Yuji Otsuka

2-dimensional distribution of dielectric constants in patterned low-k structures by a nm-probe STEM/valence EELS (V-EELS) technique

2D distribution of dielectric constants or damage in porous low-k trench structures have been characterized with nm-order space resolution by valence electron energy loss spectroscopy (V-EELS) combined with scanning transmission electron microscopy (STEM) for the first time. Kramers-Kronig analysis (KKA) was carried out to estimate dielectric constants from V-EELS spectra. The results derived from the STEM/V-EELS technique showed that the dielectric constant at a side wall was higher than that at a central region in a trench patterned porous poly-methylsilsequioxane (MSQ) film. It is shown that the STEM/V-EELS technique combined with KKA is a unique technique to investigate changes in local structures and dielectric constants of low-k films, caused by such as plasma treatments, in fine structures.

Analytical electron microscopy investigation of elemental composition and bonding structure at the Sb-doped Ni-fully-silicide/SiO2 interface

It is very important to control the elemental composition and bonding structure at the gate electrode/ gate dielectrics interface in metal-oxide-semiconductor transistor devices because this determines the threshold voltage of the gate electrode. In this study, we investigated the structure at the interface between the antimony (Sb)-doped nickel-fully-silicide gate electrode and SiO2 dielectrics by employing high-spatial resolution techniques such as energy dispersive x-ray spectroscopy and electron energy-loss spectroscopy using a scanning transmission electron microscope. In one region, we found a thin nickel layer at the NiSi/SiO2 interface originating from the migration of native oxide at the face of the poly-silicon. In another region, a Sb pileup was detected at the NiSi/SiO2 interface where the Ni L3-edge spectrum showed Ni–Sb bonding, then it was suggested that Sb atoms exist at the bottom of NiSi, substituting for Si atoms in NiSi.

Luminescence from SiO2 by Helium Ion Microscope (HIM) without any Damage Characterized by TEM-EELS

【背景】ヘリウム(He)イオン顕微鏡(Ion Microscope)(HIM)を用いた低誘電率膜やレジスト パターンに対してダメージ(材料構造変化)の少ない二次電子像観察技術、金属ピラー形成技術 を報告してきた[1-3]。しかしながら He イオンビーム(0.25nm 径)と試料との衝突現象、二次電 子発生機構の理解は不十分であり、He イオンビーム照射条件により試料表面でエッチング、ブリ スタリングが生じる場合もあり、照射条件には注意が必要である。本報告では HIM を用いて SiO2 膜に He イオンビームを標準的な二次電子像観察条件で照射した場合の SiO2膜からのルミネッセ ンス発光現象、およびその照射条件下での SiO2膜のダメージの有無を評価した結果を述べる。 【実験方法】Si 基板上に熱酸化膜を 400nm 形成し、標準的な二次電子像観察条件(加速エネルギ 30kV,イオンドーズ量 1E13~5E14/cm)で He イオンビームを照射し、SiO2膜からのルミネッセン ス、照射後の SiO2試料の TEM EELS 評価[4]を行った。 【結果と考察】ルミネッセンスは SEM CL で観察される波長 672 nm(1.85eV)以外に 281nm(4.41eV), 447nm(2.77eV)の発光が観察された(Fig.1)。447nm は He 原子スペクトルに一致するが、発光ピ ークはブロードであるため SiO2材料に起因するルミネッセンスと考えている。発光強度はドーズ 量と共に増大するが波長に変化は見られないため、この照射条件の範囲ではダメージはないもの と考えられる。TEM観察ではブリスタリングに起因するボイドは一切観察されず、Valence(V)-EELS、 ELNES による評価の結果、ダメージが存在すれば変化する 4~10eV(Fig2.)、100~120eV 領域の スペクトル形状に変化は見られなかった。したがって標準的な観察条件では EELS で検知できるレ ベルのダメージは生じていないと考えられる。ルミネッセンス発光機構に関して当日報告する。 【参考文献】[1] S. Ogawa, et al, Jpn. J. Appl. Phys., 49 (2010) 04DB12, [2] S. Ogawa, et al, Proc. of International Interconnect Technology Conference (2011), [3] K. Kohama et al, 2013 年春季応物 28a-G6-1, [4] Y. Otsuka, et al, Jpn. J. Appl. Phys., 49 111501 (2010)

Characterization of Patterned SiOC film by STEM-VEELS at Lower (80kV) Acceralation Energy

