JP2019106358A - Microwave plasma processing apparatus - Google Patents

Abstract

To provide a plasma processing apparatus having a structure that can increase plasma density.SOLUTION: There is provided a microwave plasma processing apparatus including: a microwave supply part configured to supply a microwave; a microwave emission member provided on a ceiling of a process chamber and configured to emit the microwave supplied from the microwave supply part; and a microwave transmission member provided to close an opening in the ceiling and made of a dielectric substance that transmits the microwave transmitted to a slot antenna via the microwave emission member. In the ceiling, a recess having a depth in a range of λ/4±λ/8 is formed on an outer side of the opening when a wavelength of a surface wave of the microwave traveling through the microwave transmission member and propagating along a surface of the ceiling from the opening in the ceiling is taken as λ.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a microwave plasma processing apparatus.

  A microwave is introduced into a vacuum chamber from a microwave introduction unit through a transmission window provided in an opening of a ceiling wall, and plasma processing is performed on a substrate by the action of plasma generated from gas by the power of the microwave. A processing apparatus is known (see, for example, Patent Document 1). In this plasma processing apparatus, a choke groove that attenuates the propagation of microwaves is provided around the opening. The choke groove has a propagation path length of approximately λ / 4 with respect to the free space wavelength λ of plasma, and suppresses the propagation of microwaves.

JP 2003-45848 A JP 2004-319870 JP 2005-32805 A JP, 2009-99807, A Unexamined-Japanese-Patent No. 2010-232493 JP, 2016-225047, A

  However, in Patent Document 1 described above, the position of the groove is designed according to the propagation path length of the microwave introduced into the vacuum chamber, and the plasma density can be increased by optimizing the shape of the groove. Not considered.

  One way to increase the plasma density is to increase the input power, but in this case it is necessary to prepare a plasma source with a large maximum output power. Also, the cost of production increases because more power is used during plasma processing. Therefore, a structure of a plasma processing apparatus for increasing plasma density without increasing input power is desired.

  In one aspect, the present invention provides a plasma processing apparatus having a structure capable of increasing plasma density.

In order to solve the above-mentioned subject, according to one mode, it is provided on a microwave supply part which supplies microwaves, and a ceiling wall of a processing container, and radiates microwaves supplied from the microwave supply part. And a microwave transmitting member made of a dielectric that is provided to close the opening of the ceiling wall and transmits microwaves passed through the slot antenna via the microwave emitting member. When the wavelength of a surface wave of microwaves transmitted through the microwave transmitting member and propagated from the opening of the top wall to the top wall is λ _sp , the top wall is outside the opening There is provided a microwave plasma processing apparatus, wherein a recess having a depth in the range of λ _sp / 4 ± λ _sp / 8 is formed.

  According to one aspect, it is possible to provide a plasma processing apparatus having a structure capable of increasing the plasma density.

Sectional drawing which shows an example of the microwave plasma processing apparatus which concerns on one Embodiment. The figure which shows an example of the ceiling wall which concerns on one Embodiment (AA cross section of FIG. 1). The figure which shows an example of the recessed part which concerns on one Embodiment. The figure which shows an example of the electric field cutoff efficiency of the recessed part which concerns on one Embodiment, and a comparative example. The figure for demonstrating the electric field interruption | blocking efficiency of the recessed part which concerns on one Embodiment, and a comparative example. The figure which shows an example of the evaluation result of the electric field interruption | blocking efficiency of the recessed part which concerns on one Embodiment, and a comparative example. The figure which shows an example of the evaluation result of the electric field interruption | blocking efficiency of the recessed part which concerns on one Embodiment, and a comparative example. The figure which shows an example of the ceiling wall which concerns on the modification 1 of one Embodiment (AA cross section of FIG. 1). The figure which shows an example of the ceiling wall which concerns on the modification 2 of one Embodiment (AA cross section of FIG. 1). Sectional drawing which shows an example of the recessed part of the top wall which concerns on the modification 3 of one Embodiment. Sectional drawing which shows an example of the recessed part of the top wall which concerns on the modification 4 of one Embodiment. The figure which shows an example of the relationship between wavelength (lambda) _sp of the surface wave of the microwave which concerns on the modification 4 of one embodiment, and the electron density of a plasma. The figure which shows the system used for calculation which derives the relationship between wavelength (lambda) _sp of the surface wave of a microwave, and the electron density of plasma.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and the drawings, substantially the same configuration is given the same reference numeral to omit redundant description.

[Microwave plasma processing system]
First, a microwave plasma processing apparatus 100 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an example of a microwave plasma processing apparatus 100 according to an embodiment of the present invention. The microwave plasma processing apparatus 100 has a processing container 1 for containing a wafer W. The upper portion of the processing container 1 is open, and the opening can be opened and closed by a lid 10. Thus, the lid 10 constitutes the top wall of the processing container 1.

