JP2013149790A - Plasma processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent the occurrence of an undesired resonance phenomenon without inducing the generation of a particle on a high-frequency transmission line around an upper electrode formed to be movable in up and down directions.SOLUTION: A capacitive coupling plasma processing device of cathode-coupling type comprises: a chamber 10; an upper electrode 44 provided in an upper portion of the chamber 10 to be movable in up and down directions; and a susceptor (lower electrode) 14 opposed to the upper electrode, provided that the upper electrode is arranged coaxially and in parallel with the susceptor. The upper electrode 44 has: an electrode main body 46 opposed to the susceptor 14; a conductive backing plate 48 opposed to a ceiling wall (top cover) 10b of the chamber 10; and a ring-like dielectric 52 for joining between a peripheral portion of the electrode main body 46 and a peripheral portion of the backing plate 48 so as to form a gap 50 therebetween. The backing plate 48 of the upper electrode 44 is physically and electrically connected through a bellows 72 to the chamber 10 which is a member at an earth potential.

Description

  The present invention relates to a cathode-coupled capacitively coupled plasma processing apparatus, and more particularly to an upper electrode that can move up and down.

  In general, in a capacitively coupled plasma processing apparatus, an upper electrode and a lower electrode are arranged in parallel in a processing vessel configured as a vacuum chamber, and a substrate to be processed (semiconductor wafer, glass substrate, etc.) is placed on the lower electrode. The high frequency power is applied to either one of the electrodes. Electrons are accelerated by the electric field formed between the two electrodes by this high-frequency power, and plasma is generated by impact ionization between the electrons and the processing gas, and the substrate surface is subjected to desired processing or processing by radicals or ions in the plasma. The Here, the distance between the upper electrode and the lower electrode (hereinafter referred to as “interelectrode gap”) is related to other process conditions such as pressure, and the application efficiency and stability of the high frequency power, the plasma density distribution, etc. It depends on you. Therefore, it is an important hardware process condition that affects the characteristics and results of the plasma process.

  In recent years, in such a cathode coupling type capacitively coupled plasma processing apparatus, in order to adjust the gap between electrodes, a lower electrode on the cathode side on which a substrate is placed is fixedly installed, and an upper electrode which is a counter electrode is provided. Attention has been focused on a device configuration that can move the device up and down (Patent Document 1). Such an upper electrode movable type plasma processing apparatus has an upper electrode support mechanism that supports the upper electrode so that the upper electrode can be moved in the vertical direction slightly away from the side wall of the chamber in the reduced pressure space of the chamber (processing vessel), A telescopic bellows that hermetically connects the back side region of the upper electrode and the chamber ceiling wall when viewed from the lower electrode side is provided. Since the bellows is made of a metal having high strength and durability such as stainless steel, the upper electrode is electrically connected to the chamber via the bellows and grounded. Even in the upper electrode movable type, the upper electrode is generally configured as a shower head having a large number of gas injection holes for supplying a processing gas to a plasma generation space or a processing space between both electrodes.

  When processing gas is supplied from a shower head (upper electrode) in a chamber depressurized to a predetermined pressure and high frequency power having a frequency suitable for plasma generation is applied from a high frequency power source to the lower electrode, the lower electrode and the upper electrode Plasma of the processing gas is generated by the high frequency discharge during. The generated plasma diffuses into the processing space, and high-frequency power flows through the upper electrode to the ground potential chamber. At this time, an electrical resonance phenomenon may occur on a high-frequency transmission path (hereinafter referred to as “high-frequency transmission path around the upper electrode”) from the processing space to the chamber having the ground potential via the upper electrode. The occurrence of such a resonance phenomenon is undesirable because it prevents the stable generation of plasma.

  There are a plurality of high-frequency transmission paths around the upper electrode. In particular, a resonance phenomenon on a high-frequency transmission path (hereinafter referred to as “upper electrode back side high-frequency transmission path”) from the processing space to the ground potential chamber via the upper electrode and the bellows is applied to the plasma space. In addition to high frequency power loss and bellows burning, it also induces abnormal discharge in the decompression space (ceiling space) between the back side area of the upper electrode and the chamber ceiling wall when viewed from the lower electrode side. Therefore, it is necessary to actively suppress the resonance phenomenon.

  For this purpose, it is necessary to prevent the unique resonance frequency in the high-frequency transmission path around the upper electrode from overlapping the frequency of the high-frequency power applied during plasma generation. However, in the upper electrode movable type, since the gap between the electrodes is adjusted so as to be an optimum process condition, the inductance component of the high frequency transmission line on the back side of the upper electrode varies due to expansion and contraction of the bellows. Therefore, the frequency-impedance characteristic of the high-frequency transmission line around the upper electrode also changes depending on the process conditions. That is, the resonance frequency specific to the high-frequency transmission line changes.

  More specifically, the smaller the gap between the electrodes, the longer the bellows extends and the inductance increases, so the natural resonance frequency decreases. On the contrary, the larger the gap between the electrodes, the shorter the bellows contract and the smaller the inductance thereof, so that the natural resonance frequency becomes higher. For example, when the movement range of the upper electrode (that is, the expansion / contraction range of the bellows) is 70 mm and the gap between the electrodes is continuously changed from the minimum value to the maximum value, the natural series resonance frequency is continuously reduced from less than 40 MHz to more than 60 MHz. It changes (FIG. 4 of patent document 1). Therefore, when a frequency of 40 MHz to 60 MHz is used for the high frequency for plasma generation, when the intrinsic series resonance frequency of the high frequency transmission path around the upper electrode overlaps the frequency of the high frequency for plasma generation by adjusting the gap between the electrodes, Resonance occurs.

  In order to cope with this problem, the technique of Patent Document 1 includes a conductive bypass member in a decompression space (ceiling space) between the upper electrode and the chamber ceiling wall. This bypass member is typically configured to be able to expand and contract by bending a strip-shaped aluminum thin plate, and connects the upper electrode and the chamber ceiling wall in parallel with the bellows. By providing this bypass member, the resonance point of the frequency-impedance characteristic on the high-frequency transmission line around the upper electrode can be set to a higher frequency region side, for example, more than 70 MHz (FIG. 6 of Patent Document 1). Accordingly, when the gap between the electrodes is changed from the minimum value to the maximum value, even if the gap between the electrodes is arbitrarily adjusted using a high frequency for plasma generation of 40 MHz to 60 MHz, the intrinsic series resonance frequency on the high frequency transmission path around the upper electrode Therefore, the resonance phenomenon that impairs the stability of the plasma does not occur.

