E. Arai

Effects of minute impurities (H, OH, F) on SiO/sub 2//Si interface as investigated by nuclear resonant reaction and electron spin resonance

The effects of minute amounts of impurities (H, OH, and F) in SiO/sub 2/ are investigated to obtain a guideline for improving the reliability of MOS devices. To examine the behavior of hydrogen, deuterium (D) is adopted as a tracer. The quantity of deuterium dissolved in SiO/sub 2/ is measured by the D(/sup 3/He,p)/sup 4/He nuclear resonant reaction (NRR) technique. The Influence of the impurities on the SiO/sub 2/-Si interface structure is studied by electron spin resonance (ESR) measurement. Hot-carrier injection with MOS capacitors and transistors are examined to determine the effects of minute impurities on the electrical characteristics of gate SiO/sub 2/ and the correlation of this effect with the NRR and ESR experimental results. It was found that significant amounts of D/sub 2/O are diffused into SiO/sub 2/, even at 200 degrees C, and these dissolved D/sub 2/O molecules are eliminated at temperatures above 700 degrees C. The number of unpaired bonds at the interface increases with decrease of dissolved water in SiO/sub 2/. The disappearance of the interface traps after high-temperature annealing above 800 degrees C is thought to be due to the viscous flow of SiO/sub 2/ and to the interface reoxidation. Reducing the hydrogen and relaxing the interface strain are essential for improving the MOS device endurance against hot carriers. >

Stoichiometry measurement and electric characteristics of thin‐film Ta2O5 insulator for ultra‐large‐scale integration

Elastic recoil detection and Rutherford backscattering were adapted to a stoichiometric study of thin Ta2O5 films deposited on Si substrates by means of the reactive sputtering (SP) and chemical‐vapor‐deposition (CVD) method. Before annealing the samples it was observed that (i) the atomic ratio of oxygen to tantalum in the SP films agreed with 5/2 within the experimental accuracy and (ii) the CVD films have less oxygen content than the other samples. The specimens were annealed for 30 min under the following three conditions: (a) in dry oxygen ambient at 800 °C; (b) in ozone atmosphere under ultraviolet irradiation (UV ozone) at 300 °C; and (c) two‐step treatment of (a) after the (b) process. Each oxidizing process has shown a certain positive effect on the thin CVD samples. Among them, the two‐step treatment has proven to be very effective to restore the stoichiometry of 5/2 in the CVD films. Additionally the thickness of contaminant carbon films on the surface of the samples has been reduced by anneali...

TOF ERD experiments using a 10 MeV 35Cl beam

Abstract An analysis system has been established for stoichiometry of thin layers composed of chemical elements which range from light elements to medium-heavy ones such as Fe. A beam of 10 MeV 35C1 was used to recoil nuclei from the target. The mass of recoils has been identified by a counter telescope which consists of two timing detectors for time of flight (TOF) and a surface barrier detector (SBD) for energy measurement of each particle. The detection efficiency of the TOF spectrometer was determined as a function of atomic number Z for light elements up to chlorine. Experimental results are reported for LiF/Si, BF2-implanted SiO2/Si and FeOv/C samples. Factors which affect the accuracy of the present method are discussed.

Stoichiometry and profiling of surface layers by means of TOF-E ERDA and RBS

Abstract An experimental method is established for stoichiometric analysis and profiling of the surface region of solids by adapting a TOF-E counter telescope to acquire spectra of the atomic mass and the kinetic energy of recoils. A 10 MeV 35Cl beam, delivered by a small tandem, bombards samples to eject the recoils. The samples include Ta2O5 films deposited onto Si substrates. Advantages and the limit of applicability of the present method are discussed.

A new method for atmospheric tritium measurement by a source modulation technique

Abstract A new method for the measurement of atmospheric tritium has been developed. The mixture of sample gas and pure air was fed to a large volume ionization chamber, where the mixing ratio was modulated by a sine function. For the demodulation, cross-correlation was taken between the ionization current and the modulation signal. Background due to the white-noise dark current was reduced drastically, and a detection sensitivity of 0.1 μμ Ci cm −3 was realized.

