Method of manufacturing cubic boron nitride film

Abstract

A method of manufacturing a cubic boron nitride film on a material layer of a device is performed by a plurality of atomic layer deposition cycles. Each of the at least one atomic layer deposition cycle is firstly to introduce at least one pulse of a boron-containing precursor into a reaction where the device is placed. The material layer can be formed of a sapphire, a SiC, a GaN, a AlN, etc. During the step of introducing the at least one pulse of the boron-containing precursor, a non-reactive gas plasma is introduced where the boron-containing precursor is activated by the non-reactive gas plasma. Next, a purge gas is selectively introduced into the reaction chamber. Then, a nitrogen-containing plasma is introduced into the reaction chamber. Finally, the purge gas is introduced into the reaction chamber.

Description

Technical Field

[0001] This invention relates to a method for manufacturing boron nitride thin films, and more particularly, to a method for manufacturing cubic boron nitride thin films with excellent crystallinity using a modified atomic layer deposition (ALD) process. Prior Technology

[0002] Boron nitride (BN) exhibits polymorphism in two main crystalline phases: graphitic hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN). h-BN is the most stable phase of boron nitride, with space group P63 / mmc. c-BN is as stable as diamond at high temperatures and has an F3m zincblende structure. Both phases possess exceptional chemical stability, high thermal conductivity, and wide-bandgap electrical insulating properties. The unique properties of h-BN and c-BN make them suitable for numerous applications, such as high-temperature electronics, buffer or dielectric layers in two-dimensional devices, hard coatings, lubricants, and photodetectors. Traditionally, the synthesis of h-BN and c-BN relies on chemical vapor deposition (CVD) processes at high temperatures ranging from 750 to 1500 °C. These stringent thermal conditions limit certain applications, particularly back-end integration in advanced semiconductor processes. At temperatures below 750°C, boron nitride primarily forms in an amorphous state (a-BN). Recent advances in a-BN have attracted considerable attention. Hong et al. observed an extremely low dielectric constant (k) of 1.78 on an approximately 3 nm thick a-BN film fabricated using CVD. As semiconductor technology nodes approach the angstrom level, the rapidly increasing device density exacerbates the already challenging resistive-capacitive (RC) delay in metal interconnects, leading to a significant degrade in overall wafer performance and a substantial increase in power consumption. To address these challenges, the International Roadmap for Devices and Systems proposes using materials with ultra-low dielectric constants (k²) to minimize parasitic capacitance. a-BN, with its ultra-low dielectric constant, holds promise as an excellent candidate for next-generation semiconductor interconnect dielectric materials. c-BN, on the other hand, possesses a high thermal conductivity.

[0003] With the continuous development of advanced semiconductor manufacturing technology, atomic layer deposition (ALD) technology has significant advantages over traditional CVD technology, especially in terms of large-area uniformity, high conformality, step coverage, and atomic-level control of material composition and film thickness. However, the ALD process for boron nitride encounters several obstacles, including inherently low deposition rates, limited precursor reactivity, and the requirement for high temperatures. Once an inert h-BN surface is formed during film deposition, the lack of surface active sites hinders further growth of the boron nitride film. On the other hand, although various boron precursors are available, only a few are effective for ALD due to their insufficient reactivity at low deposition temperatures, which is crucial for the self-limiting deposition of ALD. For example, triethylborane (TEB) has limited reactivity with NH3 and N2 / H2 plasmas at temperatures below its decomposition point, making it suitable for CVD processes but not for ALD processes. Therefore, alternative precursors with enhanced reactivity at low temperatures are still being investigated to improve the deposition of boron nitride thin films via ALD. Furthermore, the surface migration ability of boron atoms is generally poor, resulting in the need for further improvement in the quality of deposited boron nitride thin films. Consequently, in many studies, higher deposition temperatures are still required to achieve boron nitride thin films with good crystallinity. In particular, the process conditions required for depositing c-BN thin films via ALD are extremely stringent. Therefore, novel techniques such as electron-enhanced ALD have been explored and developed to overcome the limitations of traditional ALD processes. However, there is still significant room for improvement in previous ALD techniques for depositing cubic boron nitride thin films. Summary of the Invention

[0004] Therefore, one of the technical problems that this invention aims to solve is to provide a method for manufacturing cubic boron nitride thin films with excellent crystallinity through an atomic layer deposition process.

