Magnetically Enhanced Reactive Ion Etching Research Articles

High Rate Deep Si Etching using Capacitively Coupled Plasma

High rate deep Si etching using SF6/O2 gas chemistry by Magnetically-Enhanced Reactive Ion Etch (MERIE) system using a Dipole-Ring Magnet (DRM) is studied. It is capable of etching holes 40 μm in diameter in a Si substrate at etch rates as high as 50 μm/min. It was found that the Si etch reaction is dominated by the density of fluorine radicals, which is realized at high frequency and pressure. In holes with higher aspect ratios, it was found that the Si etch rate at the bottom of holes is determined not only by the supply of fluorine radicals, but is also influenced by an etch-inhibiting effect related to the sidewall of the hole. Using an 8 μm square mask, holes with straight sidewalls were etched to a depth of 60 μm at an etch rate of 24 μm/min.

Fabrication of near-field optical probes using advanced functional thin films for MEMS and NEMS applications

Highly efficient atomic force microscopy (AFM) cantilevers and an near-field scanning optical microscopy (NSOM) aperture array were fabricated using the functional Si 3N 4 and SiO 2 thin films for the micro electro mechanical systems (MEMS) and NEMS applications. In order to generate the cantilevers and array, a silicon nitride (Si 3N 4) thin film with a stress below 100 MPa was deposited using NH 3 and SiCl 2H 2 gases with a relative ratio of 1:5 at 140 mTorr, and 835 °C by low pressure chemical vapor deposition (LPCVD). Cantilevers of 10–100 μm in length were fabricated with Si 3N 4 thin films. Photolithography and magnetically enhanced reactive ion etching (MERIE) techniques were employed for patterning the Si 3N 4 thin films and selective bulk etching of Si was carried out using a strong alkaline solution of tetramethylammoniumhyroxide (TMAH) to generate the Si 3N 4-based cantilevers with 3D shapes. In addition, we also successfully fabricated an array of SiO 2 apertures with sub-wavelength sizes as near-field optical probe in order to examine the possible light resonance-tunneling phenomenon. Initially, a (50 × 50) array with a dimension of (5 mm × 5 mm) was fabricated on a Si wafer followed by the V-groove formation using alkaline solution Si bulk micromachining technology. The size of the aperture on top of the pyramidal array was carefully controlled with an opening rate of ∼27 nm/min using HF solution diluted by a factor of 50 using water. The Al thin film was thermally evaporated on the (50 × 50) array pattern for the fabrication of apertures with sub-wavelength sizes.

Modeling of magnetically enhanced capacitively coupled plasma sources: Two frequency discharges

Magnetically enhanced, capacitively coupled radio frequency plasma sources are finding continued use for etching of materials for microelectronics fabrication at a time when multifrequency sources are also being developed. Magnetically enhanced reactive ion etching (MERIE) sources typically use magnetic fields of tens to hundreds of Gauss parallel to the substrate to either increase the plasma density at a given pressure or to lower the operating pressure. Multifrequency sources are used to separately control the magnitude of the ion and radical fluxes (typically with a high frequency source) and the ion energy distributions (typically with a low frequency) to the substrate. In this article, the properties of a two-frequency MERIE reactor are discussed using results from a computational investigation. As in single frequency sources, the reduction in transverse electron mobility as the magnetic field increases can produce a reversal of the electric field in the sheath and an increase in voltage drop across the bulk plasma. These trends decrease ion energies and increase the angular spread of ions. Similar trends are found here, including a field reversal in the sheath at the high frequency electrode. These effects produce a coupling between the high and low frequency sources that compromise the independence of ion production and ion acceleration by the two sources.

In Situ Monitoring of Silicon Plasma Etching Using a Quantum Cascade Laser Arrangement

AbstractIn etch plasmas used for semiconductor processing, concentrations of the precursor gas NF3 and of the etch product SiF4 are measured online and in situ using a new diagnostic arrangement, the Q‐MACS Etch system, which is based on quantum cascade laser absorption spectroscopy (QCLAS). In addition, the etch rates of SiO2 layers and of the silicon wafer are monitored including plasma‐etching endpoint detection. For this purpose the Q‐MACS Etch system is working as an interferometer arrangement. The experiments are performed in an industrial, dual‐frequency, capacitively coupled, magnetically enhanced, reactive ion etcher (MERIE), which is a plasma reactor developed for dynamic random access memory (DRAM) technologies. In the spectral range 1028 ± 0.3 cm–1, the absorption cross‐sections of SiF4 and NF3 are determined to be σ = (7.7 ± 0.7) × 10–18 cm2 molecule–1 and σ = (8.7 ± 0.8) × 10–20 cm2 molecule–1, respectively.

