Recrystallized Silicon Films Research Articles

Modification of silicon waveguide structures using ion implantation induced defects

The structure of re-crystallized silicon films is investigated using transmission electron microscopy, spectroscopic ellipsometry and positron annihilation spectroscopy. Samples were prepared via amorphization of the silicon overlayer of silicon-on-insulator substrates, and subsequent thermal annealing. For an annealing temperature of 650 °C we show that the silicon film has a poly-crystalline structure. Its refractive index measured at 1550 nm is comparable to that of crystalline silicon following re-crystallization at 750 °C. Positron measurements indicate a high concentration of open-volume point defects in the re-crystallized films. We discuss the potential importance of these structures with regard to defect engineering for silicon photonic devices.

Surface morphology and impurity distribution of electron beam recrystallized silicon films on low cost substrates for solar cell absorber

A line shaped electron beam recrystallised polycrystalline silicon film on the low cost substrate was investigated for the use of the solar cell absorber. The applied EB energy density strongly influences the surface morphology of the film system. Lower EB energy density results in droplet morphology and the rougher SiO 2 capping layer due to the low fluidity. With the energy increasing, the capping layer becomes smooth and continuous and less and small pinholes form in the silicon film. Tungstendisilicide (WSi 2) is formed at the interface tungsten/silicon but also at the grain boundaries of the silicon. Because of the fast melting and cooling of the silicon film, the eutectic of silicon and tungstendisilicide mainly forms at the grain boundary of the primary silicon dendrites. The SEM-EDX analysis shows that there are no chlorine and hydrogen in the area surrounding a pinhole after recrystallization because of outgassing during the solidification.

Characterization of double gate MOSFETs fabricated by a simple method on a recrystallized silicon film

A simple process to fabricate double gate SOI MOSFET is proposed. The new device structure utilizes the bulk diffusion layer as the bottom gate. The active silicon film is formed by recrystallized amorphous silicon film using metal-induced-lateral-crystallization (MILC). While the active silicon film is not truly single crystal, the material and device characteristics show that the film is equivalent to single crystal SOI film with high defect density, like SOI wafers produced in early days. The fabricated double gate MOSFETs are characterized, which demonstrate excellent device characteristics with higher current drive and stronger immunity to short channel effects compared to the single gate devices.

Silicon thin-film UV filter for NADH fluorescence analysis

Abstract A new optical detector system for fluorescence analysis in on-chip high-speed screening arrays is described. It consists of a photodiode covered by a re-crystallized silicon film, which acts as a single-film optical filter. The crystalline structure of the silicon film has a strong influence on the optical properties of the filter. The fabrication process and characterization of a polycrystalline Si thin-film on glass are reported. The method is compatible with standard CMOS processes. The optical properties of the designed filter are such that fluorescent light of wavelengths of 420 nm or higher can be measured in the presence of (UV) excitation light (340–360 nm). A selectivity exceeding 35 dB has been demonstrated. The technique has the potential for 50 dB selectivity and higher. NADH concentration measurements in the range 0–1 mMol/l illustrate the application of the system for determination of enzymatic activity of different analytes.

Multiple layers of CMOS integrated circuits using recrystallized silicon film

This letter presents a method to fabricate high performance three-dimensional (3-D) integrated circuits based on the conventional CMOS SOI technology. The first layer of transistors is fabricated on SOI and the second layer is fabricated on large-grain polysilicon-on-insulator (LPSOI), using oxide as the interlayer dielectric. The LPSOI film is formed by the recrystallization of amorphous silicon through metal induced lateral crystallization (MILC). The grain size obtained by the LPSOI process is much larger than the transistors and the transistor performance is similar to those fabricated on the SOI layer. Three-dimensional (3-D) CMOS inverters have been demonstrated with p-channel devices stacking over the n-channel ones.

