Function Of Source Power Research Articles

Inductively coupled plasma etching of bulk, single-crystal Ga2O3

High ion density dry etching of bulk single-crystal β-Ga2O3 was carried out as a function of source power (100–800 W), chuck power (15–400 W), and frequency (13.56 or 40 MHz) in inductively coupled plasma (ICP) systems using Cl2/Ar or BCl3/Ar discharges. The highest etch rate achieved was ∼1300 Å min−1 using 800 W ICP source power and 200 W chuck power (13.56 MHz) with either Cl2/Ar or BCl3/Ar. This is still a comfortably practical set of conditions, where resist reticulation does not occur because of the effective He backside cooling of the sample in the tool and the avoidance of overly high powers in systems capable of 2000 W of source power. The etching is ion-assisted and produces anisotropic pattern transfer. The etched surface may become oxygen-deficient under strong ion-bombardment conditions. Schottky diodes fabricated on these surfaces show increased ideality factors (increasing from 1.00 to 1.29 for high power conditions) and reduced barrier heights (1.1 on reference diodes to 0.86 eV for etched surfaces). This electrically active damage is dependent on ion energy and flux during the etching. An obvious strategy is to reduce plasma powers toward the end of an etch sequence to reduce the disruption to the Ga2O3 surface.

“What did You Say, and Who do You Think You Are?” How Power Differences Affect Emotional Reactions to Prejudice

Three studies examine how power differences between targets and sources of prejudice affect targets' emotional reactions to prejudice. Study 1 first demonstrates that people do not expect powerful others to be prejudiced. Studies 2 and 3 then examine what happens when targets encounter prejudice, as a function of the source's power. Targets notice and recall prejudiced statements from powerful sources, irrespective of whether or not they are personally dependent on the source. However, results also demonstrate that personal dependency on the source determines how much targets attend to and are emotionally affected by prejudice. Emotional reactions to prejudice as a function of source power were mediated by negative expectations about future interactions.

High density plasma etching of titanium nitride metal gate electrodes for fully depleted silicon-on-insulator subthreshold transistor integration

Etching of TiN metal gate materials as a part of an integrated flow to fabricate fully depleted silicon-on-insulator ultralow-power transistors is reported. TiN etching is characterized as a function of source power, bias power, gas composition, and substrate temperature in a high density inductively coupled plasma reactor. Under the conditions used in this work, the TiN etch rate appears to be ion flux limited and exhibits a low ion enhanced etching activation energy of 0.033eV. Notching of the polysilicon layer above the TiN may occur during the polysilicon overetch step as well as the TiN overetch step. Notching is not significantly affected by charging of the underlying gate dielectric under the conditions used. By optimizing the plasma etch process conditions, TiN:SiO2 selectivity of nearly 1000:1 is achieved, and a two-step TiN main etch and TiN overetch process yields well-defined metal gate structures without severe gate profile artifacts.

Radio frequency source power effect on silicon nitride films deposited by a room-temperature pulsed-PECVD

Silicon nitride (SiN) films deposited by using a pulsed-plasma enhanced chemical vapor deposition system at room temperature were investigated as a function of radio frequency source power and duty ratio in the experimental ranges of 200–800 W and 40–90%, respectively. Diagnostic parameters, measured using a non-invasive ion energy analyzer, were related to SiN deposition rate. Decreasing the source power increased high ion energy, but decreased low ion energy. A high similarity between ion energy flux and ion energy was observed. Decreasing the source power increased the deposition rate for all duty ratios. For all the variations in the power and duty ratio, the deposition rate varied in the range of 290–640 Å/min. Decreasing the duty ratio was effective in increasing the deposition rate. The deposition rate was strongly correlated to high ion energy and high ion energy flux as a function of source power.

Chlorine dissociation fraction in an inductively coupled plasma measured by ultraviolet absorption spectroscopy

Broadband ultraviolet absorption spectroscopy of the weak Cl2 continuum between 250 and 400 nm was used to measure the molecular Cl2 density in pure chlorine inductively coupled plasmas at pressures of 15–100 mTorr and radio-frequency (rf) power up to 800 W. The depletion of the Cl2 density was greatest at high-rf power and low pressure, and reached 80% at 15 mTorr 800 W. A simple global model was developed to explain the variation of the Cl2 dissociation rate as a function of source power and total gas pressure, and was in excellent agreement with the observations.

