CN101667533B - Plasma processing method and plasma processing apparatus - Google Patents

Abstract

The invention relates to a plasma treatment method and a plasma treatment device. In the cathode coupling method, it is possible to prevent the additional deposited film on the electrode on the anode side from affecting the subsequent process, and to improve the uniformity of the treatment as much as possible. A substrate to be processed (W) is placed on a susceptor (16) of the lower electrode, and a high frequency for plasma generation is applied from a high frequency power supply (30). The upper electrode (34) disposed parallel to it above the base (16) is installed in the chamber (10) in an electrically floating state via a ring-shaped insulator (35). The upper electrode (34) A variable capacitor (86) with variable capacitance is set in the space (50) between the ceiling of the above and chamber (10). According to the processing condition, the capacitance of the variable capacitor (86) is changed by the capacitance control section (85). The ground capacitance of the upper electrode (34) is switched.

Description

Plasma treatment method and plasma treatment device

This case is a divisional application of a patent application with an application date of March 30, 2007 , an application number of 200710091348.6 , and an invention title of plasma processing method and plasma processing device .

technical field

The present invention relates to the technique of implementing plasma processing on a substrate to be processed, in particular to a capacitively coupled plasma processing device and a plasma processing method.

Background technique

In the processes of etching, deposition, oxidation, sputtering, etc. in the manufacturing process of semiconductor devices or FPD (Flat Panel Display: Flat Panel Display), plasma is often used in order to perform a good reaction at a relatively low temperature in the process gas. In the prior art, capacitively coupled plasma processing apparatuses have become the mainstream among sheet-type plasma processing apparatuses, especially plasma etching apparatuses.

Generally, in a capacitively coupled plasma processing apparatus, an upper electrode and a lower electrode are arranged in parallel in a processing container formed as a vacuum chamber, and a substrate to be processed (semiconductor wafer, glass substrate, etc.) is placed on the lower electrode. , apply a high-frequency voltage to either side of the two electrodes. The electrons are accelerated by the electric field formed between the two electrodes by the high-frequency voltage, the plasma is generated by the impact ionization of the electrons and the processing gas, and the required microprocessing (such as etching process). Here, since the side electrode to which the high frequency is applied is connected to the high frequency power supply via a blocking capacitor in the matching unit, it operates as a cathode (cathode).

In the cathode coupling method, where a high frequency is applied to the lower electrode of the supporting substrate to use it as a cathode, it is possible to introduce ions in the plasma almost vertically to the substrate by using its own bias voltage generated on the lower electrode. Perform anisotropic etching. In addition, in the cathode coupling method, in a process in which deposits such as polymers (accumulated deposits, hereinafter referred to as "deposition") are easily attached to the upper electrode, there is also sputtering by bombardment of ions incident on the upper electrode. The advantage of being able to remove a deposited film (the same is true if an oxide film is added).

Patent Document 1 Japanese Patent Application Laid-Open No. 6-283474

In a conventional capacitively coupled plasma processing apparatus using a cathode coupling method, generally, the upper electrode on the anode side to which a high-frequency voltage is not applied is DC-grounded. Usually, since the processing container is made of metal such as aluminum or stainless steel and is grounded safely, the upper electrode can be used as the ground potential through the processing container, so the upper electrode is directly attached to the ceiling of the processing container to form an integrated structure or the processing A structure in which the ceiling of the container is used as the upper electrode as it is.

However, with the miniaturization of design rules in semiconductor manufacturing processes in recent years, high-density plasma at low pressure is required. In capacitively coupled plasma processing equipment, the frequency of high-frequency electricity is gradually increasing. Recently, the standard use Frequency above 40MHz. However, as the frequency becomes higher, its high-frequency current gathers at the center of the electrode, and the density of the plasma generated in the processing space between the two electrodes is also higher at the center of the electrode than at the edge of the electrode. The problem of reduced in-plane uniformity is aggravated.

Contents of the invention

The present invention is proposed in view of the problems of the above-mentioned prior art, and its first purpose is to provide, in the cathode coupling mode, to prevent as much as possible the additional deposited film on the electrode on the anode side from affecting the subsequent process, and to improve the efficiency as much as possible. A plasma processing method and a plasma processing device for processing uniformity.

In addition, the second object of the present invention is to provide a plasma processing method and a plasma processing apparatus which, by repeating the number of times of plasma processing, even in the processing environment in the processing container The generation of time-dependent changes can also stably ensure the uniformity of treatment.

In order to achieve the above-mentioned first object, the first plasma processing method of the present invention is characterized in that: in a vacuumable, grounded processing container, the first electrode and the second electrode are arranged in parallel at a predetermined interval, by The second electrode supports the substrate to be processed so that it is opposed to the first electrode, and evacuates the inside of the processing container to a predetermined pressure, and supplies the substrate between the first electrode, the second electrode, and the side wall of the processing container. The processing space supplies the desired processing gas, and applies the first high frequency to the above-mentioned second electrode, and performs the desired processing on the above-mentioned substrate by the plasma generated in the above-mentioned processing space, wherein the above-mentioned first An electrode is installed in the above-mentioned processing container, and is electrically connected to the ground potential through the electrostatic capacitance variable part with variable electrostatic capacitance, and switches the static electricity of the above-mentioned electrostatic capacitance variable part according to the processing conditions for implementing plasma processing on the above-mentioned substrate. capacitance.

