LV15499B - SILICON CRYSTAL GROWING METHOD AND EQUIPMENT FOR ITS IMPLEMENTATION - Google Patents

Abstract

The invention relates to crystal growth, in particular to the growth of silicon crystals by induction heating without a crucible. An improved method and the necessary equipment for growing silicon crystals are proposed. The method involves growing a crystal by rotating the seed crystal (1) upward using an initial rod with a diameter no smaller than the diameter of the crystal to be grown, and a pedestal (11) that is rotated upward is positioned below the melting inductor (5 ) and is surrounded by a focusing coil (7). The method is supplemented by the fact that the pedestal (11) is heated by an annular heater (10) in the area below the focusing coil (7) which conducts heat. In addition, a device for the implementation of the method is proposed, which contains a vacuum chamber (14) equipped with a holder for the excitation crystal (2), which is vertically movable with the possibility of rotation, and a lower holder for the pedestal (11).

Description

DESCRIPTION OF THE INVENTION

[01] The invention relates to the production of silicon, such as the industrial production of silicon for microelectronics of electricity, including the production of high-power semiconductor devices such as diodes, thyristors, etc.

Prior art

[02] The aim of this production is to obtain high-quality silicon mainly by the melt extraction method [1] without the use of a crucible. This process is carried out by melting the original rod by the induction melting method and crystallizing a single crystal whose diameter differs from the original rod by not more than 20%. Due to the impossibility of producing original silicon bars with a diameter of 300 mm in the traditional Siemens process, a new technology for the production of such bars was developed, namely the technology described in patent no. LV15065. There are no visible restrictions on the diameter of the crystals grown for this technology. In addition, there is currently no equipment and technology for growing single crystals with a diameter of 300 mm using the crucible extraction method. For this reason, bars with a diameter of 300 mm and more are useful as a pedestal in the melt extraction process without the use of a crucible. In such processes, single crystals with a diameter significantly smaller (1.5 -3 times) than the diameter of the pedestal can be grown. Such technology is potentially applicable to pedestals with a diameter of 100 mm, but has not been used in practice for the last 50 years due to the fact that the development of melt extraction technology without the use of a crucible has always surpassed Siemens' original bar manufacturing process technology. The use of induction heating involves a relationship between the dimensions of the equipment (induction heaters, screens, etc.), i.e. between the elements of the growing device and the diameters of the pedestal (Dp) as well as the grown single crystal (Dc).

[03] The problems with this process are the incomplete melting of the central area of the pedestal [1], but after melting, the problems with single crystal growth, which start with the cultivation of a fine neck with a diameter of about 5 mm. If, using any technique, the central zone can be melted, then the melt in it has a relatively constant temperature. When the excitation crystal touches the surface of the melt, the temperature of which is close to the crystallization temperature of silicon, spontaneous crystallization takes place on the surface of the melt (Figure 1), so it is not possible to grow a fine neck by the method of Sausage [6]. The inner diameter of the melting inductor when grown from a pedestal should be larger than the diameter of the single crystal grown, and commercially available single crystals with a diameter of 50-200 mm are of interest. It is obvious that additional heating of the melting surface must be introduced in the process by growing a fine neck with a diameter of about 5 mm for further growth of a single crystal with a diameter of 50-200 mm.

[04] Apparatus of the FZ process [2] is known, which uses infrared heating with halogen or xenon lamps, or is used to grow laser single crystals from a pedestal. In addition, in order to create optimal growing conditions, the lamps heat the pedestal and the free surface of the melt using several lamps conditionally arranged vertically in three rows. The bottom row heats the pedestal, the middle one melts the melt close to the three-phase melting limit of the pedestal and the upper one near the three-phase crystallization limit. When working with silicon, the reflection coefficients of the surfaces (solid and liquid) differ, but both approach 90%. To compensate for the total radiation of 90 mm in diameter from a pedestal 200 mm from a pedestal 200 mm of approximately 10.5 kW, lamps with a total wattage of 105 kW, equivalent to 21 lamps of 5 kW each, must be switched on (such wattage lamps are commonly used in floodlights). to illuminate large areas such as stadiums, etc.). In addition, the cultivation process must be guided by visual observation of both boundaries of the three phases.

