Tetsuya Homma

Single-shot measurement of carrier-envelope phase changes by spectral interferometry.

We demonstrated single-shot measurements of spectral interference between a white-light continuum generated in a hollow-fiber and its second harmonic. The interference has information on the carrier-envelope phase of an input pulse to the fiber and the time delay of the blue wing of the continuum. By analyzing the observed spectral interference, we estimated shot-by-shot changes of the carrier-envelope phase. This method is useful for determining the carrier-envelope phase changes of a low-repetition-rate, high-intensity laser.

Low dielectric constant materials and methods for interlayer dielectric films in ultralarge-scale integrated circuit multilevel interconnections

This paper reviews low dielectric constant materials for interlayer dielectric films in ultralarge-scale integrated circuit (ULSI) multilevel interconnections. The trends of ULSIs in the last decade were briefly described first. Then, the requirements for interlayer dielectric film properties and their formation techniques were explained. They are: (1) a low dielectric constant, (2) a surface planarity, (3) a gap-filling capability, and (4) a low residual stress. In contrast with the requirements, the interlayer dielectric films and related technologies developed in the last decade were reviewed. In the requirements, the low dielectric constant materials are strongly required because the device performance has been limited by signal propagation time and cross-talk in the multilevel interconnections. Furthermore, the low dielectric constant is also required for reduction of power consumption in ULSI operation. Finally, the low dielectric constant materials were summarized, and future trends of the low dielectric constant interlayer dielectric film technologies are discussed.

A Room Temperature Chemical Vapor Deposition SiOF Film Formation Technology for the Interlayer in Submicron Multilevel Interconnections

A new interlayer dielectric film formation technology for multilevel interconnection by catalytic chemical vapor deposition has been developed. This technique utilizes fluorotriethoxysilane and water vapor as gas source. The films deposited at 25°C have remarkably good properties, such as tightly bonded Si‐O networks with no OH radicals, large density value (2.20 g/cm3), small residual stress (50 MPa), low leakage current, and small dielectric constant (3.7), although the film contains residual fluorine and carbon atoms with , respectively. Based on the film characterization results, we speculate that the reaction sequence for the film deposition is: hydrolysis of fluorotriethoxysilane monomers, formation of siloxane oligomers with reaction by‐product (alcohol), adsorption of the oligomers to the wafer surface, and then polymerization. The electrical conduction mechanism study revealed that the Schottky emission was dominant for the electric conduction through the film. It also has clarified that the deposition film thickness has no dependence on Al wiring widths, and is completely isotropic with no crack or keyhole in the film.

A Selective SiO2 Film‐Formation Technology Using Liquid‐Phase Deposition for Fully Planarized Multilevel Interconnections

A selective SiO 2 film-formation technology using liquid-phase deposition (LPD) around room temperature for fully planarized multilevel interconnections is developed. The LPD technique utilizes supersaturated hydrofluosilicic acid (H 2 SiF 6 ) aqueous solution as a source liquid. The LPD-SiO 2 films can be selectively formed on chemical vapor deposition (CVD) SiO 2 underlayers in the trenches between photoresist patterns or tungsten wiring with photoresist as mask. For polysilicon patterns with photoresist masks, the LPD-SiO 2 films creep along the polysilicon and photoresist sidewalls

Carrier-envelope-phase stabilized chirped-pulse amplification system scalable to higher pulse energies

We have demonstrated a carrier-envelope phase (CEP) stabilized chirped-pulse amplification (CPA) system employing a grating-based pulse stretcher and compressor and a regenerative amplifier for the first time. In addition to stabilizing the carrier-envelope offset phase of a laser oscillator, a new pulse selection method referenced to the carrier-envelope offset beat signal was introduced. The pulse-selection method is more robust against the carrier-envelope offset phase fluctuations than a simple pulse-clock dividing method. We observed a stable fringe in a self-referencing spectrum interferometry of the amplified pulse, which implies that the CEP of amplified pulse is stabilized. We also measured the effect of the beam angle change on the CEP of amplified pulses. The result demonstrates that the CEP stabilized CPA is scalable to higher-pulse energies.

An asymmetric sidewall process for high performance LDD MOSFET's

An asymmetric LDD sidewall spacer technology is presented which gives a high drivability of LDD MOSFET without sacrificing hot carrier immunity. The asymmetric spacer is fabricated by using a selective oxide deposition technique. The process implemented in a CMOS fabrication sequence requires no additional masking step. The fact that no reliability problems are introduced in the transistor characteristics by the selective oxide deposition process is also examined. >

Instability of Si-F bonds in fluorinated silicon oxide (SiOF) films formed by various techniques

