Antenna and plasma processing apparatus

An antenna includes a dielectric window and a slot plate provided at one surface of the dielectric window. The slot plate includes a plurality of slot pairs each being formed of two slots. The slot pairs are concentrically disposed about a centroid position of the slot plate and provided at positions where straight lines extending from the centroid position of the slot plate and passing through each slot pair are not overlapped with each other.

FIELD OF THE INVENTION

The present invention relates to an antenna and a plasma processing apparatus.

BACKGROUND OF THE INVENTION

Conventionally, a plasma etching apparatus using a radial line slot antenna is known (see, e.g., Japanese Patent Application Publication No. 2007-311668). In this plasma etching apparatus, a circular plate-shaped slot antenna having a plurality of slots is installed on a dielectric window of a processing chamber. The slots include a plurality of slot pairs formed of two elongated microwave radiation slots directed in different directions. The slot pairs are arranged in a double ring shape (i.e., a concentric circular shape) about the centroid position of the slot antenna. The microwave is incident on the central position of the slot antenna, emitted radially, and radiated from the slots. The microwave radiated from the slots of the slot antenna is introduced into a processing space of the processing chamber through a dielectric window made of a dielectric material. A processing gas is turned into a plasma by the energy of the microwave.

The microwave plasma generated by the radial line slot antenna has a feature that a plasma having a relatively high electron temperature of several eV which is generated just below the dielectric window (referred to as “plasma excitation region”) is diffused and becomes a plasma having a relatively low electron temperature of about 1 eV to 2 eV in a region just above a substrate and below the dielectric window by a distance of about 100 mm or more (referred to as “plasma diffusion region”). In other words, the electron temperature distribution of the plasma occurs as a function of a distance from the dielectric window.

In the radial line slot antenna type plasma etching apparatus, an etching gas is supplied to a low electron temperature region and dissociation control of the etching gas (control of the amount of etching species generated in the plasma) is performed. By doing so, etching reaction (chemical reaction on a substrate surface by the etching species) is controlled. Accordingly, the etching can be performed with high precision and damage to the substrate is considerably reduced. For example, when etching or the like is performed in a step of forming a spacer, it is possible to manufacture devices with design dimensions and reduce the damage to the substrate such as a recess or the like.

However, as the processes become various and complicated, the plasma stability needs to be further improved. For example, in the plasma etching apparatus using a radial line slot antenna described in Japanese Patent Application Publication No. 2007-311668, the radiation electric field intensity is decreased in the case of using as a processing gas a negative gas that is turned into negative ions due to attachment of electrons in the plasma diffusion region. Therefore, in order to ensure the plasma stability, it is required to control a pressure or a microwave power.

SUMMARY OF THE INVENTION

In this technical field, it is required to provide an antenna and a plasma processing apparatus capable of improving plasma stability by improving a radiation electric field intensity with respect to an input power.

An antenna in accordance with an aspect of the present invention includes a dielectric window and a slot plate. The slot plate is provided at one surface of the dielectric window. The slot plate includes a plurality of slot pairs each being formed of two slots. The slot pairs are concentrically disposed about a centroid position of the slot plate. The slot pairs are provided at positions where straight lines extending from the centroid position of the slot plate and passing through each slot pair are not overlapped with each other.

The microwave is incident on the centroid position of the slot plate and radially emitted. If the slot pairs are disposed at positions where the straight lines extending from the centroid position of the slot plate and passing through each slot pair are overlapped with each other, i.e., if the slot pairs are overlapped with each other when seen from the centroid position of the slot plate toward the outer region in the diametrical direction, the microwave is initially radiated from a slot pair close to the centroid position. Therefore, the microwave having a low electric field intensity propagates to the other slot pairs disposed on the straight line extending from the centroid position of the slot plate and passing through the slot pair close to the centroid position. Accordingly, the microwave having a low electric field intensity is radiated from the other slot pairs. Meanwhile, in the antenna, the slot pairs arranged in a concentric circular shape are provided at positions where the straight lines extending from the centroid position of the slot plate and passing through each of the slot pairs are not overlapped with each other. In other words, on the straight line extending from the centroid position of the slot plate and passing through a slot pair, other slot pairs are not provided. Accordingly, the slot pairs having a low microwave radiation efficiency for an input power can be excluded, which makes it possible to relatively improve distribution of the input power to the other slot pairs. As a result, the radiation electric field intensity with respect to the input power is improved and the plasma stability can be improved.

In the aspect, the slot plate may include a first slot group, a second slot group, a third slot group and a fourth slot group. The first slot group is spaced from the centroid position of the slot plate by a first distance. The second slot group is spaced from the centroid position of the slot plate by a second distance. The third slot group is spaced from the centroid position of the slot plate by a third distance. The fourth slot group is spaced from the centroid position of the slot plate by a fourth distance. A relationship between the first to the fourth distance satisfies the first distance<the second distance<the third distance<the fourth distance. Slots in the first slot group and slots in the second slot group which correspond to each other form a plurality of first slot pairs, and slots in the third slot group and slots in the fourth slot group which correspond to each other form a plurality of second slot pairs. A slot in the second slot group of each first slot pair is positioned on a first straight line extending from the centroid position of the slot plate and passing through a slot in the first slot group of the corresponding first slot pair. A slot in the fourth slot group of each second slot pair is positioned on a second straight line extending from the centroid position of the slot plate and passing through a slot in the third slot group of the corresponding second slot pair. All the slots are arranged such that the first straight line and the second straight line are not overlapped with each other.

With the above configuration, the slot pairs having a low microwave radiation efficiency for the input power can be excluded, which makes it possible to relatively improve distribution of the input power to the other slot pairs. As a result, the radiation electric field intensity with respect to the input power is improved and the plasma stability can be improved.

In the aspect, the number of the slots in the first slot group and the number of the slots in the second slot group may be the same number denoted by N1, and the number of the slots in the third slot group and the number of the slots in the fourth slot group may be the same number denoted by N2, wherein N2is an integer multiple of N1. With the above configuration, a plasma having high in-plane symmetry can be generated.

