Patent Application
20050241769
The disclosure of Japanese Patent Application No. JP2004-381290, filed Dec. 28, 2004, entitled “plasma processing apparatus” and Application No. JP2004-136566, filed Apr. 30, 2004, entitled “plasma processing apparatus”. The contents of that applications are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to a plasma processing apparatus and a plasma processing method to be adopted when executing a process such as etching on a substrate with plasma generated from a process gas by applying high-frequency power.
2. Description of Related Art
During the production of semiconductor devices and flat panel devices such as liquid crystal display devices, plasma processing apparatuses including plasma etching apparatuses and plasma CVD (Chemical Vapor Deposition) film forming apparatuses are utilized to execute an etching process, a film forming process and the like on workpieces such as semiconductor wafers and glass substrates.
The lower electrode is connected to the processing chamber 11 via a conductive passage 18 to constitute an anode electrode. The conductive passage 18 in this example is constituted with a shaft 18a, a support plate 18b and a bellows member 18c. The upper side of the processing chamber 11 is connected with the high-frequency power source 17 via a matching box 16 which is a grounded casing, and more specifically, it is grounded through its connection to the outer layer of the coaxial cable connecting the high-frequency power source 17 and the matching box 16.
The size of glass substrates for flat panels used in liquid crystal displays and the like among substrates that are processed in plasma processing apparatuses is expected to further increase and glass substrates as large as 1.5 m2 must be processed in plasma processing apparatuses in the near future. As a larger processing chamber 11 is utilized to handle such large glass substrates, the inductance component in the processing chamber 11 is bound to increase, to result in weaker coupling of the upper electrode 12 and the lower electrode 13, which leads to a concern that plasma may be generated between the upper electrode 12 and the wall of the processing chamber 11 (shown as capacitive coupling in
Patent Reference Literature 1 discloses a technology for controlling the diffusion of the plasma by providing an impedance adjustment circuit between the lower electrode and the ground. However, this technology whereby different settings are selected at the impedance adjustment circuit for a film forming process and for a cleaning process so as to achieve plasma conditions matching the individual processes, does not address the problems discussed above and Patent Reference Literature 1 does not disclose any solutions to these problems.
An object on the present invention, which has been completed with the background described above, is to provide a plasma processing apparatus and a plasma processing method that prevent generation of plasma between the cathode electrode and the wall of the processing chamber and make it possible to execute plasma processing on the substrate to achieve a high level of planar uniformity by generating a uniform field of plasma.
The present invention provides a plasma processing apparatus for processing a substrate with plasma generated from a process gas by supplying high-frequency power into a processing chamber, comprising a cathode electrode and an anode electrode facing opposite each other on an upper side and a lower side inside the processing chamber and insulated from the processing chamber a high-frequency power source having one end thereof connected to the cathode electrode via a matching circuit, and an impedance adjustment unit having one end thereof connected to the anode electrode and another end thereof connected to the processing chamber and containing a capacitive component, is characterized in that the substrate is placed on either the cathode electrode or the anode electrode that is located on the lower side, and the impedance adjustment unit adjusts a value of impedance occurred in a path extending from the cathode electrode to a grounded casing of the matching circuit via the plasma, the anode electrode and a wall of the processing chamber to a level lower than a value of impedance occurred in a path extending from the cathode electrode to the grounded casing of the matching circuit via the plasma and the wall of the processing chamber.
The cathode electrode and the anode electrode are described above as being “insulated from the processing chamber,” which means that they are in a fully floating state electrically relative to the processing chamber over the area excluding the impedance adjustment unit.
It is to be noted that the path extending from the cathode electrode to the grounded casing of the matching circuit via the plasma, the anode electrode and the wall of the processing chamber may also be referred to as the path extending along the direction in which the plasma achieves uniformity relative to the substrate. In addition, the path extending from the cathode electrode to the grounded casing of the matching circuit via the plasma and the wall of the processing chamber may also be referred to as the path along which the plasma density becomes higher relative to the wall of the processing chamber (i.e., the path extending along the direction in which the plasma distribution becomes non-uniform relative to the substrate).
In another aspect of the present invention, a plasma processing apparatus for processing a substrate with plasma generated from a process gas by supplying high-frequency power into a processing chamber containing a process gas, comprising a cathode electrode and an anode electrode facing opposite each other on an upper side and a lower side within the processing chamber and insulated from the processing chamber, a high-frequency power source having one end thereof connected to the cathode electrode via a matching circuit and an impedance adjustment unit having a capacitive component with one end thereof connected to the anode electrode and another end thereof connected to the processing chamber, is characterized in that the substrate is placed on either the cathode electrode or the anode electrode that is located on the lower side and that the impedance adjustment unit adjusts the value of the impedance over a path extending from the cathode electrode to the grounded casing of the matching circuit via the plasma, the anode electrode and the wall of the processing chamber so as to achieve a minimum impedance value. Through the adjustment of “the impedance over the path extending from the cathode electrode to the grounded casing f the matching circuit via the plasma, the anode electrode and the wall of the processing chamber so as to achieve a minimum impedance value”, the value of the impedance may be adjusted substantially to the minimum value and may be adjusted to a value within a 2% range (namely, 0.98x−1.02x: x=the minimum value) with respect to the minimum value.
