Single crystal silicon rod manufacturing single crystal silicon growth furnace

Abstract

This application relates to the field of single crystal growth equipment technology, and discloses a single crystal silicon growth furnace for preparing single crystal silicon rods. The furnace includes a furnace body, an outer crucible inside the furnace body, a heater outside the outer crucible, a seed crystal shaft above the outer crucible, and a feeding device fixedly installed on the outside of the furnace body. The feeding device includes a cylinder, inside which are three feeding cylinders arranged in a circumferential array. A temporary receiving device connected to the first feeding cylinder is located above the cylinder. By setting the feeding device and the temporary receiving device between the feeding tube and the outer crucible inside the furnace, and utilizing the rotating disk and U-shaped receiving disk in the temporary receiving device to rotate half a circle for temporary receiving, and coordinating with the repositioning of the three feeding cylinders, feeding, air removal, and material addition are performed respectively. This achieves continuous feeding and direct pulling without stopping the machine, while also ensuring that the added polycrystalline silicon raw material is not mixed with air, guaranteeing high efficiency and high quality of single crystal silicon growth.

Description

Technical Field

[0001] This application relates to the field of single crystal growth equipment technology, and in particular to a single crystal silicon growth furnace for preparing single crystal silicon rods. Background Technology

[0002] A single crystal silicon growth furnace (abbreviated as single crystal furnace) is a device used to manufacture silicon crystals. Currently, single crystal silicon rods are prepared using the Czochralski (CZ) method, continuous Czochralski (CCZ) method, and multiple crystal pulling (RCZ) technology. Among them, the continuous Czochralski technology has the advantages of high efficiency, low cost and high quality compared with the Czochralski and multiple crystal pulling technologies, and is recognized as the "ultimate form" of single crystal silicon preparation.

[0003] However, in existing continuous Czochralski equipment, it is necessary to consider that during continuous feeding, monocrystalline silicon is not affected by oxygen during growth. When adding polycrystalline silicon raw materials, if the polycrystalline silicon raw materials are directly added to the crucible through the feed pipe, even if protective gas is continuously introduced, it is difficult to completely remove the air from the polycrystalline silicon raw materials, which will affect the growth quality of the monocrystalline silicon rod. If valves or other methods are used to feed and vent separately, the particulate matter in the polycrystalline silicon raw materials can easily cause the valves to get stuck when closed, which will affect the growth efficiency of the monocrystalline silicon rod. Summary of the Invention

[0004] This application proposes a single-crystal silicon growth furnace for preparing single-crystal silicon rods, which has the advantages of high efficiency and high quality in single-crystal silicon growth. It solves the problem that existing single-crystal silicon growth furnaces, when using continuous Czochralski pulling, cannot simultaneously achieve both efficiency and quality when continuously feeding materials such as polycrystalline silicon.

[0005] To achieve the above objectives, this application adopts the following technical solution: a single-crystal silicon growth furnace for preparing single-crystal silicon rods, comprising a furnace body, an outer crucible inside the furnace body, a heater outside the outer crucible, a seed crystal shaft above the outer crucible, and a feeding device fixedly installed on the outside of the furnace body. The feeding device includes a cylinder, and three feeding cylinders arranged in a circumferential array inside the cylinder. The three feeding cylinders are driven to rotate synchronously by a first motor located above the cylinder. A temporary receiving device communicating with the first feeding cylinder is located above the cylinder. An air inlet pipe and an exhaust pipe are respectively connected above and below the second feeding cylinder. A discharge pipe extending into the outer crucible is connected below the third feeding cylinder.

[0006] The temporary receiving device includes a positioning tube fixedly installed above the cylinder. A rotating disk is rotatably connected to one side of the positioning tube. An inclined guide tube is fixedly connected to the outer edge of one side of the rotating disk. A rotary joint is fixedly connected to the end of the inclined guide tube away from the rotating disk. The axis of the rotary joint is on the same straight line as the axis of the rotating disk. One end of the inclined guide tube is fixedly connected to the rotating end of the rotary joint. A feeding pipe is connected to the fixed end of the rotary joint. A U-shaped receiving tray is fixedly installed on the side of the rotating disk, and the opening of the U-shaped receiving tray faces the opening of the inclined guide tube.

