Fast Etch Rate Research Articles

Dry etching and implantation characteristics of Al0.5Ga0.5P

Highly anisotropic pattern transfer into AlGaP was achieved using low pressure (1 mTorr) microwave BCl3/Ar or CH4/H2/Ar discharges. Much faster etch rates were obtained with the chlorine-based discharges and etching was initiated at lower dc biases. The electrical activation of implanted Si+ and Be+ ions was investigated at fixed dose (5×1014 cm−2) as a function of annealing temperature (500–1000 °C). Activation efficiencies of ∼50% were obtained for Be+ implantation after annealing at ≥750 °C. Activation of Si+ was less efficient and required higher annealing temperatures than for Be+. Thermally stable high resistance (≳108 Ω/⧠) regions were formed in initially n+ AlGaP by O+ implantation at doses ≳1014 cm−2 while normal damage-induced compensation was observed for lower O+ doses. No thermally stable isolation was found in O+-implanted p+ AlGaP.

Comparison of plasma chemistries for patterning InP-based laser structures

The available plasma chemistries for dry etching of In-containing III-V semiconductors used in long wavelength laser structures have been examined with respect to suitability for fabrication of thick photonic devices. Electron cyclotron resonance discharges of CH4/H2, Hl/H2, CH3l/H2 and Cl2/CH4/H2 at low pressure (1 mTorr) and low DC bias (-100 V) were characterized for InP etch rates, selectivity for etching the semiconductor over common masking material and changes to the electrical and structural properties of the etched surface. The Cl2/CH4/H2 chemistry provided the fastest etch rates but required sample temperatures of approximately=150 degrees C and dielectric masks. Microdisk lasers were fabricated to demonstrate the suitability of this plasma chemistry to photonic device processing.

Controllable layer-by-layer etching of III–V compound semiconductors with an electron cyclotron resonance source

A highly controllable etching technique, in which the etching proceeds layer by layer, has been studied using a plasma generated by an electron cyclotron resonance (ECR) source. In this etching technique, the sample is exposed to reactive chlorine radicals and low energy Ar ions separately and repeatedly. For GaAs etching, the chlorine radicals were typically generated with 35 W microwave power and the Ar ions were produced using 50 W microwave power and 6 W rf power, with a self-induced dc bias of −38 V. When there was complete coverage of the surface by reactive chlorine radicals, the etch rate was found to be independent of chlorine radical or Ar ion reaction time. Layer-by-layer etching with the etch rate in the range of 0.5 nm/cycle has been achieved on GaAs. No GaAs etching was observed at −120 °C and the etch rate increased significantly with temperature. The etch rate increased initially with microwave power used in the adsorption step, then decreased at microwave power ≳60 W due to passivation effects. Faster etch rates were obtained on samples etched at higher rf power during the etch product desorption step and/or longer distance from the ECR source. Layer-by-layer etching of GaInAs, AlInAs, and InP has been demonstrated for the first time. For GaInAs and AlInAs, etching was observed at room temperature and rf power level similar to that used for etching of GaAs. For InP, etching was obtained only at higher temperature (150 °C) and rf power (8 W) during the etch product desorption step. Etch-induced damage was minimal since electrical characteristics of Schottky diodes fabricated on the etched surface were similar to an unetched sample.

Characteristics of vinyl iodide microwave plasma etching of GaAs/AlGaAs and InP/InGaAs heterostructures

Vinyl iodide (C2H3I) microwave discharges with additions of H2 and Ar are found to provide faster etch rates than conventional CH4/H2/Ar discharges for InP, InGaAs, GaAs, and AlGaAs. This is a result of the relatively high volatilities of indium, gallium, and aluminum iodide species. The etched features are smooth and anisotropic over a wide range of do self-biases (−150 to −350 V), process pressures (1–20mTorr), and microwave powers (150–500 W). The polymer that forms on the mask during the plasma exposure can be readily removed in O2 discharges. Electron spectroscopy for chemical analysis (ESCA) showed that the etched surfaces are slightly deficient in the group V elements under most conditions, but changes to the optical properties of the semiconductors are minimal. No defects are visible by transmission electron microscopy (TEM) in GaAs or InP samples etched at dc biases ≤ −250 V.