A plasma processing apparatus for processing a substrate with plasma generated from a process gas by supplying high-frequency power into a processing chamber, comprising an upper electrode and a lower electrode facing opposite each other on an upper side and a lower side inside the processing chamber and insulated from the processing chamber, a first high-frequency power source having one end thereof connected to the upper electrode via a first matching circuit and supplying the high-frequency power within a range of 10 MHz to 30 MHz, a second high-frequency power source having one end thereof connected to the lower electrode via a second matching circuit and supplying the high-frequency power within a range of 2 MHz to 6 MHz, a first impedance adjustment unit having one end thereof connected to the lower electrode and another end thereof connected to the processing chamber and containing a capacitive component, and a second impedance adjustment unit having one end thereof connected to the upper electrode and another end thereof connected to the processing chamber and containing a capacitive component, is characterized in that the substrate is placed on the lower electrode, the first impedance adjustment unit adjusts a value of impedance occurred in a path extending from the upper electrode to a grounded casing of the first matching circuit via the plasma, the lower electrode and a wall of the processing chamber by the high-frequency power of the first high-frequency power source to a level lower than a value of impedance occurred in a path extending from the upper electrode to the grounded casing of the first matching circuit via the plasma and the wall of the processing chamber by the high-frequency power of the first high-frequency power source, and the second impedance adjustment unit adjusts a value of impedance occurred in a path extending from the lower electrode to a grounded casing of the second matching circuit via the plasma, the upper electrode and the wall of the processing chamber by the high-frequency power of the second high-frequency power source to a level lower than a value of impedance occurred in a path extending from the lower electrode to the grounded casing of the second matching circuit via the plasma and the wall of the processing chamber by the high-frequency power of the second high-frequency power source.
A plasma processing apparatus according to the present invention for processing a substrate with plasma generated from a process gas by supplying high-frequency power into a processing chamber containing the process gas achieved in another aspect of the present invention adopted in an upper electrode/lower electrode two-frequency system, comprising an upper electrode and a lower electrode facing opposite each other on an upper side and a lower side inside the processing chamber and insulated from the processing chamber, a first high-frequency power source that supplies 10 MHz to 30 MHz power with one end thereof connected to the upper electrode via a first matching circuit, a second high-frequency power source that supplies 2 MHz to 6 MHz power with one end thereof connected to the lower electrode via a second matching circuit, a first impedance adjustment unit having a capacitive component with one end thereof connected to the lower electrode and another end thereof connected to the processing chamber and a second impedance adjustment unit having a capacitive component with one end thereof connected to the upper electrode and another end thereof connected to the processing chamber, is characterized in that the substrate is placed on the lower electrode, that the first impedance adjustment unit adjusts the value of the impedance at the frequency of the first high-frequency power source over a path extending from the upper electrode to a grounded casing of the first matching circuit via the plasma, the lower electrode and the wall of the processing chamber so as to achieve a minimum impedance value and that the second impedance adjustment unit adjusts the value of the impedance at the frequency of the second high-frequency power source over a path extending from the lower electrode to a grounded casing of the second matching circuit via the plasma, the upper electrode and the processing chamber wall so as to achieve a minimum impedance value.
The present invention may also be adopted in a lower electrode two-frequency system having a first high-frequency power source and a second high-frequency power source connected to the lower electrode. In such an application, A plasma processing apparatus for processing a substrate with plasma generated from a process gas by supplying high-frequency power into a processing chamber, comprising, an upper electrode and a lower electrode facing opposite each other on an upper side and a lower side inside the processing chamber and insulated from the processing chamber, a first high-frequency power source having one end thereof connected to the lower electrode via a first matching circuit and supplying the high-frequency power within a range of 10 MHz to 30 MHz, a second high-frequency power source having one end thereof connected to the lower electrode via a second matching circuit and supplying the high-frequency power within a range of 2 MHz to 6 MHz, and a first impedance adjustment unit and a second impedance adjustment unit having one end thereof connected to the upper electrode and another end thereof connected to the processing chamber and containing a capacitive component respectively, is characterized in that the substrate is placed on the lower electrode, the first impedance adjustment unit adjusts a value of impedance occurred in a path extending from the lower electrode to a grounded casing of the first matching circuit via the plasma, the upper electrode and a wall of the processing chamber by the high-frequency power of the first high-frequency power source to a level lower than a value of impedance occurred in a path extending from the lower electrode to the grounded casing of the first matching circuit via the plasma and the wall of the processing chamber by the high-frequency power of the first high-frequency power source, and the second impedance adjustment unit adjusts a value of impedance occurred in a path extending from the lower electrode to a grounded casing of the second matching circuit via the plasma, the upper electrode and the wall of the processing chamber by the high-frequency power of the second high-frequency power source to a level lower than a value of impedance occurred in a path extending from the lower electrode to the grounded casing of the second matching circuit via the plasma and the wall of the processing chamber by the high-frequency power of the second high-frequency power source.
