NF3 Flow Research Articles

Optical diagnostic of LiNbO3 etching in NF3/Ar ICP plasma: Part I

Optical emission spectroscopy is informative and nondisturbing technique for diagnostics of various plasmas used for material treatment. In this work the distinctive features of emission spectra of NF3/Ar plasmas of various compositions formed during the plasma chemical etching of lithium niobate were studied. It was found that the wavelength region (220–290 nm) is of a particular interest for LiNbO3 etching control because it can be used to determine "endpoint" in multistep processes with sequencing of plasma etching and wet cleaning for LiF barrier layer removal. The influence of RF Inductively Coupled Plasma (ICP) power, total pressure, bias voltage, NF3 flow rate, and temperature of the susceptor was studied for five different ratios of NF3/Ar flow rates: NF3 (1.5 sccm)/Ar(9.2 sccm), NF3(7.0 sccm)/Ar(4.9 sccm), NF3(7.8 sccm)/Ar(10.8 sccm), NF3 (9.4 sccm)/Ar(3.3 sccm), NF3(11.7 sccm)/Ar(5.4 sccm). It has been shown that a decrease in total pressure and an increase in ICP power lead to an increase in the relative intensities of both argon and fluorine lines. At the same time the variations of bias voltage and susceptor temperature did not have a significant impact on spectral lines intensity of Ar and F. Optical actinometry technique was used to determine concentration of atomic fluorine in NF3/Ar plasmas at various process conditions to demonstrate a correlation between etching rate of LiNbO3 and fluorine atoms concentration.

Plasma Etching of Silicon at a High Flow and a High Pressure of NF3 in Reactive Ion Etching

Capacitively coupled plasma reactive ion etching of silicon by injecting nitrogen trifluoride (NF3) gas was conducted, and the etching process was studied with a residual gas analyzer and an optical emission spectroscopy. During the etching of silicon by the NF3 plasma, the currents of F+ and SiF+3 ions were obtained from the residual gas analyzer. At the same time, the line intensity of fluorine was measured using optical emission spectroscopy. The ion currents of F+ and SiF+3 and the line intensity of fluorine were highest for etching at high pressure. With the results of this study, the general characteristics of reactive ion etching of silicon by using NF3 plasma were confirmed. In addition, by simply changing the flow rate of NF3, a high NF3 flow rate was found to result in a high etch rate because of the reduced residence time.

Perfluorocompound Emissions Control and Kinetic Characteristics in Point-of-Use Wet-Thermal-Wet Abatement of Plasma-Enhanced Chemical Vapor Deposition Chamber Cleaning

Electric thermal oxidation of NF3 is studied in the context of kinetic and activation energy, with an emphasis on correlation with reaction rate. To improve economic feasibility of the wet-thermal-wet abatement process, the effect of NF3 flow rate, N2 flow rate, and operational temperature on decomposition of NF3 are examined. The reactions in question follow first order kinetics. It was found the rate constant is enhanced with increasing flow rate of NF3 and temperature, and decreased with increasing flow rate of N2. The highest rate constant of NF3 was 0.5501 s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for 13 liter per minute (LPM) NF3 flow rate, 70 LPM N2 flow rate, and a temperature of 725 °C. The inlet and outlet concentration of NF3 was examined utilizing Fourier-transform infrared spectroscopy for estimation of NF3 decomposition. This paper not only confirms that large amounts of NF3 can be efficiently decomposed by electric thermal oxidation, but also enhances the feasibility of this technology.

Characterization of Ammonium Silicate Residue during Polysilazane (PSZ) Dry Etching in NF3/ H2O Gas Chemistry

