JP2012178380A - Plasma processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plasma processing device which is improved in characteristics of processing, and the uniformity of a geometry resulting from the processing in a radial direction of a sample.SOLUTION: The plasma processing device comprises: a vacuum container; a processing chamber which is placed in the vacuum container, and in which plasma is formed; a sample holder placed in the processing chamber; a round plate member which is made of a dielectric and disposed over the processing chamber, and through which an electric field for forming the plasma extends; a cylindrical cavity part which is placed over the plate member, and into which the electric field is led; a cylindrical pipe line which is coupled with an upper central portion of the cavity and extends vertically, and in which the electric field is transmitted; and a generator which is placed at an end of the pipe line, and operable to generate the electric field. The cavity part includes: a first cylindrical cavity part having a bottom face formed by the plate member, and a cylindrical cavity with a large diameter; a second cylindrical cavity part located above and connected with the first cylindrical cavity part, and having a cylindrical cavity with a small diameter; and a stepped portion located and connecting between the first and second cylindrical cavity parts.

Description

  The present invention relates to a plasma processing apparatus using a magnetic field microwave and a plasma processing method, and more particularly to a plasma processing apparatus suitable for etching a deposited film on a wafer surface in a semiconductor device manufacturing process.

  According to the International Technology Roadmap for Semiconductor (ITRS), the mass production of MPU physical gate length of 22 nm node started in 2012, and the allowable gate length difference (CDU) in the wafer plane <1.0 nm Securement is necessary. Furthermore, a line for processing 450 mm wafers is expected to start in 2015. Along with this, a next-generation plasma processing apparatus is required to cope with miniaturization of semiconductor devices and an increase in wafer diameter, and in particular, plasma having high uniformity over a wide range with the above-mentioned 450 mm wafer diameter (18 inches). Source development is an urgent need.

  In the semiconductor device manufacturing process, plasma processing such as plasma etching, plasma CVD, and plasma etching is widely used. Plasma is generated by exciting high-frequency power or microwave power into the vacuum processing chamber and exciting the gas particles supplied to the inside. In the plasma processing, a substrate-like sample such as a semiconductor wafer disposed in a vacuum processing chamber is processed using this plasma.

  In other words, charged particles such as ions in the plasma are attracted to the surface of the wafer to promote a chemical reaction between radicals (active particles) formed by the plasma and a film-like material placed on the wafer surface. Then, the process of the film is advanced to obtain a desired shape. Such plasma processing is required to have shape controllability in a pressure region corresponding to miniaturization of semiconductor devices and uniformity of in-plane processing. In particular, a magnetic field microwave plasma etching system that generates plasma by generating ECR (Electron Cyclotron Resonance) using microwave 2.45 GHz and solenoid coil magnetic field (875 Gauss) generates high-density plasma at low pressure. Since it can be used, it has been used in the semiconductor manufacturing process.

  As an example of such a conventional technique, one disclosed in Japanese Patent Laid-Open No. 7-235394 (Patent Document 1) is known. In this prior art, a 2.45 GHz microwave was introduced into a cylindrical cavity by propagating through a rectangular waveguide and a circular waveguide. At this time, the microwave propagated in the TE01 mode in the rectangular waveguide and in the TE11 mode in the cylindrical waveguide. Microwaves that enter the cylindrical cavity in this mode are introduced into the vacuum processing chamber through the microwave transmission window and the shower plate. A magnetic field is formed in the axial direction of the processing chamber by a solenoid coil surrounding the vacuum processing chamber, and an 875 Gauss isomagnetic surface is formed in the radial direction. ECR is caused by an electric field of 2.45 GHz and a magnetic field of 875 Gauss, and plasma is generated in the vacuum processing chamber. Specifically, electrons receive a Lorentz force from a magnetic field, and microwaves have a cyclotron frequency. Therefore, the electrons feel an electric field having the same phase and are accelerated in a DC manner according to the electric power. For this reason, high-speed electrons promote ionization and form high-density plasma even at low pressure.

  In the cylindrical cavity of the microwave plasma etching apparatus, the TE11 mode microwave that has passed through the cylindrical waveguide is a standing wave having reflection ends at a plurality of locations in the processing chamber in the cylindrical cavity. The reflection end is an end point such as a quartz microwave transmission window, a quartz shower plate, plasma, plasma, and a portion of the processing chamber electrode (sample stage), lower end of the processing chamber, and the like. In addition, since quartz is a dielectric, it is also known that reflection is repeated between the inside of the microwave transmission window, the shower plate, the lower surface of the microwave transmission window, and the upper surface of the shower plate.

When the plasma density exceeds a certain level (in the case of a magnetic field, the electron density> 1 × 10 11 / cm ³ ), the microwave O-wave component is cut off, and the microwave is totally reflected by the plasma. From these reflection ends and the incident end of the circular waveguide, traveling waves and reflected waves interfere in a complicated manner, and standing waves having various modes, that is, wavelengths, are generated in the cylindrical cavity. A single mode of the incident wave TE11 or a standing wave of a plurality of modes in the cylindrical cavity passes through the microwave transmission window, enters the vacuum chamber, functions as a plasma ignition source, and determines the uniformity of the plasma. For this reason, conventionally, the cylindrical cavity height has been appropriately selected to generate uniform and stable high-density plasma.

JP 7-235394 A

  In the above prior art, since the TE11 mode is transmitted through the circular waveguide, the TE mode (TE11, TE21, TE01, etc.) is likely to occur even in the cylindrical cavity, and the TE mode is basically defined in the cylindrical cavity. A standing wave is generated, and a substantially uniform microwave is propagated over a wide range of the vacuum processing chamber to achieve a uniform plasma density. However, in such a technique, the plasma state that is the reflection end of the standing wave changes depending on the plasma generation parameters such as the gas type, the pressure in the vacuum processing chamber, and the magnetic field profile, so the electric field distribution in the cylindrical cavity is The knowledge that the mode other than the TE mode is generated has been obtained by the inventors' investigation.