Another plasma processing apparatus according to the present invention for processing a substrate with plasma generated from a process gas by supplying high-frequency power into a processing chamber containing the process gas, adopted in a lower electrode two-frequency system and comprising an upper electrode and a lower electrode facing opposite each other on an upper side and a lower side inside the processing chamber and insulated from the processing chamber, a first high-frequency power source that supplies 10 MHz to 30 MHz power with one end thereof connected to the lower electrode via a first matching circuit, a second high-frequency power source that supplies 2 MHz to 6 MHz power with one end thereof connected to the lower electrode with a second matching circuit and a first impedance adjustment unit and a second impedance adjustment unit each having a capacitive component with one end thereof connected to the upper electrode and another end thereof connected to the processing chamber, is characterized in that the substrate is placed on the lower electrode, that the first impedance adjustment unit adjusts the value of the impedance over a path extending from the lower electrode to a grounded casing of the first matching circuit via the plasma, the upper electrode and the wall of the processing chamber so as to achieve a minimum impedance value and that the second impedance adjustment unit adjusts the value of the impedance over a path extending from the lower electrode to a grounded casing of the second matching circuit via the plasma, the upper electrode and the processing chamber wall so as to achieve a minimum impedance value.
In each of the plasma processing apparatuses described above, the following control may be executed by the individual units in the plasma processing apparatus when adjusting the value of the impedance over the path extending along the direction in which the plasma achieves uniformity relative to the substrate to a level lower than the value of the impedance over the path through which the plasma density increases relative to the wall (i.e., the path extending along the direction in which the plasma distribution becomes non-uniform relative to the substrate) and when adjusting the value on the impedance over the path through which the plasma becomes distributed more evenly relative to the substrate so as to achieve the minimum impedance value.
Namely, it is desirable that an impedance value, which will provide a value within a 10% range with respect to the maximum high-frequency current value when the value of the high-frequency current at a specific frequency flowing to the anode electrode is altered by adjusting the value of the high-frequency impedance at the frequency, be set at each impedance adjustment unit. If the anode electrode constitutes the lower electrode, for instance, the impedance adjustment unit should be connected on its other end to the bottom of the processing chamber. To make the most of the impedance adjustment unit, it should be ensured that the other end of the impedance adjustment unit and the processing chamber are connected with each other in an area considerably distanced from the cathode electrode to avoid plasma generation occurring between the cathode electrode and the connecting area. Accordingly, the connection may be achieved at a position achieving a height equal to the height of the anode electrode in the processing chamber, or at a position on the side opposite from the side on which the anode electrode is present (e.g., on the lower side when the anode electrode constitutes the lower electrode, and on the upper side when the anode electrode constitutes the upper electrode).
The impedance adjustment unit may be constituted by using, for instance, a variable-capacity capacitor so as to allow the impedance value to be varied, or it may be achieved by using, for instance, a dielectric plate constituting a capacitive component disposed between the anode electrode and the inner surface of the processing chamber. By using an impedance adjustment unit that allows the impedance value to be varied, a plasma processing apparatus according to the present invention may adopt a structure having a control unit having stored therein data correlating each plasma processing type with the impedance adjustment value of the impedance adjustment unit (correlating each plasma processing type with an adjustment value at the first impedance adjustment unit and an adjustment value at the second impedance adjustment unit when the plasma processing apparatus includes the first and second impedance adjustment units), which outputs a control signal to be used to adjust the impedance adjustment unit by reading out an impedance adjustment value corresponding to a selected plasma processing type.
It is desirable that the plasma processing apparatus according to the present invention include a plurality of impedance adjustment units with the individual impedance adjustment units connected on one end to the anode electrode at positions distanced from one another along the longish side of the anode electrode. In an application in an upper electrode/lower electrode two-frequency system, the plasma processing apparatus should include a plurality of first impedance adjustment units with the individual impedance adjustment units connected on one end thereof to the lower electrode at positions distanced from one another along the longish side of the lower electrode and a plurality of second impedance adjustment units with the individual impedance adjustment units connected on one end thereof to the upper electrode at positions distanced from one another along the longish side of the upper electrode. In addition, according to the present invention adopted in a lower electrode two-frequency system, the plasma processing apparatus should include a plurality of first impedance adjustment units with the individual impedance adjustment units connected on one end thereof to the lower electrode at positions distanced from one another along the longish side of the lower electrode and a plurality of second impedance adjustment units with the individual impedance adjustment units connected on one end thereof to the lower electrode at positions distanced from one another along the longish side of the lower electrode.
The plasma processing apparatus having a plurality of impedance adjustment units as described above is ideal in an application in which a substrate with an area equal to or greater than 1 m2, e.g., a large rectangular substrate, and is particularly effective when the sum of the high-frequency power used in the apparatus is equal to or greater than 10 kW.
