Method for forming ruthenium thin film

Abstract

The present invention relates to a method for forming a ruthenium thin film produced using an atomic layer deposition method. In the present invention, at a high temperature at which thermal decomposition of a ruthenium precursor occurs, ammonia is injected as an additional reaction gas and a ruthenium thin film is formed. The present invention relates to a high-performance six-step (six-stage) atomic layer deposition method with which it is possible to maintain exceptional thin film characteristics. In the present invention, after a stage for injecting and purging oxygen, which is the main reaction gas, ammonia, which is an additional reaction gas, is injected and purged, thereby making it possible to enlarge ruthenium crystal grains and reduce the impurity concentration, whereby the specific resistance of the thin film is reduced. The ruthenium thin film formed in the present invention has improved characteristics over those of an existing ruthenium thin film obtained using only an oxygen reaction gas. The present invention is thereby utilized as a novel metal wiring material that replaces copper wiring, and as film formation technology.

Description

Method for forming a ruthenium thin film

[0001] The present invention relates to a method for forming a ruthenium (Ru) thin film by atomic layer deposition. ３ This invention relates to a high-temperature, high-performance, six-step ruthenium thin film formation method that uses the ruthenium ion beam.

[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 isolated parts of a semiconductor chip to regulate the flow of current and transmit 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, materials and manufacturing processes for metal wiring have been continuously developed and are 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, and 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 the size of semiconductor elements becomes smaller, the line width of metal wiring is required to be reduced to the mean free path of electrons in Cu (39 nm) or less. Furthermore, when the line width of metal wiring is reduced to the order of several nanometers, problems such as electromigration and stress-induced voids can occur, causing the resistivity of Cu wiring to exceed the bulk resistivity. 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 suitable for depositing nanometer-scale thin films. ALD uses gaseous reactants to repeatedly deposit atomic layers of a material to form a thin film. This process involves sequentially injecting and purging two materials—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. This process is repeated to create a thin film of the desired thickness. ALD also offers superior step coverage compared to other deposition techniques, enabling the growth of multilayer structures of various materials.

[0006] Japanese Patent Application Laid-Open No. 2023-139020 Special Publication No. 2017-524729 Special Publication No. 2010-525162

[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.

[0008] To achieve the above object, the present invention provides a six-step atomic layer deposition method in which ammonia, an additional reactant gas, is supplied in addition to oxygen, a primary reactant 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 reactant gases, and is a high-temperature, high-performance ruthenium film formation process.

[0009] That is, the present invention relates to a method for forming a ruthenium thin film by atomic layer deposition, which comprises using a ruthenium precursor having the following structure (tricarbonyl(trimethylenemethane)ruthenium: [Ru(TMM)(CO) ３ ]) and oxygen and ammonia as reactive gases, and a ruthenium thin film is formed by atomic layer deposition.

[0010]

[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 in which a 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 forms a ruthenium thin film by including the following steps: supplying a ruthenium precursor onto a substrate in a chamber; purging the ruthenium precursor; supplying oxygen as a main reactant gas onto the substrate; purging the main reactant gas; supplying ammonia as an additional reactant gas onto the substrate; and 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] In addition, 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.

[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.

[0019] Graph showing the resistivity, growth rate, and incubation cycle of a ruthenium thin film formed by 4-step Ru ALD. XRD pattern of a ruthenium thin film formed by 4-step Ru ALD. Graph showing the resistivity, growth rate, and incubation cycle of a ruthenium thin film formed by 6-step Ru ALD. XRD pattern of a ruthenium thin film formed by 6-step Ru ALD. Graph comparing the resistivity of ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD. Graph comparing HRXRD patterns of ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD. TEM image of a ruthenium thin film formed by 4-step Ru ALD. TEM image of a ruthenium thin film formed by 6-step Ru ALD. Graph showing the distribution of crystal grain size of a ruthenium thin film formed by 4-step Ru ALD. Graph showing the distribution of crystal grain size of a ruthenium thin film formed by 6-step Ru ALD. Diagram showing the results of composition analysis by SIMS of a ruthenium thin film formed by 4-step Ru ALD. Diagram showing the results of composition analysis by SIMS of a ruthenium thin film formed by 4-step Ru ALD. Cross-sectional TEM image of a ruthenium thin film formed on a patterned wafer by 6-step Ru ALD: TEM image of the top portion of the pattern where ruthenium is deposited. TEM image of the bottom portion of the ruthenium thin film pattern. TEM images of the top, middle, and bottom portions of the ruthenium thin film pattern.

