Chemically Assisted Ion Beam Etching Research Articles

A simple model of the chemically assisted ion beam etching yield of GaAs with Cl2 at medium current densities

We present a simple analysis of the chemically assisted ion beam etching (CAIBE) yield of a solid under exposure to an ion beam and flux of molecular chlorine, using a mass-balance approach. In this model, dichloride species formed by the dissociative chemisorption of physisorbed chlorine are removed by collisional cascade mechanisms. We show that the energy and ion flux dependences of the yield deviate from expected forms depending primarily on the surface chemisorption rate and the surface flux ratio, but even in this simple model there are reasons why the latter might not be a good parameter for the comparison of experimental data. The model describes the important features of the etch rates of GaAs in chlorine and low-energy (500–1250 eV, 0.05–0.35 mA/cm2) Ar+, including a changing energy dependence of the yield with chlorine partial pressure.

Assessing thermal Cl2 etching and regrowth as methods for surface passivation

The damage layer that results from ion beam processing ultimately limits the smallest size structure which will emit light and hence prevents the realization of low-dimensional quantum size effects. Effective surface passivation of etched structures requires both layer removal and compensation of surface states. Ultimately these two processes must be made compatible. To address this problem, we have coupled an ultrahigh-vacuum (UHV) dry-etching system to a molecular beam epitaxy (MBE) growth chamber. Material is patterned and masked outside of the combined etching/regrowth system using electron beam lithography. Samples are then loaded into the combined UHV system and vertical structures are produced by chemically assisted ion beam etching (CAIBE). These structures are then subjected to a thermal Cl2 gas etch to remove the damage layer created by the ion beam etching. Samples are subsequently transferred directly into the MBE growth chamber, where a cladding layer of Al0.3Ga0.7As is grown over the etched structure to provide passivation. In this way both the damage removal and surface passivation are achieved in-situ without the deleterious effects caused by exposure to air. We find, by low temperature cathodoluminescence, that submicrometer structures subjected to this in-situ processing display fivefold improved luminescence efficiencies. Structures etched and regrown without the thermal Cl2 etching step show no comparable improvement, indicating the damage removal is the key to improved efficiencies.

Characterization of etch rate and anisotropy in the temperature-controlled chemically assisted ion beam etching of GaAs

Independent adjustment of etch rate and sidewall profiles in chemically assisted ion beam etching (CAIBE) of GaAs is demonstrated by controlling the temperature of the sample. GaAs etch rate data as a function of sample temperature, ion beam flux, and reactive gas flow is presented for CAIBE using a 500 eV argon ion beam and molecular chlorine. At a constant etch rate of 0.5 μm/min, etch profiles ranging from vertical to crystallographically faceted are obtained. This demonstrated flexibility, combined with the inherent reproducibility of dry etching, make CAIBE an attractive choice for processing advanced semiconductor devices. To illustrate the range of capabilities available with temperature-controlled CAIBE, etched-facet laser structures, self-aligned mesas and fine tips suitable for field-emitting devices are fabricated.

Selective Chemically Assisted Ion Beam Etching of Si, Polysilicon, and SiO2 Using Ni‐Cr Masks and Cl2

The etching of single‐crystal silicon, CVD polysilicon, thermally grown silicon oxides, and Ni‐Cr masks have been studied using a chemical‐assisted ion beam etching (CAIBE) process. Etch rates were measured as functions of gas flow rate, Ar+ ion beam energy, and beam current density. Selectivities of Ni‐Cr:Si, Ni‐Cr:poly, and of 1:10, 1:9, and 1:4 were determined. Vertical profiles were obtained down to at least 100 nm linewidths using CAIBE.