For 28nm NAND flash memory, the aspect ratio of shallow trench isolation (STI) becomes large, and it makes difficult to fill STI structure by conventional oxide film without void formation. Several gap-fill methods such as high density plasma (HDP) and thermal chemical vapor deposition (CVD) are widely accepted, but they are difficult to make gap fill without void because of gap-fill margin. Recently, STI fill has been tried with polysilazane (PSZ) based inorganic spin-on dielectric (SOD) film. PSZ oxide has its good gap-fill ability, low moisture content and high etching resistance. However, PSZ oxide would produce amine etch residue during the NF3 dry etching process because of NH3component in PSZ oxide. For preventing this resudue, it is very important to control process parameters affecting the chemical reaction because the etch rate, and the surface quality depend upon the process reaction. During the STI etching back process, other layer also exposed. So, selectivity between other oxide must be considered. In this study, we have employed plasma dry etching of nitrogen trifluoride (NF3) and H2O mixtures. We studied the effect of the gas chemistry on the etching of oxides. The materials used for these experiments were thermally grown SiO2 (1000Å, 10000Å), PSZ oxide (500Å), TEOS (315Å) and ALD oxide (300Å). Samples of size 25 x 25 mm were cleaned first in diluted SC-1 [NH4OH(25%): H2O2(38%): DIW =1:2:50] at 60°C for 10 min. The etching mechanism of PSZ oxide was investigated in plasma activated NF3/H2O gas. This process generates ammonium hexafluorosilicate ((NH4)2SiF6) as a by-product. By-products were formed on the PSZ surface which was confirmed by observing N–H, NH4+ and SiF6 2-peak in ATR-FTIR spectrum. These peaks are representative of (NH4)2SiF6 powder composition. Etch rates of several SiO2 were reported as a function of H2O ratio, substrate temperature, and pressure. NF3/H2O mixtures were excited using pulsed RF plasma. The NF3 flow rate for all experiments was kept at 150 sccm. The temperatures were varied from 8 to18ºC, the chamber pressures from 7 to 9 Torr., the H2O flow rates from 1500 to 2500 sccm and process times from 20 to 100 sec. Helium was used as a carrier gas. After dry etching, an annealing process was performed. The reaction mechanism was proposed by analyzing the oxide layer surface. We used an ellipsometer to measure the oxide thickness for evaluation of the etch rate. Also, various analyzing tools such as SEM, contact angle analyzer, and FT-IR were used to characterize the surface contaminants. The optimized drying process provides the high selectivity without any residue formation.

Quantum Chemical Investigation of Si Chemical Dry Etching by Flowing NF3 into N2 Downflow Plasma

A quantum chemical investigation of the chemical dry etching of N2 downflow plasma and NF3 flow into the downflow area was carried out by the B3LYP/6-31+G(d) method. The results provide a reasonable interpretation of how the chemical dry etching of Si takes place. Experimentally, it was reported that single-crystal silicon was etched in the N2 downflow plasma with NF3 flow and the etch rate depended on the etching conditions, and it had been deduced that the etchant was F atoms produced by the reaction of N*+ NF3. It was found through our calculations that there were three reaction routes of NF3 proceeding F production in the initial reaction step, with N(2Do) and N2(A3Σu+) and by electron attachment, and it is thought that the most probable F production reaction in the downflow area is N(2Do) + NF3→N=NF2+ F and the next probable reaction is N2(A3Σu+) + NF3(3E)→N2(1Σg+) + NF2+F.

High-speed etching of SiO2 using a remote-type pin-to-plate dielectric barrier discharge at atmospheric pressure

High speed etching of SiO2 has been investigated using a remote-type dielectric barrier discharge (DBD) in-line system with a multi-pin-to-plate power electrode configuration as functions of N2/NF3 gas combination, added gases and operating frequency of a pulse power supply. The SiO2 etch rate increased with an increase in NF3 flow rate (0.2–1.0 slm) in N2 (60 slm)/NF3 but showed a maximum with an increase in N2 (30–80 slm) at 60 slm in the N2/NF3 (1 slm) gas mixture. The SiO2 etch rate was also increased with the addition of up to 0.6 slm of He or Ar gas and it was also related to the increase in fluorine atomic density in the plasma. The addition of He or Ar to the N2 (60 slm)/NF3 (1 slm) and the increase in the frequency of the pulse power increased the fluorine atomic density through the increased Penning ionization/dissociation and the increased ionization by the increased pulse-on time, respectively.

Use of a neural network to model SiC etching in a NF3 inductively coupled plasma

Using a neural network, a plasma etching of silicon carbide thin films was modelled. The etching was conducted in an inductively coupled plasma etch system and characterized by a 24 factorial experiment. The process parameters involved include radio frequency source power, bias power, pressure and gas ratio defined as a NF3 flow rate divided by the total flow rate. The prediction performance of generalized regression neural network was optimized by means of a genetic algorithm. Etch mechanisms were qualitatively estimated by exploring predicted response surfaces. The etch rate variation with the gas ratio was strongly correlated to that of either the dc bias or expected fluorine concentration. The etch rate increase with the pressure was attributed to dominant chemical etching over polymer deposition. Typical source power effect was transparent only at higher gas ratios and higher powers, presumably due to enhanced radical concentration. The source power effect strongly depended on physical phenomena accompanied by the gas ratio variation maintained in the chamber.

