JP2008182102A - Top plate member and plasma processing apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a top plate member which can improve the ignitability of plasma even when the pressure in a processing chamber is still low. <P>SOLUTION: A top plate material 58 consists of a dielectric plate 62 transmitting microwaves and is prepared in the top portion of a processing chamber 44 for vacuuming in order to apply processing to a workpiece W by plasma generated by microwaves. A recess 64 for ignition is prepared inside the processing chamber 44 of the dielectric plate 62 in order to perform electric field concentration at plasma ignition. Thereby, the ignitability of plasma can be improved even when the pressure inside the processing chamber is still low, since it can prevent film deposition while the pressure inside the processing chamber is high, electric properties of formed insulating films, etc., composed of low dielectric material can be improved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a plasma processing apparatus used when processing is performed by applying plasma generated by microwaves to a semiconductor wafer or the like, and a top plate member used therefor.

  In recent years, with increasing density and miniaturization of semiconductor products, plasma processing apparatuses are often used for various processes such as film formation, etching, and ashing in the manufacturing process of semiconductor products, and in particular, 0.1 mTorr. (13.3 mPa) to several Torr (several hundreds Pa) A microwave plasma treatment for generating a high-density plasma using microwaves because a plasma can be stably generated even in a high vacuum state where the pressure is relatively low. The device tends to be used.

  Such a plasma processing apparatus is disclosed in Patent Documents 1 to 5 and the like. Here, an example of a general plasma processing apparatus using a microwave will be schematically described with reference to FIGS. FIG. 8 is a schematic configuration diagram showing a conventional general plasma processing apparatus, and FIG. 9 is an enlarged sectional view showing a top plate member.

  In FIG. 8, the plasma processing apparatus 2 includes a mounting table 6 on which a semiconductor wafer W is mounted in a processing container 4 that can be evacuated, and microwaves are applied to a ceiling portion facing the mounting table 6. A top plate member 8 made of a dielectric plate such as transparent disc-shaped alumina, aluminum nitride, or quartz is provided in an airtight manner. The side wall of the processing vessel 4 is provided with, for example, a gas nozzle 10 as gas introduction means for introducing a predetermined gas into the vessel, and an opening 12 for loading / unloading the wafer W is provided. The part 12 is provided with a gate valve G that opens and closes the airtightly. Further, an exhaust port 14 is provided at the bottom of the processing container 4, and a vacuum exhaust system (not shown) is connected to the exhaust port 14 so that the processing container 4 can be evacuated as described above. Yes.

  A microwave introducing means 16 for introducing a microwave for plasma formation into the processing container 4 is provided above the top plate member 8. Specifically, the microwave introduction means 16 includes a disk-shaped planar antenna member 18 made of, for example, a copper plate having a thickness of about several millimeters provided on the top surface of the top plate member 8, and the planar antenna member 18. It has a slow wave member 20 made of, for example, a dielectric for shortening the wavelength of the microwave in the radial direction. The planar antenna member 18 is formed with a number of microwave radiating slots 22 made of, for example, long groove-like through holes. The slots 22 are generally arranged concentrically or spirally.

  The central conductor 24A of the coaxial waveguide 24 is connected to the planar antenna member 18, and the outer conductor 24B of the coaxial waveguide 24 is connected to the central portion of the waveguide box 25 that covers the entire slow wave member 20. It comes to connect. Then, for example, a 2.45 GHz microwave generated by the microwave generator 26 is converted into a predetermined vibration mode by the mode converter 28 and then guided to the planar antenna member 18 and the slow wave member 20. Then, while propagating the microwaves radially in the radial direction of the antenna member 18, the microwaves are radiated from the respective slots 22 provided in the planar antenna member 18, and are transmitted through the top plate member 8, so that the lower processing container 4. A microwave is introduced into the chamber, and a plasma is generated in the processing space S in the processing chamber 4 by the microwave so that the semiconductor wafer W is subjected to predetermined plasma processing such as etching or film formation. A cooler 30 for cooling the slow wave member 20 heated by the dielectric loss of microwaves is provided on the upper surface of the waveguide box 25.