In addition, the first plasma processing apparatus of the present invention is characterized in that it includes: a vacuum-exhaustable, grounded processing container; a first electrode installed in the above-mentioned processing container via an insulator or a space; A variable electrostatic capacity section for variable electrostatic capacitance between the first electrode and ground potential; disposed in parallel with the first electrode at a predetermined interval in the processing container, facing the first electrode, and supporting the processed a second electrode of the substrate; a processing gas supply unit for supplying a desired processing gas to a processing space between the first electrode, the second electrode, and the side wall of the processing container; and a processing gas supply unit for generating the processing gas in the processing space plasma, a first high-frequency power supply unit that applies a first high frequency to the second electrode; and a capacitance control that switches the capacitance of the capacitance variable unit according to processing conditions of the plasma treatment performed on the substrate. department.

In the structure of the capacitive coupling type adopted in the present invention, if the high frequency from the high frequency power supply is applied to the second electrode, the high frequency discharge between the second electrode and the first electrode and the second electrode and the processing The high-frequency discharge between the side walls (inner walls) of the container generates plasma of the processing gas in the processing space, and the generated plasma diffuses in all directions, especially upward and outward in the radial direction, and the electron current in the plasma passes through the first An electrode or the side wall of the processing vessel etc. flows to the ground.

Here, by switching the electrostatic capacitance of the electrostatic capacitance variable part according to the processing conditions of the plasma treatment, it is possible to arbitrarily switch the electrostatic capacitance around the first electrode or the ground from high capacitance (low impedance) to low capacitance (high impedance). capacitance. In particular, the high-capacitance (low-impedance) grounding mode increases the ratio of the plasma electron current flowing between the first electrode and the second electrode, thereby enhancing sputtering of ions directed at the first electrode. Effect, so it is advantageous for the treatment that the deposited film such as polymer is easy to adhere to the second electrode. In addition, the low-capacitance (high-impedance) grounding mode increases the proportion of the plasma electron current flowing between the first electrode and the side wall of the processing vessel, enabling the spatial distribution of the plasma density to radial Since the direction spreads outward, it is suitable for a process where the uniformity of the process is important and a process in which there is no problem even if the deposited film adheres to the second electrode (for example, a final process process).

In addition, a second high frequency lower than the first high frequency may be applied to the second electrode, or a desired DC voltage may be applied to the first electrode.

In order to achieve the above-mentioned second object, the second plasma processing method of the present invention is characterized in that: in a vacuumable, grounded processing container, the first electrode and the second electrode are arranged in parallel at a predetermined interval, by The second electrode supports the substrate to be processed so that it is opposed to the first electrode, and evacuates the inside of the processing container to a predetermined pressure, and supplies the substrate between the first electrode, the second electrode, and the side wall of the processing container. The processing space supplies the desired processing gas, and applies the first high frequency to the above-mentioned second electrode, and performs the desired processing on the above-mentioned substrate by the plasma generated in the above-mentioned processing space, wherein the above-mentioned first An electrode is installed in the above-mentioned processing container, and is electrically connected to the ground potential through the electrostatic capacitance variable part with variable electrostatic capacitance. capacitance.

In addition, the second plasma processing apparatus of the present invention is characterized in that it includes: a grounded processing container that can be evacuated; a first electrode installed in the above-mentioned processing container via an insulator or a space; A variable electrostatic capacity section for variable electrostatic capacitance between the first electrode and ground potential; disposed in parallel with the first electrode at a predetermined interval in the processing container, facing the first electrode, and supporting the processed a second electrode of the substrate; a processing gas supply unit for supplying a desired processing gas to a processing space between the first electrode, the second electrode, and the side wall of the processing container; and a processing gas supply unit for generating the processing gas in the processing space Plasma: a first high-frequency power supply unit that applies a first high frequency to the second electrode; and a capacitance control unit that switches the capacitance of the capacitance variable unit according to the number of substrates that are subjected to plasma processing. .

In the above-mentioned second method or apparatus, by switching the electrostatic capacitance of the above-mentioned electrostatic capacitance variable part according to the number of processed substrates to be subjected to plasma treatment, the spatial distribution characteristics of the plasma density and even the in-plane distribution of the treatment can be controlled. characteristics, resulting in the ability to stably maintain treatment uniformity.

According to a preferred embodiment of the present invention, the value of the electrostatic capacitance of the electrostatic capacitance variable part is adjusted to be large in advance, and the value of the electrostatic capacitance is decreased as the number of sheets processed increases.

According to the plasma processing method and plasma processing apparatus of the present invention, through the above-mentioned structure and function, in the cathode coupling method, it is possible to prevent the additional deposition film on the electrode on the anode side from affecting the subsequent process, and Maximize treatment uniformity. In addition, by repeating the number of times of plasma processing, uniformity of processing can be stably ensured even if a temporal change occurs in the processing environment in the processing container.

