Patent Application
20110132540
This invention relates to a plasma processing apparatus, or in particular, to a plasma processing apparatus for etching or otherwise processing a sample using a plasma formed in a processing chamber by supplying a high frequency to a coil-shaped antenna wound on the outer periphery of a processing chamber.
Generally, in the etching apparatus described above, a reaction product formed from a certain type of the processing gas and the material of the film arranged on the surface of a substrate-like sample such as a semiconductor wafer to be etched is attached to the inner wall surface of the processing chamber in the processing chamber. It is known that such a product deposited on the inner wall surface, if increased in amount, is peeled off or separated from the wall surface and, by attaching again to the sample surface, produces the contaminating matter which pollutes the sample surface.
Also, the deposition of such a product is known to deteriorate the stability of the process of etching, for example, Al2O3 with Cl2 or SiO2 with CF as a processing gas. In view of this, the conventional techniques are known to reduce the product attached to the inner wall surface of the processing chamber.
As an example of the conventional techniques, a Faraday shield is arranged between a plasma and a coil-shaped antenna wound on the outer periphery of a vacuum vessel and supplied with high-frequency power to suppress or remove the deposition on inner wall of the vacuum vessel. Such a conventional technique is disclosed, for example, in JP-A-2000-323298. According to the technique disclosed in JP-A-2000-323298, a plasma is formed in a processing chamber of an insulating material due to an induction field or a magnetic field formed by the high-frequency power supplied to a coil-shaped antenna. With the power supplied to the Faraday shield, the charged particles forming the plasma are attracted and impinged on the product on the inner wall surface of the processing chamber by the potential difference with the potential of a predetermined magnitude maintained on the inner wall of the processing chamber thereby to remove the product.
Another method using the Faraday shield is known in which the film of a specified metal is arranged on the outer wall surface of the processing chamber to function as a Faraday shield. For example, JP-A-2004-235545 discloses a technique of forming by spraying a tungsten film on the outer wall surface of a processing chamber of an insulating material.
The conventional techniques described above have posed a problem for lack of full consideration of the following points.
Specifically, in the case where a film is formed on the outer surface of the vacuum vessel as disclosed in JP-A-2004-235545, the gap between the filmy Faraday shield and the outer wall surface of the vacuum vessel is removed, so that the electrostatic capacitance between the Faraday shield and the plasma can be reduced to a minimum. As compared with the prior art, therefore, the deposition can be suppressed or removed with a higher effect on the one hand, while the fact that, as in the prior art configured of a tabular member, the Faraday shield has a planar shape with a slit portion extending in longitudinal (vertical) direction leads to the disadvantage that the electrostatic field formed by the power supplied to the Faraday shield fails to work on the portion of the processing chamber immediately under the slit portion (the inner wall surface of the processing chamber corresponding to the internal space of the slit portion).
Specifically, in the slit portion, the charged particles are not attracted to the inner wall surface of the vacuum vessel or so attracted considerably less than in the left and right non-slit portions (the inner wall surface having the outer periphery covered with a tabular or filmy member), thereby reducing the sputtering effect. As a result, a large difference develops in the amount of the attached product or deposition between the respective inner wall surface portions of the vacuum vessel corresponding to the slit and non-slit portions, and therefore, it is difficult to remove the attached product uniformly. This poses the problem that the processing operation along the peripheral direction of the sample (the peripheral direction of the processing chamber in the shape of a cylinder or a cone (truncated cone)) becomes disuniform and unstable with the result that the configuration of the Faraday shield makes it impossible to realize a uniform process.
An object of this invention is to provide a plasma processing apparatus capable of realizing a more uniform process. Another object of the invention is to provide a plasma processing apparatus which suppresses the generation of the contaminating matter for an improved yield.
In order to solve the problem described above, according to one aspect of this invention, there is provided a plasma processing apparatus in which a wafer placed on a sample stage arranged in a processing chamber inside a vacuum vessel is processed using the plasma formed in the particular processing chamber, comprising a dielectric bell jar making up the upper part of the vacuum vessel and surrounding the processing chamber, a coil-shaped antenna wound on the outer periphery of the bell jar and supplied with the high-frequency power to form the plasma, and a Faraday shield of a dielectric material formed in double layers including inner and outer layers in spaced relation to each other between the antenna and the bell jar, wherein the slits of one of the inner and outer layers of the Faraday shield are arranged to cover the film portions between the slits of the other of the inner and outer layers in staggered fashion.
