exhibit three-dimensional complicated structure. The deep trench with high aspect ratio (AR), i.e. opening/depth, is one of the components to realize the structure [1]. The atomic layer deposition (ALD) is one of techniques suitable for trench structure, because which can conformally deposit a thin film along the high AR trench structure [2,3]. The ALD film theoretically consist of the same composition with the same thickness along the trench no matter how the AR is high. In this study, we evaluated the ALD deposited SiN films along the deep trench with high AR of 3 and 7.5. 2. Experiment 10 nm-thick SiN films were deposited using alternate supply of SiH2Cl2 and NH3 precursor with plasma on the plane and trench structure with 40 nm opening and 120 or 300 nm deep, AR of 3 and 7.5 at 350, 550, 630oC, respectively. The SiN film were conformally deposited along the trench as shown in Fig. 1. The fabricated samples were evaluated using, conventional X-ray photoelectron spectroscopy (XPS) and Hard X-ray photoelectron spectroscopy (HAXPES). For the XPS and HAXPES evaluation, we carried out angle-resolved spectroscopy. As the HAXPES equipment, a laboratory-based HAXPES (Lab. HAXPES) equipment product of Scienta Omicron Inc. was used [4]. The X-ray source energy was 9,251.74 eV from liquid GaKα. The photoemission angle (Take-off angle: TOA) was varied from 90 degree to 30, with the photoelectron energy resolution of approximately 0.5 eV. 3. Results and Discussion Figure 1 illustrates the trench sample schematics with the explanation of the angle-resolved measurements. One can understand by reducing the TOA from 90 degrees, the photoelectron from the lower part of the trench side walls cannot reach to the photoelectron energy analyzer, therefore the measurement becomes top layer sensitive. Figure 2 compares the Si 1s spectra from the samples at 350oC with (blue) and without (red) trenches. The film on the flat surface, without trenches, showed mostly composed of Si-N chemical bonds, while the spectrum from the trench sample showed more Si-O bonds in the film. The films on or in the trench structure seem to be different from the flat surface, more oxide than nitride, although the ALD was performed to deposit SiN film. Figure 3 shows the angle-resolved HAXPES results for the trench sample at 350oC. From Fig. 3, it can be recognized the Si-O component in the film decreased by reducing the TOA from 90 to 60, implying there are more oxide in the lower part of trench than the upper part. Plasma activated N precursors might lose their energy (activity) during the proceeding narrow high AR trench, resulting in the non-stoichiometric film remained close to the bottom part of trench, which might be oxidized after the film deposition, although the film thickness seems to be the same for all over the trench structures. The stoichiometry uniformity was achieved by elevating the deposition temperature up to 550oC. 4. Conclusion In conclusions, we have evaluated the ALD SiN film conformally formed physically in the high AR trench and found there were possible non-uniformity in the chemical structure along the deep trench. Acknowledgements We appreciate the SPring-8 BENTEN database for the Si 1s spectra assignment. Reference [1] T. Franza et al., ACS Appl. Mater. Interfaces 9, 1858 (2017).[2] T. Antonio et al., Materials Matters 13, 55 (2018).[3] X. Meng et al., Materials 9, 1007 (2016).[4] A. Regoutz et al., Rev. Sci. Instrum. 89, 073105 (2018). Figure 1