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Effects of side wall ion reflection on maskless physical etching
Vacuum/volume 37humbers Printed in Great Britain
0042-207X/87$3.00+ .OO Pergamon Journals Ltd
516lpages 491 to 493/l 987
Abstracts Thin film deposition techniques for electronic materials F Briones, Centro National Madrid, Spain
de Microelectronica,
CSIC, 28006-
A review of the evolution of vacuum deposition techniques for thin film semiconductor materials provides a background for a description of new vacuum epitaxial techniques which have been successfully developed during the last decade, in particular MBE, MOMBE, ALE and ICD. The basic reasons are presented that allow those techniques to be considered the most promising from the point of view of industrial fabrication of advanced semiconductor devices: optimum control and reproducibility of thickness; doping level; uniformity; yield; together with the unique capability of in situ characterization of growth process and grown layers. In this context, examples of application of surface analysis and mass spectrometry techniques during MBE growth of GaAs and AlGaAs are presented with special reference to recent advances of RHEED. The possibilities of fabrication of high quality heterostructures with dimensional control of the order of atomic distances are discussed which open a new field of the physics of semiconductors and a new generation of electronic devices: two-dimensional electron gas (2DEG), quantum well structures and superlattices. The final part of the paper is concerned with the most relevant properties of those structures grown by MBE, present applications in micro- and optoelectronics and future developments of ‘band structure engineering’.
Effects of side wall ion reflection on maskless physical etching J C Moreno-Marin, J A Vallb-Abarca and A Gras-Marti, LCFCA, Departamento de Fisica, Fact&ad de Ciencias, Universidad de Alicante, Apartado 99, 03080 Alicante, Spain The effects due to the reflection of the beam on the groove wall during maskless ion milling of a surface are quantified by a tridimensional model, based on an analytical theory developed by Smith and Walls’. The model incorporates the effect of the main secondary processes that take place during etching, such as redeposition, resputtering and ion reflection at side walls*. The latter effect is the origin of the well-known trenches which are commonly observed in ion beam etching of microstructures. Two simplified models have been used depending upon the assumption that a single or a multiple elastic collision process is responsible for ion reflection. For a simple collision event between the incoming ion and a surface atom, we assume that the ions are reflected with an average scattering angle. When a multiple elastic collision process takes place, the incoming beam is reflected with a well-defined angular distribution having a maximum in the specular direction. Reasonable expressions for the input param-
eters such as sputtering yields, reflection coefficients, and energy and angular spectra of sputtered and reflected particles are used in a computer simulation of the etching process. Detailed profiles are shown for a variety of cases of practical interest, e.g. the etching of Si and GaAs with a Ga+ focused ion beam. References ‘R Smith and J M Walls, Phil Mug, A42, 235 (1980) ’ J C Moreno-Marin, J A Vallks-Abarca and A Gras-Mar& J Vat Sci Technol, B4, 322 (1986). 10
Deposition of transparent and conductive oxide thin films by activated reactive evaporation C Ferratter, E Bertran, J Esteve, J L Morenza and J M Coding, Laboratori de Capes Primes, Departament d’Electricitat i Electrdnica, Universitat de Barcelona, Au Diagonal 645,08028 Barcelona, Spain Semiconducting oxide thin films with high electrical conductivity, optical transmittance and infra-red reflectance, are used as transparent electrodes in solar cells and opto-electronic devices, and also as heat mirrors. In,O, thin films were deposited onto glass substrates kept at different temperatures in the 10&250”C range by activated reactive evaporation (ARE). The films were obtained by indium evaporation in a glow discharge oxygen plasma, created by means of a hot cathode and a ring electrode which is positively biased. The influence of the deposition parameters was studied, keeping fixed the plasma conditions: discharge density 100 mA, anode-cathode potential 100 V and pressure 1.5 x 10e3 or 2 x 10m3 mbar. The In,O, growth rate was then essentially determined by the In evaporation rate. The optical properties of the films in the visible and near infrared were obtained from the transmission spectra in the 30&2600 nm range. The mean transmittance in the visible zone has values in the 75581% range. The higher transmission corresponds to the films grown with lower In flux. The electrical properties at 300 K were studied by means of conductivity and Hall effect measurements. The conductivity has values between 48 and 4 x lo3 S cm-i. The carrier concentration and mobility range between 3 x 1019 and 4.6 x 10” cmm3, and 9 and 69 cm2 V-’ s-i respectively. These values have a strong correlation with the indium flux. Conductivity and carrier concentration increase when the indium flux increases and tend to saturation. In,O, films, 720 nm thick, with mean transmittance of 79% in the visible range and, simultaneously electrical conductivity of 2.9 x lo3 S cm-’ have been obtained. The observed correlations can be explained through a model in which oxygen vacancies originate the charge carriers. 491
0042-207X/87$3.00+ .OO Pergamon Journals Ltd
516lpages 491 to 493/l 987
Abstracts Thin film deposition techniques for electronic materials F Briones, Centro National Madrid, Spain
de Microelectronica,
CSIC, 28006-
A review of the evolution of vacuum deposition techniques for thin film semiconductor materials provides a background for a description of new vacuum epitaxial techniques which have been successfully developed during the last decade, in particular MBE, MOMBE, ALE and ICD. The basic reasons are presented that allow those techniques to be considered the most promising from the point of view of industrial fabrication of advanced semiconductor devices: optimum control and reproducibility of thickness; doping level; uniformity; yield; together with the unique capability of in situ characterization of growth process and grown layers. In this context, examples of application of surface analysis and mass spectrometry techniques during MBE growth of GaAs and AlGaAs are presented with special reference to recent advances of RHEED. The possibilities of fabrication of high quality heterostructures with dimensional control of the order of atomic distances are discussed which open a new field of the physics of semiconductors and a new generation of electronic devices: two-dimensional electron gas (2DEG), quantum well structures and superlattices. The final part of the paper is concerned with the most relevant properties of those structures grown by MBE, present applications in micro- and optoelectronics and future developments of ‘band structure engineering’.
