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无 锡 职 业 技 术 学 院毕业设计说明书（英文翻译）Preparation of polysilicon thin film Abstract: The low pressure chemical vapor deposition, solid-phase crystallization, excimer laser crystallization, rapid thermal annealing, metal-induced crystallization, and plasma enhanced chemical vapor deposition reaction is used for the preparation polysilicon thin film of several major ways. They have their different preparation principle, the crystallization mechanism, and their advantages and disadvantages.Key words: hydrogenated amorphous silicon and polysilicon grain The preparation methods of polycrystallinesilicon film 1 Introduction At the same time polysilicon thin film materials with silicon materials and the high mobility of amorphous silicon materials can be large, the advantages of low-cost preparation. Therefore, the polysilicon thin film materials of growing concern, the preparation of polycrystalline silicon thin films can be divided into two categories: one category is high-temperature process, the preparation of the temperature is higher than 600 , and the use of expensive substrate quartz, but the preparation of relatively simple. The other is low-temperature process, the processing temperature is below 600 , can be used for low-cost glass substrate, thus producing large area, but the preparation of more complex. Currently polysilicon thin film preparation methods have the following main categories: 2 low pressure chemical vapor deposition (LPCVD) This is a direct polysilicon production methods. LPCVD IC is used in the preparation of polysilicon thin film commonly used by the standard method, a fast-growing, film-forming dense, uniform and equipment, such as large-capacity features. Silane gas polysilicon thin film can be directly deposited by LPCVD method in the substrate, the typical deposition parameters are: silane pressure of 13.3 to 26.6 Pa, deposition temperature Td = 580 630 , the growth rate of 5 to 10 nm / min . The deposition temperature higher, such as ordinary glass softening temperature at 500 to 600 , it can not use cheap glass and must be used for expensive quartz substrate. LPCVD of polysilicon thin film growth, grain is preferred orientation, morphology in a V shape, containing high-density micro-twin crystal defects, and small grain size, carrier mobility rate is not big enough and to the device application subject to certain restrictions. Despite the reduction silane pressure to increase the grain size, but often accompanied by the increase of surface roughness of the carrier mobility of the devices electrical stability and have a negative impact. Solid-phase crystallization 3 (SPC) The so-called solid-phase crystallization of amorphous solids refers to the temperature of crystallization occurred below its melting after crystallization temperature. This is a kind of indirect way polysilicon production, the first to use silane gas as raw materials, with LPCVD method in about 550 of a-Si: H film, then films at 600 to a high temperature above the melting, then a lower temperature when the nucleus, with lower melting temperature of the silicon crystal in the nuclei of to continue to increase grain into polysilicon films. Use this method, the polysilicon thin film grain size depends on the thickness of thin films and crystallization temperature. Crystal annealing temperature is an important factor in the effect of the 700 following annealing temperature range, the lower the temperature, the lower the rate of nucleation, annealing at the same time the grain size can be greater, and in more than 700 , at the grain boundary movement has caused the mutual annexation of the grain, makes this temperature range, grain size increased with temperature increase. After a considerable amount of research shows that the method used in the system of grain size polysilicon thin film samples with the initial degree of the disorder closely related to T. Aoyama, and others on the initial conditions for the deposition of solid-phase crystallization of the impact of the study found that the initial material disorder, solid-phase crystallization process of nucleation rate and the lower, larger grain size. As the crystallization process of the formation of nuclei is spontaneous, therefore, SPC polysilicon thin film grain crystal orientation is random. Grain adjacent crystal orientation will be different from a high barrier, and the need for hydrogenation processing to improve the performance of SPC polysilicon. The advantages of this technology can be of large areas of films, the grain size larger than the direct deposition of polysilicon. Doping can be carried out in-situ, low cost, simple process, easy to form lines. SPC is due to the melting temperature of crystallization of amorphous silicon, high temperature of the crystallization process, the temperature is higher than 600 , usually require about 1100 , annealing time for more than 10 hours, does not apply to glass, quartz substrate materials used or Silicon, for the production of small-size devices, such as liquid crystal light valve, such as the camera viewfinder. 