Method for forming ruthenium thin film

Abstract

To provide a method for forming a ruthenium thin film having high purity and low resistance by an atomic layer vapor deposition method.SOLUTION: The present invention relates to a method for forming a ruthenium thin film by atomic layer deposition. In the present invention, a ruthenium thin film is formed by injecting ammonia as an additional reaction gas at a high temperature at which thermal decomposition of a ruthenium precursor occurs. The present invention provides a high-performance 6-step process capable of maintaining excellent thin film properties To provide an atomic layer deposition method. In the present invention, by injecting and purging ammonia, which is an additional reaction gas, after injecting and purging oxygen, which is a main reaction gas, it is possible to increase the ruthenium crystal grains and reduce the impurity concentration, thereby reducing the resistivity of the thin film. The ruthenium thin film formed in the present invention has improved characteristics as compared with a ruthenium thin film formed only by an existing oxygen reaction gas. Accordingly, the present invention can be utilized as a new metal wiring material and film formation technology that replaces copper wiring.SELECTED DRAWING: Figure 2a

Description

[Technical Field]

[0001] The present invention relates to a method for forming a ruthenium (Ru) thin film by atomic layer deposition, and more particularly to a high-temperature, high-performance, six-step method for forming a ruthenium thin film by using ammonia (NH3) as an additional reactant gas in atomic layer deposition. [Background technology]

[0002] Metal wiring is a metal line that transmits and connects electrical signals within a semiconductor chip. It is made of metals such as copper (Cu) and aluminum (Al) and is mainly used in integrated circuits (ICs) during semiconductor manufacturing. Metal wiring connects the isolated parts of a semiconductor chip, regulating the flow of current and transmitting signals. This function plays an important role in controlling the operation of electronic devices. Furthermore, metal wiring must be manufactured thin and precise due to the increasing size and density of semiconductor chips. In recent years, the materials and manufacturing processes for metal wiring have been continuously evolving, and are being designed to provide faster transmission speeds and higher reliability.

[0003] The most important characteristic of metals used in integrated circuit wiring is their resistance to current flow, so metal materials with low resistivity must be selected. In addition to the aforementioned copper (Cu) and aluminum (Al), other metal wiring materials for semiconductors include silver (Ag) and gold (Au). The resistivities of these metal wiring materials at room temperature (20°C) are as follows: silver: 1.59 μΩ·cm, gold: 2.44 μΩ·cm, aluminum: 2.82 μΩ·cm, and copper: 1.72 μΩ·cm. Of these metals, silver has the lowest bulk resistivity. However, from an economical perspective, copper is the most suitable metal wiring material and is currently used as the primary material for semiconductor metal wiring.

[0004] However, as semiconductor device dimensions continue to shrink, the line width of metal wiring must be reduced to the mean free path of electrons in copper (39 nm) or less. Furthermore, reducing the line width of metal wiring to the order of a few nanometers can cause problems such as electromigration and stress-induced voiding, which can cause the resistivity of copper wiring to exceed the bulk resistivity. These problems have led to the limitations of copper as a wiring material.

[0005] Atomic layer deposition (ALD) is a semiconductor thin film deposition technique that is suitable for depositing nanometer-scale thin films. ALD uses gaseous reactants to repeatedly deposit atomic layers of a substance to form a thin film. This process involves sequentially injecting and purging two substances: a precursor and a reactant gas. At each stage, the precursor adsorbs onto the film surface, and the reactant gas reacts with the precursor to form a new atomic layer. By repeating this process, a thin film of the desired thickness can be created. ALD also has the advantage of ensuring superior step coverage compared to other deposition techniques and enabling the growth of multilayer structures of a variety of materials. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-139020 [Patent Document 2] Special Publication No. 2017-524729 [Patent Document 3] Special Publication No. 2010-525162 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention relates to a method for forming a thin film of ruthenium (Ru), which is a promising metal wiring material, by atomic layer deposition. Specifically, the present invention provides an atomic layer deposition process that can form a thin film of ruthenium with high purity, low resistivity, and good crystallinity. [Means for solving the problem]

[0008] To achieve the above object, the present invention provides a six-step atomic layer deposition method in which ammonia, an additional reactive gas, is supplied in addition to oxygen, the main reactive gas, during the formation of a ruthenium thin film by atomic layer deposition.The present invention is a six-step atomic layer deposition method using one precursor and two reactive gases, and is a high-temperature, high-performance ruthenium film formation process.

