Plasma processing apparatus and method

A plasma processing apparatus performs a process on a substrate by using plasma. The plasma processing apparatus includes a processing chamber; a mounting table which is located in the processing chamber and on which a substrate is mounted; a gas shower head formed of a conductive material provided to face the mounting table and having at the bottom surface thereof a plurality of gas injection openings for supplying a processing gas into the processing chamber; an induction coil to which a high frequency current is supplied to generate an inductively coupled plasma in a region surrounding a space below the gas shower head; a negative voltage supplying unit for applying a negative DC voltage to the gas shower head to allow an electrical field, which is induced by the induction coil, to be drawn to a central portion of the processing region; and a unit for evacuating the processing chamber.

FIELD OF THE INVENTION

The present invention relates to a plasma processing apparatus and a plasma processing method for performing a plasma process on a substrate.

BACKGROUND OF THE INVENTION

A semiconductor device manufacturing process includes a step for performing a plasma process such as an etching process, a film forming process or the like on a surface of a semiconductor wafer (hereinafter, referred to as a “wafer”) as a substrate by using a plasma.

For example, an etching process is performed on multilayer films having different compositions, e.g., a bottom anti-reflection coating film, an amorphous carbon film, a silicon oxide film, an etching stop film and the like, which are laminated below a pattern mask in that order from the top on an silicon film of a pattern mask. Therefore, when a recess is formed in these multilayer films, an etching gas is changed for each film and, also, processing conditions such as a flow rate of the etching gas, a pressure and the like are controlled for each film. In order to uniformly etch each of the films, it is required to supply a processing gas such that the concentration thereof becomes uniform in a processing region above a wafer in accordance with the processing conditions for each film and to convert the processing gas into a plasma uniformly.

As for a method for performing a plasma process by using a plasma of a processing gas, there have been known, e.g., a CCP (capacitively coupled plasma) processing method, an ICP (inductively coupled plasma) processing method, a method using microwaves and the like.

The CCP processing method uses a parallel plate type plasma processing apparatus in which a processing gas supplied from a gas shower head formed of, e.g., a metal, and having at a bottom portion thereof a plurality of gas injection openings is converted into a plasma by applying a high frequency voltage between the gas shower head and a mounting table which mounts thereon a wafer in a processing chamber, the gas shower head being provided at a ceiling wall of the processing chamber so as to face the wafer. In this method, the processing gas is supplied from the shower head, so that the concentration distribution thereof in the processing region can be controlled even when the processing conditions such as the flow rate and the type of the processing gas are changed. Due to the uniform distribution of the concentration of the processing gas and the close installation of the mounting table and the gas shower head, the height of the processing chamber can be reduced. Moreover, the gas shower head is formed of an easily processable material, e.g., a metal, so that a cooling mechanism, e.g., a cooling water path, can be simply provided at the gas shower head. Accordingly, the temperature of the gas shower head can be easily controlled in accordance with the processing conditions.

However, in the CCP processing method, a path of a current flowing between the mounting table and the gas shower head is extremely complicated. Thus, it is difficult to uniformly convert the processing gas into the plasma, and the plasma density on the surface of the wafer is apt to be non-uniform. Accordingly, an etching rate in a diametrical direction of the wafer, for example, may be varied. Further, in this method, a high electron temperature of the plasma may inflict damages on the wafer. Moreover, a high frequency power supply needs to be connected to both or one of the mounting table and the gas shower head and, hence, the cost of the apparatus is increased.

The ICP processing method that has been conventionally used utilizes electromagnetic induction as described in, e.g., Japanese Patent Application Publication No. 2008-109155 (FIG. 1). Specifically, an ICP coil wound multiple times coaxially with respect to a wafer is provided at the ceiling wall of the processing chamber which is formed of a dielectric material, e.g., quartz. By applying a high frequency voltage to the coil, an electric field is generated in the processing chamber through the ceiling wall. The processing gas is turned into a plasma by the electric field thus generated. In this method, the electric field is generated below the coil, and the intensity of the electric field is changed in accordance with the value of the voltage applied to the coil. Accordingly, it is extremely easy to detect the plasma generation location and the concentration (amount) of the plasma. The plasma density distribution can be easily controlled by controlling the position of the coil or by dividing the coil into an inner and an outer coil respectively provided at an inner and an outer peripheral side of the wafer and controlling a voltage applied to each coil. Since the processing gas can be turned into a plasma simply by providing the coil at the ceiling wall of the processing chamber, the plasma process can be carried out cost-effectively.

However, when the coil is installed on the gas shower head formed of a metal which is provided at the ceiling wall of the processing chamber, the electric field is blocked by the gas shower head. Therefore, in order to form the uniform electric field in the processing region, the shower head formed of a metal cannot be used. However, a dielectric material, e.g., quartz, has poor workability compared to a metal, so that it is difficult to form the gas shower head by using the dielectric material in view of workability. For that reason, in case of employing such method, instead of providing the gas shower head, gas injection openings are formed at, e.g., a center portion of the ceiling wall and the sidewall of the processing chamber, and the processing gas is supplied through the gas injection openings. Hence, the uniformity of the distribution of the processing gas is decreased compared to the case of using the gas shower head. Moreover, since the concentration of the processing gas is non-uniform near the ceiling wall or the sidewall of the processing chamber, a large gap needs to be provided between the wafer (mounting table) and the ceiling wall or the sidewall of the processing chamber in order to improve the concentration distribution of the processing gas near the wafer. However, this results in scaling up of the processing chamber. Further, when the ceiling wall of the processing chamber is formed of a dielectric material, e.g., quartz, it is difficult to form a cooling water path at the ceiling wall in view of workability and, hence, it is difficult to control the temperature of the ceiling wall.

The above-described methods have advantages and disadvantageous, so that the use of only one of these methods is not enough to supply the processing gas such that the concentration distribution thereof becomes uniform in accordance with the various processing conditions and to convert the processing gas into a plasma uniformly. Thus, an etching rate, for example, may be varied in the wafer plane. In the method using microwaves as well as in the ICP processing method, it is difficult to control the flow rate of the processing gas or the temperature of the ceiling wall. In order to uniformly supply the processing gas and uniformly convert the processing gas into a plasma, there has been examined a technique for applying an ICP processing method to a CCP plasma processing apparatus by providing a dielectric member around the gas shower head formed at the ceiling wall of the processing chamber and winding a coil on the dielectric member coaxially with respect to the wafer. Besides, there has been examined a method for applying a DC voltage to a gas shower head in a CCP plasma processing apparatus, which is described in Japanese Patent Application Publication No. 2006-286813 (especially,FIG. 1). Although these methods can slightly improve the uniformity of the etching process, a method capable of performing uniform processing is still required.

As the opening diameter of the aforementioned pattern mask is reduced, the in-plane uniformity of the processing needs to be improved. Thus, as miniaturization of wiring structures progresses, more uniform plasma generation is required. When a large wafer having a diameter of, e.g., about 450 mm (18 inches), is used instead of a currently used wafer having a diameter of about 300 mm (12 inches), a large plasma suitable for the large wafer needs to be generated and, hence, a technique for ensuring more uniform plasma generation is required.

The method using microwaves has been known as one of the methods for performing a plasma process by using a plasma of a processing gas. In this method, a processing gas is converted into a plasma in a processing chamber by supplying microwaves from a microwave generating unit to an antenna installed at a ceiling wall of the processing chamber which is formed of a dielectric material, e.g., quartz. Accordingly, a plasma having a low electron temperature, for example, can be obtained.

In this method, since the ceiling wall of the processing chamber is formed of a dielectric material, the gas shower head having a plurality of gas supply holes for supplying the processing gas to the wafer cannot be installed at the ceiling wall of the processing chamber. It is difficult to form the gas shower head by using a dielectric material due to its low workability. Further, when the gas shower head formed of a metal that is easily processable is provided below the antenna, the microwaves are blocked by the gas shower head. To that end, in this apparatus, gas supply holes are formed, e.g., at the central portion of the ceiling wall of the processing chamber, and the processing gas is supplied through the gas supply holes into the processing chamber. However, this may lead to non-uniformity of the concentration distribution of the processing gas in the wafer plane. Specifically, the concentration of the processing gas tends to be high at the central portion of the processing region and low at the peripheral portion of the processing region. In order to reduce the gradient of the concentration of the processing gas near the wafer, a large gap needs to be formed between the ceiling wall of the processing chamber and the wafer. However, this results in scaling up of the processing chamber. Moreover, when the ceiling wall of the processing chamber is formed of a dielectric material, it is difficult to provide a coolant channel for circulating cooling water in the ceiling wall of the processing chamber and, accordingly, the temperature of the ceiling wall is not controllable.

Hence, in order to uniformly supply the processing gas and uniformly convert the processing gas into a plasma by microwaves, there has been examined a method in which a gas supply unit formed of a dielectric material, e.g., quartz, and having at a bottom surface thereof a plurality of gas supply holes is provided at a middle portion of the processing chamber (between the ceiling wall of the processing chamber and the wafer), which is described in, e.g., Japanese Patent Application Publication No. 2008-140998 (especially,FIG. 2and paragraphs 0027 to 0029). Further, a plurality of openings is formed at the gas supply unit so that the upper portion (ceiling wall side) and the lower portion (wafer side) of the processing chamber can communicate with each other. A gas for plasma generation, e.g., Ar gas, is turned into a plasma by microwaves in the upper portion of the processing chamber, and the plasma thus generated is directed downward to be supplied toward the wafer through the openings of the gas supply unit. Accordingly, the processing gas is turned into a plasma even in the lower portion of the gas supply unit.

