Kenkichi Suzuki

Excimer laser-induced temperature field in melting and resolidification of silicon thin films

The liquid/solid interface motion and temperature history during excimer laser annealing of 50-nm-thick Si films on fused quartz substrates are investigated by in situ nanosecond time-resolved electrical conductance, optical reflectance, and transmittance at visible and near-IR wavelengths, combined with thermal emission measurements. The temperature response, melt propagation and evolution of the recrystallization process are fundamentally different in the partial-melting and the complete-melting regimes. Because it is necessary to balance the latent heat across the propagating phase-change interface, the maximum induced temperature in the partial-melting regime remains close to the melting point of amorphous Si. The peak temperature rises in the complete-melting regime, but the nonparticipating nature of the liquid Si/fused quartz interface allows substantial supercooling (>200 K), followed by spontaneous nucleation into fine-grained material. These phase transformations are consistent with the recrysta...

Relationship between fluence gradient and lateral grain growth in spatially controlled excimer laser crystallization of amorphous silicon films

In order to clarify the relationship between excimer laser fluence gradient and the length of lateral grain growth, the excimer laser fluence used for crystallization is modulated by a beam mask. The crystallized 50-nm-thick a-Si films are secco etched in order to observe the lateral grain growth by scanning electron microscope. The fluence distribution across the pattern is measured by a negative photoresist that has a linear relationship between laser fluence and resist thickness after development. This mapped fluence distribution is utilized to deduce the fluence gradient for each laser energy output. It is shown that lateral growth length increases and the directionality of the grains improves as the fluence gradient increases. Lateral growth length as long as 1.5 μm can be driven in a 50-nm-thick a-Si film by a single excimer laser pulse without any substrate heating. Electrical conductance measurement is used to probe the solidification dynamics. The lateral solidification velocity is estimated to b...

Two-dimensional particle simulation of a sustained discharge in an alternating current plasma display panel

A plasma discharge due to a sustaining pulse of an alternating current plasma display panel was analyzed using a two-dimensional particle-in-cell code, and basic characteristics of the plasma discharge were calculated. The characteristics of the plasma discharge due to a sustaining pulse are as follows. (i) A large amount of space charge remained after drawing the discharge current. This excess space charge did not contribute to wall charge formation or ultraviolet radiation. (ii) The electron energy distribution function was evaluated and could be well fitted by the Druyvesteyn distribution in the high-energy region. The Druyvesteyn distribution was a consequence of the cross section for electron-Ne elastic scattering. (iii) The calculated ultraviolet radiation efficiency η of the plasma discharge due to a sustaining pulse was between 5.51% and 30.7%. Examination of the sensitivity of the efficiency to the electron temperature showed that reducing the electron temperature was a key to improving the effic...

In situ and ex situ diagnostics on melting and resolidification dynamics of amorphous and polycrystalline silicon thin films during excimer laser annealing

The liquid/solid interface motion and the temperature history of Si films during excimer laser annealing are observed by in situ experiments combining time-resolved (∼1 ns) electrical conductance, optical reflectivity/transmissivity at visible and near-infra-red wavelength, and thermal emission measurements. The existence of partial and complete melting regimes are detected. In the partial melting regime, the maximum temperature remains close to the melting point of amorphous Si (a-Si), since the laser energy is consumed by the latent heat of phase-change. In the complete melting regime, substantial supercooling, followed by spontaneous nucleation is observed. These phase transformations are consistent with the recrystallized poly-Si morphologies. It is also found that phase change temperature of poly-Si films is about 140 K higher than that of the a-Si films.

Hollowing and Transfer of Polymethyl Methacrylate Film Propelled by Laser Ablation of Triazeno Polymer Film

Utilizing the laser ablation of a triazeno polymer (TA) film as a driving force, materials transfer and patterning were successfully demonstrated. The prepared overlaid films consist of a source film, which is made of pyrene-doped polymethyl methacrylate (PMMA) and TA films, and a target neat PMMA film on a quartz plate. After pressing them together, a 248 nm laser pulse was irradiated from the back side of the source film. When the thickness of the TA film was 1.0 µm, slightly thicker than the penetration depth of TA of 600 nm, the pyrene-doped PMMA film was perfectly transferred to the target film.