JP 2011-204764 A

  However, the bypass member as described above may become a particle generation source due to its physical structure and expansion / contraction function. Particles generated from the bypass member in the ceiling space undesirably affect the plasma process, for example, through the gap between the upper electrode and the chamber side wall and into the processing space, causing abnormal discharge. Even if the bypass member is used, there is a limit to moving the resonance point of the frequency-impedance characteristic on the high-frequency transmission line around the upper electrode to the higher frequency region side, and it is not perfect as a resonance prevention measure.

  This is because plasma is generally a non-linear load, and therefore, in a chamber of a capacitively coupled plasma processing apparatus, harmonics having a frequency that is an integral multiple of the fundamental wave, or the sum or difference of fundamental waves or between fundamental waves and harmonics. IMD (cross modulation distortion) having a frequency of inevitably occurs. Of these harmonics and IMD, the second harmonic is the most influential, that is, the one having a large high frequency power. For this reason, for example, when a high frequency for plasma generation of 40 MHz is used, it is necessary to prevent not only the resonance at the fundamental frequency of 40 MHz but also the resonance phenomenon at the second harmonic of 80 MHz. Therefore, even when the fluctuation range of the series resonance frequency is set to a frequency higher than 70 MHz by providing the bypass member as described above, the series resonance frequency of the high-frequency transmission path around the upper electrode is adjusted to the second order by adjusting the gap between the electrodes. When it overlaps with the harmonic frequency (80 MHz), series resonance occurs. When series resonance occurs in the second harmonic, not only the problem of power loss and component burnout occurs, but also the plasma process is affected as in the case where series resonance occurs in the fundamental wave.

  The present invention solves the above-described problems of the prior art, and in the cathode coupling system in which the upper electrode as the counter electrode is configured to be movable in the vertical direction, the generation of particles on the high-frequency transmission line around the upper electrode is achieved. Provided is a capacitively coupled plasma processing apparatus that can effectively prevent the occurrence of an undesired resonance phenomenon without induction.

  Furthermore, the present invention provides a capacitively coupled plasma processing apparatus that improves the function of moving the resonance point of the frequency-impedance characteristic on the high-frequency transmission line around the upper electrode to a higher frequency region side.

  A plasma processing apparatus according to a first aspect of the present invention is a processing space between an upper electrode and a lower electrode provided opposite to each other in a cylindrical processing container capable of being evacuated to accommodate a substrate to be processed. A plasma processing apparatus for generating a plasma by high-frequency discharge of a processing gas and performing a desired processing on the substrate held on the lower electrode under the plasma, the upper electrode being removed from a side wall of the processing vessel An upper electrode support mechanism that supports the upper electrode so as to be movable in the vertical direction, and a stretchable conductive partition wall that connects the upper electrode and the ceiling wall of the processing vessel on the back side of the upper electrode when viewed from the lower electrode side. And the upper electrode has an electrode body facing the lower electrode, a conductive back plate facing the ceiling wall of the processing vessel, and a gap formed between the electrode body and the back plate. And a ring-shaped dielectric coupling the peripheral portion of the a peripheral portion backplate of the electrode body.

  In the above device configuration, when the height position of the upper electrode is changed in order to adjust the gap between the electrodes, the conductive partition wall expands and contracts and its inductance changes, and as a result, the natural resonance frequency on the high-frequency transmission path around the upper electrode is changed. Change. In particular, the series resonance frequency on the high-frequency transmission path (upper electrode back side high-frequency transmission path) from the processing space to the processing container having the ground potential via the upper electrode and the conductive partition changes.

  On the other hand, in the above device configuration, a capacitor is formed between the electrode body of the upper electrode and the back plate, and the capacitance is determined by the dielectric constant, area and thickness of the air gap. Therefore, a capacitor having a very low capacitance is inserted on the high frequency transmission line on the back side of the upper electrode, and as a result, the range in which the series resonance frequency on the high frequency transmission line on the back side of the upper electrode fluctuates with the adjustment of the gap between the electrodes is increased. It is possible to shift to a frequency region higher than the frequency of the high frequency used and even higher than the frequency of the second harmonic.

  A plasma processing apparatus according to a second aspect of the present invention provides a processing space between an upper electrode and a lower electrode that are provided opposite to each other in a cylindrical processing container that can be evacuated and accommodates a substrate to be processed. A plasma processing apparatus for generating a plasma by high-frequency discharge of a processing gas and performing a desired processing on the substrate held on the lower electrode under the plasma, the upper electrode being removed from a side wall of the processing vessel An upper electrode support mechanism that supports the upper electrode so as to be movable in the vertical direction, and a stretchable conductive partition wall that connects the upper electrode and the ceiling wall of the processing vessel on the back side of the upper electrode when viewed from the lower electrode side. The upper electrode is interposed between the electrode body and the back plate, the electrode main body facing the lower electrode, the conductive back plate facing the ceiling wall of the processing vessel Invitation And a body.

  In the above device configuration, when the height position of the upper electrode is changed in order to adjust the gap between the electrodes, the conductive partition wall expands and contracts and its inductance changes, and as a result, the natural resonance frequency on the high-frequency transmission path around the upper electrode is changed. Change. In particular, the series resonance frequency on the high-frequency transmission path (upper electrode back side high-frequency transmission path) from the processing space to the processing container having the ground potential via the upper electrode and the conductive partition changes.

  On the other hand, in the above device configuration, a capacitor is formed between the electrode body of the upper electrode and the back plate, and the capacitance is determined by the dielectric constant, area and thickness of the dielectric. Therefore, a low-capacitance capacitor is inserted on the high-frequency transmission line on the back side of the upper electrode, and as a result, the range in which the series resonant frequency on the high-frequency transmission line on the back side of the upper electrode fluctuates is shifted to the high-frequency region side. It is possible to move to a frequency region higher than the frequency of the high frequency used.

