KR102781519B1 - Method for Dry Etching of Cobalt Thin Films - Google Patents

Abstract

The present invention relates to an etching method for a cobalt thin film, and more specifically, to an etching method for a cobalt thin film which can provide a fast etching speed and an etching profile with high anisotropy (or etching slope) without re-deposition compared to conventional etching methods for cobalt thin films by applying optimal etching process conditions including the type and concentration of etching gas and etching process variables to the cobalt thin film.

Description

{Method for Dry Etching of Cobalt Thin Films}

The present invention relates to a dry etching method for a cobalt thin film, and more specifically, to an etching method for a cobalt thin film that applies optimal etching process conditions to the cobalt thin film using an etching gas containing alcohol gas.

The semiconductor device manufacturing process is demanding a reduction in device size due to increased integration, and as the wiring line width decreases, it is becoming more difficult to cleanly implement the pattern shape of small-size patterns. Accordingly, the processing technology used in the semiconductor manufacturing process is also becoming increasingly strict.

Copper or copper-based metals have been used for liquid crystal displays, gate electrodes, wiring, barrier layers, contact holes, and via holes of thin film transistors in semiconductor devices. However, recently, as the critical dimension of devices has been reduced to several tens of nm or less, the resistance of copper metal wiring has gradually increased, and copper or copper-based metals are being replaced by cobalt or cobalt-based metals.

Cobalt and cobalt-based metals have higher resistivity than copper, but show almost no electromigration and have better dry etching potential than copper, so they are currently receiving attention as next-generation metal wiring materials.

Meanwhile, in general, there are wet etching and dry etching methods in the etching process of thin films for fine patterning. However, as the size of the patterns to be etched is reduced to a size of several micrometers or nanometers, the application of wet etching becomes difficult, and the need for dry etching using plasma that is faithful to pattern transfer is highlighted.

Dry etching process is an etching method that uses low-pressure plasma, and can be divided into two types: ion milling etching and reactive ion etching, depending on the chemical reactivity of the plasma. The ion milling etching method uses argon (Ar) plasma, which is an inert gas, and the reactive ion etching method performs etching using various chemical gases.

Looking at the related prior art, cobalt etching began in the late 1990s, but no notable etching gas or etching technology for a dry etching process has been developed to date. Initially, the ion beam etching method using inert gases such as Ne, Ar, Kr, and Xe was used (JVST B18, 3539, 2000), and the RIE or ICPRIE method was used with gases such as CF ₄ /O ₂ and Cl ₂ /Ar, but satisfactory etching results were not secured (J. Kor. Rad. Waste Sco., 232, 2004). After that, in 2017, a two-step atomic layer etching method was attempted using O ₂ plasma and HCOOH vapor, and a severe undercut profile and an etching slope of approximately 60° were secured (J. Vac. Sci. Technol. A35, 05C305, 2017). In addition, atomic layer etching including vapor etching using Cl ₂ /Ar and HFAC/Ar gas mixtures has been introduced (JVST A37, 021004, 2019). The most recently reported research result was obtained by securing an etching slope of approximately 60° for a 600 nm pattern using BCl ₃ /Ar gas and the ICPRIE method at the Valiey Institute of Physics and Technology (Proceeding of SPIE, 12157 1215718, 2021).

Meanwhile, in general, when ion milling, which utilizes a physical etching mechanism, is used to etch a cobalt thin film, or when the pattern size is approximately 5 ㎛ to 10 ㎛ or less, redeposition occurs around the etched pattern to form a fence shape, as shown in (b) of Fig. 1. This is because the ion milling etching method is an etching mechanism in which a portion of the thin film material is sputtered and removed purely by the collision energy of argon (Ar) cations without a chemical reaction.

Therefore, the current dry etching process for cobalt thin films should be performed by developing the existing etching gases and new etching gases to derive the optimal etching processes, and when etching cobalt thin films for the manufacture of high-integration devices, a reactive ion etching method using a chemical reaction should be applied rather than an ion milling method using a physical etching mechanism.

Recently, high-density plasma reactive ion etching has been applied because it has a high plasma density, which enables a fast etching speed and increases the etching selectivity. In particular, cobalt metal has very low or no reactivity, so the etching speed is very slow, and therefore the etching selectivity of the cobalt thin film with respect to the etching mask is also very low. Therefore, when photoresist is used as a mask by general lithography, it is impossible to form an etched cobalt pattern depending on the etching conditions. In this case, instead of photoresist, a thin film of metal (Ti, Ta, W, TiN, Cr, etc.) or metal oxide (TiO ₂ , SiO ₂ , etc.) or Si ₃ N ₄ must be used as a mask, that is, a hard mask must be used to etch.

However, even when etching a cobalt thin film by reactive ion etching, there was a problem of re-deposition occurring on the side of the etched pattern if an inappropriate etching gas or inappropriate etching gas concentration was used, or if an inappropriate etching process was applied. In addition, when etching was performed with a non-optimized etching gas or etching condition, the occurrence of re-deposition could be reduced, but as shown in (c) of Fig. 1, the etched side slope (etching slope) was very gentle, making it difficult to apply it to the etching of a fine pattern.

Therefore, there is a continuous demand for the development of an etching technology for cobalt thin films that can provide a fast etching speed and a highly anisotropic etching profile through appropriate etching gas and its concentration control.

Korean Patent Publication No. 2021-0115794 (Publication Date: 2021.09.27.) Korean Patent Publication No. 2022-0041420 (Publication Date: 2022.04.01.)

JVST B18, 3539 (2000) J. Kor. Rad. Waste Sco., 232, 2004 J. Vac. Sci. Technol. A35, 05C305, 2017 JVST A37, 021004, 2019 Proceedings of SPIE, 12157 1215718, 2021

The main purpose of the present invention is to solve the above-described problems, and to provide a method for etching a cobalt thin film, which can prevent etching by-products from being redeposited on an etched wall surface of a cobalt thin film, alleviate plasma damage to a metal oxide semiconductor layer under the cobalt thin film without etching residues, and provide a fast etching speed and a highly anisotropic etching profile.

In order to achieve the above object, one embodiment of the present invention provides a method for etching a cobalt thin film, characterized by including the steps of: (a) patterning a cobalt thin film with a hard mask and masking it by etching; (b) converting an etching gas selected from the group consisting of an alcohol gas; a mixed gas containing an alcohol gas and an inert gas; a mixed gas containing an alcohol gas and an oxidizing gas; and a mixed gas containing an alcohol gas, an oxidizing gas, and an inert gas into plasma; and (c) etching the cobalt thin film masked in step (a) using the plasma generated in step (b).

In a preferred embodiment of the present invention, the etching selectivity of the cobalt thin film with respect to the hard mask may be characterized as being 0.4 to 1.5.

In a preferred embodiment of the present invention, the inert gas may be characterized by being at least one selected from the group consisting of He, Ne, Ar, and N ₂ .

In a preferred embodiment of the present invention, the oxidizing gas may be characterized by being at least one selected from the group consisting of oxygen, ozone, radical oxygen, and water vapor.

In a preferred embodiment of the present invention, the hard mask may be characterized by being at least one selected from the group consisting of silicon oxide (SiO ₂ ), Si ₃ N ₄ , TiO ₂ , TiN, Ti, Ta, W, Cr, and carbon (C).

