PLASMA PROCESSING APPARATUS

An inductively coupled plasma process can effectively and properly control plasma density distribution within donut-shaped plasma in a processing chamber is provided. In an inductively coupled plasma processing apparatus, a RF antenna 54 disposed above a dielectric window 52 is segmented in a diametrical direction into an inner coil 58, an intermediate coil 60, and an outer coil 62 in order to generate inductively coupled plasma. Between a first node NA and a second node NB provided in high frequency transmission lines of the high frequency power supply unit 66, a variable intermediate capacitor 86 and a variable outer capacitor 88 are electrically connected in series to the intermediate coil 60 and the outer coil 62, respectively, and a fixed or semi-fixed inner capacitor 104 is electrically connected to the inner coil 58.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, illustrative embodiments will be described with reference to the accompanying drawings.

[Entire Configuration and Operation of Apparatus]

FIG. 1illustrates a configuration of an inductively coupled plasma processing apparatus in accordance with an illustrative embodiment.

The plasma processing apparatus is configured as an inductively coupled plasma etching apparatus using a planar coil RF antenna. By way of example, the plasma etching apparatus may include a cylindrical vacuum chamber (processing chamber)10made of metal such as aluminum or stainless steel. The chamber10may be frame grounded.

Above all, there will be explained a configuration of each component which is not related to plasma generation in this inductively coupled plasma etching apparatus.

At a lower central region within the chamber10, a circular plate-shaped susceptor12may be provided horizontally. The susceptor12may mount thereon a target substrate such as a semiconductor wafer W and may serve as a high frequency electrode as well as a substrate holder. This susceptor12may be made of, for example, aluminum and may be supported by a cylindrical insulating support14which may be extended uprightly from a bottom of the chamber10.

Between a cylindrical conductive support16which is extended uprightly from a bottom of the chamber10along the periphery of the cylindrical insulating support14and an inner wall of the chamber10, an annular exhaust line18may be provided. Further, an annular baffle plate20may be provided at an upper portion or an input of the exhaust line18. Further, an exhaust port22may be provided at a bottom portion. In order for a gas flow within the chamber10to be uniformized with respect to an axis of the semiconductor wafer W on the susceptor12, multiple exhaust ports22equi-spaced from each other along a circumference may be provided. Each exhaust port22may be connected to an exhaust unit26via an exhaust pipe24. The exhaust unit26may include a vacuum pump such as a turbo molecular pump or the like. Thus, it may be possible to depressurize a plasma generation space within the chamber10to a required vacuum level. At an outside of a sidewall of the chamber10, a gate valve28configured to open and close a loading/unloading port27of the semiconductor wafer W may be provided.

The susceptor12may be electrically connected to a high frequency power supply30for RF bias via a matching unit32and a power supply rod34. This high frequency power supply30may be configured to output a variable high frequency power RFLhaving an appropriate frequency (typically, about 13.56 MHz or less) to control energies of ions attracted into the semiconductor wafer W. The matching unit32may accommodate a variable reactance matching circuit for performing matching between an impedance of the high frequency power supply30and an impedance of a load (mainly, susceptor, plasma and chamber). The matching circuit may include a blocking capacitor configured to generate a self-bias.

An electrostatic chuck36for holding the semiconductor wafer W by an electrostatic attraction force may be provided on an upper surface of the susceptor12. Further, a focus ring38may be provided around the electrostatic chuck36to annularly surround the periphery of the semiconductor wafer W. The electrostatic chuck36may be formed by placing an electrode36amade of a conductive film between a pair of insulating films36band36c.A high voltage DC power supply40may be electrically connected to the electrode36avia a switch42and a coated line43. By applying a high DC voltage from the high voltage DC power supply40, the semiconductor wafer W can be attracted to and held on the electrostatic chuck36by the electrostatic force.

A coolant cavity or a coolant path44of, e.g., a circular ring-shape, may be formed within the susceptor12. A coolant, such as cooling water cw, having a certain temperature may be supplied into and circulated through the coolant path44from a chiller unit (not illustrated) via lines46and48. By adjusting the temperature of the cooling water cw, it may be possible to control a process temperature of the semiconductor wafer W held on the electrostatic chuck36. Further, a heat transfer gas, such as a He gas, may be supplied from a heat transfer gas supply unit (not illustrated) into a space between an upper surface of the electrostatic chuck36and a rear surface of the semiconductor wafer W through a gas supply line50. Furthermore, an elevating mechanism (not shown) including lift pins configured to move up and down vertically through the susceptor12may be provided to load and unload the semiconductor wafer W.

Hereinafter, there will be explained a configuration of each component which is related to plasma generation in this inductively coupled plasma etching apparatus.

A ceiling or a ceiling plate of the chamber10may be separated relatively far from the susceptor12. A circular dielectric window52formed of, for example, a quartz plate may be airtightly provided as the ceiling plate. Above the dielectric window52, an antenna chamber56may be provided as a part of the chamber10. The antenna chamber56may accommodate therein a RF antenna54and shield this RF antenna54from the outside. Here, the RF antenna54may generate inductively coupled plasma within the chamber10.

The RF antenna54is provided in parallel to the dielectric window52. Desirably, the RF antenna54may be placed on the top surface of the dielectric window52and include an inner coil58, an intermediate coil60, and an outer coil62with a certain gap therebetween in a radial direction. The coils58,60,62are coaxially (preferably, concentrically) arranged. Further, the coils58,60,62are also arranged concentrically with each other as well as with the chamber10or the susceptor12.

