Method and apparatus for sputter deposition of optical thin films based on dual pulsed sources

Abstract

This invention discloses a method and apparatus for sputtering deposition of optical thin films based on a dual-pulse source, belonging to the field of optical thin film manufacturing technology within optical manufacturing. This invention adjusts the corresponding deposition parameters for different substrates and targets to achieve the deposition and preparation of various optical thin films. The dual-pulse source consists of a main source and an auxiliary source. High-energy charged particles generated by the main pulse source bombard the target surface, undergoing cascade collisions within several atomic layers. Energy exchange occurs between the particles and the target. When the target atoms gain sufficient energy to overcome their atomic barriers, they leave the target surface and deposit on the substrate to form a thin film. High-energy particles generated by the auxiliary pulse source bombard the surface of the growing thin film. Film molecules gain greater kinetic energy through energy and momentum transfer with the high-energy particles, resulting in enhanced film adhesion and a denser surface arrangement. This invention can achieve the preparation of multiple types of optical thin films while also improving the filling density and performance of optical thin films.

Description

Technical Field

[0001] This invention belongs to the field of optical thin film manufacturing technology in optical manufacturing, and relates to a method and apparatus for sputtering deposition of optical thin films based on a dual-pulse source. Background Technology

[0002] Optical thin films refer to one or more layers of metal films, dielectric films, or stacks of metal and dielectric films deposited on optical elements to alter the transmission characteristics of light waves. Optical thin films can reduce or increase optical characteristics such as reflection, gating of spectra, and control of polarization and phase on the surface of optical elements. They can also specifically improve the chemical, mechanical, and electrical properties of the surface of optical elements. They are an indispensable key technology in various optical and laser systems. With technological advancements, the application of optical thin films is becoming increasingly widespread, and the requirements are becoming more stringent. However, obtaining uniform and stable optical thin films remains a significant technical challenge.

[0003] Ion beam sputtering deposition, an emerging optical thin film fabrication technology, uses a high-energy ion beam to bombard a target material at a specific angle, sputtering target atoms and depositing them onto a substrate. Although optical thin films deposited by ion beam sputtering have strong adhesion to the substrate, the uniformity and stability of the deposited film on the substrate surface are difficult to guarantee due to the uncertainty of the target molecule's trajectory during sputtering.

[0004] Furthermore, the thickness of optical thin films is closely related to their optical properties. If the film thickness cannot be known during the deposition process, it cannot be guaranteed that the deposited film will meet the requirements. This necessitates rework and multiple depositions, which is cumbersome and inefficient. Additionally, the sputtered optical components are subject to environmental influences during repeated handling, affecting the adhesion between the film and the substrate, as well as the stress within the film layer, ultimately damaging its performance. Summary of the Invention

[0005] To address the issues of inconsistent uniformity and stability in thin film deposition and the inability to monitor film thickness in existing technologies, this invention provides a method and apparatus for sputtering optical thin films based on a dual-pulse source. This method allows for the adjustment of deposition parameters for different substrates and targets, enabling the deposition of various optical thin films; it also improves the fill density and performance of the optical thin films. The apparatus integrates sputtering and removal: the main pulse source provides energy to sputter target atoms from the target surface; the auxiliary pulse source provides secondary energy to the target atoms, enhancing film adhesion. Furthermore, after film preparation, a smoothing removal process can be performed on the film surface to address the inability to guarantee uniformity and stability, while also reducing film stress and improving the bonding force between the substrate and the film. This invention also utilizes a film thickness monitor to monitor the optical thickness of the film in real time during the sputtering deposition process, solving the problem of unmonitored film thickness.

[0006] The objective of this invention is achieved through the following technical solution.

[0007] The dual-pulse source-based sputtering deposition method for optical thin films consists of a main pulse source and an auxiliary pulse source. The main pulse source generates high-energy, high-momentum charged particles that bombard the target surface, resulting in cascade collisions within several atomic layers. Energy exchange occurs between the particles and the target. Once the target atoms gain sufficient energy to overcome their atomic barriers, they leave the target surface. The auxiliary pulse source provides secondary energy to the sputtered target atoms, enabling them to move onto the substrate and form an optical thin film. Simultaneously, the secondary energy from the auxiliary pulse source enhances film adhesion and results in a denser molecular arrangement of the target atoms on the surface. The secondary energy from the auxiliary pulse source also increases the filling density and refractive index of the optical thin film, reducing water vapor absorption, wavelength drift, and consequently, absorption and scattering effects. The stress σ of the film is controlled by adjusting the substrate curvature radius, as shown in the following formula:

[0008]

[0009] In the formula, E represents the Young's modulus of the substrate; d represents the thickness of the optical thin film; v represents the Poisson's ratio of the target material; R p R0 represents the radius of curvature of the substrate after film deposition; R0 represents the radius of curvature of the substrate before film deposition.

