Single crystal pulling apparatus

Abstract

This invention provides a single crystal pulling apparatus that offers excellent cooling performance for single crystals and allows for observation of the liquid level. [Solution] A single crystal pulling apparatus for the Czochralski method, comprising: a cylindrical first cooling body that surrounds the outer surface of a single crystal being grown and pulled up from a molten liquid in a crucible to cool the single crystal; an inverted conical second cooling body positioned below the first cooling body and surrounding the outer surface of the single crystal being grown to cool the single crystal; and an imaging device for observing the liquid surface of the molten liquid, wherein the inner diameter of the upper end of the second cooling body is larger than the outer diameter of the lower end of the first cooling body, and a linear optical path is formed from the liquid surface to the imaging device through the gap between the lower end of the second cooling body and the outer surface of the single crystal being grown, and through the gap between the upper end of the second cooling body and the lower end of the first cooling body.

Description

Technical Field

[0001] The present invention relates to a single crystal pulling apparatus.

Background Art

[0002] There is known a single crystal pulling apparatus using the Chokralski method, which includes a cylindrical cooling body that cools a growing single crystal by surrounding the outer peripheral surface of the growing single crystal pulled from the melt in a crucible, and an imaging device that observes the liquid surface of the melt in the crucible (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, by cooling the growing single crystal by surrounding the outer peripheral surface of the growing single crystal with a cooling body, the growing single crystal can be effectively cooled to improve the pulling speed, and it is said that the boundary region between the single crystal and the liquid surface can be observed by an imaging device through a notch provided at the lower end portion of the cooling body. However, providing a notch at the lower end portion of the cooling body has a problem of deteriorating the uniformity of the circumferential heat distribution at the notch.

[0005] An object of the present invention is to provide a single crystal pulling apparatus having excellent cooling performance of a single crystal and capable of observing the liquid surface.

Means for Solving the Problems

[0006] One aspect of the present invention is as follows.

[0007] [1] A single crystal pulling apparatus using the Chokralski method, A cylindrical first cooler surrounds the outer surface of a single crystal being grown and pulled up from the molten liquid in the crucible to cool the single crystal, A second cooling body, shaped like an inverted cone and positioned below the first cooling body, surrounds the outer surface of the single crystal being grown and cools the single crystal; It includes an imaging device for observing the liquid surface of the molten liquid, The inner diameter of the upper end of the second cooler is larger than the outer diameter of the lower end of the first cooler. A single crystal pulling apparatus, wherein a linear optical path is formed from the liquid surface through the gap between the lower end of the second cooling body and the outer surface of the single crystal being grown, and through the gap between the upper end of the second cooling body and the lower end of the first cooling body, to the imaging device.

[0008] [2] The single crystal pulling apparatus according to [1], wherein when the inner diameter of the upper end of the second cooler is A and the inner diameter of the lower end of the second cooler is B, 1.1 ≤ A / B ≤ 1.5.

[0009] [3] The single crystal pulling apparatus according to [1] or [2], wherein the distance between the lower end of the second cooling body and the outer surface of the single crystal being grown is 20 to 70 mm. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a single crystal pulling apparatus that has excellent cooling performance for single crystals and allows observation of the liquid level. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing a single crystal pulling apparatus according to one embodiment of the present invention. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] As shown in Figure 1, in one embodiment of the present invention, the single crystal pulling apparatus 1 is a single crystal pulling apparatus 1 for the Czochralski method, and includes a crucible 3 (a double crucible in which a quartz crucible is housed inside a graphite crucible) for storing a melt 4 which will be the material for the single crystal 2 such as silicon, a seed pulling apparatus 6 which pulls up a seed 5 that will come into contact with the liquid surface 4a of the melt 4 at the start of single crystal growth and serve as the starting point for the single crystal 2 to be grown, while rotating it around a central axis O, and a control device 7 which is configured by a computer or the like and controls the rotation speed and pulling speed of the seed 5 by the seed pulling apparatus 6. The seed pulling apparatus 6 includes a seed chuck 6a for holding the seed 5, a wire 6b with one end connected to the seed chuck 6a, and a hoisting device 6c for winding up the wire 6b from the other end. After immersing the lower end of seed 5 in the liquid surface 4a, the seed 5 is raised while rotating, forming a neck portion 2a at the lower end of seed 5, a shoulder portion 2b with a gradually increasing diameter, and then a roughly cylindrical straight body portion 2c centered on the central axis O.

[0014] In this embodiment, the direction perpendicular to the central axis O is called the radial direction, the direction that circles the central axis O is called the circumferential direction, and the cross-section perpendicular to the central axis O is called the cross-section.

