JPWO2018230373A1 - Plasma processing apparatus seasoning method and plasma etching method - Google Patents

Abstract

A seasoning method for stabilizing the inner surface of the plasma processing chamber by performing plasma treatment using a seasoning gas containing 2-fluorobutane and nitrogen in a preceding stage of a plasma etching process in which plasma etching is performed using an etching gas containing 2-fluorobutane. Is.

Description

  The present invention relates to a seasoning method and a plasma etching method for a plasma processing apparatus. In particular, the present invention relates to a seasoning method performed before a plasma etching step in which plasma etching is performed using an etching gas containing 2-fluorobutane, and a plasma etching method including a seasoning step according to the seasoning method.

  In the manufacture of semiconductor devices, plasma etching may be performed using an etching gas when finely processing a thin film formed on an object to be processed. In plasma etching, an object to be processed such as a wafer is placed in a plasma processing chamber (hereinafter, simply referred to as a “processing chamber”) included in a plasma processing apparatus, and plasma of an etching gas is excited to remove the object to be processed. A plasma etching process of plasma etching is performed.

Prior to the plasma etching step, it has been proposed to perform a seasoning step in order to adjust the inside of the processing chamber to a state required when producing a product such as a semiconductor wafer (see, for example, Patent Document 1). In Patent Document 1, prior to the plasma etching process of a wafer using a known general fluorocarbon gas that can be used for the etching process of CF ₄ gas, C ₄ F ₈ gas, etc., the processing chamber is set to a steady state. As a purpose, performing a seasoning process is described.

JP, 2010-147052, A

  In recent years, the usefulness of 2-fluorobutane as a new plasma etching gas is drawing attention. However, as a result of studies by the present inventors, when 2-fluorobutane is introduced into the plasma processing chamber during plasma etching, it tends to be decomposed by reacting with the material forming the surface of the processing chamber. It became clear. If 2-fluorobutane introduced into the plasma processing chamber during plasma etching is decomposed, the usefulness as a plasma etching gas may not be sufficiently enhanced.

Here, no problem has been pointed out that the conventionally known etching gases such as CF ₄ gas and C ₄ F ₈ gas are easily decomposed in the plasma etching process. Therefore, the conventional seasoning process as disclosed in Patent Document 1 exclusively deposits on the inner wall of the processing chamber so as to adjust the temperature of components in the processing chamber to a steady state and to be compatible with the plasma etching process for product wafers. It was carried out for the purpose of stabilizing the state of the inside of the processing chamber to the optimum state required at the time of production of product wafers by adjusting the state of by-products and the like. Therefore, in the conventional seasoning process as disclosed in Patent Document 1, it is not possible to effectively suppress the decomposition of the specific plasma etching gas of 2-fluorobutane in the plasma etching process.

Therefore, an object of the present invention is to provide a seasoning method for a plasma processing apparatus, which can favorably suppress the decomposition of 2-fluorobutane in the plasma etching step.
Another object of the present invention is to provide a plasma etching method capable of suppressing decomposition of 2-fluorobutane in etching gas.

  The present inventors have earnestly studied to solve the above problems. As a result, the present inventors have found that the seasoning process using a gas containing 2-fluorobutane and nitrogen can effectively suppress the decomposition of 2-fluorobutane as an etching gas in the plasma etching process. Newly found and completed the present invention.

  The present invention has an object to advantageously solve the above problems, and a seasoning method for a plasma processing apparatus of the present invention is a plasma etching step of performing plasma etching using an etching gas containing 2-fluorobutane. The first stage is characterized in that plasma treatment is performed using a seasoning gas containing 2-fluorobutane and nitrogen to stabilize the inner surface of the plasma treatment chamber. In this way, if the inside of the processing chamber is plasma-processed using the seasoning gas containing 2-fluorobutane and nitrogen in the preceding stage of the plasma etching process, it is introduced into the processing chamber as the etching gas in the plasma etching process. The decomposition of fluorobutane can be effectively suppressed.

Here, in the seasoning method of the present invention, the volume ratio of nitrogen in the seasoning gas is preferably 40% by volume or more. When the volume ratio of nitrogen in the seasoning gas is 40 vol% or more, the decomposition of 2-fluorobutane introduced into the processing chamber as the etching gas in the plasma etching step can be suppressed more effectively.
In the present specification, the “volume ratio of nitrogen in the seasoning gas” can be calculated based on the flow rate of each gas introduced into the processing chamber in the seasoning process.