  According to the plasma processing apparatus of the present invention, by having the configuration as described above, particles are generated on the high-frequency transmission path around the upper electrode in the cathode coupling method in which the upper electrode as the counter electrode is configured to be movable in the vertical direction. It is possible to effectively prevent the occurrence of an undesired resonance phenomenon without inducing. Furthermore, the function of moving the resonance point of the frequency-impedance characteristic on the high-frequency transmission line around the upper electrode to the higher frequency region side can be improved.

It is sectional drawing which shows the structure of the plasma processing apparatus in one Embodiment of this invention. It is a partial expanded sectional view which shows the main structures around the upper electrode in the said plasma processing apparatus. It is a circuit diagram which shows the equivalent circuit of the high frequency transmission path around an upper electrode in the said plasma processing apparatus. It is a partial expanded sectional view which shows the structure of the upper electrode periphery in a comparative example. It is a circuit diagram which shows the equivalent circuit of the high frequency transmission line around the upper electrode in a comparative example. It is a figure which shows the frequency-impedance characteristic of the high-frequency transmission line around an upper electrode in a comparative example. It is a figure which shows the frequency-impedance characteristic (partially estimated value) of the high frequency transmission line around an upper electrode in an Example. It is sectional drawing which shows the structure of the plasma processing apparatus in 2nd Embodiment. It is a partial expanded sectional view which shows the one modification regarding the structure of the upper electrode periphery. It is a partial expanded sectional view which shows another modification regarding the structure around an upper electrode. It is a partial expanded sectional view which shows another modification regarding the structure around an upper electrode.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[Embodiment 1]

  FIG. 1 shows the configuration of a plasma processing apparatus according to an embodiment of the present invention. This plasma processing apparatus is configured as a cathode coupling type capacitively coupled (parallel plate type) plasma etching apparatus. For example, a cylindrical vacuum chamber (processing) made of aluminum whose surface is anodized (anodized). Container) 10. The chamber 10 has a cylindrical side wall 10a, a disk-shaped upper lid 10b that airtightly covers the upper end of the side wall 10a, and a bottom wall (not shown) connected to the lower end of the side wall 10a. Is grounded.

  A susceptor support 12 that is electrically insulated from the chamber 10 is provided at the center of the bottom of the chamber 10, and a thick disk-shaped susceptor 14 made of, for example, aluminum is formed on the susceptor support 12 with the chamber 10. It is fixedly arranged coaxially. The susceptor 14 constitutes a lower electrode, on which, for example, a semiconductor wafer W is placed as a substrate to be processed.

  An electrostatic chuck 16 for holding the semiconductor wafer W is attached to the upper surface of the susceptor 14. The electrostatic chuck 16 is obtained by sandwiching an electrode 18 made of a conductive film between a pair of insulating layers or insulating sheets, and a DC power source 22 is electrically connected to the electrode 18 via a switch 20. The semiconductor wafer W can be held on the electrostatic chuck 16 by an electrostatic attraction force by a DC voltage from the DC power source 22. Although not shown in the figure, the susceptor support 12 is cooled to a constant temperature with a coolant such as cooling water, and a heat transfer gas such as He gas is passed between the upper surface of the electrostatic chuck 16 and the back surface of the semiconductor wafer W via a gas supply line. A wafer temperature control mechanism is also provided.

  Around the susceptor 14, a cylindrical inner wall member 26 made of, for example, aluminum whose surface is anodized is provided via a ring-shaped insulator 24, and between the inner wall member 26 and the side wall 10 a of the chamber 10. An annular exhaust space 27 extending to the bottom of the chamber 10 is formed. A focus ring 30 is attached on the ring-shaped insulator 24 and the inner wall member 26 via an annular dielectric 28 made of, for example, quartz. The focus ring 30 is for improving the uniformity of etching, and is made of, for example, silicon, and is disposed on the electrostatic chuck 16 so as to cover the periphery of the semiconductor wafer W.

  An exhaust port (not shown) of the chamber 10 is provided at the bottom of the exhaust space 27. An exhaust device 34 is connected to the exhaust port via an exhaust pipe 32. The exhaust device 34 has a vacuum pump such as a turbo molecular pump, and can reduce the pressure in the chamber 10 to a desired degree of vacuum. An APC valve (not shown) for controlling the pressure in the chamber 10 is provided in the middle of the exhaust pipe 32. A gate valve (not shown) for opening and closing a loading / unloading port (not shown) for the semiconductor wafer W is attached to the side wall of the chamber 10.

Two systems of high-frequency power feeding units are electrically connected to the susceptor 14. The high frequency power supply unit of the first system matches the impedance on the load side with the high frequency power source 36 that outputs a high frequency RF ₁ having a constant frequency (for example, 40.68 MHz) suitable for plasma generation. For matching. The high-frequency power supply unit of the second system includes a high-frequency power source 40 that outputs a high-frequency RF ₂ having a constant frequency (for example, 3.2 MHz) suitable for drawing ions from the plasma into the semiconductor wafer W on the susceptor 14, and the high-frequency power source. And a matching unit 42 for matching the impedance on the load side with the impedance of 40.

  The configuration around the upper electrode, which is the counter electrode, is as follows. An upper electrode 44 is provided on the upper portion of the chamber 10 so as to be parallel to the susceptor 14 and movable in the vertical direction coaxially with the susceptor 14. The upper electrode 44 includes an electrode body 46 facing the susceptor 14, a conductive back plate 48 facing the ceiling wall (upper lid) 10 b of the chamber 10, and a gap 50 between the electrode body 46 and the back plate 48. The ring-shaped dielectric 52 which couple | bonds the peripheral part of the electrode main body 46 and the peripheral part of the backplate 48 so that it may be formed.

  The electrode main body 46 of the upper electrode 44 is a thick disk-shaped conductor made of, for example, aluminum whose surface is anodized, has a gas buffer chamber 54 inside thereof, and has a number of gas vent holes 46a on its lower surface. And has a gas inlet 46b on its upper surface. In this embodiment, in order to etch silicon on the main surface of the semiconductor wafer W, a disk-shaped top plate 56 made of quartz having high etching resistance is attached to the surface (lower surface) of the electrode body 46. A large number of gas vent holes (through holes) 56 a communicating with the gas vent holes 46 a of the electrode body 46 are formed in the quartz top plate 56. The electrode body 46 and the quartz top plate 56 are integrated to form a shower head.