In the illustrative embodiment, the term “coaxial” means that central axes of multiple objects having axisymmetric shape are aligned with each other. As for multiple coils, respective coils surfaces may be offset with each other in an axial direction or may be aligned on the same plane (positioned concentrically).

Further, the inner coil58, the intermediate coil60and the outer coil62are electrically connected in parallel between a high frequency power supply line68from a high frequency power supply unit66for plasma generation and a return line70toward a ground potential member (i.e., between two nodes NAand N8). Here, the return line70as an earth line is grounded and is connected with a ground potential member (for example, the chamber10or other member) that is electrically maintained at a ground potential.

A variable capacitor86is provided between the node NBon the earth line70and the intermediate coil60. Further, a variable capacitor88is provided between the node NBon the earth line70and the outer coil62. Capacitances of these variable capacitors86and88may be independently adjusted to a desired value within a certain range by a capacitance varying unit90under the control of a main controller84. Hereinafter, a capacitor connected in series to the inner coil58will be referred to as an “inner capacitor”; a capacitor connected in series to the intermediate coil60will be referred to as an “intermediate coil”; and a capacitor connected in series to the outer coil62will be referred to as an “outer capacitor.” All these capacitors are provided between the node NAand NB.

The high frequency power supply unit66may include a high frequency power supply72and a matching unit74. The high frequency power supply72is capable of outputting a variable high frequency power RFHhaving a frequency (typically, equal to or higher than about 13.56 MHz) for generating plasma by an inductively coupled high frequency electric discharge. The matching unit74has a reactance-variable matching circuit for performing matching between an impedance of the high frequency power supply72and an impedance of load (mainly, RF antenna or plasma).

A processing gas supply unit for supplying a processing gas into the chamber10may include an annular manifold or buffer unit76; multiple sidewall gas discharge holes78; and a gas supply line82. The buffer unit76may be provided at an inside (or outside) of the sidewall of the chamber10to be located at a position slightly lower than the dielectric window52. The sidewall gas discharge holes78may be formed along a circumference at a regular interval and opened to the plasma generation space from the buffer unit76. The gas supply line82may be extended from a processing gas supply source80to the buffer unit76. The processing gas supply source80may include a flow rate controller and an opening/closing valve (not shown).

The main controller84may include, for example, a micro computer and may control an operation of each component within this plasma etching apparatus, for example, the exhaust unit26, the high frequency power supplies30and72, the matching units32and74, the switch42for the electrostatic chuck, the variable capacitors86and88, the processing gas supply source80, the chiller unit (not shown), and the heat transfer gas supply unit (not shown) as well as a whole operation (sequence) of the apparatus.

In order to perform an etching process in this inductively coupled plasma etching apparatus, when the gate valve28becomes open, the semiconductor wafer W as a process target may be loaded into the chamber10and mounted on the electrostatic chuck36. Then, after closing the gate valve28, an etching gas (generally, an mixture gas) may be introduced into the chamber10from the processing gas supply source80via the gas supply line82, the buffer unit76, and the sidewall gas discharge holes78at a certain flow rate and a flow rate ratio. Subsequently, an internal pressure of the chamber10may be controlled to be a certain level by the exhaust unit26. Further, the high frequency power supply72of the high frequency power supply unit66is turned on, and the high frequency power RFHfor plasma generation is outputted at a certain RF power level. A current of the high frequency power RFHis supplied to the inner coil58, the intermediate coil60and the outer coil62of the RF antenna54through the matching unit74, the RF power supply line68and the return line70. Meanwhile, the high frequency power supply30may be turned on to output the high frequency power RFLfor ion attraction control at a certain RF power level. This high frequency power RFLmay be applied to the susceptor12via the matching unit32and the power supply rod34. Further, a heat transfer gas (a He gas) may be supplied to a contact interface between the electrostatic chuck36and the semiconductor wafer W from the heat transfer gas supply unit. Furthermore, the switch42is turned on, and then, the heat transfer gas may be confined in the contact interface by the electrostatic force of the electrostatic chuck36.

Within the chamber10, an etching gas discharged from sidewall gas discharge holes78is diffused into a processing space below the dielectric window52. By the current of the high frequency power RFHflowing in the coils58,60and62, magnetic force lines (magnetic flux) generated around these coils are transmitted to the processing space (plasma generation space) within the chamber10via the dielectric window52. An induced electric field may be generated in an azimuth direction within the processing space. Then, electrons accelerated by this induced electric field in the azimuth direction may collide with molecules or atoms of the etching gas so as to be ionized. In the process, donut-shaped plasma may be generated.

Radicals or ions in the donut-shaped plasma may be diffused in all directions within the large processing space. To be specific, while the radicals are isotropically introduced and the ions are attracted by a DC bias, the radicals and the ions may be supplied on an upper surface (target surface) of the semiconductor wafer W. Accordingly, plasma active species may perform chemical and physical reactions on the target surface of the semiconductor wafer W so as to etch a target film into a required pattern.