Study of plasma charging-induced white pixel defect increase in CMOS active pixel sensor

Plasma process-induced “white pixel defect” (WPD) of CMOS active pixel sensor (APS) is studied for Si3N4 spacer etch back process by using a magnetically enhanced reactive ion etching (MERIE) system. WPD preferably takes place at the wafer edge region when the magnetized plasma is applied to Si3N4 etch. Plasma charging analysis reveals that the plasma charge-up characteristic is well matching the edge-intensive WPD generation, rather than the UV radiation. Plasma charging on APS transfer gate might lead to a gate leakage, which could play a role in generation of signal noise or WPD. In this article the WPD generation mechanism will be discussed from plasma charging point of view.

Process limitations of magnetically enhanced reactive ion etch equipment

In magnetically enhanced reactive ion etching (MERIE), it is conventionally understood that the etch rate increases with increasing magnetic field strength (MFS) owing to the increase in plasma density. However, it is uncertain that this can be valid under various plasma conditions. This concern was investigated by applying a statistical experimental design to an etching of aluminium thin films in a chlorine (Cl2) plasma. It was noticeable that five experimental cases were contradictory to the reported MFS effect. The major contributor was estimated to be the dominant effect of ion bombardment. The sensitivity analysis of three significant cases revealed a little interaction between MFS and Cl2 flow. Demonstrated high sensitivity of each contradictory case reveals that the process limitations of MERIE can be circumvented by controlling the process parameters.

Etch Characteristics of Al2O3 in ICP and MERIE Plasma Etchers

The etch characteristics of films were investigated for magnetically enhanced reactive ion etching (MERIE) and inductively coupled plasma (ICP) etch systems as a function of bias power, source power, and gas chemistry. Compared to pure Ar sputtering, F-, Cl-, and Br-based plasma provided a significant chemical enhancement. Fluorine containing plasma produced higher etch rates compared to Cl and Br. The selectivity for over other semiconductor materials is low for all of the investigated two-gas mixtures. A polymerizing chemistry provides acceptable selectivity to Si, and was used for a patterning of an hard mask. These structures have been transferred into the Si wafer.

Design, Fabrication, and Integration Technology of Large-Scale Microlens Array for Infrared Charge Coupled Device Application

Infrared charge coupled device (IRCCD) integration with microlens array is an effective method for improving the detecting sensitivity of IRCCD sensors. In this paper, we present the diffractive microlens array (MLA), which is manufactured by the submicron photolithography technology and magnetically enhanced reactive ion etching (MERIE) on infrared quartz substrate. The integration procedure between microlens array and PtSi Schottky-barrier IRCCD chip is introduced in detail. The optical response of IRCCD sensor with microlens array is tested and the average response increases 0.23 in the spectral range of 1.2∼5.0 μm. The measuring results show that the large-scale diffractive microlens array is able to improve the detecting sensitivity of IRCCD and that the integration technology mentioned is available.

Modeling of magnetically enhanced capacitively coupled plasma sources: Ar/C4F8/O2 discharges

Magnetically enhanced, capacitively coupled radio frequency plasma sources are finding continued use for etching of materials for microelectronics fabrication. MERIE (magnetically enhanced reactive ion etching) sources typically use magnetic fields of tens to hundreds of gauss parallel to the substrate to either increase the plasma density at a given pressure or to lower the operating pressure. The use of MERIEs for etching of dielectric materials, such as SiO2, often involves the use of complex gas mixtures, such as Ar/C4F8/O2/CO. In this paper results from a two-dimensional hybrid-fluid computational investigation of MERIE reactors operating in such mixtures are discussed. Fluxes and energy distributions for ions incident on the wafer are discussed for an industrially relevant geometry. The reduction in transverse electron mobility as the magnetic field increases produces a decrease in the sheath electric fields and a decrease in the dc bias (becoming more positive) at large magnetic fields thereby decreasing ion energies and increasing the angular spread of ions. These trends affect heavier ions more acutely than lighter ions. Subtle variations in the electrical geometrical layout of the reactor significantly affect the spatial uniformity of ion energy distributions.

