TaSiN Films Research Articles

Integration of perovskite oxide dielectrics into complementary metal–oxide–semiconductor capacitor structures using amorphous TaSiN as oxygen diffusion barrier

The high permittivity perovskite oxides have been intensively investigated for their possible application as dielectric materials for stacked capacitors in dynamic random access memory circuits. For the integration of such oxide materials into the CMOS world, a conductive diffusion barrier is indispensable. An optimized stack p++-Si/Pt/Ta21Si57N21/Ir was developed and used as the bottom electrode for the oxide dielectric. The amorphous TaSiN film as oxygen diffusion barrier showed excellent conductive properties and a good thermal stability up to 700 °C in oxygen ambient. The additional protective iridium layer improved the surface roughness after annealing. A 100-nm-thick (Ba,Sr)TiO3 film was deposited using pulsed laser deposition at 550 °C, showing very promising properties for application; the maximum relative dielectric constant at zero field is κ ≈ 470, and the leakage current density is below 10–6 A/cm2 for fields lower then ± 200 kV/cm, corresponding to an applied voltage of ± 2 V.

MOCVD of TaN Using the All‐Nitrogen‐Coordinated Precursors [Ta(NEtMe)3(N‐tBu)], [Ta(NEtMe)(N‐tBu){C(N‐iPr)2(NEtMe)}2], and [Ta(NMeEt)2(N‐tBu){Me2N‐N(SiMe3)}

AbstractThree different all nitrogen‐coordinated heteroleptic precursors, [Ta(NEtMe)3(N‐tBu)] (1), [Ta(NEtMe)(N‐tBu){C(N‐iPr)2‐(NEtMe)}2] (2), and [Ta(NMeEt)2(N‐tBu)(tdmh)] (3) (Et = ethyl, Me = methyl, tBu = tert‐butyl, iPr = isopropyl, tdmh = N‐trimethylsilyl‐N′,N′‐dimethylhydrazine) are tested in thermally activated metal–organic (MO)CVD of TaN thin films. Using 1 and 2, conducting cubic‐TaN films can be deposited (1: 4000 μΩ·cm; 2: 10000–20000 μΩ·cm), while 3 results in the formation of insulating silicon‐containing films with high levels of oxygen impurities. Raising the chemical complexity of precursors 2 and 3 with respect to 1 does not necessarily lead to high carbon incorporation, even in the absence of additional ammonia. Metal–insulator–semiconductor structures with TaN as the metal gate material are fabricated and characterized by capacitance–voltage (C–V) and current density–voltage (J–V) measurements. Precursor 3 is used to deposit insulating TaSiN(O) films in a large‐scale reactor on 150 mm prestructured metal oxide semiconductor (MOS) wafers.

Pretreatment of the TaSiN Substrate Surface for Copper-MOCVD

Effects of plasma pretreatments to the TaSiN film surface on Cu nucleation were investigated. Scanning electron microscopy (SEM) was used to measure the Cu nucleation density and to observe the morphology of the Cu film. X-ray spectroscopy (XPS) and Auger depth profiling analyses were used to investigate the bonding state of atoms and the concentrations of oxygen and nitrogen at the TaSiN film surface, respectively. Cu nucleation in Cu MOCVD is effectively enhanced by treating the underlying Ta-Si-N film surface with hydrogen plasma prior to Cu MOCVD. The Cu nucleation density in Cu MOCVD increases as the rf-power and the plasma exposure time increase in the hydrogen plasma pretreatment, but it is saturated at the rf-power of 40W and the plasma exposure time of 2min. To increase the rf-power and the plasma exposure time further would increase the plasma radiation damage for the Si substrate. Therefore, 40W and 2min are the optimal process conditions for the hydrogen pretreatment. Copper nucleation is enhanced by hydrogen plasma pretreatment because the plasma treatment removes the nitrogen and oxygen atoms from the Ta-Si-N film surface. Since Ta-Si is a substrate more favorable for Cu nucleation than Ta-Si-N(O), Cu nucleation on the Ta-Si-N film is enhanced by hydrogen plasma pretreatment of the Ta-Si-N film surface.

