CN1929096A - Plasma ashing method - Google Patents

Abstract

A plasma ashing method is used for removing a patterned resist film in a processing chamber after etching a portion of a low-k film from an object to be processed in the processing chamber by using the patterned resist film as a mask. The method includes a first step of supplying a reaction product removal gas including at least CO2 gas into the processing chamber, generating plasma of the reaction product removal gas by applying a high frequency power for the plasma generation, and removing reaction products deposited on an inner wall of the processing chamber; and a second step of supplying an ashing gas into the processing chamber, generating plasma of the ashing gas by applying a high frequency power for the plasma generation, and removing the resist film.

Description

Plasma ashing method

Technical Field

The present invention relates to a plasma ashing method for removing a resist film on an object to be processed.

Background

For example, in a semiconductor manufacturing process, a surface of a target object, for example, a semiconductor wafer (hereinafter also referred to as "wafer") is etched using a predetermined process gas with a resist film having grooves (trenches) or holes (holes) patterned as a mask, and then ashing treatment is performed to remove the remaining resist film.

As such ashing, it is known to use, for example, O₂(oxygen) gas, CO₂A method of ashing and removing a resist film by a process gas such as a gas (plasma ashing method) (see patent documents 1 and 2). Specifically, for example, while heating a wafer in a processing chamber, O is introduced into the processing chamber₂Gas to generate plasma, thereby utilizing in O₂Active species such as O (oxygen) radicals (chemical) generated during the plasma formation of the gas are ashed to remove the resist film.

Since the ashing process is performed after the etching process, if the etching process and the ashing process can be performed continuously in the same processing chamber, for example, the time for transferring the wafer to another processing chamber can be omitted, the entire processing time can be shortened, and the like, and the advantage is very remarkable.

However, if a fluorine-containing process gas (for example, a CF-based polymer) is used as the process gas in the etching process, a reaction product such as a fluoropolymer (for example, a CF-based polymer) may be deposited on the inner wall of the process chamber. If the ashing process is continuously performed in this state, reaction products such as fluoropolymers deposited on the inner wall of the chamber are dissociated again, and a film on the wafer is etched (memory effect), which may adversely affect the performance of the semiconductor device formed on the wafer. Such a phenomenon is not only the use of O₂The gas is generated as a processing gas in ashing, and CO is used₂Gas or CO gas also occurs.

On the other hand, in order to suppress the occurrence of such memory effect, there is a case where the ashing process is divided into 2A method of performing each step (see, for example, patent document 3). In the ashing process, first, in the first step, O is introduced into the process chamber without applying a bias to the wafer₂Removing the reaction product such as fluoropolymer deposited on the inner wall of the processing chamber by using the gas as a reaction product removing processing gas and generating oxygen plasmaAnd (4) removing. Next, in the second step, a bias is applied to the wafer, and ashing process gas is introduced into the processing chamber to remove the resist film on the wafer. The process of removing the resist film by such 2 steps is called hybrid ashing (hybrid ashing).

[ patent document 1]Japanese patent application laid-open No. 2003-59911

[ patent document 2]Japanese patent application laid-open No. 2001-189302

[ patent document 3]Japanese patent application laid-open No. Hei 11-145111

[ patent document 4]Japanese patent application laid-open No. 2005-101289

However, when a layer including a Low dielectric constant film (hereinafter also referred to as a "Low-k film") is formed on the bottom layer of the resist film, if the Low-k film is simply subjected to the hybrid ashing in a state where the Low-k film is exposed, the Low-k film may be damaged. Specifically, for example, when a reaction product such as a fluoropolymer deposited on the inner wall of the process chamber is removed in the first step, a part of the fluorine is dissociated again by the influence of O (oxygen) radicals or the like generated in the process chamber, and enters the Low-k film or the lower film of the Low-k film, and the Low-k film or the lower film is etched, so that C (carbon atom) contained in the Low-k film may be removed, the film quality may be deteriorated, and the dielectric constant may be increased.

In this regard, although damage to the Low-k film or the primary film can be suppressed by optimizing the process conditions in the first step so as to reduce the density of O (oxygen) radicals in the process chamber (see patent document 4), there is a limit to further suppressing damage to the Low-k film or the primary film.

Disclosure of Invention

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a plasma ashing method capable of suppressing damage to a Low dielectric constant film (Low-k film) or an underlying film formed on a target object to be processed, to be lower than that of the related art.

In order to solve the above-described problems, according to a first aspect of the present invention, there is provided a plasma ashing method for applying a patterned resist film as a mask to an object to be processed in a processing chamberAnd removing the resist film in the processing chamber after performing a process of etching a part of the low dielectric constant film, the method including: a first ashing step of supplying the material into the chamberTo contain at least CO₂Removing a reaction product of the gas from the processing gas, applying high-frequency power for plasma generation to generate plasma of the reaction product removing the processing gas, and removing the reaction product attached to the inner wall of the processing chamber; and a second ashing step of supplying an ashing gas into the processing chamber, applying a high-frequency power for plasma generation, generating a plasma of the ashing gas, and removing the resist film.

In this case, the reaction product removal treatment gas may be CO₂The single gas of the gas may also be a gas comprising CO₂A mixed gas of a gas and an inert gas. The pressure in the processing chamber in the first ashing step is preferably 30mTorr or less. The ashing gas may contain, for example, O₂Gas and CO₂Either one or both of the gases. Further, it is preferable that: the first ashing step is performed without applying a bias generating high-frequency power; the second ashing step is performed while applying a bias generating high-frequency power. The Low dielectric constant film is, for example, a porous (porous) Low-k film.

The present inventors have focused on the inclusion of CO₂Process gas of gas and gas containing O₂The damage to the low dielectric constant film or the primary coating formed on the object to be processed is very small as compared with the processing gas of the gas, and it was found that even when such CO is used₂The gas can also sufficiently remove reaction products adhering to the inner wall of the processing chamber to contain the CO₂The process gas is used as a product removal process gas in the first ashing step. Thereby, O is contained in the first ashing step₂Damage to the low dielectric constant film or the primary coating of the object to be processed in the first ashing step can be significantly reduced as compared with the case of the processing gas. In addition, the first ashing step is used for secondary treatmentSince the reaction product is removed from the inner wall of the chamber, the reaction product is not re-dissociated in the second ashing step, and the low dielectric constant film or the primary film of the object to be processed is not damaged.

In order to solve the above problems, according to a second aspect of the present invention, there is provided a plasma ashing method for removing a resist film in a processing chamber after performing a process of etching a part of the low dielectric constant film on a target object disposed on a second electrode opposing a first electrode disposed in the processing chamber using the patterned resist film as a mask, the plasma ashing method comprising: a first ashing step of supplying a gas containing at least CO into the processing chamber₂Removing a processing gas from a reaction product of the gas, generating plasma of the processing gas from which the reaction product is removed by applying a high-frequency power to the first electrode, and removing the reaction product adhering to the inner wall of the processing chamber while the high-frequency power is not applied to the second electrode; and second ashingAnd supplying an ashing gas into the processing chamber, applying a high-frequency power to the first electrode to generate plasma of the ashing gas, and removing the resist film while applying the high-frequency power to the second electrode. Thus, even when the first ashing step and the second ashing step are performed in the processing chamber in which the first electrode and the second electrode are disposed to face each other, damage to the low dielectric constant film or the primary coating of the object to be processed can be significantly reduced.

Further, it is preferable that: in the second ashing step, the frequency of the high-frequency power applied to the first electrode is the same as the frequency of the high-frequency power applied to the second electrode, and is 13MHz to 40MHz inclusive. Further, more preferably: in the second ashing step, the frequency of the high-frequency power applied to the first electrode is 27MHz or more, and the frequency of the high-frequency power applied to the second electrode is 13MHz or more and 40MHz or less. The pressure in the processing chamber in the second ashing step is preferably 400mTorr or less. Accordingly, the frequency of the high-frequency power and the pressure in the processing chamber can be set to the optimum range, and therefore, damage to the low dielectric constant film or the primary film formed on the object to be processed can be further reduced in the first ashing step and the second ashing step, and ashing can be performed at a higher speed in the second ashing step.

In order to solve the above problems, according to a third aspect of the present invention, there is provided a plasma ashing method for removing a resist film in a processing chamber after performing a process of etching a part of the low dielectric constant film on a target object on a second electrode disposed to face a first electrode disposed in the processing chamber using the patterned resist film as a mask, the plasma ashing method comprising: a first ashing step of supplying a gas containing at least CO into the processing chamber₂Removing a processing gas from a reaction product of the gas, generating plasma of the processing gas from which the reaction product is removed by applying a high-frequency power to the first electrode, and removing the reaction product adhering to the inner wall of the processing chamber while the high-frequency power is not applied to the second electrode; and a second ashing step of supplying an ashing gas into the processing chamber, generating plasma of the ashing gas by applying a high-frequency power to the second electrode without applying a high-frequency power to the first electrode, and removing the resist film while applying a high-frequency power to the second electrode.

In this way, the plasma of the ashing process gas may be generated by applying the high-frequency power to the second electrode without applying the high-frequency power to the first electrode in the second ashing step. This makes it possible to collect plasma of the ashing process gas directly above the object to be processed, and therefore, the amount of ions generated required for ashing can be increased, and the ashing of the resist film can be performed at a higher speed.

In this case, in the second ashing step, the frequency of the high-frequency power applied to the second electrode is preferably 13MHz to 40 MHz. The pressure in the processing chamber in the second ashing step is preferably 400mTorr or less.