In the aspect, a width of the slots in the first slot group may be the same as a width of the slots in the second slot group, a width of the slots in the third slot group may be the same as a width of the slots in the fourth slot group, and the width of the slots in the first slot group and the width of the slots in the second slot group may be greater than the width of the slots in the third slot group and the width of the slots in the fourth slot group. With the above configuration, the radiation electric field intensity of the first and second slot groups which are close to the centroid position of the slot plate can become lower than that of the third and fourth slot groups which are far from the centroid position of the slot plate. Since the microwave is attenuated during propagation, the radiation electric field intensity of the microwave becomes uniform over the surface of the slot plate by employing the above configuration. Accordingly, the plasma having high in-plane uniformity can be generated.

In the aspect, an angle between a diameter extending from the centroid position of the slot plate toward a target slot and a lengthwise direction of the target slot may be the same in each of the first to the fourth slot group. A slot in the first slot group and a slot in the second slot group that are positioned on the same diameter extending from the centroid position of the slot plate may be elongated in different directions. Further, a slot in the third slot group and a slot in the fourth slot group that are positioned on the same diameter extending from the centroid position of the slot plate may be elongated in different directions. With the above configuration, the reflection on two slots of a slot pair is cancelled, so that the uniformity of the radiation electric field intensity of the microwave can be improved.

In the aspect, the other surface of the dielectric window may include a flat surface surrounded by an annular first recess, and a plurality of second recesses formed in the flat surface so as to surround a centroid position of the flat surface. When seen from a direction perpendicular to a main surface of the slot plate, a centroid position of each of the second recesses may be positioned in each of the slots of the slot plate. With the above configuration, the in-plane uniformity can be further improved.

In the aspect, the second recesses may have a circular shape in a plan view. When the second recesses have a circular shape, the shape from the center has a high equivalence and, hence, stable plasma is generated.

A plasma processing apparatus in accordance with another aspect of the present invention includes an antenna, a processing chamber, a mounting table and a microwave introduction line. The antenna includes a dielectric window and a slot plate. The slot plate is provided at one surface of the dielectric window. The slot plate includes a plurality of slot pairs each being formed of two slots. The slot pairs are arranged in a concentric circular shape about a centroid position of the slot plate. The slot pairs are provided at positions where straight lines extending from the centroid position of the slot plate and passing through each slot pair are not overlapped with each other. The processing chamber includes the antenna. The mounting table is provided in the processing chamber to face the other surface of the dielectric window, and mounts thereon a substrate to be processed. The microwave introduction line connects a microwave generator and the slot plate.

The plasma processing apparatus can provide the same effect as the antenna.

EFFECT OF THE INVENTION

As described above, according to the aspects and embodiments of the present invention, there are provided an antenna and a plasma processing apparatus which are capable of improving plasma stability by improving a radiation electric field intensity with respect to an input power.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals will be used for like or corresponding parts in the respective drawings.

FIG. 1is a vertical cross sectional view of a plasma processing apparatus in accordance with an embodiment of the present invention. A plasma processing apparatus1includes a cylindrical processing chamber2. A ceiling portion of the processing chamber2is covered by a dielectric window (ceiling plate)16made of a dielectric material. The processing chamber2is made of, e.g., aluminum, and is electrically grounded. An inner wall surface of the processing chamber2is coated by an insulating protective film2fsuch as alumina or the like.

A mounting table3for mounting thereon a semiconductor wafer (hereinafter, referred to as “wafer”) as a substrate is provided at a center of a lower portion in the processing chamber2. The wafer W is held on a top surface of the mounting table3. The mounting table3is made of ceramic, e.g., alumina, alumina nitride or the like. A heater5is embedded in the mounting table3, so that the wafer W can be heated to a predetermined temperature. The heater5is connected to a heater power supply4through a wiring provided in a column.

An electrostatic chuck CK for electrostatically attracting the wafer W mounted on the mounting table3is provided on the top surface of the mounting table3. The electrostatic chuck CK is connected to a bias power supply BV for applying a bias direct current or a high frequency power (RF power) via a matching unit MG.

Provided at a bottom portion of the processing chamber2is a gas exhaust line11for exhausting a processing gas through a gas exhaust port11adisposed at a position lower than the surface of the wafer W mounted on the mounting table3. A gas exhaust unit10such as a vacuum pump or the like is connected to the gas exhaust line11via a pressure control valve PCV. The gas exhaust unit10communicates with the inside of the processing chamber2via the pressure control valve PCV. A pressure in the processing chamber2is controlled to a predetermined pressure by the pressure control valve PCV and the gas exhaust unit10.

The dielectric window16is provided at the ceiling portion of the processing chamber2through a sealing15such as an O-ring or the like for ensuring airtightness. The dielectric window16is made of a dielectric material, e.g., quartz, alumina (Al2O3), aluminum nitride (AlN) or the like. The dielectric window16transmits a microwave.

A circular plate-shaped slot plate20is provided on a top surface of the dielectric window16. The slot plate20is made of a conductive material, e.g., copper plated or coated with Ag, Au, or the like. A plurality of slots having, e.g., a T-shape or an L-shape is concentrically arranged at the slot plate20.

A dielectric plate25for compressing a wavelength of a microwave is provided on the top surface of the slot plate20. The dielectric plate25is made of a dielectric material, e.g., quartz (SiO2), alumina (Al2O3), aluminum nitride (AlN), or the like. The dielectric plate25is covered with a conductive cover26. An annular heat medium flow path27is formed in the cover26. The cover26and the dielectric plate25are controlled to a predetermined temperature by a heat medium flowing through the heat medium flow path27. In the case of a microwave of 2.45 GHz, for example, a wavelength in vacuum is about 12 cm and a wavelength in the dielectric window16made of alumina is about 3 cm to 4 cm.

A coaxial waveguide30for propagating a microwave is connected to a center of the cover26. The coaxial waveguide30includes an inner conductor31and an outer conductor32. The inner conductor31is connected to a center of the slot plate20while penetrating through a center of the dielectric plate25.

The coaxial waveguide30is connected to a microwave generator35via a mode converter37and a rectangular waveguide36. Microwaves of 860 MHZ, 915 MHz or 8.35 GHz may be used instead of the microwave of 2.45 GHz.

A microwave generated by the microwave generator35propagates through the rectangular waveguide36, the mode converter37, the coaxial waveguide30, and the dielectric plate25, which serve as a microwave introduction line. The microwave transmitted to the dielectric plate25is supplied into the processing chamber2through the slots21of the slot plate20and the dielectric window16. An electric field is formed below the dielectric window16by the microwave and a processing gas in the processing chamber2is turned into a plasma.

