Decrease In Etch Rate Research Articles

Effects of plasma conditions on the shapes of features etched in Cl2 and HBr plasmas. I. Bulk crystalline silicon etching

We have studied the effects of source and bias powers, pressure, and feed gas composition on the shapes of SiO2-masked crystalline silicon features etched in a transformer-coupled high density plasma system. Higher etching rates were obtained at higher source and bias powers, and higher pressure. The etching rates of isolated and nested trenches, isolated lines, and holes were nearly the same, indicating a negligible pattern density dependence. We did, however, observe a very weak decrease in etch rates with increasing aspect ratio at 2 mTorr in a pure Cl2 plasma. At 10 mTorr, no aspect ratio dependence was observed, except at the highest source and bias powers. Microtrenching was observed under certain plasma conditions and could be reduced by using higher bias powers. At 10 mTorr in a pure chlorine plasma, we observed a slight taper at the bottoms of the etched features and the formation of narrow microtrenches near feature corners. At 2 mTorr, the microtrenches were broader and overlapped near the center of narrow trenches to form pyramid-shaped trench bottoms. When a HBr plasma was used instead of Cl2, the etching rate decreased by 50% but the etching profiles were more vertical and the trench bottoms were flat. Isolated lines etched in the HBr plasma, however, revealed broad but shallow microtrenches near the edges of the line, suggesting that the flat trench bottoms were a result of broad microtrenches that overlapped. Trenches of 3 μm depth and aspect ratios of 7 have been obtained using either HBr or Cl2, exhibiting similar microfeatures as observed when etching shallower trenches.

Metalorganic molecular beam epitaxy/etching of III–V semiconductors

Etching of GaSb by TDMASb is observed on the surface of GaSb and GaAs at appropriate temperatures (several hundred °C) in a MOMBE chamber. RHEED intensity observation shows that the layer-by-layer mode etching takes place. When Sb 4 is supplied simultaneously, the etching rate decreases and the activation energy of etching increases. Etching reaction largely depends on surface coverage of Sb. Etching rate of GaSb by TDMASb was almost independent of crystal surface orientation. When TEGa is supplied simultaneously with TDMASb, growth takes place and the growth rate on the ( N11) surfaces ( N=5, 4, 3) was much higher compared with other surfaces. Grown samples indicate high crystal quality. BDMAAsCl also shows the etching effect on GaAs, InAs and GaSb. By using this etching effect, InAs quantum dot structures having no wetting layer were fabricated.

Low bias dry etching of III-nitrides in Cl2-based inductively coupled plasmas

Cl2-based inductively coupled plasmas (ICP) with low additional dc self-biases (−100V) produce convenient etch rates (500–1500A·min−1) for III-nitride electronic device structures. A systematic study of the effects of additive gas (Ar, N2, H2), discharge composition, process pressure, and ICP source power and chuck power on etch rate and surface morphology has been performed. The general trends are to go through a maximum in etch rate with percent Cl2 in the discharge for all three mixtures, and to have an increase (decrease) in etch rate with source power (pressure). Since the etching is strongly ion-assisted, anisotropic pattern transfer is readily achieved. Maximum etch selectivities of approximately six for InN over the other nitrides were obtained.

Characterization of Titanium Etching in Cl2 / N 2 Plasmas

The effects of etch time, nitrogen and chlorine gas flows, radio frequency power, pressure, and temperature on the etch rate of sputtered titanium films in chlorine‐nitrogen plasmas were investigated in this work. The radio frequency power was found to have the greatest effect on the etch rate, followed by the reaction pressure. The increase in Ti etch rate with radio frequency power can be attributed to increased ionization of the gases and increase in ion and electron energies in the plasma. The increase in pressure led to a decline in the etch rate, probably due to loss of chlorine through recombination reactions. It was observed that the etch rate increased with increase in chlorine for gas flows below 100 sccm. Addition of nitrogen increased the etch rate to a flow of 10 sccm due to generation of free chlorine radicals, but led to a decrease in etch rate for nitrogen flows beyond 25 sccm due to dilution effect. There was only slight dependence of etch rate on the temperature within the range of this investigation.

