JP2011077292A - Plasma processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve uniform plasma processing in a large range by optimizing a distribution of microwave regardless of change in a plasma processing condition. <P>SOLUTION: A microwave supply means supplies microwave into a vacuum processing chamber to produce plasma. An introduction part of the microwave supply means introducing microwave to the processing chamber includes a circularly polarized wave generator which converts the microwave of linearly polarized wave into the microwave of circularly polarized wave. The circularly polarized wave generator includes a square input-side wave guide tube 301 which operates at a minimum order mode, a regular polygonal or circular output-side wave guide tube 306 which operates at a minimum order mode, and a regular polygonal or circular phase adjusting wave guide tube 303 capable of propagating a plurality of linearly polarized waves of different planes of polarization at the same time. The phase adjusting wave guide tube includes adjusting means 304 and 305 which adjusts the phase or amplitude of one of linearly polarized waves of different polarized wave planes. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a plasma processing technique, and more particularly to a plasma processing technique provided with a circularly polarized wave generator for supplying a microwave whose polarization plane rotates to a processing chamber.

  A substrate used for manufacturing a semiconductor such as a semiconductor memory or a logic LSI tends to be increased in diameter to improve productivity, and a silicon substrate having a diameter of 300 mm is used for manufacturing a state-of-the-art semiconductor memory. It has become mainstream. In addition, there is an opinion that a silicon substrate having a diameter of 450 mm is necessary, and it is considered that the trend of increasing the diameter of the substrate continues.

  In these semiconductor manufacturing processes, a plasma processing apparatus is used, but it is necessary to perform uniform plasma processing on the substrate to be processed at the time of processing, and technical difficulty tends to increase as the diameter of the substrate to be processed increases. It is in.

  In order to perform uniform plasma processing on the substrate to be processed, naturally the distribution of plasma characteristics such as plasma density and temperature near the substrate to be processed is important, and the plasma distribution is optimized from the viewpoint of uniform plasma processing. Technology to do is important.

  By the way, a microwave plasma processing apparatus that generates plasma using microwave power can generate high-density plasma under low pressure, and it can easily distribute the plasma by adjusting the distribution of the static magnetic field applied to the microwave. It has features such as being controllable. For this reason, the microwave plasma processing apparatus has come to be widely used for semiconductor manufacturing and the like.

  In an apparatus that generates plasma using microwaves, by using circularly polarized microwaves, it is possible to efficiently generate electron cyclotron resonance and obtain a high-density plasma. The axial symmetry can be improved and uniform plasma treatment can be obtained (see Patent Document 1).

JP 59-114798 A

  As described above, by generating plasma using a circularly polarized microwave, it is expected that the axial symmetry of plasma is improved and the axial symmetry of plasma processing is improved. However, characteristics such as density change when plasma processing conditions are changed. For this reason, in a plasma generator using a circularly polarized wave generator optimized under a specific processing condition, if the plasma processing condition is changed, sufficient circularly polarized wave cannot be generated, and the axial symmetry of the plasma May not be secured.

  The present invention has been made in view of these problems, and provides a plasma processing apparatus capable of obtaining a uniform plasma processing over a wide range by optimizing the distribution of microwaves regardless of changes in plasma processing conditions. To do.

  In order to solve the above problems, the present invention employs the following means.

  A vacuum processing chamber capable of depressurizing the interior; a gas supply means for supplying a processing gas into the vacuum processing chamber; a microwave supply means for supplying a microwave into the vacuum processing chamber to generate plasma; and the vacuum processing chamber A substrate electrode for mounting and holding a sample as a material to be processed, and a vacuum exhaust unit connected to the vacuum processing chamber and exhausting a gas in the vacuum processing chamber, to the processing chamber of the microwave supply unit The microwave introduction unit of the present invention includes a circularly polarized wave generator that converts linearly polarized microwaves into circularly polarized microwaves, and the circularly polarized wave generator is a rectangular input side that operates in the lowest order mode. A waveguide, a regular polygonal or circular output side waveguide that operates in the lowest mode, and a regular polygonal or circular phase adjusting waveguide that can simultaneously propagate multiple linearly polarized waves with different polarization planes The phase adjusting waveguide is polarized With adjusting means for adjusting one of the phase or amplitude of the different linear polarization of.

  Since the present invention has the above-described configuration, it is possible to obtain a uniform plasma treatment in a wide range by optimizing the microwave distribution regardless of changes in the plasma treatment conditions.

