Papers by Utpal Chakrabarti
Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 1990
The reactive ion etching (RIE) of InP, InAs, InSb, InGaAs, and AlInAs in CHCl2F —or CHClF2 —based... more The reactive ion etching (RIE) of InP, InAs, InSb, InGaAs, and AlInAs in CHCl2F —or CHClF2 —based discharges was investigated as a function of plasma power density, pressure, and gas composition. For 0.56 W cm−2, 4 mTorr discharges the etch rates are in the range 125 Å min−1 (AlInAs) to 390 Å min−1 (InAs). These are comparable to the etch rates obtained with C2H6/H2 RIE under similar conditions. All of these materials exhibit smooth surface morphologies over a wide range of RIE parameters. Carrier compensation is observed to depths of ∼2000 Å in n-type InP for high power density (1.3 W cm2) etching, but lower powers yield surfaces that display reasonable Schottky diode behavior for evaporated Au contacts. Thin (20–30 Å) residue layers containing 3–9 at. % Cl and 1–3 at. % F (24 at. % for AlInAs) are present after the dry etching, although this contamination can be removed by solvent cleaning. The formation of a high concentration of AlF3 on AlInAs provides a natural etch stop for re...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1994
The diode diameter dependence of current density in mesa p–n junctions was used to measure surfac... more The diode diameter dependence of current density in mesa p–n junctions was used to measure surface recombination velocities (S) for both InGaP and AlGaAs. For InGaP, S values of 4–5×104 cm s−1 were obtained for both wet- and dry-etched mesas, and the surface was relatively insensitive to changes resulting from annealing or plasma exposure. Surface passivation by (NH4)2Sx treatment reduced the recombination velocity by a factor of 2. By contrast, AlGaAs displayed a strong sensitivity to the type of processing steps used in photonic and electronic device fabrication, with values of S as high as 9×105 cm s−1 after low temperature annealing, and as low as 3.7×104 cm s−1 after sulphide passivation.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1991
An electron cyclotron resonance plasma etching system with the capability of additionally radio-f... more An electron cyclotron resonance plasma etching system with the capability of additionally radio-frequency biasing the substrate has been used to study the etching characteristics of InP, InAs, InSb, InGaAs, and AlInAs in CH4/H2 -based discharges. The etch rates of these materials increase linearly with rf power and retain smooth surface morphologies for microwave powers below 150 W. At higher microwave powers the surface becomes rough due to preferential removal of the group V species. The quality of Au Schottky diode contacts on InP degrades for high-bias etching, but the addition of PCl3 to the discharge retards this degradation by providing an overpressure of P. The room temperature photoluminescence intensity of InP is also preserved by this PCl3 addition. We obtained highly anisotropic etching of all five semiconductors over the whole pressure range investigated (1–20 mTorr). Low-bias (25–100 V) etching occurs with rates in the range 10–140 Å min−1, dependent on the particular ...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 1992
The characteristics of plasma etching of InP, InAs, InSb, GaAs, AlGaAs, GaSb, AlInAs, InGaAs, and... more The characteristics of plasma etching of InP, InAs, InSb, GaAs, AlGaAs, GaSb, AlInAs, InGaAs, and AlInP in microwave (2.45 GHz) discharges of methyl-, ethyl-, and propyl-iodide have been examined with respect to etch rates, surface morphology, damage introduction, and etch anisotropy. The etch rates for all of these semiconductors are somewhat faster than for conventional CH4-based discharges under the same conditions of direct-current bias, pressure, and microwave power, but are not as fast as with HI discharges. Polymer deposition on the mask and within the chamber occurs as with CH4-based mixtures, but is minimized at low pressure (≤10 mTorr) and with H2 dilution. The etched surface morphologies are smooth over a wide range of plasma parameters and show roughness only under conditions of significant polymer deposition. Chemical analysis by Auger electron spectroscopy and x-ray photoelectron spectroscopy also shows that the near surface of the etched samples retains its stoichiome...
Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 1990
High rate (≤10 μm min−1 ) etching of GaAs, AlxGa1−x As, and GaSb in Cl2/Ar or SiCl4/Ar discharges... more High rate (≤10 μm min−1 ) etching of GaAs, AlxGa1−x As, and GaSb in Cl2/Ar or SiCl4/Ar discharges is reported. The etching was investigated as a function of discharge pressure, power density and composition, and changes in the etching rate of AlxGa1−xAs when SF6 was added to the gas mixtures. Highly anisotropic etching was achieved with SiCl4 for all materials, whereas a greater degree of chemical etching was evident with Cl2. Provided self-biases were ≤50 V, excellent Schottky diode characteristics were exhibited by TiPtAu contacts on SiCl4 or Cl2 etched GaAs surfaces. Energetic-ion bombardment caused carrier compensation up to 2200 Å from the surface in n-type (1017 cm−3 ) GaAs, with this depth being less for lower self-biases. Photoluminescence decreases of 2–25 times were observed after reactive ion etching of GaAs for both types of discharge. Chlorine residues were typically present to a depth of <20 Å after etching, with cleaner surfaces obtained with SiCl4 than with Cl2.
Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena, 1990
We have investigated the etch rates, residual lattice damage, surface morphologies, and chemistri... more We have investigated the etch rates, residual lattice damage, surface morphologies, and chemistries of InP, InGaAs, AlInAs, and GaAs plasma etched in electron cyclotron resonance (ECR) CH4/H2/Ar discharges. The etch rates of InP and InGaAs increase linearly with additional rf biasing of the substrate, and are approximately a factor of 2 faster than for GaAs. Under our conditions the etch rate of Al0.52Ga0.48As is very low (∼25 Å min−1) even for the addition of 100 V rf bias. In all of these materials the residual damage layer remaining after dry etching is very shallow (∼20 Å) as evidenced from Schottky barrier height and photoluminescence measurements combined with wet chemical etching. InP shows significant P depletion with the addition of rf biasing during the ECR etching while GaAs retains a near-stoichiometric surface. Hydrogen passivation of shallow donors in n-type GaAs occurs to a depth of ∼3000 Å during exposure to the CH4/H2/Ar discharge for long periods (60 min). The surf...
MRS Proceedings, 1989
ABSTRACTThe reactive ion etching of InP, InGaAs and InAlAs in CC12F2 /O 2 or C2H6 /H 2 discharges... more ABSTRACTThe reactive ion etching of InP, InGaAs and InAlAs in CC12F2 /O 2 or C2H6 /H 2 discharges was investigated as a function of the plasma parameters pressure, power density, flow rate and relative composition. The etch rates of these materials are a factor of 3-5 times faster in CC12F2 /O 2 (∼600–1000 Å · min−1) compared to C2H6 /H 2(160–320 Å · min−1). Significantly smoother morphologies are obtained with C2H6 /H 2 etching provided the composition of the plasma is no more than 10 - 20% by volume of C2H6. At higher methane compositions, polymer formation increases leading to micromasking and rough surface morphologies. Sub-surface disorder is limited to <100 Å deep for both gas chemistries for plasma power densities of 0.85 W cm−2. The C2H6 /H 2 mixture leaves an In-rich surface in all cases, but this surface is free of any residual contamination, whereas the CC12F2/O2 chemistry leaves chloro-fluorocarbon residues approximately 20–50 Å thick on the surface of all three In-ba...
[Proceedings 1991] Third International Conference Indium Phosphide and Related Materials
ABSTRACT A hybrid electron cyclotron resonance (ECR)/radiofrequency (RF) plasma etching system us... more ABSTRACT A hybrid electron cyclotron resonance (ECR)/radiofrequency (RF) plasma etching system used to study the etching characteristics of InP and InGaAs in CH4H2-based discharges is described. It was found that the materials retain smooth surface morphologies for microwave powers below 150 W. At higher microwave powers the surface becomes rough due to preferential removal of the group V species. The quality of Au Schottky diode contacts on InP degrades for high-bias etching, but the addition of PCl3 to the discharge retards this degradation by providing an overpressure of P. The room-temperature photoluminescence intensity of InP is preserved by the PCl3 addition. The use of CH3Cl in preference to CH4 to increase the etch rate of InGaAs was investigated and this appears to have few advantages since the etch rates are comparable to those with CH4/H2. The degree of polymer deposition during CH4/H2Ar etching on the type of mask used (photoresist, W, or SiO2) is discussed
MRS Proceedings, 1992
ABSTRACTA comparison is given of the dry etching characteristics of InP and related materials in ... more 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.
