A method for rapidly preparing high-temperature-resistant and high-conductivity Mo-C-based interconnection film at room temperature

Abstract

This invention relates to the field of microelectronics and integrated circuit materials technology, specifically a method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature. Addressing the problems of decreased conductivity and insufficient thermal stability caused by natural oxidation in traditional copper-based interconnect materials at technology nodes of 7 nm and below, this invention proposes molybdenum-based interconnect materials as an alternative. This invention achieves controllable and rapid preparation of high-quality molybdenum-carbon compound thin films on silicon substrates using magnetron sputtering technology. The key is the precise control of parameters such as sputtering power, carbon content, and working gas pressure, successfully preparing high-quality films with different phase structures (including MoC, Mo3C2, and Mo2C). Experimental results show that the optimized 60 nm thick Mo2C film can achieve a resistivity as low as 5.53 μΩ·cm at room temperature and maintains excellent electrical properties after high-temperature annealing at 400–600℃. This provides a key material solution for next-generation integrated circuit interconnect layers and has significant application prospects.

Description

Technical Field

[0001] This invention relates to the field of microelectronics and integrated circuit materials technology, specifically a method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature. Background Technology

[0002] In integrated circuit manufacturing processes, the electrical properties and thermal stability of interconnect materials have a decisive impact on device reliability. While traditional interconnect materials (such as Al and Cu) possess excellent conductivity, they are prone to electromigration and thermal degradation at high temperatures, leading to decreased device performance. Molybdenum (Mo), due to its high melting point (2623℃) and low resistivity (~5-8 μΩ·cm), is considered a potential alternative interconnect material. However, pure Mo films are prone to interdiffusion with the silicon substrate during high-temperature annealing, forming high-resistivity silicides (such as Mo5Si3), and its insufficient stability in oxidizing environments limits its application in advanced processes.

[0003] To improve the thermal stability of Mo thin films, existing technologies introduce carbon to form a molybdenum carbide (Mo2C) phase. Studies have shown that Mo2C has higher chemical inertness and can effectively suppress element diffusion and oxidation at high temperatures. However, existing preparation methods (such as chemical vapor deposition and reactive sputtering) have the following problems: ① Poor process controllability: The carbon content is difficult to precisely control, resulting in uneven film composition and large fluctuations in electrical properties; ② Insufficient thermal stability: Traditional Mo and Mo2C metal thin films fail at 300 / 400℃. [1,2] ③ Interface compatibility: Mo / Si or Mo2C / Si interfaces are prone to defects under thermal stress, exacerbating device failure. Furthermore, existing technologies do not address how to rapidly obtain high-quality Mo-C-based interconnect thin film materials.

[0004] [1] Akçay N, Akın N, Cömert B, Özçelik S. Temperature effects on thestructural, optical, electrical and morphological properties of the RF-sputtered Mo thin films. Journal of Materials Science: Materials in Electronics 28(2017):399-406.

[0005] [2] Kesik O, Elçi A, Kaynar BM Synthesis of Mo / Mo2C-DLC compositethin films via diffusion of plasma-generated C atoms into sputter-coated Mothin films[J]. Vacuum, 233(2025),233114008-114008. Summary of the Invention

[0006] This invention develops a method for rapidly and precisely controlling the composition of Mo and Mo2C thin films at room temperature, which combines low resistivity and high thermal stability to meet the demand of integrated circuits for high-performance interconnect materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature includes the following steps:

[0009] Step 1: Using Mo as the target material, a Mo thin film is prepared on a clean and dry silicon substrate by magnetron sputtering. The electrical properties and scanning electron microscope images of the prepared Mo thin film are tested. Based on the principle of lowest resistivity and dense surface morphology, the Mo thin film with the lowest resistivity is determined to be the best film, and the deposition parameters of the best Mo thin film are selected.

[0010] Step 2: Using Mo as the metal target and graphite as the carbon target, sputtering is performed on a clean and dry silicon substrate using the optimal deposition parameters obtained in Step 1 for the metal target and different power for the carbon target, resulting in different Mo carbide films on the silicon substrate. Then, based on the principle of the lowest resistivity, the optimal Mo carbide film is selected as the Mo-C based interconnect film.