A lower end portion of the inner conductor31connected to the slot plate20has a truncated cone shape. Therefore, the microwave can be efficiently transmitted from the coaxial waveguide30to the dielectric plate25and the slot plate20without a loss.

The microwave plasma generated by the radial line slot antenna has a feature that a plasma having a relatively high electron temperature that is generated just below the dielectric window16(hereinafter, referred to as “plasma excitation region”) is diffused and becomes a plasma having a relatively low electron temperature of about 1 eV to 2 eV in a region just above the wafer W (hereinafter, referred to as “plasma diffusion region”). In other words, unlike the plasma generated by a parallel plate type plasma processing apparatus, the microwave plasma generated by the radial line slot antenna has a feature that the electron temperature distribution of the plasma occurs as a function of a distance from the dielectric window16. More specifically, the electron temperature of several eV to about 10 eV in a region just below the dielectric window16decreases to about 1 eV to 2 eV in a region just above the wafer W. Since the wafer W is processed in the region (plasma diffusion region) where the electron temperature of the plasma is low, serious damage such as a recess or the like is not inflicted on the wafer W. If the processing gas is supplied to the region where the electron temperature of the plasma is high (plasma excitation region), the processing gas is easily excited and dissociated. If the processing gas is supplied to the region where the electron temperature of the plasma is low (the plasma diffusion region), the degree of dissociation is decreased compared to the case where the processing gas is supplied to the vicinity of the plasma excitation region.

A central introduction unit55for introducing the processing gas to the central portion of the wafer W is provided at the center of the dielectric window16at the ceiling portion of the processing chamber2. A processing gas supply line52is formed at the inner conductor31of the coaxial waveguide30. The central introduction unit55is connected to the processing gas supply line52.

The central introduction unit55includes: a cylindrical block57inserted into a cylindrical space143(seeFIG. 8) provided at the center of the dielectric window16; a gas storage space60formed to have an appropriate size between a bottom surface of the inner conductor31of the coaxial waveguide30and a top surface of the block57; and a tapered space143a(seeFIG. 8) connected to a cylindrical space having a gas injection opening59at a leading end thereof. The block57is made of a conductive material, e.g., aluminum or the like, and is electrically grounded. A plurality of central inlet openings58penetrates through the block57in a vertical direction.

InFIG. 3, the size of the gas injection opening59shown inFIG. 3is exaggeratedly shown in order to visualize the central inlet openings58. The shape of the space143ais not limited to a tapered shape and may be simply a cylindrical shape. In this case, the size of the gas injection opening59is increased as shown inFIG. 3. The central inlet openings58have a circular or elongated hole shape in a plan view in consideration of a required conductance or the like. The block57made of aluminum is coated by anodically oxidized alumina (Al2O3), yttria (Y2O3) or the like.

The processing gas supplied into the gas storage space60through the supply line52penetrating through the inner conductor31is diffused in the gas storage space60and then injected downward toward the central portion of the wafer W through the central inlet openings58of the block57.

In the processing chamber2, a ring-shaped peripheral introduction unit61for supplying a processing gas to a peripheral portion of the wafer W is provided so as to surround the periphery of the space above the wafer W. The peripheral introduction unit61is positioned below the central inlet openings58formed at the ceiling portion and above the wafer W mounted on the mounting table3. The peripheral introduction unit61is an annular hollow pipe. A plurality of peripheral inlet openings62is formed at an inner circumferential side of the peripheral introduction unit61, the peripheral inlet openings62being spaced apart from each other at a regular interval along the circumferential direction introduction unit. The processing gas is injected through the peripheral inlet openings62toward the center of the peripheral introduction unit61. The peripheral introduction unit61is made of, e.g., quartz. A supply line53made of stainless steel penetrates through the sidewall of the processing chamber2. The supply line53is connected to the peripheral introduction unit61. The processing gas supplied into the peripheral introduction unit61through the supply line53is diffused in the peripheral introduction unit61and injected toward the inner side of the peripheral introduction unit61through the peripheral inlet openings62. The processing gas injected through the peripheral inlet openings62is supplied to a space above the peripheral portion of the wafer W. Instead of providing the ring-shaped peripheral introduction unit61, a plurality of peripheral inlet openings62may be formed at the inner surface of the processing chamber2.

FIG. 2is a block diagram showing a detailed structure of a gas supply source. A gas supply source100includes a common gas source41and an additional gas source42. The common gas source41and the additional gas source42supply processing gases for plasma etching, plasma CVD processing and the like.

A common gas line45is connected to the common gas source41and also connected to a flow splitter44. The flow splitter44is provided at the common gas line45and divides the common gas line45into a first branch common gas line46and a second branch common gas line47. The flow splitter44can control a ratio of flow rates of gases flowing in the first and second branch common gas lines46and47. Here, the first branch common gas line46is connected to the central introduction unit55(seeFIG. 1) through the supply line52and supplies a central introduction gas Gc to the central introduction unit55. The second branch common gas line47is connected to the peripheral introduction unit61(seeFIG. 1) through the supply line53and supplies a peripheral introduction gas Gp to the peripheral introduction unit61.

The additional gas source42is connected to the second branch common gas line47through the additional gas line48. Further, the additional gas source42may be connected to the first branch common gas line46through an additional gas line48′. Moreover, the additional gas source42may be connected to both of the branch common gas lines46and47through the additional gas lines48and48′.

The common gas source41includes a plurality of gases G11, G12, G13and G1xand flow rate control valves41a,41b,41cand41xfor controlling flow rates of the gases, respectively. Valves V are provided at the upstream and downstream lines connected to the flow rate control valves41a,41b,41cand41x, and opens/closes the paths of the lines. The flow rate control valves41a,41b,41cand41xare connected to the common gas line45via the respective valves V.

The additional gas source42includes a plurality of gases G21, G22, G23and G2xand flow rate control valves42a,42b,42cand42xfor controlling flow rates of the gases, respectively. Valves V are provided at the upstream and downstream lines connected to the flow rate control valves42a,42b,42cand42x, and opens/closes the paths of the lines. The flow rate control valves42a,42b,42cand42xare connected to the additional gas line48via the respective valves V.