  The back plate 48 of the upper electrode 44 is, for example, a circular plate body made of aluminum whose surface is anodized, and an opening for passing a cylindrical shaft (upper electrode support member) 58 extending vertically in the center of the plate. 48a is formed. A back plate 48 is fixed to the outer peripheral surface of the lower end portion of the shaft 58. Since the electrode body 46 is fixed to the back plate 48 via the ring-shaped dielectric 52 as will be described later, it may be directly fixed to the lower end of the shaft 58, or another member may be interposed. .

  The ring-shaped dielectric 52 is made of alumina, for example, and the upper surface of the peripheral portion thereof is larger than the upper surface of the electrode body 46 so that the gap 50 is formed between the electrode body 46 and the back plate 48. The electrode main body 46 is placed on and supported by a flange portion 52a that protrudes inward in the radial direction from the inner peripheral surface thereof. In this embodiment, a ring-shaped top plate 60 made of quartz is also attached to the lower surface of the ring-shaped dielectric 52 for silicon etching. A slight gap 61 of several mm or less is formed between the outer peripheral surfaces of the back plate 48, the ring-shaped dielectric 52 and the ring-shaped top plate 60 and the side wall 10 a of the chamber 10.

  The shaft 58 is made of, for example, stainless steel, and is provided so as to be movable in the vertical direction along an insulating guide member such as a collar 62 attached to the central opening of the ceiling wall (upper lid) 10 b of the chamber 10. The upper end of the shaft 58 is coupled to a lift mechanism (not shown) above the chamber 10, and the upper electrode 44 can be moved up and down like a piston by the lift driving force of the lift mechanism and has a movable range. It can be stationary or fixed at an arbitrary height position within (for example, 70 mm).

  The inside of the shaft 58 is hollow, and the processing gas supply pipe 66 from the processing gas supply unit 64 arranged outside the chamber 10 passes through the space inside the shaft 58 to the gas inlet 46 b of the electrode body 46. It is connected. The processing gas supply pipe 66 in the illustrated configuration example includes a rigid downstream gas pipe 68 that moves up and down together with the upper electrode 44 by the driving force of the lift mechanism, and a stationary processing gas supply section 64 and a downstream gas pipe 68. It is comprised with the flexible upstream gas pipe 70 which connects the inlet port 68a.

  Adjacent to the outside of the shaft 58, a bellows 72 is attached that hermetically connects the upper electrode 44 and the ceiling wall (upper lid) 10 b of the chamber 10. The bellows 72 is made of, for example, stainless steel and functions as a stretchable partition wall that blocks pressure. By the bellows 72, a ceiling space CS is formed between the upper electrode 44 and the ceiling wall 10b of the chamber 10. The ceiling space CS communicates with the plasma generation space or the processing space PS between the electrodes 14 and 44 through a gap 61 at the chamber side wall 10a, and is a decompressed space.

  The bellows 72 has an upper end coupled to the ceiling wall 10 b of the chamber 10 and a lower end coupled to the back plate 48 of the upper electrode 44. Thereby, the back plate 48 of the upper electrode 44 is electrically connected to the chamber 10 which is a ground potential member via the bellows 72.

  The control unit 74 includes one or a plurality of microcomputers, and in accordance with software (program) and recipe information stored in an external memory or internal memory, each unit in the apparatus, in particular, the high frequency power sources 36 and 40, the matching unit 38, 42, the individual operations of the exhaust device 34, the lift mechanism, and the like (sequence) of the entire device are controlled.

  The control unit 74 stores an operation panel (not shown) for a man-machine interface including an input device such as a keyboard and a display device such as a liquid crystal display, and various data such as various programs, recipes, and setting values. An external storage device (not shown) for storage is also connected. In this embodiment, the control unit 72 is shown as one control unit, but a plurality of control units may share the functions of the control unit 74 in parallel or hierarchically.

  The basic operation of single wafer dry etching in this capacitively coupled plasma etching apparatus is performed as follows. First, the gate valve is opened and the semiconductor wafer W to be processed is loaded into the chamber 10 and placed on the electrostatic chuck 18. Then, a processing gas such as a Cl-based etching gas is introduced into the chamber 10 from the processing gas supply unit 64 at a predetermined flow rate and flow rate ratio, and the pressure in the chamber 10 is set to a set value by evacuation by the exhaust device 34. Further, the high frequency RF1 (40.68 MHz) from the high frequency power supply 36 and the high frequency RF2 (3.2 MHz) from the high frequency power supply 40 are superimposed (or singly) and applied to the susceptor 14. Further, a DC voltage is applied from the DC power source 22 to the electrode 18 of the electrostatic chuck 16 to fix the semiconductor wafer W on the electrostatic chuck 16. The etching gas discharged from the shower head (upper electrode) 44 is discharged under a high-frequency electric field between the electrodes 44 and 14, and plasma is generated in the processing space PS. The workpiece (silicon in this embodiment) on the main surface of the semiconductor wafer W is etched by radicals and ions contained in the plasma.

  In this plasma etching apparatus, the gap between the electrodes, which is one of the process conditions, can be arbitrarily adjusted by moving the upper electrode 44 up and down to change its height position. In addition, the usable range (margin) of other process conditions such as gas flow rate and RF power can be expanded.

  On the other hand, harmonics having a frequency that is an integral multiple of each fundamental wave from plasma generated in the chamber 10, or IMDs (intermodulation distortion) having a frequency that is the sum or difference of fundamental waves or between fundamental waves and harmonics. Will occur. These harmonics and IMD not only cause power loss and component burnout, but may also affect the plasma process. In the cathode coupling type capacitively coupled plasma etching apparatus, these undesirable phenomena are caused by a high-frequency transmission path from the processing space to the chamber 10 at the ground potential via the upper electrode 44, that is, a high-frequency transmission path 75 around the upper electrode. Above, especially on the high-frequency transmission path from the processing space to the chamber 10 at the ground potential via the upper electrode 44 and the bellows 72, that is, on the high-frequency transmission path 76 on the back side of the upper electrode, in series with any harmonic or IMD. It appears prominently when resonance occurs. Of course, even when series resonance occurs with respect to any of the fundamental waves on the high-frequency transmission path 75 around the upper electrode, parts on the high-frequency transmission path 75 may be burned out, which is not desirable.

