Nitrided Oxide Films Research Articles

Precursor design and engineering for low-temperature deposition of gate dielectrics for thin film transistors

ABSTRACTThe electrical and physical quality of gate and passivation dielectrics significantly impacts the device performance of thin film transistors (TFTs). The passivation dielectric also needs to act as a barrier to protect the TFT device. As low temperature TFT processing becomes a requirement for novel applications and plastic substrates, there is a need for materials innovation that enables high quality plasma enhanced chemical vapor deposition (PECVD) gate dielectric deposition. In this context, this paper discusses structure-property relationships and strategies for precursor development in silicon nitride, silicon oxycarbide (SiOC) and silicon oxide films. Experiments with passivation SiOC films demonstrate the benefit of a superior precursor (LkB-500) and standard process optimization to enable lower temperature depositions. For gate SiO2 deposition (that are used with polysilicon TFTs for example), organosilicon precursors containing different types and amounts of Si, C, O and H bonding were experimentally compared to the industry standard TEOS (tetraethoxysilane) at different process conditions and temperatures. Major differences were identified in film quality especially wet etch rate or WER (correlating to film density) and dielectric constant (k) values (correlating to moisture absorption). Gate quality SiO2 films can be deposited by choosing precursors that can minimize residual Si-OH groups and enable higher density stable moisture-free films. For e.g., the optimized precursor AP-LTO® 770 is clearly better than TEOS for low temperature PECVD depositions based on density, WER, k charge density (measured by flatband voltage or Vfb); and leakage and breakdown voltage (Vbd) measurements. The design and development of such novel precursors is a key factor to successfully enable manufacturing of advanced low temperature processed devices.

(Invited) The Surface Chemistry of Atomic Layer Deposition (ALD) Processes for Metal Nitride and Metal Oxide Film Growth

The surface and gas-phase thermal chemistry of tetrakis(ethylmethylamido)titanium (TEMAT), by itself and in the presence of water, was investigated by using transmission infrared (IR) absorption spectroscopy and tandem gas chromatography-mass spectrometry (GC-MS). It was found that the uptake of TEMAT is partially self-limiting between 140 and 280 {degree sign}C, but that a CVD component from precursor decomposition does contribute to the deposition of Ti, more apparent with increasing temperatures. It was also found that decomposition of the amido ligands on the surface leads to the formation of surface species containing C=N bonds, probably imine intermediates produced by β-hydride eliminations steps. Finally, it was determined that TEMAT can thermally decompose by itself through a reductive coupling mechanism in which N,N'-diethyl-N'N'-dimethylhydrazine is formed. In contrast, addition of water to the reaction mixture promotes a competing ligand hydrogenation reaction to form ethylmethylamine instead.

The Growth of Thin Silicon Oxide and Silicon Nitride Films at Low Temperature (400 $^{\circ}{\hbox{C}}$) and High Growth Rates for Semiconductor Device Fabrication by an Advanced Low Electron Temperature Microwave-Excited High-Density Plasma System

An advanced approach for the growth of thin and ultra-thin oxide and nitride films at low temperatures (400?C) for the fabrication of future scaled-down semiconductor electron devices is presented. This technique presents an alternative to the existing conventional thermal techniques currently employed in the IC industry, which utilize high-temperatures (800?C-1000?C) for the growth of both SiO2 and Si3N4 films. An alternative is needed since the high temperature range given above limits further down-scaling possibilities of semiconductor electronic devices. In this paper, the structure, operational principles, and performance of a microwave-excited high-density (> 1012 cm-3) plasma system, which utilizes low bombardment inert gas ion energies (<7 eV), low plasma potential (<10 V), and low electron temperature (<1 eV), is described, which yields high-integrity SiO2 and Si3N4 films grown at 400?C. The films grown by this technique were previously shown by us to demonstrate comparable or superior performance with respect to SiO2 films grown by the conventional thermal method at much higher temperatures (1000?C). The specific issue which this paper addresses is the problem of the growth rate of these films, which are grown at the above reduced temperature. This issue is important because it affects the compatibility of this fabrication approach with the need to obtain a high throughput in industrial electronic device processing. The results clearly demonstrate that both the SiO2 and Si3N4 films grown at these low temperatures (400?C) exhibited comparable growth rates to those of films thermally grown by conventional techniques at elevated temperatures (800?C-1000?C). Data is presented of Silicon Oxide (SiO2) films grown with various inert gases (He, Ar, Kr, Xe), mixed with O2. Silicon Nitride (Si3N4) films were grown by using Ar/N2, Ar/N2/H2, and Ar/NH3 gas mixtures. Both film types were grown in a vacuum chamber using different partial and total pressures of the above gases. Plasma excitation of these gases was achieved by irradiating them with microwave frequencies of 2.45 or 8.3 GHz. MOS transistors were fabricated using gate oxide grown by the above plasma system, in order to demonstrate the system's compatibility with electronic device fabrication.

