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Recently, plasma process-induced damage (PID) has garnered significant interest in the design of thin dielectric films implemented in semiconductor devices. Silicon nitride (SiN) films, a material of interest in strain engineering, are found to suffer from PID because they are exposed to various plasmas during device manufacturing processes. Only a limited amount of experimental evidence is available at present regarding plasma-induced mechanical property changes of SiN films. In this study, we investigated the mechanical property change in SiN and SiO2 films using a cyclic nanoindentation technique. We focused on the contact stiffness (S) as the principal mechanical property parameter. Firstly, a single loading/unloading test confirmed an increase in S after Ar and He plasma exposures. Subsequently, we examined the time-dependent features of damaged SiN and SiO2 films under cyclic loading/unloading. From the cyclic test, an increase in S was seen with the number of loading/unloading cycles (N) for both SiN and SiO2 films. A larger increase in S was observed for the damaged SiN, while no significant increase was seen for the damaged SiO2 films. The observed increase in S and its time dependence are attributed to the strain developed by the created defects (e.g. interstitial species) and the reconstruction and stabilization of plasma-damaged Si–N networks with created defects, respectively. The time-dependent S analysis under cyclic loading/unloading is useful for evaluating the effects of PID on the mechanical properties of thin films. [ABSTRACT FROM AUTHOR]

Plasma process-induced damage (PID) to SiN dielectric films was investigated by using an impedance (admittance)-based technique. Multi-layered equivalent circuits were introduced to assign the spatial and energy distribution of defects created in the SiN/Si system. We propose to use admittance as the principal parameter for damaged SiN/Si systems after Ar and He plasma exposures. The change in the border trap density was determined from the admittance in accumulation, whereas the interface state density and energy profile that was created was determined from the admittance in depletion. Plasma source-dependent damage-creation mechanisms are discussed. It was found that the extracted border trap density in the He plasma-damaged sample was larger than that in the Ar plasma-damaged sample under the same ion dosage. The proposed characterization scheme is useful for assessing PID to dielectric/Si systems. [ABSTRACT FROM AUTHOR]

We investigated the effects of Cu-line layouts on plasma-induced radiation damage (PRD) to interline low-k dielectric films. We carried out a finite-element-method-based three-dimensional (3D) electromagnetic simulation (EMS), in which a Drude free-electron model was implemented for the dielectric function of Cu lines. The 3D EMS analysis revealed that the electric field in the low-k films was enhanced for specific Cu-line layouts exposed to N2 plasma irradiation, while no clear electric-field enhancement was observed for Ar plasma exposure. The specific optical emission lines produced in N2 plasmas are the root cause of damage creation in the low-k dielectric films with embedded Cu lines. The 3D EMS analysis predicted that the electric field was enhanced with decreasing the line and space (L/S) widths. The prediction implies that the Cu-line-layout dependent PRD should be more prominent as device dimensions shrink. We verified the predicted results experimentally using devices with low-k films between various L/S Cu lines, in addition to a blanket wafer—without Cu lines. We found that an increasing peak in the low-k dielectric constant appeared at a specific L/S width after N2 plasma exposure and no clear increase in the dielectric constant was observed after Ar plasma exposure. The obtained experimental results are consistent with the 3D EMS analysis. We propose a damage model, where the electric field enhancement plays an important role in the low-k dielectric films with embedded Cu lines. The proposed damage model is indispensable for minimizing PRD and designing Cu layouts in future devices. [ABSTRACT FROM AUTHOR]

A microplasma thruster of the electrothermal type has been developed with X-band (f = 11 GHz) microwaves and Ar as a propellant. The emphasis was placed on an understanding of distinguished features of the microplasma generation and thrust performance by X-band microwaves, compared with those by S-band (f = 4 GHz) ones. The thruster consisted of a microplasma source 2 mm in the inner diameter and 3–12 mm long with a rod antenna on the axis, followed by a converging-diverging micronozzle. Azimuthally symmetric surface wave-excited plasmas were established by microwaves at powers of ≤6 W, with the source pressure in the range 2–50 kPa at flow rates of 10–70 sccm. The plasma generation, nozzle flow, and thrust performance were numerically analyzed using a two-dimensional fluid model, coupled with an electromagnetic model for microwaves interacting with plasmas in the source region. Simulations indicated that higher frequency f = 11 GHz with the source chamber length Ls ≈ 1/4 of the driving wavelength λ is preferred for the microplasma thruster in terms of efficient plasma generation, gas heating, and thus thrust performance as well as system compactness; moreover, in f = 11 GHz discharges with longer Ls ≈ 3λ/4, standing-wave striation-like plasma structures occur in the axial direction. Experiments were made for f = 11 and 4 GHz microwaves with the respective Ls ≈ λ/4, where the plasma electron density and gas temperature in the microplasma source were measured by optical emission spectroscopy with a small amount of H2 and N2 added. The electron density and gas temperature were in the range of (4–12) × 1019 m−3 and 800–1000 K for f = 11 GHz, being ∼10%–50% higher than those for f = 4 GHz. The thrust performance was also measured by a target-type microthrust stand, giving a thrust, specific impulse, and thrust efficiency in the range 0.2–1.8 mN, 65–90 s, and 2%–14% for f = 11 GHz, which were ∼10%–15% higher than those for f = 4 GHz. These experimental results were consistent with those of simulations, depending on microwave frequency, power, chamber size, and gas flow rate. [ABSTRACT FROM AUTHOR]

