Plasma generator

Abstract

To expand a range of a gas pressure generating an inductive coupling plasma and a gas flow amount.SOLUTION: A plasma generator generates a plasma in an inner part by introducing a gas into the inner part. The plasma generator comprises: an electric-discharge tube; a coil wound to an external periphery of the electric-discharge tube; and a lid part blocking one open of the electric-discharge tube. In the lid part, a gas introduction hole for introducing a gas into the inner part of the electric-discharge tube from an external part is formed at a position corresponded to a center shaft of the electric-discharge tube. A length of a direction of the center shaft in an upstream part from a lower end part of the lid part and an end part of the coil is equal to or less than the length of the direction of the center shaft of the coil. In each coil, the length of the direction of the center shaft in the coil of a current path part in which a current flows is shorter than that of the direction of the center shaft in the upstream part. The length of the direction of the center shaft from the lower end part of the lid part to the end part of the current path part is longer than that of the direction of the center shaft of the current path part. An inner diameter of the electric-discharge tube is shorter than the length of the direction fo the center shaft in the upstream part.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a plasma generator. [Background technology]

[0002] In semiconductor manufacturing processes, processing using plasma is performed. Plasma is generated using a plasma generator having a discharge tube into which a process gas is introduced and which generates plasma inside. Patent Documents 1 and 2 describe plasma generators that generate inductively coupled plasma (ICP).

[0003] However, in conventional plasma generators, the plasma that should be coupled with the coil flows downstream, reducing efficiency and making it impossible to stably generate ICP. For this reason, conventional plasma generators have a narrow range of gas pressures and gas flow rates at which ICP can be generated, making the conditions for stably generating ICP strict. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-161319 [Patent Document 2] Japanese Patent Publication No. 2020-057464 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above, and provides a plasma generator that generates inductively coupled plasma over a wide range of gas pressures and gas flow rates. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a plasma generator according to the present invention is a plasma generator in which a gas is introduced inside and plasma is generated inside, the plasma generator comprising: a cylindrical discharge tube made of an insulator; a conductor coil wound around the central axis of the discharge tube around the outer periphery of the discharge tube; and a lid portion closing one opening of the discharge tube, wherein the lid portion has a gas inlet hole formed at a position corresponding to the central axis of the discharge tube for introducing the gas from the outside into the inside of the discharge tube, the length in the central axis direction from a lower end of the lid portion to an end of the coil at an upstream portion is equal to or shorter than the length in the central axis direction of the coil, the length in the central axis direction of a current path portion of the coil through which current flows is shorter than the length in the central axis direction of the coil at the upstream portion, a part of the coil forms the current path portion, the length in the central axis direction from the lower end of the lid portion to the end of the current path portion is longer than the length in the central axis direction of the current path portion, and the inner diameter of the discharge tube is shorter than the length in the central axis direction of the upstream portion. [Effects of the Invention]

[0007] According to the present invention, the range of gas pressure and gas flow rate for generating inductively coupled plasma can be widened. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the configuration of a plasma generation device according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the appearance of the plasma generator according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the plasma generator according to the embodiment. [Figure 4] FIG. 4 is a diagram showing dimensions of the plasma generator according to the embodiment. [Figure 5] FIG. 5 is a diagram showing the state of plasma generation for each gas flow rate and gas pressure condition when the length from the bottom end of the lid to the top end of the coil is set to 100 mm. [Figure 6]FIG. 6 is a diagram showing plasma generation states for each gas flow rate and gas pressure condition in the plasma generator according to the embodiment. [Figure 7] FIG. 7 shows a modified example of the lid portion. DETAILED DESCRIPTION OF THE INVENTION

[0009] A plasma generation device 10 according to an embodiment will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to this embodiment.

[0010] 1 is a diagram showing the configuration of a plasma generator 10 according to an embodiment. The plasma generator 10 according to an embodiment is a device that generates inductively coupled plasma (ICP).

[0011] The plasma generation device 10 according to the embodiment includes a high-frequency power supply 12, an impedance matching circuit 14, and a plasma generator 20.