In order to solve the above problems, according to a fourth aspect of the present invention, there is provided a plasma ashing method using a patterned resist filmAs a mask, the method for removing a resist film in a processing chamber after performing a process of etching a part of a low dielectric constant film on an object to be processed disposed on an electrode which is disposed in the processing chamber and is configured to be capable of superimposing a first high frequency power and a second high frequency power having a frequency lower than the first high frequency power, the method comprising: a first ashing step of supplying a gas containing at least CO into the processing chamber₂Removing a processing gas from a reaction product of the gas, applying the first high-frequency power to the electrode to generate a plasma of the reaction product removing processing gas, and removing the reaction product adhering to the inner wall of the processing chamber without applying a second high-frequency power to the electrode; and a second ashing step of supplying an ashing gas into the processing chamber, applying a first high-frequency power to the electrode to generate plasma of the ashing gas, and removing the resist film while applying a second high-frequency power to the electrode. Thus, even when the first ashing step and the second ashing step are performed in a processing chamber having an electrode to which the firsthigh-frequency power and the second high-frequency power having a frequency lower than that of the first high-frequency power are applied in a superposed manner, damage to a low dielectric constant film or a primary film formed on an object to be processed can be significantly reduced.

In the first ashing step, the frequency of the first rf power is preferably 13MHz or higher. In this case, the frequency of the first high-frequency power in the first ashing step is preferably 27MHz or higher. In the second ashing process, the frequency of the first rf power is preferably 13MHz to 100 MHz. In this case, the second high-frequency power may be 0W. Further, it is preferable that: in the second ashing step, the frequency of the first rf power is 40MHz or more, and the frequency of the second rf power is 13MHz or less. Accordingly, the frequency of the high-frequency power and the pressure in the chamber can be set to the optimum ranges, and therefore, damage to the low dielectric constant film or the primary coating formed on the object to be processed in the first ashing step and the second ashing step can be further reduced, and ashing can be performed at a higher speed in the second ashing step.

In the present specification, 1Torr is (101325/760) Pa, and 1mTorr is (10)^-3X 101325/760) Pa, 1sccm is (10)^-6/60)m³/sec。

As described above, according to the present invention, it is possible to provide a plasma ashing method capable of suppressing damage to a Low dielectric constant film (Low-k film) or an underlying film formed on an object to be processed to be lower than that of the related art.

Drawings

Fig. 1 is a schematic configuration diagram of a plasma processing apparatus according to a first embodiment ofthe present invention.

Fig. 2 is a schematic sectional view showing a film structure of a wafer subjected to etching and ashing processes by the plasma processing apparatus shown in fig. 1.

Fig. 3 is a schematic cross-sectional view showing a film structure after etching treatment of the wafer shown in fig. 2.

Fig. 4 is a schematic cross-sectional view showing a film structure after the ashing process is performed on the wafer shown in fig. 3.

Fig. 5 is a graph showing the results of indirectly measuring the removal amount of the reaction product in the first ashing step by the reduction amount of the film.

Fig. 6 is a graph showing the results of measuring the plasma emission spectrum in the processing chamber after the first ashing step.

Fig. 7 is an explanatory diagram of a method of determining the degree of damage to the Low-k film by the first ashing procedure.

Fig. 8 is a diagram showing a relationship between the kind of the process gas used in the first ashing step and the amount of CD shift.

Fig. 9 is a graph showing the relationship between the chamber pressure and the CD shift amount in the first ashing step.

Fig. 10 is a diagram showing a relationship between the upper power and the CD shift amount in the first ashing step.

Fig. 11 is a diagram showing a relationship between an electrode gap and a CD shift amount in the first ashing step.

Fig. 12 is a graph showing the relationship between the process gas flow rate and the CD shift amount in the first ashing step.

Fig. 13 is an explanatory diagram of a method of determining the degree of damage to the Low-k film by the second ashing procedure.

Fig. 14 is a graph showing the relationship between the chamber pressure and the CD shift amount in the second ashing step.

Fig. 15 is a sectional view showing an example of the configuration of a plasma processing apparatus according to a second embodiment of the present invention.

Description of the symbols

100 plasma processing apparatus

102 process chamber

103 insulating plate

104 base support table

105 base (lower electrode)

107 temperature regulating medium chamber

108 introducing pipe

109 discharge pipe

111 Electrostatic chuck

112 electrode

113 DC power supply

114 gas passage

115 Focus ring

121 upper electrode

122 insulating material

123 blowoff hole

124 electrode plate

125 electrode support

126 gas inlet

127 gas supply pipe

128 valve

129 mass flow controller

130 process gas supply

131 exhaust pipe

132 gate valve

135 air exhaust mechanism

200 wafer

202 photoresist film

204 antireflection film

206 protective film

208 low dielectric constant film

210 groove

300 plasma processing apparatus

302 process chamber

306 lower electrode

308 upper electrode

309 gas ejection port

312 power supply device

330 magnet

332 gas inlet

336 exhaust pipe

W wafer

Detailed Description

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and the drawings, the same reference numerals are given to the constituent elements having substantially the same functional configurations, and redundant description is omitted.

(example of the configuration of the plasma processing apparatus according to the first embodiment)

First, a configuration example of a plasma processing apparatus according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows a schematic configuration of a plasma processing apparatus 100 according to a first embodiment. The plasma processing apparatus 100 is a so-called parallel-plate type plasma processing apparatus having an upper electrode as a first electrode and a lower electrode as a second electrode disposed to face the first electrode.

As shown in fig. 1, the plasma processing apparatus 100 includes a processing chamber 102 formed of a processing container made of, for example, aluminum having an anodized (alumite) surface and formed in a cylindrical shape, and the processing chamber 102 is grounded. A substantially cylindrical susceptor support table 104 for placing a target object, for example, a semiconductor wafer (hereinafter also referred to as "wafer") W, is provided on the bottom of the processing chamber 102 via an insulating plate 103 made of ceramic or the like. A susceptor 105 constituting a lower electrode is provided on the susceptor support base 104. A High Pass Filter (HPF)106 is connected to the pedestal 105.

A temperature adjusting medium chamber 107 is provided inside the base support table 104. Then, the temperature adjusting medium (for example, refrigerant) is introduced into the temperature adjusting medium chamber 107 through the introduction pipe 108, circulated, and discharged from the discharge pipe 109. By circulating the temperature adjusting medium, the susceptor 105 can be adjusted to a desired temperature.

The upper center portion of the base 105 is formed in a convex circular plate shape. An electrostatic chuck 111 having substantially the same shape as the wafer W is provided on the susceptor 105. The electrostatic chuck 111 has an electrode 112 interposed between insulating materials. A dc voltage of, for example, 1.5kV is applied to the electrostatic chuck 111 from a dc power supply 113 connected to the electrode 112. Thereby, the wafer W is electrostatically attracted by the electrostatic chuck 111.

Further, the insulating plate 103, the susceptor support table 104, the susceptor 105, and the electrostatic chuck 111 are provided with a gas passage 114 for supplying a heat transfer medium (e.g., a backside gas such as He gas) to the backside of the wafer W. The heat medium transfers heat between the susceptor 105 and the wafer W, and the wafer W is maintained at a predetermined temperature.

An annular focus ring (focus ring)115 is disposed on the upper end peripheral portion of the susceptor 105 so as to surround the wafer W placed on the electrostatic chuck 111. The focus ring 115 is made of an insulating material such as ceramic or quartz, or a conductive material. By configuring the focus ring 115, the uniformity of etching is improved.

Further, an upper electrode 121 is provided above the susceptor 105 so as to face the susceptor 105 substantially in parallel. The upper electrode 121 is supported inside the process chamber 102 by an insulating material 122. The upper electrode 121 is composed of an electrode plate 124 having a plurality of ejection holes 123 and forming a surface facing the susceptor 105, and an electrode support 125 supporting the electrode plate 124. The electrode plate 124 is formed of an insulating material or a conductive material. In the present embodiment, silicon is used as a constituent material of the electrode plate 124. The electrode support 125 is made of a conductive material such as aluminum having an alumite-treated surface. Further, the interval between the susceptor 105 and the upper electrode 121 can be adjusted.

A gas inlet 126 is provided in the center of the electrode support 125 of the upper electrode 121. The gas supply pipe 127 is connected to the gas inlet 126. A process gas supply 130 is connected to the gas supply line 127 through a valve 128 and a mass flow controller 129.

As the process gas, for example, an etching gas for plasma etching, a reaction product removing gas for ashing, an ashing gas, and the like are supplied from the process gas supply source 130. In fig. 1, only 1 process gas supply system including the gas supply pipe 127, the valve 128, the mass flow controller 129, the process gas supply source 130, and the like is shown, but the plasma processing apparatus 100 includes a plurality of process gas supply systems. For example, CF₄、O₂、N₂、CHF₃、CO₂The process gases such as Ar, He, and Xe are supplied into the process chamber 102 while flow rates thereof are controlled independently.

An exhaust pipe 131 is connected to the bottom of the process chamber 102, and an exhaust mechanism 135 is connected to the exhaust pipe 131. The exhaust mechanism 135 has a vacuum pump such as a turbo molecular pump, and adjusts the inside of the processing chamber 102 to a predetermined reduced pressure atmosphere. Further, a gate valve 132 is provided on a sidewall of the processing chamber 102. By opening the gate valve 132, the wafer W can be carried into the processing chamber 102 and carried out of the processing chamber 102.

The first high-frequency power supply 140 is connected to the upper electrode 121, and a first matching unit 141 is inserted into a power supply line thereof. In addition, a Low Pass Filter (LPF)142 is connected to the upper electrode 121. The first high-frequency power supply 140 can output first high-frequency power (high-frequency power for plasma generation) having a frequency in the range of 50to 150 MHz. By applying the first high-frequency power having such a high frequency to the upper electrode 121, plasma having a desired dissociation state and a high density can be formed in the processing chamber 102, and plasma processing under a low-pressure condition can be performed. The frequency of the first high-frequency power source 140 is preferably 50to 80MHz, and typically 60MHz or a frequency near the illustrated frequency is used.

