退火对Ge诱导晶化多晶Si薄膜结晶特性的影响

本文采用磁控溅射法, 衬底温度500 ℃下在硅衬底上分别制备具有Ge填埋层的a-Si/Ge 薄膜和a-Si薄膜, 并进行后续退火, 采用Raman光谱、X射线衍射、原子力显微镜及场发射扫描电镜等对所制薄膜样品进行结构表征. 结果表明, Ge有诱导非晶硅晶化的作用, 并得出以下重要结论: 衬底温度为500 ℃时生长的a-Si/Ge薄膜, 经600 ℃退火5 h Ge诱导非晶硅薄膜的晶化率为44%, 在相同的退火时间下退火温度提高到700 ℃, 晶化率达54%. 相同条件下, 无Ge填埋层的a-Si薄膜经800 ℃退火5 h薄膜实现晶化, 晶化率为46%. 通过Ge填埋层诱导晶化可使在相同的条件下生长的非晶硅晶薄膜的晶化温度降低约200 ℃. Ge诱导晶化多晶Si薄膜在Si(200)方向具有高度择优取向, 且在此方向对应的晶粒尺寸约为76 nm. 通过Ge诱导晶化制备多晶Si薄膜有望成为制备高质量多晶Si薄膜的一条有效途径.     

In situ spectromicroscopic study of nickel induced lateral crystallization of amorphous silicon thin film using SPESM

Scanning photoelectron spectromicroscopy (SPESM) has been used to study nickel metal induced lateral crystallization (Ni-MILC) of amorphous silicon (a-Si) thin films, produced by in situ annealing of vacuum deposited Ni patterned films on a-Si. The spatial variations in the chemical composition of the Ni-MILC of a-Si were directly imaged. High-resolution photoemission spectra of both Si 2p and Ni 3p core levels and valence band were used to evaluate morphological changes and chemical interactions. Our direct spectromicroscopic characterization clearly shows that the Ni-MILC process in UHV leads to the lower crystallization temperature and a faster crystallization speed of a-Si, and a poly-Si film with high-crystallinity can be obtained. A unified mechanism for the enhanced growth rate of the high-crystallinity poly-Si film produced by Ni-MILC in UHV is proposed.     

AlCl3-induced crystallization of amorphous silicon thin films

It is reported that the direct contact between Al and amorphous silicon (a-Si) enhances the crystallization of a-Si films. But the polycrystalline silicon (poly-Si) films crystallized by the direct contact of Al metal film suffer the problems of rough surface. In our study, we utilized the AlCl₃ vapor during the a-Si films deposition instead of Al metal film to enhance crystallization. X-ray diffraction (XRD) shows that the AlCl₃ vapor so successfully enhanced the crystallization of a-Si films that the crystallization was completed in 5 h at 540 °C. And the orientation of the poly-Si film deposited with AlCl₃ vapor is much more random than that of annealed with Al metal under layer. But the average grain size is much larger than that. Moreover, the surface of the AlCl₃-induced crystallized poly-Si film was much smoother than that of the Al-induced poly-Si film. The Al and Cl incorporation into the poly-Si film was confirmed using X-ray photoelectron spectroscopy (XPS) and found that the quantity of Al and Cl incorporated into the Si film was below the detection limit of XPS.     

铝诱导非晶硅薄膜的场致低温快速晶化及其结构表征

铝诱导非晶硅薄膜晶化可以降低退火温度、缩短退火时间，是制备多晶硅薄膜的一种重要方法.在此基础上，通过在退火过程中加入电场加速了界面处硅、铝原子间的互扩散，实现了非晶硅薄膜的快速低温晶化.实验结果表明，外加电场，退火温度为400℃，退火时间为60min时，薄膜的晶化率大于60％；退火温度为450℃退火时间为30min时，薄膜已经呈现明显的晶化现象；退火温度为500℃退火时间为15min时，薄膜的x射线多晶峰强度与非晶峰强度之比为未加电场的3—4倍. 关键词： 非晶硅薄膜 多晶硅薄膜 外加电场     

Al-Induced Crystallization Growth of Si Films by Inductively Coupled Plasma Chemical Vapour Deposition

Polycrystalline Si （poly-Si） films are in situ grown on Al-coated glass substrates by inductively coupled plasma chemical vapour deposition at a temperature as low as 350℃. Compared to the traditional annealing crystalliza- tion of amorphous Si/Al-layer structures, no layer exchange is observed and the resultant poly-Si film is much thicker than Al layer. By analysing the depth profiles of the elemental composition, no remains of A1 atoms are detected in Si layer within the limit （〈0.01 at.%） of the used evaluations. It is indicated that the poly-Si material obtained by Al-induced crystallization growth has more potential applications than that prepared by annealing the amorphous Si/Al-layer structures.     