Description of drawings

FIG. 1 is a longitudinal sectional view showing the structure of a plasma etching apparatus according to one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a configuration of a variable capacitor in the plasma etching apparatus according to the embodiment.

3 is a diagram showing another example of a configuration of a variable capacitor in the plasma etching apparatus according to the embodiment.

4 is a longitudinal sectional view showing the configuration of a plasma etching apparatus according to a modified example of the embodiment.

5 is a longitudinal sectional view showing the configuration of a plasma etching apparatus according to a modified example of the embodiment.

6 is a diagram schematically showing a pattern of high-frequency discharge in a chamber when the plasma etching apparatus according to the embodiment is switched to a high-capacitance (low-impedance) grounding mode.

7 is a diagram schematically showing a pattern of high-frequency discharge in a chamber when the plasma etching apparatus according to the embodiment is switched to a low-capacitance (high-impedance) grounding mode.

8 is a longitudinal sectional view showing the configuration of a plasma etching apparatus used in the etching method according to the embodiment.

FIG. 9 is a rough cross-sectional view showing the state of each stage of multi-steps in the etching method according to the embodiment.

Symbol Description

10 chambers (processing vessels)

16 base (lower electrode)

30 high frequency power supply

34 Upper electrode

35 ring insulator

36 electrode plates

36a Gas ejection hole

38 Electrode support

40 gas buffer chamber

42 Gas supply pipe

44 Process gas supply pipe

50 spaces

52 Insulators

64 high frequency power supply

70, 72 Capacitors

85 Capacitance Control Department

86 variable capacitor (capacitance variable part)

Detailed ways

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

In FIG. 1, the structure of the plasma processing apparatus which concerns on one Embodiment of this invention is shown. This plasma processing apparatus is configured as a cathode-coupled capacitively coupled (parallel plate type) plasma etching apparatus, for example, having a cylindrical vacuum chamber made of aluminum whose surface is treated with an aluminum oxide film (anodized treatment). Chamber (processing container) 10 . Chamber 10 is securely grounded.

At the bottom of the chamber 10 , a cylindrical susceptor support 14 is disposed via an insulating plate 12 such as ceramics, and a susceptor 16 made of, for example, aluminum is provided on the upper surface of the susceptor support 14 . The susceptor 16 constitutes a lower electrode, on which, for example, a semiconductor wafer W is placed as a substrate to be processed.

An electrostatic chuck 18 for holding the semiconductor wafer W by electrostatic attraction is provided on the upper surface of the susceptor 16 . This electrostatic chuck 18 has a structure in which an electrode 20 made of a conductive film is sandwiched between a pair of insulating layers or insulating sheets, and a DC power supply 22 is electrically connected to the electrode 20 . With the DC voltage from the DC power supply 22, the semiconductor wafer W can be attracted and held on the electrostatic chuck 18 by Coulomb force. Around the electrostatic chuck 18 , a focus ring 24 made of, for example, silicon is arranged on the upper surface of the susceptor 16 to improve the uniformity of etching. A cylindrical inner wall member 25 made of, for example, quartz is attached to the side surfaces of the susceptor 16 and the susceptor support 14 .

Inside the susceptor support 14 is provided a refrigerant chamber 26 extending in the circumferential direction, for example. A refrigerant of a predetermined temperature, such as cooling water, is circulated into the refrigerant chamber 26 via pipes 27a and 27b by a cooling unit (not shown) installed outside. The processing temperature of the semiconductor wafer W on the susceptor 16 can be controlled by the temperature of the cryogen. Furthermore, a heat transfer gas such as He gas from a heat transfer gas supply mechanism (not shown) is supplied between the upper surface of the electrostatic chuck 18 and the back surface of the semiconductor wafer W through the gas supply line 28 .

A high-frequency power supply 30 for plasma generation is electrically connected to the susceptor 16 via a matching unit 32 and a power supply rod 33 . This high-frequency power supply 30 applies a predetermined high frequency, for example, a high frequency of 40 MHz, to the susceptor 16 when plasma processing is performed in the chamber 10 .

Above the susceptor 16 , an upper electrode 34 is provided parallel to and opposite to the susceptor. The upper electrode 34 includes an electrode plate 36 made of a semiconductor material such as Si, SiC, etc. with a plurality of gas ejection holes 36a; The electrode support 38 made of processed aluminum is mounted in the chamber 10 in an electrically floating state via the ring-shaped insulator 35 . A plasma generation space or a processing space PS is formed by the upper electrode 34 , the susceptor 16 , and the side walls of the chamber 10 .

The annular insulator 35 is made of, for example, aluminum oxide (Al ₂ O ₃ ) and installed so as to airtightly close the gap between the outer peripheral surface of the upper electrode 34 and the side wall of the chamber 10, while physically supporting the upper electrode 34. , constituting a part of the electrostatic capacitance between the upper electrode 34 and the chamber 10 .

