JP6097317B2 - Plasma processing method - Google Patents

Description

The present invention relates to a technique for performing plasma processing on a substrate to be processed, and more particularly to an inductively coupled plasma processing method.

  In processes such as etching, deposition, oxidation, sputtering and the like in the manufacturing process of semiconductor devices and FPDs (Flat Panel Displays), plasma is often used in order to cause a favorable reaction to a processing gas at a relatively low temperature. Conventionally, plasma of high frequency discharge in the MHz region is often used for this type of plasma processing. Plasma by high frequency discharge is roughly classified into capacitively coupled plasma and inductively coupled plasma as more specific (device-like) plasma generation methods.

  In general, an inductively coupled plasma processing apparatus is configured such that at least a part (for example, a ceiling) of a wall of a processing container is formed of a dielectric window, and a high frequency power is applied to a coil-shaped RF antenna provided outside the dielectric window. Supply. The processing container is configured as a vacuum chamber that can be depressurized, and a processing space is set between the dielectric window and the substrate in which a substrate to be processed (for example, a semiconductor wafer, a glass substrate, etc.) is disposed in the center of the chamber. A processing gas is introduced into the system. The high-frequency current flowing through the RF antenna generates a high-frequency AC magnetic field around the RF antenna so that the magnetic lines of force pass through the dielectric window and pass through the processing space in the chamber. An induced electric field is generated in the azimuth direction in the processing space. Then, the electrons accelerated in the azimuth direction by the induced electric field cause ionization collision with the molecules and atoms of the processing gas, and a donut-shaped plasma is generated.

  By providing a large processing space in the chamber, the doughnut-shaped plasma is efficiently diffused in all directions (particularly in the radial direction), and the density of the plasma is fairly uniform on the substrate. However, using only a normal RF antenna, the plasma density uniformity obtained on the substrate is insufficient for most plasma processes. In the plasma process, improving the uniformity or controllability of the plasma density on the substrate is one of the most important issues because it affects the uniformity and reproducibility of the process and, in turn, the manufacturing yield.

  In the inductively coupled plasma processing apparatus, the plasma density distribution characteristic (profile) in the donut-shaped plasma generated near the dielectric window in the chamber is important, and the core plasma density distribution profile is It affects the characteristics (particularly uniformity) of the plasma density distribution obtained on the substrate.

  In this regard, several methods for dividing the RF antenna into a plurality of annular coils having different coil diameters have been proposed as techniques for improving the uniformity of the plasma density distribution in the radial direction. This type of RF antenna division method includes a first method in which a plurality of annular coils are connected in series (for example, Patent Document 1) and a second method in which a plurality of annular coils are connected in parallel (for example, Patent Documents). 2).

US Pat. No. 5,800,609 US Pat. No. 6,164,241

  Among the conventional RF antenna division methods as described above, in the first method, since the total coil length of the RF antenna is a large length obtained by adding all the coils, the voltage drop in the RF antenna cannot be ignored. Further, a standing wave having a current nodal portion is likely to be formed near the RF input end of the RF antenna due to the wavelength effect. For this reason, it is difficult to obtain a uniform plasma density distribution not only in the radial direction but also in the circumferential direction, and the first method is essentially not suitable for a plasma process that requires a large-diameter plasma.

  On the other hand, in the second method, since the wavelength effect and voltage drop in the RF antenna depend on the length of each coil divided in parallel, the voltage drop in the antenna is relatively small, and the wavelength effect However, it is difficult to arbitrarily control the current distribution in the RF antenna in the radial direction and thus the plasma density distribution immediately below the antenna.

  For this reason, the conventional plasma processing apparatus adopting the second method adds (connects) variable capacitors for impedance adjustment to all the coils constituting the RF antenna, and adjusts the ratio of the RF current flowing through each coil. Like to do. However, the variable capacitor is expensive, and it is not desirable in terms of cost to fill all the coils in the RF antenna with the variable capacitor. In addition, when the number of variable capacitors is large, the capacitance (parameter) to be adjusted is increased, and the adjustment work is troublesome.

  On the other hand, the conventional system cannot efficiently eliminate an undesired profile in which the plasma density is relatively high in the central portion in the radial direction. In particular, in the low-pressure process, the influence of plasma diffusion is effective, and the plasma density tends to be higher at the central portion in the radial direction, making it difficult to solve it. Moreover, in the plasma processing apparatus for large diameter, since the difference in coil diameter is large between the inner coil and the outer coil, the plasma density tends to be relatively high in the central portion in the radial direction. It has been difficult to achieve uniform plasma density distribution efficiently.

The present invention solves the problems of the prior art as described above, and can effectively and arbitrarily control the plasma density distribution in the donut-shaped plasma, and in particular, plasma under a low pressure or large aperture An inductively coupled plasma processing method is provided that can control the plasma density distribution in the radial direction to any profile efficiently and diversely.

A plasma processing method according to a first aspect of the present invention includes a processing container having a dielectric window , a substrate holding unit for holding a substrate to be processed in the processing container, and supplying a desired processing gas into the processing container. A high-frequency power having a frequency suitable for high-frequency discharge of the processing gas; a processing gas supply unit; an RF antenna provided outside the dielectric window to generate plasma of the processing gas by inductive coupling in the processing container; A plasma processing method for performing a desired plasma process on the substrate to be processed in a plasma processing apparatus having a high-frequency power supply unit for supplying the RF antenna to the RF antenna, wherein the RF antenna is mounted on the same surface parallel to the dielectric window relatively spaced in a radial direction around the central axis of the processing chamber above the inside, it is arranged intermediate and outer, high-frequency supply from the high frequency power supply portion The first node and the inner coil are electrically connected in parallel between a second node connected to retrace line leading to the ground potential member connected to the line, divided into intermediate coil and the outer coil, wherein between the first node and the second node, the intermediate coil and the electrically capacitance varying intermediate capacitor connected in series, the static coupled to the outer coil and electrically in series An outer capacitor having a variable capacitance, and the capacitance of the intermediate capacitor is variably controlled in a region lower than a series resonance point, so that a current in a direction opposite to a current flowing through the inner coil and the outer coil is intermediated Flow through the coil.

In the plasma processing method according to the first aspect, when high-frequency power is supplied to the RF antenna from the high-frequency power feeding unit, RF is generated around each coil by a high-frequency current flowing through each part of the RF antenna, that is, the inner coil, the intermediate coil, and the outer coil. A magnetic field is generated, and an induction electric field for generating high-frequency discharge of processing gas, that is, generation of donut-shaped plasma, is formed in the processing container. The generated donut-shaped plasma diffuses in all directions in the processing container .

In this plasma processing method, a variable capacitance intermediate connected in series with the intermediate coil between the first node on the high frequency power supply line side and the second node on the return line side. A capacitor and an outer capacitor of variable capacitance electrically connected in series with the outer coil are provided, and the inner capacitor and the outer coil are controlled by variably controlling the capacitance of the intermediate capacitor in a region lower than the series resonance point. By passing a current in the opposite direction to the current flowing through each of the intermediate coils, the plasma density in the processing vessel is controlled to be forcibly lowered locally near the position facing the intermediate coil, and then held in the substrate holder. The plasma density distribution in the radial direction can be freely controlled on the substrate to be processed.