Herein, “donut-shaped plasma” is not limited to only ring-shaped plasma which is generated only at the radial outside in the chamber10without being generated at the radial inside (at a central area) therein. Further, “donut-shaped plasma” may include a state where a volume or a density of the plasma generated at the radial outside is greater than that at the radial inside. Further, depending on a kind of a gas used for the processing gas, an internal pressure of the chamber10, or the like, the plasma may have other shapes instead of “a donut shape”.

In the inductively coupled plasma etching apparatus, the RF antenna54is segmented into the inner coil58, the intermediate coil60, and the outer coil62, which have different coil diameters. As a result, a wavelength effect or an electric potential difference (voltage drop) in the RF antenna54is effectively suppressed or reduced. Further, except for the inner coil58, the variable capacitors86,88are connected in series to the intermediate coil60and the outer coil62, respectively. Therefore, plasma density distribution on the semiconductor wafer W can be simply and effectively controlled.

[Basic Configuration and Operation of the RF Antenna]

FIGS. 2 and 3illustrate a basic configuration of a layout and an electric connection (circuit) of the RF antenna54in accordance with the illustrative embodiment.

As illustrated inFIG. 2, the inner coil58includes a single circular-ring shaped coil with a gap or a space Githerein, and the inner coil58has a constant radius. Further, the inner coil58is positioned near a central portion of the processing chamber10in the diametrical direction. One end of the inner coil58, i.e., an RF input terminal58in is connected to the RF power supply line68of the high frequency power supply unit66via the first node NAand the connection conductor92extending upwardly. The other end of the inner coil58, i.e., an RF output terminal58out is connected to the earth line70via the second node NBand the connection conductor94extending upwardly.

The intermediate coil60includes a single circular-ring shaped coil with a gap or a space Gmtherein, and the intermediate coil60has a constant radius. Further, the intermediate coil60is positioned at a portion of more outer than the inner coil58in the diametrical direction in a middle portion of the processing chamber10. One end of the intermediate coil60, i.e., an RF input terminal60in is adjacent to the RF input terminal58in of the inner coil58in the diametrical direction. Further, the RF input terminal60in is connected to the RF power supply line68of the high frequency power supply unit66via the first node NAand the connection conductor96extending upwardly. The other end of the intermediate coil60, i.e., an RF output terminal60out is adjacent to the RF output terminal58out of the inner coil58in the diametrical direction. Further, the RF output terminal60out is connected to the earth line70via the second node NBand the connection conductor98extending upwardly.

The outer coil62includes a single circular-ring shaped coil with a gap or a space Gotherein, and the outer coil62has a constant radius. The outer coil62is positioned at a portion of more outer than the intermediate coil60in the diametrical direction near the side wall of the processing chamber10. One end of the outer coil62, i.e., an RF input terminal62in is adjacent to the RF input terminal60in of the intermediate coil60in the diametrical direction. The RF input terminal62in is connected to the RF power supply line68of the high frequency power supply unit66via the first node NAand the connection conductor100extending upwardly. The other end of the outer coil62, i.e., an RF output terminal62out is adjacent to the RF output terminal60out of the intermediate coil60in the diametrical direction. The RF output terminal62out is connected to the earth line70via the second node NBand the connection conductor102extending upwardly.

As illustrated inFIG. 2, the connection conductors92to102upwardly extending from the RF antenna54serve as branch lines or connecting lines in horizontal directions while spaced apart from the dielectric window52at a sufficiently large distance (i.e., at considerably high positions). Accordingly, electromagnetic influence upon the coils58,60and62can be reduced.

In the above-described coil arrangement and segment connection configuration within the RF antenna54, when connecting from the high frequency power supply72to the ground potential member via the RF power supply line68, the RF antenna54, and the earth line70, more directly, when connecting from the first node NAto the second node NBvia high frequency branch transmission lines of the coils58,60,62within the RF antenna54, the directions when passing through the inner coil58, the intermediate coil60, and the outer coil62are all counterclockwise ofFIG. 2and identical to the circumferential direction.

In the inductively coupled plasma etching apparatus in accordance with the illustrative embodiment, a high frequency current supplied from the high frequency power supply unit66flows through each of component within the RF antenna54. As a result, high frequency AC magnetic fields distributed in loop shapes are formed around the inner coil58, the intermediate coil60and the outer coil62of the RF antenna54according to the Ampere's Law. Further, under the dielectric window52, magnetic force lines passing through the processing space in the radial direction are formed even in a relatively lower region.

In this case, a diametric directional (horizontal) component of a magnetic flux density in the processing space may be zero (0) constantly at a central region and a periphery of the processing chamber10regardless of a magnitude of the high frequency current. Further, the radial directional (horizontal) component of a magnetic flux density in the processing space may have a maximum value at a certain portion therebetween. A density distribution of the induced electric field in the azimuth direction generated by the AC magnetic field of the high frequency may have the same pattern as a magnetic flux density distribution in a diametrical direction. That is, an electron density distribution within the donut-shaped plasma in the diametrical direction may substantially correspond to a current split within the RF antenna54in a macro view.

The RF antenna54of the illustrative embodiment is different from a typical spiral coil wound from its center or inner peripheral end to an outer peripheral end thereof. That is, the RF antenna54includes the circular ring-shaped inner coil58localized to the central portion of the antenna; the circular ring-shaped intermediate coil60localized to the intermediate portion of the antenna; and the circular ring-shaped outer coil62localized to a peripheral portion of the antenna. A current split in the RF antenna54may be concentrated in the vicinities of each of the coils58,60and62.

