bluuebunny/crossref_metadata_2025 huggingface dataset:
New Slurry Formulation for Copper-CMP Process in a Damascene Integration Scheme
Authors: Terzieva Valentina L. , Sijmus Bram M. , Meuris Marc A. , Puppe Lothar , Passing Gerd
Published: June 2019

In this work novel slurries both for copper and tantalum nitride removal were developed. In the first step the Cu bulk is removed, by using high selective slurry, which stops on the underlying TaN barrier. The selectivity of Cu vs. TaN achieved with this slurry is larger than 1/100. High selective second step slurry is further introduced for removing the barrier material. In the present work data concerning dishing and erosion will be presented as a function of line width and pattern density across the wafer. Electrical yield measurements on shorts and opens of meander-fork structures will be discussed.
Analysis of Local Planarization with Polishing Time, Film Thickness, Chemical Non-Uniformity, Line Density, Line Width, and Pad Relaxation Property
Authors: Bian Jinru , Quanci John
Published: June 2019

Theoretical chemical mechanical polishing local planarization models as a function of polishing time and film removal are reviewed, and re-derived in a systematic and correlative way. The derived models employ pad viscoelastic and relaxation properties to explain the experimental phenomena that step height local planarization is an exponential function of line width at the same line density, and also account for the affect of pattern density and polishing of two different materials at the same time on step height planarization.
Study of Defect Generated During Cu/Black Diamond CMP Process
Authors: Wu Shaoyu , Li Ning , Kang J. M. , Lam T. W. M. , Lin B. , Selvaraj T. , Zhao S. P. , Kumar R. , Foo P. D.
Published: June 2019

Black Diamond (BD) is gaining popularity as a low k dielectric for copper/low k integration. However, because of lower hardness and more hydrophobic in nature of BD film surface comparing with those of the conventional oxide, some specific defects appear during CMP process of Cu/BD patterned wafers. In this study, the patterned wafer inspection systems, AIT II, and SEM review station are used to review and to classify such defects generated from CMP process. Using conventional Cu/Oxide CMP process, the percentage of these specific defects from Cu/BD CMP is typically more than 60 of total defect count. By modifying the composition of slurry with new additives and optimization of polishing and cleaning parameters, the total defect count can be reduced by 80%, in which the amount of specific defects is less than 5% of total defect count.
On the Role of Surface Diffusion and Its Relation to the Hydrogen Incorporation During Hydrogenated Amorphous Silicon Growth
Authors: Smets A.H.M. , Kessels W.M.M. , van de Sanden M.C.M.
Published: June 2019

The incorporation of hydrogen in vacancies and at void surfaces during hydrogenated amorphous silicon growth from a remote expanding thermal plasma (ETP) is systematically studied by variation of the mass growth flux Γa-Si:H and substrate temperatureTsub. An evident relation between the void incorporation and the growth parameters Γa-Si:H andTsubhas been observed. We speculate on a possible relation with the surface diffusion processes during deposition. An activation energy for surface diffusion during a-Si:H growth of 0.8-1.1 eV is obtained using this assertion, similar to the activation energy deduced from surface roughness evolution studies. For compact films hydrogen is predominantly present at vacancies, and a possible relation with the hydrogen removal mechanism during deposition is discussed.
Hydrosilylation of Silicon Surfaces: Crystalline versus Amorphous
Authors: Lehner Andrea , Steinhoff Georg , Brandt Martin S. , Eickhoff Martin
Published: June 2019

Using thermally induced hydrosilylation, organic molecules were covalently bonded to H-terminated crystalline silicon (111) and hydrogenated amorphous silicon (a-Si:H) surfaces. The resulting chemical surface structure was analyzed by X-ray photoelectron spectroscopy (XPS) and compared to that of silicon surfaces covered by a native oxide or terminated with hydrogen. For both kinds of substrates, the presence of oxygen on the surface is found to hinder the hydrosilylation reaction. Stable H-termination as a starting point for a successful hydrosilylation can be obtained on a-Si:H surfaces with much less technological effort than on crystalline silicon surfaces. Photoconductivity measurements of the different a-Si:H surfaces at low intensity of illumination (monomolecular recombination regime) indicate that the hydrosilylated surface has less defects than the H-terminated surfaces or surfaces covered with native oxide. Spin-dependent photoconductivity measurements identify the dominant paramagnetic defect at the hydrosilylated a-Si:H surface to be the silicon dangling bond.
Atomistic Character of Nanocrystalline and Mixed Phase Silicon
Authors: Biswas R. , Pan B. C.
Published: June 2019

Materials grown close to the phase boundary of amorphous and microcrystalline growth have the best electronic properties for solar cells. Systematic molecular dynamics methods have generated such nano-crystalline silicon, consisting of a mixed phase of nano-crystallites in an amorphous matrix, using an embedding method. An excess density of H resides on the surface of the nanocrystallites. The structure of this heterogeneous phase will be characterized by atomic distribution functions and structure factors. The electronic band structure of smaller models of nanocrystalline silicon reveals no midgap states and is similar to a-Si:H. There is a highly strained region surrounding the crystallites. The presence of localized strain region may increase the stability of the material.
Evidence For Trap-Conversion Induced Instability In Amorphous Silicon
Authors: Dalal Vikram L. , Sharma Puneet , Aziz Abdul
Published: June 2019