  The microwave plasma processing apparatus 100 performs predetermined plasma processing on a semiconductor wafer W (hereinafter, referred to as “wafer W”) by surface wave plasma of microwaves propagating on the surface of a ceiling wall. Examples of the predetermined plasma treatment include etching treatment, film formation treatment, ashing treatment, and the like.

  The processing container 1 is a substantially cylindrical container made of a metal material such as aluminum or stainless steel which is airtightly configured, and is grounded. A support ring 129 is provided on the contact surface between the processing container 1 and the lid 10, whereby the inside of the processing container 1 is airtightly sealed. The lid 10 is made of metal such as aluminum.

  The microwave plasma source 2 has a microwave output unit 30, a microwave transmission unit 40 and a microwave radiation member 50. The microwave output unit 30 outputs microwaves by distributing to a plurality of paths. The microwave output unit 30 and the microwave transmission unit 40 are an example of a microwave supply unit that supplies microwaves.

  The microwave transmission unit 40 transmits the microwaves output from the microwave output unit 30. The peripheral microwave introduction mechanism 43a and the central microwave introduction mechanism 43b provided in the microwave transmission unit 40 have a function of introducing the microwave output from the amplifier unit 42 into the microwave radiation member 50 and a function of matching the impedance. Have. The microwave radiation member 50 is provided on the lid 10 of the processing container 1.

  Under the microwave radiation member 50, six microwave transmission members 123 corresponding to the six peripheral microwave introduction mechanisms 43a are arranged at equal intervals in the circumferential direction of the lid 10 (see FIG. 1A). -See Figure 2 showing the A side). Further, one microwave transmitting member 133 corresponding to the central microwave introducing mechanism 43 b is disposed at the center of the lid 10. The microwave transmitting member 123 and the microwave transmitting member 133 are embedded in the lid 10, and the lower surface is circularly exposed in the processing chamber. The lower surfaces of the microwave transmitting members 123 and 133 are located closer to the slots 122 and 132 than the surface of the ceiling wall.

  In the peripheral microwave introduction mechanism 43a and the central microwave introduction mechanism 43b, the cylindrical outer conductor 52 and the rod-like inner conductor 53 provided inside the same are coaxially arranged, and between the outer conductor 52 and the inner conductor 53 Is a microwave transmission line 44.

  The peripheral microwave introduction mechanism 43a and the central microwave introduction mechanism 43b have a slag 54 and an impedance adjustment member 140 located at the tip thereof. The slag 54 is formed of a dielectric, and has a function of matching the impedance of the load (plasma) in the processing vessel 1 with the characteristic impedance of the microwave power source in the microwave output unit 30 by moving the slag 54. The impedance adjustment member 140 is formed of a dielectric, and adjusts the impedance of the microwave transmission line 44 by its relative dielectric constant.

  The microwave radiation member 50 is formed of a disk-like member which transmits microwaves. The microwave transmitting members 123 and 133 are provided under the microwave radiation member 50 so as to close the opening of the lid 10 through the slots 122 and 132 formed in the lid 10.

  The microwave transmitting members 123 and 133 are formed of a dielectric. The microwave radiation member 50 has spaces 121 and 131 at the center, and radiates microwaves to the microwave transmission members 123 and 133 via the slots 122 and 132 connected to the spaces 121 and 131. The microwave transmitting members 123 and 133 have a function as a dielectric window for forming microwave surface wave plasma uniformly on the surface of the ceiling wall.

The microwave transmitting members 123 and 133 may be formed of, for example, a ceramic such as quartz or alumina (Al ₂ O ₃ ), a fluorine-based resin such as polytetrafluoroethylene, or a polyimide-based resin as in the microwave radiating member 50. Good.

The microwave radiation member 50 is a dielectric having a dielectric constant larger than that of vacuum, and, for example, quartz, ceramics such as alumina (Al ₂ O ₃ ), fluorine-based resin such as polytetrafluoroethylene, polyimide-based resin, etc. It is formed by Thus, the wavelength of the microwaves transmitted through the microwave radiation member 50 is made shorter than the wavelength of the microwaves propagating in the vacuum, thereby reducing the shape of the antenna including the slots 122 and 132.

  With this configuration, the transmitted microwaves output from the microwave output unit 30 are transmitted to the microwave radiation member 50 through the microwave transmission path 44 and emitted from the microwave radiation member 50 into the processing container 1. Ru. As a result, microwave power is supplied into the processing container 1.