[0012] The high frequency power supply 12 outputs high frequency power in the RF (Radio Frequency) band. The impedance matching circuit 14 matches the impedance of the high frequency power output from the high frequency power supply 12 and supplies it to the plasma generator 20.

[0013] Gas is introduced into the plasma generator 20, which generates plasma therein. The plasma generated by the plasma generator 20 is sent to, for example, a plasma processing chamber and used for various processes such as etching.

[0014] The plasma generator 20 includes a cylindrical discharge tube 22, a conductive coil 24, and a lid 26. The discharge tube 22 is made of an insulator such as quartz or alumina.

[0015] The coil 24 is wound around the outer periphery of the discharge tube 22, centering on the central axis of the discharge tube 22. High frequency power is supplied to the coil 24 from the high frequency power source 12 via the impedance matching circuit 14.

[0016] The lid 26 is made of a metal such as aluminum and closes one opening of the discharge tube 22. Furthermore, the lid 26 is formed with a gas inlet 28 at a position corresponding to the central axis of the discharge tube 22, for introducing gas from the outside into the inside of the discharge tube 22.

[0017] In such a plasma generator 20, the inside of the discharge tube 22 is maintained in a high vacuum state, and gas is introduced into the interior through the gas inlet hole 28. The plasma generator 20 converts the gas inside the discharge tube 22 into plasma through inductive coupling with a fluctuating magnetic field generated by a high-frequency current flowing through the coil 24, thereby generating inductively coupled plasma (ICP). The generated plasma is sent to a plasma processing chamber or the like from an opening in the discharge tube 22 on the opposite side from the gas inlet hole 28.

[0018] Fig. 2 is a diagram showing the appearance of the plasma generator 20 according to the embodiment, and Fig. 3 is a diagram showing a cross section of the plasma generator 20 according to the embodiment.

[0019] Gas is introduced into the plasma generator 20 from the upper side in the drawing, and plasma is emitted from the lower side in the drawing. The upstream side of the gas flowing into the plasma generator 20 is referred to as the upper side, and the downstream side of the gas is referred to as the lower side.

[0020] The plasma generator 20 includes a discharge tube 22, an upper flange 42, an upper connecting cylinder 44, and a lid portion 26.

[0021] The discharge tube 22 is made of an insulating material such as quartz, alumina, etc. Gas that is a material for plasma passes through the inside of the discharge tube 22 in the direction of the central axis.

[0022] The upper flange 42 is made of a metal such as aluminum, and is provided near the upper side of the discharge tube 22 on the outer periphery of the discharge tube 22. The upper flange 42 has a circular outer periphery and a circular opening in the center. The central opening of the upper flange 42 coincides with the outer periphery of the discharge tube 22, and the discharge tube 22 is attached with the opening inserted.

[0023] The upper connecting tube 44 is made of a metal such as aluminum, and is attached to the upper side of the discharge tube 22. The upper connecting tube 44 is approximately cylindrical, with its inner circumference coinciding with the outer circumference of the discharge tube 22, and the discharge tube 22 is inserted inside. The upper connecting tube 44 also extends in the outer circumferential direction at its lower position. This extended portion functions as a first flange 46. The upper connecting tube 44 also extends in the outer circumferential direction at its upper position. This extended portion functions as a second flange 48.

[0024] Furthermore, a notch is formed on the inside (discharge tube 22 side) of the lower end position of the upper connecting tube 44, and an O-ring 91 is inserted into the notch. By fixing the first flange 46 and the upper flange 42 with bolts or the like, the O-ring 91 is sandwiched between the first flange 46 and the upper flange 42, and the O-ring 91 deforms, thereby sealing the gap between the discharge tube 22 and the first flange 46. This maintains airtightness above the discharge tube 22.

[0025] The cover portion 26 is disk-shaped. The cover portion 26 is fixed to the upper connecting cylinder 44 with the edge of the circle placed on a second flange 48 formed on the upper connecting cylinder 44. This allows the cover portion 26 to close one opening of the discharge tube 22.

[0026] Furthermore, the lid 26 has a gas introduction hole 28 formed at a position corresponding to the central axis of the discharge tube 22. This allows the lid 26 to introduce gas from the outside to the inside of the discharge tube 22 while maintaining the pressure inside the discharge tube 22. In the figure, four holes are formed around the gas introduction hole 28, but these four holes do not penetrate through and are used when attaching the lid 26.

