REACTOR AND METHOD FOR PRODUCTION OF SILICON

Abstract

Reactor for production of silicon, comprising a reactor volume, distinctive in that the reactor comprises or is operatively arranged to at least one means for setting a silicon-containing reaction gas for chemical vapor deposition (CVD) into rotation inside the reactor volume. Method for production of silicon.

Claims

1. (canceled)

2. A method for production of high grade pure solid silicon by chemical vapor deposition (CVD) in a reactor, the reactor having a sidewall, a top, a bottom, a substantially circular cross-section, a vertical orientation, a plurality of inlets arranged in the bottom and a single outlet in the top of the reactor arranged coaxial to a central rotation axis, the method comprising: rotating the reactor around the central rotation axis by operating a motor, wherein the motor is operatively arranged to the reactor for rotating the reactor around the central rotation axis during operation for production of the high grade pure solid silicon by CVD; heating the sidewall to CVD temperature by a heat light source arranged outside the sidewall, wherein parts of the reactor other than the sidewall do not reach CVD temperature; introducing silicon-containing reaction gas into the reactor through the plurality of inlets; separating the silicon-containing reaction gas by a centrifuge effect of the rotation, providing a highest silicon concentration of the silicon-containing reaction gas along the sidewall of the reactor and a lowest silicon concentration of the silicon-containing reaction gas along the central rotation axis; effecting CVD of high grade pure solid silicon on an inner surface of the heated sidewall while the reactor rotates; and wherein a lowest silicon concentration of the silicon-containing reaction gas accumulates along the central rotation axis and eventually flows out from the single outlet as residual gas.

3. The method according to claim 2, wherein the plurality of inlets are spread in substance evenly over the bottom of the reactor, whereby the silicon-containing reaction gas introduced into the reactor through the plurality of inlets rotates at a same speed about the central rotation axis as the reactor and the reactor gas inside a reactor volume when entering the reactor volume.

4. A method for production of high grade pure solid silicon by chemical vapor deposition (CVD) in a reactor, the reactor having a sidewall, a top, a bottom, a substantially circular cross-section, a plurality of inlets arranged in the bottom and a single outlet in the top of the reactor arranged coaxial to a central rotation axis, the method comprising: rotating the reactor around the central rotation axis by operating a motor, wherein the motor is operatively arranged to the reactor for rotating the reactor around the central rotation axis during operation for production of the high grade pure solid silicon by CVD; heating the sidewall to CVD temperature by a heat source arranged outside the sidewall, wherein parts of the reactor other than the sidewall do not reach CVD temperature; introducing silicon-containing reaction gas into the reactor through the plurality of inlets; separating the silicon-containing reaction gas by a centrifuge effect of the rotation, providing a highest silicon concentration of the silicon-containing reaction gas along the sidewall of the reactor and a lowest silicon concentration of the silicon-containing reaction gas along the central rotation axis; effecting CVD of high grade pure solid silicon on an inner surface of the heated sidewall while the reactor rotates; and wherein a lowest silicon concentration of the silicon-containing reaction gas accumulates along the central rotation axis that eventually flows out from the single outlet as residual gas.

5. The method according to claim 4, wherein: the reactor has a vertical orientation; the heating is by a heat light source arranged outside the reactor; and the silicon-containing reaction gas introduced rotates at a same speed as the gas inside the reactor volume by introducing the silicon-containing reaction gas thorough a plurality of inlets spread over a surface of the bottom.