[0007] Furthermore, the outer crucible is also provided with an inner crucible. The lower half of the inner crucible is provided with a through groove that connects to the inner cavity of the outer crucible. The bottom end of the feeding tube is located outside the inner crucible. When the seed crystal shaft is pulling the crystal inside the inner crucible, the polycrystalline silicon raw material is added to the outer crucible through the feeding tube, thereby reducing the interference of the polycrystalline silicon raw material on the liquid surface of the molten liquid inside the inner crucible.

[0008] Furthermore, the top and bottom of the cylinder are respectively fixedly connected to cover plates. Rotating blocks are installed on opposite sides of the two cover plates via plane bearings. A positioning shaft is fixedly connected in the middle between the two rotating blocks. Three feeding cylinders are fixedly arranged between the two rotating blocks. Three guide grooves are opened on the rotating blocks. The three guide grooves are respectively connected to the three feeding cylinders. The first motor is fixedly installed on the top of one of the cover plates. The first motor fixedly installed on the top of the cover plate drives the output shaft to drive the positioning shaft to rotate, thereby driving the two cover plates and the three feeding cylinders to rotate, thereby changing the position of the three feeding cylinders. This allows the three feeding cylinders to perform feeding, air discharge and feeding operations respectively, thereby achieving a continuous feeding and straight-pull effect.

[0009] Furthermore, three connecting shafts located outside the positioning shaft are fixedly connected between the two rotating blocks. The three connecting shafts are respectively located between two adjacent feeding cylinders. The two rotating blocks are connected through the connecting shafts so that the positioning shaft can drive the two rotating blocks and the three feeding cylinders to rotate stably together under the driving force of the first motor.

[0010] Furthermore, the cover plate is provided with a feeding trough that connects to one of the material guide troughs. The opening at the bottom of the positioning tube is connected to the feeding trough. The polycrystalline silicon raw material that enters the positioning tube through the inclined guide tube falls into the feeding cylinder from the opening at the bottom of the positioning tube, the feeding trough, and the material guide trough.

[0011] Furthermore, a sealing ring is provided at the connection between the feeding trough and the guiding trough. When the rotating block and the feeding cylinder rotate together relative to the cylinder body and the cover plate, the sealing of the connection between the feeding trough and the guiding trough is ensured. This allows for ventilation through the air inlet pipe and exhaust through the exhaust pipe, thus purging the air from one of the feeding cylinders. This ensures that when the polycrystalline silicon raw material in that feeding cylinder is added to the outer crucible, no air will be mixed in, thereby guaranteeing the growth quality of the monocrystalline silicon.

[0012] Furthermore, a guide block is fixedly installed at the bottom of the inner cavity of the feeding cylinder. The inner diameter of the guide block decreases uniformly from top to bottom, and the minimum inner diameter of the guide block is the same as the inner diameter of the guide groove. The polycrystalline silicon raw material in the feeding cylinder falls smoothly through the guide block's inner inclined surface.

[0013] Furthermore, an observation port is provided at the top of the side of the cylinder, and the observation port is located on one side of the feeding cylinder. The feeding cylinder is a transparent tube, which makes it convenient for the operator to know the amount of polysilicon raw material in the feeding cylinder below the temporary receiving device. Before the polysilicon raw material is filled, the second motor drives the rotating disk and the U-shaped receiving disk to rotate half a turn. When the first motor drives the three feeding cylinders to change positions, it can prevent polysilicon particles from getting stuck at the connection between the guide trough and the discharge trough.

[0014] Furthermore, a side cover is fixedly installed on the other side of the positioning tube, and a second motor is fixedly installed on the outer side of the side cover. The output shaft of the second motor is fixedly connected to a linkage shaft, and the linkage shaft is fixedly connected to a rotating disk. The axis of the linkage shaft and the axis of the rotary joint are on the same straight line. The U-shaped receiving tray is located between the linkage shaft and the inlet of the inclined guide tube. The output shaft driven by the second motor drives the linkage shaft and the rotating disk to rotate, so that the inlet of the inclined guide tube rotates from below the linkage shaft to above the linkage shaft.