  Further, as the top plate member 8, the thickness of the dielectric plate constituting the top plate member 8 may be uniformly formed over the entire surface, but in order to make the plasma density uniform in the in-plane direction of the processing space S. The top plate member 8 is devised in various ways. For example, as shown in FIG. 9 (see Patent Document 5), a concave portion 32 for canceling the microwave in this portion and avoiding electric field concentration is provided on the atmosphere side (upper surface side) of the central portion of the top plate member 8. At the same time, a microwave is provided on the lower surface side of the top plate member 8 by providing projections 34a, 34b, 34c each having a trapezoidal or triangular cross section at the center, middle periphery and outer periphery thereof. Is formed so that a stable plasma can be generated from a low pressure to a high pressure.

Japanese Patent Laid-Open No. 3-191073 JP-A-5-343334 Japanese Patent Laid-Open No. 9-181052 JP 2003-332326 A Japanese Patent Laid-Open No. 2005-100931

  By the way, as a material constituting, for example, an interlayer insulating film of a semiconductor device, a low dielectric constant material typified by, for example, a SiOC film, a SiOCH film, or a CF film, for example, a so-called Low- k materials tend to be used. In order to further improve the electrical characteristics of the interlayer insulating film made of this low dielectric constant material, the processing pressure is as low as possible within a range where a reasonable throughput can be obtained, for example, 50 mTorr (6.7 Pa). It is desired to form a film as follows.

  In this case, as is well known, if the pressure in the processing container 4 is excessively lowered, the plasma will not be ignited even if the power of the input microwave is increased. For this reason, in the prior art, when the plasma is ignited, the pressure in the processing container 4 is once set slightly higher, and when the plasma is ignited, the pressure in the processing container 4 is lowered to perform the process. I was doing. In addition, once ignited, the plasma has a characteristic that it can be maintained sufficiently stably even if the pressure in the processing container 4 is excessively lowered thereafter.

  However, as described above, if the pressure in the processing container 4 is set so high that the plasma can be ignited even when it is temporarily ignited, the film-forming gas has already flowed at the time of ignition. However, there has been a problem that a film of a low dielectric constant material is formed at a high process pressure, and the thin film deposited at this time deteriorates the electrical characteristics of the entire insulating film.

In this case, in order to improve the ignitability of the plasma, it is only necessary to form a large protrusion downward in the central portion of the lower surface of the top plate member to generate an electric field concentration. Since the electric field concentration continuously occurs in this portion even after ignition, the uniformity of the plasma density in the plane direction is greatly lost, and the above structure cannot be adopted.
The present invention has been devised to pay attention to the above problems and to effectively solve them. An object of the present invention is to provide a top plate member capable of improving the ignitability of plasma even when the pressure in the processing vessel is kept low, and a plasma processing apparatus using the top plate member.

  According to the first aspect of the present invention, there is provided a dielectric plate that is provided on a ceiling portion of a processing vessel that can be evacuated in order to perform processing with plasma generated by microwaves on an object to be processed and transmits the microwaves. In the top plate member, the top plate member is characterized in that an ignition recess for concentrating an electric field at the time of plasma ignition is provided inside the processing container of the dielectric plate.

As described above, since the ignition concave portion for concentrating the electric field at the time of plasma ignition is provided inside the processing container of the dielectric plate serving as the top plate member, the plasma can be generated even when the pressure in the processing container is kept low. Ignition can be improved.
Therefore, it is possible to prevent the film formation from being performed in a state where the pressure in the processing container is high, and thus it is possible to improve the electrical characteristics of an insulating film made of a low dielectric constant material to be formed.

In this case, for example, as described in claim 2, if the diameter D1 of the recess for ignition is a wavelength λ in the dielectric plate of the microwave, 2 · λ / 8 ≦ D ≦ 4 · λ / 8 Is within the range.
Further, for example, as described in claim 3, if the depth H of the ignition recess is a wavelength λ in the dielectric plate of the microwave, 2 · λ / 8 ≦ H ≦ 4 · λ / 8. Within range.
For example, as described in claim 4, the inner side surface of the ignition recess is set within ± 10 degrees with respect to the vertical direction.

In addition, for example, as described in claim 5, the ignition recess is formed in a trapezoidal cross-sectional protrusion that protrudes inside the processing container at the center of the dielectric plate in order to form a resonance region for the microwave. Has been.
For example, as described in claim 6, the pressure in the processing vessel is set within a range of 10 mTorr to 2 Torr when the plasma is ignited.

