Magnetic Neutral Loop Discharge Plasma Research Articles

Effect of Substrate Bias on Production and Transport of Etchant Ions in a Magnetic Neutral Loop Discharge Plasma

Production and transport of etchant ions in an RF (13.56 MHz) magnetic neutral loop (NL) discharge plasma in the presence and the absence of an ac (1.695 MHz) substrate bias were simulated using a Monte Carlo method. Under the bias, electrons accelerated near the NL were attracted to the substrate and produced more etchant ions near the substrate than in the absence of the bias. Effect of bias leading to enhancement of the ion inflow to the substrate was discussed.

Structure and dynamics of a magnetic neutral loop discharge plasma described using electron motion in a quadrupole magnetic field

Electron motion in a CF4 magnetic neutral loop discharge (NLD) plasma was simulated using a Monte Carlo method. The spatial distribution of electrons illustrated the fundamental structure of the NLD plasma, and its dynamics were depicted from the distributions of the mean electron energy, the electron energy gain and the azimuthal electron flux. The peak of mean electron energy appeared at the neutral loop (NL), which confirmed that electrons gain energy near this loop. High mean electron energy was observed not only near the NL but also along the separatrices of the quadrupole magnetic field. Energetic electrons were transported along the separatrices and induced ionization at those locations. However, the electron distribution had valleys along the separatrices, because electrons accelerated near the NL were likely to leave this region where the binding of the magnetic field is weak. The azimuthal electron flux representing the loop plasma current showed that the electron conduction path around the NL, which has conventionally been modelled as a ring conductor, has a particular directionality due to the rectification effect of antiparallel magnetic fields composing the quadrupole magnetic field. The directionality in the upper and lower regions of the quadrupole magnetic field was opposite to that in the inner and outer regions.

Numerical Simulation of Electron Transport in Electric and Magnetic Fields for Analysis of Electron Temperature and Number Density Profiles Measured in Argon Magnetic Neutral Loop Discharge Plasma

A Monte Carlo simulation of electron transport in electric and magnetic fields was performed to analyze experimental data of the electron temperature Te and electron number density ne measured in a magnetic neutral loop discharge (NLD) plasma driven in Ar at 0.13 Pa. Te and ne in the vicinity of the substrate holder were measured with a triple probe, and their radial profiles had peaks at different radial positions. The simulation reproduced these peak positions well under the chosen boundary condition that the electron reflectivity of the side wall was lower than that of the reactor ceiling and the substrate holder. It was explained that the Te peak was formed by high-energy electrons transported from the neutral loop along a separatrix of the quadrupole magnetic field and that the ne peak consisted of electrons undergoing reciprocating motion between the reactor ceiling and the substrate.

A Novel TSV Etching using NLD and VHF CCP Plasma For 3-D Stacked Devices.

In this study, the etch development of high etch rate and high aspect ratio for the fabrication of various diameters of thru silicon via is described. There are a lot of applications about TSV's methods. There TSV need to meet strict requirements with respect to high etch rate, sidewall roughness and undercut. For diameter of vias down to 10um a SiO2 hard mask based SF6/O2 etch approach is used by magnetic neutral loop discharge plasma (NLD plasma). This system can be used for oxide etching and Si etching. In the case of oxide etching, some magnetic coil currents are applied to generate magnetic neutral loop in the vacuum chamber in order to high density plasma in the low pressure below 1 Pa. On the other hand, in the case of Si etching, the pressure is raised up to 2∼10 Pa. As a result, an etched profile of TSV with diameter of 1.5 um and the etched depth of 11.5 um, aspect ratio is 7.6, was achieved. The etch rate is about 4.5 um/min. For diameter of vias up to 10um, a resist mask based and SF6/O2 etch approach is also used by very high frequency coactivity coupled plasma. VHF CCP etching system was used to high-pressure process, more than 50Pa, as a purpose to high etch rate of up to 10um pattern's TSV etching. As a result, a vertical profile of TSV with diameter of 50 um and the etched depth of 50 um, aspect ratio is 1.0, was achieved. The etch rate is about 45 um/min. NLD and VHF CCP processes are non-cycle etch methods, and to successfully smooth pattern TSV.

Observation of Characteristics of Magnetic Neutral Loop Discharge Plasma Appearing at Antenna in RF Circuit

The characteristics of magnetic neutral loop discharge (NLD) plasma have been studied by measurement of a high voltage appearing at an antenna in RF circuit. Peak-to-peak voltage Vpp at the antenna coil supplying power into plasma varied depending on the configuration and strength of the magnetic field. By analysis of the measured Vpp using the equivalent circuit model, it is deduced quantitatively that the power deposited into plasma in NLD is larger than that deposited in inductively coupled plasma (ICP).

Etching characteristics of porous silica (k=1.9) in neutral loop discharge plasma

Etching characteristics of a porous silica material (ISM-1.5™ produced in ULVAC, Inc.) were investigated and compared with those of thermal oxide. The etch rate of porous silica in magnetic neutral loop discharge plasma was approximately two times higher than that of thermal SiO2 film when linear saturated perfluorocarbon compounds were used. This may be due to the low film density of the porous silica. However, in the case of C4F8 (octafluorocyclobutane) plasma, the etch rate ratio to SiO2 was about 1.45. When C4F6 (CF2=CFCF=CF2: hexafluorobutadiene) was used, the etch rate ratio was also very low (0.6). So, the etch rate strongly depended on the gas structure, whereas the SiO2 etch rate did not depend on the gas species and was almost constant. Through mass spectrometry and x-ray photoelectron spectroscopy measurements, it was deduced that the fluorocarbon polymer formed in the pore suppressed the etch rate of porous silica in C4F8 or C4F6 plasmas.