  As an example of the TE mode in the cylindrical cavity, it is assumed that the process rate in the TE mode is uniform in the direction of the surface of the wafer (so-called in-plane direction). The profile was weak and weakly convex in the radial direction. This is also transferred to the plasma, and in the case of ICF distribution, it appears as a distribution with a large ICF current at the center and a small outer periphery, and in the case of rate distribution, it appears prominently as a distribution with a high center rate and a low outer periphery. Even if the profile is center-convex with such a plasma, by controlling the temperature difference between the center and the outer periphery of the sample table, the amount of incident ions can be changed to make the sample finish in-plane uniform. It was.

  Apart from this control on the sample stage, in the conventional cylindrical cavity structure, especially under the fluoride-based process conditions, the junction directly between the circular waveguide and the top of the cylindrical cavity is discontinuous. Thus, it has been experimentally found that two small circular plasmas (hereinafter referred to as abnormal discharges) are generated separately from the plasma generated in the processing chamber by generating an extremely strong electric field at the discontinuous portion. This abnormal discharge occurs directly under the quartz shower plate or between the quartz microwave transmission window and the shower plate. For this reason, an etching rate distribution on the wafer appears in a transferred form, and an M-type or W-type profile may be taken in the radial direction. For this reason, the rate distribution on the wafer may clearly lack uniformity in the circumferential direction and the radial direction depending on the process conditions.

  Therefore, the profile of plasma generated in the processing chamber is uniform in the circumferential direction such as convex or concave, and the radial direction can be adjusted by the temperature difference of the wafer sample stage when the gradient difference between the center and the outer circumference is small. However, since most of the difference is due to plasma, it is considered that this variation difference is further increased at a large diameter of φ450 mm.

  An object of the present invention is to provide a plasma processing apparatus in which the processing characteristics and the uniformity of the processing shape are improved in the radial direction of a sample.

  The object is to provide a vacuum vessel, a processing chamber arranged inside the vacuum vessel and forming plasma therein, a sample stage arranged in the processing chamber and on which a sample is placed, and an upper side of the processing chamber A circular plate member made of a dielectric material through which an electric field supplied to form the plasma is transmitted, and a hollow portion having a cylindrical shape which is arranged above the plate member and into which the electric field is introduced A cylindrical pipe that is connected to the center of the upper part of the cavity and extends vertically, and the electric field propagates through the inside, and a generator that is arranged at an end of the pipe and generates the electric field, A first cylindrical cavity having a cylindrical cavity having a large diameter with the plate member as a bottom surface, and a cylindrical cylinder having a small diameter disposed above and connected to the first cylindrical cavity. A second cylindrical cavity having a cavity, and the first and second It is achieved by a plasma processing apparatus provided with a step portion connecting these with the cylindrical cavity.

  Furthermore, this is achieved by providing another stepped portion for connecting the second cylindrical cavity portion and the pipe line, and a ceiling surface of the cavity portion parallel to the plate member.

  Furthermore, the ceiling surface of the second cylindrical cavity is arranged in parallel with the plate member, and the height H2 of the ceiling surface from the upper surface of the plate member is λ <H2 <5λ with respect to the wavelength λ of the electric field. This is achieved by being in the range of / 4.

  Furthermore, the ceiling surface of the first cylindrical cavity is arranged in parallel with the plate member, and the height H1 of the ceiling surface from the upper surface of the plate member is λ / 4 <H1 with respect to the wavelength λ of the electric field. This is achieved by making it within the range.

  Furthermore, this is achieved by setting the cylindrical radius R2 of the second cylindrical cavity to a range of λ / 4 <R2 with respect to the wavelength λ of the electric field.

  Furthermore, the second cylindrical cavity is arranged in alignment with the central axis of the sample stage having a cylindrical shape at the center, and the stepped portion has a cylindrical shape in a direction from the central axis toward the outer peripheral side. This is achieved by being arranged on the center side from the outer periphery of the sample stage.

  Furthermore, the electric field is a microwave electric field of 2.45 GHz, and has magnetic field generating means for supplying an 875 Gauss magnetic field in the processing chamber, and the plasma is formed by ECR in the processing chamber. Achieved.

  Furthermore, this is achieved by supplying the TE11 mode microwave from the pipe to the cavity.

It is a longitudinal cross-sectional view which shows the outline of a structure of the plasma processing apparatus which concerns on the Example of this invention. It is the longitudinal cross-sectional view which expanded and showed the electric field introduction | transduction part arrange | positioned at the upper part of the plasma processing apparatus based on the Example shown in FIG. It is a schematic diagram which shows distribution of the electric field and magnetic field in the cross section cut in the horizontal direction in the cylindrical cavity part in a prior art. It is a schematic diagram which shows distribution of the electric field and magnetic field in the cross section cut in the horizontal direction in the cylindrical cavity part in a present Example shown in FIG. It is a longitudinal cross-sectional view which shows typically the electric field in the cylindrical cavity part of the Example shown in FIG. It is a graph which shows the distribution (ICF distribution) of the in-plane direction of the sample of the ionic current which flows into the electrode in a sample stand from the plasma in the process chamber of a prior art and a present Example shown in FIG.

  In the embodiment of the plasma processing apparatus according to the present invention described below, a plurality of cylindrical portions having first and second cylindrical cavities having different diameters are connected to each other in the vertical direction concentrically. The objective which solves said subject is achieved by providing the cylindrical hollow of a step. In the plasma processing apparatus according to the embodiment of the present invention, which will be described in detail below, the waveguide and the cavity resonance part, which are configured to propagate the electric field disposed above, have a plurality of steps on the upper surface. It has a cylindrical hollow inside, and the electric field of the microwave introduced into this inside propagates to the lower processing chamber and suppresses the non-uniformity of the distribution of the introduced electric field, thereby improving the uniformity. Thus, the desired resonance and propagation distribution is achieved.