Further, in the seasoning method of the present invention, it is preferable that the residence time of the seasoning gas in the plasma processing chamber is 0.2 seconds or more and 30 seconds or less. If the residence time of the seasoning gas in the plasma processing chamber is 0.2 seconds or more and 30 seconds or less, the decomposition of 2-fluorobutane introduced into the processing chamber as the etching gas in the plasma etching step can be suppressed more effectively. You can
In the present specification, "the residence time of the seasoning gas in the plasma processing chamber" refers to the flow rate of each gas introduced into the processing chamber in the seasoning process, the volume of the processing chamber during the seasoning process, and the processing chamber during the seasoning process. Can be calculated based on the pressure.

  Here, the present invention has an object to advantageously solve the above-mentioned problems, and a plasma etching method of the present invention includes a seasoning step according to any one of the above-mentioned seasoning methods, and a step following the seasoning step. -A plasma etching step of performing plasma etching using an etching gas containing fluorobutane. After the seasoning step according to any one of the above seasoning methods, a plasma etching step of performing plasma etching using an etching gas containing 2-fluorobutane was carried out, and thus the plasma was introduced into the plasma processing chamber in the plasma etching step. It is possible to favorably suppress the decomposition of 2-fluorobutane contained in the etching gas.

According to the present invention, it is possible to provide a seasoning method for a plasma processing apparatus, which can favorably suppress decomposition of 2-fluorobutane in a plasma etching step.
Further, the present invention can provide a plasma etching method capable of suppressing decomposition of 2-fluorobutane in etching gas.

  Hereinafter, embodiments of the present invention will be described in detail. A seasoning method for a plasma processing apparatus of the present invention (hereinafter, also simply referred to as “seasoning method”) is a plasma etching method using an etching gas containing 2-fluorobutane (which may be included in a semiconductor device manufacturing process). Plasma etching method). Here, in the present specification, “seasoning” means stabilizing the inner surface of the plasma processing chamber at least before the plasma etching step. In addition to the effect of "stabilizing the surface of the plasma processing chamber" by performing the seasoning method, the seasoning process further exerts the function of "making the plasma processing chamber a steady state in the plasma etching process". May be.

(Seasoning method)
According to the seasoning method of the present invention, a plasma treatment is performed using a seasoning gas containing 2-fluorobutane and nitrogen before a plasma etching process in which plasma etching is performed using an etching gas containing 2-fluorobutane. Is a method for stabilizing the. By using a mixed gas of 2-fluorobutane and nitrogen as the seasoning gas, the decomposition of 2-fluorobutane contained in the etching gas can be effectively suppressed. The reason for this is not clear, but it is presumed that the mechanism is as follows.

  Generally, the inner surface of the processing chamber included in the plasma etching apparatus may be made of metal and / or metal compound. More specifically, the material forming the surface of the processing chamber is a metal and / or metal compound having an acid point (Lewis acid point), more specifically, aluminum oxide such as alumite (registered trademark), and stainless steel. Examples include steel and manganese steel. Among these, a plasma etching apparatus is generally provided with a processing chamber having an inner surface formed of alumite (registered trademark). Here, acid points may be exposed on the surface of the processing chamber formed of a metal and / or metal compound having acid points. When acid points exposed on the surface of the processing chamber react with 2-fluorobutane contained in the etching gas, 2-fluorobutane is decomposed. If 2-fluorobutane is decomposed, hydrogen fluoride and butenes can be produced. Therefore, according to the seasoning method of the present invention, a plasma treatment using a seasoning gas containing 2-fluorobutane and nitrogen is performed in the preceding stage of the plasma etching step, so that a film derived from 2-fluorobutane and nitrogen is formed on the surface of the treatment chamber. It is considered that the nitrogen atoms in the film suppress the decomposition action of 2-fluorobutane by the acid sites. As a result, the reaction between acid points on the surface of the processing chamber and 2-fluorobutane introduced as an etching gas in the etching step is effectively suppressed, and the decomposition of 2-fluorobutane is significantly suppressed. It is presumed to be possible.

  Furthermore, it is presumed that the above-mentioned coating can suppress further polymerization reaction after 2-fluorobutane introduced as an etching gas in the etching step is decomposed. In this way, according to the seasoning method of the present invention, 2-fluorobutane introduced as an etching gas in the etching step is decomposed in the processing chamber, and decomposition products generated by the decomposition are generated. It is presumed that it is possible to suppress the subsequent conversion into other substances such as polymerization.

