JP6569578B2 - Plasma etching method - Google Patents

Description

  The present invention relates to a plasma etching gas and a plasma etching method, and more particularly to a method capable of selectively plasma etching a silicon oxide film.

  In manufacturing a semiconductor device, plasma etching may be performed using a processing gas when a thin film formed on an object to be processed is finely processed. Such a thin film is, for example, a silicon compound film such as a silicon nitride film or a silicon oxide film, an organic film containing carbon as a main component, amorphous silicon, a photoresist composition, or the like, polycrystalline silicon, or amorphous silicon. It can be an inorganic film containing an inorganic substance as a main component, which can be formed by, for example. When one of these multiple types of thin film is to be etched and the other thin film is to be non-processed, the processing target is set against the non-processed object formed on the same object. It is necessary to etch selectively. That is, it is necessary to increase the selectivity during etching.

Therefore, conventionally, a plasma etching method for selectively etching a silicon oxide film provided on a substrate which is an object to be processed has been proposed (see, for example, Patent Documents 1 and 2). Patent Document 1 discloses a plasma etching method using a plasma etching gas containing a fluorocarbon having 3 or 4 carbon atoms having at least one unsaturated bond and / or ether bond and having a bromine atom. It is disclosed. Further, in Patent Document 2, it is represented by a general formula C _x B _ry F _z (where x, y, z are natural numbers indicating the number of atoms and satisfy the condition x ≧ 2, y + z = 2x + 2). An etching method for etching a silicon oxide-based material layer using an etching gas containing a bromofluorocarbon compound is disclosed.

International Publication No. 2012/124726 JP-A-5-152255

  In recent years, in the manufacture of semiconductor devices, there has been an increasing demand for higher accuracy of structures formed by etching. In order to increase the accuracy of the structure formed by etching, it is important to increase the selectivity during etching. However, the plasma etching methods disclosed in Patent Documents 1 and 2 have room for improvement in the etching selectivity of the silicon oxide film.

  Accordingly, an object of the present invention is to provide a plasma etching gas and a plasma etching method capable of highly selectively etching a silicon oxide film.

  The present inventors have intensively studied for the purpose of solving the above problems. Then, the present inventor uses a gas containing a bromine compound in which the ratio of the number of bromine atoms / the number of carbon atoms is within a specific range as a processing gas for plasma etching, and does not contain a fluorine atom. The present invention has been completed by finding that it can be etched with high selectivity.

That is, the present invention aims to advantageously solve the above-mentioned problems, and the plasma etching gas of the present invention has a bromine atom / carbon atom ratio of 0.4 to 1.0. It is characterized by containing a bromine compound and not containing a fluorine atom. By using a plasma etching gas containing a bromine compound having a ratio of bromine atoms / carbon atoms in the specific range and not containing fluorine atoms, the silicon oxide film can be etched with high selectivity.
Here, “selectively” etching in the present invention means that the etching selectivity is more than 1, and in particular, “etching a silicon oxide film highly selectively” means that the etching selectivity is 2 or more. , More preferably 10 or more, still more preferably infinite.
In this specification, the “etching selectivity” is a value obtained by dividing the etching depth of the processing target per unit time by the etching depth of the non-processing target. Specifically, the “etching selectivity ratio of the silicon oxide film with respect to the non-processing target” is a value obtained by dividing the etching depth of the silicon oxide film per unit time by the etching depth of the non-processing target. . Here, the non-processing target can be, for example, a silicon nitride film, an inorganic film, or an organic film.

  Here, the plasma etching gas of the present invention preferably has 2 or 3 carbon atoms in the bromine compound. This is because the etching efficiency during etching can be further improved.

  In the plasma etching gas of the present invention, the bromine compound preferably has a boiling point of 50 ° C. or lower. This is because the load on the plasma etching apparatus and the piping is small, and the plasma etching process can be made more efficient.

  In the plasma etching gas of the present invention, the bromine compound preferably contains a hydrogen atom. This is because the selectivity during etching can be further improved.