Power dependence of NF3 plasma stability for in situ chamber cleaning

We investigated the stability of NF3 plasmas for in situ chamber cleaning in a production plasma-enhanced chemical vapor deposition reactor. An rf power threshold, normalized by NF3 molar number (Pnn) and NF3 flow rate (Pnf), is observed to be PnnPnf=39 (W/μ mol)(W/sccm) for stable plasmas with high NF3 destruction efficiency. This is rationalized by the energy required to maintain sufficient electron–ion pair creation in an electronegative discharge.

Optimization and analysis of NF3 in situ chamber cleaning plasmas

We report on the optimization and analysis of a dilute NF3 in situ plasma-enhanced chemical vapor deposition chamber cleaning plasma for an Applied Materials P-5000 DxL chamber. Using design of experiments methodology, we identified and optimized operating conditions within the following process space: 10–15 mol % NF3 diluted with helium, 200–400 sccm NF3 flow rate, 2.5–3.5 Torr chamber pressure, and 950 W rf power. Optical emission spectroscopy and Fourier transform infrared spectroscopy were used to endpoint the cleaning processes and to quantify plasma effluent emissions, respectively. The results demonstrate that dilute NF3-based in situ chamber cleaning can be a viable alternative to perfluorocarbon-based in situ cleans with added benefits. The relationship between chamber clean time and fluorine atom density in the plasma is also investigated.

Plasma Decontamination Of Depleted Uranium Oxide From Stainless Steel Surfacesa

ABSTRACT: A series of single effect, RF plasma, glow discharge experiments were conducted using NF3 gas to decontaminate depleted uranium dioxide from stainless‐steel substrates. In the experiments, the plasma absorbed power was varied from 25 to 210 W, the pressure from ∼10 to 40 Pa, and the NF3 flow rate from 3 to 18.5 SCCM. Results demonstrated that UO2 can be completely removed from stainless‐steel substrates after several minutes processing at under 100 W with initial etch rates ranging from 0.2 to 7.4 μm/min. A primary etch mechanism is proposed in which F atoms created in the plasma diffuse to the surface UO2 and react to form successive intermediates of uranium fluorides and/or oxyfluorides with reactions continuing to form the volatile UF6 which desorbs into the gas phase to be pumped away. Ions created in the plasma are too low in concentration to be the primary etch mechanism, yet they can deliver enough energy to enhance the reaction process. UO2 etching is a self‐limiting process due to the formation of non‐volatile uranium oxyfluorides and fluorides which form over the UO2, slowing or completely blocking the reaction to UF6.

Silicon etching in NF3/O2 remote microwave plasmas

The etching of silicon in remote microwave discharges fed with NF3/O2 has been investigated. In situ ellipsometry and x-ray photoelectron spectroscopy (XPS) were used to monitor surface effects, while mass spectrometry was used to monitor the gas phase dynamics. Varying the microwave power from 600 to 1400 W has little effect, due to the near complete dissociation of the NF3, even at lower powers. For discharges containing pure NF3, the poly-Si etch rate increases linearly with NF3 flow. When a low proportion of O2 (O2/NF3=0.1) is added to the discharge, the etch rate increases quickly to its maximum of ∼700 nm/min. With further O2 addition, this etch rate decreases below that observed for pure NF3 processing. The fluorine concentration in the processing region decreases for all O2 additions by a dilution effect. For pure NF3 discharges, XPS measurements reveal 1–2 nm thick, highly fluorinated reaction layers with a gradual loss of fluorine content as the NF3 flow is increased. Specimens processed with both NF3 and O2 show much less surface fluorination that decreases with increasing O2 content in the feed gas. At the etch rate maximum, the observed N (1s) signal is also maximized. The reaction layer thickness increases with added O2 and continues to more than 10 nm at O2:NF3 ratios greater than unity. We discuss the enhanced reactivity of the modified Si surface and compare our results with the role of admixed N2 into the CF4/O2 system. We also injected NO directly into the effluent of NF3 and CF4/O2 discharges. For fluorine rich discharges, NO removes the modified surface layer on Si and provides for an enhanced etch rate. In the oxygen rich regime, NO injection can increase both the etch rate and the reaction layer thickness. We will present a mechanism for the enhanced etching of Si in the presence of fluorine, oxygen and the NO molecule.