Plasma-induced surface roughening and ripple formation has been studied based on Monte Carlo simulations of plasma-surface interactions and feature profile evolution during Si etching in Cl-based plasmas, with emphasis being placed on the role and effects of ion reflection from microstructural feature surfaces on incidence. The simulation model included the effects of Cl+ ion reflection (and/or its penetration into substrates) through calculating the momentum and energy conservation in successive two-body elastic collisions with substrate Si atoms every ion incidence. The "reflection coefficient ri" was then further introduced in the model (0 ≤ ri ≤ 1), representing the fraction of ions incident on surfaces with the reflection/penetration calculation scheme turned on. The coefficient ri is, in a sense, a measure of the reflection probability for impacts of an ion species onto Si surfaces relative to that for Cl+ impacts. Simulations for ion incidence angles of θi = 0°, 45°, and 75° onto substrate surfaces with incident energies in the range Ei = 20−500 eV showed that as ri is slightly decreased from unity, the roughness decreases substantially, and the ripple formation fades away: the roughness remains at the low level of stochastic roughening during etching for decreased ri ≤ ri* ≈ 0.95−0.75 (the critical ri* tends to be lower at higher Ei and θi) with no ripple structures at off-normal θi. This elucidates that the ion reflection is indispensable in surface roughening and rippling during plasma etching, and their degree relies significantly on the reflectivity of ions. Simulations further showed that at intermediate off-normal θi = 45°, the ripple wavelength increases significantly with decreasing ri, while the increase in amplitude is relatively less significant; thus, sawtooth-like ripple profiles pronounced for ri = 1 tend to be collapsed with decreasing ri. These effects of reduced ion reflection on plasma-induced surface roughening and ripple formation are discussed in terms of effectively enhanced smoothing due to neutral reactants, which competes with the roughening and rippling caused by ion bombardment. [ABSTRACT FROM AUTHOR]

Photoreflectance spectroscopy was used to characterize Si surface damage induced during Ar and CHF3/CF4/Ar plasma processing.

A new study investigates the time-dependent electric breakdown characteristics of ultrathin gate oxides by different process techniques.

Nitrogen is a very common element, comprising approximately 78% of Earth’s atmosphere, and is an important component of various electronic devices while also being essential for life. However, it is challenging to directly utilize dinitrogen because of the highly stable triple bond in this molecule. The present review examines the use of non-equilibrium plasmas to generate controlled electron impacts as a means of generating reactive nitrogen species (RNS) with high internal energy values and extremely short lifetimes. These species include ground state nitrogen atoms, excited nitrogen atoms, etc. RNS can subsequently react with oxygen and/or hydrogen to generate new highly reactive compounds and can also be used to control various cell functions and create new functional materials. Herein, plasma-processing methods intended to provide RNS serving as short-lived precursors for a range of applications are examined in detail. [ABSTRACT FROM AUTHOR]

Research has established a defect generation model which describes two time-dependent dielectric breakdown, charge-to-breakdown under constant-current injection and time-to-breakdown under constant-voltage stress in thin gate oxides impacted by plasma processing. Constant-voltage stress is not adversely affected by antenna ratio.

Gate oxide damage by plasma processing was evaluated using structures with various antenna lengths. The gate oxide damage by plasma processing was found to be monitored quantitatively by measuring the charge to breakdown, [Q.sub.BD]. From the [Q.sub.BD] measurements, we have confirmed that the degradation occurs during overetching, not in main etching. Plasma current was calculated from the decrease of [Q.sub.BD] during the etching. The breakdown spot in the gate oxide was detected by photon emission and TEM. The LOCOS structure plays an important role for the degradation by plasma damage. In this paper, it is demonstrated that the [Q.sub.BD] method is effective for realizing a highly reliable process against plasma damage.

Energetic ion bombardment during plasma etching processes creates latent defects which play a role as carrier trapping/de-trapping sites in materials. In this study, we investigated the latent defects in Si substrate created by H2 plasma exposure. In the case of light-mass ion such as H+, the created defects were difficult to detect by conventional capacitance-based methods. We found that a modified conductance method with an equivalent circuit considering the plasma-damaged layer can identify the latent defects created in Si substrates after H2 and He plasma exposures. The conductance method quantifies the areal defect densities and the characteristic time constant of carrier trapping/de-trapping processes. Then, the reconstruction of the damaged structures by a rapid thermal annealing (RTA) was evaluated. It was confirmed that the RTA changes the conductance of damaged structures in response to the annealing temperature and the total thermal budget. The obtained results suggest that the modified conductance method is an effective tool to quantify the dynamic behaviors of latent defects in Si substrates after H2 and He plasma exposures. [ABSTRACT FROM AUTHOR]

Two-dimensional axisymmetric particle-in-cell simulations with Monte Carlo collision calculations (PIC-MCC) have been conducted to investigate argon microplasma characteristics of a miniature inductively coupled plasma source with a 5-mm-diameter planar coil, where the radius and length are 5 mm and 6 mm, respectively. Coupling the rf-electromagnetic fields to the plasma is carried out based on a collisional model and a kinetic model. The former employs the cold-electron approximation and the latter incorporates warm-electron effects. The numerical analysis has been performed for pressures in the range 370-770 mTorr and at 450 MHz rf powers below 3.5 W, and then the PIC-MCC results are compared with available experimental data and fluid simulation results. The results show that a considerably thick sheath structure can be seen compared with the plasma reactor size and the electron energy distribution is non-Maxwellian over the entire plasma region. As a result, the distribution of the electron temperature is quite different from that obtained in the fluid model. The electron temperature as a function of rf power is in a reasonable agreement with experimental data. The pressure dependence of the plasma density shows different tendency between the collisional and kinetic model, implying noncollisional effects even at high pressures due to the high rf frequency, where the electron collision frequency is less than the rf driving frequency. [ABSTRACT FROM AUTHOR]