In this plasma processing method, when the capacitance of the outer capacitor is fixed to a predetermined value within the variable range and the capacitance of the intermediate capacitor is variably controlled in a region lower than the series resonance point, the inner coil and the outer coil The amount of current flowing through each of the coil currents also increases or decreases accordingly, but the ratio (balance) between the two coil currents hardly changes. Therefore, it is possible to freely control the plasma density distribution in the radial direction by adjusting to variably control only the capacitance of the intermediate capacitor while the capacitance of the outer capacitor is fixed.

A plasma processing method according to a second aspect of the present invention includes a processing container having a dielectric window, a substrate holding unit for holding a substrate to be processed in the processing container, and supplying a desired processing gas into the processing container. A high-frequency power having a frequency suitable for high-frequency discharge of the processing gas; a processing gas supply unit; an RF antenna provided outside the dielectric window to generate plasma of the processing gas by inductive coupling in the processing container; A plasma processing method for performing a desired plasma process on the substrate to be processed in a plasma processing apparatus having a high-frequency power supply unit for supplying the RF antenna to the RF antenna, wherein the RF antenna is mounted on the same surface parallel to the dielectric window The first is connected to the high-frequency power feeding section, which is disposed relatively inside, in the middle, and outside at a radial interval centering on the central axis of the processing container. Are divided into an inner coil, an intermediate coil, and an outer coil that are electrically connected in parallel between the second node connected to the return line leading to the ground potential member, and the first node and the second coil A variable capacitance intermediate capacitor electrically connected in series with the intermediate coil, and a variable capacitance outer capacitor electrically connected in series with the outer coil, between the second node and the second node; The capacitance of the outer capacitor is variably controlled in a region lower than the value of the series resonance point, and a current in a direction opposite to the current flowing through the inner coil and the intermediate coil is passed through the outer coil. The plasma in the processing vessel is confined inside the outer coil in the radial direction.

In the plasma processing method according to the second aspect, when high-frequency power is supplied from the high-frequency power feeding unit to the RF antenna, RF is generated around each coil by a high-frequency current flowing through each part of the RF antenna, that is, the inner coil, the intermediate coil, and the outer coil. A magnetic field is generated, and an induction electric field for generating high-frequency discharge of processing gas, that is, generation of donut-shaped plasma, is formed in the processing container. The generated donut-shaped plasma diffuses in all directions in the processing container.
In this plasma processing method, a variable capacitance intermediate connected in series with the intermediate coil between the first node on the high frequency power supply line side and the second node on the return line side. A capacitor and a variable capacitance outer capacitor electrically connected in series with the outer coil are provided, and the inner coil is variably controlled in a region lower than the value of the series resonance point. The substrate is held while preventing damage to the inner wall of the processing vessel by confining the plasma in the processing vessel inside the outer coil in the radial direction by passing a current in the opposite direction to the current flowing through the intermediate coil and the outer coil. The plasma density distribution in the entire radial direction can be freely controlled on the substrate to be processed held by the unit.

According to the plasma processing method of the present invention , it is possible to efficiently control the plasma density distribution in the donut-shaped plasma by the configuration and operation as described above, particularly for low-pressure plasma or large-diameter plasma. On the other hand, the plasma density distribution in the radial direction can be controlled to an arbitrary profile efficiently and variously.

It is a longitudinal cross-sectional view which shows the structure of the inductively coupled plasma processing apparatus in one Embodiment of this invention. It is a perspective view which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in embodiment. FIG. 3 shows the operation of the embodiment of FIG. FIG. 3 is an electrical connection diagram when the capacitor is entirely omitted from the RF antenna of FIG. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor used in one experiment in embodiment. It is a figure which shows the change of the coil current distribution and electron density distribution which were measured by changing the electrostatic capacitance of an intermediate capacitor in the said experiment. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in one modification of embodiment. It is a figure for demonstrating the effect | action of the Example of FIG. 6A. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in another Example. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in another Example. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in another Example. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in another Example. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in another Example. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in another Example. It is a figure which shows the layout structure and electrical connection structure of RF antenna with a variable capacitor in another Example.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
[Configuration and operation of the entire device]

  FIG. 1 shows the configuration of an inductively coupled plasma processing apparatus according to an embodiment of the present invention.

  This plasma processing apparatus is configured as an inductively coupled plasma etching apparatus using a planar coil type RF antenna, and has a cylindrical vacuum chamber (processing vessel) 10 made of metal such as aluminum or stainless steel. Yes. The chamber 10 is grounded for safety.

  First, the configuration of each part not related to plasma generation in this inductively coupled plasma etching apparatus will be described.

  A disc-shaped susceptor 12 on which, for example, a semiconductor wafer W is mounted as a substrate to be processed is horizontally disposed as a substrate holding table that also serves as a high-frequency electrode in the lower center of the chamber 10. The susceptor 12 is made of, for example, aluminum, and is supported by an insulating cylindrical support portion 14 that extends vertically upward from the bottom of the chamber 10.

  An annular exhaust path 18 is formed between the conductive cylindrical support section 16 extending vertically upward from the bottom of the chamber 10 along the outer periphery of the insulating cylindrical support section 14 and the inner wall of the chamber 10. An annular baffle plate 20 is attached to an upper portion or an inlet of 18 and an exhaust port 22 is provided at the bottom. In order to make the gas flow in the chamber 10 uniform on the axis of the semiconductor wafer W on the susceptor 12, it is preferable to provide a plurality of exhaust ports 22 at equal intervals in the circumferential direction. An exhaust device 26 is connected to each exhaust port 22 via an exhaust pipe 24. The exhaust device 26 has a vacuum pump such as a turbo molecular pump, and can depressurize the plasma processing space in the chamber 10 to a desired degree of vacuum. Outside the side wall of the chamber 10, a gate valve 28 that opens and closes a loading / unloading port 27 for the semiconductor wafer W is attached.

A high frequency power source 30 for RF bias is electrically connected to the susceptor 12 via a matching unit 32 and a power feed rod 34. The high-frequency power source 30 can output a high-frequency RF _L having a constant frequency (usually 13.56 MHz or less) suitable for controlling the energy of ions drawn into the semiconductor wafer W with variable power. The matching unit 32 accommodates a reactance variable matching circuit for matching between the impedance on the high frequency power source 30 side and the impedance on the load (mainly susceptor, plasma, chamber) side. A blocking capacitor for generating a self-bias is included in the matching circuit.

  On the upper surface of the susceptor 12, an electrostatic chuck 36 for holding the semiconductor wafer W with an electrostatic attraction force is provided, and a focus ring 38 that surrounds the periphery of the semiconductor wafer W in an annular shape is provided radially outward of the electrostatic chuck 36. Provided. The electrostatic chuck 36 is obtained by sandwiching an electrode 36 a made of a conductive film between a pair of insulating films 36 b and 36 c, and a high voltage DC power supply 40 is electrically connected to the electrode 36 a through a switch 42 and a covered wire 43. It is connected. The semiconductor wafer W can be attracted and held on the electrostatic chuck 36 with an electrostatic force by a high-voltage DC voltage applied from the DC power supply 40.