It is a figure explaining a microwave etching apparatus. It is a figure explaining a circularly polarized wave generator. It is the figure which projected the cross section of each waveguide shown in FIG. 2 on the plane perpendicular | vertical to the central axis of each waveguide. It is a figure which shows distribution of the electric field vector in a waveguide cross section. It is a figure which shows distribution of the electric field vector in a waveguide cross section. It is a figure which shows distribution of the electric field vector in a waveguide cross section. It is a figure which shows distribution of the electric field vector in a square waveguide. It is a figure which shows distribution of the electric field vector in a square waveguide. It is a figure explaining the connection state of a square waveguide and a rectangular waveguide. It is a figure which shows the cross section of the square waveguide loaded with the rectangular dielectric plate. It is a figure which shows the cross section of the square waveguide loaded with the rectangular dielectric plate. It is a figure which shows the other example of the cross section of the dielectric material plate for phase adjustment. It is a figure which shows the example which modeled the case where the circularly polarized wave generator of the structure shown in FIG. 2 is used for the part which introduce | transduces the microwave of an etching apparatus. It is a figure which shows the result of having evaluated the roundness of the circular polarization in the circular waveguide part of a plasma processing chamber. It is a figure which shows the result of having evaluated the roundness of the circular polarization in the circular waveguide part of a plasma processing chamber. It is a figure which shows the result of having evaluated the roundness of the circular polarization in the circular waveguide part of a plasma processing chamber. It is a figure which shows the result of having evaluated the roundness of the circular polarization in the circular waveguide part of a plasma processing chamber. It is a figure which shows the maximum value of circular polarization | polarized-light roundness obtained by adjusting the position of two dielectrics of a phase adjustment waveguide. It is a figure which shows the monitoring apparatus of circular polarization roundness. It is a figure which shows the microwave electric field strength distribution of the circular waveguide inner surface at the time of circular waveguide TE11 mode propagation.

  Hereinafter, embodiments will be described with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a microwave etching apparatus according to the present embodiment. As shown in FIG. 1, the microwave oscillated from the microwave source 101 is transmitted to the circular waveguide 105 through the isolator 119, the automatic matching unit 102, the rectangular waveguide 103, and the circular rectangular converter 104. . Here, the automatic matching machine 102 automatically suppresses the reflected wave by adjusting the load impedance.

  As the microwave source, a magnetron having an oscillation frequency of 2.45 GHz was used. In addition, an isolator 119 was used to protect the microwave source. The circular waveguide 105 is connected to the cavity resonator 106. The cavity resonance unit 106 has a function of adjusting the electromagnetic field distribution of the microwave to a distribution suitable for plasma processing.

  A microwave introduction window 107, a shower plate 108, and a plasma processing chamber 110 are provided below the cavity resonance unit 106. Since the shower plate 108 is directly exposed to the plasma generated in the plasma processing chamber 110, it is desirable that the shower plate 108 be made of a material that has high plasma resistance and does not adversely affect the plasma processing. As a material for the microwave introduction window 107 and the shower plate 108, quartz was used as a material that can efficiently transmit microwaves and keep the plasma processing chamber airtight.

  A minute gap (not shown) is provided between the microwave introduction window 107 and the shower plate 108, and a processing gas used for plasma processing is supplied to the gap via the gas supply system 109. The shower plate 108 is provided with a plurality of fine gas supply holes (not shown), and the processing gas is supplied to the plasma processing chamber 110 in a shower shape through the gas supply holes.

  In the plasma processing chamber 110, a substrate electrode 112 for placing a substrate 111 to be processed is installed. A bias power source 114 is connected to the substrate electrode 112 via an automatic aligner 113 to supply bias power to the substrate 111 to be processed. A frequency of 400 kHz was used as the frequency of the bias power source 114.

  A static magnetic field generator 115 is provided around the plasma processing chamber 110 to apply a static magnetic field to the plasma processing chamber 110. When the electron cyclotron resonance phenomenon, in which the microwave power is resonantly absorbed by electrons when the electron cyclotron frequency matches the microwave frequency, plasma is generated even in a high vacuum region where it is usually difficult to generate plasma. It becomes possible, and plasma processing becomes possible.

  Further, by applying a static magnetic field to the plasma processing chamber, plasma loss can be suppressed and plasma ignitability can be improved. Further, by adjusting the distribution of the static magnetic field, the plasma generation region and its diffusion can be controlled to control the plasma distribution. Further, by controlling the plasma distribution, it is possible to control the uniformity of the plasma processing performed on the substrate 111 to be processed. When the frequency of the microwave is 2.45 GHz, the magnitude of the static magnetic field that causes electron cyclotron resonance is 0.0875 Tesla. Thus, in order to utilize the electron cyclotron resonance phenomenon, it is necessary to generate a static magnetic field of 0.0875 Tesla in the plasma processing chamber, and a static magnetic field capable of generating a static magnetic field of this magnitude in any place in the processing chamber. It is desirable to use a magnetic field generator. As a static magnetic field generator, a multistage electromagnet in which a plurality of coils are combined in multiple stages was used. By using a multistage electromagnet, the static magnetic field distribution can be easily adjusted.