[0011] In this invention, a clean and dry silicon substrate is obtained through the following method:

[0012] The silicon wafer is cleaned sequentially with acetone and anhydrous ethanol under ultrasonic conditions, and then etched with a 10-25%, preferably 20%, hydrofluoric acid solution. After etching with the hydrofluoric acid solution, it is rinsed with water and dried with a protective gas. In practical applications, after each cleaning, it is rinsed with deionized water and dried with nitrogen.

[0013] In step one of this invention, when preparing Mo thin films by magnetron sputtering, the sputtering power is 15-30 W, the working pressure is 0.5-1.5 Pa, and the deposition time is 5-15 min.

[0014] In step one of this invention, the resistivity (ρ) and carrier mobility (μ) of the thin film are measured using a Hall effect testing system.

[0015] In step one of this invention, the optimal deposition parameters for the Mo thin film are: working pressure 0.7 Pa and sputtering power 20 W.

[0016] The optimal deposition parameters for Mo thin films resulted in a resistivity (ρ) of 5.09 μΩ·cm.

[0017] In step two of this invention, the sputtering power of the metal target is 20 W and the working pressure is 0.7 Pa, while the sputtering power of the carbon target is 50-130 W.

[0018] In step two of this invention, the process parameters for obtaining the optimal Mo carbide thin film are: sputtering power of the metal target is 20 W, working pressure is 0.7 Pa, and sputtering power of the carbon target is 120 W.

[0019] In step two of this invention, the resistivity (ρ) of the obtained optimal Mo carbide film is 5.53 μΩ·cm.

[0020] In steps one and two of this invention, the magnetron sputtering temperature is room temperature, preferably 25°C.

[0021] In industrial applications, the sputtering deposition rate of Mo2C can be explored first, and then a reasonable deposition time can be selected based on the actual required thickness.

[0022] In order to evaluate the thermal stability of the thin film, the present invention uses annealing treatment followed by measurement of the electrical properties of the thin film. The annealing conditions are as follows: gradient annealing is carried out under Ar atmosphere protection, the annealing temperature range is 400-800℃, the heating rate is 5℃ / min, and the holding time is 30 min.

[0023] The Mo-C based interconnect thin film material obtained in step two of this invention showed no significant failure in its electrical properties up to 600°C, and the introduction of carbon significantly improved its thermal stability.

[0024] After optimization, the Mo-C-based interconnect thin film material obtained in step two of this invention exhibits a resistivity of 10.06 μΩ·cm and an electrical conductivity of 9.94 × 10⁻⁶ after being heated at 600°C for 30 min. 4 S / cm, bulk carrier concentration is 1.04 × 10⁻⁶ 21 / cm³, mobility 597.42cm³ / V·s, surface carrier concentration 6.24×10 15 / cm 2 .

[0025] The Mo-C-based interconnect thin film material obtained in step two is used in integrated circuits, and is particularly suitable as an interconnect material in integrated circuits.

[0026] The innovation of this invention is specifically reflected in the following aspects:

[0027] ① A systematic study on the interconnect application potential of novel Mo and Mo2C metal carbide thin film materials: For the first time, a comprehensive evaluation of the electrical properties (resistivity, carrier concentration, mobility, and conductivity) and thermal stability of Mo and Mo2C metal carbides at the 7 nm node of ultra-large-scale integrated circuits (ULSI) with a thickness of 60 nm was conducted, filling the gap in the systematic research of this material system in the field of nano-interconnects.

[0028] ② Breaking through the performance bottlenecks of traditional interconnect materials: Compared with traditional Cu interconnects (which have prominent problems with thermal stability and resistivity increase) and transition metal nitrides (which have high resistivity), this invention achieves synergistic optimization of low resistivity (~5 μΩ·cm) and high thermal stability (critical temperature 500 / 600℃) by controlling the grain boundary chemical state of Mo and Mo2C metal carbides (such as carbon vacancy passivation) and interlayer stacking mode (such as orientation growth), providing a solution for interconnect materials below 7nm node.

[0029] ③ Innovation in process compatibility and scalability: We developed room temperature (25°C) magnetron co-sputtering and innovatively adopted gradient power co-sputtering to obtain Mo2C thin films with controllable stoichiometry; and we can precisely control the electrically excellent Mo2C metal carbide thin films by adjusting the C / metal target power ratio, revealing the mechanism by which carbonization treatment enhances the thermal stability of the metal / semiconductor interface.