Here, a high frequency current Ii(hereinafter, referred to as an “inner coil current”) may be regular or uniform over the loop of the inner coil58and flows in the inner coil58. A high frequency current Im(hereinafter, referred to as an “intermediate coil current”) may be regular or uniform over the loop of the intermediate coil60and flows in the intermediate coil60. A high frequency current Io(hereinafter, referred to as an “outer coil current”) may be regular or uniform over the loop of the outer coil62and flows in the outer coil62.

Therefore, in the donut-shaped plasma generated below (inside) the dielectric window52of the processing chamber10, as shown inFIG. 3), a current density (i.e. plasma density) may be remarkably increased (maximized) at positions right below the inner coil58, the intermediate coil60and the outer coil62. Thus, a current density distribution within the donut-shaped plasma may not be uniform in a diametrical direction and may have an uneven profile. However, since the plasma is diffused in all directions within the processing space of the processing chamber10, a plasma density in a vicinity of the susceptor12, i.e. on the substrate W, may become very uniform.

In the present illustrative embodiment, the inner coil58, the intermediate coil60and the outer coil62have the circular ring shapes. Further, since a regular or uniform high frequency currents flow in the circumferential directions of the coils, a plasma density distribution can constantly be uniformized in the circumferential directions of the coils in the vicinity of the susceptor12, i.e., on the substrate W as well as within the donut-shaped plasma.

Further, in the radial direction, by varying and setting the electrostatic capacitances C85and C88of the intermediate capacitor86and the outer capacitor88to have appropriate values within certain ranges, it is possible to adjust a balance between the currents Ii, Imand Ioflowing in the inner coil58, the intermediate coil60and the outer coil62, respectively. Accordingly, plasma density distribution within the donut-shaped plasma can be controlled as desired. Thus, plasma density distribution in the vicinity of the susceptor12, i.e., on the substrate W can be controlled as desired, and plasma density distribution can be easily uniformized with high accuracy.

In the illustrative embodiment, the wavelength effect and the voltage drop within the RF antenna54depend on a length of each of the coils58,60,62. Accordingly, by setting the length of each of the coils to prevent the wavelength effect from occurring in the coils58,60,62, both the wavelength effect and the voltage drop within the RF antenna54can be reduced. In order to prevent the wavelength effect, the length of each of the coils58,60,62is desirably shorter than a ¼ wavelength of the high frequency RFH.

The condition that the length of each the coil is less than a ¼ wavelength of the high frequency RFHis easily satisfied when a diameter of a coil is small, and the number of windings is small. Accordingly, in the RF antenna, the inner coil58having a smallest diameter can be easily subject to a configuration of a multiple number of windings. The outer coil62having a largest diameter is desirably subject to a single winding, rather than a multiple number of windings. The intermediate coil60depends on a diameter of the semiconductor wafer W, the frequency of the high frequency RFH, and the like. However, the intermediate coil60is desirably subject to a single winding, like the outer coil62.

[Functions of Capacitors Added to the RF Antenna]

The core technical feature of the illustrative embodiment lies in that the RF antenna54is segmented in parallel in the diametrical direction into the three coils58,60,62having different coil diameters. Further, the variable intermediate capacitor86and the variable outer capacitor88are electrically connected in series to the intermediate coil60and the outer coil62, respectively. Meanwhile, any reactance device (in particular, a capacitor) is not connected to the inner coil58.

Here, as illustrated inFIG. 4, it is assumed that no capacitor is connected to the RF antenna. In such case, more remarkable and stronger plasma than that generated directly under the intermediate coil60and the outer coil62is generated directly under the inner coil58. The reason that the remarkable and strong plasma is generated directly under the inner coil58will be described. A self-inductance L of a single circular ring-shaped coil is expressed by the formula (1) below, where a thickness (radius) of a coil conducting wire is represented as “a”, and a coil diameter (radius) is represented as “r”.

Here, μois a vacuum permeability, and the coil diameter (radius) r is a middle value between a radius of an inner periphery of a coil and a radius of an outer periphery of a coil.

From the formula (1), the self-inductance L is linearly proportional to the coil radius r. When a frequency of the high frequency is f, an impedance Z of the circular ring-shaped coil is 2πfL (Z=2πfL), and proportional to the self-inductance L. Accordingly, if the coil radiuses of the inner coil58, the intermediate coil60, and the outer coil62are, for example, about 50 mm, about 100 mm, and about 150 mm, respectively, the inner coil current Iiflows in the inner coil58, and an amount of the inner coil current Iiis approximately 2 times larger than the intermediate coil current Imflowing in the intermediate coil60, and approximately 3 times larger than the outer coil current Ioflowing in the outer coil62. Density of the plasma generated by the circular ring-shaped coils is slightly lowered in efficiency when the radiuses of the coils are small. However, the plasma density generally depends on an amount of the coil currents, regardless of the radiuses of the coils. As such, several times stronger plasma than that generated directly under the intermediate coil60and the outer coil62is generated directly under the inner coil58. Accordingly, the plasma density distribution near the susceptor12, i.e., on the semiconductor wafer W has a profile, where the central portion in the diametrical direction is protruded and becomes high.

