Optical film stress control method and vacuum coating system

Abstract

This invention discloses a method for controlling stress in optical thin films and a vacuum deposition system. The method includes: firstly, forming a viscoelastic buffer layer on the substrate surface using a precursor containing organic components in a PECVD chamber; then, transferring the substrate to a PVD chamber in a vacuum-connected environment to deposit a metal layer, and applying a pulsed bias voltage to introduce intrinsic compressive stress to pre-compensate for the thermal tensile stress generated during the subsequent cooling process; next, depositing a dielectric layer; finally, using the intrinsic compressive stress to offset the thermal tensile stress, and utilizing the viscoelasticity of the buffer layer to release the lattice mismatch shear stress between interfaces, thereby achieving mutual cancellation of the overall residual internal stress of the multilayer thin film structure. This invention effectively solves the problem of cracking or delamination caused by stress accumulation in multilayer optical thin films through a synergistic mechanism of "active pre-compensation + passive elastic absorption," significantly improving the adhesion and structural stability of the thin film on complex curved substrates.

Description

Technical Field

[0001] This invention relates to the field of optical thin film deposition technology, and more specifically to an optical thin film stress control method and a vacuum coating system. Background Technology

[0002] As precision optical devices such as automotive head-up displays (HUDs) evolve towards higher integration and wider field of view, depositing metal-dielectric composite multilayer thin films on aspherical substrates has become a mainstream industry requirement. These thin film structures typically include a metal layer for high reflectivity and a dielectric layer for phase matching or protection. However, due to the significant differences in physical properties among the metal, dielectric, and glass substrates, extremely high residual internal stresses accumulate in the thin films during fabrication and subsequent environmental changes.

[0003] These residual internal stresses mainly consist of two parts: first, the mismatch in thermal expansion coefficients of the different layers leads to enormous thermal tensile stress during the cooling stage after deposition due to shrinkage imbalance; second, the difference in lattice constants between the metal and dielectric layers results in shear stress at the heterogeneous interface. In existing single deposition processes, due to the lack of active stress regulation methods and effective physical buffering mechanisms, these accumulated stresses easily cause film cracking, warping, and even peeling from the substrate surface. This localized stress concentration is particularly pronounced when applied to aspherical substrates with complex surface curvature, severely restricting the mechanical reliability and lifespan of optical thin films. Summary of the Invention

[0004] This invention provides a method for controlling stress in optical thin films and a vacuum coating system, which aims to solve the technical problem of the difficulty in releasing the tensile stress generated by thermal shrinkage in multilayer optical thin films and the shear force of lattice mismatch between heterogeneous interfaces.

[0005] To achieve the above objectives, the present invention provides an optical thin film stress control method applied to a vacuum coating system, the vacuum coating system comprising a PECVD chamber and a PVD chamber connected to each other, the method comprising the following steps:

[0006] S1. The substrate is sent into the PECVD chamber, and a viscoelastic buffer layer is formed on the substrate surface by plasma-enhanced chemical vapor deposition using a precursor containing organic components.

[0007] S2. Under a vacuum and without exposure to the atmospheric environment, the substrate is transferred to the metal deposition station within the PVD chamber. Process gas is introduced into the PVD chamber to generate plasma. A metal layer is deposited on the surface of the buffer layer by magnetron sputtering of a metal target. Simultaneously, a pulsed bias is applied to the substrate. By controlling the electrical parameters of the pulsed bias, ions in the plasma are used to transfer momentum to the growth surface of the metal layer under the drive of the pulsed bias, thereby increasing the lattice density of the metal layer and introducing intrinsic compressive stress inside the metal layer. This intrinsic compressive stress is used to pre-compensate for the thermal tensile stress generated in the metal layer during subsequent cooling. Furthermore, the amplitude of the pulsed bias is dynamically adjusted based on the real-time temperature change of the substrate during the deposition process to maintain a real-time balance between the intrinsic compressive stress and dynamic thermal stress inside the metal layer.

[0008] S3. The substrate is transferred from the metal deposition station to the dielectric deposition station in the PVD chamber, and a dielectric layer is deposited on the surface of the metal layer by magnetron sputtering.