It has been shown recently that there are two distinct types of recovery during annealing of amorphous Silicon after degradation due to light soaking. It has been postulated that the two different kinetics of annealing point to the existence of two different types of states, with perhaps one state being charged dangling bonds and the other state being neutral dangling bonds. To see if two kinds of states exist, in this paper, we study the kinetics of degradation within the first 100 seconds, and also study the entire absorption curve at all degradation times. An analytical model is derived for early time degradation based on the conversion of a D- state into a neutral dangling band by absorption of a light generated ( the trap-to-dangling bond conversion model of Adler) and the experimental data of degradation versus light intensity fit the predictions of the model very well. The model also predicts that the Adler-type negatively charged defect states, which have a negative correlation energy, upon conversion will transform into Do states at a higher energy, and therefore, there should be a decrease in absorption corresponding to states closer to the valence band, and an increase in absorption corresponding to states near the mid-gap. For the films where such D- states are deliberately introduced by using a small oxygen (a donor atom) leak, we see strong evidence for such a behavior in absorption, with a decrease in the 1.3-1.4 eV photon energy range, and an increase in the 1.1 eV photon energy range. The increase in Do corresponds well with the decrease in photo-conductivity, even at the earliest times.
Properties of High Quality p-Type Micro-Crystalline-Si Prepared by Cat-CVD
Authors: Matsumura Hideki , Katouno Kouichi , Itoh Masaya , Masuda Atsushi
Published: June 2019

Properties of p-type μc-Si prepared by Cat-CVD (Catalytic Chemical Vapor Deposition), often called Hot-Wire CVD, are studied for possible application to window layer of a-Si solar cells. Electrical, structural and optical properties are investigated. It is concluded that Cat-CVD p-type μc-Si is a suitable material as a window layer for Cat-CVD a-Si solar cells.
Microstructure and Optical Functions of Transparent Conductors and their Impact on Collection in Amorphous Silicon Solar Cells
Authors: Ferreira G. M. , A. ChiChen , Ferlauto S. , Rovira P. I. , An Ilsin , Wronski C.R. , Collins R. W. , Ganguly G. , Kwak Joong Hwan , Lim Koeng Su
Published: June 2019

We have developed new procedures for determining the microstructure as well as the index of refraction and extinction coefficient spectra {n(E),k(E)} for textured SnO2thin films on glass used as the top contact layers and superstrate for amorphous silicon (a-Si:H) p-i-n solar cells. These procedures combine (i) multichannel Mueller matrix spectroscopy using a dual rotating-compensator spectroscopic ellipsometer in reflection from the surface of the SnO2, a measurement that is most sensitive to microstructure andn(E), and (ii) transmission spectroscopy through a double-thick SnO2sandwich contacted with index-matching fluid, a measurement that is most sensitive tok(E). An important optical loss in a-Si:H p-i-n solar cells is reflection from the SnO2/p-layer interface. In this paper, we characterize this optical loss through modeling the solar cell optical quantum efficiency and demonstrate the extent to which microscopic roughness at this interface can serve as an anti-reflection layer for enhanced collection.
Field-Assisted Germanium Induced Crystallization of Amorphous Silicon
Authors: Derakhshandeh J. , Mohajerzadeh S. , Golshani N. , Soleimani E. Asl , Robertson M.D.
Published: June 2019

A field-assisted germanium-induced crystallization of amorphous silicon on glass is reported at temperatures below 500°C. Silicon films with a thickness of 0.1um are covered with 500Å of germanium as the seed of crystallization. Applying an electric field enhances the growth from both cathode and anode sides. XRD, SEM and TEM analyses have been used to study the crystallinity of the samples which have been treated under different annealing conditions, all confirming the polycrystalline nature of the annealed silicon films. The value of the applied voltage plays a crucial role in the crystalline quality of Si layers. While samples treated without an external voltage are not polycrystalline, an electric voltage of 10 V applied for a 1cm separation between anode and cathode, seems suitable for achieving good poly-crystalline Si layers. The size of grains varies between 0.1 and 0.2μm, as observed using SEM.
A Simple Lateral Grain Growth of Poly-Si by Single Excimer Laser Crystallization of Amorphous Silicon Film Deposited on Polygon Shaped Trench
Authors: Jung Sang-Hoon , Kang Su-Hyuk , Shin Hee-Sun , Han Min-Koo
Published: June 2019

A simple lateral grain growth of polysilicon employing single excimer laser irradiation is proposed. In order to increase the size of silicon grain and to control the location of the large lateral grain, the oxide trench is employed under the amorphous silicon film in the proposed method. The proposed oxide trench, which is shaped like a triangle or a polygon with an acute angle, induces temperature gradient on the molten silicon film during the solidification. It was verified by SEM that about 2 μm-long silicon grains are successfully achieved near the oxide trench edge and the locations of lateral grains are controlled by the angular points of the diagram.
Anomalous behaviour of stain etched porous silicon photoluminescence
Authors: Guerrero-Lemus Ricardo , Ben-Hander Fathi A. , Hernández-Rodríguez Cecilio , Martínez-Duart José M.
Published: June 2019

In this work we present a comparative study of porous silicon (PS) photoluminescence for samples stain etched and electrochemically etched. The etching parameters for both types of samples have been adjusted to obtain similar porous structures. The photoluminescence spectra have been obtained varying the excitation energy between 2.48 and 3.54 eV. The variation of the excitation energy produces differences in the evolution of the emission energy maximum between both types of PS. This behaviour is attributable to the differences in oxidation level in the porous structure. Also it has been established a higher concentration of luminescent centers for stain etched PS.
Development of Vertically Integrated Imaging and Particle Sensors
Authors: Wyrsch N. , Miazza C. , Dunand S. , Shah A. , Blanc N. , Kaufmann R. , Cavalier L. , Anelli G. , Despeisse M. , Jarron P. , Moraes D. , Sirvent A. G. , Dissertori G. , Viertel G.
Published: June 2019