6. A method for production of high grade pure solid silicon by chemical vapor deposition (CVD) in a reactor, the reactor having a sidewall, a top, a bottom, a substantially circular cross-section, inlets arranged in the bottom and a single outlet arranged in the top of the reactor coaxial to a central rotation axis, the method comprising: rotating the reactor around the central rotation axis by operating a motor, wherein the motor is operatively arranged to the reactor for rotating the reactor around the central rotation axis during operation for production of the high grade pure solid silicon by CVD; heating the sidewall to CVD temperature by a heat source arranged outside the sidewall, wherein parts of the reactor other than the sidewall do not reach CVD temperature; introducing silicon-containing reaction gas into the reactor through the plurality of inlets; separating the silicon-containing reaction gas by a centrifuge effect of the rotation, providing a highest silicon concentration of the silicon-containing reaction gas along the sidewall of the reactor and a lowest silicon concentration of the silicon-containing reaction gas along the central rotation axis; effecting CVD of high grade pure solid silicon on an inner surface of the heated sidewall while the reactor rotates; and wherein a lowest silicon concentration of the silicon-containing reaction gas accumulates along the central rotation axis and eventually flows out from the single outlet as residual gas.

7. The method according to claim 6, wherein: the reactor has a vertical orientation; the heating is by a heat light source arranged outside the reactor; and the silicon-containing reaction gas introduced rotates at a same speed as the gas inside the reactor volume by introducing the silicon-containing reaction gas thorough a plurality of inlets spread over a surface of the bottom.

8. A reactor for production of high grade pure solid silicon by chemical vapor deposition (CVD), the reactor comprising: a sidewall, a top and a bottom; a substantially circular cross-section; a vertical orientation; a plurality of inlets arranged in the bottom and spread in substance evenly over the bottom of the reactor and a single outlet arranged in the top of the reactor coaxial to a central rotation axis; a motor operatively arranged to the reactor for rotating the reactor around the central rotation axis during operation for production of the high grade pure solid silicon by CVD; and a heat light source arranged outside the sidewall for heating the sidewall to CVD temperature, wherein parts of the reactor other than the sidewall do not reach CVD temperature.

9. A reactor for production of high grade pure solid silicon by chemical vapor deposition (CVD), the reactor comprising: a sidewall; a top and a bottom; a substantially circular cross-section; inlets arranged in the bottom; a single outlet arranged in the top of the reactor coaxial to a central rotation axis; a motor operatively arranged to the reactor for rotating the reactor around the central rotation axis during operation for production of the high grade pure solid silicon by CVD; and a heat source arranged outside the sidewall for heating the sidewall to CVD temperature, wherein parts of the reactor other than the sidewall do not reach CVD temperature.

10. The reactor according to claim 9, comprising: a heat source arranged outside the reactor sidewall without any structure between the heat source and the sidewall; a plurality of inlets in the bottom, the plurality of inlets spread in substance evenly over the bottom of the reactor; and a vertical orientation.

11. A reactor for production of high grade pure solid silicon by chemical vapor deposition (CVD), the reactor comprising: a sidewall; a top and a bottom; a substantially circular or polygonal cross-section; inlets arranged in the bottom and a single outlet arranged coaxial to a central rotation axis in the top of the reactor; a motor operatively arranged to the reactor for rotating the reactor around the central rotation axis during operation for production of the high grade pure solid silicon by CVD; and a heat source for heating the sidewall to CVD temperature, wherein parts of the reactor other than the sidewall do not reach CVD temperature.

12. The reactor according to claim 11, comprising: a heat source arranged outside the reactor sidewall without any structure between the heat source and the sidewall; a plurality of inlets in the bottom, the plurality of inlets spread in substance evenly over the bottom of the reactor; and a vertical orientation.

Description

FIGURES

[0029] Some embodiments of the inventions are illustrated in the drawings, wherein

[0030] FIG. 1 illustrates a vertical reactor according to the invention, with a circular or in substance circular cross-section,

[0031] FIG. 2 illustrates a vertical reactor with a helical heating device on the outside,

[0032] FIG. 3 illustrates an implementation of inlets in a bottom of a vertical reactor, and

[0033] FIG. 4 illustrates a particularly advantageous reactor according to the invention.