However, a coil has a positive reactance, and a capacitor has a negative reactance. When a capacitor is connected to a coil, the negative reactance of the capacitor removes the positive reactance of the coil. As a result, a combined reactance becomes lower than the reactance of the coil. Accordingly, increasing the amount of the inner coil current I, by connecting a capacitor to the inner coil58does not have an effect on the uniformity of the plasma density distribution, and rather, results in a reverse effect thereon.

This is the same when the coils58,60,62are configured by spiral coils having Ni, Nm, and Noturns, respectively. That is, since an inductance of each coil is proportional to the number of turns (the number of windings), an impedance of each coil is also proportional to the number of turns. Accordingly, a ratio of the coil currents (Ii, Io) flowing in the inner coil58and the outer coil62, respectively, is Ii:Io=ro*No*Ni:ri*Ni*No=ro:ri. Meanwhile, the plasma density (ni, no) generated directly under each of the coils58and62is determined by multiplying the coil current and the number of turns. Accordingly, a ratio of the plasma densities (ni, no) generated directly under the inner coil58and the outer coil62is ni:no=ro*No*Ni:ri*Ni* No=ro:ri, which depends on a ratio of radiuses. The ratio of the coil currents and the plasma densities is identically applied to the case of the inner coil58and the intermediate coil60. As described, constantly, stronger plasma than those generated directly under the intermediate coil60and the outer coil62is generated directly under the inner coil58.

Actually, an impedance of a wiring from the output terminal of the matching unit74to the corresponding coil cannot be ignored. A length of the wiring is determined by a height from the output terminal of the matching unit74to the RF antenna54. Thus, it may be assumed that the length of the wiring is the same among the inner side, the intermediate side, and the outer side. Further, it is assumed that the wiring impedance is the same at the inner side, the intermediate side, and the outer side. In such case, if the outer coil62and the inner coil58have impedances of about 75Ω and about 25Ω, respectively, when the wiring impedance is approximately about 10Ω, Ii:Io=(75+10):(25+10)=85:35=2.41:1. Thus, there is still a difference two or more times between the impedances of the coils and the wiring impedance.

When a pressure is relatively high (generally, more than about 100 mTorr), and thus, plasma is difficult to be diffused, the above-described balance is achieved at the inner side and the outer side. However, when a pressure is lowered, and thus, the plasma is easy to be diffused, a plasma density at a central portion is further protruded and becomes high.

Accordingly, there is established a theory providing that under any conditions, a plasma density directly under an innermost coil, among a multiple number of coils electrically connected in parallel to one another and having different diameters, becomes relatively high.

In the illustrative embodiment, based on the above-described theory, no capacitor is added (connected) to the inner coil58between the both terminals (between the first node NAand the second node NB) of the RF antenna54. The variable capacitors86,88are connected in series to the intermediate coil60and the outer coil62, respectively. By adjusting the electrostatic capacitances C86, C88of the variable capacitors86,88in consideration of reducing a combined reactance, the amounts of the coil currents Im, Ioflowing in the intermediate coil60and the outer coil62, respectively, are properly increased. In this manner, it is possible to conform the coil currents Ii, Im, Ioto be in substantially the same amounts. Alternatively, it is possible to make the intermediate coil current Imand/or the outer coil current Iolarger than the inner coil current Ii. Here, the increasing amounts of the coil currents Im, Ioby the variable capacitors86,88flow in the intermediate coil60and the outer coil62, and contribute to the plasma generation. Thus, no waste of high frequency power is generated.

In general, in order to correct the profile, where a plasma density is protruded and becomes high at the central portion of the diametrical direction, it is effective to adjust a ratio (balance) of the inner coil current Iiflowing in the inner coil58and the outer coil current Ioflowing in the outer coil62. In the illustrative embodiment, a ratio of the coil currents Ii, Iocan be adjusted simply by varying the electrostatic capacitance C88of the outer capacitor88.

In this case, in order to uniformize the plasma density distribution under various conditions, it is desirable to set a variable range of multiplication (Io*no) of the outer coil current lo and the number of turns no of the outer coil62to have a lower limit value smaller than and an upper limit value larger than multiplication (Ii*ni) of the inner coil current Ii and the number of turns ni of the inner coil58. The ratio of the inner coil current Ii and the outer coil current lo is proportional to a ratio of reciprocal numbers of an impedance of the inner coil58(hereinafter, referred to as an “inner impedance”) and a combined impedance of the outer coil62and the outer capacitor88(hereinafter, referred to as an “outer combined impedance”). Accordingly, if the inner impedance (fixed value) is represented as Zi, and minimum and maximum values for the outer combined impedance (variable value) are represented as Zo(min) and Zo(max), respectively, the above-described condition for a multiplication of the coil current and the number of turns is expressed as follows:

Further, the inner impedance Ziand the outer combined impedance Zodepend on their respective average coil radiuses, except for the electric connecting portion. An effect of the electric connecting portion cannot be ignored, but is not dominant. Thus, the above-described condition may be expressed as follows:

Here, Co(min) is a value of the electrostatic capacitance C88of the outer capacitor88when the outer combined impedance Zois minimum within an adjustable range. Co(max) is a value of the electrostatic capacitance C88of the outer capacitor88when the outer combined impedance Zois maximum. Co(min) and Co(max) may not be the same as the minimum value and the maximum value of the variable range. The outer combined impedance Zobecomes minimum, when the outer coil62and the outer capacitor88cause a series resonance. Co(min) is a value of the electrostatic capacitance C88of the outer capacitor88at that time. The outer combined impedance Zobecomes maximum, when the electrostatic capacitance C88of the outer capacitor88becomes apart from the series resonance point up to an upper or lower limit of the variable range. Co(max) is a value of the electrostatic capacitance C88of the outer capacitor88at that time.