  Inside the susceptor 12, for example, an annular refrigerant chamber or refrigerant flow path 44 extending in the circumferential direction is provided. A refrigerant having a predetermined temperature, such as cooling water cw, is circulated and supplied to the refrigerant chamber 44 through pipings 46 and 48 from a chiller unit (not shown). The temperature during processing of the semiconductor wafer W on the electrostatic chuck 36 can be controlled by the temperature of the cooling water cw. In this connection, a heat transfer gas such as He gas from a heat transfer gas supply unit (not shown) is supplied between the upper surface of the electrostatic chuck 36 and the back surface of the semiconductor wafer W via the gas supply pipe 50. Is done. Further, for loading / unloading of the semiconductor wafer W, lift pins that can vertically move through the susceptor 12 and a lifting mechanism (not shown) and the like are also provided.

  Next, the configuration of each part related to plasma generation in this inductively coupled plasma etching apparatus will be described.

  The ceiling or top plate of the chamber 10 is provided at a relatively large distance from the susceptor 12, and a circular dielectric window 52 made of, for example, a quartz plate is airtightly attached as the top plate. On the dielectric window 52, an antenna chamber 56 for accommodating the RF antenna 54 for generating inductively coupled plasma in the chamber 10 by electromagnetically shielding it from the outside is provided integrally with the chamber 10. .

  The RF antenna 54 is parallel to the dielectric window 52, preferably on the upper surface of the dielectric window 52, and is arranged with an inner coil 58, an intermediate coil 60, An outer coil 62 is provided. These coils 58, 60, 62 are arranged coaxially (more preferably concentrically) with each other, and are also arranged coaxially with respect to the chamber 10 or the susceptor 12.

  In the present invention, the term “coaxial” refers to a positional relationship in which the central axes overlap each other between a plurality of objects having an axially symmetric shape. This includes not only the case where they are offset from each other but also the case where they are coincident on the same plane (concentric positional relationship).

The inner coil 58, the intermediate coil 60, and the outer coil 62 are electrically connected between the high-frequency power supply line 68 from the high-frequency power supply unit 66 for plasma generation and the return line 70 leading to the ground potential member (two nodes N). _a, are connected in parallel with N between _B). Here, the return line 70 is an earth line having a ground potential, and is connected to a ground potential member (for example, the chamber 10 or another member) that is electrically maintained at the ground potential.

Between the node N _B and the intermediate coil 60 and outer coil 62 of the ground line 70 side, the variable capacitor 86 and 88 are electrically connected in series (insert). These variable capacitors 86 and 88 can be varied independently and arbitrarily within a certain range by the capacitance variable section 90 under the control of the main control section 84. Hereinafter, a capacitor connected in series with the inner coil 58 between the nodes N _A and N _B is referred to as an “inner capacitor”, and a capacitor connected in series with the intermediate coil 60 is referred to as an “intermediate capacitor”. A capacitor connected in series with 62 is referred to as an “outer capacitor”.

The high frequency power supply unit 66 includes a high frequency power source 72 and a matching unit 74. The high frequency power source 72 can output a high frequency RF _H having a constant frequency (usually 13.56 MHz or more) suitable for generating plasma by inductively coupled high frequency discharge with variable power. The matching unit 74 accommodates a reactance variable matching circuit for matching between the impedance on the high frequency power source 72 side and the impedance on the load (mainly RF antenna, plasma) side.

  A processing gas supply unit for supplying a processing gas to the processing space in the chamber 10 is an annular manifold or buffer unit 76 provided in (or outside) the side wall of the chamber 10 at a position somewhat lower than the dielectric window 52. A plurality of side wall gas discharge holes 78 facing the plasma generation space from the buffer section 76 at equal intervals in the circumferential direction, and a gas supply pipe 82 extending from the processing gas supply source 80 to the buffer section 76. The processing gas supply source 80 includes a flow rate controller and an on-off valve (not shown).

  The main control unit 84 includes, for example, a microcomputer. Each unit in the plasma etching apparatus, for example, the exhaust device 26, the high frequency power sources 30, 72, the matching units 32, 74, the electrostatic chuck switch 42, the variable capacitors 86, 88, The individual operations of the processing gas supply source 80, the chiller unit (not shown), the heat transfer gas supply unit (not shown), and the operation (sequence) of the entire apparatus are controlled.

In order to perform etching in this inductively coupled plasma etching apparatus, the gate valve 28 is first opened, and the semiconductor wafer W to be processed is loaded into the chamber 10 and placed on the electrostatic chuck 36. Then, after the gate valve 28 is closed, an etching gas (generally a mixed gas) is supplied from the processing gas supply source 80 through the gas supply pipe 82, the buffer portion 76, and the side wall gas discharge holes 78 at a predetermined flow rate and flow rate ratio. The pressure in the chamber 10 is set to a set value by the exhaust device 26. Further, the high frequency power supply 72 of the high frequency power supply unit 66 is turned on to output a high frequency RF _H for plasma generation at a predetermined RF power, and the RF antenna 54 is connected via the matching unit 74, the RF power supply line 68 and the return line 70. A high frequency RF _H current is supplied to the inner coil 58, the intermediate coil 60 and the outer coil 62. On the other hand, the high frequency power supply 30 is turned on to output a high frequency RF _L for controlling the ion attraction at a predetermined RF power, and this high frequency RF _L is applied to the susceptor 12 via the matching unit 32 and the power feed rod 34. Further, the heat transfer gas (He gas) is supplied from the heat transfer gas supply unit to the contact interface between the electrostatic chuck 36 and the semiconductor wafer W, and the electrostatic chucking force of the electrostatic chuck 36 is turned on by turning on the switch 42. The heat transfer gas is confined in the contact interface.

In the chamber 10, the etching gas discharged from the side wall gas discharge holes 78 diffuses into the processing space below the dielectric window 52. Magnetic field lines (magnetic flux) generated around the coils due to the high-frequency RF _H current flowing through the coils 58, 60, 62 of the RF antenna 54 penetrate the dielectric window 52 and process space (plasma generation space) in the chamber 10. ), An induced electric field in the azimuth direction is generated in the processing space. Electrons accelerated in the azimuth direction by the induced electric field cause ionization collision with molecules and atoms of the etching gas, and a donut-shaped plasma is generated.

  The radicals and ions of the doughnut-shaped plasma diffuse in all directions in a wide processing space, the radicals flow isotropically, and the ions are pulled by a DC bias, so that the top surface (surface to be processed) of the semiconductor wafer W To be supplied. Thus, the active species of the plasma cause a chemical reaction and a physical reaction on the surface to be processed of the semiconductor wafer W, and the film to be processed is etched into a desired pattern.

  Here, the “doughnut-shaped plasma” is not limited to a strictly ring-shaped plasma in which plasma does not stand on the radially inner side (center portion) of the chamber 10 but only on the radially outer side. This means that the volume or density of plasma on the outer side in the radial direction is larger than the inner side in the radial direction. Further, depending on conditions such as the type of gas used for the processing gas and the pressure value in the chamber 10, the “doughnut-shaped plasma” may not occur.

