Kazutoshi Shiba

Photoluminescence from anodized and thermally oxidized porous germanium

Abstract A broad photoluminescence (PL) band at ~ 1.17 eV is observed for as-anodized porous Ge (PG) at room temperature. Oxidation at 600 °C induces a new intense PL band at ~ 2.15 eV whose spectral shape remains almost unchanged with progressive oxidation. Considering this result and the observed temperature dependence and decay time of the PL from thermally oxidized PG, it has been suggested that the radiative recombination through localized states is a possible pathway of the emission.

Luminescence from Thermally Oxidized Porous Silicon

Porous silicon produced by means of anodization in an HF-based solution has been oxidized in an N2+O2 gas mixture at 900 or 1000°C to realize the ideal passivation of a porous Si surface with thermally grown oxide instead of hydrogen termination. Visible photoluminescence at room temperature has been observed for porous Si whose surface is terminated by oxygen. It is shown that the luminescence from the porous silicon is extremely stable under Ar+ laser light (488 nm) irradiation even in air at room temperature. A possible mechanism for the visible light emission is discussed on the basis of the excitation intensity dependence of the luminescence.

Optical Absorption and Photoluminescence of Self-Assembled Silicon Quantum Dots

Hemispherical silicon quantum dots with an average height of 6.3, 3.3 or 1–2 nm covered with an ultrathin SiO2 layer have been spontaneously formed on SiO2/Si(100) and quartz substrates by the thermal decomposition of pure silane at low pressure. It is found that the optical absorption edge determined from photothermal deflection spectroscopy exhibits blue shifts from 1.9 to 2.5 eV when the average dot size was decreased from 6.3 to 1–2 nm and correspondingly, the luminescence peak energy increases from 1.2 to 1.4 eV at room temperature. The large Stokes shift suggests that the localized, radiative recombination centers existing presumably in the SiO2/Si dot interface are responsible for the efficient, room-temperature luminescence from the silicon quantum dots.

Evaluation of CVD/PVD multilayered seed for electrochemical deposition of Cu-damascene interconnects

Multilayered seed for electrochemical deposition (ECD) of Cu was investigated to develop narrow-pitched, dual-damascene Cu interconnects that will be required for future ULSI devices. The seed was obtained by the physical vapor deposition (PVD) of a Cu film followed by the chemical vapor deposition (CVD) of a Cu film. The seed of the thinner CVD-Cu element and the thicker PVD-Cu element demonstrated better filling characteristics in high-aspect ratio vias. Good current-voltage characteristics were demonstrated using the multilayered seed technique with Cu dual-damascene interconnects (0.28 /spl mu/m minimum via size) resulting in a via resistance about 0.7 /spl Omega/. In addition, ring-oscillator circuits were fabricated by integrating the double-layered interconnects with a transistor having a 0.18 /spl mu/m gate width. The propagation delay per inverter, which had an interconnect with 10/sup 4/ vias, was about 6 ns. We successfully fabricated multilevel Cu-damascene interconnects, which are available for future high-speed devices using this multilayered seed technique.

A robust embedded ladder-oxide/Cu multilevel interconnect technology for 0.13 μm complementary metal oxide semiconductor generation

A robust embedded ladder-oxide (k=2.9)/copper (Cu) multilevel interconnect is demonstrated for 0.13 µm complementary metal oxide semiconductor (CMOS) generation. A stable ladder-oxide intermetal dielectric (IMD) is integrated by the Cu metallization with a minimum wiring pitch of 0.34 µm, and a single damascene (S/D) Cu-plug structure is applied. An 18% reduction in wiring capacitance is obtained compared with that in SiO2 IMDs. The superior controllability of metal thickness by the S/D process enables us to enhance the MPU maximum frequency easily. The stress-migration lifetime of vias on wide metals for the S/D Cu-plug structure is longer than that for a dual damascene (D/D) structure. Reliability test results such as electromigration (EM), the temperature dependant dielectric breakdown (TDDB) of Cu interconnects, and pressure cooker test (PCT) results are acceptable. Moreover, a high flexibility in a thermal design is obtained.