[0009] S4. The intrinsic compressive stress introduced in step S2 is used to offset the tensile stress of the metal layer caused by thermal shrinkage, and the viscoelasticity of the buffer layer is used to release the lattice mismatch shear stress between the metal layer and the dielectric layer interface, thereby achieving mutual cancellation of the overall residual internal stress of the multilayer thin film structure composed of the buffer layer, the metal layer, and the dielectric layer; wherein, the substrate is aspherical glass in the vehicle head-up display system, in steps S2 and S3, the passing speed of the substrate when passing through the metal deposition station and the dielectric deposition station is adjusted to compensate for the difference in deposition thickness caused by the surface curvature change of the aspherical glass, so that the thickness deviation of the formed metal layer and the dielectric layer on the surface of the aspherical glass is less than a preset threshold.

[0010] Preferably, the PECVD chamber is equipped with a radio frequency power supply. In step S1, the radio frequency power supply is used to excite the precursor to generate plasma, so that the precursor undergoes a polymerization reaction. By adjusting the radio frequency excitation power of the radio frequency power supply, the ratio of organic components to inorganic components in the buffer layer is controlled so that the Young's modulus of the buffer layer is less than that of the substrate.

[0011] Preferably, in step S1, the ambient pressure inside the PECVD chamber is controlled at... to Between these elements, the mean free path of the precursor molecules is made greater than their path of motion when they reach the substrate surface, thereby forming a buffer layer with a loose organic nanoporous structure on the substrate surface, and utilizing the high damping characteristics of the organic nanoporous structure to absorb the corresponding force.

[0012] Preferably, in step S2, the energy distribution of ions reaching the growth surface of the metal layer is controlled by adjusting the frequency and duty cycle of the pulse bias voltage, so as to adjust the intrinsic compressive stress of the metal layer to a predetermined threshold.

[0013] Preferably, in step S3, by alternately switching the polarity of at least two dielectric targets and making at least two dielectric targets alternately ignite, the polarity reversal guides electrons to neutralize the positive charge accumulated on the target surface, thereby improving the consistency of stress within the dielectric layer.

[0014] Preferably, the ratio of the thickness of the buffer layer to the total thickness of the multilayer thin film structure is 1:5 to 1:10, so that the optical transmittance of the multilayer thin film structure is not less than 90%, while the mechanical elastic space provided by the buffer layer releases the lattice mismatch energy generated at the interface between adjacent film layers in the multilayer thin film structure.

[0015] The present invention also provides a vacuum coating system for performing the above-described optical thin film stress control method, the vacuum coating system comprising:

[0016] PECVD chamber;

[0017] The PVD chamber is connected to the PECVD chamber, and the PVD chamber is equipped with a metal deposition station and a dielectric deposition station.

[0018] A transport mechanism is used to carry the substrate and drive the substrate sequentially through the PECVD chamber, the metal deposition station, and the dielectric deposition station;

[0019] A bias power supply, electrically connected to the substrate or the transmission mechanism, is used to apply a pulse bias voltage to the substrate at the metal deposition station.

[0020] An infrared temperature measuring device is installed in the PVD chamber to detect the temperature change of the substrate in real time during the deposition process;

[0021] The control unit is used to execute the optical thin film stress control method to coordinate and control the operating parameters of the vacuum coating system.

[0022] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0023] This invention utilizes pulsed bias voltage during PVD deposition to generate ion momentum transfer, increasing the lattice density of the metal layer while actively introducing intrinsic compressive stress onto its growth surface. This design effectively pre-compensates for the thermal tensile stress generated during subsequent cooling of the metal layer, achieving self-counterbalancing of internal stresses in the multilayer thin film structure at the microscopic physical level, thereby significantly enhancing the overall crack resistance and structural stability of the multilayer thin film system. Simultaneously, the viscoelastic buffer layer formed in situ through the PECVD process not only provides the necessary mechanical elastic space for the film system to release the lattice mismatch shear stress at the interface between the metal and dielectric layers, but also achieves an optimal balance between film toughness and strength by precisely controlling the ratio of organic to inorganic components in the buffer layer, ensuring high transparency with an optical transmittance of no less than 90% for the multilayer thin film structure.

