Method for forming ruthenium thin films

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. Specifically, it relates to a high-temperature and high-performance 6-step method for forming a ruthenium thin film by applying ammonia (NH3) as an additional reaction gas in atomic layer deposition.

Background Art

[0002] A metal wiring is a metal wire that plays a role in transmitting and connecting electrical signals within a semiconductor chip. It is manufactured from metals such as copper (Cu) and aluminum (Al), and is mainly applied to integrated circuits (ICs) in semiconductor processes. The metal wiring connects mutually separated parts of the semiconductor chip to regulate the flow of current and transmit signals. This function has an important role in controlling the operation of electronic devices. Also, due to the size and high density of semiconductor chips, the metal wiring needs to be manufactured thinly and precisely. In recent years, the materials and manufacturing process steps of metal wiring have been continuously developing and are designed to provide higher transmission speeds and high reliability.

[0003] The most important property for a metal used in integrated circuit wiring is the resistance to the flow of current, and a metal material with a low specific resistance must be selected. In addition to the above-mentioned copper (Cu) and aluminum (Al), silver (Ag), gold (Au), etc. are applied as materials for semiconductor metal wiring. The specific resistances of these metal wiring materials at room temperature of 20°C are, respectively, silver: 1.59 μΩ·cm, gold: 2.44 μΩ·cm, aluminum: 2.82 μΩ·cm, and copper: 1.72 μΩ·cm. Among these metals, the bulk specific resistance of silver is the lowest. However, considering the economic aspect, copper is the most suitable metal wiring material and is currently used as the main material for semiconductor metal wiring.

[0004] However, as semiconductor devices become smaller, the line width of metal wiring is required to be reduced to less than the mean free path of electrons in copper (39 nm). Furthermore, when the line width of metal wiring is reduced to the order of a few nanometers, problems can arise where the resistivity of the copper wiring exceeds the bulk resistivity due to electromigration and stress-induced voiding. Due to these problems, it can be said that copper as a wiring material has reached its limits.

[0005] Atomic layer deposition (ALD) is a semiconductor thin film deposition technique, particularly suitable for depositing nanometer-thick films. ALD uses reactants in a gaseous state and repeatedly deposits atomic layers of material to form a thin film. This process involves sequentially injecting and purging two substances: a precursor and a reaction gas. At each stage, the precursor adsorbs onto the thin film surface, and the reaction 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. Furthermore, ALD offers superior step coverage compared to other deposition techniques, enabling the growth of multilayer structures of various materials. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-139020 [Patent Document 2] Special Publication No. 2017-524729 [Patent Document 3] Special Publication No. 2010-525162 [Overview of the project] [Problems that the invention aims to solve]

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

[0008] To achieve the above objective, the present invention provides a 6-step atomic layer deposition method in which, in addition to oxygen, the main reaction gas, ammonia is supplied as an additional reaction gas during the ruthenium thin film formation process by atomic layer deposition. The present invention is a 6-step atomic layer deposition method using one precursor and two reaction gases, and is a high-temperature, high-performance ruthenium film deposition process.

[0009] In other words, the present invention is a method for forming a ruthenium thin film by atomic layer deposition, characterized in that a ruthenium precursor having the structure shown in Chemical Formula 1 below (tricarbonyl(trimethylenemethane)ruthenium: [Ru(TMM)(CO)3]) and oxygen and ammonia are used as reaction gases to form a ruthenium thin film by atomic layer deposition.

[0010] [ka]

[0011] In this 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, this film formation temperature of 310°C or higher is above the ALD window. The ALD window is the temperature range in which the self-termination 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 the atomic layer deposition process.

[0012] Furthermore, in this invention, oxygen is used as the main reaction gas, and ammonia is used as the additional reaction gas.

[0013] Furthermore, the ruthenium thin film formed by the present invention preferably has a resistivity of 20 μΩ·cm or less. In addition, it is preferable that the impurity content of this ruthenium thin film is 1.0 atomic% or less.

[0014] The present invention's 6-step atomic layer deposition method for forming a ruthenium thin film preferably includes the following steps to form the ruthenium thin film. • A step of supplying a ruthenium precursor onto the substrate in the chamber; • A step of purging the ruthenium precursor; • A step of supplying oxygen, which is the main reaction gas, onto the substrate; • A step of purging the main reaction gas; - A step of supplying ammonia, which is an additional reaction gas, onto the substrate; • The step of purging the additional reaction gas;

[0015] Furthermore, in the above procedure, hydrogen, hydrogen plasma, ammonia plasma, or nitrogen / hydrogen plasma may be supplied to the substrate as an additional reaction gas after the step of supplying ammonia as an additional reaction gas to the substrate and before the step of purging the additional reaction gas.

[0016] In the ruthenium thin film formation method according to the present invention, when each of the above steps is performed sequentially once, one deposition cycle is considered, it is preferable that the incubation cycle for ruthenium thin film formation is smaller than 35 of the deposition cycles.

