JP2011171750A - Plasma processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To optimize respective actions or functions of both high frequencies at the same time in a system of applying two high frequencies (or high frequencies and direct current) different in frequencies to one-side electrode of a capacitive coupling type. <P>SOLUTION: An upper electrode 80 facing a susceptor (lower electrode) 14 interposing a plasma space PS includes a first upper electrode 84 and a second upper electrode 86. A DC voltage is applied to the first upper electrode 84 functioning also as a shower head from a variable DC power source 92. A processing gas supply source 62 is connected to the inside of the first upper electrode 84 or a gas chamber through a gas supply tube 60. The second upper electrode 86 is arranged behind the first upper electrode 84, and electrically insulated from the first upper electrode 84 and a chamber 90. A plasma-generating high frequency is applied to the second upper electrode 86 through a matching unit from a high-frequency power source 96. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for performing plasma processing on a substrate to be processed, and more particularly to a capacitively coupled plasma processing apparatus of a two-frequency superimposition application method.

  Plasma is used for fine processing or processing such as etching, deposition, oxidation, sputtering, etc. in the manufacturing process of semiconductor devices and FPD (Flat Panel Display) in order to cause a favorable reaction at a relatively low temperature with the processing gas. . Conventionally, among single-wafer plasma processing apparatuses, particularly plasma etching apparatuses, capacitively coupled plasma processing apparatuses have been mainstream.

  Generally, in a capacitively coupled plasma processing apparatus, an upper electrode and a lower electrode are arranged in parallel in a processing container configured as a vacuum chamber, and a substrate to be processed (semiconductor wafer, glass substrate, etc.) is mounted on the lower electrode. And applying a high frequency to one of the two electrodes. Electrons are accelerated by the electric field formed by this high frequency, plasma is generated by impact ionization between the electrons and the processing gas, and desired fine processing (for example, etching processing) is performed on the substrate surface by radicals or ions in the plasma. .

  Recently, with the miniaturization of design rules in the manufacturing process, high-density plasma under a low pressure is required for plasma processing, and the capacitively coupled plasma processing apparatus as described above (generally, 13.56 MHz) than before. However, the frequency of a remarkably high high frequency region (40 MHz or higher) has been used. However, when the frequency of the high frequency discharge is increased, a high frequency applied from the high frequency power source to the back surface or back surface of the electrode via the feeding rod is transmitted to the electrode main surface (surface facing the plasma) by the skin effect, A high-frequency current flows from the edge portion toward the center portion on the electrode main surface. For this reason, the electric field intensity at the center of the electrode main surface is higher than the electric field intensity at the edge, and the density of the generated plasma is higher at the electrode center than at the electrode edge, and the process characteristics vary in the radial direction. The problem is becoming prominent.

  In order to cope with this problem, contrivances such as providing a mortar-shaped or tapered recess on the main surface of the electrode to which a high frequency is applied and embedding a dielectric therein are performed (for example, see Patent Document 1). According to such an electrode structure, since the impedance on the electrode center side is relatively large with respect to the plasma side and the impedance on the electrode edge side is low, the high-frequency electric field on the electrode edge side is strengthened while the electrode center side is on the side. The high frequency electric field is weakened, and the uniformity of the electric field strength or plasma density is improved. In addition, an electrode structure in which a high resistance member is provided at the center of the electrode main surface is also known, although the power consumption increases due to Joule heat (see, for example, Patent Document 2).

  On the other hand, in the capacitively coupled plasma processing apparatus, in order to individually optimize the plasma density and the selectivity of anisotropic etching, the lower electrode supporting the substrate has a relatively high frequency suitable for plasma generation. In recent years, a lower two-frequency superimposing application method that superimposes and applies a first high frequency (generally 27 MHz or higher) and a second high frequency of a relatively low frequency (generally 13.56 MHz or lower) suitable for ion attraction is becoming mainstream. (For example, refer to Patent Document 3).