Ultrahigh selective etching of Si3N4 films over SiO2 films for silicon nitride gate spacer etching

The process window for the high etching selectivity of silicon nitride to silicon oxide was investigated in CF4∕CH4 inductively coupled plasma. This work showed that the etching selectivity could be controlled by modulating the thickness of the fluorocarbon film with the flow rates of CH4 gas. The carbon content in the fluorocarbon by-product layers on the etched films was observed to play a critical role in determining the etching selectivity of silicon nitride to silicon oxide. The increase in the carbon content in the fluorocarbon films with increasing CH4 gas caused the etch rates of both silicon oxide and silicon nitride films to be reduced, eventually leading to the etch stops. The minimum effective thickness of the fluorocarbon films was estimated to be 20Å for the etch stop. The infinite etching selectivity of the silicon nitride to the silicon oxide on the blanket wafers could be achieved for the CH4 flow rate above 30SCCM (SCCM denotes cubic centimeters per minute at STP) for the CF4 flow rate of 10SCCM. NF3∕CH4 and SF6∕CH4 plasma showed etch behavior similar to CF4∕CH4 plasma.

Depositon of Dielectric Films with Inductively Coupled Plasma‐CVD in Dependence on Pressure and Two RF‐Power‐Sources

AbstractThis paper presents the investigations of thin dielectric silicon oxide (SiOx) and silicon nitride (SiNx) films deposited below 100 °C by a plasma enhanced chemical vapour deposition (PECVD) using an inductively coupled plasma (ICP)‐source. The influence of the deposition pressure and the applied RF‐power to the plasma from the ICP‐source and a second RF‐power at substrate electrode on the characteristics of the deposited films are studied. The investigated characteristics are refractive index R.I. at 632 nm, deposition rate Rdep, stress σ and etching rate Retch in buffered hydrofluoric acid (BHF). Measurements from electron spectroscopy for chemical analysis (ESCA) support the investigations. The results are discussed and compared with other PECVD deposition methods. A significant influence of the RF‐generator connected to substrate electrode on etching rate and hence on film quality is identified for SiOx but the converse effect is identified for SiNx‐films.

Thermal effects and plasma damage upon encapsulation of polymer solar cells

A barrier structure consisting of silicon oxide and silicon nitride films was deposited via plasma-enhanced chemical vapor deposition (PECVD) for the encapsulation of polymer solar cells (PSCs). The total concentration of the solution and the ratio of P3HT and PCBM on the performance of polymer solar cells were studied by UV–Vis absorption spectroscopy, atomic force microscopy and photocurrent measurement. Base on these measurements, there is a compromise between light absorption and phase separation with increasing blend concentration. The PSCs were annealed at 80, 100, 120 and 140 °C for 10–60 min to investigate the thermal effects and to estimate the best deposition temperature of the barrier layers. Nevertheless, the devices with the encapsulation of barrier layers had relatively low power conversion efficiencies (PCE) of 0.98% comparing to the devices heated in the PECVD system (1.57%) at the same condition of 80 °C for 45 min due to the plasma damage during the film deposition process. After inserting a 5-nm TiO x layer between Al/barrier structure and active layer against the plasma damage, the annealed devices presented an average PCE of 2.26% and demonstrated over 50% of their initial value after constant exposure to ambient atmosphere and sunlight for 1500 h.