Display applications of field-enforced phase transition in PLZT ceramics

Abstract Experiments to determine the applicability of field-enforced reversible transitions between antiferroelectric and ferroelectric phases in PLZT 7.9/70/30 ceramic to flat panel picture display devices reveal that the ceramic has three remarkable advantages over ordinary ferroelectric phase PLZT ceramics. They are: (1) the high transparency of the antiferroelectric PLZT 7.9/70/30 ceramic makes possible a higher contrast display material, (2) the absence of remanent polarization when no electric field is applied makes possible a faster erase display material, and (3) the linear relation between the field-induced scattered light intensity and the simultaneously induced ferroelectric polarization makes possible the control of gray-scale in a display by controlling the polarization charge switched.

Polymer resist materials for excimer ablation lithography

Abstract Excimer ablation lithography (EAL) is a new lithography suitable to TFT-LCD. Among the constituent technologies, the polymer materials for the resist is most crucial, as high ablation rates are required at low fluence. To elucidate the ablation mechanism at low fluence we specified some characteristic features through observations of about 200 polymers. The low fluence features are explained by the contributions from the primary and secondary structures, and ablation dynamic process. From the results, it is derived that polyurethane is most promising material for EAL, and the design of the secondary structure is essential to improve the ablation rate.

Excimer ablation lithography (EAL) for TFT-LCD

The excimer ablation lithography (EAL) is a process of direct patterning and removal of a resist polymer film by photo-decomposition ablation. Comparing to the conventional photolithography, EAL does not need the development process and realizes a non-vacuum dry removal of resist. The main equipment for the new processes is a kind of aligner- exposure for the resist patterning and the removal, which reduce the cost of the clean room and the equipments considerably. This is very attractive for TFT-LCD manufacturing, as it is required to reduce the cost severely. The large area patterning and high throughput are essential for TFT-LCD applications. To prove the feasibility, we fabricated an experimental equipment for ablation patterning. It is equipped with the high precision 300 X 300 mm X-Y stages and a N.A. 0.1 image lens which enable to explore the problems inherent to TFT panel of a real size. In addition, two substantial technologies were developed. One is a dielectric multilayer mask on 8 inch quartz substrate with precision enough for TFT patterns. The other is high ablation rate resist polymer. With these technologies, A4 size TFT laser was fabricated by step and scan method. The results show that EAL is in a good prospect for a new TFT manufacturing technology.

Electronic energy states in Si-doped MgO for exoelectron emission

A generalized analytical method to determine the density of energy states of electron emission source (EES) is devised by using a thermal excitation and emission model for an exoelectron in the MgO layer and the emission time constants of the exoelectron extracted from experimental stochastic distributions of discharge delay time. When applied to Si-doped MgO, the emission time constant of the exoelectron from the Si EES becomes shorter at high temperature and at short time intervals due to thermal excitation. The density of energy states of the Si EES DSi(E) shows the main peak at 736 meV, a satellite peak at 601 meV, and broad energy structures over the range of 586–896 meV. The effective number of Si EES is 5.5 times larger than that in purified MgO. The excitation energy in a Si-doped MgO cluster with a crystal structure is obtained to be 0.83 eV by using the symmetry-adapted-cluster configuration interaction method and the Si EES contributes to exoelectron emission. The thermal excitation is governed...

Global breakdown in an alternating current plasma display panel

In the alternating current plasma display panel, a widespread discharge can take place accidentally in a large number of cells in the upper or lower panel ends. The undesirable discharge is referred to as global breakdown. This is a serious problem, with consequences not only for display quality, but also for product reliability. The mechanism of the global breakdown was examined experimentally using a surface electrometer and theoretically using plasma simulation. From these examinations, the global breakdown mechanism was clarified as follows. Global breakdown was accompanied by charge separation in the horizontal direction of the panel. This charge separation was caused by electron transport downward in the panel during the address discharge. The electron transport formed a negative wall charge on the phosphor surface. When the wall voltage exceeded the insulation voltage of the protective layer, global breakdown occurred. Furthermore, it was clarified that increasing the front dielectric thickness or ...