JP 2004-363552 A JP 2000-323456 A JP 2000-156370 A

  However, in the conventional plasma processing apparatus adopting the lower two-frequency superimposition application method as described above, a high high frequency region (40 MHz or more) is used for plasma generation, and a dielectric or a high resistance member is embedded as described above. When a lower electrode with a structure in which the impedance at the center of the electrode is relatively higher than the impedance at the electrode edge is used, the electric field strength distribution on the main surface (upper surface) of the lower electrode is high with a high frequency for plasma generation. On the other hand, the uniformity is improved, but at the high frequency with a low frequency for ion attraction, the electrode center side is lower than the electrode edge side, and the uniformity is lowered. For this reason, even if the uniformity of the plasma density can be improved, there is a trade-off problem that the uniformity of the anisotropic etching accuracy is lowered in exchange.

  The present invention has been made in view of the above-described problems of the prior art, and in a system in which two high frequencies (or direct current and high frequency) having different frequencies are applied to a capacitively coupled electrode on one side. A plasma processing apparatus capable of simultaneously optimizing (or direct current and high frequency) actions or functions is provided.

  The plasma processing apparatus of the present invention includes a processing container that can be evacuated, a first electrode that is disposed in the processing container so as to face the plasma space, and a back side of the first electrode when viewed from the plasma space side. A second electrode disposed on the first electrode, a processing gas supply unit that supplies a desired processing gas to the plasma space, a first power supply unit that applies a first high frequency or direct current to the first electrode, And a second power supply unit that applies a second high frequency to the second electrode.

  In the above configuration, the first high frequency or direct current is applied to the first electrode facing the plasma space, and the second high frequency is applied to the second electrode disposed behind the first electrode. The first electrode can have an electrode structure optimal for the action of the first high frequency or direct current, and the second electrode can have the electrode structure optimum for the action of the second high frequency.

  According to a preferred aspect of the present invention, the third electrode is arranged in parallel directly opposite the first electrode across the plasma space. Then, a third high frequency is applied to the third electrode from the third power feeding unit.

  According to a preferred aspect of the present invention, a recess is formed in the main surface of the second electrode, and a dielectric is embedded in the recess. In this case, a configuration in which the thickness of the dielectric gradually decreases from the electrode center portion toward the electrode edge portion is preferable. According to such an electrode structure, when the frequency of the second high frequency is considerably increased in order to increase the plasma density, the skin effect in the second electrode is canceled and a high frequency electric field based on the second high frequency is generated in the electrode radial direction. The plasma density in the plasma space can be made uniform in the radial direction of the electrode.

  Moreover, according to the suitable one aspect | mode of this invention, the electrode structure which served as the shower head of the process gas supply part in the 1st electrode is taken.

  According to the plasma processing apparatus of the present invention, as described above, in the method of applying two high frequencies (or DC and high frequency) having different frequencies to the capacitively coupled one side electrode, the one side electrode is divided into two vertically. Thus, both high frequencies (or direct current and high frequency) are applied separately, so that the action or function of both high frequencies (or direct current and high frequency) can be optimized simultaneously.

It is a longitudinal cross-sectional view which shows the structure of the plasma etching apparatus in one Embodiment of this invention. It is a longitudinal cross-sectional view which shows the structure of the plasma etching apparatus in one modification of embodiment. It is a longitudinal cross-sectional view which shows the structure of the plasma etching apparatus by another Example of this invention.

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

  FIG. 1 shows the configuration of a plasma etching apparatus according to the first embodiment of the present invention. This plasma etching apparatus is configured as a capacitive coupling type plasma etching apparatus of a lower two-frequency superimposing application method, and has a cylindrical chamber (processing vessel) 10 made of metal made of, for example, aluminum or stainless steel. The chamber 10 is grounded for safety.