[0005] A method for manufacturing a cubic boron nitride thin film on a material layer of a device according to a preferred embodiment of the present invention is performed by a plurality of atomic layer deposition (ALD) cycles. Each ALD cycle includes the following steps: introducing at least one gas pulse containing a boron precursor into a reaction chamber, wherein the device is placed in the reaction chamber; during the step of introducing at least one gas pulse containing the boron precursor, introducing a non-reactive gas plasma, wherein the boron precursor is activated by the non-reactive gas plasma (therefore, this method is called a plasma-activated precursor (PAP)-ALD process); selectively introducing a purge gas into the reaction chamber; introducing a nitrogen-containing plasma into the reaction chamber; and introducing a purge gas into the reaction chamber. The material layer of the device may be formed of sapphire, SiC, GaN, AlN, etc.

[0006] In one specific embodiment, the cubic boron nitride thin film manufactured according to the method of a preferred embodiment of the present invention has a growth rate ranging from 0.02 to 0.12 nm / cycle per ALD cycle.

[0007] In one specific embodiment, the boron-containing precursor may be tris(dimethylamino)borane (TDMAB, B(N(CH3)2)3), boron-nitrogen cycloalkanes (B3H6N3), tetramethylammonium borohydride, boron nitride, ammonia borane (BH6N), or tris(ethylmethylamino)borane (TEMAB), etc.

[0008] In one specific embodiment, the nitrogen-containing plasma can be N2 plasma, NH3 plasma, or N2 / H2 plasma, etc.

[0009] In another specific embodiment, the nitrogen-containing plasma is formed by the excitation of a nitrogen-containing gas by a non-reactive gas plasma. The nitrogen-containing gas can be N2, NH3, or N2 / H2, etc.

[0010] In one specific embodiment, each atomic layer deposition cycle is performed at a process temperature and a vacuum level. The process temperature ranges from 100°C to 500°C, and the vacuum level ranges from 0.1 Pa to 1000 Pa.

[0011] Unlike previous ALD techniques for depositing boron nitride thin films, the cubic boron nitride thin films manufactured according to the method of the present invention have excellent properties such as superior crystal quality, high growth rate per ALD cycle, and high heat dissipation efficiency.

[0012] The advantages and spirit of this invention can be further understood from the following detailed description of the invention and the accompanying drawings. Simple Explanation of the Diagram

[0013] Figure 1 is a flowchart of each of the plurality of ALD cycles used in the method of the preferred embodiment of the present invention. Figure 2 is a schematic diagram of the PAP-ALD process, PEALD process, and ALA process of the first example of the present invention, and the ALD cycle flow diagram. Figure 3 shows the results of measuring the growth rate per cycle (GPC) and boron-nitrogen ratio (B / N ratio) of boron nitride films deposited using the PAP-ALD process, PEALD process, and ALA process in the first example of the present invention. Figure 4 shows the measurement results of the GPC of the boron nitride thin film deposited using the PAP-ALD process in the first example of the present invention, as a function of different N2 plasma exposure times (TN). Figure 5 shows the measurement results of the boron nitride thin film deposited by the PAP-ALD process used in the first example of the present invention, with the B / N ratio and carbon content (at.%) varying with different N2 plasma exposure times (TN). Figure 6 shows the measurement results of the GPC of the boron nitride thin film deposited using the PAP-ALD process in the first example of the present invention, as a function of different precursor pulse durations (TP). Figure 7 shows a high-resolution transmission electron microscopy (HRTEM) cross-sectional image of a boron nitride thin film deposited on a (0001) sapphire substrate and a platinum protective layer plated thereon in the second example of the present invention. Figure 8 shows the pattern of the inverted lattice space obtained by further using fast Fourier transformation (FFT) based on the HRTEM image in Figure 7. Implementation

[0014] The method for manufacturing a cubic boron nitride thin film on a material layer of a device according to a preferred embodiment of the present invention is performed by a plurality of ALD cycles. It should be emphasized that the device used in the method of the preferred embodiment of the present invention can be a finished or semi-finished product of devices in various fields such as semiconductors, optoelectronics, optics, and microelectromechanical systems. The aforementioned material layer of the device can be formed from sapphire, SiC, GaN, AlN, etc.

[0015] It should be noted that each ALD cycle consists of two half cycles. The fabrication of cubic boron nitride thin films using atomic layer deposition (ALD) essentially also consists of two half cycles. The first half cycle supplies boron precursors and purge gas into the reaction chamber, while the second half cycle supplies reactants containing nitrogen plasma and purge gas into the reaction chamber.

[0016] Please refer to Figure 1, which is a flowchart of each of the plurality of ALD cycles 1 used in the method of the preferred embodiment of the present invention.