[0015] Furthermore, one side of the positioning tube is rotatably connected to the rotating disk via a bearing, so that the rotating disk rotates relative to the positioning tube. A sealing ring is provided at the connection between the positioning tube and the rotating disk, and a seal is formed at the connection between the positioning tube and the rotating disk by the sealing ring to prevent the leakage of polycrystalline silicon raw material powder particles and prevent wear on the bearing.

[0016] The beneficial effects of this invention are as follows:

[0017] This application provides a single-crystal silicon growth furnace for preparing single-crystal silicon rods. By setting a feeding device and a temporary receiving device between the feeding tube and the outer crucible inside the furnace, the rotating disk and U-shaped receiving disk in the temporary receiving device rotate half a turn to temporarily receive the material. With the switching of three feeding cylinders, the feeding, air removal and feeding operations are carried out respectively. Thus, while achieving continuous feeding and Czochralski pulling without stopping the machine, it also ensures that the added polycrystalline silicon raw material is not mixed with air, ensuring high efficiency and high quality of single-crystal silicon growth. At the same time, by eliminating the repeated heating, melting and cooling processes of the Czochralski method and multiple crystal pulling methods, it also effectively saves power consumption. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort:

[0019] Figure 1 This is a schematic diagram of the structure of the present invention;

[0020] Figure 2 for Figure 1 Schematic diagram of the connection structure between the feeding device and the feeding pipe;

[0021] Figure 3 for Figure 2 A three-dimensional schematic diagram of the internal structure of the middle cylinder;

[0022] Figure 4 for Figure 2 A cross-sectional schematic diagram of the temporary material receiving device;

[0023] Figure 5 for Figure 2 Right view of the central rotating disk;

[0024] Figure 6 for Figure 5 A schematic diagram showing the state of the central rotating disk after it has rotated half a turn.

[0025] In the diagram: 1. Furnace body; 2. Supporting shaft; 3. Graphite tray; 4. Outer crucible; 5. Inner crucible; 6. Heater; 7. Molten material receiving tray; 8. Seed crystal shaft; 9. Feeding device; 901. Cylinder; 9011. Observation port; 902. Cover plate; 9021. Discharge chute; 903. Rotating block; 9031. Guide chute; 904. Positioning shaft; 905. First motor; 906. Feeding cylinder; 907. Guide block; 908. Connecting shaft; 10. Temporary receiving device; 101. Positioning tube; 102. Rotating disk; 103. Side cover; 104. Second motor; 105. Linkage shaft; 106. U-shaped receiving tray; 11. Inclined guide tube; 12. Rotary joint; 13. Feeding pipe; 14. Air inlet pipe; 15. Exhaust pipe; 16. Discharge pipe. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] like Figure 1 A single-crystal silicon growth furnace for preparing single-crystal silicon rods includes a furnace body 1. A supporting shaft 2 is installed at the bottom of the inner cavity of the furnace body 1. A graphite tray 3 is fixedly installed on the top of the supporting shaft 2. An outer crucible 4 is installed on the top of the graphite tray 3. An inner crucible 5 is also provided inside the outer crucible 4. A through groove is opened in the lower half of the inner crucible 5 to communicate with the inner cavity of the outer crucible 4. A heater 6 is located outside the outer crucible 4 inside the furnace body 1, and a melt receiving tray 7 is located below the outer crucible 4. A seed crystal shaft 8 is movably installed at the top of the inner cavity of the furnace body 1. The heater 6 heats the outer crucible 4 and the inner crucible 5 to above the melting point of silicon, so that the polycrystalline silicon in the outer crucible 4 and the inner crucible 5 is completely melted. The overflowing melt is received by the melt receiving tray 7. The seed crystal shaft 8 is controlled to descend into the inner crucible 5. After preheating to eliminate thermal shock, the seed crystal shaft 8 is controlled to be parallel to the liquid surface. Upon contact, the seed crystal tip at the bottom of the seed crystal shaft 8 is slightly melted. Simultaneously, the support shaft 2 is controlled to rotate the graphite tray 3, outer crucible 4, and inner crucible 5 together. Then, the seed crystal shaft 8 is slowly rotated and moved upwards to pull the crystal (the driving devices for rotating the support shaft 2 and moving the seed crystal shaft 8 are existing known devices, not shown in the figure, and are not the inventive point of this invention, so they will not be described in detail. The same driving method as existing single crystal silicon growth furnaces can be used). The pulling speed is reduced and the temperature is appropriately lowered to rapidly increase the crystal diameter until the target diameter is reached. When the diameter reaches the set value, the pulling speed is rapidly increased to suppress the diameter from continuing to grow laterally, so that the crystal edge smoothly transitions to vertical downward growth to form a cylinder. Cooling grooves are provided on the furnace body 1, and cooling water is continuously introduced through the cooling grooves during the crystal pulling process to achieve a cooling effect.