In this inductively coupled plasma etching apparatus, the RF antenna 54 is divided into an inner coil 58, an intermediate coil 60 and an outer coil 62 having different coil diameters, and the wavelength effect and potential difference (voltage drop) in the RF antenna 54 are effectively suppressed. Alternatively, the configuration in which the variable capacitors 86 and 88 are connected in series to the intermediate coil 60 and the outer coil 62 except for the inner coil 58 can easily and efficiently control the plasma density distribution on the semiconductor wafer W. I have to.

[Basic configuration and operation of RF antenna]

  2 and 3 show the basic configuration of the layout and electrical connection (circuit) of the RF antenna 54 in this inductively coupled plasma etching apparatus.

As shown in FIG. 2, the inner coil 58 is a single-turn annular coil with a constant radius that goes around the gap or the cut line G _i , and is located near the center of the chamber 10 in the radial direction. One end, i.e. RF inlet end 58in the inner coil 58 is connected to the RF feed line 68 of the high-frequency power supply portion 66 via the connecting conductor 92 and the first node N _A that extends upward. The other end, i.e. RF outlet end 58out of the inner coil 58 is connected to the earth line 70 via a connecting conductor 94 and the second node N _B extending upward.

Intermediate coil 60 is made constant radius single turn toroidal coils around across the gap or cut G _m, it is located in the middle portion of the chamber 10 at the outer side than the inner coil 58 in the radial direction. One end, i.e. RF inlet end 60in intermediate coil 60 is adjacent to the RF inlet end 58in the inner coil 58 in the radial direction, the high-frequency power supply unit 66 via a connection conductor 96 and the first node N _A that extends upward Are connected to the RF feed line 68. The other end, i.e. RF outlet end 60out of intermediate coil 60 is adjacent to the RF outlet 58out of the inner coil 58 in the radial direction, the earth line 70 via a connecting conductor 98 and the second node N _B extending upward It is connected.

The outer coil 62 is a single-turn annular coil with a constant radius that goes around the gap or the cut _Go, and is located outside the intermediate coil 60 and closer to the side wall of the chamber 10 in the radial direction. One end, i.e. RF inlet end 62in the outer coil 62 is adjacent to the RF inlet end 60in intermediate coil 60 in the radial direction, the high-frequency power supply unit 66 via the connection conductor 100 and the first node N _A that extends upward Are connected to the RF feed line 68. The other end, i.e. RF outlet end 62out of the outer coil 62 is adjacent to the RF outlet end 60out of intermediate coil 60 in the radial direction, the earth line 70 through the connection conductor 102 and a second node N _B extending upward It is connected.

  As shown in FIG. 2, the connecting conductors 92-102 extending above the RF antenna 54 are laterally separated (at a considerably high position) from the dielectric window 52 within the antenna chamber 56 (FIG. 1). A branch line or a jumper line is formed to reduce the electromagnetic influence on the coils 58, 60, 62.

In the coil arrangement and connection structure in the RF antenna 54 as described above, when the high-frequency power source 72 passes through the RF feed line 68, the RF antenna 54, and the ground line 70 to the ground potential member, more specifically, the first node. when traveling around the high-frequency branch transmission path of each coil 58, 60, 62 constituting the RF antenna 54 from N _a to the second node N _B, the orientation when passing through the inner coil 58, the intermediate coil 60 and outer coil 62, respectively Are counterclockwise in FIG. 2 and are the same in the direction of rotation.

  In the inductively coupled plasma etching apparatus of this embodiment, a high-frequency current supplied from the high-frequency power feeding unit 66 flows through each part in the RF antenna 54, whereby the inner coil 58, the intermediate coil 60, and the Around the outer coil 62, a high-frequency AC magnetic field distributed in a loop according to Ampere's law is generated, and the processing space extends radially in the relatively inner (lower) area below the dielectric window 52. A transverse field line is formed.

  Here, the radial direction (horizontal) component of the magnetic flux density in the processing space is always zero at the center and the peripheral portion of the chamber 10 regardless of the magnitude of the high-frequency current, and becomes a maximum somewhere in the middle. The intensity distribution of the induced electric field in the azimuth direction generated by the high-frequency AC magnetic field also shows the same distribution as the magnetic flux density in the radial direction. That is, in the radial direction, the electron density distribution in the donut-shaped plasma substantially corresponds to the current distribution in the RF antenna 54 in a macro manner.

  The RF antenna 54 in this embodiment is different from a normal spiral coil that pivots from the center or the inner peripheral end to the outer peripheral end, and the annular inner coil 58 that is localized in the center of the antenna and the antenna in the middle. A current distribution in the RF antenna 54 is a concentric shape corresponding to the position of each coil 58, 60, 62. Distribution.

Here, a uniform or uniform high-frequency current (hereinafter referred to as “inner coil current”) I _i flows through the inner coil 58 in the loop. The intermediate coil 60, within a loop uniform or uniform high frequency current (hereinafter referred to as "intermediate coil current".) I _m flows. A high-frequency current (hereinafter referred to as “outer coil current”) I _{o that} is uniform or uniform in the loop flows through the outer coil 62.

  Thus, in the donut-shaped plasma generated below (inside) the dielectric window 52 of the chamber 10, as shown in FIG. 3, in the vicinity of the position immediately below each of the inner coil 58, the intermediate coil 60 and the outer coil 62. The current density (that is, plasma density) is maximized. As described above, the current density distribution in the donut-shaped plasma is not uniform in the radial direction but has an uneven profile. However, the plasma diffuses in all directions in the processing space in the chamber 10, so that the density of the plasma is leveled near the susceptor 12, that is, on the substrate W.

  In this embodiment, all of the inner coil 58, the intermediate coil 60 and the outer coil 62 are annular coils, and a uniform or uniform high-frequency current flows in the coil circulation direction. Of course, a substantially uniform plasma density distribution can be obtained in the vicinity of the susceptor 12, that is, on the substrate W.

Further, in the radial direction, as will be described later, by changing or selecting the capacitances C ₈₆ and C ₈₈ of the intermediate capacitor 86 and the outer capacitor 88 to appropriate values within a predetermined range, the inner coil 58 and the intermediate coil can be selected. The plasma density distribution in the donut-shaped plasma can be freely controlled by adjusting the balance of the currents I _i , I _m , and I _o flowing through the outer coil 60 and the outer coil 60, respectively. Accordingly, the plasma density distribution in the vicinity of the susceptor 12, that is, on the substrate W can be freely controlled, and the uniform plasma density distribution can be easily achieved with high accuracy.

In this embodiment, the wavelength effect and voltage drop in the RF antenna 54 depends on the length of each individual coil 58, 60, 62. Therefore, by selecting the length of each coil so as not to cause the wavelength effect in the individual coils 58, 60, 62, all the problems of the wavelength effect and the voltage drop in the RF antenna 54 can be solved. In order to prevent the wavelength effect, it is desirable to make the length of each coil 58, 60, 62 shorter than a quarter wavelength of the high frequency RF _H.

