扫描电子束在绝缘衬底上生长单晶硅薄膜(SOI)的实验研究

在绝缘衬底上生长单晶硅薄膜,即SOI技术,是近年发展起来研制三维集成电路的一项新技术。本文讨论了利用扫描电子束对淀积在SiO2上的多晶硅薄膜进行改性的实验。采用籽晶液相外延形成单晶硅薄膜。本实验的重点在于摸索电子束的功率密度、扫描速度、衬底的温度和样品结构等因素对形成单晶硅薄膜质量的影响。实验取得了较好的结果,获得了20025m2的单晶区。     

THE GROWTH OF MONOCRYSTALLINE SILICON THIN FILM ON INSULATOR (SOI) BY SCANNING ELECTRON BEAM

An experiment for preparation of SOI films by using the scanning electron beam to modify the polycrystalline silicon on SiO2 is presented. This method takes on the epitaxial lateral growth of liquid phase with the crystallon to form monocrystalline silicon films. The effects of the beam power density, scanning velocity, temperature of the substrates and the construction of samples on the quality of the monocrystalline silicon films were discussed. A good experimental result has been obtained, the monocrystalline silicon zone is nearly 200×25μm2.     

A study of cracking in GaN grown on silicon by molecular beam epitaxy

It is observed that GaN layers grown on silicon substrates often crack. The crack characteristics in hexagonal GaN films on Si(111) has been characterized using scanning electron microscopy and Nomarski optical microscopy. The effects of growth temperature, layer thickness, and V/III ratios on the cracking have been analyzed. The critical thickness for crack initiation was estimated using a simple theoretical model and is shown to have good agreement with experimental results. Crack-free GaN on Si(111) of thicknesses greater than one micron is possible by using low growth temperatures.     

Highly reliable high-voltage transistors by use of the SIPOS process

The n-p-n and p-n-p high-voltage transistors showing high reliabilities have been developed by using semi-insulating polycrystalline-silicon (SIPOS) films for the surface passivation. SIPOS films are chemically vapor-deposited polycrystalline-silicon doped with oxygen or nitrogen atoms. The films employed for the surface passivation of high-voltage transistors are composed of triple layers, which are oxygen-doped SIPOS films of 0.5-µm thickness to stabilize the silicon interface, nitrogen-doped SIPOS films of 0.15-µm thickness to prevent water or sodium ions from reaching the silicon surface, and silicon dioxide films to prevent dielectric breakdown of the SIPOS films under very high-voltage operation. The n-p-n and p-n-p SIPOS transistors rated at 800 and 2500 V have been produced in planar-like structures with field-limiting rings. These transistors showed highly reliable characteristics, because the passivating SIPOS layer provides a good protection against ionic contamination and externally applied electric fields. Furthermore, 10-kV n-p-n SIPOS transistors with multiple rings have been fabricated and found that operation is stable.     

Solid-phase Crystallization of Hydrogenated Amorphous Silicon on Glass Substrates

Amorphous silicon films prepared by PECVD on glass substrate have been crystallized by conventional furnace annealing and rapid thermal annealing（RTA）, respectively. From the Raman spectra, X- ray diffraction and scanning electron microscope, it is found that the grain size is crystallized at 850 ℃ in both techniques. The thin film made by RTA is smooth and of perfect structure, the thin film annealed by FA has a highly structural disorder. An average grain size of about 30 nm is obtained by both techniques.     

脉冲准分子激光制备PCLT热释电薄膜

采用脉冲激光沉积的方法,在Pt/SiO_2/Si衬底上制备了掺Ca的(Pb,La)TiO_3薄膜。薄膜呈多晶结构,具有较好的铁电性和热释电性。由于掺Ca的作用,使薄膜的材料探测优值和电压响应优值几乎与单晶MgO衬底上的c轴取向的PbTiO_3或(Ph,La)TiO_3薄膜相比拟。这些较好的实验结果是在硅基衬底上的铁电薄膜中获得的,因而对研制单片集成的红外热释电阵列将有一定的意义。     

Specific features of photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from monosilane–hydrogen mixture

Photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from a monosilane-hydrogen mixture have been studied at a fraction of hydrogen in the mixture that corresponds to the onset of formation of a nanocrystalline phase in the structure of the films obtained. A behavior untypical of amorphous hydrogenated silicon films is observed for the photoconductivity and the spectral dependence of the absorption coefficient. The temperature dependences of the photoconductivity in the films under study are found to vary with the energy of incident photons. At a photon energy of 1.3 eV, temperature quenching of photoconductivity is observed. Prolonged illumination of the films led to a certain decrease in the absorption coefficient at photon energies in the range 1.2–1.5 eV. The results obtained are attributed to the possible presence of silicon nanocrystals in the structure of the films and to the influence of these nanocrystals on their photoelectric and optical properties.     