A controller CONT shown inFIG. 1controls the flow rate control valves41a,41b,41c,41x,42a,42b,42cand42xand the various valves V in the gas supply source and ultimately controls a partial pressure ratio of a specific gas contained in the gases Gc and GP respectively flowing in the branch common gas lines46and47. The controller CONT controls the flow rates of the respective gases and determines a flow rate and a partial pressure for each gas species in the common gas supplied to the flow splitter44. In this apparatus, it is possible to change the partial pressure for each gas species, and the gas species itself in the central introduction gas Gc supplied to the central portion of the wafer W and the peripheral introduction gas Gp supplied to the peripheral portion of the wafer W. Hence, the characteristics of the plasma processing can be variously modified.

A rare gas (Ar gas or the like) may be used as a gas G1xof the common gas source41. However, other additional gases may also be used. In the case of etching a silicon-based film such as polysilicon or the like, Ar gas, HBr gas (or Cl2gas) and O2gas are supplied as the additional gases G21, G22and G23, respectively. In the case of etching an oxide film such as SiO2or the like, Ar gas, CHF-based gas, CF-based gas, and O2gas are supplied as the additional gases G21, G22, G23and G2x, respectively. In the case of etching a nitride film such as SiN or the like, Ar gas, CF-based gas, CHF-based gas, and O2gas are supplied as the addition gases G21, G22, G23and G2x, respectively.

The CF-based gas may include C(CF3)4, C(C2F5)4, C4F8, C2F2, C5F8and the like. However, it is preferable to use C5F8in order to obtain dissociated species suitable for the etching.

In this apparatus, the same gas may be supplied from the common gas source41and the additional gas source42, or different gases may be supplied from the common gas source42and the additional gas source42.

In order to suppress dissociation of the etching gas, a plasma excitation gas and an etching gas may be supplied from the common gas source41and the additional gas source42, respectively. For example, in the case of etching a silicon-based film, Ar gas is only supplied as the plasma excitation gas from the common gas source41and HBr gas and gas are only supplied as the etching gas from the additional gas sources42.

The common gas source41may supply a common gas other than a cleaning gas such as O2, SF6or the like.

The above-described gas contains a so-called negative gas. The negative gas denotes a gas having an electron attachment cross section area at an electron energy of 10 eV or less, e.g., HBr, SF6or the like.

Here, a technique that controls a distribution ratio of the common gas by using the flow splitter44and controls the amount of gases introduced from the central inlet openings58(seeFIG. 3) and the peripheral introduction unit61(seeFIG. 1) in order to achieve uniform plasma generation and uniform processing over the surface of the wafer W is referred to as “RDC (Radical Distribution Control)”. The RDC is expressed as a ratio of the amount of gas introduced from the central inlet openings58with respect to the amount of gas introduced from the peripheral introduction unit61. In general RDC, the same gas is supplied from the central introduction unit55and the peripheral introduction unit61. An optimum RDC value is determined experimentally depending on the types of films to be etched or various conditions. A technique for further supplying an additional gas to the central introduction unit55or the peripheral introduction unit61is referred to as “ARDC (Advanced Radical Distribution Control)”.

In the etching process, by-products (etching residue or deposits) are generated by the etching. In order to improve gas flow in the processing chamber2and easily discharge the by-products to the outside of the processing chamber, it is considered to introduce gases from the central introduction unit55and the peripheral introduction unit61alternately. This can be realized by switching a RDC value temporally. For example, the by-products are removed from the processing chamber2by repeating a step of introducing a large amount of gas to the central portion of the wafer W and a step of introducing a large amount of gas to the peripheral portion of the wafer W at a predetermined cycle and controlling gas flow. From this, a uniform etching rate can be obtained.

FIG. 4is an exploded perspective view of a structure of the slot plate and its vicinity. The dielectric window16is installed at the plasma processing apparatus1such that the bottom surface thereof (where the recesses are formed) is positioned on the surface of an annular member19forming a part of the sidewall of the processing chamber2. The slot plate20is provided on top of the dielectric window16. The dielectric plate25is provided on top of the slot plate20. The dielectric window16, the slot plate20and the dielectric plate25have a circular shape in a plan view, and the centers thereof are positioned on the same axis (Z-axis).

The slot plate20has slots of various patterns. InFIG. 4, the illustration of the slots is omitted in the slot plate20for clear explanation, but instead, the slot plate20having the slots is illustrated inFIG. 5.

FIG. 5is a top view of the slot plate20. The slot plate20has a thin circular plate shape. Opposite surfaces of the slot plate20in the plate thickness direction are flat. The slot plate20has a plurality of slots penetrating therethrough in the thickness direction. A first slot133elongated in one direction and a second slot134elongated in a perpendicular direction to the first slot133adjoin to each other and form a pair. Specifically, two adjacent slots133and134form a pair and are arranged in a substantially L-shape that is disconnected at the center. In other words, the slot plate20has slot pairs140, each being formed of the first slot133extending in one direction and the second slot134extending in a perpendicular direction to the one direction. In the same manner, a slot pair140′ is formed of a third slot133′ and a fourth slot134′. Examples of the slot pairs140and140′ are illustrated in a region indicated by dotted lines inFIG. 5.

The slot pairs are divided into an inner slot pair group135disposed at an inner peripheral side and an outer slot pair group136disposed at an outer peripheral side. The inner slot pair group135has seven slot pairs140provided in an inner region of a virtual circle indicated by a dashed dotted line inFIG. 5. The outer slot pair group136has fourteen slot pairs140′ provided in an outer region of the virtual circle indicated by the dashed dotted line inFIG. 5. The slot pairs140and140′ are disposed in a concentric circular shape so as to surround the center (centroid position)138of the slot plate20.

In the inner slot pair group135, the seven slot pairs140are spaced from each other at a regular interval in the circumferential direction. With such a configuration, for the seven slot pairs140in the inner slot pair group135, one slot of each pair can be arranged at positions corresponding to the positions of the second recesses that are circular dimples. The outer slot pair group136is arranged so as not to overlap with the inner slot pair group135when seen from the center138of the slot plate20toward the outer region in the diametric direction. For this reason, in the outer slot pair group136, seven sets of two slot pairs140′ are spaced from each other at a regular interval in the circumferential direction.