[0017] Furthermore, in the ruthenium thin film formation method according to the present invention, when each of the above steps is performed sequentially once, it is preferable that the deposition rate of the ruthenium thin film is in the range of 0.13 nm / cycle to 0.16 nm / cycle. [Effects of the Invention]

[0018] In the present invention, after the supply step of oxygen which is the main reaction gas, ammonia which is the additional reaction gas is supplied to form a ruthenium thin film. According to the present invention, it is possible to form a ruthenium thin film with various physical properties improved, such as high purity, low resistance, and improved crystallinity of ruthenium purity.

Brief Description of the Drawings

[0019] [Figure 1a] Graph showing the specific resistance value, growth rate, and incubation cycle of a ruthenium thin film formed by 4-step Ru ALD. [Figure 1b] XRD pattern of a ruthenium thin film formed by 4-step Ru ALD. [Figure 2a] Graph showing the specific resistance value, growth rate, and incubation cycle of a ruthenium thin film formed by 6-step Ru ALD. [Figure 2b] XRD pattern of a ruthenium thin film formed by 6-step Ru ALD. [Figure 3a] Graph comparing the specific resistance of ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD. [Figure 3b] Figure comparing the 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 crystal grain size distribution of a ruthenium thin film by 4-step Ru ALD. [Figure 5b] Graph showing the crystal grain size distribution of a ruthenium thin film by 6-step Ru ALD. [Figure 6a] Figure showing the composition analysis result by SIMS of a ruthenium thin film by 4-step Ru ALD. [Figure 6b]This figure shows the results of SIMS compositional analysis of a ruthenium thin film using 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 upper edge of a ruthenium-deposited pattern. [Figure 8b] TEM image of the patterned bottom of a ruthenium thin film. [Figure 8c] TEM images of the top, middle, and bottom of a ruthenium thin film pattern. [Modes for carrying out the invention]

[0020] Embodiments of the present invention will be described below. In this embodiment, a ruthenium thin film was formed under specific deposition 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 reaction gas, was supplied. In the following, the conventional atomic layer deposition method described above may be referred to as the 4-step atomic layer deposition method.

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

[0022] The precursor was supplied to the ALD (Advanced Liquid Processing) stage after being contained in a stainless steel bubbler. The temperature of the ruthenium precursor bubbler was maintained at 10°C. The precursor was supplied for 10 seconds, along with 50 sccm of nitrogen carrier gas, into the reaction chamber containing the substrate. All experiments used a substrate on which silicon oxide (SiO2) was deposited at a thickness of 100 nm.

[0023] The 6-step atomic layer deposition method (6-step Ru ALD) of the present invention is an atomic layer deposition method in which a ruthenium precursor and oxygen, the main reaction gas, are injected and purged at a temperature of 310°C, above the ALD window at which thermal decomposition of the precursor occurs, and then ammonia is injected and purged as an additional reaction gas.

[0024] In the 6-step Ru ALD, the ruthenium precursor is injected for 10 seconds, followed by a purge phase injecting 50 sccm of nitrogen gas for 10 seconds. Then, oxygen is supplied as the main reaction gas at 50 sccm for 10 seconds. In the oxygen purge phase, 50 sccm of nitrogen gas is injected for 10 seconds. Next, ammonia, an additional reaction gas, is supplied at 50 sccm for 30 seconds. In the ammonia purge phase, 50 sccm of nitrogen gas is injected for 10 seconds. Therefore, the duration of each step in the 6-step Ru ALD sequence, which consists of "precursor exposure → purging → main reaction gas exposure → purging → additional reaction gas exposure → purging," is 10 seconds - 10 seconds - 10 seconds - 10 seconds - 30 seconds - 10 seconds.

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

[0026] In the 4-step Ru ALD, the ruthenium precursor is injected for 10 seconds, followed by a purge phase injecting 50 sccm of nitrogen gas for 10 seconds. Then, oxygen is supplied as the main reaction gas at 50 sccm for 10 seconds. In the oxygen purge phase, 50 sccm of nitrogen gas is injected for 10 seconds. Therefore, the duration of each step in the 4-step Ru ALD sequence, which consists of "precursor exposure → purging → main reaction gas exposure → purging," is 10 seconds - 10 seconds - 10 seconds - 10 seconds.

[0027] Under the above conditions, resistivity measurements, grain size measurements, and TEM observation of cross-sectional morphology were performed on ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD. Resistivity was calculated from the film thickness by measuring the surface resistance of the thin film.

[0028] Figure 1a shows the resistivity and growth rate (GPC:Growth) of a ruthenium thin film formed by 4-step Ru ALD. Figure 1b shows the growth rate (per cycle) and incubation cycle. Figure 1b also shows the XRD pattern of a 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:Growth) of a ruthenium thin film formed by 6-step Ru ALD. Figure 2b shows the growth rate (GPC) per cycle and incubation cycle. The growth rate (GPC) of the ruthenium thin film formed by 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. When comparing the two under similar film thickness and conditions, the resistivity of the 4-step Ru ALD was 20.1 μΩ·cm, while the resistivity of the 6-step Ru ALD was 13.4 μΩ·cm, showing a decrease of 6.7 μΩ·cm.

