Plasma Etching Of Polysilicon Research Articles

Nanoscale structure formation by plasma etching

Process of isotropic plasma etching of polysilicon to form nanostructures has been developed and optimized. Dependences of the technological characteristics of the isotropic plasma etching process of polysilicon on its operational parameters have been obtained. The results were to form nanowire silicon field effect transistors and a sensitive vibro-resonant nanoelement for an atom mass sensor.

In situ measurements of HCl during plasma etching of poly-silicon using a diodelaser absorption sensor

Tunable diode laser absorption spectroscopy is used to monitor hydrogen chloride(HCl) concentration in a commercial, high-density, low-pressure plasma reactorduring plasma etching. A near-infrared diode laser is used to scan the P(4)transition in the first overtone of HCl near 1.79 µmto measure changes in HCl levels. A variety of HBr and Cl2feedstock recipes are investigated at a process pressure of 10 mTorr asa function of rf power transformer coupled plasma, bias power andthe total flow rate. Using 50 ms averaging and a signal modulationtechnique, we estimate a minimum detectivity of 4 × 10−6in peak absorbance, which corresponds to an HCl numberdensity of ∼2 × 1011 cm−3.The diode-laser based HCl sensor is sufficiently sensitive to detect smallconcentration variations and HCl concentration correlates with poly-Si etch ratefor the conditions studied. These measurements demonstrate the feasibility of areal-time diode laser-based sensor for etch rate monitoring and the potential forprocess control.

Charge Pumping Profiling Technique for the Evaluation of Plasma-Charging-Enhanced Hot-Carrier Effect in Short-N-Channel Metal-Oxide-Semiconductor Field-Effect Transistors

Plasma etching of poly-silicon in a metal-oxide-semiconductor field-effect transistor (MOSFET) during the gate definition process induces edge damage at the gate-drain overlap edge. This edge damage will be further enhanced by the antenna effect and cause a more serious hot-carrier (HC) effect, particularly in short-channel devices. We call this phenomenon the plasma-charging-enhanced HC effect. In this paper, this plasma-charging-enhanced HC effect is evaluated by the charge pumping (CP) profiling technique, in which the enhanced damage at the gate-drain overlap gate oxide region can be identified. A three-phase plasma damage mechanism is then proposed to explain the observed effect. According to experimental results, it was shown that the interface traps generated at the gate-drain overlap edge are mainly attributed to the plasma-charging-enhanced HC effect. These interface traps (Nit) become the dominant mechanism of the drain current (ID) degradation, which increases with a reducing channel length (L). Again, the enhanced HC-effect-induced-degradation will dominate the device reliability under long-term operations.

Dc-etching of poly-silicon with fluorine chemistry

Plasma etching of poly-silicon in a dc-discharge has been studied. By using a dc plasma, it is possible to measure voltage and current separately. Hence it is possible to study the effect of both the ion flux and the gas flux onto the etched surface. The etching behaviour of CF 4, NF 6 has been investigated. The importance of the difference in electrical behaviour of the gases is pointed out. In the dc-glow discharge the etching yield/current density was observed to be equal for both n- and p-type poly-silicon. In the voltage region investigated no effect on etch rate by varying the applied voltage was observed. The etching yield was larger for the SF 6 gas than for the other gases. A pronounced excess etching effect was observed caused by the neutral surrounding gases.

The Plasma Etching of Polysilicon with CF 3Cl / Argon Discharges: II . Modeling of Ion Bombardment Energy Distributions

An experimental technique for measuring total positive‐ion‐bombardment fluxes and energy distribution is presented. It is shown that mean ion energies in (Freon® 13) plasmas can be well described by discharge electrical impedance analysis in conjunction with a simple sheath transport model. Based on the measurement of only the rms discharge current, mean ion energies are predicted. An empirical description using the mean ion energy provides a good representation of the ion energy distribution over a wide range of conditions. These results should allow estimation of ion energy distributions in other parallel plate reactors.

The Plasma Etching of Polysilicon with CF 3Cl / Argon Discharges: III . Modeling of Etching Rate and Directionality

Three kinetic models, based on experimentally measured and theoretically estimated plasma properties, are developed to describe heavily P‐doped polysilicon etching in (Freon® 13) RF discharges. The models include both chemical and ion‐assisted processes, and, therefore, predict etching directionality as well as etching rate. The results indicate the importance of relatively low energy (<30 eV) ion bombardment, and suggest that the dominant loss process for the chemical etchant is diffusion‐limited recombination at the electrode surfaces. Agreement between measured and predicted etching rates is excellent. The major trends in etching directionality are reproduced by the model, although there is some quantitative disagreement at low pressure.

Pattern profile control of polysilicon plasma etching

Profile control in plasma etching of polysilicon is described. Reactive gases are CCl2F2–H2 and CCl2F2–C2H6. Undercutting suppression and sloped wall pattern profile without undercutting are realized. Thin film formation on the etched pattern side wall is observed. These characteristics are explained by the plasma polymerization phenomena which occurs competitively with etching reaction.

Plasma etching of polysilicon and Si3N4in SF6with some impact on MOS device characteristics

Accurate delineation of the circuit materials polycrystalline silicon (poly), and silicon nitride are important requirements of most SFC process sequences. We have investigated the use of SF 6 as an active species in the parallel-plate plasma etching of these materials. For the etching of poly there is good selectivity (better the 50:1) with respect to the etch rates of SiO 2 and positive photoresist. This process has been used in the fabrication of MOS transistor with 3-µm poly-gate lengths and threshold voltages vary by less than 0.05 V both across a wafer and from wafer to wafer. Etching of nitride is less selective and less isotropic than that of poly.

Optical detector to monitor plasma etching

A simple photodetector has been developed to monitor plasma etching of polysilicon, pyrolytic silicon nitride and reactive plasma deposited silicon nitride.