Optical and electrical properties of boron nitride oxide films

Polycrystalline boron nitride oxide (BNO) films are synthesized by RF magnetron sputtering. It is found that the bandgap of the BNO film increases with increasing oxygen composition. The bandgap energy as wide as 5.5 eV is obtained with oxygen composition of 17%. The electrical resistivity is estimated to be as high as 10 13 Ωcm. Metal/BNO/metal structures are fabricated with various metals such as Ni, Cu and Al, and electrical characterization are performed for metal/BNO contacts. The true Schottky barrier heights are estimated for metal/BNO contacts. The true Schottky barrier height decreases with increasing metal work function. This behavior of the Schottky barrier height suggests that the BNO film has p-type electrical conduction.

Simulation, Fabrication and Characterization of a Tunable Bragg Reflector Based on Silicon Oxide and Silicon Nitride Dielectric Films Deposited by PECVD

of a Tunable Bragg Reflector based on dielectric silicon oxide and silicon nitride films deposited over corning-glass substrates by Plasma Enhanced Chemical Vapor Deposition at low temperatures (320 oC). The device consists of consecutive layers of silicon oxide and silicon nitride films with appropriated refractive indices and thickness to function as an interferential filter in the visible region. The optical results of these devices are comparable to the numerical simulations previously realized, showing an attenuation peak in the transmittance curve at approximately 680 nm. Also, when an angular variation between the incident light beam and the optical filter is produced, a shift in the attenuation peak is observed, which is due to a difference in the optical path of the incident beam. This behavior agrees with simulated results. When a change in temperature is applied to the optical device, a shift in the attenuation peak is also observed, which is related to the thermo-optic effect (TOE) of this kind of material. These results demonstrate that it is possible to control the optical output power of the device through the adequate control of the angle of the incident beam and/or temperature of the device.

Radical-Assisted Silcore(R)CVD of Si3N4 and SiO2 Nanolaminates

The low temperature generation of Si3N4 and SiO2 films, or nanolaminates of these films, has been developed for LPCVD vertical furnaces. These films use silcore® chemistry to deposit amorphous silicon films that are subsequently converted to silicon nitride or silicon oxide films via exposure to in-situ radicals. The gas composition during the plasma conversion step is critical for determining the final film properties.

Fabrication of nanoporous silicon nitride and silicon oxide films of controlled size andporosity for combined electrochemical and waveguide measurements

We demonstrate a method for controlled etching of vertical nano-sized pores overmacroscopic areas. The method employs particle lithography to define a pattern,for which the density can be varied in a wide range and the size of the porescan be varied independently. The particle pattern is transferred into a chromemask on the substrate. We show how a thin nano-patterned mask is sufficientto etch sub-100 nm pores in dielectric materials at an aspect ratio of 20:1. Thiscreates possibilities to reach optimal design parameters for porous waveguides forincreased sensitivity and simultaneous electrochemical measurements. The feasibilityof these applications is also demonstrated by applying the process to makingfunctional plasmon-coupled waveguides with buried electrochemical electrodes.

A Comparison of N+ type and P+ type Polysilicon Gate in High Speed Non-Volatile Memories

AbstractThe polarity of gates and the threshold voltages are primary parameters that determine the electric fields in the gate stack region of non-volatile memories. This field is central to programming, retention and the other characteristics of the devices. We have investigated the effect of the gate polysilicon polarity, experimentally, for silicon-oxide-nitride-oxide-silicon (SONOS) memory devices on silicon-on-insulator (SOI) wafers. An ultra-thin oxide-nitride-oxide (ONO) film with high trap density and strong localization of the trapping provides the scalability and retention in our structures. The effect of ONO film, grown and deposited and of doping was simulated and characterized. Retention is affected by the electric field between the control gate and the storage node. Our experiments and simulations verify the consequences of different polarity of control gates through the change in electric field that they cause in retention and erase times for n+ and p+ polysilicon gate SONOS memories is verified through the characteristic energies of the processes.