According to another aspect of the invention, there is provided a plasma processing apparatus, wherein the Faraday shield is formed of a plurality of film layers arranged on the outer peripheral wall surface of the bell jar.
According to still another aspect of the invention, there is provided a plasma processing apparatus, wherein the high-frequency power is supplied to the Faraday shield.
According to yet another aspect of the invention, there is provided a plasma processing apparatus, wherein each member between the adjacent slits of the outer Faraday shield portion is arranged to cover the whole gaps of the slits of the inner Faraday shield portion in the peripheral direction of the wafer.
According to a further aspect of the invention, there is provided a plasma processing apparatus, wherein an insulating film is arranged between the inner and outer Faraday shield portions.
According to a still further aspect of the invention, there is provided a plasma processing apparatus, wherein the inner or outer Faraday shield portion is formed by spraying.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
The plasma processing apparatus according to an embodiment of the invention is explained below with reference to the drawings.
The vessel includes the cylindrical vacuum vessel 2 and a bell jar 12 formed of an insulating material (such as quartz, ceramic or other nonconductive material) arranged above the cylindrical vacuum vessel 2 and coupled to the vacuum vessel 2 to enclose the internal cylindrical space. The bell jar 12, having a trapezoidal longitudinal section, is in the shape of a truncated cone symmetric about the vertical center axis passing through the circular cross section thereof. The vacuum processing chamber providing a space in the bell jar 12 is surrounded by the inner wall surface of the vacuum vessel 2 and the bell jar 12, which are coupled to each other in such a manner that the interior of the plasma processing apparatus 100 can be sealed hermetically against the external atmospheric environment.
The vacuum processing chamber providing the internal space of the vessel has therein a sample stage 5 on which a substrate-like sample 13 is mounted in parallel to the inner wall surface of the top flat portion of the bell jar 12. The internal space of the vacuum processing chamber above the sample stage 5 forms an area where, as described later, the pressure is reduced to a predetermined vacuum degree to generate a plasma 6 and the sample 13 is processed using the plasma 6. Also, the sample stage 5 makes up the upper part of a cylindrical sample holder 9 including the sample stage 5. The space between the outer periphery of the sample holder 9 and the cylindrical inner wall of the vacuum vessel 2 makes up the vacuum processing chamber as a passage through which a gas, containing the particles of the products generated by processing the plasma 6 formed above the sample 13, the processing gas supplied and the sample 13, is discharged by flowing down.
The coil-shaped antenna 1 is wound in a plurality of layers on the outer periphery of the outer inclined wall surface of the bell jar 12. The antenna 1 according to this embodiment, divided into a plurality of positions of different heights, has an upper antenna portion 1a and a lower antenna portion 1b. Further, a filmy Faraday shield 8 is arranged along the exterior of the inclined outer wall surface of the bell jar 12 in such a manner as to cover the particular inclined surface.
The bell jar 12 according to this embodiment is mounted on and coupled hermetically to the upper part of the vacuum vessel 2, and arranged with the circular lower end thereof located above the upper sample mounting surface of the sample stage 5 to surround the sample 13 circumferentially above it. The Faraday shield 8 arranged to cover the outer periphery of the bell jar 12 and the coil-shaped antenna 1 wound on the outside of the Faraday shield 8 are arranged to surround the outer periphery of the vacuum processing chamber to form the plasma 6 above the sample stage 5 or the sample 13 mounted thereon.
The Faraday shield 8 according to this embodiment is arranged to cover the outer wall surface including the inclined surface and the top flat portion of the bell jar 12. The Faraday shield 8 is connected in series to a high-frequency power supply (first high-frequency power supply) 10 through a matching box 3. While the sample 13 is processed, the Faraday shield 8 is maintained at a predetermined potential in its entirety and capacitively coupled to the plasma 6 having a specified potential as a dielectric material. The upper antenna portion 1a, the lower antenna portion 1b and the Faraday shield 8 are also connected with a series resonant circuit (a variable capacitor VC3 and a reactor L2) having the impedance variable magnitude in parallel between the Faraday shield 8 and the earth.
