Vacuum Ultraviolet Light Source Research Articles

Effects of dual spectral sources on the curing of polyimide films by rapid isothermal processing

There are fundamental differences between conventional furnace processing (CFP) and rapid isothermal processing (RIP). The radiation spectrum of a conventional furnace consists of photons in the infrared and longer wavelength regions, whereas the spectrum of the incoherent light sources used in RIP consists of some UV, visible, and infrared photons. As compared to CFP, the photophysical and photochemical effects associated with RIP provide the capability of lower temperature processing. However, a further reduction in processing temperature can be achieved by the use of vacuum ultraviolet (VUV) and UV light sources in conjunction with a single spectral source RIP. We provide experimental results for the dual spectral source curing of polyimide dielectric films. Our findings indicate that simultaneous exposure of polyimide samples to both VUV and conventional RIP sources during processing cured the polyimide more rapidly and at lower temperatures than did single spectral source RIP alone. These results may be of great importance for the RIP of the future generation of semiconductor devices.

Undulator radiation source NIJI-II for photo-excited processes

An undulator radiation source using a compact electron storage ring was developed for photo-excited processes. Quasi-monochromatic radiation has been available and the wavelength of the radiation is tunable from 65 to 1000 nm. The full width at half maxima (FWHM) was measured by a Seya-Namioka type monochromator and the photon fluence was measured using an ionization chamber. We present here an intense vacuum ultraviolet light source which emits a photon fluence exceeding 10 15 photons/s.

Passivation with SiO2 on HgCdTe by direct photochemical-vapor deposition*

For the first time, SiO2 layers, prepared by direct photochemical-vapor deposition, were passivated onto HgCdTe substrates using a deuterium (D2) lamp as the ultraviolet and vacuum-ultraviolet light source. It was found that the refractive index of the SiO2 films, grown at 60 °C and 0.5 Torr for a mixture of SiH4 and O2, is close to 1.462 (the refractive index of thermal silicon dioxide) when the gas ratio (SiH4/O2) is adjusted to 0.2. Various characterization techniques, such as x-ray photoemission, Auger-electron, and Fourier-transform spectroscopies were used to give a detailed study of the physical and chemical properties of the SiO2 thin films. The electrical properties of these SiO2 layers were investigated by performing high frequency (1 MHz) capacitance–voltage (C–V) and current–voltage (I–V) measurements, at 77 K. The C–V measurement shows that the minimum interface state density is 5×1010 cm−2 eV−1 with a hysteresis smaller than 0.2 V. The maximum dielectric strength observed from I–V measurement is around 580 kV/cm.

Pulsed field ionization threshold photoelectron spectroscopy with coherent vacuum ultraviolet: NO+(a 3Σ+ v=0,1,2)←NO(X 2Π1/2)

We report pulsed field ionization spectra of an ionic electronically excited state, specifically, the NO+(a 3Σ+ v+=0,1,2)←NO(X 2Π1/2) transition. A coherent vacuum ultraviolet light source provides single photon excitation, which enables a direct measurement of the ionization potentials for the three vibrational levels — I.P.(v+=0)=126 392±1.5 cm−1, I.P.(v+=1)=127 653±1.5 cm−1, and I.P.(v+=2)=128 884±1.5 cm−1. The rotational structure of these spectra has been simulated using a standard model for rotational line strengths in a photoelectron spectrum, and this simulation shows the strong atomic p orbital character of the initial NO orbital from which the electron is photoionized. However, our data show that the rotational line strengths are strongly dependent on the final vibrational state of NO+, in disagreement with the theoretical model. Also, the spectrum for the v+=1 state of NO+ is strongly affected by the presence of a strong autoionizing Rydberg resonance at the same photon energy, which leads to a complex resonance.