<Seasoning gas>
The seasoning gas contains 2-fluorobutane and nitrogen. Here, the volume ratio of nitrogen in the seasoning gas is preferably 40% by volume or more, more preferably 50% by volume or more, preferably 99% by volume or less, and 95% by volume or less. Is more preferable, and 90% by volume or less is further preferable. When the volume ratio of nitrogen in the seasoning gas is within the above range, the decomposition of 2-fluorobutane in the plasma etching step can be effectively suppressed. The volume ratio of 2-fluorobutane in the seasoning gas is preferably 1% by volume or more, more preferably 5% by volume or more, further preferably 10% by volume or more, and 60% by volume or less. Is preferable and 50% by volume or less is more preferable. In particular, by appropriately adjusting the volume ratio of nitrogen and 2-fluorobutane in the seasoning gas, the atomic weight of nitrogen in the coating and the thickness of the coating can be appropriately balanced, and as a result, a better 2 -It is presumed that it becomes possible to obtain the effect of suppressing decomposition of fluorobutane. For example, if the volume ratio of nitrogen in the seasoning gas is set to the above lower limit value or more, it is possible to sufficiently suppress the decomposition of 2-fluorobutane in the plasma etching step by sufficiently increasing the amount of nitrogen atoms in the coating film. Inferred. Further, if the volume ratio of nitrogen in the seasoning gas is not more than the above upper limit value, the film formed by the seasoning gas is sufficiently thickened or densified to form a film formed on the surface of the processing chamber. It is presumed that it is possible to make it difficult to detach from the inner surface of the processing chamber in the plasma etching process.

  The “volume ratio of nitrogen in the seasoning gas” can be calculated based on the flow rate of each gas introduced into the processing chamber in the seasoning process. Here, in general, each gas source that can be connected to the plasma etching apparatus can be a gas containing a single gas species with high purity. The “gas containing a single gas species in high purity” is a gas that does not substantially contain other gas species, and for example, 99.99% by volume or more, preferably 100% by volume is a single gas species. Is a gas occupied by. Therefore, the flow rate supplied from each gas source substantially corresponds to the volume ratio of each gas introduced into the processing chamber.

Here, it is preferable that the seasoning gas does not include any gas other than 2-fluorobutane and nitrogen (that is, the third component). However, it does not exclude that the seasoning gas contains a third component. When the seasoning gas contains the third component, the volume ratio of the third component may be less than 50% by volume based on 100% by volume of the entire seasoning gas. The third component is not particularly limited and includes a gas that can be introduced into the processing chamber in the subsequent plasma etching step. Specific examples of such a third component include rare gases such as helium gas, argon gas, neon gas, krypton gas, and xenon gas; oxygen; and fluorocarbon gases other than 2-fluorobutane, hydrocarbons. Gas etc. are mentioned. Note that other fluorocarbon gases include fluoromethane (CH ₃ F), difluoromethane (CH ₂ F ₂ ), trifluoromethane (CHF ₃ ), and tetrafluoromethane (CF ₄ ). Further, examples of the hydrocarbon gas include methane (CH ₄ ) and ethane (C ₂ H ₆ ).

  In the seasoning method of the present invention, a high-frequency electric field is applied to the seasoning gas containing at least 2-fluorobutane and nitrogen to cause glow discharge, and various components contained in the seasoning gas are chemically activated ions. , Separation of active species such as electrons, and neutral species. Various conditions such as an electric field that can be applied to the seasoning gas are not particularly limited, and known plasma processing conditions can be followed.

<Stay time>
In the seasoning method of the present invention, the residence time of the seasoning gas in the processing chamber is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and preferably 30 seconds or less, 20 seconds. The following is more preferable. When the residence time of the seasoning gas in the plasma processing chamber is within the above range, the plasma during seasoning can be stabilized, and a necessary and sufficient amount of nitrogen atoms can be introduced into the film. As a result, the decomposition of 2-fluorobutane introduced into the processing chamber as an etching gas in the plasma etching step can be suppressed more effectively. As described above, the residence time is the flow rate of the seasoning gas introduced into the processing chamber in the seasoning process (hereinafter, also referred to as “gas flow rate”), the volume of the processing chamber during the seasoning process (hereinafter, also referred to as “processing chamber volume”). And the pressure in the processing chamber during the seasoning process (hereinafter, also referred to as “processing chamber pressure”). Specifically, it can be calculated according to the following equation (1). The coefficient 78.95 in the following equation (1) is a coefficient for unit conversion.