The second rf power supply 150 is connected to the susceptor 105 as a lower electrode, and a second matching unit 151 is inserted into a power supply line thereof. The second high-frequency power supply 150 can output second high-frequency power (bias generating high-frequency power) having a frequency in the range of several hundred kHz to ten and several MHz. By applying the second high-frequency power having a frequency in such a range to the susceptor 105, an appropriate action of ions can be applied without damaging the wafer W. The frequency of the second high-frequency power supply 150 is typically 2MHz, 3.2MHz, 13.56MHz, or the like as shown in the figure. In this embodiment 2 MHz.

The second high-frequency power is usually used as the bias generating high-frequency power, but the second high-frequency power may be used as the plasma generating high-frequency power when the second high-frequency power is applied without applying the first high-frequency power. This makes it possible to collect plasma of the ashing process gas directly above the wafer, and therefore, the amount of ions generated required for ashing, which will be described later, can be increased, and the resist film can be ashed at a higher speed.

(specific example of film Structure of wafer)

Next, a specific example of the film structure of a wafer subjected to etching and ashing processes by the plasma processing apparatus 100 shown in fig. 1 will be described with reference to fig. 2.

As shown in fig. 2, the wafer 200 has a film structure in which a Low dielectric constant film (hereinafter referred to as "Low-k film") 208, a protective film 206, a reflection preventing film (BARC) 204, and a photoresist film 202 are sequentially stacked. In addition, in addition to an etching stopper film made of a SiC material such as a SiCN film or a SiC film, a metal layer such as a Cu (copper) wiring layer and various semiconductor layers may be formed on a silicon substrate constituting the main body of the wafer 200 under the low dielectric constant film 208.

As a Low dielectric constant material constituting the Low-k film 208, for example,a porous type Low-k film (porous Low-k film) is used. In order to cope with a problem of wiring delay due to reduction in design rule (design rule) of a semiconductor integrated circuit, a porous structure such as a porous Low-k film is used as an interlayer insulating film. This enables the interlayer insulating film to have a further low dielectric constant.

Examples of such porous Low-k films include films obtained by making porous coating films having a siloxane structure, such as HSQ (Hydrogen-silanes-Quioxane) and MSQ (Methyl-Hydrogen-siloxanes-Quioxane), and films obtained by making porous CVD films, such as SiOCH films. Among them, the SiOCH film is also expressed as a SiOC film, and generally contains Si, O, C, and H as constituent elements. As the Low-K film 208 in this embodiment, a porous Low-K film composed of an SiOCH film having a relative dielectric constant K of 2.5 is used, and the film thickness thereof is 480 nm.

The coating film having a porous structure as described above is formed, for example, as follows. That is, a solution containing a precursor (precursor) of an insulating film constituent material and a template (template) is spin-coated on a substrate, and then the substrate is made porous by heat treatment. The CVD film having a porous structure is formed by appropriately selecting conditions such as a film forming gas.

Further, since the porous Low-k film is a porous insulating film, adhesion to other films, film strength, and the like may be reduced. Therefore, in the case of using a porous type Low-k film as the Low-k film 208, the protective film 206 is formed on the upper portion thereof. Examples of the protective film 206 include a SiCN film and SiO₂Films, and the like. As the protective film 206 in this embodiment, a SiCN film is used, and the film thickness thereof is 120 nm. In addition, the Low-k film formed on the wafer is exemplified by a porous Low-k film,but is not limited thereto.

The resist material constituting the photoresist film 202 is, for example, a type sensitive to KrF light (wavelength 248nm), and the film thickness thereof is 410 nm. Thus, a so-called line-and-space (trench) having a line width of 200nm is patterned in advance in a photolithography process at a ratio of a line width to a line width of 1: 2.

When the photoresist film 202 is exposed to KrF light, the antireflection film 204 functions to suppress reflected light from the underlayer. This enables finer patterning. The thickness of the antireflection film 204 in the present embodiment is 60 nm.

(specific example of treatment to a wafer)

Here, a specific example of the process performed on the wafer 200 shown in fig. 2 by using the plasma processing apparatus 100 shown in fig. 1 will be described. First, the wafer 200 shown in fig. 2 is carried into the processing chamber 102 of the plasma processing apparatus 100 shown in fig. 1, and the plasma etching process is performed on the wafer 200. This prevents the reflective film 204, the protective film 206, and the Low-k film 208 from being etched, thereby forming grooves 210 (see fig. 3). For example, the ratio of the line width of the trench 210 to the line width between lines is 1: 2, and the line width is 200 nm. Next, the plasma ashing process of the present invention is performed on the wafer 200 in the same process chamber 102. Thereby, the resist film 202 and the antireflection film 204 are removed (see fig. 4).

Here, a specific example of the plasma etching process will be described. Here, for example, the plasma etching process is performed by sequentially performing the first to third etching steps. First, in the first etching step, the anti-reflection film 204 is etched using the patterned photoresist film 202 as a mask. As the processing conditions for performing the first etching step, for example, the pressure in the processing chamber 102 is adjusted to 50mTorr, the high-frequency power applied to the upper electrode 121 is set to 1000W, and the high-frequency power applied to the susceptor (lower electrode) 105 is set to 100W. In addition, CF is used₄The flow rate of the process gas was set to 100 sccm. The pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 10Torr at the center (center) portion and 35Torr at the edge (edge) portion. The processing time in the first etching step is set to, for example, 60 sec.

Next, in the second etching step, the protective film 206 is etched using the patterned photoresist film 202 as a mask. As the processing conditions for performing the second etching step, for example, the pressure in the processing chamber 102 is adjusted to 50mTorr, the high frequency power applied to the upper electrode 121 is set to 500W, and the substrate is subjected to the etching treatmentThe high-frequency power applied to the socket (lower electrode) 105 was set to 500W. In addition, use of C₄F₈、Ar、N₂The flow ratio (C) of the respective gases is set as a process gas₄F₈Gas flow of Ar/N₂The gas flow rate of (1) was set to 5sccm/100sccm/100 sccm. The pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 10Torr at the center and 35Torr at the edge. The processing time in the second etching step is set to, for example, 60 sec.

Next, in the third etching step, the Low-k film 208 is etched. As in carrying outIn the third etching step, the pressure in the processing chamber 102 is adjusted to 75mTorr, the high-frequency power applied to the upper electrode 121 is set to 1000W, and the high-frequency power applied to the susceptor (lower electrode) 105 is set to 300W, for example. In addition,CF is used₄Ar mixed gas as a process gas, and the flow ratio (CF) of each gas₄The gas flow rate of Ar/the gas flow rate of Ar) was set to 100sccm/100 sccm. The pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 10Torr at the center and 35Torr at the edge. The processing time in the third etching step is set to, for example, 70 sec.

By the plasma etching treatment in the first to third etching steps, for example, as shown in fig. 3, a groove 210 is formed in the Low-k film 208. The ratio of the line width of the groove 210 to the line width between lines is, for example, 1: 2, and the line width is, for example, 200 nm. Next, in the plasma etching process, a plasma ashing process for removing the photoresist film 202 is performed on the wafer 200 in the same processing chamber 102.

However, when the plasma etching process as described above is performed, F (fluorine) contained in the process gas adheres to the inner wall of the process chamber 102 and gradually deposits as a fluoropolymer. When the plasma ashing process is performed from this state for the purpose of removing only the photoresist film 202, the fluoropolymer deposited on the inner wall of the processing chamber 102 is dissociated again, and the Low-k film 208 is etched, thereby changing the width and depth of the groove.

Therefore, the plasma ashing process according to the present embodiment is mainly performed in the following two steps: a first ashing step of removing reaction products such as fluoropolymer (for example, CF-based fluoropolymer) deposited on the inner wall of the processing chamber 102; and a second ashing process for removing the photoresist film 202. First, the fluoropolymer deposited on the inner wall of the processing chamber 102 is removed by performing the first ashing step. Thus, in the second ashing step, the fluorine polymer is not dissociated again to etch the Low-k film 208.

However, if the conventional method using O is used in the first ashing step of the plasma ashing process₂When a process gas mainly containing a gas is used as a reaction product removing process gas, the Low-k film and the underlying film (e.g., an etching stopper film) of the Low-k film are easily damaged. For example, when removing the fluoropolymer attached to the inner wall of the processing chamber 102, a part of fluorine is dissociated again by the O radicals generated in the processing chamber 102 and enters the Low-k film or the underlying film, and there is a possibility that the Low-k film or the underlying film is reduced or the film quality of the Low-k film is deteriorated and the dielectric constant is increased. In addition, in the first ashing step, O is contained because of the use₂The C (carbon atoms) contained in the Low-k film is generated by O in the processing chamber 102The Low-k film may be deteriorated due to the dissociation of radicals, etc., and the dielectric constant (k value) of the Low-k film may be increased.

In this case, although it is possible to suppress damage to the Low-k film or the underlying film by optimizing the process conditions in the first ashing step so as to reduce the density of O (oxygen) radicals in the process chamber 102, there is a limit to further suppress damage to the Low-k film or the underlying film.

Therefore, the present inventors have found that, when a trial and error is conducted by newly examining the reaction product removal process gas used in the first ashing step: even if CO is used in the first ashing process₂The process gas mainly containing O can be used as a reaction product for removing the process gas₂Similarly, the reaction products such as the fluoropolymer deposited on the inner wall of the processing chamber 102 are sufficiently removed by the process gas as a main body.

Presumably: for example, it will be in the form of CO₂When the process gas mainly used is converted into plasma, CO is generated₂ ⁺(CO₂Ion), the CO₂The ions are accelerated by the potential difference between the plasma potential and the inner wall of the processing chamber 102, collide with the inner wall, are dispersed on the inner wall surface, and are gasified into CO gas and COF gas by chemical reactions such as the following chemical formulas (1-1) and (1-2)₂Gas, thereby removing the fluoropolymer (e.g., CF-based fluoropolymer) deposited on the inner walls of the process chamber 102.