In the present embodiment, an opening width of the first slot133, i.e., a distance W1between one wall130aand the other wall130bextended in the lengthwise direction of the first slot133, is set to 14 mm. A length of the first slot133in the lengthwise direction indicated by W2inFIG. 5, i.e., a length W2between one end130cand the other end130dof the first slot133in the lengthwise direction, is set to 35 mm. Although the width W1and the length W2may be changed within a range of ±10%, the apparatus can operate even when the width and the length are not within such ranges. A ratio W1/W2of the short side to the long side in the first slot133is 14/35=0.4. The opening shape of the first slot133is the same as that of the second slot134. That is, if the first slot133is rotated by an angle of 90°, the rotated first slot133becomes the second slot134. When an elongated hole such as a slot is formed, the length ratio W1/W2is smaller than 1.

An opening width W3of the fourth slot134′ is smaller than an opening width W1of the first slot133. In other words, the opening width W1of the first slot133is larger than the opening width W3of the fourth slot134′. Here, the opening width W3of the fourth slot134′ is, e.g., 10 mm. A length of the fourth slot134′ in the lengthwise direction which is denoted by W4inFIG. 5is the same as the length W2of the first slot133. Although the width W3and the length W4may be changed within a range of ±10%, the apparatus can operate even when the width and the length are not within such ranges. A ratio W3/W4of the short side to the long side in the fourth slot134′ is 10/35≈0.29. The opening shape of the fourth slot134′ is the same as that of the third slot133′. That is, if the third slot133′ is rotated by an angle of 90°, the rotated third slot133′ becomes the fourth slot134′. When an elongated hole such as a slot is formed, the length ratio W3/W4is smaller than 1.

A through-hole137is formed at the center of the slot plate20in the diametrical direction. A reference hole139is formed through the slot plate20in the plate thickness direction thereof at an outer region of the outer slot pair group136in order to allow the slot plate20to be easily positioned in the circumferential direction thereof. Therefore, the position of the slot plate20in the circumferential direction with respect to the processing chamber2or the dielectric window16is determined by using the reference hole139as a mark. The slot plate20has rotational symmetry about the center138in the diametrical direction except the reference hole139.

Further, the structure of the slot plate20will be described in detail. The slot plate20includes: a first slot group133spaced from the centroid position138of the slot plate20by a first distance K1(indicated by a circle K1); a second slot group134spaced from the centroid position138by a second distance K2(indicated by a circle K2); a third slot group133′ spaced from the centroid position138by a third distance K3(indicated by a circle K3); and a fourth slot group134′ spaced from the centroid position138by a fourth distance K4(indicated by a circle K4).

Here, the first to the fourth distances K1to K4have a relationship of K1<K2<K3<K4. An angle between a lengthwise direction of a target slot (one of the slots133,134,133′ and134′) and straight lines (a first straight line R1and a second straight line R2or R3) extending from the centroid position138of the slot plate and passing through the target slot is the same in each of the first to the fourth slot group133,134,133′ and134′.

The slot133of the first slot group and the slot134of the second slot group which are positioned on the same diameter (on the first straight line R1) extending from the centroid position138of the slot plate20are elongated in different directions (orthogonally in this example). The slot133′ of the third slot group and the slot134′ of the fourth slot group which are positioned on the same diameter (on the second straight line R2or R3) extending from the center138of the slot plate20are elongated in different directions (orthogonally in this example). The slots133,134,133′,134′ are arranged such that the straight line R1and the straight line R2, or the straight line R1and the straight line R3are not overlapped with each other. For example, the angle between the straight line R1and the straight line R2, or the angle between the straight line R1and the straight line R3is greater than or equal to 10°. With such a configuration, the slots having a low microwave radiation efficiency for the input power can be excluded, which makes it possible to relatively improve distribution of the input power to the other slots. As a result, the radiation electric field intensity with respect to the input power is improved and the plasma stability can be improved.

The number of the slots133of the first slot group and the number of the slots134of the second slot group are the same, the number being N1. The number of the slots133′ of the third slot group and the number of the slots134′ of the fourth slot group are the same, the number being N2. N2is an integer multiple of N1. With this configuration, a plasma having high in-plane symmetry can be generated.

FIG. 6is a top view of the dielectric window.FIG. 8is a cross sectional view of the dielectric window. The dielectric window16has a substantially circular plate shape and has a predetermined plate thickness. The dielectric window16is made of a dielectric material. Specifically, the dielectric window16is made of quartz, alumina or the like. The slot plate20is provided on a top surface159of the dielectric window16.

A through-hole142penetrating through the dielectric plate16in a plate thickness direction thereof, i.e., in a perpendicular direction to a sheet surface ofFIG. 6is formed at the center of the dielectric plate16in a diametrical direction thereof. A lower region of the through-hole142serves as a gas supply port of the central introduction unit55and an upper region of the through-hole142serves as a recess143where the block57of the central introduction unit55is disposed. A central axis144aof the dielectric window16to the diametrical direction is indicated by a dashed dotted line inFIG. 8.

An annular first recess147that is tapered inwardly in the plate thickness direction of the dielectric window16is formed at an outer region of a flat surface146in the diametrical direction. The flat surface146is a bottom surface of the dielectric window16facing a space where the plasma is generated when the dielectric window16is attached to the plasma processing apparatus. The flat surface146is disposed at a central region of the dielectric window16in the diametrical direction. At the central flat surface146, circular second recesses153(153ato153g) are formed at a regular interval along the circumferential direction of the flat surface146. The annular first recess147includes: an inner tapered surface148tapered outward from the outer edge of the flat surface146, i.e., inclined with respect to the flat surface146; a flat bottom surface149extending straightly outward from the inner tapered surface148in the diametrical direction, i.e., in parallel to the flat surface146; and an outer tapered surface150tapered outward from the bottom surface149, i.e., inclined with respect to the bottom surface149.

Angles of the tapered surfaces, i.e., an angle defined by an extended direction of the inner tapered surface148with respect to the bottom surface149and an angle defined by an extended direction of the outer tapered surface150with respect to the bottom surface149, are properly set. In the present embodiment, the angles are all the same at any position in the circumferential direction. The inner tapered surface148, the bottom surface149, and the outer tapered surface150form a continuous smooth curved surface. Further, an outer peripheral flat surface152extending straightly outward in the diametrical direction, i.e., in parallel to the flat surface146, is provided at a radially outer region from the outer tapered surface150. The outer peripheral flat surface152serves as a supporting surface for the dielectric window16.

The dielectric window16is attached to the processing chamber2such that the outer peripheral flat surface152is positioned at an upper end surface of the annular member19(seeFIG. 4).