Studies on metal/benzocyclobutene (BCB) interface and adhesion

Interfacial characteristics such as chemical reaction, metal diffusion, and morphology were investigated for Cu/BCB, Cr/BCB and Ti/BCB structures. Using Auger and XPS depth profiling, the formation of titanium carbide and chromium oxide was confirmed at the metal/BCB interface. Annealing at 250°C for extended periods resulted in the diffusion of Cu, Cr and Ti into the BCB and subsequent formation of Cu-Si, CrSi2 and Ti-Si compound precipitates. The reaction is a thermal diffusion controlled process which is dependent on time and temperature. Ar sputtering treatment of BCB film before metallization was found to roughen the surface, resulting in metal spikes which penetrate into the roughened BCB film. However, the peel strength of metals on BCB was only about 177 g cm_1presumably due to the brittleness of the BCB film. The etch rates of the BCB film in a reactive ion etcher (RIE) and a plasma etcher were measured using Ar, O2, O2 + CF4, and O2 + SF6 gas mixtures. Faster etch rates were obtained when CF4 and SF6 were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO2 formed by exposure of Si-containing BCB film to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O2 and O2 + CF4 plasmas oxidized the carbo-siloxane linkage (C—Si—O) of the BCB, resulting in the formation of SiO2 on the surface. The O2 + SF6 plasma, however, did not produce the surface SiO2, because of its faster Si and SiO2 etch rates.

Small Diameter Dry Etched Via Holes in GaAs

ABSTRACTTwo techniques for fabricating through-wafer via holes in 2-4 mil thick GaAs substrates were examined. In the first, Ni or thick photoresist masks were used for patterning 30 μm diameter vias by ECR-rf dry etching using low pressure (10-20 mTorr), low bias (– 150V) BCI3/C12 discharges. Microwave enhancement of these discharges produced faster etch rates but a greater degree of isotropic material removal at a given pressure. Reducing the process pressure produces extremely anisotropic features with high aspect ratio. The BC13-to-C12 ratio must be kept to ≥5:1 to maintain the anisotropy. A novel laser drilling technique was also examined - in this case a Q-switched beam with high energy density was used to ablate material in each pass of the beam, producing a via in approximately 40 passes. This is a maskless procedure capable of producing any desired via hole pattern, but currently there is no selectivity for ablating GaAs over a front-side metal film.

Intrinsic mechanism of smooth and rough morphology in etching of InP by Cl2 determined by infrared laser interferometry

The effect of Cl2 pressure and substrate temperature (Ts) on the absolute, steady-state etch rates of InP(100) has been measured with ∼1% accuracy from ∼0.02 to 1000 Å/sec by infrared laser interferometry. An unexpected finding was that the etch rate could exceed the calculated evaporation rate of InCl3 by a factor of 50, indicating a weaker binding energy of InCl3 to InP relative to itself. At sufficiently low Ts, the measured slow etch rate is only a factor of ∼3.5 above that predicted from the evaporation rate of InCl3. The transition between the fast and slow etch rates occurs as a first-order phase transition at a substrate temperature, T*s, which depends on the Cl2 pressure. If InP is etched at T*s, the surface roughens while at other Ts the surface remains smooth. The explanation for the surface roughening is that at T*s, InCl3 nucleates to form InCl3 islands. At T*s the etch rate is approximately fifteen times slower where the InP surface is covered by InCl3 compared to the bare InP surface. The large differential etch rates for bare and InCl3 covered InP produces a rough surface morphology. Below T*s, the surface is completely covered by an InCl3 multilayer and etches uniformly although slowly at the nominal InCl3 vaporization rate. This mechanism of surface roughening is intrinsic to the Cl2+InP reaction.

Etching of photoresist using oxygen plasma generated by a multipolar electron cyclotron resonance source

Etching of photoresist in an O2 plasma generated by an electron cyclotron resonance source (ECR) was investigated. The ECR source was a microwave multipolar reactor at 2.45 GHz, and the stage was connected to a rf power supply at 13.56 MHz. Effects of microwave power, rf power, ECR source to sample distance, and pressure on photoresist etch rate were characterized. It has been found that the photoresist etch rate increases with microwave and rf power, but decreases with source to sample distance. With microwave power at 1000 W and rf power at 300 W, smooth morphology and fast etch rate at 1.61 μm/min were obtained. Self-induced dc bias voltage increases with rf power and source to sample distance, but decreases with microwave power. Etch rate uniformity better than 0.5% was obtained across 7.5 cm diam wafer even with a very close source to sample distance of 3 cm. Etch profile can be varied depending on the etch conditions. Vertical profile in polyimide has been obtained using a trilayer resist scheme.

Iodine-Based dry Etching Chemistries for InP and Related Compounds

ABSTRACTA comparison is given of the dry etching characteristics of InP and related materials in high ion density (>1011 cm−2 ) microwave discharges of HI, CH3I, C2H5I, C3H7I and C2H3I. The InIx species are more volatile than their InClx counterparts near room temperature and rapid etch rates can therefore be achieved without the need for sample heating. HI discharges provide faster etch rates than the halocarbon-based mixtures, but are more corrosive. All of these gas chemistries offer faster rates than conventional CH4/H2 mixtures. Halocarbon-iodide discharges still suffer from polymer deposition on the mask and within the reactor, as with CH4/H2. AES analysis shows an absence of contaminating residues with all of the iodine-based chemistries, and highly anisotropic features are obtained since the etching is driven by ion-enhanced desorption of the reaction products.