Therefore, it is necessary to devise so that series resonance does not occur on the high-frequency transmission path 75 around the upper electrode with respect to any of the fundamental wave, harmonics, and IMD. However, it is the second harmonic that has the greatest influence among the harmonics and the IMD, that is, has a large high frequency power, and it is practically sufficient if series resonance is prevented by the fundamental wave and the second harmonic. When the high frequency RF ₁ of 40.68 MHz is used for plasma generation as in this embodiment, series resonance should be prevented at the fundamental frequency of 40.68 MHz and the second harmonic frequency of 81.36 MHz. .

Of course, it is necessary to prevent series resonance with respect to the high frequency RF ₂ (3.2 MHz) for ion attraction and its second harmonic (6.4 MHz). However, normally, in this type of upper electrode movable plasma processing apparatus, even if the gap between the electrodes is minimized, the natural series resonance frequency of the high-frequency transmission path 75 around the upper electrode does not become several tens of MHz or less. Therefore, series resonance does not become a problem for the high frequency RF2 (3.2 MHz) and its second harmonic (6.4 MHz).

In this embodiment, instead of providing a bypass member as disclosed in Patent Document 1, the generation of particles on the high-frequency transmission path around the upper electrode is induced by specially contriving the configuration of the upper electrode 44 itself. Therefore, it is possible to reliably prevent the occurrence of series resonance at the high frequency RF ₁ for plasma generation, and also to reliably prevent series resonance at the second harmonic.

  The upper electrode 44 in this embodiment includes an electrode main body 46 that faces the susceptor 14 through the processing space PS, and the ceiling wall 10b of the chamber 10 in the ceiling space CS, as shown in an enlarged view in FIG. A ring-shaped dielectric that connects the periphery of the electrode body 46 and the periphery of the back plate 48 such that a gap 50 is formed between the opposing conductive back plate 48 and the electrode body 46 and the back plate 48. The body 52 is comprised. In FIG. 2 (and FIGS. 4, 9 to 11), the inner peripheral surface of the ring-shaped dielectric 52 and / or the ring-shaped top plate 60 is simplified to a flat surface for easy illustration and understanding. It has become.

FIG. 3 shows an equivalent circuit of the high-frequency transmission path 75 around the upper electrode. In this equivalent circuit, capacitors C ₅₆ and C ₅₀ , a coil L ₇₂ and a resistor R ₇₂ form a series circuit between the boundary surface 44S and the ground potential, and correspond to the upper electrode back side high-frequency transmission line 76.

Here, the capacitor C ₅₆ is provided by a quartz top plate 56 attached to the lower surface of the electrode body 46, and its capacitance is determined by the dielectric constant, area and thickness of the quartz top plate 56. The capacitor C ₅₀ is formed between the electrode body 46 and the back plate 46 of the upper electrode 44, and the capacitance is mainly determined by the dielectric constant, area, and thickness of the air gap 50. The coil L ₇₂ is given by the inductor portion of the bellows 72, and its inductance depends on the material, shape and size of the bellows 72, but varies depending on the length of the bellows 72. That is, the shorter the bellows 72 are shortened, the smaller the inductance is. The longer the bellows 72 is elongated, the larger the inductance is. The resistance R ₇₂ is given by the resistance of the bellows 72, and the resistance value is determined by the material, shape and size of the bellows 72 and does not depend on the length of the bellows 72. The capacitor C ₆₁ is a capacitor that exists in the high-frequency transmission path from the boundary surface 44S through the gap 61 to the chamber side wall 10a in parallel with the high-frequency transmission path 76 on the back side of the upper electrode. It depends on the dimensions and does not depend on the height position of the upper electrode 44.

  Here, as a comparative example, as shown in FIG. 4, a configuration in which each element of the back plate 48, the gap 50, and the ring-shaped dielectric 52 is omitted from the upper electrode 44 will be considered. In this comparative example, the lower end of the bellows 72 is coupled to the upper surface (back surface) of the electrode body 46.

FIG. 5 shows an equivalent circuit of the high-frequency transmission line 75 ′ around the upper electrode in this comparative example. Capacitor C _56, C ₅₀ in the equivalent circuit, coils L ₇₂ and resistor R _72, the capacitor C _56, C ₅₀ in the equivalent circuit of the embodiment (FIG. 3), respectively the same as the coil L ₇₂ and resistor R _72. That is, if omitted capacitor C ₅₀ from the equivalent circuit of the embodiment (FIG. 3), the equivalent circuit of the comparative example (FIG. 5). In other words, when the capacitor C ₅₀ is added to the equivalent circuit of the comparative example (FIG. 5), the equivalent circuit of the embodiment (FIG. 3) is obtained.

  By the way, the structure around the upper electrode in the comparative example is substantially the same as the structure around the upper electrode in Patent Document 1 except for the bypass member. Therefore, when the material, shape and size of the chamber, upper electrode, bellows, susceptor, etc. are the same as those around the upper electrode in Patent Document 1, the frequency-impedance characteristic of the high-frequency transmission path 75 'around the upper electrode is shown in FIG. (FIG. 6 corresponds to FIG. 4 of Patent Document 1).

In FIG. 6, “when the gap is minimum” means when the gap between the electrodes is minimized, that is, when the bellows 72 becomes the longest and the inductance becomes the maximum value L _72max . The inherent series resonance frequency f _S1 and parallel resonance frequency f _P1 in the high-frequency transmission line 75 ′ around the upper electrode at this time are theoretically expressed by the following equations (1) and (2) from the equivalent circuit of FIG.
f _S1 = 1 / _2π√ (L _72max · C ₅₆ ) (1)
f _P1 = 1 / _2π√ {(L _72max · C ₅₆ · C ₆₁ / (C ₅₆ + C ₆₁ )}} (2)
However, C ₅₆ and C ₆₁ are capacitances of the capacitors C ₅₆ and C ₆₁ .