Reactive Ion Etching of RuO2 Films: The Role of Additive Gases in O2 Discharge

In a previous work, we had reported that the etch rate of RuO2 thin films in an oxygen discharge exhibits an anomalously strong increase (1625 A/min) when a small amount of additive gas such as CF3CFH2 (2.5% by mole fraction) is introduced. Furthermore, the etch rate was suppressed by a large factor when the mole fraction of CF3CFH2 gas in the feed was increased. In this work, we have explored the underlying mechanism for this behavior. Several gases, such as CF3CFH2 (HCFC-134), N 2 , and SF 6 were added to the oxygen discharge to investigate the etch mechanism. Atomic oxygen was found to be the dominant active species reacting with RuO 2 films to form volatile RuO 4 products. In low concentrations, additive gases in the oxygen discharge were found to increase the generation rate of O atoms, thereby enhancing the etch rate. This was confirmed through loading effect studies; the etch rate was found to decrease with increasing sample area. HCFC-134 gas had the strongest effect in increasing the generation rate (G), and accordingly, addition of small amount of CF 3 CFH 2 in oxygen discharge yielded the highest etch rate. The decrease in etch rate with increasing mole fraction of CF3CFH2 in the feed (>5%) was attributed to the reaction of F atoms with RuO 2 to form surface residue layers that occupied surface reaction sites thus impeding the reaction between O and RuO 2 . The formation of the surface residue layer was validated through X-ray photoelectron spectroscopy studies.

Numerical study of the etch anisotropy in low-pressure, high-density plasma etching

Evolution of etched profiles has been numerically studied during low-pressure, high-density (LPHD) plasma etching of Si in Cl2. The surface etch rates were calculated using a reaction model of synergism between incoming ions and neutral reactants, including the spread of ion angular distributions due to their thermal motions and the transport of neutrals arising from the reemission on surfaces in a microstructure. Etched profiles were then simulated using a so-called two-dimensional string algorithm to examine the effects of ion temperature kTi and energy (or sheath voltage) eVs on the etch anisotropy for different neutral-to-ion flux ratios Γn/Γi toward the substrate. Numerical results indicated that in typical Cl2 LPHD plasma etching environments, where the neutral-to-ion flux ratio is Γn/Γi∼1 and the ratio of sheath voltage to ion temperature is eVs/kTi∼100, the chlorinated surface coverage is microscopically nonuniform in etched features: The coverage is very low at the bottom (α∼0.1), whereas the sidewall surface (α∼1) is almost saturated with neutrals. This microscopic nonuniformity of the coverage in etched features is the proposed mechanism responsible for the inversely tapered profiles that often occur in LPHD plasma etching. Additionally, the decrease in vertical etch rate in microstructures or the reactive-ion-etching lag due to neutral shadowing effects is also found to become significant in LPHD plasma etching. At such a low flux ratio of Γn/Γi∼1, more directional ions with a higher ratio of eVs/kTi≳500 are required for the anisotropic etching; e.g., for an ion energy (or sheath voltage) of eVs=50 eV, the ion temperature in a plasma is required to be kTi≲0.1 eV.

Cl2-Based Dry Etching Of The AIGaInN System In Inductively Coupled Plasmas

AbstractCl2-based Inductively Coupled Plamas with low additional dc self-biases(−100V) produce convenient etch rates(500–1500Å.min−1) for GaN, AIN, InN, InAiN and InGaN. A systematic study of the effects of additive gas(Ar, N2, H2), discharge composition and ICP source power and chuck power on etch rate and surface morphology has been performed. The general trends are to go through a maximum in etch rate with percent C12 in the discharge for all three mixtures, and to have an increase(decrease) in etch rate with source power(pressure). Since the etching is strongly ion-assisted, anisotropic pattern transfer is readily achieved. Maximum etch selectivities of approximately 6 for InN over the other nitrides were obtained.

Role of nitrogen in the downstream etching of silicon nitride

Chemical downstream etching of silicon nitride (Si3N4) requires the addition of nitrogen to the discharge for obtaining efficient etch rates. A 10% addition of N2 to a CF4/O2 discharge (CF4/O2 = 1.2, 0.525 Torr) causes a factor of 6 increase in the Si3N4 etch rate and a 8% decrease in the silicon dioxide etch rate. The result is selectivities approaching 9:1. Importantly, the conversion of CF4 to F and F-containing reactive species by the discharge decreases or remains constant as nitrogen is added to the discharge mix, indicating that the etching reaction is not limited by delivery of these species to the substrate. By measuring the amount of NO and NO2 in the etch chamber, it is found that the NO concentration increases by a factor of 6 as N2 is added, while the amount of NO2 remains small and constant. The NO signal is significantly reduced during nitride etching compared to the signal observed during a discharge with an empty etch chamber, implying that the increase in Si3N4 etch rate is related to the formation of NO in the discharge. This view is consistent with the observation that an NF3 plasma in a quartz discharge tube results in a nitride etch rate which is a factor of 2 higher than for the same discharge in a sapphire tube. The conclusion is that the oxygen liberated by erosion of the quartz tube allows the formation of NO. That NO is a key Si3N4 etch reactant was confirmed by performing a series of experiments in which N2, NO, NO2, and N2O were injected into the discharge and then downstream in the reaction chamber during a CF4/O2 discharge. Nitride etch rates increased significantly upon injection of NO into both discharge and etch chamber as compared to injection of the other NxOy species.

