Seiichiro Kawamura

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.

Three-dimensional CMOS IC's Fabricated by using beam recrystallization

A three-dimensional (3-D) CMOS integrated circuit 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 8.2 ns. In the present experiment, a double-layer of silicon-nitride and phospho-silicate-glass (PSG) film has been used as an intermediate insulating layer between the top and the bottom devices. This CMOS structure and the process technology we have developed here can be the basis for realizing a multilayered 3-D device composed of vertically stacked transistors with separate gates and an insulating layer in between.

Effect of fluorine in chemical‐vapor‐deposited tungsten silicide film on electrical breakdown of SiO2 film

The effect of fluorine in chemical‐vapor‐deposited tungsten silicide film on electrical breakdown of SiO2 film was investigated. Fluorine diffuses into the SiO2 film through the upper layer of poly Si above 800 °C. At 1000 °C, fluorine diffuses into the SiO2 film to a concentration on the order of 1020 cm−3. Electrical breakdown field of the SiO2 film degrades remarkably at 1000 °C. However, it was clear that the diffusion of fluorine was blocked by a thin chemical‐vapor‐deposited Si3N4 layer on the SiO2 film. In this case, the degradation of SiO2 film was not observed. From the above results, it is concluded that the diffusion of fluorine included in the chemical‐vapor‐deposited tungsten silicide film is one of the causes in degradation of electrical breakdown of the SiO2 film when the chemical‐vapor‐deposited tungsten silicide film was used as a gate electrode in metal oxide semiconductor integrated circuits.

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.

A Study of Hot-Carrier-Effects in SOI-MOSFETs Using Photon Emission

The hot-carrier effects of SOI-!,!OSFHIs have been studied, for ttre first. time, using photon emission from hot carriers. The emission of the SOI!,IOSFHIs is observed not only in the drain region but also the source region. The emission nechanism at the source region is possibly electron-hole recombination. The total photo intensity from a SOf-!{OSFET indicates the strengttr of imtrnct ionization. The relation between the hot-carrier-lifetime and the photo intensity in SOI-MOSFETs is similar to that between the lifetime and the substrate current in bulk MOSFHIs. llhe photon emj.ssion is a good index for hot-carrier-degradation measurements in SOI devices.

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.