  The number of peripheral microwave introduction mechanisms 43a and the number of central microwave introduction mechanisms 43b are not limited to those shown in the present embodiment. For example, only one central microwave introduction mechanism 43b may be provided, and the peripheral microwave introduction mechanism 43a may not be provided. That is, the number of the peripheral microwave introduction mechanisms 43a may be zero or one or more.

The lid 10 is formed of a metal such as aluminum, and a gas inlet 62 having a shower structure is formed inside. A gas supply source 22 is connected to the gas introduction unit 62 via a gas supply pipe 111. The gas is supplied from the gas supply source 22, and is supplied to the inside of the processing container 1 from the plurality of gas supply holes 60 of the gas introduction unit 62 via the gas supply pipe 111. The gas introduction unit 62 is an example of a gas shower head that supplies a gas from a plurality of gas supply holes 60 formed in the ceiling wall of the processing container 1. Examples of the gas include, for example, Ar gas, and a mixed gas of Ar gas and N ₂ gas.

  A mounting table 11 for mounting the wafer W is provided in the processing container 1. The mounting table 11 is supported by a support member 12 erected at the center of the bottom of the processing container 1 via an insulating member 12 a. As a material which comprises the mounting base 11 and the supporting member 12, metal, such as aluminum etc. which carried out the alumite process (anodizing process) of the surface, and the insulation members (ceramics etc.) which had the electrode for high frequencies inside are illustrated. The mounting table 11 may be provided with an electrostatic chuck for electrostatically attracting the wafer W, a temperature control mechanism, a gas flow path for supplying a heat transfer gas to the back surface of the wafer W, and the like.

  A high frequency bias power supply 14 is connected to the mounting table 11 via a matching unit 13. The supply of high frequency power from the high frequency bias power supply 14 to the mounting table 11 causes ions in the plasma to be drawn to the wafer W side. The high frequency bias power supply 14 may not be provided depending on the characteristics of the plasma processing.

  An exhaust pipe 15 is connected to the bottom of the processing container 1, and an exhaust device 16 including a vacuum pump is connected to the exhaust pipe 15. When the exhaust device 16 is operated, the inside of the processing container 1 is exhausted, whereby the inside of the processing container 1 is rapidly depressurized to a predetermined degree of vacuum. A loading / unloading port 17 for loading / unloading the wafer W and a gate valve 18 for opening / closing the loading / unloading port 17 are provided on the side wall of the processing container 1.

  Each unit of the microwave plasma processing apparatus 100 is controlled by the control unit 3. The control unit 3 includes a microprocessor 4, a read only memory (ROM) 5, and a random access memory (RAM) 6. The ROM 5 and the RAM 6 store a process sequence which is a process sequence and control parameters of the microwave plasma processing apparatus 100. The microprocessor 4 controls each part of the microwave plasma processing apparatus 100 based on the process sequence and the process recipe. In addition, the control unit 3 includes the touch panel 7 and the display 8, and can perform input when performing predetermined control according to the process sequence and the process recipe, and display of a result.

  When plasma processing is performed in the microwave plasma processing apparatus 100 having such a configuration, first, the wafer W is held from the gate valve 18 opened through the loading / unloading port 17 in the processing container 1 while being held on the transfer arm. It is mounted on the mounting table 11. The pressure inside the processing container 1 is maintained at a predetermined degree of vacuum by the exhaust device 16. Gas is introduced into the processing container 1 from the gas introduction unit 62 in a shower shape.

  The surface waves of the microwaves radiated through the microwave radiation member 50, the slots 122 and 132, and the microwave transmission members 123 and 133 propagate on the surface of the ceiling wall. Then, the gas is ionized and dissociated by the electric field of the surface wave to generate surface wave plasma of microwaves in the vicinity of the surface of the ceiling wall. The wafer W is subjected to plasma processing in the processing space U between the ceiling wall of the processing container 1 and the mounting table 11 using this surface wave plasma.

[Concave part]
The front surface (rear surface) of the top wall of the lid 10 of the microwave plasma processing apparatus 100 according to this embodiment of the configuration will be described with reference to FIG. 2 showing the A-A plane of FIG. On the surface of the ceiling wall, six microwave transmitting members 123 are provided at equal intervals in the circumferential direction on the peripheral side, and one microwave transmitting member 133 is provided. Each microwave transmission member 123 is exposed from the opening of the top wall of the peripheral portion, and the microwave transmission member 133 is exposed from the opening of the central top wall. In the top wall, seven recesses (grooves) 70 are formed in a ring shape so as to surround each of the top wall openings to which the microwave transmitting members 123 and 133 are exposed.

Assuming that the wavelength of the surface wave of the microwaves transmitting through each of the microwave transmitting members 123 and 133 and propagating from the opening of the ceiling wall to the surface of the ceiling wall is λ _sp , the depth of λ _sp / 4 That is, it is formed in about 5 mm-7 mm. However, the depth of the recess 70 is not limited to lambda _sp / 4, it may be in the range of _{λ sp / 4 ± λ sp /} 8.

