JP2007080850A - Plasma ashing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress damage given to a low dielectric constant film (Low-k film) formed on a workpiece and a base film more than before. <P>SOLUTION: A plasma ashing method has a first ashing process for supplying reaction product removal raw gas comprising CO<SB>2</SB>gas into a treatment chamber 102, generating plasma of reaction product removal raw gas by applying high frequency power to an upper electrode 121, and removing a reaction product attached to an inner wall of the treatment chamber in a state where high frequency power is not applied to a lower electrode; and a second ashing process for supplying ashing raw gas into the treatment chamber, generating plasma of ashing raw gas by applying high frequency power to the upper electrode, and removing a resist film in a state where high frequency power is applied to the lower electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  For example, in a semiconductor manufacturing process, an etching process is performed using a predetermined processing gas using a resist film in which trenches and holes are patterned on the surface of an object to be processed such as a semiconductor wafer (hereinafter also referred to as “wafer”). After that, an ashing process for removing the remaining resist film is performed.

As such an ashing process, there is known a method (plasma ashing method) for removing a resist film by ashing by using a processing gas such as O ₂ (oxygen) gas, CO gas, CO ₂ gas, etc. (Patent Document) 1 and 2). Specifically, for example, by heating the wafer in the processing chamber and introducing O ₂ gas into the processing chamber to generate plasma, the activity of O (oxygen) radicals and the like generated when the O ₂ gas is turned into plasma. The resist film is removed by ashing with seeds.

  As described above, since the ashing process is performed after the etching process, if the etching process and the ashing process can be continuously performed in the same processing chamber, for example, the time for transferring the wafer to another processing chamber is omitted, and the entire process is performed. There are significant advantages such as shortening of processing time.

However, if, for example, a fluorine-containing processing gas (for example, a CF-based processing gas) is used as a processing gas in the etching process, a reaction product such as a fluorine polymer (for example, a CF-based polymer) may be deposited on the inner wall of the processing chamber. If the ashing process is continuously performed in this state, a reaction product such as fluorine polymer deposited on the inner wall of the processing chamber is re-dissociated and the film on the wafer is etched (memory effect). As a result, the performance of the semiconductor device formed on the wafer may be adversely affected. Such a phenomenon occurs not only when O ₂ gas is used as a processing gas for ashing, but also when CO ₂ gas or CO gas is used.

On the other hand, in order to suppress the occurrence of such a memory effect, there is a method of performing ashing processing in two steps (see, for example, Patent Document 3). In such an ashing process, first, in the first step, an oxygen plasma is generated by introducing O ₂ gas as a reaction product removing process gas into the process chamber without applying a bias voltage to the wafer, thereby generating an oxygen plasma in the process chamber. Reaction products such as fluorine polymer deposited on the inner wall are removed. Next, in the second step, a bias voltage is applied to the wafer, an ashing gas is introduced into the processing chamber, and the resist film on the wafer is removed. The process of removing the resist film in such two steps is called hybrid ashing.

JP 2003-59911 A JP 2001-189302 A Japanese Patent Laid-Open No. 11-145111 JP 2005-101289 A

  However, when a layer including a low dielectric constant film (hereinafter also referred to as “Low-k film”) is formed below the resist film, the hybrid film is simply exposed with the Low-k film exposed. If ashing is performed, the Low-k film may be damaged. Specifically, for example, when a reaction product such as a fluorine polymer deposited on the inner wall of the processing chamber is removed in the first step, a part of the fluorine such as an O (oxygen) radical generated in the processing chamber The film is re-dissociated by the influence and implanted into the Low-k film or the underlying film of the Low-k film, the Low-k film or the underlying film is etched, or C (carbon atoms) contained in the Low-k film There is a risk that the film quality may change due to desorption and the dielectric constant may increase.

  In this respect, it is possible to suppress damage to the low-k film and the base film by optimizing the process conditions of the first step and reducing the O (oxygen) radical density in the processing chamber (Patent Document). 4), there is a limit to further suppress damage to the Low-k film and the underlying film.

  Therefore, the present invention has been made in view of such problems, and the object of the present invention is to damage the low dielectric constant film (Low-k film) and the base film formed on the object to be processed. An object of the present invention is to provide a plasma ashing method that can be suppressed more than ever.

In order to solve the above-described problems, according to one aspect of the present invention, a process for etching a part of a low dielectric constant film is performed on a target object in a processing chamber using a patterned resist film as a mask. Then, a plasma ashing method for removing the resist film in the processing chamber, wherein a reaction product removing processing gas containing at least CO ₂ gas is supplied into the processing chamber, and a high frequency power for plasma generation is applied to react. A first ashing step for generating a plasma of a product removal processing gas to remove reaction products adhering to the inner wall of the processing chamber, supplying an ashing processing gas into the processing chamber, and applying a high frequency power for plasma generation And a second ashing step of generating a plasma of the ashing gas and removing the resist film. A laser ashing method is provided.

In this case, the reaction product removing process gas may be a single gas CO ₂ gas, or a mixed gas containing the CO ₂ gas and an inert gas. The pressure in the processing chamber in the first ashing process is preferably 30 mTorr or less. Further, the ashing gas includes, for example, one or both of O ₂ gas and CO ₂ gas. Preferably, the first ashing step is performed without applying a bias voltage generating high frequency power, and the second ashing step is preferably performed with a bias voltage generating high frequency power applied. The low dielectric constant film is, for example, a porous low-k film.

In the present invention, the processing gas containing CO ₂ gas is much less damaging to the low dielectric constant film and the base film formed on the object to be processed than the processing gas containing O ₂ gas. with attention, found that the reaction product is also adhered to the inner wall of the processing chamber by such a CO ₂ gas can be removed sufficiently, the process gas containing the CO ₂ gas as a product removal process gas in the first ashing step Applied. As a result, the damage to the low dielectric constant film and the base film of the object to be processed in the first ashing process can be greatly reduced as compared with the case where the processing gas containing O ₂ gas is used in the first ashing process. . In addition, since the reaction product is removed from the inner wall of the processing chamber by the first ashing process, the reaction product is re-dissociated in the subsequent second ashing process to damage the low dielectric constant film and the base film of the object to be processed. Nothing will happen.

In order to solve the above problems, according to another aspect of the present invention, a patterned resist is formed on an object to be processed on a second electrode disposed opposite to a first electrode disposed in a processing chamber. A plasma ashing method for removing the resist film in the process chamber after performing a process of etching a part of the low dielectric constant film using the film as a mask, wherein the reaction chamber contains at least CO ₂ gas. A product removal treatment gas is supplied, a high frequency power is applied to the first electrode to generate a plasma of a reaction product removal treatment gas, and the inner wall of the treatment chamber is not applied with the high frequency power to the second electrode. A first ashing step for removing reaction products adhering to the substrate, supplying an ashing gas into the processing chamber, and applying a high frequency power to the first electrode, There is provided a plasma ashing method comprising: a second ashing step of removing a resist film in a state in which a zigzag is generated and high frequency power is applied to the second electrode. According to this, even when the first ashing process and the second ashing process are performed in the processing chamber in which the first electrode and the second electrode are arranged to face each other, damage to the low dielectric constant film and the base film of the object to be processed is reduced. It can be greatly reduced.

  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 the frequency is preferably 13 MHz to 40 MHz. . In the second ashing step, the frequency of the high frequency power applied to the first electrode is preferably 27 MHz or more, and the frequency of the high frequency power applied to the second electrode is more preferably 13 MHz to 40 MHz. Furthermore, the pressure in the processing chamber in the second ashing step is preferably 400 mTorr or less. As a result, the frequency of the high-frequency power and the pressure in the processing chamber can be set within an optimum range, so that the low dielectric constant film and the base film formed on the object to be processed in the first ashing process and the second ashing process. Can be further reduced, and ashing can be performed at a higher speed in the second ashing step.

In order to solve the above problems, according to another aspect of the present invention, a patterned resist is formed on an object to be processed on a second electrode disposed opposite to a first electrode disposed in a processing chamber. A plasma ashing method for removing the resist film in the process chamber after performing a process of etching a part of the low dielectric constant film using the film as a mask, wherein the reaction chamber contains at least CO ₂ gas. A product removal treatment gas is supplied, a high frequency power is applied to the first electrode to generate a plasma of a reaction product removal treatment gas, and the inner wall of the treatment chamber is not applied with the high frequency power to the second electrode. A first ashing step for removing reaction products adhering to the first electrode, supplying an ashing gas into the processing chamber, and applying high frequency power to the second electrode without applying high frequency power to the first electrode. A plasma ashing method comprising: a second ashing step of applying an electric power to generate a plasma of an ashing treatment gas and removing the resist film in a state where a high frequency power is applied to the second electrode. Is done.

  As described above, in the second ashing process, plasma of the ashing gas may be generated by applying high frequency power to the second electrode without applying high frequency power to the first electrode. As a result, the plasma of the ashing gas can be generated immediately above the object to be processed, so that the amount of ions required for ashing can be increased and the resist film can be ashed 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 13 MHz to 40 MHz. The pressure in the processing chamber in the second ashing step is preferably 400 mTorr or less.