  According to a seventh aspect of the present invention, there is provided a processing container in which a ceiling portion is opened so that the inside can be evacuated, a mounting table provided in the processing container for mounting an object to be processed, and the processing container A gas introducing means for introducing the gas in the interior; the top plate member according to any one of the above-mentioned, which is airtightly attached to the opening of the ceiling portion; and the microwaves into the processing container via the top plate member A plasma processing apparatus comprising: a microwave introduction means for introduction.

In this case, for example, as described in claim 8, the microwave introducing means generates a microwave with a planar antenna member provided on the top plate member and formed with a plurality of slots for radiating microwaves. And a waveguide for guiding the microwave generated by the microwave generator to the planar antenna member.
Further, for example, as described in claim 9, the microwave introducing means generates the microwave, and a waveguide provided on the top plate member and formed with a plurality of slots for radiating microwaves. And a microwave generator.

  According to a tenth aspect of the present invention, there is provided a processing container in which a ceiling portion is opened so that the inside can be evacuated, a mounting table provided in the processing container for mounting an object to be processed, and the processing container A gas introducing means for introducing the gas in the interior; the top plate member according to any one of the above-mentioned, which is airtightly attached to the opening of the ceiling portion; and the microwaves into the processing container via the top plate member When performing plasma processing using a plasma processing apparatus having a microwave introducing means to be introduced and a control means for controlling the operation of the entire apparatus, the pressure in the processing vessel is within a range of 10 mTorr to 2 Torr when the plasma is ignited. A storage medium for storing a program for controlling the plasma processing apparatus to be set to

According to the top plate member and the plasma processing apparatus using the same according to the present invention, the following excellent operational effects can be exhibited.
An ignition recess for concentrating the electric field when plasma is ignited is provided inside the processing vessel of the dielectric plate as the top plate member, improving plasma ignitability even when the pressure in the processing vessel is kept low Can be made.
Therefore, it is possible to prevent the film formation from being performed in a state where the pressure in the processing container is high, and thus it is possible to improve the electrical characteristics of an insulating film made of a low dielectric constant material to be formed.

Hereinafter, an embodiment of a top plate member and a plasma processing apparatus using the same according to the present invention will be described in detail with reference to the accompanying drawings.
1 is a block diagram showing a first embodiment of a plasma processing apparatus according to the present invention, FIG. 2 is an enlarged sectional view showing a top plate member used in the plasma processing apparatus shown in FIG. 1, and FIG. FIG. 4 is a graph showing the relationship between the diameter of the recess for ignition provided in the top plate member and the electric field strength during plasma ignition.

  As shown in the figure, this plasma processing apparatus 42 has a processing container 44 whose side wall and bottom are made of a conductor such as aluminum and which is formed into a cylindrical shape, for example, a cylindrical shape. A sealed processing space S is formed, and plasma is formed in the processing space S. The processing container 44 itself is grounded.

In the processing container 44, a mounting table 46 on which, for example, a semiconductor wafer W as a target object is mounted is accommodated on the upper surface. The mounting table 46 is formed in a substantially disc shape made flat, for example, by anodized aluminum or the like, and is erected from the bottom of the container via a support 47 made of, for example, an insulating material.
An electrostatic chuck or a clamp mechanism (not shown) for holding the wafer is provided on the upper surface of the mounting table 46. The mounting table 46 may be connected to a high frequency power source for bias of 13.56 MHz, for example. Moreover, you may provide the heater for heating in this mounting base 46 as needed. The mounting table 46 is provided with lifter pins (not shown) that push up the wafer W when the wafer W is loaded and unloaded.

  As a gas introduction means 48, a plasma gas supply nozzle 48a made of quartz pipe for supplying a plasma gas, for example, argon gas, or a process gas, for example, a deposition gas, is introduced into the side wall of the processing container 44. For example, a processing gas supply nozzle 48b made of quartz pipe is provided, and the respective gases can be supplied from these nozzles 48a and 48b while controlling the flow rate. For example, a quartz shower head may be used as the gas introducing means 48.

  The container side wall is provided with an opening 50 for loading / unloading the wafer into / from the inside of the container, and the opening 50 is provided with a gate valve 52 that opens and closes when the wafer is loaded / unloaded. In addition, an exhaust port 54 is provided at the bottom of the container, and an exhaust path 56 connected to a vacuum pump and a pressure control valve (not shown) is connected to the exhaust port 54, and the processing container 44 is used as necessary. The inside can be evacuated to a predetermined pressure.

