Reactive Sputter Etching Research Articles

Poly (phenyl methacrylate-co-methacrylic acid) as a dry-etching durable positive electron resist

Copolymers of phenyl methacrylate and methacrylic acid (φ-MAC) have been investigated as dry-etching durable positive electron resists. φ-MAC's are preheated above 170°C to crosslink the polymers by intermolecular acid anhydride bonds. The crosslinked φ-MAC's become insoluble and do not swell even in development with strong solvents. They also have excellent thermal stability. These properties contribute to their high sensitivity of 5 µC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , γ(contrast) = 2.0, and resolution finer than 0.2-µm line patterns (65 µC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). φ-MAC's have excellent dry-etching durabilities (e.g., 2 times stronger than PMMA in reactive sputter etching) and good adhesion to the substrate due to the protective effect of benzene rings and the adherent effect of carboxylic acid groups, respectively. The good properties of φ-MAC's make them prospective in the submicrometer electron lithography.

Poly (Phenyl Methacrylate-Co-Methacrylic Acid) as a Dry-Etching Durable Positive Electron Resist

Copolymers of phenyl methacrylate and methacrylic acid (phi-MAC) have been investigated as dry-etching durable positive electron resists. phi-MAC's are preheated above 170/spl deg/C to crosslink the polymers by intermolecular acid anhydride bonds. The crosslinked phi-MAC's become insoluble and do not swell even in development with strong solvents. They also have excellent thermal stability. These properties contribute to their high sensitivity of 5 µC/cm/sup 2/, gamma(contrast) = 2.0, and resolution finer than 0.2-/spl mu/m line patterns (65 /spl mu/C/cm/sup 2/). phi-MAC's have excellent dry-etching durabilities (e.g., 2 times stronger than PMMA in reactive sputter etching) and good adhesion to the substrate due to the protective effect of benzene rings and the adherent effect of carboxylic acid groups, respectively. The good properties of phi-MAC's make them prospective in the submicrometer electron lithography.

Identification and Elimination of Gate Oxide Defect Origin Produced during Selective Field Oxidation

Gate oxide defects induced by selective oxidation processes have been investigated by a copper decoration technique. Gate oxide defects are randomly distributed throughout active device regions and are not locally situated at the edges of isolation oxides. The density of gate oxide film defects has been found to agree with that of masking film defects produced by selective oxidation. Furthermore, by making use of a contrived novel processing, it has been confirmed that each location of gate oxide defects coincides with that of masking film defects induced by selective oxidation. The gate oxide defects are attributed to gate oxide thinning, which results from some Si nitride points formed on the Si substrate through masking defects induced during selective oxidation. Not only an additional sacrifice oxidation, followed by etchback of the resultant oxide, but also a plasma reactive sputter etching procedure prior to gate oxidation have been found to have a remarkable effect on gate oxide defect elimination.

Multimode Deposited Silica Waveguide and its Application to an Optical Branching Circuit

A fabrication procedure has been developed for multimode deposited silica waveguide (DS guide), consisting of uniform and thick glass layer formation for core and cladding, and amorphous Si mask film for reactive sputter etching. The embedded multimode DS guide with a square core cross section has a transmission loss of 1.3 dB/cm at 633 nm wavelength. Waveguide parameters, such as core dimension, refractive index, and index difference, are similar to those of a multi-mode silica fiber. A multimode optical branching circuit with eight output ports was demonstrated by the above fabrication procedure. Excess insertion loss was 2 dB.

Multimode deposited silica waveguide and its application to an optical branching circuit

A fabrication procedure has been developed for multimode deposited silica waveguide (DS guide), consisting of uniform and thick glass layer formation for core and cladding, and amorphous Si mask film for reactive sputter etching. The embedded multimode DS guide with a square core cross section has a transmission loss of 1.3 dB/cm at 633 nm wavelength. Waveguide parameters, such as core dimension, refractive index, and index difference, are similar to those of a multi-mode silica fiber. A multimode optical branching circuit with eight output ports was demonstrated by the above fabrication procedure. Excess insertion loss was 2 dB.

Summary Abstract: NMOS silicide/polysilicon gates by lift‐off/reactive sputter etching

Summary Abstract: NMOS silicide/polysilicon gates by lift‐off/reactive sputter etching

Dry Cleaning of Si Surface Contamination by Reactive Sputter Etching

A dry cleaning method is needed at present in Si wafer processing. We investigated the removal of Na contamination from an Si surface by a reactive sputter etching method. The surface contamination was analyzed by SIMS, AES and ESCA, and the results showed that this dry cleaning technique can decrease Na contamination under low gas pressure and high RF power if a CF4+O2 gas mixture is used. However, a saturated Na contamination value exists because of reattachment of Na atoms sputtered from the surface of the sample, the cathode and the chamber walls. Fluorine plays an important role in removing the Na. Na atoms combine with F atoms, and are then sputtered from the surface in this cleaning method. F and C atoms are removed from the surface as COx and COFx as the relative flow rate (O2/CF4) increases.