[0009] That is, the present invention provides a method for forming a ruthenium thin film by atomic layer deposition, characterized in that a ruthenium thin film is formed by atomic layer deposition using a ruthenium precursor (tricarbonyl(trimethylenemethane)ruthenium: [Ru(TMM)(CO)]) having the structure of Chemical Formula 1 below, and oxygen and ammonia as reactive gases.

[0010] [ka]

[0011] In the present invention, a ruthenium thin film can be formed at a temperature of 310°C or higher. This film formation temperature of 310°C or higher is a temperature at which thermal decomposition of the precursor can occur. Furthermore, a film formation temperature of 310°C or higher is a temperature above the ALD window. The ALD window is the temperature range within which the self-limiting mechanism of surface chemical reactions (a mechanism that suppresses further adsorption of precursor atoms onto the layer of precursor atoms adsorbed on the substrate surface) can operate in an atomic layer deposition process.

[0012] In the present invention, the main reactant gas is oxygen and the additional reactant gas is ammonia.

[0013] The ruthenium thin film formed by the present invention preferably has a resistivity of 20 μΩ·cm or less, and more preferably has an impurity content of 1.0 atomic % or less.

[0014] The method for forming a ruthenium thin film by a 6-step atomic layer deposition method of the present invention preferably includes the following steps to form a ruthenium thin film. providing a ruthenium precursor onto the substrate in the chamber; purging the ruthenium precursor; supplying oxygen as a main reactive gas onto the substrate; purging the main reaction gas; supplying ammonia as an additional reactive gas onto the substrate; purging the additional reactant gas;

[0015] In the above, after the step of supplying ammonia as an additional reactive gas onto the substrate and before the step of purging the additional reactive gas, hydrogen, hydrogen plasma, ammonia plasma, or nitrogen / hydrogen plasma may be supplied onto the substrate as an additional reactive gas.

[0016] In the method for forming a ruthenium thin film according to the present invention, when one deposition cycle is defined as performing each of the above steps once in sequence, it is preferable that the incubation cycle for forming the ruthenium thin film is shorter than 35 deposition cycles.

[0017] Furthermore, in the method for forming a ruthenium thin film according to the present invention, when one deposition cycle is defined as performing each of the above steps once in sequence, the deposition rate of the ruthenium thin film is preferably in the range of 0.13 nm / cycle to 0.16 nm / cycle. [Effects of the Invention]

[0018] In the present invention, a ruthenium thin film is formed by supplying ammonia as an additional reactant gas after supplying oxygen as a main reactant gas, and the present invention makes it possible to form a ruthenium thin film with various improved physical properties, such as high ruthenium purity, low resistance, and improved crystallinity. [Brief explanation of the drawings]