Integrated imaging and particle sensors have been developed using thin-film on ASIC technology. For this purpose, hydrogenated amorphous silicon diodes, in various configurations, have been optimized for imaging and direct particle detection. These devices were first deposited on glass substrates and later on CMOS readout chips. With an optimization of the material properties and of the diode, a dark current of 1 pA/cm2 could be achieved on p-i-n structures at reverse bias voltage of 1 V. CMOS imagers, incorporating these optimized diodes were then fabricated and characterized. Very thick diodes (with thicknesses up to 50 μm) were also optimized and deposited on glass and on CMOS readout chips. Particle detectors in TFA technology with 12 and 30 μm a-Si:H n-i-p diodes have been fabricated and characterized using light pulse illumination. Direct detection of single low-energy beta particles has been demonstrated.
An Amorphous Silicon Photoconductor for UV Detection
Authors: Hillebrand Matthias , Blecher Frank , Sterzel Jürgen , Böhm Markus
Published: June 2019

An amorphous silicon photoconductor to detect wavelengths between 180 nm to 550 nm without scintillator is presented. The photoconductor is based on a coplanar configuration of the electrodes, similar to measurement structures to determine material characteristics of amorphous layers, e.g. for the Constant Photocurrent Method (CPM). After passing through a thin transparent passivation layer, the incident radiation is directly absorbed in the intrinsic a-Si:H material. The carrier collecting electrical field is applied perpendicular to the incoming light. Test structures have been fabricated with 80 nm thick sputtered chromium contacts on top of a 60 nm carbonized hydrogenated i-layer and a SixNx passivation layer with a thickness of about 36 nm. The spacing between the Schottky contacts is varied between 3 μm and 100 μm. They are deposited on top or below the a-SiC:H layer. First experiments with this simple coplanar design show that with an increasing voltage a shift towards UV wavelengths can be observed. The new UV detector is applicable in the field of TFA image sensors (Thin Film on ASIC) and in the new Lab-on-a-Chip concept presently under development at the institute for microsystem technologies.
Post-transit Analysis of Transient Photocurrents from High-Deposition-Rate a-Si:H Samples
Authors: Brinza Monica , Kessel W.M.M. , Smets Arno H.M , Sanden M.C.M van de , Adriaenssens Guy J.
Published: June 2019

An interpretation of post-transit photocurrents in a time-of-flight experiment in terms of the underlying density of localized gap states in the sample is presented for the case of hydrogenated amorphous silicon cells prepared by the expanding thermal plasma technique. It is pointed out that part of the observed current is not generated by re-emission of trapped photo-generated charge and should, therefore, not be used for density-of-states calculations.
Thin Film Cavity Ringdown Spectroscopy and Second Harmonic Generation on Thin a-Si:H Films
Authors: Aarts I.M.P. , Hoex B. , Gielis J.J.H. , Leewis C.M. , Smets A.H.M. , Engeln R. , Nesládek M. , Kessels W.M.M. , Sanden M.C.M. van de
Published: June 2019

A set of 8 rf deposited a-Si:H thin films of various thickness (4-1031nm) have been used to explore the applicability of two optical techniques, thin film cavity ringdown spectroscopy (tfCRDS) and second harmonic generation (SHG), for the measurement of small defect-related absorptions. In this paper we will give a first overview of the different aspects of these techniques, which are novel in the field of amorphous silicon materials. It is shown that tf-CRDS is capable of measuring defect-related absorptions (associated with dangling bonds) as small as 10-7 for a single measurement, without the need for elaborate calibration procedures. The results are compared with photothermal deflection spectroscopy (PDS) for a broad spectral range (0.7 – 1.7 eV) and show good agreement. Furthermore the existence of a defect-rich surface layer with a defect density of 1.1×1012 cm-2 has been proven. The absorption spectrum of a 4 nm thin film has revealed a different spectral signature than a bulk dominated (1031 nm) film. The SHG experiments on a-Si:H films have shown that the second harmonic signal arises from the surface states and polarization dependent studies have revealed that the surface states probed have an ∞m-symmetry. From this it can be deduced that the absorbing surface states are isotropically distributed. A spectral scan suggests that the second harmonic signal, whose origin has not been unrevealed yet, has a resonance at an incident photon energy of 1.22 eV.
Time-Resolved Switching Studies in a-Si:H and Related Films
Authors: Stradins P. , Jackson W. B. , Branz H. M. , Hu J. , Perkins C.L. , Wang Qi
Published: June 2019

Switching in a-Si:H and a-Si:HNx layers is investigated by pulse current transient and Auger scanning microspectroscopy measurements. Switching in a-Si:H with Ag and Cr contacts exhibits 2 different regimes depending on the voltage pulse polarity. With a positive top Ag contact, switching occurs in nanoseconds after a certain latency time, which depends on voltage exponentially. For a negative Ag contact, there is no latency time provided the voltage exceeds a certain critical value. This might be related to interface effects on contact properties or field-assisted metal diffusion. Scanning Auger element micromaps reveal metallic filaments in the switched films. They contain both Ag and Cr throughout the film thickness. Two phases of the filament formation are suggested – a precursor phase and a post-switching phase characterized by local heating and atomic diffusion. Soft and hard switching are observed in a-Si:HNx films simultaneously and their rates depend strongly on the contact material and applied voltage. Soft switching might be related to the charge trapping in this wide bandgap material.
Threshold Voltage Performance of a-Si:H TFTs for Analog Applications
Authors: Karim K.S. , Sakariya K. , Nathan A.
Published: June 2019

