Apparatus for plasma processing

A plasma processing apparatus that generates a uniform plasma, thus allowing uniform processing of large-diameter wafers. The cylindrical apparatus includes a wafer mounting table, a silica plate providing an airtight seal, a microwave supplier for propagating a microwave in TE11 mode, and a cylindrical waveguide connected at one end to the microwave supplier. A radial waveguide box is connected between the other end of the cylindrical waveguide and the silica plate. The radial waveguide box extends radially outward from the cylindrical waveguide, forming a flange and defining an interior waveguide space. A disc-shaped slot antenna is located at the lower end of the radial waveguide box, above the silica plate. A circularly-polarized wave converter disposed in the cylindrical waveguide rotates the TE11-mode microwave about the axis of the cylindrical waveguide, and sends the rotating microwave to the radial waveguide box.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a plasma processing apparatus utilizing a microwave.

BACKGROUND OF THE INVENTION

Conventionally, there is known a plasma processing apparatus which includes a flat antenna, as shown in FIG.18.

This plasma processing apparatus71comprises a processing container73generally shaped to be cylindrical with a bottom and a silica plate75formed on the ceiling part of the processing container73in an airtight manner thereby to define a closed processing space S in the processing container73. Accommodated in the processing container73is a mounting table77on which a semiconductor wafer W is mounted. This mounting table77is connected to a bias high-frequency power source79through power lines. Further, a gas nozzle81is arranged in the sidewall of the processing container73, for introducing a process gas into the container. The processing container73is also provided, on a bottom thereof, with exhaust ports85connected with a not-shown vacuum pump.

On the other hand, a flat antenna member87is arranged on the top of the silica plate75sealing up the upside of the processing container73. The flat antenna member87is constituted as a bottom plate of a radial waveguide box89consisting of a low and disc-shaped hollow cylindrical container. The flat antenna member87is attached to a top surface of the silica plate75. A coaxial waveguide93has its outer tube93A connected to the center of an upper face of the disc-shaped radial waveguide box89. The coaxial waveguide93is also connected, at the other end, with a microwave generator91. In the coaxial waveguide93, an inside cable93B is connected to the center of the disc-shaped antenna member87.

The disc-shaped antenna member87is made from a copper plate having a number of slits95formed therein. Further, in the radial waveguide box89, a dielectric material97of predetermined dielectric constant is accommodated to shorten the wavelength of a microwave thereby accomplishing a short guide wavelength.

With the above structure, a microwave generated in the microwave generator91is propagated in the coaxial waveguide93and successively dispersed in the radial waveguide box89in the radial direction. Then, the microwave is discharged downward from the slits95of the antenna member87thereby to form a plasma in the processing container73.

However, since cables inside the coaxial waveguide are easy to be heated in the above processing apparatus71, such an overheating operation may cause an abnormal discharging of electricity in the apparatus. In order to prevent the occurrence of abnormal discharging, it is necessary to provide the “so-slender” inside cable with a cooling mechanism. However, this countermeasure would cause the structure of the apparatus to be complicated with an excessive increase in manufacturing cost. Additionally, since the countermeasure requires a supporting structure for the inside cable, a new problem arises in that it might take a great deal of time to adjust an impedance accompanied by the provision of the supporting structure.

Further, due to the generation of uneven electric field formed below the flat antenna member87, the processing apparatus71has a problem of producing an uneven treatment on the wafer W. In detail, an electric field emitted downward from the slits95of the flat antenna member87is reflected on an inner wall of the processing container73to produce an uneven electric field in the processing container. Thus, the above processing apparatus betrays an uneven treatment in processing wafers, especially, large-diameter wafers.

In order to solve the above-mentioned problems, the object of the present invention is to provide a plasma processing apparatus which is capable of prevention of heat-generation of the cable inside the coaxial waveguide and which can form a uniform electromagnetic field in the processing container.

DISCLOSURE OF THE INVENTION

The first feature of the present invention resides in a plasma processing apparatus which comprises:a processing container shaped to be a cylinder with a bottom, the processing container having, inside thereof, a mounting table for mounting an object to be processed thereon;a lid body made of a dielectric material to cover an upper opening of the processing container;a microwave supplier for supplying a microwave;a cylindrical waveguide having one end connected to the microwave supplier, the cylindrical waveguide being formed so as to extend from the microwave supplier toward the lid body thereby defining a waveguide space in the cylindrical waveguide;a radial waveguide box connected to the other end of the cylindrical waveguide and also formed so as to extend from the other end of the cylindrical waveguide radially outward in form of a flange and successively extend downward therefrom in form of a sidewall, the radial waveguide box defining another waveguide space therein; anda slot antenna arranged along the lid body to cover a lower opening of the radial waveguide box, the slot antenna having a plurality of slots formed therein.

