Giora Yaron

Capacitance voltage characterization of poly SiSiO2Si structures

Abstract The high frequency C-V characteristics of poly SiSiO 2 Si capacitors have been studied. It is shown that the poly SiSiO 2 Si capacitor C - V characteristics are significantly different from the corresponding metal-SiO 2 Si capacitor due to field penetration into the poly Si layer. A comparison of the theoretical and measured C-V characteristics gives an estimate of the surface state charge density at the poly SiSiO 2 interface and indicates that the surface potential behavior of this interface is trap and surface state dominated up to poly silicon impurity concentrations of approximately 10 17 cm −3 .

Application of laser annealing techniques to increase channel mobility in silicon on sapphire transistors

Laser annealing techniques were successfully incorporated into standard metal‐oxide‐semiconductor silicon‐on‐sapphrie (MOS/SOS) processing to increase transistor channel mobility. Silicon islands were photolithographically defined and chemically etched (by KOH) on standard SOS wafers. The islands were exposed to radiation from an excimer laser (λ=2490 A) having a pulse duration of 25 nsec, a beam size in the range 0.1–0.2 cm2, and an energy density in the range 0.5–1.0 J/cm2. Using standard processing techniques, MOS transistors were fabricated and characterized. It was found that MOS transistors fabricated over islands exposed to a beam having an energy density of 0.8 J/cm2 exhibit a 30% increase in channel mobility.

Characterization of phosphorus implanted low pressure chemical vapor deposited polycrystalline silicon

Abstract Thin (3000–5000A) low pressure chemically vapor deposited (LPCVD) films of polycrystalline silicon suitable for microelectronics applications have been deposited from silane at 600°C and at a pressure of 0.25 Torr. The films were phosphorus implanted at 150 KeV and electrically characterized with the annealing conditions and film thickness as parameters, over a resistivity range of four orders of magnitude (10 3 –10 7 Ω/□) . Annealing during silox deposition was found to result in a lower film resistivity than annealing done in nitrogen atmosphere. Resistivity measurements as a function of temperature indicate that the electrical activation energy is a linear function of 1 N ( N is the doping concentration), changing from 0.056 eV for a doping concentration of 8.9 × 10 18 cm −3 to 0.310 eV for doping concentration of 3.3 × 10 18 cm −3 . The grain boundary trap density was found to have a logarithmically decreasing dependence on the polysilicon thickness, decreasing from 1.3 × 10 13 cm −2 for 2850A polysilicon film to 8.3 × 10 12 cm −2 for 4500A polysilicon film.

Laser annealing effects on the electrical characteristics of SOS transistors

Abstract Successful incorporation of laser annealing techniques into standard processing methods requires that the electrical characteristics of the devices not be degraded. In this work, a range of energy densities from pulsed u.v. and visible lasers which can be utilized in silicon on sapphire (SOS) technology to improve device performance without introducing any deleterious side effects is determined experimentally. Silicon islands were photolithographically defined and chemically etched (KOH) on standard SOS wafers which were subsequently exposed to pulsed (25 nsec) ruby ( λ = 6943 A ) and excimer ( λ = 2490 A ) laser radiation. Comparative studies of the effect of front and back side (through the sapphire) irradiation of the silicon on device performance were conducted. Using standard processing techniques, MOS transistors were fabricated after laser irradiation and electrically characterized. It was found that under certain conditions utilization of lasers in SOS processing, can result in an increase in the interface state density at both the top 〈100〉 Si-SiO2 interface and the bottom Al2O3-Si interface. However, a set of conditions exists, in which it is possible to apply laser annealing to standard SOS processing so as to increase MOS/SOS transistor channel mobility by over 30% without causing any degradation of the device electrical characteristics.

Large photoenhancement of hydrogen-implanted quantized accumulation layers on ZnO surfaces

We report in this letter on an interesting and unexpected effect which is not fully understood yet. Strong hydrogen‐implanted accumulation layers on ZnO surfaces, produced and maintained at 80 K, can be further enhanced by illumination with visible light. The enhancement attained is surprisingly large, amounting to a twofold increase in surface electron density, up to 6×1014 cm−2. The photoenhanced layer is less than 10–20 A in width, thus constituting a two‐dimensional electron system, which is by far the strongest ever attained on any semiconductor surface. Measurements of the electron transport characteristics and of the spectral response of the photoenhancement process are presented.