Structure and grain boundary defects of recrystallized silicon films prepared from amorphus silicon deposited using disilane

The structure of polycrystalline Si (poly-Si) films, prepared by annealing amorphous Si (a-Si) films deposited using Si2H6, has been investigated by x-ray diffraction (XRD), Raman scattering, transmission electron microscopy (TEM), and electron spin resonance, as functions of deposition conditions, such as deposition temperature Td (450–580 °C) of the a-Si and annealing time under a fixed temperature of 600 °C. A dominant texture of the poly-Si films changed from a 〈100〉 texture for Td below 530 °C to a 〈111〉 for Td above 530 °C, independent of the deposition rate of the a-Si films and of the film thickness. Although the XRD grain size was independent of Td, the TEM grain size increased from 1.0 to 2.5 μm with decreasing Td. It is suggested that the increase in this TEM size is caused by enhanced lateral growth of 〈100〉 grains due to the presence of strain. The spin density Ns and the factor g were found to first increase with the annealing time, and rapidly decreased after the films were crystallized. It is also found that the value of g for the poly-Si films decreased from 2.0051 to 2.0048 with decreasing Td. Furthermore, effects of post-hydrogenation on the poly-Si films with different textures were investigated, and a structural change of the boundary regions in the poly-Si films is discussed in connection with a change in the dominant texture, through the corresponding change in g.

Single-crystal silicon microblocks produced by a selective recrystallization technique

A previously reported ac magnetic-field technique has here been applied to selective recrystallization on quartz substrates of polysilicon thin films which had been patterned into specific microblock designs. With the recrystallization it has been possible to produce single-crystal silicon microblocks of a maximum size of approximately 60×40×2 μm,3 large enough for the fabrication of high-performance thin-film transistors. Microblocks used in the experiments were of two types: ‘‘network’’ rectangles, connected on the wafer two dimensionally with polysilicon paths, and ‘‘isolated’’ rectangles adjacent to the network rectangles. The surface morphology of the recrystallized silicon films was observed with scanning electron microscopy. While no grain boundaries were found on the surfaces of the recrystallized network rectangles, many grain boundaries were observed to remain on the recrystallized isolated rectangles. X-ray diffractions for the recrystallized network rectangles were measured with a microfocused x-ray beam, and the recrystallized network rectangles were confirmed to be single-crystal silicon microblocks of good crystal quality. It had been expected that network rectangles would be more greatly heated, as compared to isolated rectangles, by the eddy currents induced by the ac magnetic fields, and the observed higher quality of network-rectangle recrystallization has verified that anticipated eddy-current contribution.

Structure of recrystallized silicon films prepared from amorphous silicon deposited using disilane

The structure of polycrystalline Si (poly-Si) films, prepared by annealing of amorphous Si films deposited using Si2H6 and SiH4, has been investigated as a function of deposition temperature Td (450–580 °C) and annealing temperature Ta (550–1000 °C). A dominant texture of the poly-Si films changed from 〈100〉 for Td below 500 °C to 〈111〉 texture for Td above 500 °C, independent of Ta. For Ta lower than 650 °C, a greater grain size was obtained by the use of Si2H6 rather than SiH4. It was suggested that the changes of these texture and grain size, respectively, are mainly controlled by Td and the deposition rate of the amorphous Si films.

Measurement of Viscoelastic Stress Relief in Patterned Silicon-on-Insulator Composite Structures With Raman Spectroscopy

ABSTRACTRaman spectroscopy has been utilized to measure room-temperature residual strain in the active device layer of laser-recrystallized silicon-on-insulator (SOI) composite structures. The SOI composite structures were fabricated on synthetic fused-silica substrates, and the composites contained a phosphosilicate glass (PSG) layer to provide high-temperature stress relief. Conventional masking and etching techniques were used to selectively pattern the polycrys-talline silicon layer into isolated square islands prior to recrystallization. The biaxial in-plane stress in recrystallized films was calculated from the measured strain-induced first-order Stokes Raman wavenumber shifts, and the results indicate that 200- μm-square recrystallized silicon islands have significantly lower in-plane stress values than continuous recrystallized silicon films. These measurements provide a preliminary confirmation of the dependence of the time constant for viscoelastic stress relief on the in-plane pattern dimension.

