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Float zone silicon from electron beam grown rods

Periodic Reporting for period 1 - EBFZ (Float zone silicon from electron beam grown rods)

Reporting period: 2016-10-01 to 2017-03-31

"The aim of our project is to expand the use of the FZ process for the production of silicon single crystals as a method of obtaining the purest and perfect single crystals in the industry. The total annual sales of silicon wafers for microelectronics and solar energy in 2015 amounted to 24 billion dollars. USA, about 50% of this amount is the production of bulk crystals. At the same time, silicon in the final cost of electronic products is about 1%, and in the cost of solar power plants - about 10% and largely determines the quality of these products. The main problem of limiting the application of the FZ process is the price of the supply rods obtained in the Siemens process. The price of rods is several times higher than the price of silicon rock because of the low speed of the process of obtaining quality rods suitable for growing single crystals of silicon FZ. We set ourselves the technical task of substantially reducing the cost of these single crystals. Another important area of work is to increase the diameter of the rods suitable for subsequent FZ processes. As a result of removing the restriction on the diameter of the rods produced in the coming decades, the problem of obtaining initial rods without cracks with high density with a low surface profile with a price slightly higher than polycrystalline silicon in pieces will disappear. Turnover of the secondary products in FZ production will be possible.
The first stage of the company's activity was the creation of equipment and technologies for growing rods with electron beam heating; The second stage was to create industrial equipment and pulling of rods (EBR) with a diameter of 200 mm, suitable for the subsequent production of silicon monocrystals. Currently, rods up to 200 mm in diameter are produced in our own EBR plant
Profit is planned by introducing an innovative process of EBR growth into production. The process is carried out on its own unique equipment and is protected by several patents owned by the company and the main investor. The economic effect is achieved through the use of cheap raw materials and technological processes with the formation of EBR at a low price (less than USD 50 per kg) compared to the existing on the market polycrystalline silicon rods manufactured by extended Siemens with a price of $85-120 / kg. In addition, EBR does not impair the properties of the end products.
The industrial target is FZ single crystals (FZSC) with a diameter of 200 mm, which we plan to produce at our facility on standard equipment FZ35. We'll use our EBR as feeding rods for such process.
The economic goal is to reduce prices for silicon wafers with the same or even better quality for manufacturers of power semiconductor electronics and photovoltaic materials and expand sales by replacing other types of silicon.
Social goals - reduction of energy consumption, effective reduction of CO2 emissions in the production of rods, improving the possibility of using FZ silicon in solar energy due to increased efficiency of solar cells.
The essence of the changes to KEPP EU can be summarized as follows: the extended process of manufacturing Siemens rods is replaced by the much shorter process of Siemens and added EBR pulling. In the same process, the scrap of extremely pure single crystals (TOP & TAILS) is used for direct recirculation in the FZ process. The novelty of our project is the advanced technology of manufacturing large diameter silicone rods using electron beam heating in the so-called process of melting the skull, which was considered impossible for a long time. Fig. 1.
As our preliminary market study showed, the introduction of a ""new"" product, the novelty of which is in a new production technology, from a supplier, which is ""new"" to the market has proved to be difficult for both reasons. The market where the goods are to be introduced has high requirements for the product, while given product's price bears a small influence on the cost of the final goods, the quality of the product determines the quality and durability of the final goods to a large extent.Therefore the main focus has shifted to the business plan development and, first and foremost, launching the product to the market; as well as speeding the implementation of the part of the business plan, which appears feasible to the enterprise.
The enterprise successfully concluded contracts for the sale of such single crystals in the market of permanent presence. The volume of contracts awarded for 2018-19 is more than 50% of the FZ equipment capacity planned for installation in 2017. Such loading of equipment makes it possible, on the basis of its own production, to train the personnel without prejudice to the accepted commercial obligations. As the efficiency of personnel increases, reserve capacity will allow them to aggressively enter new markets. To enter these markets, the enterprise has concluded two distribution agreements with partners, whose activity coincides with the target markets of the enterprise. For the first half of 2018, the ISO 9000 quality system certification is scheduled.
The enterprise also faces a number of technical and organizational tasks, the most important of which are
- Increase the purity of the rods grown in the process with electron beam heating to the level of polycrystalline silicon of electronic quality produced in the Siemens process. This task involves a number of steps. First, the purity of FZ single crystals and polycrystalline silicon measured by current control methods directly on the grown rods. Secondly, control of grown and standard single crystals obtained from the rods of their own production by all accepted control methods. It should be noted that in the selected marketing strategy this not simple process is not a limiting for the development of markets, because at the first stage for the production of FZ single crystals will be used ordinary silicon from Siemens processes, as more understandable to potential buyers.
- the most acute for the company is the development of FZ technology in full and training of personnel in cost-effective process management. This task includes a complex of technology for growing single crystals with a diameter of up to 100 mm, consisting of at least two parts - the technology of crystals with a diameter of 65 mm and more than 75 mm. In addition, it is necessary to master the doping processes directly in the process of growing from the gas phase, which requires the mastering of special devices, as well as neutron doping, which includes a method for calculating the dose of irradiation of single crystals in a nuclear reactor and the technology for the subsequent removal of radiation defects;
- Development of technical requirements for equipment, selection of equipment, finished equipment and participation in the project with European co-financing of the acquisition of innovative equipment by small enterprises.