In FIG. 6, the series resonance frequency f _S1 is about 38 MHz, and the parallel resonance frequency f _P1 is about 45 MHz.

Further, “when the gap is maximum” is when the gap between the electrodes is maximized, that is, when the bellows 72 is the shortest and the inductance becomes the minimum value L _72min . The inherent series resonance frequency f _S2 and parallel resonance frequency f _P2 in the high-frequency transmission line 75 ′ around the upper electrode at this time are theoretically expressed by the following equations (3) and (4) from the equivalent circuit of FIG.
f _S2 = 1 / _2π√ (L _72minx · C ₅₆ ) (3)
f _P2 = 1 / _2π√ {(L _{72 min} · C ₅₆ · C ₆₁ / (C ₅₆ + C ₆₁ )}} (4)

In FIG. 6, the series resonance frequency f _S2 is about 64 MHz, and the parallel resonance frequency f _P2 is about 75 MHz.

As described above, the upper electrode 44 of the embodiment has a configuration including the back plate 48, the gap 50, and the ring-shaped dielectric 52 in addition to the electrode main body 46 and the quartz top plate 56. A capacitor C ₅₀ is included on the back side high-frequency transmission line 76. In this case, the capacitor C ₅₀ is connected in series with the capacitor C _56, and the combined capacitance C _S is expressed by the following equation (5).
C _S = C ₅₀ · C ₅₆ / (C ₅₀ + C ₅₆ ) (5)
However, C ₅₀ and C ₅₆ are capacitances of the capacitors C ₅₀ and C ₅₆ .

Here, the capacitance of the capacitor C ₅₀ is the dielectric constant epsilon ₅₀ of gap 50, S ₅₀ the area, and the thickness and d _50, expressed by the following equation (6).
C ₅₀ = ε ₅₀ · S ₅₀ / d ₅₀ ··· (6)

On the other hand, the capacitance of the capacitor C ₅₆ is expressed by the following equation (7), where the dielectric constant of the quartz top plate 56 is ε ₅₆ , the area is S ₅₆ , and the thickness is d ₅₆ .
C ₅₆ = ε ₅₆ · S ₅₆ / d ₅₆ ··· (7)

The dielectric constant ε ₅₀ of the air gap 50 is 1, which is about ¼ of the dielectric constant ε ₅₆ of the quartz top plate 56. The area S ₅₀ of the air gap 50 is smaller than the area S ₅₆ of the quartz ceiling plate 56 (only approximate area fraction of the center opening 48a of the back 48 small), for example 0.8 times that. Thus, for example, and the thickness d ₅₀ of the gap 50 is the same as the thickness d ₅₆ of the quartz ceiling plate 56, the formula (6), a C ₅₀ = 0.2 C ₅₆ (7), from equation (5) C _S ≈0.17C ₅₆

As described above, according to the embodiment, the capacitor C ₅₀ formed by the back plate 48 of the upper electrode 44, the gap 50 and the ring-shaped dielectric 52 is provided on the upper electrode rear side high-frequency transmission line 76, so that the upper electrode rear side is provided. The synthetic capacity C _S on the high-frequency transmission line 76 can be significantly reduced. Thus, the resonance point of the frequency-impedance characteristic of the high-frequency transmission line 75 around the upper electrode in the embodiment is higher than the resonance point of the frequency-impedance characteristic of the high-frequency transmission line 75 ′ around the upper electrode in the comparative example. Can be moved greatly to. That is, if C _S ≈KC ₅₆ (K is a coefficient smaller than 1), the frequency-impedance characteristic (particularly each resonance point) can be made to have a high frequency as a whole by about 1 / √K times.

The theoretical series resonance frequency f _S1 and the parallel resonance frequency f _P1 of the high-frequency transmission line 75 around the upper electrode at the “minimum gap” are theoretically expressed by the following equations (8) and (9) from the equivalent circuit of FIG. Represented.
f _S1 = 1 / _2π√ (L _72max · C _S ) (8)
f _P1 = 1 / _2π√ {(L _72max · C _S · C ₆₁ / (C _S + C ₆₁ )} (9)
However, C _S and C ₆₁ are capacitances of the capacitors C _S and C ₆₁ .

Further, the intrinsic series resonance frequency f _S1 and the parallel resonance frequency f _P1 of the high-frequency transmission line 75 around the upper electrode at the “maximum gap” are theoretically expressed by the following equations (10) and (11) from the equivalent circuit of FIG. Represented.
f _S2 = 1 / _2π√ (L _72minx · C _S ) (10)
f _P2 = 1 / _2π√ {(L _{72 min} · C _S · C ₆₁ / (C _S + C ₆₁ )} (11)

When the thickness d ₅₀ of the gap 50 is the same as the thickness d ₅₆ of the quartz top plate 56 and C _S ≈0.17C ₅₆ as in the above example, the frequency-impedance characteristic of the high-frequency transmission line 75 around the upper electrode is set. Is as shown in FIG. Here, the natural series resonance frequency f _S1 at the “minimum gap” is about 93 MHz (38 × 1 / √0.17), and the natural series resonance frequency f _S1 at the “maximum gap” is about 156 MHz (64 × 1). /√0.17). When the gap between the electrodes is between the minimum value and the maximum value, the natural series resonance frequency f _S is an intermediate value between about 93 MHz and about 156 MHz.

Note that the values of the natural parallel resonance frequencies f _P1 and f _P2 at the “minimum gap” and “maximum gap” according to the embodiment also depend on the capacitance of the capacitor C ₆₁ , and thus the natural parallel resonance frequency f _P1 in the comparative example. , F _P2 (known) and the value of K in the relational expression C _S ≈KC ₅₆ (known) cannot be calculated. However, since K is a coefficient smaller than 1, inherent parallel resonance frequency f _P1, f _P2 in the embodiment shifts to a higher frequency region side than inherent parallel resonance frequency f _P1, f _P2 in the comparative example, and the formula (8) ( 10) and the expressions (9) and (11), they exist in a frequency region higher than the natural series string resonance frequencies f _S1 and f _{S2 in the} embodiment. Therefore, the parallel resonance point shown in FIG. 7 is an estimate and is not calculated.