Characterization of defects in Si films on SiO2 layer

SOI (Silicon-on-lnsulator) offers many advantages for integrated circuits including faster switching speed, high packing density, radiation resistance, and latch-up free. It can also be used in the integration of high voltage devices and/ or sensors. Defect-free Si films with a small interior stress are required for the application mentioned above. Therefore a heat-sink and a valley entrainment structure (Fig. 1) were made in order to confine defects to predetermined locations and to leave the other areas of the recrystallized silicon film defect-free.Using a cross—section specimen electron microscopy we have observed some kinds of defects in unseeded rapid zone-melting-recrystallized (RZMR) Si films which were prepared with a RF-induced graphite strip heater system. The scanning speed of the graphite strip heater is 11 mm / sec. Fig.2 shows a cross-section image of a valley structure specimen. Not any defect has been found in region A, which means that about 10μm wide defect-free Si film can be obtained by the process. Region C is an unpatterned normal area with a uniform thickness.The subgrain boundaries (SGBs) with an interval less than 6μm were observed in the region C.

A laser-recrystallization technique for silicon-TFT integrated circuits on quartz substrates and its application to small-size monolithic active-matrix LCD's

The laser-recrystallization technique utilizes the connected-island structure for forming recrystallized silicon films with enlarged grain size controlled by the thermal gradient. This technique has been used to fabricate the driver circuits of small-size monolithic active-matrix liquid-crystal displays. A horizontal driver circuit with partially recrystallized silicon thin-film transistors (TFTs) has been successfully fabricated on quartz substrates, together with a vertical driver and active-matrix TFT circuits. The operating frequency of the fabricated horizontal driver circuits can be as high as 10 MHz under a clock voltage of 5 V. >

High-quality stacked CMOS inverter

A stacked CMOS technology with enhanced device performance and small geometries is discussed. Surface-channel mobilities were measured to be 700 cm/sup 2//V-s for bulk n-channel devices and 165 cm/sup 2//V-s for the top PMOS transistors. Excellent subthreshold slope of 100 mV/decade and leakage currents below 150-fA/ mu m channel width were measured for both device types. The low-impurity crystalline silicon film on top of the bulk devices was produced by local epitaxial overgrowth, an important alternative to recrystallized silicon films for three-dimensional CMOS circuits. The structure is planarized and requires only size masks with reduced processing time.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Large-area defect-free silicon-on-insulator films by zone-melt recrystallization

Large areas of defect-free silicon-on-insulator (SOI) films have been obtained by softening (lowering the viscosity) a layer underlying the silicon film. During zone-melt recrystallization this sublayer provides a stress relief mechanism and relieves mechanical constraints for the growing crystal. Using this technique we have been able to obtain recrystallized silicon films that show significant improvement over the typical material obtained in samples without the soft layer recrystallized under identical conditions. We have reproducibly obtained SOI films that contain large areas that are free of subgrain boundaries as well as other defects such as twin boundaries and threading dislocations.

Study of the laser-recrystallized film with a control of grain boundary location by using surrounding antireflection cap method

A modified technique for unseeded laser-recrystallization of poly-crystalline silicon films deposited on amorphous insulators has been developed whereby grain boundary location in the recrystallized silicon film can be controlled. In this technique, the silicon film is encapsulated with an antireflection cap with windows and then recrystallized by cw-Ar ion laser irradiation. Grain boundaries are removed from the silicon film at the place where the window is opened because of a temperature gradient due to a change in laserbeam absorption in the silicon film. The (100) texture is observed in the grain-boundary-free areas although the silicon shows (110) texture before the recrystallization. An SOI/ MOSFET has been fabricated in the recrystallized film. The channel regions of MOS-FET’s are aligned in the window regions. Field-effect mobility of 490 cm2/Vs is obtained for n-channel MOSFET’s. Source-to-drain leakage current of 5fA/μm is obtained at drain voltage of 5V and back-gate voltage of -100V for the W/L = 10 μ/2 μm MOSFET.