Electron Transport in Nonorthogonal Crossed DC Electric and Magnetic Fields

Transport and plasma chemistry in magnetized plasma sources for plasma processing are become increasingly important. Beyond the plasma shaping and confinement associated with magnetic fields in magnetically enhanced reactive ion etching (MERIE) tools, magnetized inductively coupled plasmas and conventional magnetrons, there are electron-kinetics-driven chemistry functions as well. It is difficult to capture these effects using conventional fluid or hybrid approaches, as it is not straightforward how to map transport and kinetic macroparameters onto common orthogonal grids. This paper addresses this issue by characterizing macroparameters (also known as swarm parameters) as a function of crossed electric and magnetic field crossing angle for Cl2 and SiH4. Scaling or mapping criteria (i.e., mapping of swarm parameters onto an orthogonal numerical grid) are described to be a function of the relative position of the energy threshold of collision processes and the mean electron energy. Using these criteria, the transport or kinetic parameters may be mapped either by angle cosines or by their components on an orthogonal grid. Significant exceptions to this occur for certain inelastic processes. When threshold energies coincide with the mean electron energy, it is not possible to determine simple mapping criteria independent of exact knowledge of how the parameters behave at a specific crossing angle.

Modeling of magnetically enhanced capacitively coupled plasma sources: Ar discharges

Magnetically enhanced capacitively coupled plasma sources use transverse static magnetic fields to modify the performance of low pressure radio frequency discharges. Magnetically enhanced reactive ion etching (MERIE) sources typically use magnetic fields of tens to hundreds of Gauss parallel to the substrate to increase the plasma density at a given pressure or to lower the operating pressure. In this article results from a two-dimensional hybrid-fluid computational investigation of MERIE reactors with plasmas sustained in argon are discussed for an industrially relevant geometry. The reduction in electron cross field mobility as the magnetic field increases produces a systematic decrease in the dc bias (becoming more positive). This decrease is accompanied by a decrease in the energy and increase in angular spread of the ion flux to the substrate. Similar trends are observed when decreasing pressure for a constant magnetic field. Although for constant power the magnitudes of ion fluxes to the substrate increase with moderate magnetic fields, the fluxes decreased at larger magnetic fields. These trends are due, in part, to a reduction in the contributions of more efficient multistep ionization.

Parallel Simulations of Relaxation in Electron Transport in Crossed Electric and Magnetic Fields

Simulations of magnetized [or magnetically enhanced reactive ion etch (MERIE)] plasma sources are increasingly in demand with the advent of 300 mm technology in which plasma sources (like MERIE tools) are believed will play a prominent role. Resolving locality issues and understanding how electrons relax in electric and magnetic fields are important in the understanding of electron heating and the resolution of numerical issues associated with the simulations of these phenomena. In this paper describing Monte Carlo simulations of electron swarms, it is shown that electron swarms in crossed electric and magnetic fields have appreciable relaxation times related to their evolution to steady-state mean electron energy. These times are correlated to relaxation lengths that are on the order of 0.1 cm to 10 cm and increase with increasing reduced magnetic field. The times and distances are parameterized over the ranges of 100–106 G/Torr and 28–1415 Td. Finally, parallelization through Java-based remote method invocation and distributed computing is presented as a successful approach for solving large-particle-number Monte Carlo simulations, the type of which are employed in this study.

Energetic neutral fluxes towards surfaces in a magnetically enhanced reactive ion etch-like reactor

In very large scale integrated microelectronics fabrication magnetically enhanced reactive ion etch (MERIE) reactors are established for many dry etch processes of conducting or dielectric materials. Angularly and energetically resolved distributions of the surfaces incident particles (ions and neutrals) as well as the fluxes of ions and neutrals play an essential role for feature scale profile evolution. The focus of this work is set on the calculation of the neutral to ion fluxes ratio. Therefore the MERIE reactor’s boundary sheath is simulated by the technology-oriented computer aided design simulation tool hybrid plasma sheath model (HPSM). HPSM consists of a self-consistent coupling of a fluid dynamical part to a Monte Carlo part. The sheath and presheath regions are described in one unified model. Energetic neutrals impinging the surface can be monitored in addition to the positive ion species. Simulations with parameters in the range of about 100 mTorr, rf voltages of a few 100 V, magnetic fields of about 90 G, and plasma powers of about 1000 W are presented. The simulations show that the flux of the energetic neutrals compared to the flux of the ions is not neglectable and that the neutral flux makes an important contribution to the energy budget of the surface impinging particles.