Effects of Ar inductively coupled plasma exposure on 4H-SiC Schottky rectifiers

4H-SiC Schottky rectifiers were exposed to inductively coupled Ar plasmas as a function of source power (150–750 W), rf chuck power (75–350 W), and process pressure (5–30 mTorr). The reverse breakdown voltage (VB) was increased by increases in both incident ion energy and ion flux, with the former having the strongest influence. As an example, Ar plasma exposure at ion energies of ∼335 eV led to an increase in VB from approximately −500 to −950 V. These results suggest strategies for minimizing plasma-induced damage during both deposition and etching steps used in the fabrication of SiC rectifiers.

Etch characteristics of HfO2 films on Si substrates

The etch rates and mechanisms for HfO2 thin films in Cl2-, SF6- or CH4/H2-based plasmas were measured as a function of source power, r.f. chuck power and discharge composition. Both Cl2- and SF6-based plasmas produced some degree of chemical enhancement in the etch mechanism. Selectivities between 0.2 and 5 were obtained for Si over HfO2 in these two plasma chemistries. High fidelity pattern transfer was achieved for photoresist-masked HfO2/Si structures etched with Cl2/Ar over a broad range of pressures or with SF6/Ar at low pressures. The surface morphologies of both HfO2 and Si were smooth over a wide range of etching conditions.

Schottky diode measurements of dry etch damage in n- and p-type GaN

n- and p-type GaN was exposed to inductively coupled plasma of N2, H2, Ar, or Cl2/Ar, as a function of source power (0–1000 W) and rf chuck power (20–250 W). For n-GaN, there was a strong reduction in diode reverse breakdown voltage and an increase in forward and reverse currents, while for p-GaN the reverse breakdown voltage increased. These results are consistent with creation of point defects with shallow donor nature that increase the conductivity of initially n-type GaN or decrease the conductivity of p-type GaN. Annealing at 750 °C under N2 produced significant recovery of the electrical properties, while wet etch removal of 500–600 Å of the surface produced a full recovery. For completed n-type mesa diodes exposed to Ar or Cl2/Ar discharges, the low bias forward currents increased by several orders of magnitude. The exposed surfaces became N2 deficient in all cases.

Inductively coupled plasma damage in GaN Schottky diodes

The effects of H2 or N2 plasma exposure on the current–voltage characteristics of GaN Schottky diodes were examined as a function of source power and rf chuck power. Under all conditions there was a strong reduction in diode reverse breakdown voltage and an increase in forward and reverse currents. The results are consistent with creation of a thin (⩽600 Å) n-type conducting surface region after ion bombardment of the GaN surface. Much of the degradation in diode quality can be recovered by annealing in N2 at 750 °C.

Effect of inert gas additive species on Cl 2 high density plasma etching of compound semiconductors : Part II. InP, InSb, InGaP and InGaAs

The effects of the additive noble gases He, Ar and Xe on chlorine-based inductively coupled plasma etching of InP, InSb, InGaP and InGaAs were studied as a function of source power, chuck power and discharge composition. The etch rates of all materials with Cl 2/He and Cl 2/Xe are greater than with Cl 2/Ar. Etch rates in excess of 4.8 μm/min for InP and InSb with Cl 2/He or Cl 2/Xe, 0.9 μm/min for InGaP with Cl 2/Xe, and 3.8 μm/min for InGaAs with Cl 2/Xe were obtained at 750 W ICP power, 250 W rf power, ∼15% Cl 2 and 5 mTorr. All three plasma chemistries produced smooth morphologies for the etched InGaP surfaces, while the etched surface of InP showed rough morphology under all conditions.

New plasma chemistries for dry etching of InGaAlP alloys: BI3 and BBr3

Inductively coupled plasma etching of InGaP, AlInP and AlGaP in BI3 or BBr3 discharges was investigated as a function of source power, dc chuck bias and plasma composition. InGaP etches at the fastest rates (>6000 Å min−1) in both chemistries, followed by AlGaP. It is found that AlInP provides an excellent etch stop for the other two materials in both mixtures. The InGaP surface morphology improves with increasing BI3 or BBr3 content, and with increasing dc chuck bias. The etched features for this material are highly anisotropic. Etch selectivities for InGaP over SiO2 and SiNx of ⩾8 are obtained in both plasma chemistries, and there is no etch incubation time with either mixture, indicating that both can scavenge the native oxide on InGaP, AlGaP and AlInP.