Depth profiling of porous silicon surface by means of heavy-ion TOF ERDA

Abstract In recent years the properties of porous silicon, especially the photoluminescence have found widespread interest. In order to acquire more information on this unique material we have performed depth profiling of hydrogen, carbon, oxygen, fluorine and silicon. Among these elements, we have observed a tight correlation between the form of the hydrogen profile and the intensity of photoluminescence. The probe beam for the heavy ion TOF ERDA consisted of 13.6 MeV 35 C1 ions accelerated by a small tandem. A time-of-flight spectrometer was adapted to register heavy recoils where the mass was determined by simultaneously measuring the kinetic energy and flight time of each recoiled particle using a surface barrier detector (SBD) and two timing detectors, respectively. In order to measure hydrogen recoils we employed a conventional ERD counter consisting of 6 μm mylar foil and a SBD set at a somewhat larger angle than the TOF.

Thermal behavior of fluorine in SiO2 and Si investigated by the 19F(p,αγ) 16O reaction and secondary‐ion mass spectrometry

Thermal changes of implanted fluorine distributions in a SiO2 film and a (100)‐oriented Si single crystal were investigated by the 19F(p, αγ) 16O reaction and secondary‐ion mass spectrometry. Fluorine in the Si accumulates to a damaged region (consistent with a Monte Carlo simulation) after annealing above 700 °C for 30 min. This effect is not observed in the SiO2. Once the fluorine is trapped by the damaged region, nearly 80% of the fluorine stays in the silicon after annealing at 800 °C. In contrast, only 10% of implanted fluorine remains in the SiO2 after annealing at 800 °C. These effects are explained by assuming the difference in the natures of imperfections in these samples. Above 1000 °C, most of the fluorine diffuses out of both systems.

Investigation of fluorine in SiO2 and on Si surface by the 19F(p,αγ)16O reaction, secondary‐ion mass spectrometry, and x‐ray photoelectron spectroscopy

A fluorinated thermal SiO2, grown after HF surface treatment without de‐ionized water rinse, was estimated to contain ∼3×1013 cm−2 of fluorine by the 19F(p,αγ)16O reaction. Secondary‐ion mass spectrometry data indicate that the SiF distribution is peaked at the SiO2/Si interface in the fluorinated oxide. The time‐dependent change of the absolute amount of fluorine on the HF‐treated silicon surface as a function of storage time in air or in vacuum was also investigated by the 19F(p,αγ)16O reaction. The initial number of fluorine atoms on the HF‐treated silicon surface was estimated to be ∼1015 cm−2 before substantial desorption took place. Fluorine atoms desorb from the silicon surface much more rapidly if the sample is stored in air than in vacuum. These results were also supported by the x‐ray photoelectron spectroscopy measurement.

Pulse height defect of low energy ions in surface barrier detectors

Abstract Data of pulse height defects (PHD) of silicon surface barrier detectors (SBD) are very important for the particle mass assignment by means of TOF measurements. We have measured pulse height signals from SBD for protons (control) and five heavy ion species ( 16 O, 19 F, 28 Si, 35 Cl, 81 Br) in the incident energy range of 2–8 MeV. The experimental data have been best-fitted to a proposed empirical formula which reproduces PHD values for all particles with A = 16–80 in this energy range. The experimental results are discussed by comparing them with defect values calculated by using the TRIM code and with values calculated by the empirical formula proposed by Kaufman.

Experimental studies on the optimization of the accelerating field distribution in an IH lineac

Abstract A new method is being studied to control the accelerating field distribution in an IH lineac with a high energy gain. In spite of its high shunt impedance, a shortcoming of an IH structure is that a concentration of accelerating field occurs at the low-energy section of the cavity. One of the practical methods to control the accelerating-gap voltages is adjusting the electric-capacity distribution of the structure. This method, however, is not always suitable for an IH lineac when the particle-energy gain is larger than the incident particle energy. The basic idea of our experiments is to utilize an inductive method to “tune” the accelerating field distribution. In order to test the applicability of this method, accelerating field distributions and shunt impedances are measured in terms of these “tuner” configurations by using 1 4 scale models. The results are compared with the calculations based on a four-terminal network simulation.