The potential of the Faraday shield 8 is adjusted to a predetermined level by the matching box 3 including the series resonant circuit. Especially, the potential of the Faraday shield 8 according to this embodiment is adjustable to an arbitrary positive or negative value as well as the earth potential. This value can be set, for example, to attract the charged particles in the plasma in the vacuum processing chamber toward the Faraday shield 8 and impinge them on the surface of the bell jar 12. By the impingement of the charged particles, the product deposited is released again physically or chemically into the internal space of the vacuum processing chamber thereby to reduce the deposition.
A gas feed pipe 4a connecting the vacuum vessel 2 and a gas source 4 of the processing gas supplied into the vacuum processing chamber is coupled to the upper end portion of the vacuum vessel 2. The processing gas flowing in the gas feed pipe 4a from the gas source 4 is supplied into the vacuum processing chamber from an opening facing it. Also, by the operation of an exhaust unit 7 arranged under and coupled to the vacuum vessel 2, the gas in the vacuum processing chamber is discharged from an opening at the lower part of the vacuum processing chamber communicating with the exhaust unit 7, so that the internal pressure of the vacuum processing chamber is reduced to a predetermined level.
The exhaust unit 7 includes an exhaust pump such as a turbo molecular pump generally used in the technical field of the invention, and an opening communicating between the exhaust pump and the interior of the vacuum processing chamber is formed at a designed horizontal distance from the center axis of the sample stage 5 under the vacuum vessel 2. On the path communicating between this opening and the inlet of the exhaust pump, there are horizontally arranged a plurality of exhaust valves adapted to increase or decrease the open area of the particular path by rotating around the axis thereof. The pressure is regulated by rotating these exhaust valves to adjust the flow area of the path and the exhaustion rate.
The processing gas supplied into the vacuum processing chamber through the gas feed pipe 4a is converted into a plasma by the operation of the electric field or the magnetic field generated by the power supplied to the upper antenna portion 1a and the lower antenna portion 1b. The electrode arranged in the sample stage 5 is connected with a substrate bias power supply (second high-frequency power supply) 11, from which power is supplied to the electrode thereby to form the bias potential above the sample stage 5 and the sample 13 placed thereon. In accordance with the potential difference between this bias potential and the potential of the plasma 6, the charged particles such as ions existing in the plasma 6 can be attracted onto the sample 13 so that the sample 13 can be processed at a high processing rate as desired.
Incidentally, the power supplied from the high-frequency power supply 10 is the high-frequency power of, for example, 13.56 MH or a higher frequency in VHF band. By supplying this high frequency power to the antenna 1 or the Faraday shield 8, an induction field or a magnetic field is formed to generate the plasma 6 in the vacuum processing chamber. In the process, the impedance of the antenna 1 is rendered to coincide with the output impedance of the high-frequency power supply 10 using the matching box 3, thereby making it possible to suppress the power reflection. According to this embodiment, variable capacitors VC1, VC2 connected in the form of an inverted L as shown, for example, are used as the matching box 3.
According to this embodiment, the sample 13 such as a semiconductor wafer is transported through a carrier chamber (held by a vacuum robot arm not shown) coupled to the outer side wall of the internally decompressed vacuum vessel 2, and after being delivered onto a plurality of pins on the sample stage 5 in the vacuum processing chamber, placed on the circular upper surface of the sample stage 5 and held there by adsorption. With a heat transmission gas supplied between the back of the sample 13 and the sample stage 5, the particles of the processing gas supplied into the vacuum processing chamber above the sample 13 are dissociated by the induction or magnetic field supplied from the antenna 1. In this way, a plasma due to the inductive coupling, i.e. the plasma 6 of what is called the induction type is formed. At the same time, the substrate bias is formed above the sample 13 and the sample is processed by the power supplied to the electrode in the sample stage 5.
A predetermined process of the sample 13 is started and, after detection of the end of the process, the adsorption is ceased and the sample 13 is retrieved in the reverse order of the delivery steps.
According to this embodiment, the Faraday shield 8 exhibits a crucial effect in generating the plasma 6. In the absence of the Faraday shield 8, each part of the coil of the antenna 1 impressed with a voltage by the high-frequency power supplied to the antenna 1 would have an arbitrary potential. As a result, the electrostatic coupling would occur between the coil of the antenna 1 and the plasma 6 having a potential in the vacuum processing chamber. Therefore, the inner wall surface of the bell jar 12 in the neighborhood of the antenna 1 wound on the outer periphery of the inclined surface portion would be locally scraped off by the impingement of the charged particles from the plasma 6, and the inner wall surface of the vacuum processing chamber would be consumed unevenly.