[0019] [Figure 1a] Graph showing the resistivity, growth rate, and incubation cycle of ruthenium thin films formed by 4-step Ru ALD. [Figure 1b] XRD pattern of ruthenium thin film formed by 4-step Ru ALD. [Figure 2a] Graph showing the resistivity, growth rate, and incubation cycle of ruthenium thin films formed by 6-step Ru ALD. [Figure 2b] XRD pattern of ruthenium thin film formed by 6-step Ru ALD. [Figure 3a] Graph comparing the resistivity of ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD. [Figure 3b] Figure comparing HRXRD patterns of ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD. [Figure 4a] TEM image of a ruthenium thin film formed by 4-step Ru ALD. [Figure 4b] TEM image of a ruthenium thin film formed by 6-step Ru ALD. [Figure 5a] Graph showing the distribution of crystal grain size in ruthenium thin films grown by 4-step Ru ALD. [Figure 5b] Graph showing the distribution of crystal grain size in ruthenium thin films grown by 6-step Ru ALD. [Figure 6a] Figure 1 shows the results of SIMS composition analysis of a ruthenium thin film grown by 4-step Ru ALD. [Figure 6b]Figure 1 shows the results of SIMS composition analysis of a ruthenium thin film grown by 4-step Ru ALD. [Figure 7] Cross-sectional TEM image of a ruthenium thin film formed on a patterned wafer using 6-step Ru ALD [Figure 8a] TEM image of the top edge of the pattern where ruthenium was deposited. [Figure 8b] TEM image of the bottom of a ruthenium thin film pattern. [Figure 8c] TEM images of the top, middle, and bottom of a ruthenium thin film pattern. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present invention will now be described. In this embodiment, a ruthenium thin film was formed under specific film formation conditions using the 6-step atomic layer deposition method according to the present invention. For comparison with the present invention, a ruthenium thin film was also formed using a conventional atomic layer deposition method in which only oxygen, the main reactive gas, was supplied. Note that, hereinafter, this conventional atomic layer deposition method may be referred to as a 4-step atomic layer deposition method.

[0021] The precursor of the ruthenium thin film used was the ruthenium precursor shown in Chemical Formula 1 above (tricarbonyl(trimethylenemethane)ruthenium: [Ru(TMM)(CO)3]). An NCD ALD tool (Lucida d200, NCD Co., Ltd.) was used as the apparatus and reactor for producing the ruthenium thin film. During the process of forming the ruthenium thin film by atomic layer deposition, the measured temperature of the substrate was maintained at 310°C.

[0022] The precursor was contained in a stainless steel bubbler and used for ALD. The temperature of the ruthenium precursor bubbler was maintained at 10°C. The precursor was delivered for 10 seconds, and was supplied to the reaction chamber containing the substrate along with 50 sccm of nitrogen carrier gas. All experiments were performed using a silicon substrate with 100 nm of silicon oxide (SiO2) deposited on it.

[0023] The 6-step atomic layer deposition method (6-step Ru ALD) of the present invention involves injecting and purging a ruthenium precursor and oxygen, the main reactive gas, at a temperature of 310°C, above the ALD window where thermal decomposition of the precursor occurs, followed by injecting and purging ammonia as an additional reactive gas.

[0024] In the 6-step Ru ALD, the ruthenium precursor is injected for 10 seconds, followed by a 10-second purge step in which 50 sccm of nitrogen gas is injected. Then, oxygen, the main reactant gas, is supplied at 50 sccm for 10 seconds. In the oxygen purge step, 50 sccm of nitrogen gas is injected for 10 seconds. Then, ammonia, the additional reactant gas, is supplied at 50 sccm for 30 seconds. In the ammonia purge step, 50 sccm of nitrogen gas is injected for 10 seconds. Therefore, the time required for each step in the 6-step Ru ALD sequence, consisting of precursor exposure → purging → main reactant gas exposure → purging → additional reactant gas exposure → purging, is 10 seconds, 10 seconds, 10 seconds, 10 seconds, 30 seconds, and 10 seconds.

[0025] In contrast to the 6-step Ru ALD described above, the 4-step atomic layer deposition method (4-step Ru ALD) uses only a ruthenium precursor and oxygen as the main reactive gas at a temperature of 310°C, above the ALD window where thermal decomposition of the precursor occurs.

