The present application is based on and claims priority of Japanese patent application No. 2010-269875 filed on Dec. 3, 2010, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to plasma processing apparatuses, and more specifically, relates to inductively coupled plasma processing apparatuses.
2. Description of the Related Art
In the field of semiconductor device fabrication, inductively coupled plasma processing apparatuses are used to perform etching and surface treatments. In this type of plasma processing apparatus, a few turns of induction coils are arranged on the outer side of a vacuum chamber of the apparatus and radio frequency current is supplied to the coils so as to feed power to generate plasma. At this time, stray capacitance occurs between the induction coils and plasma, causing local damages of the vacuum chamber. Japanese patent application laid-open publication No. 2007-158373 (patent document 1) discloses an apparatus capable of preventing this problem by disposing a Faraday shield composed of a conductor between the induction coils and plasma.
It is known that regardless of the type of inductively coupled plasma source being applied, the generated plasma becomes uneven along the circumferential direction of the induction coils, since uneven current distribution along the induction coils is unavoidable. This phenomenon causes the eccentricity of plasma in which the center axis of plasma diffused above the wafer is displaced from the center axis of the induction coils. Plasma eccentricity is also considered to be caused by the influence of magnetic fields, wherein Japanese patent application laid-open publication No. 2004-22988 (patent document 2) discloses an apparatus for covering the whole body of the plasma processing chamber with a magnetic member to shield the magnetic fields, thereby solving the above-mentioned problem of influence of magnetic fields.
The present inventors have also confirmed via experiment that eccentricity of distribution of plasma diffused above the wafer occurs by the influence of magnetic fields. In the experiment, plasma processing was performed by disposing an approximately 0.4 mT magnet to the outer circumference of the plasma processing chamber 1. As a result, it was discovered that a minute magnetic field as small as 0.4 mT created by the magnet caused the plasma distribution diffused above the wafer to be varied greatly. It has been recognized that plasma is possibly influenced by even a minute magnetic field as small as geomagnetism. The above-mentioned phenomenon may also be caused by the magnetic field created via a vacuum pressure gauge or a motor disposed on the processing apparatus. The eccentricity of plasma diffused above the wafer influenced by the magnetic field is caused by the generated plasma being diffused obliquely toward the wafer by the influence of the magnetic field. When etching is performed while the plasma diffused above the wafer has eccentricity, the uniformity and verticalness of the etching process is deteriorated. Demands are increasing for higher accuracy and higher speed of etching processes, and the influence of magnetic fields cannot be ignored in order to realize stable etching processes. The following three problems occur when the art disclosed in patent document 2 is adopted to solve the influence of magnetic fields. The first problem is the problem of performance. Plasma processing chambers must have openings for transferring samples to be processed or for evacuating processing gases, so that it is actually impossible to shield magnetic fields. Moreover, when the chamber is covered by a magnetic member, induction loss occurs within the magnetic member due to the induction magnetic field generated by the induction coils, according to which the plasma generating ability is deteriorated. The second problem is related to the mounting process. A significant change of design is required to cover the whole chamber with the magnetic member, and dangers during operation increase along with the increased chances of handling heavy loads during assembly. The third problem relates to costs. According to the art disclosed in patent document 2, a large amount of magnetic materials capable of covering the plasma processing chamber must be used, which requires a large amount of costs. These three problems are extremely serious in manufacturing mass production apparatuses. Other than the above-mentioned influence of magnetic fields, the eccentricity of plasma caused by the oblique diffusion of plasma mentioned above may also occur due to the eccentricity of vacuum within the plasma processing chamber 1. Thus, the present invention aims at solving the three problems mentioned above and the influence of vacuum eccentricity, not by shielding magnetic fields but by providing a plasma processing apparatus having a means for generating plasma capable of correcting the eccentricity of plasma diffused above the wafer caused by magnetic fields and vacuum eccentricity.
SUMMARY OF THE INVENTION
The present invention provides a plasma processing apparatus comprising a vacuum processing chamber in which a sample is processed via plasma, a gas supply means for supplying gas into the vacuum processing chamber, a sample stage disposed within the vacuum processing chamber on which the sample is placed, an induction coil disposed outside the vacuum processing chamber, a radio frequency power supply for supplying radio frequency power to the induction coil, a Faraday shield being capacitively coupled with the plasma, and an eccentricity correction means disposed between the induction coil and a dielectric sealing window constituting an upper surface of the vacuum processing chamber, wherein the eccentricity correction means generates a plasma capable of correcting the eccentricity of the plasma.