According to the present invention, the generation of plasma between the cathode electrode and the wall of the processing chamber is controlled and, as a result, a plasma process can be executed on the substrate to achieve a high level of planar uniformity by generating evenly distributed plasma.
The plasma processing apparatus achieved in the first embodiment of the present invention as an etching apparatus for etching a glass substrate for a liquid crystal display device is now explained. Reference numeral 2 in
The upper electrode 3 is connected with a high-frequency power source 4 via a matching circuit 41 and a conductive passage 40. In addition, a matching box 42 is disposed so as to surround the opening 30 at the processing chamber 2 and to hold therein the matching circuit 41. The top portion of the matching box 42 extends as an outer layer portion 43 which constitutes, together with the conductive passage 40, a coaxial cable 44, and the outer layer portion 43 is grounded. In this example, the matching box 42 constitutes a grounded casing of the matching circuit.
In the processing chamber 2, a lower electrode 5 to be also used as a stage on which a substrate 10 is placed is disposed at the bottom, and the lower electrode 5 is supported at a support portion 51 via an insulating member 50. Thus, the lower electrode 5 is fully floating with respect to the processing chamber 2 electrically. At the center of the lower surface of the support portion 51, a protective pipe 52 passing through an opening 20 formed at the bottom wall of the processing chamber 2 and extending downward is disposed. The protective pipe 52 is supported on its bottom side by a conductive support plate 53 having a diameter larger than that of the protective pipe 52, which also seals the pipe. At the peripheral edge of the support plate 53, the lower end of a conductive bellows member 54 is fixed, and the upper end of the bellows member 54 is fixed to the opening edge of the opening 20 at the processing chamber 2. The bellows member 54 pneumatically seals the inner space in which the protective pipe 52 is disposed from the atmosphere side space, and the stage 5 is allowed to move up/down by an elevator mechanism (not shown) via the support plate 53.
One end of a conductive passage 55 disposed within the protective pipe 51 is connected to the lower electrode 5, with an impedance adjustment unit 6 disposed in the conductive passage 55. Another end of the conductive passage 55 is connected to the bottom of the processing chamber 2 via the support plate 53 and the bellows member 54. A portion of the processing chamber 2 located in the vicinity of the upper electrode 3, e.g., the upper surface of the processing chamber 2, is grounded via the matching box 42 and then the outer layer portion 43 of the coaxial cable 44, as explained earlier. The upper electrode 3 and the lower electrode 5 are respectively equivalent to a cathode electrode and an anode electrode in this example.
An evacuation passage 21 is connected to the side wall of the processing chamber 2, with a vacuum evacuation means 22 connected to the evacuation passage 21. In addition, a gate valve 24 used to open/close a transfer port 23 through which the substrate 10 is transferred is disposed at the side wall of the processing chamber 2.
In the structure described above, a high-frequency current flows through the path extending from the high-frequency power source 4 to the ground sequentially via the matching circuit 41, the upper electrode 3, the plasma, the lower electrode 5, the impedance adjustment unit 6, the processing chamber 2, the matching box 42 and the outer layer portion 43 of the coaxial cable 44. Since there is a concern that the high-frequency current may flow to the wall of the processing chamber 2 from the upper electrode 3 via the plasma as explained in reference to the related art, the impedance in the path (the return path) extending from the lower electrode 5 to the top of the processing chamber 2 is adjusted with the impedance adjustment unit 6.
The object of the embodiment is to adjust the impedance j (−1/ωC1+ωL−1/ωC) over the path extending from the lower electrode 5 to the top of the processing chamber 2 to a level lower than the impedance over the path extending from the upper electrode 3 through the plasma and then the wall of the processing chamber 2 through which the plasma density increases relative to the wall by canceling out the capacitance (C1) of the plasma and the inductance (L) in the path extending from the lower electrode 5 to the top of the processing chamber 2 with the capacitive component (C) of the impedance adjustment unit 6. For these purposes, the impedance adjustment unit 6 includes a capacitive component. Such an impedance adjustment unit 6 may be achieved by adopting any of various modes. For instance, the impedance adjustment unit 6 may be constituted by using a variable-capacity capacitor 61, as shown in
While the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate should be ideally reduced by ascertaining the values of the electrical current flowing through the path in correspondence to varying impedance values assumed at the impedance adjustment unit 6 through tests conducted as detailed later and selecting an impedance value corresponding to the maximum current value, i.e., by setting a value that will minimize the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate, it is desirable to ensure that a value corresponding to a current value within a 2% range with respect to the maximum value or at least a 10% range with respect to the maximum current value in a practical application.