资料来源 360毕业设计网 4 excimer laser crystallization (ELA) The laser crystallization of solid-phase crystallization of polysilicon is desirable, the use of the laser pulse transient high-energy incident to the amorphous silicon thin film surface, in the 100 nm thick film surface depth of production of heat effect, a - Si thin film in an instant to 10 , so as to achieve a p-Si-Si the changes. During this process, the laser pulse transient (15 50 ns) energy is a-Si thin film and assimilation into a phase change, and therefore, there will be no excessive heat conduction to the film substrate, a reasonable choice of laser wavelength and power , the use of laser heating can enable a-Si film to the melting temperature and ensure that the temperature of the substrate below 450 , the glass substrates can be used as a substrate, we realized p-Si thin film preparation, and be able to satisfy the LCD OEL on the transparent substrate requirements. Its main advantage of the short pulse width (15 50 ns), substrate heating small. Also available through select mixed crystal, amorphous silicon and polysilicon that is a mixture of. Excimer laser annealing of the crystal mechanism: laser radiation to the surface of a-Si, the surface temperature reached its melting point is reached when the crystal energy density of the domain of Ec. A-Si in the laser radiation energy absorption, and aroused the imbalance in the electronic - hole right, increasing the free energy of electronic conductivity, thermal electron - hole in the heat of the time of radiation-free way to own energy Lattice pass, the surface very rapidly in recent warming, as a large number of amorphous silicon materials gap states and the deep-level, non-radiative transition process is the main compound, and so they have a higher conversion efficiency of light, and heat, if laser Energy density Ec domain of energy density, that is, heated to melting point temperature semiconductor, thin film surface melting, melting will be to the forefront of about 10 m / s speed internal-depth material, after laser irradiation, a certain depth of the thin film layer melting, stop after irradiation, to start melting layer 108-1010 K / s speed cooling, solid-phase and liquid-phase will be the interface between 1-2 m / s to the speed of the surface, cooling after crystallization into polycrystalline thin films, as with the increase of laser energy density, grain size increases, when melted completely amorphous film, film grain or grain into microcrystalline, if laser energy density is less than the energy density of Ec domain, the energy absorbed by not enough to make the surface temperature to the melting point, the film does not crystallization. Under normal circumstances, increase energy density, grain size increased, the film corresponding increase mobility, when the Si film almost all melted, the largest grain. However, the laser energy restrictions, we should not greatly increased, but much of the energy density of the migration rate has dropped. Laser wavelength effects on the crystallization of great influence, the longer the wavelength, laser energy more deeply into the Si film, the better the effect of crystallization. ELA Preparation of polysilicon thin film grain, space selective doped high efficiency, small defects in the crystal, electrical properties, and high rates of migration to 400 cm2/vs, comprehensive performance is the best low-temperature polycrystalline Silicon Films. Process maturity, has been the large-scale production line equipment, but it also has its own shortcomings, the grain size of the laser power-sensitive, large area of less uniform. Repeatability poor, the high cost of equipment, maintenance complex. 5 Rapid Thermal Annealing (RTA) Generally speaking, the rapid annealing process consists of three stages: the warming phase, the stabilization phase and cooling phase. When the annealing furnace power opened, with time and temperature on the rise, as this stage heating stage. Unit time of the change in temperature is very easy to control. After the heating process, the temperature in a stable stage. Finally, when the power switch off the annealing furnace, the temperature decreases with time on this stage, known as the cooling stage. Hydrogenated amorphous silicon used as the initial material, annealing. Equilibrium temperature control in more than 600 , nanocrystalline silicon grains in the form of amorphous silicon thin films, and by the formation of the nanocrystalline silicon grains with the size of the process of annealing temperature and the speed of change. In the heating process, the unit of time if a large amount of temperature change (such as 100 / s), nanocrystalline silicon grains formed by the smaller (1.6 15 nm); if unit time temperature variation of the smaller (eg 1 / s), nanometer silicon particles larger (23 46 nm). Further experiments showed that: extended annealing time and annealing temperature increase does not change the form of nanocrystalline silicon grain size, and in annealing, the temperature rise is directly affected by the formation of the nanocrystalline silicon grain size. In order to clarify the change of temperature on the speed of nanocrystalline silicon formed by the grain size of the impact of the growth in the use of crystal nucleation theory. Crystal Growth in the need to be two steps: the first step is a nuclear, and the second step is growth. That is to say. The need for adequate first step in the growth of crystal Aberdeen. The results showed that: a warming impact speed of the Aberdeen crystal density. Unit time if large temperature change, the Aberdeen crystal density; on the contrary, if the unit time small amount of temperature change, the Aberdeen crystal density. RTA annealing at elevated annealing temperature or extended annealing time and can not be eliminated in the amorphous thin films of the Qing Xue, and others made from amorphous silicon, a fractal growth to the growth of silicon nanotechnology: fractal growth. From down to up, as long as the temperature is not too high so that adjacent nanometer silicon island is not melting, then even if the annealing temperature increase or extend the annealing time which can completely eliminate the amorphous part. RTA prepared by annealing polysilicon small grain size, grain boundary internal crystal density, high density material defects, and high-temperature annealing method is not suitable for the preparation of a glass substrate polysilicon. 