The arrangement of the present invention enables to correct the eccentricity of plasma diffused above the wafer and to achieve the desired etching performance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of the plasma processing apparatus according to the present invention;
FIG. 2 is a view showing the position for arranging a conductor ring;
FIG. 3 is a view showing the diffusion of plasma in a state where no magnetic field exists;
FIG. 4 is a view showing the diffusion of plasma when a magnetic field is applied from outside the plasma processing chamber;
FIG. 5 is a view showing the correction of eccentricity of plasma when the conductor ring is applied;
FIG. 6 is a view showing the concept of operation of the conductor ring;
FIG. 7 is a view showing the shape of the conductor ring; and
FIG. 8 is a view showing the verification result of the effect according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now, a preferred embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a cross-sectional view of a plasma processing apparatus according to the present invention. A plasma processing chamber 1 is composed of a window 1a which is a parallel plate dielectric sealing window formed of an insulating material (a nonconductive material such as alumina (Al2O3) ceramics) having a plasma generating section formed therein, and a chamber 1b having arranged therein a sample stage 3 for mounting a sample 2 which is a wafer. An induction coil 4 is arranged on the outer side of the window 1a. The induction coil 4 is divided into two lines, an inner circumference coil 4a and an outer circumference coil 4b each having two turns, through which current flows in the direction shown by the arrows in the drawing. Further, a plate-shaped Faraday shield 6 capacitively coupled with plasma 5 is disposed between the window 1a and the induction coils 4, wherein the induction coils 4 and the Faraday shield 6 are series-connected via a matching box 7 to a first radio frequency power supply 8. A variable capacitor and a coil are disposed within the matching box 7. Therefore, current can be flown independently to two branched lines of the inner circumference coil 4a and the outer circumference coil 4b, and this current and the voltage applied to the Faraday shield 6 can be controlled. Furthermore, a capacitor is disposed in the matching box for suppressing the reflection of radio frequency power of 13.56 MHz or 27.12 MHz generated from the first radio frequency power supply 8, for example.
While feeding processing gas from a gas supply device 9 into the plasma processing chamber 1, the pressure within the plasma processing chamber 1 is decompressed to a predetermined pressure via a vacuum device 10. Processing gas is fed from the gas supply device 9 to the plasma processing chamber 1, and plasma is generated by the processing gas via the action of an electric field created via the Faraday shield 6 and the induction magnetic field created via the induction coils 4. A second radio frequency power supply 11 is connected to the sample stage 3. A bias power is applied from the second radio frequency power supply 11 to the sample stage 3 so as to draw ions existing within the plasma 5 toward the sample 2. The Faraday shield 6 is composed of a metallic conductor having vertical striped slits and arranged to be superposed to the window 1a. Thus, the present apparatus realizes a function to prevent local damages of the window 1a caused by the stray capacitance between the induction coils 4 and plasma 5, and a function to maintain the inner wall of the plasma processing chamber 1 to a most suitable condition by applying uniformly-sized capacitive coupling actively controlled via the matching box 7 to the plasma.
As shown in FIG. 2, the conductor ring 12 according to the present invention is disposed between the induction coils 4 and the Faraday shield 6, and further arranged to be in conduction with the Faraday shield 6. The conductor ring 12 is disposed between the induction coils 4 and the Faraday shield 6 according to the present embodiment, but equivalent functions can be realized by arranging the conductor ring 12 between the induction coils 4 and the window 1a.
The plasma processing apparatus of the present invention as described above enables to generate plasma capable of correcting the eccentricity of plasma diffused above the sample 2 caused by the influence of the magnetic field other than the induction magnetic field generated by the induction coils 4. This is due to the following operation of the present invention. As shown in FIG. 3, when there are no influences by magnetic fields other than the induction magnetic field created via the induction coils 4, the generated plasma 5a is diffused straight toward the sample 2, so that the plasma does not have any eccentricity. Next, as shown in FIG. 4, if there are influences caused by magnetic fields other than the induction magnetic field created via the induction coils 4, the generated plasma 5a will be diffused obliquely, so that the plasma diffused above the sample has eccentricity. Therefore, as shown in FIG. 5, the plasma processing apparatus according to the present invention enables to generate plasma 5b capable of correcting the eccentricity of plasma diffused above the sample 2, so that the eccentricity of plasma diffused above the sample 2 can be improved. Plasma correcting the eccentricity of plasma diffused above the sample 2 refers to a plasma capable of correcting the eccentricity in advance so that the plasma diffused obliquely above the sample 2 does not have eccentricity. Next, a means for generating the plasma capable of correcting the eccentricity of plasma diffused above the sample 2 mentioned above will be described. As shown in FIG. 6, since a conductor ring 12 which is a ring-shaped conductor is disposed between the induction coils 4 and the Faraday shield 6, inductive current 13a flows along the circumference of the conductor ring 12 in the direction to cancel out the induction magnetic field generated from the induction coils. Further, since the conductor ring 12 is in conduction with the Faraday shield 6, an inductive current 