Such processing gas supply method enables uniform distribution of the processing gas compared to the method for supplying the processing gas from the central portion of the ceiling wall of the processing chamber. However, in this method, the openings are formed at the gas supply unit, so that the amount of the processing gas is small below the openings, and a plasma is non-uniformly generated. As a consequence, the arrangement pattern of the openings may be transferred to the wafer.

As the opening diameter of the pattern mask is reduced, the in-plane uniformity of the processing is required. Hence, as miniaturization of wiring structures progresses, a plasma needs to be generated more uniformly. When a large wafer having a diameter of, e.g., about 450 mm (18 inches) is used instead of a wafer having a diameter of, e.g., about 300 mm (12 inches), a technique for ensuring more uniform plasma generation is required in order to generate a large plasma suitable for the large wafer. In the large wafer, the uniformity of the plasma process may be deteriorated in the circumferential direction, so that a technique for improving the uniformity of the plasma distribution in the circumferential direction as well as the diametrical direction is required.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides a plasma processing apparatus and a plasma processing method capable of performing a plasma process on a substrate with high in-plane uniformity.

In accordance with an aspect of the present invention, there is provided a plasma processing apparatus for processing a substrate by using a plasma, including: a processing chamber; a mounting table, provided in the processing chamber, for mounting thereon a substrate; a gas shower head formed of a conductive material provided to face the mounting table, the gas shower head having at a bottom surface thereof a plurality of gas injection openings for supplying a processing gas into the processing chamber; an induction coil to which a high frequency current is supplied to generate an inductively coupled plasma in a region surrounding a space below the gas shower head; a negative voltage supply unit for applying a negative DC voltage to the gas shower head to allow an electric field induced by the induction coil to be drawn to a central portion in a processing region; and a unit for evacuating the processing chamber.

With such configuration, when the plasma process is performed on the substrate, the processing gas is uniformly supplied to the substrate from the gas shower head formed of a conductive material and facing the mounting table mounting thereon the substrate, and the inductively coupled plasma is generated in the region surrounding the space below the gas shower head. Further, a thick DC sheath is formed below the gas shower head by applying a DC voltage to the gas shower head, and the plasma is diffused to the central portion via the DC sheath.

Accordingly, while using the inductively coupled plasma, the processing gas can be uniformly supplied from the gas shower head and the plasma can be generated uniformly along the surface of the substrate and also in the space below the gas shower head. As a result, the plasma process having high in-plane uniformity can be performed on the substrate.

Preferably, the induction coil is wound around an axis extending in a direction parallel with the substrate and perpendicular to a diametrical direction of the processing chamber.

Further, the induction coil is preferably provided in a plural number along a circumferential direction of the processing chamber.

Preferably, the induction coil is wound in an angular shape having a side parallel with the substrate.

Preferably, the induction coil is provided above the processing chamber, and a ceiling wall of the processing chamber around the gas shower head is formed of a dielectric material.

Preferably, the induction coil is buried in a dielectric material and forms a part of a ceiling wall of the processing chamber.

Preferably, at least a bottom surface portion of the gas shower head is formed of silicon.

Preferably, the plasma processing apparatus further includes: a storage unit storing, in corresponding relationship, recipes of processes to be performed on the substrate, values of the negative DC voltage, and values of the high frequency power supplied to the induction coil; and a control unit for outputting a control signal by reading out a value of the negative DC voltage and a value of the high frequency power in accordance with a specific recipe from the storing unit.

In accordance with another aspect of the present invention, there is provided a plasma processing method for processing a substrate by a plasma, including: mounting a substrate on a mounting table in a processing chamber; forming an electric field in a region surrounding a space below a gas shower head formed of a conductive material and disposed to face the mounting table by supplying a high frequency current to an induction coil positioned outwardly of the gas shower head in a diametrical direction of the processing chamber; supplying a processing gas into the processing chamber through gas injection openings formed at a bottom surface of the gas shower head to allow the processing gas to be converted into a plasma by the electric field; and applying a negative DC voltage to the gas shower head to allow the electric field induced by the induction coil to be drawn to the central portion of a processing region.

Preferably, the induction coil is wound around an axis extending in a direction parallel with the substrate and perpendicular to the diametrical direction of the processing chamber.

Preferably, the induction coil is provided in a plural number along the circumferential direction of the processing chamber.

Preferably, the induction coil is wound in an angular shape having a side parallel with the substrate.

Preferably, the plasma processing method further includes reading out a value of a negative DC voltage and a value of a high frequency power supplied to the induction coil in accordance with a specific recipe from a storage unit storing, in corresponding relationship, recipes of processes to be performed on the substrate, values of the negative DC voltage and values of the high frequency power supplied to the induction coil.

In accordance with still another aspect of the present invention, there is provided a storage medium that is used for a plasma processing apparatus for processing a substrate and stores therein a computer program operating on a computer, wherein the computer program has instructions for performing the plasma processing method described above.

In accordance with still another aspect of the present invention, there is provided a plasma processing apparatus for processing a substrate by a plasma, including: a mounting table, provided in a processing chamber, for mounting thereon a substrate; a gas shower head formed of a conductive material provided to face the mounting table, the gas shower head having at a bottom surface a plurality of gas injection openings for supplying a processing gas into the processing chamber; a microwave supply unit to which microwaves are supplied to convert a processing gas into a plasma in a region surrounding a space below the gas shower head; a negative voltage supply unit for applying a negative DC voltage to the gas shower head to allow an electric field induced by the induction coil to be drawn to a central portion of a processing region; and a unit for evacuating the processing chamber.

With such configuration, when the plasma process is performed on the substrate, the processing gas is uniformly supplied to the substrate from the gas shower head formed of a conductive material and facing the mounting table mounting thereon the substrate, and the plasma is generated in the region surrounding the space below the gas shower head by the microwaves. Further, a thick DC sheath is formed below the gas shower head by applying a DC voltage to the gas shower head, and the plasma is diffused to the central portion via the DC sheath.

Accordingly, while using the plasma generated by the microwaves, the processing gas can be uniformly supplied from the gas shower head and the plasma can be generated uniformly along the surface of the substrate and also in the space below the gas shower head. As a result, the plasma process having high in-plane uniformity can be performed on the substrate.

Since the plasma can be uniformly generated by the microwaves along the circumferential direction of the region surrounding the space below gas shower head, the plasma process having high in-plane uniformity can be carried out.

Preferably, the microwave supply unit is provided in a plural number along the circumferential direction of the processing chamber.

Preferably, a ceiling wall of the processing chamber around the gas shower head is formed of a dielectric material, and the microwave supply unit is provided above the ceiling wall.

Preferably, an opening is formed at a ceiling wall of the processing chamber, the opening being positioned below the microwave supply unit and around the gas shower head, and the microwave supply unit is airtightly provided at the processing chamber to block the opening.

Preferably, the plasma processing apparatus further includes: a storage unit storing, in corresponding relationship, recipes of processes to be performed on the substrate and values of the negative DC voltage; a control unit for outputting a control signal by reading out a value of the negative DC voltage in accordance with a specific recipe from the storing unit.

Alternatively, the plasma processing apparatus further includes: a storage unit storing, in corresponding relationship, recipes of processes to be performed on the substrate, values of the negative DC voltage, and values of the microwave power supplied to the microwave supply unit; and a control unit for outputting a control signal by reading out a value of the negative DC voltage and a value of the microwave power in accordance with a certain recipe from the storing unit.

In this case, preferably, the microwave supply unit is provided in a plural number along the circumferential direction of the processing chamber; the storage unit stores, in corresponding relationship, recipes and values of the microwave power supplied to each of the microwave supply units; and the control unit outputs a control signal by reading out a value of the microwave power supplied to each of the microwave supply units in accordance with the recipe.

DETAILED DESCRIPTION OF THE EMBODIMENT

A plasma processing apparatus in accordance with a first embodiment of the present invention will be described with reference toFIGS. 1 to 5. This plasma processing apparatus performs a plasma process, e.g., an etching process, on a semiconductor wafer (hereinafter, referred to as a “wafer”) as a substrate by a plasma of a processing gas. The following is brief description of the wafer W. The wafer W has a silicon base film and films laminated thereon. The laminated films include a photoresist mask formed of, e.g., an organic material, and having a predetermined pattern, a bottom anti-reflection coating film formed of, e.g., an organic film, an amorphous carbon film, an insulating film (SiO2film or SiCOH film) or a Poly-Si (polycrystalline silicon) film, an etching stop film formed of, e.g., an inorganic film, and the like, which are laminated in that order from the top. As will be described later, the plasma processing apparatus performs an etching process to form a recess in the films laminated on the base layer through the pattern of the photoresist mask.

The plasma processing apparatus includes a processing chamber21formed of a vacuum chamber, and a mounting table disposed at the center of the bottom surface of the processing chamber21. The processing chamber21is electrically grounded. A gas exhaust port22is formed on the bottom surface of the processing chamber21at a side of the mounting table3. A vacuum exhaust unit23including a vacuum pump or the like is connected to the gas exhaust port22via a gas exhaust line24having a pressure control valve24aas a pressure control unit. The pressure control valve24aand the vacuum exhaust unit23constitute a unit for exhausting the processing chamber21to a vacuum state. Formed at a sidewall of the processing chamber21is a transfer opening25for loading and unloading a wafer W. The transfer opening25can be closed and opened by a gate valve26.