In order to solve the above-described problem, according to another aspect of the present invention, the first high-frequency power and the second high-frequency power having a frequency lower than the first high-frequency power can be superimposed and applied in the processing chamber. Plasma that removes the resist film in the processing chamber after performing a process of etching a part of the low dielectric constant film on the object to be processed on the configured electrode using the patterned resist film as a mask In the ashing method, a reaction product removal processing gas containing at least CO ₂ gas is supplied into the processing chamber, and the first high frequency power is applied to the electrode to generate a plasma of the reaction product removal processing gas. A first ashing step for removing a reaction product adhering to the inner wall of the processing chamber without applying a second high-frequency power to the electrode; and an ashing processing gas in the processing chamber. A second ashing step of removing the resist film in a state where a first high frequency power is applied to the electrode to generate plasma of an ashing gas and a second high frequency power is applied to the electrode. A plasma ashing method is provided. According to this, there is a case where the first ashing process and the second ashing process are performed in a processing chamber including an electrode that superimposes and applies the first high-frequency power and the second high-frequency power having a frequency lower than the first high-frequency power. Thus, damage to the low dielectric constant film and the base film formed on the object to be processed can be greatly reduced.

  Moreover, it is preferable that the frequency of the said 1st high frequency electric power in the said 1st ashing process is 13 MHz or more. In this case, it is preferable that the frequency of the first high-frequency power in the first ashing step is 27 MHz or more. Moreover, it is preferable that the frequency of the said 1st high frequency electric power in the said 2nd ashing process is 13 MHz or more and 100 MHz or less. In this case, the second high frequency power may be 0 W. Moreover, it is preferable that the frequency of the said 1st high frequency electric power in the said 2nd ashing process is 40 MHz or more, and the frequency of the said 2nd high frequency electric power is 13 MHz or less. As a result, the frequency of the high-frequency power and the pressure in the processing chamber can be set within an optimum range, so that the low dielectric constant film and the base film formed on the object to be processed in the first ashing process and the second ashing process. Can be further reduced, and ashing can be performed at a higher speed in the second ashing step.

In this specification, 1 Torr is (101325/760) Pa, 1 mTorr is (10 ⁻³ × 101325/760) Pa, and 1 sccm is (10 ⁻⁶ / 60) m ³ / 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) and a base film formed on a workpiece more than ever. Is.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

(Configuration example of plasma processing apparatus according to the first embodiment)
First, a configuration example of the plasma processing apparatus according to the 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 the first embodiment. The plasma processing apparatus 100 is a so-called parallel plate type plasma processing apparatus that includes 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 has a processing chamber 102 constituted by a processing container formed into a cylindrical shape made of aluminum whose surface is anodized (anodized), for example. The processing chamber 102 is grounded. A substantially cylindrical susceptor support base 104 for placing an object to be processed, for example, a semiconductor wafer (hereinafter also referred to as “wafer”) W, is provided at the bottom of the processing chamber 102 via an insulating plate 103 such as ceramic. It has been. A susceptor 105 constituting a lower electrode is provided on the susceptor support 104. A high pass filter (HPF) 106 is connected to the susceptor 105.

  Inside the susceptor support 104, a temperature control medium chamber 107 is provided. Then, a temperature control medium (for example, a refrigerant) is introduced into the temperature control medium chamber 107 through the introduction pipe 108, circulated, and discharged from the discharge pipe 109. By such circulation of the temperature control medium, the susceptor 105 can be adjusted to a desired temperature.

  The susceptor 105 is formed in a disc shape whose upper central portion is convex. On the susceptor 105, an electrostatic chuck 111 having substantially the same shape as the wafer W is provided. The electrostatic chuck 111 has a configuration in which an electrode 112 is interposed between insulating materials. The electrostatic chuck 111 is applied with a DC voltage of, for example, 1.5 kV from a DC power supply 113 connected to the electrode 112. As a result, the wafer W is electrostatically attracted to the electrostatic chuck 111.

  The insulating plate 103, the susceptor support 104, the susceptor 105, and the electrostatic chuck 111 are formed with a gas passage 114 for supplying a heat transfer medium (for example, a backside gas such as He gas) to the back surface of the wafer W. Has been. Heat transfer is performed between the susceptor 105 and the wafer W via the heat transfer medium, and the wafer W is maintained at a predetermined temperature.

  An annular focus ring 115 is disposed on the upper peripheral edge 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 ceramics or quartz, or a conductive material. By arranging 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 processing chamber 102 via an insulating material 122. The upper electrode 121 includes an electrode plate 124 that forms a surface facing the susceptor 105 and has a large number of discharge holes 123, and an electrode support 125 that supports 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 the constituent material of the electrode plate 124. The electrode support 125 is made of, for example, a conductive material such as aluminum whose surface is anodized. Note that the distance between the susceptor 105 and the upper electrode 121 can be adjusted.

  A gas inlet 126 is provided at the center of the electrode support 125 in the upper electrode 121. A gas supply pipe 127 is connected to the gas inlet 126. Further, a processing gas supply source 130 is connected to the gas supply pipe 127 via a valve 128 and a mass flow controller 129.

From the processing gas supply source 130, for example, an etching gas for plasma etching, a reaction product removal gas to be described later for ashing, an ashing gas, and the like are supplied as a processing gas. FIG. 1 shows only one processing gas supply system including a gas supply pipe 127, a valve 128, a mass flow controller 129, a processing gas supply source 130, and the like, but the plasma processing apparatus 100 includes a plurality of processing gases. A gas supply system is provided. For example, processing gases such as CF ₄ , O ₂ , N ₂ , CHF ₃ , CO ₂ , Ar, He, and Xe are independently controlled in flow rate and supplied into the processing chamber 102.

  An exhaust pipe 131 is connected to the bottom of the processing chamber 102, and an exhaust mechanism 135 is connected to the exhaust pipe 131. The exhaust mechanism 135 includes a vacuum pump such as a turbo molecular pump, and adjusts the inside of the processing chamber 102 to a predetermined reduced pressure atmosphere. A gate valve 132 is provided on the side wall of the processing chamber 102. By opening the gate valve 132, the wafer W can be loaded into the processing chamber 102 and the wafer W can be unloaded from the processing chamber 102.

  A first high-frequency power source 140 is connected to the upper electrode 121, and a first matching unit 141 is interposed in the power supply line. Further, 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 50 to 150 MHz. By applying the first high-frequency power having a high frequency to the upper electrode 121 in this way, a high-density plasma can be formed in a preferable dissociated state in the processing chamber 102, and plasma processing under a low-pressure condition is possible. Become. The frequency of the first high-frequency power of the first high-frequency power source 140 is preferably 50 to 80 MHz, and typically, the illustrated frequency of 60 MHz or the vicinity thereof is used.

  A second high-frequency power source 150 is connected to the susceptor 105 as the lower electrode, and a second matching unit 151 is inserted in the power supply line. The second high frequency power supply 150 can output second high frequency power (high frequency power for bias voltage generation) having a frequency in the range of several hundred kHz to several tens of MHz. By applying the second high frequency power having a frequency in such a range to the susceptor 105, an appropriate ion action can be given without damaging the wafer W. The frequency of the second high frequency power of the second high frequency power supply 150 is typically 2 MHz, 3.2 MHz, 13.56 MHz, or the like shown in the figure. In this embodiment, it is 2 MHz.

  The second high frequency power is normally used as a bias voltage generating high frequency power. However, when the second high frequency power is applied without applying the first high frequency power, the second high frequency power is used for generating plasma. It may be used as high frequency power. As a result, the plasma of the ashing gas can be generated immediately above the wafer, so that the amount of ions necessary for ashing described later can be increased, and the resist film can be ashed at a higher speed.

(Specific example of wafer film structure)
Next, a specific example of the film structure of a wafer to be etched and ashed by the plasma processing apparatus 100 shown in FIG. 1 will be described with reference to FIG.

  As shown in FIG. 2, a wafer 200 includes a low dielectric constant film (hereinafter referred to as “Low-k film”) 208, a protective film 206, an antireflection film (BARC) 204, and a photoresist film. A film structure 202 is sequentially stacked. Under the low dielectric constant film 208, a metal layer such as a Cu (copper) wiring layer and various semiconductor layers are provided on the wafer 200, in addition to an etching stop film made of a SiC material such as a SiCN film or a SiC film. You may form on the silicon substrate which comprises a main body.

  As a low dielectric constant material constituting the low-k film 208, for example, a porous low-k film (porous low-k film) is used. A porous structure such as a porous low-k film is adopted as an interlayer insulating film in order to cope with the problem of wiring delay accompanying the reduction of the design rule of a semiconductor integrated circuit. Thereby, the dielectric constant of the interlayer insulating film can be further reduced.

  As such porous low-k film, a porous coating system film having a siloxane structure such as HSQ (Hydrogen-Silses-Quioxane) or MSQ (Methyl-hydrogen-Silses-Quioxane), SiOCH film, etc. The CVD film is made porous. Of these, the SiOCH film is sometimes referred to as an SiOC film, and usually contains Si, O, C, and H as constituent elements. As the Low-k film 208 in this embodiment, a porous Low-k film made of a SiOCH film having a relative dielectric constant K = 2.5 is used, and the film thickness is 480 nm.