Composition, oxidation, and optical properties of fluorinated silicon nitride film by inductively coupled plasma enhanced chemical vapor deposition

Amorphous fluorinated silicon nitride films have been deposited with the variation of NF3 flow rate using SiH4, N2, Ar, and NF3 gases by inductively coupled plasma enhanced chemical vapor deposition for the first time, and the absolute composition, oxidation mechanism, and optical properties were investigated. The absolute composition including hydrogen was performed by means of elastic recoil detection time of flight. It was found that the oxygen and fluorine contents in the film dramatically increased, but the hydrogen content decreased to below 4 at.% as the NF3 flow rate increased. The oxidation mechanism could be explained in terms of the incorporation of the activated residual oxygen species in the chamber into the film with unstable open structure by the fluorine-added plasma. It was shown that the density and optical properties such as refractive index, absorption coefficient, and optical energy gap depended on the film composition. The variations of the above properties for fluorinated silicon nitride film could be interpreted by the contents of fluorine and oxygen with high electronegativity.

Preparation and Electrochemical Properties of Carbonaceous Thin Films Prepared by C2H4/NF3 Glow Discharge Plasma

Carbonaceous thin films were prepared from ethylene, argon and nitrogen trifluoride (NF3) by plasma assisted chemical vapor deposition (PCVD). The carbon thin films were characterized by scanning electron microscope (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) and then their electrochemical properties were studied by cyclic voltammetry and charge and discharge.measurements. From SEM image carbon thin films were flat and pin-hole free. XPS spectra indicate that nitrogen and fluorine atoms are not contained in carbon thin films. Crystallinity of the films are affected by the NF3 flow rate from Raman spectra. The difference of the NF3 flow rates also affected the results of cyclic voltammetry and charge and discharge measurements. Correlation of the NF3 flow rate and the electrochemical properties of carbon thin films was discussed.

Remote Plasma-Enhanced CVD of Fluorinated Silicon Nitride Films

An investigation has been made of the effect of dilution of nitrogen with NF3 on the properties of silicon nitride deposited by remote plasma-enhanced CVD (PECVD). For NF3/N2 mixtures with < 1.5% NF3, fluorinated films with the structure of silicon nitride are formed but the total concentration of bonded hydrogen in the films decreases with increasing NF3 flow rate, which leads to an improvement of the electrical properties of the films compared with unfluorinated films. Such films could be of interest for device applications. For NF3/N2 mixtures with NF3 > 1.5 %, films with the structure of silicon dioxide are formed, but they do not contain enough oxygen to give typical SiO2 IR spectra. It is suggested that the silicon dioxide structure arises because of isoelectronic substitution of oxygen by NF.

The Applicability of Fluorinated Silicon Nitride Film As Bottom Antireflective Layer In Deep Ultraviolet Lithography

AbstractThis study describes the use of fluorinated silicon nitride film as a bottom antireflective layer (BARL) material suitable for line-patterning in quarter-micron KrF excimer laser lithography. For the structures of photoresist/BARL (300Å)/c-Si and photoresist/BARL (300 Å )/W-Si at a wavelength of 248nm, 0% reflectance could be achieved when the refractive index (n) and extinction coefficient (k) values of the film are 2.11 and 0.68 or 2.05 and 0.59, respectively. The fluorinated silicon nitride thin films on p-type (100) Si substrates obtained by inductively coupled plasma enhanced CVD have been evaluated with the variations of NF3 flow rates under the two conditions of SiH4:N2=2:15 and 3:20 (seem). The films optical constants and reflectance were investigated by spectroscopic ellipsometry combined with a reflectance simulation program. The film n and k values at 248nm vary in the ranges of 1.67~2.35 and 0.01~0.69, respectively, depending on gas flow ratio of SiH4:N2:NF3. Low reflectance of below 5% can be obtained from reflectance simulation for two deposition conditions with a BARL thickness of 300Å. In addition, the reflectance could be reduced to almost 0% by controlling film thickness. Finally, the antireflective layer performance was investigated using KrF excimer laser lithography.