As described, no capacitor is connected to the inner coil58, and the outer capacitor88is connected in series to the outer coil62. By varying the electrostatic capacitance C88of the outer capacitor88, the ratio of the inner coil current Iiand the outer coil current Iois properly adjusted. Also, a general profile of the plasma density distribution within the donut-shaped plasma generated directly under the RF antenna54(in particular, balance between the central portion and the peripheral portion) can be properly controlled.

In the illustrative embodiment, the intermediate coil60is arranged between the inner coil58and the outer coil62. The variable intermediate capacitor86is connected in series to the intermediate coil60. This configuration is intended to minutely control the plasma density distribution (in particular, at the intermediate portion) within the donut-shaped plasma. The configuration is useful when generating plasma under a low pressure or generating plasma of a large diameter.

Instead of providing the intermediate coil60, it is considered to form the outer coil62in a spiral shape to cover the area of the intermediate portion of the antenna54with the outer coil62. In this case, however, the same coil current Ioflows in all sections of the outer coil62. Thus, the plasma density directly under the intermediate portion of the antenna may become relatively high. It becomes difficult to achieve a uniform profile, for example, in the diametrical direction.

In actual processes, there is a case where a desirable profile (e.g., flat) in the whole diametrical direction is obtained by forcibly reducing the plasma density within the donut-shaped plasma directly under the intermediate portion of the antenna. In particular, this situation easily occurs when an amount of the outer coil current Iois rapidly increased in order to raise peripheral plasma density to a desired level.

In this case, the intermediate capacitor86is used effectively. That is, the electrostatic capacitance C86of the intermediate capacitor86is varied in a range lower than a value of a series resonance point. As a result, a combined reactance of the intermediate coil60and the intermediate capacitor86(hereinafter, referred to as an “intermediate combined reactance”) becomes a negative value. Accordingly, the intermediate coil current Imflows in a direction opposite to the circumferential direction and in a certain current amount (in particular, it is also possible to slightly increase the current amount from the state of substantially zero (0)). Accordingly, the plasma density within the donut-shaped plasma directly under the intermediate coil can be locally and easily controlled. Furthermore, the plasma density distribution in the whole diametrical direction near the susceptor12, i.e., on the semiconductor wafer W can be easily controlled.

The function of the intermediate capacitor86has been verified by the experiment shown inFIGS. 5A and 5B. In the experiment, as illustrated inFIG. 5A, the inner coil58of the RF antenna54is formed with two windings (2 turns) having a diameter of about 100 mm. The intermediate coil60and the outer coil62are formed with a single winding (single turn) having diameters of about 200 mm and about 300 mm, respectively. As primary process conditions, the frequency of the high frequency RFHis about 13.56 MHz, the RF power is about 1500 W, a pressure in the processing chamber10is about 100 mTorr, the processing gas is a mixture gas of Ar and O2, and a flow rate of the processing gas is Ar/O2=about 300/30 sccm.

In the experiment, the electrostatic capacitance C88of the outer capacitor88is fixed at about 560 pF. The electrostatic capacitance C86of the intermediate capacitor86is varied to about 13 pF, to about 40 pF, and to about 64 pF. In this case, it is confirmed that as shown inFIG. 5B, the intermediate coil current Imis changed to about −0.4 A, to about −5.0 A, and to about −11.2 A, and the electron density Ne(i.e., plasma density) near a portion directly under the intermediate coil60can be locally and properly lowered. When C86is about 13 pF, the inner and outer coil currents Ii, Ioare about 16.4 A and about 18.3 A, respectively. When C86is about 40 pF, the inner and outer coil currents Ii, Ioare about 17.4 A and about 19.4 A, respectively. When C86is about 64 pF, the inner and outer coil currents Ii, Ioare about 19.0 A and about 20.1 A, respectively. If an amount of the intermediate coil current Imflowing in the opposite direction increases, amounts of the inner coil current Iiand the outer coil current Io, which flow in the forward direction, slightly increase. However, a ratio (balance) of the coil currents Ii, Iousually does not vary.

With respect to other functions in the RF antenna54of the present illustrative embodiment, it is possible to vary the electrostatic capacitance C88of the outer capacitor88in a range lower than the value of the series resonance point. As a result, a combined reactance of the outer coil62and the outer capacitor88(hereinafter, referred to as an “outer combined reactance”) becomes a negative value. Accordingly, it is possible to make the outer coil current Ioflow in the opposite direction. For example, if plasma diffuses excessively toward the outer side of the diametrical direction within the processing chamber10, the inner wall of the processing chamber10may be easily damaged. In such case, it is possible to make the coil current Ioflow in a direction opposite to the outer coil62, thereby confining the plasma in the inner side of the outer coil62. As a result, the damage of the inner wall in the processing chamber10can be prevented. This function is effective, for example, when a multiple number of intermediate coils60having different coil diameters are arranged while being spaced from one another in the diametrical direction, or when the outer coil62is arranged at a further outer side of the diametrical direction than the susceptor12.