The electrode support 38 has a gas buffer chamber 40 inside it, and has a plurality of gas vent holes 38a connected from the gas buffer chamber 40 to the gas ejection holes 36a of the electrode plate 36 on its lower surface. The processing gas supply part 44 is connected to the gas buffer chamber 40 through the gas supply pipe 42 . When a predetermined processing gas is introduced into the gas buffer chamber 40 from the processing gas supply unit 44, it is sprayed from the gas discharge holes 36a of the electrode plate 36 toward the semiconductor wafer W on the susceptor 16 in a shower-like manner to the processing space PS. Handle gas. In this way, the upper electrode 34 also serves as a shower head for supplying the processing gas to the processing space PS.

In addition, a passage (not shown) flowing through a refrigerant such as cooling water is provided inside the electrode support body 38, and the whole of the upper electrode 34, especially the electrode plate 36, is adjusted to a specified value by means of an external cooling unit through the refrigerant. temperature. In addition, in order to stabilize the temperature control of the upper electrode 34, a heater (not shown) composed of a resistance heating element, for example, may be installed inside or on the electrode support 38.

A gap having an appropriate gap size is provided between the upper surface of the upper electrode 34 and the ceiling of the chamber 10 , and a space 50 is formed there. Although this space 50 can be an atmospheric space, it is preferably constituted as a vacuum space, which not only realizes the thermal isolation between the upper electrode 34 and the chamber 10 and the ambient temperature, but also prevents the gap between the upper electrode 34 and the chamber 10 by virtue of the removal of gas. The discharge function. When the space 50 is evacuated in this way, it is evacuated separately from the processing space PS, and the vacuum state is maintained by the airtight structure. In this embodiment, in order to further improve the discharge prevention function, all or part of the inner wall of the space 50 is covered with a sheet-shaped insulator 52 (only the upper side is shown in the figure). A heat-resistant polyimide-based resin can be suitably used for the insulator 52 , but Teflon (registered trademark), quartz, or the like can also be used.

The annular space formed between the susceptor 16 , the susceptor support 14 and the side wall of the chamber 10 serves as an exhaust space, and an exhaust port 54 of the chamber 10 is provided at the bottom of the exhaust space. An exhaust device 58 is connected to the exhaust port 54 through an exhaust pipe 56 . The exhaust device 58 has a vacuum pump such as a turbomolecular pump, and can depressurize the interior of the chamber 10, especially the processing space PS, to a desired vacuum degree. In addition, a gate valve 62 for opening and closing the loading and unloading port 60 of the semiconductor wafer W is attached to the side wall of the chamber 10 .

In this plasma etching apparatus, a variable capacitor 86 with variable capacitance is provided in the space 50 , and the capacitance of the variable capacitor 86 can be changed by a capacitance control unit 85 provided outside the chamber 10 , for example, on the upper surface.

Here, a configuration example of the variable capacitor 86 is shown in FIGS. 2 and 3 . The variable capacitor 86 has a conductor plate 88 movable between a first position on top of or close to the upper electrode 34 and a second position separated upward from the upper electrode 34; and moving the conductor plate 88 up and down Or change the position of the operating mechanism, such as the operating rod 90. Here, a capacitor is formed between the conductor plate 88 and the upper electrode 34 . The greater the area of the conductor plate 88, the greater the sensitivity or range in which the capacitance can be varied can become. The operating mechanism 90 of FIG. 2 is made of a conductive material, or a material that is conductive to high frequencies or a material that has low impedance to high frequencies, and is grounded directly or via the chamber 10 . The operating mechanism 90 of FIG. 3 may be made of insulating material. The electrostatic capacity control unit 85 has, for example, a stepping motor capable of arbitrarily controlling the amount of rotation, and a motion conversion mechanism (such as a ball screw mechanism) that converts the rotation of the rotational drive shaft of the stepping motor into the linear (elevating) motion of the operating mechanism 90. ) etc., the capacitance of the variable capacitor 86 can be continuously changed by variable control of the height position of the conductor plate 88 . The closer the conductor plate 88 is to the ceiling surface of the chamber 10, the smaller the ground capacitance of the upper electrode 34 becomes. Conversely, the closer the conductor plate 88 is to the upper surface of the upper electrode 34, the larger the ground capacitance of the upper electrode 34 becomes. In an extreme case, the ground capacitance can be infinitely increased by bringing the conductive plate 88 into contact with the upper electrode 34 and grounding the upper electrode 34 .

In FIG. 4 , a capacitance variable unit 85 according to another embodiment is shown. In this embodiment, an annular insulator 35 is provided between the upper electrode 34 and the side wall of the chamber 10, and an annular liquid storage chamber 94 is formed in the annular insulator, so that it can be accessed from the chamber 10 through the pipe 92. A structure in which a liquid Q with a suitable dielectric constant (for example, an organic solvent like Galden) is derived and introduced from the outside. By changing the type (permittivity) or the amount of the dielectric liquid Q, the capacitance of the entire annular insulator 35 and the ground capacitance of the upper electrode 34 can be varied.