Temperature dependence of the etch rate and selectivity of silicon nitride over silicon dioxide in remote plasma NF3/Cl2

The etch rates and selectivity of Si3N4 over SiO2 have been investigated by microwave discharging a mixture of NF3 and Cl2 and flowing the resultant fluorine and chlorine atoms and interhalogenous molecules simultaneously over a silicon wafer covered with low pressure chemical vapor deposition (LPCVD) Si3N4, and a wafer covered with thermally grown SiO2. The temperature dependence of the etch rates of Si3N4 and SiO2 in the NF3/Cl2 mixture was examined in the range from 25 to 500 °C, and the selectivity of the nitride etch over the oxide etch as well as nitride etch rate was found to increase with increasing temperature. It was also found that both etch rates and selectivities increase with NF3 flow rates within the range used in this study.

Nearly isotropic etching of 6H-SiC in NF3 and O2 using a remote plasma

Nearly isotropic etching of the 6H-SiC carbon face has been achieved in a remote plasma at 330 °C using a mixture of O2 and NF3 in argon. Using evaporated aluminum as a mask, undercutting has been observed to a distance equal to the etch depth. The etch rate is a function of the ratio of O2 to NF3 flow rates and of temperature, peaking strongly to 220 nm/min at 82% oxygen for 330 °C. Smooth surfaces were obtained for gas ratios leading to the maximum etch rate, and also for a NF3-argon mixture, with significant roughening observed for other O2-NF3-argon mixtures. In the absence of a practical wet etch for SiC, this procedure is promising for isotropic etching in SiC device processing.

I.r. spectra resolution in fluorinated silicon nitride films

The broad I.r. Si-N band (700–1200 cm−1) in fluorinated silicon nitride films has been resolved. I.r. spectra of the samples have been fitted using Gaussian curves centred in positions determined from the maxima of the negative second derivative of the digitized spectra. In silicon nitride films deposited by plasma-assisted chemical vapour deposition from SiH4-NF3-NH3-N2 gas mixtures-SiFn radicals (n=1–3) incorporated in their structures have been detected. The relative concentrations of the different fluorine radicals present in the network depend on the NF3 flow ratio used. As the flow ratio increases above 0.5, -SiF and-SiF2 concentrations in the film reach the steady state. However, an appreciable increase in-SiF3 and [-SiF2-] n concentrations has been observed.

Magnetron-Enhanced Reactive-Ion-Etching of Al-1%Si-2%Cu Alloy

ABSTRACTPlasma etching of Al-1%Si-2%Cu presents serious challenges in corrosion, residue, and critical dimension (CD) control in single wafer etchers. One approach is to pattern the metal with oxide mask so chlorine can no longer be trapped in resist and sidewall polymers to cause corrosion. The magnetron-enhanced reactive-ion-etching (MERIE) offers a high degree of ionization at very low pressure, so anisotropic etching with reasonably high etch rate can be achieved even without sidewall protection. This paper summarizes our MERIE process characterization in terms of the effects of SiCl4 flow rate and plasma power on selectivity and CD control using an oxide mask. Typical etching was performed at 1000 watts and 40 sccm SiCl4 with the unthrottled pressure at 4.0 mTorr and a self-induced dc bias of 75 V. A 2-minute NF3 plasma at 250 watts and 100 sccm of NF3 flow served as the passivation step. This metal etch process has been successfully implemented in a doublelayer-metal interconnect technology.

Deposition of Fluorinated Silicon Nitride using Plasma Enhanced Chemical Vapor Deposition Technique

ABSTRACTHigh hydrogen content of ammonia/silane deposited silicon nitride films has been linked to instability in electronic devices such as MOSFET's MNOSFET's and TFT's. Fluorine has been proposed to help reduce the hydrogen content of these films. In this work, NF3 was used as a fluorinating agent. Optical and electrical properties were studied as a function of NF3 flow rate. A maximum optical gap of 5.3 eV was obtained with NF3 as compared to 3.2 eV without. The dielectric strength improved from 4 to 10 MV/cm with the addition of NF3. FTIR data show that the Si-N peak shifts to higher wave numbers and the Si-H peak drops below the detection limit with the addition of NF3. Also, the broad Si-N peak at 850 cm-1 is composed of many individual peaks which become discernable when a stainless steel screen is placed in front of the substrate. As the NF3 concentration is increased, a new peak at 1030–1060 cm-1 appears. This may be associated with a N-F vibration (1030 cm-1).