  Further, as shown in FIG. 2, the diameter of the inner peripheral side of the recess 70 is in the range of φ + 10 mm to 100 mm with respect to the diameter φ of the opening of the top wall where the microwave transmitting members 123 and 133 are exposed. If the diameter on the inner peripheral side of the recess 70 is in the range of φ + 10 mm to 100 mm, a plurality of ring-shaped recesses 70 may be formed concentrically.

[Evaluation of recess]
Next, an example of the evaluation result of the recess will be described with reference to FIG. FIG. 3A and FIG. 3B show an example of the comparative example, and the convex portion 71 is formed in a ring shape so as to surround each of the openings of the top wall where the microwave transmitting members 123 and 133 are exposed. . The height from the surface of the ceiling wall of the convex portion 71 in FIG. 3A is 5 mm, and the height from the surface of the convex portion 71 in FIG. 3B is 10 mm.

  FIG. 3C is an example of the present embodiment, in which concave portions 70a and 70b having a depth of 5 mm, which are an example of the concave portion 70, are formed in a ring shape in a double manner.

  FIG. 3D is an example of the present embodiment, and a convex portion is formed between the concave portions 70a and 70b having a depth of 5 mm. The protrusion protrudes 10 mm from the bottom of the recess 70 a, 70 b, that is, 5 mm from the surface of the ceiling wall.

In such a configuration, microwave surface wave plasma was generated under the following process conditions.
<Process condition>
Gas type Ar gas microwave power 400 W
Microwave frequency 860 MHz
Pressure 10Pa
The results are shown in FIG. The graph of (a) of FIG. 4 shows an example of the state of the electric field of the surface wave plasma propagating on the surface of the ceiling wall. The horizontal axis indicates the distance R (mm) from the center of the ceiling wall (right end of the graph), and the vertical axis indicates the electric field intensity Power (mW) of the surface wave plasma. The -70 mm line on the horizontal axis is the position where the convex portion 71 or the concave portion 70 is formed. According to this, FIG. 3 (c) is more than “a” when the convex 71 of FIG. 3 (a) is formed and “b” when the convex 71 of FIG. 3 (b) is formed. In the case where the concave portion 70 is formed, the direction of “c” in the case where the concave portion 70 of FIG. 3D is formed is on the outer peripheral side than the position where the convex portion 71 or the concave portion 70 is formed. The electric field strength of the surface wave plasma is low. That is, by providing the concave portion on the surface of the ceiling wall rather than the convex portion, the blocking efficiency of the electric field of the surface wave plasma can be enhanced. Further, by providing the concave portion 70 having a depth of 5 mm shown in FIG. 3C, the electric field cutoff efficiency of surface wave plasma is more than providing the concave portion shown in FIG. 3D (height of 10 mm at the center) Is found to be higher.

From the above evaluation results, it was found that it is preferable to form a recess of about 5 mm, ie, a depth of λ _sp / 4, so as to surround each of the ceiling wall openings to which the microwave transmitting members 123 and 133 are exposed. . In addition, it was found that the blocking efficiency of the electric field of the surface wave plasma when the convex portions were provided so as to surround each of the openings of the ceiling wall was lower than that when the concave portions were provided. The wavelength λ _sp of the surface wave of microwaves propagating from the opening of the ceiling wall to the surface of the ceiling wall is, in other words, the wavelength of the surface wave of microwaves flowing on the surface of plasma, and the free space wavelength of plasma in vacuum It will be about 1/10 to 1/20 of.

  The graph of (b) of FIG. 4 shows an example of the electron density of the plasma generated under the above process conditions. In addition, the electron density of plasma is synonymous with plasma density.

  The “c” in the graph of FIG. 4B, that is, the electron density of the plasma when the recess 70 of FIG. 3C is formed, is the electron density inside the −70 mm line on the horizontal axis. “A” (that is, when the protrusion 71 in FIG. 3A is formed), “b” (that is, when the protrusion 71 in FIG. 3B is formed) and “d” (that is, It is found that the height is significantly higher than when the recess 70 in FIG. 3 (d) is formed. As a result, it was found that the power absorption efficiency inside the recess can be increased by an amount corresponding to +200 W in the example of FIG. 4 by providing the recess having a depth of 5 mm so as to surround each of the openings of the ceiling wall.

  The reason for the high blocking efficiency of the electric field of the surface wave plasma when the depth of the recess is designed to be 5 mm will be described with reference to FIG. The left side of the central axis O of the microwave transmitting member 123 of FIG. 5 shows a model in the case where the recesses 70a and 70b of FIG. 3C are formed, and the right side of the central axis O of the microwave transmitting member 123 of FIG. , 70b are shown.