[0015] The single crystal pulling apparatus 1 includes a main chamber 8 in which a crucible 3 is placed, having an outer peripheral wall 8a with a circular cross-sectional shape, a top wall 8b which is annular in top view and connected to the upper end of the outer peripheral wall 8a, and a bottom wall 8c which is connected to the lower end of the outer peripheral wall 8a; and a pull chamber 9 in which a single crystal 2 being grown is pulled up and introduced, having a peripheral wall 9a which extends upward from the inner peripheral edge of the top wall 8b of the main chamber 8, and a top wall 9b which is connected to the upper end of the peripheral wall 9a. Inside the main chamber 8 are a heater 10 which surrounds the outer circumference of the crucible 3 and heats it, and an insulating material 11 which surrounds the outer circumference of the crucible 3 and keeps the crucible 3 warm.

[0016] The single crystal pulling apparatus 1 has a cylindrical first cooling body 12 that cools the growing single crystal 2 by surrounding the outer peripheral surface of the single crystal 2 pulled up from the liquid surface 4a and has a circular cross-sectional shape centered on the central axis O. The first cooling body 12 extends downward from the inner peripheral edge of the ceiling wall 8b of the main chamber 8. The first cooling body 12 may have a cylindrical configuration or a conical or inverted conical configuration. From the viewpoint of enhancing the cooling performance, it is preferable that the first cooling body 12 has a configuration having a flow path inside through which a cooling medium for cooling the first cooling body 12 by heat exchange flows.

[0017] The single crystal pulling apparatus 1 has a second cooling body 13 that is disposed below the first cooling body 12 and cools the growing single crystal 2 by surrounding the outer peripheral surface of the single crystal 2. The second cooling body 13 has an inverted conical cylindrical shape centered on the central axis O. That is, the inner diameter A of the upper end of the second cooling body 13 is larger than the outer diameter B of the lower end of the second cooling body 13. From the viewpoint of enhancing the cooling performance, it is preferable that the second cooling body 13 has a configuration having a flow path inside through which a cooling medium for cooling the second cooling body 13 by heat exchange flows.

[0018] The single crystal pulling apparatus 1 has an imaging device 14 for observing the liquid surface 4a. The imaging device 14 is, for example, a camera, a scanner, or an image sensor. The imaging device 14 is preferably provided outside a window portion 15 made of a light-transmitting material provided on the ceiling wall 8b of the main chamber 8 and observes the liquid surface 4a through the window portion 15 as in the present embodiment.

[0019] In the present embodiment, the inner diameter A of the upper end of the second cooling body 13 is larger than the outer diameter C of the lower end of the first cooling body 12, and a linear optical path L reaching the imaging device 14 is formed from the liquid surface 4a through a gap G1 between the lower end of the second cooling body 13 and the outer peripheral surface of the growing single crystal 2 and a gap G2 between the upper end of the second cooling body 13 and the lower end of the first cooling body 12.

[0020] According to the above configuration, not only the cooling performance of the cylindrical first coolant 12 is exerted, but also the cooling performance of the second coolant 13 with its lower end approaching the liquid surface 4a is exerted. Therefore, there is an effect that the cooling effect on the growing single crystal 2 is extremely high. Moreover, since the shape of the second coolant 13 is an inverted conical shape, the viewing range of the imaging device 14 is enlarged, and an optical path L passing between the second coolant 13, the first coolant 12, and the growing single crystal 2 can be secured. Thus, the liquid surface 4a can be observed by the imaging device 14. Particularly in this embodiment, as shown in FIG. 1, since the optical path L includes the boundary between the growing single crystal 2 and the melt 4, the boundary can be observed, and the diameter control of the growing single crystal 2 becomes possible. Further, by observing the liquid surface 4a, it is also possible to control the distance (gap) between the liquid surface 4a and the lower end of a heat shield 16 described later to a predetermined value.

[0021] When the inner diameter of the upper end of the second coolant 13 is A and the inner diameter of the lower end of the second coolant 13 is B as described above, it is preferable that 1.1 ≦ A / B ≦ 1.5. By setting 1.1 ≦ A / B, it becomes easy to secure the optical path L necessary for observing the liquid surface 4a by the imaging device 14. By setting A / B ≦ 1.5, it is possible to suppress the second coolant 13 from being too far away from the growing single crystal 2 and the cooling effect by the second coolant 13 from decreasing too much.

[0022] The distance D between the lower end of the inner peripheral surface of the second coolant 13 and the outer peripheral surface of the growing single crystal 2 is preferably 20 to 70 mm. By setting the distance D to 20 mm or more, it becomes easy to secure the optical path L while suppressing the contact between the second coolant 13 and the growing single crystal 2. By setting the distance D to 70 mm or less, it is possible to suppress the cooling effect by the second coolant 13 from decreasing too much. The vertical length E from the upper end to the lower end of the second coolant 13 is preferably 100 to 400 mm.

[0023] It is preferable that the lower end of the first cooler 12 is located below the upper end of the second cooler 13. With this configuration, the lower end of the first cooler 12 can compensate for the cooling effect that decreases as the upper end of the second cooler 13 widens. It is preferable that the lower end of the first cooler 12 is located at a height that does not obstruct the optical path L that includes the boundary between the growing single crystal 2 and the melt 4.