  A susceptor 14 serving as a lower electrode and a substrate holding table is provided on the bottom surface of the chamber 10 via an annular insulating member 12 made of ceramic, for example. The susceptor 14 has an upper susceptor electrode 16 and a lower susceptor electrode 18 that constitute the first and second lower electrodes in the present invention, respectively.

  An annular or cylindrical power supply body 20 is disposed on the annular insulating member 12, and the upper susceptor electrode 16 is mounted substantially horizontally on the cylindrical power supply body 20. The upper susceptor electrode 16 is a circular flat plate electrode having a diameter that is slightly larger than that of the substrate to be processed, for example, the semiconductor wafer W, and is preferably a conductive material having a high resistivity, such as tungsten (W) or silicon (Si), for the reason described later. Etc. The annular insulating member 12 is made of a low resistivity material such as aluminum with little transmission loss.

  A first high frequency power source 22 is electrically connected to the upper susceptor electrode 16 via a matching unit 24, a power feeding rod 26, and a cylindrical power feeding body 20. The first high frequency power supply 22 outputs a first high frequency of a predetermined frequency, for example, 2 MHz, which contributes mainly to the drawing of ions into the semiconductor wafer W held on the susceptor 14 with a desired power. The first high frequency (2 MHz) from the first high frequency power supply 22 is supplied to the upper susceptor electrode 16 through the matching unit 24, the power supply rod 26 and the cylindrical power supply body 20. And it is emitted toward the plasma space PS above the main surface (upper surface) of the upper susceptor electrode 16.

  The lower susceptor electrode 18 is a circular substantially flat electrode made of a conductive material having a low resistivity, for example, aluminum. It is disposed inside the annular insulating member 12 and directly below the upper susceptor electrode 16 in a state of being electrically insulated from the surroundings (16, 20). As shown in the drawing, a tapered concave portion is formed on the main surface (upper surface) of the lower susceptor electrode 18 so that the center of the electrode is at the bottom, and a dielectric 28 is embedded in the concave portion. Such an electrode structure is for improving the uniformity of the electric field strength or plasma density in the electrode radial direction, and uses the technique described in Patent Document 1 (Japanese Patent Laid-Open No. 2004-363552). The gaps between the lower susceptor electrode 18 and the annular insulating member 12 and the upper susceptor electrode 16 are closed with, for example, a cylindrical insulator 30 and a disc insulator 32 made of ceramic in order to prevent discharge. preferable.

  A second high frequency power supply 34 is electrically connected to the lower susceptor electrode 18 via a matching unit 36 and a power feed rod 38. The second high frequency power supply 34 outputs a predetermined frequency, for example, a high frequency of 40 MHz, which mainly contributes to plasma generation, with a desired power. The second high frequency (40 MHz) from the second high frequency power supply 34 is supplied to the lower susceptor electrode 18 through the matching unit 36 and the power feed rod 38. And it is emitted toward the plasma space PS above the main surface (upper surface) of the lower susceptor electrode 18.

  An electrostatic chuck 40 is provided on the upper surface of the upper susceptor electrode 16 to hold the semiconductor wafer W with an electrostatic adsorption force. The electrostatic chuck 40 is obtained by sandwiching an electrode 42 made of a conductive film between a pair of insulating layers or insulating sheets 44, and a DC power supply 46 is electrically connected to the electrode 42. The semiconductor wafer W can be attracted and held on the chuck by a Coulomb force by a DC voltage from the DC power supply 46. Around the electrostatic chuck 40, a focus ring 48 made of, for example, silicon is arranged to improve etching uniformity. A cylindrical inner wall member 50 made of, for example, quartz is attached to the outer peripheral surfaces of the annular insulating member 12 and the cylindrical power feeder 20.