Aluminium-induced crystallization of amorphous silicon films deposited by DC magnetron sputtering on glasses

Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550 °C during 4 h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum-annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evidence that crystallization is initiated at 450 °C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450 °C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC).     

On the Discontinuity of Polycrystalline Silicon Thin Films Realized by Aluminum-Induced Crystallization of PECVD-Deposited Amorphous Si

Crystallization of glass/Aluminum (50, 100, 200 nm) /hydrogenated amorphous silicon (a-Si:H) (50, 100, 200 nm) samples by Aluminum-induced crystallization (AIC) is investigated in this article. After annealing and wet etching, we found that the continuity of the polycrystalline silicon (poly-Si) thin films was strongly dependent on the double layer thicknesses. Increasing the a-Si:H/Al layer thickness ratio would improve the film microcosmic continuity. However, too thick Si layer might cause convex or peeling off during annealing. Scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX) are introduced to analyze the process of the peeling off. When the thickness ratio of a-Si:H/Al layer is around 1 to 1.5 and a-Si:H layer is less than 200 nm, the poly-Si film has a good continuity. Hall measurements are introduced to determine the electrical properties. Raman spectroscopy and X-ray diffraction (XRD) results show that the poly-Si film is completely crystallized and has a preferential (111) orientation.     

Reaction between amorphous Si and crystalline Al in Al/Si and Si/Al bilayers: microstructural and thermodynamic analysis of layer exchange

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/Si and Si/Al bilayers was studied upon annealing at 250 °C by X-ray diffraction and Auger electron spectroscopy. The Al/a-Si bilayers and a-Si/Al bilayers were prepared by sputter deposition on single-crystal silicon wafers with a silicon-oxide film on top. During the isothermal annealing a layer-exchange process occurred in both types of bilayers. A continuous polycrystalline silicon (poly-Si) film was formed within, and thereby gradually replacing, the initial Al metal layer. The sublayer sequence in the original bilayer influenced the speed of the poly-Si formation and the layer-exchange process. After annealing, the Al fiber texture in the as-deposited bilayers had become stronger, the Al crystallites had grown laterally, and the macrostress in the Al layer had been released. The amorphous Si layer had crystallized into an aggregate of nanocrystals with {111} planes parallel to the surface, with a crystallite size of about 15–25 nm. An extensive analysis of the Gibbs energy change due to annealing showed that the layer exchange may be promoted by the release of elastic energy and grain growth for the Al phase. PACS 05.70.Jk; 61.43.Dq; 68.35.Rh; 61.72.Cc; 68.55.Jk     

Thermal transport in melting and recrystallization of amorphous and polycrystalline Si thin films

The liquid-solid interface motion and temperature history of thin Si films during excimer laser annealing are observed by in situ experiments combining time-resolved (~1 ns) electrical conductance, optical reflectance/transmittance at visible and near-IR wavelengths and thermal emission measurements. For laser energy densities causing partial melting, the maximum temperature remains close to the melting point of amorphous silicon (a-Si). When complete melting occurs, substantial supercooling is observed, followed by spontaneous nucleation. These phase transformations are consistent with the recrystallized poly-Si morphologies. It is also found that the melting of poly-Si occurs close to the melting point of crystalline silicon. This temperature is higher than the melting point of a-Si by about 100-150 K.     

Evolution of surface morphology during the growth of amorphous and polycrystalline silicon films

The evolution of the surface morphology of LPCVD poly-Si films (deposition temperature 620°C), a-Si films (deposition temperature 550°C) and poly-Si films, obtained by the crystallization of a-Si is investigated in the thickness range 40–500 nm. It is found that upon an increase in the thickness from 40 to 500 nm, the surface roughness (parameters S _q , S _z , S _v ) is increased for poly-Si, while in the case of a-Si and poly-Si obtained by crystallization a-Si, on the contrary, decreases. The correlation length (S _al ) increases for all three types of silicon films. Poly-Si films, obtained by the crystallization of a-Si, as compared to LPCVD poly-Si films have a significantly lower surface roughness, respectively, S _q two times less at a thickness of 40 nm and sixteen times less at 500 nm. In contrast to thick films, thin a-Si films (at thicknesses of less than 40 nm) have a granular structure, which is especially pronounced at an average thickness of about 20 nm and there is a maximum on the dependence of the roughness S _q on the thickness.     

