Yupu Li

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...

Analysis of thin‐film silicon‐on‐insulator structures formed by low‐energy oxygen ion implantation

The characteristics of the formation and growth of buried oxide layers, formed by oxygen implantation into silicon at lower energies (50–140‐keV 16O+), have been studied using secondary‐ion mass spectrometry. Some results have been checked and compared with the results obtained by Rutherford backscattering and cross‐sectional transmission electron microscopy. The critical doses, required to form a continuous buried stoichiometric oxide layer during implantation (ΦIc) and after annealing (ΦAc) have been estimated from experimental results. The thicknesses of the silicon overlayer (TASi) and buried silicon dioxide layer (TASiO2) for the annealed wafers have also been estimated. A set of semi‐empirical formulas for ΦIc, ΦAc, TASi, and TASiO2 has been introduced. These formulas can be used to quickly calculate the critical doses and the layer thickness values.

Formation of thin silicon films using low energy oxygen ion implantation

Abstract SIMOX (separation by implanted oxygen) is an established technique to produce device worthy silicon-on-insulator structures. Current interest in thin film fully depleted CMOS devices in SIMOX material has placed emphasis on producing silicon overlayers of 100 nm thickness or less. Thin film SIMOX substrates have been prepared using halogen lamps, to preheat and provide background heating during oxygen ion implantation in the relatively low energy range 50–140 keV. The resulting structures have been studied by RBS, cross-sectional TEM and SIMS. This paper reports on the crystalline quality of the silicon overlayers and discusses the viability of low energy oxygen implantation to produce thin film SIMOX structures suitable for VLSI device fabrication.

4-11 Mu-M Infrared-Emission and 300 K Light-Emitting-Diodes From Arsenic-Rich Inas1-Xsbx Strained-Layer Superlattices

Arsenic-rich InAs/lnAs1-xSbx strained layer superlattices (SLSs) grown on GaAs substrates by molecular beam epitaxy (MBE) are studied for their potential application as infrared emitters. The long-wavelength emission (4-11 mu m) is highly sensitive to superlattice design parameters and is accounted for by a large type-II band offset, greater than in previously studied antimony-rich InSb/lnAs1-xSbx SLSs. High internal PL efficiencies (>10%) and intense luminescence emission were observed at these long wavelengths despite large dislocation densities. Initial unoptimized InAs/lnAs1-xSbx SLS light emitting diodes gave approximately=200 nW of lambda =5 mu m emission at 300 K.

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 )

Low energy, oxygen dose optimization for thin film separation by implanted oxygen

Low energy oxygen ions of 50 to 70 keV were implanted to doses of 1 × 1018 O+ cm−2 for the formation of separation by implanted oxygen (SIMOX) substrates. Owing to the reduced energy straggle of the low energy ions, it is possible to achieve a buried oxide layer with a lower dose (than with higher energies) which offers the potential advantage of a reduced fabrication cost for SIMOX material. However, defects, including threading dislocations and silicon islands near the lower SiO2Si interface, have been observed in low energy oxygen implanted material. A recipe to reduce the density of these islands is proposed, involving implantation of a dose of oxygen which is less than the critical dose Φc required to form a continuous layer of stoichiometric SiO2 during implantation. This not only reduces the density of silicon islands but also the ion implantation damage in the silicon overlayer is reduced and hence, after annealing, fewer threading dislocations (less than 105 cm−2) are present. The actual dose was determined experimentally for oxygen ions of energy 70 keV and a substrate temperature of 680 °C and was found to be approximately 0.33 × 1018O+ cm−2.

Oxygen isotopic exchange between an 18O+ implanted Si layer and a natural SiO2 capping layer during high‐temperature annealing

To understand the effects of the SiO2 capping layer on the growing buried SiO2 layer a silicon wafer was implanted at 680 °C with 90 keV 18O+ to a dose of 4.3×1017 18O+/cm2. After the deposition of an ∼500 nm natural SiO2 cap by the plasma sputtering, one piece of the implanted wafer was annealed at 1360 °C for 6 h in a quartz silica tube in flowing nitrogen. There is clear evidence of diffusional mixing of the oxygen isotopes from the cap into the 18O+ implanted layer during this annealing step, indeed a surprisingly large amount has taken place, in that approximately 41% of 18O contained within the buried SiO2 layer has been exchanged with the cap.

Study of the microstructure of low energy (70 keV) oxygen implanted silicon

Device grade (100) single crystal silicon wafers have been implanted with 70 keV oxygen ions over a dose range from 3.3×1017 /cm2 to 10×1017/cm2 at a temperature of 680 °C. The wafers were subsequently annealed at 1320 °C for 6 h. Transmission electron microscopy and ion channeling studies show that both the as‐implanted microstructure and the damage distribution play an important role in determining the final microstructure of the annealed wafer. As the dose increases so does both the values of χmin for both as‐implanted and annealed wafers, and the threading dislocation density in the silicon overlayer of the annealed wafers. For the wafer implanted with 70 keV oxygen ions at the lowest dose (3.3×1017/cm2), the threading dislocation density in the silicon overlayer after annealing was less than 105/cm2.

A study of 2H trapping in YBa2Cu2O7−δ /LaAlO3 〈100〉 samples under 2H+ irradiation

A c‐axis oriented YBa2Cu3O7−δ film, 180–230 nm thick, deposited onto 〈100〉 LaAlO3 by dc sputtering was irradiated at room temperature with 50 keV 2H+ (deuterium) ions to a dose of 1×1016 cm−2. Secondary‐ion‐mass spectroscopy analysis shows that after implantation the implanted 2H is trapped in both the film and the substrate. For example, when the thickness of the YBCO film is equal to ∼180 nm, it contains about 4.5% of the retained dose. The as‐implanted 2H distribution is essentially Gaussian‐like and the depth (Rp) of maximum 2H concentration is ∼485 nm. It is obvious that the target crystallinity has to be taken into account for the range data, since the experiment values (Rp,Rp, and ΔRp) are obviously larger than the corresponding values from the transport of ions in matter code. This implantation makes the YBa2Cu3O7−δ film more granular. Within the irradiated LaAlO3 substrate, a damaged band was observed by cross‐sectional transmission electron microscopy, which was centered at about 85% of Rp(exp).

SIMS, RBS, ion channelling, and TEM studies of the low energy SIMOX structures

Abstract Device grade single crystal 〈100〉 silicon wafers have been implanted with 70 keV oxygen ions over a dose range from 3.3 × 1017 to 10 × 1017/cm2 at 680 °C and subsequently annealed at 1320 °C for 2 or 6 h. Secondary ion mass spectrometry (SIMS), Rutherford backscattering (RBS), ion channelling, and planar and cross sectional transmission electron microscopy (TEM) have been used to follow the evolution of the as-implanted and annealed structures. It has been shown that the mechanisms responsible for the buried oxide layer formation at 70 keV appear to be similar to those at 200 keV, with the as-implanted microstructure playing an important role in determining the final structure of the annealed wafer. As the dose increases the values of Xmin in the as-implanted and annealed samples increases as does the threading dislocation density in the silicon overlayer of the annealed wafers. Increasing anneal time (from 2 to 6 h) improves the two interfaces (Si/SiO2 and SiO2 /Si), but has little effect on the dislocation density and the distribution of silicon islands.