  In the present embodiment, the microwave propagated through the circular waveguide in the TE11 mode is converted into the TM12 mode in the cylindrical cavity. Thereby, plasma stronger than before is formed at a position between the center of the vacuum processing chamber and the wall surface. Thus, nonuniformity of plasma density and intensity distribution is reduced, and processing with improved uniformity can be performed.

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

〔Example〕
FIG. 1 is a longitudinal sectional view schematically showing the configuration of a plasma processing apparatus according to an embodiment of the present invention. In this figure, the plasma processing apparatus 100 according to the present embodiment generates and propagates a vacuum vessel having a processing chamber 114 having a cylindrical shape therein, and an electric field that is disposed above the chamber and introduced into the processing chamber 114. And an exhaust section that is disposed below the vacuum chamber and exhausts gas, products, and plasma particles from the vacuum chamber to the outside of the vacuum chamber.

  The electric field introduction section is roughly divided into a waveguide in which a magnetron 101 which is a means for forming a microwave electric field having a frequency of 2.45 GHz and a pipe having a rectangular shape and a circular shape are connected to each other at the end. And a resonance part having a cylindrical interior space connected to the lower end portion of the waveguide and covering the processing chamber 114 above the processing chamber 114, and these are connected and arranged in the order of description. ing. A microwave having a frequency of 2.45 GHz formed by being excited by the magnetron 101 disposed at the end portion (left end portion in the drawing) of the waveguide portion constitutes the waveguide portion, and the magnetron 101 is provided at one end portion thereof. It propagates inside the rectangular waveguide 102 installed on the side surface.

  The waveguide section is arranged at the upper part and extends in the horizontal direction in the figure, and is connected to the electric field forming means at one end thereof, and a rectangular waveguide 102 having a rectangular cross section. The rectangular waveguide 102 has a circular waveguide 104 which is connected to the lower end of the rectangular waveguide 102 and extends in the vertical direction and has a circular cross section. Inside the rectangular waveguide 102 and the circular waveguide 104, the microwave electric field propagates toward the end of the waveguide portion with a specific mode as a dominant distribution of its intensity or density. In this embodiment, a directional coupler and an automatic matching unit 103 are provided on the upper surface between one end and the other end of the rectangular waveguide 102.

  In this embodiment, in this embodiment, a TE01 mode is provided and a microwave electric field propagates through the rectangular waveguide 102 and propagates toward the right end in the figure. The electric field that has reached the right end of the rectangular waveguide 102 is introduced into the circular waveguide 104 that is connected and disposed below through the conversion waveguide. Inside the circular waveguide 104, the electric field has a TE11 mode as a dominant distribution and propagates toward the lower end in the lower part of the figure.

  The circular waveguide 104 includes a dielectric material 305 such as quartz for the circular polarization mode conversion of the electric field inside the circular tube. The dielectric material 305 has a cylindrical shape and is densely arranged in contact with the inner wall surface in the tube. When this dielectric material 305 is inserted at a position in the 45-degree direction with respect to the TE11 mode combined electric field vector, the TE11 mode electric field introduced is delayed by 90 degrees in phase, so that the circularly polarized wave rotated in the circumferential direction at the exit can do.

  The electric field rotating in the circumferential direction in the circular cross section of the circular waveguide 104 is such that the intensity or density distribution of the electric field is suppressed from being nonuniform in time and the uniformity is improved. The uniformity of the intensity or density distribution of the plasma formed in the processing chamber by introducing such an electric field downward is also improved.

  The electric field that rotates in the circumferential direction of the cross section and has the TE11 mode, which is a predetermined mode, and reaches the end of the circular waveguide 104 is introduced into a cylindrical cavity connected to it below the lower end. As described above, the cylindrical cavity portion of the present embodiment has an internal cavity in which cylindrical shapes having two different diameters are concentrically connected in the vertical direction, and the first cylinder which is a lower cylindrical cavity portion. The diameter of the second cylindrical cavity 107 disposed above the diameter of the cavity 106 is made smaller.

  In the present embodiment, the first cylindrical cavity has the same diameter as that of the processing chamber 114 disposed below and having a concentric cylindrical shape. The lower end portion of the circular waveguide 104 is a circular portion disposed at the center of a ring-shaped disk 107 ′ that constitutes the upper surface of the second cylindrical cavity portion 107 disposed above the first cylindrical cavity portion 106. The second cylindrical cavity 107 and the circular waveguide 104 are communicated with each other by being connected along the inner peripheral edge of the opening and communicating the circular opening and the inside of the circular waveguide 104.

  The electric field of microwave which is circularly polarized wave introduced into the cylindrical cavity by being introduced into the second cylindrical cavity 107 has a predetermined intensity and density distribution and propagation mode in the cylindrical cavity. The microwave introduction window 108 which is a disc made of a dielectric material such as quartz and which is disposed concentrically with the bottom surface of the first cylindrical cavity 106 and the inside of the processing chamber 114 And is introduced into the processing chamber 114 through the shower plate 109, which is a disc made of a dielectric material such as quartz, which constitutes the ceiling surface thereof.

  Note that the electric field introducing unit includes one or three systems of solenoid coils 110 and a yoke 111 arranged so as to surround the vacuum vessel and the cylindrical cavity that constitute the processing chamber 114 and above the outer periphery and upper surface of the side wall. is doing. These form a static magnetic field in the axial direction inside the processing chamber 114 by the supplied DC power.

  The microwave introduction window 108 has sealing means such as an O-ring that hermetically seals the inside and the outside of the lower processing chamber 114 at the outer peripheral edge thereof. By this sealing means, the inside and outside of the processing chamber 114 that is depressurized during processing to a predetermined degree of vacuum is sealed so that the desired pressure difference can be maintained.