Reactive ion etching of glasses: Composition dependence

Magnetically enhanced reactive ion etching (MERIE) of silicate and phosphate glasses was examined in CF 4/CHF 3 and Ar plasmas. The etch depths were measured by profilometery to obtain etching rates as a function of plasma power, plasma composition and glass composition. It was found that in fluorocarbon plasmas, the etch rate of glasses decreases as the concentration of less-volatile oxides in the glass increases. These etching rates were interpreted in terms of ion-enhanced chemical reaction and physical sputtering. The compositions of the etched surfaces were determined with X-ray photoelectron spectroscopy (XPS). A high chemical reaction rate between the reactive (ion) species in the plasma and the glass surface was observed during the early stages of etching which lead to depletion of highly volatile species (SiF 4 and BF 3) and accumulation of less volatile species (AlF 3, BaF 2, NaF, etc.). At longer times, the glass surface reached a steady state composition (of the less volatile species) and subsequent etching was dominated by physical sputtering.

Effect of Etching Process Deviations and Photoresist Stripping on Contact Yield of Copper Dual Damascene Metallization

Dual damascene technology imposes strict requirements on etch and strip modules. One of them is to avoid exposure of copper on via bottoms during etching and subsequent plasma photoresist stripping (PRS) as it may lead to oxidation and contamination of copper and thus decrease contact yield. Therefore, etching should be reliably tuned for retaining some thickness of the protective cap dielectric in vias of targeted size. However, deviations of etching parameters in mass production may deteriorate selectivity and uniformity, resulting in partial or full exposure of copper in vias. In this case the effect of PRS on copper surfaces must be taken into consideration. This paper presents the study of copper surface oxidation and contamination and their effect on contact resistance and yield for three different PRS recipes: plasma at 40°C in a magnetically enhanced reactive ion etching (MERIE) reactor and and downstream plasma at 250°C in an inductively coupled plasma (ICP) reactor. It was found that PRS in the MERIE reactor and PRS in the ICP reactor oxidized the surface of copper to different depths but both processes did not reduce the yield of Kelvin vias and via chains. At the same time, plasma in an ICP reactor resulted in total failure of via chains in which copper was exposed before PRS (via size larger than 0.32 μm). Further implications of these results on dual-damascene process flow, mechanism of failure, and advantages of low-temperature PRS are discussed. © 2002 The Electrochemical Society. All rights reserved.

Investigation of in situ trench etching process and Bosch process for fabricating high-aspect-ratio beams for microelectromechanical systems

The etching processes and mechanisms for sidewall formation were investigated for the in situ trench etching and releasing process, using a magnetically enhanced reactive ion etcher (MERIE), and for the Bosch process, using an inductively coupled plasma (ICP) etcher. For the Bosch process, almost vertical sidewall profiles were obtained up to etching depth of ∼100 μm. The average height of the scallops on the sidewall was ∼70 nm and the average erosion underneath the mask was ∼0.4 μm, when trenches 50 μm deep were formed. This limited the fabrication capability of small feature sized microelectromechanical system structures of less than ∼1 μm. For the in situ processes using MERIE, the reactive ion etching (RIE) lag was significant when the etching depth reached ∼50 μm. The RIE lag was significantly reduced when the ICP was used at pressure below 50 mTorr. Scallops and undercuts were not observed when the in situ process was used. Anger electron spectroscopy and x-ray photoelectron spectroscopy analysis revealed that the sidewall passivation layer from the in situ process consisted of SiOx (1<x<2, where x varies with sidewall thickness) and small amount of F.

Characterization of Via Etching in CHF3/CF4Magnetically Enhanced Reactive Ion Etching Using Neural Networks

This study characterizes an oxide etching process in a magnetically enhanced reactive ion etching (MERIE) reactor with a CHF 3 /CF 4 gas chemistry. We use a statistical 2 4-1 experimental design plus one center point to characterize the relationships between the process factors and etch responses. The factors that we varied in the design include RF power, pressure, and gas composition, and the modeled etch responses were the etch rate, etch selectivity to TiN, and uniformity. The developed models produced 3D response plots. Etching of SiO 2 mainly depends on F density and ion bombardment. SiO 2 etch selectivity to TiN sensitively depends on the F density in the plasma and the effects of ion bombardment. The process conditions for a high etch selectivity are a 03 to 0.5 CF 4 flow ratio and a -600 V to -650 V DC bias voltage according to the process pressure in our experiment. Etching uniformity was improved with an increase in the CF 4 flow ratio in the gas mixture, an increase in the source power, and a higher pressure. Our characterization of via etching in a CHF 3 /CF 4 MERIE using neural networks was successful, economical, and effective. The results provide highly valuable information about etching mechanisms and optimum etching conditions.