And the ceiling part of the processing container 44 is opened, and the top plate member 58 is airtightly provided here through a seal member 60 such as an O-ring. The top plate member 60 is configured by a dielectric plate 62 that transmits a microwave such as a ceramic member such as aluminum nitride (AlN) or aluminum oxide (Al ₂ O ₃ ), or a microwave such as quartz. . The thickness of the dielectric plate 62 is set to, for example, about 20 mm in consideration of pressure resistance. An ignition recess 64, which is a feature of the present invention, is provided on the lower surface of the dielectric plate 62 and facing the inside of the processing container 44, that is, the inside of the processing container. It has been. The structure of the top plate member 58 such as the ignition recess 64 will be described later.

  A microwave introducing means 66 for introducing a microwave into the processing container 44 through the top plate member 58 is provided on the upper surface side of the top plate member 58. Specifically, the microwave introducing means 66 has a planar antenna member 68 provided on the top surface of the top plate member 58, and a slow wave member having a high dielectric constant characteristic on the planar antenna member 68. 70 is provided. The planar antenna member 68 is configured as a bottom plate of a wave guide box 72 made of a conductive hollow cylindrical container covering the entire upper surface of the slow wave member 70, and is opposed to the mounting table 46 in the processing container 44. Provided.

  The waveguide box 72 and the peripheral portion of the planar antenna member 68 are both grounded, and an outer tube 74a of the coaxial waveguide 74 is connected to the center of the upper portion of the waveguide box 72, and an inner conductor 74b inside. Is connected to the central portion of the planar antenna member 68 through a through hole at the center of the slow wave member 70. The coaxial waveguide 74 is connected to a 2.45 GHz microwave generator (microwave generating means) 82 having a matching circuit 80 via a mode converter 76 and a rectangular waveguide 78, for example. Microwaves are propagated to the planar antenna member 68. Therefore, the mode converter 76 is interposed in the middle of the waveguide formed by the rectangular waveguide 78 and the coaxial waveguide 74.

  Here, for example, a TE mode microwave is emitted from the microwave generator 82, which is converted into, for example, a TEM mode by the mode converter 76 and propagated through the coaxial waveguide 74. This frequency is not limited to 2.45 GHz, and other frequencies such as 8.35 GHz or 1.98 GHz may be used. A ceiling cooling jacket (not shown) may be provided above the waveguide box 72. The slow wave member 70 having high dielectric constant characteristics provided in the waveguide box 72 on the upper surface side of the planar antenna member 68 shortens the in-tube wavelength of the microwave due to this wavelength shortening effect. . As the slow wave member 70, for example, the same material as that of the dielectric plate 62 can be used.

  The planar antenna member 68 is made of, for example, a copper plate or an aluminum plate, which is a conductive material having a diameter of 300 to 400 mm and a thickness of 1 to several mm, for example, in the case of an 8-inch wafer, although it depends on the wafer size. The surface of this disk is, for example, silver-plated. The circular plate is formed with a number of slots 84 made of, for example, long groove-like through holes for emitting microwaves. The arrangement form of the slots 84 is not particularly limited. For example, the slots 84 may be arranged concentrically, spirally, or radially, or may be distributed uniformly over the entire antenna member.

  The dielectric plate 62 forming the top plate member 58 is formed to be substantially flat on the upper surface side, whereas on the lower surface side, that is, the surface facing the processing space S of the processing container 44. A protrusion as disclosed in Japanese Patent Application Laid-Open No. 2005-100931 is formed. Specifically, as shown in FIGS. 2 and 3, protrusions 86, 88, and 90 are formed at the central portion, the middle peripheral portion, and the outer peripheral portion, which are microwave introduction portions of the dielectric plate 62, respectively. The thickness of the dielectric plate 62 is changed. Here, the peripheral surface of the protrusion 86 at the center is a tapered surface 86a, the inner and outer peripheral surfaces of the protrusion 88 at the middle periphery are tapered surfaces 88a, and the inner periphery of the protrusion 90 at the outer periphery. Has a tapered surface 90a.

  The protrusion 90 on the outer periphery and the protrusion 88 on the middle periphery are formed in a ring shape along the circumferential direction of the dielectric plate 62, and the protrusion 90 has a tapered surface on the inner peripheral side, and the protrusion 88. The inner and outer peripheral sides are tapered surfaces.