In the illustrative embodiment, by making at least one of the electrostatic capacitances C86, C88of the intermediate capacitor86and the outer capacitor88close to a value when a series resonance is generated, it is possible to reduce the inner coil current Iiflowing in the inner coil58. By making at least one of the electrostatic capacitances C86, C88of the intermediate capacitor86and the outer capacitor88apart from the value when the series resonance is generated, it is possible to increase the inner coil current Ii. That is, the inner coil current Ii, the intermediate coil current Im, and the outer coil current Ioare in a ratio of Ii:Im:Io=(1/Zi):(1/Zm):(1/ Zo). Accordingly, as C86and/or C88are close to the value when the series resonance is generated, Zmand/or Zobecome smaller values. Here, Imand/or Ioare relatively increased, and Iibecomes smaller. Meanwhile, as C86and/or C88are apart from the value when the series resonance is generated, Z, and/or Zobecome large values. Here, Imand/or Ioare relatively decreased, and Iibecomes larger. [Another testing example or a modified example for the RF antenna]

In the illustrative embodiment, in controlling (in particular, uniformizing) the plasma density distribution, no capacitor is connected to the inner coil58, considering that an amount of the inner coil current does not need to be varied in order to increase the current amount thereof.

However, there is a case where positively or forcibly controlling an amount of the inner coil current Iiis effective. For example, when a pressure in the processing chamber10is low, the plasma tends to be gathered at a central portion of the diametrical direction. As described above, this problem may be resolved by varying the electrostatic capacitance C88of the outer capacitor88and adjusting a ratio of the inner coil current Iiand the outer coil current Io. However, the problem may not be completely resolved.

As illustrated inFIGS. 6A and 6B, the fixed or semi-fixed inner capacitor104is electrically connected in series to the inner coil58between the first node NAand the second node NBin the RF antenna54. In this configuration, it is also possible to select or adjust the electrostatic capacitance C104of the inner capacitor104to be a desired value. As a result, a combined reactance Xiof the inner coil58and the inner capacitor104(hereinafter, referred to as an “inner combined reactance”) becomes a desired value. When the fixed or semi-fixed capacitor104and the variable outer capacitor88are provided, the condition formulas (2) and (3) are also applied with respect to the number of turns of each of the coils or the variable control of the electrostatic capacitance C88of the outer capacitor88.

Although a freedom degree or an accuracy of the plasma density distribution control is somewhat decreased, in order to reduce costs, a variable capacitor for the inner capacitor104and a fixed or semi-fixed capacitor for the outer capacitor88may be used, as illustrated inFIGS. 7A and 7B. Although not illustrated herein, a fixed or semi-fixed capacitor for the intermediate capacitor86may be used. Further, the intermediate capacitor86may be omitted.

When the fixed or semi-fixed outer capacitor88and the variable inner capacitor104are provided, in uniformizing the plasma density distribution under various conditions, it is desirable to set a variable range of multiplication (Ii*ni) of the inner coil current Iiand the number of turns niof the inner coil58to have a lower limit value smaller and an upper limit value larger than multiplication (Io*no) of the outer coil current Ioand the number of turns (no) of the outer coil62. The ratio of the inner coil current Iiand the outer coil current Iois proportional to a ratio of reciprocal numbers of the combined impedance (inner combined impedance) of the inner coil58and the inner capacitor104, and the combined impedance (outer combined impedance) of the outer coil62and the outer capacitor88. Accordingly, if the outer impedance (fixed value) is represented as Zo, and minimum and maximum values of the inner combined impedance (variable value) are represented as Zi(min) and Zi(max), respectively, the above-described condition for the multiplication of the coil current and the number of turns is expressed as follows:

The inner combined impedance Ziand the outer combined impedance Zodepend on their respective average coil radiuses, except for the electric connecting portion. An effect of the electric connecting portion cannot be ignored, but is not dominant. Thus, the above-described condition may be expressed as follows:

Here, Ci(min) is a value of the electrostatic capacitance C104of the inner capacitor104when the inner combined impedance Ziis minimum within an adjustable range. Ci(max) is a value of the electrostatic capacitance C104of the inner capacitor104when the inner combined impedance Ziis maximum. Ci(min) and Ci(max) may not be the same as a minimum value and a maximum value of the variable range of C104. The inner combined impedance Zibecomes minimum, when the inner coil58and the inner capacitor104cause a series resonance. Ci(min) is a value of the electrostatic capacitance C104of the inner capacitor104at that time. Further, the inner combined impedance Zibecomes maximum, when the electrostatic capacitance C104of the inner capacitor104becomes apart from the series resonance point up to an upper or lower limit of the variable range. Ci(max) is a value of the electrostatic capacitance C104of the inner capacitor104at that time.

The variable inner capacitor104is connected to the inner coil58, and a fixed or semi-fixed outer capacitor88is connected in series to the outer coil62. By varying the electrostatic capacitance C104of the inner capacitor104, the ratio of the inner coil current Iiand the outer coil current Iois properly adjusted. Also, it is possible to properly control a profile of the plasma density distribution within the donut-shaped plasma generated directly under the RF antenna54(in particular, a balance of the central portion and the peripheral portion).

In accordance with a modified example, in order to positively or forcibly reduce the amount of the inner coil current Ii, a variable inductor106may be electrically connected in series to the inner coil58between the first node NAand the second node NB. Also, it is possible to substitute the intermediate capacitor86with another variable inductor, or it is possible to omit the outer capacitor88for reducing costs.