  Another object of the present invention is to advantageously solve the above-mentioned problems, and the plasma etching method of the present invention is a plasma etching method for plasma-etching a target object having a silicon oxide film and a silicon nitride film. A preparatory step of placing the object to be processed in a processing container, and an etching step of plasma etching the silicon oxide film on the object to be processed by plasma of any of the plasma etching gases described above. The etching selectivity of the silicon oxide film to the silicon nitride film is 2 or more, and the etching selectivity of the silicon oxide film to the organic film and / or inorganic film is 2 or more. According to the plasma etching method using a plasma etching gas containing a bromine compound in which the ratio of bromine atoms / carbon atoms is within the specific range and not containing fluorine atoms, the silicon oxide film is highly selectively etched. be able to.

  According to the present invention, it is possible to provide a plasma etching gas and a plasma etching method capable of highly selectively etching a silicon oxide film.

  Hereinafter, embodiments of the present invention will be described in detail. The plasma etching gas and the plasma etching method of the present invention can be used in a semiconductor device manufacturing process. The plasma etching method of the present invention is a plasma etching method capable of performing plasma etching on a target object having a silicon oxide film and a silicon nitride film. The object to be processed is not particularly limited as long as it is an object that can be processed by plasma etching, and can be any object. Examples of the object to be processed include a glass substrate, a silicon single crystal wafer, and a gallium-arsenide substrate. For example, when a silicon single crystal wafer is used as an object to be processed, for example, a silicon nitride film, a silicon oxide film, an organic film, and / or an inorganic film is formed on the object to be processed as necessary. Is formed.

In this specification, “silicon nitride film” refers to a film formed of a silicon compound containing nitrogen atoms such as Si ₃ N ₄ (SiN), SiCN, SiBCN, or the like. Further, in the present specification, the “silicon oxide film” refers to a film formed of a silicon compound containing oxygen atoms such as SiO ₂ , SiOC, and SiOCH. Furthermore, in this specification, “organic film” refers to a film containing carbon as a main component. “Mainly containing carbon” means that the ratio of carbon contained in the material forming the film is more than 50% by mass. Specifically, carbon-based materials such as amorphous carbon, photoresist compositions, etc. This means a film formed by (hereinafter also referred to as a resist film). Examples of the photoresist composition include a KrF resist composition, an ArF resist composition, and an X-ray resist composition. Furthermore, in the present invention, the “inorganic film” is a film containing an inorganic substance as a main component other than a silicon oxide film or a silicon nitride film, and means a film in which more than 50% of the material forming the film is an inorganic substance. Specific examples include a polycrystalline silicon film and an amorphous silicon film.

  In the plasma etching method of the present invention, “etching” refers to a technique of etching a very highly integrated fine pattern on a target object used in a semiconductor device manufacturing process or the like. “Plasma etching” is a process in which a high frequency electric field is applied to a processing gas to cause glow discharge, and the processing gas is separated into chemically active ions, electrons, and neutral species and etched with these active species. A technique for performing etching by utilizing a chemical reaction with a target material and a reaction caused by physical collision.

(Plasma etching gas)
The plasma etching gas of the present invention needs to contain a bromine compound having a ratio of bromine atoms / carbon atoms of 0.4 or more and 1.0 or less, and no fluorine atoms. According to such plasma etching gas, the silicon oxide film can be highly selectively etched with respect to the silicon nitride film. Examples of the plasma etching gas that satisfies the above conditions include an organic bromine compound having a carbon-bromine bond, and specifically, bromoethane that can be represented by the general formula C ₂ H ₅ Br, a general formula C ₂ H ₃ Br And vinyl bromide represented by the general formula CH ₃ Br.