LEOS 1992 Summer Topical Meeting Digest on Broadband Analog and Digital Optoelectronics, Optical Multiple Access Networks, Integrated Optoelectronics, and Smart Pixels
A novel dry etch mixture based on HI/H2 is shown to be a universal etchant for In-based semicondu... more A novel dry etch mixture based on HI/H2 is shown to be a universal etchant for In-based semiconductors, giving rise to highly anisotropic features with smooth surface morphologies. At low DC self bias (-100 V) and low pressure (1 mTorr), etch rates for all III-V materials of >2000 Å-min-1 are possible for high HI percentages in the discharge, whereas rates >1 μm-min-1 are obtained at higher pressures and DC biases. These etch rates are approximately an order of magnitude faster than for CH4/H2/Ar mixtures under the same conditions. Moreover, there is no polymer deposition on the mask or within the reactor chamber with HI/H2. Auger electron spectroscopy reveals residue-free, stoichiometric surfaces after dry etching in this mixture. Results of etching with electron cyclotron resonance discharges of HBr/Ar, HBr/CH4, and HBr/H2 are also discussed. It is concluded that the HI/H2/Ar chemistry provides a strong alternative to CH4/H2/Ar, particularly for the etching of deep features
SPIE Proceedings, 1996
Prior to the full maturation of electro-absorption modulated laser technology, directly modulated... more Prior to the full maturation of electro-absorption modulated laser technology, directly modulated 1.55 micrometer distributed feedback lasers will continue to play a central role in long haul, high bit rate, optical communications systems. Maintaining a competitive advantage, however, requires that these devices be optimized for long fiber length transmission, high power, and low cost. In this talk we discuss the
Materials Science Forum, 1992
Semiconductor Science and Technology, 1992
ABSTRACT Three different discharge chemistries for dry etching of gratings in InP laser structure... more ABSTRACT Three different discharge chemistries for dry etching of gratings in InP laser structures have been investigated. Each type of plasma (HI/H2, CH4/H2, C2H6/H2) yields controllable etch rates that are constant with etching time. Lower DC self-biases can be used with HI/H2 because of the greater volatility of the group III etch products. The C2H6/H2 mixture produces excessive polymer deposition on the photoresist mask at process pressures &gt;or=10 mTorr. The rectangular shape of the gratings is preserved during overgrowth by organo-metallic vapour phase epitaxy.
Semiconductor Science and Technology, 1991
ABSTRACT The authors report the first demonstration of featureless surface morphology on InP plas... more ABSTRACT The authors report the first demonstration of featureless surface morphology on InP plasma etched in CH4/H2/Ar electron cyclotron resonance (ECR) discharges. At a plasma composition of 5 CH4/17 H2/8 Ar it is necessary to limit the microwave input power to &lt;or=150 W in the reactor order to achieve smooth etching. At microwave powers above this value, the authors observe increasingly rough surfaces. This is ascribed to faster removal of phosphorus than indium because of an imbalance of active hydrogen (removing P as PH3) to methyl radicals (which are the active species in forming the In etch product). The addition of Ar to the discharge enhances the etch rate by a factor &gt;or=3 compared with CH4/H2 alone, indicating that some additional degree of ion bombardment is necessary with this gas chemistry even under ECR conditions. Degradation of the InP photoluminescence as a result of plasma etching at bias voltages less than 150 V can be completely quenched by the addition of PCl3 to the discharge. This provides a phosphorus partial pressure during the etch, maintaining the stoichiometry of the InP surface.
Semiconductor Science and Technology, 1991
ABSTRACT A common feature of mesa structures formed by dry etching of III-V materials is the pres... more ABSTRACT A common feature of mesa structures formed by dry etching of III-V materials is the presence of corrugations or ribbing on the mesa sidewalls. The authors show that this sidewall roughness results from a replication of the roughness present at the edges of the masking material on the semiconductor. Using a photoresist mask free of sidewall roughness they demonstrate that it is possible to achieve a completely smooth mesa in InP with CH4/H2/Ar plasma etching. This is particularly important in minimizing light scattering in certain types of long wavelength lasers. It is also shown that the mask sidewall roughness does not worsen during the plasma exposure, even for long (2 h) etching runs.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1991
Electron cyclotron resonance (ECR) discharges are characterized by low ion energies (515 eV) and ... more Electron cyclotron resonance (ECR) discharges are characterized by low ion energies (515 eV) and high densities of active species. This makes them excellent candidates for high rate, low damage dry etching of III-V semiconductors. We have investigated the use of ECR discharges of CH,/H,/Ar for etching InP, InGaAs, AlInAs and GaAs as a function of additional rf biasing of the sample, and in this article present the InP results. In contrast to the results with conventional reactive ion etching (RIE), ECR discharges lead to very shallow (-20 A) damaged layers on these materials and much less disruption of the electrical quality of the etched surface. For example, RIE of InP leads to nonstoichiometric, In-rich surfaces to which one cannot make a Schottky contact. Removal of at least 150 A of material is required before the integrity of the surface is restored. We have been able to achieve excellent rectifying contacts on ECR-etched InP without the need for wet chemical treatment of the surface. Optical and chemical analysis of the ECR etching shows that it clearly is a Low damage process relative to the more conventional dry etch methods.