[0010] Furthermore, according to equations (2), (3), and (4), the optical thickness d of the deposited film is determined by the desired optical properties of the optical thin film:

[0011]

[0012] In the formula, R represents the reflectivity of the film layer; δ represents the phase thickness of the film layer; n 0-2 λ represents the refractive index of air, film, and substrate, respectively; m represents the wavelength; and m is the number of extreme points.

[0013] Analysis of the above formulas (2), (3), and (4) shows that the optical thickness of the film is related to the optical performance required by the film. The optical thickness of the film is monitored in real time by a film thickness monitoring instrument to ensure that the deposited film meets the required standards.

[0014] This invention discloses a sputtering deposition optical thin film apparatus based on a dual-pulse source, mainly composed of a main pulse source, an auxiliary pulse source, a target stage, a deposition stage, a light emitting device, a film thickness monitor, a target material, and a substrate. The main pulse source, auxiliary pulse source, target stage, and deposition stage are placed in a vacuum chamber. The target material is fixed on the target stage. The substrate is fixed on the deposition stage. The pulse beam emitted by the main pulse source bombards the surface of the target material, sputtering target atoms. The pulse beam emitted by the auxiliary pulse source assists the target atoms in adhering to the substrate surface. The light emitting device irradiates the substrate surface. The film thickness monitor monitors the thickness of the film deposited on the substrate surface in real time.

[0015] The method for thin film deposition using the above-mentioned dual-pulse source-based sputtering deposition optical thin film apparatus includes the following steps:

[0016] Step 1: After cleaning the target and substrate materials with a lint-free cloth soaked in a mixture of ethanol and ether, place them into the target stage and worktable in the vacuum chamber respectively; before deposition, drive the auxiliary pulse ion source to clean the target and substrate to remove surface impurities and reduce film stress.

[0017] Step 2: Start the vacuum pump to evacuate the vacuum chamber; achieve different vacuum levels according to the requirements of different optical thin films;

[0018] Step 3: Drive and turn on the main pulse source to bombard the target material; at the same time, turn on the auxiliary pulse source to provide further energy to the sputtered target molecules so as to achieve deposition on the substrate surface.

[0019] Step 4: Turn on the film thickness monitor; monitor the film thickness in real time until the film meets the optical property requirements; after the film deposition is completed, the auxiliary pulse source can also sweep away unstable molecules in the film to ensure the uniformity and stability of the film.

[0020] Step 5: Inspect the film layer; After the film layer is prepared, the thickness and performance of the prepared film layer need to be tested to ensure that the sputtered optical thin film meets the preset requirements; The thin film prepared by the dual-pulse source sputtering deposition method has the effects of high uniformity, smooth surface and stable optical properties.

[0021] In the aforementioned device, the end face of the target stage is parallel to the end face of the worktable, and the main pulse source and the target stage are on the same plane. The main pulse source can be flipped so that the emitted pulse beam can bombard the surface of the target stage. The auxiliary pulse source is on the same plane as the worktable, and the auxiliary pulse source can also be flipped so that the pulse beam emitted by the auxiliary pulse source can provide secondary energy to the target molecules sputtered by the main pulse source, thereby enabling the target molecules to deposit on the substrate surface to form a film.

[0022] The film thickness monitoring instrument works by emitting light from a light-emitting device onto the film layer. After reflection, the light is received by the film thickness monitoring instrument to obtain data for analyzing the optical properties of the film layer. The light passes through a beam splitter in the film thickness monitoring instrument, which separates the incident light into reflected light and transmitted light. The reflected light passes through a photocell to form a contrasting electrical signal that enters the display. The transmitted light passes through a high-reflection mirror and is focused by a lens to converge the beam onto a monochromator. The monochromator converts the weakened light signal into an electrical signal, which serves as another input signal for the differential amplifier and enters the display. The optical thickness of the film layer is obtained by comparing the two electrical signals.

[0023] The above-mentioned method for sputtering optical thin films based on dual-pulse sources includes the following deposition parameters: the voltage of the main pulse source is 800-1500V and the anode current is 0.3-0.4mA; the voltage of the auxiliary pulse source is 200-400eV and the anode current is 1.1-1.8mA.