With the above constitution, it becomes unnecessary to consider the heat-generation of cables inside the coaxial waveguide and also possible to establish a uniform electromagnetic field in the processing container.

The second feature of the present invention resides in that the slot antenna is provided, at its part opposing an opening of the other end of the cylindrical waveguide, with a bump projecting toward the cylindrical waveguide inside the radial waveguide box. With this arrangement, it is possible to accomplish both introduction and propagation of a microwave from the cylindrical waveguide into the radial waveguide box effectively.

The third feature of the present invention resides in that the bump is shaped to be generally conical.

The fourth feature of the present invention resides in that the microwave to be propagated from the microwave supplier to the radial waveguide box through the cylindrical waveguide box is identical to a microwave in TM01 mode.

The fifth feature of the present invention resides in that the microwave to be propagated from the microwave supplier to the radial waveguide box through the cylindrical waveguide box is identical to a microwave in TE11 mode.

The sixth feature of the present invention resides in that the plasma processing apparatus further comprises a circularly-polarized wave converter which is arranged in the cylindrical waveguide between the microwave supplier and the radial waveguide box to rotate the microwave in TE11 mode about an axis of the cylindrical waveguide thereby transmitting a resulting circularly-polarized wave to the radial waveguide box. With the structure mentioned above, it is possible to make an electromagnetic field in the processing container uniform, thereby preventing an unevenness in producing a plasma.

The seventh feature of the present invention resides in that the slot antenna is a radiation type of antenna.

The eighth feature of the present invention resides in that the slots of the slot antenna are arranged coaxially.

The ninth feature of the present invention resides in that the slots of the slot antenna are arranged spirally.

The tenth feature of the present invention resides in that the slot antenna is a leak type of antenna.

The eleventh feature of the present invention resides in that the slots of the slot antenna are arranged coaxially.

The twelfth feature of the present invention resides in that the slots of the slot antenna are arranged spirally.

The thirteenth feature of the present invention resides in that the slots of the slot antenna are arranged on a periphery of a polygon.

The fourteenth feature of the present invention resides in that the slots of the slot antenna are arranged on radiation lines.

The fifteenth feature of the present invention resides in that a periphery between the slot antenna and the processing container has a absorbing member arranged to absorb a high frequency wave.

The sixteenth feature of the present invention resides in that the slot antenna is held by struts each made of a dielectric material. With this structure, it is possible to produce a uniform plasma.

The seventeenth feature of the present invention resides in that an interior of the radial waveguide box is filled up with a dielectric material. With this structure, it is possible to prevent a deformation of the slot antenna.

The eighteenth feature of the present invention resides in that an outer periphery inside the radial waveguide box has a absorbing member arranged to absorb a high frequency wave.

The nineteenth feature of the present invention resides in that the plasma processing apparatus further comprises, between the microwave supplier and the cylindrical waveguide:a rectangular waveguide extending from the microwave supplier;a circular-and-rectangular converter arranged between the rectangular waveguide and the cylindrical waveguide; anda cylindrical dummy load having its one end connected to the cylindrical waveguide between the circular-and rectangular converter and the circularly-polarized wave converter, the other end of the cylindrical dummy load having a microwave absorber.

The twentieth feature of the present invention resides in that the dummy load is provided, at its connecting part with the cylindrical waveguide, with a partition wall which separates an interior of the cylindrical waveguide and an interior of the dummy load and has a slit formed to be parallel with an axial direction of the cylindrical waveguide.

The twenty-first feature of the present invention resides in that the plasma processing apparatus further comprises a rod-shaped reflector arranged in the waveguide between the cylindrical waveguide and the circular-and-rectangular converter, the rod-shaped reflector consisting of a conductor bridged in a direction substantially perpendicular to an axis of the cylindrical waveguide and substantially perpendicular to an extending direction of the dummy load.

The twenty-second feature of the present invention resides in that the reflector is a plate body along a plane containing the axis of the cylindrical waveguide.

The twenty-third feature of the present invention resides in that an axis of the dummy load is arranged in a position apart from the reflector toward the circularly-polarized wave converter by a quarter of guide wavelength of a standing wave reflected by the reflector.

