AVS2010 Session TF-ThP: Thin Film Poster Session II

With the advent of pulsed magnetron direct current (DC) sputter deposition technology, there have been gains made in the deposition of various inorganic thin films.¹ Most notably used for reactive sputtering of oxides and nitrides, pulsed DC sputtering has led to the deposition of dense coatings with improved properties such as adhesion and wear. The property changes have been attributed to the differences in flux and energy of the species involved with growth.

In this work, we explore the effects of using pulsed DC methods for sputtering monolithic ~ 200 nm-thick nickel films. The power supply used for this study is the Advanced Energy Pinnacle Plus 10kW series, which allows for continuous or pulsed DC sputtering modes. We demonstrate the effects of argon sputter pressure (1-25mT) on residual stress, film density and film resistivity for various pulsed DC processes and contrast these with the properties formed during continuous DC sputtering. For the pulsed DC experiments we show how these three film properties (stress, density and resistivity) depend on argon pressure for each of four different pulse frequencies (50, 150, 250 and 350 kHz - reversal time is held at 1.0 μs). Residual stress is determined through wafer curvature methodologies – working within the assumptions of Stoney’s­ equation². Film density determined using x-ray reflectivity. Room temperature resistivity is determined using four-point probe instruments.

In general, the stress can be tailored during pulsed DC and constant DC sputtering by adjusting argon sputter pressure. For most conditions, the films are in a state of in-plane tensile stress after deposition and cooldown although near-zero stress can be obtained at lower pressures. Pulse frequency is shown to have a minor effect on residual stress for most processes. However, frequency has a greater effect on stress at the lower sputter pressures (1-5mT). We further evaluate the stress of all films in terms of intrinsic and extrinsic contributions to isolate the role of pulsed DC sputtering process parameters on intrinsic stress. Extrinsic stress effects (due to mismatch in thermal expansion coefficients) are factored out from the final, residual stress using known temperatures achieved during deposition and the mechanical properties of the film and substrate.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Co., for the United States Department of Energy’s National Nuclear Security Administration under Contract No. DEAC04-94AL85000.

References:

1) J. Lin, J.J. Moore, W.D. Sproul, B. Mishra and Z. Wu, Thin Solid Films 518 (2009) 1566.

2) G.G Stoney, Proc. Roy. Soc. Ser A, 82 (1909) 172

Glancing Angle Deposition (GLAD)¹ thin films are increasingly used in optical and sensor devices that benefit from the unique refractive properties or ultra-high surface area. Extending the use of GLAD films to energy devices, epitomised by the fields of photovoltaics² and fuel cell catalysis³, increases the complexity in desired film requirements. High electrical conductivity along the length of GLAD structures - normal to the substrate plane - is necessary in order to exploit the high surface area of GLAD films in electronic devices. To date, GLAD has been applied to a variety of metals and conductive oxides^4-6, and preliminary trends outline a relationship between the angle of incident flux, film density and in-plane resistivity. More specifically, it has been found that as the oblique deposition angle increases, the in-plane resistivity also increases. This relationship has been attributed to a decrease in film density resulting in diminished conductive pathways. Electrical anisotropy has also been observed, with differing in-plane resistivity for parallel and perpendicular directions with respect to the nanocolumns formed.^4-6 A thorough study of both in-plane and through-post conductivity as a function of film composition, morphology, porosity, and crystallinity / phase is required to understand the complex interplay between film morphology and corresponding electrical properties. Quantifying differences between vertical and lateral-plane characteristics of GLAD films requires expanding on established techniques for in-plane measurements (which largely neglect morphological effects) and tailoring techniques to apply directly to GLAD films. It has been found that external boundaries begin to dominate standard bulk scattering mechanisms as film thickness decreases, resulting in an inverse relationship between film thickness and resistivity.⁷ Subsequently, the extensive boundaries present in GLAD films between and within individual features can result in complex electrical behaviour. We will quantify the variations in both in-plane and through-post conductivity through the use of direct and indirect experimental approaches, and relate the results to deposition parameters suitable for forming GLAD films of desirable conductivity.

[1] M.M. Haweye et al., J. Vac. Sci. Technol. A, 25, 1317, (2007).

[2] N. Li et al., Appl. Phys. Lett., 95, 123309, (2009).

[3] A. Bonakdarpour et al., Appl. Catal. A., 349, 110 (2008).

[4] J. Lintymer et al., Surf. & Coat. Tech. 174-175, 316, (2003).

[5] K.D. Harris et al., Adv. Funct. Mater., 18, 2147, (2008).