[0024] The single crystal pulling apparatus 1, as in this embodiment, preferably has a heat shield 16 that divides the inside of the main chamber 8 into a lower space S1 and an upper space S2, and has an opening 16a in the center of the top view that connects the lower space S1 and the upper space S2. The single crystal 2 being grown passes from the liquid surface 4a through the opening 16a and is pulled into the pull chamber 9 while being cooled by the second cooler 13 and the first cooler 12 in the upper space S2. The inert gas such as argon introduced into the pull chamber 9 flows in the following order: radially inside the first cooler 12, radially inside the second cooler 13, the opening 16a of the heat shield 16, between the liquid surface 4a and the heat shield 16, and between the outer surface of the crucible 3 and the heat insulating material 11, and is discharged from an outlet (not shown) provided at the bottom of the main chamber 8.

[0025] Preferably, the heat shield 16 has, as in this embodiment, an annular bottom wall portion 16b in a top view with an opening 16a in the center of the top view, a cylindrical wall portion 16c extending upward from the outer peripheral edge of the bottom wall portion 16b, and an annular flange wall portion 16d in a top view that extends radially outward from the upper end of the cylindrical wall portion 16c and connects to the outer peripheral wall 8a of the main chamber 8. In this embodiment, the bottom wall portion 16b is shown as extending horizontally in the radial direction, but the bottom wall portion 16b may be inclined downward from the cylindrical wall portion 16c toward the liquid surface 4a.

[0026] From the viewpoint of reliably introducing an inert gas into the heat shield 16, it is preferable that the lower end of the first cooler 12 is located below the upper end of the cylindrical wall portion 16c of the heat shield 16. Furthermore, it is desirable to position the second cooler 13 inside the heat shield 16 so as to cool the single crystal 2 immediately after growth as possible. From this viewpoint, it is preferable that the upper end of the second cooler 13 is located below the upper end of the cylindrical wall portion 16c of the heat shield 16, and that the inner diameter A of the upper end of the second cooler 13 is smaller than the inner diameter of the upper end of the cylindrical wall portion 16c of the heat shield 16. It is preferable that the lower end of the second cooler 13 is located above the inner periphery of the bottom wall portion 16b of the heat shield 16, and that the inner diameter A of the lower end of the second cooler 13 is greater than or equal to the inner diameter of the inner periphery of the bottom wall portion 16b of the heat shield 16. This prevents the evaporated material evaporating from the melt 4 from adhering to and solidifying on the lower end of the second cooler 13, and prevents the adhering and solidified material from falling into the melt 4 and causing the single crystal 4 being grown to develop dislocations. It is preferable to set the inner diameter of the bottom wall portion 16b of the heat shield 16 to a size that does not obstruct the optical path L that includes the boundary between the single crystal 2 being grown and the melt 4.

[0027] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and the embodiments described above can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0028] 1. Single crystal pulling apparatus 2 Single crystals 2a Neck section 2b Shoulder section 2c Straight body part 3 Crucible 4. Melt 4a Liquid level 5th seed 6 Seed Lifting Device 6a Seed Chuck 6b Wire 6c hoisting device 7 Control device 8 Main Chamber 8a Outer wall 8b Ceiling wall 8c bottom wall 9 Pull Chamber 9a Peripheral wall 9b Top wall 10 Heaters 11. Insulation 12. First Cooler 13. Second Cooler 14 Imaging device 15 Window section 16. Heat shield 16a aperture 16b Bottom wall 16c Cylinder wall 16d Flange wall section A Inner diameter B Inner diameter C Outer diameter D distance E Length G1 Gap G2 Gap L optical path O center axis S1 lower space S2 upper space

Claims

1. A single crystal pulling apparatus using the Czochralski method, A cylindrical first cooler surrounds the outer surface of a single crystal being grown and pulled out of the molten liquid in the crucible to cool the single crystal, A second cooling body, shaped like an inverted cone and positioned below the first cooling body, surrounds the outer surface of the single crystal being grown and cools the single crystal; It includes an imaging device for observing the liquid surface of the molten liquid, The inner diameter of the upper end of the second cooler is larger than the outer diameter of the lower end of the first cooler. A single crystal pulling apparatus, wherein a linear optical path is formed from the liquid surface through the gap between the lower end of the second cooling body and the outer surface of the single crystal being grown, and through the gap between the upper end of the second cooling body and the lower end of the first cooling body, to the imaging device.

2. The single crystal pulling apparatus according to claim 1, wherein when the inner diameter of the upper end of the second cooling body is A and the inner diameter of the lower end of the second cooling body is B, 1.1 ≤ A / B ≤ 1.

5.

3. The single crystal pulling apparatus according to claim 1 or 2, wherein the distance between the lower end of the second cooling body and the outer surface of the single crystal being grown is 20 to 70 mm.

Images