As described above, in the plasma etching apparatus of this embodiment, the plasma on the high-frequency transmission path 76 around the upper electrode is adjusted no matter how the gap between the electrodes is adjusted by changing the height position of the upper electrode 44 by the lift mechanism. In addition to completely avoiding series resonance at the generating high frequency RF ₁ (40.68 MHz), series resonance at its second harmonic (81.36 MHz) can also be completely avoided.

[Other Embodiments or Modifications]

  FIG. 8 shows the configuration of the plasma processing apparatus in the second embodiment of the present invention. The second embodiment differs from the first embodiment described above in a configuration including a DC power supply unit 80, a switch 82, and a filter circuit 84 in order to apply a DC voltage to the electrode body 46 of the upper electrode 44. Yes, everything else is the same as in the first embodiment.

The DC power supply unit 80 is composed of a variable DC power supply, for example, and is configured to output a DC voltage V _DC of −2000 to +1000 V. Alternatively, as another form, the DC power supply unit 80 may include a plurality of DC power supplies that output different DC voltages, and selectively output one of the plurality of DC voltages. The polarity and absolute value of the output (voltage, current) of the DC power supply unit 80 and on / off switching of the switch 82 are controlled by the control unit 74.

  A DC grounding component (not shown) made of a conductive material such as Si or SiC is attached to an appropriate location facing the processing space PS in the chamber 10. This DC grounding component is always grounded via a grounding line (not shown).

The filter circuit 84 applies the DC voltage _VDC from the DC power supply unit 80 to the electrode body 46 of the upper electrode 44, while the high frequency current that has entered from the susceptor 12 through the processing space PS and the upper electrode 44 is grounded. So that it does not flow to the DC power supply unit 80 side. Although not shown, the filter circuit 84 is composed of, for example, an LC ladder circuit, and a high-frequency transmission path (hereinafter referred to as “upper electrode”) from the processing space PS to the ground potential via the electrode body 46 of the upper electrode 44 and the filter circuit 84. It is referred to as a “DC application system high-frequency transmission line.”) The inductance of the coil and the capacitance of the capacitor in the LC ladder circuit are selected so that resonance does not occur on 86. These coils and capacitors are commercially available electronic components, and their inductance and capacitance can be selected without being restricted by hardware. The upper electrode DC application system high-frequency transmission path 86 is in an electrically parallel relationship with the high-frequency transmission path 75 around the upper electrode or the high-frequency transmission path 76 around the upper electrode as viewed from the plasma side, and is independent from each other with respect to series resonance. There is a relationship.

In the configuration including such an upper DC bias mechanism, for example, a negative DC voltage V _DC is applied to the electrode body 46 of the upper electrode 44 to thereby form a photoresist film (especially an ArF resist) used as a plasma etching mask. The etching resistance of the film) can be enhanced.

When plasma is generated in the chamber 10, an ion sheath (hereinafter referred to as “upper electrode sheath”) is formed between the plasma and the upper electrode 44. This upper electrode sheath acts as a capacitor for high frequency power. Therefore, the high-frequency transmission path from the plasma to the ground potential through the electrode body 46 of the upper electrode sheath and the upper electrode 44 is located above the entrance of the high-frequency transmission path 75 around the upper electrode and the high-frequency transmission path 86 around the upper electrode DC application system. This corresponds to an electrode sheath capacitor added in series. Here, the capacitor of the upper electrode sheath changes its thickness (and hence its capacitance) according to the process conditions (pressure, RF power, gas type, etc.) and the DC voltage _VDC , and the larger the sheath thickness, the more The capacitance decreases, and the capacitance increases as the sheath thickness decreases. Therefore, due to the presence of the upper electrode sheath, the series resonance frequency slightly shifts toward the higher frequency region, and the amount of movement increases as the sheath thickness increases.

9 to 11 show modifications of the upper electrode in the present invention. In the modification of FIG. 9, the space of the gap 50 in the upper electrode 44 is filled with a dielectric 88 to form an electrode structure without the gap 50. In this case, the capacitance of the capacitor C ₈₈ formed between the electrode body 46 and the back plate 46 of the upper electrode 44 is mainly determined by the dielectric constant, area, and thickness of the dielectric 88. Therefore, the material of the dielectric 88 is preferably a low dielectric constant. For example, in the case of using a quartz dielectric 88, the capacitance of the capacitor C ₈₈ is about four times the capacitance of the capacitor C ₅₀ of the case of providing the air gap 50. Nevertheless, the combined capacitance C _S of the quartz top plate 56 and the capacitor C ₅₆ is C _S ≈0.5C ₅₆ from the above equation (5), and the series resonance frequency in the frequency-impedance characteristic of the high-frequency transmission path 75 around the upper electrode. Can be shifted to the right by about 1 / √0.5 times on the frequency axis. That is, the series resonance frequency of “when the gap is minimum” can be shifted to about 54 MHz. Therefore, in this case, series resonance can be prevented at least for the fundamental frequency 40.68 MHz of the high frequency RF ₁ for plasma generation.

  In the modified example of FIG. 10, the peripheral portion of the back plate 48 is extended downward to wrap around the outer peripheral surface of the dielectric 88. Basically, it conforms to the modification of FIG.

In the modification of FIG. 11, a conductor, for example, an electrode plate 90 made of silicon is attached to the lower surface of the electrode body 46. For example, when the silicon oxide film is etched on the main surface of the semiconductor wafer W, such a silicon electrode plate 90 is used as a top plate. In this case, the capacitor C ₅₆ is eliminated in the high-frequency transmission path 75 around the upper electrode, and the capacitor C _{50 is the} only capacitor on the high-frequency transmission path 76 on the back side of the upper electrode. However, the capacitance of the capacitor C ₅₀ is very small as described above. For example, when the thickness of the gap 50 is the same as the thickness of the quartz top plate 56, C ₅₀ ≈0.2C ₅₆ . Therefore, in this case, the series resonance frequency in the frequency-impedance characteristic of the high-frequency transmission line 75 around the upper electrode can be shifted to the right by about 1 / √0.2 times. That is, the series resonance frequency of “when the gap is minimum” can be shifted to about 84 MHz. Therefore, in this case, the series resonance at the fundamental frequency of 40.68 MHz of the high frequency RF1 for plasma generation can be prevented, and the series resonance at 81.36 MHz of the second harmonic can also be prevented.