Due to the presence of the annular first recess147, a region where the thickness of the dielectric window16is continuously changed is formed at the outer region of the dielectric window16in the diametrical direction. Accordingly, a resonance region where the dielectric window has a thickness suitable for various processing conditions for plasma generation can be formed. As a result, high stability of the plasma can be obtained at the outer region in the diametrical direction under various processing conditions.

The second recesses153(153ato153g) recessed inwardly from the flat surface146in the plate thickness direction of the dielectric window16are formed at a radially inner region of the annular first recess147. The second recesses153have a circular shape in a plan view. Each of the second recesses153has a cylindrical inner wall surface and a flat bottom surface. Since a circle is a polygon having infinite corners, the second recesses153may have a polygonal shape having finite corners in a plan view. It is considered that the plasma is generated in the recess when the microwaves are introduced. If the recess has a circular shape when seen from the top, the shape from the center has high uniformity, so that the plasma can be stably generated.

In the present embodiment, the total number of the second recesses153is seven. The number of the second recesses153is equal to that of the inner slot pairs. The seven second recesses153ato153ghave the same shape. That is, the recessed shapes, and the depths and diameters of the recesses and the like of the second recesses153ato153gare all the same. The seven second recesses153ato153gare spaced from each other at a regular interval so as to have rotation symmetry about the center156of the dielectric window16in the diametrical direction. When seen from the plate thickness direction of the dielectric window16, centers157ato157gof the circular seven second recesses153ato153gare positioned on a circle158having the same center156as the dielectric window16. Therefore, when the dielectric window16is rotated by about 51.42° (=360°/7) about the center156of the dielectric window16, the same shape as before the rotation is obtained. The circle158is indicated by a dashed dotted line inFIG. 6. A diameter of the circle158is 154 mm. A diameter of the second recesses153ato153gis 30 mm.

A depth of the second recesses153(153ato153g), i.e., a distance L3between the flat surface146and the bottom surface155inFIG. 8, is properly set. It is set to about 32 mm in the present embodiment. The diameter of the second recesses153and the distance from the bottom surfaces of the second recesses153to the top surface of the dielectric window are set to be ¼ of a wavelength λg of the microwave introduced thereto. In the present embodiment, the diameter of the dielectric window16is about 460 mm. The diameter of the circle158, the diameter of the recesses153, the diameter of the dielectric window16and the depth of the recesses153may vary within a range of ±10%. However, conditions for operating the apparatus are not limited thereto and the apparatus can operate as long as the plasma is confined in the recesses. If the diameter or depth of the recesses close to the center is increased, the plasma density becomes higher at the central portion than at the peripheral portion. In that case, the balance therebetween may be controlled.

Due to the presence of the second recesses153ato153g, the electric field of the microwave can concentrate in the recesses and a mode can be firmly locked at the inner region of the dielectric window16in the diametrical direction. In this case, since the region where the mode is firmly locked can be obtained at the inner region of the dielectric window16in the diametrical direction regardless of various changes in processing conditions, the plasma can be stably and uniformly generated and, thus, the substrate can be more uniformly processed over the surface. Especially, the second recesses153ato153ghave rotation symmetry, so that the region where the mode is firmly locked at the inner region of the dielectric window16in the diametrical direction can have a high axial symmetry. As a result, the generated plasma has a high axial symmetry.

The dielectric window16configured as described above has a wide range of process margin and the generated plasma has a high axial symmetry.

FIG. 7is a plan view showing the antenna70formed by combining the slot plate20and the dielectric window16.FIG. 7illustrates the radial line slot antenna seen from the bottom along the Z-axis shown inFIG. 1. In the plan view, the outer tapered surface150and the slots134′ of the fourth slot group (the fourth slot group from the center) are partially overlapped with each other. Further, the annular flat bottom surface149and the slots133′ of the third slot group (the third slot group from the center) are overlapped with each other.

Furthermore, in the plan view, the inner tapered surface148and the slots134of the second slot group (the second slot group from the center) are overlapped with each other. The slots133of the innermost first slot group are positioned on the flat surface146. The centroid positions of the second recesses153are overlapped with the slots133.

FIGS. 9A and 9Bare a perspective view and a cross sectional view showing a structure around the slot133and the recess153, respectively. As shown inFIG. 9A, the slot133is positioned directly above the recess153. When the microwave is introduced, a plasma PS is generated in the recess153by the electric field generated in the width direction of the slot133(seeFIG. 9B).

FIGS. 10A and 10Bshow the position relation between the slots and the second recess.FIG. 10Ashows the case where the centroid G2of the second recess153is set to a position where the electric field E from the slot133is selectively introduced. Due to the introduction of the microwave, the electric field E is generated in the width direction of the slots133and134. In this example, the centroid position G1of the slot133and the centroid position G2of the second recess153coincide with each other, and the centroid position G2of the second recess153is positioned in the slot133. In this case, the plasma is reliably confined in the second recess153, so that there are little fluctuation in the plasma state and little in-plane variation of the plasma state in spite of changes in various conditions. Especially, since the second recesses153are formed at the central flat surface146(seeFIG. 7), a surface surrounding a single recess153has a high equivalence and, thus, the degree of plasma confinement becomes high.

Meanwhile,FIG. 10Bshows the case where the centroid position G2of the second recess153is set to a position where the electric fields E from the slots133and134are introduced. In other words, inFIG. 10B, the centroid position G1of the slot133is separated from the center G2of the second recess153and the centroid position G2of the second recess153is not positioned in the slot133. In this case, the microwaves are not easily introduced into the recess153compared to the case shown inFIG. 10A. Accordingly, the plasma density is decreased and there may be fluctuation in plasma generation.

Next, an antenna of a comparative example will be briefly described in order to explain the operational effect of the antenna70and the plasma processing apparatus1of the present embodiment.