Role of etch products in polysilicon etching in a high-density chlorine discharge

For low-pressure, high-density plasma systems, etch products can play a significant role in affecting plasma parameters such a.s species concentration and electron temperature. The residence time of etch products in the chamber can he long, hence depleting the concentration of the reactants, and leading to a decrease in etch rate. We use a spatially averaged global model including both gas phase and surface chemistry to study Cl2 etching of polvsilicon. Etch products leaving the wafer surface are assioned to he SiCL2 and SiCl4. These species can be fragmented and ionized by collisions with energetic electrons, generating neutral and charged SiCl, products (x=0–4). Two limiting cases of the etch mechanism are found. an ion flux-limited regime and a neutral reactant-limited regime. The high degree of dissociation in high-density plasmas leads to the formation of elemental silicon, which can deposit on the chamber walls and wafer surface. We include surface models for both the wall and the wafer to better understand the role of etch products as a function of flowrate, pressure, and input pwer. A phenomenological model for the surface chemistry is based on available experimental data. We consider the two limiting conditions of nonreactive and reactive walls. These models are perfectly reflective walls, where all silicon-containing species are reflected; and reactive walls, which act as reactive sites for the formation of SiCl2 and SiCl4 etch products. The two limiting conditions give significantly different results. A decrease in the absolute atomic silicon density and a weaker dependence of etch rate on flowrate are observed for the reactive wall.

Electron cyclotron resonance plasma etching of silicon dioxide for deep-submicron ultralarge scale integrations

Silicon dioxide etching technology for deep-submicron ultralarge scale integration has been developed using an electron cyclotron resonance (ECR) plasma etcher. The optimum conditions for silicon dioxide etching are obtained in terms of etch rate, geometrical controllability, and radiation damage by fully utilizing such advantages of the ECR plasma etcher as low-pressure operation, high plasma density, and independent control of ion energy and plasma discharge. High selectivity is also found at low pressures with C4F8/CH3F. The technology has been successfully applied to the formation of 0.35 μm contact holes with an aspect ratio of 4 without a decrease in etch rate.

Electrochemical etch-stop characteristics of TMAH:IPA solutions

Abstract The characteristics of electrochemical etching of silicon in concentrated (25 wt.%) and dilute (2.5 wt.%) tetramethyl ammonium hydroxide (TMAH) and in 25 wt.% TMAH: 17 vol.% isopropyl alcohol (IPA) solutions are presented. I–V curves and the variation of the etch rate in the direction with the applied potential have been obtained for n- and p-type silicon. The difference in the passivation potential (PP) of n- and p-type silicon is more significant for dilute TMAH solutions and is practically unaffected by the presence of IPA. The silicon etch rate is smaller for n-type than for p-type silicon, the difference being more pronounced when no IPA is used. In any case, the etch rate decreases abruptly at potentials anodic to the PP. Surprisingly, a pronounced decrease in the etch rate of n-type silicon is observed for potentials negative with respect to the open-circuit potential. The results obtained are applied to the fabrication of thin membranes and for monocrystalline silicon microbridges.

Monte Carlo simulation and measurement of silicon reactive ion etching profiles

A two-dimensional plasma etching model based on the simbad Monte Carlo thin-film growth simulation program has been modified to include ion-enhanced etch processes. The modified program has been applied to a study of sidewall passivation in the etching of silicon in a CF4/O2 plasma. Experimentally measured mask undercut in the etching of 0.8-μm-wide lines was reduced from 150 Å/min to virtually zero with an increase in oxygen from 8% to 45% of total gas flow. The corresponding decrease in etch rate was from about 750 to 325 Å/min. Simulations account for this change based on competition between oxidation and flourine etching of the silicon surface. Reactive gases follow collisionless trajectories at the simulation scale and have a high probability of diffuse re-emission following contact with the surface. This simulation method extends current profile simulation capabilities for a well-known etching chemistry.