In a preferred embodiment of the present invention, the etching gas of step (b) may be characterized by containing 50 vol% to 100 vol% of alcohol gas with respect to the total volume of the etching gas.

In a preferred embodiment of the present invention, the mixed gas containing the oxidizing gas of step (b) may be characterized by containing 10 vol% to 20 vol% of the oxidizing gas with respect to the total volume of the mixed gas.

In a preferred embodiment of the present invention, the plasma treatment in step (b) may be performed by injecting gas at a process pressure of 0.13 Pa to 1.3 Pa and applying a coil high-frequency power (ICP rf power) of 300 W to 700 W and a dc-bias voltage of 200 V to 400 V.

In a preferred embodiment of the present invention, the etching in step (c) may be characterized in that it is performed by one method selected from the group consisting of high-density plasma reactive ion etching including inductively coupled plasma reactive ion etching, self-enhanced reactive ion etching, reactive ion etching, vapor etching, atomic layer etching, and pulse-modulated high-density plasma reactive ion etching.

In a preferred embodiment of the present invention, the method may further comprise a post-treatment step of removing etching residue using a mixed solution containing ammonia water, hydrogen peroxide, and water after step (c).

Another embodiment of the present invention provides a cobalt thin film etched by the above-described etching method and characterized by having an etching slope of 70° or more.

The etching method of a cobalt thin film according to the present invention applies optimal etching process conditions as well as optimal etching gas and optimal etching gas concentration, thereby providing a fast etching speed and a highly anisotropic etching profile without etching residue and without re-deposition compared to conventional etching methods of a cobalt thin film, and thus can be applied to all devices and apparatuses in which a cobalt thin film is used.

In addition, the present invention does not require an additional configuration for heating the substrate, and can etch a cobalt thin film at a low temperature.

Figure 1 schematically illustrates the side structure before/after thin film etching. (a) is the thin film structure before etching, (b) is the thin film structure etched by the conventional ion milling etching method or reactive ion etching method, (c) is the thin film structure etched by the conventional reactive ion etching method, and (d) is the etching profile of the sample after ideal etching.
FIG. 2 is a schematic diagram of a dry etching method for a cobalt thin film according to an embodiment of the present invention, wherein (i) is a thin film structure in which a photoresist mask (PR mask) on a hard mask/cobalt thin film is patterned, (ii) is a thin film structure in which a hard mask is etched using the patterned photoresist mask, (iii) is a thin film structure in which the photoresist mask on the etched hard mask is removed, and (iv) is a thin film structure after etching of the cobalt thin film using the etched hard mask.
Figure 3 is a graph showing the change in etching rate and etching selectivity of a cobalt thin film and a hard mask according to the concentration of C ₂ H ₅ OH in a C ₂ H ₅ OH/Ar mixed gas among etching gases.
Figure 4 is a SEM image of a cobalt thin film etched according to the C ₂ H ₅ OH concentration in a C ₂ H ₅ OH/Ar mixed gas among etching gases, where (a) is a side view of a thin film etched in Comparative Example 1, (b) is a side view of a thin film etched in Example 4, (c) is a side view of a thin film etched in Example 3, (d) is a side view of a thin film etched in Example 2, and (e) is a side view of a thin film etched in Example 1.
Figure 5 shows SEM images of cobalt thin films treated according to the component ratio of the mixed solution, where (a) is a side view of a thin film treated in Example 5, (b) is a side view of a thin film treated in Example 6, (c) is a side view of a thin film treated in Example 7, (d) is a side view of a thin film treated in Example 8, and (e) is a side view of a thin film treated in Example 9.
Figure 6 is a SEM image of an etched cobalt thin film before/after the mixed solution treatment in the post-processing step, where (a) is a side view of the cobalt thin film of Example 4, (b) is a side view of the cobalt thin film of Example 3, (c) is a side view of the cobalt thin film of Example 2, and (d) is a side view of the cobalt thin film of Example 1. In addition, (e) is a side view of the cobalt thin film of Example 13, (f) is a side view of the cobalt thin film of Example 12, (g) is a side view of the cobalt thin film of Example 6, and (h) is a side view of the cobalt thin film of Example 10.
Figure 7 is a graph showing the change in etching rate and etching selectivity of a cobalt thin film and a hard mask according to the O ₂ concentration in a C ₂ H ₅ OH/O ₂ /Ar mixed gas among etching gases. (a) is the case where C ₂ H ₅ OH is 50 vol% in the C ₂ H ₅ OH/O ₂ /Ar mixed gas, and (b) is the case where C ₂ H ₅ OH is 75 vol% in the C ₂ H ₅ OH/O ₂ /Ar mixed gas.
Figure 8 is a SEM image of a cobalt thin film before and after mixed solution treatment according to the O ₂ concentration in the C ₂ H ₅ OH/O ₂ /Ar mixed gas among etching gases, where (a) is a side view of a cobalt thin film of Example 3, (b) is a side view of a cobalt thin film of Example 16, (c) is a side view of a cobalt thin film of Example 15, (d) is a side view of a cobalt thin film of Example 14, (e) is a side view of a cobalt thin film of Example 13, (f) is a side view of a cobalt thin film of Example 11, (g) is a side view of a cobalt thin film of Example 24, (h) is a side view of a cobalt thin film of Example 23, (i) is a side view of a cobalt thin film of Example 22, and (j) is a side view of a cobalt thin film of Example 21.
Figure 9 is a SEM image of a cobalt thin film before and after mixed solution treatment according to the O ₂ concentration in the C ₂ H ₅ OH/O ₂ /Ar mixed gas among etching gases, where (a) is a side view of a cobalt thin film of Example 2, (b) is a side view of a cobalt thin film of Example 20, (c) is a side view of a cobalt thin film of Example 19, (d) is a side view of a cobalt thin film of Example 18, (e) is a side view of a cobalt thin film of Example 17, (f) is a side view of a cobalt thin film of Example 6, (g) is a side view of a cobalt thin film of Example 28, (h) is a side view of a cobalt thin film of Example 27, (i) is a side view of a cobalt thin film of Example 26, and (j) is a side view of a cobalt thin film of Example 25.
Figure 10 is a graph showing the change in etching rate and etching selectivity of a cobalt thin film and a hard mask according to ICP rf power in an etching gas of 75 vol% C ₂ H ₅ OH/Ar.
Figure 11 is a SEM image of a cobalt thin film before and after mixed solution treatment of the cobalt thin film etched according to ICP rf power in an etching gas of 75 vol% C ₂ H ₅ OH/Ar, where (a) is a side view of the cobalt thin film of Example 29, (b) is a side view of the cobalt thin film of Example 2, (c) is a side view of the cobalt thin film of Example 30, (d) is a side view of the cobalt thin film of Example 35, (e) is a side view of the cobalt thin film of Example 6, and (f) is a side view of the cobalt thin film of Example 36.
Figure 12 is a graph showing the change in etching rate and etching selectivity of a cobalt thin film and a hard mask according to dc-bias voltage in an etching gas of 75 vol% C ₂ H ₅ OH/Ar.
Figure 13 shows SEM images of cobalt thin films before and after mixed solution treatment in an etching gas of 75 vol% C ₂ H ₅ OH/Ar at a dc-bias voltage, where (a) is a side view of the cobalt thin film of Example 31, (b) is a side view of the cobalt thin film of Example 2, (c) is a side view of the cobalt thin film of Example 32, (d) is a side view of the cobalt thin film of Example 37, (e) is a side view of the cobalt thin film of Example 6, and (f) is a side view of the cobalt thin film of Example 38.
Figure 14 is a graph showing the change in etching rate and etching selectivity of a cobalt thin film and a hard mask according to pressure in an etching gas of 75 vol% C ₂ H ₅ OH/Ar.
Figure 15 is a SEM image of a cobalt thin film before and after the mixed solution treatment of the cobalt thin film etched under pressure in an etching gas of 75 vol% C ₂ H ₅ OH/Ar, where (a) is a side view of the cobalt thin film of Example 33, (b) is a side view of the cobalt thin film of Example 2, (c) is a side view of the cobalt thin film of Example 34, (d) is a side view of the cobalt thin film of Example 39, (e) is a side view of the cobalt thin film of Example 6, and (f) is a side view of the cobalt thin film of Example 40.
Figure 16 is a graph measuring the sizes of active species in plasma generated according to the mixing ratio of C ₂ H ₅ OH and Ar in a C ₂ H ₅ OH/Ar mixed gas among etching gases. (a) is a graph comparing the sizes of various active species as the concentration of C ₂ H ₅ OH increases, and (b) is a graph showing the ratio of each active species to the intensity of Ar.
Figure 17 shows the XPS analysis results for the surfaces of cobalt thin films before etching and cobalt thin films etched in Examples 1 to 4, where (a) is Co 2p, (b) is O 1s, and (c) is C 1s.
Figure 18 is an etching profile SEM image of the cobalt thin film etched in Examples 2 to 4, where (a) is an etching profile image of the cobalt thin film etched in Example 4, (b) is an etching profile image of the cobalt thin film etched in Example 3, and (c) is an etching profile image of the cobalt thin film etched in Example 2.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In general, the nomenclature used herein is well known and commonly used in the art.

Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

The present invention relates to an etching method for a cobalt thin film, characterized by comprising the steps of: (a) patterning a cobalt thin film with a hard mask and masking it by etching; (b) converting an etching gas selected from the group consisting of an alcohol gas; a mixed gas containing an alcohol gas and an inert gas; a mixed gas containing an alcohol gas and an oxidizing gas; and a mixed gas containing an alcohol gas, an oxidizing gas, and an inert gas into plasma; and (c) etching the cobalt thin film masked with the hard mask in step (a) using the plasma generated in step (b).

Specifically, the main purpose of the present invention is to form a pattern by etching using a conventional dry etching method without forming a pattern by the current damascene process on a cobalt thin film that can be widely used as a semiconductor material such as electrodes and wiring in next-generation semiconductor devices and display devices. To achieve this, the present invention develops a new appropriate etching gas and provides an etching method for a cobalt thin film that can provide a fast etching speed and a highly anisotropic etching profile without etching residues and without re-deposition.

The present invention is described in detail step by step below.

The etching method of a cobalt thin film according to the present invention first patterns the cobalt thin film with a hard mask and masks it by etching [step (a)].

The above step (a) is, as an example, as shown in FIG. 2, first, a hard mask (SiO ₂ mask)/cobalt thin film (Co) is patterned with a photoresist mask (PR mask) to mask the hard mask/cobalt thin film [FIG. 2(i)], and a gas such as C ₂ F ₆ /Cl ₂ /Ar is converted to plasma. Thereafter, the hard mask is etched from the masked hard mask/cobalt thin film using the generated C ₂ F ₆ /Cl ₂ /Ar plasma [FIG. 2(ii)]. Thereafter, in order to remove the photoresist mask, oxygen gas is converted to plasma, and the photoresist mask is removed from the thin film using the generated oxygen plasma [FIG. 2(iii)], thereby obtaining a cobalt thin film masked by the hard mask. In this way, the cobalt thin film is etched using the hard mask from the thin film from which the photoresist mask has been removed.

The hard mask used in the step (a) above may be one selected from among ceramic series such as silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), titanium dioxide (TiO ₂ ), metal series such as Ti, TiN, Ta, W, and amorphous carbon, but is not limited thereto. The hard mask is satisfactory as long as it is a material that exhibits a slow etching speed and high etching selectivity with respect to the etching gas of the present invention, and specifically, it is preferably silicon dioxide (SiO ₂ ).

The patterning of the above silicon dioxide hard mask is formed by patterning a SiO ₂ thin film using a general photoresist through a lithography process, and then etching using a gas such as C ₂ F ₆ /Ar. The SiO ₂ thin film etched at a concentration of 25 vol% to 30 vol% C ₂ F can obtain a vertical etching slope of about 85° or more.

Thereafter, in the present invention, the etching gas is plasma-plasmaized to etch the cobalt thin film [step (b)].

In the case where only pure inert gas (e.g. argon gas) was used as a conventional etching gas, there were problems such as a large amount of redeposited material being generated around the etched cobalt thin film because physical etching was performed by argon ions.

Accordingly, the present invention has the advantage of not allowing by-products to be re-deposited around the cobalt thin film after etching by using alcohol gas as an etching gas for the cobalt thin film.

In the present invention, the edible gas may be alcohol gas alone, a mixed gas containing alcohol gas, and preferably may be selected from the group consisting of alcohol gas; a mixed gas containing alcohol gas and an inert gas; a mixed gas containing alcohol gas and an oxidizing gas; and a mixed gas containing alcohol gas, an oxidizing gas, and an inert gas.

The alcohol gas may be used without limitation as long as it is a gaseous organic compound in which a hydroxyl group (-OH) is bonded to a saturated carbon atom, and preferably, it may be an alcohol gas having 1 to 5 carbon atoms, and more preferably, it may be ethanol.

In addition, the etching gas may be, as an embodiment, a mixed gas containing at least one inert gas selected from the group consisting of He, Ne, Ar, and N ₂ in the alcohol gas, and as another embodiment, a mixed gas containing at least one oxidizing gas selected from the group consisting of oxygen, ozone, radical oxygen, and water vapor in the alcohol gas, and as yet another embodiment, a mixed gas containing the inert gas and the oxidizing gas in the alcohol gas.

At this time, the alcohol gas may contain 25 vol% to 100 vol%, preferably 50 vol% to 100 vol%, based on the total volume of the etching gas. If the alcohol gas in the etching gas is less than 25 vol%, a problem may occur in which a redeposition material is generated around the etched thin film and a fine pattern of cobalt cannot be formed.

In addition, in the case of a mixed gas containing an oxidizing gas among the etching gases, the content of the oxidizing gas may be preferably contained in an amount of 10 vol% to 20 vol%, more preferably 15 vol% to 20 vol%, based on the total volume of the etching gas. When the content of the oxidizing gas satisfies the above range, the etching selectivity and etching slope of the cobalt thin film can be improved without redeposition.

In the present invention, plasma generation can be performed by injecting gas at a process pressure of 0.13 Pa to 1.3 Pa, applying coil high-frequency power (ICP rf power) of 300 W to 700 W, and applying dc-bias voltage of 200 V to 400 V.