[6] D. Vick et al., J. Vac. Sci. Technol. A, 24, 156, (2006).

[7] A.F. Mayada, M. Shatzkes, Phys. Rev. B, 1, 1382 (1970).

The atomic layer deposition (ALD) of high quality metal nitrides at low process temperatures has remained a challenge. The use of organometallic precursors to reduce the deposition temperature can lead to carbon incorporation and poor electrical performance. One possibility is to use halide precursors together with hydrazine instead of ammonia for the ALD of metal nitrides. Thermochemical calculations indicate that heats of reaction are more favorable and reaction temperatures should be lower with hydrazine. In this work, TiN ALD was performed using titanium tetrachloride (TiCl₄) and hydrazine (N₂H₄). In situ quartz crystal microbalance (QCM) measurements revealed a TiN ALD growth rate of 16 ng/cm² at 225°C. The TiCl₄ and N₂H₄ reactions were both observed to be self-limiting. At higher temperatures, TiN ALD is difficult to examine using the QCM because of thermal stability issues. X-ray diffraction (XRD) and X-ray reflectivity (XRR) studies revealed that TiN ALD deposited at 275°C resulted in the purest cubic polycrystalline TiN film. TiN ALD at 275^oC also displayed the highest growth rate of 0.36 Å/cycle and a film density of 4.7 g/cm³. Fourier transform infrared (FTIR) studies of the TiCl₄ and N₂H₄ reactions at 275°C observed that primary (-NH₂) and secondary (-NH) amines are formed after hydrazine exposures. The FTIR spectra contained no evidence of any chlorine-containing salt on the surface. Elemental analysis of the TiN ALD grown at 275^oC revealed no chlorine impurities within the X-ray photoelectron (XPS) instrument detection limit of 1 at%. However, oxygen was present at 14 at% that is attributed to oxidation after exposure to air. The use of hydrazine should facilitate the deposition of TiN ALD films at process temperatures <300°C.

Thin film bulk acoustic resonators (FBAR) and bulk acoustic wave (BAW) filters based on piezoelectric aluminum nitride (AlN) thin films are widely employed for different wireless applications. As the resonance frequency of the resonator is determined by the thickness of the AlN layer, there is essential interest of using ultra-thin 100-200 nm films to extend the current technology from 1-2 to 5-10 GHz range. Reactive magnetron sputtering is a method of choice enabling formation of the films with a high degree of c-axis texture; however it is challenging to deposit such thin films with acceptable piezoelectric coefficients due to their drastically downward crystallinity compared to 500-2000 nm thick films required for lower frequency devices.

In this study, we use reactive sputtering technology with a dual cathode ac powered S-Gun magnetron [1]. The quality of the c-axis crystal orientation is characterized by the full width at half maximum (FWHM) of the AlN (0002) X-ray diffraction peak. AlN films deposited by the S-Gun on low-doped Si wafers exhibit a strong crystal orientation, which is improved with increasing film thickness. It is more sophisticated to achieve the same crystal orientation when the film is deposited on a metal bottom electrode, as it is required for the FBAR and BAW devices. Therefore, formation of well-textured underlying electrodes is essential, especially if the AlN films are relatively thin.

The crystal orientation of common electrode metals and alloys deposited on Si, SiO₂, SiC, and diamond-like substrates is greatly enhanced by depositing a thin AlN seed layer underneath the metal. In the paper, we will discuss the critical conditions and process steps required for producing ultra-thin highly textured AlN films. For this purpose, we have developed a two-step sputter deposition process enabling better conditions for AlN nucleation. After preliminary rf plasma treatment of the substrate surface, the first 20-50 nm thick AlN layer is deposited at elevated temperature with higher nitrogen concentration in Ar-N₂ gas mixture, stimulating growth of higher quality columnar grains with the increase of AlN film thickness.

The results obtained for 100 and 200 nm thick AlN films deposited onto different metal electrodes (Mo, Cr, Ir) are presented in the paper.

The sputter technology has demonstrated high efficiency in producing very thin (100 nm) AlN films exhibiting superior crystallinity with FWHM < 2.5˚on Mo electrode, which is equal to or even better than the value for the deposition on Si substrates.

[1] V. V. Felmetsger, P. N. Laptev, and S. M. Tanner, Surf. & Coat. Technol., 204 (2009) 840-844.