Residence time [sec] = 78.95 x processing chamber pressure [torr] x processing chamber volume [L] / gas flow rate [sccm] ・ ・ ・ (1)

Here, the gas flow rate can be appropriately changed by adjusting the set flow rate of the gas supply mechanism provided in the plasma etching apparatus. Further, the processing chamber pressure can be appropriately changed by a pressure adjusting mechanism provided in the plasma etching apparatus.

(Plasma etching method)
Hereinafter, an example of the plasma etching method of the present invention including a seasoning step according to the above-described seasoning method will be described. Such a plasma etching method is characterized by including a seasoning step according to the seasoning method of the present invention described above, and a plasma etching step of performing plasma etching using an etching gas containing 2-fluorobutane, which is subsequent to the seasoning step. . According to the plasma etching method of the present invention, it is possible to proceed with etching while suppressing decomposition of 2-fluorobutane contained in the etching gas in the etching step. The term "etching" refers to a technique used in a semiconductor device manufacturing process or the like to etch a very highly integrated fine pattern on a processed object that includes a processed object and a non-processed object. In particular, "plasma etching" means applying a high-frequency electric field to the etching gas to cause glow discharge, separating the etching gas into chemically active ions, electrons, and neutral species, and etching these active species and etching. It refers to a technique of performing etching by utilizing a chemical reaction between a target material and a reaction due to physical collision between these active species and the etching target material.

The plasma etching method is not particularly limited and can be carried out using a general plasma etching apparatus. Among them, it is preferable to use a reactive ion etching (RIE) device. Examples of the RIE device include a helicon wave type plasma etching device, a high frequency induction type plasma etching device, a parallel plate type plasma etching device, a magnetron type plasma etching device, and a microwave type plasma etching device. Here, a parallel plate type plasma etching apparatus, a high frequency induction type plasma etching apparatus, and a microwave type plasma etching apparatus can be preferably used for the plasma etching method including the seasoning method of the present invention. This is because plasma in the high density region can be easily generated.
Hereinafter, as an example of the plasma etching method of the present invention, a plasma etching method including performing an arbitrary cleaning step, a seasoning step, and a plasma etching step in this order will be described.

<Cleaning process>
In the cleaning step, for example, a dummy object to be processed such as a dummy wafer is introduced into the processing chamber, and then the processing chamber is degassed to a vacuum. Here, the “dummy” means a wafer / object to be processed which is different from the wafer / object to be processed in the plasma etching process. That is, the wafer or the like introduced into the processing chamber in the cleaning step is used only for adjusting the environment inside the processing chamber, and is not a final product. Note that the same dummy object to be processed can be left mounted in the processing chamber through the cleaning step and the seasoning step described later. Further, it is not essential to place the dummy object to be processed in the processing chamber in the cleaning step and / or the seasoning step.

Then, a predetermined cleaning gas is introduced into the vacuumed processing chamber. Here, the cleaning gas is not particularly limited, and oxygen, tetrafluoromethane (CF ₄ ), nitrogen trifluoride (NF ₃ ), or a mixed gas thereof can be used.

<Seasoning process>
Then, in the seasoning step, while exhausting the cleaning gas from the processing chamber, the above-described seasoning gas is introduced into the processing chamber, and a high frequency electric field is applied to the seasoning gas in the processing chamber to cause glow discharge, A plasma of seasoning gas is generated. According to such a seasoning process, the surface of the processing chamber can be stabilized. At this time, the dummy wafer that has been introduced into the processing chamber in the cleaning process can be used as it is.

  Further, in the seasoning step, the temperature of the dummy wafer may be adjusted to, for example, -50 ° C or higher and 120 ° C or lower. The temperature of the dummy wafer and the like can be controlled by using a cooling gas such as helium gas and a cooling device. When a parallel plate type plasma etching apparatus having an upper electrode of 60 MHz and a lower electrode of 2 MHz and a distance between these electrodes of 35 mm is used as the plasma etching apparatus, the power supplied to the upper electrode is 100 W or more and 2000 W or less. The power supplied to the lower electrode can be freely combined within the range of 0 W or more and 600 W or less. Furthermore, the upper electrode temperature can be freely combined within the range of 20 ° C. to 180 ° C., and the processing chamber wall surface temperature can be freely combined within the range of 20 ° C. to 180 ° C.