[0028] like Figures 1-4 A feeding device 9 is fixedly installed on one side of the top of the furnace body 1. The feeding device 9 includes a cylinder 901. A cover plate 902 is fixedly installed on the top and bottom of the cylinder 901. A rotating block 903 is installed on the opposite side of the two cover plates 902 through a plane bearing. A positioning shaft 904 is fixedly connected in the middle between the two rotating blocks 903. A first motor 905 that drives the positioning shaft 904 to rotate is fixedly installed on one of the cover plates 902. The positioning shaft 904 is movably sleeved with the cover plate 902. Three feeding cylinders 906 located outside the positioning shaft 904 are fixedly fitted between the two rotating blocks 903. The three feeding cylinders 906 are arranged in a circumferential array on the cover plate 902. A guide groove 9031 communicating with the feeding cylinders 906 is opened on each of the two rotating blocks 903.

[0029] A guide block 907 is fixedly installed at the bottom of the inner cavity of the feeding cylinder 906. The inner diameter of the guide block 907 decreases uniformly from top to bottom, and the minimum inner diameter of the guide block 907 is the same as the inner diameter of the guide groove 9031, so that the polycrystalline silicon raw material in the feeding cylinder 906 can fall smoothly.

[0030] Three connecting shafts 908 located outside the positioning shaft 904 are fixedly connected between the two rotating blocks 903. The three connecting shafts 908 are respectively arranged between two adjacent feeding cylinders 906. The two rotating blocks 903 are connected through the connecting shafts 908 so that the positioning shaft 904 can drive the two rotating blocks 903 and the three feeding cylinders 906 to rotate stably together under the driving force of the first motor 905.

[0031] A temporary receiving device 10 and an air inlet pipe 14 are fixedly installed on the cover plate 902 at the top of the cylinder 901. An exhaust pipe 15 and a discharge pipe 16 are connected to the cover plate 902 at the bottom of the cylinder 901. The temporary receiving device 10, the air inlet pipe 14, the exhaust pipe 15, and the discharge pipe 16 are respectively connected to three feeding cylinders 906. The bottom end of the discharge pipe 16 extends into the outer crucible 4, and the bottom end of the discharge pipe 16 is located outside the inner crucible 5. A discharge trough 9021 is opened on the cover plate 902, which is connected to one of the guide troughs 9031. A sealing ring is provided at the connection between the discharge trough 9021 and the guide trough 9031. The temporary receiving device 10 includes a positioning pipe 101. The pipe opening at the bottom of the positioning pipe 101 is connected to the discharge trough 9021. A rotating disk 102 is rotatably connected to one side of the positioning pipe 101 through a bearing. The positioning pipe 101 and the cover plate 902 are connected to each other. A sealing ring is provided at the connection part. A side cover 103 is fixedly installed on the other side of the positioning tube 101. A second motor 104 is fixedly installed on the outer side of the side cover 103. The output shaft of the second motor 104 is fixedly connected to a linkage shaft 105. The linkage shaft 105 is fixedly connected to the rotating disk 102. The output shaft is driven by the second motor 104 to drive the linkage shaft 105 and the rotating disk 102 to rotate. An inclined guide tube 11 is fixedly connected to the outer edge of one side of the rotating disk 102. A rotary joint 12 is fixedly connected to the end of the inclined guide tube 11 away from the rotating disk 102. The axis of the rotary joint 12 is on the same straight line as the axis of the linkage shaft 105 and the rotating disk 102. One end of the inclined guide tube 11 is fixedly connected to the rotating end of the rotary joint 12. A feeding pipe 13 is connected to the fixed end of the rotary joint 12. The feeding pipe 13 can be set as a spiral conveying pipe.