The functions and the advantages of the embodiment described above are now explained. After the substrate 10 is transferred into the processing chamber 2 on a transfer arm (not shown) from a load lock chamber (not shown) by opening the gate valve 24, the substrate 10 is transferred onto the lower electrode 5 through cooperation of the transfer arm and an elevator pin (not shown) passing through the lower electrode 5. Then, the gate valve 24 is closed, the process gas is supplied into the processing chamber 2 from the process gas supply unit 33 via the upper electrode 3, and the pressure inside the processing chamber 2 is maintained at a predetermined level by evacuating the processing chamber 2 vacuously with the vacuum evacuation means 22. The process gas becomes excited as 10 kW high-frequency power at, for instance, 10 MHz to 30 MHz frequency from the high-frequency power source 4 is applied between the upper electrode 3 and the lower electrode 5, thereby generating plasma. The process gas may be constituted with, for instance, a gas containing halogen such as a gas containing a halogen compound, an oxygen gas and an argon gas or the like.
As the plasma is generated, the high-frequency current flows through the path extending from the upper electrode 3 to the ground sequentially via the plasma, the lower electrode 5, the impedance adjustment unit 6, the processing chamber 2, the matching box 42 and the outer layer portion 43 of the coaxial cable 44 along the direction in which the plasma becomes more uniform relative to the substrate. Since the value of the impedance in the path is set substantially to the minimum value, smaller than the value of the impedance in the path extending from the upper electrode 3 to the ground sequentially via the plasma, the processing chamber 2, the matching box 42 and the outer layer portion 43 of the coaxial cable 44, plasma is not generated readily between the upper electrode 3 and the wall of the processing chamber 2. As a result, the plasma is allowed to concentrate in the space between the upper electrode 3 and the lower electrode 5 and the plasma present above the substrate 10 achieves a high level of planar uniformity. As the surface of the substrate 10 is etched with this plasma achieving a high level of planar uniformity, the etching rate sustains a high level of consistency and thus, uniform etching is achieved within the plane. In addition, the damage to or wear of the inner wall of the processing chamber 2 and internal parts is minimized.
In the embodiment, optimal adjustment values to be set at the impedance adjustment unit 6 in correspondence to various types of processing may be stored in memory as, for instance, a table at a storage unit of a control unit 7, the optimal adjustment value corresponding to a specific processing type having been selected may be read out from the data, e.g., the table and a control signal may be output from the control unit 7 to an actuator at the impedance adjustment unit 6 which may be a motor for driving the trim mechanism of the variable-capacity capacitor, as shown in
In the embodiment, when processing the substrate with plasma generated by applying high-frequency power to the space between the cathode electrode and the anode electrode, the impedance adjustment unit having a capacitive component, which is disposed between the anode electrode (constituted with the electrode facing opposite the electrode connected with the high-frequency power source) and the processing chamber, adjusts the value of the impedance in the path extending from the cathode electrode to the grounded casing of the matching circuit via the plasma, the anode electrode and the processing chamber wall to a level lower than the value of the impedance in the path extending from the cathode electrode to the grounded casing of the matching circuit via the plasma and the processing chamber wall. As a result, plasma is not generated readily in the space between the cathode electrode and the processing chamber wall and plasma with highly consistent distribution is generated to enable plasma processing with a high level of planar uniformity at the substrate.
(Variations of the First Embodiment)
In a variation of the embodiment, the plasma processing apparatus include a plurality of impedance adjustment units e.g., impedance adjustment units 6A, 6B and 6C, as shown in
To explain the plasma processing apparatus in further detail in reference to a specific example, if the plasma intensity is high around the center, the capacitive value at the impedance adjustment unit 6B corresponding to the central area is increased so as to raise the value of the impedance between the lower electrode 5 and the processing chamber 2 over the central area and the capacity values at the impedance adjustment units 6A and 6C corresponding to the peripheral areas are reduced so as to shift the plasma with the high intensity from the center toward the periphery. It is a prerequisite in such an embodiment that the impedance values at the individual impedance adjustment units 6A, 6B and 6C be set so as to adjust the value of the impedance over the path extending along the direction in which the plasma becomes more uniform relative to the substrate as described earlier, including the value of the impedance at the parallel connection circuit constituted with the impedance adjustment unit 6A, 6B and 6C to a level lower than the value of the impedance over the path extending from the upper electrode 3 and then through the plasma and along the wall of the processing chamber 2, through which the plasma density increases relative to the wall. The intensity of the plasma over the plane of the substrate 10 can be fine-adjusted by adjusting the impedance values at the individual impedance adjustment units while satisfying the prerequisite, which proves extremely effective for generating highly consistent plasma to process large size substrates. Bearing in mind that it is difficult to sustain plasma in a uniform state over the plane of a large size substrate with an area of 1 m2 or more, e.g., a rectangular substrate used for a flat panel display, the inventor learned that the plasma consistency can be improved and any abnormal discharge that might otherwise occur locally can be prevented by fine-adjusting the plasma distribution. The structure having a plurality of impedance adjustment units is particularly effective when the sum of the high-frequency power is significant at 10 kW or more, since an abnormal discharge tends to occur readily under such circumstances.
As shown in
When dividing the lower electrode 5 into separate impedance adjustment areas, as described above, it does not need to be divided into three areas and instead, it may be halved both longitudinally and laterally to form four divided areas, for instance, and in such a case, an impedance adjustment unit should be provided in correspondence to each of the four divided areas.