Thus, main matter to be dealt with within the project is the localization of technological processes within the enterprise, mainly, the FZ growth process for FZSC production.
Negotiations with a number of potential consumers, considering the possibility of testing silicon produced using the new technology, failed - the only price argument was insufficient for potential buyers to bear at least the minimum costs for testing a completely unknown product from the Unknown supplier.
Therefore, the main attention was paid to the development of the business plan and, first of all, the launch of the product on the market; And also accelerate the implementation of part of the business plan, which is practically possible for the enterprise.
During the development of the business plan and coaching by Uwe Welhausen, a SWOT analysis of the EBR's growth project was carried out, which revealed a number of strengths and weaknesses. Weaknesses of the project included:
1) Lack of direct relations with customers, since manufacturers of FZ either offer too low a price, or ensure the growth of single crystals as a service with subsequent sales of FZ by themselves, which weakens the position in the commodity market.
2) Absence of own powers of the Federal Law - as a consequence 1)
3) Target chain of product cost creation, there are a number of services and subcontractors: FZSC growth, part of quality control measurements, doping and annealing of neutron transmutation, wafers.
4) Difficult access to capital due to lack of similar enterprises and low credibility of potential creditors to the likelihood of project implementation.
Thus, the main issue that should be considered within the framework of the project is the localization of technological processes in the enterprise, mainly the process of FZSC production growth.
As a result of localization, a number of products should become feasible:
1. FZSC, or alloyed in the process of metallurgical growth - FZSCD, or unalloyed - with high resistance-FZSCHR
2. FZSC NTD is a product created in cooperation with European or Russian nuclear plants or research centers
3. Si plates are made of one kind of single crystals, manufactured in cooperation at the request of the customer.
Testing of single crystals in the customer's energy devices is planned after growing single crystals of silicon FZ with a diameter of 44-100 mm at their own capacities.
The next step is the growth of single crystals of 150 mm (as an intermediate stage) and a diameter of 200 mm. The timeframe for the production of the furnace for the growth process is about 12 months, the development of the technology of growth of 150 mm - 6 months, the development of technology for 200 mm - 6-12 months. Therefore, given the time it takes to finance the attraction, we consider it prudent to begin this process in 2017 to begin the production of 200 mm single crystals by 2019.
With regard to raising funds At the time of writing the loan was drawn from SEB Bank in the amount of 200 000 euro for a period of five years; An agreement was signed on the delivery of a vacuum chamber for a future FZSC furnace with a 6-month grace period. A contract was signed for the supply of equipment for the mechanical processing of silicon and the missing measuring equipment. Equipment available in the company for chemical and thermal processing is sufficient for the current localization of production.
In the process of EBR growth, the influence of the operation of the electron beam energy source on the process was noted; In particular, the size of the focal spot on the surface and the quality of focusing. It is known that the size of the focal spot and the energy actually applied to the spot significantly affect the amount of heat actually transferred to the melt. Consequently, it became necessary to detect the signals from the batteries and the electron beam heater and the need to control them to handle the resulting oscillations. In the course of the project, a model of such a power source was developed.
On the basis of experimental work, the ratios of the sizes of a container with water cooling, a crucible and a rod for growing were established. The results of the studies were taken as a basis for the design of the bath (Fig. 2). As a result of experimental work, several crystals with a mass of up to 80 kg with a diameter of up to 240 mm grew during six months. The EBR of the process 27 shown in FIG. 2 was separately and compared with a 150 mm diameter FZSC portion. Insulation of a quartz crucible from melt is possible in scheme of the process in a silicon skull is applicable. With such a scheme of the process, the diameter of the growing crystal decreases, and
we have pulled silicon rods with a diameter of 145-168 mm in process No. 21.
However, a study of the same sample by FTIR spectroscopy showed that the concentration of the controlled impurities along the crystal length increases. In the case of aluminum, which easily leaves the silicon melt in a vacuum, this fact clearly indicates the addition of impurities to the EBB during the process. This assumption was confirmed in the course of studying the wear of the surfaces of the cathode and the anode of an electron beam gun. The results of ingot monitoring No. 27 are shown in Fig. 3, where the N-HR sample is from a standard single crystal FZ, sample No. 3-2 is from the bottom of the grown EB, and sample No. 5-2 is from the melt residues.
It can be seen that the difference between the impurity concentration B; Na; Ta; W; K in N-HR (standard single crystal of silicon FZ, where the content of these impurities can not exceed 1E10 atoms / cm3), and the melt remains are very small. So, we analyze these kinds of impurities. For other impurities, the N-HR and N3-2 samples are very similar.
Conclusions: 1. As a result of the project, a business plan was developed that significantly changed the approach to entering the product into the market. The enterprise has started to implement the above-mentioned business plan both in parts, covering the work with suppliers and customers, and in the part concerning the localization of production.
2. EBRs with a diameter of more than 200 mm were obtained, which became an important technical task for the EBFZ project. 3. A high level of purity of the rods has been achieved, sources of additional potential impurities have been determined - the volume of the gas discharge and the beam of the electron beam gun; The gas-dynamic window, which secures the gas flow from the gun to the melt, has been designed and satisfactorily tested. 4. The developer implementing plans for the localization of production and marketing of products.
The company for the first time in the world has developed, manufactured and operated a unique equipment for growing melt silicon rods with a diameter of more than 200 mm with the use of electron beam heating. We are established by the ratio of the dimensions of the elements of the tooling, which determine the diameter of the drawn rods. The geometric characteristics of the equipment in combination with these relationships allow us to hope that it is possible to grow rods with a diameter of up to 300 mm in the existing equipment. Fig 4.