[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 was the ruthenium precursor shown in Chemical Formula 1 (tricarbonyl(trimethylenemethane)ruthenium: [Ru(TMM)(CO) ３]) was used. An NCD ALD tool (Lucida d200, NCD Co., Ltd.) was used as the apparatus and reactor for producing the ruthenium thin film. In 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 precursors were contained in a stainless steel bubbler and used for ALD. The temperature of the bubbler for the ruthenium precursor was maintained at 10°C. The precursor was supplied for 10 seconds, together with 50 sccm of nitrogen carrier gas, into the reaction chamber containing the substrate. All experiments were performed using silicon oxide (SiO ２ The substrate used was a substrate on which 100 nm of SiO 2 was deposited.

[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, which is the main reactive gas, at a temperature of 310°C, above the ALD window where thermal decomposition of the precursor occurs, and then injecting and purging ammonia, which is an additional reactive gas.

[0024] In the 6-step Ru ALD, a ruthenium precursor is injected for 10 seconds, followed by a purge step in which 50 sccm of nitrogen gas is injected for 10 seconds. 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, the 4-step atomic layer deposition (4-step Ru ALD) is an atomic layer deposition method that uses only a ruthenium precursor and oxygen as the main reactive gas at a temperature of 310°C, which is above the ALD window where thermal decomposition of the precursor occurs.

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

[0027] Ruthenium thin films formed by 4-step Ru ALD and 6-step Ru ALD under the above conditions were subjected to resistivity measurement, crystal grain size measurement, and TEM observation of cross-sectional morphology. The resistivity was calculated from the film thickness by measuring the sheet resistance of the thin film.

[0028] Figure 1a shows the resistivity, growth rate (GPC: Growth Per Cycle), and incubation cycles for a ruthenium thin film 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, growth rate (GPC: Growth Per Cycle), and incubation cycles for a ruthenium thin film formed by 6-step Ru ALD. Figure 2b shows the XRD pattern of the ruthenium thin film formed by 6-step Ru ALD. 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] 3a is a graph comparing 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 film was 20.1 μΩ cm, while the resistivity of the 6-step Ru ALD film was 13.4 μΩ cm, confirming a decrease of 6.7 μΩ cm.

[0031] Figure 3b shows the results of analysis of a ruthenium thin film using high-resolution X-ray diffraction analysis (HRXRD, analysis equipment: Bruker, D8 DISCOVERY). 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 shows a TEM image of a ruthenium thin film grown by 4-step Ru ALD, and Figure 4b shows 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 are the results of measurements on 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. The injection of 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 of the ruthenium thin film formed by 4-step Ru ALD, and Figure 6b shows the analysis results of 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 the injection of ammonia, an additional reactive gas, in 6-step Ru ALD is effective in reducing the impurity concentration.

[0034] Finally, we show 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 8a and 8b, the ruthenium thin film formed by the 6-step Ru ALD of this embodiment is uniformly formed in the pattern.

[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 accommodate the ever-increasing shrinkage of metal wiring. The present invention is suitable for forming metal wiring for various semiconductor devices, and can particularly accommodate the miniaturization of wiring in ultra-miniaturized semiconductor devices.

Claims

1. A method for forming a ruthenium thin film by atomic layer deposition, comprising using a ruthenium precursor having the structure of Chemical Formula 1 below and oxygen and ammonia as reactive gases to form a ruthenium thin film by atomic layer deposition.

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

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

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

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

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

9. A method for forming a ruthenium thin film by atomic layer deposition according to claim 6, wherein when each of the steps is performed once in sequence to form one deposition cycle, 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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