  A disc-shaped shower plate 109 is disposed below the microwave introduction window 108 with a predetermined gap therebetween. A plurality of through holes are arranged in a predetermined range in the center of the shower plate 109, and a processing gas is introduced into the processing chamber 114 through these. The processing gas passes through a supply line connected to a gas source (not shown), is introduced into a gap between the microwave introduction window 108 and the shower plate 109, diffuses in the gap, and communicates with the gap. By flowing into the processing chamber 114 from above through the through-holes, non-uniform distribution of the processing gas in the processing chamber 114 is reduced.

  Below the shower plate 109 inside the processing chamber 114, a sample stage 116 having a cylindrical shape and having a disk-shaped electrode made of a conductive material on which a semiconductor wafer as a sample is placed is disposed. . The sample stage 116 is disposed with a gap between the cylindrical side wall of the processing chamber 114 and is connected to the side wall by a plurality of support beams in the horizontal direction (left and right in the figure). The sample stage 116 is held in a so-called hollow state by opening a space below the sample stage 116 in the processing chamber 114 inside the vacuum vessel by these support beams.

  Below the vacuum vessel, there is disposed an exhaust unit for exhausting the inside of the processing chamber 114 and adjusting the inside to a predetermined pressure during processing. Under the processing chamber 114 and directly below the sample stage 116, there is an opening through which processing gas introduced into the processing chamber 114, particles formed during the processing, particles such as plasma flow out. And particles are discharged from this opening through the flow path.

  In the plasma processing apparatus 100 according to the present embodiment, an exhaust unit is formed below the opening, and the cross-sectional area of the flow path is determined by rotating around a rotation axis that is arranged to intersect the axial direction of the flow path. A variable valve 113 having a plurality of plate-like flaps for increasing and decreasing, and a turbo molecular pump 112, which is a vacuum pump having an inlet connected to an outlet of the flow path, are arranged below the variable valve 113. By adjusting the rotational operation of the turbo molecular pump 112 and the variable valve 113 together with the amount speed of introduction of the processing gas introduced from the introduction hole through the gap from the gas source, the pressure inside the processing chamber 114 is predetermined. The degree of vacuum is adjusted.

  The plasma processing apparatus 100 is connected to a transfer container which is another vacuum container (not shown) constituting a transfer chamber whose pressure is reduced to the same degree of vacuum as that of the process chamber 114 on the side wall of the vacuum container. The transfer chamber is opened and closed by an open / close valve such as a gate valve (not shown). A sample that has been transported while being placed on transport means such as a robot arm (not shown) in the transport chamber in a state where a gas such as Ar is introduced into the processing chamber 114 and reduced in pressure to a predetermined degree of vacuum, Is opened to the sample table 116 side above the mounting surface constituting the upper surface of the sample table 116 in the processing chamber 114.

  After the gate valve is closed and the inside of the processing chamber 114 is hermetically sealed from the outside, the sample is placed on the mounting surface of the sample table 116 and is sucked and held by an electrostatic chucking means (not shown). A heat conductive gas for promoting heat transfer between the surface and the mounting surface is supplied from an introduction port disposed on the mounting surface.

  A processing gas is introduced into the processing chamber 114 from a plurality of introduction holes arranged in a region of a predetermined radius at the center of the shower plate 109 arranged in parallel to the upper surface of the sample table 116. . Further, the inside of the processing chamber 114 is evacuated by the operation of the turbo molecular pump 112 and the variable valve 113 in the exhaust section through an opening arranged immediately below the sample stage 114, and the inside is depressurized. The inside is adjusted to a pressure of a predetermined degree of vacuum in the range of 0.05 to 5 Pa.

  In this state, an electric field of 2.45 GHz is introduced from above into the processing chamber 114 through the microwave introduction window 108 and the shower plate 109, and formed in parallel with the solenoid coil 110 to generate the electric field and ECR of 2.45 GHz. A static magnetic field of 875 Gauss strength is introduced to occur. The processing gas is excited by the ECR generated by the interaction between the electric field and the magnetic field, and the plasma 115 is formed in the processing chamber 114.

  When the plasma 115 is formed, a high frequency power of 400 kHz to 13.56 MHz is electrically connected to an electrode made of a conductive member (not shown) disposed in the sample stage 116 on which the sample is placed. One or two systems are applied from the high frequency power source 117. A bias potential is formed on the mounting surface of the sample table 116 or above the upper surface of the sample by the supplied high-frequency power, and charged particles such as ions in the plasma 115 are attracted to the sample surface by the potential difference between the potential of the plasma 115 and the bias potential. It collides with the film to be processed on the sample surface. Using the incident energy at the time of the collision, the reaction between the highly active particles generated in the plasma 115 and the material constituting the film is promoted, and the film structure including the film is etched into a desired shape.

  When it is detected that the etching process has a desired shape or that the process of the film to be processed has reached the end point, the supply of high-frequency power is stopped and the plasma 115 disappears. Thereafter, the supply of the thermally conductive gas introduced to the back surface of the sample is stopped and the adsorption and holding on the mounting surface using the electrostatic force of the sample are released, and the sample is placed on the sample table 116. It is detached from the mounting surface and removed.

  Thereafter, the gate valve is opened, and the sample is carried out into the processing chamber 114 or the transfer chamber outside the vacuum container by the robot arm. Next, when there is a sample to be processed in the processing chamber 114, the sample is again carried into the processing chamber 114 by the robot arm, placed on the sample table 116, and processed in the same manner as described above.

  The operation of each part of the plasma processing apparatus 100 during the processing of the sample is adjusted by a control unit (not shown). Each unit has detection means such as a sensor for detecting the state of operation, and the detection unit and the control unit are communicably connected by a communication unit. The control unit determines a state from the received signal from the detection means and calculates a command signal to each unit, and stores a state from the received signal and calculates a determination and a command. A command from a computing unit having an interface for exchanging a command signal from a computing unit or a signal output from a detection unit with a communication unit, such as a semiconductor memory or a hard disk drive for storing the program of Based on the signal, the operation of each unit is performed in an appropriate amount at an appropriate timing.