Interface Charges at the Back Surface of Seeded, Recrystallized Silicon Films

Interface charges at the back of seeded, recrystallized silicon films on insulating oxide layers were investigated and compared to those at the back of unseeded films. Both the fixed charge density and the interface trap density were found to be appreciably lower for the seeded devices than for unseeded devices. A recrystallization technique which melted the silicon film a minimum number of times produced the lowest interface charge densities. The differences between seeded and unseeded structures may be related to the higher charge densities expected for grain orientations other than {100} or to traps located at the grain boundaries near the back surface of the silicon film.

Electrical properties of halogen lamp recrystallized silicon films on SiO2

The electrical properties of halogen lamp recrystallized silicon films on oxide-coated Si substrates have been investigated by capacitance technique and transport measurements. Bulk and interface defect densities revealed by deep level transient spectroscopy are lower than 5×1011 cm−3 and 1010 eV−1 cm−2, respectively. However, the generation lifetimes on the order of 0.1 μs, obtained from pulsed metal-oxide-semiconductor (MOS) capacitor techniques, cannot be accounted for by bulk or surface generation, given the very low defect densities observed. The source of defects may be the subgrain boundaries. Electron mobility measured from depletion-mode MOS transistors ( μ=700 cm2/V s) is comparable to that obtainable in bulk-type material. Subgrain boundaries do not appear to have a significant effect on carrier transport.

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.

A current conduction mechanism in laser recrystallized silicon metal-oxide-semiconductor transistors

Laser recrystallization is a method used for improving the quality of deposited silicon films by enlarging the grain sizes and reducing the density of defect states in the films. N-channel MOS transistors were fabricated on silicon films that had been recrystallized by an argon ion laser at different power levels. These transistors showed electrical characteristics similar, but somewhat inferior to those devices fabricated on single crystal silicon substrates. These differences are attributed to the presence of trapping states at the grain boundaries of the crystallites in the recrystallized silicon. A coulombic scattering model is presented to explain these differences. In the case of films annealed at low laser power, an additional factor of nonuniform trap state distribution is invoked to explain device characteristics. This model provides an adequate explanation for the observed transport properties of transistors fabricated from recrystallized silicon films.

Silicon photodetector integrated on a lithium tantalate substrate

We report the fabrication of metal-oxide-semiconductor field-effect transistors (MOSFET’s) in laser recrystallized silicon films on a lithium tantalate substrate with an intervening silicon dioxide layer. Deposited polycrystalline silicon films were irradiated with a scanning focused argon ion laser beam which caused melting and subsequent crystallization of the silicon film into crystallites suitable for MOSFET fabrication. Melting and recrystallization of the silicon film without damaging the substrate were accomplished by irradiation with 0.3–0.4 W of argon ion laser power focused to a 50-μm-diam spot. Transistor channel mobility was measured to be 50 cm2/Vs. When operated as integrated photodetectors, a responsivity of approximately 0.5 A/W was measured. Theoretical operation of these MOSFET’s as integrated photodetectors is derived and compared to observed operation.

Zone-melting recrystallization of polycrystalline silicon films on fused silica substrates using RF-Heated carbon susceptor

High-quality recrystallized silicon films on fused silica substrates have been produced with a new micro-zone-melting method using an RF-heated carbon susceptor. In this method, the fused silica substrate, on which a 0.5-1.0-µm-thick polycrystalline silicon film encapsulated with a 1.2-µm-thick CVD-SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> layer has been deposited, is moved across the carbon susceptor surface, which has a narrow-strip high-temperature zone. Recrystallized silicon films with