No abstract

Polycrystalline lead oxide (PbO) film is an excellent candidate material for a direct conversion X-ray detector. However, the thick-bulky film tends to significantly reduce the charge collection efficiency for recombination process, and the effective number of electron-hole pairs is lower than that of thin film, because it is difficult to fabricate high-dense and thick PbO films. In this paper, we first synthesized nano-sized PbO particles that could be used in a novel high-efficiency flat panel X-ray detector using a simple solution/combustion method. Energy dispersive X-ray spectrometry, X-ray diffraction, and field emission scanning electron microscopy were used to analyze the component ratio and morphology of the PbO particles as a function of annealing temperature. Then, 150-mm-thick PbO films were deposited on glass substrates using a particle-in-binder method at room temperature. The influences of annealing before deposition on the X-ray detection characteristics of the PbO films were investigated in detail. The key parameters-the dark current, X-ray sensitivity, signal-to-noise ratio, and signal decay-were measured. The annealing conditions strongly affected the electrical properties of the PbO films. The X-ray sensitivity of films annealed in oxygen gas increased dramatically with increasing annealing temperatures up to 500 C.

Copper thin films are deposited on amorphous' tungsten nitride diffusion barrier by metalorganic chemical vapor deposition method. The resistivity of Cu film is considerably higher than those of Cu films deposited on SiO,, borophospho-silica glass, and Si due to substratedriven reaction. RBS, XTEM and XRD measurements clearly show that 100-800 A amorphous W,N,, layer successfully executes the role of diffusion barrier for Cu during the annealing process at 800 OC for 30 min.

We implanted 6×1016–3×1017 nitrogen ions/cm2 into 100 nm thick tungsten thin films with acceleration energies of 20–60 KeV. As a result, the thermal stability of N+-implanted W thin films is greatly improved from 700 to 900 °C because polycrystalline W thin films change into nanostructured films after N+ implantation. The W thin film implanted at 40 KeV and 3×1017 ions/cm2 effectively prevents Cu diffusion after an annealing at 800 °C for 30 min. When the acceleration energy and dosage are higher or lower than this optimum condition, thermal stability of the N+-implanted W film is degraded due to surface damage of Si substrate and partially nanostructured W thin film.

Nitrogen-implanted W thin film (W-N+) has been proposed as a new diffusion barrier for Cu metallization. The crystalline phase of W-N+ thin film is transformed from polycrystalline to amorphous by the implantation of 1–3 ×1017 N+/cm2. However, if the dosage of N+ is less than 6 ×1016 N+/cm2 it is difficult to form the amorphous phase in the W film. The comparison of this amorphized W-N+ diffusion barrier with the conventional W film shows that the amorphized W-N+ diffusion barrier is very effective for preventing the Cu diffusion even at the annealing temperature of 800°C for 30 min, whereas the conventional W film cannot withstand annealing at 600°C for 30 min. Our result at 800°C for 30 min is a new and excellent record for preventing Cu diffusion.