Processing of titanium films on silicon using a multiscanned electron beam

A multiscanned electron beam has been used to process titanium films thermally on single-crystal silicon. The redistribution of titanium and the composition of the processed films were studied by Rutherford backscattering. Oxygen contamination within the titanium is found to control the reaction rate. Processing conditions have been established which give stoichiometric TiSi2 layers and the removal of oxygen from the system. These results have been confirmed by Auger analysis and the surface texture has been examined using scanning electron microscopy.     

High‐quality surface passivation of silicon solar cells in an industrial‐type inline plasma silicon nitride deposition system

We have studied the surface passivation of silicon by deposition of silicon nitride (SiN) in an industrial‐type inline plasma‐enhanced chemical vapor deposition (PECVD) reactor designed for the continuous coating of silicon solar cells with high throughput. An optimization study for the passivation of low‐resistivity p‐type silicon has been performed exploring the dependence of the film quality on key deposition parameters of the system. With the optimized films, excellent passivation properties have been obtained, both on undiffused p‐type silicon and on phosphorus‐diffused n⁺ emitters. Using a simple design, solar cells with conversion efficiencies above 20% have been fabricated to prove the efficacy of the inline PECVD SiN. The passivation properties of the films are on a par with those of high‐quality films prepared in small‐area laboratory PECVD reactors. Copyright © 2004 John Wiley & Sons, Ltd.     

Subthreshold slope of thin-film SOI MOSFET's

Silicon-on-insulator (SOI) n-channel transistors have been made in thin (90 nm) silicon films. Both modeling and experimental results show that excellent subthreshold slopes can be obtained (62 mV/ decade) when the silicon film thickness is smaller than the maximum depletion depth in the transistor channel. For comparison, the subthreshold slope of transistors made in thicker films is also reported.     

Improved micromorph solar cells by means of mixed‐phase n‐doped silicon oxide layers

A good light trapping scheme is necessary to improve the performance of amorphous/microcrystalline silicon tandem cells. This is generally achieved by using a highly reflective transparent conducting oxide/metal back contact plus an intermediate reflector between the component cells. In this work, the use of doped silicon oxide as alternative n‐layer in micromorph solar cells is proposed as a means to obtain high current values using a simple Ag back contact and no extra reflector between the component cells n‐doped silicon oxide layers with a wide range of optical and electrical properties have been prepared. The influence of different deposition regimes on the material properties has been studied. The main findings are the following: (i) when carbon dioxide is added to the gas mixture, sufficiently high hydrogen dilution is necessary to widen the transition region from highly conductive microcrystalline‐like films to amorphous material characterized by low electrical conductivity; (ii) lower refractive index values are found with lower deposition pressure. Optimal n‐doped silicon oxide layers have been used in both component cells of micromorph devices, adopting a simple Ag back contact. Higher current values for both cells are obtained in comparison with the values obtained using standard n‐doped microcrystalline silicon, whereas similar values of fill factor and open circuit voltage are measured. The current enhancement is particularly evident for the bottom cell, as revealed by the increased spectral response in the red/infrared region. The results prove the high potential of n‐doped silicon oxide as ideal reflector for thin‐film silicon solar cells. Copyright © 2011 John Wiley & Sons, Ltd.     

Ion-sensitive field-effect transistors with inorganic gate oxide for pH sensing

Ion-sensitive field-effect transistors (ISFET's) have been fabricated by using silicon films on sapphire substrates (SOS). Using this structure SiO2, ZrO2, and Ta2O5films are examined as hydrogenion-sensitive materials, and Ta2O5film has been found to have the highest pH sensitivity (56 mV/pH) among them. The measured pH sensitivity of this SOS-ISFET's is compared with the theoretical sensitivity based on the site-binding model of proton dissociation reaction on the metal oxide film and good agreement between them is obtained.     

Multilayer vapor-phase epitaxial silicon millimeter-wave IMPATT diodes

A new procedure has been developed for fabricating small-area silicon avalanche diodes directly on a plated copper heat sink. The process incorporates multilayer vapor-phase epitaxially grown silicon and a preferential electrochemical etching technique to fabricate thin uniform silicon films; 6 µ thick films on 2-cm diameter wafers have been obtained reproducibly with little difficulty. Inverted mesa diodes 30-40 µ in diameter have been formed by etching through the unmasked area of the thinned silicon wafer. Implementation of this technology has resulted in single drift region p⁺-n-n⁺diodes that generate over ¼ W CW power with 6-percent efficiency at 60 GHz.     