DETAILED DESCRIPTION

[0034] Referring to FIG. 1, the reactor is a closed or in substance closed cylindrical or polygonal vessel with wall (1), top plate (7) and bottom plate (4), preferably produced from/made of silicon of metallurgical purity or purer. Alternatively, the reactor is made of other feasible materials. A polygonal vessel will be assembled from plain plates. The reactor is surrounded by heating elements (3) formed as a spiral or a helix around the reactor, either complete or divided into sections. Said heating elements can also be implemented as short, straight elements, sloping so that they add up to an approximate spiral. The reaction gas (6) which is fed in through the bottom plate (4) is a silicon-containing gas, preferably SiH.sub.4 or SiHCl.sub.3, in most cases mixed with H.sub.2 gas. Referring to FIGS. 2 and 3, the bottom plate (4) of the reactor comprises one or more through-going holes (5) which function as nozzles for the reaction gas (6). The holes can ideally be positioned on a line between the center of the cylinder and the cylinder wall, in such a way that new nozzles can be put to use as the wall grows inwardly. Possibly, several nozzles can be arranged around the circumference. The nozzle holes (5) are designed in such a way that the gas flow acquires a tangential (12) as well as a vertical velocity component. This is achieved in that the sloping holes extend through the bottom plate, seen from one side, as illustrated by FIG. 3. The angle of the holes is preferably equal to the helix angle, the slope angle, of the heating elements. Thereby, the gas flow will obtain a rotation (14) about the center line of the reactor and follow the inside of the cylinder wall (2) as it moves vertically upward. The top plate (7) also comprises holes (8) through which the residual gas (9) can escape, which gas is residue of the reaction gas (6), consisting mainly of H.sub.2, in a nearly ideal process. The hole (8) in the top plate (7) is positioned in the center, in such a way that the silicon-poor residual gas (9) can escape, whereas the remaining reaction gas (6) can rotate along the reactor wall (2) until as much as possible of the silicon has been liberated. It may be advantageous if the hole (8) is tubular shaped and extends somewhat downwardly into the reactor. This could cause a cyclone effect, which could further increase the utilization of the reaction gas. A gas flow with reaction gas (6) is fed through the holes (5) in the bottom plate (4) at ideal velocity, preferably with parallel streamlines, that is, in such a way that a helical flow extends all the way to the top of the reactor. The reaction gas (6) enters the bottom of the reactor, tangential to the inside of the wall (2) at an upwardly inclined angle. Thus, the gas will follow the wall (2) and rotate about the center line of the reactor. Silicon is deposited onto the heated wall (2) and the depositions form a helix (10) on the inside of the reactor wall (2) due to the position of the heating elements (3) and the varying heating of the reactor wall. The residual gas (9) will finally escape through the hole (8) in the top plate (7).

[0035] The bottom plate (4) can be equipped with a concentric hole (11) in order to allow vertical injection of additional reaction gas (6). This could contribute to an even more balanced deposition of silicon in the vertical direction of the reactor, particularly if the flow velocity of the helical flow is considerably larger than the flow velocity of the vertical injection flow. The centric gas beam of reaction gas will be caught by the rotation reaction gas (14) and forced outwardly towards the inside of the reactor wall (2). It is advantageous if the vertical deposition can be controlled through the cross-section of the centric hole (11) and the gas beam up through the centric hole (11). In a polygonal vessel the bottom plate can be additionally equipped with vertical holes (15), positioned in each corner in the transition between two sidewalls. By feeding a vertical gas flow with reaction gas through the holes (15) for some time when initiating the reactor, silicon can quickly deposit between the sidewalls, hence sealing the reactor. Thereby a very early limitation of the leakage of silicon-containing gas is achieved, as the leakage causes a gradual sealing of the joints, causing a polygonal vessel to obtain a more circular inner cross-section, which is advantageous for the rotation. Leaked silicon-containing gas can however deposit onto the reactor wall, particularly onto a heat light heated reactor wall.