Abstract Instability of Si—F bonds in fluorinated silicon oxide (SiOF) films is studied. Al wiring corrosion and underlayer SiO 2 etching problems are the major issues for the use of SiOF interlayer dielectric films. To clarify the mechanism, three kinds of SiOF films have been used for this study. They are: (i) a fluorinated silicon oxide (SiOF) film prepared by room-temperature chemical vapour deposition (RTCVD) using fluorotriethoxysilane and pure water as gas sources; (ii) a fluorinated spin-on-glass (SOG) film prepared by fluorotrialkoxysilane vapor treatment (FAST); and (iii) a room-temperature liquid phase deposition (LPD) SiOF film. The initial refractive indices for the RTCVD-SiOF, FAST-SOG and LPD-SiOF films are 1.400, 1.398 and 1.433, respectively. After conducting a pressure cooker test (PCT) at 125 °C for 520 h, the refractive indices for the RTCVD-SiOF, FAST-SOG and LPD-SiOF films increase to 1.450,1.440 and 1.436, respectively. The Si—O bond peak absorption coefficient for the LPD-SiOF film decreases at the early stage of PCT, but those for the RTCVD-SiOF and FAST-SOG films increase at the early stage of PCT. The initial Si—F bond peak absorption coefficient for the RTCVD-SiOF film is much higher than those for the LPD-SiOF and FAST-SOG films. It decreases drastically in the PCT time ranging from 0 to 140 h. The Si—F bond peak absorption coefficients for the FAST-SOG and LPD-SiOF films show a slow reduction, as compared with that for the RTCVD-SiOF film at the early stage of PCT. Although the OH peak absorption coefficients for the RTCVD-SiOF and FAST-SOG films increase at the early stage of PCT and level off at 50 h, that for the LPD-SiOF film increases at 306 h. After conducting 520 h PCT, concentrations of fluorine atoms for the RTCVD-SiOF and FAST-SOG films decrease by three orders and two orders of magnitudes, respectively. However, the LPD-SiOF film has a limited change in the fluorine concentration, as compared with those for the RTCVD-SiOF and FAST-SOG films. The thicknesses for all of the films remain almost unchanged after PCT for 520 h.

Xenon Flash Lamp Annealing of Poly-Si Thin Films

We have investigated xenon (Xe) flash lamp annealing for the crystallization of amorphous silicon (a-Si) films for polycrystalline silicon (poly-Si) thin film transistors on glass substrates. The Xe flash lamp emits white light with a wavelength range of 400-800 nm for 40 μs, thereby instantaneously supplying the energy necessary to crystallize a-Si films to poly-Si films. The distance between electrodes in the lamp is 1000 mm, the bore diameter is 10 mm, and the peak voltage is up to 20 kV. The sample structure is a-Si (50 nm)/SiOx (100 nm) deposited on a glass substrate by plasma-enhanced chemical vapor deposition using SiH 4 gas. An average grain size of 500 nm is obtained without substrate heating during Xe flash lamp annealing when the light energy density is 1.82 J/cm 2 . The grain size is less than 50 nm at 1.55-1.78 J/cm 2 , and a significant grain growth occurs at 1.82 J/cm 2 . The light energy is absorbed by the whole a-Si film, because the Xe flash lamp emits light with a wide wavelength range of 400-800 nm. Therefore, when the light energy exceeds its threshold at which the a-Si film melting point is observed, a-Si films can be partially melted and subsequently crystallized at the top and bottom surfaces, thereby forming large-grain poly-Si.

Properties of Fluorinated Silicon Oxide Films Formed Using Fluorotriethoxysilane for Interlayer Dielectrics in Multilevel Interconnections

Properties of a fluorinated silicon oxide (SiOF) film for interlayer dielectrics in multilevel interconnections of ultralarge-scale integrated circuits (ULSIs) are investigated. The SiOF films are formed by a room temperature chemical vapor deposition (RTCVD) technique using fluorotriethoxysilane [FSi(OC 2 H 5 ) 3 , FTES] and pure water as gas sources. The SiOF film property changes by annealing at 400 or 900°C are studied. Although the Si-O bond absorption peak position in the Fourier transform infrared (FTIR) spectrum is not changed by 400°C annealing, the peak position for the 900°C annealed SiOF films shifts to low wave numbers. The full width at half-maximum (FWHM) of the Si-O bond absorption peak increases by 400°C annealing, and it further increases by 900°C annealing. The tendency of the Si-F bond peak absorption coefficient change is inverse to the change of FWHM, indicating that fluorine influences the Si-O bond nature. Other properties such as the fluorine atomic concentration, refractive index, etching rate, shrinkage, residual stress, and leakage current density are changed by the annealing. These property changes are due to changes in the chemical bonding structure. No crack is observed for the SiOF films formed on aluminum wiring patterns after 400°C annealing.

Stability of a new polyimide siloxane film as interlayer dielectrics of ULSI multilevel interconnections

Abstract Stability of a new polyimide siloxane (PSI) film as interlayer dielectrics of ULSI multilevel interconnections is studied. The PSI films, involving Si-phenyl bonds, are designed to have a three-dimensional polymer structure by crosslinking through Si-O bonds. It has been revealed that the PSI films are more stable than conventional polyimide films in terms of thermal and electrical properties at high temperatures. The PSI films decomposition temperature is as high as 500°C. The coefficient of thermal expansion is 4 × 10−5 K−1 in the temperatures of 25–450°C. The abrupt thermal expansion that usually occurs at around 270°C for conventional polyimide films is eliminated. The residual stress for the PSI films is less than 20 MPa, and is lower than for conventional polyimide films. Leakage currents through the PSI films at temperatures above 100°C are over one order of magnitude lower than those through conventional polyimide films. Good surface planarization characteristics are obtained for the PSI films by decreasing the molecular weight and viscosity of the polyamic acid solutions. No void is observed acid the films formed on 2.4 μm thick silicon dioxide lines with 1.1 μm width and 1.5 μm spacing, using polyamic acid solutions with precursor molecular weights ranging from 2900 to 9600.