When the above process pressure is less than 0.13 Pa, the generated plasma may become unstable, and the mean free path may increase, which may increase the physical collisions of ions and radicals with the cobalt thin film, which may increase the occurrence of redeposition on the side of the thin film. When it exceeds 1.3 Pa, the amount of ions, radicals, etc. in the plasma may relatively increase, but their mean free paths may decrease, which may cause frequent physical collisions, ultimately resulting in a slow etching rate and a low etching slope.

If the coil high-frequency power (ICP rf power) of the above plasma is lower than 300 W, the etching speed may be too slow and polymer deposition may occur instead of etching, and if it is higher than 700 W, a problem of serious re-deposition after etching may occur.

In addition, when the DC bias voltage is less than 200 V, the overall voltage applied to the thin film to be etched is low, so not only is the amount of ions, radicals, etc. generated by plasma transferred to the sample small, but in particular, due to the slow (weak) acceleration of the ions, a pattern with a slow etching speed and a relatively low etching slope is obtained, and polymer deposition may occur on the etching side, and a high DC bias voltage exceeding 400 V may improve the etching speed and etching slope, but etching redeposition may occur due to ion bombardment applied to the thin film, and at the same time, etch damage may occur in the thin film, which may cause a problem of deterioration in the electrical characteristics of devices to be manufactured in the future.

In the etching method of a cobalt thin film according to the present invention, by etching the cobalt thin film using plasma generated using the etching gas, the cobalt thin film can be etched at a high speed, re-deposition on the etched surface can be suppressed, and an etching profile with high anisotropy can be provided.

Thereafter, in step (c), the masked cobalt thin film of step (a) is etched using the plasma generated in step (b).

The etching of the above masked cobalt thin film can be performed by one method selected from the group consisting of high-density plasma reactive ion etching including inductively coupled plasma reactive ion etching, self-enhanced reactive ion etching, reactive ion etching, vapor etching, atomic layer etching, and pulse-modulated high-density plasma reactive ion etching.

The above etching method is capable of generating high-density plasma and connecting an independent RF power to the substrate side to apply a bias voltage to the substrate, thereby enabling high-energy collisions of ions with the substrate, and the broken chemical bonds then chemically react with radicals coming down from inside the plasma to cause etching. In addition, if the volatility of the reaction products by the chemical reaction is low, redeposition occurs on the etched side, and at this time, the physical sputtering of ions on the substrate helps to detach the redeposited materials.

In particular, high-density plasma ion etching method obtains high-density plasma by transferring energy to electrons in plasma generated inside the chamber by applying power to an external coil, and has the advantages of fast etching speed and no damage due to ion bombardment.

Also, reactive ion etching is a technology to remove materials from the wafer surface through a reactive chemical process and a physical process using ion bombardment. Magnetically enhanced reactive ion etching is an etching method that combines physical and chemical methods with a magnetically enhanced reactive ion etching reaction. Plasma with a magnetic field generates high-density plasma and allows operation even at low pressure, and has the advantage of maintaining the directionality and uniformity of etching, especially in the case of etching with high aspect ratio characteristics. However, it is difficult to obtain the above effects when using a general low-density reactive ion etching method, and accordingly, there are problems in that an appropriate etching speed and anisotropic etching are not performed.

The etching in the above step (c) is performed by high-energy collision of ions with the cobalt thin film, and the resulting chemical bonds cause a chemical reaction with radicals within the plasma. At this time, if the volatility of the reaction products due to the chemical reaction is low, redeposition occurs on the etched side, but the physical sputtering of ions onto the substrate helps to detach the redeposited materials, thereby suppressing redeposition.

At this time, the temperature of the etching substrate loaded with the cobalt thin film is 10° C. to 25° C. In the present invention, a configuration for heating the etching substrate is not required when etching the cobalt thin film, and etching can be performed at a low temperature by applying a cooling fluid of 10° C. to the etching substrate.

If the etching substrate must be heated to 150°C or higher as in the conventional etching method, first of all, since a vacuum seal such as an O-ring cannot be used under the substrate, a substrate with a special structure must be provided, which increases the unit cost of the equipment, and furthermore, since the substrate must be heated to a high temperature of 150°C for a considerable period of time, this may cause diffusion of materials already deposited or patterned/etched on the substrate, causing unwanted materials (elements) to move up or down the thin film layer, which may cause deterioration or deterioration of the characteristics of the device.

Meanwhile, the etching method of a cobalt thin film according to the present invention may further include a post-treatment step [step (d)] of removing etching residue or redeposited material using a mixed solution containing ammonia water, hydrogen peroxide, and water after step (c).

The mixed solution containing the above ammonia water, hydrogen peroxide and water may preferably have a volume ratio of ammonia water, hydrogen peroxide and water of 1:1:2 to 10, and more preferably, the volume ratio of ammonia water, hydrogen peroxide and water may have a volume ratio of 1:1:3 to 7.

A mixed solution containing ammonia water, hydrogen peroxide, and water in the above content range can remove etching residues or redeposited materials on the surface of a cobalt thin film without additional etching of the surface of the thin film.

The cobalt thin film manufactured by the etching method according to the present invention has an etching selectivity of 0.4 to 1.5 with respect to a hard mask, and an etching slope of the cobalt thin film of 70° or more, thereby providing an excellent anisotropic profile [(iv) of FIG. 2]. The etching selectivity refers to the etching rate of the cobalt thin film with respect to the etching rate of the hard mask, and can be calculated as shown in Equation 1 below.

Etch selectivity = (etching rate of cobalt thin film)/(etching rate of hard mask)...Equation 1

Hereinafter, the present invention will be described in more detail by way of preferred embodiments. However, it will be apparent to those skilled in the art that these embodiments are intended to explain the present invention more specifically and that the scope of the present invention is not limited thereby.

<Example 1>

A cobalt thin film (500 nm thick) masked with a SiO ₂ hard mask was positioned 120 mm away from the ICP coil, and ethanol (C ₂ H ₅ OH) gas or a mixture of ethanol (C ₂ H ₅ OH) gas and argon (Ar) gas as an etching gas was flowed at 20 sccm at a process pressure of 0.67 Pa, and a coil high-frequency power of 500 W and a DC bias of 300 V were applied to form plasma, thereby etching the cobalt thin film patterned with the hard mask. The ratio of the mixed gas is shown in Table 1.