Work Function Characterization of TaSiN and TaCN Electrodes Using CV, IV, IPE and SKPM

Work function of TaSiN (TaCN) films on HfO2 or SiO2 gate dielectrics is investigated for the first time using a combination of Capacitance-Voltage, Fowler- Nordheim tunneling, internal Photoemission, and scanning Kelevin probe microscopy methods, which consistently show ~0.2 eV work function difference between these two metals. These results indicate that Fermi-level pinning on HfO2 is not an issue for these metal systems. SKPM gives qualitative results. Beveled structure and complicated modeling are needed for the potential quantitative application of SKPM in metal/high-k systems. The capacitive-voltage and internal photoemission measurements were performed on the same test structures. Work function values extracted from these two methods agree well.

TaSiN diffusion barriers deposited by reactive magnetron sputtering

Due to its resistance to oxidation, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced memory devices. In this study we report on the properties of TaSiN thin films deposited by reactive magnetron sputtering of a TaSi 2 target in an Ar/N 2 atmosphere. We especially focus on the influence of deposition parameters (pressure and power density) on TaSiN film properties. To study oxidation resistance, films are processed by rapid thermal annealing in 18O 2 at 650 °C. The concentration depth profiles of 18O were measured via the narrow resonance of 18O( p, α) 15N at 151 keV (FWHM = 100 eV). Whatever the power density, films deposited above 2 Pa are porous and exhibit high resistivity. Ta 26Si 47N 27 deposited at 0.5 Pa with a power density of 2.65 W/cm 2 exhibits high density, low resistivity, and good oxidation resistance.

Enhancement of Ru nucleation by pretreatments of the underlying TaSiN film surface in Ru MOCVD

Surface pretreatment of the underlying film to enhance Ru nucleation is essential in molecular organic chemical vapor deposition (MOCVD) of Ru. In the present work, effects of argon plasma, hydrogen plasma, and palladium sputtering treatments of the Ta–Si–N film surface on Ru nucleation in Ru MOCVD were investigated using scanning electron microscopy (SEM) and Auger electron emission spectrometry (AES) analyses. It was found from the analysis results that palladium sputtering treatment is the most efficient, argon plasma treatment is the next, and hydrogen plasma treatment is the third in enhancing Ru nucleation. Also, the mechanism through which Ru nucleation is enhanced by these pretreatments and why the nucleation enhancing efficiencies of these three pretreatments are different are discussed.

Effects of Hydrogen Plasma Treatment of the Underlying TaSiN Film Surface on the Copper Nucleation in Copper MOCVD

MOCVD is one of the major deposition techniques for Cu thin films and Ta-Si-N is one of promising barrier metal candidates for Cu with high thermal stability. Effects of hydrogen plasma pretreatment of the underlying Ta-Si-N film surface on the Cu nucleation in Cu MOCVD were investigated using scanning electron microscopy, X-ray photoelectron spectroscopy and Auger electron emission spectrometry analyses. Cu nucleation in MOCVD is enhanced as the rf-power and the plasma exposure time are increased in the hydrogen plasma pretreatment. The optimal plasma treatment process condition is the rf-power of 40W and the plasma exposure time of 2min. The hydrogen gas flow rate in the hydrogen plasma pretreatment process does not affect Cu nucleation much. The mechanism through which Cu nucleation is enhanced by the hydrogen plasma pretreatment of the Ta-Si-N film surface is that the nitrogen and oxygen atoms at the Ta-Si-N film surface are effectively removed by the plasma treatment. Consequently the chemical composition was changed from Ta-Si-N(O) into Ta-Si at the Ta-Si-N film surface, which is favorable for Cu nucleation.