  Further, the protrusion 86 at the center is formed in a trapezoidal cross section or a frustoconical shape, and the side surface is a tapered surface. Here, when microwaves are introduced from the planar antenna member 68 to the dielectric plate 62 side, the plasma generated immediately below the dielectric plate 62 acts as a reflector strong against microwaves (such plasma is referred to as “ This microwave is referred to as “surface wave plasma”, and is oscillated in the (up and down) plane direction while being repeatedly reflected on the upper surface side and the lower surface side in the dielectric plate 62 to become a standing wave. In this case, since one side surface or both side surfaces of the projections 86, 88, 90 are tapered surfaces, the amplitude that vibrates in the surface direction in the dielectric plate 62 and the projections 86, 88, There is a portion where the thickness in the plane direction at 90 coincides, and a resonance region can be formed there to increase the plasma density.

  As described above, an ignition recess 64 for concentrating the electric field at the time of plasma ignition is formed corresponding to the central portion of the dielectric plate 62, that is, the microwave introduction portion for introducing the microwave from above. . Here, the ignition recess 64 is formed at the center of the projection 86 at the center. The recess 64 for ignition is a hole having a circular cross section, and its diameter D is λ when the wavelength of the microwave in the dielectric plate 62 is λ in order to cause plasma ignition even at a low process pressure of 50 mTorr or less. It is set to be in the range of 2 · λ / 8 ≦ D ≦ 4 · λ / 8. In this case, the diameter D is preferably set to 3 · λ / 8.

  Further, the depth H of this ignition recess 64 is also set to be in the range of 2 · λ / 8 ≦ H ≦ 4 · λ / 8. The function required for the ignition recess 64 is that electric field concentration occurs in this portion during plasma ignition, and the electric field concentration is eliminated after plasma ignition in order to improve the uniformity of the plasma density in the processing space S. In order to satisfy such a function, the above-described dimensional condition of the ignition recess 64 is required. Of the above dimensional conditions, the condition of the diameter D of the ignition recess 64 is particularly important.

  That is, when the diameter D deviates from the above-mentioned range, the electric field is not sufficiently concentrated, and the plasma cannot be ignited at a low pressure of 50 mTorr or less. In this embodiment, as an example, the diameter D is set to about 20 mm, and the depth H is set to about 10 mm. Further, the inner side surface 64a of the ignition recess 64 is preferably set within an angle range of ± 10 degrees with respect to the vertical direction (gravity direction) 94, and the side surface 64a deviates from this angular range. If the taper surface has a large inclination, sufficient electric field concentration does not occur in this portion, and plasma ignition cannot be caused.

  The overall operation of the plasma processing apparatus 42 formed in this way is controlled by a control means 96 made of, for example, a computer, and the computer program for performing this operation is a flexible disk or CD (Compact). Disc), a storage medium 98 such as a flash memory or a hard disk. Specifically, supply of each gas and flow control, supply of microwaves and high frequencies, power control, control of process temperature and process pressure, and the like are performed according to commands from the control means 96.

  Next, a processing method performed using the plasma processing apparatus 42 configured as described above will be described. First, the gate valve 52 is opened, the semiconductor wafer W is accommodated in the processing container 44 by the transfer arm (not shown) through the opening 50, and the wafer W is loaded by moving the lifter pins (not shown) up and down. It is mounted on the mounting surface on the upper surface of the mounting table 46.

  Then, for example, argon gas is supplied from the plasma gas supply nozzle 48a into the processing container 44 while controlling the flow rate, and the film forming gas is controlled from the processing gas supply nozzle 48b according to the processing mode. While supplying. At the same time, the microwave generated by the microwave generator 82 is supplied to the planar antenna member 68 through the rectangular waveguide 78 and the coaxial waveguide 74 to reduce the wavelength in the processing space S by the slow wave member 70. Then, a predetermined microwave treatment is performed by generating plasma in the processing space S.

  Here, for example, a 2.45 GHz TE mode microwave generated by the microwave generator 82 propagates through the rectangular waveguide 78 and then converted to a TEM mode by the mode converter 76. As described above, the wave propagates through the coaxial waveguide 74 and reaches the planar antenna member 68 in the waveguide box 72, and radiates from the center of the disk-shaped planar antenna member 68 to which the internal conductor 74b is connected. The microwave is introduced into the processing space S immediately below the planar antenna member 68 through the top plate member 58 from the slots 84 formed in the planar antenna member 68 while propagating to the peripheral portion. The argon gas excited by the microwave is dissociated and turned into plasma, and diffused downward to activate the processing gas to create active species. By the action of the active species, a predetermined plasma treatment is performed on the surface of the wafer W. Will be given.

