K.G. Stephens

Electrical, Rutherford backscattering and transmission electron microscopy studies of furnace annealed zinc implanted GaAs

Abstract Electrical, Rutherford backscattering and transmission electron microscopy measurements have been carried out on GaAs samples implanted with 150 keV, 1.10 15 zinc ions/cm 2 and furnace annealed in the temperature range from room temperature to 900°C. A correlation between three types of measurement technique was established and four distinct annealing stages have been identified. For perfect recrystallization and maximum electrical activation an annealing temperature of 900°C is required. The maximum peak hole concentration was in the range 1–2.10 19 holes/cm 3 .

High quality silicon on insulator structures formed by the thermal redistribution of implanted nitrogen

Silicon wafers have been implanted with 200‐keV 14N+ ions to doses between 0.25 and 1.4×1018 N+ cm−2 at a temperature of 500 °C and have been annealed at 1200 °C for 2 and 8 h. Rapid redistribution of the implanted nitrogen occurs, against the macroscopic concentration gradient, in samples implanted with doses below that required to directly synthesize stoichiometric Si3N4. This leads to the formation of a continuous buried layer of either amorphous or polycrystalline Si3N4. The surface layer is high quality single crystal silicon (χmin =0.043) containing no polycrystalline material nor precipitates. The Si‐Si3N4 interfaces are extremely abrupt but with an irregularity of ∼100 and ∼50 A at the upper and lower interfaces, respectively.

Formation of buried insulating layers in silicon by the implantation of high doses of oxygen

Abstract Silicon wafers have been implanted with 200 keV oxygen to dosss of up to 2.4 × 10 18 O + /cm 2 at implantation temperatures of 325°C to 600°C. Rutherford backscattering and SIMS show the oxygen depth distribution is insensitive to the implantation temperature but is modified by subsequent high-temperature processing. Multiple laser irradiations produced a single crystal layer at the surface by LPE regrowth but better crystallinity is observed in samples which have been furnace annealed, when a layer of 1000 A thickness is formed which is denuded of oxygen. Preferred conditions to form a silicon on insulator structure (SOI) suitable for VLSI device technology are implantation temperature 400–500°C followed by furnace annealing at 1150°C for 2–4 h with an SiO 2 cap.

Doping of III–V compound semiconductors by ion implantation

Abstract The use of ion implantation to dope III–V compound semiconductors is growing in importance because it can be applied in the manufacture of discrete devices such as LEDs, lasers and FETs and increasingly, in the production of both linear and digital integrated circuits. As in silicon technology, the advantages of implantation include good control over depth profiles and sheet carrier concentration, good reproducibility, and good uniformity. With compounds, however, there is probably a greater need to know the depth variation of the carrier concentration, as well as the percentage electrical activation of the dopant atoms and the measurement of profiles is discussed together with the problems of annealing. Dissociation and loss ofthe volatile component during annealing has to be avoided, and therefore various annealing methods have been tried in order to establish the best technique for particular applications. Recent progress in these annealing studies are discussed. The effects of the substrate on the resultant carrier concentration profile is also reviewed since the redistribution of impurities due to damage and subsequent heat treatment can vary considerably with starting material, annealing schedule, ion, dose, dose rate, etc., and is thus an important factor in making devices. The production of n-type, p-type and semi-insulating layers is reviewed and a brief summary given of recent device applications.

Annealing of zinc‐implanted GaAs

A study of ion‐implanted zinc in GaAs has been made using three annealing techniques: e‐beam, graphite strip heating, and furnace annealing in an arsine ambient. The highest hole concentrations, 7–8×1019 cm−3, were obtained using electron‐beam annealing. Graphite strip heating and electron‐beam annealing were able to electrically activate 100% of the implanted dose. The effect of strain on the activation of the zinc has been demonstrated by comparing chemical‐vapor‐deposited Si3N4 with reactively evaporated AlN encapsulants.

Silicon on insulator structures formed by the implantation of high doses of reactive ions

Silicon on insulator structures have been formed by implanting O+ and N+ ions into (100) silicon. The structures have been evaluated by RBS and SIMS techniques. In oxygen implanted substrates, the thickness and crystal quality of the surface layer is found to be insensitive to the ion energy. The thickness increases with anneal temperature over the range 1100°C to 1200°C and has a maximum value when the substrate temperature during implantation is 500°C. Nitrogen implanted wafers have a thicker single crystal layer with very abrupt Si/Si3N4 interfaces.