The twenty-fourth feature of the present invention resides in that the plasma processing apparatus further comprises a tuner arranged in the cylindrical waveguide between the circularly-polarized wave and the radial waveguide box to adjust an impedance in the cylindrical waveguide thereby to reflect a microwave, which has been returned by reflection of the radial waveguide box, toward the radial waveguide box.

The twenty-fifth feature of the present invention resides in that the tuner comprises:a plurality of stubs projecting from an inner circumferential wall of the cylindrical waveguide inwardly in a radial direction thereof, with respective adjustable projecting amounts;a stub driver for driving the stubs in the radial direction;a detector arranged inside the cylindrical waveguide between the stubs and the circularly-polarized converter to detect an intensity of electromagnetic field of a microwave in the cylindrical waveguide; anda controller for driving the stub driver on a basis of the intensity of electromagnetic field of the microwave detected by the detector thereby to change respective positions of the stubs in the radial direction for adjustment of an impedance, the controller for controlling the microwave, which has been returned from the part of the radial waveguide box, so as to reflect toward the radial waveguide box.

The twenty-sixth feature of the present invention resides in that the stubs are complete in twelve stubs which are arranged on an inner circumferential face of the cylindrical waveguide and which consist of four stubs arranged at regular intervals in a circumferential direction of the cylindrical waveguide for each level and also lined three deep along an axial direction of the cylindrical waveguide.

The twenty-seventh feature of the present invention resides in a plasma processing method for a plasma processing apparatus. In this method, the plasma processing apparatus includes: a processing container accommodating an object to be processed therein and having an upper opening covered by a lid body made of a dielectric material; a microwave supplier for supplying a microwave; a cylindrical waveguide having one end connected to the microwave supplier, the cylindrical waveguide being formed so as to extend from the microwave supplier toward the lid body thereby defining a waveguide space in the cylindrical waveguide; a radial waveguide box connected to the other end of the cylindrical waveguide and also formed so as to extend from the other end of the cylindrical waveguide radially outward and successively extend downward therefrom in form of a sidewall, the radial waveguide box defining another waveguide space therein; a slot antenna adapted so as to cover a lower opening of the radial waveguide box; and a circularly-polarized wave converter for rotating a microwave in TE11 mode supplied from the microwave supplier about an axis of the cylindrical waveguide thereby transmitting the microwave as a circularly-polarized wave to the radial waveguide box. This plasma processing method comprises the steps of:rotating the microwave in TE11 mode supplied from the microwave supplier about the axis of the cylindrical waveguide thereby transmitting the microwave as the circularly-polarized wave to the radial waveguide box;monitoring a microwave which has been reflected by the part of the radial waveguide box and subsequently returned therefrom;tuning the so-reflected microwave on a basis of a result at the monitoring step; andproducing a uniform plasma in the processing container by the tuning step.

BEST MODE OF EMBODIMENTS OF THE INVENTION

With reference to attached drawings, a plasma processing apparatus in accordance with one embodiment of the present invention will be described below, in detail.FIG. 1is a sectional view of an example of the plasma processing apparatus of the present invention.FIG. 2is a view showing a section of a circularly polarized wave converter, taken along a line II—II of FIG.1.

Although the plasma processing apparatus is embodied by a plasma etching apparatus in this embodiment, it is a matter of course that the present invention is not limited to this example only. The plasma etching apparatus2includes a processing container4having its sidewall and bottom made of a conductive material, such as aluminum, and shaped to be a cylinder with a bottom as a whole. The ceiling part of the processing container4is opened. A silica plate8having a thickness to endure a vacuum pressure is disposed on the opened ceiling part through a sealing member6, such as O-ring, in an airtight manner, thereby to form a sealed processing space S in the container.

In the processing container4, a mounting table10is accommodated to mount a semiconductor wafer W as an object to be processed, on a top surface of the table. Using “Alumite-processed” aluminum, the mounting table10is formed in the shape of a general column which is provided, at a center thereof, with a flattened projection. The lower part of the mounting table10is supported by a supporting table12shaped to be columnar by aluminum as well. The supporting table12is mounted on the bottom of the processing container4through an insulator14.

On the top surface of the mounting table10, there are provided an electrostatic chuck (not shown) and a clamping mechanism (not shown) for holding a wafer. The mounting table10is connected to a matching box18and a “bias” high-frequency power source20. The supporting table12for supporting the mounting table10is provided with a cooling jacket22for passage of a cooling water for cooling a wafer at the plasma processing.