Integration of high dielectric Ba 0.5Sr 0.5TiO 3 films into amorphous TaSiN barrier layer structures

The high- k dielectric material (Ba,Sr)TiO 3 has been intensively investigated for possible applications in dynamic random access memory circuits. During the BST deposition process in O 2 ambient, typically at 650°C, the diffusion of oxygen through the bottom electrode into the poly Si plug must be prevented. Amorphous TaSiN films are excellent candidates as oxygen barrier layers. Ba 0.5Sr 0.5TiO 3 (BST) films with thickness of 100 nm were deposited on the electrode structure SiO 2/TaSiN/Pt. The sol–gel method was used to grow the BST films. The barrier effect for oxygen diffusion is studied in TaSiN layers with thickness of 50 nm, which were deposited by a reactive sputter process. X-ray photoemission spectroscopy results confirm that this amorphous material is a suitable barrier against oxygen diffusion at 650°C. The BST films, deposited at 650°C and post-annealed at 650°C show a dielectric constant of 100 at 100 kHz and a dissipation factor of less than 5%.

High-resolution energy-dispersive x-ray spectroscopic analysis of ultrathin ion diffusion barriers using microcalorimetry

The advent of microcalorimetry for x-ray detectors holds the promise for high-resolution compositional microanalysis applicable to nanometer-scale devices and structures. To demonstrate this capability, microcalorimeter-based energy dispersive x-ray spectroscopy (EDS) has been used to analyze ultrathin TaSiN films under development as ion diffusion barriers in sub-0.1 μm integrated circuit interconnect structures. Microanalysis of TaSiN films has been carried out using microcalorimetry-based EDS for comparison with similar data acquired using conventional Si(Li) EDS detectors. The elimination of elemental peak overlaps provided by the improved energy resolution of the microcalorimeter x-ray detector is demonstrated for TaSiN EDS spectra from films as thin as 3.5 nm. In addition, variation of the electron probe beam energy is examined to reduce the x-ray generation volume relative to the TaSiN film thickness. It is shown that microcalorimetery-based EDS is a potentially powerful technique for the characterization/metrology of ultrathin barrier films used for microelectronics, with x-ray energy-resolving capabilities similar to techniques such as wavelength dispersive spectroscopy.

Study of poly-Si/TaSiN/Pt structure for stacked capacitors

ABSTRACTDue to its high oxidation resistance, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced memory devices. In this work, we report on the properties of TaSiN thin films deposited by reactive magnetron sputtering of a TaSi2 target. We have mainly studied the influence of deposition pressure and power density on film properties (composition, density, resistivity). The oxidation resistance of TaSiN films has been investigated at typical conditions for crystallization of perovskite dielectrics. The as-deposited and annealed samples were characterized using Rutherford backscattering spectroscopy and nuclear reaction analysis for atomic composition and XPS for chemical bonding. To study oxidation resistance, films have been processed in 18O2. The concentration depth profiles of 18O was measured after thermal treatments via the narrow resonances of 18O(p,α)15N at 151 keV (fwhm=100eV). The different results suggest that a pressure of 0.5 Pa, a power density of 2.63W/cm2 and a gas flow ratio N2/Ar of 5% allow to perform TaSiN films with high density, low resistivity and good oxidation resistance.

Diffusion Barrier Characteristics of TaSiN for Pt/TaSiN/Poly-Si Electrode Structure of Semiconductor Memory Device

The TaSiN barrier layers for Pt/TaSiN/poly-Si structure were prepared by dc reactive magnetron sputtering. The resistivity of as-deposited films with an optimum composition of was about 1,277 μΩ cm. The TaSiN films are amorphous over a wide range of annealing temperatures up to 900°C and showed an abrupt increase of resistivity at annealing temperatures of 700 and 750°C because of the formation of amorphous phase onto TaSiN films. The characteristics of Pt/TaSiN/poly-Si structure before and after annealing at various temperatures became linear, which is indicative of Ohmic characteristics, independent of annealing temperature. The contact resistivities of Pt/TaSiN/poly-Si structures with increasing annealing temperature up to 700°C did not vary greatly compared with those of as-deposited electrode structures. The specific contact resistivities of as-deposited and annealed structures at 700°C were about and respectively. © 2001 The Electrochemical Society. All rights reserved.

