A method of reducing damage to a substrate when growing a thin film using PEALD

Abstract

The application discloses a method for reducing damage to a substrate when growing a film using PEALD, and belongs to the field of inorganic materials. First, the selected substrate is cleaned to remove surface contamination and oxides; then the cleaned substrate is immediately placed into a PEALD reaction chamber, and after the temperature reaches a deposition temperature, the temperature is kept stable for at least 20 minutes; finally, before epitaxial nitride film needs plasma, an oxide film without plasma source is first epitaxially formed to form a protective layer, which can effectively avoid damage to the substrate by plasma, maintain stable chamber pressure, and improve the interface quality between the epitaxial film and the substrate; on the other hand, for a device, the oxide is usually used as a High k material for a gate medium layer, can effectively reduce the leakage current, and further improves the performance of the device.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials and relates to a plasma-enhanced atomic layer deposition (PEALD) technique, specifically a method for reducing damage to the substrate when growing thin films using PEALD. Background Technology

[0002] With the rapid development of the microelectronics field, the performance and size of traditional Si power devices have approached their theoretical limits, making it difficult to continue developing towards high-speed applications. III-V compound semiconductors, mainly represented by GaAs, GaN, and SiC, are gradually replacing silicon-based materials and are widely used in communication, high-frequency, and high-power microwave devices due to their high electron mobility, large band gap, high breakdown field strength, and high temperature resistance.

[0003] Common methods for epitaxial III-V compound semiconductors include MOCVD and MBE. However, these methods typically require high temperatures (above 800°C) to deposit thin films. High-temperature deposition has the following main disadvantages: 1. Excessively high deposition temperatures make it difficult to precisely control film thickness, which is crucial for microelectronic devices; 2. When cooling at high deposition temperatures, if the thermal expansion coefficients of the substrate and the epitaxial film are different, it will cause large biaxial stress and cracking inside the film, affecting device performance; 3. High-temperature deposition can cause the decomposition of substrates such as GaAs; 4. Flexible substrate materials such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), Kapton, and graphene can all be used to fabricate optoelectronic devices, but high-temperature deposition is incompatible with temperature-sensitive device layers and flexible substrates, limiting further applications.

[0004] Atomic layer deposition (ALD) is a low-temperature epitaxial thin film technology that has attracted widespread attention. ALD is a method of forming thin films layer by layer by alternately introducing gaseous precursors into a reaction chamber and causing gas-solidification reactions on the substrate surface. ALD typically consists of two half-reaction sequences, A and B, and features surface self-limitation. Thin films deposited using ALD offer advantages such as precise thickness control, excellent three-dimensional conformality, large-area uniformity, and low growth temperature. With the continuous reduction in the size of microelectronic and deep submicron chip devices and the continuous increase in device aspect ratio, the thickness of materials used has decreased to a few nanometers, allowing the advantages of ALD to be fully demonstrated. In 2007, Intel launched the first high-frequency microprocessor with a 45nm gate dielectric layer fabricated using ALD. To date, technologies such as TaSiO2 have been widely adopted in this field. x Materials such as HfO2 and Al2O3 have been successfully used by ALD as high-k dielectrics for III-V compounds.

[0005] According to the reaction type, ALD can be divided into two types: thermal ALD and PEALD. Unlike traditional thermal ALD, PEALD uses high-energy, highly active plasma as a precursor. Commonly used plasma gases include O2, N2, NH3, H2, Ar, etc., to grow oxides, nitrides, compound semiconductors, etc.

[0006] In semiconductor manufacturing, plasma is widely used in processes such as thin film deposition, etching, ion implantation, and photoresist removal. Gases are dissociated by a radio frequency source to form plasma, which then physically bombards and chemically etches the material under the influence of an accelerating electric field. Plasma is primarily composed of high-energy electrons and atomic nuclei, forming an ion paste. When plasma is used to treat a material, plasma-active particles adsorb onto the material. As the accumulated plasma charge increases, a plasma current is formed, which can easily lead to plasma-induced damage (PID).

