MHz Inductively Coupled Plasma Research Articles

Ion motion above a biased wafer in a plasma etching reactor

The behavior of ions in the plasma is an essential component in the process of industrial etching. We studied the motions and energy distribution of argon ions in a inductively coupled plasma (ICP) etching tool, by the method of laser induced fluorescence (LIF). The silicon wafer clamped to a chuck at the bottom of the chamber was biased with a 1 MHz 1–1.2 kV peak-to-peak sinusoidal voltage. The plasma is formed with a 2 MHz ICP coil pulsed at 10 Hz. Sheath thickness was measured at different phases of the bias waveform. The experiment also compared the ion motions with and without wafer bias, as well as different switch-on time of wafer bias. For all cases, ion energy distribution functions and the two-dimensional flow pattern were studied near the center and edge of the wafer. Significant vortex flows were observed near the wafer edge. Experiments in which the wafer was biased in the plasma afterglow resulted in a narrow distribution of ion energy close to the bias voltage at the vicinity of the wafer, and the ion incident angle on the wafer was the smallest. The results were compared to simulations using the Hybrid Plasma Equipment Model code.

On mechanisms influencing etching/polymerization balance in multi-component fluorocarbon gas mixtures

In this work, we performed both experimental and model-based study of plasma parameters, steady-state gas phase compositions and heterogeneous process kinetics in CF4 + C4F8 + Ar and CF4 + CHF3 + Ar gas mixtures under the condition of 13.56 MHz inductively-coupled plasma. As constant input parameters we used gas pressure (6 mTorr) and input power (700 W) while variable ones were fluorocarbon component ratios and bias power. It was found that the substitution of CF4 for any second fluorocarbon gas a) results in rather weak effects on electrons- and ions-related plasma characteristics (especially in the case of C4F8); and b) causes sufficient changes in kinetics of neutral species that accelerate the formation of polymerizing radicals and suppress the F atoms density (especially in the case of CHF3). The latter is due to the effective decay of F atoms in the CHFx + F → CFx + HF reaction family. On the contrary, the variation of bias power does not influence kinetics of plasma active species, but changes only the ion bombardment intensity (and thus, the ion-induced reaction kinetics) through the negative dc bias voltage. The phenomenological (based on the gas-phase-related tracing parameters) analysis of heterogeneous process kinetics indicated that the fluorocarbon gas ratio represents the more effective tool to adjust etching characteristics, polymerization rate and the fluorocarbon film thickness. The last two values were found to be always higher in C4F8 - containing plasmas.

Effects of aspect ratio on electron loss mechanisms and plasma uniformity in cylindrical inductively coupled plasma

The aspect ratio (AR) of discharge geometry is an important parameter in view of inductively coupled plasma (ICP) source design. AR is defined as the ratio of chamber radius (R) and chamber height (L). The effects of the AR on plasma parameters and uniformity are investigated in a 2 MHz ICP source. The argon discharge is performed in two chambers of AR = 0.72 and 0.35 with different heights, and the effects of AR on electron loss mechanisms are studied using a global model. The results show a tendency for generation of higher density plasma with better uniformity in the case of AR = 0.72 at 0.5–2 Pa. The difference in electron density is caused by the differences in the volume. The observations on plasma uniformity are explained by the study of the electron loss mechanism. The accumulation of electrons is weakened by axial diffusion at the chamber center in the case of AR = 0.72. The difference in plasma uniformity between the two chambers diminishes with the increase in the gas pressure from 0.5 to 2 Pa, which results from the fact that the electron diffusion along the axial direction becomes more difficult. At higher pressures from 5–10 Pa, the ambipolar diffusion loss of electrons to the chamber wall becomes more difficult with the increase in pressure due to frequent collisions. Therefore, the electron accumulation in the discharge center is more evident in the chamber with AR = 0.72, which deteriorates the plasma uniformity. The above study can give a reference to the design of cylindrical ICP sources for practical applications.

Pulsed beam tests at the SANAEM RFQ beamline

A proton beamline consisting of an inductively coupled plasma (ICP) source, two solenoid magnets, two steerer magnets and a radio frequency quadrupole (RFQ) is developed at the Turkish Atomic Energy Authority’s (TAEA) Saraykoy Nuclear Research and Training Center (SNRTC-SANAEM) in Ankara. In Q4 of 2016, the RFQ was installed in the beamline. The high power tests of the RF power supply and the RF transmission line were done successfully. The high power RF conditioning of the RFQ was performed recently. The 13.56 MHz ICP source was tested in two different conditions, CW and pulsed. The characterization of the proton beam was done with ACCTs, Faraday cups and a pepper-pot emittance meter. Beam transverse emittance was measured in between the two solenoids of the LEBT. The measured beam is then reconstructed at the entrance of the RFQ by using computer simulations to determine the optimum solenoid currents for acceptance matching of the beam. This paper will introduce the pulsed beam test results at the SANAEM RFQ beamline. In addition, the high power RF conditioning of the RFQ will be discussed.

Effect of Dual Radio Frequency Bias Power on SiO2 Sputter Etching in Inductively Coupled Plasma

Dual radio frequency (RF) powers are widely used with commercial plasma etchers for various nanoscale patterns. However, it is challenging to understand the relationship among the dual RF powers and the etching processes. In this work, the effect of the dual RF bias powers on SiO2 sputter etching was investigated in inductively coupled plasma (ICP). The relationship was studied among 2[Formula: see text]MHz and 27.12[Formula: see text]MHz RF bias powers, a 13.56[Formula: see text]MHz ICP source power, the ion bombardment energy, the ion density and the etching rate. The results show that the ion density of Ar plasma can be controlled in the region of 109–10[Formula: see text] ions/cm3, and DC self-bias can be controlled by controlling the ratio of dual RF bias powers while the ion density is maintained with the operation of source power. This work reveals that the dual RF bias powers expand the process window of the ion density and the ion bombardment energy independently in the ICP plasma source. The sputter etching rate is also modeled using the ion-enhanced etching model, and the model shows good agreement with the etching rate data.