[0027] A connecting member 49 is provided between the lid portion 26 and the second flange 48. The connecting member 49 is an annular member made of a metal such as aluminum, and is composed of an annular inner ring, an outer ring, and an O-ring provided between the two. When the lid portion 26 and the second flange 48 are attached with the connecting member 49 sandwiched between them, the O-ring can maintain airtightness between the lid portion 26 and the second flange 48. The lid portion 26 and the second flange 48 may also be formed integrally. This eliminates the need for the connecting member 49, thereby reducing costs.

[0028] The plasma generator 20 further includes a coil 24. The coil 24 is provided in a central region in the central axis direction of the discharge tube 22. The outer circumferential shape of the cross section of the coil 24 is rectangular, for example, square. The coil 24 is a linear conductor, and is wound around the outer periphery of the discharge tube 22 at a predetermined pitch for a predetermined number of turns, centered on the central axis of the discharge tube 22. As a result, the coil 24 is wound around the outer periphery of the discharge tube 22, centered on the central axis of the discharge tube 22.

[0029] The coil 24 is hollow and includes a cooling pipe 52 through which a refrigerant flows. The coil 24 is also provided with a first connection portion 54 at one end and a second connection portion 56 at the other end. One of the first connection portion 54 and the second connection portion 56 is a connecting jig for introducing the refrigerant into the cooling pipe 52 inside the coil 24, and the other is a connecting jig for sending the refrigerant out of the cooling pipe 52 of the coil 24. This allows the refrigerant to flow through the cooling pipe 52 inside the coil 24 from one end to the other end, cooling the coil 24 and the discharge tube 22. By including such a cooling pipe 52, the coil 24 can efficiently cool the heat generated by the coil 24.

[0030] Furthermore, a first electrode 62 and a second electrode 64 are provided midway between one end and the other end of the coil 24. High-frequency power is supplied to the first electrode 62 and the second electrode 64 from the impedance matching circuit 14. As a result, a current corresponding to the high-frequency power flows between the first electrode 62 and the second electrode 64 in the coil 24, and the coil 24 can generate a high-frequency magnetic field.

[0031] Furthermore, the plasma generator 20 includes a lower flange 72 and a lower connecting tube 74 .

[0032] The lower flange 72 is made of a metal such as aluminum, and is provided on the outer periphery of the discharge tube 22, near the lower side of the discharge tube 22. The outer periphery of the lower flange 72 is circular, and the center has a circular opening. The center opening of the lower flange 72 coincides with the outer periphery of the discharge tube 22, and the discharge tube 22 is attached with the opening inserted.

[0033] The lower connecting tube 74 is made of a metal such as aluminum, and is attached to the lower side of the discharge tube 22. The lower connecting tube 74 is approximately cylindrical, with its inner circumference coinciding with the outer circumference of the discharge tube 22, and the discharge tube 22 is inserted inside. The lower connecting tube 74 also extends in the outer circumferential direction at its upper position. This extended portion functions as a third flange 76. The upper connecting tube 44 also extends in the outer circumferential direction at its lower position. This extended portion functions as a fourth flange 78.

[0034] Furthermore, the plasma generator 20 includes a cooling pipe support portion 82 and a lower cooling pipe 84 .

[0035] The cooling pipe support part 82 is made of a metal such as aluminum, and is provided above the lower flange 72 on the outer periphery of the discharge tube 22. The cooling pipe support part 82 holds the lower cooling pipe 84. The cooling pipe support part 82 extends upward along the outer periphery of the discharge tube 22.

[0036] Furthermore, a notch is formed on the inside (discharge tube 22 side) of the lower end position of the cooling pipe support part 82, and an O-ring 92 is inserted into the notch. By fixing the cooling pipe support part 82 and the lower flange 72 with bolts or the like, the O-ring 92 becomes sandwiched between the cooling pipe support part 82 and the lower flange 72, and the O-ring 92 deforms, thereby sealing the gap between the discharge tube 22 and the cooling pipe support part 82. This maintains airtightness below the discharge tube 22.