Further, this change in the wall surface state changes the coupling between the antenna 1 and the plasma 6 in the bell jar 12, resulting in the adverse effect of changing the etching characteristic such as the etching rate, uniformity or the processing verticality on the surface of the sample 13. To alleviate this problem, the plasma 6 and the Faraday shield 8 are arranged and a predetermined potential is applied to the Faraday shield 8 to reduce the potential difference between the inner wall surface of the bell jar 12 and the plasma 6. Furthermore, as in this invention, the potential supplied to and formed in the Faraday shield 8 is adjusted in such a manner as to remove the deposits attached on the inner wall surface of the bell jar 12 by the impingement of the charged particles from the plasma 6. In this way, the consumption of the inner wall surface of the bell jar 12 can be suppressed while at the same time preventing the change in uniformity and the secular variation of the process for an improved yield.
In the conventional processing apparatus using the Faraday shield 8 described above, a large difference occurs in the amount of deposits between the inner wall surface of the bell jar 12 immediately under the slits and the material between the slits of the Faraday shield 8. Specifically, a large amount of deposits are attached on the inner wall surface of the bell jar 12 just inside the slits, whereas the deposits just inside the material between the slits are small in amount. Thus, the deposits on the inner wall of the vacuum processing chamber are attached unevenly along the periphery of the sample 13 or the cylindrical periphery of the vacuum processing chamber, with the result that the sample is processed unevenly along the peripheral direction.
A gas ring 14 is an annular member arranged under the circular lower end of the bell jar 12 around the outer periphery of the vacuum processing chamber. This gas ring 14 is a member arranged at a point where at least one opening through which the processing gas supplied as described above is introduced into the vacuum processing chamber faces the vacuum processing chamber. The gas ring 14 has formed therein a gas passage, not shown, through which the processing gas (for example, Cl2, BCl3, CO or carbon fluoride such as C4F8, C5F8 or CF4) supplied from the gas feed pipe 4a flows. The processing gas, after passing through the gas passage, flows out into the vacuum processing chamber from a gas outlet 16 formed on the surface of the gas ring 14 facing the interior of the vacuum processing chamber.
According to this embodiment, an annular anti-deposition plate 15 covers, through a gap, the internal wall surface of the gas ring 14 facing the vacuum processing chamber to prevent the products or other attached substances from being deposited on the surface of the gas ring 14, or especially, the gas outlet 16. The processing gas introduced from the gas outlet 16 into the vacuum processing chamber, after passing through an outlet opening 15a formed on the anti-deposition plate 15, flows into and diffuses in the space above the sample 13. Incidentally, according to this embodiment, the anti-deposition plate 15 has the upper end thereof arranged between the lower end surface of the bell jar 12 and the upper end surface of the gas ring 14. Nevertheless, the anti-deposition plate 15 may alternatively be arranged in such a manner that the upper end portion thereof extends to cover the inner wall surface of the lower end portion of the bell jar 12.
According to this embodiment, the Faraday shield 8 is configured of a conductive thin film 17 covering the outer peripheral wall surface of the bell jar 12. Especially, as shown in
These layers are formed by a specified method on the outer surface of the bell jar 12. Especially, according to this embodiment, the layers are formed by spraying. As the result of forming the Faraday shield 8 and the insulating layers 18 by spraying as thin films, the accurate thickness of the films can be secured in both peripheral and vertical directions. As a result, the distance between the Faraday shield 8 and the plasma 6 can be accurately controlled on the one hand, and the uniformity of the amount of the substances deposited on the inner wall surface of the bell jar 12 is improved so that the deposits on the inner wall surface of the bell jar can be removed uniformly on the other hand.
Further, the configuration in which the Faraday shield 8 is formed of a plurality of layers arranged at a predetermined distance from each other makes it possible to remove the deposits with a lower voltage (Faraday shield voltage; FSV) applied to the Faraday shield 8. As a result, the consumption of the inner wall surface of the bell jar 12 by the Faraday shield 8 having the slits is alleviated. Incidentally, the principle of cleaning the inner wall surface of the bell jar 12 by the Faraday shield 8 and the method of optimizing the FSV are described in detail in JP-A-2004-235545.