  Here, in this embodiment, in order to improve the electrical characteristics of the low dielectric constant (Low-k) thin film (insulating film) formed by plasma CVD, the pressure in the processing vessel 44, that is, the process pressure is set. During the film formation, including when the plasma is ignited, the pressure is always set to a low pressure, for example, 50 mTorr or less.

  In this case, in the conventional plasma processing apparatus, if the pressure at the time of plasma ignition is 50 mTorr or less, the pressure is too low and the plasma does not ignite. Therefore, the pressure in the processing vessel is set slightly high at the time of plasma ignition. However, in the present invention, as described above, the lower surface of the central portion (microwave introduction portion) of the dielectric plate 62 constituting the top plate member 58 is ignited. Since the concave portion 64 is provided, electric field concentration occurs in this portion, and plasma ignition can be generated even at a low pressure of 50 mTorr or less in the processing vessel 44. Once the plasma is ignited, the film forming process is performed while the pressure in the processing container 44, that is, the process pressure is maintained at 50 mTorr or less.

  In this case, once the plasma is ignited, the electric field concentration in the igniting recess 64 is eliminated, so that the plasma density in this portion does not become excessively high. As described above, once the plasma is generated in the processing space S as described above, the microwave propagates outward in the radial direction while reflecting up and down in the dielectric plate 62 by the surface wave plasma described above, and from the peripheral portion. This is because the dimensions of the ignition recess 64 are set so that the reflected waves cancel each other in the ignition recess 64.

  Further, here, since the protrusions 86, 88, and 90 having tapered surfaces are provided at the central portion, the middle peripheral portion, and the peripheral portion of the dielectric plate 62, respectively, this is also described in Japanese Patent Laid-Open No. 2005-100931. As described above, since the resonance region can be formed under any plasma conditions, for example, the plasma density can be increased and the plasma can be stably formed even if the process pressure changes.

  Here, the relationship between the diameter D of the ignition recess 64 and the electric field strength on the inner peripheral surface of the ignition recess 64 during plasma ignition (more specifically, the edge portion between the side surface and the bottom surface of the recess) was evaluated. The evaluation result will be described with reference to FIG. In FIG. 4, λ represents the wavelength of the microwave in the dielectric plate 62. As is clear from FIG. 4, when the diameter D is 3 · λ / 8, the electric field strength is the largest and the electric field concentration occurs, which is the peak point of the electric field strength. The electric field strength is rapidly decreasing. At 2 · λ / 8 and 4 · λ / 8, the electric field strength is reduced to about 65% of the electric field strength at the peak. When the electric field concentration is lower than the electric field strength at this time, the electric field concentration is 50 mTorr or less. Plasma ignition did not occur at low pressure. Therefore, it can be understood that the upper limit of the diameter D of the ignition recess 64 is 4 · λ / 8, and the lower limit is 2 · λ / 8. In the actual plasma processing, unless the film quality is a problem, the upper limit of the process pressure including the pressure at the time of plasma ignition is about 2 Torr.

As described above, since the ignition concave portion 64 for concentrating the electric field at the time of plasma ignition is provided inside the processing container 44 of the dielectric plate 62 to be the top plate member 58, the pressure in the processing container 44 is lowered. Even if this is done, the ignitability of the plasma can be improved.
Therefore, it is possible to prevent the film formation from being performed in a state where the pressure in the processing container 44 is high, and thus it is possible to improve the electrical characteristics of an insulating film made of a low dielectric constant material to be formed.

<Change in electric field strength by simulation>
Next, since the change of the electric field strength in the top plate member at the time of plasma ignition was obtained by simulation, the simulation result will be described. FIG. 5 is a schematic diagram showing the simulation results of the electric field strength of the conventional top plate member and the top plate member of the present invention during plasma ignition. FIG. 5 (A) shows a conventional top plate member, and FIG. 5 (B) shows the top plate member of the present invention, both showing the electric field distribution during plasma ignition and the state of the electric field distribution after plasma ignition.

  The conventional top plate member 8 shown in FIG. 5 (A) has the same structure as that described in FIG. 9, and the material thereof is made of aluminum nitride. The diameter D1 of the recess formed in the upper surface of the central portion is In order to cancel the microwave propagating here and prevent electric field concentration, it is set to about 30 mm. Further, the top plate member of the present invention shown in FIG. 5B uses the one described above, and the material thereof is made of aluminum nitride, and the diameter D of the ignition recess 64 is set to 20 mm. Both microwave frequencies are 2.45 GHz.