[0007] Therefore, when plasma directly acts on a substrate, the following disadvantages arise: 1. Undesirable side reactions: When the substrate comes into contact with highly reactive plasma, surface oxidation and nitriding may occur. 2. Impact damage to the substrate: When high-energy particles collide with the substrate surface, it leads to the breaking of chemical bonds, atomic substitution, and surface charge accumulation, causing degradation of the electrical performance of semiconductor devices. 3. Radiation damage: When a large number of electrons in the plasma collide with the surface, they activate atoms or molecules in the reaction process, causing particles to become excited. When unstable excited particles return to the ground state, they release energy through electromagnetic radiation, with energies as high as 10 eV. Such high energy can excite electronic transitions in materials such as nitrides and oxides, leading to the formation of more defects in the thin film.

[0008] For substrates, charge accumulation on the substrate surface is easy to occur, leading to degradation of the electrical performance of semiconductor devices. For devices, when plasma is used to etch the gate dielectric layer, the plasma charge can be unevenly distributed across the thin gate dielectric or metal layer. When enough charge accumulates, a potential difference will appear between the gate dielectric layer and the substrate, resulting in leakage current. As the size of MOS transistors decreases, these charges will further increase, severely affecting the performance of MOS transistors and significantly reducing the reliability and lifespan of the device and even the entire chip.

[0009] To address the aforementioned problems, this invention provides a method for reducing substrate damage during PEALD thin film growth. This method involves epitaxially growing an oxide film without a plasma source before using a plasma-source epitaxial layer to form a protective layer. This protective layer effectively prevents plasma damage to the substrate, maintains stable chamber pressure, and improves the interface quality between the epitaxial film and the substrate. Furthermore, for devices, oxides are typically used as High-k materials in the gate dielectric layer, effectively reducing leakage current and further enhancing device performance. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for reducing damage to the substrate when growing thin films using PEALD, so as to solve the problems of plasma damage to the substrate, poor interface quality between the substrate and the epitaxial film, and poor electrical properties during PEALD thin film deposition.

[0011] To achieve the above and other related objectives, the present invention provides a method for reducing damage to the substrate when growing thin films using PEALD, comprising the following steps:

[0012] 1) Place the substrate on a polytetrafluoroethylene support and perform a standardized cleaning process;

[0013] 2) Quickly place the cleaned substrate into the plasma-enhanced atomic layer deposition reaction chamber, and after the temperature reaches the deposition temperature, keep it for at least 20 minutes to allow the temperature to stabilize.

[0014] 3) Select H2O / O3 source and metal source without plasma to deposit oxide thin films at 200-300℃;

[0015] 4) Select plasma source and metal source to deposit nitride thin film at 200-350℃.

[0016] Optionally, the substrate in step 1) includes, but is not limited to, GaAs substrates and flexible substrates. Flexible substrates include polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), Kapton, graphene, two-dimensional templates, etc.

[0017] Among commonly used substrates for epitaxial semiconductor thin films, GaAs substrates are easily dissociated, easily etched, and have high electron mobility; flexible substrates such as Kapton possess excellent mechanical, dielectric, radiation resistance, and solvent resistance properties; graphene has advantages such as ultrathinness, transparency, flexibility, and high mobility, which are very much in line with the development trend of microelectronics. However, these types of substrates are susceptible to damage from plasma bombardment. In 2013, Harish C. Barshilia et al. reported that Ar+O2 plasma treatment could cause chemical bond breakage in Kapton substrates; in 2018, Petro Deminskyi et al. reported that N2 plasma or N2 / H2 plasma could damage graphene substrates. In 2021, Dan Fang et al. found that the surface roughness of GaAs substrates treated with NH3 plasma increased with increasing plasma power.

[0018] With the rapid development of the microelectronics field, the size of CMOS devices needs to be continuously reduced to meet large-scale integration requirements. GaAs substrates, with their large bandgap, high breakdown electric field, and high electron mobility, have become the ideal choice for fabricating high-frequency and high-speed devices. However, the surface of GaAs substrates contains natural oxide layers such as Ga2O3 and As2O5. These oxide layers have a loose structure and poor stability, resulting in a high interface state density at the GaAs-oxide interface, leading to a severe Fermi level pinning effect. When GaAs is used as the substrate for epitaxial High k gate dielectric layer or other thin films, high-energy plasma bombardment of the GaAs substrate can easily break the Ga-As bonds, causing substrate damage and increasing the chamber pressure, which is detrimental to the fabrication of high-quality epitaxial thin films and MOS devices.