The condition of less than ¼ wavelength regarding the coil length is more easily satisfied as the coil diameter is smaller and the number of turns is smaller. Therefore, the inner coil 58 having the smallest coil diameter in the RF antenna 54 can easily adopt a multi-turn configuration. On the other hand, the outer coil 62 having the largest coil diameter is preferably a single winding rather than a plurality of windings. Although the intermediate coil 60 depends on the diameter of the semiconductor wafer W, the frequency of the high-frequency RF _H , and the like, normally, like the outer coil 62, a single winding is desirable.

[Function of capacitor added to RF antenna]

  The main feature of this embodiment is that the RF antenna 54 is divided in parallel into three coils 58, 60, 62 having different coil diameters in the radial direction, and the intermediate coil 60 and the outer coil 62 are provided with a variable intermediate capacitor 86 and Each of the outer capacitors 88 is electrically connected in series, while no reactance element (particularly a capacitor) is connected to the inner coil 58.

Here, consider a case where no capacitor is added anywhere in the RF antenna 54 as shown in FIG. In this case, plasma that is significantly darker than that immediately below the intermediate coil 60 and the outer coil 62 is generated immediately below the inner coil 58. The reason is as follows. That is, the self-inductance L of a single-turn annular coil having a coil lead wire with a thickness (radius) of a and a coil diameter (radius) of r is expressed by the following equation (1).
Where μ _o is the vacuum permeability. The coil diameter (radius) r is an intermediate value between the radius of the inner circumference of the coil and the radius of the outer circumference of the coil.

From the above equation (1), the self-inductance L is approximately linearly proportional to the coil radius r. The impedance Z of such an annular coil is Z = 2πfL, where f is a high frequency, and is proportional to the self-inductance L. Accordingly, the inner coil 58, the coil radius for example 50mm of intermediate coil 60 and outer coil 62, 100 mm, when a 150 mm, about twice the intermediate coil current I _m flowing through the intermediate coil 60 to the inner coil 58, the outer coil 62 An inner coil current I _{i that} is about three times the flowing outer coil current I _o flows. The density of the plasma generated by the annular coil is slightly lower in efficiency as the radius is smaller, but it depends on the amount of coil current regardless of the radius. For this reason, plasma several times deeper than that immediately below the intermediate coil 60 and the outer coil 62 is generated immediately below the inner coil 58. As a result, the plasma density distribution in the vicinity of the susceptor 12, that is, on the semiconductor wafer W has a profile in which the central portion in the radial direction protrudes and becomes high.

Incidentally, the coil has a positive reactance, and the capacitor has a negative reactance. Therefore, when a capacitor is connected to the coil, the combined reactance is lower than the reactance of the coil because the negative reactance of the capacitor cancels the positive reactance of the coil. Therefore, connecting the capacitor to the inner coil 58 to increase the current amount of the inner coil current I _i is not effective for making the plasma density distribution uniform, but rather has an adverse effect.

This also applies in the case of a configuration using Subairaru shaped coil of each coil 58, 60 and 62 respectively N _i, N _m, N _o turn. That is, since the inductance of each coil is proportional to the number of turns (number of turns), each impedance is also proportional to the number of turns. Therefore, the ratio of the coil currents I _i and I _o flowing through the inner coil 58 and the outer coil 62 is as follows: I _i : I _o = _ro * N _o * N _i : r _i * N _i * N _o = _ro : r _i . On the other hand, the densities n _i and n _o of plasma generated immediately below both coils 58 and 62 are determined by the coil current × the number of turns. Therefore, the ratio of the densities n _i and n _o of the plasma generated immediately below the inner coil 58 and the outer coil 62 is n _i : n _o = _ro * N _o * N _i : r _i * N _i * N _o = r _o: r _i next, also in this case determined by the radius of the ratio. The same is true between the inner coil 58 and the intermediate coil 60. As described above, plasma that is always deeper than that immediately below the intermediate coil 60 and the outer coil 62 is generated immediately below the inner coil 58.

In reality, the impedance of the wiring from the exit of the matching unit 74 to the coil cannot be ignored. Since the length of the wiring is determined in the height direction from the exit of the matching unit 74 to the RF antenna 54, it may be assumed that the length of the wiring is the same between the inside, the middle, and the outside, and the wiring impedance is the inside and the middle.・ Assume that they are equal on the outside. Then, for example, when the outer coil 62 and the inner coil 58 have impedances of 75Ω and 25Ω, respectively, and the wiring impedance is approximately 10Ω, I _i : I _o = (75 + 10) :( 25 + 10) = 85: 35 = It becomes 2.41: 1, and there is still a difference of more than twice.

  If the pressure is relatively high (usually 100 mTorr or more) and the effect of plasma diffusion is difficult to achieve, the balance between the inside and the outside will be as described above. The plasma density of the portion further protrudes and becomes higher.

  Thus, under any condition, a law is established that the plasma density is relatively high directly below the innermost coil among the plurality of coils having different coil diameters electrically connected in parallel.

In this embodiment, based on the above knowledge, no capacitor is added (connected) to the inner coil 58 between both terminals of the RF antenna 54 (between the first and second nodes N _A and N _B ). In addition, variable capacitors 86 and 88 are connected in series to the intermediate coil 60 and the outer coil 62, and by adjusting the capacitances C ₈₆ and C ₈₈ of the variable capacitors ₈₆ and ₈₈ in a direction to lower the combined reactance, the intermediate coil 60 is set. The coil currents I _m , I _o flowing through the outer coil 62 and the outer coil 62 are appropriately increased so that the coil currents I _i , I _m , I _o are substantially equal in magnitude, or from the inner coil current I _i . The intermediate coil current _Im and / or the outer coil current _Io can be increased. Here, since the increments of the coil currents I _m and I _o due to the variable capacitors 86 and 88 all flow through the intermediate coil 60 and the outer coil 62 and contribute to plasma generation, waste of high frequency power does not occur.

In general, in order to correct the profile in which the plasma density protrudes and increases at the central portion in the radial direction, the ratio between the inner coil current I _i flowing through the inner coil 58 and the outer coil current I _o flowing through the outer coil 62 (roughly, It is efficient to adjust the balance. In this embodiment, in order to adjust the ratio between the two coil currents I _i and I _o , only the capacitance C ₈₈ of the outer capacitor 88 needs to be varied.

