Etched Features Research Articles

Characterization of iodoheptafluoropropane as a dielectric etchant. I. Process performance evaluation

1- and 2-iodoheptafluoropropane were characterized extensively as potential replacement etchants for perfluorocompounds used in an oxide etch application. In the present study, via holes of critical dimension down to 0.35 μm were etched in an inductively coupled high density plasma tool. Oxide etch rate, mask and stop layer selectivities, and feature profile were among the principal metrics used to evaluate the performance of these compounds. A conventional (C3F8-based) etch process was used as a reference. Process behavior as a function of a number of variables—namely source power, bias power, etch gas flow, additive gas CH3F) flow, roof, wall, and chiller temperatures, and pressure was studied. While good etch rates and feature profiles were obtained, mask and stop layer selectivity was found to be limited. As a supplement to the experimental work, a set of ab initio quantum chemical calculations was undertaken to obtain enthalpies of dissociation for each of the bonds in the iodoheptafluoropropane molecules in order to better understand their dissociation pathways in plasma environments. Part I focuses on trends in process behavior as a function of the variables explored and discusses key mechanisms responsible for the observed effects. Parts II and III will focus on deposited film characterization and global warming emissions, respectively.

P‐42: Effects of Deposition Temperature on the Etched Feature of Thin Chromium Film and Their Application to Field Emitter Arrays (FEAs)

AbstractThe etched features of the thin Chromium (Cr) films deposited on SiO2‐Si substrate were investigated as a function of substrate temperature during rf‐sputtering deposition. In this work, the changes of both the grain structures and crystallographic orientations of sputtered Cr‐films as a function of substrate temperature were examined by Scanning Electron Microscopy (SEM) and X‐Ray Diffraction (XRD) measurement. In these measurements, we found that the tapering angle (θt) of thin Cr‐film after reactive ion etching depends on the deposition condition, especially, substrate temperature during rf‐sputtering process. Based on the obtained results, we fabricated the two kinds of Cr‐gated Mo‐tip field emitter arrays (FEAs): one is a FEAs with tapered gate electrode (tapering gated FEAs, θt ≤ 90°) and the other is a FEAs with tapering‐free gate electrode (non‐tapering gated FEAs, θt = 90°), compared the electron emission characteristics for this two kinds of FEAs.

Mechanisms of Pb(zr0.53Ti0.47)O3 thin film etching with ECR/RF reactor

Ferroelectric capacitive devices for memory and MEMS applications require patterned ferroelectric thin films with high anisotropic etched features. In this paper, physical and chemical parameters during etching of Pb(Zr0.53Ti0.47)O3 (PZT) by a dual frequency ECR/RF reactor have been investigated. The removal characteristics of blanket films and films with a patterned mask were investigated as a function of gas chemistry (Ar, halogen gases), substrate bias RF power and working pressure (from 5 × 10−4 Pa to 1Pa). The etch processes were characterized in terms of etch rate, selectivity and mask stability. High etching rate processes (up to 70 nm/min with removable photoresist mask) were obtained and micron scale patterns were demonstrated. The impact of the etch process on the PZT surface layer modification was characterized by AFM, SEM, TEM and XPS. A strong influence of process chemistry and RF bias power on etching selectivity and surface topography (roughness, involatile residues) was observed. No surface damage layer was detected by Transmission Electron Microscopy. However, XPS revealed fluorine (up to 34%) and chlorine radicals (below 10%) in a 10nm thick surface layer.

Electron cyclotron resonance plasma etching of GaSb-based alloys

Electron cyclotron resonance plasma etching is used to fabricate submicrometer-scale GaInAsSb/AlGaAsSb multiple-quantum-well structures. Smooth and anisotropic features at low substrate bias were obtained under appropriate conditions. The etch quality was investigated with photoluminescence spectroscopy; luminescence data from the etched features agree well with a model that assumes a low-damage etching process.