  The propagation of the electric field in the cylindrical cavity of the present embodiment will be described with reference to FIG. FIG. 2 is an enlarged longitudinal sectional view showing the electric field introducing portion disposed at the upper part of the plasma processing apparatus according to the embodiment shown in FIG. In this figure, a processing chamber 114 is formed below the microwave introduction window 108 to show a discharge portion where plasma 115 is formed in a cylindrical inner space and a cylindrical side wall portion of a vacuum vessel surrounding the discharge portion. However, the lower part of the vacuum vessel is not shown. In addition, as for the portions where the same reference numerals as those in FIG.

  In this embodiment, when the microwave electric field propagating through the circular waveguide 104 reaches the lower end of the circular waveguide 104, the microwave electric field is connected to the cylinder and has a larger diameter than the radius of the circular waveguide 104. It is introduced into a circular cavity with a shaped cavity inside. The cylindrical cavity of the present embodiment has a large diameter having a diameter R1 having a size that is the same as the radius from the center of the processing chamber 114 having a cylindrical shape to the inner wall surface thereof or that can be regarded as this. A first cylindrical cavity portion 106, and a second cylindrical cavity portion 107 having a small diameter having a diameter R2 smaller than the diameter R1 and concentrically connected to the upper portion of the first cylindrical cavity portion 106; have.

  Further, the upper part of the second cylindrical cavity 107 is a ring-shaped flat disk having a circular space at the center, and the lower surface thereof is the ceiling surface of the cylindrical space in the second cylindrical cavity 107. A second upper surface plate 107 'is provided. The circular opening at the center of the second upper surface plate 107 ′ faces the upwardly connected circular waveguide 104, and the second cylindrical cavity 107 and the circular waveguide 104 are circular openings inside. It is communicated by. Further, in the present embodiment, the radius of the inner peripheral edge of the circular opening has a size that is similar to the inner diameter of the circular waveguide 104 and can be regarded as the same, so that the inner diameter of the second upper surface plate 107 ′ The peripheral end is connected to a lower end portion having a circular opening of the circular waveguide 104 and a flange on the outer peripheral side thereof.

  Further, the upper portion of the first cylindrical cavity 106 is a ring-shaped flat disk having a circular space at the center, and the lower surface thereof is the ceiling surface of the cylindrical space in the first cylindrical cavity 106. A first top plate 106 'is provided. The circular opening at the center of the first upper surface plate 106 ′ faces the upwardly connected second cylindrical cavity 107, and the first cylindrical cavity 106 and the second cylindrical cavity 107 are separated from each other. The inside is communicated by a circular opening at the center of the first upper surface plate 106 '.

  Furthermore, in this embodiment, the radius of the inner peripheral edge of the circular opening has a size that is similar to the radius of the second cylindrical cavity 107 or the cylindrical space inside the second cylindrical cavity 107 and can be regarded as the same. The inner peripheral end of the circular opening of one upper surface plate 106 ′ is connected to the circular lower end of the cylindrical side wall of the second cylindrical cavity 107. Each of the first cylindrical cavity 106 and the second cylindrical cavity 107 of the present embodiment is concentric with the vertical waveguide 104, the lower microwave introduction window 108, and the vertical axis of the processing chamber 114 having a cylindrical shape. These are located in the same shape and are arranged coaxially. Side walls constituting the respective cylinders of the first cylindrical cavity portion 106 and the second cylindrical cavity portion 107 are arranged in parallel to the axis, and the lower end of the side wall of the second cylindrical cavity portion 107 and the first cylindrical cavity portion 107 are arranged. The first cylindrical cavity 106 and the second cylindrical cavity 107 are stepped so as to be connected to the upper surface plate 106 'in a substantially vertical manner, and the entire cylindrical cavity has a plurality of stages (two stages). It has a cylindrical shape.

  The microwave electric field that has traveled into the cylindrical cavity having such a configuration diffuses in the second cylindrical cavity 107 having a small diameter (primary diffusion). The diffused electric field is distributed and proceeds evenly vertically and horizontally starting from the inner periphery of the circular opening of the second upper surface plate 107 ′ or the circular lower end of the circular waveguide 104. Then, the electric field traveling toward the outer peripheral side of the circular opening is reflected by the inner wall surface of the second cylindrical cavity 107 and further interferes with the electric field diffusing toward the outer peripheral side, so that the standing wave as a steady state. Occurs.

  Such an electric field formed in the second cylindrical cavity 107 propagates downward and is also introduced into the first cylindrical cavity 106. As a result, similarly to the operation at the connection portion between the second cylindrical cavity 107 and the circular waveguide 104, the electric field rises and falls starting from the inner periphery of the circular opening at the center of the first upper surface plate 106 '. Disperses evenly from side to side and proceeds to diffuse (secondary diffusion) And it reflects on the inner side wall surface of the 1st cylindrical cavity part 106, interferes with a subsequent electric field, and the standing wave as a steady state generate | occur | produces.

  The standing waves of the two microwave electric fields generated inside the two upper and lower cylindrical spaces propagate downward in the cylindrical cavity, pass through the microwave introduction window 108 and the shower plate 109, and pass through the processing chamber 114. The plasma 115 is formed by exciting the processing gas introduced into the processing chamber 114. The standing wave in the cylindrical cavity is reflected by the entire configuration of the processing chamber 114 such as the microwave introduction window 108, the shower plate 109, the plasma 115, the upper surface of the sample table 116, and the like. It is formed in the wave introduction window 108 and the cylindrical cavity, and is in a steady state.

  The distribution of the electric field or magnetic field inside the cylindrical cavity between this embodiment and the prior art will be described in comparison with FIGS. FIG. 3 is a diagram schematically showing an electric field or magnetic field distribution inside a cylindrical cavity in the prior art.