  A vacuum exhaust pump 118 is connected to the plasma processing chamber 110 via a valve 116 and a conductance variable valve 117. As the vacuum exhaust pump 118, a turbo molecular pump whose exhaust side was exhausted by a rotary pump was used. The pressure in the plasma processing chamber 110 is monitored by a pressure gauge 120. The conductance variable valve 117 includes a mechanism that maintains a constant pressure by controlling the exhaust speed for exhausting the gas supplied by the processing gas supply system 109 or the gas generated during the etching process.

  Next, the circular polarization of electromagnetic waves (microwaves) supplied to the plasma processing chamber via the circular waveguide 105 will be briefly described.

  The plane of polarization refers to a plane composed of the traveling direction of the electromagnetic wave and the direction of the electric field vector. In the following, the electric field vector is defined on the central axis of the waveguide with respect to the plane of polarization. Further, the circularly polarized wave refers to an electromagnetic wave whose polarization plane rotates with time. On the other hand, an electromagnetic wave whose polarization plane does not rotate is called a linearly polarized wave. In circular polarization, the trajectory formed by the end point of the electric field vector is a circle or an ellipse. The case of an ellipse is sometimes called elliptically polarized wave. It is known that circularly polarized waves can be generated, for example, by superimposing two equal-amplitude linearly polarized waves whose polarization planes are orthogonal to each other with a phase shifted by 90 °. When superimposing two linearly polarized waves to generate circularly polarized waves, it is not always necessary that the planes of polarization be orthogonal, and circularly polarized waves can be generated by adjusting the amplitude and phase even at other angles. be able to. Moreover, not only two linearly polarized waves but also three or more linearly polarized waves can be superimposed to generate circularly polarized waves.

  Here, a circularly polarized wave generator capable of improving the uniformity of plasma processing by optimizing the degree of circular polarization (roundness) corresponding to the state fluctuation of the plasma was devised. In other words, by providing a mechanism that can adjust the phase and amplitude of each mode in a waveguide that allows multiple modes with different polarization planes to propagate simultaneously, a structure that can always obtain circular polarization with high roundness can be obtained. investigated.

  A hollow waveguide having a rectangular or circular cross section is often used for microwave transmission. This is because these waveguides have clear transmission characteristics and low power loss. There are various waveguides in which a plurality of modes having different polarization planes can propagate. However, considering an axially symmetric plasma processing, it is desirable to use a waveguide having a regular polygon such as a square or a circular cross section.

  There are various known mechanisms that can adjust the phase and amplitude of each mode of electromagnetic wave propagating in the waveguide. For example, a method of inserting a conductor rod having a variable insertion length called a stub into a waveguide, a structure in which a waveguide is branched, and a variable length waveguide having one end short-circuited is connected to the branch. There is a method of loading a movable dielectric plate.

  FIG. 2 is a diagram illustrating a circularly polarized wave generator. In FIG. 2, a square waveguide 303 having a square cross section is used as a waveguide capable of propagating electromagnetic waves of a plurality of modes having different polarization planes, and the position is variable as a mechanism for adjusting the phase and amplitude of the electromagnetic waves of each mode. Although the dielectric plates 304 and 305 are used, the circularly polarized wave generator can be configured by combining other waveguides or other mechanisms capable of adjusting the phase and amplitude.

  The frequency of the microwave was 2.45 GHz. The microwave is introduced from the rectangular waveguide section 301 into the waveguide 303 having a square cross section through the matching waveguide 302. In the waveguide 303 having a square cross section, two dielectric plates 304 and 305 whose positions are variable are loaded in a direction perpendicular to each other. Further, a circular waveguide 306 is connected to the square waveguide 303.

  FIG. 3 is a diagram in which a cross section of each waveguide is projected onto a plane perpendicular to the central axis of each waveguide. The long side or the short side of the rectangular waveguide section 301 cross section and the side of the square waveguide 303 cross section intersect at an angle of 45 degrees.

  For structures with a simple geometric shape such as a rectangular waveguide or circular waveguide, the propagation characteristics and electromagnetic field distribution inside the waveguide have been clarified. He is familiar with “Wave Engineering” and Morikita Publishing.

  A rectangular waveguide 301 having a cross section standardized under the name WRJ-2 of 109.2 mm × 54.6 mm was used. In the WRJ-2 standard rectangular waveguide, it is known that a microwave having a frequency of 2.45 GHz can propagate only in the lowest-order rectangular waveguide TE11 mode.