In addition, a control signal indicating the capacitance (target value) of variable capacitor 86 is given to capacitance control unit 85 from controller 96 that controls the operation of each part in the plasma processing apparatus and the sequence of the entire apparatus.

In this plasma etching apparatus, to perform etching, first, the gate valve 62 is opened, and the semiconductor wafer W to be processed is carried into the chamber 10 and placed on the upper surface of the electrostatic chuck 18 . Then, the processing gas, that is, the etching gas (generally, a mixed gas) is introduced into the chamber 10 from the processing gas supply part 44 according to a predetermined flow rate or flow ratio, and the chamber 10 is evacuated by the vacuum exhaust device 58. The pressure inside becomes the set value. In addition, a high frequency (40 MHz) is applied to the susceptor 16 by a high frequency power supply 30 at a predetermined power. In addition, a DC voltage is applied from a DC power supply 22 to the electrodes 20 of the electrostatic chuck 18 to fix the semiconductor wafer W on the electrostatic chuck 18 . The etching gas discharged from the shower head of the upper electrode 34 is converted into plasma by high-frequency electric discharge in the processing space PS, and the film on the main surface of the semiconductor wafer W is etched by radicals or ions generated by the plasma.

This capacitively coupled plasma etching device applies high-frequency electricity of 40 MHz or higher to the susceptor (lower electrode) 16 to increase the density of the plasma in a preferred dissociated state, even under lower pressure conditions. Can form high-density plasma. In addition, the cathode coupling method is used, and ions in the plasma are introduced almost vertically onto the wafer W by the self-bias voltage generated on the susceptor 16, thereby enabling anisotropic etching.

In addition, a first high frequency with a relatively high frequency (for example, 40 MHz) suitable for plasma generation and a second high frequency with a relatively low frequency (for example, 2 MHz) suitable for ion introduction are superimposed and applied to the lower electrode. The overlapping application of the lower two frequencies is also possible. As such an apparatus configuration, for example, as shown in FIG. 5 , a high-frequency power supply 64 for supplying the second high-frequency power to the base 16, a matching unit 66, and a power supply rod 68 may be added. In such a lower two-frequency overlapping application method, the density of the plasma generated in the processing space PS can be optimized by the first high frequency (40 MHz), and the density of the plasma generated on the susceptor 16 can be optimized by the second high frequency (2 MHz). Self-bias voltage or ion layer optimization can achieve more selective anisotropic etching.

Next, the function of the variable capacitor (capacitance variable unit) 86 in this plasma etching apparatus will be described. In FIGS. 6 and 7 , the upper electrode 34 is electrically connected (grounded) to the chamber 10 at the ground potential via a variable capacitor 86 and capacitors 70 and 72 which are fixed capacitors. Here, the capacitor 70 is a capacitance (fixed capacitance) existing between the upper electrode 34 and the side wall of the chamber 10 , and is mainly provided by the annular insulator 35 . On the other hand, the capacitor 72 is parallel to the variable capacitor 86 and is a capacitor (fixed capacitor) existing between the upper electrode 34 and the ceiling of the chamber 10 . The electrostatic capacitance around the upper electrode 34 or the ground capacitance is given as a composite capacitance obtained by adding the capacitance of the variable capacitor 86 and the capacitances of the capacitors 70 and 72 .

First, the capacitance of the variable capacitor 86 is increased, and when the ground capacitance (synthetic capacitance) of the upper capacitor 34 is selected to be, for example, 20,000 pF or more (in an extreme case, the conductive plate 88 is brought into contact with the upper electrode plate 34, and In the case of an infinite capacitance value), the function will be described. In this case, as shown in FIG. 6, if the high frequency from the high frequency power supply 30 is applied to the susceptor 16, by virtue of the high frequency discharge between the susceptor 16 and the upper electrode 34 and in the susceptor 16 The high-frequency discharge between the side wall of the chamber 10 generates plasma of the processing gas in the processing space PS, and the generated plasma diffuses in all directions, especially upward and outward in the radial direction, and the electron current in the plasma passes through the upper part. The electrodes 34 and the side walls of the chamber 10 etc. flow toward the ground. Here, on the base 16, the higher the frequency of the high frequency, the easier it is for the high frequency current to concentrate in the central part of the base by the skin effect, and since the upper electrode 34 directly opposite is grounded via a high capacitance, that is, a low impedance, A relatively low proportion of the electron current in the plasma goes to the side walls of the chamber 10, most of it goes to the upper electrode 34, and to its central part. As a result, the spatial distribution characteristic of the plasma density tends to be a mountain-shaped distribution profile in which the central portion of the electrode is the highest and becomes lower as it moves toward the outer peripheral portion in the radial direction. However, on the other hand, by flowing a large amount of high-frequency current or electron current to the upper electrode 34 , the incident amount of ions on the upper electrode 34 due to its own bias increases, thereby enhancing the sputtering effect.