  In the conventional technique, the circular waveguide and the upper lid and the connecting part of the cylindrical cavity connected below the circular waveguide have a step on the surface, and the electric field distribution becomes discontinuous, resulting in a stronger electric field than other parts. There was a risk of abnormal discharge occurring locally. With respect to this point, the distribution in a cross section obtained by cutting the inside of the cylindrical cavity portion in the horizontal direction in the prior art will be described as an electric field distribution as shown in FIG. Further, in parallel with this, a magnetic field in which the electric field is directed in this distribution is formed and applied by the solenoid coil 110. At this time, the contour distribution of the magnetic field lines of the magnetic field is as shown in FIG.

  As shown in these drawings, in the conventional technique, the increase and decrease in the values of electric field and magnetic field strength and density occur in the vicinity of the center of the processing chamber 114 in the cylindrical cavity directly under the circular waveguide. Such electric field and magnetic field distribution (electromagnetic field) rotates in the circumferential direction of the circular cross section of the cylindrical cavity, and periodically varies in accordance with the period of one rotation. The distribution of intensity and density in the radial direction of the lower processing chamber is considered to be a TM11 mode having a maximum (mountain) at a predetermined radial position, for example, a position immediately below the peripheral edge of the circular waveguide. In the processing using plasma formed according to the electric field or magnetic field distribution, there is an influence that the local maximum exists near the central axis of the processing chamber, such as the radius of the cross section of the circular waveguide, depending on the process conditions. Processing characteristics, such as a distribution (rate profile) of the etching rate (rate) in the radial direction on the surface of the sample, resulting in a difference exceeding the allowable range in the shape after processing in the in-plane direction of the sample. It was happening.

  In the present embodiment, the second cylindrical cavity 107 having a small diameter is connected and disposed above the first cylindrical cavity 106. As described above, the inner surface of the side wall at the lower end of the side wall of the second cylindrical cavity 107 and the lower surface of the first upper surface plate 106 ′ of the first cylindrical cavity 106 are connected substantially perpendicularly. The distribution of the electric field formed inside the connection portion becomes discontinuous inside the so-called protruding corner portion, and a strong electric field Ez propagating downward from the connection portion is locally generated.

  A strong electric field Ez generated by the discontinuity of the electric field distribution is generated between the circular opening at the center of the second upper surface plate 107 ′ of the second cylindrical cavity 107 and the lower end of the circular waveguide 104. It also occurs in the connecting portion, and in the cylindrical cavity portion of this embodiment, it is directly below the inner peripheral edge at the lower end portion of the circular waveguide 104 and immediately below the lower end portion of the side wall of the second cylindrical cavity portion 107. Ez is provided at two positions in the radial direction from the central axis. A superposition of the strong electric field Ez and the electric field propagating downward from the cylindrical cavity propagates into the processing chamber 114.

  FIG. 4A shows an electric field distribution in a horizontal section in the first cylindrical cavity 106 in the present embodiment. Further, as in the prior art, a magnetic field perpendicular to the direction of the electric field is generated and applied by the solenoid coil 110, and the distribution thereof is as shown in FIG.

  As shown in this figure, the distribution of the electric field in the first cylindrical cavity 106 in this embodiment has a TM12 mode, and the electric field of this distribution has a predetermined value in the circumferential direction of the cross section of the cylindrical cavity. By rotating with a period, intensity and density fluctuate periodically. When considering the average over time per unit time, the distribution of the electric field in the first cylindrical cavity 106 in the present embodiment is from the electric field Ez in a plurality (two places) in the radial direction. It is strongly influenced, and typically has a plurality (two) maximums (mountains) in the radial direction.

  The electric field in the cylindrical empty groove of the present embodiment will be described with reference to FIG. 5. FIG. 5 is a longitudinal sectional view schematically showing the electric field in the cylindrical cavity portion of the embodiment shown in FIG. In particular, the diameter of the first cylindrical cavity portion 106 having the same diameter as that of the processing chamber 114 and the second cylindrical cavity portion 107 having a small diameter connected to the first cylindrical cavity portion 107 below the circular waveguide 104 is connected to the first cylindrical cavity portion 106. Λ / 4 <R2, and λ <H2 <λ + λ / 4 (= 5λ / 4) and λ / 4 <H1 with respect to the wavelength λ of the standing wave of the electric field in the cylindrical cavity The generation of standing waves in the case will be described.

  As in the case of FIG. 2, in this figure, the electric field introduction portion of the embodiment shown in FIG. 1 is shown enlarged, and a processing chamber 114 is formed below the microwave introduction window 108 to form a cylindrical shape. The discharge portion where the plasma 115 is formed in the space inside and the cylindrical side wall portion of the vacuum vessel surrounding the discharge portion are shown, but the lower portion of the vacuum vessel is not shown. Further, the magnetron 101 and the rectangular waveguide 102 extending in the horizontal direction are not shown. Further, the portions where the same reference numerals as those in FIG. 1 are quoted are omitted because they are not particularly necessary.

  In this figure, the microwave electric field introduced from the lower end of the circular waveguide 104 into the second cylindrical cavity 107 causes diffusion in the internal cavity (primary diffusion). That is, the electric field is uniformly propagated from the lower end of the circular waveguide 104 or the inner peripheral edge of the opening of the central portion of the second upper surface plate 107 ′ to the upper, lower, left and right. The electric field that has traveled toward the outer periphery of the second cylindrical cavity 107 is reflected by the vertical inner wall surface of the second cylindrical cavity 107 to cause interference with the subsequent diffusing electric field, resulting in the second cylindrical cavity. A standing wave as a steady state is generated in the unit 107. Such an electric field distribution is discontinuous at the connection portion 401 between the inner wall surface at the lower end portion of the circular waveguide 104 arranged approximately vertically and the lower surface of the second upper surface plate 107 ′. Thus, an electric field Ez2 having a large intensity is generated in the connecting portion 401 in the Z direction (downward in the drawing, the direction of the central axis of the circular waveguide 104 or the processing chamber 114).