Arranged in the sidewall of the processing container4is a gas nozzle24which is made of a silica pipe, for introducing an etching gas as the processing gas into the container. The nozzle24is connected to a processing-gas source32through a gas supply path26interposing a mass-flow controller28and a closing valve30therein.

On the periphery of the sidewall of the processing container4, there is provided, along the circumferential direction, a magnetic-field generator34, such as electromagnetic coil and permanent magnet, which generates a magnetic field in the processing space S to confine a so-produced plasma therein. Note, the magnetic-field generator34is not always required to produce a plasma and therefore, the generator may be eliminated in the modification.

The processing container4is also provided, at a bottom thereof, with exhaust ports36which are connected to a not-shown vacuum pump for allowing an interior of the processing container4to be evacuated into a designated pressure.

A microwave generator50is arranged above the silica plate8of the processing container4. A cylindrical waveguide52is connected to the microwave generator50so that a microwave generated by the generator50can be propagated in the waveguide52. As to the microwave, there can be employed microwaves in TM01 mode and TE11 mode. Particularly, it is desirable to use a circularly polarized microwave in TE11 mode in view of preventing an unevenness in producing a plasma. The operation in case of using the microwave in TE11 mode will be described as follows.

A radial waveguide box54is connected to the cylindrical waveguide52. A circularly-polarized wave converter56is disposed between the radial waveguide box54and the microwave generator50. Although there exist various kinds of circularly-polarized wave converters, this embodiment employs a circularly-polarized wave converter that, as shown inFIG. 2, two metallic columnar projections58are arranged on an inside wall of the cylindrical waveguide so as to face each other in one or plural pairs in the axial direction. The columnar projections58are positioned in respective directions at an angle of 45 with a main direction of an electric field of the TE11-mode microwave propagated from the microwave generator. This circularly-polarized wave converter rotates the main direction of an electric field of the TE11-mode microwave from the microwave generator50, about the axis of the cylindrical waveguide as a rotational center.

Being connected to the lower end of the cylindrical waveguide52, the radial waveguide box54has a flange part57extending from the lower end of the cylindrical waveguide52outward in the radial direction and a wall part59extending from the outer margin of the flange part57downward toward the silica plate8. On the lower opening of the radial waveguide box54, a slot antenna60in the form of a disc-shaped copper plate is fitted so as to overlay the above opening thereby to define a waveguide space therein. The slot antenna60is held by struts130of dielectric materials projecting from the flange part57downward, thereby preventing a deformation of the antenna.

This disc-shaped slot antenna60, which is a type of radiation antenna, has a structure similar to that of a “microwave” flat antenna to be used for communication and produces a plasma by a microwave radiated from the antenna plate. In the slot antenna60, the interval of slots is set to λg/2 or λg (λg: guide wavelength) both exhibiting a high efficiency in radiating a microwave. In this embodiment, as shown inFIG. 3, many pairs of slots101in general V-shaped arrangement are formed on concentric circles on the slot antenna. Note, as the antenna of radiation type, there may be recommended a slot antenna105where many pairs of slots103in general V-shaped arrangement are formed in a spiral manner, as shown in FIG.4.

Alternatively, the slot antenna used in this apparatus may be represented by a leak type of antenna that produces a plasma by a microwave leaking out of the antenna. The interval of slots in this leak-type antenna is normally from λ/3 to λ/40 or thereabout, which is narrower than that of the radiation-type antenna, as shown with a slot antenna107ofFIG. 5where a number of slots109are arranged on concentric circles. As to the leak-type slot antenna, there exist a slot antenna111ofFIG. 6having a number of slots113formed in spiral, a slot antenna115ofFIG. 7having a number of slots117formed in hexagonal and a slot antenna119ofFIG. 8having a number of slots121formed in radial.

Inside the radial waveguide box54, a metallic bump64is formed at the center of the disc-shaped antenna member60. This bump64is shaped so as to be a cone projecting toward the lower opening of the cylindrical waveguide52and also having a spherical tip. Owing to this provision of the bump64, it is possible to guide and propagate an electromagnetic field, which has been propagated in the cylindrical waveguide52, into the radial waveguide box54.