  In order to control the temperature of the semiconductor wafer W placed on the susceptor 14, a refrigerant chamber or a refrigerant passage (not shown) is provided inside the upper susceptor electrode 16, and the external chiller unit (not shown) A configuration in which a coolant having a predetermined temperature, such as cooling water, is circulated and supplied to the coolant passage is also possible. Similarly, in order to control the temperature of the semiconductor wafer W, a heat transfer gas such as He gas from a heat transfer gas supply mechanism (not shown) is supplied to the upper surface of the electrostatic chuck 40 via a gas supply line (not shown). It is also possible to supply between the semiconductor wafer W and the back surface of the semiconductor wafer W.

  On the ceiling of the chamber 10, there is provided a shower head 52 that is parallel to the susceptor 12 and also serves as an upper electrode of the ground potential. The shower head 52 includes a lower electrode plate 54 having a large number of gas vent holes 54a, and an electrode support 56 that detachably supports the electrode plate 54. The electrode plate 54 is made of, for example, Si or SiC, and the electrode support 56 is made of, for example, anodized aluminum. A gas chamber 58 is provided inside the electrode support 56, and a processing gas supply source 62 is connected to the gas chamber 58 via a gas supply pipe 60. A mass flow controller (MFC) 64 and a gas flow pipe 60 are connected to the gas supply pipe 60. An open / close valve 66 is provided. When a predetermined processing gas is introduced from the processing gas supply source 62 into the gas chamber 58, the processing gas is ejected in a shower shape from the gas ejection holes 54 a of the electrode plate 54 toward the semiconductor wafer W on the susceptor 14. It has become.

  An annular space formed between the susceptor 14 and the side wall of the chamber 10 is an exhaust space, and an exhaust port 68 of the chamber 10 is provided at the bottom of the exhaust space. An exhaust device 72 is connected to the exhaust port 68 via an exhaust pipe 70. The exhaust device 72 has a vacuum pump such as a turbo molecular pump, and can depressurize the interior of the chamber 10, particularly the plasma processing space, to a desired degree of vacuum. A gate valve 76 that opens and closes the loading / unloading port 74 for the semiconductor wafer W is attached to the side wall of the chamber 10.

  In order to perform etching in this plasma etching apparatus, first, the gate valve 76 is opened, and the semiconductor wafer W to be processed is loaded into the chamber 10 and placed on the electrostatic chuck 40. Then, a predetermined processing gas, that is, an etching gas (generally a mixed gas) is introduced into the chamber 10 from the processing gas supply source 62 at a predetermined flow rate and flow rate ratio, and the pressure in the chamber 10 is set to a set value by vacuum evacuation by the exhaust device 72. To. Furthermore, a first high frequency (2 MHz) is applied from the first high frequency power supply 22 to the upper susceptor electrode 16 at a predetermined power, and at the same time, a second high frequency (40 MHz) is applied from the second high frequency power supply 34 to the lower susceptor electrode. 18 is applied. Further, a DC voltage is applied from the DC power supply 46 to the electrode 42 of the electrostatic chuck 40 to fix the semiconductor wafer W on the electrostatic chuck 40. The etching gas discharged from the upper electrode or the shower head 52 is converted into plasma by high-frequency discharge in the processing space PS, and the film on the main surface of the semiconductor wafer W is etched by radicals and ions generated from the plasma.

  In this capacitively coupled plasma etching apparatus, by applying a second high frequency of a relatively high frequency suitable for plasma generation of 40 MHz to the lower susceptor electrode 18 of the susceptor 14, the plasma is densified in a preferable dissociation state, and the pressure is lower. High density plasma can be formed even under the above conditions. At the same time, by applying a first high frequency of a relatively low frequency suitable for ion attraction of 2 MHz to the upper susceptor electrode 16 of the susceptor 14, anisotropy having high selectivity with respect to the semiconductor wafer W above the susceptor 14. Etching can be performed.

  Next, the operation of the susceptor 14 which is a characteristic part of the present invention in the plasma etching apparatus of this embodiment will be described in detail.