…(1-1)

…(1-2)

Further, it can be seen that: in the first ashing treatment, CO is used₂In the case of a process gas mainly containing O₂The effect of suppressing damage to the Low-k film or the primary film is greater in the case of the main process gas. This is presumably because: using with CO₂The main conditions and uses of the process gas are O₂O radicals are less likely to be generated than in the case of a process gas mainly containing CO₂It is very stable and does not have the ability to detach C (carbon atom) from a Low-k film or the like, and therefore, the Low-k film or the primary coating is hardly damaged.

Therefore, the plasma ashing treatment method of the present invention uses CO in the first ashing step₂The process gas mainly containing the gas is used as a reaction product removing gas. Thus, damage to the Low-k film or the primary film (e.g., etching of the Low-k film or the like, deterioration of the film quality of the Low-k film, etc.) can be suppressed to be lower than in the conventional technique. Further, the first ashing step is performed to remove deposits such as fluoropolymer deposited on the inner wall of the processing chamber 102, and thenIn the second ashing stepWith CO₂The ashing process gas is mainly a process gas, and thus, the effect of suppressing damage to the Low-k film or the primary film can be reliably exerted.

Further, by optimizing other parameters in the processing conditions of the first ashing step and the second ashing step, damage to the Low-k film or the etching stopper film can be further suppressed, and as a result, the film quality of the Low-k film 208 can be kept in a better state.

Here, an example of the process conditions applied to such a plasma ashing process is shown. First, as processing conditions in the first ashing step in which the plasma ashing process is performed, for example, the pressure in the processing chamber 102 is adjusted to 20mTorr, the gap between the upper electrode 121 and the susceptor 105 is adjusted to 35mm, the high-frequency power (for example, 60MHz) applied to the upper electrode 121 is set to 300W, and the high-frequency power applied to the susceptor (lower electrode) 105 is set to 0W (that is, the high-frequency power is not applied to the susceptor 105). In addition, CO is used₂The gas being a process gas, CO₂The gas flow rate of (3) was set to 750 sccm. The pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 15Torr at the center portion and 40Torr at the edge portion. The temperature set in the processing chamber 102 was set to 60 ℃ for the upper electrode, 60 ℃ for the side wall, and 0 ℃ for the lower electrode.

As the processing conditions for performing the second ashing step, for example, the pressure in the processing chamber 102 is adjusted to 200mTorr, the gap between the upper electrode 121 and the susceptor 105 is adjusted to 50mm, the high-frequency power applied to the upper electrode 121 is set to 0W (i.e., the high-frequency power is not applied to the upper electrode 121), and the high-frequency power (e.g., the frequency of 2MHz) applied to the susceptor (lower electrode) 105 is set to 300W. In addition, CO is used₂The flow rate of the gas as a process gas was set to 700 sccm. The pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 10Torr at the center and 35Torr at the edge. The temperature set in the processing chamber 102 was set to 60 ℃ for the upper electrode, 50 ℃ for the side wall, and 40 ℃ for the lower electrode.

(experiment on the effect of removing reaction product in the first ashing step)

Here, the catalyst is practically used in the form of CO₂The experimental results of whether or not the reaction product such as fluoropolymer deposited on the inner wall of the processing chamber 102 can be removed by subjecting the process gas as a main body to the first ashing step will be described. Here, as a comparative example, O was used₂The same experiment was also performed for the first ashing process using the main process gas. In this experiment, SiO was formed over the entire surface of the wafer₂Film samples (hereinafter referred to as "SiO₂Cover sample (blanket) ") by measuring SiO₂Indirectly measuring the amount of film reduction accumulated on the inner wall of the treatment chamberThe amount of the reaction product such as the fluoropolymer described above. Namely, use is made of: the more reaction products such as fluoropolymers deposited on the inner wall of the chamber are removed by the first ashingstep, the more SiO₂SiO coating of the sample₂The less the film reduction of the film.

Specifically, first, the plasma etching process in the first to third etching steps is performed on a silicon substrate prepared as a dummy (dummy) substrate in the same processing line as described above, and thereby a reaction product such as a fluoropolymer is deposited on the inner wall of the processing chamber 102. Next, a first ashing step for removing reaction products such as fluoropolymers deposited on the inner wall of the processing chamber 102 is performed.

After the first ashing step is completed, the silicon substrate is taken out, and instead, SiO measured in advance is used₂SiO film thickness₂After the cover sample is carried into the processing chamber 102, the pressure in the processing chamber 102 is set to 15mTorr, the high-frequency power (for example, 60MHz) applied to the upper electrode 121 is set to 300W, the high-frequency power applied to the susceptor (lower electrode) 105 is set to 400W, and O is supplied into the processing chamber 102 at a flow rate of 300sccm₂Gas, processing for 60sec only, and SiO measurement₂Film reduction of the film.

O was used in the first ashing step of the experiment₂The process conditions in the case of the main process gas are as follows. That is, the pressure in the processing chamber 102 is adjusted to 20mTorr, and the gap between the upper electrode 121 and the susceptor 105 is adjustedThe total 35mm is set such that the high-frequency power (for example, 60MHz frequency) applied to the upper electrode 121 is 300W, and the high-frequency power applied to the susceptor (lower electrode) 105 is 0W (that is, the high-frequency power is not applied to the susceptor 105). In addition, Ar and O are used₂The flow ratio of each gas (Ar gas flow/O) is set as the process gas₂The gas flow rate of (3) was set to 550sccm/200 sccm. And SiO is mixed with₂The pressure of the back surface cooling gas (back surface gas) covering the sample was set to 15Torr at the center and 40Torr at the edge. The temperature set in the processing chamber 102 was set to 60 ℃ for the upper electrode, 60 ℃ for the side wall, and 0 ℃ for the lower electrode.

In the first ashing step of this experiment, CO was used₂The process conditions in the case of the main process gas are: the above-mentioned use is made of O₂The process gas under the process conditions in the case of the process gas mainly containing CO₂Gaseous monomer, CO₂The flow rate ratio of the gas was set to 750 sccm.

The measurement results of the film reduction amount thus obtained are shown in fig. 5. In fig. 5, a plot (plot) indicated by a circle is obtained by using Ar and O in the first ashing process₂The amount of film reduction in the case of the mixed gas of (1) as a process gas, and the drawing of the quadrangle is shown by using CO₂Gas monomer is used asIs the amount of reduction of the film in the case of processing gas. In this experiment, the first ashing process was performed for each process gas for 0sec (before the first ashing process), 30sec, and 60sec, and the amount of reduction in film was measured and plotted. For example, the amount of film reduction in the case of running the first ashing process for 60sec, using Ar and O₂The mixed gas (2) is 30.3 ANG when used as a process gas, and CO is used₂The gas monomer was 32.6 angstroms as the process gas.

In addition, the upper broken line in FIG. 5 is SiO₂SiO coating of the sample₂The initial value of the film thickness of the film, that is, the film thickness before the first ashing step (51.2 angstroms). The lower dotted line in FIG. 5 is a process chamber 102 which is cleaned without performing a plasma etching process and uses Ar and O₂As a processing gas, onlyThe film thickness (27.0 angstrom) in the case of performing the first ashing process for, for example, 1 minute. Therefore, the upper broken line (51.2 angstroms) in fig. 5 corresponds to the film thickness before removing the reaction product such as fluoropolymer deposited on the inner wall of the process chamber, and the lower broken line (27.0 angstroms) in fig. 5 corresponds to the film thickness after completely removing the reaction product such as fluoropolymer deposited on the inner wall of the process chamber.

As is clear from the experimental results shown in FIG. 5, Ar/O was used₂And the use of CO₂In the case of the gas alone, the amount of reduction of the film is almost the same, so even if CO is used₂A treatment gas of a gas monomer, Ar and O can be used₂The mixed gas of (3) similarly removes reaction products such as fluoropolymers deposited on the inner wall of the chamber.

Next, the following description will discuss the case where CO is used₂The plasma emission spectrum in the processing chamber was measured after the first ashing step was performed on the main process gas. In the experiment shown in FIG. 5, CO was used for the utilization₂SiO after the first ashing step in which the process gas of the gas monomer was run for 60sec only₂Coating the sample, when determining its SiO₂When the amount of film reduction was observed, the generation of O was measured₂Fig. 6 shows the results of plasma emission spectra in the processing chamber during plasma processing.

In addition, as a comparative example, O was generated in a clean processing chamber in which a reaction product such as fluoropolymer was not deposited on the inner wall of the processing chamber₂In the case of plasma, the plasma emission spectrum in the processing chamber was measured, and the results are shown superimposed in fig. 6. That is, in fig. 6, a graph indicated by a thick line is a plasma emission spectrum of a clean processing chamber, and a graph indicated by a thin line is a plasma emission spectrum of a processing chamber after a first ashing process is performed after a plasma etching process.

In fig. 6, the vertical axis represents emission intensity and the horizontal axis represents wavelength. The wavelength range is 500 nm-800 nm. Further, the plasma luminescence spectrum was measured using a spectroscope.

According to the experimental results shown in fig. 6, CO was used after the plasma etching treatment was performed₂Since the plasma emission spectrum of the chamber in which the first ashing step was performed with the single process gas was substantially the same as that of the chamber in which the inner wall of the chamber was cleaned without deposition of the reaction product such as fluoropolymer, it was found that CO was used for the plasma emission spectrum₂The first ashing step is performed using a process gas mainly composed of a gas, and reaction products such as fluoropolymers deposited on the inner wall of the chamber by the plasma etching process are reliably removed. Further, other elements do not remain in the processing chamber, and the processing chamber is in the same state as a clean processing chamber.