  Here, in completing the present invention, first, when the gas of bromine compound is used as the plasma etching gas, the present inventors set the number of Br atoms contained in the bromine compound to 0.4, which is the number of C atoms. It has been found that a bromine compound gas less than twice cannot selectively etch a silicon oxide film. Furthermore, as a result of repeated investigations by the present inventors, if the plasma etching gas contains fluorine atoms, the silicon nitride film is easily etched, and the silicon oxide film is selectively etched with respect to the silicon nitride film. It turns out that you can't. Furthermore, the present inventors have also found that when the number of Br atoms contained in the bromine compound exceeds 1.0 times the number of C atoms, it is not suitable as a plasma etching gas. Therefore, the present inventors, based on these findings, contains a bromine compound having a bromine atom / carbon atom ratio of 0.4 or more and 1.0 or less, and a gas containing no fluorine atom, The present invention has been completed by finding that it can be suitably used as a plasma etching gas for selectively processing a silicon oxide film with respect to a silicon nitride film.

  Further, in the plasma etching gas, the bromine compound preferably has 2 or 3 carbon atoms. If the number of carbon atoms of the bromine compound contained in the plasma etching gas is 2 or 3, when used as the plasma etching gas, formation of desorbed species is easy, and the etching efficiency can be improved.

  In the plasma etching gas, the boiling point of the bromine compound is preferably 50 ° C. or less, and more preferably 40 ° C. or less. If the boiling point of the bromine compound contained in the plasma etching gas is 50 ° C. or less, when introducing the plasma etching gas into the plasma etching apparatus, liquefaction in the piping or the like is prevented, and occurrence of failures due to liquefaction is avoided. Therefore, the plasma etching process can be made efficient.

Further, in the plasma etching gas, the bromine compound described above preferably further contains a hydrogen atom. More specifically, it is preferable that the bromine compound contains a carbon-hydrogen bond and can generate active species such as radicals and ions of CH _α (α is an integer) under plasma conditions. This is because these active species have relatively low reactivity with the silicon nitride film, and the silicon oxide film can be more selectively etched with respect to the silicon nitride film. Furthermore, since the bromine compound contains hydrogen, hydrogen radicals in the gas phase react with fluorine radicals to form hydrogen fluoride, reducing fluorine radicals, which are etchants of the silicon nitride film. By being suppressed, the etching selectivity of the silicon oxide film with respect to the silicon nitride film can be further improved.

(Plasma etching method)
The plasma etching method of the present invention is a plasma etching method for plasma-etching a target object having a silicon oxide film and a silicon nitride film. In addition, the plasma etching method of the present invention includes a preparation step of placing the object to be processed in the processing container, and an etching step of plasma etching the silicon oxide film on the object to be processed by the plasma of the plasma etching gas described above. Including. In the plasma etching method of the present invention, the etching rate of the silicon oxide film is at least twice the etching rate of the silicon nitride film, and the etching rate of the silicon oxide film is the etching rate of the organic film and / or the inorganic film. More than twice the speed. Hereinafter, each step will be described.

<Preparation process>
First, an object to be processed is placed in a dry etching chamber (that is, a processing container) provided in a plasma etching apparatus, and the inside of the processing container is evacuated and evacuated. In addition, the plasma etching method of this invention is not specifically limited, It can implement using a general plasma etching apparatus. Among these, it is preferable to use a reactive ion etching (RIE) apparatus. Examples of the RIE apparatus include a helicon wave type plasma etching apparatus, a high frequency induction type plasma etching apparatus, a parallel plate type plasma etching apparatus, a magnetron type plasma etching apparatus, and a microwave type plasma etching apparatus. In the present invention, a parallel plate type plasma etching apparatus, a high frequency induction type plasma etching apparatus, and a microwave type plasma etching apparatus can be suitably used. This is because plasma in a high density region can be easily generated.

  Furthermore, in the preparation step, the temperature of the object to be processed is, for example, −50 ° C. or higher, more preferably −20 ° C. or higher, further preferably −10 ° C. or higher, preferably 300 ° C. or lower, more preferably 200 ° C. or lower, Preferably, you may adjust to 100 degrees C or less. Note that the temperature of the object to be processed can be controlled using a cooling gas such as helium gas and a cooling device, for example. Thereto, the above-described plasma etching gas and, optionally, oxygen gas and rare gas are introduced at a predetermined speed and pressure. The introduction rate of the plasma etching gas may be determined in proportion to the mixing ratio of various gases in the processing gas. And while supplying process gas in a process container, the pressure in a process container is normally hold | maintained in the range of 0.0013 Pa or more and 1300 Pa or less, Preferably, 0.13 Pa or more and 5 Pa or less.