A space defined by the radial waveguide box54and the disc-shaped antenna member60is filled by a dielectric material66. In the circumferential part between the slot antenna60and the processing container4, an absorber68for absorbing a high-frequency wave is arranged to prevent the reflection of an electromagnetic field. Such an absorber may be arranged in an outer circumferential part inside the radial waveguide box54.

Next, the operation of the above-constructed apparatus of the embodiment will be described. First, a semiconductor wafer W is transported through a not-shown gate valve by a transfer arm and accommodated in the processing container4. Then, by moving lifter pins (not shown) up and down, the wafer W is mounted on a mounting surface of the mounting table10. Next, an etching gas whose flow rate is controlled is supplied from the gas nozzle24while a pressure in the processing container4is maintained to a designated pressure. At the same time, a microwave generated from the microwave generator50is introduced into the processing space S to produce a plasma for etching. During this operation, the application of a bias high-frequency power on the mounting table10allows an electrically-negative potential to be generated on the mounting table10, thereby allowing ions to be extracted from the plasma effectively. Note, the magnetic field generator34on the sidewall of the processing container4is provided to generate a magnetic field for confining the plasma in the container. Therefore, it is possible to produce a plasma by the microwave from the disc-shaped antenna member60, irrespective of the presence of the magnetic field generator.

In the above-mentioned structure, the “TE11 mode” microwave generated from the microwave generator50reaches the circularly-polarized wave converter56through the cylindrical waveguide52. There, the “TE11 mode” microwave is rotated about the axis of the cylindrical waveguide52and reaches the waveguide's connecting part with the radial waveguide box54. At this connecting part, as shown in FIG.9, a horizontal electric field E of the “TE11 mode” microwave is divided into left and right by the bump64and subsequently propagated toward the periphery of the radial waveguide box while changing the direction of the electric field vertically. Hereat, the so-divided electric fields are deviated from each other by an angle of 180°, on both sides of the bump64. Then, the microwave propagated toward the periphery generates an electromagnetic field in the processing space beneath the disc-shaped slot antenna60, so that the plasma is produced by the above electromagnetic field.

Hereat, since the microwave propagated in the cylindrical waveguide52is in the TE mode, an electric field F generated in the processing container4through the disc-shaped slot antenna60is unevenly and strongly distributed in the direction of the electric field E in the cylindrical waveguide52, as shown in FIG.10. Despite that, since the microwave propagated in the cylindrical waveguide52rotates about the axis of the cylindrical waveguide, the intensive electric field (parts) F is rotated as well. Therefore, in the processing space S below the disc-shaped slot antenna60, an intensity of the electromagnetic field is so equalized that an even and uniform plasma can be produced over a wide range in the space. Accordingly, when processing even a large-diameter wafer, it is possible to accomplish a uniform processing in the surface of the wafer.

As mentioned above, this plasma processing apparatus includes the processing container4shaped to be a cylinder with a bottom and having, inside thereof, the mounting table10for mounting the wafer W thereon, the silica plate8for covering the upper opening of the processing container4in an airtight manner, the microwave supplier50for supplying the “TE11 mode” microwave, the cylindrical waveguide52having one end connected to the microwave supplier50to extend toward the silica plate8and also defining a waveguide space therein, the radial waveguide box54connected to the other end of the cylindrical waveguide52and also shaped to extend from the other end of the cylindrical waveguide52radially outward thereby forming a flange and successively extend toward the lid body downward thereby forming a sidewall and defining a waveguide space therein, the disc-shaped slot antenna60arranged along the silica plate8to cover the lower opening of the radial waveguide box54and having the plural slots101, and the circularly-polarized wave converter56disposed in the cylindrical waveguide52between the microwave supplier50and the radial waveguide box54to rotate the “TE11 mode” microwave provided from the microwave supplier50about the axis of the cylindrical waveguide52and further send the rotating microwave to the radial waveguide box54. Therefore, it is possible to rotate the “TE11 mode” microwave, which has been propagated in the cylindrical waveguide52, about the axis of the cylindrical waveguide and also possible to cause the microwave having its phase reversed to be propagated toward the periphery of the radial waveguide box54. Accordingly, in the processing space S below the disc-shaped slot antenna60, it is possible to make an intensity of plasma even and uniform over a wide range in the space. Thus, when processing even a large-diameter wafer, it is possible to accomplish a uniform processing in the surface of the wafer. Additionally, it is possible to prevent cables inside the coaxial waveguide from being heated.