  FIG. 4 is a diagram schematically showing the electric field vector distribution in the cross section of the waveguide when propagating through the rectangular waveguide in the TE10 mode. Within the rectangular waveguide cross section, the TE10 mode electric field vector is distributed perpendicular to the long side of the rectangular cross section. The electric field distribution is uniform in the direction perpendicular to the long side, is high near the center of the long side, and is low at the end.

  FIG. 5 is a diagram showing the electric field vector distribution in the waveguide cross section of the TE11 mode, which is the lowest order mode of the circular waveguide. Since the circular waveguide is structurally symmetric with respect to the central axis, it has a degree of freedom of rotation as shown in FIG. For example, in the circular waveguide TE11 mode shown in FIG. 5, the electric field vector is in the vertical direction on the central axis, but the whole is rotated by 90 ° with respect to the central axis so that the electric field vector is in the horizontal direction on the central axis. The modes shown in (1) can also propagate at the same time. The electric field vectors in both modes are orthogonal to each other at each point on the circular waveguide cross section. Further, when the phase difference between both modes is shifted by 90 °, the electric field vector is temporally rotated due to the superposition of both modes, and circular polarization can be obtained.

  7 and 8 are diagrams showing the electric field distribution of the propagation mode in the square waveguide. Since the cross section is square, the mode shown in FIG. 7 in which the electric field vector is in the vertical direction and the mode shown in FIG. 8 in the horizontal direction can be propagated simultaneously. In the case of a square cross section with a side of 80 mm, a microwave with a frequency of 2.45 GHz can propagate only in the square waveguide TE10 mode and the square waveguide TE01 mode shown in FIGS. reference). Furthermore, a circularly polarized wave can be obtained by setting the phase difference between both modes to 90 ° and superimposing electromagnetic waves of both modes of equal amplitude.

  Next, a method of obtaining electromagnetic waves of equal amplitude TE10 mode and TE01 mode in a square waveguide will be described.

  As shown in FIG. 9, a square waveguide 303 and a rectangular waveguide 301 are connected with their central axes aligned, and are arranged so that the square or quadrilateral sides of each crossing cross at an angle of 45 °. With this arrangement, the direction of the electric field vector of the TE10 mode of the rectangular waveguide and the TE10 mode of the square waveguide and the TE01 mode of the square waveguide are superimposed on the central axis of both waveguides. The directions of the electric field vectors can be matched, and the square waveguide can excite the TE10 mode and the TE01 mode of equal amplitude in the square waveguide.

  As shown in FIG. 9, when the rectangular waveguide 301 and the square waveguide 303 are simply connected, a reflected wave is generated at the connection surface, and the microwave power cannot be used efficiently. Therefore, it is desirable to connect a matching waveguide for reducing reflected waves between the two waveguides. In the matching waveguide, the width of the rectangular waveguide 301 is slightly narrowed as shown in FIG. 2, and this portion is used as a matching waveguide, and the width and length thereof are adjusted to reduce the reflected wave. When the cross-sectional size of the rectangular waveguide is 109.2 mm × 54.6 mm and the cross-sectional size of the square waveguide is 80 mm × 80 mm, the matching waveguide has a reflected wave when the cross-section is 80 mm × 54.6 mm and the length is 35 mm. Became the minimum.

  Next, a method for adjusting the phase difference between the TE10 mode and TE01 mode electromagnetic waves propagating in the square waveguide in the square waveguide will be described with reference to FIGS.

  FIG. 10 is a diagram showing a cross section of a square waveguide loaded with, for example, a rectangular dielectric plate 1201. An operation rod 1202 is connected to the dielectric plate 1201, and the position of the dielectric plate 1201 can be adjusted by operating the operation rod 1202 from the outside of the phase adjustment waveguide. The operation rod 1202 was made of the same dielectric as the dielectric plate 1201. Further, the TE10 mode electric field vector propagating through the square waveguide is indicated by a chain line arrow.

  As shown in FIG. 10, the TE10 mode electric field propagating in the square waveguide is uniform in the direction of the electric field vector, and is high near the center of the waveguide and small near the inner wall of the waveguide. When the dielectric plate 1201 is disposed near the center of the square waveguide, the dielectric plate is disposed at a position where the microwave electric field intensity is high, and the influence on the microwave propagating in the waveguide is large. On the other hand, when the dielectric plate 1201 is disposed at a position where the microwave electric field near the waveguide wall is small, the influence of the dielectric is reduced.

