R. Kögler

Amorphization and recrystallization of 6H‐SiC by ion‐beam irradiation

Amorphization of 6H‐SiC with 200 keV Ge+ ions at room temperature and subsequent ion‐beam‐induced epitaxial crystallization (IBIEC) with 300 keV Si+ ions at 480 °C have been studied by Rutherford backscattering spectrometry/channeling and transmission electron microscopy analysis. Experimental results on amorphous layer thicknesses have been compared with trim calculations in association with the critical energy density model. Density changes during amorphization have been observed by step height measurements. Particular attention has been directed to the crystal quality and a possible polytype transformation during the IBIEC regrowth. The IBIEC process consists of two stages and results in a multilayer structure. In the initial phase an epitaxial growth of 6H‐SiC has been obtained. With increasing IBIEC dose the epitaxial growth changes to columnar growth and is stopped by polycrystallization of 3C polytype in the near‐surface region.

Ion‐beam synthesis of amorphous SiC films: Structural analysis and recrystallization

The analysis of SiC films obtained by carbon ion implantation into amorphous Si (preamorphized by Ge ion implantation) has been performed by infrared and Raman scattering spectroscopies, transmission electron microscopy, Rutherford backscattering, and x‐ray photoelectron spectroscopy (XPS). The data obtained show the formation of an amorphous Si1−xCx layer on top of the amorphous Si one by successive Ge and C implantations. The fitting of the XPS spectra indicates the presence of about 70% of Si–C bonds in addition to the Si–Si and C–C ones in the implanted region, with a composition in the range 0.35<x<0.6. This points out the existence of a partial chemical order in the layer, in between the cases of perfect mixing and complete chemical order. Recrystallization of the layers has been achieved by ion‐beam induced epitaxial crystallization (IBIEC), which gives rise to a nanocrystalline SiC layer. However, recrystallization is not complete, observing still the presence of Si–Si and C–C bonds in an amorphou...

Complete recrystallization of amorphous silicon carbide layers by ion irradiation

Ion‐beam‐induced recrystallization of amorphous surface layers on single‐crystalline silicon carbide substrates (6H–SiC) has been investigated at temperatures of 500 and 1050 °C by cross‐sectional transmission electron microscopy and Rutherford backscattering spectrometry and channeling. It is shown, that ion irradiation substantially reduces the onset temperature of both the epitaxial layer regrowth and the random nucleation of crystalline grains. Two recrystallization regimes have been found. At 500 °C ion‐beam‐induced random nucleation (IBIRN) of crystalline grains strongly competes with ion‐beam‐induced epitaxial crystallization (IBIEC) and polycrystalline material stops the epitaxial regrowth front in an early stage. At a temperature of 1050 °C IBIEC dominates over IBIRN and a complete, but disturbed epitaxial regrowth is obtained.

Carrier Profiling of Individual Si Nanowires by Scanning Spreading Resistance Microscopy

Individual silicon nanowires (NWs) doped either by ion implantation or by in situ dopant incorporation during NW growth were investigated by scanning spreading resistance microscopy (SSRM). The carrier profiles across the axial cross sections of the NWs are derived from the measured spreading resistance values and calibrated by the known carrier concentrations of the connected Si substrate or epi-layer. In the case of the phosphorus ion-implanted and subsequently annealed NWs, the SSRM profiles revealed a radial core-shell distribution of the activated dopants. The carrier concentration close to the surface of a phosphorus-doped NW is found to be by a factor of 6-7 higher than the value in the core and on average only 25% of the implanted phosphorus is electrically active. In contrast, for the in situ boron-doped NW the activation rate of the boron atoms is significantly higher than for phosphorus atoms. Some specific features of SSRM experiments of Si NWs are discussed including the possibility of three-dimensional measurements.

Spectroscopic characterization of phases formed by high-dose carbon ion implantation in silicon

High‐dose carbon‐ion‐implanted Si samples have been analyzed by infrared spectroscopy, Raman scattering, and x‐ray photoelectron spectroscopy (XPS) correlated with transmission electron microscopy. Samples were implanted at room temperature and 500 °C with doses between 1017 and 1018 C+/cm2. Some of the samples were implanted at room temperature with the surface covered by a capping oxide layer. Implanting at room temperature leads to the formation of a surface carbon‐rich amorphous layer, in addition to the buried implanted layer. The dependence of this layer on the capping oxide suggests this layer to be determined by carbon migration toward the surface, rather than surface contamination. Implanting at 500 °C, no carbon‐rich surface layer is observed and the SiC buried layer is formed by crystalline β‐SiC precipitates aligned with the Si matrix. The concentration of SiC in this region as measured by XPS is higher than for the room‐temperature implantation.

