Thin Diffusion Barrier Layer Research Articles

SiOxNy back-contact barriers for CZTSe thin-film solar cells.

The formation of molybdenum diselenide (MoSe2) is widely observed at the back-contact interface for copper zinc tin selenide (CZTSe) thin-film solar cells. Depending on individual selenium (Se) supply and thermal conditions for forming CZTSe absorbers on molybdenum (Mo) substrates, the thickness of MoSe2 can vary from a few hundreds of nanometers up to ≈ 1 μm, which is comparable to the commonly adopted thickness of 1 ~ 1.5 μm for CZTSe absorbers. In this study, for controlling the thickness of interfacial MoSe2, thin diffusion barrier layers of silicon oxynitride (SiOxNy) are deposited onto Mo layers prior to the growth of CZTSe absorbers in the fabrication process. As a result, a reduction in the thicknesses of MoSe2 layers is achieved. In terms of energy conversion efficiency (η), CZTSe solar cells grown on Mo/SiOxNy back contacts suffer a deterioration as the SiOxNy layers get thicker. CZTSe solar cells grown on Mo/SiOxNy/Mo back contacts preserve their efficiencies at ≈ 11% with thin 10 nm SiOxNy layers.

Low-Temperature Aluminum-Aluminum Wafer Bonding

Thermo-compression wafer bonding is a key technology for the wafer-level production of hermetically sealed cavities, which are essential for the functioning of many microelectromechanical systems (MEMS). Aluminum, with its low material price, high thermal and electrical conductivities and its complementary metal oxide semiconductor (CMOS) compatibility, is a promising candidate for the fabrication of CMOS-MEMS, in which the sensor/actuator part is bonded to the electrical circuit. The chemically highly stable oxide layer on the Al surface cannot be removed by conventional methods. It acts as a thin diffusion barrier layer between the two aluminum metallization layers, and therefore inhibits successful low temperature Al-Al wafer bonding. So far, effective Al-Al wafer bonding has required extreme processing temperatures of >300°C and high contact pressures. Typically, 450°C-550°C led to bonded Al-Al wafers with incorporated alumina (Al2O2) precipitates and reasonable bonding quality. By using the EVG®580 ComBond®system, in which the aluminum oxide is first removed physically, followed by bonding of the two metallization layers – both performed in a high vacuum cluster – for the first time successful Al-Al wafer bonding was feasible at a temperature of 100°C. In the present work, the microstructure of structured and unstructured aluminum films on silicon substrates was characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). C-mode scanning acoustic microscopy (C-SAM), TEM and energy dispersive x-ray spectroscopy (EDXS) interface studies of Al-Al wafer pairs bonded with this novel method revealed oxide-free, atomic contact and grain growth across the original interface. Further, the bond strength was characterized based on dicing yield and pull tests.

Vapor Phase Self-Assembled Monolayers for CMOS BEOL Barrier Layers

As the Back - End - of - Line (BEOL) Interconnects are scaling down to nanometer regime with multiple levels of metallization , need for ultra thin diffusion barrier layers arise. Self assembled monolayer (SAM) is an ideal solution to satisfy the requirement of an ultra thin barrier layer to avoid Copper difussion. However, wet chemical processes are preferably avoided in Complimentary - Metal - Oxide - Semiconductor (CMOS) fabrication process. Accordingly , a novel technique to form SAM of Zinc (||) tetraphenyl hydroxy porphyrin (ZnTPPOH) in vapor phase on Inter - Layer Dielectric (ILD) materials is developed in present work to suit the industry process flow and be integreable in CMOS fabrication. The vapor phase SAM formation of ZnTPPOH is investigated employing different techniques and studies from simple contact angle measurements, spectroscopic measurements such as x-ray photoelectron spectroscopy (XPS) , fourier transform infrared spectroscopy (FTIR) , Ultra Violet - Visible Spectroscopy (UV - Vis) , and the atomic force microscopy (AFM) , etc. The vapor phase SAM of ZnTPPOH was formed on different ILD materials such as Black Diamond , Hydrogen silsesquioxane , etc and also on Silicon dioxide substrates. Selective formation of SAM in vapor phase was studied using different substrates such as Gold , Copper , etc . The vapor phase SAM was incorporated in Metal - Oxide - Semiconductor Capacitor (MOSCAP) structure. Copper was used as metal and the Vapor phase SAM was formed on Oxide / ILD materials so as to sandwich between the Copper and ILD, to repel and isolate the Copper in order to avoid any diffusion of Copper into the ILD materials. Capacitance - Voltage (CV) measurements , Current - Voltage characterization were done under bias and temperature stress on the MOSCAP devices to investigate the electrical performance of MOSCAP device and efficiency of ZnTPPOH vapor phase SAM as a barrier layer. Similarly blanket MOSCAP stack was formed and subjected to temperature stress and the extent of copper diffusion was investigated using (SIMS). Scanning electron microscopy (SEM) and scotch tape tests were done to observe improvement in adhesion of Copper to the ILD materials. The vapor phase SAM process was optimized and devloped to suit the CMOS technology and demonstrated as an effective copper diffusion barrier layer for interconnects. This technique opens up a whole new set of opportunities to scale down the barrier layer thickness. Integrating such bottom-up approach within the CMOS fabrication process would make scaling to 7nm and beyond possible where interface layers, dielectrics, and semiconductor films will be on a molecular level. Figure 1