Evaluation of Pentafluoroethane and 1,1-Difluoroethane for a Dielectric Etch Application in an Inductively Coupled Plasma Etch Tool

In this work, a combination of two hydrofluorocarbon compounds, pentafluoroethane (FC-125, C2HF5) and 1,1-difluoroethane (FC-152a, CF2H–CH3), was evaluated as a potential replacement for perfluorocompounds in dielectric etch applications. A high aspect ratio oxide via etch was used as the test vehicle for this study, which was conducted in a commercial inductively coupled high density plasma etch tool. Both process and emissions data were collected and compared to those provided by a process utilizing a standard perfluorinated etch chemistry (C2F6). Global warming (CF4, C2F6, CHF3) and hygroscopic gas (HF, SiF4) emissions were characterized using Fourier transform infrared (FTIR) spectroscopy. FC-125/FC-152a was found to produce significant reductions in global warming emissions, on the order of 68 to 76% relative to the reference process. Although etch stopping, caused by a high degree of polymer deposition inside the etched features, was observed, process data otherwise appeared promising for an initial study, with good resist selectivity and etch rates being achieved.

Analysis of peculiar structural defects created in GaAs by diffusion of copper

High spatial resolution and high-sensitivity techniques, such as DSL etching, AFM and TEM, have been used to analyse peculiar structural defects created in GaAs by Cu diffusion. They consist of (1) entangled grown-in dislocations surrounded by dislocation loops, (2) clusters of dislocation loops and (3) {0 0 1} complex planar defects revealed as square-like etch features on the (0 0 1) etch surface or as 〈1 0 0〉 linear etch features when these planar defects lie in the (1 0 0) or (0 1 0) planes perpendicular to the sample surface. The 〈1 0 0〉 linear defects are due to straight dislocation segments decorated by precipitates whereas the (0 0 1) defects are ascribed to loops from the clusters of type (2) that have selectively grown to a size much larger than the other ones. All these defects are surrounded by regions of enhanced etch rate. Their formation is ascribed to the interaction between point defects created during Cu diffusion that presumably occurs by the kick-out mechanism, whereby Cu Ga and Ga interstitials are formed.

Recent advances in defect-selective etching of GaN

In this communication two defect-selective etching methods for GaN are evaluated and critically compared: (i) orthodox etching in molten bases (KOH–NaOH eutectic denoted E) and in hot H 2SO 4/H 3PO 4 acids (denoted HH etching) and (ii) photoelectrochemical (PEC) etching in aqueous KOH solutions. The parameters of etching are given for different type of materials, i.e. bulk crystals and epitaxial layers, for both Ga- and N-polar {0 0 0 1} surfaces. It is shown that molten bases are effective in revealing nano-pipes, inversion domains (IDs) and some dislocations, but the optimal etching parameters depend on the type of material, type and density of defects and polarity. Both orthodox etchants that result in the formation of pits on dislocations are also suitable for revealing micro-defects in heavily Mg-doped GaN single crystals but instead of pits, protruding etch features are formed. The reliability and limitations of these etching methods in revealing defects are demonstrated by means of transmission electron microscopy (TEM) calibration and by the selective formation of etch pits on dislocations introduced by indentation. Comparison with PEC etching, newly developed for GaN, is briefly discussed.

Heavy mineral weathering under acidic soil conditions

The weathering of heavy minerals in acid soil profiles (pH 4–5) has been studied in terms of their relative mineral proportions and by using the surface etching features of apatite and hornblende grains. An increasing stability order of: apatite, titanite, hornblende, garnet, epidote, zircon is found in the 45–63 μm coarse-silt fraction of soils developed on tills in southwestern Sweden. In glaciofluvial deposits, sorting processes during deposition have largely determined the variations in heavy mineral content of soils, and only the dissolution of apatite is significant. Hornblende etching is more extensive in soils with low hornblende content, indicating that the release of cations relative to the amount of hornblende is greater in such soils.

X-ray photoelectron spectroscopy analyses of oxide-masked organic polymers etched in high density plasmas using SO2/O2 gas mixtures

Top surface imaging processes are considered as attractive schemes for future lithographic processes. A major issue associated with these schemes is the dry development step which implies the obtention of anisotropic resist profiles. This anisotropy is achieve by adding SO2 to O2 gas mixtures. In this work, oxide-masked organic resist features are etched in high density plasma sources using SO2/O2 gas mixtures. The chemical constituents present on the tops, sidewalls, and bottoms of the etched features are determined by quasi in situ x-ray photoelectron spectroscopy (XPS). XPS analyses show that when using SO2/O2 gas mixtures, a thin passivation layer is formed on the sidewalls of the polymer features. This layer is mainly formed by sulfur atoms present on the polymer surface in elemental state or bonded to carbon atoms. This film is thick enough to minimize the spontaneous etching reaction of oxygen atoms with the organic resist. Samples are also analyzed after air exposure in order to determine the air-induced modification of the reactive layers formed during the dry development step. XPS analyses show that the sulfur-based passivation layer formed during the etch process interact with water moisture to form sulfur-based acids.