[05] There is a known method and apparatus for growing single crystals [3], which uses combined heating - basic induction heating, for the usual FZ process and additional heating using infrared lamps. In addition, the surface of the growing single crystal is heated by lamps and the control effect of the crystallization surface shape is obtained. The direct application of this or a similar process is not possible when growing a single crystal by the FZ method from a pedestal.

[06] A method of crystal growth [4] is known, in which the growth takes place by electron beam heating and provides the necessary conditions for the single crystal to grow from the minimum diameter to the specified one by increasing the arc radius described by the focal points of the beam on the melt surface. This method is carried out in a vacuum which is incompatible with the cultivation of large diameter silicon single crystals and using a crucible which runs counter to the intended purpose of growing single crystals without contact with the container.

[07] There is a known method and apparatus for its implementation [5], which uses a short-circuit ring installed below the melting inductor and an additional pedestal heater located under the short-circuit ring to improve the melting of the pedestal. Thus, cultivation is performed by independent heating of the melt and heating of the pedestal, which allows to compensate for the transfer of basic heat to a process that takes place through the surface of the pedestal. Despite the large internal diameter of the inductor, this method and device allows the central area of the pedestal to be completely melted. However, the introduction of an excitation crystal with a diameter of 5 mm results in uncontrolled crystallization as described in [1] and shown in Figure 1. Using excitation crystals with a larger diameter, such as 12 mm, the process continues to be difficult to control and does not provide stable fine-neck growth conditions according to the Six method [6]. In addition, it is known that using inductors with an inner diameter of 30-40 mm, such a process is possible, and single crystals were obtained [7, 8].

Purpose and essence of the invention

[08] The present inventions solve the problem of obtaining silicon single crystals using a pedestal, while the diameter of the single crystal is significantly smaller than the original pedestal, providing the conditions for growing the fine neck required for the growth of single crystals without dislocations. The present invention makes it possible to use original rods - pedestals - with a diameter of 200-400 mm and to obtain commercially efficient FZ quality silicon single crystals.

[09] The technical result is the fact that in order to obtain FZ silicon single crystals with a diameter of 100-200 mm, using a pedestal, conditions are provided for growing single crystals without dislocations, starting from fine neck cultivation by the Six method [6] and ending with a fixed diameter single crystal. reproducible growth. In addition, the initial production of bar-pedestals can be concentrated in large diameters, ie from 200 to 400 mm, which leads to an increase in the productivity of bar-growing equipment used as a pedestal and thus to a reduction in the price of pedestals and a decrease in the price of FZ silicon single crystals. the cost price of raw materials is about 50%.

[10] The technical result is obtained by using an initial rod with a diameter of not less than, but mainly 2 times the diameter of the crystal to be grown, by induction heating of silicon crystals without the use of a crucible, including crystal growth by moving the excitation crystal with the rotation upwards. . The original pedestal bar (11) (Figures 2 to 4) is located under the inductor (5), is fed upwards by rotation, and is covered at the top with a focusing coil (7), which blocks additional heating of the side surface of the pedestal with inductor (5), but under the coil (7) the pedestal (11) is heated by a ring heater (10). The inner diameter of the inductor (5) is smaller than the diameter of the pedestal (11), the closed focusing coil (7) is 10-20 mm larger than the diameter of the pedestal (11), but the ring heater (10) has a ring shape and is mounted under the focusing coils (7) and form a heating ring (12) on the pedestal surface (11). According to the proposed method, in order to ensure the control of the accident-free process, the cultivation of the fine neck and the crystal cone is performed by using additional surface heating with variable power between the crystallization front and the inner diameter of the melting inductor. For this purpose, for example, infrared radiation (Fig. 2) from lamps (21) equipped with elliptical reflectors (22) and mounted above the melt with the possibility of controlling the direction of the beam is used for additional heating, or at least two electron beam sources are used for additional heating. (31) (Fig. 3), each of which moves on the surface of the melt in a circle with a certain radius and central angle. The electron beam sources themselves (31) are located above the melt. The intermediate induction heater (41) (Fig. 4) forms a local heating ring of the melt surface with a diameter smaller than the diameter of the heating ring from the basic inductor (5), growing a fine neck (2) of the cone (3). After use, the intermediate induction heater (41) is moved vertically upwards.