[0017] As shown in Figure 1, each ALD cycle 1 first executes step S10, in which at least one gas pulse containing a boron precursor is introduced into the reaction chamber. The components are placed inside the reaction chamber.

[0018] In one specific embodiment, the boron-containing precursor may be tris(dimethylamino)borane (TDMAB, C3H12BN), boron-nitrogen cycloalkanes (B(N(CH3)2)3), tetramethylammonium borohydride, boron nitride, ammonia borane (BH6N), or tris(ethylmethylamino)borane (TEMAB), etc.

[0019] Next, each ALD cycle 1 executes step S12, during the step of introducing at least one gas pulse of the boron-containing precursor, a non-reactive gas plasma is introduced, wherein the boron-containing precursor is activated by the non-reactive gas plasma.

[0020] In one specific embodiment, the non-reactive gas plasma can be an inert gas plasma such as Ar plasma, Ne plasma, or He plasma.

[0021] Next, each ALD cycle 1 system executes step S14, selectively introducing a flushing gas into the reaction chamber. In one specific embodiment, the flushing gas can be an inert gas (e.g., argon, helium) or a non-reactive gas (e.g., nitrogen). In practical applications, the flushing gas can also serve as a precursor carrier gas.

[0022] Next, each ALD cycle 1 system performs step S16, introducing nitrogen-containing plasma into the reaction chamber.

[0023] Finally, each ALD cycle 1 system performs step S18, introducing flushing gas into the reaction chamber.

[0024] In one specific embodiment, the nitrogen-containing plasma can be N2 plasma, NH3 plasma, or N2 / H2 plasma, etc.

[0025] In another specific embodiment, the nitrogen-containing plasma is formed by the excitation of a nitrogen-containing gas by a non-reactive gas plasma. The nitrogen-containing gas can be N2, NH3, or N2 / H2, etc.

[0026] In one specific embodiment, each ALD cycle is performed at a process temperature and a vacuum level. The process temperature ranges from 100°C to 500°C, and the vacuum level ranges from 0.1 Pa to 1000 Pa.

[0027] In one specific embodiment, the cubic boron nitride thin film manufactured by the method of a preferred embodiment of the present invention has a growth rate per ALD cycle ranging from 0.02 to 0.12 nm / cycle.

[0028] The first example of this invention involves fabricating a cubic boron nitride thin film on a (0001) sapphire substrate using the method described in this invention. In this first example, TDMAB is used as the boron-containing precursor, N2 is used as the nitrogen supply source, and Ar plasma is used to activate the boron-containing precursor at a process temperature of 300°C. The process used in this first example is also called the plasma-activated precursor ALD (PAP-ALD) process, and is referred to herein as the PAP-ALD process. In contrast, prior art based on ALD, including plasma-enhanced atomic layer deposition (PEALD) and atomic layer annealing (ALA) processes, has also been used to fabricate boron nitride thin films on (0001) sapphire substrates, using TDMAB as the boron-containing precursor, N2 as the nitrogen supply source, and Ar plasma. The PAP-ALD process, PEALD process, and ALD cycle flow of the ALA process of the first example of the present invention are shown in Figure 2.

[0029] As shown in Figure 2, in the PAP-ALD process of the first example of this invention, the introduction of Ar plasma and the introduction of TDMAB gas pulses overlap in time to activate TDMAB; the introduction of Ar plasma also overlaps in time with the introduction of N2 gas to excite N2 to form N2 plasma. In the PEALD process, the introduction of Ar plasma and the introduction of N2 gas overlap in time to excite N2 to form N2 plasma. In the ALA process, the introduction of Ar plasma and the introduction of N2 gas overlap in time to excite N2 to form N2 plasma, and before the start of the next ALD cycle, Ar plasma is introduced to bombard the film surface with non-reactive gas plasma to anneal the formed boron nitride film.

[0030] Please refer to Figure 3. Figure 3 shows the boron nitride films deposited using the PAP-ALD process, PEALD process, and ALA process in the first example of this invention, and the results of measuring the growth rate (GPC) and boron-nitrogen ratio (B / N ratio) per ALD cycle. The results shown in Figure 3 indicate that the GPC of the deposited boron nitride film is very low for the conventional PEALD process, and the B / N ratio deviates significantly from the ideal 1:1. To alleviate these problems, plasma treatment is added before the precursor gas pulse step in the ALD process to achieve the ALA process. By introducing plasma, energy is transferred to the film, which activates the film surface and promotes atomic migration. Although the ALA process produces a slightly higher GPC and a more 1:1 B / N ratio for the boron nitride film compared to the conventional PEALD process, the improvement is still negligible. The low GPC of the boron nitride film observed in the conventional PEALD process and ALA process reveals the inherent defect of the low reactivity of the TDMAB precursor.