Of course, by increasing the thickness d ₅₀ of the gap 50, it can be further enhanced transfer effect described above. For example, if d ₅₀ is doubled, C ₅₀ ≈0.1C ₅₆ . Therefore, in this case, the series resonance frequency in the frequency-impedance characteristic of the high-frequency transmission line 75 around the upper electrode can be shifted to the right by about 1 / √0.1 times on the frequency axis. That is, the series resonance frequency of “when the gap is minimum” can be shifted to about 118 MHz.

In this way, by providing the gap ₅₀ that gives the small capacitor C ₅₀ inside the upper electrode 44, the series resonance frequency in the frequency-impedance characteristic of the high-frequency transmission path 75 around the upper electrode is greatly increased to the right (higher frequency region side). Thus, the series resonance at the high frequency RF ₁ for plasma generation and the series resonance at the second harmonic can be surely prevented.

  Further, the configuration in which the gap 50 is provided inside the upper electrode 44 has a significantly lower volume, weight, and cost of the entire upper electrode 44 than the configuration in which the gap 50 is filled with the dielectric 88 (FIGS. 9 and 10). There is also an advantage.

  Of course, the upper electrode structure according to the present invention and the bypass member described in Patent Document 1 can be used in combination. In particular, when the upper electrode 44 has an electrode structure without the gap 50 in the present invention, the combined use with the bypass member may be practical. In that case, the bypass member is light in terms of the effect of moving the resonance point of the frequency-impedance characteristic to the higher frequency region side, so it is optimal from another viewpoint such as prevention of particle generation, cost reduction, or ease of installation. The configuration can be taken.

  The present invention is not limited to the plasma etching apparatus as in the above-described embodiment, and is a cathode coupling type capacitively coupled plasma processing apparatus that performs an arbitrary plasma process such as plasma CVD, plasma ALD, plasma oxidation, plasma nitridation, and sputtering. Applicable. The substrate to be treated in the present invention is not limited to a semiconductor wafer, and a flat panel display, organic EL, various substrates for solar cells, a photomask, a CD substrate, a printed substrate, and the like are also possible.

10 chamber 10a chamber side wall 10b chamber ceiling (top lid)
14 Susceptor (lower electrode)
34 Exhaust device 36, 40 High frequency power supply 38, 42 Matching device 44 Upper electrode (shower head)
46 Electrode body 50 Void 52 Ring-shaped dielectric 64 Processing gas supply unit 74 Control unit 75 High frequency transmission path around upper electrode 76 High frequency transmission path on the back side of upper electrode 80 DC power supply unit 84 Filter circuit

Claims (10)

Generating plasma by high-frequency discharge of a processing gas in a processing space between an upper electrode and a lower electrode provided opposite to each other in a cylindrical processing vessel capable of being evacuated to accommodate a substrate to be taken in and out; A plasma processing apparatus for performing a desired process on the substrate held on the lower electrode under plasma,
An upper electrode support mechanism for supporting the upper electrode so as to be movable in the vertical direction away from the side wall of the processing vessel;
A stretchable conductive partition wall connecting the upper electrode and the ceiling wall of the processing vessel on the back side of the upper electrode as viewed from the lower electrode side;
The upper electrode has an electrode body facing the lower electrode, a conductive back plate facing the ceiling wall of the processing vessel, and a gap formed between the electrode body and the back plate. A ring-shaped dielectric that connects the peripheral portion and the peripheral portion of the back plate;
Plasma processing equipment.   The plasma processing apparatus according to claim 1, further comprising a first high-frequency power source that applies a first high-frequency power for mainly generating plasma to the lower electrode.   3. The plasma processing apparatus according to claim 2, wherein the lower electrode has a second high-frequency power source for applying a second high-frequency power mainly for drawing ions from the plasma to the substrate on the first electrode.   A high frequency from the boundary surface between the processing space and the upper electrode to the ground potential via the upper electrode at a height position of the upper electrode that minimizes the gap between the electrodes under the upper electrode support mechanism. 4. The plasma processing apparatus according to claim 2, wherein a series resonance frequency existing in a frequency-impedance characteristic when a transmission path is expected is higher than a frequency of the first high frequency.   A high frequency from the boundary surface between the processing space and the upper electrode to the ground potential via the upper electrode at a height position of the upper electrode that minimizes the gap between the electrodes under the upper electrode support mechanism. The plasma processing apparatus according to claim 2 or 3, wherein a series resonance frequency existing in a frequency-impedance characteristic when a transmission path is expected is higher than a frequency of a second harmonic of the first high frequency. Generating plasma by high-frequency discharge of a processing gas in a processing space between an upper electrode and a lower electrode provided opposite to each other in a cylindrical processing vessel capable of being evacuated to accommodate a substrate to be taken in and out; A plasma processing apparatus for performing a desired process on the substrate held on the lower electrode under plasma,
An upper electrode support mechanism for supporting the upper electrode so as to be movable in the vertical direction away from the side wall of the processing vessel;
A stretchable conductive partition wall connecting the upper electrode and the ceiling wall of the processing vessel on the back side of the upper electrode as viewed from the lower electrode side;
The upper electrode includes an electrode body facing the lower electrode, a conductive back plate facing the ceiling wall of the processing container, and a dielectric interposed between the electrode body and the back plate.
Plasma processing equipment.   The plasma processing apparatus according to claim 6, further comprising a first high-frequency power source that applies a first high-frequency power for mainly generating plasma to the lower electrode.   The plasma processing apparatus according to claim 7, wherein the lower electrode has a second high-frequency power source for applying a second high-frequency power for mainly drawing ions from the plasma to the substrate on the first electrode.   A frequency when a high-frequency transmission path from the boundary surface between the processing space and the upper electrode to the ground potential through the upper electrode is expected at the height position of the upper electrode where the gap between the electrodes is minimized. The plasma processing apparatus according to claim 6, wherein a series resonance frequency existing in the impedance characteristic is higher than a frequency of the first high frequency.   The plasma processing apparatus according to any one of claims 1 to 9, further comprising a DC power source that applies a DC voltage to the electrode body of the upper electrode via a filter circuit.

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