Dielectric and diffusion barrier multilayer for Cu(In,Ga)Se2 solar cells integration on stainless steel sheet

For the fabrication of monolithically integrated flexible Cu(In, Ga)Se2, CIGS modules on stainless steel, individual photovoltaic cells must be insulated from metal substrates by a barrier layer that can sustain high thermal treatments. In this work, a combination of sol–gel (organosilane-sol) and sputtered SiAlxOy forming thin diffusion barrier layers (TDBL) was prepared on stainless steel substrates. The deposition of organosilane-sol dielectric layers on the commercial stainless steel (maximal roughness, Rz=500nm and Root Mean Square roughness, RMS=56nm) induces a planarization of the surface (RMS=16.4nm, Rz=176nm). The DC leakage current through the dielectric layers was measured for the metal-insulator-metal (MIM) junctions that act as capacitors. This method allowed us to assess the quality of our TDBL insulating layer and its lateral uniformity. Indeed, evaluating a ratio of the number of valid MIM capacitors to the number of tested MIM capacitors, a yield of~95% and 50% has been reached respectively with non-annealed and annealed samples based on sol–gel double layers. A yield of 100% was achieved for sol–gel double layers reinforced with a sputtered SiAlxOy coating and a third sol–gel monolayer. Since this yield is obtained on several samples, it can be extrapolated to any substrate size. Furthermore, according to Glow Discharge Optical Emission Spectroscopy and Time of Flight Secondary Ion Mass Spectroscopy measurements, these barrier layers exhibit excellent barrier properties against the diffusion of undesired atoms which could otherwise spoil the electronic and optical properties of CIGS photovoltaic cells.

Structural Characterization of a Manganese Oxide Barrier Layer Formed by Chemical Vapor Deposition for Advanced Interconnects Application on SiOC Dielectric Substrates

We investigated the microstructure and growth behavior of a manganese oxide layer deposited on SiOC substrates for the purpose of providing a new method to form a thin diffusion barrier layer for advanced LSI interconnections. The Mn oxide layer was formed by chemical vapor deposition (CVD), using bis(ethylcyclopentadienyl)Mn as a precursor and H2 as a carrier gas at 300 °C for 30 min. The Mn oxide layer could be formed on plasma-treated SiOC, but not on as-received SiOC. By using thermal desorption spectroscopy (TDS), moisture absorption in SiOC was evidenced after plasma treatment, using various gases of O2, N2, and Ar. Two adsorbed moisture components, physisorbed (α) and chemisorbed (β, γ), were observed which were responsible for the formation of crystalline MnOx and amorphous MnSixOy, respectively. The position of the Mn oxide layer was also investigated by measuring the variation of the SiOC thickness. The Mn oxide layer was formed within the SiOC substrate. The result indicates that the Mn oxide barrier layer would have no influence on the line resistance value, but influences on the dielectric capacitance value.

Reactively Sputtered Mo–V Nitride Thin Films as Ternary Diffusion Barriers for Copper Metallization

The effectiveness and performance of Mo-based ternary nitride films as copper diffusion barriers were investigated. Thermally stable Mo–V nitride thin diffusion barrier layers were deposited using radio frequency reactive magnetron sputtering and their barrier capability was evaluated and studied. Cu/Mo–V nitride/Si structures were fabricated and annealed at different temperatures. The agglomeration of Cu and the formation of due to high-temperature annealing were probed using scanning electron microscopy/energy-dispersive X-ray spectroscopy. The drastic increase in sheet resistance after annealing at was found to take place due to the formation of highly resistive , also evident from X-ray diffraction patterns. The formation of inverted pyramidal structure of at the interface penetrated into the Si substrate corroborated the breakdown of the barrier layer at . Our results suggest that an 8 nm thick Mo–V nitride barrier can effectively prevent the formation of up to high annealing temperatures.