The formation of compound layers in silicon by ion beam synthesis

Abstract The technique of ion beam synthesis (IBS) using high doses of energetic ions has been successfully implemented to produce a variety of compounds, the physical properties of which are dependent on the implanted species and range from insulators, e.g. SiO 2 , through semiconductors, e.g. SiC, to conductors, e.g. CoSi 2 . In this paper we study the evolution of these compounds and compare and contrast their methods of formation. To demonstrate the versatility of the technique we look at three examples of IBS layers: (1) To date most of the interest in IBS has concentrated on the production of buried oxide layers for silicon-on-insulator (SOI) device applications. Recently it has been shown that by using a series of sequential implants and high-temperature anneals the defect density in the silicon overlayer can be dramatically reduced. To study how this process occurs, we followed the redistribution of the implanted species during implantation and annealing using both 16 O + and 18 O + . (2) Buried CoSi 2 layers can be fabricated in (100) single-crystal silicon by implanting high doses of energetic cobalt ions at elevated temperatures. For the higher doses (≥ 4 × 10 17 O + /cm 2 at 350 keV), a continuous coherent layer of CoSi 2 grows epitaxially during implantation. For lower doses, precipitates of both A- and B-type CoSi 2 are observed. After annealing at 1000° C for 30 min, single-crystal aligned layers are produced for the higher doses, while for lower doses discrete octahedral A-type precipitates are formed. (3) The microstructures of synthesized SiC layers are more complex than analogous synthesized oxide or silicide layers. Unlike buried oxide layers, the carbon concentration at the peak of the implanted distribution does not saturate at a value equivalent to that in the stoichiometric compound, but continues to rise, reflecting the lower diffusivity of the C in the synthesized compound layer. To achieve chemical segregation of the implanted carbon, very-high-temperature (≥ 1300°C), long-time (typically 20 h) anneals are required. At the interface with the silicon substrate the synthesized layer grows with a degree of epitaxy. This is also found to occur during implantation if the temperature is ≥ 650° C.

Electrical activity and radiation damage in ion implanted cadmium telluride

Abstract Single crystals of semi-insulating cadmium telluride have been implanted with 50 keV argon ions and 100 keV indium, tellurium and bismuth ions in an attempt to reduce the resistivity of the implanted layer by the injection of free carriers. Carrier concentrations were determined from sheet resistivity and Hall measurements. The highest percentage (∽ 30%) of electrically active ions to the total number implanted was measured for a dose of 1014 indium ions/cm2 implanted into a substrate held at 200°C. Although some activity was generated by bismuth ions, tellurium and argon ions produced no measurable electrical changes. The backscattering and channelling of hetium ions was used to study the damage produced by the different ions under different implant and annealing conditions. The technique was also used to measure the bismuth atom concentration retained by samples after various annealing stages. Some of the increases in electrical activity could be correlated with reductions in radiation damage. ...

Annealing of selenium‐implanted GaAs

The electrical and structural properties of 1×1014 Se+ cm−2, 100–400 kV and 5×1012 Se++ cm−2, 350‐kV implants into (100) semi‐insulating GaAs have been studied. Peak carrier concentrations of 5×1018 cm−3 have been measured and mobilities >4000 cm2 V−1 s−1 obtained for low‐dose implants (n=1–2×1017 cm−3) by annealing samples on a graphite strip heater. Si3N4 and AlN have been used as encapsulants. Comparisons are made with capless annealing in an arsine ambient.

SIMS analysis of silicon on insulator structures formed by high-dose O+ implantation into silicon

Abstract Silicon on insulator (SOI) structures are promising candidates for the fabrication of VLSI circuits with very high packing densities. The preparation of such structures can now be achieved by high dose implantation of reactive ion species such as oxygen to produce buried layers of SiO2 in silicon. In this paper we report experiments to depth profile these layered structures by SIMS. SOI samples have been prepared by implantating (100) silicon wafers with 400 keV molecular oxygen ions at a dose of 1.8×1018 O+ cm−2. During the implantation the wafers were maintained at temperatures between 325 and 600°C, using beam heating, which achieved in situ-annealing and ensured that the top silicon layer remained single crystal. Analysis was carried out on an Atomika DIDA-II spectrometer using 10 keV Ar+ ions with a low current density of less than 1 mA cm−2. During analysis negative secondary ions were monitored which provided a high detection sensitivity for oxygen and revealed fine detail in the measured yields with reflected both the composition and structure of the samples. Depth distributions of the oxygen compare well with results obtained by other techniques, including Rutherford backscattering and sectional TEM. It has been shown that prolonged high temperature annealing leads to diffusion of oxygen with the formation of a denuded layer of thickness 1000–1500 A which is of a suitable quality for successful fabrication of high performance MOS devices.