变温退火制备铝诱导大晶粒多晶硅薄膜的机理研究

为了缩短铝诱导法制备大晶粒多晶硅薄膜的退火时间,用射频磁控溅射法在玻璃衬底上沉积了a-Si/SiO2/Al叠层膜,并用两种方法进行变温退火.分析了变温退火工艺对铝诱导晶化过程的影响,着重讨论了退火过程中温度由低温升到高温时不形成小晶粒的机理和条件.研究表明,当退火温度升高时,是否形成小晶粒取决于晶粒半径、耗尽层厚度和相邻晶粒间距三者之间的关系.     

Crystallization of sputter deposited amorphous metal thin films

We have studied the crystallization of DC sputter deposited amorphous W-Si alloys under three separate conditions: free standing films, amorphous films deposited on Si substrates, and films with one of four different overlayers. In the case of the free standing films the crystallization temperature versus composition was measured by differential thermal analysis (DTA) for films with Si contents from 5 at% to 38 at%. Films with Si concentrations of 38% to 22% were amorphous as deposited, while those with less Si were crystalline. The crystallization temperature was a strong function of composition with a maximum T_c of 915°C (at a heating rate of 20 K/min) in alloys with 28% Si. Overlayers of W, Cu, Au and Al were investigated. Both the W and Cu overlayers had little effect on the stability of the underlying W-Si, while both the Au and Al reduced the crystallization temperature by at least 100°C. The results reported here reinforce the observation that the choice of overlayer plays a critical role in determining the overall stability of metallization systems that include amorphous layers as diffusion barriers.     

The influence of a poly-Si intermediate layer on the crystallization behaviour of Ni-Ti SMA magnetron sputtered thin films

Shape memory alloy Ni-Ti thin films as sputtered are amorphous if the substrate is not intentionally heated during deposition. Therefore, these films have to be heat treated to induce crystallization in order to exhibit the shape-memory effect. Several films have been prepared by dc magnetron sputtering and then studied concerning the influence of the type of substrate (single-crystal Si, polycrystalline Si) on the crystallization kinetics and the final structure. The structural development of the films during crystallization (at a constant temperature of 430 °C) has been studied by X-ray diffraction in grazing incidence geometry off-plane (GIXD) at a synchrotron-radiation beamline. These experiments allow us to establish a correlation between the deposition conditions and the kinetics of crystallization. For films deposited at an electrode distance of 70 mm on a Si(100) substrate, a longer crystallization time is needed compared with films obtained at 40 mm, for otherwise fixed deposition parameters. The analysis of the nucleation kinetics by using the Johnson–Mehl–Avrami equation leads to exponents between 2.6 and 3. The presence of an intermediate layer of poly-Si drastically enhances the crystallization process. Additionally, ex situ annealing of identical samples at 500 °C during 1 h and complementary characterization of the structure and morphology of the films by cross-sectional transmission electron microscopy and selected-area electron diffraction were performed. The temperature dependence of the electrical resistivity was measured, identifying the phase transformation temperature ranges. An increase of the overall resistivity with the precipitation of Ni₄Ti₃ has been detected. Results obtained by X-ray reflectometry and GIXD suggest that during crystallization excess nickel is driven into an amorphous region ahead of the crystal/amorphous interface, thus leading to a higher concentration of Ni at the surface and further precipitation of Ni₄Ti₃. PACS 81.15.Cd; 61.10.Nz; 68.55.Jk     

Fabrication of large-grain polycrystalline silicon for solar cells

The rapid recrystallization of a-Si films utilizing excimer laser crystallization (ELC) is investigated. The melt duration of liquid silicon (liquid Si) is measured by in-situ time-resolved optical measurements during ELC. The grain size of crystallized poly-Si films are characterized by FE-SEM. The substrate temperature as a function of the longest melt duration of liquid Si for different Si film thicknesses are presented. In-situ timeresolved optical measurements reveal that the longest melt duration of 400-nm-thick a-Si thin films at a substrate temperature of 500 °C is 1714 ns. The diameter of the disk grain as large as 4.7 μm is produced by ELC, which can be applied to solar cells with a high conversion efficiency and reliability.     

纳米β-FeSi2/a-Si多层膜室温光致发光分析

采用射频磁控溅射的方法,在Si（100）基片上制备了纳米β-FeSi₂/Si多层结构,利用X射线衍射、透射电子显微镜、光致发光光谱等表征技术,研究了β-FeSi₂/Si多层结构的结构、成分和光致发光特性.研究结果表明：利用磁控溅射法得到的Fe/Si多层膜,室温下能够检测到β-FeSi₂的1.53 μm处光致发光信号;未退火时多层膜是（非晶的FeSi₂+β-FeSi₂颗粒）/非晶Si结构,退火后则是 关键词： 2')" href="#">β-FeSi₂ 磁控溅射 XRD 光致发光光谱     