In this embodiment, too, adjustment values to be selected for the individual impedance adjustment units 6A, 6B and 6C should be stored in memory at the storage unit of the control unit 7 in correspondence to each type of processing and the optimal impedance values should be set at the individual impedance adjustment units 6A, 6B and 6C in correspondence to a selected processing type, as shown in
In addition, instead of using a capacitive element such as a variable-capacity capacitor or a fixed capacity capacitor to constitute an impedance adjustment unit 6, a dielectric plate or the like that constitutes a capacitive component may be used as shown in
In the example presented in
While the high-frequency power source 4 is connected to the upper electrode 3 in the embodiment described above, the high-frequency power source 4 may instead be connected to the lower electrode 5. In such a case, the impedance adjustment unit 6 should be connected between the upper electrode 3 and an upper portion of the processing chamber 2, e.g., the upper surface of the processing chamber 2. While the impedance adjustment unit 6 may be disposed between the upper electrode 3 and the side wall of the processing chamber 2 under these circumstances, it is not desirable to dispose the impedance adjustment unit at a position lower than the upper electrode 3.
By adopting the variation in which a plurality of impedance adjustment units are employed with the individual impedance adjustment units connected on one side to the anode electrode at positions distanced from one another along the longish side of the anode electrode and the impedance can be thus adjusted individually for each of the plurality of divided areas of the anode electrode defined along the plane of the substrate, the plasma distribution can be adjusted more accurately compared to an impedance adjustment over a single area and, as a result, highly consistent plasma is achieved. For instance, as it becomes difficult to achieve a highly consistent plasma state within the plane when handling a large substrate with an area of 1 m2 or more, the plasma consistency can be improved and also an abnormal discharge that might otherwise occur locally can be prevented by fine-adjusting the plasma distribution. The structure having a plurality of impedance adjustment units is particularly effective when the sum of the high-frequency power is significant at 10 kW or more since an abnormal discharge tends to occur readily under such circumstances.
The second embodiment of the present invention is adopted in an upper electrode/lower electrode two-frequency type plasma processing apparatus having a high-frequency power source 4 disposed in conjunction with the upper electrode 3 and a high-frequency power source 100 disposed in conjunction with the lower electrode 5, as shown in
The matching circuits 41 and 103 in this example respectively constitute a first matching circuit and a second matching circuit. The high-frequency power sources 4 and 100 respectively constitute a first high-frequency power source and a second high-frequency power source, and the first high-frequency power source 4 located on the upper side outputs, for instance, 10 kW high-frequency power with a frequency of 10 MHz to 30 MHz, whereas the second high-frequency power source 100 located on the lower side outputs, for instance, 3 kW high-frequency power with a frequency of 2 MHz to 6 MHz. The high-frequency power output from the first high-frequency power source 4 activates the process gas, whereas the power output from the second high-frequency power source 100 attracts the ions in the plasma toward the substrate 10. It is to be noted that the matching boxes 42 and 102 respectively constitute a grounded casing for the first matching circuit and a grounded casing for the second matching circuit in the embodiment. Although not shown in
A plurality of impedance adjustment units 9A and 9C are disposed between the upper electrode 3 and the matching box 42, and the impedance adjustment units 9A and 9C are connected to an upper portion, e.g., the ceiling, of the processing chamber 2 via the matching box 42. While the illustration includes two impedance adjustment units 9A and 9C on the upper side and two impedance adjustment units 6A and 6C on the lower side, three or more impedance adjustment units may be provided on each side or a single impedance adjustment unit may be provided on each side. In addition, the matching box 42 constitutes the grounded casing for the first matching circuit 41, which allows the high-frequency current from the first high-frequency power source 4 to return to the high-frequency power source 4 through the top portion of the processing chamber 2, and the matching box 102 constitutes the grounded casing for the second matching circuit 103, which allows the high-frequency current from the second high-frequency power source 100 to return to the high-frequency power source 100 from the bottom portion of the processing chamber 2.
The lower impedance adjustment units 6A and 6C constitute a first impedance adjustment units in conjunction with which a filter for allowing the high-frequency component corresponding to the high-frequency band of the first high-frequency power source 4 alone to pass through is provided. The upper impedance adjustment units 9A and 9C constitute second impedance adjustment units in conjunction with which a filter for allowing the high-frequency component corresponding to the high-frequency band of the second high-frequency power source 100 alone to pass through is provided. Namely, the high-frequency current from the first high-frequency power source 4 flows through a path extending from the high-frequency power source 4 to the ground sequentially via the matching circuit 41, the upper electrode 3, the plasma, the lower electrode 5, the impedance adjustment units 6A and 6C, the processing chamber 2, the matching box 42 and the outer layer portion 43 of the coaxial cable 44, whereas the high-frequency current from the second high-frequency power source 100 flows through a path extending from the high-frequency power source 100 to the ground sequentially via the matching circuit 103, the lower electrode 5, the plasma, the upper electrode 3, the impedance adjustment units 9A and 9C, the processing chamber 2, the matching box 102 and the outer layer portion 105 of the coaxial cable 104.