RIE of SiO 2 in doped and undoped fluorocarbon plasmas

SiO 2 and Si 3N 4 on top of polycrystalline silicon, titanium silicide and gallium arsenide have been selectively etched by reactive sputter etching in glow discharges of CF 4 and CHF 3. It is observed that for SiO 2 an infinite degree of selectivity can be obtained by admixing minor amounts of methane (<5%) to CHF 3. By a proper adjustment of the operating conditions, i.e. power, gas-flow, total pressure and the CH 4 to fluorocarbon ratio, we are able to control the rate of carbon deposition in such a way that etching takes place in exposed areas, releasing oxygen or nitrogen under the influence of energetic particle bombardment. The ion-assisted chemical reaction between oxygen or nitrogen and the polymerizing species, forming volatile products, together with the physical sputtering, makes these areas accessible to fluorine-containing species responsible for the chemical etching of SiO 2. The importance of carbon deposition and oxygen release under energetic particle bombardment is demonstrated by resting the samples on different cathode materials and by sputter etching in an argon/methane atmosphere. These experiments confirm that prevention of carbon build-up by released oxygen is the main mechanism responsible for the high etch rate ratio between SiO 2 and Si in reactive ion etching.

U-Groove Isolation Technology for High Density Bipolar LSI's

A new isolation technology for high packing density bipolar LSI's has been developed. This technology is composed of two main processes, U-groove formation and U-groove filling. The U-grooves are formed by anisotropic etching and reactive sputter etching of silicon. The grooves, covered with a composite Si3N4/SiO2 layer, are filled with polysilicon. Surface planarity is achieved by selective etching of the polysilicon. An ECL integrated circuit fabricated using the U-groove isolation (U-Iso) technology exibits a minimum isolation distance of 3 µm, an isolation voltage of 50 V, an isolation capacitance of 0.2 pF, and a propagation delay time, measured by ringoscillator, of 0.3 ns/gate.

Electron-beam lithography for small MOSFET's

Electron-beam lithography with a novel multilevel resist structure together with two-dimensional process and device modeling and dry processing with reactive sputter etching have been employed to produce silicon-gate NMOS devices with micrometer and submicrometer channel lengths. Results for transistors and ring oscillators are reported.

Reactive sputter etching of Si, SiO2, Cr, Al, and other materials with gas mixtures based on CF4 and Cl2

All etching processes require control of the relative etch rates of the mask and substrate materials. This is especially important in vacuum-etching processes where directional etching is often obtained at the expense of increased mask etch rate. Etch rate control requires good control of the etching parameters, and here at a constant gas flow of 2×10−2 Pa m3/s we use target voltage (peak-to-peak) and partial pressure of reactant species as controlled variables rather than power density and total pressure, as is common practice. SiO2 and Si etch rates in CF4 with a Si target were found to vary as P1/2V2 where V is the peak-to-peak target voltage (varied between 0.6 kV and 2.9 kV) and P is the reactant gas pressure varied between 0.35 Pa (2.7 μm) and 14.3 Pa (110 μm). Cr and Al rates varied as V3, but were almost independent of pressure. These differences enable accurate selection of relative etch rates and appropriate masks. For instance, SiO2/Cr etch rate ratios as high as 50:1 may be achieved for 3.7 Pa of CF4 at 0.8 kV peak-to-peak target voltage. Chlorine mixed with CF4 enables the properties of the two gases to be combined. Thus, by adjusting only the gas mixture from pure CF4 to pure Cl2, the Si/SiO2 etch rate ratio can be continuously varied between 0.33 and 6, respectively, at 1.3 kV peak-to-peak target voltage, 3.7 Pa pressure, and with substrates on a Si target.

Reactive sputter etching of silicon with very low mask-material etch rates

Directional etching of deep structures in silicon is often made difficult by a high mask erosion rate. Recent results have given a Si/SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> etch rate ratio of up to 8 without the undercut problems associated with other selective etches. In this paper a new selectivity mechanism is described which can reproducibly give Si/SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> etch rate ratios of more than 100 with a nonloading target, and more than about 50 with a loading target. Similar etch ratios are also obtained with masks of MgF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , Al, and Cr. The inherently high Si/SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> etch rate ratio obtained in Ar/Cl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> discharges is here enhanced by causing selective deposition of SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> onto slowly etched materials. The silicon may be obtained from the target, or, for easier control, from input gases such as SiCl <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> . The deposition rate is controlled by the oxygen concentration. The results of etching deep grooves in Si are presented. Etch-mask faceting and Si surface decoration appear to limit the attainable etch rate ratios with fine structures; however, 18-µm-deep gratings of 4.5-µm period have been etched in Si.