<Examples 2 to 4 and comparative examples>

A cobalt thin film was etched using the same method as in Example 1, but the component ratio of the etching gas was replaced with the conditions described in Table 1.

division ICP rf Power
(W) DC bias
voltage
(V) Chamber pressure
(Pa) Etching gas
C ₂ H ₅ OH
(vol%) Ar
(vol%) Example 1 500 300 0.67 100 - Example 2 500 300 0.67 75 25 Example 3 500 300 0.67 50 50 Example 4 500 300 0.67 25 75 Comparative Example 1 500 300 0.67 - 100

<Examples 5 to 12>

In Examples 1 to 4, the etched cobalt thin films were each washed for 20 minutes using a mixed solution containing ammonia water (NH ₄ OH), hydrogen peroxide (H ₂ O ₂ ), and water (DI water) in the content ratios shown in Table 2 below.

division Etched cobalt thin film Mixed solution (volume ratio) NH ₄ OH H ₂ O ₂ DI water Example 5 Example 2 1 1 3 Example 6 Example 2 1 1 5 Example 7 Example 2 1 1 7 Example 8 Example 2 1 - 5 Example 9 Example 2 1 2 5 Example 10 Example 1 1 1 5 Example 11 Example 3 1 1 5 Example 12 Example 4 1 1 5

<Examples 13 to 20>

A cobalt thin film was etched using the same method as in Example 1, but the component ratio of the etching gas was replaced with the conditions described in Table 3.

division Etching gas C ₂ H ₅ OH (vol%) Ar (vol%) O ₂ (vol%) Example 13 50 20 20 Example 14 50 35 15 Example 15 50 40 10 Example 16 50 45 5 Example 17 75 5 20 Example 18 75 10 15 Example 19 75 15 10 Example 20 75 20 5

<Examples 21 to 28>

In Examples 14 to 17, the etched cobalt thin films were each washed for 20 minutes using a mixed solution containing ammonia water (NH ₄ OH), hydrogen peroxide (H ₂ O ₂ ), and water (DI water) in the content ratios shown in Table 4 below.

division Etched cobalt thin film Mixed solution (volume ratio) NH ₄ OH H ₂ O ₂ DI water Example 21 Example 13 1 1 5 Example 22 Example 14 1 1 5 Example 23 Example 15 1 1 5 Example 24 Example 16 1 1 5 Example 25 Example 17 1 1 5 Example 26 Example 18 1 1 5 Example 27 Example 19 1 1 5 Example 28 Example 20 1 1 5

<Examples 29 and 34>

The cobalt thin film was etched using the same method as in Example 1, but the plasma conditions were changed to the conditions in Table 5 below to perform etching of the cobalt thin film.

division ICP rf Power
(W) DC bias
voltage
(V) Chamber pressure
(Pa) Etching gas
C ₂ H ₅ OH
(vol%) Ar
(vol%) Example 29 300 300 0.67 75 25 Example 30 700 300 0.67 75 25 Example 31 500 200 0.67 75 25 Example 32 500 400 0.67 75 25 Example 33 500 300 0.13 75 25 Example 34 500 300 1.3 75 25

<Examples 35 to 40>

In Examples 29 to 34, the etched cobalt thin films were each washed for 20 minutes using a mixed solution containing ammonia water (NH ₄ OH), hydrogen peroxide (H ₂ O ₂ ), and water (DI water) in the content ratios shown in Table 6 below.

division Etched cobalt thin film Mixed solution (volume ratio) NH ₄ OH H ₂ O ₂ DI water Example 35 Example 29 1 1 5 Example 36 Example 30 1 1 5 Example 37 Example 31 1 1 5 Example 38 Example 32 1 1 5 Example 39 Example 33 1 1 5 Example 40 Example 34 1 1 5

<Experimental Example 1: Measurement of etching rate and etching selectivity of cobalt thin film according to mixing ratio of etching gas>

In order to determine the etching rate and selectivity of cobalt thin films according to the mixing ratio of etching gases C ₂ H ₅ OH and Ar [cobalt thin film (Co) etching rate/hard mask (SiO ₂ ) etching rate], the etching rates for thin films etched in Examples 1 to 4 and Comparative Example 1 were measured, and the results are shown in Fig. 3.

As shown in Fig. 3, as the concentration of C ₂ H ₅ OH/Ar increased, the etching rates of the cobalt thin film and the hard mask simultaneously and gradually decreased, and also, since the etching rate of the cobalt thin film was faster than that of the SiO ₂ hard mask, the etching selectivity of the cobalt thin film over the SiO ₂ hard mask was found to be 1 to 1.4.

As a result, the etching rate did not increase but decreased as the C ₂ H ₅ OH gas increased, which did not follow the typical reactive ion etching mechanism. This was judged to be because the addition of C ₂ H ₅ OH gas to pure argon gas caused a polymer containing CH _x to be deposited on the cobalt thin film, and an oxide film was formed on the surface by the -OH groups, which decreased the overall etching rate of the thin film.

<Experimental Example 2: Observation of etched cobalt thin film according to the mixing ratio of etching gas>

In order to observe the etched surface of the cobalt thin film according to the mixing ratio of the etching gas, C ₂ H ₅ OH and Ar, the side surfaces of the thin films etched in Examples 1 to 4 and Comparative Example 1 were measured using SEM (Hitachi SE-4300), and the results are shown in Fig. 4. At this time, Fig. 4(a) is a side view of the cobalt thin film etched in Comparative Example 1, Fig. 4(b) is a side view of the cobalt thin film etched in Example 4, Fig. 4(c) is a side view of the cobalt thin film etched in Example 3, Fig. 4(d) is a side view of the cobalt thin film etched in Example 2, and Fig. 4(e) is a side view image of the cobalt thin film etched in Example 1.

As shown in Fig. 4, in cobalt etched in pure argon (Comparative Example 1), significant redeposition was observed to be formed on the pattern side. This was judged to be the result of physical sputtering of the argon ions onto the cobalt thin film. As the C ₂ H ₅ OH concentration increased from 25 vol% to 100 vol%, redeposition on the side of the etched cobalt thin film gradually decreased, and it was confirmed that almost no redeposition was observed on the side of the thin film under the 100 vol% C ₂ H ₅ OH condition.

<Experimental Example 3: Observation of post-processed cobalt thin film according to the component ratio of the mixed solution>

In order to observe the etched surface of the cobalt thin film treated according to the mixing ratio of the _NH4OH , _H2O2 , and DI water components of the mixed solution in the post-processing step, the side surfaces of the thin films treated in Examples ₅ to 9 were observed using SEM (Hitachi SE-4300), and the results are shown in Fig. 5. At this time, Fig. 5(a) is a side view of the cobalt thin film treated in Example 5, Fig. 5(b) is a side view of the cobalt thin film treated in Example 6, Fig. 5(c) is a side view of the cobalt thin film treated in Example 7, Fig. 5(d) is a side view of the cobalt thin film treated in Example 8, and Fig. 5(e) is a side view image of the cobalt thin film treated in Example 9.

As shown in FIG. 5, in a mixed solution composed of NH ₄ OH : H ₂ O ₂ : DI water, when the volume ratio of NH ₄ OH : H ₂ O ₂ : DI water was 1 : 1 : 3 (Example 5), the redeposited materials generated on the cobalt side were removed, but the side appeared rough, and when the volume ratio of NH ₄ OH : H ₂ O ₂ : DI water was 1 : 1 : 7 (Example 7), it was observed that the redeposited materials on the cobalt side were not completely removed. Also, in the case of a solution having a volume ratio of NH ₄ OH : H ₂ O ₂ : DI water of 1 : 0 : 5, i.e., a solution without adding H ₂ O ₂ (Example 8), it was observed that some of the redeposition material on the side of the cobalt thin film was removed, but it was observed that both sides of the cobalt thin film were etched, whereas in the case of a volume ratio of NH ₄ OH : H ₂ O ₂ : DI water of 1 : 2 : 5 (Example 9), it was observed that the redeposition material was not sufficiently removed and the side became very rough. As a result, it was found that a mixed solution having a volume ratio of NH ₄ OH : H ₂ O ₂ : DI water of 1 : 1 : 5 showed the best post-treatment effect.