Design of precursors for the CVD of inorganic thin films

Applications of inorganic thin films in the electronics industry have spurred activity in the area of chemical vapor deposition (CVD). This article discusses the increasingly sophisticated design strategies for precursor complexes through a series of case studies on CVD of metal oxide and metal nitride films.

Polishing of ILD and STI by the LHA pad

This paper examines whether a polishing pad with abrasive grain can be adapted for oxide CMP (ILD CMP and STI CMP), which is currently performed by free abrasive polishing. Using the Loosely Held Abrasive (LHA) pad that is effective in the polishing of silicon wafers, silicon oxide and silicon nitride films are polished, and the polishing selectivity and performance are investigated. In the CMP of a silicon oxide film, it is revealed that the removal rate using the combination of the LHA pad and water is 1.6 times more than that using slurry and is compatible in the almost equivalent non-uniformity within a wafer. In free abrasive polishing, the polishing selectivity of a silicon oxide film is 1.4 times that of a silicon nitride film; however, in the case of the LHA pad, it was revealed that the polishing selectivity is 10 times or more. The LHA pad, which is a polishing pad with abrasive grain, can be adapted for ILD CMP and STI CMP, and the polishing selectivity and performance is better than free abrasive polishing.

Control of Nitrogen Depth Profile and Chemical Bonding State in Silicon Oxynitride Films Formed by Radical Nitridation

Chemical bonding states and depth profiles of nitrogen in radical nitrided silicon oxide film formed in Ar/N2 plasma excited by microwave has been investigated using X-ray photoelectron spectroscopy with HF step etching. The main chemical bonding state of nitrogen atom is Si3≡N configuration, and the other unknown bonding state (termed Nhigh) is observed, whose peak energy shift is about +4.8 eV. The nitrogen atoms forming Si3≡N configuration accumulate only at the film surface and those forming Nhigh configuration are distributed deeper in the films. The Nhigh bond is very weak because it is desorbed completely at low temperature (300–500°C). Although the nitrogen atoms forming Nhigh configuration are removed by post O2-annealing, those forming Si3≡N configuration migrate toward the film/substrate interface and they increase negative bias temperature instability. In the case of ultra thin film, nitriding species forming Nhigh bond reach the film/substrate interface and form Si3≡N bond at the interface. Suppression of the generation of nitriding species forming Nhigh bond in the plasma is very important. It is clear that Nhigh bond is reduced using Ar/NH3 plasma.

Characterization of a Magnetron Plasma for Deposition of Titanium Oxide and Titanium Nitride Films

AbstractExperimental results for the energy distribution of electrons and plasma ions in a magnetron discharge with a titanium target and with pure argon, argon/nitrogen and argon/oxygen mixtures as working gas are reported. Typical electron temperatures measured 6.5 … 9.5 cm above the magnetron target range between 2–3.5 eV. Typical values for the plasma potential are in the 0.4–2 V range, as are mean ion energies measured with the help of energy‐resolved mass spectrometry. Deposited titanium films show some dependencies on oxygen flow and on substrate bias. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Reactive sputtering of iron in Ar–N2 and Ar–O2 mixtures

This paper reports on the preparation of iron nitride and iron oxide films by DC reactive magnetron sputtering. The reactivity of the Fe–N2 and Fe–O2 systems is compared by the measurement of the total pressure in the deposition chamber, the iron target voltage and the films' growth rate as a function of the reactive gas flow rate. The Fe–N2 system does not exhibit an instability phenomenon and the total pressure is quite proportional to the nitrogen flow rate. This system exhibits a low reactivity as confirmed by the effect of the nitrogen flow rate on the films' growth rate. On the other hand, a hysteresis loop occurs for the Fe–O2 system, indicating a higher reactivity for this last system.