  Examples of the rare gas that can be optionally supplied into the processing container together with the plasma etching gas include at least one selected from the group consisting of helium gas, argon gas, neon gas, krypton gas, and xenon gas. Especially, argon gas can be used conveniently as a noble gas. By using a rare gas or oxygen gas mixed with the processing gas, the etching rate can be adjusted as necessary. In the case where a rare gas is mixed and used as a processing gas, the mixing ratio of the rare gas is usually 20000 parts by volume or less, preferably 15000 parts by volume or less with respect to 100 parts by volume of the plasma etching gas described above. When oxygen gas is mixed with the processing gas, the mixing ratio of the oxygen gas is usually 1 part by volume or more, preferably 30 parts by volume or more, usually 5000 volumes with respect to 100 parts by volume of the plasma etching gas described above. Part or less, preferably 200 parts by volume or less.

  In addition, plasma etching gas and each gas such as rare gas and oxygen gas that can optionally be used in combination with plasma etching gas are usually filled and transported independently in a container such as a cylinder, and plasma etching apparatus Connected and installed. Then, by opening a valve such as a cylinder, each gas is introduced into the processing container that receives the action of plasma at a predetermined ratio, and the plasma acts on each gas to advance the etching in an etching process described later. Can do.

<Etching process>
The etching process is a process in which the silicon oxide film on the object to be processed is selectively plasma etched with respect to a non-processed object by plasma of a plasma etching gas. Such selective etching uses a plasma etching gas that contains a bromine compound having a ratio of bromine atoms / carbon atoms of 0.4 to 1.0 and does not contain fluorine atoms, as described above. Can be implemented. The non-processing object can be a silicon nitride film, an organic film, and / or an inorganic film. More specifically, the non-processing target can be an Si ₃ N ₄ film and an organic film and / or a polycrystalline silicon film formed of an ArF resist composition. In particular, the etching selectivity of the silicon oxide film to the silicon nitride film and the etching selectivity of the silicon oxide film to the organic film and / or the inorganic film in the etching process are 2 or more, preferably 10 or more, and infinite. It is more preferable that
In addition, it is desirable to perform an etching process in a high-density plasma atmosphere from a viewpoint of expressing the effect of plasma etching better. The plasma density in the etching step is not particularly limited, and is preferably 10 ¹² / cm ³ or more, more preferably 10 ¹² / cm ³ or more and 10 ¹³ / cm ³ or less.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
The object to be processed, the plasma etching apparatus, and the plasma etching conditions used in the examples and the comparative examples were as follows. In addition, the etching selectivity in Examples and Comparative Examples was evaluated as follows.

<To-be-processed object>
A plurality of chip pieces of a silicon single crystal wafer were prepared as objects to be processed. The prepared chip pieces of a plurality of silicon single crystal wafers include those having a silicon nitride film (Si ₃ N ₄ film) on the surface, those having a silicon oxide film (SiO ₂ film) on the surface, and polycrystalline on the surface Some have a silicon film (Si film) and others have a film (ArF film) formed of an ArF resist composition on the surface. The ArF film was a film formed using a commercially available chemically amplified ArF resist composition based on (meth) acrylic resin (the content ratio of the methacrylic resin is more than 50% by mass).
<Plasma etching equipment>
A parallel plate type plasma plasma etching apparatus was used as the plasma etching apparatus. The parallel plate type plasma etching apparatus has an upper electrode and a lower electrode in an etching chamber (processing vessel), and the distance between the lower surface of the upper electrode and the upper surface of the lower electrode was 35 mm. The frequency of the upper electrode of the parallel plate type plasma generator was 60 MHz, and the frequency of the lower electrode was 2 MHz.
<Plasma etching conditions>
The etching process was performed by setting the power of the upper electrode to 500 W, the power of the lower electrode to 200 W, and keeping the pressure in the processing container constant at 2.7 Pa (about 20 mTorr). The temperature conditions were such that the temperature of the upper electrode was 80 ° C., the temperature of the side wall of the processing vessel was 60 ° C., and the temperature of the lower electrode was 20 ° C. The temperature of the object to be processed was 20 ° C., the same as the temperature of the lower electrode. In the examples and comparative examples, the plasma etching time was 60 seconds. Therefore, the values of the etching depths of the objects to be processed obtained in Examples and Comparative Examples correspond to the etching rate per minute of each plasma etching method as it is.

