Jun-Ying Zhang

Efficient excimer ultraviolet sources from a dielectric barrier discharge in rare‐gas/halogen mixtures

The generation of excimer radiation in mixtures of the rare‐gases Kr or Xe together with chlorine gas has been investigated by a dielectric barrier discharge. The characteristics of the emission spectra of the excimers formed, centered around 222 and 308 nm, were obtained for different gas mixtures and total gas pressures using an ultraviolet (UV) monochromator. The influence of the gas mixture, chlorine gas concentration, total gas pressure, and buffer gas dependence of the UV intensity has been investigated using chemical actinometry. Conversion efficiencies (from input electrical to output optical energy) as high as 15% can be achieved under optimal conditions. This low‐cost and high‐power excimer lamp system can provide an interesting alternative to conventional UV lamps for industrial large‐scale UV processes.

Efficient XeI* excimer ultraviolet sources from a dielectric barrier discharge

A dielectric barrier discharge in mixtures of xenon and iodine to provide intense narrow band ultraviolet (UV) radiation at λ=253 nm (XeI*) has been investigated. The characteristics of the emission spectra of the excited dimer (excimer) and UV intensity formed from mixtures of xenon and iodine for different total gas pressures are reported. The absolute UV output power of the XeI* lamp has been determined using actinometry based on the photohydrate of uridine. The electrical power dependence of the UV intensity generated as well as the conversion efficiency of the lamps has also been studied. Conversion efficiencies (from input electrical to output optical energy) as high as 22.5% have been achieved for an electrical power input of 70 W, with 15.75 W of optical output being generated.

Low temperature photo-oxidation of silicon using a xenon excimer lamp

Low temperature (250 °C) photo-oxidation of silicon initiated by a Xe2* excimer lamp operating at a wavelength of 172 nm has been investigated. The induced reaction rate of 0.1 nm/min is 90 times greater than thermal oxidation at 612 °C and more than three times greater than that previously obtained at 350 °C using a low pressure mercury lamp. It was found to be strongly dependent upon oxygen pressure with the highest rates being achievable below 10 mbar. Ellipsometry, Fourier transform infrared spectroscopy, capacitance–voltage, and current–voltage measurements have been employed to characterize the oxide films and designate them as high quality.

Characteristics of high quality tantalum oxide films deposited by photoinduced chemical vapor deposition

A method is presented for the photodeposition of tantalum oxide films from tantalum ethoxide and nitrous oxide using 172 nm radiation. The composition of the tantalum oxides deposited by this technique was determined by x-ray photoelectron spectroscopy while the optical and electrical properties were characterized using ellipsometry, capacitance–voltage, and current–voltage techniques. A leakage current density as low as 3.2×10−7 A cm−2 at a voltage of 10 V is obtained for the as-grown films. This is several orders of magnitude better than for any other Ta2O5 films deposited using either conventional or plasma-chemical vapor deposition techniques.

Decomposition mechanisms of thin palladium acetate film with excimer UV radiation

Pre-nucleation of surfaces with palladium from thin palladium acetate films on a range of substrate materials by UV-induced decomposition is described. The optical transmission of the films after irradiation with incoherent UV radiation from several excimer lamp sources provided information about the deposition rate at different UV intensities and exposure times using three different wavelengths: λ = 172 nm (Xe 2 * ), λ = 222 nm (KrCl * ), and λ = 308 nm (Xecl * ). The gaseous products produced during UV exposure were measured using mass spectrometry (MS). The decomposed products such as H 2 O, CO 2 , + CCH 3 , + COCH 3 and + CH 3 were observed. The decomposition mechanism of palladium acetate is discussed and a simple model calculation describing photolytic decomposition processes in the thin palladium acetate films is presented. Results will be compared to those obtained by laser and thermal decomposition of palladium acetate. The deposited palladium can act as an activator for subsequent pattemed chemical metal deposition techniques in which micrometer thick copper, nickel, or gold layers with good electrical resistivity are applied.

