Yeu-Long Jiang

Very Low Temperature Deposition of Polycrystalline Si Films Fabricated by Hydrogen Dilution with Electron Cyclotron Resonance Chemical Vapor Deposition

Characteristics of polycrystalline silicon films deposited both on SiO2 and Corning 7059 glass substrates are presented in this paper. The silicon films were deposited by a hydrogen dilution method using electron cyclotron resonance chemical vapor deposition at 250° C without any thermal or laser annealing. The hydrogen dilution ratio was between 90% and 99%. The geometric configuration and surface morphology of polycrystalline silicon films were studied by atomic force microscopy. The largest grain size of the deposited silicon films, identified by plan-view transmission electron microscopy dark-field imaging, was about 1 µ m. From Raman spectrum, the crystalline fraction of polycrystalline silicon films was identified to be nearly 100%. The polycrystalline silicon was found to be preferentially - and -oriented, from the X-ray diffraction pattern.

Rapid Energy Transfer Annealing for the Crystallization of Amorphous Silicon

A rapid energy transfer annealing using an energy plate efficiently transferring photon energy to heat energy and by adjusting gas heat conduction can provide high energy transfer efficiency and controllability to rapidly crystallize amorphous silicon to polysilicon. The X-ray diffraction (XRD), Raman scattering, transmission electron microscopy (TEM), atomic force microscopy (AFM), and I-V measurements demonstrate that both thin and thick a-Si films can be fully crystallized within 20 three-second 850°C pulses annealing, that the films before and after annealing have the same roughness of about 1.3 nm and the conductivities of about 1.0 ×10-10 and 2.3 ×10-7 (Ωcm)-1, respectively.

Operating principles and performance of a novel a-Si:H p-i-n-based X-ray detector for medical image applications

This work develops a novel hydrogenated amorphous silicon (a-Si:H) p-i-n photodiode-based X-ray detector aimed at medical image applications. The new detector consists of an a-Si:H p-i-n photodiode and a stacked dielectric layer, deposited on the p-layer (n-i-p-SiN/sub x/) or the n-layer (p-i-n-SiN/sub x/) of the p-i-n photodiode, as the main charge storage element. This detector operates as a capacitor and is connected in parallel to a reverse-biased p-i-n photodiode during the detection cycle to accumulate photon-converted charges. The junction capacitance (C/sub j/) of the p-i-n diode was enhanced by this stacked dielectric layer without reducing the active area of the detector. The design of the charge storage capacity and the photon-charge transfer efficiency can be optimized separately for various applications. Moreover, the linearity, dynamic range of operation, and data retention capacity of the detector were found to be markedly improved by the enlarged capacitance in the detector. The operating principles and performance of this novel device are discussed, and the corresponding control sequence of the switch of the device array is also addressed. The experimental results proved that this novel structure is valid and can be applied to construct effectively a two-dimensional detection array, offering considerable advantages of the novel device in X-ray medical image applications.

Design issues of two-dimensional amorphous silicon position-sensitive detectors

Abstract The two-dimensional amorphous silicon position-sensitive detector (PSD) is usually in the form of large-area, continuous p-i-n silicon layer structure coupled with resistive layers next to the p and n Si layers. The device has many applications (e.g. light position measurements, light-pen input devices, etc.) and can be fabricated by using low-cost PECVD process. When used as a light-pen-based input device, several material-related design issues must be critically considered for achieving acceptable performance. The present work addresses three important issues, namely the spectral response of PSD, the uniformity requirement of the resistive layers, and the design of optical filter on the input side of PSD. They correspond to the signal-to-noise ratio of the device, the accuracy of light-position determination, and the integration problem with liquid crystal displays (LCD), respectively. Analytical analysis and computer simulation results draw the following important conclusions: (1) red-light-sensitive PSD can be obtained by properly tuning the thickness of p-layer and i-layer, which suppress the interference of background light when using the input device under sun light or similar illumination (2) the spot size of input light has little effect on position determination, as long as the size does not differ too much from that of required resolution. And a conservative uniformity requirement for the resistive layers can be obtained as |Δh/h|≤4/n with n being the required number of pixels of display and h being the film thickness (3) multi-layered filters made of oxides can be deposited on PSD to reflect non-signal light for LCD display while preserving the input-signal when the PSD is placed under a TN LCD.