Amorphous silicon (a-Si:H) thin-film transistors (TFT) used in emerging, non-switch applications such as analog amplifiers or active loads, often have a bias at the drain terminal in addition to the gate that can alter their threshold voltage (VT) stability performance. At small gate voltages (0 ≤ VST ≤ 15 V) where the defect state creation instability mechanism is dominant, the presence of a bias at the TFT drain is found to decrease the shift in VT (ΔVT) compared to the ΔVT in the absence of a drain bias. In this paper, a ΔVT model accounting for TFT drain bias, is used to predict the performance of a-Si:H analog circuits in active pixel sensor (APS) medical xray imaging and active matrix, organic light emitting diode (AMOLED) display applications.
Localised States in Microcrystalline Silicon Photovoltaic Structures Studied by Post-Transit Time-of-Flight Spectroscopy
Authors: Reynolds Steve , Smirnov Vladimir , Main Charlie , Carius Reinhard , Finger Friedhelm
Published: June 2019

Post-transit time-of-flight spectroscopy has been used to study the density of states distribution in hot-wire CVD microcrystalline silicon pin solar cell structures. For an absorber layer Raman scattering intensity ratio ICRS of 0.4 or less, behaviour consistent with multiple-trapping carrier transport is observed and may be interpreted in terms of a conduction-band tail of some 18 meV slope plus a broad defect bump of order 1017 cm-3 centered at 0.55 eV relative to the mobility edge. As ICRS is increased beyond 0.4, the temperature-dependence of the photocurrent transient becomes inconsistent with multiple-trapping and above 0.6 the decays are almost temperature-independent. By comparing data taken at 300 K, it may be inferred from the multiple-trapping model that localised states between 0.35 and 0.5 eV are associated with the presence of columns or clusters of nanocrystals and those deeper than 0.5 eV with the amorphous tissue. Results are compared with previous work on coplanar and sandwich structures.
Helium Versus Hydrogen Dilution of Silane in the Deposition of Polymorphous Silicon Films: Effects on the Structure and the Transport Properties
Authors: Saadane O. , Lebib S. , Kharchenko A.V. , Suendo V. , Longeaud C. , Cabarrocas P. Roca i
Published: June 2019

We compare the deposition rate, hydrogen incorporation and optoelectronic properties of hydrogenated polymorphous silicon films produced either by the decomposition of silane-hydrogen or of silane-helium mixtures. Our results clearly show that He dilution allows to drastically reduce the RF power needed to achieve the same deposition rate as in the case of H2 dilution. Infrared spectroscopy and hydrogen effusion experiments show clear differences in the hydrogen bonding and content in both series of films. Interestingly, both He and hydrogen dilution result in films with improved transport properties, in particular the hole diffusion length, with respect to standard amorphous silicon. These results indicate that He dilution is a good alternative to H2 dilution to prepare intrinsic layers for solar cells.
Surface Roughness Study of Low-temperature PECVD a-Si:H.
Authors: Dalakos George T. , Plawsky Joel L. , Persans Peter D.
Published: June 2019

Surface topography of a-Si:H thin films, deposited at 75°C by Plasma-enhanced Chemical Vapor Deposition (PECVD) has been examined using helium/silane feedstock mixtures under different substrate bias conditions. Notable differences in the surface roughness evolution are shown for films deposited in “cathodic” versus “anodic” mode – where the substrate is placed on the powered and grounded electrode respectively. Smooth and apparently featureless surfaces result from deposition on RF powered surfaces, upon which a self-bias induces high-energy ion bombardment. Rougher surfaces result from films deposited on electrically grounded surfaces. These anodic films show that after a transition period, surface roughness grows linearly with processing time, exhibiting mounded type growth as evidenced by 2-D power spectral density functions of surface height measurements. Linear growth in roughness has been predicted for shadow growth models assuming film precursor sticking coefficients of one and random angle approach of film precursor species. Growth of this nature has not been reported before in a-Si:H studies, which usually assume directional deposition conditions and sticking coefficients less than unity – occurring even at low processing temperatures.
Electrical and Optical Properties of Amorphous and Microcrystalline Hydrogenated Silicon Films Deposited Using Saddle Field Glow Discharge
Authors: Milostnaya I. , Allen T. , Gaspari F. , Kherani N.P. , Yeghikyan D. , Roes W.L. , Kosteski T. , Zukotynski S.
Published: June 2019

Amorphous (a-Si:H) and microcrystalline (μc-Si:H) hydrogenated silicon films were obtained using DC saddle field glow discharge. The structure of the films was determined by Raman spectroscopy, SEM and TEM. The optoelectronic characteristics of both a-Si:H and μcSi:H were investigated using FTIR, UV/VIS spectroscopy, dark electrical conductivity (σd) and photoconductivity (σph) measurements. Boron and phosphorous doping of a-Si:H and μc-Si:H films was also investigated. The results show that both a-Si:H and μc-Si:H undoped films are highly resistive (σd=10-8-10-10 Ω-1cm-1). The doping efficiency of μc-Si:H films is much higher than a-Si:H films. The Tauc gap for a-Si:H was in the range 1.8-1.9 eV and for μc-Si:H films it was in the range 1.9-2.5 eV. The photoconductivity measurements of undoped films indicate a higher photosensitivity of a-Si:H films (σph/σd=104)than that of μc-Si:H films (σph/σd=10-100).
Properties of Nanocrystalline Germanium-Carbon Films and Devices
Authors: Niu X.J. , Dalal Vikram L. , Noack Max
Published: June 2019