[0030] This invention not only expands the application boundaries of Mo and Mo2C metal carbides in the field of semiconductor interconnects, but also provides a material basis and process roadmap for overcoming the limitations of Moore's Law. The materials prepared by the method developed in this invention are easily applied to integrated circuit interconnect structures. Attached Figure Description

[0031] Figure 1 The resistivity of Mo and Mo2C films at different annealing temperatures is compared between sample No. 2 obtained in Example 1 and sample No. 14 obtained in Example 2.

[0032] Figure 2 The conductivity of Mo and Mo2C films at different annealing temperatures is compared between sample No. 2 obtained in Example 1 and sample No. 14 obtained in Example 2.

[0033] Figure 3 The migration rates of Mo and Mo2C films obtained from Example 1 (sample 2) and Example 2 (sample 14) are compared at different annealing temperatures.

[0034] Figure 4The comparison shows the surface carrier mobility of Mo and Mo2C films at different annealing temperatures between sample No. 2 obtained in Example 1 and sample No. 14 obtained in Example 2.

[0035] Figure 5 The comparison shows the bulk carrier mobility of Mo and Mo2C films at different annealing temperatures between sample No. 2 obtained in Example 1 and sample No. 14 obtained in Example 2.

[0036] Figure 6 SEM images of sample No. 2 obtained in Example 1 at different annealing temperatures: (a) 25℃; (b) 400℃; (c) 500℃; (d) 600℃; (e) 650℃; (f) 700℃;

[0037] Figure 7 AFM morphology analysis of sample No. 2 obtained in Example 1 at different annealing temperatures: (a) 25℃, Ra=0.951nm; (b) 400℃, Ra=1.08nm; (c) 500℃, Ra=1.14nm; (d) 600℃, Ra=1.20nm; (e) 650℃, Ra=1.42nm; (f) 700℃, Ra=2.16nm.

[0038] Figure 8 SEM morphology analysis of sample No. 14 obtained in Example 2 at different annealing temperatures: (a) 25℃; (b) 400℃; (c) 600℃; (d) 700℃; (e) 750℃; (f) 800℃;

[0039] Figure 9 AFM morphology analysis of sample No. 14 obtained in Example 2 at different annealing temperatures: (a) 25℃, Ra=0.553 nm; (b) 400℃, Ra=0.83 nm; (c) 600℃, Ra=1.79 nm; (d) 700℃, Ra=4.65 nm; (e) 750℃, Ra=7.79 nm; (f) 800℃, Ra=20 nm. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solution of the invention, the invention will be further described in detail below with reference to specific embodiments.

[0041] Example 1 (Exploratory Experiment)

[0042] First, ultrasonically clean the silicon wafer in acetone for 10 minutes, then ultrasonically clean it in anhydrous ethanol for 10 minutes, and blow it dry. Next, clean it with 20% hydrofluoric acid for 10 minutes, then rinse it with deionized water, and finally clean it with anhydrous ethanol for 10 minutes and blow it dry.

[0043] ① Mo Metal Thin Film Preparation: Mo metal thin films were prepared using magnetron sputtering, and the variation of film uniformity under different power, working pressure, and sputtering rate (achieved by controlling sputtering time) conditions was investigated. First, multiple power levels (e.g., 15W, 20W, 25W…) and pressure ranges (e.g., 0.5 Pa, 0.7 Pa, 1 Pa…) were set to determine the optimal conditions. Then, the effect of sputtering rate at different time intervals on film thickness uniformity was evaluated by adjusting the sputtering time (e.g., 5-20 minutes). Finally, the structure and surface morphology of the prepared films were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) to identify the most uniform Mo film fabrication conditions achievable by optimizing sputtering time under specific power and pressure. The electrical properties of the Mo films obtained under different conditions are shown in Tables 1 and 2.

[0044]

[0045]

[0046] Series Example 2

[0047] Mo2C thin film preparation: First, keeping the process unchanged, Mo thin films were prepared under a working gas pressure of 0.7 Pa and a sputtering power of 20 W. Then, co-sputtering was used to change the sputtering power of the carbon target (55 W, 65 W, 70 W, 75 W, 80 W, 85 W, 90 W, 95 W, 120 W, 130 W) to produce uniform materials with different Mo-C ratios.