<Experimental Example 4: Observation of cobalt thin film before and after treatment with mixed solution>

In order to compare and observe the cobalt thin films before and after treatment with the mixed solution in the post-treatment step, the side surfaces of the cobalt thin films of Examples 1 to 4 and the cobalt thin films of Examples 6 and 10 to 13, which were treated with the mixed solution having a volume ratio of NH ₄ OH, H ₂ O ₂ and DI water of 1: 1: 5, were observed using SEM (Hitachi SE-4300), and the results are shown in Fig. 6. Fig. 6(a) is a side view of the cobalt thin film of Example 4, Fig. 6(b) is a side view of the cobalt thin film of Example 3, Fig. 6(c) is a side view of the cobalt thin film of Example 2, and Fig. 6(d) is a side view image of the cobalt thin film of Example 1. Also, FIG. 6(e) is a side view of the cobalt thin film of Example 13, FIG. 6(f) is a side view of the cobalt thin film of Example 12, FIG. 6(g) is a side view of the cobalt thin film of Example 6, and FIG. 6(h) is a side view image of the cobalt thin film of Example 10.

As shown in Fig. 6, the redeposition on the side of the etched cobalt thin film was reduced in the etching gas of 75 vol% C ₂ H ₅ OH/Ar or higher as already explained in Fig. 4 (Fig. 4d, Fig. 4e), and when these etched cobalt thin films (Examples 3 and 4) were treated with a mixed solution, the cobalt thin films etched in the etching gas of 25 vol% C ₂ H ₅ OH/Ar and 50 vol% C ₂ H ₅ OH/Ar (Examples 12 and 13) had almost no removal of the etching redeposition materials [Fig. 6(e), Fig. 6(f)], and the cobalt thin films etched in the 75 vol% C ₂ H ₅ OH/Ar and 100 vol% C ₂ H ₅ OH (Examples 1 and 2) had no etching sidewalls (Examples 6 and 10). It was observed that the redeposited materials were completely removed (Fig. 6(g) and Fig. 6(h)].

<Experimental Example 5: Measurement of etching rate and etching selectivity of cobalt thin film according to mixing ratio of etching gas>

In order to determine the etching rate and selectivity of cobalt thin films according to the mixing ratio of C ₂ H ₅ OH, O ₂ and Ar as etching gases [cobalt thin film (Co) etching rate/hard mask (SiO ₂ ) etching rate], the etching rates for the thin films etched in Examples 2 and 3 and Examples 14 to 21 were measured, and the results are shown in Fig. 7. At this time, Fig. 7(a) shows the case where C ₂ H ₅ OH is 50 vol% among the mixed gas of C ₂ H ₅ OH, O ₂ and Ar as etching gases, and Fig. 7(b) shows the case where C ₂ H ₅ OH is 75 vol% among the mixed gas of C ₂ H ₅ OH, O ₂ and Ar as etching gases.

As shown in Fig. 7, when a cobalt thin film is etched using an etching gas mixed with oxygen (O ₂ ), the cobalt thin film is oxidized to form cobalt oxide (CoO _x ) or cobalt compounds containing oxygen, thereby increasing the reactivity with ethanol gas and consequently reducing etching redeposition.

<Experimental Example 6: Observation of cobalt thin film before and after treatment with mixed solution>

In order to compare and observe the cobalt thin films before and after treatment with the mixed solution in the post-treatment step, the cobalt thin films of Examples 2, 3, and 13 to 20 and the etched cobalt thin films of the above examples were treated with a mixed solution having a volume ratio of NH ₄ OH, H ₂ O ₂ and DI water of 1: 1: 5, and the side surfaces of the cobalt thin films of Examples 6, 11, and 21 to 28 were observed using SEM (Hitachi SE-4300), and the results are shown in FIGS. 8 and 9.

At this time, FIG. 8(a) is a side view of the cobalt thin film of Example 3, FIG. 8(b) is a side view of the cobalt thin film of Example 16, FIG. 8(c) is a side view of the cobalt thin film of Example 15, FIG. 8(d) is a side view of the cobalt thin film of Example 14, and FIG. 8(e) is a side view image of the cobalt thin film of Example 13. In addition, FIG. 8(f) is a side view of the cobalt thin film of Example 11, FIG. 8(g) is a side view of the cobalt thin film of Example 24, FIG. 8(h) is a side view of the cobalt thin film of Example 23, FIG. 8(i) is a side view of the cobalt thin film of Example 22, and FIG. 8(j) is a side view image of the cobalt thin film of Example 21.

Meanwhile, FIG. 9(a) is a side view of a cobalt thin film of Example 2, FIG. 9(b) is a side view of a cobalt thin film of Example 20, FIG. 9(c) is a side view of a cobalt thin film of Example 19, FIG. 9(d) is a side view of a cobalt thin film of Example 18, and FIG. 9(e) is a side image of a cobalt thin film of Example 17. In addition, FIG. 9(f) is a side view of a cobalt thin film of Example 6, FIG. 9(g) is a side view of a cobalt thin film of Example 28, FIG. 9(h) is a side view of a cobalt thin film of Example 27, FIG. 9(i) is a side view of a cobalt thin film of Example 26, and FIG. 9(j) is a side view image of a cobalt thin film of Example 25.

As shown in Fig. 8, the etching profile of the cobalt thin film (Example 3) etched in ₅₀ % _C2H5OH /Ar showed severe redeposition on the etching side. However, when 5 vol% to 20 vol% _O2 gas was added (Examples 21 to 24), the etching redeposition significantly decreased and the etching slope was also improved to about 75° or more. In particular, when 15 vol% to 20 vol% _O2 gas was added to the etching gas (Examples 21 and 22), almost no redeposition was observed on the side. When these etched cobalt thin films were treated with a mixed solution in the post-treatment step, when 10 vol% to 20 vol% _O2 was added as the etching gas (Examples 21 to 23), the etching redeposition on the side was completely eliminated.

In addition, as shown in FIG. 9, the etching profile of the cobalt thin film (Example 2) etched with an etching gas of 75% C ₂ H ₅ OH/Ar showed that redeposition occurred on the etching side. However, when 5 vol% to 20 vol% O ₂ gas was added to the etching gas (Examples 25 to 28), the etching redeposition significantly decreased and the etching slope was also improved to about 80° or more. In particular, when 15 vol% to 20 vol% O ₂ gas was added (Examples 25 and 26), almost no redeposition was observed on the etching side. When these etched samples were treated with a mixed solution in the post-treatment step, the etching redeposition on the etching side of the cobalt thin film was completely removed.

<Experimental Example 7: Etching rate and thin film analysis according to ICP rf power>

In order to measure the etching rate and etching selectivity of cobalt and hard mask (SiO ₂ ) according to the change in ICP rf power, which is one of the main variables of etching, the etching rate and etching selectivity were measured for the thin films of Example 2 and Examples 29 and 30 etched according to the change in ICP rf power, and the results are shown in Fig. 10.

As shown in Fig. 10, as the ICP rf power increased, the etching rate of cobalt increased almost linearly, but the etching rate of the hard mask (SiO ₂ ) increased slightly. Accordingly, it was confirmed that the etching selectivity of the cobalt thin film with respect to the hard mask (SiO ₂ ) was between 0.8 and 1.4.