[0031] In the PAP-ALD process of the first example of this invention, the plasma treatment induces the dissociation of precursor molecules, thus directly increasing their reactivity by breaking chemical bonds, thereby increasing the GPC of the boron nitride film. Furthermore, the boron nitride film deposited using the PAP-ALD process in the first example of this invention has a B / N ratio close to 1, thanks to enhanced interaction between the surface and the pre-activated precursor. The significant difference between the PAP-ALD process of the first example of this invention and the PEALD and ALA processes demonstrates the crucial role of precursor reactivity in boron nitride film deposition. According to the method of this invention, a novel process for depositing boron nitride films is proposed, introducing a non-reactive gas plasma into the precursor gas pulse step of ALD to increase precursor reactivity, thereby significantly improving the deposition rate of boron nitride films. According to the method of this invention, the process is improved without the need to develop new precursors, thereby reducing the dependence of conventional ALD processes on specific chemicals.

[0032] Please refer to Figures 4, 5, and 6. Figure 4 shows the GPC measurement results of the boron nitride film deposited using the PAP-ALD process in the first example of the present invention, with varying N2 plasma exposure times (TN) (i.e., the duration of N2 plasma introduction). Figure 5 shows the B / N ratio and carbon content (at.%) of the boron nitride film deposited using the PAP-ALD process in the first example of the present invention, with varying N2 plasma exposure times (TN). Figure 6 shows the GPC measurement results of the boron nitride film deposited using the PAP-ALD process in the first example of the present invention, with varying precursor pulse durations (TP). Figure 4 shows that the GPC of the boron nitride film deposited using the PAP-ALD process in the first example of the present invention decreases with increasing TN and reaches saturation when TN ≥ 120 seconds. On the other hand, Figure 5 shows that when TN is less than 120 seconds, the boron nitride film has a higher carbon content, which is attributed to residues generated by TDMAB. As shown in Figures 4 and 5, the observed relationship between GPC, carbon content, and TN shows a positive correlation between GPC and residual carbon content. Figure 5 also shows that as TN increases, carbon content decreases, and the B / N ratio approaches the ideal 1:1 ratio. It is noteworthy that when TN is greater than 120 seconds, the boron nitride film deposited using the PAP-ALD process in the first example of this invention remains in the saturation region in terms of GPC, B / N ratio, and carbon content. Plasma treatment of the precursor may raise concerns about whether the PAP-ALD process in the first example of this invention follows the self-limiting deposition characteristic of the ALD process. To answer this question, please examine the relationship between GPC and TP shown in Figure 6. Once TP exceeds 0.1 seconds, GPC rapidly saturates, indicating that the deposition of the PAP-ALD process in the first example of this invention exhibits self-limiting deposition characteristics. The adsorption of dissociated TDMAB on the surface provides a boron source for thin film deposition. With sufficient exposure to N2 plasma, surface groups form BN bonds, creating a nitrogen-terminated surface. This ensures that the PAP-ALD process of the first example of this invention follows the self-limiting deposition mechanism of the ALD process. Considering the observed behavior of GPC, carbon content, and B / N ratio, TN and TP are set at 240 seconds and 0.1 seconds, respectively, within the saturation region during the subsequent boron nitride thin film deposition process. Thus, the boron nitride thin film manufactured according to the method of the preferred embodiment of this invention exhibits a growth rate ranging from 0.02 to 0.12 nm / cycle per ALD cycle.

[0033] Please refer to Figures 7 and 8. Figure 7 is an HRTEM cross-sectional photograph of a boron nitride thin film deposited on a (0001) sapphire substrate and a platinum (Pt) protective layer plated thereon, according to the second example of the present invention. Figure 8 is a pattern of the inverted lattice space obtained by fast Fourier transformation (FFT) based on the HRTEM cross-sectional photograph of Figure 7. The HRTEM photograph of Figure 7 shows that the boron nitride thin film crystallizes on the (0001) sapphire substrate in a face-centered cubic structure. As shown in Figure 7, the c-BN lattice is formed directly on the lattice of the (0001) sapphire without any amorphous layer intervention. The epitaxial relationship between c-BN and sapphire is

[0111] cBN / /

[0001] sapphire and [11 ]cBN / / [2 0]sapphire, which can be established from the FFT diffraction pattern in Figure 8. Since c-BN has a three-dimensional diamond-like structure with strong sp3 bonds, it can be grown using ALD technology.