Nanocrystalline Germanium-Carbon alloys, denoted by nc- (Ge,C):H, are a potentially useful new electronic material whose bandgap can be varied by changing the Ge:C ratios. We have shown previously that nanocrystalline (Ge,C):H films can be grown using remote ECR plasma deposition. In this paper, we report on the crystal structure, electron mobility and some device related properties of these materials. The materials were grown using mixtures of either Germane and methane, with significant hydrogen dilution, or from mixtures of ethylene and germane, also with significant hydrogen dilution. X-ray diffraction measurements indicated a predominantly <111> crystal structure. The grain size was in the range of 10 nm. Raman measurements clearly show the 300 cm-1 Ge peak in the films. Electron Hall mobilities were measured in these films and were found to be in the range of 2.5-3 cm2/V-sec. Proof-of-concept p+nn+ junction devices were fabricated and showed distinct photovoltaic properties. The open circuit voltage was found to be a strong function of the itnerfaces between n+ and n layers, and between p+ and n layers. The use of an amorphous n+/n interface at the back of the improved the device performance significantly. Capacitance measurements indicated that the device behaved according to standard p/n junction theory, with the n- doping in the base layer being in the 1017/cm3 range. Thus, the base layer was not intrinsic, but rather n type, as may be expected for a crystalline as opposed to amorphous material. Quantum efficiency data indicated that as C was added to the material, the edge of the QE curve shifted to higher photon energies, indicating larger bandgaps.
High Temperature n- and p-type Doped Microcrystalline Silicon Layers Grown by VHF PECVD Layer-by-Layer Deposition
Authors: Gordijn A. , Rath J.K. , Schropp R.E.I.
Published: June 2019

Due to the high temperatures used for high deposition rate microcrystalline (μc-Si:H) and polycrystalline silicon, there is a need for compact and temperature-stable doped layers. In this study we report on films grown by the layer-by-layer method (LbL) using VHF PECVD. Growth of an amorphous silicon layer is alternated by a hydrogen plasma treatment. In LbL, the surface reactions are separated time-wise from the nucleation in the bulk. We observed that it is possible to incorporate dopant atoms in the layer, without disturbing the nucleation. Even at high substrate temperatures (up to 400°C) doped layers can be made microcrystalline. At these temperatures, in the continuous wave case, crystallinity is hindered, which is generally attributed to the out-diffusion of hydrogen from the surface and the presence of impurities (dopants).

We observe that the parameter window for the treatment time for p-layers is smaller compared to n-layers. Moreover we observe that for high temperatures, the nucleation of p-layers is more adversely affected than for n-layers. Thin, doped layers have been structurally, optically and electrically characterized. The best n-layer made at 400°C, with a thickness of only 31 nm, had an activation energy of 0.056 eV and a dark conductivity of 2.7 S/cm, while the best p-layer made at 350°C, with a thickness of 29 nm, had an activation energy of 0.11 V and a dark conductivity of 0.1 S/cm. The suitability of these high temperature n-layers has been demonstrated in an n-i-p microcrystalline silicon solar cell with an unoptimized μc-Si:H i-layer deposited at 250°C and without buffer. The Voc of the cell is 0.48 V and the fill factor is 70 %.
Deposition of Device Quality μc-Si Films and Solar Cells at High Rates by HWCVD in a W Filament Regime where W/Si Formation is Minimal
Authors: Iwaniczko E. , Mahan A.H. , Yan B. , Gedvilas L.N. , Williamson D.L. , Nelson B.P.
Published: June 2019

μc-Si has traditionally been deposited by Hot Wire CVD at a low filament temperature. At these temperatures, silicides rapidly form on the filament surface, leading in the case of a tungsten filament to both film reproducibility and filament lifetime issues. By depositing films consecutively using identical deposition parameters, these issues are chronicled for a filament temperature of ∼ 1750°C. Upon increasing the filament temperature to ∼ 1825-1850°C, these reproducibility and lifetime issues disappear and, by lowering both the substrate temperature and chamber pressure, device quality μc-Si is deposited at high deposition rates in a filament regime where tungsten silicide formation is minimal. Both single junction and tandem solar cells are fabricated using this material, confirming the validity of this approach.
Hole Drift-Mobility Measurements in Contemporary Amorphous Silicon
Authors: Dinca S. , Ganguly G. , Lu Z. , Schiff E. A. , Vlahos V. , Wronski C. R. , Yuan Q.
Published: June 2019

We present hole drift-mobility measurements on hydrogenated amorphous silicon from several laboratories. These temperature-dependent measurements show significant variations of the hole mobility for the differing samples. Under standard conditions (displacement/field ratio of 2×10-9 cm2/V), hole mobilities reach values as large as 0.01 cm2/Vs at room-temperature; these values are improved about tenfold over drift-mobilities of materials made a decade or so ago. The improvement is due partly to narrowing of the exponential bandtail of the valence band, but there is presently little other insight into how deposition procedures affect the hole drift-mobility.
Recombination in n-i-p (Substrate) a-Si:H Solar Cells with Silicon Carbide and Protocrystalline p-Layers
Authors: Vlahos V. , Deng J. , Pearce J.M. , Koval R.J. , Ferreira G.M. , Collins R.W. , Wronski C.R.
Published: June 2019