The mounting table3includes a lower electrode31and a supporting body32supporting the lower electrode31from the bottom. The mounting table3is disposed on the bottom surface of the processing chamber21via an insulation member33. An electrostatic chuck34is provided on the mounting table3, and the wafer W is electrostatically attracted and held on the mounting table3by applying a voltage from a high voltage DC power supply35to the electrostatic chuck34.

Formed in the mounting table3is a temperature control medium path37through which a temperature control medium flows. The temperature of the wafer W is controlled by the temperature control medium. Further, a gas channel for supplying a thermally conductive gas as a backside gas to the backside of the wafer W is formed in the mounting table3. The gas channel38opens at a plurality of locations on the top surface of the mounting table3. A plurality of through holes34acommunicating with the gas channel38is formed in the electrostatic chuck34. The backside gas is supplied to the backside of the wafer W through the through holes34a.

A high frequency bias power supply31afor supplying a high frequency power of about 0 W to 4000 having a frequency of, e.g., 13.56 MHz is connected to the lower electrode31via a matching unit31b. As will be described later, ions in the plasma are attracted toward the wafer W by the high frequency bias power supplied from the high frequency bias power supply31a.

Further, a focus ring39is disposed on the outer peripheral edge portion of the lower electrode31to surround the electrostatic chuck34. The plasma is converged toward the wafer W on the mounting table3through the focus ring39.

A gas shower head4forming an inner ceiling plate is disposed at the center of the ceiling wall of the processing chamber21so as to face the mounting table3. The gas shower head4includes an electrode42formed of a conductive material, e.g., aluminum, and having a circular recess on a bottom surface thereof, and a supporting member forming a circular-plate shaped shower plate which is formed of a conductive material, e.g., polycrystalline silicon, and covers the bottom surface of the electrode42. Although the conductive member in this example is a semiconductor, it may be a conductor, e.g., a metal. The space defined by the electrode42and the supporting member serves as a gas diffusion space41for diffusing the processing gas.

A DC power supply53serving as a negative voltage supply unit for applying a negative DC voltage of, e.g., about 0 V to −2000 V, is connected to the electrode42via a switch52. Upon plasma generation, a sheath having a thickness determined by a value of a voltage applied by the DC power supply53is formed in the region below the gas shower head4. Due to the formation of the sheath, the electric field formed (induced) at the peripheral portion of the processing region by an induction coil70to be described later can be drawn to the central portion of the processing region.

A processing gas supply line45communicating with a gas diffusion space41is formed in a central portion of the electrode42. A processing gas supply system49is connected to an upstream side of the processing gas supply line45via a gas supply line48. The processing gas supply system49supplies a processing gas to the wafer W. In this example, a gaseous mixture of an etching gas for performing an etching process, e.g., fluorocarbon gas, chlorine (Cl2) gas, carbon monoxide (CO) gas, hydrogen bromide (HBr) gas, ozone (O3) gas or the like, and a dilution gas such as Ar gas or the like is supplied as a processing gas into the processing chamber21. Although it is not illustrated, the processing gas supply system49includes a plurality of branch lines provided with, e.g., valves or flow rate control units, and gas sources connected to the respective branch lines. Each of the gas sources stores therein the etching gas or the dilution gas. Hence, a specific etching gas and Ar gas can be supplied at a desired flow rate ratio in accordance with types of etching target films to be etched.

The supporting member43is airtightly pressed against the electrode42via, e.g., a sealing member (not shown) formed at the peripheral edge portion of the top surface thereof. Further, a plurality of gas injection openings44is formed at the supporting member43so that the gas can be supplied from the gas diffusion space41to the wafer W with high in-plane uniformity. In this example, in order to deal with a wafer W having a diameter of, e.g., about 12 inches, the outermost gas injection openings44formed in the gas shower head4are positioned at locations separated from the center of the processing chamber21by, e.g., about 12.0 cm. The outermost gas injection openings44may be positioned at locations separated from the center by about 15 cm (outer edge of the wafer W), or may be positioned closer to the center compared to the locations thereof in this example. The minimum size of the gas shower head4is set within a range which ensures high in-plane uniformity of the gas distribution in the wafer W.

A ring-shaped region surrounding the gas shower head4at the ceiling wall of the processing chamber21includes an outer ceiling plate60which is formed of a dielectric material, e.g., quartz. The outer ceiling plate60and the gas shower head4are airtightly coupled through a ring-shaped sealing member (not shown) formed at, e.g., an inner peripheral end of the outer ceiling plate60, and are fixed such that the vertical positions of the lower end surfaces thereof are located at the same height. The outer ceiling plate60is supported at the outer peripheral end thereof by the sidewall of the processing chamber21. Here, the vertical position of the outer peripheral end of the ceiling wall is higher than that of the inner peripheral end of the ceiling wall so that the ceiling wall (the gas shower head4and the outer ceiling plate60) of the processing chamber21are positioned inside the processing chamber21, which allows the gas shower head4and the mounting table3to be disposed close to each other. Moreover, a ring-shaped groove61is formed at the upper end portion of the sidewall of the processing chamber21along the circumferential direction. A sealing member62, e.g., an O-ring or the like, is accommodated in the groove61. When the inner atmosphere of the processing chamber21is exhausted to vacuum by the vacuum exhaust unit23, the outer ceiling plate60is drawn against the processing chamber21, and airtightness of the processing chamber21is maintained by the sealing member62.

As shown inFIG. 2, the induction coil70as an induction conductor around which a conductive line formed of, e.g., a metal, is wound multiple times in an angular shape is provided at a plurality of, e.g., eight, locations spaced apart from each other at regular intervals along the circumferential direction of the outer ceiling plate60. More specifically, each of the induction coils70is formed by winding a conductive line around portions corresponding to sides of a polygon (triangle or more), an octagon in this example, in the horizontal plane of the processing chamber21. An inductively coupled plasma is generated by electromagnetic induction in the region below the induction coils70in the processing chamber21, i.e., the region surrounding the space below the gas shower head, via the outer ceiling plate60. The induction coils70are connected in parallel with a high frequency power supply71for supplying a high frequency power of about 500 W to 3000 having a frequency of, e.g., 13.56 MHz. By supplying a high frequency current to the induction coils70, an electric field Er induced in the winding direction of the induction coils70and an electric field Ez induced in a (vertical) direction perpendicular to the central axes of the induction coils70are generated. Here, the induction coils70are arranged such that the electric field Er is directed from the peripheral portion of the processing chamber21to the central portion thereof and vise versa (along the diametrical direction of the processing chamber21). For convenience,FIG. 3shows an enlarged view of one of the induction coils70. Although the illustration is simplified inFIGS. 2 and 3, the induction coils70are formed of multi-wound conductive lines.FIG. 1is a vertical cross sectional view of the processing chamber21which is taken along line I-I inFIG. 2.

Although it is not shown inFIG. 1, the gas shower head4has a cooling unit. Specifically, as shown inFIGS. 4A and 4B, the cooling unit includes a temperature control medium path110that is horizontally formed in a serpentine shape so as not to interfere with the processing gas supply line45in the electrode42. The temperature of the gas shower head4can be controlled by circulating a temperature control medium, e.g., water, having a temperature controlled to a predetermined level in the temperature control medium path110via a temperature control fluid port111.FIG. 4Ais a vertical cross sectional view of the gas shower head4which are taken along line IV-IV inFIG. 4B.

As shown inFIG. 5, a control unit7is connected to the plasma processing apparatus. The control unit7includes a CPU11, a work memory13, and a memory14as a data storage. The memory14is provided with areas for storing processing conditions for each recipe, such as a type of a film to be etched (etching target film), a type of an etching gas, a gas flow rate, a processing pressure, a value of a high frequency power supplied to the induction coils70, a value of a negative DC voltage applied from the DC power supply53and the like.

As described above, different types of multilayer films are laminated on the wafer W. Hence, when an etching process is performed on these multilayer films, an etching gas needs to be changed for each film and, also, the flow rate of the etching gas, the processing pressure and the like need to be changed for each film. In order to perform a uniform etching process over the surface of the wafer W, the etching gas needs to be converted into a plasma uniformly over the surface of each film. Especially, a plasma needs to be generated uniformly in the diametrical direction of the wafer W. In the present embodiment, in order to improve the in-plane uniformity of the amount (concentration) of the plasma generated by the electric field, the intensity of the electric field generated at the peripheral portion of the processing region by the induction coils70and the intensity of the electric field induced to the central portion of the processing chamber by the negative DC voltage are controlled, on a film basis, by controlling the value of the negative voltage applied to the gas shower head4. To do so, a value of a voltage to be applied to the gas shower head4is obtained in advance on a film (recipe) basis by performing tests or calculations, and the obtained value is stored in the memory14on a recipe basis. Without obtaining the value of the voltage in advance on a recipe basis, the corresponding value may be obtained whenever the process is performed.

The program12has an instruction for the CPU11to read out a recipe corresponding to a film to be etched from the memory14to the work memory13and send a control signal to each unit of the plasma processing apparatus in accordance with the recipe to thereby execute steps to be described later and perform an etching process. Generally, this program (including a program for inputting and displaying processing parameters)12is stored in the storage unit8, e.g., a hard disk, a compact disk, a magneto-optical disk, a memory card or the like, and installed from the storage unit8to the control unit7(the program storage unit12thereof).