<Etching selectivity>
In Examples and Comparative Examples, film thicknesses of various wafers before and after etching were measured with an ellipsometer, and the etching rate was calculated from the measured values. In the examples and comparative examples, the etching time was all 60 seconds, so the value obtained by subtracting the film thickness after etching from the film thickness before etching corresponds to the value of the etching rate as it is. And the etching selectivity was computed from the obtained speed | rate according to the following formula | equation. When the value serving as the denominator is 0 or less, the selection ratio is assumed to be infinite (∞). Further, when the numerator value was 0 or less, the selectivity was indicated as “−” because measurement was impossible. A larger etching selectivity value means that the film to be etched is preferentially etched, and in particular, when the etching selectivity value is ∞, The film (ie, the silicon nitride film, polycrystalline silicon film, or ArF film that is the non-processed object) was not etched at all, or rather the deposit was formed on the non-processed film and was protected. Means. On the other hand, when the molecular value is 0 or less, the film to be etched (that is, the silicon oxide film) is not etched at all, or rather a deposit is generated on the silicon oxide film. Means. In this case, it means that the etching reaction does not proceed in the etching process, but rather the deposition reaction proceeds.
Etching selectivity ratio of silicon oxide film to silicon nitride film (SiO ₂ / SiN) = (etching rate of SiO ₂ film / etching rate of Si ₃ N ₄ film)
Etching selectivity ratio of silicon oxide film to polycrystalline silicon film (SiO ₂ / Si) = (etching rate of SiO ₂ film / etching rate of Si film)
Etching ratio of silicon oxide film to ArF film (SiO ₂ / ArF) = (SiO ₂ film etching rate / ArF film etching rate)

Example 1
First, in the preparation step, a target object having a Si ₃ N ₄ film on the surface, a target object having a SiO ₂ film on the surface, a target object having a Si film on the surface, and an ArF surface on the surface. One to-be-processed object which has a film | membrane was arrange | positioned 1 each, and the inside of a processing container was evacuated. Then, bromoethane (C ₂ H ₅ Br, number of bromine atoms / number of carbon atoms = 0.5, boiling point 38 ° C.) gas is supplied at a rate of 25 sccm, oxygen gas at a rate of 10 sccm, and argon gas at 200 sccm. Introduced at a rate, the etching process was performed under the plasma etching conditions described above. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

(Example 2)
The etching process was performed in the same manner as in Example 1 except that the oxygen gas introduction rate was changed to 15 sccm. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

(Comparative Example 1)
Instead of bromoethane gas, 2-bromo-3,3,3, -trifluoropropene (C ₃ H ₂ BrF ₃ , number of bromine atoms / number of carbon atoms = 0.3, boiling point 34 ° C.) gas treated at 25 sccm The etching process was performed in the same manner as in Example 1 except that it was introduced into the container. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

(Comparative Example 2)
Instead of bromoethane gas, 2-bromo-3,3,3, -trifluoropropene (C ₃ H ₂ BrF ₃ , number of bromine atoms / number of carbon atoms = 0.3, boiling point 34 ° C.) gas treated at 25 sccm The etching process was performed in the same manner as in Example 2 except that it was introduced into the container. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

(Comparative Examples 3 to 10)
Instead of bromoethane gas, 2-bromo-3,3,3, -trifluoropropene (C ₃ H ₂ BrF ₃ , number of bromine atoms / number of carbon atoms = 0.3, boiling point 34 ° C.) gas in the processing vessel Etching was conducted in the same manner as in Example 1 except that the introduction rate of 2-bromo-3,3,3, -trifluoropropene gas and the introduction rate of oxygen gas were changed as shown in Table 1. The process was performed. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