On the other hand, when the capacitance of the variable capacitor 86 is lowered, and the ground capacitance (synthetic capacitance) of the upper electrode 34 is selected to be, for example, 250 pF or less, the plasma distribution in the processing space PS becomes Radially outward expansion. In such a case, if a high frequency is applied to the susceptor 16 from the high frequency power supply 30 , by virtue of the high frequency discharge between the susceptor 16 and the upper electrode 34 and between the susceptor 16 and the side wall of the chamber 10 The high-frequency discharge will also generate plasma of etching gas in the processing space PS, and the generated plasma will diffuse upward and outward in the radial direction, and the electron current in the plasma will pass through the upper electrode 34 or the side wall of the chamber 10, etc. flow to the earth. Therefore, on the susceptor 16, the high-frequency current tends to concentrate at the central portion of the susceptor as in the case of FIG. 6 . However, since the ground capacitance or impedance of the upper electrode 34 is low, even if the high-frequency current is concentrated in the central portion of the susceptor 16, it is difficult to flow from there to the upper electrode 34 directly opposite. Therefore, the proportion of the electron current flowing to the side wall of the chamber 10 in the plasma is absolutely not low, and according to the value of the capacitance to ground, that is, according to the capacitance value of the variable capacitor 86, it is possible to control the current flow on the base 16 and the upper electrode respectively. 34 and between the pedestal 16 and the side walls of the chamber 10, the ratio of the electron currents is arbitrarily controlled. On the other hand, if the high-frequency current or electron current flowing to the upper electrode 34 decreases, the incident amount of ions on the upper electrode 34 and the sputtering effect may also decrease.

As described above, the plasma etching apparatus of this embodiment has a structure capable of changing the electrostatic capacitance of the electrostatic capacitance variable portion 86, by appropriately switching the ground capacitance of the upper electrode 34 according to processing conditions, in particular, selecting a high-capacitance ground (low-impedance ground). ) mode or low-capacitance grounding (high-impedance) mode can optimize the balance or trade-off between preventing or even reducing the memory effect described later and process uniformity, thereby improving the processability of the overall process.

Next, an example of a specific plasma etching process performed by the plasma etching apparatus of this embodiment will be described. This etching process forms a connection hole (via hole) in an organic low-k film as an interlayer insulating film, and is a process using the lower two-frequency superposition method (FIG. 5).

FIG. 8 shows a detailed configuration example of the processing gas supply unit 44 in this embodiment. The main gas supply pipe 42 is connected to supply sources of various source gases via individual dedicated or branch gas supply pipes as a process gas supply system. In this embodiment, as will be described later, six types of CF ₄ , CHF ₃ , CH ₃ F, C ₄ F ₈ , Ar, and N ₂ are used as the source gas of the mixed gas for etching. The gas supply sources 100-110 of raw material gas. Mass flow controllers (MFCs) 100 a to 110 a and on-off valves 100 b to 110 b that can be independently and arbitrarily controlled by the controller 96 are provided on the respective dedicated gas supply pipes.

(0.1μm)的膜厚的氮化硅(SiN)膜，由例如CVD(Chemical Vapor Deposition：化学气相沉积)法形成。有机系low-k膜116是例如具有1μm的膜厚的SiOC系low-k膜，由例如CVD法形成。掩模118是抗蚀剂膜，由通常的光刻形成，在通孔的开孔位置具有开口部118a。On the main surface of the semiconductor wafer W to be etched, as shown in (a) of FIG. layer 114 , an organic low-k film (interlayer insulating film) 116 , and a mask 118 . The wiring layer 112 is, for example, a Cu wiring layer, and is formed by, for example, dual damascene processing. Barrier layer 114 is, for example, having

The silicon nitride (SiN) film with a film thickness of (0.1 μm) is formed by, for example, a CVD (Chemical Vapor Deposition: Chemical Vapor Deposition) method. The organic low-k film 116 is, for example, a SiOC-based low-k film having a film thickness of 1 μm, and is formed by, for example, a CVD method. The mask 118 is a resist film formed by ordinary photolithography, and has an opening 118a at the opening position of the via hole.

In this embodiment, three-step etching is performed on the semiconductor wafer W of the object to be processed. First, as a first step, etching of a deposition process is performed. The main etching conditions of this first step are as follows.

Processing gas: CF ₄ /CH ₃ F/N ₂ = flow 50/5/100sccm

Pressure in the chamber: 20mTorr

High frequency power: 40MHz/2MHz＝1000/0W

In this first step, perfluorocarbon-based CH ₃ F was used as an etching gas. Then, H molecules decomposed by the plasma in CH ₃ F quickly react with F and are exhausted as HF, whereby C is likely to remain. As a result, a large amount of carbon-based deposits occurs and adheres to the opening 118a and the upper surface of the resist mask 118 nearby, and serves as a protective film for improving the mask selectivity in subsequent steps. However, by generating a large amount of polymer, and since the second high frequency (2 MHz) is not applied on the susceptor 16 (ie, due to weak ion incidence toward the upper electrode 34 ), deposits easily adhere to the upper electrode 34 .