Materials Science and Engineering: B, 1994
For some dry etching applications in IlI-V semiconductors, such as via hole formation in InP subs... more For some dry etching applications in IlI-V semiconductors, such as via hole formation in InP substrates, the currently used plasma chemistries have etch rates that are up to a factor of 30 too slow. We report on the development of 3 new classes of discharge chemistries, namely C1 2 /CH 4 /H 2 /Ar at 150 0 C (yielding InP etch rates of >1 gm • min-I at 1 mTorr and-80V dc), HBr/H 2 for selective etching of InGaAs over AlInAs, and iodine-based plasmas (HI/H 2 , CH 3 I/H 2) that offer rapid anisotropic etching of all III-V materials at room temperature. In all cases, Electron Cyclotron Resonance sources (either multipolar or magnetic mirror) with additional rf biasing of the sample position are utilized to obtain low damage pattern transfer processes that generally use metal contacts on device structures as self-aligned etch masks. The temperature dependence of etch rates with these new chemistries display non-Arrhenius behavior in the range 50-250°C and a detailed study of the phenomenon are reported. Electrical, optical and chemical analysis of the etched surfaces show that it is possible to achieve essentially damage-free pattern transfer.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1994
Electron cyclotron resonance discharges of HBr/H2/Ar and HI/H2/Ar were used to etch III–V semicon... more Electron cyclotron resonance discharges of HBr/H2/Ar and HI/H2/Ar were used to etch III–V semiconductors at temperatures in the range 50–250 °C. The increase in etch rates is non-Arrhenius for both chemistries, but enhancements of up to a factor of 50 are seen, depending on the material, with rates of ∼1 μm min−1 for InP at 250 °C at 1 mTorr, −200 V dc and 250 W of microwave power. InP surfaces show a smooth-to-rough transition at ∼150 °C in HBr-based discharges, with degraded anisotropy of the etched features. Both GaAs and AlGaAs are more resistant to this surface roughening, but preferential loss of As occurs at elevated temperatures. Similar results were obtained with HI-based discharges, with loss of the group V element above ∼100 °C. The electrical properties of all three materials are affected by the etch treatments, with creation of a highly conducting surface layer on InP and hydrogen passivation of dopants occurring in GaAs and AlGaAs. The latter can be reversed by anneali...
Journal of The Electrochemical Society, 1990
ABSTRACT The reactive ion etching of , , , , and in or discharges was investigated as a function ... more ABSTRACT The reactive ion etching of , , , , and in or discharges was investigated as a function of the plasma parameters power density, pressure, and relative composition as well as etching time. The etch rates of all of these materials with the exception of are faster in in comparison to , and show a similar dependence on power density and discharge composition. The variation of etch rates with pressure, however, are quite different for the two gas mixtures, with all of the materials going through a maximum at 60–80 mtorr for , while continuing to show a monotonic increase with pressure for . The surface morphologies after RIE with either type of discharge are generally quite rough, although smooth etching can be obtained under appropriate conditions. Increased reverse bias currents are observed in Au/n‐type Schottky diodes after RIE, with higher currents for low pressure or high self‐bias etching. Photoluminescence decreases from are also observed after RIE, ranging in magnitude from 2–10 times. The depth of point defect introduction by energetic ion bombardment is limited to &lt;200Å in for RIE at 50 mtorr and dc biases on the samples of 50V. Chlorine‐containing residues are present typically to a depth of ∼40Å on all of the material after RIE in either type of discharge. The addition of to both gas mixtures leads to a high selectivity for and over because of the formation of a thin involatile layer of on the .
Journal of Crystal Growth, 1991
The effect of mesa shape on the planarity of InP regrowths produced by atmospheric pressure and l... more The effect of mesa shape on the planarity of InP regrowths produced by atmospheric pressure and low pressure (0.1 atm) selective (Si0 2 masked) metalorganic vapor phase epitaxy (MOVPE) is investigated. We find that for two separate atmospheric pressure reactor configurations (vertical and horizontal with a factor of 4 difference in growth rate), relatively planar regrowths are reproducibly obtained only when the mesa is non-reentrant, that is, with the narrowest portion of the mesa at the top in contact with the mask. For reentrant mesas grown at atmospheric pressure, the non-planarity is characterized by a large lateral growth rate at the top of the mesa just underneath the mask and by a very small growth rate underneath the volume of large lateral growth, the combination of which results in deep trenches on the side of the mesa and mask overgrowth from the edges. On the other hand, selective MOVPE at low pressure results in planar regrowths on the same reentrant mesas that had produced extremely non-planar regrowths during atmospheric pressure growth.
Uploads
Papers by Utpal Chakrabarti