Effects of side wall ion reflection on maskless physical etching J C Moreno-Marin, J A Vallb-Abarca and A Gras-Marti, LCFCA, Departamento de Fisica, Fact&ad de Ciencias, Universidad de Alicante, Apartado 99, 03080 Alicante, Spain The effects due to the reflection of the beam on the groove wall during maskless ion milling of a surface are quantified by a tridimensional model, based on an analytical theory developed by Smith and Walls’. The model incorporates the effect of the main secondary processes that take place during etching, such as redeposition, resputtering and ion reflection at side walls*. The latter effect is the origin of the well-known trenches which are commonly observed in ion beam etching of microstructures. Two simplified models have been used depending upon the assumption that a single or a multiple elastic collision process is responsible for ion reflection. For a simple collision event between the incoming ion and a surface atom, we assume that the ions are reflected with an average scattering angle. When a multiple elastic collision process takes place, the incoming beam is reflected with a well-defined angular distribution having a maximum in the specular direction. Reasonable expressions for the input param-
eters such as sputtering yields, reflection coefficients, and energy and angular spectra of sputtered and reflected particles are used in a computer simulation of the etching process. Detailed profiles are shown for a variety of cases of practical interest, e.g. the etching of Si and GaAs with a Ga+ focused ion beam. References ‘R Smith and J M Walls, Phil Mug, A42, 235 (1980) ’ J C Moreno-Marin, J A Vallks-Abarca and A Gras-Mar& J Vat Sci Technol, B4, 322 (1986). 10
Deposition of transparent and conductive oxide thin films by activated reactive evaporation C Ferratter, E Bertran, J Esteve, J L Morenza and J M Coding, Laboratori de Capes Primes, Departament d’Electricitat i Electrdnica, Universitat de Barcelona, Au Diagonal 645,08028 Barcelona, Spain Semiconducting oxide thin films with high electrical conductivity, optical transmittance and infra-red reflectance, are used as transparent electrodes in solar cells and opto-electronic devices, and also as heat mirrors. In,O, thin films were deposited onto glass substrates kept at different temperatures in the 10&250”C range by activated reactive evaporation (ARE). The films were obtained by indium evaporation in a glow discharge oxygen plasma, created by means of a hot cathode and a ring electrode which is positively biased. The influence of the deposition parameters was studied, keeping fixed the plasma conditions: discharge density 100 mA, anode-cathode potential 100 V and pressure 1.5 x 10e3 or 2 x 10m3 mbar. The In,O, growth rate was then essentially determined by the In evaporation rate. The optical properties of the films in the visible and near infrared were obtained from the transmission spectra in the 30&2600 nm range. The mean transmittance in the visible zone has values in the 75581% range. The higher transmission corresponds to the films grown with lower In flux. The electrical properties at 300 K were studied by means of conductivity and Hall effect measurements. The conductivity has values between 48 and 4 x lo3 S cm-i. The carrier concentration and mobility range between 3 x 1019 and 4.6 x 10” cmm3, and 9 and 69 cm2 V-’ s-i respectively. These values have a strong correlation with the indium flux. Conductivity and carrier concentration increase when the indium flux increases and tend to saturation. In,O, films, 720 nm thick, with mean transmittance of 79% in the visible range and, simultaneously electrical conductivity of 2.9 x lo3 S cm-’ have been obtained. The observed correlations can be explained through a model in which oxygen vacancies originate the charge carriers. 491