  As described above, the susceptor 14 is vertically divided into the upper susceptor electrode 16 and the lower susceptor electrode 18, and a first high frequency (2 MHz) from the first high frequency power supply 22 is applied to the upper susceptor electrode 16, A second high frequency (40 MHz) from the second high frequency power supply 34 is applied to the lower susceptor electrode 18.

  Here, the upper susceptor electrode 16 is a flat electrode having a single material and a constant plate thickness. The surface thickness when the first high-frequency (2 MHz) current having a low frequency flows through the main surface of the upper susceptor electrode 16 is thick (the skin effect is small), and is almost from each position on the electrode main surface without being biased toward the center of the electrode. It is uniformly emitted into the plasma space PS. Thereby, the intensity distribution of the high frequency electric field formed on the susceptor 14 by the first high frequency (2 MHz) can be made substantially uniform in the electrode radial direction. Therefore, the amount of ions attracted to the semiconductor wafer W following the high-frequency electric field can be made uniform in each part of the wafer surface, and the anisotropic etching shape or selectivity in-plane uniformity can be improved. it can.

  On the other hand, the lower susceptor electrode 18 has a tapered recess formed on the electrode main surface (upper surface) as described above, and the dielectric 28 is embedded in the recess. For the current of the second high frequency (40 MHz) with a considerably high frequency and a thin skin thickness (large skin effect), the action of suppressing the concentration at the center of the electrode works, and it is almost uniform from each position on the electrode main surface. To the plasma space PS. Thereby, the intensity distribution of the high frequency electric field formed on the susceptor 14 by the second high frequency (40 MHz) can be made substantially uniform in the electrode radial direction. Therefore, the magnitude of the high-frequency current or electron current that collides with gas molecules in the plasma space PS due to acceleration by the high-frequency electric field, and hence the plasma density, can be made uniform directly on the wafer, and the in-plane uniformity of the etching rate can be improved. it can.

  When a high-frequency current is emitted from the lower susceptor electrode 18 toward the plasma space PS, an eddy current flows through the upper susceptor electrode 16, and a magnetic field generated by this eddy current causes high-frequency straight travel from the lower susceptor electrode 18. Work to hinder. Therefore, in this embodiment, the upper susceptor electrode 16 is made of a material having a high resistivity to suppress the eddy current, and the high frequency emitted from the lower susceptor electrode 18 toward the plasma space PS is increased. 16 is less affected.

  As mentioned above, although preferred embodiment of this invention was described, embodiment mentioned above does not limit this invention. Those skilled in the art can make various modifications and changes in specific embodiments without departing from the technical idea and technical scope of the present invention.

  For example, the electrode structure of the lower susceptor electrode 18 in the above-described embodiment is merely an example. The lower susceptor electrode 18 can employ various electrode structures as disclosed in, for example, the above-mentioned Patent Document 1 in order to improve the uniformity of the electric field strength or plasma density in the electrode radial direction. Is independent of the upper susceptor electrode 16, it is possible to adopt a more free electrode structure.

  For example, as shown in FIG. 2, the lower susceptor electrode 18 is formed in a ring shape, and the second high frequency emitted from the lower susceptor electrode 18 toward the plasma space PS is relatively weakened relatively and actively at the center of the electrode. It is also possible to do. Further, by forming the lower susceptor electrode 18 like this in a ring shape, the power feeding rod 26 connected to the upper susceptor electrode 16 can be passed through the central opening of the lower susceptor electrode 18. In this case, the gap between the power supply rod 26 and the inner peripheral surface of the lower susceptor electrode 18 may be closed with a cylindrical insulator 78.

  The present invention can also be applied to a method of applying a high frequency to the upper electrode side. For example, the modification shown in FIG. 3 is an application of the present invention to the upper electrode 80 in a capacitively coupled plasma etching apparatus that applies high frequencies having different frequencies to the upper electrode 80 and the susceptor (lower electrode) 82. is there. The upper electrode 80 includes a first upper electrode 84 facing the susceptor 82 directly below the plasma space PS, and a second upper electrode 86 disposed behind or above the first upper electrode 84. ing.