  Such an electric field in the second cylindrical cavity 107 is introduced into the first cylindrical cavity 106 connected to propagate downward. The introduced electric field diffuses in the cavity in the first cylindrical cavity 106 (secondary diffusion), similar to the electric field from the circular waveguide 104 described above. At this time, similarly to the second cylindrical cavity 107, the diffuse reflection is performed around the connection part 403 that forms a step between the second cylindrical cavity 107 and the first cylindrical cavity 106. A wavefront is generated, and an electric field Ez1 having a strong intensity locally in the Z direction is generated. As a result, electric lines of force 404 are generated in which the connecting portion 403 between the first cylindrical cavity portion 106 and the second cylindrical cavity portion 107 that form a step is used as a spring outlet and a suction inlet.

  In this embodiment having such a distribution, the electric field Ez1 generated immediately below the periphery of the lower end portion of the circular waveguide 104 and the electric field Ez2 generated immediately below the lower end portion of the side wall of the second cylindrical cavity portion 107. The intensity distribution of the electric field obtained by the superimposing of the radii and the non-uniformity in the radial direction (horizontal direction, r direction in the figure) in the processing chamber 114 disposed below or in the plane where the ECR occurs is uniformly approached. As described above, the values of the height H1 of the first cylindrical cavity portion 106 and the height H2 of the second cylindrical cavity portion 107 are appropriately adjusted and set. As a result, non-uniformity in plasma density and intensity between the center and the outer periphery of the processing chamber 114 is reduced, and from the center of the sample placed on the mounting surface of the processing chamber 114 or the lower sample stage 116 to the outer periphery. A plasma with improved uniformity in the radial direction is formed.

  In this embodiment, the effective wavelength λ in the free space of the TM12 mode is 130 to 140 mm. From this, the distance H2 from the upper surface of the microwave introduction window 108 to the ceiling surface (the lower surface of the second upper surface plate 107 ′) of the space in the second cylindrical cavity 107 is λ <H2 <λ + λ / 4 (= It is preferable to be in the range of 5λ / 4). Further, the distance H1 between the ceiling surface of the first cylindrical cavity 106 (the lower surface of the first upper surface plate 106 ') and the upper surface of the microwave introduction window 108 efficiently propagates the effective wavelength and lowers the processing chamber. In order to introduce it into 114, the range of λ / 4 <H1 is preferable. Further, in this embodiment, the distance (radius) R1 from the central axis to the side wall of the first cylindrical cavity portion 106 is equal to the diameter of the processing chamber 114 having a cylindrical shape or its discharge portion. The distance (radius) R2 between the central axis of the cylindrical cavity 107 and the side wall is preferably in the range of λ / 4 <R2.

  In the first cylindrical cavity portion 106, an electric field having a distribution resulting from superimposing these Ez1 and Ez2 is propagated downward. The first distribution is such that the distribution of plasma in the processing chamber 114 formed below becomes a desired distribution, for example, a distribution in which the uniformity of density or intensity is improved from the center to the outside in the radial direction. The height H1 and radius of the cylindrical cavity portion 106, the height 402 of the second cylindrical cavity portion, and the radius R2 are adjusted and set to appropriate values. For example, in order to provide a radial gradient of the desired density and strength, between the upper surface of the microwave introduction window 108 and the ceiling surface of the first cylindrical cavity portion 106 and the ceiling surface of the second cylindrical cavity portion 107. After adjusting and setting the distance H1, H2 between the distances, the sample is processed.

  By satisfying such conditions, the electric fields from the two cylindrical cavities propagate downward and are efficiently absorbed by the ECR plane formed in the processing chamber 114. As a result, plasma with higher density and reduced non-uniformity is generated from the center to the outer periphery of the processing chamber 114.

  As described above, in the conventional technique, the distribution is such that the intensity and density of plasma decrease from the center to the outer periphery, particularly in the outer periphery. On the other hand, in this embodiment, regions where the intensity or density of the electric field is locally high are arranged at a plurality of locations on the outer peripheral side in the radial direction from the center of the processing chamber 114. For this reason, the problem of the prior art in which the density and strength are significantly reduced from the center to the outer peripheral portion of the processing chamber 114 is suppressed, and the gradient of density and strength over the outer peripheral portion is made lower than that of the prior art. Plasma with improved uniformity in the radial direction can be formed. In this example, as a result of confirming the ICF distribution above the sample on the sample stage and the characteristics of the etching process, for example, the distribution of the processing rate, a result in which the uniformity is improved as compared with the conventional technique is obtained. ing.

  Further, by inserting a dielectric material 105 for generating circularly polarized waves into the circular waveguide 104 and changing the phase of the TE11 mode in the circular waveguide 104 by 45 degrees, uniform TE11 is obtained at the incident end of the cylindrical cavity. A mode is obtained. For this reason, the effect of improving the uniformity of the plasma generated in the processing chamber 114 can be obtained by the radial distribution improvement by the TM mode and the circumferential distribution improvement by the circular polarization. It goes without saying that the radical distribution obtained by such plasma is effective for isotropic etching of the film to be processed on the upper surface of the sample. Thereby, it is possible to provide a plasma processing apparatus with improved processing performance for a sample having a large diameter.

  The user can adjust the shape of the cylindrical cavity of the present embodiment by moving the heights H1 and H2 of the first upper surface plate 106 ′ and the second upper surface plate 107 ′ in the vertical direction. . Although not shown in the drawing, electric field leakage such as a choke flange which short-circuits the side wall and the upper surface plate along with the relative movement between the first upper surface plate 106 ′ and the second upper surface plate 107 ′ together with the relative movement between the side walls. Means for suppressing this are provided.

  In addition, the radius R2 of the second cylindrical cavity 107 of the present embodiment is set to a value smaller than the outer shape of the sample stage 116 having a cylindrical shape disposed below. Further, the value is larger than the diameter of the outer peripheral edge of the mounting surface arranged on the upper surface of the sample table 116. With such an arrangement, a portion (radius position) where the electric field density due to the electric field EZ2 generated in the connection portion 403 is strong can be formed inside the outer shape of the sample table 116 and on the outer peripheral side of the sample. Accordingly, the electric field EZ1, EZ2 generated at the radial position corresponding to the connection portion 403 and the connection portion 401 greatly reduces the distribution of the plasma density and strength in the radial direction of the sample in the outer peripheral portion of the sample. It is possible to suppress the occurrence of the problem of the prior art that the radial characteristics of the process become non-uniform, and perform plasma processing with improved uniformity.