6 plasma enhanced chemical reaction vapor deposition (PECVD) Plasma-enhanced chemical reaction vapor deposition (PECVD) glow discharge method is used to activate the electronic chemical vapor deposition reaction. Initially, the gas due to high-energy cosmic rays, such as ultraviolet radiation, the inevitable slight ionization, there is a small number of electronic. Filling in a rarefied gas containers in response to the introduction of excitation source (for example, DC high voltage, RF, pulse power, etc.), electronic role in the acceleration of the electric field under the energy, when it and the gas of neutral particles in a non-elastic collision, is likely to produce secondary electrons, so the conduct of repeated collisions and ionization, the result will be a great number of ions and electrons. As an equal number of positive and negative particles. Therefore, called plasma, and in the form of luminescence release excess energy, a glow. In the plasma, because of the quality of electron and ion difference between the two exchange collision energy through the process has been relatively slow, so in the plasma of charged particles within their reach its thermodynamic equilibrium state, then this will not be the plasma reunification of the temperature, only the so-called electronic temperature and ion temperature. At this point the temperature can reach 104 electronic , and the elements, atomic, ion temperature is only 25 to 300 . Therefore, from a macroeconomic perspective, this plasma temperature is not high, but its internal electronic state is a high-energy, high chemical activity. If more than excited by the energy required by the chemical reaction thermal activation, when excited by the electron energy (1 to 10 eV) to open the molecular bond, leading to the activity of a chemical substance. Therefore, the original need to be carried out under the high-temperature chemical reaction, through discharge plasma role in the low temperature even at room temperature, can also occur. PECVD deposition of the process can be summed up in three stages: 1.SiH4 decomposition activity of a particle Si, H, SiH2 and SiH3; 2. Activity particles in the substrate surface adsorption and diffusion; 3. Substrate is adsorbed on the surface of molecules in the reaction of Poly-Si layer, and released H2; On the surface, in a plasma-assisted deposition process, the ions, and the Netherlands, the Group of sedimentary surface bombardment role is affecting the quality of crystallization one of the important factors. Overcome the impact of this bias is applied through the inhibition or enhancement. PECVD technology for the use of polycrystalline silicon thin film crystallization process, there are two main points of view. Activity is a first adsorption particles to the substrate surface, the recurrence of the various movements, response surface dissociation process, which a crystalline structure, therefore, the surface of the substrate crystal film on the state of play a very important role. another kind of space that is the reaction gas film crystallization temperature play a more important role, that is a phase First of all the structure of particles formed in the area of space plasma, and later spread to the substrate surface grow into polycrystalline film. For SiH4: H2 gas system, a study shows that in the conditions of high hydrogen-doped, when using the RF PECVD polysilicon thin film deposition method, it must adopt substrate heated to 600 above approach can promote the initial stage of growth nucleus formation. When the substrate temperature is less than 300 , only a hydrogenated amorphous silicon (a-Si: H) films. To SiH4: H2 gas source for polysilicon deposition temperature higher than 600 general, are high-temperature process does not apply to the glass substrate. At present, there are reports by SiC14: H2 or SiF4: H2 gas source for polysilicon deposition, lower temperature, about 300 polysilicon can be obtained, but with a polysilicon CVD Preparation of small grain size, and generally does, over 50 nm, grain deficit, the more the grain boundary. 7 horizontal metal induction (MILC) In the early 20th century found a 90-Si add some metals such as Al, Cu, Au, Ag, Ni deposition in the a-Si: H or ion implantation to the a-Si: H film itself, to reduce a-Si p-Si changes to the phase change energy, after the Ni / a-Si: H annealing to enable a-Si thin film crystallization, below the crystallization temperature can be 500 . But because of a failure in the TFT metal pollution in the application. Subsequently found Ni horizontal-induced crystallization can be avoided twins produced, nickel silicide and the lattice constant of silicon is similar and appropriate low-immiscible phase change energy, the use of nickel-metal induced a-Si thin film crystallization method transverse polysilicon thin film. Lateral Crystallization of polysilicon thin film on the surface smooth, with long grain and the grain boundary for the characteristics of the grain boundary barrier height below SPC polysilicon grain boundary barrier height, therefore, MILC TFT has excellent performance, but not deal with the need for hydrogenation. Use of metals such as nickel, in the amorphous silicon film formed on the surface induced by layer, and a metal Ni-Si interface in the silicide formation NiSi2 use silicide and the release of latent heat at the interface due to the lattice lost wrong position and the crystal lattice , a-Si atoms in the interface recrystallization, grain formation of polysilicon, NiSi2 layer destruction, Ni atoms gradually to the a-Si layer the bottom of migration, re-silicide formation NiSi2 so repeatedly been a-Si layer is basically all crystal , and its general induced temperature at 500 , and the duration of about 1 hour O, the annealing time and the film thickness. Metal-induced crystallization of amorphous silicon thin films prepared by polysilicon with high uniformity and low cost, linked to the outside metal mask can also be amorphous silicon crystal, growth temperature at 500 . However, the current MILC its crystallization rate remains high, as t