Wavelength conversion of quadrupled Nd:YAG laser radiation to the vacuum ultraviolet by anti-Stokes stimulated Raman scattering

Up-converted beams of a conventional quadrupled Nd:YAG laser by anti-Stokes Raman scattering in hydrogen are characterized as a vacuum ultraviolet light source. The beams diverge with the increase of the hydrogen pressure and also with the increase of the order of anti-Stokes scattering. Although the profiles of anti-Stokes beams vary from a Gaussian-like shape to a typical ring shape, the maximum energy conversion is always obtained with a near-Gaussian beam profile. The output energy ranges from 5.9 mJ for the first-order anti-Stokes wave (240 nm) to 8 μJ for the ninth-order anti-Stokes wave (133 nm). The energy of the sixth-order anti-Stokes wave (160 nm) fluctuates ±45% of the average output energy. The beam characteristics are described well by a model on the basis of phase matching between four waves related to each Raman process.

Disk-shaped vacuum ultraviolet light source driven by microwave discharge for photoexcited processes

An efficient vacuum ultraviolet light source of large diameter has been developed for use in photoexcited processes. It has a novel structure in which microwaves propagating through a sapphire window break down Xe gas enclosed in a disk-shaped volume and thereby produce intense emission from Xe at a wavelength of 147 nm. By optimizing the pulse width and the repetition rate, we obtained an illuminance of more than 3 mW/cm2 at the window surface. When this lamp was used as a source for photoinduced chemical vapor deposition of hydrogenated amorphous silicon films, a deposition rate of 5 nm/min was attained.

Theoretical study of a vacuum ultraviolet F2 excimer lamp (157 nm) excited by microwave discharge

A high-efficiency operation of a vacuum ultraviolet (VUV) incoherent light source of a F2 excimer lamp [157 nm:F2(D′)-F2(A′)] excited by a pulsed microwave discharge has theoretically been studied. Despite the low-pressure (300 Torr) operation, an intrinsic efficiency of 10.6% and a F2(D′) formation efficiency of 17.4% were found to be obtainable at an optimum F2 concentration (0.5%) using He/F2 mixtures. The F2(D′) state is mainly produced by energy transfer reaction from F*. Using a 300 Torr mixture of He/F2=99.5/0.5(%), a photon extraction efficiency of 60.9% is achievable with a low energy loss (39.1%) by collisional quenching. The corresponding optical output of 50.0 μJ/cm3 is achievable at an excitation rate of 100 W/cm3 and an excitation pulse width of 9.0 μs. Since it can be operated at high repetition frequency of up to 55 kHz using conventional devices, an average output power of 2.75 W/cm3 is achievable.

Study of Hydrogen Vacuum-Ultraviolet Light Sources for Submicron Lithography

The output properties of hydrogen light sources and the resist parameters, such as spectral sensitivity and absorption coefficient, in the vacuum-ultraviolet (VUV) region were investigated. A very low exposure energy of about 1 mJ/cm2 was obtained by employing a very thin polymethyl methacrylate film and the VUV light of hydrogen microwave discharge. Contact photolithography using a Si/MgF2 mask and a trilayer resist system showed that submicron patterns as small as 0.2 µm had been replicated at an exposure time of under 30 s.

Large area VUV source for thin film processing

A large area disc shaped vacuum ultraviolet (VUV) light source, from 2 cm to 20 cm in diameter, has been developed. It employs a soft vacuum electron beam emitted from a cathode of ring shape to excite the disc shaped plasma. The Lyman alpha emission 2p 2P0-1s 2S at the wavelength of 121.6 nm, dominates the emission spectra when running a hydrogen discharge while the N I line 3s 4P-2p 4S0 at 120.0 nm, dominates in a disc shaped nitrogen discharge. The 121.5 nm 4d 2D-2p 2P0 line of He II is observed to dominate in the helium discharge when measurements are made through a 10-15 cm long column of neutral helium. The intensity of VUV emission has a measured uniformity of ±6% over the central 15 cm of the 20 cm diameter disc using atomic helium, molecular N2 and H2. The windowless disc plasma is also a source of radical and excited atomic gas species. VUV photons, excited species, and radicals can all assist dissociation of CVD feedstock reactants via volume photo-absorption and sensitized atom-molecule collisions, respectively. In addition, the excited radical flux and VUV impingement on the film may also assist heterogeneous surface reactions and increase surface mobility of absorbed species. Thin films of aluminum nitride, Si3N4, and hydrogenated amorphous silicon have been deposited at temperatures between 100-400°C. The deposited films show significant improvement over other photo-assisted CVD processes in the film quality achieved, the substrate temperature required and the maximum deposition rates achieved.

