Preparation of polycrystalline silicon thin-film (part 1)
To reduce material waste, reduce costs, monocrystalline silicon and polycrystalline silicon solar cells are advancing the development thin. Satellite M55 battery Tecra A3 battery In this crystalline silicon thin-film batteries nanocrystalline grain size from millimeters up to now have, for convenience, they are collectively known as community photovoltaic cells polycrystalline silicon thin film solar. As the production of polycrystalline silicon thin film, low cost, efficiency, good stability, high efficiency of opto-electronic conversion of recent years that people in the colony of optical technology, techniques of passive restraint and technologies such as the carrier continued progress, polycrystalline silicon thin film batteries of the growing popularity of attention, the future solar cells will become major competitors. In considering how to cut a thin silicon at the same time, people moved towards the poly-silicon thin-film battery research.
Preparation of polycrystalline silicon thin film There are several ways in which the deposit chemical vapor deposition (CVD) is the preparation most widely used of the polycrystalline silicon thin film method. In this method, source gases such as silane (SiH4) in the plasma (PECVD), catalysis (Hot-Wire CVD) There are various methods such as the feasibility of the process of decomposition. After the decomposition of material in the gas phase reaction, after a series of arrival of the substrate and deposit growth. Tecra A4 battery Tecra A5 battery In most cases, using diluted hydrogen source gas to prepare a thin film of polysilicon, while the pure silane to prepare thin films of amorphous silicon. However, evaporation by electron beam (EBE) has its unique advantages compared to the vapor deposition method using the gas source, the solid silicon material as raw EBE may have a higher use raw materials. In addition, to obtain a better quality of polycrystalline silicon thin film, but also by two-step method (two-step process) for the preparation of polycrystalline silicon thin film, namely: first, by CVD, or the Evaporation by electron beam (EBE), the rule of law was thin film amorphous silicon, and solid phase crystallization method (SPC) method or rapid thermal annealing (RTP) as the film of poly-silicon thin obtained as a result.
1, Chemical Vapor Deposition Method
1. Deposits chemical vapor plasma (PECVD) method
Plasma-enhanced chemical vapor deposition (PECVD) L61 is a kind of method of chemical deposition vapor is in the chemical deposition at low pressure steam, while the use of the influence of discharge plasma glow on the process using PECVD technology may be in non-silicon substrates, the small grains of polysilicon thin film preparation. Tecra A6 battery Tecra A7 battery
Using plasma enhanced chemical vapor method for preparing the deposits of polysilicon thin film process, currently led by a combination of both SiH4 and H2 gas as a source of gas, if the mere introduction of a pure SiH4 gas, PECVD deposition of the substrate from above films are thin films of amorphous silicon. In the process of depositing thin films of polycrystalline silicon by method of radio-frequency glow discharge (Radio Frequency Glow Discharge) decomposition of silane under the effect of RF power, silane gas is decomposed into a number of new particles : atoms, radicals, and different ions and plasma. These new particles through the migration process of dehydrogenation of a series of complex post-deposition on the substrate. Overall, a deposition process of thin films of polycrystalline silicon can be divided into two phases: the decomposition of SiH4 gas and groups filing. The decomposition of SiH4 gas is divided into two phases: first, in the glow discharge, the collision of high energy electrons with SiH4 gas to decompose SiH4. Micro-reaction process of the deposition process in Figure 1.
At the same time, because in general the deposition pressure, gas molecules and groups of free range is about 10-3 ~ 10-2cm, much smaller than the size of the reaction chamber, in which the diffusion process on the substrate between them due to collision with each other and the emergence of new reactions, the main type of reaction are: A1175 MacBook Pro 15 inch battery A1078
In which the concentration of the diffusion equation group can be expressed as follows:
Where G () x is the production rate, the concentration of N in the core group, D is the diffusion coefficient, N for the SiH4 concentration, k as the core group and the reaction rate of SiH4. From this equation, we can see that people with high reactivity, low diffusion coefficient, the higher the concentration of groups is very difficult to reach the substrate, while for SiH 3 groups due to its inability to react with SiH4 and has a high diffusion coefficient, is likely to spread the surface of the substrate plate and depositing a film.
The process of thin film deposition, but also contains two processes, namely, the groups filing process and molecules or atoms of the film surface in the desorption process. In the growth of the hair surface should be possible: the growth of surface-H, SiH 3 groups SI and growth of the surface to form dangling bonds Si-Si Bond Bond; Si-Si bonding binding growth thin films. Due to the presence of hydrogen atoms, SiH 3 did not reach the growth surface, bonding with the dangling bonds If, while the group will continue to spread SiH 3 migration. So non-H thin film processing is a long process of health is an important step. The H by thermal excitation and the atomic or molecular H2 in the form of spontaneous release of the surface, you can also group with the surface or react with the release of ions, such as: A1045 PowerBook G4 15 battery
≡ Si-When expressed on the surface and thin-film bond network structure of the synthesis of silicon atoms.
The foregoing is based on pure silane and hydrogen gas source for the reaction to the use of plasma enhanced chemical vapor deposition mechanism of growth of deposits of polysilicon thin film analysis. Throughout the reaction process, when the SiH4 concentration exceeds a certain critical value can produce a variety of polyhedra has been shaped Si particles, the nucleation of these fine particles will be homogeneous if, and adsorption of SiH4 thin If the reaction nuclear generating surface of the particles continue to grow the film even further growth.