[0032] A U-shaped receiving tray 106 is fixedly installed on the side of the rotating disk 102 between the linkage shaft 105 and the pipe opening of the inclined guide tube 11. The two ends of the U-shaped receiving tray 106 and the inner wall of the positioning tube 101 are reserved with a gap for the passage of polycrystalline silicon raw materials, and the opening of the U-shaped receiving tray 106 faces the pipe opening of the inclined guide tube 11.

[0033] In use, granular polycrystalline silicon raw material is continuously fed through the feeding pipe 13. The polycrystalline silicon raw material enters the positioning pipe 101 through the rotary joint 12 and the inclined guide pipe 11, and then enters one of the feeding cylinders 906 through the feeding trough 9021 and the guide trough 9031. An observation port 9011 is opened on the top side of the cylinder 901, and the observation port 9011 is located on one side of the feeding cylinder 906. The feeding cylinder 906 is a transparent tube. Before the polycrystalline silicon raw material fills the inner cavity of the feeding cylinder 906, the output shaft driven by the second motor 104 drives the linkage shaft 105, the rotating disk 102 and the inclined guide pipe 11 to rotate half a turn. Figure 6 The process involves rotating the U-shaped receiving tray 106 below the inclined guide tube 11. At this time, the polysilicon material entering the positioning tube 101 through the inclined guide tube 11 is temporarily stored in the U-shaped receiving tray 106. All the polysilicon material in the positioning tube 101 enters the feeding cylinder 906. Then, the first motor 905 drives the output shaft to rotate the feeding cylinder 906, the two rotating blocks 903, and the three feeding cylinders 906 together by 120 degrees, that is, to change the position of the three feeding cylinders 906. At this time, when the rotating block 903 rotates relative to the discharge trough 9021, since all the polysilicon material is located in the feeding cylinder 906 and the newly added polysilicon material enters the U-shaped receiving tray 106, the problem of the polysilicon material not getting stuck at the connection between the guide trough 9031 and the discharge trough 9021 is avoided.

[0034] The polysilicon raw material feeding cylinder 906 is rotated to maintain communication with the air inlet pipe 14 and the exhaust pipe 15. Protective gas is continuously supplied through the air inlet pipe 14, and the air inside the feeding cylinder 906 is discharged through the exhaust pipe 15. During the exhaust process, the second motor 104 drives the linkage shaft 105 and the rotating disk 102 to reset and rotate half a turn, so that the opening of the U-shaped receiving tray 106 faces downward again. The polysilicon raw material in the U-shaped receiving tray 106 and the positioning tube 101 falls back into the feeding cylinder 906 below through the feeding groove 9021 and the guide groove 9031. Before the polysilicon raw material fills the inner cavity of the feeding cylinder 906, the adjacent polysilicon raw material feeding cylinder 906 is simultaneously filled. After the air inside is completely removed, the first motor 905 is started to drive the output shaft, which in turn drives the positioning shaft 904, the two rotating blocks 903, and the three feeding cylinders 906 to rotate 120 degrees. The positions of the three feeding cylinders 906 are then changed. After the air is removed, the feeding cylinder 906 rotates to the top of the feeding tube 16. The polycrystalline silicon raw material in the feeding cylinder 906 falls into the outer crucible 4 and is heated to a molten state by the heater 6, thus achieving continuous feeding. This allows the crystal pulling and feeding processes to be carried out in parallel, eliminating the need to stop the furnace, cool, dismantle, clean, reload, and remelt after each silicon rod is pulled. This eliminates the non-productive waiting time in the traditional process and improves the efficiency of crystal pulling.