The first impedance adjustment units 6A and 6B adjust the value of the impedance at the high-frequency of the first high-frequency power source 4 over the path extending from the upper electrode 3 to the matching box 42 (the grounded casing of the first matching circuit) via the plasma, the lower electrode 5 and the wall of the processing chamber 2 along the direction in which the plasma becomes more uniform relative to the substrate, to a level lower than the value of the impedance at the high frequency of the first high-frequency power source 4 over the path extending from the upper electrode 3 to the matching box 42 via the plasma and the wall of the processing chamber 2 along the direction in which the plasma density increases relative to the wall. While the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate should be ideally reduced by ascertaining the values of the electrical current flowing from the first high-frequency power source 4 through the path extending along the direction in which the plasma becomes more uniform relative to the substrate in correspondence to varying impedance values and selecting an impedance value corresponding to the maximum current value, i.e., by setting a value that will minimize the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate, it should be insured in a practical application that a value corresponding to a current value within a 2% range with respect to the maximum current value or at least within a 10% range with respect to the maximum current value is set. The value of the current in the path extending along the direction in which the plasma becomes more uniform relative to the substrate may be determined as the sum of the current values provided by, for instance, ammeters connected to the impedance adjustment units 6A and 6C.
The second impedance adjustment units 9A and 9C adjust the value of the impedance at the high-frequency of the second high-frequency power source 100 over the path extending from the lower electrode 5 to the matching box 102 via the plasma, the upper electrode 3 and the wall of the processing chamber 2 along the direction in which the plasma becomes more uniform relative to the substrate to a level lower than the value of the impedance at the high-frequency of the second high-frequency power source 100 over the path extending from the lower electrode 5 to the matching box 102 via the plasma and the wall of the processing chamber 2 along the direction in which the plasma density increases relative to the wall. While the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate should be ideally reduced by ascertaining the values of the electrical current flowing from the second high-frequency power source 100 through the path extending along the direction in which the plasma becomes more uniform relative to the substrate in correspondence to varying impedance values and selecting an impedance value corresponding to the maximum current value, it should be ensured in a practical application that a value corresponding to a current value within a 2% range with respect to the maximum value or at least a 10% range with respect to the maximum current value is set.
The third embodiment of the present invention is adopted in a lower electrode two-frequency type plasma processing apparatus having a first high-frequency power source 4 and a second high-frequency power source 100 both provided in conjunction with the lower electrode 5, as shown in
A plurality of first impedance adjustment units, e.g., three impedance adjustment units 6A to 6C, and a plurality of second impedance adjustment units, e.g., three impedance adjustment units 9A to 9C, are individually connected on one end thereof to the upper electrode 3, and the ends of the impedance adjustment units 6A to 6C and 9A to 9C on the other side are connected to an upper portion, e.g., the ceiling, of the processing chamber 2 via a conductive cover member 56 covering the opening 30 of the processing chamber 2. Instead of providing three first impedance adjustment units and three second impedance adjustment units, a first impedance adjustment unit constituted with a single impedance adjustment unit and a second impedance adjustment unit constituted with a single impedance adjustment unit may be used, or the number of impedance adjustment units included in the first and second impedance adjustment units may be two or four or more. In this example, too, a filter for allowing only the high-frequency component corresponding to the high-frequency band of the first high-frequency power source 4 to pass through is provided in conjunction with the first impedance adjustment units 6A to 6C. In addition, a filter for allowing only the high-frequency component corresponding to the high-frequency band of the second high-frequency power source 100 to pass through is provided in conjunction with the second impedance adjustment units 9A to 9C.
In addition, the matching box 42 is used both as the grounded casing for the first matching circuit, which allows the high-frequency current from the first high-frequency power source 4 to return to the high-frequency power source 4 through the bottom of the processing chamber 2, and the grounded casing for the second matching circuit, which allows the high-frequency current from the second high-frequency power source 100 to return to the high-frequency power source 100 through the bottom of the processing chamber 2.
The high-frequency current from the first high-frequency power source 4 flows through the path extending from the high-frequency power source 4 to the matching box 42 sequentially via the matching circuit 41, the lower electrode 5, the plasma, the upper electrode 3, the first impedance adjustment units 6A to 6C and the processing chamber 2, whereas the high-frequency current from the second high-frequency power source 100 flows through the path extending from the high-frequency power source 100 to the matching box 42 sequentially via the matching circuit 103, the lower electrode 5, the plasma, the upper electrode 3, the second impedance adjustment units 9A to 9C and the processing chamber 2.