Ramp test behavior of high O/U fuel

The effect of increased fuel oxygen potential on fuel behavior has been studied by fabricating and irradiating urania fuel with an average O/U ratio of 2.05. The fuel was fabricated by re-sintering standard urania pellets in a controlled oxygen potential environment and irradiated in a segmented rod bundle in a US BWR. Pre-irradiation ceramographic characterization of the pellets revealed the well-known Widmanstätten precipitation of U 4O 9 platelets in the UO 2 matrix. The high O/U fuel pellets were clad in Zircaloy-2 and irradiated to over 20 MWd/kgU. Ramp tests were performed in a test reactor and detailed post-irradiation examinations of both ramped and non-ramped rods have been performed. The cladding inner surface condition, fission gas release and swelling behavior of high O/U fuel have been characterized and compared with standard UO 2 pellets. Although fuel microstructural features in ramp-tested high O/U fuel showed evidence of higher fuel temperatures and/or enhanced transport processes, fission gas release to the fuel rod free space was less than for similarly tested standard UO 2 fuel. However, fuel swelling and cladding strains were significantly greater. In spite of high cladding strains, PCI crack propagation was inhibited in the high O/U fuel rods. Evidence is presented that the crystallographically oriented etch features often noted in peripheral regions of high burnup fuels are not an indication of higher oxides of uranium.

Reactive ion beam etching of GaAs and related compounds in an inductively coupled plasma of Cl2–Ar mixture

Reactive ion beam etching (RIBE) of GaAs, GaP, AlGaAs, and GaSb was performed in a Cl2–Ar mixture using an inductively coupled plasma source. The etch rates and yields were strongly affected by ion energy and substrate temperature. The RIBE was dominated by ion-assisted etching at <600 eV and by physical sputtering beyond 600 eV. The temperature dependence of the etch rates revealed three different regimes, depending on the substrate temperature: (1) sputtering-etch limited, (2) products-desorption limited, and (3) mass-transfer limited regions. GaSb showed the overall highest etch rates, while GaAs and AlGaAs were etched at the same rates. The etched features showed extremely smooth morphologies with anisotropic sidewalls.

Biochemical evolution II: origin of life in tubular microstructures on weathered feldspar surfaces.

Mineral surfaces were important during the emergence of life on Earth because the assembly of the necessary complex biomolecules by random collisions in dilute aqueous solutions is implausible. Most silicate mineral surfaces are hydrophilic and organophobic and unsuitable for catalytic reactions, but some silica-rich surfaces of partly dealuminated feldspars and zeolites are organophilic and potentially catalytic. Weathered alkali feldspar crystals from granitic rocks at Shap, north west England, contain abundant tubular etch pits, typically 0.4-0.6 microm wide, forming an orthogonal honeycomb network in a surface zone 50 microm thick, with 2-3 x 10(6) intersections per mm2 of crystal surface. Surviving metamorphic rocks demonstrate that granites and acidic surface water were present on the Earth's surface by approximately 3.8 Ga. By analogy with Shap granite, honeycombed feldspar has considerable potential as a natural catalytic surface for the start of biochemical evolution. Biomolecules should have become available by catalysis of amino acids, etc. The honeycomb would have provided access to various mineral inclusions in the feldspar, particularly apatite and oxides, which contain phosphorus and transition metals necessary for energetic life. The organized environment would have protected complex molecules from dispersion into dilute solutions, from hydrolysis, and from UV radiation. Sub-micrometer tubes in the honeycomb might have acted as rudimentary cell walls for proto-organisms, which ultimately evolved a lipid lid giving further shelter from the hostile outside environment. A lid would finally have become a complete cell wall permitting detachment and flotation in primordial "soup." Etch features on weathered alkali feldspar from Shap match the shape of overlying soil bacteria.

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.

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.