In such a case, as shown in FIG. 5 , the capacitance of the variable capacitor 86 is increased for the ground capacitance of the upper electrode 34 to switch to a high-capacitance ground (low impedance) mode, and in extreme cases, it becomes a short-circuit ground. Thereby, the incident efficiency of ions to the upper electrode 34 is improved, sputtering is promoted, and an additional deposited film can be avoided.

附近的深度的时候结束。在该第一步骤结束之际，停止供给CF₄/CH₃F/N₂的混合气体，即在关闭开关阀100b、104b、110b的同时，将高频电源30的输出置于关闭(off)。但是，排气装置58的排气动作保持原来的状态继续。As shown in FIG. 9(b), in this first step, the bottom of the hole 116a formed in the organic low-k film 116 reaches a predetermined depth, for example,

near the end of the depth. When the first step is completed, the supply of the mixed gas of CF ₄ /CH ₃ F/N ₂ is stopped, that is, the output of the high-frequency power supply 30 is turned off (off) while closing the on-off valves 100b, 104b, and 110b. . However, the exhaust operation of the exhaust device 58 continues as it is.

Then, as a second step, main etching is performed. The main etching conditions in this second step are as follows.

Process gas: CHF ₃ /CF ₄ /Ar/N ₂ = flow 40/30/1000/150sccm

Pressure in the chamber: 30mTorr

High frequency power: 40MHz/2MHz＝1000/1000W

In the second step, high-speed anisotropic etching is performed by adding ion-assisted etching by ion irradiation to plasma-assisted etching by chemical reaction. At this time, since the second-step process starts without adding the deposited film formed in the preceding first-step process to the upper electrode 34 , it is not affected by the first-step process.

However, in the process of the second step, a large amount of polymer is produced from perfluorocarbon-based CHF ₃ , and even if it is not as in the first step, it is easy to be additionally deposited on the upper electrode 34, and the process time is relatively long. In the case of , there is a greater possibility that the deposited film accumulates and grows larger.

In view of this point, even in the second step, the ground capacitance of the upper electrode 34 is made into a high-capacitance ground mode as shown in FIG. 5 , and in extreme cases, it becomes a short-circuit ground. As a result, the incident efficiency of ions to the upper electrode 34 is improved, ion sputtering is promoted, and an additional deposited film can be avoided.

As shown in FIG. 9(c), the second step reaches a predetermined depth at the bottom of the hole 116a of the organic low-k film 116, for example, near the end of the depth. When this step ends, the on-off valves 102b, 100b, 108b, and 110b are closed to stop the supply of the mixed gas of CHF ₃ /CF ₄ /Ar/N ₂ . At the same time, the outputs of the two high-frequency power supplies 30, 64 are temporarily turned off.

Then, as the final third step, overetching is performed. Main etching conditions in this third step are as follows.

Process gas: C ₄ F ₈ /Ar/N ₂ = flow 6/1000/150sccm

Pressure in the chamber: 50mTorr

High frequency power: 40MHz/2MHz＝1000/1000W

In the third step, the organic low-k film 116 is etched up to the base film (silicon nitride) 62 while maintaining the anisotropy (vertical shape) of the hole 116 a. Even in such a case, since the process of the third step is started without adding the deposited film formed in the process of the previous second step to the upper electrode 34, it is not affected by the process of the second step. Influence.

The C ₄ F ₈ /Ar/N ₂ mixed gas used in the etching gas in the treatment of the third step has such an advantage that the selectivity ratio to the base film (silicon nitride) 62 is high, although polymerization of fluorocarbons occurs matter, its production amount is relatively small, and there is no subsequent processing of the third step. That is, in the processing of the third step, even if a deposited film is added to the upper electrode 34, it is not necessary to consider the effect (memory effect) that the subsequent processing is affected by the previous processing due to the deposited film. In addition, for example, a deposited film attached to the upper electrode 34 or the side wall of the chamber 10 can be additionally removed by plasma cleaning.

In view of this, in the third step, the ground capacitance of the upper electrode 34 is switched to the low capacitance ground (high impedance) mode shown in FIG. 6 . In this way, the electron current flowing between the base 16 and the upper electrode 34 can be relatively reduced, and the electron current flowing between the base 16 and the side wall of the chamber 10 can be relatively increased, which can The density of the plasma generated in the processing space PS is expanded radially outward.

In such a case, although the etching rate on the semiconductor wafer W can also be uniformized spatially (especially in the radial direction), it is preferable to make the etching rate relatively higher in the edge portion than in the central portion. That is, in the previous first and second steps, the ground capacitance of the upper electrode 34 was set high due to the emphasis on preventing the above-mentioned memory effect, so the plasma density was relatively high in the central part and high in the peripheral part. Therefore, the etching rate for via hole formation tends to be relatively high in the central part and low in the peripheral part. As a result, at the end of the second step, there is a spatial (particularly radial) deviation in the depth of the bottom of the hole 116a, being relatively deep at the center and relatively shallow at the edge.