As shown in FIG. 5A, in the conventional top plate member 8, even when the plasma is ignited and after the plasma is ignited, there is almost no electric field concentration at the center of the top plate member. It can be understood that the electric field distribution is relatively uniform and the plasma is stably formed.
On the other hand, in the top plate member 58 of the present invention shown in FIG. 5 (B), it can be understood that a large electric field concentration is generated in the central portion of the ignition recess 64 when the plasma is ignited. Once the plasma is ignited and the plasma is stabilized, it can be understood that the electric field concentration in the ignition recess 64 is eliminated and the electric field distribution is relatively uniform.

  Thus, it was confirmed from the simulation that the top plate member 58 of the present invention caused electric field concentration in the ignition recess 64 only during plasma ignition, and that this electric field concentration could be eliminated after ignition.

<Verification of actual top plate member>
Next, the top plate member used in the above-described simulation was actually produced, and the presence or absence of plasma ignition was verified. The result will be described.
FIG. 6 is a diagram showing the results when verifying the presence or absence of plasma ignition between the conventional top plate member and the top plate member of the present invention. Here, the pressure at the time of plasma ignition in the processing vessel is variously changed within a range of 10 to 200 mTorr, and the microwave power is also variously changed within a range of 1000 to 3000 watts.

  Ar gas is supplied as a plasma gas. In the figure, “◯” indicates that plasma ignition occurred, and no mark (blank) indicates that plasma ignition could not be performed. As shown in FIG. 6A, in the case of the conventional top plate member, when the pressure in the processing vessel is in the range of 80 to 200 mTorr, plasma ignition occurs in all the microwave powers in the range of 1000 to 3000 watts. However, when the pressure was 50 mTorr or less, plasma ignition did not occur no matter how the microwave power was changed within the above range.

  On the other hand, in the case of the top plate member of the present invention shown in FIG. 6B, if the pressure in the processing container is in the range of 80 to 200 mTorr, the conventional top plate member of FIG. Similarly, plasma ignition occurred in all of the range of 1000 to 3000 watts. Further, when the pressure in the processing vessel is within a range of 10 to 50 mTorr, plasma ignition does not occur when the microwave power is within a range of 1000 to 1600 watts, but plasma ignition can be performed within a range of 1800 to 3000 watts. did it. Generally, the microwave power is often used in the vicinity of about 2500 watts. Therefore, according to the top plate member of the present invention, the conventional top plate member could not perform plasma ignition. It was confirmed that plasma ignition could be sufficiently performed even at a low pressure of 10 to 50 mTorr.

<Second embodiment>
In the first embodiment, the case where the projecting portions 86, 88, 90 are provided on the lower surface of the top plate member 58 has been described, but one type selected from these three types of projecting portions or Only two types of protrusions may be provided, or an ignition recess may be provided on a top plate member having a flat bottom surface where no protrusions are provided. FIG. 7 shows a cross-sectional view of the second embodiment of the top plate member of the present invention, in which an ignition recess 64 is provided in the center of the top plate member 58 having a flat bottom surface (planar shape). Shows the case.

  The dimensional conditions of the diameter and depth of the ignition recess 64 are the same as those in the first embodiment. In the case of the second embodiment, the uniformity of the electric field distribution is slightly lower than in the case of the first embodiment, but plasma ignition can be caused even at a low pressure of about 10 to 50 mTorr. The same operational effects as in the first embodiment can be exhibited.

In the present embodiment, the plasma processing apparatus using the planar antenna member 68 as a part of the microwave introducing means 66 has been described as an example. However, the present invention is not limited thereto, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-40397. As described above, a so-called waveguide slot type plasma processing apparatus in which a slot is directly formed on the lower surface of the annular rectangular waveguide and the waveguide with the slot is directly installed on the upper surface of the top plate member. The present invention can also be applied to.
Although the plasma film formation process is described as an example of the plasma process here, the present invention can be applied to all plasma processes such as a plasma etching process, a plasma ashing process, and a plasma cooling process.