[0037] The lower cooling pipe 84 is wound around the outer periphery of the discharge tube 22 at the upper portion of the lower flange 72 by approximately one turn.

[0038] The lower cooling pipe 84 has a third connection part 86 provided at one end thereof and a fourth connection part 88 provided at the other end thereof. One of the third connection part 86 and the fourth connection part 88 is a connection jig for introducing the refrigerant into the lower cooling pipe 84, and the other is a connection jig for sending the refrigerant out of the lower cooling pipe 84. This enables the lower cooling pipe 84 to cool the discharge tubes 22.

[0039] In the plasma generator 20 configured as described above, gas serving as a plasma material is introduced into the interior through the gas inlet 28, and high-frequency power is supplied to the coil 24. First, the plasma generator 20 ionizes the gas inside the discharge tube 22, which is kept in a vacuum state, using the voltage of the coil 24 to generate capacitively coupled plasma (CCP). Then, when the current flowing through the coil 24 increases, the plasma generator 20 generates an induced magnetic field, generating inductively coupled plasma (ICP). The plasma generator 20 according to this embodiment can stably generate and maintain inductively coupled plasma (ICP).

[0040] FIG. 4 is a diagram for explaining an example of conditions under which inductively coupled plasma (ICP) can be stably generated and maintained over a wide range of gas pressures and gas flow rates.

[0041] Here, the section from the lower end of the lid portion 26 to the upstream end of the coil 24 is referred to as the upstream portion 102. The length of the upstream portion 102 in the central axis direction is equal to or less than the length of the coil 24 in the central axis direction. The length of the coil 24 in the central axis direction is the length in the central axis direction from the end of the coil 24 to which the first connection portion 54 is connected to the end to which the second connection portion 56 is connected.

[0042] The portion of the coil 24 through which current flows, i.e., the portion from the first electrode 62 to the second electrode 64, is defined as a current path portion 104. The length of the current path portion 104 in the central axis direction is shorter than the length of the upstream portion 102 in the central axis direction.

[0043] Furthermore, the length in the central axis direction from the lower end of the lid portion 26 to the upstream end of the current path portion 104 is longer than the length of the current path portion 104 in the central axis direction.

[0044] The inner diameter of the discharge tube 22 is shorter than the length of the upstream portion 102 in the central axis direction.

[0045] With the above configuration, the plasma generator 20 can stably generate and maintain the generation of inductively coupled plasma (ICP).

[0046] More specific dimensional examples are given below.

[0047] First, the inner diameter of the discharge tube 22 is 73 mm. The gas introduction hole 28 is circular and has an inner diameter of 4 mm. The length in the central axis direction of the upstream portion 102 is 126 mm. The length in the central axis direction of the coil 24 is 130 mm.

[0048] The coil 24 has a square cross section measuring 10 mm on each side. The coil 24 is wound 10 times at a pitch of 13 mm. The current path portion 104 comprises six of the 10 turns. For example, the current path portion 104 is the portion from the third turn to the eighth turn from the top. Therefore, the length of the current path portion 104 of the coil 24 in the central axis direction is 78 mm. Furthermore, the length of the current path portion 104 in the central axis direction from the bottom end of the lid portion 26 to the upstream end of the current path portion 104 is 152 mm.

[0049] A high frequency voltage of 1.7 MHz or more and 2.3 MHz or less is applied to the coil 24. Furthermore, the gas introduced from the gas introduction hole 28 is O 2 is.

[0050] Fig. 5 is a diagram showing the state of plasma generation for each gas flow rate and gas pressure condition in a conventional device in which the length from the bottom end of the lid 26 to the top end of the coil is set to 100 mm. Fig. 6 is a diagram showing the state of plasma generation for each gas flow rate and gas pressure condition in the plasma generator 20 created under the conditions shown in Fig. 4.

[0051] 5 and 6 show gas flow rate (sccm) on the vertical axis and gas pressure (Pa) on the horizontal axis, and show whether plasma can be ignited, whether plasma cannot be ignited, or whether plasma can be ignited but discharge cannot be maintained for each gas flow rate and gas pressure. 2 The figure shows the plasma generation state when a high frequency voltage of 1.7 MHz or more and 2.3 MHz or less is applied while maintaining impedance matching.