  The operation rod 1202 is structured to be exposed to the outside of the square waveguide through a hole provided in the tube wall of the square waveguide. The diameter of the hole was 7 mm. The material of the operation rod 1202 was alumina ceramics. It is known that the relative dielectric constant of alumina ceramics is about 9.7. In a circular waveguide with a diameter of 7 mm loaded with alumina ceramics having a relative dielectric constant of 9.7, the cutoff frequency of the circular waveguide TE11 mode, which is the lowest order mode, is 8.1 GHz. ”Can be calculated theoretically. That is, it can be seen that the microwave of frequency 2.45 GHz is lower than the cut-off frequency and cannot propagate through the circular waveguide (hole). Since the diameter of the operation rod 1201 is smaller than the diameter of the hole 7 mm, the cutoff frequency of the hole is expected to be further increased. Here, although the tube wall thickness of the square waveguide was 20 mm, 2.45 GHz microwaves did not leak from the hole.

  In general, it is known that the wavelength of an electromagnetic wave is shortened to 1 / √ε in a dielectric having a relative dielectric constant ε. In this embodiment, alumina ceramics is used as the material of the dielectric plate 1201. As described above, when the dielectric plate 1201 is disposed at the center of the waveguide, the influence of the dielectric plate is increased, and the wavelength shortening effect of the TE10 mode electromagnetic wave propagating through the square waveguide is increased. On the other hand, when the dielectric plate 1201 is disposed near the wall of the waveguide, the influence of the dielectric plate is reduced and the wavelength shortening effect is small. Therefore, the wavelength shortening effect can be continuously adjusted by continuously moving the position of the dielectric plate 1201. Further, the phase of the TE10 mode electromagnetic wave at the output end of the phase adjusting waveguide is changed by the wavelength shortening effect. That is, by adjusting the position of the dielectric plate 1201, the phase at the output end of the square waveguide can be continuously controlled.

  FIG. 11 is a diagram illustrating a case where a TE01 mode electromagnetic wave propagating through a square waveguide is incident on the phase adjusting waveguide. The direction of the microwave electric field differs by 90 ° between the square waveguide TE01 mode and the square waveguide TE10 mode. That is, as shown in FIG. 11, since the electric field vector of the square waveguide TE01 mode is uniform in the direction in which the dielectric plate can move, the electric field in the dielectric plate can be adjusted even if the position of the dielectric plate is adjusted. The strength hardly changes. For this reason, even if the position of the dielectric plate is adjusted, the wavelength shortening effect on the square waveguide TE01 mode hardly changes. That is, the phase of the square waveguide TE01 mode at the output end of the phase adjusting waveguide hardly changes.

  FIG. 12 is a diagram showing another example of the cross section of the phase adjusting dielectric plate. In FIG. 12, the right side is the microwave incident side and the left side is the output side. The dielectric plate 1401 has a parallelogram shape. By making the shape of the dielectric plate 1401 a parallelogram, it is possible to suppress a sudden change in the degree of influence of the dielectric plate 1401 on the microwave incident side and the output side. Thereby, the reflection of the microwaves caused by the dielectric plate can be reduced. By arranging the operation bars 1402 and 1403 in a region where the TE01 mode electric field of the square waveguide near the waveguide wall is small, the influence of the operation bar insertion is reduced. Further, the distance D in the microwave traveling direction between the operation rod 1402 and the operation rod 1403 is set to ¼ of the wavelength of the square waveguide TE01 mode or the square waveguide TE10 mode. With this setting, the path length difference between the reflected wave generated by the operating rod 1402 and the reflected wave generated by the operating rod 1403 is ½ wavelength. it can.

  The reflected wave generated by the dielectric plate 1401 is smaller when the plate is thinner, but the adjustment width of the phase difference is smaller. In addition, the longer the length in the microwave traveling direction, the larger the adjustment range of the phase difference. In this embodiment, the height of the dielectric plate is 79 mm, the length in the microwave traveling direction is 80 mm, and the thickness is 5 mm. When the influence of the reflection of the microwave can be ignored, the shape of the dielectric plate 1401 may be, for example, a rectangle that is advantageous for manufacturing. The number of operating bars may be one, but it is desirable to use two or more operating bars in order to stabilize the position of the dielectric plate 1401. Although the parallelogram has been described as the shape of the dielectric plate, the shape is not limited to this shape, and other shapes such as a rhombus, an ellipse, and a polygon may be used.

  As described above, by adjusting the position of the dielectric plate, the phase of the TE10 mode propagating through the square waveguide changes greatly, but the phase of the TE01 mode propagating through the square waveguide changes little. The phase difference between the two can be adjusted.

  In the above, the phase adjustment waveguide for adjusting the phase of the TE10 mode electromagnetic wave propagating in the square waveguide has been described. However, the phase adjustment waveguide for the square waveguide TE01 mode is configured with the same structure. Can do. The phase adjustment waveguide for the square waveguide TE01 mode has a structure in which the phase adjustment waveguide for the TE10 mode is rotated by 90 ° with respect to the central axis. By using these two square waveguides, the phases of the TE10 mode and TE01 mode electromagnetic waves propagating in the square waveguide can be changed almost independently.