[0034] Due to the symmetry of the

[0001] axis of sapphire, c-BN can grow along two orientations, and their epitaxial relationship is as follows:

[0111] cBN / /

[0001] sapphire and [11 ]cBN / / [2 0]sapphire, and the equivalent relation:

[0111] cBN / /

[0001] sapphire and [11 ]cBN / / [11 0]sapphire. During film growth, adjacent crystal domains with these orientations may form twin structures, not due to mechanical deformation, but due to coalescence between crystal nuclei with twinning relationships. c-BN and c-BN' in Figure 7 represent the observed twin structures, and the FFT diffraction pattern in Figure 8 confirms this. The (111) interface between c-BN and c-BN' is a typical Σ3(111) boundary. In Figure 7, the lateral gaps caused by the growth of different c-BN and c-BN' grains are filled by boron nitride (w-BN) crystals with a wurtzite structure. w-BN structures typically appear in c-BN subjected to significant shear stress and act as bicrystalline boundaries between adjacent c-BN and c-BN' grains. Generally, c-BN is usually transformed from h-BN under extreme conditions, requiring high pressure (4~18 GPa) and high temperature (1500~3230℃), similar to the transformation of graphite into diamond. Compared to this traditional synthesis method, the temperature for forming c-BN thin films on (0001) sapphire substrates using the PAP-ALD process according to the present invention is very low, only 300℃, representing a significant advancement in c-BN synthesis technology. In addition to the reactivity of plasma-activated precursors, the energy provided by the plasma to the deposited film can also promote the movement and rearrangement of adsorbed atoms, ultimately promoting the formation of c-BN epitaxial structures. Obviously, unlike previous techniques that required extremely stringent process conditions to deposit c-BN thin films, the method according to the present invention can deposit c-BN thin films under less stringent process conditions.

[0035] Through the detailed description of the preferred embodiments above, it is believed that it can be clearly understood that the cubic boron nitride thin film manufactured by the method of the present invention has excellent crystal quality, high growth rate per ALD cycle, and low process temperature.

[0036] The detailed description of the preferred embodiments above is intended to more clearly illustrate the features and spirit of the present invention, and is not intended to limit the scope of the invention to the preferred embodiments disclosed above. Rather, the aim is to cover various modifications and equivalent arrangements within the scope of the patent claims made by this invention. Therefore, the scope of the patent claims made by this invention should be interpreted in the broadest possible sense based on the foregoing description, so as to cover all possible modifications and equivalent arrangements.

[0037] 1: Atomic layer deposition cycle S10~S18: Process Steps

Claims

1. A method for manufacturing a cubic boron nitride thin film on a material layer of an element, the method being performed by a plurality of atomic layer deposition cycles, each atomic layer deposition cycle comprising the following steps: (a) introducing at least one gas pulse of a boron-containing precursor into a reaction chamber, wherein the element is placed in the reaction chamber, the material layer being formed of one selected from the group consisting of sapphire, silicon carbide, gallium nitride, and aluminum nitride; (b) during step (a), introducing a non-reactive gas plasma, wherein the boron-containing precursor is activated by the non-reactive gas plasma; (c) selectively introducing a flushing gas into the reaction chamber; (d) introducing a nitrogen-containing plasma into the reaction chamber; and (e) introducing the flushing gas into the reaction chamber.

2. The method as described in claim 1, wherein the growth rate of one of the cubic boron nitride thin films per atomic layer deposition cycle ranges from 0.02 to 0.12 nm / cycle.

3. The method as claimed in claim 1, wherein the boron-containing precursor is selected from the group consisting of tris(dimethylamino)borane (TDMAB, B(N(CH3)2)3), boron-nitrogen cycloalkanes (B3H6N3), tetramethylammonium borohydride, boron nitride, ammonia borane (BH6N), and tris(ethylmethylamino)borane (TEMAB).

4. The method as described in claim 1, wherein the nitrogen-containing plasma is selected from the group consisting of N2 plasma, NH3 plasma and N2 / H2 plasma.

5. The method as claimed in claim 1, wherein the nitrogen-containing plasma is formed by the excitation of a nitrogen-containing gas by the non-reactive gas plasma, and the nitrogen-containing gas system is selected from the group consisting of N2, NH3, and N2 / H2.

6. The method as described in claim 1, wherein each atomic layer deposition cycle is performed at a process temperature and a vacuum level, the process temperature ranging from 100°C to 500°C and the vacuum level ranging from 0.1 Pa to 1000 Pa.

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