[0036] A gas flow with reaction gas (6) will be exposed to the heated reactor wall (2) and silicon is deposited by CVD. Most silicon will deposit onto where the wall is hottest, that is, in the area closest to the heating elements. Thus the depositions will form a helix (10) on the inside of the cylinder wall, equal to the helical heating devices. This helix (10) will aid the gas flow in maintaining the rotation inside the reactor. As the helical shaped depositions increase in thickness, the temperature differences in the silicon wall (2) will even out, and deposition will therefore occur more evenly onto the whole reactor wall (1). The whole reactor is removed and replaced with a new silicon reactor when the tube has grown tight and is filled with pure silicon all the way to the center of the reactor, or as far as it is economically justifiable to run the process. The increasing wall thickness will leave less and less volume for the silicon-containing gas (6), and production per hour will decrease over time and stop completely when the tube is clogged. The heating elements (3) are preferably heat light sources positioned outside the reactor, transmitting the heat through radiation or contact heat to the outer surfaces of the reactor. The heat light source is, as aforementioned, shaped as a spiral around the reactor or as a number of sloping heating elements which together form a spiral or a helix around the reactor. Additionally, the heating devices can be divided into sections on top of each other in order to be able to control the temperature individually in the height of the reactor. The heat is lead from the heat light source (3) through the silicon wall (1) to the inside of the wall (2) which will constitute the hottest surface inside the reactor, onto which surface the depositions advantageously occur.

[0037] Referring to FIG. 4, the reactor is a closed or nearly closed cylindrical or polygonal (three or more sides) vessel with wall (1), top plate (7) and bottom plate (4). A polygonal vessel will be assembled from plane plates. The vessel is preferably made of a non-contaminating material, preferably silicon of sufficient purity so that in substance the whole reactor can be utilized further in the production. The reactor is thus meant to be used only once, in a batch process. The reactor is surrounded by heating devices (3), either complete or divided into sections. The heating elements can possibly be stationary, rod shaped elements. The reaction gas (6) which is fed in through the bottom plate (4) is a silicon-containing gas, preferably SiH4 or gas with silicon fines, in most cases mixed with H.sub.2 gas. The bottom plate (4) of the reactor comprises one or more through-going straight holes (17) which function as nozzles for the reaction gas (6). The holes (17) can be positioned in an infinite number of ways and can be shaped in many different ways, depending on the desirable flow pattern. Holes (17) between the center of the cylinder and the cylinder wall might be sensible, so that new nozzles can be put to use as the wall is growing inwards. The top plate (7) also comprises holes (8) in order to let the residual gas (9) escape, which is residue from the reaction gas (6) and consists mainly of H.sub.2, in a nearly ideal process. The hole (8) in the top plate (7) is positioned in the center, in such a way that the silicon-poor residual gas (9) can escape, whereas the remaining reaction gas (6) can stay in the reactor until as much as possible of the silicon has been liberated. It might also be advantageous if the hole (8) is tubularly shaped and extends somewhat downwardly into the reactor. This could cause a cyclone effect, which could further increase the utilization of the reaction gas.

[0038] A gas flow with reaction gas (6) is fed through the holes (17) in the bottom plate (4) at optimal velocity, advantageously resulting in parallel streamlines or flow pattern. The reaction gas (6) enters through the bottom plate (4) and moves upwardly through the reactor. By putting the whole reactor into rotation (16), the reaction gas (6) will be exposed to centripetal acceleration which forces the gas (6) towards the wall of the reactor. The silicon-containing gas is substantially heavier than the residual gas (9) and will thus be exposed to the larger force. This results in the silicon-containing gas (6) being forced closest to the heated wall (2) onto which the silicon is deposited, whereas the residual gas (9) has to yield and move closer to the center of the reactor. The residual gas (9) will finally escape through the hole (8) in the top plate (7). The reactor can possibly be vertical, sloping or with inlets at the top and outlets at the bottom. The reaction gas (6) is exposed to centripetal forces in that the whole or parts of the reactor is rotating (16) at a sufficient rotation velocity. This can be achieved in that a motor 19 (shown in FIG. 4) puts the reactor into rotation (16). It is generally only necessary to rotate the reactor walls (1), however, it is advantageous if the bottom and top plate (4 and 7) also rotate (16) in order to achieve the best possible flow pattern. If it, due to construction considerations, is more expedient to let heating elements (3), measuring devices (not shown in figure), insulation (not shown in figure) and other elements surrounding the reactor, rotate with the reactor, this is possible. Gas going in (6) and out (9) needs to travel through special couplings (18) allowing rotation, such as a swivel coupling. Most of the electronics and measuring devices (not shown in figure) can advantageously be wireless.