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

In addition, since the porous Low-k film makes the insulating film porous, there is a possibility that the adhesion with other films, film strength, and the like may be reduced. For this reason, when a porous Low-k film is used as the Low-k film 208, a protective film 206 is formed thereon. Examples of the protective film 206 include a SiCN film and a SiO ₂ film. As the protective film 206 in this embodiment, a SiCN film is used, and the film thickness is 120 nm. In addition, as a Low-k film | membrane formed on a wafer, although the porous Low-k film | membrane is mentioned as an example, it is not restricted to this.

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

  The antireflection film 204 functions to suppress the reflected light from the underlayer when the photoresist film 202 is exposed with KrF light. Thereby, finer patterning becomes possible. Note that the film thickness of the antireflection film 204 in this embodiment is 60 nm.

(Specific example of processing applied to wafer)
Here, a specific example of processing performed on the wafer 200 shown in FIG. 2 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 wafer 200 is subjected to plasma etching. Thus, the antireflection film 204, the protective film 206, and the low-k film 208 are etched to form the trench 210 (see FIG. 3). For example, the ratio of the line width to the line width of the trench 210 is 1: 2, and the line width is 200 nm. Subsequently, the plasma ashing process according to the present invention is performed on the wafer 200 in the same processing 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 executing the first to third etching steps. First, in the first etching process, the antireflection film 204 is etched using the patterned photoresist film 202 as a mask. As the process conditions for performing this first etching step, for example, the pressure in the processing chamber 102 is adjusted to 50 mTorr, the high frequency power applied to the upper electrode 121 is 1000 W, and the high frequency power applied to the susceptor (lower electrode) 105 is 100 W. Further, CF ₄ is used as a processing gas, and its flow rate is set to 100 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 10 Torr and the edge portion 35 Torr. The processing time of the first etching step is set to 60 seconds, for example.

Next, in the second etching step, the protective film 206 is etched using the patterned photoresist film 202 as a mask. As the process conditions for performing this second etching step, for example, the pressure in the processing chamber 102 is adjusted to 50 mTorr, the high frequency power applied to the upper electrode 121 is 500 W, and the high frequency power applied to the susceptor (lower electrode) 105 is 500 W. Further, a mixed gas of C ₄ F ₈ , Ar, and N ₂ is used as the processing gas, and the flow rate ratio of each gas (C ₄ F ₈ gas flow rate / Ar gas flow rate / N ₂ gas flow rate) is 5 sccm / 100 sccm. / 100 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 10 Torr and the edge portion 35 Torr. The processing time of the second etching process is set to 60 seconds, for example.

Next, in the third etching step, the low-k film 208 is etched. As the process conditions for performing this third etching step, for example, the pressure in the processing chamber 102 is adjusted to 75 mTorr, the high frequency power applied to the upper electrode 121 is 1000 W, and the high frequency power applied to the susceptor (lower electrode) 105 is 300W. Further, a mixed gas of CF ₄ and Ar is used as the processing gas, and the flow rate ratio of each gas (the gas flow rate of CF ₄ / the gas flow rate of Ar) is set to 100 sccm / 100 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 10 Torr and the edge portion 35 Torr. For example, the processing time of the third etching step is 70 seconds.

  By such plasma etching processes in the first to third etching steps, for example, a trench 210 is formed in the low-k film 208 as shown in FIG. The ratio between the line width and the line width of the trench 210 is, for example, 1: 2, and the line width is, for example, 200 nm. Following such a 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.

  By the way, when the plasma etching process as described above is performed, F (fluorine) contained in the processing gas adheres to the inner wall of the processing chamber 102 and gradually accumulates as a fluorine polymer. From this state, when the plasma ashing process is performed only for the purpose of removing the photoresist film 202, the fluorine polymer deposited on the inner wall of the processing chamber 102 is re-dissociated, and the Low-k film 208 is etched to form the width of the trench. And the depth will change.

  For this reason, in the plasma ashing process according to the present embodiment, a first ashing process for removing a reaction product such as a fluorine polymer (for example, CF-based fluorine polymer) deposited mainly on the inner wall of the processing chamber 102, and the photoresist film 202. The second ashing process is performed separately. First, the fluorine polymer deposited on the inner wall of the processing chamber 102 is removed by performing the first ashing process. Thus, in the subsequent second ashing process, the fluorine polymer is not re-dissociated and the low-k film 208 is not etched.

By the way, in the first ashing process of the plasma ashing process, if a conventional process gas mainly composed of O ₂ gas is used as a reaction product removal process gas, the low-k film or the low-k film is used. The underlying film (for example, an etching stop film) is easily damaged. For example, when the fluorine polymer attached to the inner wall of the processing chamber 102 is removed, a part of the fluorine is re-dissociated by the O radical generated in the processing chamber 102 and is driven into the Low-k film or the base film. , The low-k film or the base film may be scraped, or the film quality of the low-k film may deteriorate and the dielectric constant may increase. In addition, the low-k film is altered due to desorption of C (carbon atoms) contained in the low-k film by O radicals generated in the processing chamber 102 by the O ₂ -containing plasma in the first ashing process, and the result In particular, the dielectric constant (k value) of the low-k film may be increased.

  In this case, it is possible to suppress damage to the Low-k film and the base film by optimizing the process conditions of the first ashing process and reducing the O (oxygen) radical density in the processing chamber 102. , There is a limit to further suppress damage to the Low-k film and the underlying film.

For this reason, the present inventors reviewed the reaction product removal processing gas used in the first ashing process and repeated experiments. As a result, in the first ashing process, the processing gas mainly composed of CO ₂ was treated with the reaction product removal processing. It has been found that reaction products such as fluorine polymer deposited (deposited) on the inner wall of the processing chamber 102 can be sufficiently removed by using it as a gas as well as a processing gas mainly composed of O ₂ .

For example, when a processing gas mainly composed of CO ₂ is converted into plasma, CO ₂ ⁺ (CO ₂ ions) are generated, and the CO ₂ ions are accelerated by the potential difference between the plasma potential and the inner wall of the processing chamber 102 and collide with the inner wall. Fluorine polymer (for example, CF polymer) that is dispersed on the inner wall surface and vaporized as CO gas or COF ₂ gas by a chemical reaction such as the following chemical formulas (1-1) and (1-2) and deposited on the inner wall of the processing chamber 102. It is inferred that the fluorine-based polymer) is removed.

CO ₂ ⁺ (CO ₂ ion) + CF ₂ + e ⁻ (electron) → CO ↑ + COF ₂ ↑
... (1-1)

CO ₂ ⁺ (CO ₂ ion) + C + e ⁻ (electron) → 2CO ↑
... (1-2)

Further, when a processing gas mainly composed of CO ₂ is used in the first ashing process, the effect of suppressing damage to the Low-k film and the base film is greater than when a processing gas mainly composed of O ₂ is used. I also understood that. This is because, when a processing gas mainly composed of CO ₂ is used, O radicals are less likely to be generated than when a processing gas mainly composed of O ₂ is used, and CO ₂ is very stable, In this case, it is presumed that the low-k film and the base film are not easily damaged because they do not have the ability to desorb C (carbon atoms) from the low-k film.

Therefore, in the plasma ashing processing method according to the present invention, the processing gas mainly composed of CO ₂ gas is used as the reaction product removal gas in the first ashing step. As a result, damage to the Low-k film and the base film (for example, etching into the Low-k film and the deterioration of the quality of the Low-k film) can be suppressed more than before. Further, by removing the deposits such as fluorine polymer deposited on the inner wall of the processing chamber 102 by performing the first ashing process, the processing gas mainly composed of CO ₂ gas is also used in the subsequent second ashing process. By using it as an ashing gas, it is possible to reliably exhibit the effect of suppressing damage to the Low-k film and the base film.

  Furthermore, by optimizing other parameters in the process conditions of the first ashing process and the second ashing process, damage to the low-k film and the etching stop film can be further suppressed, and as a result, the low-k The film quality of the film 208 can be kept in a better state.

Here, an example of process conditions applied to such a plasma ashing process is shown. First, as process conditions for performing the first ashing process in the plasma ashing process, for example, the pressure in the processing chamber 102 is adjusted to 20 mTorr, the interval between the upper electrode 121 and the susceptor 105 is adjusted to 35 mm, and the process is applied to the upper electrode 121. The high frequency power (for example, frequency 60 MHz) is 300 W, and the high frequency power applied to the susceptor (lower electrode) 105 is 0 W (that is, no high frequency power is applied to the susceptor 105). Further, CO ₂ gas is used as the processing gas, and the gas flow rate of CO ₂ is set to 750 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 15 Torr and the edge portion 40 Torr. The set temperature in the processing chamber 102 is 60 ° C. for the upper electrode, 60 ° C. for the side wall, and 0 ° C. for the lower electrode.