Although this plasma processing apparatus is capable of producing a uniform plasma in the processing space as mentioned above, there has been found a slight unevenness in the distribution of plasma in accordance with a more detailed measurement. It is believed that this phenomenon comes from the following reasons.

That is, as shown inFIG. 11, a “TE11 mode” traveling wave155falling in an upper cylindrical waveguide151is rotated in a clockwise direction by the circularly-polarized wave converter56and falls in a lower cylindrical waveguide153while rotating as shown with a reference numeral157. This microwave157is divided into left and right by the bump64and directs toward the periphery of the radial waveguide box54, so that the microwave is propagated into the processing space through the disc-shaped slot antenna60. Nevertheless, this microwave is extremely partially reflected by the slot antenna60in the processing container, so that the so-reflected microwave is propagated upward in the lower cylindrical waveguide153while retracing in the opposite route, as shown with a reference numeral159. When this microwave reaches the upper cylindrical waveguide151through the circularly-polarized wave converter56, it becomes a “TE11 mode” microwave that does not rotate, as shown with a reference numeral161. This microwave is reflected on a waveguide's connecting part173with a rectangular waveguide171, so that the phase of microwave is reversed. Then, the so-reflected microwave as a traveling wave, falls in the cylindrical waveguide151, as shown with a reference numeral163. Next, by passing through the circularly-polarized wave converter56again, the microwave is rotated and falls in the lower cylindrical waveguide153, as shown with a reference numeral165. Here, due to a plane of polarization different from that of the traveling wave155by an angle of 90°, the microwave165rotates in the counter-clockwise direction against the rotating direction of the microwave157. In this way, it is supposed that the distribution of microwave becomes uneven because the microwave165in the counter-clockwise direction interferes with the proper microwave157in the clockwise direction.

Provided to improve such a drawback is a plasma processing apparatus200of the second embodiment which is shown inFIGS. 12to14.

InFIG. 12, reference numeral201designates a rectangular waveguide. The rectangular waveguide201is connected to a not-shown microwave generator. The rectangular waveguide201is bent at a corner part203by an angle of 90° and further connected to a circular-and-rectangular converter205. A cylindrical waveguide207is connected to the circular-and-rectangular converter205. Below the cylindrical waveguide207, there is provided a circularly-polarized wave converter209which rotates a microwave in TE11 mode about an axis of the converter. A flange-shaped radial waveguide box211is connected to the lower part of the circularly-polarized wave converter209succeeding the cylindrical waveguide207, allowing a microwave to be propagated from the slot antenna on a lower face of the radial waveguide box211into the processing container.

In the above plasma processing apparatus, a dummy load215in the form of a rectangular cylinder is arranged on the upper part of the cylindrical waveguide207, in the vicinity of a waveguide's connecting part213with the circular-and-rectangular converter205. This dummy load215extends in a direction perpendicular to the axis of the cylindrical waveguide207, at a position of a distance L away from the connecting part between the cylindrical waveguide207and the circular-and-rectangular converter205. Hereat, it is desirable that when a microwave propagated in the cylindrical waveguide207in the opposite direction is reflected at the connecting part213thereby to form a standing wave, the distance L becomes equal to a quarter of a wavelength of the standing wave and further, the dummy load215has its axis positioned at an antinode of the standing wave. The dummy load215is provided, at an end thereof, with a microwave absorber217. For example, as shown inFIG. 14, the microwave absorber217may be formed to be a cone storing water therein, allowing a microwave to be absorbed by the cone. The dummy load215is provided, in its part close to the cylindrical waveguide207, with a shutter219which makes it possible to interrupt the absorption of microwave by the dummy load215optionally. At the connecting part of the dummy load215with the cylindrical waveguide207, a shield plate221is provided with a slit223in parallel with the axis of the cylindrical waveguide207. The slit223is formed to have, for example, a length of 50 to 120 mm and a width of 2 to 20 mm. Additionally, at the connecting part213, a rod-shaped reflecting plate225is arranged so as to be perpendicular to the axis of the cylindrical waveguide and also a projecting direction of the dummy load215. The reflecting plate225is made of conductor and shaped in the form of a plate in a direction along a plane containing the axis of the cylindrical waveguide207.