A study was carried out on hydrogenated amorphous silicon (a-Si:H) n-i-p (substrate) solar cell structures with p-a-SiC:H and highly diluted p-Si:H layers grown with different dilution ratios R=[H2]/[SiH4]. The contributions of the recombination at the p/i interfaces to the forward bias dark current characteristics were identified and quantified for the different cell structures. In both cell structures the role of the p/i interfaces was identified and it is found that the lowest p/i interface recombination is obtained with protocrystalline p-Si:H layers having no microcrystalline component. The results with p-Si:H layers are attributed not only to their properties but also to the subsurface modification of the intrinsic layer. Evidence is also presented that points to the beneficial effects of the high hydrogen dilution and power used in the deposition of these p-layers in creating the p/i interface regions. The limitations on 1 sun open circuit voltage (VOC) imposed by the p/i recombination present in all the cell structures is consistent with the mechanisms proposed by Deng et al.[1]. The results presented here also point to why the 1 sun VOC in protocrystalline p-Si:H solar cells is higher than that in p-a-SiC:H cells.
Combinatorial Approach to Thin-Film Silicon Materials and Devices
Authors: Wang Qi , Tessler Leandro R. , Moutinho Helio , To Bobby , Perkins John , Han Daxing , Ginley Dave , Branz Howard M.
Published: June 2019

We apply combinatorial approaches to thin-film Si materials and device research. Our hot-wire chemical vapor deposition chamber is fitted with substrate xyz translation, a motorized shutter, and interchangable shadow masks to implement various combinatorial methods. For example, we have explored, in detail, the transition region through which thin Si changes from amorphous to microcrystalline silicon. This transition is very sensitive to deposition parameters such as hydrogen-to-silane dilution of the source gas, chamber pressure, and substrate temperature. A material library, on just a few substrates, led to a three-dimensional map of the transition as it occurs in our deposition system. This map guides our scientific studies and enables us to use several distinct transition materials in our solar-cell optimization research. We also grew thickness-graded wedge samples spanning the amorphous-to-microcrystalline Si transition. These single stripes map the temporal change of the thin silicon phase onto a single spatial dimension. Therefore, the structural, optical, and electrical properties can easily be studied through the phase transition. We have examined the nature of the phase change on the wedges with Raman spectroscopy, atomic force microscopy, extended x-ray absorption fine structure (EXAFS), x-ray absorption near-edge spectroscopy (XANES), ultraviolet reflectivity, and other techniques. Combinatorial techniques also accelerate our device research. In solar cells, for example, the combinatorial approach has significantly accelerated the optimization process of p-, i-, n-, and buffer layers through wide exploration of the complex space of growth parameters and layer thicknesses. Again, only a few deposition runs are needed. It has also been useful to correlate the materials properties of single layers in a device to their performance in the device. We achieve this by depositing layers that extend beyond the device dimensions to permit independent characterization of the layers. Not only has the combinatorial approach greatly increased the rate of materials and device experimentation in our laboratory, it has also been a powerful tool leading to a better understanding of structure-property relationships in thin-film Si.
A Study of Atomic Layer Deposition and Reactive Plasma Compatibilitywith Mesoporous Organosilicate Glass Films
Authors: Ryan E. Todd , Freeman Melissa , Svedberg Lynne , Lee J.J. , Guenther Todd , Connor Jim , Yu Katie , Sun Jianing , Gidley David W.
Published: June 2019

The compatibility of ALD and CVD metal deposition with mesoporous and microporous carbon-doped organosilicate glass (OSG) films was examined. Blanket film studies using TEM, TOF-SIMS, and positron lifetime spectroscopy demonstrate that ALD Wand TaN penetrate deep into the mesoporous film via the film's connected pore structure. In contrast, metal penetration into microporous OSG films was not observed. He and NH3 plasma pretreatments to the mesoporous OSG film surface did not seal the mesopores to ALD metal penetration, but the plasmas did damage the bulk of the mesoporous OSG film with varying severity. The results indicate that porosity, pore size, and/or pore structure regulate ALD/CVD precursor diffusion and that ALD metal deposition is a good probe of pore sealing strategies.
Adhesion Enhancement for Multiple Level Cu/SiLKTM Integration
Authors: Chen X. T. , Lu D. , Tan Y. T. , Chen Y. W. , Foo P. D.
Published: June 2019

The effects of various integration processes on the adhesion of SiLKTM to the Ta barrier layer were studied. We have found that the H2/He reactive plasma clean treatment (RPC) causes poor adhesion between these two layers. The results obtained from TOF-SIMS showed that hydrogen plasma had caused damage to the SiLK surface causing molecular fragmentation. Hydrogen had also been chemically incorporated into SiLK to form a hydrogen-saturated surface. To improve adhesion, an argon sputtering process was employed to remove this altered SiLK surface layer. Adhesion was found to have been improved and no delamination was observed even up to integration of 7 metal layers.
Quantitative Measurements of Subcritical Debonding of Cu Films from Glass Substrates
Authors: Pang M. , Baker S.P.
Published: June 2019

Subcritical debonding of Cu films from silicate glass substrates has been studied using a driver film method. In this method, a highly stressed Cr overlayer is imposed to debond the target Cu film from the substrate. Substrates included a commercial flat panel display glass and glasses having composition (2SiO2)x(CaO·Al2O3)1-x. A range of strain energy densities for driving interfacial crack growth was provided by depositing Cr driver layers with varying thickness. The film debond velocity was obtained experimentally. The stresses in Cu and Cr were measured and used to obtain the strain energy release rate. The effect of oxygen concentration and substrate composition on subcritical debonding was studied. A kinetic crack model previously developed for bulk ceramics was modified and applied. Differences in adhesion could be attributed to differences in density of strong Cu-O bonds across the interface.
Deposition and Characteristics of Tantalum Nitride films by Plasma Assisted Atomic Layer Deposition as Cu Diffusion Barrier
Authors: Na Kyoung-Il , Park Se-Jong , Jeong Woo-Cheol , Kim Se-Hoon , Boo Sung-Eun , Bae Nam-Jin , Lee Jung-Hee
Published: June 2019