The loop shape of each of the coils58,60,62in the RF antenna54is not limited to a circular shape. For example, as illustrated inFIG. 9, the loop shape of each of the coils58,60,62may be square according to the shape of the target object to be processed. When the loop shape of each of the coils58,60,62is polygonal, the variable intermediate capacitor86and the outer capacitor88may be electrically connected in series to the intermediate coil60and the outer coil62, respectively, and no capacitor may be connected to the inner coil58.

An inductance L of a rectangular coil, where lengths of two sides are represented as “a” and “b”, and a thickness of the coil is represented as a radius “d”, is expressed by the formula (6) below.

As shown from the formula (6), the inductance L of the rectangular coil is substantially proportional to the lengths of the two sides “a”, “b”. Accordingly, even when no capacitor is connected to the inner coil58as the same as in the circular coil, the plasma density distribution can be simply or easily controlled by the intermediate capacitor 86 and the outer capacitor88.

FIG. 10shows an example where the coils (inner coil58/intermediate coil60/outer coil62) of the RF antenna54are formed with a pair of spiral coils. The coils are arranged in a spatially and electrically parallel. The spiral coils may be used unless the wavelength effect is really a problem.

In the illustrated configuration example, the inner coil58is formed with a pair of spiral coils58a,58bhaving a multiple number of turns (respectively, 2 turns in the illustrated example) and being deviated 180° from the circumferential direction. The spiral coils58a,58bare electrically connected in parallel between a node NCprovided at a downstream side lower than the node NAof the high frequency power supply72and a node NDprovided at an upstream side higher than the node NBof the earth line70.

The intermediate coil60is formed with a pair of spiral coils60a,60beach having a multiple number of turns (respectively, 2 turns in the illustrated example) and being deviated 180° from the circumferential direction. The spiral coils60a,60bare electrically connected in parallel between a node NEprovided at a downstream side lower than the node NAof the high frequency power supply72and a node NFprovided at an upstream side higher than the node NB(and the intermediate capacitor86) of the earth line70.

The outer coil62is formed with a pair of spiral coils62a,62beach having a multiple number of turns (respectively, 2 turns in the illustrated example) and being deviated 180° from the circumferential direction. The spiral coils62a,62bare electrically connected in parallel between a node NGprovided at a downstream side lower than the node NAof the high frequency power supply72and a node NHprovided at an upstream side higher than the node NB(and the outer capacitor88) of the earth line70.

When the inner coil58, the intermediate coil60, and the outer coil62are segmented into ki, km, and kospiral coils in parallel, respectively, if no capacitor is connected to the RF antenna54, a ratio of plasma densities ni, nm, no, which is generated directly under the coils58,60,62, respectively, is expressed by an approximation equation (3) below.

As in the illustrated example, if the number of segments ki, km, kois the same (2 segments), the plasma density generated directly under the inner coil58, i.e., the plasma in the central portion becomes relatively higher. In this case, the most desirable configuration is that no capacitor is connected to the inner coil58, and the variable intermediate capacitor86and the outer capacitor88are connected in series to the intermediate coil60and the outer coil62, respectively.

With respect to another modified example, as illustrated inFIG. 11, it is possible to connect an intermediate capacitor86and an outer capacitor88between the first node NAof the high frequency power supply72and the RF inlet terminals60in,62in of the intermediate coil60and the outer coil62. Connecting a capacitor or an inductor for adjusting impedance between the first node NAand each of the coils may be applied to another experimental example or another modified example (FIGS. 6A,8,9, and10).

FIG. 12illustrates the configuration where an output common capacitor108is connected between the second node NBand the earth line70(or on the earth line70) at the terminal end of the RF antenna54, and electrically connected in series to all the coils58,60,62of the RF antenna54. The output terminal (terminal end) common capacitor 108 may be a common fixed capacitor or a variable capacitor.

The output terminal (terminal end) common capacitor108has a function of adjusting the whole impedance of the RF antenna54, and a function of suppressing ion sputter performed on the ceiling plate or the dielectric window52by serially raising the whole potential of the RF antenna54from a ground potential.

Although not illustrated herein, it is possible to provide other coils at the diametrical direction inner side of the inner coil58and/or the diametrical direction outer side of the outer coil62in the RF antenna54. As a result, total 4 or more coils are arranged in the diametrical direction at intervals while being electrically connected in parallel to one another.

In the above-described embodiment, the illustrated configuration of the inductively coupled plasma etching apparatus is nothing more than an example. Not only each component of the plasma generating mechanism but also each component which is not directly relevant to plasma generation can be modified in various manners.

By way of example, the basic shape of the RF antenna may be a dome shape besides the planar shape mentioned above. Further, it may be also possible to have configuration in which a processing gas is introduced into the chamber10from the processing gas supply unit through a ceiling. Furthermore, it may be also possible not to apply a high frequency power RFLfor DC bias control to the susceptor12.

The inductively coupled plasma processing apparatus or the inductively coupled plasma processing method of the present disclosure can be applied to, not limited to a plasma etching technology, other plasma processes such as plasma CVD, plasma oxidation, plasma nitridation, and sputtering. Further, the target substrate in the present disclosure may include, but is not limited to a semiconductor wafer, various kinds of substrates for a flat panel display or photo mask, a CD substrate, and a print substrate.