In the above-mentioned structure of the present invention, when a microwave, which has be propagated from the radial waveguide box211in the opposite direction, passes through the circularly-polarized wave converter209and reaches the connecting part213between the cylindrical waveguide207and the circular-and-rectangular converter205, the microwave reflects at the connecting part213without entering into the rectangular waveguide201. Particularly, since the plasma processing apparatus200has the reflecting plate225arranged at the connecting part213, the microwave is reflected at the plate225thereby to form a standing wave C having a node at the reflecting plate225, as shown in FIG.14. Since the axis of the dummy load215, i.e. a center of the slit is positioned apart from the connecting part213by a quarter of a wavelength of the standing wave, the antinode of the standing wave C coincides with the center of the slit223. Then, the standing wave is propagated into the dummy load215through the slit223and subsequently absorbed in the absorber217.

In this way, since the microwave reflected from the radial waveguide box211is absorbed in the dummy load, there is no possibility that the microwave is propagated toward the radial waveguide box211again. That is, since the uniformity of the microwave propagated from the radial waveguide box211into the processing container is not disturbed, it is possible to maintain the uniformity of plasma in the processing container at a higher level.

FIGS. 15 and 16are respective diagrams showing experimental results of the above-mentioned effect. These figures are obtained by measuring the intensity of saturated ionic currents on the mounting table. The measurement has been carried out at a center R1of the mounting table and also in respective angular positions in the circumferential direction of respective circumferences of radii R2, R3and R4(the outermost circumference). The measuring results are designated in the form of graphs.

In these figures,FIG. 15illustrates the measured saturated ionic currents on condition of closing the shutter219in the dummy load215, that is, an inactivated condition of the dummy load215. From this figure, it will be understood that, in the state of the inactivated dummy load215, the saturated ionic currents on the mounting table vary widely in the circumferential direction and additionally, such a tendency is remarkable in the outer peripheral position particularly.

To the contrary,FIG. 16shows a situation to open the shutter219, in other words, an activated condition of the dummy load215. From this figure, it will be understood that the saturated ionic currents on the mounting table represent respective constant values in all cases of both circumferential direction and radial direction and therefore, an influence due to the reflection of microwave is reduced remarkably.

Referring toFIG. 17, we describe a plasma processing apparatus300in accordance with the third embodiment whose effect is similar to that of the second embodiment.

The cylindrical waveguide207is provided, at a lower part thereof, with a tuner311. This tuner311has a plurality of stubs313formed to project from the inner circumferential face of the lower part of the cylindrical waveguide207inward in the radial direction. By projecting into the cylindrical waveguide207, these stubs313operate to change an impedance thereby to drive the microwave, which has been reflected by the radial waveguide box211, back to the same box211. The number of stubs313is twelve in total: four stubs each at regular intervals of an angle of 90° in the circumferential direction; and three pairs of stubs at regular intervals in the axial direction of the cylindrical waveguide. For these stubs313, there are provided stub drivers315which drive the stubs313to the radial direction, respectively.

Detectors317are arranged on the inner circumferential face of the cylindrical waveguide207between the stubs313and the circularly-polarized wave converters209. The detectors317are provided to detect the microwave that has been reflected by the radial waveguide box211. The number of detectors317is twelve in total: four detectors each at regular intervals of an angle of 90° in the circumferential direction; and three pairs of detectors at regular intervals of λg/8 in the axial direction.

The apparatus further includes a controller319. Based on the intensity of an electromagnetic field of microwave measured by the detectors317, the controller319drives the stub drivers315to change the positions of the stubs313in the radial direction, thereby adjusting an impedance in tuning.

With the constitution mentioned above, the microwave propagated from the radial waveguide box211in the opposite direction is detected by the detectors317and the so-obtained measurement is transmitted to the controller319. Then, on a basis of the intensity of the electromagnetic field of microwave measured by the detectors317, the controller319calculates the positions of the stubs313in the radial direction required to reflect the microwave, which has been returned from the part of the radial waveguide box211, toward the same box211again. Continuously, the controller319outputs a drive command of the stubs313to the stub drivers315. In accordance with the drive command, each of the stub drivers315changes the radial-directional position of the stub313to adjust the impedance for tuning, whereby the returned microwave is reflected toward the radial waveguide box211.

In this way, according to the plasma processing apparatus300, since the reflection wave from the radial waveguide box is tuned and reflected in front of the circularly-polarized wave converter209, the rotating direction of the circularly-polarized wave is not reversed. Accordingly, it is possible to propagate a uniform microwave from the slot antenna, thereby accomplishing a uniform plasma processing.

Next, the matching operation for circularly-polarized wave by this tuner will be described.