Electron Energy Loss Spectroscopy (EELS) equipped with Transmission Electron Microscope (TEM) at lower-kV has been carried out or precise characterization of nm-order structures of low-k interconnect dielectrics. Structural changes after plasma processes such as dry etch and ashing were characterized by using valence EELS (V-EELS) at lower accelerating voltage such as 80keV. Because the electron irradiation damage and the unexpected effects of Cerencov radiation can be significantly ignored at low-kV VEELS, so that we could derive more precise dielectric constant profile than characterization at conventional 200 kV. Introduction For a rapid development of low-k materials in copper metallization for ULSI devices, nm-order characterization methods of low-k materials after several processes such as dry etching, metal sputter deposition are required to optimize materials and processes quickly. We have already proposed a dielectric constant measurement technique by VEELS [1]. Recently some difficulties were pointed out to measure the dielectric constant from VEELS [2] so that it is not an easy way to characterize damages in the low-k materials. In this study, low accelerating voltage VEELS has been applied to eliminate electron beam damages and Cerenkov radiation loss in characterization of of process damage in low-k materials with higher spatial resolution. Experimental A porous SiOC (p-SiOC) of k=2.4 patterned structure on a SiO2 layer with Cu interconnect (Ta/TaN barrier) was used for characterization. A TEM cross sectional specimen was prepared by a FIB method. The STEM-VEELS analysis was performed with JEOL ARM200 at 80keV, equipped with GATAN Imaging Filter (Quantum). Typical energy resolution was 0.4eV FMHM. EELS were recorded with the illumination semi-angle α of about 10.0 m-rad and the collection semi-angle β of about 40 m-rad at probe diameter of 0.2nm. Specimen thickness t was determined from the VEELS of SiO2 region by the log-ratio method [3], in this study absolute specimen thickness was 115nm. We assumed that the thickness of TEM specimen was constant by FIB thinning and normalized by thickness for Kramers-Kronig analysis (KKA) [4]. Regards to Cerenkov radiation loss, we ignored it because the low kV EELS such as at 80keV obtain information only from low refractive index materials [2]. Results and Discussion Figure 1 shows a STEM image of the patterned SiOC structure with a Cu wiring and figure 2 shows spatially resolved VEELS loss functions from the sidewall of the Cu wiring to 25nm inner region of SiOC. In Fig.2, 2-3eV peaks gradually increased near the sidewall in the area of 10nm. In our previous study, Carbon composition gradually decreased in the area of 40nm [5]. So these peaks presumably appered not because of the compositional change such as carbon depletion directly. In Figure 2, there was another broad intensity distribution around 5-6eV, which was not seen in loss function of SiO2. An origin of this peak is attributed to the existence of methyl group in the SiOC structure. The intensity of 5-6eV was gradually decreased and slightly shifted to higher energy close to the sidewall. Fig. 1. Bright field STEM image of the patterned p-SiOC film. 20nm Cu SiOC -779Extended Abstracts of the 2011 International Conference on Solid State Devices and Materials, Nagoya, 2011, pp779-780 C-4-2

Relative Density Characterization of Patterned Low-k material by VEELS

Electron Energy Loss Spectroscopy (EELS) equipped with Transmission Electron Microscope (TEM) has been carried out to characterize nm-order structures of low-k interconnect dielectrics. Both compositional and structural change after plasma processes such as dry etch and ashing were performed by using conventional core EELS (core electron excitation region: C-EELS) for the compositional analysis and valence EELS (V-EELS) for relative thickness measurement, and results were discussed related to density of lowk dielectrics regions in a Cu/Low-k interconnect cross-secrion. Introduction For a rapid development of low-k materials in copper metallization for ULSI devices, nm-order characterization methods of low-k materials after several processes such as dry etching, metal sputter deposition are required to optimize materials and processes quickly. We have already reported a dielectric constant measurement technique by VEELS [1]. Recently some difficulties were pointed out to measure the dielectric constant from VEELS [2] so that it is not an easy way to characterize damages in the low-k materials. In this study, a 2-dimensional relative thickness measurement has been applied to obtain density or process damage information of low-k materials at higher spatial resolution by VEELS combined with conventional compositional analysis by core-EELS (CEELS). Experimental A porous SiOC (p-SiOC) of k=2.4 patterned structure on a SiO2 layer with Cu interconnect (Ta/TaN barrier) was used for characterization. A TEM cross sectional specimen was prepared by a FIB method. The TEM, STEM, EELS analysis were performed with JEOL JEM-2100F at 200keV, equipped with GATAN Imaging Filter (Tridiem). Typical energy resolution was 0.8eV FMHM. EELS were recorded with the illumination semi-angle α of about 5.0 m-rad and the collection semi-angle β of about 40 m-rad at probe diameter of 1 nm. Specimen thickness t was determined from the low-loss region of the EELS by the log-ratio method [3],

Micro Beam IR Characterization of Narrow Width (-100 nm) Low-k Spaces Between Cu Lines Correlated with Valence EELS Evaluation

Low-k materials of 100 nm width (low-k spaces) between Cu lines in 200 nm pitch Cu / Low-k interconnect samples were characterized by a micro beam IR for the first time, and obtained results were verified in comparison with valence electron energy loss spectroscopy (V-EELS) combined with scanning transmission electron microscopy (STEM). The results derived from the IR technique showed that a metallization process onto a low-k trench resulted in a heavier damage compared to a trench formation processes such as dry etch or ash, and Si-CH3 / Si-O bond intensity ratio decreased from a bottom region of a space up to a cap layer interface, namely the top region was more damaged than the bottom region. V-EELS characterization agreed the IR results.

New Aspects of Nano-meter Structures of Porous Low-k Films and Their Impacts on Cu/Low-k Processes for 65 nm and Beyond TEM Tells What?

Nano-meter order structures of porous low-k films have been successfully characterized by a transmission electron microscopy (TEM). Two proposed applications will be presented in this paper. Using a TEM tomographic technique, 3-dimensional structures of pores in porous low-k films have been quantitatively evaluated and it was shown how the pore structures influenced on materials penetration phenomena into the porous structures. A valence electron energy loss spectroscopy (V-EELS) combined with a scanning TEM (STEM) clearly showed distributions or change of dielectric constants in the porous low-k trench structures with nm-order spatial resolution induced by plasma processes such as dry etch and ash with or without change in composition.