  More specifically, the first upper electrode 84 has an electrode structure that also serves as a shower head, and is attached in a state of being electrically insulated from the chamber 90 by a ring-shaped dielectric 88, that is, in a floating state. . A DC voltage is applied to the first upper electrode 84 from a variable DC power source 92. A processing gas supply source 62 is connected to the inside of the first upper electrode 84 or the gas chamber via a gas supply pipe 60.

  The second upper electrode 86 may have an electrode structure similar to that of the lower susceptor electrode 18 in the above embodiment, and is arranged in an inverted direction (facing downward). The periphery is surrounded by an insulator 94 and is electrically insulated from the first upper electrode 84 and the chamber 90. A high frequency (eg, 60 MHz) for plasma generation is applied to the second upper electrode 86 from a high frequency power source 96 through a matching unit (not shown).

  The susceptor 82 is formed in a normal disk shape, and has an electrode structure for holding the semiconductor wafer W on the upper surface thereof. The susceptor 82 has a high frequency for ion attraction (not shown) from a high frequency power source 98 via a matching unit (not shown). For example, 13.56 MHz) is applied.

  In this plasma etching apparatus, plasma made uniform in the electrode radial direction can be generated by the high frequency (60 MHz) emitted from the second upper electrode 86 toward the plasma space PS. Further, ions can be drawn into the semiconductor wafer W almost uniformly in the radial direction of the electrode by the high frequency (13.56 MHz) emitted from the susceptor 82 toward the plasma space PS independently of the high frequency for plasma generation (60 MHz). .

  The first upper electrode 86 is made of a material having a high resistivity such as tungsten or silicon, as in the above-described embodiment, and does not interfere with the high frequency (60 MHz) from the second upper electrode 86 toward the plasma space PS. Good. Further, various actions (for example, an action for controlling the plasma potential and an action for increasing the plasma density) can be applied to the plasma by the DC voltage applied from the DC power supply 92.

  The present invention is not limited to plasma etching as in the above embodiment, but can be applied to other plasma processes such as plasma CVD, plasma oxidation, plasma nitridation, and sputtering. In addition, the substrate to be processed in the present invention is not limited to a semiconductor wafer, and a flat panel display substrate, a photomask, a CD substrate, a printed substrate, and the like are also possible.

10 Chamber 14 Susceptor 16 Upper susceptor electrode 18 Lower susceptor electrode
22 First high frequency power source 30, 32 Insulator 34 Second high frequency power source 52 Upper electrode (shower head)
62 Processing gas supply source 80 Upper electrode 82 Susceptor 84 First upper electrode 86 Second upper electrode 90 Chamber 92 Variable DC power supply 96, 98 High frequency power supply

Claims (6)

A processing container capable of being evacuated;
A first electrode arranged to face the plasma space in the processing vessel;
A second electrode disposed behind the first electrode when viewed from the plasma space side;
A processing gas supply unit for supplying a desired processing gas to the plasma space;
A first power feeding unit that applies a first high frequency or direct current to the first electrode;
A plasma processing apparatus, comprising: a second power supply unit that applies a second high frequency to the second electrode.   2. The plasma processing apparatus according to claim 1, further comprising a third electrode disposed in parallel with and directly opposite to the first electrode across the plasma space.   The plasma processing apparatus according to claim 2, further comprising a third power feeding unit that applies a third high frequency to the third electrode.   The plasma processing apparatus according to claim 1, wherein the processing gas supply unit includes a shower head provided on the first electrode so as to eject the processing gas in a shower shape.   The plasma processing apparatus according to any one of claims 1 to 4, wherein a recess is formed in a main surface of the second lower electrode, and a dielectric is embedded in the recess.   The plasma processing apparatus according to claim 5, wherein a thickness of the dielectric gradually decreases from an electrode center portion toward an electrode edge portion.

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