Application of magnetic neutral loop discharge plasma in deep silica etching

The electron temperature Te is one of the key parameters for process plasma because the decomposition of most reactive gases depends on the kinetic energy of electrons in the plasma. Pressure is another important parameter in the etching process for microelectromechanical systems (MEMS). Low pressure can avoid etch product substrate redepositing by reducing the collision between neutral particles and etch products in the gas phase. Also, low pressure may reduce the scattering of incident ions in the sheath that may reduce the negative taper angle for trench etching. Therefore, this study is focused on low pressure (<0.67 Pa), low Te plasma production for optical MEMS etching processes. To reduce the Te and keep the high density of the plasma, use of a parallel turn antenna was proposed and it was applied in magnetic neutral loop discharge plasma, where the Te is desirably reduced to about 2.5 eV while the density is about 1.2×1011 cm−3 at pressure of 0.2 Pa. With this improvement in plasma production, fused quartz and chemical vapor deposition SiO2 were successfully etched in a trench 5–40 μm deep at a high etch rate of over 500 nm/min. The vertical angles are about 90° and the surface roughness is less than 50 nm as evaluated by a scanning electron microscope picture, where Cr, WSi and Si were used as hard masks of SiO2 in order to achieve the selectivity required.

Investigation of the Conditions Required for the Formation of a Magnetic Neutral Loop Discharge Plasma

In order to reveal the conditions required for the formation of a neutral loop discharge (NLD) plasma, distributions of excited atoms that are closely related to the distributions of the ionization rates were measured under various discharge conditions. Measurements of the distributions of these excited atoms were performed by laser induced fluorescence spectroscopy and optical emission spectroscopy. It was found that the results of these measurements were consistent with the theoretically predicted dependencies of electron heating on the magnetic field strength, the radio frequency (RF) electric field, and the frequency of the RF source. In addition, it was shown that the effects of electron-neutral collisions and of the finite size of the device set limitations on the formation of the NLD plasma.

Low-k materials etching in magnetic neutral loop discharge plasma

Low-k materials etching for FLARE™ and a porous silica were carried out in a magnetic neutral loop discharge plasma at low pressure, below 1 Pa. Fluorinated carbon molecules were used as etching gases for porous silica. The etch rate of the porous silica was approximately two times higher than that of thermal SiO2. This result means that consumption of perfluoro compound (PFC) gases is suppressed below at approximately half volumes. And organic low-k materials etching where ammonia gas or a gas mixture of nitrogen and hydrogen were used instead of PFC gas is an environmentally friendly process. After investigating an influence of a N2/H2 mixture ratio in the organic materials etch process, a good experimental condition to get a low microloading profile was found at a N2 ratio of 70%–80%. Under this condition N2+ and N2H+ ions were dominant, and the signal intensity of the N2H+ ion showed a maximum value in the mass spectrum. This may mean N2+ and N2H+ ions play an important role for a low microloading etching. The nitrogen may be adsorbed on the surface and a thin passivation film may be created on the sidewall surface.

Very uniform and high aspect ratio anisotropy SiO2 etching process in magnetic neutral loop discharge plasma

Magnetic neutral loop discharge (NLD) plasma is a new type for dry etching process characterized by effective coupling of the input electric field electron electron motion near the magnetic neutral loop (NL) region. Therefore, dense plasma can be produced and controlled spatially by changing the position of the NL. Uniformity was controlled by changing the radius of NL temporally during the etching using a repetition frequency of 0.1 Hz, so that the deviation of the SiO2 etch rate was within 2% (3σ) on 200-mm-diam wafer. In nanoscale pattern etching processes, we found that CHF2+ ions played an important role in very high aspect ratio profile etching. In CHF2+ ion-rich plasma, ZEP photoresist patterned 20 nm space was successfully etched 800 nm in depth at the pressure of about 0.3 Pa, using CH2F2, C4F8, and O2.

Application of magnetic neutral loop discharge plasma to SiO 2 etching process

The applicability of the NLD plasma etching apparatus to the 0.1 μm wafer process was verified through the experiments. The uniformity of the SiO 2 etch rate was obtained within 1.6% (3% as 3 σ value) on 200 mm wafer, by applying a functional current to the magnetic coil with 0.1 Hz. A super-fine trench pattern with 20 nm width and 800 nm depth was also successfully fabricated with an electron beam resist mask in a C 4F 8+CH 2F 2 plasma at 0.3 Pa.

Usefulness of Magnetic Neutral Loop Discharge Plasma in Plasma Processing

Usefulness in plasma processing is demonstrated for a plasma produced in a closed magnetic neutral loop, which consists of zero magnetic field points connected continuously. A preliminary experiment was carried out to show the advantage of magnetic neutral loop discharge (NLD) plasma in sputter etching processing of SiO2/Si wafer in the lower Ar gas pressure range. The experiment shows that a high-density plasma was obtained for Ar gas lower than 0.1 Pa and the sputter etching rate is 3 times higher than that for the usual inductively coupled plasma (ICP). In a large-loop case, the sputter etching profile obtained has a peak at a radius along the azimuthal direction. This implies that a uniform etching profile could be realized by controlling the radius of the neutral loop during process operation. The NLD plasma current induced with an rf primary one-turn antenna coil reaches up to one-third of that of the primary.