Sn-doped In₂O₃ (ITO) thin films find wide applications as an electrode material for photovoltaic devices. Optical transparency, electrical properties and surface roughness are the major parameters which need to be optimized for obtained device quality films for such applications. In the present work 100 nm thick ITO films were deposited on quartz substrates at room temperature using a vapor deposition technique, where a pulsed electron beam was used to ablate the target material. A series of films were deposited by varying the oxygen pressure in chamber during growth from 3.1mTorr to 20mTorr. Various characterization techniques were applied: x-ray diffraction, atomic force microscopy, four-point probe, Hall analysis, and Spectrophotometry were used to investigate the structure, surface morphology, electrical, and optical properties of these films. The best samples had a film resistivity of 6.8E^-4ohm*cm, and an average transmittance of 80% in the visible spectrum. The influence of post annealing on the film properties was also be presented.

Molybdenum oxynitride films were deposited on the p-type Si(100) substrate using radio frequency (r.f.) magnetron sputtering technique at different nitrogen gas ratio from 0 to 100%. Molybdenum oxynitride films were investigated by atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), and X-ray photoelectron spectroscopy (XPS).

In recent years, atomic layer deposition (ALD) has emerged as a technology platform for nanofabrication [1]. This interest has evolved from its intrinsic advantages; inherent thickness control, the ability to prepare highly conformal pin-hole free films, low temperature film growth and its large area uniformity. These redeeming characteristics have broadened the application of ALD films in such diverse areas as encapsulation of nanoparticles [2], templating of complex structures [3] and the modification of membranes [4].

The deposition of atomic layer protective coatings on flexible polymers and metals is another target application to improve the lifetime performance of functional materials that may be susceptible to degradation [5]. In particular, the ingress of moisture and atmospheric gases as well as the effects of abrasion and thermal cycling can significantly diminish a material’s suitability in cases where its bulk properties meet all other requirements. Inorganic barrier coatings on flexible substrates are subject to additional constraints where the mechanical strength and adhesion of the protective coating are particularly important.

In this study, ALD alumina coatings were deposited on flexible substrates including polycarbonate, polyethylene naphthalate (PEN), copper and titanium, to investigate their toughness and adhesion under tensile load. In addition, the effect of deposition conditions on the performance of these protective coatings will be presented.

1. H. Kim, H.B.R. Lee, and W.J. Maeng, Thin Solid Films, 517 (2009) 2563-2580.
2. J.R. Scheffe, A. Frances, D.M. King, X. Liang, B.A. Branch, A.S. Cavanagh, S.M. George, and A.W. Weimer, Thin Solid Films, 517 (2009) 1874-1879.
3. G. Triani, P.J. Evans, D.J. Attard, K.E. Prince, J Bartlett, S. Tan, and R.P. Burford, J. Mater. Chem., 16 (2006) 1355-1359.
4. L.Velleman, G. Triani, P.J. Evans, J. G. Shapter, and D. Losic, Micropor. Mesopor. Mater. 126 (2009) 87-94.
5. T. Hirkikorpi, M. Vaha-Nissi, T. Mustonen, E.Iiskola and M. Karppinen, Thin Solid Films, 518 (2010) 2654-2658

Deposition temperature uniformity of GaN based MQW(multiple quantum well) layers is an important key which affects the wavelength uniformity of white LEDs. Two types of heater were tested: a resistive and inductive heater. Varying the gap between the heater and the susceptor, temperature uniformity was assessed by infra-red images for both cases of a static and a rotating susceptor. The best non-uniformity of resistive heater was obtained at 3 mm gap, 6.2%. Rotating the susceptor at 2.5 rpm over the induction heater gave 4.3% of temperature non-uniformity. Temperature distribution of the graphite susceptor over the induction heater was numerically modelled and agreed with experimental results.

ZnO:Al (AZO) thin film was prepared on glass substrate with various substrate temperatures by RF magnetron sputtering deposition. Various substrate temperatures and 500 ℃ annealing on the electrical and optical properties of as-deposited AZO film were investigated by Hall measurement and spectrometer. The minimum resistivity of the as-deposited AZO film was 1.0 X 10^-3 ohm cm at the substrate temperature of 300 ℃. After annealing, the resistivity of all films was improved. The optimum resistivity of AZO thin film is 5.6 X 10^-4 ohm cm. The average transmittance of AZO thin films in the visible range was decreased with increased substrate temperature. It was found that the minimum resistivity and maximum average transmittance of 82% in the visible range were at substrate temperature of 300 ℃ and after 500 ℃ annealing.