Here, in the final third step, conversely, by making the plasma density relatively low in the central portion and relatively high in the peripheral portion and making the etching rate on the semiconductor wafer W relatively low in the central portion, The edge portion is relatively high, and the variation in etching depth so far can be offset to a certain extent. Thereby, the in-plane uniformity of the etching rate through the overall processing of the first to third steps can be improved.

As described above, according to this embodiment, the ground capacitance of the upper electrode 34 is variably configured, and depending on the processing conditions, for example, in the continuous processing, when the previous processing tends to additionally deposit a film on the upper electrode 34, in this processing Switching the ground capacitance of the upper electrode 34 to a high-capacitance ground (low impedance) mode makes it difficult to add a deposited film on the upper electrode 34, which can prevent or reduce the influence or memory effect on subsequent processing. In addition, when it is difficult to add a deposition film on the upper electrode 34 or a final process, the ground capacitance of the upper electrode 34 is switched to a low-capacitance ground (high impedance) mode, so that the plasma generated in the processing space PS The density spreads outward in the radial direction, thereby improving the processing uniformity.

The through-hole etching of the organic low-k film in the above-mentioned embodiment is an example, and the present invention is applicable to any multi-step process, and of course, is also applicable to a single-step process. In addition, a DC power supply (not shown) is electrically connected to the upper electrode 34, and a structure or a method in which an arbitrary DC voltage is applied to the upper electrode 34 is also possible. In such a case, the upper electrode 34 functions as a direct current in a state of being electrically floating from the potential of the chamber 10 , that is, from the ground potential.

In addition, as another embodiment, the value of the electrostatic capacitance may be changed according to the number of wafers processed. In general, as the temperature of components inside the chamber increases due to plasma, the etching rate at the edge of the wafer tends to decrease. Therefore, especially in the early stage of etching, the etching rate at the center of the wafer is increased synchronously with the increase of the etching rate at the edge of the wafer to maintain uniformity. The electrostatic capacitance value of the portion becomes smaller, so that the reduction of the etching rate at the edge portion of the wafer is reduced.

The high-frequency frequency used in the above-mentioned embodiments is an example, and any frequency may be used according to the processing. In addition, various modifications may be made to the structure of each part in the device. In particular, the configuration of the capacitance variable unit 86 in the above embodiment is an example, and any capacitor configuration that can change the capacitance around the upper electrode 34 or the ground capacitance within a desired range can be employed. Although the above-described embodiments relate to a plasma etching device and a plasma etching method, the present invention can also be applied to other plasma processing devices and processing methods such as plasma CVD, plasma oxidation, plasma nitridation, and sputtering. In addition, the substrate to be processed in the present invention is not limited to a semiconductor wafer, and may be various substrates for flat panel displays, photomasks, CD substrates, printed substrates, and the like.

Claims (7)

1. A plasma processing device, characterized in that, comprising: Vacuum-ventable, grounded processing containers; a first electrode mounted within the processing vessel via an insulator or a space; an electrostatic capacitance variable portion electrically connected between the first electrode and a ground potential in an annular insulator provided between the first electrode and a side wall of the processing container An annular liquid storage chamber is formed, and a liquid having a predetermined dielectric constant is introduced into the liquid storage chamber from the outside of the processing container through a pipe, or a liquid having a predetermined dielectric constant is led out from the liquid storage chamber to the outside of the processing container. The dielectric constant of the liquid, so that the electrostatic capacitance is variable; a second electrode that is arranged in parallel with the first electrode at a predetermined interval in the processing container, and faces the first electrode, and supports the substrate to be processed; a processing gas supply part that supplies a desired processing gas to a processing space between the first electrode, the second electrode, and a side wall of the processing container; a first high frequency power supply unit that applies a first high frequency to the second electrode in order to generate plasma of the process gas in the process space; and The capacitance control unit switches the capacitance of the capacitance variable unit according to processing conditions of the plasma treatment of the substrate to be subjected to plasma treatment or the number of processed substrates. 2. The plasma processing device according to claim 1, characterized in that: The electrostatic capacity control unit increases the value of the electrostatic capacity of the electrostatic capacity variable unit in advance, and decreases the value of the electrostatic capacity as the number of sheets processed increases. 3. The plasma processing device according to claim 1, characterized in that: The capacitance control unit switches the capacitance of the capacitance variable unit to high when the deposition film can be attached to the first electrode, and switches the capacitance of the capacitance variable unit to high when the deposition film cannot be attached to the first electrode. When on, switch the electrostatic capacitance of the electrostatic capacitance variable part to low. 4. The plasma processing device according to claim 1, characterized in that: In the multi-step process, the capacitance control unit switches the capacitance of the variable capacitance unit to high during the processing of each step except the last step, and switches the capacitance of the variable unit to high during the processing of the last step. The electrostatic capacitance of the electrostatic capacitance variable part is switched to low. 5. The plasma processing device according to claim 1, characterized in that: The capacitance variable unit has a variable capacitor. 6. The plasma processing device according to claim 1, characterized in that: A second high frequency lower than that of the first high frequency is applied to the second electrode. 7. The plasma processing device according to claim 1, characterized in that: A DC power supply is provided for applying a desired DC voltage to the first electrode.

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