[11] The essence of the method is based on the fact that the equipment with high-frequency induction heating has a reactor (14) (Fig. 5) and pedestal (11) as well as excitation single crystal (1) holders with the possibility of cutting and axis movement (not shown in the figures). shown below), a sequentially closed focusing coil (7) is installed under the inductor (5), which is cooled by water, and a ring heater (10), and above the inductor (5) is one of the additional heating sources, namely infrared lamps (21) (Fig. 2) with elliptical reflectors (22) or electron beam sources (31) (Fig. 3), or an intermediate induction heater (41) (Fig. 4). The pedestal (11) is heated using a ring heater (10) and concentrating the heat dissipation in the heating ring (12) on the surface of the pedestal (11), which should be sufficient to reduce axial heat dissipation from the melting surface, and then activating a selected additional heat source and melt the upper part of the pedestal (11). The excitation single crystal (1) is applied to the melt, connected to the melting zone (6) and the fine neck (2) with a diameter of about 5 mm is grown by the Sausage method [6] until all dislocations are removed, and then the conical parts of the single crystal (3) are started. cultivation. The inductor (5) is then switched on and, by gradually reducing the heating from the auxiliary heater (21) or (31) or (41) used, the heating from the inductor (5) is increased so that it can carry out the main part of the growing process. In this case, the heat (Q2) supplied to the heating ring (12) is distributed to dissipate heat along the surface of the pedestal (11) upwards (Q21), downwards (Q22) and radially heating the pedestal (Q23). The heat flows (Q21) and (Q23) result in the heating of the result, which is directed to the central zone (15) of the pedestal (11). Thus, the heat dissipation (Q3) decreases, which is shown in Figure 5 as a compensating heat flow (Q31). In this case, the closed focusing coil (7), by generating heat dissipation (Q5), blocks the heating of the surface of the pedestal (11) by the inductor (5) and conducts the excess heat (Q21) released in the heating ring (12). In addition, the heat dissipation (Q5), which is increased by the focusing coil (7), allows to increase the heat dissipation (Q1) from the inductor (5) and to improve the heating of the melt, resulting in heating of the central area (15) of the pedestal (11).

Examples of implementation of the invention

[12] The method is implemented as follows. The original pedestal (11) is attached to the high-frequency heating unit in the lower holder (not shown), which is fed to the inductor (5) (Fig. 2). A closed focusing coil (7) is installed under the inductor (5) at a distance L1, which is cooled with water. A ring heater (10) is located around the pedestal (11). In our version, the ring heater (10) is a two-wire inductor. In addition, the height of the ring heater (10) is L3 and it is located at a distance L2 from the closed focusing coil (7), which is cooled by water. Mount an excitation single crystal (1) with the required crystallographic orientation in the upper holder. Above the inductor (5) are mounted 4 halogen lamps (21) with 5 kW power in elliptical reflectors (22), selected in such a way that the focal length F2 allows to maintain the allowable temperature on the reflector surface, while the focal length F1 and the elliptical reflector shape focus the lamps radiation on the surface of the pedestal in the optimal focal spot, for example, with a diameter of 10 mm. The lamps (21) with reflectors (22) are mounted on drives (not shown) which are protected from heating by screens which allow the lamps (21) with reflectors (22) to be radially rotated and to move vertically. The reactor (14) is closed and a pure argon atmosphere is created in the apparatus. The process takes place in an argon stream (24), passing it through dividers (23) in the direction of the reflectors (22), thus creating a gas overflow of the lamps (21) and reflectors (22). Next, the pedestal (11) is placed in the ring heater (10), it is supplied with current and the rays of the lamps (21) are placed on the upper section of the pedestal. When turning, heat the pedestal (11) to the transition position. Then the pedestal (11) starts to move upwards, approaching the lower section of the inductor (5). Switch on the high-frequency current of the inductor (5) and create a molten zone. Place the centers of the focal spots on the optimal arc, for example 30 mm, and lower the excitation crystal. The excitation single crystal (1) is connected to the melt in the zone (6) and, after melting the excitation single crystal (1), a fine neck (2) is grown, while the temperature in the melt zone (6) near the excitation crystal is regulated by changing the current supplied to the lamps (21). After growing the fine neck (2), gradually increase the diameter of the growing crystal (4), forming a cone (3) to the specified diameter. In addition, the lamps (21) and the reflectors (22) gradually radiate radially from the growing axis and change the power supplied to the lamps (21) to ensure a smooth growth of the single crystal cone section. The power supplied to the ring heater (10) is selected so as to avoid the formation of a protrusion of the pedestal (11) in the central area (15), which can reach a growing crystal (4), and a constant power is maintained throughout the process. Pull out the cylindrical part of the excitation single crystal (1) at a certain speed, which is proportional to the ratio of the diameters of the squares of the speed of the pedestal (11). The pedestal (11) and excitation single crystal (1) are rotated at optimal speeds. Instead of lamps (21), an intermediate induction heater (41) can be used, which has the possibility to move vertically (Fig. 4) or at least two electron beam sources (31) (Fig. 3). Using electron beam sources (31), the process is started without switching on the inductor (5) under reduced pressure in the atmosphere of hydrogen (33) fed through the annular feeder (32). Next, the inductor (5) is switched on, as the cone (3) grows, the power supply to the inductor (5) increases, at the same time as the hydrogen pressure increases. In addition, the power supplied to the electron beam source (31) gradually decreases, but the supply hydrogen is replaced by a mixture of argon and then by pure argon.