The process conditions for performing the second ashing step include, for example, adjusting the pressure in the processing chamber 102 to 200 mTorr, the interval between the upper electrode 121 and the susceptor 105 to 50 mm, and the high frequency power applied to the upper electrode 121 to 0 W (ie, , No high frequency power is applied to the upper electrode 121), and high frequency power (for example, frequency 2 MHz) applied to the susceptor (lower electrode) 105 is 300 W. Further, CO ₂ gas is used as the processing gas, and its flow rate is set to 700 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 10 Torr and the edge portion 35 Torr. The set temperature in the processing chamber 102 is 60 ° C. for the upper electrode, 50 ° C. for the side wall, and 40 ° C. for the lower electrode.

(Experiment on reaction product removal effect of first ashing step)
Here, as a result of conducting an experiment on whether or not a reaction product such as a fluorine polymer deposited on the inner wall of the processing chamber 102 can be removed by actually performing the first ashing process using a processing gas mainly containing CO _2. Will be described. Here, the same experiment was conducted for the first ashing process using a processing gas mainly composed of O ₂ as a comparative example. In this experiment, a sample in which a SiO ₂ film is formed on the entire wafer surface (hereinafter referred to as “SiO ₂ blanket sample”) is used to measure the amount of SiO ₂ film reduction, and indirectly on the inner wall of the processing chamber. The removal amount of the reaction product such as the deposited fluorine polymer is measured. That is, the amount of reduction of the SiO ₂ film of the SiO ₂ blanket sample is reduced as the amount of the reaction product such as fluorine polymer deposited on the inner wall of the processing chamber is removed by the first ashing process. It is.

  Specifically, first, a silicon substrate prepared as a dummy substrate is subjected to plasma etching processing by the first to third etching steps under the same process conditions as described above, whereby a fluorine polymer is formed on the inner wall of the processing chamber 102. The reaction product such as is deposited. Subsequently, a first ashing process for removing reaction products such as fluorine polymer deposited on the inner wall of the processing chamber 102 is performed.

After the completion of the first ashing process, the silicon substrate is taken out, and a SiO ₂ blanket sample whose SiO ₂ film thickness has been measured is loaded into the processing chamber 102 and then the pressure in the processing chamber 102 is applied to the upper electrode 121 at 15 mTorr. A high frequency power (for example, a frequency of 60 MHz) is set to 300 W, a high frequency power applied to the susceptor (lower electrode) 105 is set to 400 W, and a process process for supplying O ₂ gas into the processing chamber 102 at a flow rate of 300 sccm is performed for a time of 60 seconds. , The amount of reduction of the SiO ₂ film is measured.

The process conditions when a processing gas mainly composed of O ₂ is used in the first ashing step in this experiment are as follows. That is, the pressure in the processing chamber 102 is adjusted to 20 mTorr, the distance between the upper electrode 121 and the susceptor 105 is adjusted to 35 mm, high frequency power (for example, frequency 60 MHz) applied to the upper electrode 121 is applied to 300 W, and the susceptor (lower electrode) 105 is applied. The high frequency power to be set is 0 W (that is, no high frequency power is applied to the susceptor 105). Further, a mixed gas of Ar and O ₂ is used as the processing gas, and the flow rate ratio of each gas (Ar gas flow rate / O ₂ gas flow rate) is set to 550 sccm / 200 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the SiO ₂ blanket sample is set to the center portion 15 Torr and the edge portion 40 Torr. The set temperature in the processing chamber 102 is 60 ° C. for the upper electrode, 60 ° C. for the side wall, and 0 ° C. for the lower electrode.

Process conditions in a process gas of CO ₂ mainly in the first ashing step in this experiment, the process gas in the process conditions the CO ₂ gas alone in the case of using a process gas consisting mainly of O ₂ as described above Instead, the flow rate ratio of CO ₂ gas is set to 750 sccm.

FIG. 5 shows the measurement results of the film loss obtained in this way. In FIG. 5, the plots indicated by circles indicate the amount of film loss when a mixed gas of Ar and O ₂ is used as the processing gas in the first ashing process, and the plots indicated by squares use CO ₂ gas alone as the processing gas. This is the amount of film loss. In this experiment, the first ashing process was performed with each processing gas for 0 sec (before the first ashing process), 30 sec, and 60 sec, and the amount of film loss was measured and plotted. For example, when the first ashing process is performed for 60 seconds, the amount of film reduction is 30.3 angstroms for the processing gas of the mixed gas of Ar and O ₂ and 32.6 angstroms for the processing gas of the single CO ₂ gas.

The upper dotted line in FIG. 5 is the initial value of the SiO ₂ film thickness of the SiO ₂ blanket sample, that is, the film thickness before the first ashing process (51.2 Å). The lower dotted line in FIG. 5 indicates the film thickness when the first ashing process is performed, for example, for only one minute using a mixed gas of Ar and O ₂ as a processing gas in a clean processing chamber 102 where the plasma etching process is not performed. (27.0 angstroms). Accordingly, the upper dotted line (51.2 Å) in FIG. 5 corresponds to the film thickness before the reaction product such as fluorine polymer deposited on the inner wall of the processing chamber is removed, and the lower dotted line ( 27.0 angstroms) corresponds to the film thickness after the reaction product such as fluorine polymer deposited on the inner wall of the processing chamber is completely removed.

According to the experimental result shown in FIG. 5, since in the case of using a CO ₂ gas alone when using a mixed gas of Ar / O _2, has substantially the same film thickness reduction, the CO ₂ gas alone It can be seen that the reaction product such as fluorine polymer deposited on the inner wall of the processing chamber is removed even in the case of the processing gas using the same gas as the processing gas using the mixed gas of Ar and O ₂ .

Next, the results of measuring the plasma emission spectrum in the processing chamber after performing the first ashing process using the processing gas mainly composed of CO ₂ will be described. Here, in the experiment shown in FIG. 5, for the SiO ₂ blanket sample in which the first ashing process was performed for 60 seconds using the processing gas using the CO ₂ gas alone, the amount of reduction of the SiO ₂ film was measured. FIG. 6 shows the result of measuring the plasma emission spectrum in the processing chamber when O ₂ plasma was generated.

FIG. 6 shows a plasma emission spectrum in the processing chamber when a O ₂ plasma is generated in a clean processing chamber in which a reaction product such as a fluorine polymer is not deposited on the inner wall of the processing chamber as a comparative example. The measurement results are shown superimposed. That is, in FIG. 6, the graph indicated by the thick line is the plasma emission spectrum of the clean process chamber, and the graph indicated by the thin line is the plasma emission spectrum of the process chamber in which the first ashing process is performed after the plasma etching process.

  The vertical axis in FIG. 6 represents the emission intensity, and the horizontal axis represents the wavelength. The wavelength range is 500 nm to 800 nm. The plasma emission spectrum was measured using a spectroscope.

According to the experimental results shown in FIG. 6, the processing chamber in which the first ashing process is performed using the processing gas of CO ₂ gas alone after the plasma etching process is performed is a reaction product such as a fluorine polymer on the inner wall of the processing chamber. Since the plasma emission spectrum is almost the same as in the case of a clean processing chamber in which no silicon is deposited, the first ashing process is performed by using a processing gas mainly composed of CO ₂ to surely perform the plasma etching process. It can be seen that the reaction product such as fluorine polymer deposited on the inner wall of the processing chamber is removed. Moreover, no other elements remain in the processing chamber, and the state is similar to that of a clean processing chamber.

(Experiment on the effect of suppressing damage to the Low-k film in the first ashing process)
Next, the result of an experiment conducted on the effect of suppressing damage to the low-k film in the first ashing process will be described. Here, the first ashing process is performed on the wafer 200 shown in FIG. 3 that has been subjected to the plasma etching process using the plasma processing apparatus 100 according to the present embodiment, and the degree of damage to the Low-k film is determined. taking measurement.

  In this experiment, the degree of damage that the first ashing process gives to the low-k film is determined by immersing the sample wafer 200 in hydrofluoric acid (HF) solution and using the erosion amount of the low-k film at that time as a reference. To do. This determination method utilizes the property that a low-k film with good film quality does not dissolve in hydrofluoric acid, but a low-k film whose composition has changed, such as C (carbon atom) dissociation, dissolves in hydrofluoric acid. is there. Hereinafter, this determination method will be described in detail with reference to FIG.

  When the plasma etching process is performed on the wafer 200 shown in FIG. 3, a trench 210 is formed in the low-k film 208 of the wafer 200 as shown in FIG. Subsequently, a first ashing process is performed on the wafer 200 shown in FIG. In this first ashing step, the photoresist film 202 is not removed, so that the film structure of the wafer 200 remains the same as in FIG. The wafer 200 after the first ashing process is shown in FIG.

  However, when the wafer 200 after the first ashing process shown in FIG. 7A is immersed in hydrofluoric acid, the exposed wall of the low-k film 208 is damaged by the first ashing process. As shown in (b), the exposed wall of the low-k film 208 is melted.