In this case, in order to uniform the plasma density distribution under various conditions, the outer coil current I _o and the variable range of the product I _o * n _o number of turns n _o of the outer coil 62 and inner coil current I _i inside It is desirable to have a lower limit value and a larger upper limit value than the product I _i * n _{i of the} number of turns n _i of the coil 58. The ratio of the inner coil current I _i and the outer coil current I _o is referred to as the impedance of the inner coil 58 (hereinafter referred to as “inner impedance”) and the combined impedance of the outer coil 62 and the outer capacitor 88 (hereinafter referred to as “outer combined impedance”). ), The inner impedance (fixed value) is Z _i , and the minimum and maximum values of the outer composite impedance (variable value) are Z _{o (min)} and Z _{o (max)} respectively. The above-mentioned condition regarding the coil current × the number of turns is expressed as follows.
... (2)

Further, the inner impedance Z _i and the outer combined impedance Z _o depend on the average coil radius except for the connection portion. Since the influence of the connection part cannot be ignored but is not a dominant influence, the above condition can also be expressed as follows.
... (3)

Here, C _{o (min)} is the value of the capacitance C ₈₈ of the outer capacitor 88 when the outer combined impedance Z _o is minimized within the adjustable range. _{Co (max)} is the value of the capacitance C ₈₈ of the outer capacitor 88 when the outer combined impedance Z _o is maximized within the adjustable range. _{Incidentally, C o (min), C} o (max) does not necessarily match the minimum and maximum values of the variable range of C _88. The outer combined impedance Z _o is minimized when the outer coil 62 and the outer capacitor 88 cause series resonance, and C _{o (min)} is the value of the capacitance C ₈₈ of the outer capacitor 88 at that time. . Further, the outer synthetic impedance Z _o is maximum is at either the time went away from the series resonance point capacitance C ₈₈ of the outer capacitor 88 up to the upper limit or the lower limit of the variable range, C _{o (max)} is the value of the capacitance C ₈₈ of the outer capacitor 88 at that time.

In this way, the inner coil 58 is not connected to the inner coil 58, but the outer capacitor 88 is connected in series to the outer coil 62, and the capacitance C ₈₈ of the outer capacitor ₈₈ is varied, whereby the inner coil current I _i and the outer coil 58 are changed. The ratio of the coil current I _o is arbitrarily adjusted, and the rough profile (particularly the balance between the central portion and the peripheral portion) of the plasma density distribution in the donut-shaped plasma generated immediately below the RF antenna 54 can be arbitrarily controlled. it can.

  In this embodiment, an intermediate coil 60 is further disposed between the inner coil 58 and the outer coil 62, and a variable intermediate capacitor 86 is also connected in series to the intermediate coil 60. This is for finely controlling the plasma density distribution (especially the intermediate portion) in the donut-shaped plasma, and is particularly useful when generating a plasma under a low pressure or a large-diameter plasma.

Instead of providing the intermediate coil 60, for example, a configuration in which the outer coil 62 is formed in a spiral shape and the region of the intermediate portion of the antenna 54 is covered by the outer coil 62 is also conceivable. However, in that case, since the same coil current _Io flows in all the sections of the outer coil 62, the plasma density tends to be relatively high immediately below the intermediate portion of the antenna. For example, the profile is uniform in the radial direction. It becomes difficult.

In an actual process, it is sometimes possible to obtain a desirable profile (for example, flat) in the entire radial direction by forcibly lowering the plasma density in the donut-shaped plasma directly under the antenna intermediate portion. In particular, this situation is likely to occur when the amount of the outer coil current _Io is increased to increase the plasma density in the periphery to a desired level.

In such a case, the intermediate capacitor 86 can function effectively. That is, the capacitance C ₈₆ of the intermediate capacitor 86 is set to a value at the series resonance point so that the combined reactance (hereinafter referred to as “intermediate combined reactance”) X _{m of} the intermediate coil 60 and the intermediate capacitor 86 becomes a negative value. Can be varied in a low region. Thus, in the opposite direction of the intermediate coil current I _m in the circumferential direction, yet (it is also possible to slightly increase from particular most 0 state) any amount of current flows, whereby the donut immediately below the intermediate coil 60 The plasma density in the plasma can be freely controlled locally, and the plasma density distribution in the entire radial direction can be freely controlled in the vicinity of the susceptor 12, that is, on the semiconductor wafer W.

The function of the intermediate capacitor 86 as described above has been confirmed by an experiment as shown in FIG. In this experiment, as shown in FIG. 5A, in the RF antenna 54, the inner coil 58 is formed in two turns (two turns) with a diameter of 100 mm, and the intermediate coil 60 and the outer coil 62 are single wound with a diameter of 200 mm and 300 mm, respectively. (1 turn). As main process conditions, the frequency of the high frequency RF _H is 13.56 MHz, the RF power is 1500 W, the pressure in the chamber 10 is 100 mTorr, the processing gas is a mixed gas of Ar and O ₂ , and the gas flow rate is Ar / O ₂ = 300. / 30 sccm.

In this experiment, by fixing the capacitance C ₈₈ of the outer capacitor 88 to 560 pF, the capacitance C ₈₆ of the intermediate condenser 86 13 pF, 40 pF, when the variable to 64PF, intermediate coil current I _m as shown in FIG. 5B There -0.4A, -5.0A, changes and -11.2A, be lowered in the vicinity immediately below the intermediate coil 60 electron density (i.e. plasma density) N _e locally and any could be confirmed. The inner and outer coil currents I _i and I _o are 16.4 A and 18.3 A when C ₈₆ = 13 pF, and 17.4 A and 19.4 A when C ₈₆ = 40 pF, respectively. When C ₈₆ = 40 pF, they were 19.0 A and 20.1 A, respectively. As you increase the amount of current of the intermediate coil current I _m flowing in the opposite direction, the current amount of the inner coil current I _i and the outer coil current I _o flows in the forward direction is also somewhat increased by hung thereto, both the coil current I _i , I _o ratio (balance) is hardly changed.

As another function of the RF antenna 54 of this embodiment, the static capacitance of the outer capacitor 88 is set so that the combined reactance of the outer coil 62 and the outer capacitor 88 (hereinafter referred to as “outer combined reactance”) X _o becomes a negative value. It is also possible to vary the capacitance C ₈₈ in a region lower than the value of the series resonance point, thereby allowing the outer coil current I ₀ to flow in the reverse direction. For example, when the plasma spreads too far outward in the radial direction and the inner wall of the chamber 10 is susceptible to damage, the plasma is confined inside the outer coil 62 by applying a reverse coil current I _o to the outer coil 62, 10 Damage to the inner wall can be suppressed. This function is particularly useful when, for example, a plurality of intermediate coils 60 having different coil diameters are arranged at intervals in the radial direction, or when the outer coil 62 is arranged radially outside the susceptor 12.

In this embodiment, at least one of the capacitances C ₈₆ and C ₈₈ of the intermediate capacitor 86 and the outer capacitor 88 is brought close to the value at the time of causing the series resonance, so that the inner coil current I _i flowing through the inner coil 58 is increased. Can be reduced. Further, it is possible to increase the inner coil current I _i by separating at least one of the capacitances C ₈₆ and C ₈₈ of the intermediate capacitor 86 and the outer capacitor 88 from the value at which series resonance occurs. That is, between the inner coil current I _i , the intermediate coil current _Im and the outer coil current I _o , I _i : I _m : I _o = (1 / Z _i ) :( 1 / Z _m ) :( 1 / Z _o ). Therefore, when C ₈₆ and / or C ₈₈ are brought close to the value at which series resonance occurs, Z _m and / or Z _o become smaller as the series resonance is approached, so that relatively I _m and / or I _o becomes larger and I _i becomes relatively smaller. Also, if C ₈₆ and / or C ₈₈ are separated from the value at which the series resonance occurs, Z _m and / or Z _o become so large as to move away from the series resonance, so that relatively I _m and / or I _o becomes smaller and I _i becomes relatively larger.