Growth kinetics and polysilicon formation by aluminium-induced crystallization on glass-ceramic substrates

In this work, we present extended structural properties of poly-Si thin films fabricated by aluminium-induced crystallization (AIC) of amorphous silicon (a-Si) on high-temperature glass-ceramic substrates. The silicon nucleation kinetics on glass-ceramic substrates was investigated by optical microscopy. The crystalline quality of the films was studied by micro-Raman spectroscopy as a function of exchange annealing conditions. By means of electron backscattering diffraction (EBSD), we have analyzed the effect of thermal annealing on silicon grain size and its distribution, intra- and inter-grains defects, and on the grains preferential crystallographic orientation. The optimal thermal annealing condition, allowing 100% crystallized polysilicon large grains with an average grain size of 26 μm and 〈100〉 oriented, acquired a thermal budget of 475°C and 8 h.     

Synthesis of nanocrystalline ZnTiO3 perovskite thin films by sol-gel process assisted by microwave irradiation

Nanocrystalline ZnTiO₃ thin films have been grown on Si (1 0 0) at room temperature by using simple, cost effective sol-gel process assisted by microwave irradiation for thermal treatment. For comparison purpose the deposited films have subjected to two kinds of annealing treatments: first set by using conventional annealing and second set by irradiating the deposited films at different microwave powers for 10 min. In both treated films, formation of cubic phase ZnTiO₃ structure has been observed. It is evident that there is a dramatic structural modification when the deposited films are exposed to microwave. It is evident that there is a dramatic change in the morphological properties of the films irradiated in microwave compared to the conventional annealing temperature. Microwave exposed films have shown 19% of Zn, 19% of Ti and 62% of O in the films close to the stiochiometry of the ZnTiO₃, where as annealed films have shown 18% of Zn, 17.5% of Ti, and 64.5% of O in the films of ZnTiO₃. Plausible mechanism for the formation of cubic phase of ZnTiO₃ at low microwave powers has also been discussed. This new innovative microwave heating could open a door for the advanced technologies to cut down the process cost in post treatment of the materials.     

Thermal annealing of a-Si:H/a-SiNx:H multilayers

The crystallinity of Si/SiN_x multilayers annealed by a rapid thermal process and furnace annealing is investigated by a Raman-scattering technique and transmission electron microscopy. It is found that the crystallization temperature varies from 900 °C to 1000 °C when the thickness of a-Si:H decreases from 4.0 nm to 2.0 nm. Raman measurements imply that the high crystallization temperature for the a-Si:H sublayers originates from the confinement modulated by the interfaces between a-Si:H and a-SiN_x:H. In addition to the annealing temperature, the thermal process also plays an important role in crystallization of a-Si sublayers. The a-Si:H sublayers thinner than 4.0 nm can not be crystallized by furnace annealing for 30 min, even when the annealing temperature is as high as 1000 °C. In contrast, rapid thermal annealing is advantageous for nucleation and crystallization. The origin of process-dependent crystallization in constrained a-Si:H is briefly discussed. Received: 11 April 2001 / Accepted: 20 June 2001 / Published online: 30 August 2001     

Origins of interdiffusion, crystallization and layer exchange in crystalline Al/amorphous Si layer systems

Aluminium-induced crystallization of amorphous silicon (a-Si) in Al/a-Si and a-Si/Al bilayers was studied upon annealing at low temperatures between 165 and 250 °C, by X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Upon annealing the inward diffusion of Si along grain boundaries in Al takes place, followed by crystallization of this diffused Si. Continuous annealing leads to (more or less) layer exchange in both types of bilayers. The change in bulk energy of the Al phase (release of macrostress and microstrain, increase of grain size) promotes the occurrence of layer exchange, whereas changes in surface and interface energies counteract the layer exchange.     

不同形貌衬底上铝诱导poly-Si薄膜的制备及表征

以表面平整、粗糙的玻璃为衬底,在不同衬底温度下直流磁控溅射沉积a-Si薄膜,制备成glass/a-Si/Al样品,经退火处理制备了poly-Si薄膜。分别采用Raman光谱、XRD光谱等手段研究了衬底粗糙度以及衬底温度对铝诱导晶化(AIC)制备的poly-Si品质的影响。Raman光谱表明：所有样品在521 cm-1都有尖锐、对称的Raman峰出现,表明样品完全结晶;XRD结果表明：poly-Si在(111)晶向择优生长;XRD在(111)处的半高宽值(FWHM)表明：玻璃衬底的形貌和a-Si沉积的温度对poly-Si的品质产生影响。200 ℃可能是AIC制备poly-Si薄膜时沉积a-Si时的最适温度。