Chemically Assisted Ion Beam Etching (CAIBE)- a New Technique for TEM Specimen Preparation of Materials

ABSTRACTChemically assisted ion beam etching (CAIBE) is widely practiced in the semiconductor industry. In the electron microscopy field, the CAIBE technique offers a new method for preparing specimens that are difficult to make by conventional inert gas milling techniques, e.g. indium containing type III-V compound semiconductors. CAIBE employs a collimated, molecular beam of a reactive species, e.g. iodine in combination with a conventional inert gas fast atom beam for thinning TEM specimens. CAIBE should not be confused with reactive ion beam etching (RIBE) which takes a chemically active species (e.g. iodine) and converts it into a beam of fast ions directed at the sample. CAIBE has three major advantages over (RIBE): i) corrosion of the ion gun components does not occur, ii) much smaller quantities of reactive gas are required and hence pump maintenance and pollution problems are minimized, iii) a wider range of chemicals may be used. Superior results are obtained if CAIBE is done on only one side of the specimen at a time. This is achieved using a new type of specimen holder post which enables very low angle milling and minimizes specimen contamination by sputtering from the holder. This new technique is described and results from iodine CAIBE milling, iodine RIBE milling and argon ion milling are compared for InP, InSb and GaAs as well as metals like tungsten. Also, the beneficial effects of very low angle (∼1°) argon ion milling in preparing specimens of silicide containing Si based IC wafers is reported.

Self-aligned chemically assisted ion-beam-etched GaAs/(Al,Ga)As turning mirrors for photonic applications

It is shown that totally reflecting turning mirrors can be fabricated in GaAs/(Al,Ga)As graded-index separate-confinement-heterostructure single-quantum-well (GRIN-SCH SQW) material using Ti metal masking and Cl/sub 2/ chemically assisted ion-beam-etching (CAIBE). Combined with ridge waveguides, these techniques have been used to make turning-mirror cleaved-facet lasers that have acceptable external slope efficiencies with a modest estimated increase in threshold current. Scanning electron microscope examination of the mirrors indicates some residual roughness attributed to the edge definition of the deposited titanium film. The mirror loss is estimated to be 68% for these particular turning mirrors. These components, which continue to be developed and improved, are being applied to increasingly sophisticated and demanding photonic programs. >

Chemically assisted ion beam etching process for high quality laser mirrors

A process for the fabrication of mirror facets for AlGaAs/GaAs laser diodes is described. The major requirements for the fabrication of high quality mirrors have been fulfilled by using Cl 2/Ar chemically assisted ion beam etching (CAIBE) and a new multilayer mask structure that produces the smoothest facets. The fabricated AlGaAs/GaAs SQW-GRIN-SCH lasers with etched mirrors show characteristics similar to those of lasers with cleaved mirrors on the same substrate. Results of on-wafer testing of laser threshold uniformity by means of monitor diodes indicate the potential of the process for laser integration and full wafer fabrication and testing.

Chemically assisted ion beam etching of polycrystalline and (100)tungsten

A chemically assisted ion beam etching (CAIBE) technique is described which employs an ion beam from an electron bombardment ion source and a directed flux of ClF3 neutrals. This technique enables the etching of tungsten foils and films in excess of 40 μ thick with good anisotropy and pattern definition over areas 30 mm2, and with a high degree of selectivity. (100)tungsten foils etched with this process exhibit preferred orientation etching, while polycrystalline tungsten films exhibit high etch rates. This technique can be used to pattern the dispenser cathode surfaces serving as electron emitters in traveling wave tubes to a controlled porosity.

Chemically Assisted Ion Beam Etching of Tungsten using ClF3

A chemically assisted ion beam etching (CAIBE) technique is described which employs an ion beam from an electron bombardment ion source and a directed flux of ClF3 neutrals. This technique enables the etching of tungsten foils and films in excess of 40 μm thick with good anisotropy and pattern definition over areas 5 mm2, and with a high degree of selectivity. (100) tungsten foils etched with this process exhibit preferred orientation etching, while polycrystalline tungsten films exhibit high etch rates approximately 80% that of (100) orientation tungsten.

Ion-beam etching, and chemically-assisted ion-beam etching to produce x-ray masks for synchrotron-radiation-lithography

Gold patterns for x-ray masks can by obtain through pattern transfer in gold-absorbers by method of Ion-Beam Etching and Chemical Assisted Ion-Beam Etching. This work presents results of pattern transfer by soft mask (resist) and hard mask (metal layer) through a three-stage etching process in Au-absorber and a resulting wall inclination of approx 860 (quasiperpendicular).