Electrically active defects generated by MERIE and RIE-mode plasmas in thin SiO 2-Si structures

The effect of both RIE and high-density nonuniform magnetically enhanced reactive ion etching (MERIE)-type plasmas on the properties of thin oxide (11–13 nm) MOS capacitors as well as FETs without gate has been investigated. The results reveal the vulnerability of the oxide and its interface with Si to the plasma process — the interface is much more sensitive. The creation of defects in the form of fixed oxide charge, bulk traps, slow states and interface states is found. The damage level is a function of both the discharge conditions (including plasma exposure time) and the initial Si-SiO 2 structure parameters, the plasma conditions having a priority impact. The damage process is very rapid particularly in the first seconds (up to 30 s) of plasma exposure. The effects become highly process dependent as the plasma time increases. The plasma induced defects degrade the inversion carrier mobility and change the dominant scattering mechanism in the inversion channel. The damage leads to an excess leakage current and decreases the breakdown fields. A strong linear correlation between plasma induced leakage current and plasma created positive charge is detected. It is established that the build-up damage depends on plasma nonuniformity, but the non uniformity is neither the only nor the dominating factor. The nature of process induced defects and the influence of plasma components are discussed. It is proposed that generated interface states are mainly attributed to VUV and ion bombardment, whereas the high values of positive oxide charge are due to the charging effect. The type of plasma induced defects (oxide traps or interface states) and the energy distribution of interface states strongly depend on the relative contribution (or domination) of the different plasma components. A room temperature annealing of MERIE-type plasma induced interface states is established. The reduction depends only on the starting postplasma treatment level of interface states and the effects responsible for this reduction take place very close to the Si-SiO 2 interface. (The fixed oxide charge is stable and it does not change at all.) The process seems to be controlled by moisture transport to the Si-SiO 2 interface. By means of X-ray photo electron spectroscopy it is found that 5 min exposure of thin thermal SiO 2 to N 2-RIE mode plasma causes structural modifications, which manifest only as a deterioration of oxide quality without actual nitration of the oxide. The presence of a small constant amount of SiO species through the oxide and a broadening of Si-SiO 2 interface region are detected. The nature of the electrically active plasma induced defects by both plasma processes — RIE and MERIE is equal — the bond defects in the oxide and at the interface: the oxide charge is associated with E′ centers and the interface states with P b centers.

Magnetically Enhanced Reactive Ion Etching of Lead Zirconate Titanate Thin Film by CHF3 Plasma

A metal-organic deposition (MOD) derived Pb (Zr0.53Ti0.47)O3 thin film was patterned using magnetically enhanced reactive ion etching (MERIE) which promised a relatively high etching rate, large etch anisotropy and good selectivity for lead zirconate titanate (PZT). The etched surface of PZT thin films was investigated by X- ray photoelectron spectroscopy (XPS). It was found that PbF2, ZrF4 and polymers containing C, H and F were formed and remained on the etched surface while no titanium fluoride was formed during the etching process. The major factor that restricts the realization of a high etching rate is the removal of PbF2. Fluoride that remained on the surface could be removed by annealing after etching.

Advanced plasma technology in microelectronics

The current status and future trends of plasma technology for microelectronics are discussed. The low pressure high density plasma (HDP) source is advantageous for the etching of a gate electrode and a small deep contact hole. However, the high temperature electrons in the HDP may induce profile defects, notch and sidewall etching, and may degrade the electrical quality of the gate oxide. By lowering the electron temperature with the pulse plasma technique, the etch profile of the gate electrode was improved. Platinum, the suggested storage electrode for the capacitor of the next generation ULSI, was etched in a magnetically enhanced reactive ion etching (MERIE) plasma. With the etching chemistry of Cl 2/O 2/Ar, it was etched with the slope of up-to 80°. In SiO 2 etching, the HDP is advantageous for less RIE-lag. We also need to control the polymerization for the critical dimension (CD) control and for the selectivities to the resist, silicon, and also to Si 3N 4 for the self-aligned contact (SAC). It was shown that it is possible to control the dissociation of radicals in the plasma and the surface reaction with a phase-controlled pulse plasma. The chemistry C 4F 8/CH 3F/Ar was shown to achieve the requirements for the SAC hole etching, but the process window was quite narrow. Also, the HDP-CVD SiO 2 and SiOF have shown better gap filling capability, film quality and more favorable deposition profiles than conventional CVD oxides. We also discussed the results of the application of HDP-CVD oxide to the trench isolation and the intermetal dielectrics (IMDs). The film characteristics of fluorine doped HDP-CVD SiO 2 (SiOF) as a low dielectric material was found to be very stable with uniform film properties even after high temperature stressing at 350°C for 100 h.