Hereinafter, the operation of the plasma processing apparatus will be described with reference toFIGS. 6 to 10. First, a recipe for an etching target film formed on the surface of the wafer W is read out from the memory14to the work memory13. In this example, the etching target film is, e.g., a bottom anti-reflection coating film, so that the recipe for this film is read out. Next, the wafer W is loaded from a vacuum transfer chamber (not shown) maintained at a vacuum atmosphere into the processing chamber21by a substrate transfer unit (not shown) and mounted on the mounting table3. Thereafter, the gate valve26is closed, and the inside of the processing chamber21is fully evacuated by the vacuum exhaust unit23by fully opening the pressure control valve24a, for example. At the same time, the temperature control medium having a temperature controlled to a predetermined level and the backside gas are supplied from the temperature control medium channel37and the gas channel38, thereby controlling the temperature of the wafer W to a predetermined level. By circulating in the temperature control medium path110the temperature control medium having a temperature controlled to a predetermined level through the temperature control fluid port111, the temperature of the gas shower head4is controlled to a predetermined level.

Next, a high frequency power having a frequency of, e.g., 13.56 MHz, is supplied to the induction coils70at a power level of about 2000 W and, also, a high frequency bias power is supplied from the high frequency power supply31ato the mounting table3. By supplying the high frequency power to the induction coils70, an electric field of a TM mode is generated in the region surrounding the space below the gas shower head4through the outer ceiling plate60. This electric field includes a vertical electric field Ez and a horizontal electric field Er (directed from the peripheral portion of the processing region to the central portion of the gas shower head4and vise versa) along the diametrical direction of the wafer W. A negative DC voltage having a predetermined level, e.g., about −500 V, is applied to the gas shower head4. Due to the application of the negative DC voltage, a negative electric field is generated near the bottom surface of the gas shower head4.

Then, Ar gas is supplied together with the etching gas from the processing gas supply system49into the processing chamber21, thereby controlling the pressure in the processing chamber21to a predetermined level, e.g., about 2.67 Pa (20 mTorr). Ar gas is activated at a low energy level and thus is preferably supplied into the processing chamber21together with the etching gas. The processing gas as a gaseous mixture of the etching gas and Ar gas is diffused into the processing chamber21and turned into a plasma below the induction coils70by the TM mode electric field. Accordingly, an inductively coupled plasma including Ar+ions or ions and electrons of the etching gas material is generated. The plasma generated at the peripheral portion of the processing region is diffused to the central portion of the gas shower head4in the processing chamber21. The gas at the central portion is turned into a plasma by the plasma diffused to the central portion. Hence, a plasma80is generated horizontally over the entire processing region. If a negative DC voltage is not applied to the gas shower head4, a plasma is generated mainly in the region below the induction coils70, and the plasma density at the central portion becomes lower than that at the peripheral portion, as can be seen fromFIG. 6. InFIG. 6, the region where the plasma density is high is indicated by oblique lines.

However, in the present embodiment, the negative DC voltage is applied to the gas shower head4, so that a negative electric field is generated in a region near the bottom surface of the gas shower head4, and a thick DC sheath75is formed immediately therebelow. The DC sheath75has a thickness determined by the value of the negative DC voltage. Further, the electric field Er is directed toward the central portion of the gas shower head4and passes through the DC sheath75. Accordingly, a plasma is uniformly generated over the surface of the wafer W. The reason thereof is considered as follows. As shown inFIG. 7, the plasma generated below the induction coils70is drawn within the DC sheath75by the electric field Er, and the processing gas is turned into a plasma at the central portion by the electric field Er and the plasma drawn to the central portion. Therefore, the plasma density is increased at the boundary between the DC sheath75and the plasma region or a region close thereto. Hence, as shown inFIG. 8, the high-density plasma is generated below the DC sheath75as well as below the induction coils70.

When the electrons in the plasma80collide with the etching gas or Ar gas, the corresponding gas is turned into a plasma. Then, electrons generated from this plasma collide with the etching gas or Ar gas, so that the sequential generation of plasma is continued to increase the density of the plasma80. The high-density inductively coupled plasma generated by the induction coils70is diffused to the region below the gas shower head4via the DC sheath75and directed downward toward the wafer W by a downward exhaust flow. As a consequence, a highly uniform plasma80is generated over the surface of the wafer W.

As shown inFIG. 9, positive ions in the plasma, e.g., Ar+ions, are strongly attracted by the negative electric field of the DC sheath75and thus collide with the gas shower head4. As a result of the collision, secondary electrons are generated from the gas shower head4and accelerated in the DC sheath75. The accelerated secondary electrons are directed downward, and the processing gas is turned into a plasma by these secondary electrons. Therefore, the density of the plasma80above the wafer W is increased, and the in-plane uniformity of the plasma density is further improved.

As shown inFIG. 10, ions in the plasma are attracted toward the wafer W by the high frequency bias power from the high frequency power supply31a, so that a vertical etching process is carried out. The bottom anti-reflection coating film is etched until the amorphous carbon film formed under the bottom anti-reflection film is exposed.

Thereafter, the supply of the etching gas and Ar gas is stopped and, also, the supply of the high frequency power to the induction coils70and the application of the negative DC voltage to the shower head4are stopped. Next, the processing chamber21is exhausted to vacuum, and a recipe for an amorphous carbon film to be etched is read out from the memory14to etch the amorphous carbon film. Then, in the same manner, a recipe for a film formed under the amorphous carbon film is read out to perform an etching process on the film formed thereunder.

In accordance with the aforementioned embodiment, the gas shower head4having a conductive member is provided at the central portion of the ceiling wall of the processing chamber21, so that the gas can be supplied uniformly over the surface of the wafer W. Further, an inductively coupled plasma is generated by the induction coils70in the region surrounding the space below the gas shower head4, and the DC sheath75is formed below the gas shower head4by applying a negative DC voltage to the gas shower head4. The plasma is diffused to the central portion via the DC sheath75. Accordingly, while using the inductively coupled plasma, the gas can be uniformly supplied from the gas shower head4and the plasma80can be generated uniformly along the surface of the wafer W and also in the space below the gas shower head4. As a result, the plasma process having high in-plane uniformity, e.g., the etching process in this example, can be performed on the wafer W.

Further, the plasma80having high in-plane uniformity in accordance with the processing recipe can be easily obtained by controlling the thickness of the DC sheath75by adjusting the negative DC voltage applied to the gas shower head4. In this plasma processing apparatus, the inductively coupled plasma80can be generated simply by providing the induction coils70above the ceiling plate (outer ceiling plate60) of the processing chamber21. Thus, the plasma processing apparatus of the present embodiment has a simple configuration and can be achieved cost effectively. Although a conventional inductively coupled plasma processing apparatus is disadvantageous in that it is difficult to supply a gas to a substrate having a large area, the plasma processing apparatus of the present embodiment does not have such disadvantage.

In the above-described apparatus, the gas shower head4may be physically eroded through a so-called sputtering by impact of Ar+ions. Since, however, the bottom surface of the gas shower head4is formed of silicon, there is no fear of contamination. Besides, the etching gas is uniformly supplied from the gas shower head4, so that the gas shower head4and the mounting table3can be disposed adjacent to each other and the height of the processing chamber21can be reduced. Further, the temperature of the gas shower head4can be controlled on a recipe basis by forming the temperature control medium path110substantially throughout the supporting member43.

In the above example, the in-plane uniformity of the plasma density is improved by controlling the value of the negative DC voltage applied to the gas shower head4. However, the uniformity of the plasma density may also be controlled by controlling the vale of the high frequency power supplied to the induction coils70as well as the value of the negative DC voltage or by controlling the value of the high frequency power supplied to the induction coil70while maintaining the negative DC voltage at a predetermined value.

In the above-described embodiment, the induction coils70are wound in an angular shape and, thus, a large electric field Er directed from the peripheral portion to the central portion of the processing chamber21and vise versa can be obtained. The induction coils70may be wound in a circular shape or in an elliptical shape of which a long axis is extended from the peripheral portion to the central portion of the processing chamber21. Moreover, in order to generate an electric field in the processing chamber21, a plurality of rod-shaped antennas may be radially arranged from the central portion to the peripheral portion of the processing chamber21instead of using the induction coils70.

Furthermore, in the above-described embodiment, the induction coils70are wound around the sides of the octagon of which center corresponds to the center of the processing chamber21when viewed from above such that the electric field Er generated in the processing chamber21among the electric fields Er induced by the induction coils70is directed toward the center of the processing chamber21. However, as shown inFIG. 11, the induction coils70may be wound around axes slanted with respect to the respective sides in the horizontal plane. In that case, the electric field Er has components directed from the peripheral portion to the central portion of the processing chamber21, and these electric field components are positioned within the DC sheath75. Further, a control unit for controlling an impedance may be provided for each of the induction coils70to control a high frequency supplied to each of the induction coil70. The induction coils70may be connected in series instead of being connected in parallel. Or, a high frequency power supply may be provided for each of the induction coils70to control a value of a high frequency current supplied to each of the induction coils70.

In the above-described embodiment, the induction coils70are installed above the outer ceiling plate60. However, as shown inFIG. 12, the outer ceiling plate60may be configured as a divided structure including an upper portion100and a lower portion101, and the induction coils70may be accommodated in, e.g., a plurality of recesses102formed at the lower portion101while being spaced from each other at regular intervals along the circumferential direction. In that case, the effects of the above-described example are obtained. In other words, the etching gas is uniformly converted into a plasma, and the in-plane uniformity of the etching process is achieved. Instead of accommodating the induction coils70in the outer ceiling plate60, the induction coils70may be installed below the outer ceiling plate60in the processing chamber21. In this case, it is preferable to install an insulation member103between the outer ceiling plate60formed of, e.g., a conductive material, and the gas shower head4, as shown inFIG. 13.