Thin tantalum pentoxide films deposited by photo-induced CVD

Abstract Thin tantalum pentoxide films have been grown on Si(100) and quartz substrates by photo-induced chemical vapour deposition (CVD) using a 172 nm xenon excimer lamp. The effects of gas pressure and substrate temperature on the properties of the film formed have been studied using ellipsometry, Fourier transform infrared spectrometry and ultraviolet spectrophotometry. An optical transmittance of around 90% in the visible region of the spectrum was obtained at different pressures. Low temperature (400°C) annealing under vacuum ultraviolet (VUV) irradiation is shown to remove any suboxides present in the as-deposited films. Physical and optical characterization both reveal good film qualities, rendering this new technique promising for low temperature microelectronic and optoelectronic material processing.

Thin tantalum oxide films prepared by 172 nm Excimer lamp irradiation using sol–gel method

Abstract Thin homogeneous tantalum oxide films have been prepared on Si(100) substrates by spin-coating using the sol–gel approach as well as a novel VUV irradiation step using a 172 nm excimer lamp. The effects of spin-on speed, irradiation time and substrate temperature on the films formed have been studied. X-ray photoelectron spectroscopy (XPS) was employed to examine the elemental content during the process and showed that the carbon content, which is considered to be harmful to the electrical properties, can be reduced to the extent of being essentially zero. Ellipsometry, Fourier transform infrared spectroscopy, capacitance–voltage and current–voltage measurements were also employed to characterise the oxide films prepared at different substrate temperatures in the range of 100°C to 450°C and indicate that some of the films were of high quality. A significant reduction in the leakage current has been achieved by this technique without any high-temperature annealing.

Growth of tantalum pentoxide film by pulsed laser deposition

Abstract Thin films of Ta 2 O 5 have been deposited on quartz and silicon substrates by 532-nm (Nd:YAG) pulsed laser deposition (PLD) in various O 2 gas environments. The influence of the deposition parameters, such as oxygen pressure, substrate temperature and annealing under UV irradiation using a 172-nm excimer lamp, on the properties of the grown films, has been studied. The refractive index of the films increases with increasing pressure of O 2 . X-ray diffraction measurements show that the as-deposited films are amorphous at temperatures below 500°C and possess orthorhombic (β-Ta 2 O 5 ) crystal structure at temperatures above 600°C. The optical properties determined by UV spectrophotometry also strongly depend on the deposition parameters. At O 2 pressures above 0.15 mbar, the refractive index of the films was about 2.12 which is close to the bulk Ta 2 O 5 value of 2.2. Optical transmittance around 85% in the visible region of the spectrum was obtained at an oxygen pressure of 0.2 mbar.

Investigations of photo-induced decomposition of palladium acetate for electroless copper plating

Photo-induced decomposition of palladium acetate films has been performed by using argon and xenon excimer vacuum ultraviolet (VUV) sources that emit radiation peaking at wavelengths of 126 and 172 nm, respectively. VUV irradiation of a substrate treated with palladium acetate results in the formation of palladium, which acts as a catalyst for subsequent copper plating by means of an electroless bath. A selective copper pattern can thus be formed in a simple process using a contact mask. The surface morphology of films on silicon substrates has been investigated using an atomic force microscope (AFM) and a scanning electron microscope (SEM). Exposure conditions were found to affect the morphology and density of the Pd activation layer. The electrical resistivity of the films, measured by four-point probe, and the adhesion strength of copper on the Pd-nucleated substrate, were both found to be dependent on the thickness of the palladium.

Thin tantalum and tantalum oxide films grown by pulsed laser deposition

The growth of tantalum and tantalum oxide films grown on Si (1 0 0) and quartz by 532 nm (Nd:YAG) pulsed laser deposition (PLD) in various O2 gas environments has been investigated. Ellipsometry has been used to determine the refractive index and thickness of the films whilst Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and UV spectrophotometry were used to identify tantalum and tantalum oxide formation and optical transmittance as well as optical constants. The FTIR, XPS and UV spectra reveal a strong dependence of the film properties on the O2 gas pressure used. The results showed that oxygen pressure could be used to control the composition of the films. XPS analysis showed that the composition of the layers changed from Ta2O5 to metal tantalum as the oxygen pressure was varied from 0.2 to 0.005 mbar. Under optimum deposition conditions, the refractive index of the oxide layers was found to be around 2:10 0:05 which is close to the value of the bulk Ta2O5 of 2.2 while an optical transmittance in the visible region of the spectrum up to 90% was obtained. These properties compare very favourably with those of films produced by other techniques. # 2000 Elsevier Science B.V. All rights reserved.