(experiment on the effect of suppressing damage to Low-k film in the first ashing step)

Next, the results of experiments conducted on the effect of the first ashing step to suppress damage to the Low-k film will be described. Here, the wafer 200 shown in fig. 3 after the above-described plasma etching treatment was performed using the plasma processing apparatus 100of the present embodiment was subjected to the first ashing step, and the degree of damage to the Low-k film was measured.

In this experiment, the wafer 200 as a sample was immersed in a hydrofluoric acid (HF) solution, and the degree of damage to the Low-k film by the first ashing step was determined based on the amount of etching of the Low-k film at that time. This determination method utilizes the property that: the Low-k film having good film quality is insoluble in hydrofluoric acid, and the Low-k film having a composition changed by dissociation of C (carbon atom) or the like is soluble in hydrofluoric acid. This determination method will be described in detail below with reference to fig. 7.

When the wafer 200 shown in fig. 2 is subjected to a plasma etching process, a groove 210 is formed on the Low-k film 208 of the wafer 200 as shown in fig. 3. Next, the wafer 200 shown in fig. 3 is subjected to a first ashing process. In this first ashing step, the photoresist film 202 is not removed, and thus the film structure of the wafer 200 remains the same as that of fig. 3. Fig. 7(a) shows the wafer 200 after the first ashing step.

However, when the wafer 200 after the first ashing step shown in fig. 7(a) is immersed in a hydrofluoric acid solution, if the exposed wall of the Low-k film 208 is damaged by the first ashing step, the exposed wall of the Low-k film 208 dissolves as shown in fig. 7 (b).

The dissolution loss Δ d corresponds to the range of the Low-k film 208 in which the composition changes due to dissociation of C (carbon atom) or the like, and the greater the dissolution loss Δ d, the greater the damage to the Low-k film 208 by the first ashing treatment. As shown in fig. 7, the dissolution loss Δ d is expressed as a change in the groove width (or the opening diameter of the hole) of the groove (CD (Critical Dimensions) shift). Therefore, in the experiment of the first ashing step, the dissolution loss Δ d was defined as the groove width (or hole diameter) d of the groove of the Low-k film 208 before immersion in the hydrofluoric acid solution₀The width (or diameter) d of the groove corresponding to the Low-k film 208 immersed in the hydrofluoric acid solution₁Difference (Δ d ═ d)₁-d₀)。Then, the degree of damage of the Low-k film was determined by using the dissolution loss Δ d as the CD offset.

In the method for determining damage of the Low-k film, CO used in the first ashing step is measured₂The results of the damage (CD shift amount) of the Low-k film in the case of the main process gas will be described. Here, as comparative examples, the CD shift amount after the plasma etching before the first ashing step and the CD shift amount used in the first ashing step were also set to O₂The CD shift amount in the case of the main process gas was measured.

O is used in the first ashing step₂The process conditions in the case of the main process gas are as follows. That is, the pressure in the processing chamber 102 is set to 20mTorr, the high-frequency power (for example, 60MHz) applied to the upper electrode 121 is set to 300W, and the high-frequency power applied to the susceptor (lower electrode) 105 is set to 0W (that is, the high-frequency power is not applied to the susceptor 105). In addition, Ar and O are used₂The flow ratio of each gas (Ar gas flow/O) is set as the process gas₂The gas flow rate of (3) was set to 550sccm/200 sccm. The processing time in the first ashing step was set to 30 sec.

In addition, CO is used in the first ashing step₂The process conditions in the case of the main process gas are: the above-mentioned use is made of O₂Process gas under process conditions in the case of a process gas mainly composed of a gasChange to CO₂Gaseous monomer, CO₂The flow rate of the gas was set to 750 sccm. The processing time in the first ashing step was set to 45 sec.

The measurement results of the CD shift amount thus obtained are shown in fig. 8. In FIG. 8, the amount of CD shift indicating the degree of damage of the Low-k film is shown as a bar graph. According to the measurement results shown in FIG. 8, the measured value is expressed as CO₂The CD offset after the first ashing step using a single gas as a process gas is reduced to Ar and O₂The mixed gas (2) is substantially 50% of the CD shift amount after the first ashing process of the process gas. Therefore, it can be seen that: using CO₂In the case of using a gaseous monomer as the processing gas, Ar and O are used₂The effect of suppressing damage to the Low-k film is greater in the case of the mixed gas of (2) as a process gas.

Furthermore, it can be seen that: with CO₂Since the CD shift amount after the first ashing step using a single gas as a process gas is substantially the same as the CD shift amount before the first ashing step, CO is used for the operation₂In the first ashing step in which a gas monomer is used as a process gas, a reaction product such as a fluoropolymer deposited on the inner wall of the chamber can be removed without causing any damage to the Low-k film.

(experiments on other parameters of the first ashing Process)

Next, various parameters of the ashing process conditions were changed, and reference was made to FIG. 3The experimental result of the first ashing process performed on the wafer 200 after the plasma etching process of (1) will be described with respect to the optimum process conditions that can improve the effect of reducing the damage to the Low-k film 208. In this experiment, the pressure in the chamber, the high-frequency power (upper power) applied to the upper electrode, the electrode gap between the upper electrode 121 and the susceptor (lower electrode) 105, and CO were measured₂/(CO₂+ Ar) flow ratio (%) was set to 3 levels, and the ashing conditions (NO 1to NO9) shown in table 1 below were formed by a combination of these levels, and the first ashing step was performed under each of the ashing conditions (NO 1to NO 9).

Further, the pressure of the backside cooling gas (backside gas) of the wafer 200 was fixed to 10Torr at the center and 35Torr at the edge, and the upper electrode was fixed to 60 ℃, the side wall to 50 ℃ and the lower electrode to 40 ℃ at the set temperature in the processing chamber 102.

[ TABLE 1]

The results obtained by the experiment of the first ashing step will be described. First, the relationship between the chamber pressure and the CD shift amount is shown in fig. 9. Specifically, fig. 9 is a graph in which the CD shift amounts at the process chamber pressures of 30mTorr, 20mTorr, and 10mTorr in the above table 1 are plotted as broken lines. That is, in fig. 9, the average value of the CD shift amount for each level of the chamber pressure is plotted. From the experimental results of fig. 9, the CD shift amount was almost the same in the range of the chamber pressure of 10mTorr to 30mTorr, and favorable results were obtained that the CD shift amount could be suppressed to approximately 20nm or less. Therefore, the pressure in the chamber is preferably 30mTorr or less.

Next, fig. 10 shows the relationship between the high-frequency power (upper power) applied to the upper electrode and the CD shift amount. Specifically, fig. 10 is a graph in which the CD shift amounts when the upper power levels in table 1 are 400W, 800W, and 1200W are plotted as broken lines. That is, in fig. 10, the average value of the CD shift amounts for each level of the upper power is plotted. From the experimental results of fig. 10, it is understood that: in the range of 400W to 1200W, the CD shift amount tends to decrease slightly as the upper power is increased. Furthermore, the CD shift amount can be suppressed to about 20 nm.

The upper power (high-frequency power for plasma generation) and the frequency thereof are sufficient to be at least sufficient to ignite plasma. In contrast, the high-frequency power (high-frequency power for bias generation) applied to the lower electrode in the first ashing process is preferably not applied (0W).

Next, fig. 11 shows the relationship between the electrode gap between the upper electrode and the lower electrode and the CD shift amount. Specifically, fig. 11 is a graph in which the CD shift amounts at the electrode spacing levels of 30mm, 45mm, and 60mm in table 1 are plotted as broken lines. That is, in fig. 11, the average value of the CD shift amounts of the respective levels of the electrode interval is plotted. From the experimental results of fig. 11, it is understood that: in the range of 30mm to 60mm in the electrode interval, the smaller the CD shift amount tends to be. Furthermore, the CD shift amount can be suppressed to about 20nm or less.

Then, CO is introduced₂/(CO₂FIG. 12 shows the relationship between the flow rate ratio (%) of + Ar) and the amount of CD offset. Specifically, FIG. 12 shows the contents of CO in Table 1₂/(CO₂+ Ar) the CD shift amounts at 50%, 75%, 100% gradation of the flow rate ratio (%) are plotted as broken lines. That is, in FIG. 12, CO is plotted₂/(CO₂+ Ar) average value of CD shift amount for each level of flow ratio (%). From the experimentalresults of fig. 12, it is understood that: in CO₂/(CO₂+ Ar) flow rate ratio (%) was in the range of 50% to 100%, and the CD offset amounts were almost the same, and good results were obtained that the CD offset amount could be suppressed to approximately 20nm or less. In addition, from this experiment, it is found that: for example, in the first ashing step, CO is not used only₂In the case of a treatment gas of gaseous monomers, and in the case of using CO₂And CO in the case of a mixed gas of Ar and₂the case of the gas alone similarly suppresses the CD shift amount.

(second ashing Process experiment)

Next, the optimum (or optimum range) of the process conditions for maintaining the film quality of the Low-k film 208 in a good state will be described with reference to the experimental results after the second ashing process is performed on the wafer 200 shown in fig. 3 while changing various parameters. In addition, the experiment for finding the optimum process conditions for the second ashing step is not limited to the following description, and is performed by placing the wafer 200 having the grooves in the so-called clean processing chamber 102 in which the reaction product such as fluoropolymer is not deposited on the inner wall of the processing chamber 102. This is because the experimental result does not include the influence of the first ashing step.

In this experiment, as in the case of the experiment of the first ashing step described above, the wafer as a sample was immersed in a hydrofluoric acid (HF) solution, and the degree of damage to the Low-k film by the plasma ashing treatment was determined based on the amount of etching of the Low-k film at that time. This determination method will be described in detail below with reference to fig. 13.