[0024] Beneficial effects:

[0025] 1. The present invention discloses a method and apparatus for sputtering deposition of optical thin films based on a dual-pulse source. By adjusting the corresponding deposition parameters for different substrates and targets, various optical thin films can be deposited and prepared. At the same time, the filling density and performance of the optical thin films can be improved.

[0026] 2. This invention discloses a method and apparatus for sputtering deposition of optical thin films based on a dual-pulse source. The dual-pulse source integrates sputtering and removal. High-energy charged particles generated by the main pulse source bombard the target surface, and energy exchange occurs between the particles and the target. When the target atoms gain sufficient energy to overcome their atomic barriers, they leave the target surface and deposit on the substrate surface to form a thin film. The auxiliary pulse source generates high-energy particles that bombard the surface of the growing thin film. Film molecules gain greater kinetic energy through energy and momentum transfer with the high-energy particles, resulting in enhanced film adhesion and a denser surface arrangement. Simultaneously, the auxiliary pulse source can clean the substrate and target surfaces before film deposition to remove surface impurities, which is beneficial for improving the adhesion between the substrate and the thin film. After film deposition, the auxiliary pulse source can still clean the film surface to ensure the uniformity of the film.

[0027] 3. The present invention discloses a method and apparatus for sputtering deposition of optical thin films based on a dual-pulse source. The optical thickness of the thin film is calculated according to the performance requirements of the thin film, and the optical thickness of the optical thin film is monitored in real time during the sputtering process by a film thickness monitoring instrument. This enables the precise manufacturing of optical thin films and has the advantages of high processing efficiency and low cost. Attached Figure Description

[0028] Figure 1 This is a diagram of a dual-pulse source sputtering deposition device for optical thin films.

[0029] Figure 2This is a schematic diagram of the sputtering deposition principle;

[0030] Figure 3 This is a schematic diagram of the optical thin film growth process;

[0031] Figure 4 This is a schematic diagram of a film thickness monitoring instrument.

[0032] Among them, 1—vacuum pump, 2—vacuum chamber, 3—auxiliary pulse source, 4—light emitting device, 5—fixture, 6—target stage, 7—target material, 8—film thickness monitor, 9—main pulse source, 10—substrate, 11—work stage, 12—target material molecule, 13—beam splitter, 14—high reflection mirror, 15—lens, 16—monochromator, 17—display instrument, 18—photocell. Detailed Implementation

[0033] The invention will be further illustrated below with reference to the accompanying figures.

[0034] Figure 1 The diagram shows a dual-pulse source sputtering deposition apparatus for optical thin films, which comprises a vacuum system, a deposition system, and a control system. The vacuum system consists of a vacuum pump 1 and a vacuum chamber 2, with the deposition system housed within the vacuum chamber 2. The vacuum pump 1 is controlled by the system control module, selecting the appropriate vacuum level based on the characteristics of the target material 7 and the substrate material 10. The deposition system comprises a main pulse source 9 and an auxiliary pulse source 3, a target stage 6, and a deposition stage 11. The target material 7 is fixed to the target stage 6 using clamps 5, and the substrate material 10 is fixed to the deposition stage 11 using clamps 5.

[0035] Figure 2 This is a schematic diagram illustrating the principle of sputtering deposition. The main pulse source bombards the target material, causing the target molecules to gain energy and escape from the target surface. A secondary pulse source provides additional energy, allowing them to reach the substrate material surface. The target molecules diffuse and aggregate on the substrate material surface, forming stable nuclei and ultimately creating an optical thin film on the substrate material surface, such as... Figure 3 As shown. Figure 4 This is a schematic diagram of the film thickness monitoring instrument. Light passes through a beam splitter 13 in the instrument, splitting the incident light into reflected and transmitted light. The reflected light passes through a photocell 18 to form a contrasting electrical signal, which enters the display 17. The transmitted light passes through a high-reflection mirror 14 and is focused by a lens 15, converging the beam onto a monochromator 16. The monochromator 16 converts the weakened light signal into an electrical signal, which serves as another input signal for the differential amplifier and enters the display 17. The optical thickness of the film is obtained by comparing the two electrical signals.

[0036] Example 1

[0037] This embodiment is used for the deposition of optical thin films on the surfaces of optical components such as optical mirrors and hard and brittle materials in optical systems. For example, when depositing tantalum dioxide optical thin films on the surface of a high-reflectivity quartz mirror in a solar simulator, the film reflectivity is required to reach 99%. The appropriate deposition parameters are selected according to the substrate and target material; the optical thickness of the film is determined by the optical properties that the optical thin film needs to achieve.