Effect of ion angular distributions on microloading in oxygen reactive-ion etching of submicrometer polymer trenches

The etch rate of the resist by energetic reactive ions (O+, O+2) from a 13.56 MHz plasma was studied as a function of the aspect ratio. Using a trilevel sequence, submicrometer grooves with widths of 500, 200, 100, and 50 nm are etched with an oxygen rf plasma in a parallel-plate reactor. Pattern transfer into the polymer photoresist proceeds via a thin silicon nitride mask. With increasing aspect ratio a decrease in etch rate is observed for increasing etch time resulting in a diminished etch depth for small width grooves. This effect is commonly called microloading and its origin is subject to many discussions. With the assumption that lower local etch rates are caused by the characteristics of particle fluxes entering the structures it is necessary to consider the ion energy distributions and the ion angular distributions of O+ and O+2 emerging from the oxygen rf plasma bombarding the surface to be structured. The measurement of ion angular impact energy distributions of O+ and O+2 is performed in an apparatus simulating a parallel-plate rf reactor. Through a small orifice in the rf-powered electrode ions are sampled and are analyzed in a quadrupole mass spectrometer equipped with an energy filter. Tilting the detection system with the vertex lying in the orifice, mass selected ion energy distributions are measured at each angle. O+2 energy distributions consist of the well-known peaked structures caused by charge-exchange collisions in the plasma sheath. The angular distributions are characterized by mace-shaped structures with an angular width of about 2° accompanied by wings with intensity maxima at about ±2° for most of the experimental conditions considered. O+ energy distributions consist of bimodal split high-energy peaks and continuous intensities between 50 eV and the maximal energy defined by the potential drop across the sheath. The angular distributions of the high-energy O+ ions have widths between 2° and 6° while the continuous part of the ion energy distributions exhibits angular widths between 7° and 11°. The phenomena observed in the ion energy distributions and ion angular distributions are a result of scattering mechanisms of ions with O2 parent gas molecules in the plasma sheath. The experimental ion angular distributions are used to model the effect of lower local etch rates. Assuming that direct impingement of particles onto the bottom surface of a structure is the dominant ablation mechanism it is possible to correlate the effect of lower local etch rates with the angularly broadened flux of O+ ions.

Selective Wet Etching of GaInP , GaAs , and InP in Solutions of HCl , CH 3 COOH , and H 2 O 2

The wet chemical etching of , , and in solutions of has been evaluated. In the absence of the oxidant, , the solutions etch and with high selectively over but rough surfaces are formed. When is added, smoother surfaces are obtained and depending on the concentration, the etchant can be made highly selective for . The etch rate of these mixtures varies strongly with the age of the solution, initially increasing and then gradually declining. The increase in etch rate is attributed to the formation of in solution from the reaction of with , and the eventual decrease in etch rate to the gradual evaporation of from solution. The in these mixtures functions as a nonaqueous solvent. In dilute solutions slow etch rates and smooth surfaces can be obtained for all three materials, suggesting that this etchant may be useful for recessing layers for heterostructure electronic and optoelectronic device applications.

An electrochemical and X-ray photoelectron spectroscopic study into the mechanism of Ti + W alloy etching in H 2O 2 solutions

One of the most striking aspects of etching Ti + W alloys in aqueous H 2O 2 solutions is the decrease in etch rate under improved mass transport conditions. This aspect was studied by X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. XPS results showed that Ti dissolves preferentially and that a W oxide film (WO x) is formed at the surface during etching. The valence of W in this oxide is between IV and VI. The WO x film is thicker for a rotating Ti + W sample than for a stationary one. The electrochemical experiments showed that H 2O 2 is reduced at the WO x covered surface. Intermediates of this reduction reaction (most probably OH . radicals) interact with WO x and enhance further oxidation into the soluble WO 5 2− ion. Removal of these intermediates by improved mass transport conditions and/or better supply of the stabilizing agent in H 2O 2 solutions results in lower etch rates.

Rapid thermal annealing effects on the properties of plasma-enhanced chemical vapor deposited tungsten films

Tungsten films have been deposited onto single-crystal silicon (Si) and silicon dioxide (SiO2) by plasma-enhanced chemical vapor deposition with WF6-SiH4-H2 chemistry: the annealing effect on these films has been investigated by rapid thermal annealing. The deposition rate of the tungsten films on both sides of Si and SiO2 is linearly dependent on the SiH4/WF6 ratio up to 1 and the deposition rate is not increased beyond this ratio (SiH4/WF6=1). Phase transition from α-W to β-W and silicidation are observed under the annealing at 900 °C for 15 s in W films on Si. On the other hand, resistivities of W films on SiO2 are decreased under the same annealing condition. The resistivity reduction in W films on SiO2 is believed to be the results of the grain growth and point, line defect removal, and out-diffusion of impurity atoms such as oxygen, fluorine, and silicon. In addition to this grain growth, the intensities of x-ray diffraction peaks are increased after the rapid thermal annealing. Etching process of the tungsten layer has been performed with a reactive ion etcher using CF4-O2 etchant. The etch rate of the as-deposited tungsten film is about 7800 Å/min, and decreases with increase of annealing temperature to about 4600 Å/min for the tungsten films annealed at 1000 °C for 15 s. This decrease in etch rate is believed to be caused by the decreases of the absorption site for etching sources due to grain growth and defect removal.