As a result:
1. For the first time, silicon rods with a diameter of more than 200 mm were obtained in the skull-melting process with electron-beam heating.
2. For the first time, the rods applicable to the FZ process (produced dislocation-free single crystals) because of their high purity were obtained. This enables us to use raw materials with rational purity levels and re-use our own secondary FZSC.
3. For the first time, electron-beam heating is combined with the receipt of high-purity materials
4. The potential of the technology developed is absolutely essential. For a number of technological reasons, the source rod may not differ in diameter from the growing single crystal by more than 20%. Next, after the FZSC diameter of 200 mm, a technological standard of 300 mm should be expected. Thus, the initial rod must be of a diameter of at least 250 mm. The designed equipment must ensure obtaining of rods with a diameter of 300 mm, and a diameter of 225 mm has already been produced. For the first time in the world, rods with a diameter of more than 225 mm were obtained, while the diameter of the rods from the widespread Siemens process does not exceed 175 mm.
The production of such rods makes it possible to grow FZ single crystals of the same diameter, which will significantly reduce the backlog of FZ technology, in which the maximum diameter of a single crystal is 200 mm, while the technology of crucible growth allows the production of silicon up to 450 mm in diameter.

It is established that the electron-beam heaters with cold cathode used wear out during melting. Wear products are supplied with the plasma-forming gas to the silicon melt and contaminate it. A technical solution has been developed, it is essential to limit the penetration of these gases to the melt. As a result, the purity of the rods was substantially improved. A comparative analysis of the purity of rods, monocrystalline and multicrystalline silicon, standardly used in solar energy, has shown that at today's level of technology, rods are substantially cleaner than the products used in solar energy.
The resulting rods are cleaner than single crystals and polycrystals of silicon used in solar energy and in the near future will reach the level of purity of the Siemens process. Of these rods are grown FZSC of various diameters. The characteristics of single crystals measured by standard methods on the standard equipment of one of the FZSC manufacturers showed that the parameters of single crystals correspond to the standard specification for FZSC. Comparative analysis of energy consumption for the production of FZ rods in the long-term Siemens process and production in a short Siemens process of lump silicon with subsequent growth of rods from the melt with electron beam heating showed that the energy intensity of the proposed process is less by 30-40%.
For the first time in the world, a complete turnover of technological residues of FZ production of single crystals within the FZ production cycle has been obtained. This leads both to a reduction in the price of silicon produced, and to a decrease in the consumption of high-purity lump silicon from the Siemens process. As a result, the required amount of such silicon decreases, and the need for processes using multi-stage rectification of chlorosilanes decreases before silicon precipitation in the hydrogen reduction reactor.