Dual Damascene Interconnect Technology for 130-nm-node Complementary Metal–Oxide–Semiconductor Devices Using Ladder-Oxide Film

A 0.34-µm-pitch Cu dual damascene interconnect technology using a low-k ladder-oxide film (k=2.9) is developed for 130-nm-node complementary metal oxide semiconductor (CMOS) devices. Photoresist poisoning was improved by adopting the ladder-oxide film with annealing before the photolithography step. The fence structures around via openings caused poor Cu gap filling. The problem was solved by controlling the filling height of a bottom anti-reflective coating and by eliminating the photoresist poisoning. Furthermore, no degradation of the ladder-oxide film upon photoresist stripping was observed. It was demonstrated that these technologies could be applied to a product-level application-specific integrated circuit chip with a seven-level Cu interconnect.

Fabrication of silicon nanocrystallites by oxidation/annealing of polysilane films and their luminescence properties

Abstract Hydrogenated polysilane films prepared from a SiH 4 plasma were oxidized at room temperature and subsequently annealed at temperatures ranging from 800 to 1000 °C. It is found that the 1000 °C annealed films consist of Si nanocrystallites embedded in SiO 2 and exhibit stable intense luminescence peaked at ∼1.5 eV under 488 nm excitation at room temperature. On the basis of the temperature and excitation power dependences of the steady-state and time-resolved luminescence from the annealed films, radiative recombination is thought to occur through localized states in the Si/SiO 2 interface region.

Multilevel Aluminum Dual-Damascene Interconnects for Process-Step Reduction in 0.18 µm ULSIs

Multilevel Al dual-damascene interconnects are fabricated with laminated SiO2/SiON films for the reduction of the number of steps in the fabrication process. In the dual-damascene structure composed of the SiO2 in the line area and the SiON in the via area, the SiON films act not only as the etch-stop layer for line-trench formation but also as the absorbent layer in KrF lithography, thus reducing the number of steps in the fabrication process by 17%. The Al dual-damascene interconnects have a small via resistance of 1–2 Ω/via at a 0.28 µm diameter. The low resistance is retained in the stacked via structure. This process is especially applicable for fabricating the lower level interconnects in low-cost, 0.18 µm complementary-metal-oxide-semiconductor ULSI.

Device-grade a-SiGe:H alloys prepared by nanometer deposition/H2 plasma annealing method

Abstract Hydrogenated amorphous silicon-germanium (a-SiGe:H) alloys are fabricated by alternately repeating a 3 nm thick a-SiGe:H deposition and subsequent hydrogen plasma annealing at various rf power densities and substrate temperatures. The bonded-hydrogen content decreases with increasing rf power density or substrate temperature. It is found that the hydrogen-annealed films with an optical bandgap of 1.45–1.52 eV exhibit high photoconductivity (> 10 −5 S/cm) under AM1 light (100 mW/cm 2 ) illumination and high photosensitivity (> 10 4 ). A significant reduction of the gap states due to the hydrogen annealing is also suggested from the luminescence properties as well as the substitutional doping efficiency.

Luminescence Study of Thermally-Oxidized Porous Si under Subgap or Overgap Excitation

The temperature dependence and the temporal decay of photoluminescence from thermally-oxidized porous silicon have been studied under 1.80 or 2.54 eV excitation which is below or above the optical bandgap value of 2.2 eV determined from the luminescence excitation spectrum. No significant difference between luminescence spectra under the subgap and the overgap excitation is observed at emission energies below 1.65 eV. The luminescence under the subgap excitation exhibits a weak temperature dependence compared to the overgap excitation case. This can be interpreted in terms of the suppressed thermal emission-rate for carriers photogenerated near the radiative recombination centers to the extended states. It is also revealed that, in the pulsed subgap excitation, the luminescence shows a fast decay in the time region below 1 µs and a slow decay component follows, as observed in the case of the pulsed overgap excitation. The carriers photogenerated directly at radiative recombination centers or neighboring sites under the subgap excitation are likely to be responsible for the observed fast decay.