This loss amount Δd corresponds to the range of the Low-k film 208 in which the composition has changed due to the dissociation of C (carbon atoms) or the like, and the first ashing process is performed as the loss amount Δd increases. The 208 is being damaged greatly. As shown in FIG. 7, the loss amount Δd appears as a change (CD (Critical Dimensions) shift) in the trench width (or hole opening diameter). Therefore, in the experiment of the first ashing step, the amount of loss Δd was dipped in the trench width (or hole diameter) d ₀ of the trench of the Low-k film 208 before being dipped in the hydrofluoric acid solution, and in the hydrofluoric acid solution. A difference (Δd = d ₁ −d ₀ ) from the trench width (or hole diameter) d ₁ of the trench of the later Low-k film 208 is assumed. Then, the degree of damage of the Low-k film is determined by using the amount of loss Δd as the CD shift amount.

The result of measuring the damage (CD shift amount) of the Low-k film in the case of using the processing gas mainly composed of CO ₂ in the first ashing process by such a damage determination method of the Low-k film will be described. Here, as a comparative example, the CD shift amount after the plasma etching process and before the first ashing step, and the CD shift amount when using a processing gas mainly composed of O ₂ in the first ashing step were also measured.

In addition, the process conditions when a process gas mainly composed of O ₂ is used in the first ashing process are as follows. That is, the pressure in the processing chamber 102 is 20 mTorr, the high frequency power applied to the upper electrode 121 (for example, frequency 60 MHz) is 300 W, the high frequency power applied to the susceptor (lower electrode) 105 is 0 W (that is, high frequency power is applied to the susceptor 105. Not applied). Further, a mixed gas of Ar and O ₂ is used as the processing gas, and the flow rate ratio of each gas (Ar gas flow rate / O ₂ gas flow rate) is set to 550 sccm / 200 sccm. The processing time of the first ashing process is 30 seconds.

Also, the process conditions in a process gas of CO ₂ mainly in the first ashing step, a process gas in the process conditions in a process gas consisting mainly of O ₂ as described above CO ₂ gas alone In other words, the flow rate of CO ₂ gas is set to 750 sccm. The processing time of the first ashing process is 45 seconds.

The measurement result of the CD shift amount obtained in this way is shown in FIG. In FIG. 8, the CD shift amount indicating the degree of damage of the Low-k film is represented by a bar graph. According to the measurement result shown in FIG. 8, the CD shift amount after the first ashing process using the CO ₂ gas alone as the processing gas is the CD after the first ashing process using the mixed gas of Ar and O ₂ as the processing gas. It is reduced to about 50% of the shift amount. Therefore, it can be seen that when CO ₂ gas alone is used as the processing gas, the effect of suppressing damage to the Low-k film is greater than when the mixed gas of Ar and O ₂ is used as the processing gas.

Moreover, the CD shift after the first ashing step of the process gas of CO ₂ gas alone, first to since it is substantially the same as the CD shift amount before the first ashing step, a process gas of CO ₂ gas alone It can be seen that when the ashing process is performed, reaction products such as fluorine polymer deposited on the inner wall of the processing chamber can be removed with almost no damage to the Low-k film.

(Experiment on other parameters of the first ashing process)
Next, the effect of reducing damage to the low-k film 208 is described with reference to the experimental results of performing the first ashing process on the wafer 200 after the plasma etching process shown in FIG. 3 while changing various parameters of the ashing process conditions. The optimum process conditions that can improve the process will be described. In this experiment, the pressure in the processing chamber, the high-frequency power applied to the upper electrode (upper power), the electrode spacing between the upper electrode 121 and the susceptor (lower electrode) 105, and the CO ₂ / (CO ₂ + Ar) flow rate ratio (%) were 3 respectively. Two levels were set, ashing process conditions (NO1 to NO9) as shown in Table 1 below were created by combining these levels, and the first ashing process was executed according to each ashing process condition (NO1 to NO9).

  The pressure of the backside cooling gas (backside gas) of the wafer 200 is fixed to the center portion 10 Torr and the edge portion 35 Torr, and the set temperature in the processing chamber 102 is set to 60 ° C. for the upper electrode and 50 ° for the side wall portion. The bottom electrode was fixed at 40 ° C.

  A result obtained by the experiment of the first ashing process will be described. First, FIG. 9 shows the relationship between the processing chamber pressure and the CD shift amount. Specifically, FIG. 9 is a line graph showing the CD shift amount when the processing chamber pressure level is 30 mTorr, 20 mTorr, and 10 mTorr in Table 1 above. That is, in FIG. 9, the average CD shift amount at each level of the processing chamber pressure is plotted. According to the experimental results of FIG. 9, the CD shift amount is almost the same in the processing chamber pressure range of 10 mTorr to 30 mTorr, and the good result that the CD shift amount can be suppressed to about 20 nm or less is obtained. It was. Therefore, the pressure in the processing chamber is preferably 30 mTorr 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 line graph showing the CD shift amount when the upper power level in Table 1 is 400 W, 800 W, and 1200 W. That is, FIG. 10 plots the average CD shift amount at each level of the upper power. According to the experimental results shown in FIG. 10, it can be seen that when the upper power is in the range of 400 W to 1200 W, the CD shift amount tends to be slightly smaller as the upper power is increased. Moreover, a good result was obtained that the CD shift amount could be suppressed to about 20 nm.

  The upper power (high frequency power for plasma generation) and its frequency need only be at least enough to ignite the plasma. On the other hand, it is preferable not to apply high frequency power (high frequency power for bias voltage generation) to be applied to the lower electrode in the first ashing process (0 W).

  Next, FIG. 11 shows the relationship between the electrode interval between the upper electrode and the lower electrode and the CD shift amount. Specifically, FIG. 11 is a line graph showing the CD shift amount when the electrode spacing level in Table 1 is 30 mm, 45 mm, and 60 mm. That is, FIG. 11 plots the average CD shift amount at each level of the electrode spacing. According to the experimental results of FIG. 11, it can be seen that the CD shift amount tends to be slightly smaller as the electrode interval is reduced in the range of 30 mm to 60 mm. In addition, a good result was obtained that the CD shift amount could be suppressed to about 20 nm or less.

Next, FIG. 12 shows the relationship between the CO ₂ / (CO ₂ + Ar) flow rate ratio (%) and the CD shift amount. Specifically, FIG. 12 is a line graph showing the CD shift amount when the level of the CO ₂ / (CO ₂ + Ar) flow rate ratio (%) in Table 1 is 50%, 75%, and 100%. . That is, in FIG. 12, the average of the CD shift amount at each level of the CO ₂ / (CO ₂ + Ar) flow rate ratio (%) is plotted. According to the experimental results of FIG. 12, the CD shift amount is almost the same when the CO ₂ / (CO ₂ + Ar) flow rate ratio (%) is in the range of 50% to 100%, and the CD shift amount is about 20 nm or less. The good result that it was able to be suppressed to was obtained. Further, according to this experiment, for example, in the case of using the processing gas of CO ₂ gas alone in the first ashing process, the case of using a mixed gas of CO ₂ and Ar is the same as in the case of CO ₂ gas alone. It can be seen that the amount of CD shift can be suppressed. Note that

(Experiment regarding the second ashing process)
Next, referring to the experimental results of performing the second ashing process on the wafer 200 shown in FIG. 3 while changing various parameters, it is optimum to keep the film quality of the low-k film 208 in a good state (or The process conditions (in the optimal range) will be described. Unless otherwise specified, the experiment for finding the optimum process conditions for the second ashing process is a so-called clean process chamber 102 in which a reaction product such as a fluorine polymer is not deposited on the inner wall of the process chamber 102. This is performed by setting a wafer 200 in which a trench is formed. This is to prevent the influence of the first ashing process from being included in the experimental result.

  Also in this experiment, as in the case of the experiment of the first ashing process described above, the degree of damage that the plasma ashing process gives to the Low-k film is soaked in a hydrofluoric acid (HF) solution. The erosion amount of the low-k film is determined as a reference. Hereinafter, this determination method will be described in detail with reference to FIG.

  When the second ashing process is performed on the wafer 200 shown in FIG. 4, the photoresist film 202 is removed by the second ashing process, so that the film structure of the wafer 200 is as shown in FIG. The wafer 200 after the second ashing process is shown in FIG.

  When the wafer 200 after the second ashing process shown in FIG. 13A is immersed in a hydrofluoric acid solution, if the Low-k film 208 is damaged in the second ashing process, it is shown in FIG. 13B. Thus, the exposed side wall of the low-k film 208 is melted.

This loss amount Δd corresponds to the range of the Low-k film 208 in which the composition has changed due to dissociation of C (carbon atoms) and the like, and the loss amount Δd is large as in the case of the first ashing step. As the plasma ashing process is performed, the Low-k film 208 is greatly damaged. The loss Δd appears as a change (CD shift) in the trench width (or hole opening diameter) as shown in FIG. In practice, the trench (or hole) CD shift may be different in the depth direction. Therefore, in the experiment of the second ashing step, the upper groove width (or upper hole diameter) d _1t , the bottom groove width (or bottom hole diameter) d _1b , the groove of the Low-k film 208 after being immersed in the hydrofluoric acid solution The depth (or hole depth) d _1h is measured, and the amount of loss Δd is obtained. Specifically, if the groove width (or hole diameter) of the low-k film 208 before being immersed in the hydrofluoric acid solution is d _0t and the groove depth (or hole depth) is d _0h , the upper groove width (Or top hole diameter), bottom groove width (or bottom hole diameter), groove depth (or hole depth) loss, that is, CD shift amounts Δd _1t , Δd _1b , Δd _1h are respectively Δd _1t = d _1t −d _0t , Δd _1b = d _1b −d _0t , Δd _1h = d _1h −d _0h . For example, the average value Δd ₁ of these CD shift amounts Δd _1t , Δd _1b , Δd _1h is determined as the degree of damage to the Low-k film.