[0019] Optionally, the cleaning step of GaAs substrate in step 1) is as follows: The GaAs substrate is sequentially immersed in acetone, alcohol, and deionized water, and sonicated for 3-10 minutes to remove surface oil and organic matter; then, the GaAs substrate is immersed in an HF aqueous solution (HF:deionized water = 1:10) for 2-5 minutes to remove surface oxides. The cleaned substrate is then immersed in a 20-26% (NH4)2S aqueous solution by weight for 10-40 minutes to remove oxides from the GaAs surface. Finally, the sample is rinsed with plenty of deionized water and dried with N2.

[0020] Optionally, the deposition temperature in step 2) is 200-350℃.

[0021] Optionally, the metal source in step 3) includes one of TMG, TEG, TMA, TDMAH, and BDEAS; the deposited oxide film includes, but is not limited to, Ga2O3, Al2O3, HfO2, SiO2, etc.

[0022] Optionally, the plasma source in step 4) includes one of N2 plasma, NH3 plasma source, and N2 / H2 / Ar plasma, and the deposited nitride film includes, but is not limited to, GaN, AlN, InN, Si3N4, etc.

[0023] Optionally, in step 3), the pulse time of the H2O source is 0.1-0.3s, the pulse time of the metal source is 0.1-0.5s, and an inert gas such as argon (Ar), helium (He), or nitrogen (N2) is selected as the carrier gas to flush away the byproducts generated by the reaction and excess reaction source after each pulse.

[0024] Optionally, in step 4), the plasma power is 60-200W, the metal source pulse time is 0.1-0.5s, the plasma source pulse time is 25-40s, and an inert gas such as argon (Ar), helium (He), or nitrogen (N2) is selected as the carrier gas to flush away the byproducts generated by the reaction and excess reaction source after each pulse.

[0025] Optionally, the oxide film deposited in step 3) undergoes 10-50 ALD cycles.

[0026] Optionally, the nitride film deposited in step 4) has a PEALD cycle count of 100-300 cycles.

[0027] As described above, the present invention has the following beneficial effects:

[0028] (1) The present invention uses ALD technology to epitaxial thin films, which can obtain thin films with good density and uniformity and precise controllable thickness at the angstrom level at a lower temperature. It can be widely used in processes such as depositing metal gates, gate dielectric layers and interconnect diffusion barrier layers.

[0029] (2) In this invention, an oxide layer without a plasma source is deposited as a protective layer before the thin film required for epitaxy. This avoids direct contact between the plasma and the GaAs substrate, preventing Ga-As bond breakage and providing a stable surface. For GaAs-based devices, the epitaxial protective layer can reduce the interface state density between the gate dielectric material and the GaAs substrate, reduce the Fermi level pinning effect, and further improve the electrical performance of the device.

[0030] (3) When using MOCVD, MBE and other technologies to epitaxially grow thin films on flexible substrates, the flexible substrates are difficult to withstand high temperatures. Usually, the method is to epitaxially grow thin films on sapphire or Si substrates and then transfer them to flexible substrates. However, using ALD technology can avoid damage to the flexible substrates caused by high temperatures and can also greatly avoid the decrease in yield caused by film transfer, thus reducing production costs. Attached Figure Description

[0031] Figure 1 The diagram shown is a process flow diagram of an embodiment of the present invention.

[0032] Figure 2 The diagram shows a pulse diagram and a structural diagram of the deposition of an Al2O3 thin film on a GaAs substrate in this invention.

[0033] Figure 3 The diagram shows a pulse diagram and a structural diagram of the deposition of an AlN thin film on a GaAs substrate in this invention.

[0034] Among them, there is a 10-GaAs substrate; a 20-Al2O3 thin film; and a 30-AlN thin film. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0036] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0037] Example 1

[0038] Figure 1 This is a process flow diagram of the method for reducing substrate damage when growing thin films using PEALD according to the present invention. In this embodiment, GaAs substrate 10 is preferred, and the process method includes at least the following steps:

[0039] Substrate cleaning: GaAs substrate 10 is sequentially immersed in acetone, alcohol, and deionized water, and sonicated for 3-10 minutes to remove surface oil and organic matter; in this embodiment, 5 minutes is preferred. Then, GaAs substrate 10 is immersed in an HF aqueous solution (HF:deionized water = 1:10) for 2-5 minutes to remove surface oxides; in this embodiment, 2 minutes is preferred. The cleaned substrate is then immersed in a 20-26% (NH4)2S aqueous solution by weight for 10-40 minutes to remove oxides from the GaAs surface; in this embodiment, 20 minutes is preferred. Finally, the sample is rinsed with plenty of deionized water and dried with N2.