  The state in which the surface wave S of microwaves propagates is schematically shown in the left central view of FIG. 5 in which the region B on the left side from the central axis O is enlarged. The state in which the surface wave S of microwaves propagates is schematically shown in the right center view of FIG. 5 in which the region C on the right side from the central axis is enlarged.

  In the surface wave of the microwave shown in the enlarged view of the region B, a surface wave Sa which goes straight on the surface of the ceiling without entering the inside of the recesses 70a and 70b, and the surface of the ceiling enter the inside of the recesses 70a and 70b There is a surface wave Sb that travels while traveling.

  The surface wave Sb advancing while entering the inside of the concave portions 70a and 70b propagates inside the concave portions 70a and 70b, is reflected at the bottom and reciprocates, and merges with the surface wave Sa. At the confluence point, the phase of the surface wave Sb deviates from the phase of the surface wave Sa by a distance λg / 2 (= (λg / 4) × 2) when reciprocating inside the concave portions 70a and 70b. As a result, as shown in the lower left surface waves Sa and Sb in FIG. 5, the merged surface waves Sa and Sb cancel each other. Thereby, when the depths of the recesses 70a and 70b are designed to be 5 mm, the blocking efficiency of the electric field of the surface wave plasma becomes high, the power absorption efficiency inside the recesses 70a and 70b can be improved, and the plasma density can be increased. .

  On the other hand, in the surface wave of the microwave shown in the enlarged view of the region C, the phase of the surface wave Sb advancing into the inside of the concave portions 70a and 70b is the phase shift of .lamda. It deviates from the phase of the surface wave Sa. Since the phase shift in the case of FIG. 3C is λg / 2, the phase of the surface wave Sb deviates from the phase of the surface wave Sa by λg. As a result, as shown in the lower right surface waves Sa and Sb in FIG. 5, the merged surface waves Sa and Sb strengthen each other.

  From the above reasons, the blocking efficiency of the electric field of the surface wave plasma of microwaves by the recesses 70a and 70b of FIG. 3D is the blocking of the electric field of the surface wave plasma of microwaves by the recesses 70a and 70b of FIG. It is lower than the efficiency. As a result, as shown in FIG. 4A, the electric field intensity of “d” outside the −70 mm line on the horizontal axis is higher than the electric field intensity of “c”. Thereby, the power absorption efficiency shown to "c" of FIG.4 (b) is notably higher than the power absorption efficiency shown to "d" of FIG.4 (b). As a result, in the recesses 70a and 70b in FIG. 3D, it is difficult to increase the plasma density inside the recesses 70a and 70b as compared to the case where the recesses 70a and 70b in FIG. all right.

  From the above, on the surface of the ceiling wall of the microwave plasma processing apparatus 100 according to the present embodiment, the ring has a diameter within the range of diameter φ + 10 mm to 100 mm on the outer peripheral side with respect to the diameter φ of the opening of the ceiling wall The recess 70 is formed in the shape of a depth of about 5 mm (ie, λg / 4). The number of the recesses 70 may be one or more. However, it is preferable that the number of the recesses 70 is more than one because the electric field blocking efficiency can be further enhanced.

  In the microwave plasma processing apparatus 100 according to the present embodiment, seven microwave transmission units 40, microwave radiation members 50, slots 122 and 132, and seven microwave transmission members 123 and 133 are provided. It may be alone. Also in this case, one recess 70 is provided so as to surround the outer periphery of one microwave transmitting member.

[Variation of process conditions (pressure, gas species) and electric field cutoff efficiency]
Next, with reference to FIG. 6 and FIG. 7, an example of the evaluation result of the electric field interruption | blocking efficiency of the recessed part which concerns on this embodiment is demonstrated, comparing with a comparative example. FIG. 6 shows an example of the electric field intensity of microwave surface wave plasma propagating to the surface of the ceiling wall when the process conditions of pressure and gas species are changed. FIG. 7 shows an example of the electron density of plasma when the process conditions of pressure and gas species are changed.

According to FIG. 6, in the case where the concave portion 70 with a depth of 5 mm is provided on the surface of the ceiling wall, Ref. The electric field strength is lower on the outer side than the -70 mm line in which the recess 70 is formed in any of 6 Pa, 10 Pa, and 20 Pa as compared with the case where the recess shown in FIG. It turned out that there is an electric field interruption efficiency. Further, according to FIG. 7, when the concave portion 70 with a depth of 5 mm is provided on the surface of the ceiling wall, Ref. The plasma density is 1.3 times to 1 in the region inside the −70 mm line where the recess 70 is formed in any of 6 Pa, 10 Pa, and 20 Pa, as compared with the case where the recess shown by is not provided. It turned out that it is increasing about 0.5 times. It is considered that the provision of the recess 70 having a depth of 5 mm improves the absorption of microwave input power into the plasma, and the plasma density increases up to 1.5 times the input power. These results were similar in any of Ar gas plasma or Ar gas and N ₂ gas plasma.