In the above-described example, the induction coils70are installed at a plurality of locations along the circumferential direction. However, as shown inFIG. 14, the induction coils70may be connected as a single induction coil provided along the circumferential direction. In this case, an electric field Er directed from the peripheral portion to the central portion is generated in the processing chamber21. Therefore, the electric field Er penetrates the DC sheath75formed below the gas shower head4, and the effects of the above-described embodiment can be obtained.

In order to form an electric field in the processing chamber21, a star-connected or a delta-connected three-phase coil other than a single-phase coil may be provided along the circumferential direction of the processing chamber21. Further, the technical scope of the present invention includes the case where the shower plate of the gas shower head4in the processing region is formed of a conductive material and a negative voltage is applied to the shower plate connected to the DC power supply53via the conductive path.

Although the etching process is described as an example of the plasma process in the above-described examples, the plasma processing apparatus of the present invention may be applied to, e.g., an etching apparatus or a film forming apparatus employing a CVD (Chemical Vapor Deposition) method using a plasma. For example, in the film forming apparatus, a value of a negative DC voltage applied to the gas shower head4is controlled in accordance with processing conditions such as a type or a flow rate of a film forming gas, a pressure and the like. Hence, the film forming process can be performed at a uniform film forming rate across the surface.

The following is description of a test performed by using a CCP apparatus to monitor an electron density change caused by applying a negative DC voltage from the negative DC power supply53to the gas shower head4.

The difference in the electron density below the gas shower head4between the case of applying a negative DC voltage (900 V) to the gas shower head4and the case of applying no negative DC voltage thereto was compared by using an electron density measuring probe.

FIG. 15showed that the electron density below the gas shower head4was increased by applying a negative DC voltage to the gas shower head4. In other words, positive ions between the gas shower head4and the mounting table3were attracted toward the gas shower head4by the DC sheath, and positive ions (Ar+) in the plasma collided with the gas shower head4, which results in generation of electrons.

Although it was not illustrated, another test or calculation showed that the electron density was increased by applying a negative DC voltage of about 200 V or more to the gas shower head4.

Next, simulation (calculation) using COMSOL as an electromagnetic field calculation software was performed to monitor the change in the density distribution of the TM mode electric field generated in the processing chamber21by winding the induction coils70as shown inFIG. 3and applying a negative DC voltage to the gas shower head4.

The calculation was performed in the case where a high frequency power having a high frequency of 13.56 MHz was supplied to the induction coils70at a power level of about 1500 W. Further, the calculation was performed in the cases where the DC sheaths75having different thicknesses of about 1 mm, 5 mm and 10 mm were generated below the gas shower head4by applying a negative DC voltage to the gas shower head4. Further, the intensity of the electric field absorbed by the processing gas was monitored in the right half space of the processing chamber21. The electron density of the plasma below the DC sheath75can be evaluated by the absorbed electric field intensity (the intensity of the electric field absorbed by the processing gas).

As shown in (a) ofFIG. 16, even when the thickness of the DC sheath was about 1 mm, in the region below the DC sheath75, the region of the absorbed electric field intensity was extended to the area close to the central portion of the processing chamber21. From the above, it was found that the TM mode electric field was extended toward the central portion of the wafer W. Further, (b) and (c) ofFIG. 16showed that the TM mode electric field generated below the induction coils70was further extended to the central portion of the wafer W by increasing the thickness of the DC sheath, i.e., by increasing the negative DC voltage applied to the gas shower head4.

Thereafter, the simulation calculation was performed in the case where the coil was wound coaxially with respect to the wafer W so as to generate the electric field (electric field in θ direction: TE mode) coaxially with respect to the peripheral edge portion of the wafer W as in the apparatus described in Japanese Patent Application Publication No. 2008-109155.

As a result, as shown inFIG. 17, the region where the absorbed electric field intensity was high was positioned below the coil, and the electric field was not extended to the central portion of the wafer W. Such tendency was not changed even when the thickness of the DC sheath was increased. From this, it was found that the formation of the TM mode electric field was required to extend the electric field generated by the coil to the central portion of the wafer W.

Hence, as described above, in the present embodiment, the induction coils70need to be wound to have a portion substantially parallel with the diametrical direction of the wafer W and a portion substantially parallel with the vertical direction to thereby generate the electric field Er and the electrical field Ez.

Hereinafter, another embodiment in which the plasma processing apparatus of the present invention is applied to a plasma etching apparatus will be described with reference toFIGS. 18 to 26.

The plasma processing apparatus includes a processing chamber1021formed of a vacuum chamber, and a mounting table1003disposed at the center of the bottom surface of the processing chamber1021. The processing chamber1021is electrically grounded. A gas exhaust port1022is formed on the bottom surface of the processing chamber1021at a side of the mounting table1003. A vacuum exhaust unit1023including a vacuum pump or the like is connected to the gas exhaust port1022via a gas exhaust line1024having a pressure control valve1024aas a pressure control unit. The pressure control valve1024aand the vacuum exhaust unit1023constitute a unit for exhausting the processing chamber1021to a vacuum state. Formed at a sidewall of the processing chamber1021is a transfer opening1025for loading and unloading a wafer W. The transfer opening1025can be closed and opened by a gate valve1026.

The mounting table1003includes a lower electrode1031and a supporting body1032supporting the lower electrode1031from the bottom. The mounting table1003is disposed on the bottom surface of the processing chamber1021via an insulation member1033. An electrostatic chuck1034is provided on the mounting table1003, and the wafer W is electrostatically attracted and held on the mounting table1003by applying a voltage from a high voltage DC power supply1035to the electrostatic chuck1034.

Formed in the mounting table1003is a temperature control medium path1037through which a temperature control medium flows. The temperature of the wafer W is controlled by the temperature control medium. Further, a gas channel1038for supplying a thermally conductive gas as a backside gas to the backside of the wafer W is formed in the mounting table1003. The gas channel1038opens at a plurality of locations on the top surface of the mounting table1003. A plurality of through holes1034acommunicating with the gas channel1038is formed in the electrostatic chuck1034. The backside gas is supplied to the backside of the wafer W through the through holes1034a.

A high frequency bias power supply1031afor supplying a high frequency power of about 0 W to 4000 W having a frequency of, e.g., 13.56 MHz is connected to the lower electrode1031via a matching unit1031b. As will be described later, ions in the plasma are attracted toward the wafer W by the high frequency bias power supplied from the high frequency bias power supply1031a.

Further, a focus ring1039is disposed on an outer peripheral edge portion of the lower electrode1031to surround the electrostatic chuck1034. The plasma is converged toward the wafer W on the mounting table1003through the focus ring1039.

A gas shower head1004forming an inner ceiling plate is disposed at the center of the ceiling wall of the processing chamber1021so as to face the mounting table1003. The gas shower head1004includes an electrode1042formed of a conductive material, e.g., aluminum, and having a circular recess on a bottom surface thereof, and a supporting member1043forming a circular-plate shaped shower plate which is formed of a conductive material, e.g., polycrystalline silicon, and covers the bottom surface of the electrode1042. Although the conductive member in this example is a semiconductor, it may be a conductor, e.g., a metal. The space defined by the electrode1042and the supporting member1043serves as a gas diffusion space1041for diffusing the processing gas.

A DC power supply1053serving as a negative voltage supply unit for applying a negative DC voltage of, e.g., about 0 V to −2000 V, is connected to the electrode1042via a switch1052. Upon plasma generation, a sheath having a thickness determined by a value of a voltage applied by the DC power supply1053is formed in the region below the gas shower head1004. Due to the formation of the sheath, the electric field formed (induced) at the peripheral portion of the processing region by an antenna unit1070to be described later can be drawn to the central portion of the processing region.

A processing gas supply line1045communicating with a gas diffusion space1041is formed in a central portion of the electrode1042. A processing gas supply system1049is connected to an upstream side of the processing gas supply line1045via a gas supply line1048. The processing gas supply system1049supplies a processing gas to the wafer W. In this example, a gaseous mixture of an etching gas for performing an etching process, e.g., fluorocarbon gas, chlorine (Cl2) gas, carbon monoxide (CO) gas, hydrogen bromide (HBr) gas, ozone (O3) gas or the like, and a dilution gas such as Ar gas or the like is supplied as a processing gas into the processing chamber1021. Although it is not illustrated, the processing gas supply system1049includes a plurality of branch lines provided with, e.g., valves or flow rate control units, and gas sources connected to the respective branch lines. Each of the gas sources stores therein the etching gas or the dilution gas. Hence, a specific etching gas and Ar gas can be supplied at a desired flow rate ratio in accordance with types of etching target films to be etched.

The supporting member1043is airtightly pressed against the electrode1042via, e.g., a sealing member (not shown) formed at the peripheral edge portion of the top surface thereof. Further, a plurality of gas injection openings1044is formed at the supporting member1043so that the gas can be supplied from the gas diffusion space1041to the wafer W with high in-plane uniformity. In this example, in order to deal with a wafer W having a diameter of, e.g., about 12 inches, the outermost gas injection openings1044formed in the gas shower head1004are positioned at locations separated from the center of the processing chamber1021by, e.g., about 12.0 cm. The outermost gas injection openings1044may be positioned at locations separated from the center by about 15 cm (outer edge of the wafer W), or may be positioned closer to the center compared to the locations thereof in this example. The minimum size of the gas shower head1004is set within a range which ensures high in-plane uniformity of the gas distribution in the wafer W.