(Comparative Example 11)
The etching process was performed in the same manner as in Example 1 except that carbon tetrafluoride (CF ₄ ) was introduced into the processing vessel at a rate of 5 sccm in addition to bromoethane gas, oxygen gas, and argon gas. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

(Comparative Example 12)
Instead of bromoethane gas, 2-bromo-1-propene (C ₃ H ₅ Br, number of bromine atoms / number of carbon atoms = 0.3, boiling point 48 ° C.) gas was introduced into the processing vessel at 25 sccm, The etching process was performed in the same manner as in Example 1. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

(Comparative Examples 13-18)
The etching process was performed in the same manner as in Comparative Example 12 except that the supply amount of 2-bromo-1-propene gas was changed as shown in Table 1. Table 1 shows the results of evaluating the etching selectivity of the obtained object to be processed according to the method described above.

Table 1 shows the following. First, as in Examples 1 and 2, when a bromoethane gas having a bromine atom / carbon atom ratio of 0.5 and containing no fluorine atoms is used as a plasma etching gas, silicon for all non-processing objects is used. It can be seen that the etching selectivity of the oxide film is infinite, and the silicon oxide film can be etched with high selectivity. On the other hand, in Comparative Examples 1 to 18 using a plasma etching gas containing a fluorine atom and / or containing a bromine compound having a bromine atom / carbon atom ratio of less than 0.4, the silicon nitride film The etching selectivity of the silicon oxide film is less than 2, or the etching selectivity of the silicon oxide film to the Si film and / or ArF film is less than 2, and the silicon oxide film could not be etched with high selectivity. I understand.
In particular, in the case where 2-bromo-3,3,3, -trifluoropropene gas having a bromine atom number / carbon atom ratio of Comparative Examples 1 to 10 is 0.3, the plasma etching gas is processed. The deposited film is deposited on the target silicon oxide film, or the etching speed of the silicon nitride film is equal to or higher than the etching speed of the silicon oxide film, so that the silicon oxide film cannot be selectively etched. I understand that.
In addition, in the plasma etching gas containing the bromoethane gas having a bromine / carbon atom ratio of 0.5 and a small amount of carbon tetrafluoride used in Comparative Example 11, the silicon oxide film to be processed is used. It can be seen that the silicon oxide film cannot be selectively etched because the deposited film is also deposited on the top.
Further, in Comparative Examples 12 to 14 and 16 to 18 in which 2-bromo-1-propene gas containing no fluorine and having a bromine atom / carbon atom ratio of 0.3 was used as a plasma etching gas, The deposited film is deposited on the target silicon oxide film, or the etching speed of the silicon nitride film is relatively high, so the etching selectivity value is low as less than 2, and the silicon oxide film can be selectively etched. You can see that there wasn't.
In particular, in Comparative Example 15 using 2-bromo-1-propene gas as the plasma etching gas, the etching selectivity of the silicon oxide film to the silicon nitride film is good, but the silicon oxide film is compared to the Si film and ArF film. It can be seen that the film could not be selectively etched.

  According to the present invention, the silicon oxide film can be etched with high selectivity.

Claims (4)

A plasma etching method for plasma etching a target object having a silicon oxide film and a silicon nitride film,
A preparation step of placing the object to be processed in a processing container;
The silicon oxide film on the object to be processed by plasma of a plasma etching gas containing a bromine compound having a ratio of bromine atoms / carbon atoms of 0.4 to 1.0 and not containing fluorine atoms An etching process for plasma etching,
The etching selectivity of the silicon oxide film to the silicon nitride film is 2 or more, and the etching selectivity ratio of the silicon oxide film to the organic film and / or inorganic film is 2 or more.
Plasma etching method . The plasma etching method according to claim 1, wherein the bromine compound has 2 or 3 carbon atoms. The plasma etching method according to claim 1, wherein the bromine compound has a boiling point of 50 ° C. or less. The plasma etching method according to claim 1, wherein the bromine compound contains a hydrogen atom.