[0026] In the 4-step Ru ALD, the ruthenium precursor is injected for 10 seconds, followed by a 10-second purge step in which 50 sccm of nitrogen gas is injected. Then, oxygen is supplied as the main reactant gas at 50 sccm for 10 seconds. The oxygen purge step involves injecting 50 sccm of nitrogen gas for 10 seconds. Therefore, the total time required for each step in the 4-step Ru ALD sequence (precursor exposure → purging → main reactant gas exposure → purging) is 10 seconds, 10 seconds, 10 seconds, and 10 seconds.

[0027] Under the above conditions, the resistivity and grain size of ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD were measured, and their cross-sectional morphology was observed by TEM. The resistivity was calculated from the film thickness by measuring the sheet resistance of the thin film.

[0028] Figure 1a shows the resistivity and growth rate (GPC) of ruthenium thin films formed by 4-step Ru ALD. Figure 1b shows the XRD pattern of the ruthenium thin film formed by 4-step Ru ALD. The growth rate of the ruthenium thin film by 4-step Ru ALD was 2.6 Å / cycle, and the incubation cycle was 0.

[0029] Figure 2a shows the resistivity and growth rate (GPC) of ruthenium thin films formed by 6-step Ru ALD. Figure 2b shows the XRD pattern of the ruthenium thin film formed by the 6-step Ru ALD. The growth rate (GPC) of the ruthenium thin film formed by the 6-step Ru ALD was 1.3 Å / cycle, and the incubation cycle was 33.

[0030] Figure 3a compares the resistivity of ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD. Comparing the two under similar film thickness and conditions, the resistivity of the 4-step Ru ALD was 20.1 μΩ·cm, while that of the 6-step Ru ALD was 13.4 μΩ·cm, confirming a 6.7 μΩ·cm decrease in resistivity.

[0031] Figure 3b shows the high-resolution X-ray diffraction analysis (HRXRD, analysis equipment: Bruker, D8 These are the results of an analysis of a ruthenium thin film using the DISCOVERY (STEM) system. The analysis results are for a 24.3 nm thick thin film grown by 4-step Ru ALD and a 26.7 nm thick thin film grown by 6-step Ru ALD. The ruthenium thin film exhibits a hexagonal close-packed (HCP) polycrystalline structure, with diffraction peaks appearing on the (100), (002), (101), (102), and (110) planes. This figure shows that the ruthenium thin film grown by 6-step Ru ALD has higher peak intensities than the 4-step Ru ALD, confirming improved crystallinity.

[0032] Figure 4a is a TEM image of a ruthenium thin film grown by 4-step Ru ALD, and Figure 4b is a TEM image of a ruthenium thin film grown by 6-step Ru ALD. Figure 5a shows the grain size distribution of a ruthenium thin film grown by 4-step Ru ALD. Figure 5b shows the grain size distribution of a ruthenium thin film grown by 6-step Ru ALD. These grain size distributions were measured for 100 crystals. The average grain size of the ruthenium thin film grown by 4-step Ru ALD was 13.7 nm, and the average grain size of the ruthenium thin film grown by 6-step Ru ALD was 19.2 nm. Injecting ammonia, an additional reactive gas, into the 6-step Ru ALD process increased the average grain size of the ruthenium thin film by 5.5 nm.

[0033] The composition of the ruthenium thin films (after 250 cycles) formed by each process was analyzed by secondary ion mass spectrometry (SIMS). Figure 6a shows the analysis results for the ruthenium thin film formed by the 4-step Ru ALD process, and Figure 6b shows the analysis results for the ruthenium thin film formed by the 6-step Ru ALD process. The ruthenium thin film formed by the 4-step Ru ALD process contained 0.56 atomic % carbon, 0.98 atomic % oxygen, and other impurities, with a ruthenium concentration of 97.80 atomic %. On the other hand, the ruthenium thin film formed by the 6-step Ru ALD process contained 0.04 atomic % carbon, 0.27 atomic % oxygen, and other impurities, with a ruthenium concentration of 99.6 atomic %. It can be seen that the addition of ammonia as an additional reactive gas during the 6-step Ru ALD process effectively reduces the impurity concentration.