[0024] Furthermore, this invention demonstrates significant advantages in process control precision. Through dynamic closed-loop adjustment of pulse bias frequency, duty cycle, and real-time temperature feedback, it achieves digital quantitative control of stress compensation, ensuring the quality stability of the thin film under different thermal load conditions and complex production environments. For special applications such as automotive head-up display systems using aspherical substrates, this invention effectively compensates for differences in deposition thickness caused by variations in substrate surface curvature by adjusting the substrate's passage speed through the deposition station, fundamentally eliminating the potential for failure due to localized stress concentration. Combined with an integrated design that connects the PECVD and PVD chambers without disrupting the vacuum, and a polarity reversal technology for the dielectric target, this invention completely avoids interface contamination while further ensuring high consistency of internal stress in the film layer during large-scale continuous production, providing comprehensive technical support for the reliable fabrication of high-precision optical devices. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the vacuum coating system according to an embodiment of the present invention;

[0026] Figure 2 This is a cross-sectional view of the substrate and multilayer thin film structure in an embodiment of the present invention;

[0027] Figure 3 This is a circuit control block diagram of the vacuum coating system in an embodiment of the present invention.

[0028] Explanation of reference numerals in the attached figures: 10, Vacuum coating system; 11, PECVD chamber; 111, Radio frequency power supply; 12, PVD chamber; 121, Metal deposition station; 122, Dielectric deposition station; 13, Vacuum isolation channel; 131, Isolation valve actuator; 14, Transmission mechanism; 15, Bias power supply; 16, Control unit; 17, Infrared temperature measurement device; 1, Substrate; 2, Buffer layer; 3, Metal layer; 4, Dielectric layer. Detailed Implementation

[0029] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0030] This embodiment provides a vacuum coating system 10. For example... Figure 1 As shown, the vacuum coating system 10 mainly includes a PECVD chamber 11 and a PVD chamber 12 that are interconnected, and a vacuum isolation channel 13 located between the PECVD chamber 11 and the PVD chamber 12, which serves as a physical isolation and vacuum transition. The vacuum isolation channel 13 is equipped with a highly airtight vacuum gate valve, which is driven to open and close by an isolation valve driver 131. This maintains independent pressure environments for the PECVD chamber 11 and the PVD chamber 12 during the process and ensures that the high concentration of organic precursor gas in the PECVD chamber 11 does not diffuse into the PVD chamber 12 and contaminate the target material.

[0031] The vacuum coating system 10 has a transmission mechanism 14 running through it. In this embodiment, the transmission mechanism 14 is a linear guide bracket driven by a servo motor or a magnetic levitation transmission plate, used to carry the substrate 1 (such as aspherical glass in an automotive HUD system) and drive it sequentially through each process station. In addition, the vacuum coating system 10 is equipped with an RF power supply 111, a bias power supply 15, and an infrared temperature measurement device 17. Figure 1 and Figure 3 As can be seen, the bias power supply 15 is electrically connected to the transmission mechanism 14 located at the metal deposition station 121 inside the PVD chamber 12 via a conductive slip ring. The infrared temperature measuring device 17 is installed on the top of the PVD chamber 12 and points towards the metal deposition station 121, and is used to detect the real-time temperature during the deposition process.

[0032] like Figure 3 As shown, the operation of the vacuum coating system 10 is uniformly scheduled by the control unit 16. The control unit 16 is electrically connected to the radio frequency power supply 111, the bias power supply 15, the transmission mechanism 14, the infrared temperature measuring device 17, and the isolation valve driver 131. By receiving feedback signals from the infrared temperature measuring device 17, the control unit 16 adjusts the output parameters of the bias power supply 15 in real time and coordinates the movement of the isolation valve driver 131 and the transmission mechanism 14 to achieve automated closed-loop control of the entire process.

[0033] In the specific process flow, the first step S1 is to construct a viscoelastic buffer layer 2 on the surface of the substrate 1. The substrate 1 is first fed into the PECVD chamber 11 by the transmission mechanism 14. A precursor containing organic components (such as hexamethyldisiloxane) is introduced into the PECVD chamber 11, and plasma is generated under the excitation of the radio frequency power supply 111. The control unit 16 adjusts the excitation power of the radio frequency power supply 111 to a predetermined value between 200W and 800W (for example, set to 500W) to precisely control the degree of polymerization of the precursor molecules, so that the Young's modulus of the buffer layer 2 is significantly lower than that of the substrate 1.