When the wafer 200 shown in fig. 3 is subjected to the second ashing step, the photoresist film 202 is removed by the second ashing step, and thus the film structure of the wafer 200 is the same as that shown in fig. 4. Fig. 13(a) shows the wafer 200 after the second ashing step.

When the wafer 200 after the second ashing step shown in fig. 13(a) is immersed in a hydrofluoric acid solution, if the Low-k film 208 is damaged in the second ashing process, the exposed sidewall of the Low-k film 208 dissolves as shown in fig. 13 (b).

The dissolution loss amount Δ d corresponds to the range of the Low-k film 208 in which the composition changes due to dissociation of C (carbon atom) or the like, and as in the case of the first ashing step, the greater the dissolution loss amount Δ d, the greater the damage to the Low-k film 208 by the plasma ashing process. As shown in fig. 13, the dissolution loss Δ d is expressed as a change in groove width (or opening diameter of a hole) of the groove (CD shift). In practice, the CD offset of the grooves (or holes) may differ in the depth direction. Therefore, in the experiment of the second ashing step, the upper groove width (or upper aperture diameter) d of the Low-k film 208 after immersion in the hydrofluoric acid solution was measured_1tBottom slot width (or bottom aperture) d_1bAnd groove depth (or hole depth) d_1hThe dissolution loss amounts Δ d were obtained. Specifically, if the groove width (or the aperture diameter) of the Low-k film 208 before immersion in the hydrofluoric acid solution is d_otD represents a groove depth (or a hole depth)_ohThe amount of dissolution loss of the upper groove width (or upper hole diameter), the bottom groove width (or bottom hole diameter), and the groove depth (or hole depth), that is, the CD offset Δ d_1t、Δd_1b、Δd_1hRespectively as follows: Δ d_1t＝d_1t-d_ot、Δd_1b＝d_1b-d_ot、Δd_1h＝d_1h-d_oh. For example, mixing these CD offset Δ D_1t、Δd_1b、Δd_1hAverage value of (a) d₁The degree of damage of the Low-k film was determined.

(pressure dependency of treatment Chamber in second ashing Process)

The results of the experiment concerning the pressure dependence in the chamber in the second ashing step will be described using the above-described determination method. Here, the wafer 200 shown in fig. 4, on which the above-described plasma etching process was performed using the plasma processing apparatus 100 of the present embodiment, was subjected to the second ashing process with the pressure in the chamber changed, and the degree of damage (CD shift amount) to the Low-k film and the ashing rate (ashing rate) were measured.

In this experiment, the second ashing process was performed to measure the CD offset (Δ d) of the Low-k film 208 for the case where the chamber pressure was set to a Low pressure of 15mTorr and the case where the chamber pressure was set to a high pressure of 200mTorr_1t、Δd_1b、Δd_1h) And Ashing Rate (AR). The results of this experiment are shown in table 2 below.

Other process conditions for performing the second ashing process with the chamber pressure at 200mTorr are as follows. That is, the distance between the upper electrode 121 and the susceptor (lower electrode) 105 was adjusted to 55mm, the high-frequency power applied to the upper electrode 121 was set to 0W (i.e., the high-frequency power was not applied to the upper electrode 121), and the high-frequency power (e.g., frequency 2MHz) applied to the susceptor (lower electrode) 105 was set to 300W. In addition, CO is used₂The flow rate of the process gas was set to 700 sccm. The pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 10Torr at the center and 35Torr at the edge. The set temperature in the processing chamber 102 was set to 60 ℃ for the upper electrode, 50 ℃ for the side wall, and 40 ℃ for the lower electrode. The processing time in the second ashing step was set to 44 sec.

Other process conditions for performing the second ashing step with the chamber pressure set to a low pressure of 15mTorr are as follows. That is, the distance between the upper electrode 121 and the susceptor (lower electrode) 105 was adjusted to 55mm, and the high frequency applied to the upper electrode 121 was adjustedThe power (frequency 60MHz) was 500W, and the high-frequency power (frequency 2MHz) applied to the susceptor (lower electrode) 105 was 100W. In addition, CO is used₂The flow rate of the gas as a process gas was set to 300 sccm. Further, the pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 10Torr at the center portion and 35Torr at the edge portion. The set temperature in the processing chamber 102 was set to 60 ℃ for the upper electrode, 50 ℃ for the side wall, and 40 ℃ for the lower electrode. The processing time in the second ashing step was set to 66 sec.

[ TABLE 2]

From the experimental results shown in table 2, it is understood that in the range where the chamber pressure is 200mTorr or less, the chamber pressure is high, the CD shift amount is small, and the damage to the Low-k film 208 is also reduced. In addition, when the pressure in the chamber is 200mTorr, it is needless to say that the CD shift amount becomes a lower value than that of the conventional art even if the pressure in the chamber is reduced to about 15 mTorr. As is clear from the experimental results shown in table 2, the Ashing Rate (AR) is increased due to the high pressure in the chamber, and the ashing can be performed at a higher rate. Therefore, the pressure in the chamber in the second ashing step is preferably high.

In addition, for other samples composed of a Low-k film having a lower dielectric constant value than that of the Low-k film of the wafer 200 (which is a film having an etching stopper film composed of SiC film, a porous type Low-k film composed of MSQ film, SiO)₂A wafer having a film structure in which hard masks such as films are sequentially stacked, grooves are formed in a porous Low-k film), and a second ashing process is performed by changing the pressure in the chamber in the same manner as described above to measure the CD shift amount. However, the CD shift amount at this time is determined using a sample having an etching stopper film, and therefore, it is used as the amount of change in the groove width (or the pore diameter) defined in the experiment of the first ashing step. The results are shown in fig. 14. In this experiment, the second ashing step was also performed to measure the CD shift amount in the range where the chamber pressure exceeded 200 mTorr.

As is clear from the experimental results shown in fig. 14, the pressure in the chamber was as high as about 200mTorr, and the CD shift amount was small, and therefore, the same tendency was observed as in the case shown in table 2. However, it can be seen that: if the pressure in the chamber exceeds 200mTorr, the CD offset gradually increases, and at 400mTorr or more, the CD offset tends to increase sharply. Therefore, the pressure in the chamber in the second ashing step is preferably high as described above, but the pressure in the chamber is preferably less than 400mTorr from the viewpoint of the effect of suppressing damage to the Low-k film 208.

(frequency dependence of second radio frequency Power in thesecond ashing step)

Next, the experimental result of the frequency dependence of the second rf power applied to the susceptor (lower electrode) 105 in the second ashing step will be described. Here, the plasma processing apparatus 100 of the present embodiment was used to perform the second ashing process by changing the frequency of the second rf power again for the same sample as the wafer 200, and measure the degree of damage (CD shift amount) to the Low-k film and the ashing rate.

In this experiment, the second ashing process was performed to measure the CD shift amount (Δ d) of the Low-k film 208 when the frequency of the second high-frequency power was set to 2MHz and 13.56Hz_1t、Δd_1b、Δd_1h) And Ashing Rate (AR). The results of this experiment are shown belowTable 3 below.

Other processing conditions for performing the second ashing process with the frequency of the second rf power set to 2MHz are as follows. That is, the distance between the upper electrode 121 and the susceptor (lower electrode) 105 was adjusted to 55mm, the high-frequency power applied to the upper electrode 121 was set to 0W (i.e., the high-frequency power was not applied to the upper electrode 121), and the high-frequency power applied to the susceptor (lower electrode) 105 was set to 300W. In addition, CO is used₂The flow rate of the gas as a process gas was set to 700 sccm. Further, the pressure of the back surface cooling gas (back surface gas) of the wafer 200 was set to 10Torr at the center portion and 35Torr at the edge portion. The temperature set in the processing chamber 102 was set to 60 ℃ for the upper electrode, 50 ℃ for the side wall, andthe lower electrode was set at 40 ℃. The processing time in the second ashing step was set to 44 sec. In this case, the voltage Vpp of one cycle from peak (peak) to peak of the ac component of the second high-frequency power (2MHz, 300W) is 1300V. The Vpp changes in accordance with the state of plasma excited in the processing chamber, for example, a change in plasma density, and therefore can be used as an index of the plasma state.

In addition, as for other processing conditions when the second ashing process is performed with the frequency of the second high-frequency power set to 13.56MHz, the high-frequency power applied to the susceptor (lower electrode) 105 was 1100W, and the processing time in the second ashing process was 21 sec. The other processing conditions are the same as those in the case where the frequency of the second rf power is 2MHz, and therefore, the description thereof is omitted. In this case, the voltage Vpp of one cycle from peak (peak) to peak of the ac component of the second high-frequency power (13.56MHz, 1100W) is 1200V, which is substantially the same as the above-described case where the frequency of the second high-frequency power is 2 MHz.

[ TABLE 3]

From the experimental results shown in table 3, it is understood that in the range where the frequency of the second rf power is 13.56MHz or less, the frequency of the second rf power is high, the CD shift amount is slightly reduced, and the damage to the Low-k film 208 is also slightly reduced. In addition, in the range where the frequency of the second rf power is 13.56MHz or less, it is needless to say that the CD shift amount is a lower value than that of the conventional technique even if the frequency is reduced to about 2MHz in the case where the frequency of the second rf power is 13.56 MHz. As is clear from the experimental results shown in table 3, the frequency of the second high-frequency power is high, the ashing time is short, and the ashing can be performed at a higher rate. Therefore, thefrequency of the second rf power in the second ashing step is preferably high.

Thus, it is presumed that: the higher frequency of the second high-frequency power enables ashing at a higher rate because the higher frequency enables more ions (CO) to be used₂ ⁺Etc.) is ashed. That is to say that the first and second electrodes,since the plasma density becomes higher as the frequency becomes higher, the current easily flows and the voltage value decreases. Therefore, the second radio frequency power (power) needs to be increased so as not to decrease the voltage value. In the above specific example, the second high-frequency power was increased from 300W to 1100W. The second high-frequency power is larger, and ions (CO) generated by the plasma₂ ⁺Etc.) are also increased, more ions can be used for ashing.

