A. Nejim

Visible photoluminescence at room temperature from microcrystalline silicon precipitates in SiO2 formed by ion implantation

We have investigated the photoluminescence of microcrystalline silicon formed in SiO2 layers by ion beam synthesis. 28Si+ ions over the dose range 1 × 1017 to 6 × 1017 cm−2 at energies of 150 keV and 200 keV were implanted into thermal oxide. Samples were annealed in a halogen lamp furnace at temperatures of 900°C, 1100°C and 1300°C for times between 15 and 120 min. The implanted layers were analysed by Rutherford Backscattering Spectroscopy (RBS), Cross-Sectional Transmission Electron Microscope (XTEM) and Photoluminescence (PL) (80 K to 300 K) using an Ar laser of 488 nm wavelength. Room temperature (300 K) visible photoluminescence has been observed from all the samples. XTEM confirms the existence of Si microcrystals (within the SiO2 layers), which typically have a diameter within the range of 2–15 nm. The luminescence peak wavelength was about 600 nm or 800 nm, depending upon processing. Changes in the peak wavelength and intensity from these samples and other samples in which the crystallites were reduced in size by thermal oxidation, show trends which are generally consistent with quantum confinement, however, other mechanisms cannot be ruled out.

An investigation of as‐implanted material formed by high dose 40 keV oxygen implantation into silicon at 550 °C

Device grade 〈100〉 single crystal silicon wafers have been implanted with 40 keV oxygen ions (16O+) over the dose range of 1×1017–8×1017/cm2 at a temperature of 550±10 °C. Transmission electron microscopy, ion channeling, and secondary ion mass spectroscopy studies show that during implantation the critical dose required to form a buried oxygen‐rich amorphous (SiOx, x<2) layer is lower than 1×1017 O+/cm2. As the dose increases from 1×1017 to 4×1017/cm2 the thickness of the buried SiOx layer increases and there is a corresponding decrease in the thickness of the single crystal silicon top layer, with the oxygen concentration and residual radiation damage playing important roles in determining its position and thickness. A dose of 5×1017/cm2 results in a continuous surface amorphous layer, with a buried SiO2 sublayer being formed in the region corresponding to the implanted oxygen peak. With further increasing dose, the buried SiO2 sublayer grows primarily towards the surface. The results for the sample imp...

SIC BURIED LAYER FORMATION BY ION BEAM SYNTHESIS AT 950 C

Carbon implantation into Si at a temperature of 950 °C and at doses in the range of 0.2×1018 to 1×1018 cm−2 at 200 keV results in the formation of β‐SiC buried layers having the same orientation as the Si matrix. Under these conditions redistribution of the implanted species occurs enabling the formation of a buried layer of β‐SiC with an overlayer of high quality single crystal Si which is free of structural defects. The quality of the Si overlayer and the β‐SiC buried layer was investigated by Rutherford backscattering and transmission electron microscopy. A mechanism for the formation of the β‐SiC without the generation of defects in the Si matrix is proposed.

Transient enhanced diffusion in preamorphized silicon: the role of the surface

Abstract Experiments on the depth dependence of transient enhanced diffusion (TED) of boron during rapid thermal annealing of Ge-preamorphized layers reveal a linear decrease in the diffusion enhancement between the end-of-range (EOR) defect band and the surface. This behavior, which indicates a quasi-steady-state distribution of excess interstitials, emitted from the EOR band and absorbed at the surface, is observed for annealing times as short as 1 s at 900°C. Using an etching procedure we vary the distance xEOR from the EOR band to the surface in the range 80–175 nm, and observe how this influences the interstitial supersaturation, s(x). The supersaturations at the EOR band and the surface remain unchanged, while the gradient ds/dx, and thus the flux to the surface, varies inversely with xEOR. This confirms the validity of earlier modelling of EOR defect evolution in terms of Ostwald ripening, and provides conclusive evidence that the surface is the dominant sink for interstitials during TED.

Is there an effect of the proximity of a “free-surface” on the formation of End-Of-Range defects?

Abstract We have studied the effect of the proximity of the wafer surface on the formation of End-Of-Range defects. These experiments are aimed at elucidating the behavior, upon annealing, of the Si self-interstitial supersaturation responsible for transient enhanced diffusion of boron in pre-amorphized silicon wafers. By implanting with Ge at constant energy while carefully etching away increasing thicknesses of the amorphous layer the nucleation and growth of End-Of-Range defects have been studied by transmission electron microscopy. Clearly, no influence in the loop population can be shown even when using state-of-the-art “quantitative” electron microscopy. These results are explained by considering that the c a interface is a diffusion barrier for the Si self-interstitial atoms during the nucleation stage, i.e., when the supersaturation is high. Only after the solid phase epitaxial regrowth, i.e., during the coalescence of the loops when the supersaturation is already low, the surface can interact with the loops. However, this interaction is not measurable through the observation of extended defects and this leads to simplifying assumptions for the simulation of Transient Enhanced or Retarded Diffusion in pre-amorphized Si wafers.

