Motoo Nakano

Recrystallization of Si on amorphous substrates by doughnut‐shaped cw Ar laser beam

Continuous single‐crystal Si films longer than 600 μm over SiO2 have been produced with or without lateral epitaxial growth from bulk silicon seed by changing the mode structure of the cw Ar laser beam. The thermal profile of the laser spot is controlled by using a doughnut‐shaped beam instead of usual Gaussian one to suppress competitive nucleation from side edges of the molten zone. The result indicates that the liquid‐solid interface line profile is the most essential limiting parameter on the mechanism of regrowth.

Laser recrystallization of Si over SiO2 with a heat‐sink structure

Complete single crystalline silicon films over SiO2 have been produced with a heat‐sink structure designed for best utilization of temperature gradients during resolidification process induced by an incident cw Ar laser beam. The structure includes device regions with thin SiO2 layers which act as a heat sink to the substrate and the peripheral regions with thick SiO2 layers. By using this technique, residual grain boundaries in the laser recrystallized silicon over insulator can be eliminated. N‐channel metal‐oxide‐semiconductor field‐effect transistors fabricated in the recrystallized silicon films with a heat‐sink structure exhibit good device characteristics, having a surface electron mobility of 500 cm2/V s which is comparable to that of bulk devices.

Laser‐induced lateral epitaxial growth of silicon over silicon dioxide with locally varied encapsulation

The effect and use of locally varied encapsulation thickness has been demonstrated in cw Ar laser‐ induced lateral epitaxial growth of silicon (Si) layers over silicon dioxide (SiO2) islands. The reflectivity of the laser light has been separately controlled in each region of the Si seed or the SiO2 island by changing the thicknesses of SiO2 and/or silicon nitride (Si3N4) caps. The technique essentially eliminates the surface ripples and thermal detachment of the laser‐recrystallized Si layer, producing single crystalline layers over SiO2 islands as large as 15×80 μm and 20×40 μm.

Single crystalline Si islands on an amorphous insulating layer recrystallized by an indirect laser heating technique for three‐dimensional integrated circuits

A new laser recrystallizing technique for producing single crystalline Si islands on an amorphous insulating layer has been developed. Si islands are recrystallized by indirect Ar ion laser heating utilizing a Si cap. This technique is an effective recrystallizing method for fabricating three‐dimensional integrated circuits. During recrystallization, this technique easily and stably produces a desired temperature profile to eliminate grain boundaries in recrystallized Si islands; the interior of the Si islands is kept cooler than the periphery and crystal growth begins from the interior. This desired temperature profile is realized because an Ar ion laser power is absorbed in the Si cap and heat flow takes place to the Si islands laterally as well as vertically from the heated Si cap through a separation cap. Damage to the underlying layer is not observed, which suggests that the laser beam power is cut in the Si cap. No grain boundaries are observed in more than 90% of the Si islands recrystallized with ...

Lateral Epitaxial Growth in Poly-Si Film over SiO2 from Single-Si Seed by Scanning CW Ar Laser Annealing

CVD poly-Si films 0.4 µm thick were deposited on (100) Si-substrate having a thermally grown SiO2 0.4 µm thick. The samples were then annealed to melt and recrystallize the poly-Si films with scanning cw Ar laser. Laser-annealing in a unidirectional mode with overlapped beams was found to produce a single crystal (100) Si as large as 36 µm in maximum width and more than 140 µm in length in the poly-Si film on SiO2 along the Si seed. However, the lateral epitaxial growth was restricted in size by formation of long crystallites from unannealed poly-Si peripheries and of grain boundaries probably due to the stresses generated by the poly-Si/SiO2 interface.

3-D SOI/CMOS

Three-dimensional (3-D) SOI/CMOS has been expected to be a novel structure which offers the possibilities of high packing density and high speed function. This paper summarizes some of the properties of 3-D SOI/CMOS such as fabricating processes, characteristics and practical structures.

Melt‐width enhancement in the recrystallization of polycrystalline silicon‐on‐insulator by twin‐laser‐beam‐induced substrate interheating

A new method to recrystallize polycrystalline silicon on amorphous insulating layers is developed using twin cw argon laser beams. It is found that the melt width of twin beams can exceed that of a single beam by a factor of 4. This effect is explained by a model of substrate interheating between twin laser spots. Using this technique, a large silicon single crystalline grain as large as 1.8 mm long and 20 μm wide was obtained on thermal oxide coated silicon wafers even for the substrate kept at room temperature during laser irradiation.

Degradation in Bi-Sr-Ca-Cu-O Thin Films Exposed to Water

A study of Bi-Sr-Ca-Cu-O thin films soaked in water demonstrated that film superconductivity was degraded by exposure to water. ICP analysis showed that Sr and Ca, but no Bi and Cu, largely dissolved. EPMA analysis indicated that dissolution took place mostly in nonsuperconducting grains. By contrast, XRD patterns showed no significant change after soaking. That is, superconducting grains were indeed stable, but nonsuperconducting grains were notably degraded in polycrystalline films, with a consequent lowering of overall superconductivity.

3-Dimensional SOI/CMOS IC's fabricated by beam recrystallization

A 3-Dimensional (3-D) CMOS integration with a structure, in which one type of transistor is fabricated directly above a transistor of the opposite type with separate gates and an insulator in between, has successfully been fabricated by using laser beam recrystallization. Seven-stage ring oscillators fabricated in the 3-D structure have a propagation delay of 430psec per stage at a supply voltage of 5V, which is comparable to that of single-crystal Si devices. This CMOS structure and the process technologies we have developed in this work can be the basis for realizing a multi-layered 3-D integration composed of vertically stacked transistors with separate gates and an insulating layer in between.

3-D high-voltage CMOS ICs by recrystallized SOI merged with bulk control-unit

A three-dimensional (3-D)high-voltage flat-panel display scan driver composed of high-voltage offset-gate SOI output circuits merged with low-voltage bulk CMOS control-units has successfully been fabricated by using a CW-Ar laser recrystallization technology. The SOI high-voltage circuits are operated as a power-supply voltage of 60 ∼ 180V with an output current of more than 100mA for a channel length of 10µm and offset length of 20µm. With this technology, a monolithic integration of high-voltage output circuits and well-established low-voltage bulk VLSI can easily be realized.