[0040] Protective layer film growth: The passivated GaAs substrate 10 is rapidly placed into the plasma-enhanced atomic layer deposition (PEALD) reaction chamber. In this embodiment, H2O and TMA are preferably used as the O source and Al source, respectively, to deposit an Al2O3 film 20. Figure 2 As shown. Specific growth parameters are as follows:

[0041] Deposition temperature in the reaction chamber: 250℃;

[0042] TMA pulse duration: 0.1s;

[0043] H2O source time: 0.1s;

[0044] Purging time: 30s;

[0045] Deposition cycle: 50 cycles.

[0046] The carrier gas can be selected from inert gases such as argon (Ar), helium (He), and nitrogen (N2). In this embodiment, Ar is preferred as the carrier gas. On the one hand, it is used to carry the source into the reaction chamber; on the other hand, it carries the unreacted source and the by-products generated by the reaction out of the reaction chamber.

[0047] Plasma thin film growth: In this embodiment, TMA and Ar / N2 / H2 mixed gas are preferably used as the Al source and plasma N source, respectively, to deposit an AlN thin film 30, as shown below. Figure 3 As shown, the specific growth parameters are as follows:

[0048] Deposition temperature in the reaction chamber: 250℃;

[0049] TMA pulse duration: 0.1s;

[0050] Plasma N-source time: 30s;

[0051] Purging time: 30s;

[0052] Plasma power: 70W;

[0053] Deposition cycle: 100 cycles.

[0054] Epitaxial Al2O3 film before epitaxial AlN film reduces plasma damage to GaAs substrate, maintains stable chamber pressure, improves interface quality between gate dielectric and GaAs substrate, effectively reduces Fermi level pinning effect, and further enhances electrical performance of GaAs-based devices.

[0055] Example 2

[0056] Since the process flow in this embodiment is the same as that in Embodiment 1, except for the material being deposited, the process flow diagram is still as shown for the sake of simplicity. Figure 1 As shown, the process method includes at least the following steps:

[0057] Substrate cleaning: The GaAs substrate is sequentially immersed in acetone, alcohol, and deionized water, and sonicated for 3-10 minutes to remove surface oil and organic matter; in this embodiment, 5 minutes is preferred. Then, the GaAs substrate is immersed in an HF aqueous solution (HF:deionized water = 1:10) for 2-5 minutes to remove surface oxides; in this embodiment, 5 minutes is preferred. The cleaned substrate is then immersed in a 20-26% (NH4)2S aqueous solution by weight for 10-40 minutes to remove oxides from the GaAs surface; in this embodiment, 30 minutes is preferred. Finally, the sample is rinsed with plenty of deionized water and dried with N2.

[0058] Protective layer film growth: The passivated GaAs substrate is rapidly placed into the plasma-enhanced atomic layer deposition (PEALD) chamber. In this embodiment, H2O and TMG are preferably used as the O source and Ga source, respectively, to deposit a Ga2O3 film. The specific growth parameters are as follows:

[0059] Deposition temperature in the reaction chamber: 300℃;

[0060] TMG pulse duration: 0.1s;

[0061] H2O source time: 0.1s;

[0062] Purging time: 30s;

[0063] Deposition cycle: 50 cycles.

[0064] Plasma growth of thin films: In this embodiment, TMG and Ar / N2 / H2 mixed gas are preferably used as Ga source and plasma N source, respectively, to deposit GaN thin films. The specific growth parameters are as follows:

[0065] Deposition temperature in the reaction chamber: 300℃;

[0066] TMG pulse duration: 0.1s;

[0067] Plasma N-source time: 30s;

[0068] Purging time: 30s;

[0069] Plasma power: 100W;

[0070] Deposition cycle: 200 cycles.

[0071] This embodiment has the same effect as Embodiment 1.