TiN Etching and Its Effects on Tungsten Etching in SF6/Ar Helicon Plasma

Etching characteristics of TiN film have been investigated in SF6/Ar helicon plasma. The etch rate of TiN film increases with increasing source power, bias power and temperature, exhibits a maximum at a moderate pressure as a function of pressure. A possible mechanism of titanium fluoride formation is proposed based on the results of optical emission spectroscopy (OES). In order to determine the effect of titanium fluorides on tungsten etching, the loading effect in tungsten etchback is investigated as a function of source power, bias power and temperature. Using secondary ion mass spectrometry (SIMS), the relative concentrations of titanium fluorides redeposited on tungsten are measured by varying the bias power and temperature. The loading effect is reduced by enhancing the redeposition of titanium fluorides on a tungsten plug with increasing source and bias power. The loading effect is also retarded by lowering the temperature.

Mechanism of Tungsten Atom Formation in Tungsten Etchback Using SF 6/Ar Helicon Plasma

The formation mechanism of tungsten (W) atoms in tungsten etching has been investigated with the /Ar helicon plasma. The etch rate of W films decreases with increasing flow rate of Ar in the /Ar gas mixture while the density of tungsten atoms increases as measured by optical emission spectroscopy. Tungsten films are rarely etched with pure Ar plasma. The density of tungsten atoms generated by a direct sputtering is much less than the one in /Ar plasma. By comparing the etch rate with the relative intensity of W atom as a function of source power and bias power, it was found that tungsten atoms are mainly formed through the dissociation reaction of stable product, , and further by electron impact. The loading effect in tungsten etchback can be suppressed by enhancing the redeposition of (y and z ⩾ 0) by‐products by increasing the source power. The suppression mechanism of the loading effect is investigated by an in situ monitoring of optical emission of tungsten atoms generated during overetching in tungsten etchback.

Comparison of advanced plasma sources for etching applications. V. Polysilicon etching rate, uniformity, profile control, and bulk plasma properties in a helical resonator plasma source

Etching of polysilicon features using a helical resonator plasma source is evaluated. Performance metrics consist of etching rate, etching rate uniformity, and profile control using HBr/O2–He gas-phase chemistry. The effect of source power, rf-bias power, and reactor pressure on etching rate and uniformity is examined using a response surface experiment. Feature profile control is determined by examining nested and isolated lines and trenches using oxide mask/polysilicon/oxide structures. Good uniformity and vertical profiles are obtained at low reactor pressures, high source power, and rf-bias between 50 and 60 W. The operating point for best uniformity is at 3.5 mTorr, 3000 W source power, and 53 W rf-bias power. At this point, the etching rate is 3700 Å/min and the nonuniformity is less than 1.0%, over 125-mm-diam wafers. Radial profiles of electron temperature and ion density near the wafer surface are presented as a function of source power, rf-bias power, and reactor pressure. The ion density was found to be in the mid-1011 cm−3 range and electron temperatures were 5–7 eV. An increase in source power and reactor pressure results in an increase in ion density; however, the electron temperature shows a weaker dependence. Finally, these results are compared to those using helicon and multipole electron cyclotron resonance plasma sources evaluated in previous studies. We found that all three plasma sources provide high ion density at low pressures to meet performance demands for polysilicon etching; however, the helical resonator source offers somewhat higher etching rate and better bulk plasma uniformity.

The relative frequency of broad-lined and narrow-lined active galactic nuclei: implications for unified schemes

I discuss evidence concerning the relative occurrence of narrow-lined and broad-lined active galactic nuclei (AGN), in optical, IR, X-ray, and radio-selected samples. Both narrow-lined AGN and reddened broad-lined AGN occur more frequently at lower source powers. There is marginal evidence that narrow-lined AGN were more common in the past. Narrow-lined objects have weaker [O III] at a given radio power. These data are inconsistent with the simplest unified scheme where a similar thick molecular torus surrounds all AGN, and with the simplest modification, that the torus geometrical thickness is a function of source power.