A ring-shaped region surrounding the gas shower head1004at the ceiling wall of the processing chamber1021includes an outer ceiling plate1060which is formed of a dielectric material, e.g., quartz. The outer ceiling plate1060and the gas shower head1004are airtightly coupled through a ring-shaped sealing member (not shown) formed at, e.g., an inner peripheral end of the outer ceiling plate1060, and are fixed such that the vertical positions of the lower end surfaces thereof are located at the same height. The outer ceiling plate1060is supported at the outer peripheral end thereof by the sidewall of the processing chamber1021. Here, the vertical position of the outer peripheral end of the ceiling wall is higher than that of the inner peripheral end of the ceiling wall so that the ceiling wall (the gas shower head1004and the outer ceiling plate1060) of the processing chamber1021are positioned inside the processing chamber1021, which allows the gas shower head1004and the mounting table1003to be positioned close to each other. Moreover, a ring-shaped groove1061is formed at the upper end portion of the sidewall of the processing chamber1021along the circumferential direction. A sealing member1062, e.g., an O-ring or the like, is accommodated in the groove1061. When the inner atmosphere of the processing chamber1021is exhausted to vacuum by the vacuum exhaust unit1023, the outer ceiling plate1060is drawn against the processing chamber1021, and airtightness of the processing chamber1021is maintained by the sealing member1062.

As shown inFIG. 19, antenna modules1071constituting a microwave supply unit are provided at a plurality of, e.g., eight, locations spaced apart from each other at regular intervals along the circumferential direction of the outer ceiling plate1060. The antenna modules1071are connected in parallel with a microwave output unit1080, and a plasma is generated in the region below the antenna modules1071, i.e., the region surrounding the space below the gas shower head1004, by the microwave electric field. By supplying the microwaves to the antenna modules1071and employing the slot arrangement ofFIG. 23, the electric field Er directed from the peripheral portion to the central portion of the processing chamber1021and vise versa is formed along the circumferential direction. These antenna modules1071constitute an antenna unit1070.

As shown inFIG. 20, the microwave output unit1080includes a power supply unit1081for supplying a power of, e.g., about 500 W to 3000 W, a microwave oscillator1082for oscillating microwaves having a frequency of, e.g., 2.45 GHz, an amplifier1083for amplifying the oscillated microwaves, and a distributor1084for distributing the microwave to the antenna modules1071. Each of the antenna modules1071has an amplifier section1072for amplifying the microwave distributed by the distributor1084, a tuner1073for matching impedances, and an antenna section1074for radiating the amplified microwave into the processing chamber1021. The amplifier section1072has a phase shifter1075, a variable gain amplifier1076for controlling a level of the microwave power supplied to each of the antenna modules1071, a main amplifier1077serving as a solid state amplifier, and an isolator1078for separating the microwave reflected by the antenna section1074and returning to the main amplifier1077.

The phase shifter1075is configured to shift the phase of the microwave by using a slag tuner, and the radiation characteristics of the microwave can be modulated by controlling the slag tuner. The phase shifter1075shifts the phase of the microwave applied to each of the antenna modules1071by using the slag tuner, so that the directivity of the microwave can be controlled and, also, the plasma distribution can be adjusted. Or, a circular polarized wave can be obtained by varying the direction of slots1101ato be described later by about 90° between neighboring antenna modules1071to shift the phase of the microwave by about 90° between the neighboring antenna modules1071.

Hereinafter, the detailed configuration of the antenna modules1071will be described. As shown inFIG. 21, the tuner1073and the antenna section1074are accommodated in that order from the top in a substantially cylindrical housing1100formed of, e.g., a metal. The housing1100has a lower portion having an outwardly swollen shape and serves as an outer conductor of a coaxial tube. As shown inFIG. 22, the antenna section1074includes: an approximately circular plate-shaped planar slot antenna1101having two arc-shaped slots1101adisposed opposite to each other; a ring-shaped wave retardation member1105provided above the planar slot antenna1101, for controlling the plasma density by shortening the wavelength of the microwave in vacuum; and a ceiling plate1106provided below the planar slot antenna1101and formed of a dielectric material, e.g., quartz, ceramics or the like. A metal rod1102serving as an inner conductor of the coaxial tube is connected to the central portion of the top surface of the planar slot antenna1101and extended upward through the inner peripheral side of the wave retardation member1105.

As shown inFIG. 23, in each of the antenna modules1071, two slots1101aare provided opposite to each other substantially in the diametrical direction of the gas shower head1004.FIG. 23schematically shows the shape of the slot1101a. As shown inFIG. 22, the slots1101aare preferably formed in an arc shape. Preferably, each of the planar slot antennas1101has two slots1101aas in this example or four slots1101aspaced apart from each other at regular intervals along the circumferential direction.

The ceiling plate1106allows the microwaves supplied from the microwave output unit1080to be introduced into the processing chamber1021therethrough.

The tuner1073has two ring-shaped slags1108formed of a dielectric material, e.g., quartz. The slags1108are spaced apart from each other in a vertical direction and the metal rod1102vertically extends through the slags1108. Further, the slags1108are connected to a driving unit1109provided outside the housing1100through arms1109aextending from the outer side of the housing1100to be vertically movable. A controller1109bis connected to the driving unit1109and controls vertical positions L1and L2of the slags1108in each of the antenna modules1701such that the impedance of the antenna modules1071seen from the microwave output unit1080becomes about 50Ω in accordance with the instruction from a control unit1007to be described later.

A power supply excitation plate1110for non-contact supply is provided above the tuner1073so as to be connected to the upper end of the metal rod1102. The power supply excitation plate1110includes a dielectric board1115formed of a printed circuit board (PCB) or the like, and a ring-shaped dielectric member1112provided below the dielectric board1115and formed of a dielectric material, e.g., quartz. As shown inFIG. 24, two microstrip lines1116formed of a conductor, e.g., Cu or the like, are formed at the backside of the dielectric board1115. The microstrip lines1116extend opposite to each other from the outer periphery toward the center with the leading ends thereof separated from each other.

Connectors1118are attached to the end portions of the microstrip lines1116at the circumferential edge of the dielectric board1115and connected to the amplifier section1072. Therefore, the (spatially) combined microwave power is supplied from the two connectors1118to the tuner1073. A single pair or three or more pairs of the microstrip lines1116and the connectors1118may be provided instead of two pairs of the microstrip lines1116and the connectors1118. InFIG. 21, reference numeral “1114” indicates a reflecting plate for reflecting the microwaves.

A circular plate-shaped slot antenna1113formed by copper plating and having two arc-shaped slots1113aopposite to each other as in the aforementioned planar slot antenna1101is provided at the bottom surface of the dielectric member1112. In each of the antenna modules1071, the slots1113aare arranged in the same orientation as that of the slots1101aofFIG. 23, and the slots1113ahave a length of, e.g., about ½×λg (λg: wavelength of the microwave in the waveguide). The dielectric member1112serves as a resonator together with the slot antenna1113and has a central portion through which a central conductor1117extends to connect the bottom surface of the dielectric board1115with the slot antenna1113. The slots1113amay be provided at a plurality of, e.g., four, locations spaced apart from each other at regular intervals along the circumferential direction, or may be formed in, e.g., a linear shape, instead of the arc shape. Besides, the power may be supplied to make a monopole antenna in which the microwave has a wavelength of ¼×λg without providing the slots1113a.FIG. 18is a vertical cross sectional view of the processing chamber1021which is taken along line XVIII-XVIII inFIG. 19. InFIG. 19, the illustration of the power supply excitation plate1110is omitted.

Although it is not shown inFIG. 18, the gas shower head1004has a cooling unit. Specifically, as shown inFIGS. 25A and 25B, the cooling unit includes a temperature control medium path1310that is horizontally formed in a serpentine shape so as not to interfere with the processing gas supply line1045in the electrode1042. The temperature of the gas shower head1004can be controlled by circulating the control medium having a temperature controlled to a predetermined level, e.g., water, in the temperature control medium path1310via a temperature control fluid port1311.FIG. 25Ais a vertical cross sectional view of the gas shower head4which is taken along line XXV-XXV inFIG. 25B.

As shown inFIG. 26, a control unit1007is connected to the plasma processing apparatus. The control unit1007includes a CPU1011, (a program storage unit for storing) a program1012, a work memory1013, and a memory1014as a data storage. The memory1014is provided with areas for storing processing conditions for each recipe, such as a type of a film to be etched (etching target film), a type of an etching gas, a gas flow rate, a processing pressure, a temperature of the gas shower head1004, a value of a high frequency power supplied to each of the antenna modules1071, a value of a negative DC voltage applied from the DC power supply1053and the like.

As will be described later, different types of multilayer films are laminated on the wafer W. Hence, when an etching process is performed on these multilayer films, an etching gas needs to be changed for each film and, also, the flow rate of the etching gas, the processing pressure and the like need to be changed for each film. In order to perform a uniform etching process over the surface of the wafer W, the etching gas needs to be converted into a plasma uniformly over the surface of each film. Especially, a plasma needs to be generated uniformly in the diametrical direction of the wafer W. In the present embodiment, in order to improve the in-plane uniformity of the amount (concentration) of the plasma generated by the electric, the intensity of the electric field generated at the peripheral portion of the processing region by the antenna modules1071and the intensity of the electric field induced to the central portion of the processing chamber by the negative DC voltage are controlled on a film basis by controlling the value of the negative voltage applied to the gas shower head1004.