In addition, in order to observe the state of the etched cobalt thin film according to the change in ICP rf power, the thin films of Examples 2 and 29 and 30 etched according to the change in CP rf power and the thin films of Examples 6, 35 and 36 treated using a mixed solution (NH ₄ OH : H ₂ O ₂ : DI water = 1 : 1 : 5) in the post-processing step were photographed and observed for comparison using SEM (Hitachi SE-4300), and the results are shown in Fig. 11. At this time, Fig. 11(a) is the cobalt thin film of Example 29, Fig. 11(b) is the cobalt thin film of Example 2, and Fig. 11(c) is the cobalt thin film of Example 30. Also, Fig. 11(d) is a cobalt thin film of Example 35, Fig. 11(e) is a cobalt thin film of Example 6, and Fig. 11(f) is a cobalt thin film of Example 36.

As shown in Fig. 11, in terms of the etching profile, the redeposition after etching was significantly reduced under the rf power condition of 300 W, and under the etching condition of 700 W, the redeposition material increased somewhat on the sides of the hard mask and the cobalt thin film after etching, but the etch slope was greatly improved. In general, when the ICP rf power increases, the plasma density in the reactor increases, which generates more radicals and more cations, thereby increasing the etching rates of the thin films and also helping the anisotropy of the etching profile. However, if the etching mechanism does not follow the reactive ion etching mechanism, redeposition may occur. When these etched cobalt thin films were post-treated with a mixed solution, the redeposition material on the side of the thin film was completely removed in the cases of 300 W and 500 W, but it was confirmed that some of the redeposition material remained in the case of 700 W.

<Experimental Example 8: Etching rate and thin film analysis according to dc-bias voltage>

In order to measure the etching rate and etching selectivity of cobalt and hard mask (SiO ₂ ) according to the change in dc-bias voltage, which is one of the main variables of etching, the etching rate and etching selectivity were measured for the thin films of Example 2 and Examples 31 and 32 etched according to the change in dc-bias voltage, and the results are shown in Fig. 12.

As shown in Fig. 12, the etching rate of the cobalt thin film gradually increased as the dc-bias voltage increased from 200 V to 400 V, and the etching rate of the SiO ₂ hard mask also increased as it increased from 200 V to 300 V, but there was no significant change at 400 V. The etching selectivity of the cobalt thin film to the SiO ₂ hard mask was confirmed to be in the range of 0.9 to 1.4.

In addition, in order to observe the state of the etched cobalt thin film according to the change in dc-bias voltage, the thin films of Examples 2, 31, and 32 etched according to the change in dc-bias voltage and the side surfaces of the thin films of Examples 6, 37, and 38 treated with a mixed solution (NH ₄ OH : H ₂ O ₂ : DI water = 1 : 1 : 5) were photographed by SEM (Hitachi SE-4300) for comparative observation, and the results are shown in Fig. 13. At this time, Fig. 13(a) is a side image of the cobalt thin film of Example 31, Fig. 13(b) is a side image of the cobalt thin film of Example 2, and Fig. 13(c) is a side image of the cobalt thin film of Example 32. Also, FIG. 13(d) is a side view of the cobalt thin film of Example 37, FIG. 13(e) is a side view of the cobalt thin film of Example 6, and FIG. 13(f) is a side view image of the cobalt thin film of Example 38.

As shown in Fig. 13, when examining the etching profile results, the cobalt thin films etched under the conditions of 200 V and 300 V dc-bias voltage (Example 31 and Example 2) showed a small amount of redeposited material similarly on the etching side, but the cobalt thin film etched under the condition of 400 V dc-bias voltage (Example 32) showed a significant amount of redeposited material on the etching side. When these etched thin films were treated with a mixed solution in the post-processing step, the redeposited material on the etched side (Example 37 and Example 6) was completely removed under the conditions of 200 V and 300 V dc-bias voltage, but the redeposited material on the etching side (Example 38) was not completely removed under the condition of 400 V dc-bias voltage. It was determined that when the dc-bias voltage increases, the positive ions in the plasma are attracted to the substrate with greater energy and collide strongly, removing the thin film or removing the etching products remaining on the surface. However, if only a strong collision occurs on the substrate without a chemical reaction on the surface, the sidewall of the etching pattern undergoes redeposition.

<Experimental Example 9: Etching rate and thin film analysis according to etching process pressure>

In order to measure the etching rate and etching selectivity of cobalt and hard mask (SiO ₂ ) according to the change in etching process pressure, which is one of the main variables of etching, the etching rate and etching selectivity were measured for the thin films of Example 2 and Examples 33 and 34 etched according to the change in chamber pressure, and the results are shown in Fig. 14.

As shown in Fig. 14, the etching rate of the cobalt thin film decreased slightly as the pressure decreased from 0.13 Pa to 1.3 Pa, and the etching rate of the hard mask (SiO ₂ ) increased at 0.67 Pa and then decreased again at 1.3 Pa. The etching selectivity of the cobalt thin film to the hard mask (SiO ₂ ) varied between approximately 0.9 and 1.8 and showed the largest value at the process pressure of 0.13 Pa.

In addition, in order to observe the state of the etched cobalt thin film according to the pressure change, the thin films of Examples 2 and 33 and 34 etched according to the pressure change and the thin films of Examples 6, 39 and 40 treated with a mixed solution (NH ₄ OH : H ₂ O ₂ : DI water = 1 : 1 : 5) were photographed and observed sideways with SEM (Hitachi SE-4300) for comparison, and the results are shown in Fig. 15. At this time, Fig. 15(a) is a side view of the cobalt thin film of Example 33, Fig. 15(b) is a side image of the cobalt thin film of Example 2, and Fig. 15(c) is a side view of the cobalt thin film of Example 34. Also, FIG. 15(d) is a side view of the cobalt thin film of Example 39, FIG. 15(e) is a side view of the cobalt thin film of Example 6, and FIG. 15(f) is a side view image of the cobalt thin film of Example 40.

As shown in Fig. 15, in the cobalt thin film etched at a chamber pressure of 0.13 Pa (Example 33), redeposition occurred on the sidewall of the cobalt thin film, and in the cobalt thin film etched at a chamber pressure of 1.3 Pa (Example 34), redeposition was also observed on the sidewall, but in the cobalt thin film etched at a pressure of 0.67 Pa (Example 2), the smallest amount of redeposition was observed. As a result of treating these etched thin films with a mixed solution, it was observed that the redeposited material on the sidewall was removed under all conditions of each pressure. However, in the post-treated cobalt thin films (Examples 39 and 40) etched at process pressures of 0.13 Pa and 1.3 Pa, the etched sidewalls were somewhat roughened, and it was observed that the redeposited material on the sidewalls of the thin film was not completely removed. Therefore, the process pressure of 0.67 Pa was determined to be the optimal condition.

These results are generally judged to be because at a low pressure of 0.13 Pa, the mean free path increases significantly, allowing radicals or ions generated in the plasma to effectively reach the thin film surface without collision, allowing more radicals and ions to participate in reactions such as chemical reactions and sputtering with the thin film surface, thereby increasing the etching rate. However, the redeposited material on the side of the thin film increases, and the anisotropy of the etching profile increases, resulting in a more vertical etching profile.