The Effects of Dose and Target Temperature on Low Energy SIMOX Layers

The critical doses required to form a continuous buried stoichiometric oxide layer for 70 keV oxygen implantation either during implantation, Φ c 1 , or after implantation and annealing, Φ c A , are ≃7×10 17 O . /cm 2 and ≃3×10 17 O . /cm 2 , respectively. The dislocation density in the silicon overlayer and the distribution and density of silicon islands in the buried SiO 2 layer of the annealed (70 keV) SIMOX (separated by implantation of oxygen) samples are strongly dependent on the oxygen dose (Φ) and the target temperature (T i )

INTERSTITIAL TRAPPING EFFICIENCY OF C+ IMPLANTED INTO PREAMORPHISED SILICON : CONTROL OF EOR DEFECTS

Abstract The trapping of Si interstitials by C + implantation has been quantified by following the evolution of EOR defects during thermal annealing. Si (100) n-type wafers have been preamorphised by the implantation of 150 keV Ge + ions to a dose of 2 × 10 15 ions/cm 2 to form a 175 nm thick amorphous layer, followed by C + implantation at 65 keV ( R p = 175 nm to doses ranging from 3 × 10 13 ions/cm 2 to 3 × 10 15 ions/cm 2 . All samples were then annealed at 1000°C for 15 s. These structures have been investigated by RBS, TEM and SIMS. The mean radius of the EOR loops monotonically decreases with increasing dose of C + ions while their density increases. The number of Si self-interstitials stored in the loops also decreases with increasing carbon dose. This effect is associated with the capture of Si self-interstitials by SiC complexes. The effective trapping efficiency of carbon is about 1.18 interstitials per carbon atom, which is consistent with values obtained from studies of B transient enhanced diffusion.

FORMATION OF EXTENDED DEFECTS AND STRAIN RELAXATION IN ION BEAM SYNTHESISED SIGE ALLOYS

Abstract Single crystal SiGe alloy layers have been fabricated by implantation of Ge+ ions at energies ranging from 70 to 400 keV, followed by Si+ post-amorphisation and S olid P hase E pitaxial G rowth (SPEG). It is found that for each Ge+ implantation energy a critical value of the peak germanium concentration exists above which extended defects nucleate in the vicinity of the peak of the germanium depth profile and extend up to the surface. A critical value of the elastic energy stored in the structures ( ∼300 mJ / m 2 ) has been determined above which ion beam synthesised SiGe alloys relax, independently of the implantation energy. This empirical model has been found to successfully account for the results obtained in this work as well as in many other studies reported in the literature. For a regrowth temperature of 700°C, all samples investigated by XRD have been found to be almost fully strained, including samples containing relaxation-induced defects, indicating that, under these conditions, the energy transferred to the defects is very low. Complete strain relaxation is achieved after a second anneal step at 1000°C.

Characterization of extended defects in SiGe alloys formed by high dose Ge+ implantation into Si

The synthesis of SiGe/Si heterostructures by Ge+ ion implantation is reported. 400 keV Ge+ ions were implanted at doses ranging from 3 × 1016 to 10 × 1016 ions/cm2 into (001) Si wafers, followed by Si+ amorphisation and low temperature Solid Phase Epitaxial Regrowth (SPER). TEM investigations show that strained alloys can be fabricated if the elastic strain energy (Eel) of the SiGe layer does not exceed a critical value (E′el) of about 300 mJ/m2, which is independent of the implantation energy. Our analysis also suggests that “hairpin” dislocations are formed as strain relieving defects in relaxed structures. A “strain relaxation” model is proposed to explain their formation.

The formation of 3C-SiC in crystalline Si by carbon implantation at 950°C and annealing : a structural study

Abstract 3C-SiC(cubic) was formed by carbon implantation into (001) and (111)Si with doses ranging between 0.2 × 1018 and 1 × 1018cm−2 at 200 keV. During implantation the samples were maintained at a temperature ≈ 950°C and they were subsequently annealed at 1250°C for 6 h. In all samples a buried 3C-SiC layer was formed, which consists of a high density of 3C-SiC precipitates having the same orientation as the Si matrix. The coherency of the SiC precipitates with the Si matrix is shown for the first time by high resolution transmission electron microscopy (HRTEM) observations. The 22% misfit between the two lattices is accommodated by misfit dislocations, which form loops around the precipitates. From the shift of the displacement type moirepatterns which were formed by superposition of the mismatched 3C-SiC and Si lattices the portion of the misfit accommodated by partial dislocations was deduced. The stability of the SiC precipitates during the high temperature anneal is shown. A mechanism for the formation of the 3C-SiC, without the generation of defects in the Si matrix, is proposed. Low dose high temperature carbon implantation through a SiO2 capping layer into the near surface region of the underlying silicon results in the preferential nucleation and growth of 3C-SiC on the silicon side of the SiO2/Si interface, the advantages of such structures are discussed.