For a diffusion barrier against Cu, tantalum nitride (TaN) films have been successfully deposited by both conventional thermal atomic layer deposition (ALD) and plasma assisted atomic layer deposition (PAALD), using pentakis (ethylmethlyamino) tantalum (PEMAT) and ammonia (NH3) as precursors. The growth rate of PAALD TaN at substrate temperature 250° was slightly higher than that of ALD TaN (0.80 Å/cycle for PAALD and 0.75 Å/cycle for ALD). Density of TaN films deposited by PAALD was as high as 11.0 g/cm3, considerably higher compared to the value of 8.3 g/cm3 obtained by ALD. The N: Ta ratio for ALD TaN was 44: 37 in composition and the film contained approximately 8∼10 atomic % carbon and 11 atomic % oxygen impurities. On the other hand, the ratio for PAALD TaN layers was 47: 44 and the respective carbon and oxygen contents of TaN layers decreased to 3 atomic % and 4 atomic %. The stability of 10 nm-thick TaN films as a Cu diffusion barrier was tested through thermal annealing for 30 minutes in N2 ambient and characterized by XRD, which proves the PAALD deposited TaN film to maintain better barrier properties against Cu below 800°.
Vapor Treatment of Copper Surface Using Organic Acids
Authors: Ishikawa Kenji , Yagishita Teruo , Nakamura Moritaka
Published: June 2019

The mechanism for cleaning Cu surfaces using the vapor from organic acids was studied by infrared reflection-absorption spectroscopy (IR-RAS) and by analysis of products collected using a cold-trap placed downstream of a reactor. When formic acid vapor was exposed to oxidized Cu samples heated to about 200°C for about a half an hour, the oxides were reduced. The surface seemed to have a shiny metallic appearance but no Cu-containing volatile products were collected, and the decomposition of formic acid molecules into CO2 was observed. In contrast, using acetic acid vapor, Cu-containing etching products were collected and identified as a dinuclear Cu (II) acetate complex. The vapor treatment using formic and acetic acids can be reduced Cu oxides to have metallic Cu surfaces. Furthermore, controlling temperature and choice of organic acids enabled the advantageous establishment of a control for the reduction in, and etching of, the Cu oxides.
Impact of Annealing on the Resistivity of Ultrafine Cu Damascene Interconnects
Authors: Steinlesberger G. , Engelhardt M. , Schindler G. , Steinhögl W. , Traving M. , Hönlein W. , Bertagnolli E.
Published: June 2019

The influence of different annealing conditions on the electrical resistivity of copper damascene interconnects with lateral dimensions down to sub-50 nm was studied. Different thermal treatments after copper plating as well as annealing processes in addition to the final anneal step were carried out in order to study the microstructural change of copper damascene lines. It was found that rapid thermal annealing (RTA) at high temperatures (600°C) leads to an enlargement of the Cu grains by a factor of 2 for wide lines, whereas a significant impact of annealing on the median grain size of ultrafine lines was not observed. This is attributed to the geometrical limitation of the grain growth process. As a result, the size effect in Cu nano-interconnects which is mainly determined by grain boundaries acting as scattering sites for electrons cannot be reduced significantly by using thermal treatments.
A Novel Technique to Re-construct 3D Void in Passivated Metal Interconnects
Authors: Tan Cher Ming , Gan Zhenghao , Zhang Guan , Prasad Krishnamachar , Zhang Dao Hua
Published: June 2019

In the present work, a novel method is proposed to re-construct voids in passivated metal interconnections. In this method, the conventional SEM and EBIC systems are assembled and utilized without much modification. In principle, a constant current is applied to the metal interconnections while an electron beam is scanning and impinging upon the surface of the sample. The voltage at the terminals is monitored simultaneously during electron beam scanning. Resistance change, and hence voltage perturbation are expected when the electron beam approaches the defective area, caused by uneven electron beam heating (EBH) and heat transmission. Information on defects or voids is thus obtained by analyzing the voltage alteration. Finite element simulation showed that the recorded voltage perturbation is not dependent of the length of the interconnect, but a linear function of the void volume. Thus, the method is essentially useful as the metal length has increased tremendously in copper technology. In addition, it can provide the void size and depth, with the possibility to reconstruct the entire void shape in 3D.
AlCu Pattern Generation on 3D StructuredWafer Using Multi Level Exposure Method on Electrodeposited Polymer Material
Authors: Sharma Vineet , Suriadi Arief B. , Berauer Frank , Mittelstadt Laurie S.
Published: June 2019