The first impedance adjustment units 6A to 6C adjust the value of the impedance at the high frequency of the first high-frequency power source 4 over the path extending from the lower electrode 5 to the matching box 42 via the plasma, the upper electrode 3 and the wall of the processing chamber 2 along the direction in which the plasma becomes more uniform relative to the substrate to a level lower than the value of the impedance at the high frequency of the first high-frequency power source 4 over the path extending from the lower electrode 5 to the matching box 42 via the plasma and the wall of the processing chamber 2 along the direction in which the plasma density increases relative to the wall. While the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate should be ideally reduced by ascertaining the values of the electrical current flowing from the first high-frequency power source 4 through the path extending along the direction in which the plasma becomes more uniform relative to the substrate in correspondence to varying impedance values and selecting an impedance value corresponding to the maximum current value, i.e., by setting a value that will minimize the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate, it should be insured in a practical application that a value corresponding to a current value within a 2% range with respect to the maximum current value or at least within a 10% range with respect to the maximum current value is set.
The second impedance adjustment units 9A to 9C adjust the value of the impedance at the high frequency of the second high-frequency power source 100 over the path extending from the lower electrode 5 to the matching box 42 via the plasma, the upper electrode 3 and the wall of the processing chamber 2 along the direction in which the plasma becomes more uniform relative to the substrate to a level lower than the value of the impedance at the high frequency of the second high-frequency power source 100 over the path extending from the lower electrode 5 to the matching box 42 via the plasma and the wall of processing chamber 2 along the direction in which the plasma density increases relative to the wall. While the impedance in the path extending along the direction in which the plasma becomes more uniform relative to the substrate should be ideally reduced by ascertaining the values of the electrical current flowing from the second high-frequency power source 100 through the path extending along the direction in which the plasma becomes more uniform relative to the substrate in correspondence to varying impedance values and selecting an impedance value corresponding to the maximum current value, it should be ensured in a practical application that a value corresponding to a current value within a 2% range with respect to the maximum value or at least a 10% range with respect to the maximum current value is set.
It is to be noted that the impedance adjustment units achieved in the embodiments shown in
The optimal distance between the upper electrode 3 and the lower electrode 5 and the optimal processing pressure to be assumed in an apparatus having the high-frequency power source 4 connected to the upper electrode 3, as shown in
(Tests)
Next, tests conducted to verify the advantages of the embodiments of the present invention are described.
(Test 1)
A Test Method
A plane parallel plasma processing apparatus such as that shown in
The trimmers of the variable-capacity capacitors were adjusted to various positions so as to set the impedance at the impedance adjustment units were set to different values. The state of the plasma generated in the processing chamber was visually observed, the current flowing through the conductive path extending between the impedance adjustment units and the processing chamber (the current flowing to the lower electrode) was detected and the voltage at the upper electrode was measured at each impedance setting. The plasma was generated with the distance between the upper electrode and the lower electrode set to 60 mm, a mixed gas containing SF6 gas, HCl gas and He gas was used as the plasma generating gas, the frequency and the level of the power output from the high-frequency power source set to 13.56 MHz and 7.5 kW and the pressure set to 20 Pa (150 mTorr).
B Test Results
As the test results indicate, the lower current peaked at 79 A and the best plasma state was achieved at 79 A. The plasma state with the lower current at 78 A was evaluated to be fairly good and the plasma state with the lower current at 72 A was evaluated to be slightly poor. In addition, the plasma state at 66 A or lower was very poor. Accordingly, the impedance value should be adjusted so as to substantially maximize the lower current. With the measuring error and the like taken into consideration, it is desirable to ensure that the lower current is within a 10% range with respect to the maximum value and it is even more desirable to assure a lower current within a 2% range with respect to the maximum value. When the lower current value is substantially maximized, the upper voltage value, too, is substantially maximized, which means that the value of the impedance between the lower electrode and the processing chamber is substantially minimized. In other words, when the lower current value is substantially maximized, the level of the current flowing from the upper electrode to the wall of the processing chamber via the plasma is substantially at the minimum level and, under such circumstances, the plasma consistency is improved without an electrical discharge occurring between the upper electrode and the wall of the processing chamber.
(Test 2)
A Test Method
A two-frequency type plane parallel plasma processing apparatus such as that shown in
In addition, five impedance adjustment units were provided in conjunction with the high-frequency component from the high-frequency power source 4 of the upper side at positions corresponding to the four corners and the center of the rectangular substrate and likewise, five impedance adjustment units were provided in conjunction with the high-frequency component from the high-frequency power source 100 of the lower side at positions corresponding to the four corners and the center of the rectangular substrate. Each impedance adjustment unit was constituted by connecting in series a variable-capacity capacitor and an inductor, as shown in
B Test Results
The results of the test are presented in
The operations of the individual units in the plasma processing apparatus achieved in each of the embodiments described above are related with one another and thus they may be considered to be steps in an operational sequence. But assuming such a perspective, the present invention can be embodied as a plasma processing method.
While the invention has been particularly shown and described with respect to preferred embodiments thereof by referring to the attached drawings, the present invention is not limited to these examples and it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit, scope and teaching of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2004-136566 | Apr 2004 | JP | national |
| JP2004-381290 | Dec 2004 | JP | national |