As described above, the higher the frequency of the second high-frequency power, the higher the second high-frequency power needs to be, and the higher the second high-frequency power is, the higher the ashing speed can be performed. Further, the degree to which the magnitude of the second high-frequency power can be increased depends on the performance of the plasma processing apparatus, and therefore, the frequency of the second high-frequency power which is currently in practical use is more preferably 13MHz to 40 MHz.

In the present embodiment, CO is used₂The case where the gas is used as the process gas in the second ashing step has been described, but the gas is not limited thereto, and O may be used₂Gas, in addition, CO may also be used₂And O₂The mixed gas of (1).

(preferable treatment conditions for plasma ashing treatment)

Based on the above experimental results, the optimum process conditions for the plasma ashing process performed using the plasma processing apparatus 100 according to the first embodiment are shown in table 4 below.

[ TABLE 4]

As shown in table 4, the pressure in the chamber in the first ashing step is preferably 30mTorr or less. The reaction product-removing treatment gas is preferably CO₂However, CO may also be used₂And Ar. The first high-frequency power in the first ashing step may be set to any frequency as long as it is sufficient that at least plasma can be ignited. In contrast, the second high-frequency power is preferably 0W (not applied to the lower electrode).

In addition, in the second ashing process, the chamber pressure is preferably less than 400 mTorr. The ashing gas may use O₂Or CO₂Or any one of their mixed gases. The first high-frequency power in the second ashing step is most preferably 0W (not applied to the upper electrode), and if the first high-frequency power is applied, it is preferable that the power is as low as possible and the frequency is 27MHz or higher. On the other hand, the frequency of the second high-frequency power is preferably 13 to 40MHz, and the second high-frequency power is preferably determined according to the frequency.

By performing the plasma ashing process under such process conditions, damage to the Low-k film or the primary coating formed on the wafer can be suppressed to be lower than in the prior art. In particular, the first ashing step has a large effect of suppressing damage to the Low-k film. In addition, ashing can be performed at a higher rate in the second ashing process.

(example of the configuration of the plasma processing apparatus according to the second embodiment)

Next, a configuration example of a plasma processing apparatus according to a second embodiment of the present invention will be described with reference to the drawings. Fig. 15 shows a schematic configuration of a plasma processing apparatus 300 according to a second embodiment. The plasma processing apparatus 300 shown in fig. 15 is a plasma processing apparatus of the following type: a first high-frequency power (high-frequency power for plasma generation) having a high frequency of, for example, 40MHz and a second high-frequency power (high-frequency power for bias generation) having a low frequency of, for example, 3.2MHz are superimposed and applied to one electrode (lower electrode) serving also as a mounting table. The plasma ashing method according to the present invention can also be applied to the plasma processing apparatus 300 of this type.

As shown in fig. 15, the plasma processing apparatus 300 includes a processing chamber 302 including a grounded and airtight processing container 304. In the processing chamber 302, a conductive lower electrode 306 also serving as a mounting table on which a wafer W is mounted is disposed so as to be movable up and down. The lower electrode 306 is maintained at a predetermined temperature by a temperature adjustment mechanism (not shown), and a heat transfer gas is supplied between the wafer W and the lower electrode 306 at a predetermined pressure from a heat transfer gas supply mechanism (not shown). An upper electrode 308 is formed at a position facing the mounting surface of the lower electrode 306.

A gas inlet 332 connected to a gas supply source (not shown) is formed in an upper portion of the processing chamber 302 to introduce a predetermined processing gas into the processing chamber 302. Is introduced intoThe process gas introduced into the process chamber 302 is introduced onto the wafer W through a plurality of gas outlets 309 formed in the upper electrode 308. For example CF₄Gas, CHF₃Gas, C₄F₈Gas, O₂Gas, He gas, Ar gas, N₂Gases, and mixtures thereof, may be introduced into the process chamber 302 as process gases.

An exhaust pipe 336 connected to an exhaust valve and an exhaust mechanism (not shown) is provided at a lower portion of the processing chamber 302. The process chamber 302 is evacuated through the exhaust pipe 336 and maintained at a predetermined vacuum level, for example, 50 mTorr. Further, a magnet 330 is provided on a side surface of the processing chamber 302, and a magnetic field (multi-pole magnetic field) for confining plasma is formed near the inner wall of the processing chamber 302 by the magnet 330. The strength of the magnetic field is variable.

A power supply device 312 that supplies power of 2 frequencies overlapping is connected to the lower electrode 306. The power supply device 312 includes a first power supply unit 314 that supplies first high-frequency power of a first frequency, and a second high-frequency power supply unit 316 that supplies second high-frequency power of a second frequency lower than the first frequency.

The first power supply mechanism 314 includes a first filter 318, a first matching unit 320, and a first power supply 322, which are connected in this order from the lower electrode 306 side. The first filter 318 prevents the power component of the second frequency from entering the first matching unit 320. The first matching unit 320 matches the first high-frequency power component. The first frequency is for example 100 MHz.

The second power supply mechanism 316 includes a second filter 324, a second matching unit 326, and a second power source 328, which are connected in this order from the lower electrode 306 side. The second filter 324 prevents the power component of the first frequency from entering the second matching unit 326 side. The second matching unit 326 matches the second high-frequency power component, and the second frequency is, for example, 3.2 MHz.

In the plasma processing apparatus 300 configured as described above, the process gas introduced into the processing chamber 302 is changed into a plasma state by the 2 kinds of high-frequency power output from the power supply 312 and the horizontal magnetic field formed by the magnet 330, and the etching process and the ashing process are performed on the wafer W by the energy of the ions and radicals accelerated by the generated self-bias.

(specific example of applying treatment to wafer)

The plasma processing apparatus 300 of the present embodiment configured as described above performs, for example, etching processing on the wafer 200 shown in fig. 3 and continuously performs ashing processing in the same processing chamber, as in the plasma processing apparatus 100 of the first embodiment shown in fig. 1.

Here, a specific example of the plasma etching process will be described. Here, for example, the plasma etching process is performed by sequentially performing the first to third etching steps. First, atIn the first etching step, the anti-reflection film 204 is etched using the patterned photoresist film 202 as a mask. As the processing conditions for performing the first etching step, for example, the pressure in the processing chamber 302 is adjusted to 10mTorr, the first high-frequency power (for example, 100MHz) applied from the first power source 322 to the lower electrode 306 is 1500W, and the second high-frequency power (for example, 3.2MHz) applied from the second power source 328 to the lower electrode 306 is 0W (that is, the second high-frequency power is not applied). In addition, CF is used₄As a process gas.

Next, in the second etching step, the protective film 206 and the Low-k film 208 are etched using the patterned photoresist film 202 as a mask. As the processing conditions for performing the second etching step, for example, the pressure in the processing chamber 302 is adjusted to 50mTorr, the first high-frequency power (for example, 100MHz) applied from the first power source 322 to the lower electrode 306 is set to 2000W, and the second high-frequency power (for example, 3.2MHz) applied from the second power source 328 to the lower electrode 306 is set to 200W. In addition, CF is used₄And Ar as a process gas.

By performing the above first and second etching processes, for example, as shown in fig. 3, a groove 210 is formed on the Low-k film 208. Next, in the plasma etching process, a plasma ashing process for removing the photoresist film 202 is performed on the wafer 200 in the same processing chamber 302.

According to the plasma processing method in which 2 kinds of high-frequency power are applied to the lower electrode in a superimposed manner using the plasma processing apparatus 300, the plasma density and the bias voltage can be independently controlled. Further, since the high-frequency power is applied only to the lower electrode and the high-frequency power does not need to be applied to the upper electrode, there is an advantage that the apparatus structure is not complicated.

However, in the plasma processing method in which 2 kinds of high-frequency power are applied to the lower electrode in a superimposed manner, after etching the Low-k film using a resist film as a mask using a processing gas containing F (fluorine), in the same processing chamber, if O is used₂When the resist film is ashed by the main process gas, the bias is generated by the first high-frequency power even if the second high-frequency power is set to 0W. In the ashing, fluorine used in the plasma etching process remains in the chamber, and fluorine is accelerated in the direction of the Low-k film and the underlying film by the bias voltage, thereby possibly reducing the Low-k film or the underlying film.

In this regard, the plasma ashing process according to the present invention is performed using CO in the first ashing process₂Since the resist film can be removed in the second ashing step after the fluorine remaining in the processing chamber is removed by the main processing gas, the occurrence of the fluorine residue on the Low-k film or the primary coating film can be suppressedThe damage of (2).

(first high-frequency Power and second high-frequency Power)

When the plasma ashing process is performed using the plasma processing apparatus 300 of the type in which 2 kinds of powers having different frequencies are applied to the lower electrode, the first high-frequency power and the second high-frequency power are preferably set as follows.

First, the frequency of the first high-frequency power in the first ashing step is preferably set to a frequency at which plasma ignition can be performed even at a low pressure in the chamber of 30mTorr or less. Specifically, the frequency is preferably 13MHz or more. The first high-frequency power is preferably set according to the frequency. The second rf power in the first ashing step is preferably 0W.

The frequency of the first rf power in the second ashing step is preferably 13MHz to 40 MHz. In this case, the second high-frequency power is preferably set to 0W, but the second high-frequency power may be applied. In this case, the damage to the Low-k film 208 when the first high-frequency power is set to 13.56MHz and the second high-frequency power is set to 0W is the same as the experimental results shown in table 3 when the second high-frequency power applied to the lower electrode in the plasma processingapparatus 100 is set to 13.56 MHz. This also makes it possible to suppress damage to the Low-k film 208 lower than in the prior art, shorten the ashing time, and perform ashing at a higher rate.