Normal photolithography tools have focal depth limitations and are unable to meet the expectations of high resolution photolithography on highly topographic structures. This paper shows a cost effective and promising technique of combining two different approaches to achieve critical dimensions of traces on slope pattern continuity on highly topographic structures. Electrophoretically deposited photoresist is used on 3-D structured wafers. This photoresist coating technique is fairly known in the MEMS industries to achieve uniform and conformal photoresist films on 3D surfaces. Multi step exposures are used to expose electrophoretically deposited photoresist. AlCu (Cu-0.5%), 0.47-0.53 μm thick metal film is deposited on 3D structured silicon substrate to plate photoresist. By combining these two novel methods, metal (AlCu) traces of 75 μm line width and 150 μm pitch (from top flat to down the slope) have been demonstrated on isotropically etched 350 μm deep trenches with 5-10% line width loss.
Supercritical Carbon Dioxide-based Fluids Used as a Recovery Tool for Low-k Materials
Authors: Orozco-Teran Rosa A. , Gorman Brian P. , Zhang Zhengping , Mueller Dennis W. , Reidy Richard F.
Published: June 2019

Conventional ash strippers can easily damage most porous low-k materials, causing increased dielectric constants and decreased film thicknesses. This effect is more prominent in carbon containing porous low-k materials such as methylsilsesquioxane (MSQ). Ashed MSQ films exhibit increased water adsorption and dielectric constants due to the removal of methyl groups and structural damage caused by interaction with plasma species. Supercritical carbon dioxide (SC-CO2), has attracted considerable attention due its low cost, low critical point temperatures and pressures, and environmentally benign nature. This work describes the effects of SC-CO2 in combination with silylating agents on O2 ash-damaged MSQ films. FTIR, sessiledrop goniometric contact angle measurements, and SEM were used to monitor changes in the films' chemical bonding, composition, and microstructure.
Mechanical Properties of Organosilicon Thin Films Deposited from Cyclic and Acyclic Precursors using Water as an Oxidant.
Authors: Burkey Daniel D. , Gleason Karen K.
Published: June 2019

Pulsed-plasma chemical vapor deposition was used to deposit thin films from four different organosilicon (OSG) precursors, using water as the oxidant. The OSG precursors varied in structure (cyclic or acyclic), chemical composition (siloxane or silane), and type of organic substituent. Significant differences in final film structure were observed based on precursor identity, with the primary result being that cyclic siloxane precursors yielded films with a greater degree of crosslinking. The identity of the organic substituents was shown to affect the crosslinking potential, in that more reactive side groups, such as vinyl groups, facilitated the formation of crosslinking groups. At low power (200 W), film structure was dictated by precursor identity, whereas at high power (400 W), film structure became more uniform and precursor identity was less important. Mechanical properties tracked with plasma power, with low power samples being relatively soft, with hardness values between 0.126 GPa and 0.536 GPa. Samples produced at higher powers are more extensively crosslinked, resulting in enhanced mechanical properties. Samples produced at high powers had hardness values between 0.679 and 3.22 GPa, depending upon precursor identity. Dielectric constants ranged between 2.3 and 4.0.
Nanoporous Silica Films Derived from Structural Controllable Poly(silsesquioxane) Oligomers by Templating
Authors: Liu Wei-Chih , Yu Yang-Yen , Chen Wen-Chang
Published: June 2019

In this study, nanoporous silica films were prepared from the poly(hydrogen silsesquioxane)(HSSQ) and a templating agent. Three different kinds of the HSSQ with different molecular weight and Si-OH end group content were prepared through the variation of the water/triethoxysilane ratio or pH. The templaing agent for generating nanopore was triphenylsilanol (TPS). The experimental results of refractive index, dielectric constant, and FE-SEM supported the formation of the nano-size pores in the prepared silica films. The dielectric constant of the prepared nanoporous thin films could be reduced form 2.89 (porosity: 12%) to 1.85 (porosity: 58%) by increasing the added TPS. The surface roughness of the prepared nanoporous silica film in comparison with the film thickness was less than 1%. For successful generating small and uniform nanopore in the film, low molecular weight or high Si-OH content of the prepared HSSQ would be required. The current approach is useful for preparing new kinds of low dielectric constant materials.
The characterization and preparation of porous low dielectric films using various cyclodextrins as template materials
Authors: Yim Jin-Heong , Kim Jung-Bae , Jeong Hyun-Dam , Lyu Yi-Yeoul , Mah Sang Kook , Hyeon-Lee Jingyu , Lee Kwang Hee , Chang Seok , Pu Lyong Sun , Hu Y. F. , Sun J.N. , Gidley D.W.
Published: June 2019

Porous low dielectric films containing nano pores (∼20Å) with low dielectric constant (<2.2), have been prepared by using various kinds of cyclodextrin derivatives as porogenic materials. The pore structure such as pore size and interconnectivity can be controlled by changing functional groups of the cyclodextrin derivatives. We found that mechanical properties of porous low-k thin film prepared with mCSSQ (modified cyclic silsesquioxane) precursor and cyclodextrin derivatives were correlated with the pore interconnection length. The longer the interconnection length of nanopores in the thin film, the worse the mechanical properties of the thin film (such as hardness and modulus) even though the pore diameter of the films were microporous (∼2nm).
Effects of Supercritical CO2 Drying and Photoresist Strip on Low-k Films
Authors: Reidy R.F. , Zhang Zhengping , Orozco-Teran R.A. , Gorman B.P. , Mueller D.W.
Published: June 2019

Future interlayer dielectric (ILD) requirements necessitate reductions in dielectric constant to 2.1 within four years. Due to gaseous-like transport properties and near liquid-like densities, supercritical methods have been developed to dry and strip resist from these highly porous materials. Although a non-polar molecule, the solvating capability of supercritical CO2 (SCCO2) can be tailored by varying pressure, temperature, and co-solvents. This flexibility has been employed to remove photoresist and moisture from porous low-k films. The results of these experiments have been characterized using FTIR, ellipsometry, and SEM.