Field-drifting resonant tunneling through a-Si:H/a-Si/sub 1-x/C/sub x/:H quantum wells at different locations of the i-layer of a p-i-n structure

The transport of photogenerated carriers perpendicular to the quantum wells in the p-i-n structure is discussed. The field-drifting resonant tunneling through the a-Si:H/a-Si/sub 1-x/C/sub x/:H double-barrier (or three-barrier) quantum wells, located at different positions of the i-layer, was studied. The room-temperature resonant-tunneling behavior is observed when the quantum well structure is embedded in the middle second of the i-layer. The results provide further evidence of quantum size effects in amorphous-silicon-based superlattice structures. >

Rapid and Efficient Recrystallization and Activation of Implanted Phosphorus Doping in Laser-Annealed Polysilicon by Rapid Energy Transfer Annealing

Phosphorus atoms that are implanted as dopants in laser-annealed polysilicon films are recrystallized and activated by rapid energy transfer annealing (RETA). After five pulses of RETA annealing, with a total process time of 90 s, the implanted, damaged amorphous silicon films are fully recrystallized into polysilicon films. Transmission electron microscopic images clearly reveal that these amorphous regions fully recover the original grain structure and the surface topography of the polysilicon film preceding implantation. The current versus voltage (I-V) measurements demonstrate that the implanted phosphorus atoms are efficiently activated. The sheet resistance of the annealed film after annealing is approximately 280 Ω/square, which is around the same order as obtained for excimer laser-annealed films.

Hydrogenated amorphous silicon a-Si:Hx/a-Si:Hy compositional superlattices : Profiling the lattice-constant-scale spatial change of the designed Si-H bonding configurations

Hydrogenated amorphous silicon a-Si:Hx∕a-Si:Hy compositional superlattices are produced by periodic switching two pulse-wave modulation plasmas. Simply varying the on and off times of pulse waves selectively controls the Si–H bonding configurations and yields a-Si:Hx∕a-Si:Hy superlattices with spatial periodic change of the designed monohydride (SiH) bonds and polyhydride (SiH2)n bonds over ultrathin periods (4.5–2.5nm) with lattice-constant sublayer thicknesses (2.5–0.75nm). The superlattice structures are identified by the observation of x-ray Bragg’s diffraction peaks. The bandgap and refractive index are controlled by the spatial distribution of different Si–H bonds and changing sublayer thickness in superlattice structure.

Fast Grain Growth of Metal-Induced Lateral Crystallization of Amorphous Silicon Using Rapid Energy Transfer Annealing

In this work, we examine the acceleration of the grain growth of the nickel (Ni) metal-induced lateral crystallization (MILC) of amorphous silicon by rapid energy transfer annealing (RETA). An extremely high grain growth rate, exceeding 3.4 µm/min, was obtained using five pulses of RETA annealing, since nickel silicide mediated faster grain growth than that obtained by random nucleation, and the metastable internal energy of the a-Si film was relaxed at a high temperature. Transmission electron microscopy (TEM) images and energy dispersive X-ray (EDX) spectra reveal that the laterally crystallized polysilicon regions incorporate large grains with little contamination by residual Ni atoms.

An innovative a-Si:H p-i-n based X-ray medical image detector for low dosage and long exposure applications

Abstract An innovative hydrogenated amorphous silicon (a-Si:H) p-i-n photodiode based X-ray detector for medical imaging applications was developed in this work, and the improvements of the device were also discussed. The detector consists of an a-Si:H p-i-n photodiode and a stacked dielectric layer, such as silicon nitride (SiNx), deposited on p-layer of this p-i-n diode (n-i-p-SiNx), as the major charge storage element. The detector operates as a capacitor, formed by this dielectric layer, in parallel with a reverse-biased p-i-n diode during the detection cycle. Consequently, the capacitance, for accumulating the photon-converted charges, of the p-i-n diode was enlarged by this stacked dielectric layer without decreasing the active area of the detector. As a result, the dynamic range, linearity and data retention capability of this novel detector are significantly improved. In particular, the photo sensitivity and charge storage capability of this novel detector can be separately optimized, and the drastically improved data retention, due to the high density and long release time of the trapped electrons in p-layer of the p-i-n diode, could facilitate this novel detector to be employed in the low dosage flux and long exposure applications.

Ultra-shallow junction formation using implantation through capping nitride layer on source/drain extension

Method for forming ultra-shallow p+/n is demonstrated for 0.15 µm p-type metal-oxide-semiconductor field-effect transistor (pMOSFET). The approach includes a capping ultra-thin nitride on the source/drain extension regions followed by a low energy source/drain (S/D) extension implantation. Ultra shallow p+/n junctions can be obtained with depth of 27 nm and sheet resistivity of 1007 Ω/.