Control of Crystalline Structure and Electrical Properties of TaSiN Thin Film Formed by Reactive RF-Sputtering

The crystalline structure, thermal stability, and electrical properties of TaN and TaSiN thin films formed by reactive RF-sputtering with a broad range of N and Si composition ratios were investigated. TaSiN with a Si/(Si+Ta) ratio less than 25% were crystalline, whereas that with a ratio more than 25% was amorphous, regardless of the N2 partial pressure. The amorphous films exhibited excellent thermal stability with no crystallization up to 900°C. Crystalline films consisted of columnar grains with sizes ranging from 20–30 nm. Electrical resistivity showed a strong dependence on the Si and N composition ratios. However, amorphous films deposited at low N2 partial pressure exhibited constant resistivity, regardless of the Si/Ta ratio. These results clarify that the crystalline structure and electrical resistivity of TaSiN films can be controlled by varying the Si and N composition ratios.

In Situ Study of Barrier Layers Using Spectroscopic Ellipsometry and Mass Spectroscopy of Recoiled Ions

ABSTRACTAn in situ study of barrier layers using spectroscopic ellipsometry (SE) and Time-of-Flight (ToF) mass spectroscopy of recoiled ions (MSRI) is presented. First the formation of copper silicides has been observed by real-time SE and in situ MSRI in annealed Cu/Si samples. Second TaSiN films as barrier layers for copper interconnects were investigated. Failure of the TaSiN layers in Cu/TaSiN/Si samples was detected by real-time SE during annealing and confirmed by in situ MSRI. The effect of nitrogen concentration on TaSiN film performance as a barrier was also examined. The stability of both TiN and TaSiN films as barriers for electrodes for dynamic random access memory (DRAM) devices has been studied. It is shown that a combination of in situ SE and MSRI can be used to monitor the evolution of barrier layers and detect the failure of barriers in real-time.

Layered TaSiN as an Oxidation Resistant Electrically Conductive Barrier

TaSiN films deposited as layered TaN–SiN structures of various compositions have been examined for their oxidation resistant properties during annealing in oxygen at annealing conditions commonly used to prepare perovskite dielectrics. The films have been characterized by Rutherford backscattering analysis (RBS), x-ray diffraction (XRD), and electrical resistivity measurements. Films with less than 15 at.% Si showed some resistance to oxidation after annealing for 1 min at 650 °C but became fully oxidized after longer anneals. Increasing the Si content up to 28 at.% increasingly improved the oxidation resistance of the alloys to the point where the films resisted complete oxidation for up to 5 min at 700 °C. For alloys with greater than 28 at.% Si, no oxidation could be detected by RBS or electrical measurements for anneals up to 5 min at 700 °C. Furthermore, these high Si content alloys were still conductive with resistivities of near 1000 μΩ cm. It was also found that TaSiN and lead lanthanum titanate (PLT) interact strongly during annealing, and another nonoxidizing barrier metal, such as Pt, is required between the two materials if TaSiN is to be used as an electrode/barrier with lead-based perovskites.

Evaluation of LPCVD MeSiN (MeTa, Ti, W, Re) diffusion barriers for Cu metallizations

LPCVD MeSiN (MeRe, W, Ti, Ta) thin films were investigated for use as diffusion barriers between Cu overlayer and oxidized silicon substrates. Gaseous precursors were silane, in situ fabricated metal chloride, ammonia, hydrogen and argon. Thermodynamic simulations of the MeSiN and the CVD MeSiNClHAr systems were combined with the experimental study. It was shown that the existence (titanium and tantalum) or non-existence (rhenium and tungsten) of stable metal nitrides could explain the differences observed in the morphology of the four systems. Amorphous or nanocrystallized ReSiN and WSiN whereas crystallized TiSiN and TaSiN films were deposited. The ReSiN an WSiN layers crystallization temperature was found to be around 1173 K. Their morphology, thermal stability, resistivity and the performances of the four copper metallized MeSiN systems were evaluated. WSiN material appeared as the most promising diffusion barrier thanks to its morphology, resistivity around 1 mΩ cm and performances in blocking copper diffusion.