For example, the amount of the plasma generated by the microwave electric field can be uniformly distributed in the circumferential direction by controlling, on a film basis, the microwave power supplied to each of the antenna modules1071by the variable gain amplifier1076. In other words, in the present embodiment, the amount of the plasma can be uniformly distributed on the surface of each film of the wafer W (in the diametrical and the circumferential direction). To do so, a value of a voltage to be applied to the gas shower head1004and a value of a microwave power to be supplied to the antenna modules1071are obtained in advance on a film (recipe) basis by performing tests or calculations, and the obtained values are stored on a recipe basis. Without obtaining the values in advance on a recipe basis, the corresponding values may be obtained whenever the process is performed. Further, only the negative DC voltage may be changed on a recipe basis while fixing the value of the microwave power to be supplied to the antenna modules1071to the same level in a plurality of recipes.

The program1012has an instruction for the CPU1011to read out a recipe corresponding to a film to be etched from the memory1014to the work memory1013and send a control signal to each unit of the plasma processing apparatus in accordance with the recipe to thereby execute steps to be described later and perform an etching process. Generally, this program (including a program for inputting and displaying processing parameters)1012is stored in the storage unit1008, e.g., a hard disk, a compact disk, a magneto-optical disk, a memory card or the like, and installed from the storage unit1008to the control unit1007(the program storage unit1012thereof).

Hereinafter, the operation of the plasma processing apparatus will be described with reference toFIGS. 27 to 31.

The following is brief description of a semiconductor wafer (hereinafter, referred to as a “wafer”) W as a substrate to be processed. The wafer W has a silicon film and films laminated thereon. The laminated films include a photoresist mask having a predetermined pattern, a bottom anti-reflection coating film formed of, e.g., an organic film, an amorphous carbon film, an insulating film (SiO2film or SiCOH film) or a Poly-Si (polycrystalline silicon) film, an etching stop film formed of, e.g., an inorganic film, and the like, which are laminated in that order from the top.

First, a recipe for an etching target film formed on the surface of the wafer W is read out from the memory1014to the work memory1013. In this example, the etching target film is, e.g., a bottom anti-reflection coating film, so that the recipe for this film is read out. Next, the wafer W is loaded from a vacuum transfer chamber (not shown) maintained at a vacuum atmosphere into the processing chamber1021by a substrate transfer unit (not shown) and mounted on the mounting table1003. Thereafter, the gate valve1026is closed, and the inside of the processing chamber1021is fully evacuated by the vacuum exhaust unit1023by fully opening the pressure control valve1024a, for example. At the same time, the temperature control medium having a temperature controlled to a predetermined level and the backside gas are supplied from the temperature control medium channel1037and the gas channel1038, thereby controlling the temperature of the wafer W to a predetermined level. By circulating in the temperature control medium path1310the temperature control medium having a temperature controlled to a predetermined level through the temperature control fluid port1311, the temperature of the gas shower head1004is controlled to a predetermined level.

Next, a microwave power having a frequency of, e.g., 2.45 GHz, is supplied at a power level of, e.g., about 0 W to 4000 W, from the microwave output unit1080to the antenna modules1071and, also, a high frequency bias power is supplied from the high frequency power supply1031ato the mounting table1003. The microwave oscillated by the microwave oscillator1082of the microwave output unit1080is amplified by the amplifier1083and then distributed to the antenna modules1071by the distributor1084. The microwaves are amplified by the variable gain amplifier1076and the main amplifier1077in each of the antenna modules1071and output from the two microstrip lines1116. Then, the microwaves are combined and supplied into the processing chamber1021via the planar slot antenna1101.

By supplying the microwaves to the antenna modules1071and employing the slot arrangement ofFIG. 23, the electric field Er directed in the diametrical direction of the wafer W (from the central portion to the peripheral portion of the processing chamber1021and vice versa) along the circumferential direction is formed in the region surrounding the space below the gas shower head1004through the outer ceiling plate1060. Further, a negative DC voltage of, e.g., about −500 V, is applied to the gas shower head1004. Due to the application of the negative DC voltage, a negative electric field is formed near the bottom surface of the gas shower head1004.

Then, Ar gas is supplied together with the etching gas from the processing gas supply system1049into the processing chamber1021, thereby controlling the pressure in the processing chamber1021to a predetermined level, e.g., about 5.3 Pa (40 mTorr). Ar gas is activated at a low energy and thus is preferably supplied into the processing chamber1021together with the etching gas. The processing gas as a gaseous mixture of the etching gas and Ar gas is diffused into the processing chamber1021and turned into a plasma below the antenna modules1071by the electric field Er. The plasma thus generated includes Ar+ions, ions and electrons of the etching gas material and the like. The plasma generated at the peripheral portion of the processing region is diffused to the central portion of the gas shower head1004in the processing chamber1021. The gas at the central portion is turned into a plasma by the plasma diffused to the central portion. Hence, a plasma1080is generated horizontally over the entire processing region. If a negative DC voltage is not applied to the gas shower head1004, a plasma is generated mainly in the region below the antenna modules1071, and the plasma density at the central portion becomes lower than that at the peripheral portion, as can be seen fromFIG. 27. InFIG. 27, the region where the plasma density is high is indicated by oblique lines.

However, in the present embodiment, the negative DC voltage is applied to the gas shower head1004, so that a negative electric field is generated in a region near the bottom surface of the gas shower head1004, and a thick DC sheath1001is formed immediately therebelow. The DC sheath1001has a thickness determined by the value of the negative DC voltage. Further, as shown inFIG. 28, the electric field Er is directed toward the central portion of the gas shower head1004and penetrates the DC sheath1001. Accordingly, a plasma is uniformly generated over the surface of the wafer W. The reason thereof is considered as follows.

In other words, the electric field Er generated at the peripheral edge of the gas shower head1004is strongly attracted toward the central portion of the gas shower head1004by the DC sheath1001, which leads to generation of an electric field having a high intensity below the gas shower head1004. Hence, the processing gas injected from the gas shower head1004is instantly turned into a plasma by the electric field attracted toward the region below the gas shower head1004. Even if the processing gas is not turned into a plasma by the electric field, when the processing gas reaches the region below the antenna modules1071, it is turned into a plasma by the high-intensity electric field Er in that region. Further, when the processing gas that has not been turned into a plasma reaches the region below the DC sheath1001, it is turned into a plasma by absorbing the electric field energy from the DC sheath1001.

When the plasma1002flows downward and the electrons in the plasma1002collide with the processing gas, the processing gas is turned into a plasma. Then, electrons generated from this plasma collide with the processing gas, so that the sequential generation of plasma is continued to increase the density of the plasma1002as shown inFIG. 29. The electric field Er by the antenna modules1071is diffused to the region below the gas shower head1004via the DC sheath1001, and the plasma1002generated by this electric field is directed downward toward the wafer W by a downward exhaust flow. As a consequence, a highly uniform plasma1002is generated over the surface of the wafer W (in the diametrical and the circumferential direction).

As shown inFIG. 30, positive ions in the plasma, e.g., Ar+ions, are strongly attracted by the negative electric field of the DC sheath1001and thus collide with the gas shower head1004. As a result of the collision, secondary electrons are generated from the gas shower head1004and accelerated in the DC sheath1001. The accelerated secondary electrons directed downward, and the processing gas is turned into a plasma by these secondary electrons. Therefore, the density of the plasma1002above the wafer W is increased, and the in-plane uniformity of the plasma density is further improved.

As shown inFIG. 31, ions in the plasma are attracted toward the wafer W by the high frequency bias power from the high frequency power supply1031a, so that a vertical etching process is carried out. The bottom anti-reflection coating film is etched until the amorphous carbon film formed under the bottom anti-reflection film is exposed.

Thereafter, the supply of the etching gas and Ar gas is stopped and, also, the supply of the microwaves to the antenna modules1071and the application of the negative DC voltage to the shower head1004are stopped. Next, the processing chamber1021is exhausted to vacuum, and a recipe for an amorphous carbon film to be etched is read from the memory1014to etch the amorphous carbon film. Then, in the same manner, a recipe for a film formed under the amorphous carbon film is read out to perform an etching process on the film formed thereunder.

In accordance with the aforementioned embodiment, the gas shower head1004having a conductive member is provided at the central portion of the ceiling wall of the processing chamber1021, so that the gas can be supplied uniformly over the surface of the wafer W. Further, a plasma is uniformly generated by the antenna modules1071in the region surrounding the space below the gas shower head1004along the circumferential direction, and the DC sheath1001is formed therebelow by applying a negative DC voltage to the gas shower head1004. The plasma1002is diffused to the central portion via the DC sheath1001. Accordingly, while using the microwaves, the gas can be uniformly supplied from the gas shower head1004and the plasma1002can be generated uniformly along the surface of the wafer W and also in the space below the gas shower head1004. As a result, the plasma process having high in-plane uniformity, e.g., the etching process in this example, can be performed on the wafer W.

Further, the plasma1002having high in-plane uniformity in accordance with the processing recipe can be easily obtained by controlling the thickness of the DC sheath1001by the negative DC voltage applied to the gas shower head1004and controlling the microwave power supplied to each of the antenna modules1071. In this plasma processing apparatus, the plasma1002using microwaves can be generated simply by providing the antenna modules1071above the ceiling plate (outer ceiling plate1060) of the processing chamber1021. Thus, the plasma processing apparatus of the present embodiment has a simple configuration and can be achieved cost effectively. Although a conventional plasma processing apparatus is disadvantageous in that it is difficult to supply a gas to a substrate having a large area, the plasma processing apparatus of the present embodiment does not have such disadvantage.