The operation and effect of the present embodiment will be described with reference to FIG. FIG. 6 is a graph showing the in-plane direction distribution (ICF distribution) of the ion current flowing from the plasma 115 into the electrode in the sample stage 116 from the plasma 115 in the processing chamber 114 of the present embodiment shown in FIG. It is. In the example of this figure, the processing gas used for forming the plasma 115 is a mixed gas of Cl ₂ / HBr / O ₂ / Ar, the pressure in the processing chamber 114 is 0.4 Pa, and the mounting surface of the sample stage 116 This is a result obtained when the height of the ECR plane from the surface of the substrate is 165 mm, and the power of the supplied microwave is 1200 W in the case of the conventional cylindrical cavity, and 1800 W in this embodiment.

  The conventional technique shows a distribution in which the ion current at the center is high and the outer periphery is low. For this reason, the plasma distribution has a convex shape. In particular, it is considered that the density of the ion current is remarkably reduced in the region of the outer peripheral portion (150 mm or more) of the sample, and the density and intensity of the plasma 115 are also greatly reduced in the outer peripheral portion. The uniformity in the in-plane direction of the sample processing according to the conventional technique under this condition was 11%.

  On the other hand, in the case of the present embodiment, it is shown that the ion current is high in the vicinity of 150 mm in the radial direction from the center of the sample stage 116. On the other hand, the ICF shows a low distribution at the center and the outer periphery of the sample. In other words, the intensity and density of the plasma under the above conditions of the present embodiment have an M-shaped distribution. And the uniformity about the in-plane direction of the process of the sample on the said conditions became 5%.

  The above detection data shows the most uniform result among the detections in the process under a plurality of conditions by changing the microwave power to a plurality of values along with the height of the ECR plane. In addition, uniformity improvement results were obtained even under fluoride process conditions.

  Needless to say, in a state of high uniformity, radicals are evenly irradiated onto the wafer, which is advantageous for radical-induced etching. In particular, the diffusion degree of ionized electrons and ions is large under high pressure conditions (3 Pa to 10 Pa), radicals are dominant over ions on the wafer, and variations in shape and rate within the wafer surface are improved even at high pressures.

  As described above, according to the present embodiment, the nonuniformity of the density and intensity distribution of the plasma formed in the processing chamber is reduced, and the processing characteristics and the uniformity of the processing shape are improved in the radial direction of the sample. A plasma processing apparatus can be provided.

101 Magnetron 102 Rectangular waveguide 103 Automatic matching box 104 Circular waveguide 105 Dielectric material 106 First cylindrical cavity 107 Second cylindrical cavity 108 Microwave introduction window 109 Shower plate 110 Solenoid coil 111 Yoke 112 Turbo molecule Pump 113 Variable valve 114 Processing chamber 115 Plasma 116 Sample stage 117 High frequency power supply 401, 403 Connection portion 402 Height of second cylindrical cavity 404 Electric field lines

Claims (8)

A vacuum chamber, a processing chamber disposed inside the vacuum chamber and generating plasma therein, a sample stage disposed in the processing chamber and having a sample placed thereon, and disposed above the processing chamber. A circular plate member made of a dielectric material through which an electric field supplied to form plasma is transmitted, a hollow portion having a cylindrical shape that is disposed above the plate member and into which the entire electric field is introduced, and A cylindrical pipe that is connected to the center of the upper part and extends up and down to propagate the electric field, and a generator that is arranged at an end of the pipe and generates the electric field,
A first cylindrical cavity having a large-diameter cylindrical cavity with the plate member as a bottom surface, and a small-diameter cylindrical shape connected to and disposed above the first cylindrical cavity A plasma processing apparatus comprising: a second cylindrical cavity portion having a cavity; and a step portion connecting the first cylindrical cavity portion and the second cylindrical cavity portion. The plasma processing apparatus according to claim 1,
The plasma processing apparatus provided with another level | step-difference part which connects these between the said 2nd cylindrical cavity part and the said pipe line, and the surface where the ceiling surface of a cavity part is parallel to the said plate member. The plasma processing apparatus according to claim 1 or 2,
The ceiling surface of the second cylindrical cavity is arranged in parallel with the plate member, and the height H2 of the ceiling surface from the upper surface of the plate member is λ <H2 <5λ / 4 with respect to the wavelength λ of the electric field. Plasma processing equipment made to range. The plasma processing apparatus according to any one of claims 1 to 3,
The ceiling surface of the first cylindrical cavity is arranged in parallel with the plate member, and the height H1 of the ceiling surface from the upper surface of the plate member is in the range of λ / 4 <H1 with respect to the wavelength λ of the electric field. Plasma processing apparatus. The plasma processing apparatus according to any one of claims 1 to 4,
The plasma processing apparatus, wherein a cylindrical radius R2 of the second cylindrical cavity is in a range of λ / 4 <R2 with respect to the wavelength λ of the electric field. A plasma processing apparatus according to any one of claims 1 to 5,
The second cylindrical cavity is arranged in alignment with the central axis of the sample stage having a cylindrical shape at the center, and the stepped part has a cylindrical shape in a direction from the central axis toward the outer peripheral side. A plasma processing apparatus disposed on the center side from the outer periphery. A plasma processing apparatus according to any one of claims 1 to 7,
A plasma processing apparatus, wherein the electric field is a microwave electric field of 2.45 GHz, has magnetic field generating means for supplying a magnetic field of 875 Gauss in the processing chamber, and the plasma is formed by ECR in the processing chamber. The plasma processing apparatus according to claim 7,
A plasma processing apparatus in which the microwave of the TE11 mode is supplied from the pipe to the cavity.