[0072] In summary, this invention provides a method for reducing substrate damage during PEALD thin film growth. This method first cleans and passivates the substrate with sulfur, effectively removing contaminants and oxides from the GaAs substrate surface and forming a stable interface. Before depositing the epitaxial III-nitride thin film, an Al₂O₃ layer that does not require a plasma source is deposited, effectively reducing plasma damage to the substrate and maintaining stable deposition pressure. This improves the interface quality between the gate dielectric and the GaAs substrate, effectively reducing the Fermi level pinning effect and further enhancing the electrical performance of GaAs-based devices. This method has the same effect on flexible substrates. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial applicability.

[0073] The above two embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Those skilled in the art can also achieve the purpose of the present invention by selecting other preferred parameters based on the content of the present invention.

[0074] The embodiments described above are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. It should be noted that any simple modifications, equivalent changes, or alterations made to the above embodiments by those skilled in the art without departing from the technical solution and essence of the present invention are within the scope of the present invention.

Claims

1. A method for reducing damage to the substrate when growing thin films using PEALD, characterized in that, Includes the following steps: 1) Place the substrate on a polytetrafluoroethylene support and perform a standardized cleaning process; 2) Quickly place the cleaned substrate into the plasma-enhanced atomic layer deposition reaction chamber, and after the temperature reaches the deposition temperature, keep it for at least 20 minutes to allow the temperature to stabilize. 3) Select an H2O source or O3 source and a metal source that do not use plasma to deposit oxide thin films at 200-300℃; 4) Select plasma and metal sources to deposit nitride films at 200-350℃; The substrate mentioned in step 1) includes a GaAs substrate and a flexible substrate. The flexible substrate includes polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polycarbonate (PC), Kapton, graphene, and a two-dimensional template. The cleaning steps for the GaAs substrate in step 1) are as follows: the GaAs substrate is sequentially immersed in acetone, alcohol, and deionized water and sonicated for 3-10 minutes to remove surface oil and organic matter; then the GaAs substrate is immersed in an HF aqueous solution for 2-5 minutes to remove surface oxides; the HF:deionized water ratio in the HF aqueous solution is 1:10; the cleaned substrate is immersed in a 20-26% (NH4)2S aqueous solution by weight for 10-40 minutes to remove oxides on the GaAs surface; finally, the sample is rinsed with a large amount of deionized water and dried with N2.

2. The method for reducing damage to the substrate when growing thin films using PEALD according to claim 1, characterized in that, The deposition temperature in step 2) is 200-350℃.

3. The method for reducing damage to the substrate when growing thin films using PEALD according to claim 1, characterized in that, The metal source in step 3) includes one of TMG, TEG, TMA, TDMAH, and BDEAS; the deposited thin film includes Ga2O3, Al2O3, HfO2, and SiO2.

4. The method for reducing damage to the substrate when growing thin films using PEALD according to claim 1, characterized in that, The plasma source in step 4) includes one of N2 plasma, NH3 plasma source, and N2 / H2 / Ar plasma, and the deposited thin film includes GaN, AlN, InN, and Si3N4.

5. The method for reducing damage to the substrate when growing thin films using PEALD according to claim 1, characterized in that, In step 3), the pulse time of the H2O source is 0.1-0.3s, and the pulse time of the metal source is 0.1-0.5s. Argon (Ar), helium (He), and nitrogen (N2) are selected as carrier gases to flush away the byproducts and excess reaction sources generated in the reaction after each pulse.

6. The method for reducing damage to the substrate when growing thin films using PEALD according to claim 1, characterized in that, In step 4), the plasma power is 60-200W, the metal source pulse time is 0.1-0.5s, the plasma source pulse time is 25-40s, and argon (Ar), helium (He), and nitrogen (N2) are selected as carrier gases to flush away the byproducts and excess reaction source generated by the reaction after each pulse.

7. The method for reducing damage to the substrate when growing thin films using PEALD according to claim 1, characterized in that, The oxide film deposited in step 3) has an ALD cycle count of 10-50 cycles.

8. The method for reducing damage to the substrate when growing thin films using PEALD according to claim 1, characterized in that, The nitride film deposited in step 4) has a PEALD cycle count of 100-300 cycles.

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