We have found a hole trap related to hydrogen and carbon in p-type crystalline silicon after hydrogen and deuterium injection by chemical etching and plasma exposure. It was found from deep-level transient spectroscopy that this center is located at 0.33 eV above the valence band and shows no Poole–Frenkel effect in electric fields lower than 6×103 V/cm. The depth profiling technique using deep-level transient spectroscopy indicated that this center is distributed over the range 1–7 μm from the surface with densities of 1011–1013 cm−3, depending on the hydrogenation method. On the other hand, secondary ions mass spectroscopy revealed that the majority of deuterium injected into silicon exists within a much shallower region less than 60 nm from the surface with higher densities of 1018–1020 cm−3. We have therefore concluded that the majority of injected hydrogen stays in the near-surface region probably in the form of a molecule and larger clusters and only the minority diffuses into the bulk in an atomic form to form an electrically active complex with carbon. We performed annealing experiments to investigate the thermal stability of the complex. It was stable in the dark up to 100 °C, above which it was completely annihilated in first-order kinetics with an activation energy of about 1.7 eV. The illumination of band gap light with and without a reverse bias at room temperature and at 50 °C induced no effect on the stability of the trap. This is contrast to the photoinduced annihilation of a recently observed electron trap related also to hydrogen and carbon and with comparable thermal stability in n-type silicon. These similarities and differences between the two traps and the comparison of the present results with the recently published theoretical calculations of the total energy of hydrogen configurations in the hydrogen-carbon complex suggest that the previously observed electron trap and the presently observed hole trap arise from two different defects with similar origins and structures and are tentatively ascribed to the electronic states of ‘‘bond-centered’’ and ‘‘anti-bonding of carbon’’ configurations of hydrogen in the hydrogen-carbon complex, respectively.

A stacked image sensor with a 0.9 μm pixel size fabricated by using organic photoconductive film (OPF) was realized. It is the first trial to introduce an active material, that is, an organic semiconductor into the BEOL process. This pixel structure is fabricated by using a standard 45 nm BEOL process. However, after OPF deposition, it is essential to restrict the thermal budget and to avoid oxygen, moisture, and plasma irradiation. By controlling the above conditions, a demonstration of a stacked image sensor with OPF, which has high sensitivity, high saturation charge, and a wide incident light angle, was successfully performed.Introduction As the pixel size of image sensors shrinks, new technologies dependant on BEOL, such as lightpipes [1], the separation walls of on-chip color filters (OCFs) [2], and backside illumination (BSI) [3], have been widely developed and introduced into mass production recently. Pixel size has shrunk to nearly 1.0 μm.However, as silicon has a low absorption coefficient, the depth of photodiodes should be larger than 3 μm to ensure sensitivity regardless of pixel size, i.e., as pixel size becomes small, the aspect ratio of photodiode must be large. As a result, the leakage of light to the neighboring pixels in a photodiode increases. This leads to narrow incident light angles.To suppress the leakage of light and achieve wide incident light angles at a small pixel size, it is necessary to develop a stacked image sensor with another photoconductive film that works effectively even if it becomes thinner.Recently, organic semiconductors have been applied to photoelectric conversion devices, such as light emitting diodes, illumination, and solar cells [4, 5]. Some organic materials have a higher absorption coefficient than does silicon, as shown in Fig. 1. Therefore, in image sensors, the thickness of photoelectric conversion film (photodiode) can be decreased to under 0.5 μm by using organic materials, as shown in Fig. 2. This makes it possible to have both a high sensitivity and a wide incident light angle [6] at a pixel size under 1.0 μm.Because organic photoconductive film (OPF) is not so robust, there are some problems that must be overcome in order to introduce it into the BEOL process. It is necessary to restrict the thermal budget and to avoid oxygen, moisture, and plasma irradiation, which includes ultraviolet light.In addition to the above problems, in stacked image sensors, which are different from normal CMOS image sensors, the capacitance of lower pixel electrodes as well as plugs affects the electronic crosstalk of adjacent pixels, so that deciding both the pixel structure and the position of the lower pixel electrodes becomes important problem.In this work, to solve the above problems, we considered where the OPF, lower pixel electrodes, and global layer should be placed and proposed two structures: an "OPF over global layer" and an "OPF under global layer."Pixel Structure using OPF This stacked image sensor used 45 nm CMOS technologies on a 300 mm wafer. Three Cu fine laye...

No abstract

No abstract

No abstract