In the plasma processing apparatus 300, the first high-frequency power is applied to the lower electrode, and therefore, the frequency of the first high-frequency power in the second ashing step can be set to 40MHz or higher. This is because of the following reason, for example. That is, in the plasma processing apparatus 300 shown in fig. 15, since the first high-frequency power is applied to the lower electrode, the plasma is concentrated directly above the wafer, and therefore, the ion increment number is increased as compared with the case where the first high-frequency power is applied to the upper electrode as in the plasma processing apparatus 100 shown in fig. 1.

In this case, ashing is mainly performed by the ions, but the ions lose energy on the wafer surface, and thus the film formed on the wafer is less susceptible to the ashing. Therefore, even if the frequency of the first high-frequency power applied to the lower electrode is increased to increase the power of the first high-frequency power, the Low-k film 208 is less likely to be affected by the ashing.

In contrast, if the frequency of the first rf power applied to the upper electrode 121 of the plasma processing apparatus 100 shown in fig. 1 is set to 40MHz or higher to increase the power of the first rf power, the Low-k film 208 is damaged more. This is because of the following reason, for example. That is, since the first high frequency power is applied to the upper electrode 121 to generate plasma, the plasma is dense in the vicinity of the upper electrode 121 and is thin in the vicinity of the wafer apart from the upper electrode 121. Therefore, radicals are likely to be generated in the vicinity of the upper electrode 121,but the radicals have a long lifetime, and therefore, the radicals increase in the vicinity of the wafer.

In the case of ashing by radicals, unlike the above ions, not only the surface of the wafer is ashed but also the film is ashed. Thus, if the power of the first rf power applied to the upper electrode is increased, the number of radicals increases, and the damage to the Low-k film 208 increases. Further, it can be considered that: when the power of the first high-frequency power applied to the lower electrode is increased, the radical increases, the ashing rate increases, and the ashing time is shortened, so that the Low-k film 208 is less likely to be affected by damage.

In addition, since the plasma density rapidly increases when the frequency of the first high-frequency power of the second ashing process is 40MHz or more, it is preferable to accelerate the plasma by setting the frequency of the second high-frequency power to 13MHz or less in order to increase the ion energy (assist). However, depending on the frequency of the first high-frequency power, the frequency of the second high-frequency power may be set to 0W.

Here, the experimental results of performing the second ashing process with the frequency of the first rf power set to 100MHz and the frequency of the second rf power set to 3.2MHz are described. Here, the second ashing process was performed on the wafer 200 shown in fig. 4 using the plasma processing apparatus 300 of the present embodiment, and the degree of damage to the Low-k film (CD shift amount) and the ashing rate were measured. The results of this experiment are shown in table 5 below.

In addition, other processing conditions for performing the second ashing step in this experiment are as follows. That is, the pressure in the chamber is set to 50mTorr, the first high-frequency power applied to the lower electrode is set to 400W, and the second high-frequency power applied to the lower electrode is set to 300W. In addition, CO is used₂The flow rate of the process gas was set to 700sccm, and the magnetic field strength was set to 300G. The pressure of the back side cooling gas (back side gas) of the wafer 200 is set to be middleThe core was set at 10Torr, and the edge was set at 50 Torr. The set temperature in the processing chamber 102 was 50 ℃ for the upper electrode, 60 ℃ for the side wall, and 40 ℃ for the lower electrode. The processing time in the second ashing step was set to 44 sec.

[ TABLE 5]

From the experimental results shown in table 5 above, it can be seen that: even if the first high-frequency power is increased to 100MHz, the CD offset is sufficiently small, and the damage to the Low-k film 208 is small. Further, from the experimental results shown in table 5 above, it is clear that: the Ashing Rate (AR) also becomes large, and ashing can be performed at a higher rate. Therefore, in the plasma processing apparatus 300, the frequency of the first high-frequency power in the second ashing step is preferably 40MHz or more.

Note that the optimum ranges of the process conditions other than the first high-frequency power and the second high-frequency power, for example, the chamber pressure, the process gas, and the like, in the plasma ashing process performed in the plasma processing apparatus 300 are substantially the same as those in the case of the plasma processing apparatus 100 shown in fig. 1, and therefore, the description thereof will be omitted.

The preferred embodiments of the present invention have been described above with reference to the drawings, but it is needless to say that the present invention is not limited to these examples. It should be understood that: various modifications and alterations that can be made by those skilled in the art within the scope of the claims will be apparent, and these are also within the technical scope of the present invention.

Industrial applicability

The present invention can be applied to a plasma ashing method for removing a resist film on an object to be processed.

Claims (20)

1. A plasma ashing method for removing a resist film in a processing chamber after performing a process for etching a part of a low dielectric constant film on an object to be processed in the processing chamber using a patterned resist film as a mask, the plasma ashing method comprising:

a first ashing step of supplying a gas containing at least CO into the processing chamber₂Removing a reaction product of the gas from the processing gas, applying a high-frequency power for plasma generation to generate a plasma of the reaction product removing processing gas, and removing the reaction product adhering to the inner wall of the processing chamber; and

and a second ashing step of supplying an ashing gas into the processing chamber, applying a high-frequency power for plasma generation, generating plasma of the ashing gas, and removing the resist film.

2. The plasma ashing process of claim 1, wherein:

the reaction product removal treatment gas is CO₂A gas.

3. The plasma ashing process of claim 1, wherein:

the reaction product removal process gas contains CO₂Gases and inert gases.

4. The plasma ashing process of claim 1, wherein:

the pressure in the processing chamber in the first ashing step is 30mTorr or less.

5. The plasma ashing process of claim 1, wherein:

the ashing process gas comprises O₂Gas and CO₂Either one or both of the gases.

6. The plasma ashing process of claim 1, wherein:

the first ashing step is performed without applying a bias generating high-frequency power,

the second ashing step is performed in a state where a bias generating high-frequency power is applied.

7. The plasma ashing process of claim 1, wherein:

the Low dielectric constant film is a porous type Low-k film.

8. A plasma ashing method for removing a resist film in a processing chamber after performing a process of etching a part of a low dielectric constant film on an object to be processed on a second electrode disposed to face a first electrode disposed in the processing chamber using a patterned resist film as a mask, the plasma ashing method comprising:

a first ashing step of supplying a gas containing at least CO into the processing chamber₂Removing a reaction product of a gas from the processing gas, applying a high-frequency power to the first electrode to generate a plasma of the reaction product-removed processing gas, and removing the reaction product adhering to the inner wall of the processing chamber without applyingthe high-frequency power to the second electrode; and

and a second ashing step of supplying an ashing gas into the processing chamber, applying a high-frequency power to the first electrode to generate plasma of the ashing gas, and removing the resist film while applying the high-frequency power to the second electrode.

9. The plasma ashing process of claim 8, wherein:

in the second ashing step, the frequency of the high-frequency power applied to the first electrode is the same as the frequency of the high-frequency power applied to the second electrode, and is 13MHz to 40MHz inclusive.

10. The plasma ashing process of claim 8, wherein:

in the second ashing step, the frequency of the high-frequency power applied to the first electrode is 27MHz or more, and the frequency of the high-frequency power applied to the second electrode is 13MHz or more and 40MHz or less.

11. The plasma ashing process of claim 8, wherein:

the pressure in the processing chamber in the second ashing step is 400mTorr or less.

12. A plasma ashing method for removing a resist film in a processing chamber after performing a process of etching a part of a low dielectric constant film on an object to be processed on a second electrode disposed to face a first electrode disposed in the processing chamber using a patterned resist film as a mask, the plasma ashing method comprising:

a first ashing step of supplying a gas containing at least CO into the processing chamber₂Reaction of gasesA product removing process gas for generating plasma of the reaction product removing process gas by applying a high-frequency power to the first electrode and removing the reaction product adhered to the inner wall of the process chamber in a state where the high-frequency power is not applied to the second electrode; and

and a second ashing step of supplying an ashing gas into the processing chamber, generating plasma of the ashing gas by applying a high-frequency power to the second electrode without applying a high-frequency power to the first electrode, and removing the resist film while applying a high-frequency power to the second electrode.

13. The plasma ashing process of claim 12, wherein:

in the second ashing step, the frequency of the high-frequency power applied to the second electrode is 13MHz to 40 MHz.

14. The plasma ashing process of claim 12, wherein:

the pressure in the processing chamber in the second ashing step is 400mTorr or less.

15. A plasma ashing method for removing a resist film in a processing chamber after performing a process of etching a part of a low dielectric constant film on an object to be processed disposed in the processing chamber and configured to be capable of superimposing a first high frequency power and a second high frequency power having a frequency lower than the first high frequency power, using the patterned resist film as a mask, the method comprising:

a first ashing step of supplying a gas containing at least CO into the processing chamber₂Removing a reaction product of a gas from a process gas, applying the first high-frequency power to the electrode to generate a plasma of the reaction product-removed process gas, and removing the reaction product adhering to the inner wall of the process chamber without applying a second high-frequency power to the electrode; and

and a second ashing step of supplying an ashing gas into the processing chamber, applying a first high-frequency power to the electrode to generate plasma of the ashing gas, and removing the resist film while applying a second high-frequency power to the electrode.

16. The plasma ashing process of claim 15, wherein:

the frequency of the first high-frequency power in the first ashing step is 13MHz or more.

17. The plasma ashing process of claim 15, wherein:

the frequency of the first high-frequency power in the first ashing step is 27MHz or more.

18. The plasma ashing process of claim 15, wherein:

the frequency of the first high-frequency power in the second ashing step is 13MHz to 100 MHz.

19. The plasma ashing process of claim 18, wherein:

the second high-frequency power in the second ashing step is 0W.

20. The plasma ashing process of claim 15, wherein:

in the second ashing step, the frequency of the first rf power is 40MHz or more, and the frequency of the second rf power is 13MHz or less.

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