[Other Embodiments or Modifications Related to RF Antenna]

In the above embodiment, in order to control the plasma density distribution (particularly to make it uniform), a capacitor is attached to the inner coil 58 from the viewpoint that it is not necessary to vary the amount of the inner coil current I _{i in} the increasing direction. I did not put it.

However, it may be useful to positively or forcibly control the amount of inner coil current I _i . For example, when the pressure in the chamber 10 is low, the plasma tends to collect at the radial center. This problem can be largely dealt with by adjusting the ratio of the inner coil current I _i and the outer coil current I _o by changing the capacitance C ₈₈ of the outer capacitor 88 as described above. There are cases where it cannot be completed.

Therefore, as shown in FIGS. 6A and 6B, the RF antenna 54, a first node N _A and the inner coil 58 and electrically inside the capacitor 104 in the fixed or semi-fixed in series between the second node N _B Connecting. Also in this configuration, the capacitance C ₁₀₄ of the inner capacitor 104 is set to an appropriate value so that the combined reactance (hereinafter referred to as “inner combined reactance”) X _{i of} the inner coil 58 and the inner capacitor 104 becomes a desired value. Can be selected or adjusted. When the fixed or semi-fixed inner capacitor 104 and the variable outer capacitor 88 are provided in this way, the same conditional expression (2) as described above regarding the variable control of the number of turns of each coil and the capacitance C ₈₈ of the outer capacitor 88 is provided. , (3) applies.

  Although the degree of freedom or accuracy of plasma density distribution control is sacrificed to some extent, as shown in FIGS. 7A and 7B, a variable capacitor is used for the inner capacitor 104 and a fixed or semi-fixed capacitor is used for the outer capacitor 88 to reduce costs. Although not shown in the drawing, a configuration in which a fixed or semi-fixed capacitor is used for the intermediate capacitor 86, and a configuration in which the intermediate capacitor 86 is omitted is also possible.

When the fixed or semi-fixed outer capacitor 88 and the variable inner capacitor 104 are provided in this way, the inner coil current I _i and the number n of turns of the inner coil 58 can be used to equalize the plasma density distribution under various conditions. it is desirable that the variable range of the product I _i * n _i of _i has a smaller lower limit greater upper limit than the product I ₀ * n _o number of turns n _o of the outer coil current I _o and the outer coil 62. The ratio of the inner coil current I _i and the outer coil current I _{o is} the ratio of the reciprocal of the combined impedance (inner combined impedance) of the inner coil 58 and the inner capacitor 104 and the combined impedance (outer combined impedance) of the outer coil 62 and the outer capacitor 88. Since the outer impedance (fixed value) is Z ₀ , and the minimum and maximum values of the inner composite impedance (variable value) are Z _{i (min)} and Z _{i (max)} , respectively, this coil current x number of turns The above condition is expressed as follows.
... (4)

Further, the inner combined impedance Z _i and the outer combined impedance Z _o depend on the average coil radius except for the connection portion. Since the influence of the connection part cannot be ignored but is not a dominant influence, the above condition can also be expressed as follows.
... (5)
Here, C _{i (min)} is the value of the capacitance C ₁₀₄ of the inner capacitor 104 when the inner combined impedance Z _i is minimized within the adjustable range. C _{i (max)} is the value of the capacitance of the inner capacitor 104 when the inner combined impedance Z _i is maximized within the adjustable range. Note that C _{i (min)} and C _{i (max)} do not necessarily match the minimum and maximum values of the variable range of C ₁₀₄ . The inner composite impedance Z _i is minimized when the inner coil 58 and the inner capacitor 104 cause series resonance, and C _{i (min)} is the value of the capacitance C ₁₀₄ of the inner capacitor 104 at that time. . Further, the inner synthetic impedance Z _i is maximum is at either the time went away from the series resonance point capacitance C ₁₀₄ of the inner condenser 104 to the upper or lower limit of the variable range, C _{i (max)} is the value of the capacitance C ₁₀₄ of the inner capacitor 104 at that time.

In this way, the variable inner capacitor 104 is connected to the inner coil 58, and the fixed or semi-fixed outer capacitor 88 is connected in series to the outer coil 62, so that the capacitance C ₁₀₄ of the inner capacitor 104 can be varied. Thus, the ratio of the inner coil current I _i and the outer coil current I _o is arbitrarily adjusted, and a rough profile of the plasma density distribution in the donut-shaped plasma generated immediately below the RF antenna 54 (particularly between the central portion and the peripheral portion). (Balance) can be controlled arbitrarily.

As a modification, in order to reduce the amount of current of the inner coil current I _i positively or forcibly, as shown in FIG. 8, the inner coil 58 between the first node N _A and the second node N _B It is also possible to connect a preferably variable inductor 106 electrically in series. In this case, a configuration in which the intermediate capacitor 86 is replaced with another variable inductor, or a configuration in which the outer capacitor 88 is omitted for cost reduction is possible.

  The loop shape of each of the coils 58, 60, 62 constituting the RF antenna 54 of this embodiment is not limited to a circle, and may be a rectangle as shown in FIG. Good. Thus, even when the loop shape of the coils 58, 60, 62 is polygonal, a variable intermediate capacitor 86 and an outer capacitor 88 are electrically connected in series to the intermediate coil 60 and the outer coil 62, respectively, A configuration in which no capacitor is connected to the coil 58 can be suitably employed.

In addition, the inductance L of the rectangular coil having the lengths of two sides of a and b and the winding thickness of radius d is expressed by the following equation (6).
... (6)
As can be seen from this equation (6), the inductance L of the rectangular coil is approximately proportional to the length of the two sides a and b. Therefore, as in the case of the circular coil, the plasma density distribution can be easily and arbitrarily controlled by the intermediate capacitor 86 and the outer capacitor 88 without providing the inner coil 58 with a capacitor.

  FIG. 10 shows an example in which each of the coils (inner coil 58 / intermediate coil 60 / outer coil 62) constituting the RF antenna 54 is composed of a pair of spiral coils in a spatially and electrically parallel relationship. Such a spiral coil may be used when the wavelength effect is not a significant problem.

In the illustrated configuration example, the inner coil 58 includes a pair of spiral coils 58a and 58b that translate by being shifted by 180 ° in the circumferential direction (two turns in the illustrated example). These spiral coils 58a, 58b is, the node N _D that is provided on the upstream side of the node N _B than the node N _A of the high frequency power source 72 side is provided on the downstream side node N _C and the ground line 70 side Are electrically connected in parallel.

The intermediate coil 60 is composed of a pair of spiral coils 60a and 60b (two turns in the illustrated example) that translate by being shifted by 180 ° in the circumferential direction. These spiral coils 60a, 60b rather than the node N _B of the node N _E and the ground line side which is provided on the downstream side than the node N _A of the high frequency power source 72 side (more than intermediate capacitor 86) provided on the upstream side It is electrically connected in parallel between the node N _F, which is.

