(Invited) Evaluation of Chemical and Physical Conformality for SiN x Films Deposited on Trench Substrate By Atomic Layer Deposition

Abstract

I. Introduction State-of-the-art large-scale integrated circuit (LSI) requires three-dimensional complicated structures to further increase its packing density. High aspect ratio (AR), i.e. depth over opening, trench is one of the components to realize such kind of structure [1]. The trench surface often needs to be covered by insulator film, which is desired to have excellent conformality both in the physical and chemical viewpoints. The atomic layer deposition (ALD) is one of techniques suitable for such a requirement [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, namely perfect conformality. In this study, we evaluated the ALD SiN x films along the trench with AR of 3 and 7.5. II. Experimen We deposited 10 nm-thick SiN x films using alternate supply of SiH2Cl2 and plasma enhanced NH3 precursors 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 and 630oC, respectively. The fabricated samples were evaluated using hard X-ray photoelectron spectroscopy (HAXPES), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscope (TEM) with energy dispersive X-ray spectroscopy (EDX). For the HAXPES evaluation, we carried out angle-resolved spectroscopy.Figure 1 shows a schematic diagram of angle-resolved HAXPES in the trench sample. Since the detection area changes with take-off angle (TOA), the SiN x film at the trench top is mainly evaluated at TOA 90. On the other hand, when the TOA is 75 or 60, the SiN x film on the trench sidewall is also evaluated.As the HAXPES equipment, a laboratory-based HAXPES (Lab. HAXPES) produced by ScientaOmicron Inc. was used [4]. The X-ray source energy was 9,251.74 eV from liquid GaKa. The photoelectron energy resolution was approximately 0.5 eV. III. Results and Discussion Figure 2 shows the EDX mapping of Si, O, and N atoms in AR7.5 sample deposited at 350oC. From Fig. 2 (a), nitrogen atoms are conformality distributed along the Si trench substrate. And Fig. 2 (b) shows that there is a large amount of oxygen atoms on the surface of the SiN x film at the trench sidewall. These results suggests that the oxygen atoms in the air may have bonded to nitrogen deficient bonds in the SiN x film formed on the trench sidewall. Figure 3 shows the Si 1s spectra from the AR7.5 trench sample deposited at 350oC using the angle-resolved HAXPES and the chemical shifts calculated from the Si 1s spectra. From Fig. 3 (a), the 1838.6 eV peak is assigned to the Si-Si bond of the Si substrate, and the peak around 1842 eV is assigned to Si-N bonds. The vertical axis in Fig. 3 (b) is the chemical shifts from the Si-Si bonds detected in the Si substrate. In other words, smaller shift indicates that the SiN x film has a non-stoichiometric characteristic with more N deficiencies. As shown in Fig. 3, the chemical shifts became smaller as the TOA decreased. Since the detection area of angle-resolved HAXPES with TOA75 and 60 is the top and sidewall of the trench structure, we consider that the photoelectrons originating from the nitrogen deficiency dominated from the trench sidewall. These results can be explained by the energy-loss of the plasma activated precursor in the trench structure while ALD process. We consider that the deactivation of the precursor prevented the formation of stoichiometric SiN x film on the trench sidewall, and that the N-deficient area was bonded by oxygen after exposure to the atmosphere. The stoichiometry uniformity was achieved by elevating the deposition temperature up to 550oC. IV. Conclusion In conclusion, we have evaluated the ALD SiN x film in the trench structure and found there were possible non-uniformity in the chemical structure along the trench although physically formed with excellent conformality. 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