Interstitial-type defects away from the projected ion range in high energy ion implanted and annealed silicon

Defects in high energy ion implanted silicon have been investigated, especially in the depth range around half of the projected ion range RP/2 after annealing at temperatures between 700 and 1000 °C. Preferable trapping of metals just in this depth range proves the existence of defects there. No vacancy-like defects could be detected by variable energy positron annihilation spectroscopy after annealing at temperatures T>800 °C. Instead, interstitial-type defects were observed in the RP/2 region using cross section transmission electron microscopy of a specimen prepared under special conditions. The results indicate the presence of small interstitial agglomerates at RP/2 which remain after high temperature annealing.

CRYSTALLIZATION AND SURFACE EROSION OF SIC BY ION IRRADIATION AT ELEVATED TEMPERATURES

The effects of high dose ion irradiation through amorphous surface layers on single crystalline 6H–SiC at elevated temperatures are studied in detail. Material swelling, subsequent densification, and surface erosion are quantified for irradiation at 500 °C. Ion beam induced recrystallization is investigated in the temperature range between 300 and 1300 °C. The results demonstrate that undisturbed epitaxial regrowth of an amorphous surface layer in (0001)-oriented 6H–SiC cannot be achieved by ion irradiation. The shift of the amorphous/crystalline interface observed by Rutherford backscattering spectrometry/channeling analysis is a consequence of columnar growth and surface erosion. The columnar growth starts inside the heavily damaged transition region between the amorphous surface layer and the single crystalline bulk material. It is stopped by random nucleation which is strongly enhanced by ion irradiation in the temperature range between 300 and 1000 °C. Neither the interface roughness nor the kind of ...

Ex situ n and p doping of vertical epitaxial?short silicon nanowires by ion?implantation

Vertical epitaxial short (200-300 nm long) silicon nanowires (Si NWs) grown by molecular beam epitaxy on Si(111) substrates were separately doped p- and n-type ex situ by implanting with B, P and As ions respectively at room temperature. Multi-energy implantations were used for each case, with fluences of the order of 10(13)-10(14) cm(-2), and the NWs were subsequently annealed by rapid thermal annealing (RTA). Transmission electron microscopy showed no residual defect in the volume of the NWs. Electrical measurements of single NWs with a Pt/Ir tip inside a scanning electron microscope (SEM) showed significant increase of electrical conductivity of the implanted NWs compared to that of a nominally undoped NW. The p-type, i.e. B-implanted, NWs showed the conductivity expected from the intended doping level. However, the n-type NWs, i.e. P- and As-implanted ones, showed one to two orders of magnitude lower conductivity. We think that a stronger surface depletion is mainly responsible for this behavior of the n-type NWs.

Synthesis of SiC Microstructures in Si Technology by High Dose Carbon Implantation: Etch‐Stop Properties

The use of high dose carbon ion implantation in Si for the production of membranes and microstructures is investigated. Si wafers were implanted with carbon doses of 10{sup 17} and 5 {times} 10{sup 17} cm{sup {minus}2}, at an energy of 300 keV and a temperature of 500 C. The structural analysis of these samples revealed the formation of a highly stable buried layer of crystalline {beta}-SiC precipitates aligned with the Si matrix. The etch-stop properties of this layer have been investigated using tetramethyl-ammonium hydroxide as etchant solution. Secondary ion mass spectrometry measurements performed on the etched samples have allowed an estimate of the minimum dose needed for obtaining an etch-stop layer to a value in the range 2 to 3 {times} 10{sup 17} ions/cm{sup 2}. This behavior has been explained assuming the existence of a percolation process in a SiC/Si binary system. Finally, very thin crystalline membranes and self-standing structures with average surface roughness in the range 6 to 7 nm have been obtained.

Radiation damage and annealing behaviour of Ge+-implanted SiC

Abstract In recent years, single-crystal SiC has become an important electronic material due to its excellent physical and chemical properties. The present paper reports a study of the defect reduction and recrysallisation during annealing of Ge+-implanted 6H-SiC. Implants have been performed at 200 keV with doses of 1 × 1014 and 1 × 1015 cm−2. Furnace annealing has been carried out at temperatures of 500, 950 and 1500°C. Three analytical techniques including Rutherford backscattering spectrometry in conjunction with channelling (RBS/C), positron annihilation spectroscopy (PAS) and cross-sectional transmission electron microscopy (XTEM) have been employed for sample characterisation. It has been shown that damage removal is more complicated than in ion-implanted Si. The recrystallisation of amorphised SiC layers has been found to be unsatisfactory for temperatures up to 1500°C. The use of ion-beam-induced epitaxial crystallisation (IBIEC) has been more successful as lattice regrowth, although still imperfect, has been observed to occur at a temperature as low as 500°C.