  Furthermore, a circular waveguide was connected to the output side of the square waveguide. This is because the circular waveguide has a symmetrical structure with respect to the central axis, and therefore has good matching with circularly polarized waves. The diameter of the circular waveguide is such that only the TE11 mode, which is the lowest order mode, can propagate. The reflected wave at the connection surface of the square waveguide and the circular waveguide is small, and a matching waveguide or the like is unnecessary. If the reflected wave at the connection surface cannot be ignored, a matching circular waveguide is placed between both waveguides, and the reflected wave is reduced by adjusting the diameter and length of the matching circular waveguide. can do.

  Circularly polarized waves can be rotated clockwise or counterclockwise. It is known that the circularly polarized wave in a plasma to which a static magnetic field is applied has different radio wave absorption characteristics between a clockwise circularly polarized wave and a counterclockwise circularly polarized wave with respect to the direction of the static magnetic field. In the circularly polarized wave generator shown in FIG. 2, the rotation direction of the circularly polarized wave can be controlled to the left or right depending on the positions of the two dielectric plates. However, from the viewpoint of optimizing the plasma processing characteristics, it is clockwise or counterclockwise. Around circular polarization can be selected.

  The trajectory of the electric field vector end point of the circularly polarized wave is usually an ellipse as described above, and the ratio of the length of the short axis to the length of the long axis of the ellipse is called the circularity of the circularly polarized wave. The degree of polarization was quantified. A roundness of 1 indicates complete circular polarization, and zero indicates linear polarization.

  FIG. 13 is an example in which the case where the circularly polarized wave generator having the structure shown in FIG. 2 is used for the part where the microwave of the etching apparatus shown in FIG. 1 is introduced is modeled. The roundness of was evaluated. The circularly polarized wave generator shown in FIG. 2 was used in combination with a circular rectangular converter 104 in FIG. 1 in combination with an E corner that changes the traveling direction of the microwave by 90 degrees.

  It is assumed that the E corner has a sufficiently small reflection. The circularly polarized wave generator has a rectangular waveguide on the input side and a circular waveguide on the output side, and has a function to circularly polarize the microwave input with linearly polarized waves. The plasma processing chamber uses a circular waveguide as an input port and consumes microwave power mainly by internal plasma. For the circularly polarized wave generator, microwave electromagnetic field analysis was performed by the finite element method, and the scattering matrix was calculated and numerically modeled. Two methods were used for calculating the scattering matrix of the circularly polarized wave generator. One method is to directly calculate the scattering matrix by modeling the entire circularly polarized wave generator using the finite element method, and the other method is to divide the circularly polarized wave generator into several parts and model each using the finite element method. This is a method of calculating the scattering matrix and numerically synthesizing the scattering matrix of each part to calculate the entire scattering matrix.

  A finite element model in which the position of the dielectric plate was changed for the waveguide for phase adjustment was created, the scattering matrix was calculated for each, and the scattering matrix of the entire circularly polarized wave generator was obtained numerically. The plasma processing chamber was modeled as having a certain reflection coefficient. The reflection coefficient of the plasma processing chamber is treated as a parameter because it varies greatly depending on the plasma processing conditions. The scattering matrix was calculated for each part of the model shown in FIG. 2 by the above-described method, and the roundness of the incident reflected wave and the circularly polarized wave of each part was calculated.

  As described above, the circularly polarized wave in the circular waveguide can be handled as a superposition of two linearly polarized waves whose polarization planes are orthogonal. That is, two linearly polarized waves whose polarization planes are orthogonal to the output port of the circularly polarized wave generator and the input port of the plasma processing chamber are considered, and these incident and reflected waves are analyzed using a scattering matrix. The roundness of the circularly polarized wave was calculated from the amplitude and phase of the two orthogonally polarized waves orthogonal to each other.

  FIGS. 14A, 14B, 14C, and 14D show the results of evaluating the roundness of circularly polarized waves in a circular waveguide portion that is a microwave input port of the plasma processing chamber. 14A shows the case where the reflection coefficient of the plasma processing chamber is 0, FIG. 14B shows the case where the reflection coefficient of the plasma processing chamber is 0.2, and FIG. 14C shows the reflection coefficient of the plasma processing chamber. 14 shows a case where the reflection coefficient of the plasma processing chamber is 0.6. In the figure, L1 and L2 respectively indicate the dielectric plate position of the TE10 mode phase adjustment waveguide and the TE01 mode phase adjustment waveguide. The position where the dielectric plate was in close contact with the waveguide wall was zero, and the distance between the waveguide wall and the dielectric plate surface was taken as the distance. When the reflection coefficient of the plasma processing chamber is zero and there is no reflection (FIG. 14A), a high roundness can be obtained in a relatively wide region. However, when the absolute value of the reflection coefficient increases and the reflected waves increase, It can be seen that the region where the circularity of high circular polarization can be obtained becomes narrow.