[0048] Before preparing the molybdenum carbide thin film, the sputtering rate was initially determined. This experiment employed magnetron co-sputtering. Under the previously optimized sputtering process parameters, Mo and C targets were co-sputtered for 10 minutes. The sputtering power of the C target was varied (70W, 80W, 90W), ultimately determining the sputtering rate of the Mo₂C thin film to be 3.6 nm / min. Under this sputtering rate, the sputtering power and estimated sputtering time were adjusted to obtain a film of the desired thickness.

[0049] Then, the electrical properties, microstructure, crystallinity, and thermal stability (400-800℃) of molybdenum thin films prepared by reactive magnetron sputtering and Mo2C thin films prepared by magnetron co-sputtering were compared and studied.

[0050]

[0051] For a comparison of the performance of sample No. 2 in Example 1 and sample No. 8 in Example 2 at different annealing temperatures, see [link to documentation]. Figure 1-5In Example 1, the preparation conditions for sample 2 were: Mo target sputtering power of 20 W, gas pressure range of 0.7 Pa, and sputtering time of 18 minutes. In Example 2, the preparation conditions for sample 14 were: Mo target sputtering power of 20 W, gas pressure range of 0.7 Pa, and sputtering time of 17 minutes; and C target sputtering power of 120 W, gas pressure range of 0.7 Pa, and sputtering time of 17 minutes. For samples 8-15 in Table 3, all other conditions were the same, the difference being the use of different C target sputtering powers.

Claims

1. A method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature, characterized in that, Includes the following steps: Step 1: Using Mo as the target material, a Mo thin film is prepared on a clean and dry silicon substrate by magnetron sputtering. The electrical properties and scanning electron microscope images of the prepared Mo thin film are tested. Based on the principle of lowest resistivity and dense surface morphology, the Mo thin film with the lowest resistivity is determined to be the best film, and the deposition parameters of the best Mo thin film are selected. Step 2: Using Mo as the metal target and graphite as the carbon target, sputtering is performed on a clean and dry silicon substrate using the optimal deposition parameters obtained in Step 1 for the metal target and different power for the carbon target, resulting in different Mo carbide films on the silicon substrate. Then, based on the principle of the lowest resistivity, the optimal Mo carbide film is selected as the Mo-C based interconnect film.

2. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: A clean and dry silicon substrate is obtained through the following method: The silicon wafer is cleaned sequentially with acetone and anhydrous ethanol under ultrasonic conditions, and then etched with a 10-25%, preferably 20%, hydrofluoric acid solution. After etching with hydrofluoric acid solution, it is rinsed with water and dried with protective gas.

3. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: In step one, when preparing Mo thin films by magnetron sputtering, the sputtering power is 15-30 W, the working pressure is 0.5-1.5 Pa, and the deposition time is 5-15 min.

4. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: In step one, the optimal deposition parameters for the Mo thin film are: working pressure 0.7 Pa and sputtering power 20 W.

5. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: In step two, the sputtering power of the metal target is 20 W and the working pressure is 0.7 Pa, while the sputtering power of the carbon target is 50-130 W.

6. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: In step two, the process parameters for obtaining the optimal Mo carbide thin film are: sputtering power of the metal target is 20 W, working pressure is 0.7 Pa, and sputtering power of the carbon target is 120 W.

7. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: In step two, the resistivity ρ of the obtained optimal Mo carbide film is 5.53 μΩ·cm.

8. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: In steps one and two, the magnetron sputtering temperature is room temperature, preferably 25°C.

9. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: To evaluate the thermal stability of the thin film, the electrical properties of the thin film were measured after annealing. The annealing conditions were as follows: gradient annealing was carried out under Ar atmosphere protection, the annealing temperature range was 400-800℃, the heating rate was 5℃ / min, and the holding time was 30 min.

10. The method for rapidly preparing Mo-C-based interconnect thin film materials at room temperature according to claim 1, characterized in that: The Mo-C based interconnect thin film material obtained in step two is used in integrated circuits.

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