Studies of PQ-100(TM) Polyquinoline Film for Multichip Module(MCM) Applications

AbstractOxygen and O2+CF4 RIE showed faster etch rate of PQ-100 film than nonoxygen containing RIE, and caused rough surface morphology. Ti shows good adhesion to the PQ-100 film because of Ti-O and possible Ti-N compound formation at the interface. No diffusion of Ti and Ti-containing precipitates were observed at the Ti/PQ interface even at temperatures of 250 °C. In contrast to the Ti/PQ interface, Cu showed very poor adhesion to the PQ film because of weak chemical bonding. Cu reaction compounds were not observed at the interface at the 250 °C annealing. Ti adhesion to the PQ-100 film was good for control, RIE modified, and water-boiled cases. Initial studies suggest a reduction in peel strength at 250 °C annealing, although this topic must be further addressed to understand the exact mechanism.

Etching of GaAs and InP using a hybrid microwave and radio-frequency system

A hybrid system consisting of a multipolar electron cyclotron resonance source driven by a microwave power supply at 2.45 GHz and a radio-frequency (rf) powered electrode at 13.56 MHz is used for the etching of GaAs and InP. Both CCl2F2 and Cl2 are used as the gas sources, and the effect of rf and microwave power, pressure, as well as flow rate on etch rate and surface morphology are evaluated. Fast etch rate up to 3.4 μm/min is obtained for GaAs. Etch rate increases with rf power and decreases with microwave power when CCl2F2 is used. Optical emission and x-ray photoelectron measurements indicate that more C-related compounds are generated when microwave power is on. With Cl2 addition, etch rate increases with microwave power and smoother morphology is obtained. Etching for InP yields smooth morphology at a typical rate of 50 nm/min.

Etch rate studies of base catalyzed hydrolysis of polyimide film. II

AbstractThe influence of a potassium carbonate (K2CO3) additive on the base catalyzed hydrolysis of polyimide (Kapton†) film in aqueous potassium hydroxide (KOH) was determined experimentally. The etch rate is significantly greater for KOH/K2CO3 solutions compared with solutions composed of KOH only. The experimental order of the reaction with respect to the KOH concentration was found to be 1.5. In addition, the rate was found to increase linearly with respect to the K2CO3 concentration at a fixed KOH concentration. Visual observations of a thinner gel layer on the surface of the film, combined with increased solubility of the etch by‐products in KOH/K2CO3 relative to KOH, help to explain the difference in etch rate. It appears the ability of K2CO3 to enhance the solubility of the hydrolyzed polyimide (polyamic acid salt) results in faster etch rates.

Measurements of etch rate and film stoichiometry variations during plasma etching of lead-lanthanum-zirconium-titanate thin films

Plasma etching of lead-lanthanum-zirconium-titanate (PLZT) ferroelectric thin films using a dc hollow-cathode discharge in CF4 and dilute HCl has been investigated. The etch rate and film stoichiometry variations of sputter-deposited lead-lanthanum-titanate (PLT), and solution-deposited PLT, lead-zirconium-titanate (PZT), and PLZT have been measured over a wide range of etching conditions. Etching does not take place at room temperature, but requires substrate heating above 200 °C. Etch rate and film stoichiometry varied strongly as a function of substrate temperature, gas mixture, and film preparation method. For sputter-deposited films, the fastest etch rates of 6500 Å/h were obtained using a mixture of CF4 and dilute HCl. Etch rates for solution-deposited films were higher than for sputter-deposited films, reaching 2000 Å/min in CF4.

Hybrid electron cyclotron resonance-RF plasma etching of TiNx thin films grown by low pressure rapid thermal metalorganic chemical vapour deposition

The use of F-based (SF6/O2, CF4/O2 and CHF3/O2) electron cyclotron resonance discharges for dry etching of TiNx films deposited onto InP by low pressure (3-10 Torr), rapid thermal metalorganic chemical vapour deposition is described. Etch rates of 50-100 AA min-1 are obtained for low DC biasing (-100 V) of the sample, giving rise to anisotropic features, infinite selectivity of etching TiNx over InP, and minimal damage to the semiconductor. SF6/O2 mixtures offer the fastest etch rates, while CHF3/O2 discharges produce significant polymer deposition under high pressure (20 mTorr) or high microwave power (>200 W) etching conditions.

Studies on the Surface Modification of Benzocyclobutene(BCB) Film By Plasma Ions

ABSTRACTThe etch rates of BCB film in a reactive ion etcher(RIE) were measured using Ar, O2, O2+CF4, and O2+SF6 gas mixtures. Faster etch rates were obtained when CF4 and SF6 were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO2 formed by exposure to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O2 and O2+CF4 plasma oxidized the carbo-siloxane linkage (C-Si-O) of the BCB, resulting in the formation of SiO2 on the surface. The O2 +SF6 plasma, however, did not produce the surface SiO2, because of its faster Si and SiO2 etch rates. Ar ion sputtering following the plasma modification, restored the surface chemical composition to a state similar to the initial BCB surface.