The outer coil 62 is composed of a pair of spiral coils 62a and 62b each having a plurality of turns (two turns in the illustrated example) that are translated by 180 ° in the circumferential direction. These spiral coils 62a, 62b rather than the node N _B of the high frequency power source 72 side of the node N nodes arranged downstream of the _A N _G and the earth line 70 side (more than the outer capacitor 88) on the upstream side It is electrically connected in parallel with the provided node _NH .

Thus, the inner coil 58, respectively k _i the intermediate coil 60 and outer coil 62, k _m, when divided in parallel to the k _o number of spiral coils, when the capacitor does not stick at all to the RF antenna 54, each coil The ratio of the densities n _i , n _m , and n _o of plasma generated immediately below 58, 60, and 62 is expressed by the following approximate expression (7).
_{n i: n m: n o} ≒ (k i / ri) :( k m / ri) :( k o / ri) ··· (7)

Therefore, as in the illustrated example, the division number k _i, k _m, if k _o is the same (2), the relative plasma density of the plasma, i.e. the central portion generated just below the inner coil 58 It will be very high. In such a case, a configuration in which a variable intermediate capacitor 86 and an outer capacitor 88 are connected in series to the intermediate coil 60 and the outer coil 62 without connecting a capacitor to the inner coil 58 is most desirable.

As another modification, as shown in FIG. 11, the intermediate capacitor 86 and the outer capacitor 88 RF inlet end 60in the first node of the high frequency power source 72 side N _A and the intermediate coil 60 and outer coil 62, and 62in It is also possible to connect each of them in between. As described above, the configuration in which the capacitor or inductor for adjusting the impedance is connected between the first node N _A and each coil can be applied to other embodiments or modifications (FIGS. 6A, 8, 9, and 10). Is also applicable.

12, at the end side of the RF antenna 54, i.e. the second node N _B and between the earth line 70 (or ground line 70 above) in all coils 58, 60, 62 electrically in the RF antenna 54 The structure provided with the output side common capacitor | condenser 108 connected in series is shown. The common capacitor 108 on the output side (termination) may normally be a fixed capacitor, but may be a variable capacitor.

  The output-side (termination) common capacitor 108 not only has a function of adjusting the overall impedance of the RF antenna 54, but also raises the overall potential of the RF antenna 54 from the ground potential in a DC manner, so that the top plate or the dielectric window 52 has the function of suppressing ion sputtering.

  Although not shown in the figure, in the RF antenna 54, another coil is disposed radially inside the inner coil 58 and / or radially outside the outer coil 62, and a total of four or more coils are spaced in the radial direction. It is also possible to arrange them in parallel and electrically connect them in parallel.

  The configuration of the inductively coupled plasma etching apparatus in the above-described embodiment is an example, and various modifications can be made to the configuration of each part not directly related to plasma generation as well as each part of the plasma generation mechanism.

For example, as a basic form of the RF antenna, a type other than the planar type, such as a dome type, is possible. A configuration in which the processing gas is introduced into the chamber 10 from the ceiling in the processing gas supply unit is also possible, and a configuration in which the high frequency RF _L for DC bias control is not applied to the susceptor 12 is also possible.

  Furthermore, the inductively coupled plasma processing apparatus or plasma processing method according to the present invention is not limited to the technical field of plasma etching, and can be applied to other plasma processes such as plasma CVD, plasma oxidation, plasma nitridation, and sputtering. . Further, the substrate to be processed in the present invention is not limited to a semiconductor wafer, and various substrates for flat panel displays, photomasks, CD substrates, printed substrates, and the like are also possible.

DESCRIPTION OF SYMBOLS 10 Chamber 12 Susceptor 26 Exhaust device 52 Dielectric window 54 RF antenna 58 Inner coil 60 Intermediate coil 62 Outer coil 66 High frequency electric power feeding part 70 Ground line 72 High frequency power source for plasma generation 74 Matching device 80 Processing gas supply source 84 Main control part 86 Intermediate capacitor 88 Outer capacitor 90 Capacitance variable section

Claims (6)

A processing container having a dielectric window, a substrate holding part for holding a substrate to be processed in the processing container, a processing gas supply part for supplying a desired processing gas into the processing container, and inductive coupling in the processing container An RF antenna provided outside the dielectric window, and a high-frequency power feeding unit that supplies high-frequency power having a frequency suitable for high-frequency discharge of the processing gas to the RF antenna. A plasma processing method for performing desired plasma processing on the substrate to be processed in a plasma processing apparatus,
The RF antennas are disposed on the same plane parallel to the dielectric window and relatively radially inwardly, centered and centered on the central axis of the processing vessel, respectively, on the inner side, the middle side and the outer side. An inner coil, an intermediate coil and an outer coil electrically connected in parallel between a first node connected to the high-frequency power supply line from the section and a second node connected to the return line leading to the ground potential member Divided into coils,
A variable capacitance intermediate capacitor electrically connected in series with the intermediate coil, and a static electricity electrically connected in series with the outer coil, between the first node and the second node. With a variable capacitance outer capacitor,
The capacitance of the intermediate capacitor is variably controlled in a region lower than a series resonance point, and a current in a direction opposite to the current flowing through the inner coil and the outer coil is passed through the intermediate coil.
Plasma processing method.   The capacitance of either or both of the intermediate capacitor and the outer capacitor is adjusted so as to approach a value at the time of causing a series resonance in order to control the current flowing through the inner coil in a decreasing direction. The plasma processing method as described in 2.   2. The capacitance of one or both of the intermediate capacitor and the outer capacitor is adjusted in a direction away from a value when series resonance occurs in order to control the current flowing through the inner coil in an increasing direction. The plasma processing method as described in 2.   The plasma processing method according to claim 1, wherein capacitances of the intermediate capacitor and the outer capacitor are adjusted so that a plasma density on the substrate to be processed is uniform in a radial direction. A processing container having a dielectric window, a substrate holding part for holding a substrate to be processed in the processing container, a processing gas supply part for supplying a desired processing gas into the processing container, and inductive coupling in the processing container An RF antenna provided outside the dielectric window, and a high-frequency power feeding unit that supplies high-frequency power having a frequency suitable for high-frequency discharge of the processing gas to the RF antenna. A plasma processing method for performing desired plasma processing on the substrate to be processed in a plasma processing apparatus,
The RF antennas are disposed on the same plane parallel to the dielectric window and relatively radially inwardly, centered and centered on the central axis of the processing vessel, respectively, on the inner side, the middle side and the outer side. An inner coil, an intermediate coil and an outer coil electrically connected in parallel between a first node connected to the high-frequency power supply line from the section and a second node connected to the return line leading to the ground potential member Divided into coils,
A variable capacitance intermediate capacitor electrically connected in series with the intermediate coil, and a static electricity electrically connected in series with the outer coil, between the first node and the second node. With a variable capacitance outer capacitor,
The capacitance of the outer capacitor is variably controlled in a region lower than the value of the series resonance point, and a current in a direction opposite to the current flowing through the inner coil and the intermediate coil is passed through the outer coil, and the processing is performed. Confining the plasma in the vessel radially inside the outer coil;
Plasma processing method. The plasma processing method according to claim 5 , wherein the outer capacitor is disposed radially outside the substrate holding portion.