  FIG. 15 shows the maximum circular polarization roundness in the circular waveguide portion of the plasma processing chamber obtained by adjusting the positions of the two dielectrics (304, 305) of the phase adjusting waveguide shown in FIG. Indicates the value. Each of the dielectric positions was adjusted in a range of 0 to 40 mm at a pitch of 2 mm. As shown in FIG. 14, when the absolute value of the reflection coefficient of the plasma processing chamber increases, the region where the circular polarization roundness is high is narrowed. It can be seen that the maximum value of can be adjusted to a high roundness. The phase of the reflection coefficient can be adjusted by adjusting the length of the circular waveguide portion between the circularly polarized wave generator and the plasma processing chamber, and can be adjusted to a high roundness.

  FIG. 16 is a diagram showing a monitor device for circular polarization roundness. In order to adjust the circular polarization roundness by adjusting the dielectric position of the phase adjusting waveguide, it is desirable that the circular polarization roundness can be monitored in real time. In this monitor device, seven electric field detectors 1801 are connected at a pitch of 30 ° around a circular waveguide in which only the circular waveguide TE11 mode can propagate. The electric field detector 1801 can detect the magnitude of the electric field in the vicinity of the inner surface of the circular waveguide with each probe. The disturbance of the electromagnetic field in the circular waveguide due to the installation of the probe is minimized. The circularly polarized wave roundness monitor device is disposed between the circularly polarized wave generator and the plasma processing chamber, and can monitor the circularly polarized wave roundness. A method for monitoring circular polarization roundness will be described below.

As described above, the circularly polarized wave can be expressed by superimposing two linearly polarized waves having the same amplitude and having the same plane of polarization and different temporal phases by 90 °. Consider a circular waveguide with dimensions that can only take the TE11 mode, which is the lowest order mode of the circular waveguide. According to the “microwave engineering”, the electric field on the wall of the circular waveguide TE11 can be distributed according to the equation (1) because the waveguide inner wall has only a component perpendicular to the inner surface due to boundary conditions. Are known

A is a constant, φ is an angle. Further, the electric field on the waveguide inner wall in the TE11 mode of a circular waveguide whose plane of polarization is orthogonal and the temporal phase is different by 90 ° can be expressed by equation (2).

j is an imaginary unit, B is a constant.

Since only the distribution of the electric field on the inner surface of the circular waveguide is considered, the constant A is set to 1.

In this case, the constant B corresponds to the circular polarization roundness, and when it is zero, it becomes a linear polarization, and when B is ± 1, it becomes a complete circular polarization. Since the electric field detected by the electric field detector in the circularly polarized circularity monitor device has the amplitude of equation (4), the absolute value is as follows.

  The circularly polarized wave roundness B can be obtained by applying the measured value by each electric field detector to the equation (5).

  FIG. 17 shows the microwave electric field intensity distribution on the inner surface of the circular waveguide in the circular waveguide TE11 mode. The horizontal axis represents an angle indicating the position of the inner surface of the circular waveguide, and circularly polarized circularity is taken as a parameter. The vertical axis indicates the microwave electric field intensity in terms of amplitude, and is normalized so that the maximum value is 1. Since the circular waveguide capable of propagating only the TE11 mode, which is the lowest order mode of the circular waveguide, is used, it is not necessary to consider the electric field distribution of other modes. In the case of perfect circular polarization with a circular polarization roundness of 1, the microwave electric field strength is constant everywhere on the inner surface. On the other hand, in the case of a linearly polarized wave with a circular polarization roundness of zero, the distribution follows the circular waveguide TE11 mode. Except for the ideal case of circular polarization roundness 1, the same pattern is shown with a period of 180 °. The electric field detector 1901 may be arranged over the entire circumference of 360 °. However, by installing the electric field detector 1901 within a range of 180 °, it is possible to observe a change in one cycle. In addition, since the maximum value and the minimum value of the electric field come at positions 90 ° apart, it is possible to observe the maximum value or the minimum value by observing in the range of 90 °. For this reason, it is theoretically possible to calculate the circular polarization roundness even if the observation position is narrowed to a range of 90 °. Note that the electric field detectors 1901 are desirably arranged at a fine pitch.