Specifically, the conductive films 17a of tungsten, the insulating layer 18a as a thin film of alumina, the conductive films 17b of tungsten and the insulating layer 18b of alumina are arranged in that order upward (outward) from the outer peripheral surface of the bell jar 12. The conductive films 17b on the upper side and the conductive films 17a on the lower side are arranged to cover the whole of the inclined surface and the top of the bell jar 12, respectively, and have a plurality of slits extending vertically, i.e. in the direction crossing the direction (horizontal direction in this embodiment) in which the antenna 1 is wound.
These slits are arranged to prevent the situation in which the reverse electromotive current generated in the Faraday shield 8 by the induction or magnetic field of the plasma 6 or the antenna 1 flows in the direction hampering the formation of the electric or magnetic field, as the case may be. For this purpose, the slits are arranged at many points over as wide a range as possible covered by the electric or magnetic field. In short, the configuration shown in
Also, the film portions of the upper conductive films 17b between the slits are arranged to cover the outside (upper portion) of the slits of the lower conductive films 17a. Specifically, the slits of one of the conductive films 17a, 17b are covered by the material between the slits of the other of the conductive films 17a, 17b. In other words, the conductive films 17a, 17b of the Faraday shield 8 arranged in multiple layers are formed with the plurality of the slits and the material therebetween in staggered fashion.
The relative positions of the horizontal ends of the film portions between the slits of the conductive films 17a, 17b, as shown in
In the case where a large gap is developed between the end points of the film portion between the slits of the upper and lower conductive films 17a, 17b as indicated by character a in
To realize the layer structure of the Faraday shield 8 according to this embodiment, each film is formed as described below. Specifically, the conductive films 17a, 17b each have the thickness of 100 μm and the insulating layers 18a, 18b each have the thickness of 150 μm. This invention, however, is not limited to these thickness values, but the thickness of each film is set appropriately in such a way as not to generate the circumferential current in the conductive films 17a, 17b as a whole. Further, the widths of each slit and each film portion between the slits are appropriately selected in accordance with the specification including the magnitude of the supplied power, the frequency, the material of the bell jar 12 and the thickness.
Also, according to this embodiment, the lower layers and the insulating layer 18b are both arranged to cover the whole of the top portion and the inclined surface portion of the bell jar 12, so that the conductive films 17a, 17b are not exposed to the atmosphere. At the time of cleaning by removing the bell jar 12 from the plasma processing apparatus 100 proper, therefore, the conductive films 17a, 17b are corroded less in contact with the atmosphere or the cleaning material, thereby facilitating the handling for an improved cleaning efficiency.
Next, the operation of the electrostatic or magnetic field according to this embodiment is explained with reference to
In the configuration of the conventional Faraday shield 8 shown in
According to this embodiment, on the other hand, as shown in
On the other hand, although the slits of the upper and lower conductive films 17a, 17b are covered by the film portions, the induction field or the magnetic field from the antenna 1 passes through the vertically stacked insulating layers 18a, 18b between the conductive films 17a, 17b, and an electric or magnetic field can be formed in the vacuum processing chamber through the bell jar 12 from the slit portion of the conductive film 17a. As a result, the electric or magnetic field required to maintain the ignition of the plasma 6 is prevented from extremely deteriorating the Faraday shield 8 having the configuration according to this embodiment as compared with the conventional technique.
As described above, according to this embodiment, the amount of consumption of or deposition on the inner wall surface of the vacuum processing chamber with the outer peripheral wall surface thereof covered by the Faraday shield 8 is uniformized along the peripheral direction of the sample 13 or the vacuum processing chamber, thereby realizing a plasma processing apparatus improved in reliability and service life. Also, the sample is processed uniformly along the peripheral direction on the one hand, and the generation of contaminating matter is suppressed while at the same time assuring the uniform distribution of the contaminating matter on the other hand, resulting in an improved processing efficiency and yield.
The configuration of the invention described above is not limited to this embodiment, but can be appropriately selected in accordance with the required specification without adversely affecting the operation and effects with the improved reliability and efficiency. For example, according to this embodiment, the high-frequency power is supplied to the Faraday shield 8, and by forming a bias potential on the inner wall surface of the bell jar 12, the charged particles are attracted. As in the conventional technique, however, the grounding potential may alternatively be employed and the supplied power may be adjusted to attach the deposits appropriately and maintain a uniform amount of the deposits.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-279035 | Dec 2009 | JP | national |