[0039] The reaction gas (6) will reach the same rotation as the reactor, and will thus have no tangential velocity component relative to the reactor wall (2), only a small velocity component upwardly along the reactor wall (2). This results in a small relative velocity between the reaction gas (6) and the wall (2) onto which it should deposit, which is advantageous in order to avoid the formation of particles or fines. The centripetal forces arising due to the rotation (16) will force the reaction gas (6) outwardly towards the reactor wall (1). The gas will be separated in that the heaviest molecules are exposed to the largest forces, thus, they will be positioned closest to the wall. The light molecules will have to yield to the heavier ones, thus being positioned closer to the rotation axis. In this particular case, this is especially advantageous in that the silicon-containing reaction gas (6) is substantially heavier than the residual gas (9) from which most of the silicon has been liberated. Thus, a gradient with heavy reaction gas (6) closest to the wall and light residual gas (9) inwardly towards the center of the reactor will form. This results in a higher deposition rate due to the fact that the reaction surface (2) quickly will be provided with new reaction gas. This will most likely also increase the gas utilization, decreasing the silicon concentration in the exhaust gas.

[0040] In a polygonal vessel, the bottom plate can additionally be equipped with vertical holes (15) positioned in each corner in the transition between two sidewalls. By feeding a vertical gas flow with reaction gas through the holes (15) for some time when initiating the reactor, silicon will quickly deposit between the sidewalls, thus nearly sealing the reactor. This can be done before the reactor starts rotating. Thereby an early limitation of the leakage of silicon-containing gas is achieved, as the leakage causes a gradual sealing of the joints and a polygonal vessel obtains a more circular inner cross-section. A gas flow with reaction gas (6) will be exposed to the hot reactor wall (2) and silicon will deposit by chemical vapor deposition (CVD). More silicon will deposit where the wall is hottest, thus, the deposition can be controlled in such a way that the depositions will be evenly distributed throughout the whole reactor. The whole reactor is removed and replaced with a new reactor when the reactor has grown tight and is filled with pure silicon all the way to the center of the reactor, or as far as it is economically justifiable to run the process. The increasing wall thickness will lead to less and less volume for the silicon-containing gas (6) and the production per hour will decrease over time and stop completely when the tube is clogged.

[0041] When the reactor is so full that it is no longer expedient to keep running the process, gas injection, rotation and heat supply are stopped. The reactor is removed from the vessel with the heating elements (3) and a new, empty reactor is inserted, in such a way that the CVD process can be started anew. Hence, it is not a continuous process but a batch process, however, the change can occur so rapidly that the highest possible production is achieved. The reactor filled with silicon can be brought directly to further processing, for example into a melting furnace. When using another material than silicon in the reactor walls (1), bottom plate (4) and/or top plate (7), this material needs to be removed, for example by machining, before the reactor can be used in further processing. The outer dimensions of the reactor can be adapted to the further processing.

[0042] The heating elements (3) are preferably heat light sources positioned outside the reactor, transmitting the heat through radiation or contact heat to the outer surfaces of the reactor. The heating devices may be divided into several sections on top of each other in order to be able to control the temperature individually in the height of the reactor. The heat is conducted from the heat light source (3) through the silicon wall (1) to the inside of the wall (2), which constitutes the hottest surface inside the reactor, onto which surface the deposition advantageously occurs. Heat light sources can also be arranged on the bottom or top plate, protected in that the heat light sources are coaxially arranged in an inert/cooling gas inlet, which is particularly advantageous and energy efficient in that heating occurs directly on the surface onto which deposition of silicon takes place. The reactor and method of the invention comprises features and/or steps as described, mention or illustrated in this document, in any operative combination, which combinations are embodiments of the reactor and method of the invention, respectively.