FIG. 11is a top view of a slot plate of the comparative example. In this slot plate20, the slot pairs240and240′ are arranged in a concentric circular shape around the center (centroid position)238of the slot plate20. The inner slot pair group disposed at an inner peripheral side includes seven slot pairs240. The outer slot pair group disposed at the outer peripheral side includes twenty-eight slot pairs240′. An opening width of the slot167of the slot pair240, i.e., a distance W5between one wall168aand the other wall168bboth extending in a lengthwise direction of the slot167, is set to 6 mm. The length W5is about one half of the length W1of the slot133of the aforementioned slot plate. A length W6in a lengthwise direction of the slot167, i.e., a length between one end168cand the other end168din the lengthwise direction of the slot167, is set to 35 mm. The length W6is the same as the length W2of the slot133of the aforementioned slot plate. A ratio W5/W6of the short side to the long side in the slot167is 6/35≈0.17. The other structures of the slot are the same as those of the slot plate20shown inFIG. 5, so that the description thereof will be omitted.FIG. 12is a top view of a dielectric window of the comparative example. The dielectric window16of the comparative example does not have the second recesses formed on the flat surface146.

As shown inFIG. 11, in the comparative example, the slot pairs240and240′ are disposed at positions where straight lines R4extending from the centroid position238of the slot plate20and passing through each of the slot pairs240and240′ are overlapped with each other (coincide with each other). That is, the slot pairs240and240′ are overlapped when seen from the centroid position238of the slot plate toward the outer region in the diametrical direction. In that case, the microwave incident on the centroid position238of the slot plate20is initially radiated from the slot pair240close to the centroid position238. Therefore, the microwave having a low electric field intensity propagates to the other slot pair240′ disposed on the straight line R4extending from the centroid position238and passing through the corresponding slot pair240. Accordingly, the microwave having a low electric field intensity is radiated from the other slot pair240′.

On the other hand, in the antenna70and the plasma processing apparatus1of the present embodiment, the slot pairs140and140′ arranged in a concentric circular shape are provided at positions where the straight lines R1to R3extending from the centroid position138of the slot plate passing through the slot pairs140and140′ are not overlapped with each other. In other words, other slot pairs are not provided on the straight line R1extending from the centroid position138of the slot plate20toward the slot pair140. Accordingly, the slot pairs having a low microwave radiation efficiency for an input power can be excluded, which makes it possible to relatively improve distribution of the input power to the other slot pairs. As a result, the radiation electric field intensity with respect to the input power is improved. When the radiation electric field intensity with respect to the input power is improved, a sheet-shaped high-density plasma can be generated directly below the ceiling plate and, thus, the plasma stability can be improved. As a result, a pressure range where the plasma is stable is increased and, hence, the expansion of the processing region can be expected.

As described above, a negative gas has an electron attachment cross section area at the electron energy of 10 eV or less. Therefore, the negative gas is easily turned into negative ions due to the attachment of electrons in the plasma diffusion region. Accordingly, in the plasma processing using a negative gas, electrons and negative ions exist together as negative charges in the plasma. When the electrons are attached to the negative gas, loss is caused. In order to maintain stability of a plasma, it is required to increase the number of electrons that are generated to compensate the loss. Accordingly, in the plasma processing using a negative gas, the electric field intensity needs to be improved compared to the case of using other gases. In the antenna70and the plasma processing apparatus1of the present embodiment, the radiation electric field intensity with respect to the input power can be improved. Hence, the stability of the plasma can be improved even when a negative gas is used. Especially, it is expected that an etching process inflicts less damage at a pressure range from an intermediate pressure (e.g., about 50 mTorr (6.5 Pa)) in which negative ions are easily generated to a high pressure.

In the antenna70and the plasma processing apparatus1of the present embodiment, the width W1of the slots of the first and second slot groups is greater than the width W3of the slots of the third and fourth slot groups. As the opening width of the slot is increased, the electric field of the introduced microwave is decreased. When the opening width of the slot is decreased, the microwave can be more strongly radiated. Therefore, it is possible to lower the radiation electric field intensity of the first and second slot groups close to the centroid position138of the slot plate20than that of the third and fourth slot groups far from the centroid position138of the slot plate20. The microwave is attenuated during propagation. Therefore, the radiation electric field intensity of the microwave becomes uniform over the surface of the slot plate by employing the above-described configuration. As a result, a plasma having high in-plane uniformity can be generated.

In the antenna70and the plasma processing apparatus1of the present embodiment, when seen from a direction perpendicular to the main surface of the slot plate20, the centroid positions of the second recesses153are positioned in the slots133of the slot plate20. Accordingly, the plasma having high uniformity can be generated and the in-plane uniformity of the processing amount can be improved. Such a plasma processing apparatus1may be used for film deposition as well as etching.

While various embodiments have been described above, the present invention may be modified without being limited to the above embodiments. For example, although the above embodiments have described an example in which the slot pairs are arranged in the form of two concentric circular rings, the slot pairs may be arranged in the form of three or more circular rings.

TEST EXAMPLES

Hereinafter, test examples and comparative examples which have been carried out by the present inventors will be described to explain the above-described effect.

(Examination of Improvement of Electric Field Intensity)

Test Example 1

The antenna including the antenna plate shown inFIG. 5and the dielectric window shown inFIG. 6was used.

Comparative Example 1

The antenna including the antenna plate shown inFIG. 11and the dielectric window shown inFIG. 12was used.

In the test example 1 and the comparative example 1, the simulation of an electric field intensity was executed. The case where the microwave was totally transmitted and the case where the microwave was totally reflected were simulated. The results thereof are shown inFIG. 13.FIG. 13shows the radial line slot antenna seen from the bottom along the Z-axis shown inFIG. 1. InFIG. 13, the distribution of the electric field intensity was illustrated in monotone. InFIG. 13, a highest electric field intensity is illustrated by white color and a lowest electric field intensity is illustrated by black color. As can be seen fromFIG. 13, white portions are wider in the test example 1 than the comparative example 1. This shows that the radiation electric field intensity with respect to the input power is improved in the antenna of the present embodiment.

(Examination of Improvement of Plasma Stability)

Test Example 2

In the plasma processing apparatus1including the antenna70having the antenna plate shown inFIG. 5and the dielectric window shown inFIG. 6, a plasma was generated by inputting microwave and applying RF and plasma stability was evaluated while varying a pressure.

The plasma stability was evaluated on two patterns: a pattern of increasing a pressure from 40 mTorr (5.2 Pa) to 200 mTorr (26 Pa) and a pattern of decreasing a pressure from 200 mTorr (26 Pa) to 40 mTorr (5.2 Pa).