When the pressure in the processing container is in the range of 5 Pa to 50 Pa, the appropriate value of the depth of the recess 70 changes with the frequency of the microwave, and the appropriate value of the position of the recess 70 changes with the pressure and the gas type. Specifically, in the case of the mixed gas of Ar / N ₂ , the appropriate value of the position of the recess 70 becomes more inward as the pressure is increased. Further, in the case of Ar gas, the lower the pressure, the more the position of the concave portion 70 becomes to the outside.

[Modification]
Finally, the recess 70 of the ceiling wall according to the modification will be described with reference to FIGS. FIG. 8 is a diagram (an example of a cross section taken along the line A-A of FIG. 1) illustrating an example of the ceiling wall according to the first modification of the embodiment. FIG. 9 is a diagram (an example of a cross section taken along the line A-A in FIG. 1) illustrating an example of the ceiling wall according to the second modification of the embodiment. FIG. 10 is a cross-sectional view showing an example of the recess of the ceiling wall according to the third modification of the present embodiment.

(Modification 1)
In the recess 70 according to the first modification shown in FIG. 8, two openings 70 d are formed at positions facing the recess 70 in accordance with the positions of the microwave transmitting members 123 adjacent in the circumferential direction. The opening 70 d is at the same height as the surface of the ceiling wall and is a portion without the recess 70. A part of the surface wave of the microwaves is propagated from the opening 70 d to the outer peripheral side of the recess 70. The end of the opening 70d is formed in parallel, but is not limited thereto, and it is preferable to open at an angle range of approximately 30 ° to 60 °.

  Thus, by providing two openings 70 d opened to the side of the microwave transmitting member 123 adjacent to each other in the circumferential direction in each recess 70, surface waves of microwaves propagating through the ceiling wall from the opening 70 d A part of the plasma leaks to the outside of the recess 70. Thereby, the plasma density can be increased in the region inside each concave portion 70 while preventing the plasma density between the adjacent microwave transmitting members 123 from being lowered. As a result, process performance can be improved.

(Modification 2)
One recess 70 according to the second modification shown in FIG. 9 is formed in a ring shape so as to surround the entire opening of the ceiling wall where the plurality of microwave transmitting members 123 and 133 are exposed. Also by this, the power absorption efficiency can be improved inside the recess 70, and the plasma density can be increased. As a result, process performance can be improved.

(Modification 3)
In the recess 70 according to the third modification shown in FIG. 10A, the side wall 70e is formed in a tapered shape so as to be inclined inward toward the bottom. Further, as shown in FIG. 10 (b), the inner wall surface of the recess 70 may be coated with a protective film 70f of yttria (Y ₂ O ₃ ) by thermal spraying. The protective film 70f of yttria is not limited to the case where the side surface of the recess 70 has a tapered shape, and may coat the side surface and the bottom surface of the vertical shaped recess 70. Thereby, the plasma resistance in the recess 70 can be improved, and the generation of particles can be prevented. In any case of FIG. 10A and FIG. 10B, the depth of the recess 70 is preferably about 5 mm. Furthermore, the recess 70 formed in the present embodiment and the first to third modifications may be a perfect circle or an ellipse.

  As described above, in the microwave plasma processing apparatus 100 according to the present embodiment, the ceiling wall is λg outside the predetermined distance from the opening of the ceiling wall (the microwave radiation area, the position of the microwave transmitting members 123 and 133). Recesses 70 having a depth of / 4 or λg / 4 ± λg / 8 are formed. Thus, the recess 70 can increase the blocking efficiency of the electric field of the surface wave plasma of microwaves, improve the power absorption efficiency inside the recess 70, and increase the plasma density. As a result, process performance can be improved.

(Modification 4)
Next, the recessed part 70 of the top wall which concerns on the modification 4 of one Embodiment is demonstrated, referring FIG. In the fourth modification, the electron density of the plasma changes exponentially with respect to the wavelength λ _sp of the surface wave of the microwave outside the opening of the lid 10 closed by the microwave transmitting members 123 and 133. And two or more recesses of different depths are formed.

In FIG. 11A, five recesses 70g, 70h, 70i, 70j, 70k of different depths are formed such that the electron density of plasma changes exponentially with respect to the wavelength λ _sp . In FIG. 11B, two recesses 70m and 70n of different depths are formed such that the electron density of plasma changes exponentially with respect to the wavelength λ _sp . The recesses 70g, 70h, 70i, 70j, 70k and the recesses 70m, 70n are also collectively referred to as the recess 70.