[0035] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A single-crystal silicon growth furnace for preparing single-crystal silicon rods, comprising a furnace body, an outer crucible disposed inside the furnace body, a heater disposed outside the outer crucible, a seed crystal shaft disposed above the outer crucible, and a feeding device fixedly installed on the outer side of the furnace body, characterized in that, The feeding device includes a cylinder, inside which are three feeding cylinders arranged in a circumferential array. The three feeding cylinders are driven to rotate synchronously by a first motor located above the cylinder. A temporary receiving device connected to the first feeding cylinder is located above the cylinder. An air inlet pipe and an exhaust pipe are connected to the top and bottom of the second feeding cylinder, respectively. A discharge pipe extending into the outer crucible is connected to the bottom of the third feeding cylinder. The temporary receiving device includes a positioning tube fixedly installed above the cylinder. A rotating disk is rotatably connected to one side of the positioning tube. An inclined guide tube is fixedly connected to the outer edge of one side of the rotating disk. A rotary joint is fixedly connected to the end of the inclined guide tube away from the rotating disk. The axis of the rotary joint is on the same straight line as the axis of the rotating disk. One end of the inclined guide tube is fixedly connected to the rotating end of the rotary joint. A feeding pipe is connected to the fixed end of the rotary joint. A U-shaped receiving tray is fixedly installed on the side of the rotating disk, and the opening of the U-shaped receiving tray faces the opening of the inclined guide tube.

2. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 1, characterized in that, The outer crucible is further provided with an inner crucible. The lower half of the inner crucible has a through groove that connects to the inner cavity of the outer crucible. The bottom end of the feed pipe is located outside the inner crucible.

3. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 1, characterized in that, The top and bottom of the cylinder are respectively fixedly connected to cover plates. Rotating blocks are installed on opposite sides of the two cover plates via plane bearings. A positioning shaft is fixedly connected in the middle between the two rotating blocks. Three feeding cylinders are fixedly arranged between the two rotating blocks. Three guide grooves are opened on the rotating blocks. The three guide grooves are respectively connected to the three feeding cylinders. The first motor is fixedly installed on the top of one of the cover plates.

4. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 3, characterized in that, Three connecting shafts located outside the positioning shaft are fixedly connected between the two rotating blocks. The three connecting shafts are respectively located between two adjacent feeding cylinders.

5. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 3, characterized in that, The cover plate has a discharge trough that connects to one of the guide troughs, and the bottom opening of the positioning tube is connected to the discharge trough.

6. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 5, characterized in that, A sealing ring is provided at the connection between the feeding trough and the guiding trough.

7. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 3, characterized in that, A guide block is fixedly installed at the bottom of the inner cavity of the feeding cylinder. The inner diameter of the guide block decreases uniformly from top to bottom, and the minimum inner diameter of the guide block is the same as the inner diameter of the guide groove.

8. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 1, characterized in that, An observation port is provided at the top of the side of the cylinder, and the observation port is located on one side of the feeding cylinder, which is a transparent tube.

9. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 1, characterized in that, A side cover is fixedly installed on the other side of the positioning tube, and a second motor is fixedly installed on the outside of the side cover. The output shaft of the second motor is fixedly connected to a linkage shaft, which is fixedly connected to the rotating disk. The axis of the linkage shaft and the axis of the rotary joint are on the same straight line. The U-shaped receiving tray is located between the linkage shaft and the inclined guide tube opening.

10. The single-crystal silicon growth furnace for preparing single-crystal silicon rods according to claim 9, characterized in that, One side of the positioning tube is rotatably connected to the rotating disk via a bearing, and a sealing ring is provided at the connection between the positioning tube and the rotating disk.

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