반응성 증착용 펄스 플라즈마 공정의 진단

A real-time monitoring of an immersed antenna type inductively coupled plasma (ICP) was done with optical emission spectroscopy (OES) to check the reports that sputtered atom density is decreasing as the ICP power is increased. At 10 mTorr pressure of Ar, Mg was sputtered by a bipolar pulsed power supply into 2 MHz ICP which has an insulator covered 2.5 turn antenna. Emitted light was collected in two different positions: above the target and inside the ICP region. With 100 W of Mg sputtering power, the intensities of Mg I (285.06 nm), Mg II (279.48 nm), Ar I (420.1 nm) were increased constantly with ICP power from 100 W to 600 W. At 500 W, the intensity of exceeded that of Mg under PID controlled discharge voltage of 180 V. The ratio of Mg II/Mg I was increased from 0.45 to 2.71 approximately 6 times.

Diagnostic of Surface Wave Plasma for Oxide Etching in Comparison with Inductive RF Plasma

Surface wave plasma (SWP) and inductively coupled plasma (ICP) reactors are high plasma density, unmagnetized sources that show promise for use in next-generation etching processes. We compare the 2.45 GHz SWP with the 13.56 MHz ICP in terms of the radical composition in C4F8/Ar discharges and the electron energy distribution function (EEDF). A comparison of the two plasmas was carefully made in an identical plasma vessel at the same wall temperature where an antenna coupler on a quartz plate was changed from an expanded waveguide for SWP to a loop coil for ICP. Reactive species measurement at the same electron density under the same gas conditions showed marked differences. First, the dissociation degree of C4F8 at the same electron density is higher in ICP than in SWP. Second, neutral radical densities (CF3, CF2) at the same electron density are several times higher in SWP than in ICP, and ICP has a high F radical density. Third, as regards ionic composition, ICP contains more Ar+ and less fluorocarbon ions (CmFn+), while large molecular ions (C2F4+, C3F3+, C3F5+) exist in SWP. In conclusion, ICP is more dissociative than SWP at the same electron density. This result is tentatively attributed to the difference in the EEDFs of the two plasmas, since optical emission spectroscopy of Ar I suggests 1.5–2 times more high-energy (>14 eV) electrons in ICP than in SWP.

Characterization of 100 MHz inductively coupled plasma (ICP) by comparison with 13.56 MHz ICP

The effect of the excitation frequency on the dissociative process of the C4F8 gas was investigated by comparing a 100 MHz [very high-frequency (VHF)] inductively coupled plasma (ICP) with a 13.56 MHz [radio frequency (rf)] ICP. The same apparatus except for the wave generator and matching network was used for both ICPs in order to investigate the frequency effect as precisely as possible. The electron density and electron temperature in an Ar plasma were measured by using a Langmuir probe. From the dependence of the radial distribution of the Ne on the ICP source power, it was found that the rf ICP was produced in a cylindrical space under the coil area, while the VHF ICP was generated throughout the reactor. In C4F8/Ar plasma, the CFx (x=1, 2, 3) radical densities near the reactor wall were measured by using appearance mass spectrometry, and the F radical density was measured by using actinometry through the optical emission spectroscopy of Ar (750.4 nm) and F (703.7 nm). The degree of dissociation of the C4F8 in the VHF ICP was higher than that in the rf ICP, but the CF2/F density ratio in the VHF ICP was 3–5 times that in the rf ICP. This result indicates that the dissociation of high-molecule gases, including C4F8, proceeds more easily in the VHF ICP than in rf ICP and that there is much less dissociation of high-order radicals (e.g., CF2+e→CF+F+e) in VHF ICP than there is in rf ICP. Hence, VHF ICP suppresses F radical generation better than rf ICP.

Air-argon inductively coupled plasma for organic solution analysis: spectral characteristics and analytical performances

A low power air-argon inductively coupled plasma (ICP) obtained on a commercial 40.68 MHz ICP spectrometer has been used for organic solution analysis. Spectroscopic studies show that in air-argon ICP, the molecular bands from hydrocarbons of organic samples such as CN and C 2 are largely depressed or even eliminated. The effects of operating conditions such as air ratio and ICP power on the signal-to-background ratio of atomic and ionic lines for organic solution in air-argon ICP are similar to those for aqueous solution. Detection limits for some elements in methyl-isobutyl ketone (MIBK) solution have also been measured and compared with those obtained by argon ICP. For most atomic lines and some ionic lines, the detection limits in air-argon ICP are better than those in pure argon ICP. A 50% air-argon ICP has been applied to the determination of metallic elements in waste oil diluted with xylene and in nickel naphthenate diluted with MIBK. The analytical results are satisfactory.

Analytical performance evaluation of a 40.68 MHz inductively coupled plasma mass spectrometer

The instrumentation of a new 40.68 MHz inductively coupled plasma (ICP) mass spectrometer is described. An optimization study has been carried out for the instrument. Of the many operating parameters, the carrier argon flow rate is the most sensitive and the optimum carrier argon flow rate is found to be much lower than the literature values for a 27.12 MHz ICP mass spectrometer. The analytical performance of the instrument, i.e., the detection limits, background mass spectrum and formation of oxides and doubly charged ions is also evaluated.