As to the circularly-polarized wave in TE11 mode in the circular waveguide, the rectangular waveguide is replaced by the circular waveguide thereby to produce the “TE11 mode” circularly-polarized wave by the circularly-polarized wave generator having a phase plate etc. arranged in the part of the circular waveguide.

It is noted that the reflection wave from the load of the circular waveguide travels in the opposite direction of the traveling wave and rotates in the same direction as the traveling wave.

Therefore, in the part of the circular waveguide, a standing wave produced by the reflection wave is identical to a standing wave of the TE11 mode (not a circularly-polarized wave) in the axial direction of the waveguide at a position of a constant angle.

As to the angular direction, since a standing wave is generated in the circumference, it is also possible to detect the standing wave in this direction.

As to the detection of the standing wave, there are provided three to five styluses at regular intervals of λg/8 of the guide wavelength, so that the detector detects a microwave detected by the styluses (three to five styluses at regular intervals of an angle of 45° in the circumferential direction).

For example, in case of detecting the standing wave by four styluses, the absolute value of voltage is calculated by the following expression.
|V|=|Vi|√{square root over ( )}[1+|Γ|2+2|Γ| cos (θ−2β1)]

Therefore, there are established the following expressions.
V1−V3=4K|Vi|2|Γ| cos θ
V4−V2=4K|Vi|2|Γ| sin θ

Since this signal contains the information of both reflection coefficient |Γ| and phase θ, if normalizing the member of 4K|Vi|2in the above equations, then the values of |Γ| cos θ, |Γ| sin θ are calculated to allow an impedance of load to be calculated.

Alternatively, in case of detecting the standing wave by three styluses, there are established the following expressions:
V1=K|Vi|2(1+|Γ|2+2|Γ| cos θ)
V2=K|Vi|2(1+|Γ|2−2|Γ| sin θ)
V3=K|Vi|2(1+|Γ|2−2|Γ| cos θ)
V1−V3=4K|Vi|2|Γ|2cos θ
[(V1+V3)/2]−V2=4K|Vi|2|Γ| sin θ

Similarly, the values of |Γ| cos θ, |Γ| sin θ are calculated to obtain the impedance of load in calculation.

Note, even if there are provided, at regular intervals of an angle of 45° in the circumferential direction of the circular waveguide, three or more detection terminals in place of the detectors in the axial direction, the impedance of load can be calculated similarly.

That is, the use of either three to four detectors in the axial direction or four detectors in the circumferential direction employing allows an automatic matching operation to be realized.

If only calculating the positions of three stubs arranged at intervals of (λg/8) to (λg/4) (recommended) by using the so-calculated impedance of load by means of a microcomputer and subsequently adjusting the positions of three stubs, then a matching can be accomplished.

When the stubs of plural number (e.g. four) are arranged in the circumferential direction, the circumferential balance for circular polarized wave is so improved as to allow of automatic matching against the large reflection of load.

Note, although the plasma processing apparatus200equipped with the dummy load215and the plasma processing apparatus300equipped with the tuner311have been described independently of each other in the above-mentioned embodiments, the present invention is applicable to a plasma processing apparatus equipped with both of dummy load and tuner, of course.

Additionally, although the plasma processing apparatus is applied to the plasma etching apparatus in common with the above embodiments, the present invention may be applied to other processes, for example, film-deposition process, process to improve properties of film, etc.

According to the present invention, the plasma processing apparatus includes the processing container shaped to be a cylinder with a bottom, the processing container having, inside thereof, the mounting table for mounting an object to be processed thereon, the lid body made of a dielectric material to cover an upper opening of the processing container, the microwave supplier for supplying a microwave, the cylindrical waveguide having one end connected to the microwave supplier, the cylindrical waveguide being formed so as to extend from the microwave supplier toward the lid body thereby defining a waveguide space in the cylindrical waveguide, the radial waveguide box connected to the other end of the cylindrical waveguide and also formed so as to extend from the other end of the cylindrical waveguide radially outward in form of a flange and successively extend downward therefrom in form of a sidewall, the radial waveguide box defining another waveguide space therein and the slot antenna arranged along the lid body to cover a lower opening of the radial waveguide box, the slot antenna having a plurality of slots formed therein. Therefore, it is possible to prevent an inside cable from generating heat, which might be caused in using a coaxial waveguide. Furthermore, it is possible to produce a uniform plasma in the processing container, thereby allowing an even treatment to be applied on even a large-diameter wafer.