Vacuum ultraviolet photobiology with synchrotron radiation.

The vacuum-ultraviolet (VUV) region of the electromagnetic spectrum is situated between the far-UV and X-ray regions. It covers a vast range of photon energy from 6.20 eV (200 nm) to 41.3 eV (30 nm). In a broader sense, it covers several hundred eV. The spectral regions on both sides of the VUV are relatively easy in biological experimentations since atmospheric conditions pose no obstacles. In contrast, VUV experiments are difficult to perform with living systems because of the necessity of maintaining the target in a vacuum. Besides, photon sources available for VUV experiments have been limited. In the work by Boyle (1916) we see what seems to be the earliest work on biological experiments with VUV radiation. He irradiated microorganisms with VUV radiation through a fluorite crystal plate. Blank and Arnold (1935) reported the killing of Bacillus spores by 110–130 nm photons. Heinmets and Taylor (1952) treated bacterial cells by passing them in aqueous suspension through an electrical arc. More recently, Jagger et al., (1967) studied VUV effects on Streptomyces conidia by successive use of cutoff filters down to 155 nm. These experiments avoided the vacuum problem either by using vacuum-resistant spores or by special innovations for the VUV irradiation. Apart from living materials, biomolecules, like proteins, can be dried in vacuum and thus become suitable for VUV irradiation. Setlow et al., (1959) were probably the first to perform inactivation experiments with enzymes using monochromatic light in the VUV region. Wirths and Jung (1972) and Sontag and Dertinger (1975) irradiated DNA and bacteriophages in vacuum with dispersed VUV radiation using a conventional light source. Although these biological effects, for which a sensitive assay technique is available, could be investigated by conventional VUV light sources, precise product analysis in the chemical sense is almost unthinkable with them due to the lack of intensity after monochromatization. Rare gas discharge lamps such as the one using bromine (Ito and Kobayashi, 1976) or an excimer laser (Green et al., 1987) could provide intense monochromatic VUV radiation but are greatly limited in the number of wavelengths that are available. Synchrotron radiation (SR) is a breakthrough as a VUV radiation source.

Windowless Wide Area Vuv Lamp for Energy Assisted CVD

ABSTRACTA ring shaped cold cathode electron gun provides a large area disc shaped vacuum ultraviolet (VUV) light source up to 20 cm in diameter. The windowless disc plasma is also a source of radical and excited atomic gas species. VUV photons, excited species, and radicals can all assist dissociation of CVD feedstock reactants via volume photo-absorption and sensitized atom-molecule collisions, respectively. In addition, the excited radical flux and VUV impingement on the film may also assist heterogeneous surface reactions and increase surface mobility of absorbed species. Thin films of aluminum nitride, Si3N4, and hydrogenated amorphous silicon have been deposited at temperatures between 100°C - 400°C. The deposited films show significant improvement over other photoassisted CVD processes in the film quality achieved, the substrate temperature required and the maximum deposition rates.

Optimization of Tunable VUV Light Generation by Two-Photon-Resonant Four Wave Sum-Mixing in Mg Vapour

A tunable VUV (vacuum ultraviolet) light source by two-photon-resonant four wave sum-mixing in a Mg vapour was developed for detection of carbon atoms in plasma devices. In order to optimize VUV generation, parametric dependences of the operational characteristics on buffer gases and fundamental laser intensities were experimentally investigated, and the effect of the spatial matching between two fundamental beams on the phase matching condition was theoretically studied. An output power of 7 W (1010photons/pulse) was obtained at a resonance line of a carbon atom (156.1nm).