(Process chamber pressure dependence in the second ashing process)
Using the determination method as described above, experimental results on the pressure dependence of the second ashing process in the processing chamber will be described. Here, the second ashing process is performed on the wafer 200 shown in FIG. 4 that has been subjected to the above-described plasma etching process using the plasma processing apparatus 100 according to the present embodiment, while changing the pressure in the processing chamber, and the Low-k film is formed. The degree of damage (CD shift amount) and the ashing rate are measured.

In this experiment, the second ashing process is performed when the processing chamber pressure is set to a low pressure of 15 mTorr and the high pressure of 200 mTorr, and the CD shift amount (Δd _1t , Δd _1b , Δd _1h ) of the Low-k film 208 is executed. And the ashing rate (AR) was measured. The results of this experiment are shown in Table 2 below.

Other process conditions when performing the second ashing process with the processing chamber pressure set to a high pressure of 200 mTorr are as follows. That is, the distance between the upper electrode 121 and the susceptor (lower electrode) 105 is adjusted to 55 mm, the high frequency power applied to the upper electrode 121 is 0 W (that is, no high frequency power is applied to the upper electrode 121), and the susceptor (lower electrode). ) The high frequency power (for example, frequency 2 MHz) applied to 105 is set to 300 W. Further, CO ₂ gas is used as the processing gas, and its flow rate is set to 700 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 10 Torr and the edge portion 35 Torr. The set temperature in the processing chamber 102 is 60 ° C. for the upper electrode, 50 ° C. for the side wall, and 40 ° C. for the lower electrode. The processing time of this second ashing process is 44 seconds.

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

  According to the experimental results shown in Table 2 above, it can be seen that when the processing chamber pressure is 200 mTorr or less, the higher the processing chamber pressure, the smaller the CD shift amount and the less damage to the Low-k film 208. . In addition, when the processing chamber pressure is 200 mTorr, even if the processing chamber pressure is lowered to about 15 mTorr, the CD shift amount is lower than before. Also, according to the experimental results shown in Table 2, it can be seen that the higher the pressure in the processing chamber, the larger the ashing rate (AR) and the higher the ashing rate. Therefore, it is preferable that the pressure in the processing chamber in the second ashing process is high.

Further, another sample made of a low-k film having a lower dielectric constant than the low-k film of the wafer 200 (an etching stop film made of an SiC film, a porous low-k film made of an MSQ film, an SiO ₂ film, etc.) Wafer having a film structure laminated in the order of the hard masks and having a trench formed in the porous low-k film), the pressure in the processing chamber is changed in the same manner as described above to perform the second ashing process. The CD shift amount was measured. However, since the CD shift amount at this time is obtained by using a sample having an etching stop film, it is a change amount of the trench groove width (or hole diameter) defined in the experiment of the first ashing process. . The result is shown in FIG. In this experiment, the second ashing process was performed even in a range where the processing chamber pressure exceeded 200 mTorr, and the CD shift amount was measured.

  According to the experimental results shown in FIG. 14, until the processing chamber pressure is around 200 mTorr, the higher the processing chamber pressure is, the smaller the CD shift amount is. Recognize. However, it has been found that when the pressure in the processing chamber exceeds 200 mTorr, the CD shift amount gradually increases, and when it exceeds 400 mTorr, the CD shift amount tends to increase rapidly. Therefore, as described above, it is preferable that the pressure in the processing chamber in the second ashing process is high, but it is preferable that the pressure in the processing chamber is less than 400 mTorr from the viewpoint of the effect of suppressing damage to the Low-k film 208.

(Dependency of frequency of second high frequency power in second ashing step)
Next, experimental results on the frequency dependence of the second high frequency power applied to the susceptor (lower electrode) 105 in the second ashing step will be described. Here, by using the plasma processing apparatus 100 according to the present embodiment, the second ashing process is performed again on the same sample as the wafer 200 by changing the frequency of the second high-frequency power, and the damage given to the Low-k film. And the ashing rate are measured.

In this experiment, the second ashing process is executed when the frequency of the second high-frequency power is 2 MHz and 13.56 Hz, and the CD shift amount (Δd _1t , Δd _1b , Δd _{1h) of the} low-k film 208 is executed. ) And ashing rate (AR) were measured. The results of this experiment are shown in Table 3 below.

Other process conditions when performing the second ashing process with the frequency of the second high-frequency power set to 2 MHz are as follows. That is, the distance between the upper electrode 121 and the susceptor (lower electrode) 105 is adjusted to 55 mm, the high frequency power applied to the upper electrode 121 is 0 W (that is, no high frequency power is applied to the upper electrode 121), and the susceptor (lower electrode). ) The high frequency power applied to 105 is set to 300 W. Further, CO ₂ gas is used as the processing gas, and its flow rate is set to 700 sccm. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 10 Torr and the edge portion 35 Torr. The set temperature in the processing chamber 102 is 60 ° C. for the upper electrode, 50 ° C. for the side wall, and 40 ° C. for the lower electrode. The processing time of this second ashing process is 44 seconds. In this case, the voltage Vpp for one cycle from the peak to the peak of the AC component of the second high-frequency power (2 MHz, 300 W) is 1300V. Since this Vpp fluctuates in response to the state of plasma excited in the processing chamber, for example, a change in plasma density, it can be an indicator of the plasma state.

  As for other process conditions when performing the second ashing process with the frequency of the second high-frequency power set to 13.56 MHz, the high-frequency power applied to the susceptor (lower electrode) 105 is set to 1100 W, and the processing of the second ashing process is performed. The time is 21 sec. The other process conditions are the same as those in the case where the frequency of the second high-frequency power is 2 MHz, and the description thereof is omitted. In this case, the voltage Vpp for one period from the peak to the peak of the AC component of the second high-frequency power (13.56 MHz, 1100 W) is 1200 V, which is almost the same as when the frequency of the second high-frequency power is 2 MHz. It is the same.

  According to the experimental results shown in Table 3 above, in the range where the frequency of the second high-frequency power is 13.56 MHz or less, the higher the frequency of the second high-frequency power, the smaller the CD shift amount, but the lower − It can be seen that the damage given to the k film 208 is slightly reduced. In addition, in the range where the frequency of the second high-frequency power is 13.56 MHz or less, the CD shift amount is lower than before even when the frequency of the second high-frequency power is 13.56 MHz, even if the frequency is lowered to about 2 MHz. Value. Also, according to the experimental results shown in Table 3, it can be seen that the higher the frequency of the second high-frequency power, the shorter the ashing time, and the higher the ashing time. Therefore, it is preferable that the frequency of the second high-frequency power in the second ashing step is higher.

As described above, the higher the frequency of the second high-frequency power, the higher the speed of ashing is because the higher the frequency, the more ashing can be performed by ions (CO ₂ ^{+ and the} like). It is guessed. That is, the higher the frequency, the higher the plasma density, so that current flows easily and the voltage value decreases. For this reason, in order to prevent the voltage value from decreasing, it is necessary to increase the second high-frequency power (power). In the above specific example, the second high frequency power is increased from 300 W to 1100 W. As the second high-frequency power is larger, the number of ions (CO ₂ ^{+ and the} like) generated by the plasma increases, so that ashing can be performed with more ions.

  Thus, it is necessary to increase the second high frequency power as the frequency of the second high frequency power is increased, and ashing can be performed at higher speed as the second high frequency power is increased. Since how much the magnitude of the second high-frequency power can be increased depends on the performance of the plasma processing apparatus, the practical frequency of the second high-frequency power is 13 MHz to 40 MHz is more preferable.

In the present embodiment, the case where CO ₂ is used as the processing gas in the second ashing process has been described. However, the present invention is not limited to this, and O ₂ may be used, and CO ₂ and O ₂ may be used. You may use the mixed gas of.

(Preferred process conditions in plasma ashing treatment)
Based on the above experimental results, the optimum process conditions of the plasma ashing process performed using the plasma processing apparatus 100 according to the first embodiment are shown in Table 4 below.

As shown in Table 4 above, in the first ashing process, the pressure in the processing chamber is preferably 30 mTorr or less. The reaction product removal treatment gas is preferably CO _2, but a mixed gas of CO ₂ and Ar may be used. The first high frequency power in the first ashing process is sufficient if it is at least a power capable of plasma ignition. The frequency in this case may be set arbitrarily. On the other hand, the second high frequency power is preferably 0 W (not applied to the lower electrode).

In the second ashing process, the processing chamber pressure is preferably less than 400 mTorr. As the ashing treatment gas, either O _2, CO ₂ or a mixed gas thereof may be used. The first high frequency power in the second ashing step is most preferably 0 W (not applied to the upper electrode), and if the first high frequency power is applied, it is preferable that the frequency be as low as possible and the frequency be 27 MHz or higher. On the other hand, the frequency of the second high-frequency power is preferably 13 to 40 MHz, 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 and the base film formed on the wafer can be suppressed more than ever. In particular, the effect of suppressing damage to the low-k film in the first ashing step is great. In the second ashing step, ashing can be performed at a higher speed.