<Experimental Example 10: C in etching gas ₂ H ₅ OES analysis according to the mixing ratio of OH and Ar>

The sizes of active species in the plasma generated according to the mixing ratio of C ₂ H ₅ OH and Ar in the C ₂ H ₅ OH/Ar mixed gas among the etching gases were measured by OES (optical emission spectroscopy), and the results are shown in Fig. 16. At this time, the process conditions were that ethanol (C ₂ H ₅ OH) gas or a mixed gas of ethanol (C ₂ H ₅ OH) gas and argon (Ar) gas, which are etching gases, were flowed at 20 sccm at a pressure of 0.67 Pa, and 500 W of coil high-frequency power and 300 V of DC bias were applied to form the plasma. Fig. 16(a) compares the sizes of various active species as the concentration of C ₂ H ₅ OH increases, and (b) is a graph showing the ratio of each active species to the intensity of Ar.

As shown in Fig. 16, among the various active species in the plasma in the C ₂ H ₅ OH/Ar mixed gas, the intensity was high in the order of [H], [C], [O], [OH], and [CH], and the intensity of each active species gradually decreased as the C ₂ H ₅ OH concentration increased. In addition, it was determined that the plasma density of the mixed gas decreased as the C ₂ H ₅ OH concentration increased and the Ar concentration decreased. In conclusion, it was determined that each active species in the plasma partially reacted with the cobalt thin film to generate cobalt compounds and that the volatility of these was low.

<Experimental Example 11: C in etching gas ₂ H ₅ XPS analysis according to the mixing ratio of OH and Ar>

In order to determine whether there is a chemical reaction of the cobalt thin film according to the mixing ratio of C ₂ H ₅ OH and Ar in the etching gas, XPS (Xray Photoelectron spectroscopy, ThermoScientific K-alpha) was analyzed on the surfaces of the cobalt thin films before etching (Before etching) and the cobalt thin films etched in Examples 1 to 4, and the results are shown in Fig. 17. At this time, Fig. 17(a) shows Co 2p, Fig. 17(b) shows O 1s, and Fig. 17(c) shows C 1s.

As shown in Fig. 17(a), when examining the narrow scan results for the Co 2p peak, it was determined that the surface of the cobalt thin film before etching was partially oxidized to CoO, and that CoO and Co(OH) ₂ compounds were generated on the surface of the cobalt thin film after etching with C ₂ H ₅ OH gas. However, no significant change was observed in the amount of cobalt compounds as the C ₂ H ₅ OH concentration increased.

As shown in Fig. 17(b), no cobalt oxide was observed on the surface of the cobalt thin film before etching in the narrow scans of the O 1s peak, whereas the formation of cobalt oxides of Co ₃ O ₄ and CoO and cobalt hydroxide of Co(OH) ₂ was confirmed in the cobalt thin film etched in 25 vol% C ₂ H ₅ OH/Ar etching gas (Example 4). In addition, it was observed that CoO _x oxide slightly decreased while Co(OH) ₂ slightly increased as the C ₂ H ₅ OH concentration increased.

Finally, Fig. 17(c) is a graph showing narrow scans of the C 1s peak. It was observed that when the cobalt thin film is etched with C ₂ H ₅ OH/Ar gas, carbides containing CH or CC are generated on the surface of the cobalt thin film. Although this causes a decrease in the etching rate of the cobalt thin film, it forms a kind of protective film on the side of the thin film being etched, which increases the vertical anisotropic etching and is a factor that increases the etching slope. From the results of the narrow scans of Co 2p and O 1s, it was determined that CoO _x and Co(OH) ₂ were generated under the etching conditions of C ₂ H ₅ OH, which is the reason why the etching redeposition decreased after etching.

<Experimental Example 12: C in etching gas ₂ H ₅ Etching profile measurement according to the mixing ratio of OH and Ar>

In order to measure the etching profile according to the mixing ratio of C ₂ H ₅ OH and Ar in the etching gas, the SiO ₂ hard mask was removed from the cobalt thin films etched in Examples 2 to 4 using C ₂ F ₆ /Ar gas, and then measured using SEM. The results are shown in Fig. 18. At this time, Fig. 18(a) is the etching profile of the cobalt thin film etched in Example 4, Fig. 18(b) is the etching profile of the cobalt thin film etched in Example 3, and Fig. 18(c) is the etching profile of the cobalt thin film etched in Example 2.

As shown in Fig. 18, the side surface of the cobalt thin film etched in Example 4 was rough and had an etching inclination of about 60°, the side surface of the cobalt thin film etched in Example 3 was found to have an etching inclination of about 65°, and the side surface of the cobalt thin film etched in Example 2 was found to have a smooth etching inclination of about 77°.

The specific parts of the present invention have been described in detail above, but are not limited to those illustrated in the drawings. It will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and that the scope of the present invention is not limited thereby. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (11)

(a) a step of patterning a cobalt thin film with a hard mask and masking it by etching;
(b) a step of plasma-forming an etching gas selected from the group consisting of alcohol gas; a mixed gas containing alcohol gas and an inert gas; a mixed gas containing alcohol gas and an oxidizing gas; and a mixed gas containing alcohol gas, an oxidizing gas, and an inert gas; and
(c) a step of etching the cobalt thin film masked in step (a) using the plasma generated in step (b),
The plasma generation in the above step (b) is performed by injecting gas at a process pressure of 0.13 Pa to 1.3 Pa, applying a coil high-frequency power (ICP rf power) of 300 W to 700 W, and a dc-bias voltage of 200 V to 400 V.
A method for etching a cobalt thin film, characterized in that the etching of the step (c) is performed by one method selected from the group consisting of high-density plasma reactive ion etching including inductively coupled plasma reactive ion etching, self-enhanced reactive ion etching, reactive ion etching, vapor etching, atomic layer etching, and pulse-modulated high-density plasma reactive ion etching.
In the first paragraph,
A method for etching a cobalt thin film, characterized in that the etching selectivity of the cobalt thin film with respect to the hard mask is 0.4 to 1.5.
In the first paragraph,
A method for etching a cobalt thin film, characterized in that the above inert gas is at least one selected from the group consisting of He, Ne, Ar, and N _2.
In the first paragraph,
A method for etching a cobalt thin film, characterized in that the oxidizing gas is at least one selected from the group consisting of oxygen, ozone, radical oxygen, and water vapor.
In the first paragraph,
A method for etching a cobalt thin film, characterized in that the hard mask is at least one selected from the group consisting of silicon oxide (SiO ₂ ), Si ₃ N ₄ , TiO ₂ , TiN, Ti, Ta, W, Cr, and carbon (C).
In the first paragraph,
A method for etching a cobalt thin film, characterized in that the etching gas of the step (b) contains 50 vol% to 100 vol% of alcohol gas with respect to the total volume of the etching gas.
In the first paragraph,
A method for etching a cobalt thin film, characterized in that the mixed gas containing the oxidizing gas of step (b) contains 10 vol% to 20 vol% of the oxidizing gas based on the total volume of the mixed gas.
delete delete In the first paragraph,
A method for etching a cobalt thin film, characterized in that it further comprises a post-treatment step of removing etched residue using a mixed solution containing ammonia water, hydrogen peroxide, and water after the step (c) above.
A cobalt thin film etched by the method described in any one of claims 1 to 7 and 10, and characterized by having an etching slope of 70° or more.