Vacuum Ultraviolet Light Source Using Electrodeless Discharge

A new type of vacuum ultraviolet light source employing electrodeless pulse discharge was studied, and the discharge conditions needed to obtain stable VUV radiation were investigated. The argon discharge spectra between 50 nm and 110 nm were studied, and the number of photons detected through a monochromator was estimated to be 2.5×1011 cm-2s-1 at a photon energy of 13.48 eV, a pressure of 5 mTorr of argon, and a flow rate of 12 cm3/min.

Extreme Vacuum Ultraviolet Light Source Developed

Extreme Vacuum Ultraviolet Light Source Developed

Emission spectra of CF3 radicals. III. Spectra and quenching of CF3 emission bands produced in the VUV photolyses of CF3Cl and CF3Br

Fluorescence in the photolysis of CF3Cl and CF3Br was investigated using various vacuum ultraviolet light sources of atomic lines (Ar, Kr, H, and O). Both UV and visible emission bands of CF3 were observed as in the case of the photolysis of CF3H. Lower v′ levels of the emission bands were excited when CF3X was photolyzed by the lower energy incident light. In the case of CF3Cl, the emission bands were observed by the hydrogen Lyman alpha line, but no emission was observed by the krypton lamp with a CaF2 window. The threshold energy required to produce the UV and visible emission bands should be in the region 10.03–10.20 eV for CF3Cl. The energy separation between the fluorescing upper state and the ground state of CF3 is smaller than 6.52 eV. The emission bands were quenched by the addition of N2. Vibrational relaxation was predominant in the emission bands when He was added. Total intensity of the UV emission bands decreased and that of the visible emission bands increased by the addition of He. The results show that the UV and visible emission bands of CF3 would not originate from the same electronically excited state. Collision induced cross transfer from the state associated with the UV emission to that associated with the visible emission was observed.

A high power radiation source in the vacuum ultraviolet

A sliding spark over solid xenon has been developed with the object to serve as a vacuum-ultraviolet light source for the photoionization of gases, especially hydrogen and inert gases. An intensity of 1·1012 Watt/cm3 sr at 800 A has been observed, lasting about 5 μsec. The emitting area was approximately 1.6 cm2. This light source has been used to irradiate a test gas of xenon at 0.4 m Torr. An electron density of 2·1012 cm−3 was detected at a distance of 80 cm with an 8 mm microwave interferometer.

A low conductance optical slit for windowless vacuum ultraviolet light sources

An optical slit that does not use a window material but which nevertheless has a low conductance for gas flow is described. It has a high efficiency ( approximately=40%) for transmitting vacuum ultraviolet light.

High Intensity Hot Filament Vacuum Ultraviolet Light Source

We describe a simple modification of a McPherson-Hinteregger-type capillary discharge lamp which converts it from a cold cathode discharge to a hot filament discharge. This results in about a 10-fold intensity increase in the 7–12 eV photon energy range and about a fourfold increase in operating time between cleanings. The spectral output power is presented.

Collisional Deactivation of O(1S)

Absolute rate coefficients for the collisional deactivation of O(1S) have been measured for CO2, CO, SF6, O2, H2O, NH3, CH4, C2H4, C2H6N2O, NO, NO2, H2, N2, He, Ne, Ar, Kr, and Xe. The measurements have been made with a lifetime technique in which O(1S) is produced in the photodissociation of CO2 by a pulsed vacuum-ultraviolet light source The rate coefficients were obtained from time-resolved measurements of the intensity of the O(1S → 1D) line at 5577 Å. Deactivation of O(1S) by collision induced radiation has been observed for H2, N2, Ar, Kr, and Xe.

New Excitation Unit for Rare Gas Continua in the Vacuum Ultraviolet

An excitation unit for vacuum ultraviolet light sources based on a thyratron-controlled modulator has been developed to excite rare gas continua. With this unit the Hopfield helium continuum in the 580–1100 Å wavelength region is obtained with improved intensity and stability so that a bandwidth of slightly less than 0.25 Å can be used with a 2.2-m normal incidence vacuum monochromator and photo- electric scanning detection. The application of this excitation unit to study of the rare gas continua and to absorption cross-section measurements in hydrogen is illustrated.