The case of etching a silicon-based film such as polysilicon or the like was selected as a model example, and Ar/HBr was used as a processing gas. Three gas conditions were prepared. In a first gas condition, flow rates of Ar/HBr were set to 1000 (sccm)/600 (sccm). In a second gas condition, flow rates of Ar/HBr were set to 800 (sccm)/800 (sccm). In a third gas condition, flow rates of Ar/HBr were set to 600 (sccm)/1000 (sccm). HBr is a negative gas.

A microwave power (microwave generator35) was set to 3000 W and a RF power (bias power supply BV) was set to 150 W.

Comparative Example 2

In the plasma processing apparatus including the antenna having the antenna plate shown inFIG. 11and the dielectric window shown inFIG. 12, a plasma was generated by inputting microwave and applying RF and plasma stability was evaluated while varying a pressure. The pressure and the gas conditions were set to be the same as those in the test example 2.

The plasma stability was evaluated by classifying the plasma generated under the above conditions into four categories including Stable, Unstable, RF-hunting and Relatively-unstable.FIGS. 14A to 14Dare views for explaining the category classification. As shown inFIG. 14A, the plasma stability was determined to be “Stable” when time-dependent microwave power reflection is constant (within a predetermined threshold value with respect to a reference value) and time-dependent RF power reflection is constant (within a predetermined threshold value with respect to a reference value). As shown inFIG. 14B, the plasma stability was determined to be “Unstable” when the time-dependent microwave power reflection is not constant (not within the threshold value with respect to the reference value) and the time-dependent RF power reflection is not constant (not within the threshold value with respect to the reference value). As shown inFIG. 14C, the plasma stability was determined to be “RF-hunting” when the time-dependent microwave power reflection is constant (within the predetermined threshold value with respect to the reference value) and the time-dependent RF power reflection is not constant (not within the predetermined threshold value with respect to the reference value). As shown inFIG. 14D, the plasma stability was determined to be “Relatively-unstable” when the time-dependent microwave power reflection or the time-dependent RF reflection power has a peak value (instantly exceeding the predetermined threshold value with respect to the reference value). The results thereof are shown inFIGS. 15A and 15B.

As can be seen from the test results of the test example 2 and the comparative example 2 shown inFIGS. 15A and 15B, the plasma was stable in the test example 2. In the comparative example 2, the plasma was unstable at an intermediate pressure range (50 mTorr (6.5 Pa)) in the case of using the negative gas. In contrast, in the test example 2, the plasma stability was improved at an intermediate pressure range even in the case of using the negative gas.

Test Example 3

The microwave power was set to 2000 W. The other conditions were set to be the same as those in the test example 2.

Comparative Example 3

The microwave power was set to 2000 W. The other conditions were set to be the same as those in the comparative example 2.

The test example 3 and the comparative example 3 were evaluated by the above-described evaluation method. The results thereof are shown inFIGS. 16A and 16B.

As can be seen from the test results of the test example 3 and the comparative example 3 shown inFIGS. 16A and 16B, the plasma was stable in the test example 3. In the comparative example 3, the plasma was unstable at the intermediate pressure range or above (50 mTorr (6.5 Pa) or above) in the case of using the negative gas. In contrast, in the test example 3, the plasma stability was improved at the intermediate pressure range or above even in the case of using the negative gas.

Test Example 4

The case of cleaning the apparatus was selected as a model example, and SF6/O2was used as a processing gas. Three gas conditions were prepared. In a first gas condition, flow rates of SF6/O2were set to 50 sccm/150 sccm. In a second gas condition, flow rates of SF6/O2were set to 100 sccm/100 sccm. In a third gas condition, flow rates of SF6/O2were set to 150 sccm/50 sccm. SF6is a negative gas.

The RF power was set to 0 W. The other conditions were set to be the same as those in the test example 2.

Comparative Example 4

The case of cleaning the apparatus was selected as a model example, and SF6/O2was used as a processing gas. Three gas conditions were prepared. In a first gas condition, flow rates of SF6/O2were set to 50 sccm/150 sccm. In a second gas condition, flow rates of SF6/O2were set to 100 sccm/100 sccm. In a third gas condition, flow rates of SF6/O2were set to 150 sccm/50 sccm. SF6is a negative gas.

The RF power was set to 0 W. The other conditions were set to be the same as those in the comparative example 2.

The test example 4 and the comparative example 4 were evaluated by the above-described evaluation method. The results thereof are shown inFIG. 17.

As can be seen from the test results of the test example 4 and the comparative example 4 shown inFIG. 17, the plasma was stable in the test example 4. In the comparative, example 4, the plasma was unstable at the intermediate pressure range or above (50 mTorr (6.5 Pa) or above) in the case of using the negative gas. In contrast, in the test example 4, the plasma stability was improved at the intermediate pressure range or above even in the case of using the negative gas.

(Examination of Stability of Plasma Discharge)

Test Example 5

A time-dependent emission intensity was acquired to examine stability of plasma discharge after a predetermined period of time has elapsed from ignition. The followings are the processing conditions.

Gas Flow Rates

Gas Flow Rates

That is, the ignition was performed by using Ar and then, a plasma of the negative gas was generated.

FIGS. 18A to 18Cshow the results thereof.FIG. 18Ashows the result of time dependence of emission intensity of Ar.FIG. 18Bshows the result of time dependence of emission intensity of O.FIG. 18Cshows the result of time dependence of emission intensity of F. Conventionally, when Ar plasma emission is shifted to O or F plasma emission (e.g., around 20 seconds), O plasma or F plasma is once extinguished and then generated, so that the emission intensity becomes zero around 20 seconds. On the other hand, in the test example 5 shown inFIGS. 18A to 18C, even when Ar plasma emission was shifted to O or F plasma emission, the temporary stop of the plasma discharge did not occur. Accordingly, it is seen that in the test example 5, the plasma stability was improved even when using the negative gas.

Test Example 6

Time dependent emission intensity was acquired to examine stability of plasma discharge after a predetermined period of time has elapsed from the ignition. The microwave power was set to 2500 W. The other conditions were set to be the same as those in the test example 5.

FIGS. 19A to 19Cshow the results thereof.FIG. 19Ashows the result of time dependence of emission intensity of Ar.FIG. 19Bshows the result of time dependence of emission intensity of O.FIG. 19Cshows the result of the time dependence of emission intensity of F. As can be seen fromFIGS. 19A to 19C, the plasma stability was improved even when using the negative gas, as in the case shown inFIGS. 18A to 18C.

While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.