[0034] Meanwhile, the control unit 16 controls the ambient pressure inside the PECVD chamber 11 to be within a certain range. to Between (e.g., set to) Utilizing the longer mean free path of particles under low pressure, a buffer layer 2 with a loose organic nanoporous structure is deposited on the surface of substrate 1. This microporous structure possesses high damping characteristics, effectively releasing energy at the interfaces of various film layers during subsequent processes. In this embodiment, the thickness of buffer layer 2 is 20 nm, and the total thickness of the multilayer thin film structure is 160 nm, with a thickness ratio of 1:8. This ratio ensures that the optical transmittance of the entire multilayer thin film structure is not less than 90% while providing sufficient mechanical elastic space for the entire multilayer thin film structure.

[0035] Subsequently, the vacuum isolation channel 13 is opened, and the transmission mechanism 14 drives the substrate 1 into the metal deposition station 121 of the PVD chamber 12 to perform step S2. While the magnetron sputtering metal target deposits the metal layer 3, the bias power supply 15 applies a pulsed bias to the substrate 1 through the transmission mechanism 14. The control unit 16 adjusts the frequency of the bias power supply 15 between 50 kHz and 250 kHz (e.g., 100 kHz) and the duty cycle between 10% and 50% (e.g., 30%) to increase the lattice density of the metal layer 3 using ion momentum transfer and actively introduces intrinsic compressive stress to pre-compensate for subsequent thermal tensile stress. During this process, the control unit 16 dynamically adjusts the amplitude of the bias power supply 15 (e.g., fine-tuning between 100V and 400V) based on the real-time temperature rise data monitored by the infrared thermometer 17 to maintain the real-time stress balance within the metal layer 3.

[0036] Then, in step S3, the transport mechanism 14 transports the substrate 1 to the dielectric deposition station 122 to deposit the dielectric layer 4. To improve the consistency of internal stress, the system eliminates charge accumulation by alternately switching the polarities of the two dielectric targets. For aspherical substrates, the control unit 16 adjusts the moving speed of the transport mechanism 14 in real time according to the surface curvature change (e.g., reducing the speed from 50 mm / s to 30 mm / s in edge areas with small curvature radii) to compensate for the deposition thickness difference caused by curvature changes, so that the thickness deviation between the formed metal layer 3 and dielectric layer 4 is less than a preset threshold.

[0037] Finally, in step S4, the system utilizes the intrinsic compressive stress pre-stored within the metal layer 3 to counteract the thermal tensile stress generated by cooling. Simultaneously, it leverages the viscoelasticity of the buffer layer 2 to release the shear stress caused by lattice mismatch at the interfaces between the metal layer 3 and the dielectric layer 4, and between the substrate 1 and the metal layer 3. Figure 2 As can be seen, a stable multilayer thin film structure consisting of a buffer layer 2, a metal layer 3, and a dielectric layer 4 was ultimately formed on substrate 1. This synergistic mechanism of "active pre-compensation + passive elastic absorption" ensures the adhesion and structural stability of precision optical devices in complex environments.