  Then, under such conditions, it is preferable to adjust the flow rate of the seasoning gas so that the staying time of the seasoning gas in the seasoning process is within the range described above (0.2 seconds or more and 30 seconds or less). Even in the cleaning process, the temperature of the dummy wafer and various settings of the etching apparatus can be freely combined within the range described above for the seasoning process.

<Plasma etching process>
A plasma etching process is performed subsequent to the seasoning process. In the plasma etching method of the present invention, since the plasma etching step is performed after the seasoning step, 2-fluorobutane introduced as an etching gas into the processing chamber is suppressed from being decomposed in the etching step, and the etching is performed. The efficiency can be improved. In the present specification, “to perform the plasma etching step after the seasoning step” means that impurities are introduced into the processing chamber directly or continuously to the seasoning step or between the seasoning step and the plasma etching step. It means that the plasma etching process is performed by only allowing the intervening of other steps that do not infiltrate the inside of the processing chamber and can substantially change the state of the processing chamber.

  More specifically, as another step that can make the state of the processing chamber substantially unchanged, the seasoning gas is exhausted from the processing chamber after the seasoning process is completed, the processing chamber is evacuated, and the dummy is removed from the processing chamber. It is possible to interpose the etching preparation step, which is a step of unloading the object to be processed and carrying in the object to be processed such as a wafer into the processing chamber. When the dummy object is carried out of the processing chamber in the etching preparation step / when the object is carried into the processing chamber, for example, the dummy object is carried out to a vacuum chamber such as a load lock chamber and the like. It is possible to carry the object to be processed, which has been stored in the same room, into the processing chamber. By doing so, the state in the processing chamber can be kept substantially unchanged between the seasoning step and the plasma etching step. The etching preparation process may be a sub-step included in the plasma etching process as a process forming a part of the plasma etching process. Note that it is necessary that no other process such as a cleaning process that can change the composition of the atmosphere in the processing chamber is interposed between the plasma etching process and the seasoning process, which is a process immediately before the plasma etching process.

  Further, it is possible to intervene an operation of exhausting the seasoning gas from the processing chamber to create a vacuum in the processing chamber between the seasoning process and the plasma etching process. In other words, other steps can be interposed between the end of the seasoning process and the start of the plasma etching process as long as it is possible to prevent impurities from entering the processing chamber.

  As described above, the plasma etching step and the seasoning step are preferably performed directly and continuously, but as described above, impurities are not introduced into the processing chamber and the state inside the processing chamber is substantially changed. However, sub-steps such as an etching preparation process, an exhaust operation, etc. may be interposed.

In the plasma etching process, plasma etching is performed using an etching gas containing 2-fluorobutane. In addition to 2-fluorobutane, the etching gas may optionally contain a fluorocarbon gas other than 2-fluorobutane or a halogen-based gas other than fluorine. Further, one or more kinds of other gases that can be selected from rare gas, oxygen, nitrogen, etc. may be mixed and used as an additive gas with respect to the etching gas. Other fluorocarbon gases other than 2-fluorobutane that can be used in the plasma etching process include fluoromethane (CH ₃ F), difluoromethane (CH ₂ F ₂ ), trifluoromethane (CHF ₃ ), and tetrafluoromethane ( CF ₄ ) and the like. In addition, examples of the rare gas include helium gas, argon gas, neon gas, krypton gas, and xenon gas. By using an additive gas mixed with the etching gas, the etching rate in the plasma etching step can be adjusted as necessary.

  The etching gas is not particularly limited as long as it contains 2-fluorobutane, and may have any composition. In particular, when the volume ratio of 2-fluorobutane is preferably 1% by volume or more, and more preferably 3% by volume or more with 100% by volume of the entire etching gas, suppression of decomposition of 2-fluorobutane in the etching gas. The effect can be obtained more significantly. The mixing ratio of the additive gas to the etching gas is not particularly limited and can be set arbitrarily. In other words, the mixing ratio of the additive gas to the etching gas can be set arbitrarily from the viewpoint of the required etching rate and the like. Further, the temperature of the object to be processed such as a wafer, the temperature in the processing chamber, and various setting conditions in the etching apparatus can be appropriately adjusted as necessary.