Reactive ion etching of InP with Br2-containing gases to produce smooth, vertical walls: Fabrication of etched-faceted lasers

We describe the reactive ion etching of InP using a mixture of Br2 and either N2 or Ar. We report the first fabrication of straight vertical walls in InP at a very fast etching rate of 2 μm/min. By using a mixture of Br2 and Ar and raising the substrate temperature, smooth walls are obtained. To demonstrate that the etched walls can be used as laser mirrors, we fabricated etched-faceted lasers with threshold currents of 19.0 mA for a laser with one etched and one cleaved facet and 26.6 mA for a laser with two etched facets.

Fabrication of Deep Cavities in Silicon Using Deposited Chrome-Gold Mask

Thin and uniform diaphragm structure is the most important parameter in influencing sensitivity in silicon pressure sensors. A simple technique using gold deposited films for masking and an etching mode with faster etch rates yielding repeatable and uniform multiple cavities in silicon has been developed. The process is compatible with batch fabrication with high yield.

Anisotropic plasma etching of polysilicon using SF6 and CFCl3

Undercutting of polysilicon overetched in fluorine-based plasmas has been limited to 0.1 μ per edge by adding small amounts of CFCl3 to SF6. This 0.1 μ undercut occurs during the initial etching stage and does not increase with overetch. To test possible mechanisms, these experiments were repeated with CHF3 and Cl2 used in place of CFCl3. It was found that Cl and photoresist are responsible for passivating the sidewalls of the polysilcon lines. This passivation is relatively insensitive to exact amount of CFCl3 added. Etch rate measurements were made for polysilicon, SiO2, and AZ 1470 photoresist and found to be essentially indistinguishable from those obtained in pure SF6 etching, thus the fast polysilicon etch rate and good selectivity characteristics of SF6 etching are preserved. The ability to etch polysilicon without sacrificing linewidth, selectivity, or etch rate makes CFCl3/SF6 plasma etching very useful for VLSI processing.

Characteristics of submicron pores obtained by chemical etching of nuclear tracks in polycarbonate films

Calibrated pores in the range 102–2×103 Å have been obtained by chemical etching of polycarbonate thin films irradiated with high energy krypton ions (500 MeV, Kr25+). Both the amorphous and the crystalline forms of polycarbonate (Makrofol, Bayer), further designated by their respective trade names N and KG, have been investigated up to thicknesses of 60 μm, close to the theoretical ion range of 77 μm. From conductivity studies, three different domains have been separated around the ion track: A highly damaged core of radius ?50 Å with a fast etching rate vT ≊104 Å/min, an intermediate zone of radius ?500 Å with an etching rate vI = 0.9 Å/min, an outer region with an etching rate equal to that of the undamaged material, vG = 0.47 Å/min. These observations are compatible with the delta ray model for track formation in plastic materials. Scanning electron microscope investigations have revealed that the pores formed in the N material are straight cylinders with a narrow distribution of the pore entrance diameters. On the other hand, the pores for the KG type are much less uniform and appear to be tapered, the difference between the two sides of the membrane being as much as 50%. These characteristics could be related to inhomogeneities in the morphological structure due to (i) the finite size of the crystalline domains and (ii) an asymetric manufacturer’s processing of the film surfaces.

Depth of Saw and Lap Damage in Germanium

AbstractA study utilizing an application of X-ray diffraction analysis has been made to determine the depth of surface damage in s ingle-crystal wafers of germanium. Damage was introduced by mechanical lapping and sawing. A scintillation-counter double-crystal diffractometer system was used with a 3-m evacuated collitnator. This experimental arrangement employed the (220) reflection, from a silicon monochromator, using Cu Kα1 radiation. All wafers were taken from dislocation-free crystals which were subsequently centerless ground, sawed, lapped, and etched. Half-widths were determined for the sawed and lapped conditions. Successive etchings were used to remove the damaged surface layer with the resulting halfwidths being plotted as a function of thickness removed and etching time.The depths of damage—8.0 ± 0.7 μ for sawing and 3.0 ± 0.7 μ for lapping—were indicated by the depth at which the line breadth measurements reached a limiting value. For crystals used in this study, the median value for this limiting half-width was 28″. The experimental data expressing the rate of etching indicates the presence of two separate rates—one for the damaged material and one for the undamaged substrate. An unexpected finding is a faster etch rate for the undamaged material than that observed for the damaged layer. Quite good correlation is obtained between the depth of damage as determined by X-ray and etching techniques.