[13] Example of method implementation. The original pedestal (11) with a diameter of 200 mm and a length of 1.5 m is secured by equipment with high-frequency heating in the lower holder (not shown). An inductor (5) with an inner diameter of 130 mm and an outer diameter of 240 mm and a thickness of 5 mm is shown schematically in Figures 2 to 5. A closed water-cooled focusing coil (7) with a height of 12 mm and a diameter of 215x245 mm is installed 20 mm below the inductor (5). A ring heater (10) is arranged around the pedestal (11) in the form of a two-winding inductor with a diameter of 210 x 230 mm and a distance of 15 mm between the windings fed by a generator with a frequency of 5-100 kHz.

[14] A single crystal of the required crystallographic orientation (1) is mounted in the upper holder. The reactor (14) is closed, vacuumed and then filled with argon. The process takes place in a stream of argon (24), fed through manifolds (23) in the direction of the reflectors (22), thus creating a gas overflow of the lamps (21) and reflectors (22).

[15] After creating an argon atmosphere in the chamber of the device (14), insert the pedestal (11) into the ring heater (10), but not into the focusing ring, and turn on the lamps (21) and the ring heater (10). Heat the pedestal (11) to the transition position, set the required power of the ring heater (10) and lamps (21) and move the pedestal 5-7 mm from the lower section of the inductor (5). Switch on the high-frequency current of the inductor (5) and create a molten zone (6) in the upper section of the pedestal (11). Install the centers of the focal spots of the lamps (21) at a distance of 15 mm from the axis in two mutually perpendicular diameters. The excitation single crystal (1) rotating at 15-30 rpm is lowered, connected to the zone of the melt (6) and, after the excitation of the excitation single crystal (1), begins to grow a fine neck (2) with a diameter of Less than the diameter of the excitation single crystal (1) and a length of 30100 mm until the dislocations are removed. In addition, the temperature in the melting zone (6) in the vicinity of the excitation single crystal (1) is regulated by changing the power supplied to the lamps (21). After growing the narrow neck (2), gradually increase the diameter of the growing crystal (4), forming a cone (3) to the specified diameter. In addition, the lamps (21) and the reflectors (22) are gradually removed radially from the growing axis and the power supplied to the lamps (21) is changed to ensure an even growth of the cone part of the single crystal (1). As soon as the cone diameter reaches 60 mm and up to a diameter of 90 mm, the power supplied to the lamps (21) is gradually reduced and the power supplied to the inductor (5) is increased. The diameter of the growing crystal (4) is gradually increased by forming a cone (3) until a diameter of 100 mm is reached with a vertical ascent rate of the excitation single crystal (1) of 1-3 mm / min. The power supplied to the ring heater (10) is chosen so that no protrusion forms in the central area (15) of the pedestal (11) which can reach the growing crystal (4). In the described process, power from 5 to 18 kW was supplied to the inductor (5), 11 kW to the ring heater (10) and from 0.5 to 4.5 kW to each lamp (21). The growing single crystal (4) was extracted at a speed of 3 mm / min with a rotation of 7 rpm; the pedestal (11) was fed at a speed of 0.75 mm / min with a rotation speed of 0.3 rpm. As a result, a 1.2 m long single crystal was grown (4).