  Recesses 70 g, 70 h, 70 i, 70 j and 70 k shown in FIG. 11A are formed on the back surface of the top wall outside the opening of the lid 10. Recesses 70m and 70n shown in FIG. 11 (b) are formed on the side wall of the top wall outside the opening. FIGS. 11A and 11B may be combined.

The depth of the two or more recesses 70 is preferably as shallow as possible from the opening of the lid 10 and as deep as possible from the opening. However, it may be deeper as it is closer to the opening of the lid 10 and shallower as it is farther from the opening. Further, the number of the recesses 70 is not limited to this, and in the case of a plurality, the number may be three or four or more. Moreover, although it is preferable that the space _| interval of the recessed part 70 is about (lambda) _sp / 4 and is equal intervals, it is not restricted to this. Further, the two or more recesses 70 shown in the fourth modification can be applied in combination with the position and the shape of the second recess 70 shown in the first, the second and the third modifications.

  Thereby, the surface wave (electromagnetic wave) of a microwave can be cut by the recessed part 70, maintaining the electron density of plasma in a high state. The reason is described below.

FIG. 12 is a graph showing the relationship between the wavelength λ _sp of the surface wave of microwaves in the sheath and the electron density of the plasma according to the fourth modification of the embodiment. The horizontal axis x indicates the electron density of plasma, and the vertical axis y indicates 1⁄4 of the wavelength λ _sp of the surface wave of the microwave. In the process gas region indicated by the broken line, the wavelength λ _sp / 4 and the electron density of the plasma become substantially linear in the process gas used for plasma processing. In addition, λ _sp / 4 and the electron density of the plasma are substantially linear also in the above-mentioned region from the process gas region to the argon gas used for plasma processing.

In this graph, since the plasma electron density for the wavelength lambda _{sp / 4} is displayed on a logarithmic function, the plasma electron density for the wavelength lambda _{sp / 4} in the process gas area that changes exponentially I understand. That is, in the process gas region, the wavelength λ _sp changes exponentially depending on the electron density of the plasma. In other words, since the wavelength λ _sp / 4 of the surface wave of the microwave changes depending on the electron density of plasma, the recess 70 should be formed to a depth of wavelength λ _sp / 4 corresponding to the electron density of the target plasma. Is preferred.

  Using the above-described plasma characteristics, as shown in FIGS. 11A and 11B, a plurality of recesses 70 of different depths are provided which are exponentially changed in accordance with the electron density of plasma. As a result, it is possible to form a plurality of recesses 70 that target electron density regions corresponding to process conditions. As a result, it is possible to cut microwave surface waves in the recess 70 while maintaining a high electron density of plasma.

The relationship between the wavelength λ _{sp of the} microwave surface wave and the electron density of the plasma shown in the graph of FIG. 12 is derived as follows. FIG. 13 shows a sheath under the lid 10 provided in the (y, z) direction as a system used for calculation to derive the relationship between the wavelength λ _sp of the microwave surface wave and the electron density of the plasma. The state in which the plasma was formed is shown. Assuming that the relative permittivity of the sheath is ε _r (= 1) and the relative permittivity of the plasma is ε _p , the equation (1) is derived from the Maxwell equation and the equation of motion of electrons.

(Ε _p / ε _r ) × (α / β) tan _h (αs) + 1 = 0 (1)
α indicates the number of microwaves in the x direction in the sheath. β represents the number of microwaves in the x direction in the plasma. s represents the thickness of the sheath.

  α is represented by Formula (2), and β is represented by Formula (3).

α ² = k ^2- (ω / c) ² (2)
β ² = k ² -ε _p (ω / c) ² (3)
Equation (3) can be transformed into the following equation (4).

γ is the collision frequency of electrons and neutral particles, which is determined by the pressure of the system. ω is the angular velocity of the microwave of the input frequency, and c is the velocity of light. ω _p is the electron plasma frequency, which is a function of the electron density of the plasma.

  K of Formula (2) shows the wave number of the surface wave of the microwave in the sheath of z direction. K of Formula (4) shows the wave number of the surface wave of the microwave in the plasma of z direction. The wavenumbers of the two in the z-direction interface between the sheath and the plasma shown in FIG.

  By substituting α and β defined by Equation (2) and Equation (4) into Equation (1), the following Equation (5) is derived.

λ _sp = 2π / Re (k) (5)
Since the relationship between the wave number k of the surface wave of the microwave in the plasma and the electron density ω _p is linked from the equation (4), the wavelength λ _sp of the surface wave of the microwave derived from the equation (5) and the microwave The relational expression with the wave number k of the surface wave indicates the relationship between the wavelength λ _sp of the surface wave and the electron density ω _p .