(Configuration example of plasma processing apparatus according to the second embodiment)
Next, a configuration example of a plasma processing apparatus according to the 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 the second embodiment. The plasma processing apparatus 300 shown in FIG. 15 compares the first high-frequency power (plasma generating high-frequency power) having a relatively high frequency of, for example, 40 MHz with one electrode (lower electrode) also serving as a mounting table, for example, 3.2 MHz. This is a plasma processing apparatus of a type that superimposes and applies a second high-frequency power having a low frequency (high-frequency power for generating a bias voltage). The plasma ashing method according to the present invention can also be applied to this type of plasma processing apparatus 300.

  As shown in FIG. 15, the plasma processing apparatus 300 includes a processing chamber 302 constituted by, for example, a grounded airtight processing container 304. A conductive lower electrode 306 that also serves as a mounting table on which the wafer W is mounted is disposed in the processing chamber 302 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 the heat transfer gas is supplied at a predetermined pressure from the heat transfer gas supply mechanism (not shown) between the wafer W and the lower electrode 306. Supplied. An upper electrode 308 is formed at a position facing the mounting surface of the lower electrode 306.

Further, a gas introduction port 332 connected to a gas supply source (not shown) is formed in the upper portion of the processing chamber 302 so that a predetermined processing gas is introduced into the processing chamber 302. Yes. The processing gas introduced into the processing chamber 302 is introduced onto the wafer W from a plurality of gas discharge ports 309 formed in the upper electrode 308. For example, CF ₄ gas, CHF ₃ gas, C ₄ F ₈ gas, O ₂ gas, He gas, Ar gas, N ₂ gas, and a mixed gas thereof are introduced into the processing chamber 302 as a processing gas.

  An exhaust pipe 336 connected to an exhaust valve and an exhaust mechanism (not shown) is provided below the processing chamber 302. The inside of the processing chamber 302 is evacuated through the exhaust pipe 336, thereby maintaining a predetermined degree of vacuum, for example, 50 mTorr. A magnet 330 is provided on the side of the processing chamber 302, and a magnetic field (multipole magnetic field) for confining plasma in the vicinity of the inner wall of the processing chamber 302 is formed by the magnet 330. The intensity of this magnetic field is variable.

  Connected to the lower electrode 306 is a power supply device 312 for supplying two-frequency superimposed power. The power supply device 312 includes a first power supply mechanism 314 that supplies a first high-frequency power having a first frequency, and a second high-frequency power supply mechanism 316 that supplies a second high-frequency power having a second frequency lower than the first frequency. It is configured.

  The first power supply mechanism 314 includes a first filter 318, a first matching unit 320, and a first power source 322 that are sequentially connected 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 side. The first matching unit 320 matches the first high frequency power component. The first frequency is 100 MHz, for example.

  The second power supply mechanism 316 includes a second filter 324, a second matching unit 326, and a second power source 328 that are sequentially connected 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. The second frequency is, for example, 3.2 MHz.

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

(Specific example of processing applied to wafer)
The plasma processing apparatus 300 according to the present embodiment configured as described above performs, for example, an etching process on the wafer 200 illustrated in FIG. 3 in the same manner as the plasma processing apparatus 100 according to the first embodiment illustrated in FIG. The ashing process is continuously performed in the same processing chamber.

Here, a specific example of the plasma etching process will be described. Here, for example, the plasma etching process is performed by sequentially executing the first to third etching steps. First, in the first etching step, the antireflection film 204 is etched using the patterned photoresist film 202 as a mask. As process conditions for performing the first etching step, for example, the pressure in the processing chamber 302 is adjusted to 10 mTorr, and a first high frequency power (for example, 100 MHz) applied from the first power source 322 to the lower electrode 306 is 1500 W, The second high frequency power (for example, 3.2 MHz) applied from the second power source 328 to the lower electrode 306 is set to 0 W (that is, the second high frequency power is not applied). Further, CF ₄ is used as a processing 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 process conditions for performing the second etching step, for example, the pressure in the processing chamber 302 is adjusted to 50 mTorr, and the first high frequency power (for example, 100 MHz) applied from the first power source 322 to the lower electrode 306 is 2000 W, The second high frequency power (for example, 3.2 MHz) applied from the second power source 328 to the lower electrode 306 is set to 200 W. Further, a mixed gas of CF ₄ and Ar is used as the processing gas.

  By performing the above first and second etching steps, a trench 210 is formed in the Low-k film 208 as shown in FIG. 3, for example. Following such a 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.

  By the way, according to the plasma processing method in which two types of high-frequency power are superimposed and applied to the lower electrode using such a plasma processing apparatus 300, the plasma density and the bias voltage can be controlled independently. In addition, since it is not necessary to apply high-frequency power only to the lower electrode and to apply high-frequency power to the upper electrode, there is an advantage that the device structure is not complicated.

However, according to such a plasma processing method in which two types of high-frequency power are superimposedly applied to the lower electrode, the same process is performed after the low-k film is etched using a processing gas containing F (fluorine) using the resist film as a mask. If ashing of the resist film is performed using a processing gas mainly composed of O ₂ in the processing chamber, even if the second high-frequency power is set to 0 W, a bias voltage is generated by the first high-frequency power. In ashing, the fluorine used in the plasma etching process as described above remains in the processing chamber, and the fluorine is accelerated toward the low-k film and the base film by the bias voltage, and the low-k film and the base film are removed. There is a risk of scraping.

In this regard, according to the plasma ashing process of the present invention, the fluorine remaining in the processing chamber is removed using a processing gas mainly composed of CO ₂ in the first ashing process, and then the resist film is formed in the second ashing process. Since it can be removed, damage to the Low-k film and the base film can be suppressed.

(First high frequency power and second high frequency power)
Further, when the plasma ashing process is performed using the plasma processing apparatus 300 of the type that applies power of two different frequencies to the lower electrode, the first high-frequency power and the second high-frequency power are set as follows. It is preferable to set.

  First, the frequency of the first high-frequency power in the first ashing step is preferably set to a frequency that can ignite plasma even at a low pressure in the processing chamber of 30 mTorr or less. Specifically, the frequency is preferably 13 MHz or more. The first high-frequency power is preferably set according to the frequency. Moreover, it is preferable that the 2nd high frequency electric power in a 1st ashing process is 0W.

  The frequency of the first high frequency power in the second ashing process is preferably 13 MHz to 40 MHz. In this case, the second high frequency power is preferably 0 W, but the second high frequency power may be applied. In this case, regarding the damage given to the Low-k film 208 when the first high-frequency power is 13.56 MHz and the second high-frequency power is 0 W, the second high-frequency power applied to the lower electrode in the plasma processing apparatus 100 described above. The result is the same as the experimental result shown in Table 3 in which is set to 13.56 MHz. According to this, the damage given to the Low-k film 208 can be suppressed more than before, the ashing time is shortened, and ashing can be performed at a higher speed.

  Further, since the first high frequency power in the plasma processing apparatus 300 is applied to the lower electrode, the frequency of the first high frequency power in the second ashing step may be 40 MHz or more. This is due to the following reasons, 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, plasma is generated immediately above the wafer, so that it is applied to the upper electrode as in the plasma processing apparatus 100 shown in FIG. However, the number of ions increases.

  In this case, ashing proceeds mainly by these ions. However, since ions lose energy on the wafer surface, they are hardly affected by ashing even in the film formed on the wafer. For this reason, 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 hardly affected by ashing.

  On the other hand, if the frequency of the first high-frequency power applied to the upper electrode 121 of the plasma processing apparatus 100 shown in FIG. Becomes larger. This is due to the following reasons, for example. That is, since the first high frequency power is applied to the upper electrode 121 to generate plasma, the plasma is dark near the upper electrode 121 and the plasma is thin near the wafer far from the upper electrode 121. For this reason, radicals are likely to be generated in the vicinity of the upper electrode 121, and since the radicals have a long lifetime, they also increase in the vicinity of the wafer.

  In the case of ashing by radicals, unlike the above-described ions, ashing is performed not only on the wafer surface but also in the film. As described above, when the power of the first high-frequency power applied to the upper electrode is increased, radicals increase and damage to the low-k film 208 increases. When the power of the first high-frequency power applied to the lower electrode is increased, radicals also increase, but the ashing rate is increased and the ashing time is shortened, so that the effect of receiving damage to the Low-k film 208 is increased. It seems difficult to receive.

  Note that when the frequency of the first high-frequency power in the second ashing process is set to 40 MHz or higher, the plasma density rapidly increases. Therefore, in order to increase ion energy, the frequency of the second high-frequency power is set to 13 MHz or lower. It is preferable to assist. However, the frequency of the second high-frequency power may be set to 0 W depending on the frequency of the first high-frequency power.