[16] The speed of the pedestal (11) was then reduced to 0.6 mm / min, the opposite cone was formed (not shown) and the grown crystal was separated from the melt (6). The power supplied to the ring heater (10) was increased to 9 kW, but the power supplied to the inductor (5) was reduced to 10 kW and the pedestal (11) moved downwards. The pedestal (11) was moved down until the distance from the surface of the crystallized silicon to the inductor (5) reached 70 mm. The power supplied to the ring heater (10) was then reduced to "0" within 60 minutes. 350 mm of the pedestal (11) were used. The grown dislocation single crystal was unloaded, then the process was repeated. A total of 4 single crystals 1.1-1.2 m in length were grown from one pedestal (11) (excluding the length of the cone and the fine neck (2)).

[17] The method uses an apparatus comprising a reactor (14) and induction heating through an inductor (5) fed by a generator above 1 MHz, a heater (10) fed by a generator below 100 kHz . The reactor (14) is equipped with an exciter single crystal (1) holder capable of vertical movement and rotation (not shown) and a pedestal (11) holder with vertical movement and rotation (not shown).

[18] A reactor (14), below the inductor (5), at a distance L1, is fitted with a water-cooled closed focusing coil (7). A pedestal heater (10) with a height of L3 is installed below the focusing coil (7) at a distance of L2. In addition, the value of L1 is selected from the range (0.08-0.12) * Dp; L2 is (0.10-0.15) * Dp, but the heater (10) is a two-wire inductor. L3 heater height (10) is (0.2-0.3) * Dp.

Description of drawings

[19] Figure 1: Spontaneous crystallization of silicon around an excitation crystal;

[20] Figure 2: Scheme of process implementation using additional heating with lamps;

[21] Figure 3: Scheme of process implementation using additional heating with electron beams;

[22] Figure 4: Scheme of process implementation using additional heating with inductor;

[23] Figure 5: Distribution of heat flows in the process.

[24] Symbols on the drawings: excitation single crystal (1), fine single crystal neck (2), cone (3), growing crystal diameter (4), inductor (5), melting zone (6), focusing coil (7), heater (10), pedestal surface (11), heating ring (12), reactor (14), pedestal central zone (15), lamps (21), elliptical reflectors (22), divider (23), gas (argon) channel ( 24), electron beam source (31), annular feeder (32), supply gas (hydrogen / argon) (33), intermediate induction heater (41).

Sources of information

[1] Kravtsov A. “Float zone single crystals for testing rods, pulled under electron beam heating”, et al 2019 IOP Conf. Ser .: Mater. Sci. Eng. 503 012022

[2] Petition application no. US20100307406A1, filing date 12.08.2010.

[3] Petition application no. US9422634B2, filing date 05.12.2012.

[4] Petition application no. US3494804, filed July 15, 1968.

[5] Petition application no. Р-18-81, application date17.10.2018.

[6] Petition application no. US2961305 A, filed December 27, 1957.

[7], Michael Wūnscher, Helge Riemann, Birgit Hallmann-Seifert, Anke Lüdge, "Crucible-free Crystal Pulling of Germanium", Leibniz-Institut for Crystal Growth, Berlin / Germany, Scientific Seminar on the Application of Germanium Detectors in Basic Research at Tsinghua University, Beijing / China, March 23-30, 2011, Second Edition, 2, pp. 241-279;

[8] Petition application no. US3275417, filing date 15.10.1963.11

Claims (3)

A method of growing silicon crystals by induction heating, comprising growing the crystal by moving the excitation single crystal (1) upwardly, using a pedestal (11) having a diameter not less than the diameter of the crystal to be grown and greater than the inner diameter of the inductor (5). , in addition, the pedestal (11) is fed upwards in the melting zone and is melted, characterized in that the crystal fine neck (2) and the cone (3) are grown by additional heating of the melt surface with a moving power source of variable power. A method according to claim 1, wherein at least two electron beam sources (31) are used as additional heating sources, each of which moves in an arc on a melt surface with a defined radius and a central angle. A device for growing crystals, comprising a reactor (14) equipped with an upper holder for the excitation crystal (2) and a lower holder for the pedestal (11), both holders having the possibility of rotation and axis movement, an inductor (5), a closed focusing coil (7) ) and a ring heater (10), all of which are forcibly cooled, in that additional heaters in the form of infrared lamps (21) fitted with movable elliptical reflectors (22) are mounted above the inductor (5).