Improved stacked‐structure oxide by laser annealing

Laser annealing techniques were successfully incorporated into standard MOS processing to improve the quality of oxides grown over polycrystalline silicon (polysilicon). Polysilicon films (5000 A thick) deposited over 1000 A SiO2, grown over (100) bulk Si were exposed to a short pulse (20 nsec) of ruby laser radiation at an energy density of 1 J/cm2 and subsequently oxidized at 925 °C. The resulting oxides over the polysilicon were found to have leakage currents which are lower by over three orders of magnitude than oxides grown over polysilicon films which were not laser annealed. C‐V measurements taken on the underlying polysilicon‐SiO2‐Si structure indicate that no deleterious effects were produced in the underlying structure by the laser radiation.

ELECTRICAL CHARACTERISTICS OF LASER-ANNEALED POLYSILICON RESISTORS FOR DEVICE APPLICATIONS

Laser annealing of polysilicon was studied and used to improve the control and reproducibility of resistors fabricated from ion-implanted polysilicon films (0.5 μ m). We found that, with particular laser annealing conditions, a ±10% variation in the doping concentration results in only a factor of two change in the resistivity, which is at least a factor of five improvement over thermally annealed polysilicon resistors. This improvement is attributed not only to increased polysilicon grain sizes but also to a significant reduction in the grain boundary trap density. Analysis of resistivity data in terms of the carrier trapping model shows that the grain boundary trap density is reduced from 8.5 × 10 12 cm –2 for thermally annealed resistors to 1.1 × 10 12 cm –2 for laser-annealed resistors.

Persistent photoenhancement of hydrogen-implanted quantized accumulation layers on ZnO surfaces

Abstract Strong hydrogen-implanted accumulation layers on ZnO surfaces, produced and maintained at 80 K, can be further enhanced by illumination with visible light. The attainable enhancement is surprisingly large, resulting in an enormous surface electron density of up to 6 × 10 14 cm −2 , and persists indefinitely after the light is switched off. The photoenhanced layer is practically identical in width (10–20 A) and transport characteristics to the implanted layer upon which it is based. Thus, it constitutes, just as the initial hydrogen-implanted layer, a two-dimensional electron accumulation layer, by far the strongest ever attained on any semiconductor surface. The photoenhancement effect is not fully understood. Various aspects of this effect are studied in an attempt to gain some insight into the processes involved. On the basis of the results presented we tentatively suggest that latent centers consisting of H + 2 species are introduced by the hydrogen implantation, in addition to the fully ionized proton donors responsible for the implanted accumulation layer. Illumination dissociates these species and shifts the protons so produced into sites in which they become fully ionized, thus augmenting the surface electron density of the implanted surface.

CW LASER ANNEALING OF ION-IMPLANTED POLYCRYSTALLINE SILICON FILMS

Resistivity changes and structural modifications produced in phosphorus implanted polysilicon films by cw laser radiation are presented and discussed. Samples containing implant doses of 1 × 10 12 cm –2 to 5 × 10 14 cm –2 at 150 keV were irradiated at laser power levels of 2 W to 12 W and with repetitive scans at constant laser power. As the implant dose is decreased, higher laser powers are required to produce large decreases in polysilicon resistivity. Although large grains are formed at high laser powers, significant resistivity decreases in the high dose implants can be achieved using multiple scans at lower laser powers where large grains are not produced. These results are discussed in terms of reduction of trapping states and selective desegregation of dopants from grain boundaries.

Photogeneration of narrow quantum wells on ZnO surfaces

Abstract Visible-light illumination of accumulation layers on Zn0 surfaces produced by hydrogen-ion implantation at 80 K results in a substantial enhancement of the surface electron density, up to the enormous value of 6x1014 cm-2. The photoenhanced layer persists indefinitely after the light is switched off, and has an effective width of 10–20 A. On the basis of the results presented we tentatively suggest that in addition to the fully-ionized proton donors responsible for the initial implanted accumulation layer, H2+ ions are also introduced beneath the surface by the hydrogen implantation. Illumination dissociates these species and shifts the protons so produced into sites in which they become fully ionized, thus augmenting the surface electron density of the implanted surface.