13b is also flown therethrough. Therefore, by arranging the conductor ring 12 on the Faraday shield 6 at an eccentric position displaced from the center axis of the induction coils 4 so that the inductive current 13a and the inductive current 13b flow in the position where the plasma density must be decreased or where the plasma diffused above the sample 2 is positioned eccentrically, the mutual inductance between the induction coils 4 and the plasma can be varied, according to which a plasma capable of correcting the eccentricity of plasma diffused above the sample 2 can be generated. Furthermore, according to the operation of the present invention mentioned above, the eccentricity of the plasma diffused above the sample 2 is improved, so that the eccentricity of plasma diffused above the sample 2 caused by the influence of vacuum eccentricity can also be improved similarly as the eccentricity of plasma diffused above the sample 2 caused by the above-described influence of magnetic fields. Furthermore, the conductor ring 12 is in conduction with the Faraday shield 6 according to the present embodiment, but the conductor ring 12 can be in conduction with anything capable of creating a closed loop through which inductive current flows, so that the conductor ring 12 can be in conduction with the chamber 1b or the cover of the matching box 7, for example. Next, an example of the shape of the conductor ring 12 is shown in FIG. 7. The conductor ring 12 according to the present invention is a ring-shaped member as shown in FIG. 7(a) formed for example of a conductor such as aluminum or stainless steel. Further, the ring-like shape is not restricted to the shape illustrated in FIG. 7(a), and the conductor ring can also be a comb-shaped conductor ring as shown in FIG. 7(b). Further, since the conductor ring 12 according to the present invention is in conduction with the Faraday shield 6, it does not have to be ring-shaped. Thus, the conductor ring 12 can be in a divided form as shown in FIG. 7(c). Moreover, a plurality of or multiple varieties of conductor rings can be used simultaneously. The conductor ring 12 is to be disposed independently so that it can cope with any eccentric position of plasma distribution. Since the conductor ring can be installed independently, it becomes possible to perform adjustment in response to inter-instrument differences.
Next, the result of verification of the effect of the present invention via the etching rate will be described. FIG. 8 is a drawing showing the result of verification, wherein the illustrated etching rate measurement is the in-plane distribution of etching rate of the sample when a sample having an alumina (Al2O3) thin film is etched using a chlorine-based gas (mixed gas of Cl2 gas and BCl3 gas) in an inductively coupled plasma etching apparatus designed to etch a Ø 200 mm sample in which the plasma eccentricity is especially significant. Further, the graph showing the in-plane distribution of etching rate of samples illustrates in contour the in-plane distribution of etching rate of samples at designated points on the sample measured before and after processing using a film thickness measurement device. The contour lines show that the areas having lighter colors have high etching rates and the areas having darker colors have low etching rates. The effect of the present invention was verified by computing the average of the in-plane etching rate at respective points, the in-plane uniformity of the etching rate and the eccentricity ratio. The eccentricity ratio is an index showing the level of eccentricity of plasma diffused above the sample 2, wherein smaller values of eccentricity ratio indicate smaller eccentricity.
First, according to the prior art plasma processing apparatus as shown in FIG. 8(a), the etching rate at the lower right side of the drawing is high in the in-plane distribution of the sample. This is caused by the eccentricity of the plasma at the lower right side due to the influence of magnetic fields. Next, the in-plane distribution of etching rate of the sample when a magnet is disposed on the outer circumference of the prior art plasma processing apparatus is shown in FIG. 8(b). As a result of etching rate measurement performed by disposing a north pole and a south pole of a magnet (0.4 mT) at areas shown in FIG. 8(b), the portion where etching rate was high has moved to the upper right side of the sample. This is caused by the distribution of the induction magnetic field being varied by disposing the magnet. Further, as mentioned above, the position of eccentricity of plasma diffused above the sample 2 can be estimated based on the result of in-plane etching rate distribution of the sample when magnetic fields are generated at various locations. By disposing the conductor ring 12 to correspond to the estimated result of eccentricity position, the eccentricity of plasma diffused on the sample 2 can be improved. Next, as shown in FIG. 8(c), according to the in-plane distribution of etching rate of the sample to which the present invention is applied, the eccentricity ratio of the plasma has been improved from 8.6% to 2.7%, and along therewith, the in-plane uniformity of etching rate of the sample has been improved from 8.3% to 5.8%.
The present embodiment has been illustrated based on an example in which the location of eccentricity of the plasma diffused above the sample has been estimated based on the measurement of in-plane distribution of etching rate of the sample, but the estimation of location of eccentricity of the plasma diffused above the sample can also be performed based for example on ion current flux measurement or plasma density distribution measurement using probes.
As described above, the plasma processing apparatus according to the present invention provides an eccentricity correction means for generating a plasma capable of correcting the eccentricity of plasma diffused above the sample, thereby improving the eccentricity of plasma diffused above the sample caused by the influence of magnetic fields or by the eccentricity of vacuum within the plasma processing chamber.
Patent Application
20120138229