<Deviation rate>
Here, according to the seasoning step according to the seasoning method of the present invention and the plasma etching method of the present invention including the seasoning step, the decomposition of 2-fluorobutane in the plasma etching step can be favorably suppressed. Therefore, in the plasma etching process performed in the processing chamber after the seasoning process, decomposition of 2-fluorobutane contained in the etching gas is suppressed. This can be confirmed, for example, by the low value of the "deviation rate" that can be calculated according to the description in Examples described later. The “deviation rate” is an actual measurement of the gas introduced into the processing chamber, which can be calculated based on the internal pressure increase rate in the processing chamber, with the set flow rate when introducing 2-fluorobutane being 100 (%). It is a value indicating how much the gas flow rate (hereinafter, also referred to as “actually measured flow rate”) deviates from the set flow rate.

  As mentioned above, it is believed that the decomposition of 2-fluorobutane may result in decomposition products such as hydrogen fluoride and butenes. As a result, it is considered that the pressure inside the processing chamber becomes higher than the assumed internal pressure when the decomposition products are generated, as compared with the case where only 2-fluorobutane exists in the processing chamber. In other words, 2-fluorobutane introduced into the processing chamber is not decomposed, and the pressure inside the processing chamber and the decomposition of 2-fluorobutane assuming that the state at the time of introduction is maintained in the processing chamber have occurred. The pressure in the processing chamber may be different. Based on this, the pressure in the processing chamber in the plasma etching step was measured over time, and the "actually measured flow rate" of 2-fluorobutane introduced into the processing chamber was calculated backward from the rising rate of the pressure in the processing chamber, By calculating the deviation from the set flow rate, it is possible to grasp how much the 2-fluorobutane introduced into the processing chamber is decomposed.

  Furthermore, if the generated decomposition products are polymerized after the decomposition of 2-fluorobutane, the pressure inside the processing chamber may be lower than the assumed internal pressure. In this case, the “actually measured flow rate” calculated back from the rising rate of the processing chamber pressure may be a value lower than the set flow rate. Even in this case, by calculating the difference between the actually measured flow rate and the set flow rate, it is possible to grasp how much 2-fluorobutane introduced into the processing chamber is converted into another substance.

  Even if it is assumed that both decomposition and polymerization occur in the processing chamber, unless the volume increase due to decomposition and the volume decrease due to polymerization do not completely coincide with each other between the measured flow rate and the set flow rate, Some divergence may occur. The probability that such a perfect match will occur is extremely low. In addition, the studies conducted by the present inventors have revealed that the progress of polymerization basically requires a longer time than the decomposition reaction. Therefore, based on the value of the deviation rate as described above, it is possible to determine whether or not 2-fluorobutane introduced as an etching gas has been converted into another substance mainly through a decomposition reaction.

  In any case, the fact that the divergence rate is calculated means that most of 2-fluorobutane introduced into the processing chamber is decomposed by reacting with the surface of the processing chamber, or is polymerized, etc. It can mean that it has been converted to the substance. The large value of the deviation rate means that the rate of conversion of 2-fluorobutane introduced as an etching gas into another substance is large even if the cancellation due to the decomposition and the polymerization is taken into consideration. Therefore, the value of the deviation rate is preferably as small as possible from an industrial viewpoint, but specifically, it is preferably 10% or less, and more preferably 5% or less. The deviation rate may of course be 0%.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples, and the type of processing gas used, the conditions of seasoning, etc. can be changed without departing from the gist of the present invention.
In Examples and Comparative Examples, the effect of suppressing the decomposition of 2-fluorobutane was evaluated using the "deviation rate" which is a value calculated as follows. In addition, the staying time of the seasoning gas in the seasoning process in Examples and Comparative Examples was calculated as follows.

<Deviation rate>
After the 120-second seasoning step performed according to the examples and comparative examples, 2-fluorobutane was introduced into the processing chamber at a set flow rate of 40 sccm for 210 seconds. Then, the rising speed of the pressure inside the processing chamber was obtained, and the "actually measured flow rate" of the gas actually introduced into the processing chamber was calculated from the rising speed. Then, the deviation rate was calculated according to the following equation (2).

Deviation rate [%] = √ ((measured flow rate / set flow rate-1) ^ 2) × 100 ... (2)

<Stay time>
The residence time of the seasoning gas in the seasoning process according to the examples and comparative examples was calculated according to the following formula (1).