  Here, an experimental result in which the second ashing process is performed with the frequency of the first high-frequency power set to 100 MHz and the frequency of the second high-frequency power set to 3.2 MHz will be described. Here, the second ashing process is performed on the wafer 200 shown in FIG. 4 using the plasma processing apparatus 300 according to the present embodiment, and the degree of damage (CD shift amount) given to the Low-k film and the ashing are performed. The rate was measured. The experimental results are shown in Table 5 below.

Other process conditions when performing the second ashing process in this experiment are as follows. That is, the processing chamber pressure is 50 mTorr, the first high-frequency power applied to the lower electrode is 400 W, and the second high-frequency power applied to the lower electrode is 300 W. Further, CO ₂ gas is used as the processing gas, the flow rate is set to 700 sccm, and the magnetic field strength is set to 300 G. Further, the pressure of the back surface cooling gas (backside gas) of the wafer 200 is set to the center portion 10 Torr and the edge portion 50 Torr. The set temperature in the processing chamber 102 is 50 ° C. for the upper electrode, 60 ° C. for the side wall, and 40 ° C. for the lower electrode. The processing time of this second ashing process is 44 seconds.

  According to the experimental results shown in Table 5, it can be seen that even if the first high frequency power is increased to 100 MHz, the CD shift amount is sufficiently small and the damage given to the Low-k film 208 is small. Also, according to the experimental results shown in Table 5 above, it can be seen that the ashing rate (AR) is also increased and ashing can be performed at a higher speed. Therefore, in the plasma processing apparatus 300, it is preferable that the frequency of the first high-frequency power in the second ashing process is 40 MHz or more.

  For the optimum range of process conditions other than the first high-frequency power and the second high-frequency power, for example, the pressure in the processing chamber and the processing gas, when performing the plasma ashing process in the plasma processing apparatus 300, the plasma processing apparatus shown in FIG. Since it is almost the same as the case of 100, the description is omitted.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

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

It is a schematic block diagram of the plasma processing apparatus concerning 1st Embodiment of this invention. It is a schematic sectional drawing which shows the film | membrane structure of the wafer by which an etching process and an ashing process are performed by the plasma processing apparatus shown in FIG. It is a schematic sectional drawing which shows the film | membrane structure after performing the etching process to the wafer shown in FIG. It is a schematic sectional drawing which shows the film | membrane structure after performing the ashing process to the wafer shown in FIG. It is a figure which shows the result of having indirectly measured the removal amount of the reaction product in a 1st ashing process by the film | membrane reduction amount. It is a figure which shows the result of having measured the plasma emission spectrum in the process chamber after a 1st ashing process. It is explanatory drawing of the method of determining the extent of the damage of the Low-k film | membrane by a 1st ashing process. It is a figure which shows the relationship between the process gas kind used at a 1st ashing process, and CD shift amount. It is a figure which shows the relationship between the process chamber pressure and CD shift amount in a 1st ashing process. It is a figure which shows the relationship between the top electric power and CD shift amount in a 1st ashing process. It is a figure which shows the relationship between the electrode space | interval and CD shift amount in a 1st ashing process. It is a figure which shows the relationship between the process gas flow rate and CD shift amount in a 1st ashing process. It is explanatory drawing of the method of determining the extent of the damage of the Low-k film | membrane by a 2nd ashing process. It is a figure which shows the relationship between the process chamber pressure and CD shift amount in a 2nd ashing process. It is sectional drawing which shows the structural example of the plasma processing apparatus concerning 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Plasma processing apparatus 102 Processing chamber 103 Insulation board 104 Susceptor support stand 105 Susceptor (lower electrode)
107 temperature control medium chamber 108 introduction 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 discharge hole 124 electrode plate 125 electrode support 126 gas introduction port 127 gas supply pipe 128 valve 129 mass flow controller 130 processing gas supply source 131 exhaust pipe 132 gate valve 135 exhaust mechanism 200 wafer 202 photoresist film 204 antireflection film 206 protective film 208 low dielectric constant film 210 trench 300 plasma processing apparatus 302 processing chamber 306 lower electrode 308 Upper electrode 309 Gas outlet 312 Power supply device 330 Magnet 332 Gas inlet 336 Exhaust pipe W Wafer

Claims (20)

A plasma ashing method for removing a resist film in the processing chamber after performing a processing for etching a part of the low dielectric constant film on a target object in the processing chamber using a patterned resist film as a mask. There,
A reaction product removal treatment gas containing at least CO ₂ gas is supplied into the treatment chamber, and plasma of the reaction product removal treatment gas is generated by applying a high frequency power for plasma generation, and adheres to the inner wall of the treatment chamber A first ashing step for removing reaction products to be removed;
A second ashing step of removing the resist film by supplying an ashing process gas into the processing chamber and applying a plasma generating high frequency power to generate plasma of the ashing process gas;
A plasma ashing method comprising: The plasma ashing method according to claim 1, wherein the reaction product removal processing gas is CO ₂ gas. The plasma ashing method according to claim 1, wherein the reaction product removal processing gas contains CO ₂ gas and inert gas. The plasma ashing method according to claim 1, wherein the pressure in the processing chamber in the first ashing step is 30 mTorr or less. The plasma ashing method according to claim 1, wherein the ashing gas includes one or both of O ₂ gas and CO ₂ gas. The first ashing step is performed without applying a high frequency power for generating a bias voltage,
2. The plasma ashing method according to claim 1, wherein the second ashing step is performed in a state where a high frequency power for generating a bias voltage is applied. The plasma ashing method according to claim 1, wherein the low dielectric constant film is a porous low-k film. A process of etching a part of the low dielectric constant film on the object to be processed on the second electrode disposed opposite to the first electrode disposed in the processing chamber using the patterned resist film as a mask. A plasma ashing method for removing the resist film in the processing chamber after performing,
A reaction product removal treatment gas containing at least CO ₂ gas is supplied into the treatment chamber, high frequency power is applied to the first electrode to generate a plasma of the reaction product removal treatment gas, and the second electrode A first ashing step for removing reaction products adhering to the inner wall of the processing chamber without applying high-frequency power;
An ashing gas is supplied into the processing chamber, high frequency power is applied to the first electrode to generate plasma of the ashing gas, and the resist film is removed with high frequency power applied to the second electrode. A second ashing step;
A plasma ashing method comprising: 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 the frequency is from 13 MHz to 40 MHz. The plasma ashing method according to claim 8. 9. The frequency of the high frequency power applied to the first electrode in the second ashing step is 27 MHz or more, and the frequency of the high frequency power applied to the second electrode is from 13 MHz to 40 MHz. The plasma ashing method as described in 2. 9. The plasma ashing method according to claim 8, wherein the pressure in the processing chamber in the second ashing step is 400 mTorr or less. A process of etching a part of the low dielectric constant film on the object to be processed on the second electrode disposed opposite to the first electrode disposed in the processing chamber using the patterned resist film as a mask. A plasma ashing method for removing the resist film in the processing chamber after performing,
A reaction product removal treatment gas containing at least CO ₂ gas is supplied into the treatment chamber, high frequency power is applied to the first electrode to generate a plasma of the reaction product removal treatment gas, and the second electrode A first ashing step for removing reaction products adhering to the inner wall of the processing chamber without applying high-frequency power;
An ashing process gas is supplied into the processing chamber, and a high frequency power is applied to the second electrode without applying a high frequency power to the first electrode to generate a plasma of an ashing process gas to the second electrode. A second ashing step of removing the resist film in a state where high-frequency power is applied;
A plasma ashing method comprising: The plasma ashing method according to claim 12, wherein in the second ashing step, the frequency of the high frequency power applied to the second electrode is 13 MHz or more and 40 MHz or less. The plasma ashing method according to claim 12, wherein the pressure in the processing chamber in the second ashing step is 400 mTorr or less. A resist film patterned in an object to be processed on an electrode arranged in a processing chamber and configured to be able to superimpose a first high-frequency power and a second high-frequency power having a frequency lower than the first high-frequency power. A plasma ashing method for removing the resist film in the processing chamber after performing a process of etching a part of the low dielectric constant film using as a mask,
A reaction product removal treatment gas containing at least CO ₂ gas is supplied into the treatment chamber, the first high frequency power is applied to the electrode to generate a plasma of the reaction product removal treatment gas, and (2) a first ashing step for removing reaction products adhering to the inner wall of the processing chamber without applying high-frequency power;
An ashing gas is supplied into the processing chamber, a first high frequency power is applied to the electrode to generate plasma of the ashing gas, and the resist film is removed in a state where the second high frequency power is applied to the electrode. A second ashing step;
A plasma ashing method comprising: The plasma ashing method according to claim 15, wherein the frequency of the first high-frequency power in the first ashing step is 13 MHz or more. The plasma ashing method according to claim 15, wherein the frequency of the first high-frequency power in the first ashing step is 27 MHz or more. The plasma ashing method according to claim 15, wherein a frequency of the first high-frequency power in the second ashing step is 13 MHz or more and 100 MHz or less. The plasma ashing method according to claim 18, wherein the second high frequency power in the second ashing step is 0W. The plasma ashing method according to claim 15, wherein the frequency of the first high frequency power in the second ashing step is 40 MHz or more, and the frequency of the second high frequency power is 13 MHz or less.

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