[0031] Figure 3b shows high-resolution X-ray diffraction analysis (HRXRD, analyzer: Bruker, D8). This is the result of analyzing ruthenium thin films using DISCOVERY. The analysis results are for a 24.3 nm thick thin film prepared using 4-step Ru ALD and a 26.7 nm thick thin film prepared using 6-step Ru ALD. The ruthenium thin films exhibit a hexagonal close-packed (HCP) polycrystalline structure with diffraction peaks appearing at the (100), (002), (101), (102), and (110) planes. From this figure, it can be seen that the ruthenium thin film prepared using 6-step Ru ALD has higher peak intensity than the 4-step Ru ALD, confirming improved crystallinity.

[0032] Figure 4a shows a TEM image of a ruthenium thin film obtained by 4-step Ru ALD, and Figure 4b shows a TEM image of a ruthenium thin film obtained by 6-step Ru ALD. Figure 5a shows the grain size distribution of the ruthenium thin film obtained by 4-step Ru ALD. Figure 5b shows the grain size distribution of the ruthenium thin film obtained by 6-step Ru ALD. These grain size distributions are the results of measurements taken for 100 crystals. The average grain size of the ruthenium thin film obtained by 4-step Ru ALD was 13.7 nm, and the average grain size of the ruthenium thin film obtained by 6-step Ru ALD was 19.2 nm. By injecting ammonia, an additional reaction gas, into the 6-step Ru ALD, the average grain size of the ruthenium thin film increased by 5.5 nm.

[0033] The ruthenium thin films formed in each process (after 250 cycles) were analyzed for composition by secondary ion mass spectrometry (SIMS). Figure 6a shows the analysis results for the ruthenium thin film formed by 4-step Ru ALD, and Figure 6b shows the analysis results for the ruthenium thin film formed by 6-step Ru ALD. The ruthenium thin film formed by 4-step Ru ALD 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 6-step Ru ALD contained 0.04 atomic% carbon, 0.27 atomic% oxygen, and other impurities, with a ruthenium concentration of 99.6 atomic%. It can be said that injecting ammonia as an additional reaction gas in 6-step Ru ALD has the effect of reducing the concentration of impurities.

[0034] Finally, the results of forming a ruthenium thin film on a patterned wafer using the 6-step Ru ALD of the present invention are shown. Figure 7 is a TEM image of a ruthenium thin film formed on a patterned wafer using 6-step Ru ALD (200 cycles). Figure 8a is a TEM image of the upper part of the pattern where ruthenium was deposited, and Figure 8b is a TEM image of the bottom part. Figure 8c is a TEM image of the upper (Top), middle (Middle), and bottom (Bottom) parts of the ruthenium deposited film.

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

[0036] As described above, the 6-step atomic layer deposition method for forming a ruthenium thin film according to the present invention can deposit a ruthenium thin film with high purity and low resistivity. Ruthenium has a mean free path of internal electrons of approximately 10.8 nm, which is much shorter than that of copper. Ruthenium has a higher melting point than copper and exhibits high resistance to electromigration. Therefore, it can effectively address the future trend of reducing the line width of metal wiring. The present invention is suitable for forming metal wiring in various semiconductor devices, and in particular, it can address the miniaturization of wiring in ultra-miniature semiconductor devices.

Claims

1. In a method for forming ruthenium thin films by atomic layer deposition, Using a ruthenium precursor having the structure shown in Chemical Formula 1 below, and oxygen as the main reaction gas and ammonia as an additional reaction gas, A method for forming a ruthenium thin film, characterized by forming a ruthenium thin film by an atomic layer deposition method in which each of the following steps is performed sequentially once, forming one deposition cycle. A step of supplying the ruthenium precursor onto the substrate in the chamber; A step of purging the ruthenium precursor; A step of supplying oxygen, which is the main reaction gas, onto the substrate; A step of purging the main reaction gas; A step of supplying the additional reaction gas, ammonia, onto the substrate; The step of purging the additional reaction gas; 【Chemistry 1】

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

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

4. The method for forming a ruthenium thin film according to claim 2 or claim 3, wherein the resistivity of the ruthenium thin film is 20 μΩ·cm or less.

5. A method for forming a ruthenium thin film according to claim 2 or claim 3, wherein the impurity content of the ruthenium thin film is 1.0 atomic% or less.

6. A ruthenium thin film formation method according to claim 1, comprising the step of supplying ammonia as an additional reaction gas onto the substrate, followed by the step of supplying hydrogen, hydrogen plasma, ammonia plasma, or nitrogen / hydrogen plasma as an additional reaction gas onto the substrate.

7. A method for forming a ruthenium thin film by atomic layer deposition according to Claim 1, When each of the above steps is performed sequentially once, one deposition cycle is defined as this process. A method for forming a ruthenium thin film in which the incubation cycle for ruthenium thin film formation is shorter than the 35 cycles of the deposition cycle.

8. A method for forming a ruthenium thin film by atomic layer deposition according to Claim 1, When each of the above steps is performed sequentially once, one deposition cycle is defined as this process. A method for forming a ruthenium thin film in which 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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