Residence time [sec] = 78.95 x processing chamber pressure [torr] x processing chamber volume [L] / gas flow rate [sccm] ・ ・ ・ (1)

(Example 1)
As the plasma etching apparatus, a parallel plate type plasma etching apparatus having an upper electrode of 60 MHz, a lower electrode of 2 MHz and a distance between these electrodes of 35 mm was used. The internal volume of the processing chamber of this parallel plate type plasma etching apparatus was 30 L.
In the seasoning step, the power supplied to the upper electrode was 500 W, the temperature of the upper electrode was 80 ° C., the surface temperature of the processing chamber wall was 80 ° C., the power supplied to the lower electrode was 0 W, and the processing chamber pressure was kept constant at 0.08 torr. For cooling the lower part, the cooling unit was set to 20 ° C. and the helium pressure was set to 1000 Pa. Here, as the seasoning gas, 2-fluorobutane was introduced into the processing chamber at a set flow rate of 40 sccm and nitrogen at a set flow rate of 40 sccm. This state was maintained for 120 seconds, and the seasoning process was performed. Then, when the deviation rate and the staying time were calculated according to the above method, the results were as shown in Table 1.

(Examples 2 to 5)
The seasoning step was performed in the same manner as in Example 1 except that the set flow rates of 2-fluorobutane and nitrogen set as the seasoning gas were changed as shown in Table 1. Then, when the deviation rate and the staying time were calculated according to the above method, the results were as shown in Table 1.

(Comparative Example 1)
When the deviation rate and the residence time were calculated according to the above method without performing the seasoning step, the results were as shown in Table 1.

(Comparative Examples 2 to 7)
The seasoning process was performed in the same manner as in Example 1 except that the composition of the seasoning gas was changed as shown in Table 1. Then, when the deviation rate and the staying time were calculated according to the above method, the results were as shown in Table 1.

From Table 1, in Examples 1 to 5 in which 2-fluorobutane was introduced into the processing chamber after the seasoning process using the seasoning gas containing 2-fluorobutane and nitrogen, the deviation rate was as low as 10% or less, and plasma etching was performed. It can be seen that the decomposition of 2-fluorobutane that can be introduced as an etching gas in the process can be suppressed well.
On the other hand, it can be seen from Comparative Example 1 that when the seasoning step was not performed, the deviation rate was high and the decomposition of 2-fluorobutane had occurred.
In addition, from Comparative Examples 2 to 3 and 6 to 7, nitrogen, 2-fluorobutane, and general etching gas such as octafluorocyclobutane (C ₄ F ₈ ) and fluoromethane (CH ₃ F) were separately seasoned. It can be seen that even when used in the process, the dissociation rate was high and the decomposition of 2-fluorobutane could not be suppressed.
Furthermore, in Comparative Example 4, the seasoning step was performed under the same conditions as in Example 1 except that argon was used instead of nitrogen, but the deviation rate was high at about 19%, and 2-fluorobutane other than nitrogen was used. It can be seen that the effect of suppressing decomposition of 2-fluorobutane cannot be obtained by the seasoning method using the seasoning gas obtained by mixing the above inert gas.
Then, in Comparative Example 5, the seasoning process is performed under the same conditions as in Example 1 except that octafluorocyclobutane (C ₄ F ₈ ) is used instead of 2-fluorobutane, but the deviation rate exceeds 50%. Therefore, it is understood that the effect of suppressing decomposition of 2-fluorobutane cannot be obtained by the seasoning method using the seasoning gas obtained by mixing the fluorocarbon other than 2-fluorobutane and nitrogen.

According to the present invention, it is possible to provide a seasoning method for a plasma processing apparatus, which can favorably suppress decomposition of 2-fluorobutane in a plasma etching step.
According to the present invention, it is possible to provide a plasma etching method capable of suppressing decomposition of 2-fluorobutane in etching gas.

Claims (4)

  A seasoning method for stabilizing the inner surface of the plasma processing chamber by performing plasma processing using a seasoning gas containing 2-fluorobutane and nitrogen in a preceding stage of a plasma etching process in which plasma etching is performed using an etching gas containing 2-fluorobutane. .   The seasoning method according to claim 1, wherein a volume ratio of nitrogen in the seasoning gas is 40% by volume or more.   The seasoning method according to claim 1, wherein the residence time of the seasoning gas in the plasma processing chamber is 0.2 seconds or more and 30 seconds or less. A seasoning step according to the seasoning method according to any one of claims 1 to 3, and a plasma etching step that follows the seasoning step and performs plasma etching using an etching gas containing 2-fluorobutane;
And a plasma etching method including.