In Vivo Biostability of CVD Silicon Oxide and Silicon Nitride Films

AbstractLow pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) silicon oxide and silicon nitride films were implanted subcutaneously in a rat model to study in vivo behavior of the films. Silicon chips coated with the films of interest were implanted for up to one year, and film thickness was evaluated by spectrophotometry and sectioning. Dissolution rates were estimated to be 0.33 nm/day for LPCVD silicon nitride, 2.0 nm/day for PECVD silicon nitride, and 3.5 nm/day for PECVD silicon oxide. A similar PECVD silicon oxide dissolution rate was observed on a silicon oxide / silicon nitride / silicon oxide stack that was sectioned by focused ion beam etching. These results provide a biostability reference for designing implantable microfabricated devices that feature exposed ceramic films.

Optical and electronic properties of plasma-deposited hydrogenated amorphous carbon nitride and carbon oxide films

A comparative investigation of the nanostructural vs. electronic properties of DECR plasma deposited carbon nitride and carbon oxide alloys provides new insights in the changes of the sp 2-clusters and sp 3 matrix resulting from the decrease in the average coordination number, as N and O atoms are increasingly incorporated. This review emphasizes the similar incorporation efficiency of N and O atoms in the carbon matrix as a function of the gas phase mixture (C 2H 2, N 2) or (C 2H 2, O 2), the decrease in the alloy density deduced from Nuclear Reaction Analysis and optical measurements, and the better ordering of the sp 2-hybridized carbon phase evidenced by Raman studies. Opposite variations in the ohmic conductivity σ( T), apparent activation energy E ACT and hopping transport parameters (related to the localization parameter N( E F) γ −3) are found as a function of the (N/N+C) and (O/O+C) stoichiometries. This surprising result gives evidence of some competition between the improved ordering of the sp 2 phase shown by Raman spectra in both alloys (stronger in a-C 1− x N x :H with a large influence of aromatic clusters) and the increasing polymer-like character of the sp 3 matrix, dominant in a-C 1− x O x :H films where the weaker connectivity of the sp 3 matrix is attributed to two-fold bonded oxygen atoms C–O–C and terminating C O groups. The role of π and π* states localization is discussed in the context of bandtail hopping conductivity.

Reactive magnetron sputtering of copper, silver, and gold

Copper, silver, and gold targets were sputtered in various reactive gas mixtures (Ar–N2, Ar–O2, and Ar–CH4) to compare the reactivity of noble metal atoms during the sputtering process. The evolution of the film's growth rate and the variation of the reactive gas partial pressure vs. the reactive gas flow rate were investigated for each kind of metal. The structure of the deposited films was characterised by X-ray diffraction. Electrical resistivity of the coatings was determined at room temperature. The optical band gap of oxides and nitrides films were deduced from UV–visible transmission measurements. The reactive sputtering of copper target leads to the synthesis of Cu3N, Cu2O, Cu4O3, or CuO films. No copper carbide films were deposited. Depending on the methane flow rate, Cu/C films were either nanocomposite coatings (nc-Cu/a-C:H) or amorphous. Silver oxide (Ag2O) films were formed by reactive sputtering of a silver target in Ar–O2 mixtures. On the other hand, the reactive sputtering method did not allow the synthesis of silver nitride nor gold oxide films.

Flash Memory Scaling

AbstractIn order to meet technology scaling in the field of solid-state memory and data storage, the mainstream transistor-based flash technologies will start evolving to incorporate material and structural innovations. Dielectric scaling in nonvolatile memories is approaching the point where new approaches will be required to meet the scaling requirements while simultaneously meeting the reliability and performance requirements of future products. High-dielectric-constant materials are being explored as possible candidates to replace the traditional SiO2 and ONO (oxide/nitride/oxide) films used today in memory cells. Likewise, planar-based memory cell scaling is approaching the point where scaling constraints force exploration of new materials and nonplanar, three-dimensional scaling alternatives. This article will review the current status and discuss the approaches being explored to provide scaling solutions for future transistor floating-gate-based nonvolatile memory products. Based on the introduction of material innovations, it is expected that the planar transistor-based flash memory cells can scale through at least the end of the decade (2010) using techniques that are available today or projected to be available in the near future. More complex, structural innovations will be required to achieve further scaling.