Since the photoinduced decomposition of water on TiO₂ electrodes were discovered, semiconductor based on photocatalyst has attracted extensive interest. TiO₂ is anticipated as one of materials which are alternative for existing solar cell technology type based on a silicon type. TiO₂ shows relatively high reactivity and chemical stability under UV light whose energy exceeds the band gap of 3.2 eV in the anatase crystalline phase. The sun can provide an abundant source of photons. However, UV light accounts for the only small fraction (~5 %) of the sun’s energy compared to the visible region (45 %). Many techniques have been examined to achieve this purpose, including the doping of TiO₂ with transition metals (such as Cr, Fe, Ni, V).

In this study, TiO₂ film has been prepared by reactive magnetron sputtering using a Ti target in an Ar/O₂ gas mixture. Fe addition was performed by Fe sputtering onto those TiO₂ films. Composition and microstructure of these films were investigated by X-ray photoelectron spectroscopy and X-ray diffraction, respectively. Chromatic change of a methylene blue solution was applied to a photocatalytic property. Light irradiation to the TiO₂ film in a methylene blue solution was carried out using a commercial sterilizing lamp as ultraviolet light and artificial sun light as visible light. Transmittance of a methylene blue solution was measured by a spectrophotometer. Furthermore, photocurrent between the TiO₂ film and a platinum electrode was measured by a volt-ampere characteristic using an unresisted ammeter in a KCl solution of 0.5 mol/ℓ.

The crystal structure of TiO₂ turned from a ruttile type into an anatase type with increase of O₂ gas flow rate. Photocatalytic characteristic of an anatase type showed the higher value under ultraviolet light, while the difference in the crystallographic structure was not obserbed under visible light. The effect of adding Fe was obtained at the Fe-added sample basing TiO₂ prepared with O₂ gas flow rate of 1.5 and 2.0 sccm. It was considered that the charge separation between an electron and a hole was enhanced by adding Fe to the TiO₂ surface. The optimum thickness of the Fe film was about 0.1 nm.

Surface and interface properties of thin films are critical for the growth and commercialization of microelectronics and Photovoltaics (PV) products. During the development of these thin film materials, chemical and structural characterization of surfaces at each film layer and interfaces between different layers are essential to aid product development and manufacture process for optimum products.

This presentation will focus on the applications of applying integrated methods/techniques to support thin film construction using Atomic Layer Deposition (ALD) and Physical Vapor Deposition (PVD) methods, including the study of surface composition and morphology, surface treatment, inter-layer diffusion, and film stoichiometry.

Titanium dioxide (TiO₂) has considerable properties such as photocatalytic effect, dye-sensitized photovoltaic effect, photoinduced hydrophilicity and transparent electrod. Among all these properties photocatalytic property has been interested by many researchers because of its promised application such as antifouling effect and ability to decompose environmental pollution materials. However, TiO₂ has a high band gap (3.0 ~ 3.2 eV) so that the most photocatalytic effect occurs under UV irradiation. In order to improve TiO₂ behavior under visible light, there is many researchers have used various methods such as gas or metal doping.

In this study N⁺ ion implantation was used to improve the optical properties of TiO₂ films, which were prepared by reactive magnetron sputtering on glass substrate (corning #1737). The substrate was sputtered by Ar ions in order to clean the surface before the TiO₂ thin film formation. Titanium (Ti) was sputtered from Ti target in an Ar / O₂ gas and the substrate was hated at 200 ^oC. The total film thickness was around 145nm with a deposition rate of 0.025nm/sec. N⁺ ion was irradiated to TiO₂ thin film at 15keV in acceleration voltage and 40µA/cm² in ion current density with a various irradiation doses from 2.5×10¹⁵ to 250×10¹⁵ions/cm². Film thickness of the samples was measured by Avantes optical spectrometers system (AvaSpe-2048). The structure was determined by X-ray diffraction (XRD: MAC Science High quality XG M18XCE) with CuKα (0.154nm) radiation at an incident angle of 0.3º, and the composition was characterized by X-ray photoelectron spectroscopy. The photocataylitic property was measured by a methylene blue immersion test. The spectrophotometer (SHIMADZU UV-2550) was used to measure the difference in light absorption at a wave length of 665nm and also was used to measure the optical band gap for ion irradiated films.

N⁺ ion implanted TiO₂ films showed a narrower optical band gap than unirradiation films, i.e. N⁺ was substituted for O and created a new energy level. Optical band gap was changed from 3.58 to 3.5 eV at sample of 12.510¹⁵ions/cm² ion irradiation dose, this sample was showed a maximum photocatalytic activity for visible light.