Analysis of Nonuniformities in the Plasma Etching of Silicon with CF 4 / O 2

Experimental and modeling work has been performed to examine the effects of reactor pressure, etchant gas flow rate, and wafer location on the uniformity of plasma etching silicon using in a parallel‐plate‐radial flow reactor. Intrawafer etch rates were measured at 12 points across a 3 in. wafer at pressures between 125 and 200 mtorr, 70°C, and gas residence times between 1.28 and 2.14s. Depending on the operating conditions, an edge‐to‐center decrease in etch rate of 5–25% was observed. A combined reactor/reaction model is able to predict this degree of nonuniformity. Uniformity was improved by increasing the reactor pressure and decreasing the flow rate of the etchant gas. Etch uniformity was also found to be a function of wafer location within the reactor. Data are presented which show the influences of process parameters on both etch rate magnitude and uniformity.

Formation of etch-stop structures utilizing ion-beam synthesized buried oxide and nitride layers in silicon

With advanced micromechanical devices the ability to form, with highly reproducible results, useful etch-stop layers is becoming increasingly important. A novel etch-stop method of fabricating thin silicon structures is proposed. The approach is based on the use of buried compound layers produced by the implantation of reactive O + and N + ions into single-crystal silicon. The etch-stop properties of these layers are assessed and a conceivable mechanism for the decrease of etch rate for ethylenediamine—pyrocatechol—water(EPW) solution is outlined. It is demonstrated that such substrates incorporating implantation-synthesized oxide or nitride layers have relevance to the micromachining of silicon.

X‐ray photoelectron and Auger electron spectroscopy studies of photochemical vapor deposition silicon nitrides

Silicon nitride films, deposited by a low‐temperature photochemical vapor deposition method, were characterized by optical, physical, and chemical methods. The film reflectivity was a function of the wavelength of the incident beam and varied from 0.45 to 0.02 in the 4000–7000 Å region. These values changed upon annealing at high temperatures. Film uniformity, in terms of thickness and refractive index, was good over the substrate (±5% and ±0.5%, respectively). The refractive index was 1.95 in the as‐deposited condition and upon annealing exhibited a significant increase due to densification and a decrease in the nonstoichiometric nitride component along with a concurrent increase in the Si3N4 and excess Si amounts. The dramatic decrease in etch rate in buffered HF, from ∼1200 Å/min in the as‐deposited condition to <80 Å/min after annealing at 800 °C, was also consistent with the above observations. The pinhole density in these films also decreased considerably after annealing (from ∼100/cm2 to <15/cm2). X‐ray photoelectron and Auger electron spectroscopy were used to characterize the composition of these films. The composition profiles exhibited good uniformity through the films, with oxygen and carbon contamination limited to within 100 Å from the surface. The Si 2p photoelectron and the Si KLL Auger electron spectra were broad and upon deconvolution indicated the presence of four different silicon containing species. These were identified as SiO2, stoichiometric nitride (Si3N4), nonstoichiometric nitride (SiNx, 0<x≤1), and excess silicon bonded with hydrogen (SiHy, 0<y<2). SiO2 was detected only on the surface, due to exposure to atmosphere. After high‐temperature annealing, the intensities of the nonstoichiometric nitride component in both the Si 2p and the Si KLL spectra decreased and the intensities of the Si3N4 and excess Si peaks increased suggesting partial decomposition of SiNx to Si3N4 and excess Si.

Pre-Irradiation Studies in Silicate Glass

The pre-irradiation annealing was studied in the temperature range of 100 … 350 °C for silicate glass at different annealing times. The annealing raising the tracks density. The optimum annealing temperature was 250 °C. The annealing time was found to be hardly effected at the first hundred hours. The preannealing was found to be the hardness of the silicate glass so that the bulk etching rate decreases. The activation energy for bulk etching was found to be (0.3135 eV), the annealing did not change its value.