  By using a monitoring device that detects the circular polarization roundness, that is, so that the difference between the maximum value and the minimum value of the electric field value detected by each electric field detector constituting the monitoring device is minimized. By adjusting the length of insertion of the dielectric plate of the wave generator, the circular polarization roundness can be controlled to the maximum. Adjustment of the insertion length of the dielectric plate of the circularly polarized wave generator is achieved by combining a control device that automatically controls based on the monitor value of the circularly polarized wave monitoring device and a dielectric plate drive device. It is possible to optimally control the roundness.

  The present invention is not limited to the plasma etching apparatus shown in FIG. 1, but can be applied to plasma etching apparatuses using other plasma generation methods. In addition, the dimensions of each part illustrated are examples when the microwave frequency is 2.45 GHz.

  As described above, according to the present embodiment, the degree of circular polarization of the microwave is monitored in real time using the monitor device including a plurality of electric field detectors, and the circular polarization according to the monitoring result. By adjusting the insertion length of the dielectric plate constituting the generator and adjusting the characteristics of the circularly polarized wave generator, the degree of circularly polarized wave can be adjusted optimally, and the axial symmetry of plasma processing is always maintained. Can be secured.

DESCRIPTION OF SYMBOLS 101 Microwave source 102 Automatic matching machine 103 Rectangular waveguide 104 Circular rectangular converter 105 Circular waveguide 106 Cavity resonance part 107 Microwave introduction window 108 Shower plate 109 Processing gas supply system 110 Plasma processing chamber 111 Substrate 112 Substrate Electrode 113 Automatic matching machine 114 Bias power supply 115 Static magnetic field generator 116 Valve 117 Variable conductance valve 118 Vacuum pump 119 Isolator 120 Pressure gauge 202 Dielectric plate 201 Incident side circular waveguide 401 Rectangular waveguide section 402 Matching waveguide Tube 403 Square waveguide 404, 405 Dielectric plate 406 Circular waveguide 1201 Dielectric plate 1202 Operation rod 1401 Dielectric plate 1402, 1403 Operation rod 1801 Electric field detector

Claims (4)

A vacuum processing chamber capable of reducing the pressure inside,
Gas supply means for supplying a processing gas into the vacuum processing chamber;
Microwave supply means for generating a plasma by supplying a microwave into the vacuum processing chamber;
A substrate electrode for mounting and holding a sample as a material to be processed in the vacuum processing chamber;
A vacuum exhaust means connected to the vacuum processing chamber and exhausting the gas in the vacuum processing chamber;
The microwave introduction unit to the processing chamber of the microwave supply unit includes a circularly polarized wave generator that converts a linearly polarized microwave into a circularly polarized microwave,
The circularly polarized wave generator includes a rectangular input side waveguide operating in the lowest order mode, a regular polygonal or circular output side waveguide operating in the lowest order mode, and a plurality of different polarization planes. It has a regular polygon or circular phase adjustment waveguide that can propagate linearly polarized waves simultaneously,
The plasma processing apparatus, wherein the phase adjusting waveguide includes adjusting means for adjusting one phase or amplitude of linearly polarized waves having different polarization planes. The plasma processing apparatus according to claim 1,
The plasma processing apparatus according to claim 1, wherein the adjusting means is a means for changing a position of a dielectric plate, which is inserted along the traveling direction of the microwave in the phase adjusting waveguide, perpendicular to the traveling direction.   The adjusting means adjusts the position of the dielectric plate so that a difference between detection outputs of a plurality of monitors for detecting an electric field provided in a circumferential direction of the vacuum processing chamber is minimized. apparatus. A vacuum processing chamber capable of reducing the pressure inside,
Gas supply means for supplying a processing gas into the vacuum processing chamber;
Microwave supply means for generating a plasma by supplying a microwave into the vacuum processing chamber;
A substrate electrode for mounting and holding a sample as a material to be processed in the vacuum processing chamber;
A vacuum exhaust means connected to the vacuum processing chamber and exhausting the gas in the vacuum processing chamber;
In the plasma processing method of converting linearly polarized microwaves into circularly polarized microwaves and supplying them to a vacuum processing chamber, and performing plasma processing on the sample,
A circularly polarized wave generator that converts linearly polarized microwaves into circularly polarized microwaves is a square input-side force waveguide that operates in the lowest order mode and a regular polygon that operates in the lowest order mode. Or a circular output side waveguide, a regular polygonal or circular phase adjusting waveguide capable of simultaneously propagating a plurality of linearly polarized waves with different polarization planes, and one phase of a linearly polarized wave with different polarization planes or An adjusting means for adjusting the amplitude is provided, and the adjusting means is provided in the phase adjusting waveguide so that a difference between detection outputs of a plurality of monitors for detecting an electric field provided in a circumferential direction of the vacuum processing chamber is minimized. And adjusting the position of the dielectric plate.