Furthermore, the Ar gas is described as an example of the plasma gas here, but the present invention is not limited to this, and other rare gases such as He and Ne may be used. Any gas that can be dissociated may be used.
Although the semiconductor wafer is described as an example of the object to be processed here, the present invention is not limited thereto, and the present invention can be applied to a glass substrate, an LCD substrate, a ceramic substrate, and the like.

It is a block diagram which shows 1st Example of the plasma processing apparatus which concerns on this invention. It is an expanded sectional view which shows the top plate member used for the plasma processing apparatus shown in FIG. It is a top view which shows the lower surface of a top-plate member. It is a graph which shows the relationship between the diameter of the recessed part for ignition provided in the top-plate member, and the electric field strength in the internal peripheral surface of the recessed part for ignition at the time of plasma ignition. It is a schematic diagram which shows the simulation result of the electric field strength of the conventional top plate member at the time of plasma ignition, and the top plate member of this invention. It is a figure which shows the result when verifying the presence or absence of the plasma ignition of the conventional top plate member and the top plate member of this invention. It is sectional drawing which shows 2nd Example of the top-plate member of this invention. It is a schematic block diagram which shows the conventional general plasma processing apparatus. It is an expanded sectional view which shows the top-plate member of the conventional general plasma processing apparatus.

Explanation of symbols

Reference Signs List 42 Plasma processing apparatus 44 Processing vessel 46 Mounting table 48 Gas introduction means 58 Top plate member 62 Dielectric plate 64 Recessed portion for ignition 66 Microwave introduction means 68 Planar antenna member 70 Slow wave member 74 Coaxial waveguide 82 Microwave generator 84 Slot 86, 88, 90 Protrusion 96 Control means 98 Storage medium W Semiconductor wafer (object to be processed)

Claims (10)

In a top plate member made of a dielectric plate that is provided on a ceiling portion of a processing vessel that can be evacuated to perform processing by plasma generated by microwaves on an object to be processed, and transmits the microwaves,
A top plate member configured to provide an ignition recess for concentrating an electric field during plasma ignition inside the processing container of the dielectric plate. 2. The diameter D1 of the ignition recess is in the range of 2 · λ / 8 ≦ D ≦ 4 · λ / 8, where the wavelength of the microwave in the dielectric plate is λ. The top plate member described. The depth H of the recess for ignition is in the range of 2 · λ / 8 ≦ H ≦ 4 · λ / 8, where the wavelength of the microwave in the dielectric plate is λ. The top plate member according to 1 or 2. The top plate member according to any one of claims 1 to 3, wherein an inner side surface of the ignition recess is set within ± 10 degrees with respect to a vertical direction. 2. The ignition recessed portion is formed in a trapezoidal projection having a trapezoidal cross section projecting inside a processing container at a central portion of the dielectric plate in order to form a resonance region for the microwave. The top plate member in any one of thru | or 4. The top plate member according to any one of claims 1 to 5, wherein the pressure in the processing container is set in a range of 10 mTorr to 2 Torr when the plasma is ignited. A processing vessel in which the ceiling is opened and the inside can be evacuated;
A mounting table provided in the processing container for mounting the object to be processed;
Gas introduction means for introducing gas in the processing container;
The top plate member according to any one of claims 1 to 6, which is airtightly attached to the opening of the ceiling portion,
Microwave introduction means for introducing microwaves into the processing container through the top plate member;
A plasma processing apparatus comprising: The microwave introducing means is
A planar antenna member provided on the top plate member and formed with a plurality of slots for radiating microwaves;
A microwave generator for generating microwaves;
A waveguide for guiding the microwave generated by the microwave generator to the planar antenna member;
The plasma processing apparatus according to claim 7, further comprising: The microwave introducing means is
A waveguide provided on the top plate member and formed with a plurality of slots for radiating microwaves;
A microwave generator for generating the microwave;
The plasma processing apparatus according to claim 7, further comprising: A processing vessel in which the ceiling is opened and the inside can be evacuated;
A mounting table provided in the processing container for mounting the object to be processed;
Gas introduction means for introducing gas in the processing container;
The top plate member according to any one of claims 1 to 6, which is airtightly attached to the opening of the ceiling portion,
Microwave introduction means for introducing microwaves into the processing container through the top plate member;
When performing plasma processing using a plasma processing apparatus having control means for controlling the operation of the entire apparatus,
A storage medium for storing a program for controlling the plasma processing apparatus so that the pressure in the processing container is set within a range of 10 mTorr to 2 Torr when the plasma is ignited.

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