Gallium nitride whiskers formed by selective photoenhanced wet etching of dislocations

Gallium nitride is used to fabricate high brightness blue and green light-emitting diodes in spite of high densities of extended structural defects. We describe a photoelectrochemical etching process that reveals the dislocation microstructure of n-type GaN films by selectively removing material between dislocations. The GaN whiskers formed by the etching have diameters between 10 and 50 nm and lengths of up to 1 μm. A correlation between the etched features and threading dislocations in the unetched film is confirmed through transmission electron microscopy studies. The whisker formation is believed to be indicative of electrical activity at dislocations in GaN.

Carbon nanotube tipped atomic force microscopy for measurement of <100 nm etch morphology on semiconductors

The use of carbon nanotubes as tips in atomic force microscopy for a systematic study of dry etching pattern transfer in GaAs is described. The GaAs samples are patterned via electron beam lithography and then etched using magnetron reactive ion or chemically assisted ion beam processing. The technique allows diagnosis, in air, of etched features with scale sizes of <100 nm.

Inductively coupled plasma etching of bulk 6H-SiC and thin-film SiCN in NF3 chemistries

A parametric study of the etching characteristics of 6H p+ and n+ SiC and thin-film SiC0.5N0.5 in inductively coupled plasma (ICP) NF3/O2 and NF3/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF3 percentage and rf chuck power. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tin-oxide masks display relatively good etch selectivity over SiC (maximum of ∼70:1), while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF3:O2 conditions.

Germanium etching in high density plasmas for 0.18 μm complementary metal–oxide–semiconductor gate patterning applications

Oxide masked polysilicon/polygermanium 0.18 μm gates were etched in high density plasma sources. Using gas mixtures of Cl2 and HBr with O2 which are commonly used for polysilicon, we observed strong deformation of the poly-Si/poly-Ge gate profiles, whereas perfectly anisotropic etching profiles were obtained for poly-Si gates. A multistep etching recipe was developed allowing anisotropic etching profiles to be obtained while maintaining a good selectivity to the gate oxide when using a Cl2/N2 gas mixture. The chemical constituents present on the tops, sidewalls, and bottoms of the etched features were determined by x-ray photoelectron spectroscopy (XPS). XPS analyses have shown that when using a Cl2/N2 gas mixture, a thin GeNx passivation layer is formed on the sidewalls of the poly-Ge features.

Co on stepped Cu(100) surfaces: A comparison of experimental data with Monte Carlo growth simulations

Monte Carlo simulations of the growth of Co/Cu(100) in the presence of steps, terraces, and kinks were performed. The beginning stages of Co growth enhance the roughening of step edges. Interdiffusion increases with increasing temperature and decreasing growth rate. Varying the step orientation from 〈100〉 to 〈110〉 produced a steady decrease in interdiffusion. The lateral width of the interdiffused region in steps (10%–90% concentration) is ∼0.7–1.5 nm. Decreasing the Co–Cu binding energy produced an increase in the frequency of double-height islands and step edge decoration. A value of ∼0.21 eV/nearest neighbor bond produced step edge decoration indicative of a Schwoebel barrier with very few double-height islands. Simulation results were compared to growth results obtained via nanometer resolution ultrahigh vacuum scanning electron microscopy. Island statistics compare favorably with growth results. Experimentally observed large etching features at steps were not well reproduced by the model, suggesting an exchange mechanism may be important.

Low Bias Dry Etching of Sic and Sicn in ICP NF3 Discharges

ABSTRACTA parametric study of the etching characteristics of 6H p+ and n+ SiC and thin film SiC0.8N0.2 in Inductively Coupled Plasma NF3/O2 and NF3/Ar discharges has been performed. The etch rates in both chemistries increase monotonically with NF3 percentage and rf chuck power reaching 3500Å·min−1 for SiC and 7500 Å·min−1 for SiCN. The etch rates go through a maximum with increasing ICP source power, which is explained by a trade-off between the increasing ion flux and the decreasing ion energy. The anisotropy of the etched features is also a function of ion flux, ion energy and atomic fluorine neutral concentration. Indium-tinoxide( ITO) masks display relatively good etch selectivity over SiC(maximum of 70:1) while photoresist etches more rapidly than SiC. The surface roughness of SiC is essentially independent of plasma composition for NF3/O2 discharges, while extensive surface degradation occurs for SiCN under high NF3:O2 conditions. The high ion flux available in the ICP tool allows etching even at very low dc self-biases, ≤ −10V, leading to very low damage pattern transfer.