In the above-described apparatus, the gas shower head1004may be physically eroded through a so-called sputtering by impact of Ar+ions. Since, however, the bottom surface of the gas shower head1004is formed of silicon, there is no fear of contamination. Besides, the etching gas is uniformly supplied from the gas shower head1004, so that the gas shower head1004and the mounting table1003can be disposed adjacent to each other, and the height of the processing chamber1021can be reduced. Further, the temperature of the gas shower head1004can be controlled on a recipe basis by forming the temperature control medium path1310substantially throughout the supporting member1043.

In the above example, the antenna modules1071are installed above the outer ceiling plate1060. However, as shown inFIG. 32, the antenna modules1071can be airtightly buried in circular openings1120formed at a plurality of, e.g., eight, locations along the circumferential direction of the outer ceiling plate1060while being spaced apart from each other at regular intervals. In this case, by cutting an upper portion of each of the openings1120in a larger size than a lower portion thereof, an annular engaging stepped portion1121is formed at the lower portion of the opening1120, and the antenna module1071is airtightly maintained by engaging the step surface of the engaging stepped portion1121with the engaged surfaces corresponding to the lower peripheral edge of the antenna module1071via, e.g., an O-ring or the like. In the plasma etching processing apparatus configured as described above, the plasma is uniformly generated across the surface and the same effects as that of the above example are obtained.

At this time, the region below the antenna modules1071communicates with the processing region, so that the outer ceiling plate1060may be formed of a metal, e.g., aluminum. Further, the antenna modules1071may be installed below the outer ceiling plate1060in the processing chamber1021. In this case as well, the outer ceiling plate1060may be formed of a conductive material, e.g., a metal. When the outer ceiling plate1060is formed of a conductive material as in the above-described example, it is preferable to install an insulation member between the outer ceiling plate1060and the gas shower head1004.

Although it is not illustrated, the outer ceiling plate1060may be configured as a divided structure including an upper portion and a lower portion formed of a dielectric material, and the antenna modules1071may be accommodated in, e.g., a plurality of recesses formed at the lower portion while being spaced from each other at regular intervals along the circumferential direction. In that case, the effects of the above-described example are obtained. In other words, the etching gas is uniformly converted into a plasma, and the in-plane uniformity of the etching process is achieved.

In the above example, the plasma uniformity in the diametrical direction is improved by controlling the value of the negative DC voltage applied to the gas shower head1004. However, the uniformity of the plasma density in the diametrical direction can be improved also by controlling the value of the microwave power supplied to each of the antenna modules1071while maintaining the negative DC voltage at a predetermined value. Moreover, in the above example, the amount of the plasma is uniformly distributed in the circumferential direction by controlling the microwave power supplied to each of the antenna modules1071in the circumferential direction. However, when the amount of the plasma has extremely small variation in the circumferential direction, the microwave of the same power level can be supplied to each of the antenna modules1071. Furthermore, in order to improve the uniformity of the concentration of the plasma1002in the circumferential direction, the phase of the microwave may be controlled solely or together with the power of the microwave.

In the above example, a plurality of antenna modules1071is arranged along the circumferential direction. However, an antenna unit1200serving as a microwave supply unit may be provided to cover the ceiling wall (the gas shower head1004and the outer ceiling plate1060) of the processing chamber1021. This example will be described with reference toFIGS. 33 and 34. Like reference numerals will be given to like parts in the plasma etching processing apparatus ofFIG. 18, and redundant description thereof will be omitted.

The antenna unit1200includes a flat antenna main body1201formed of a copper plate having a thickness of, e.g., about 1 mm, and having a circular shape viewed from above, and a planar antenna member (slot plate)1203having a plurality of slots1202for generating, e.g., a circular polarized wave. The antenna main body1201has a circular opening at a bottom surface thereof, and the planar antenna member1203blocks the opening formed at the bottom surface of the antenna main body1201. The antenna main body1201and the slot member1203are formed of conductors, and serves as a flat circular waveguide. Moreover, the bottom surface of the planar antenna member1203is in close contact with the top surface (the gas shower head1004and the outer ceiling plate1060) of the processing chamber1021.

As shown inFIG. 34, a plurality of slots1202, each having a pair of slots1202aand1202bdisposed in a substantially T shape with a slight gap therebetween, is arranged in a coaxial shape or a spiral shape along the circumferential direction. The slots1202aand1202bare arranged so as to be substantially perpendicular to each other, so that a circular polarized wave having two polarized wave components perpendicular to each other is radiated. At this time, the microwave is radiated as a substantially planar wave from the planar antenna member1203by arranging the pairs of slots1202aand1202bwith an interval corresponding to the wavelength of the microwave compressed by a phase retardation plate1204to be described later.

In order to reduce the wavelength of the microwave in the circular waveguide, the phase retardation plate1204formed of a low-loss dielectric material, e.g., aluminum oxide (Al2O3), silicon nitride (Si3N4) or the like, is installed between the planar antenna member1203and the antenna main body1201. The antenna main body1201, the planar antenna member1203and the phase retardation plate1204constitute a radial line slot antenna.

A microwave generating unit1206is connected to the top surface of the antenna unit1200via the coaxial waveguide1205. Therefore, the microwave having a frequency of, e.g., 2.45 GHz or 8.3 GHz, is supplied to the antenna unit1200. The coaxial waveguide1205includes an outer waveguide1206A and an inner central conductor1206B. The waveguide1206A is connected to the antenna main body1201, and the central conductor1206B is connected to the planar antenna member1203via an opening formed at the phase retardation plate1204.

In this plasma etching apparatus, the microwave having a frequency of, e.g., 2.45 GHz, is supplied at a power level of about 500 W to 3000 W from the microwave generating unit1206. The microwave propagates through the coaxial waveguide1205in a TM mode or TE mode and reaches the planar antenna member1203of the antenna unit1200. As shown inFIG. 35, the microwave propagates radially from the central portion of the planar antenna member1203toward the peripheral portion thereof and is emitted through the slots1202aand1202binto the processing chamber1201via the outer ceiling plate1060. Accordingly, an electric field Er is uniformly generated along the circumferential direction in the peripheral region surrounding the space below the gas shower head1004. Further, as in the above example, the electric field Er is strongly attracted by the DC sheath1101generated below the gas shower head1004by applying a negative DC voltage of, e.g., about 0 V to −2000 V, from the DC power supply1053. Hence, as in the above example, the plasma is uniformly generated across the surface (in the circumferential and the diametrical direction), and an etching process is carried out with high verticality. As a result, this plasma etching processing apparatus can also provide the same effect as that of the examples described above.

In this case, as shown inFIG. 32, the openings1120may be formed at the outer ceiling plate1060along the circumferential direction. Or, a ring-shaped opening may be formed so as to surround the gas shower head1004without providing the outer ceiling plate1060. In that case, the gas shower head1004is fixed to the antenna unit1200, and the lower circumferential surface of the antenna main body1201and the upper circumferential surface of the processing chamber1021are brought into airtight contact with each other. Further, the technical scope of the present invention includes the case where the shower plate (the supporting member1043) of the gas shower head1004in the processing region is formed of a conductive material and a negative voltage is applied to the shower plate connected to the DC power supply1053via the conductive path.

In the above examples, an etching process is described as an example of a plasma process. However, the plasma processing apparatus of the present invention may be applied to, e.g., a film forming apparatus employing a CVD (Chemical Vapor Deposition) method using a plasma or an ashing apparatus. For example, in a film forming apparatus, a value of a negative DC voltage applied to the gas shower head4is adjusted in accordance with processing conditions such as a type or a flow rate of a film forming gas, a pressure and the like, to thereby perform a film forming process at a uniform film forming rate across the surface.

As shown inFIG. 35, the simulation (calculation) using COMSOL as an electromagnetic field calculation software was performed to monitor the change in the density distribution of the electric field Er (TM mode electric field) generated in the processing chamber1021in the case of installing the antenna modules1071and applying a negative DC voltage to the gas shower head1004.

The calculation was performed in the case where microwaves having a frequency of, e.g., 1.8 GHz, were supplied to the antenna modules1071at a power level of about 2000 W. Further, the calculation was performed in the cases where the DC sheaths1001having different thicknesses of about 1 mm, 5 mm and 10 mm were generated below the gas shower head1004by applying a negative DC voltage to the gas shower head1004. Moreover, the intensity of the electric field absorbed by the plasma (processing gas) was monitored in the right half space of the processing chamber1021. The electron density of the plasma below the DC sheath1001can be evaluated by the absorbed electric field intensity.

As shown in (a) and (b) ofFIG. 36, as the thickness of the DC sheath1001was increased from about 1 mm to about 5 mm, the region of the absorbed electric field intensity was extended under the region below the DC sheath1001to the central portion of the processing chamber1021. From this, it was found that the electric filed Er was extended toward the central portion of the wafer W, which led to improvement of the in-plane uniformity of the plasma density. Further, (c) ofFIG. 36showed that the electric field Er generated below the antenna modules1071was further drawn toward the central portion of the wafer W by increasing the thickness of the DC sheath1001, i.e., increasing the negative DC voltage applied to the gas shower head1004.