[0038] This specification and accompanying drawings are merely illustrative examples of this application and are intended to cover any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Therefore, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. An optical thin film stress control method applied to a vacuum coating system (10), the vacuum coating system (10) comprising a PECVD chamber (11) and a PVD chamber (12) connected to each other, characterized in that, The method includes the following steps: S1. The substrate (1) is sent into the PECVD chamber (11), and a viscoelastic buffer layer (2) is formed on the surface of the substrate (1) by plasma-enhanced chemical vapor deposition using a precursor containing organic components. S2. Under the condition of maintaining vacuum and not being exposed to the atmospheric environment, the substrate (1) is transferred to the metal deposition station (121) in the PVD chamber (12); process gas is introduced into the PVD chamber (12) and plasma is generated. Metal layer (3) is deposited on the surface of buffer layer (2) by magnetron sputtering of metal target. At the same time, a pulse bias voltage is applied to the substrate (1), and by controlling the electrical parameters of the pulse bias voltage, the ions in the plasma are used to transfer momentum to the growth surface of the metal layer (3) under the drive of the pulse bias voltage, so as to increase the lattice density of the metal layer (3) and introduce intrinsic compressive stress inside the metal layer (3). The intrinsic compressive stress is used to pre-compensate the thermal tensile stress generated in the metal layer (3) during the subsequent cooling process. Furthermore, the amplitude of the pulse bias voltage is dynamically adjusted according to the real-time temperature change of the substrate (1) during the deposition process to maintain the real-time balance between intrinsic compressive stress and dynamic thermal stress inside the metal layer (3). S3. The substrate (1) is transferred from the metal deposition station (121) to the dielectric deposition station (122) in the PVD chamber (12), and a dielectric layer (4) is deposited on the surface of the metal layer (3) by magnetron sputtering. S4. The intrinsic compressive stress introduced in step S2 is used to offset the tensile stress of the metal layer (3) caused by thermal shrinkage, and the viscoelasticity of the buffer layer (2) is used to release the lattice mismatch shear stress between the metal layer (3) and the dielectric layer (4), so as to achieve mutual offset of the overall residual internal stress of the multilayer thin film structure composed of the buffer layer (2), the metal layer (3) and the dielectric layer (4); wherein, the substrate (1) is the aspherical glass in the vehicle head-up display system. In steps S2 and S3, the passing speed of the substrate (1) when passing through the metal deposition station (121) and the dielectric deposition station (122) is adjusted to compensate for the difference in deposition thickness caused by the change in the surface curvature of the aspherical glass, so that the thickness deviation of the metal layer (3) and the dielectric layer (4) on the surface of the aspherical glass is less than a preset threshold.

2. The method according to claim 1, characterized in that, The PECVD chamber (11) is equipped with a radio frequency power supply (111). In step S1, the radio frequency power supply (111) is used to excite the precursor to generate plasma so that the precursor undergoes a polymerization reaction. By adjusting the radio frequency excitation power of the radio frequency power supply (111), the ratio of organic components to inorganic components in the buffer layer (2) is controlled so that the Young's modulus of the buffer layer (2) is less than that of the substrate (1).

3. The method according to claim 1, characterized in that, In step S1, the environmental pressure inside the PECVD chamber (11) is controlled at... to Between them, the mean free path of the precursor molecules is made greater than the path of motion when they reach the surface of the substrate (1), thereby forming the buffer layer (2) with a loose organic nanoporous structure on the surface of the substrate (1), and utilizing the high damping characteristics of the organic nanoporous structure to absorb the corresponding force.

4. The method according to claim 1, characterized in that, In step S2, the energy distribution of ions reaching the growth surface of the metal layer (3) is controlled by adjusting the frequency and duty cycle of the pulse bias voltage, so as to adjust the intrinsic compressive stress of the metal layer (3) to a predetermined threshold.

5. The method according to claim 1, characterized in that: In step S3, by alternately switching the polarity of at least two dielectric targets and making at least two dielectric targets alternately glow, the polarity reversal guides electrons to neutralize the positive charge accumulated on the target surface, thereby improving the consistency of the internal stress of the dielectric layer (4).

6. The method according to claim 1, characterized in that: The thickness of the buffer layer (2) is in the ratio of 1:5 to 1:10 to the total thickness of the multilayer thin film structure, so that the optical transmittance of the multilayer thin film structure is not less than 90%, and at the same time, the mechanical elastic space provided by the buffer layer (2) is used to release the lattice mismatch energy generated at the interface between adjacent film layers in the multilayer thin film structure.

7. A vacuum coating system (10) for performing the optical thin film stress control method according to any one of claims 1 to 6, characterized in that, The vacuum coating system (10) includes: PECVD chamber (11); The PVD chamber (12) is connected to the PECVD chamber (11), and the PVD chamber (12) is provided with a metal deposition station (121) and a dielectric deposition station (122). The transfer mechanism (14) is used to carry the substrate (1) and drive the substrate (1) to pass sequentially through the PECVD chamber (11), the metal deposition station (121) and the dielectric deposition station (122). A bias power supply (15), electrically connected to the substrate (1) or the transmission mechanism (14), is used to apply a pulse bias to the substrate (1) at the metal deposition station (121); An infrared temperature measuring device (17) is installed in the PVD chamber (12) to detect the temperature change of the substrate (1) in real time during the deposition process; The control unit (16) is used to execute the optical thin film stress control method to coordinate and control the operating parameters of the vacuum coating system (10).

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