Comprehensive Analysis for PDA Effect on SiO2/SiNx/Si Stacked Structure Using Multiple Technique
Authors: Sakata Tomohiro , Takahashi Kumiko , Takemoto Noriyuki , Inoue Keiko , Sugimoto Tomomi , Tanahashi Yusaku , Ogawa Shingo 
Published: December 2024

Silicon nitride (SiNx) thin film in multi-stacked structure plays an important role as a charge trapping layer in flash memory device such as Silicon-Oxide-Nitride-Oxide-Silicon (SOMOS) and Metal-Oxide-Nitride-Oxide-Semiconductor (MONOS) memory [1, 2]. Thus, the performances of these memory devices strongly depend on the qualities of dielectric films which are controlled by deposition and annealing condition. Hence, the systematic evaluation of the quality of dielectric film in multi-stacked layers has been required to understand the chemical composition within each layer.

In this study, comprehensive analysis for the annealing effect on SiO2/SiNx/Si stacked structure can be performed by multiple technique.

The chemical components of SiNx films in SiO2/SiNx /Si-sub. stacked structures were evaluated by photoelectron spectroscopy (PES), X-ray reflectivity (XRR), Fourier transform–infrared (FT-IR) and secondary ion mass spectrometer (SIMS) analyses. SiNx (5 nm) and SiO2 (5 nm) were sequentially deposited on Si substrate by plasma enhanced atomic layer deposition (PEALD). Then, SiO2/SiNx /Si-sub. stacked structures were fabricated. The post deposition annealing (PDA) was conducted at 1000 ºC under N2 for 90 seconds. The chemical compositions of stacked layers were analyzed by PES using monochromated Cr-Kα (5.4 keV) and Al-Kα (1.5 keV) as the excitation source.

To understand the chemical compositions of the stacked layers, PES with Cr-Kα was performed. In Si 1s core-level spectra, four components assigned to Si0, SiNx (Si-rich), SiNx and SiO2 were observed. SiNx (Si-rich) represents excess silicon in SiNx matrix [3]. The components of SiNx (Si-rich) and SiNx decreased after annealing. Furthermore, the component assigned to SiON increased after 1000 ºC annealing. These results indicate that the SiNx layer was oxidized by PDA treatment. It plausibly originates from the SiO2/ SiNx interface reaction and oxygen diffusion into SiNx layer.

Next, silanol group (Si-OH) within SiO2 layer that is key factor of the electric property was analyzed by using chemical modification-PES with Al-Kα. In conventional PES, the peak derived from Si-OH can not be separated from the main peak of O-Si derived from SiO2 in O1s spectra. In chemical modification PES, Si-OH is labeled by the reagent contained in fluorine as the sample treatment.

Thus, quantitative analysis of Si-OH is available by analyzing the concentration of fluorine. In this result, the amount of Si-OH within SiO2 layer was reduced by PDA treatment. This result is in good agreement with FT-IR and SIMS results.

In summary, complementary analysis to help elucidate the properties of dielectric film is indispensable for the optimization of fabrication process and the realization of high-performance memory devices.

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