2. Very high frequency plasma enhanced chemical deposition from vapor phase (VHF-PECVD)
Using conventional radio deposition plasma chemical vapor frequency (RF-PECVD) Preparation of thin films of polycrystalline silicon, to achieve the low temperature deposition, you must use a dilution of the high hydrogen silane as reactive gas, so the deposit rate is limited, it is difficult to satisfy practical application. Polysilicon thin-film deposition rate as the increase in effective ways of one of the very high plasma deposition chemical vapor frequency (VHF-PECVD) technique in materials polysilicon thin-layer preparation and the application of research is a very wide range of applications. IBM ThinkPad R51 battery IBM ThinkPad R52 battery
VHF-PECVD deposition technique has been able to dramatically improve the rate of deposition of thin films of polycrystalline silicon, mainly because the excitation of plasma more conventional VHF radio frequency plasma: l) the electron temperature below 2 ) the benefits of greater electron density.
VHF-PECVD deposition equipment, mainly from the three bedroom PIN, vacuum system, the system of gas supply, the power of incentives and heating of substrate and other major unit.
PIN 3 reaction chamber is opened a window Watch P bedrooms and a bathroom-type N and N, respectively P-type materials, the deposition room, I for the preparation of the intrinsic layer of material, the valve between the chamber reaction to isolate, thin film deposition process to work independently of each other.
At the end of the vacuum system is divided into the vacuum system and exhaust system into two parts. The end of the vacuum system includes a turbo-molecular pump and a pre-class mechanical pump, exhaust system, an independent not connect to each chamber of three mechanical pumps. Reaction gas firm Gas line dedicated to provide all the working chamber pressure by meter route air traffic, Zhengzhou University Graduate Thesis Chapter II Preparation of polycrystalline silicon thin film technology and the growth of the flowmeter mass on the principle of the creation and control, and through the regulation of emissions of exhaust gas pumps mechanical size before opening valves to control the working pressure of reaction chamber . F4812A HSTNN-lB31 PB991A
Inspiring a dedicated power supply for VHF. Energy mainly by the signal generator, amplifier, corresponding devices, frequency and power meter, components, etc..
If the filing system is the device by converting the old power supply system, heating system put in place because the original design of the main defects in the electrode substrate is located in a high frequency power introduced in the electrodes of the following processing of the raw film deposition, surface growth, likely to fall into powder that such damage, thus affecting the quality of materials in thin layers, which affect the preparation of solar batteries is particularly important.
PIN Mimuro compartment continuous VHF PECVD deposition equipment for the parallel plate capacitor electrode structure and the performance of electrodes in place, the distance between the electrodes in adjustable between 1.5-3.5cm, common electrode spacing of about 2.5cm. Deposit system for thin films of this at the end of a vacuum better than 5 × 10-5PA. Working gas for the hydrogen dilution of silane gas flow in the measurement of mass flow meters and control the operating range of gas pressure of O-200Pao power incentive points with four VHF operating frequency: 60MHz , 70MHz, 80MHz, 40MHz, the output of O-100W, power of size to be headed by a meter. PA3383U-1BRS PA3395U-1BRS PA3534U-1BRS
3. Chemical deposition at low vapor pressure LPCVD
Low pressure deposition chemical vapor (LPCVD) method containing mainly silicon in the gas chamber, by heating near the surface of the substrate by stimulating the decomposition, the decomposition of silicon and hydrogen and the formation of under them have a variety of groups took place near the surface reaction, the silicon film formed on the substrate. Was significantly lower than in O.1MPa work under pressure in terms of peripheral LPCVD, low pressure can increase throttle response studio and reaction products through the ability of the boundary layer diffusion. At the same time, to partially offset the impact of downward pressure may increase the total quantity of reactive gas in the gas in the concentration ratio. Compared to the normal pressure CVD equipment, low pressure chemical deposition vapor pressures of work, almost as low as l00Pa, resulting in response to the gas diffusion coefficient increased by about three orders of magnitude . Despite pressure to reduce the thickness of the surface layer of the substrate border has increased, but the flow of gas can also be increased accordingly. Thus, the overall result is greatly improved rate of thin film deposition. Low pressure deposition chemical vapor (LPCVD) method will only come into contact with the gas to the surface at high temperature deposition of thin films, while the lower surface temperature of contact is not filed. Low-pressure chemical vapor deposition method has the advantage of the longer period the reaction chamber can be kept clean. Under normal circumstances, the use of heterogeneous substrate LPCVD thin films directly deposited polycrystalline silicon grain size is below 500nm, the grain can be obtained in this way more and good quality polysilicon thin films. apple PowerBook G4 12 inch battery apple MacBook 13 inch battery During LPCVD epitaxial growth substrate before cleaning, and taking the region by adjusting the reaction temperature and pressure to change the deposition rate of thin film materials and performance. Low deposition device chemical vapor pressure and atmospheric general features of hot wall-type The main difference is that it requires a vacuum pump to maintain pressure throughout the system works.