Single-crystal silicon transistors in laser-crystallized thin films on bulk glass

High-performance thin-film transistors (TFT) have been fabricated in single-crystal silicon thin films on bulk fused silica. Deposited films of polycrystalline silicon were patterned to control nucleation and growth of single-crystal material in pre-selected areas and encapsulated with a dielectric layer (e.g., SiO2) in preparation for laser crystallization. Patterning also minimized microcracking during crystallization. The patterned silicon layer was crystallized with a scanning CO2laser, which produced islands with preferred crystal orientation. The single crystallinity of the islands was established with transmission electron microscopy after transistor evaluation. The silicon islands were processed with conventional microelectronic techniques to form metal-oxide-semiconductor-field-effect transistors operating in the n-channel enhancement mode. The devices display exceptional electrical characteristics with "low-field" channel mobilities > 1000 cm²/V sec and leakage currents < 10 pA, for a Channel length of 12 µm and width of 20 µm. Achievement of high-performance TFT's with the combined features of microcrack suppression, preferred orientation, and selected-area crystallization render CO2- laser processing of silicon films a viable and versatile basis for a silicon-on-insulator technology.     

在Si(111)上磁控溅射碳化硅薄膜的H2退火效应

用射频磁控溅射法在常温硅衬底上制备了碳化硅薄膜并研究了氢退火对薄膜的影响.用傅里叶红外透射谱(FTIR)、X射线衍射(XRD)、X光电子能谱(XPS)、扫描电镜(SEM)及原子力显微镜(AFM)对薄膜样品进行了结构、组分和形貌分析.结果表明:高温退火后SiC膜的晶化程度明显提高,而且在薄膜中观察到了碳纳米线的形成.     

Amorphous-silicon thin-film transistor with liquid phase depositionof silicon dioxide gate insulator

The liquid phase deposition of silicon dioxide (LPD-SiO₂) at 50°C has been successfully applied as the gate insulator for inverted, staggered amorphous silicon thin-film transistors (TFTs). The maximum field-effect mobility of the TFTs, estimated from the saturation region, was 0.53 cm²/V-s, comparable to that obtained for conventional, silicon nitride (SiN_x ) gate transistors. The threshold voltage and subthreshold swing were 6.2 V and 0.76 V/decade, respectively. Interface and bulk characteristics are as good as those obtained for silicon nitride (SiN _x) films deposited by plasma enhanced chemical vapor deposition     

Characteristics of thermally nitrided silicon dioxide film and plasma enhancement

After reviewing characteristics of thermally nitrided silicon dioxide films, plasma enhanced nitridation is described. The plasma technique makes possible reduction of the nitridation temperature by activating reaction species. Silicon dioxide films of about 10 nm thickness were nitrided in ammonia gas plasma, for example, at 1000‡C and at a pressure of 40 Pa. From the results of the AES depth profiles and the N_ss distribution, good dielectric and interfacial properties have been obtained via plasma nitridation. The plasma nitroxide films are useful for gate insulators of small MOSFETs in future VLSI.     

Improvement of the Crystallinity of Silicon Films Deposited by Hot-Wire Chemical Vapor Deposition with Negative Substrate Bias

We have investigated the effect of negative substrate bias on microcrystalline silicon films deposited on glass and stainless steel by hot-wire chemical vapor deposition (HWCVD) to gain insight into the effect of negative substrate bias on crystallization. Structural characterization of the silicon films was performed by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy. It was found that the crystallinity of the films is obviously improved by applying the substrate bias, especially for films on stainless steel. At hot-wire temperature of 1800°C and negative substrate bias of ?800 V, grain size as large as 200 nm was obtained on stainless-steel substrate with crystalline fraction 9% higher than that of films deposited on glass and 15% higher than that of films deposited without substrate bias. It is deduced that the improvement of the crystallinity is mainly related to the accelerated electrons emitted from the hot wires. The differences in this improvement between different substrates are caused by the different electrical potential of the substrates. A solar cell fabricated by HWCVD with ?800 V substrate bias is demonstrated, showing an obviously higher conversion efficiency than that without substrate bias.     

Deposition of the IV–VI films by the hot-wall method on silicon substrates 100 mm in diameter

An experimental installation for the deposition of films of IV–VI compounds by the hot-wall method on silicon substrates 100 mm in diameter is described. The PbTe films on silicon wafers with orientation (100) are obtained and investigated. The PbTe films have a continuous mirror surface and repeat the substrate orientation. The peculiarities of obtaining such films are discussed.     

Laser forming of silicon films using nanoparticle precursor

Polycrystalline silicon films containing cubic silicon crystallites of size 3–4 μm have been formed on nickel substrates by fusing and sintering silicon nanoparticle precursors using a laser. A mechanism for the fusion and sintering of these nanoparticles, resulting in reduced heat input and continuous film formation by surface and grain boundary diffusion, is discussed. Films were characterized by optical microscopy, scanning electron microscopy, energydispersive spectroscopy, and Raman spectroscopy. Films were doped with n- as well as p-type dopants by using a laser doping technique and their current-voltage (I–V) characteristics were measured.