[0052] As shown in Figure 5, in a conventional device in which the length from the bottom end of the lid portion 26 to the top end of the coil is 100 mm, plasma can be ignited in the range of 180 Pa to 210 Pa when the gas flow rate is 4000 sccm, but plasma discharge cannot be maintained when the gas flow rate is 5000 sccm or more.

[0053] In contrast, as shown in Fig. 6, the plasma generator 20 according to the embodiment is capable of igniting plasma in a range of 180 Pa to 250 Pa, even when the gas flow rate is 10,000 sccm. As such, the plasma generator 20 according to the embodiment has a significantly wider range of gas pressure and gas flow rate at which plasma ignition and discharge can be maintained. In particular, when Fig. 5 and Fig. 6 are compared, the plasma generator 20 according to the embodiment is capable of igniting plasma and maintaining discharge even when a gas flow rate more than twice as high is used.

[0054] FIG. 7 shows a modified example of the lid portion 26. In FIG.

[0055] The lid portion 26 according to the modified example may be formed integrally with the upper connecting cylinder 44, as shown in Fig. 7. The lid portion 26 according to the modified example is cylindrical, with one opening closed by a lid 120. The lid portion 26 according to the modified example has an inner diameter that matches the outer diameter of the discharge tube 22, into which the upper end of the discharge tube 22 is inserted. In addition, the lid portion 26 has a flange similar to the first flange 46 formed on the upper connecting cylinder 44, provided on the outer periphery of the end on the opening side.

[0056] In addition, in the lid portion 26 according to the modified example, the lid 120 has a gas introduction hole 28 formed at a position corresponding to the central axis of the discharge tube 22 .

[0057] The lid part 26 according to this modification is attached to the upper side of the discharge tube 22 in place of the upper connecting cylinder 44. This allows the lid part 26 to introduce gas from the outside to the inside of the discharge tube 22 while maintaining the pressure inside the discharge tube 22.

[0058] Such a plasma generator 20 can reduce the number of parts and facilitate installation work and the like.

[0059] Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. Various modifications can be made to the embodiments. [Explanation of symbols]

[0060] 10 plasma generator, 12 high frequency power supply, 14 impedance matching circuit, 20 plasma generator, 22 discharge tube, 24 coil, 26 lid portion, 28 gas inlet hole, 44 upper connecting tube, 52 cooling tube, 74 lower connecting tube, 102 upstream portion, 104 current path portion

Claims

1. A plasma generator into which a gas is introduced and which generates plasma therein, A cylindrical discharge tube made of an insulator, a conductor coil wound around the outer periphery of the discharge tube and centered on the central axis of the discharge tube; a cover portion that closes one opening of the discharge tube; Equipped with the lid portion has a gas inlet hole formed at a position corresponding to the central axis of the discharge tube for introducing the gas from the outside into the discharge tube, a length in the central axis direction from a lower end of the lid portion to an end of the coil at an upstream portion is equal to or less than a length in the central axis direction of the coil, a length of the coil in a central axis direction of a current path portion through which a current flows is shorter than a length of the coil in the central axis direction of the upstream portion; a part of the coil is the current path portion, and a length in the central axis direction from a lower end of the lid portion to an end of the current path portion is longer than a length in the central axis direction of the current path portion; The inner diameter of the discharge tube is shorter than the length in the central axis direction of the upstream portion. Plasma generator.

2. The gas introduction hole has an inner diameter of 4 mm and is a circle. The length of the upstream portion in the central axial direction is 126 mm, The inner diameter of the discharge tube is 73 mm. The coil is made of a square conductor with a cross section of 10 mm square wound 10 times at a pitch of 13 mm, of which 6 turns form the current path portion. The plasma generator of claim 1 .

3. The coil is hollow and configured to allow a refrigerant to flow inside.

3. The plasma generator according to claim 1 or 2.

4. A high frequency voltage of 1.7 MHz or more and 2.3 MHz or less is applied to the coil.

4. The plasma generator according to claim 1.

5. The gas is O ２ is 5. The plasma generator according to claim 1.

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