From the above, the graph of FIG. 12 is derived based on the equation (4) and the equation (5), and the wavelength λ _sp of the surface wave of the microwave depends on the electron density of the plasma and can be changed by the electron density of the plasma all right.

Therefore, electrons meeting the process conditions are obtained so that the effect of blocking the surface waves by the recess 70 can be obtained in response to the surface waves of various wavelengths λ _sp that change according to the electron density of various plasmas in the process condition region. A plurality of recesses 70 of which the depth varies exponentially are formed corresponding to the area of density. This can increase the probability that at least one of the plurality of recesses 70 will be a groove having a depth of approximately λ _sp / 4 corresponding to the region of the electron density that matches the process conditions. In other words, by forming the plurality of recesses 70 whose depth changes exponentially, it is possible to maximize the effect of the recesses 70 to increase the blocking efficiency of the electric field of the microwave surface wave plasma. Thereby, the power absorption efficiency in the inside of the recessed part 70 can be improved, and plasma density can be increased. As a result, process performance can be improved.

  As mentioned above, although the microwave plasma processing apparatus was demonstrated by the said embodiment and its modification, the microwave plasma processing apparatus concerning this invention is not limited to the said embodiment, Various deformation | transformation within the scope of the present invention And improvements are possible. Matters described in the above plurality of embodiments can be combined without contradiction.

  In the present specification, the wafer W has been described, but the object to be processed by plasma processing is not limited to the wafer W, and various substrates used for LCD (Liquid Crystal Display), FPD (Flat Panel Display), etc. It may be.

DESCRIPTION OF SYMBOLS 1 processing container 2 microwave plasma source 3 control part 10 lid 11 mounting base 14 high frequency bias power supply 22 gas supply source 30 microwave output part 40 microwave transmission part 43a peripheral microwave introduction mechanism 43b central microwave introduction mechanism 44 microwave Transmission path 50 microwave radiation member 52 outer conductor 53 inner conductor 54 slag 60 gas supply hole 62 gas introduction portion 70, 70a, 70b recessed portion 70d opening portion 100 microwave plasma processing apparatus 122, 132 slot 123, 133 microwave transparent member U Processing space

Claims (9)

A microwave supply unit for supplying microwaves;
A microwave radiation member provided on the top wall of the processing vessel and radiating the microwave supplied from the microwave supply unit;
And a dielectric microwave transmitting member provided to close the opening of the ceiling wall and transmitting microwaves passed through the slot antenna through the microwave radiating member;
When the wavelength of a surface wave of microwaves transmitted through the microwave transmitting member and propagating from the opening of the top wall to the surface of the top wall is λ _sp , the top wall is λ outside the opening _The microwave plasma processing apparatus in which the recessed part of the depth of the range of _sp / 4 +/- (lambda) _sp / 8 is formed. The recess is formed one or more at a distance of 10 mm to 100 mm outward from the end of the opening of the ceiling wall.
The microwave plasma processing apparatus according to claim 1. A plurality of openings of the ceiling wall are provided in the circumferential direction of the ceiling wall, and a plurality of the microwave transmitting members are provided to close the openings of the plurality of ceiling walls,
The recess is formed in a ring shape so as to surround the entire opening of the plurality of ceiling walls to which the plurality of microwave transmitting members are exposed.
The microwave plasma processing apparatus of Claim 1 or 2. A plurality of openings of the ceiling wall are provided in the circumferential direction of the ceiling wall, and a plurality of the microwave transmitting members are provided to close the openings of the plurality of ceiling walls,
The recess is formed in a ring shape so as to surround each of a plurality of openings of the top wall where the plurality of microwave transmitting members are exposed.
The microwave plasma processing apparatus of Claim 1 or 2. The recess corresponding to each of the plurality of microwave transmitting members has an opening without a recess at a position corresponding to or in the vicinity of the facing position of the adjacent microwave transmitting members.
The microwave plasma processing apparatus according to claim 4. The recess is formed in a tapered shape.
The microwave plasma processing apparatus as described in any one of Claims 1-5. The inner wall surface of the recess is coated with yttria,
The microwave plasma processing apparatus as described in any one of Claims 1-6. Outside the opening, two or more recesses of different depths are formed such that the electron density of the plasma changes exponentially with respect to the wavelength λ _sp of the microwave surface wave.
The microwave plasma processing apparatus as described in any one of Claims 1-7. The recess is formed on at least one of the side surface or the back surface of the ceiling wall outside the opening.
The microwave plasma processing apparatus according to any one of claims 1 to 8.

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