Plasma Sprayed Diffusion Barrier Layers Based on Doped Perovskite-Type LaCrO3 at Substrate-Anode Interface in Solid Oxide Fuel Cells

In the thin-film solid oxide fuel cell (SOFC) concept of the German Aerospace Center (DLR) in Stuttgart, the entire membrane electrode assembly (MEA) is deposited onto a porous metallic substrate by an integrated multistep vacuum plasma spray (VPS) process. This concept enables the production of very thin and stable electrodes and electrolyte layers with a total cell thickness of only 100–120μm. In this concept, the porous ferrite substrate material predominantly acts as mechanical cell support and as fuel gas distributor. In general, ferrite substrate alloys with high chromium and low manganese content show both excellent corrosion stability and adequate thermal expansion behavior. Nevertheless, at the high process temperature in the SOFC of ∼800°C, atomic transport processes can show a detrimental effect on cell performance, at least at the required long-term operation. Problems arise, in particular, through diffusion processes of Fe-, Cr-, and Ni-species between the Ni/8YSZ anode and the ferrite steel-based substrate material. This can induce significant structure changes both in the anode and the substrate. As a reliable solution of this key problem, a plasma sprayed thin diffusion barrier layer is seen at the interface between anode and substrate, which consists of an electrically conductive and chemically stable ceramic component. For this purpose, some doped perovskite-type LaCrO3, such as La1−xSrxCrO3−δ, La1−xCaxCrO3−δ, or La1−xSrxCr1−yCoyO3−δ were investigated and tested carefully at DLR. These types of perovskites show a high potential to fulfill all the required properties that are needed for the applicability as an anode-side diffusion barrier layer. The paper focuses on basic investigations of differently doped LaCrO3 compounds under SOFC-relevant conditions concerning thermal expansion, electrical conductivity, chemical stability, etc. Furthermore, first results of electrically and electrochemically characterized half cells carried out with some qualified doped LaCrO3 are shown. Finally, the diffusion barrier layer is demonstrated as a new SOFC component that is effective at cell operating conditions.

TiSiN films produced by chemical vapor deposition as diffusion barriers for Cu metallization

The decrease in microelectronic device dimensions and the continuous effort to increase the speed and performance of devices have led to the need to replace the current metallization of Al(Cu) with Cu. This metal must be isolated from the neighboring dielectrics by a thin diffusion barrier layer. The currently employed diffusion barrier materials are Ta and TaN produced by advanced physical vapor deposition methods. The need for conformality and for the use of extremely thin layers serves as a driving force to look for chemical vapor deposition as the future deposition method. TiSiN films produced by using a cyclic process of thermal decomposition of tetrakis-dimethylamino-titanium followed by H2/N2 plasma and a flash of SiH4 are attractive candidates as diffusion barriers for Cu metallization in future devices. In this research, we have extensively studied the barrier integrity using secondary ion mass spectroscopy (SIMS) depth profiling and SECCO etch-pitting test. The sample configuration used was Cu/barrier/Si. Cu diffusion was detected by SIMS after annealing at 500 °C. Etch pits were first found after annealing at 600 °C. It was found that the plasma treatment is the main factor improving the barriers ability to prevent Cu diffusion to the substrate, most probably due to the higher density of the treated film, while the addition of SiH4 only slightly improves the barriers integrity due to the formation of Si3N4. A correlation between the TiSiN microstructure and its barrier integrity is proposed.

Properties of Sputtered Bilayer WNx/W Diffusion Barriers between Si and Cu

ABSTRACTCopper interconnect metallizations in next generation integrated circuits will require thin diffusion barrier layers (<20 nm) between the Cu and low-k dielectric which may also function as seed layers for subsequent material depositions. One possible structure entails a multicomponent diffusion barrier with a lower resistivity component, such as W on WNx. In this study, sputtered WNx/W bilayer thin films were investigated as diffusion barriers between Si and Cu. The total thickness of the WNx/W bilayer was fixed at 20 nm while the WNx thickness was varied from 0 to 20 nm. After deposition of the barrier films, a 100 nm thick Cu film was sputtered over the top of the á-W and amorphous WNx bilayer. The as-deposited WNx/W film stress was found to be strongly dependent on the relative amount of WNx and W present and the addition of a Cu overlayer was found to mitigate the stress levels. The WNx/W barriers remained stable after 650°C anneals and exhibited phase transformations to W2N. Microstructural characterization using transmission electron microscopy and x-ray diffraction and chemical analysis by x-ray photoelectron spectroscopy of the films were used to identify the as-deposited and transformed phases.

Diffusional breakdown of a Ag diffusion barrier in a Cu-Ag-Ni diffusion triple

A diffusion triple with copper and nickel sandwiching a thin diffusion barrier layer of silver was annealed for various times at 760 °C. Silver exhibits a limited solubility (0.135 atom fraction) for copper and a slight (0.01) solubility for nickel at 760 °C. The Ag barrier was breached by successive processes of Cu interdiffusion, interface instability of the Ag-Ni interface, and growth of Cu-Ni protrusions from the Ag-Ni interface to ultimately bridge the Ag barrier. The kinetics of widening of the Ag barrier were determined and interpreted in terms of the diffusion concentration profiles and the plastic deformation of the Ag barrier by the Cu-Ni protrusions.