[0034] Finally, we present the results of forming a ruthenium thin film on a patterned wafer using the 6-step Ru ALD method of the present invention. Figure 7 shows a TEM image of a ruthenium thin film formed on a patterned wafer using 6-step Ru ALD (200 cycles). Figure 8a shows a TEM image of the top portion of the pattern on which ruthenium was deposited, and Figure 8b shows a TEM image of the bottom portion. Figure 8c shows TEM images of the top, middle, and bottom portions of the ruthenium deposited film.

[0035] The holes in the patterned wafer had a height (depth) of 2.4 μm, a width at the bottom (bottom dimension) of 0.073 μm, and a width at the top (top dimension) of 0.14 μm. Therefore, the aspect ratio was 32.8 at the bottom and 16.7 at the top. The aspect ratio of the pattern is the ratio of the height to the width of the pattern. As can be seen from FIGS. 7 and 8, the ruthenium thin film formed by the 6-step Ru ALD of this embodiment is uniformly formed in the pattern. [Industrial Applicability]

[0036] As described above, the method for forming a ruthenium thin film using the six-step atomic layer deposition method according to the present invention can form a high-purity, low-resistivity ruthenium thin film. The mean free path of ruthenium electrons is approximately 10.8 nm, which is much shorter than that of copper. Ruthenium has a higher melting point than copper and high electromigration resistance. Therefore, it can effectively respond to the ever-increasing shrinkage of metal wiring. The present invention is suitable for forming metal wiring for various semiconductor devices, and can particularly respond to the miniaturization of wiring in ultra-miniaturized semiconductor devices.

Claims

1. In a method for forming a ruthenium thin film by atomic layer deposition, A method for forming a ruthenium thin film, comprising forming a ruthenium thin film by atomic layer deposition using a ruthenium precursor having the following chemical formula 1 and oxygen and ammonia as reactive gases. 【Chemistry 1】

2. 2. The method for forming a thin ruthenium film according to claim 1, wherein the thin ruthenium film is formed at a temperature of 310° C. or higher.

3. 3. The method for forming a thin ruthenium film according to claim 2, wherein the main reactant gas is oxygen and the additional reactant gas is ammonia.

4. 4. The method for forming a ruthenium thin film according to claim 2, wherein the resistivity of the ruthenium thin film is 20 μΩ·cm or less.

5. 4. The method for forming a thin ruthenium film according to claim 2, wherein the impurity content of the thin ruthenium film is 1.0 atomic % or less.

6. 2. The method for forming a ruthenium thin film by atomic layer deposition according to claim 1, providing a ruthenium precursor onto the substrate in the chamber; purging the ruthenium precursor; supplying oxygen as a primary reactive gas onto the substrate; purging the main reactant gas; supplying ammonia as an additional reactive gas onto the substrate; purging the additional reactant gas; A method for forming a ruthenium thin film, comprising:

7. 7. The method of claim 6, further comprising the step of supplying hydrogen, hydrogen plasma, ammonia plasma, or nitrogen / hydrogen plasma as an additional reactive gas onto the substrate after the step of supplying ammonia as an additional reactive gas onto the substrate.

8. 7. The method for forming a ruthenium thin film by atomic layer deposition according to claim 6, When each of the above steps is performed once in sequence, one deposition cycle is defined as: A method for forming a ruthenium thin film, wherein the incubation cycle for forming the ruthenium thin film is less than 35 cycles of the deposition cycle.

9. 7. The method for forming a ruthenium thin film by atomic layer deposition according to claim 6, When each of the above steps is performed once in sequence, one deposition cycle is defined as: A method for forming a ruthenium thin film, wherein the deposition rate of the ruthenium thin film is in the range of 0.13 nm / cycle to 0.16 nm / cycle.

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