Dry etching durability of positive electron resists

AbstractThe effects of positive electron resist structures and G values for scission on dry etching durability have been studied with regard to plasma etching, reactive sputter etching, and plasma ashing. Polymers of aromatic methacrylates, especially poly(α‐methylstyrene), all of which contain a benzene ring in the side chain, exhibit superior durability for each etching system. On the other hand, polymers of fluorinated and chlorinated methacrylates show low durability compared with the nonsubstituted polymethacrylates. In addition, they vary in durability with respect to the etching gas used. The sputtering effect which is induced by ion bombardment in flat bed‐type reactors produces a significant loss in thickness of positive resists. Rough correlations between dry etching rates and Gs(scission) as the indication of sensitivity were obtained. The large dispersion of the correlations implies the possibility of more useful positive electron resists of high durability and high sensitivity.

Thick zone plate fabrication using reactive sputter etching

Reactive sputter etching has been used to produce patterns for thick micro-Fresnel zone plates. An integral aluminum mask was formed on 50 μm thick Mylar, and the exposed Mylar was etched in oxygen. Gold was then electroplated into the pattern to form a micro-Fresnel zone plate 40 μm thick.

Use of Mass Spectra for End Point Detection in Etching SiO2 Films on Si

A study has been made on a monitoring technique using mass spectra in etching SiO2 films on Si substrates by reactive sputter etching. The 85SiF3+ mass peak proved to be a more effective indicator for the monitoring than the 16O+ mass peak. The end point determined by this monitoring technique was confirmed by XPS surface analysis. The signal decrement ratio at the SiO2-Si interface was denoted as a function of the etch rates of SiO2 and Si, and the sample area. This decrement ratio shows good agreement with the experimental results at various etching powers. This monitoring technique, using the 85SiF3+ mass peak, turns out to be more effective than emission spectrometry in the SiO2-Si system from the viewpoints of signal-to-noise ratio and signal stability.

Optical directional coupler using deposited silica waveguides (DS guides)

A new optical directional coupler using embedded single-mode glass waveguides is presented. The glass waveguides, called deposited silica waveguides (DS guides), were fabricated by depositing doped glass on a silica substrate after forming grooves by reactive sputter etching. Waveguide transmission loss was measured to be 1.3 dB/cm, and fiber-to-waveguide coupling loss was 0.1 dB. Using a tunable monochromatic light source, 96 percent power transfer or 14 dB isolation was measured. The DS guide directional coupler is compatible with single-mode fiber and is expected to be a useful component for future wavelength division multiplexing transmission systems.

Surface Damage on Si Substrates Caused by Reactive Sputter Etching

Surface damage on silicon substrates caused by RSE has been investigated. Defects are classified into four categories in order of destruction, namely, precipitates surrounded by elastic strain field, surface roughness pattern, polycrystalline and amorphous silicon, and no defects, based on the results of TEM and RHEED observation. In particular, precipitates which reach a depth more than 500 Å were found to cause OSF. The surface damage consists of contamination (C, F, O) layer, C and defect mixed layer, and defect layer in order from the top. The degree of these defects and contaminations expand with increasing power density and etching duration. RSE conditions, where no defects are formed, were determined, e.g., within 1 minute at 0.4 W cm-2.

Polyimide liftoff technology for high-density LSI metallization

A new liftoff technology, in which a metallization layer can be deposited at high temperatures, is developed to provide two-level highly packed interconnection metallization. A heat-resistant polymide, PIQ®, is employed as the liftoff layer. The reverse pattern of the metallization is formed by reactive sputter etching of the PIQ layer around a thin Mo mask. After metallization layer deposition, lift-off is carried out by electrolytic etching of the Mo mask, thus removing the layer deposited on PIQ. A higher packing density of interlevel connection is also accomplished by adopting exposed via holes. Utilizing this technology, fine-featured smoothly tapered metallization patterns can be obtained almost irrespective of the underlying topology. The minimum pitches of the first level, second level, and via holes are 5, 7, and 7 µm, respectively. This technology does not appear to be detrimental to bipolar device characteristics. A 4096-bit high-speed bipolar memory LSI with two-level highly packed interconnection metallization was produced experimentally utilizing this liftoff technology.

Optical Spectroscopy in Reactive Sputter Etching and Its Application to Process Control

Optical emission spectra in the reactive sputter etching (RSE) of Si, SiO2 and Si3N4 have been investigated using a spectrometer with a collimating system. Emission lines of Si, F, CN and N2 reflecting the reaction products in the RSE of Si3N4 were observed. From the dependence of these lines on the etching conditions, the active species in RSE was found to be not F radicals, but CFx ions. The applicability of these lines for use as the end point monitor was also investigated. In addition, the plasma gas temperature was determined by rotational analysis of plasma etching and RSE in C2F6 gas mixed with O2 or C2H4 gas.

Deposited silica waveguide for intergrated optical circuits

Embedded single and multimode waveguides on fused quartz substrates have been fabricated by high-speed silica deposition and accurate reactive sputter etching by a C2F6 gas plasma. These waveguides have rectangular cross sections with an aspect ratio close to unity. Total waveguide loss was approximately 5 dB/cm, and absorption loss measured by laser calorimetry at 637-nm wavelength was less than 0.1 dB/cm.