[0038] The method for thin film deposition using a dual-pulse source sputtering optical thin film deposition apparatus is implemented in the following steps:

[0039] Step 1: After cleaning the tantalum dioxide target 7 and the quartz substrate 10 with a lint-free cloth soaked in a mixture of ethanol and ether, they are placed into the target stage 6 and the worktable 11 in the vacuum chamber 2 and clamped and fixed with the fixture 5. Before deposition, the auxiliary pulse source 3 is driven to perform surface cleaning on the single crystal silicon 7 and the silicon carbide substrate 10 to remove surface impurities and reduce film stress.

[0040] Step 2: Start vacuum pump 1 to evacuate vacuum chamber 2; according to the requirements of the optical thin film of tantalum dioxide target 7 and quartz substrate 10, achieve a vacuum level of 1.33 × 10⁻⁶. -6 Pa.

[0041] Step 3: Drive and turn on the power of the main pulse source 9 to bombard the tantalum dioxide target 7; at the same time, turn on the auxiliary pulse source to provide further energy to the sputtered tantalum dioxide molecules so as to achieve deposition on the surface of the quartz substrate 10.

[0042] Step 4: Turn on the film thickness monitor 8; monitor the film thickness in real time until the tantalum dioxide film meets the optical property requirements. After the film deposition is completed, the auxiliary pulse source 3 can also sweep away unstable molecules in the film to ensure the uniformity and stability of the film.

[0043] Step 5: Inspect the film; After the tantalum dioxide film is prepared, its performance needs to be tested. The tantalum dioxide film prepared by the dual-pulse source sputtering deposition method has the effects of high uniformity, smooth surface and stable optical properties.

[0044] The deposition parameters in this embodiment include: the voltage of the main pulse source is 500V and the anode current is 0.5mA; the voltage of the auxiliary pulse source is 200V and the anode current is 1.2mA.

[0045] In this embodiment, the tantalum dioxide film material sputtered onto a quartz substrate is a high-reflectivity film with a center wavelength of 632.8 nm. The experiment ultimately achieved a center wavelength reflectivity greater than 99.99%, a transmittance of 0, and an optical film thickness of 150 nm.

[0046] Example 2

[0047] This embodiment is used for the deposition of optical thin films on the surfaces of optical components such as optical mirrors and hard, brittle materials in optical systems. For example, when depositing silicon dioxide on the surface of silicon carbide lenses in a Shenguang ignition device, a reflectivity of over 98% is required. Appropriate deposition parameters are selected based on the silicon carbide substrate and the silicon dioxide target material; the optical thickness of the film is determined by the desired optical properties of the thin film.

[0048] The method for thin film deposition using a dual-pulse source sputtering optical thin film deposition apparatus is implemented in the following steps:

[0049] Step 1: After cleaning the silicon dioxide 7 and silicon carbide substrate 10 with a lint-free cloth soaked in a mixture of ethanol and ether, they are placed into the target stage 6 and worktable 11 in the vacuum chamber 2 and clamped and fixed with the fixture 5. Before deposition, the auxiliary pulse source 3 is driven to clean the silicon dioxide 7 and silicon carbide substrate 10 to remove surface impurities and reduce film stress.

[0050] Step 2: Start vacuum pump 1 to evacuate vacuum chamber 2; according to the requirements of optical thin films on single-crystal silicon and silicon carbide substrate materials, achieve a vacuum level of 1.0 × 10⁻⁶. -6 Pa.

[0051] Step 3: Drive and turn on the power of the main pulse source 9 to bombard the single-crystal silicon target 7; at the same time, turn on the auxiliary pulse source to provide further energy to the sputtered single-crystal silicon molecules so as to achieve deposition on the bottom surface of silicon carbide 10.

[0052] Step 4: Turn on the film thickness monitor 8; monitor the film thickness in real time until the silica film meets the optical property requirements. After film deposition is completed, the auxiliary pulse source 3 can also clean up unstable molecules in the film to ensure the uniformity and stability of the film.

[0053] Step 5: Inspect the film layer; After the silica film layer is prepared, its performance needs to be tested. Thin films prepared by dual-pulse source ion beam sputtering deposition exhibit high uniformity, smooth surface, and stable optical properties.

[0054] The deposition parameters in this embodiment include: the voltage of the main pulse source is 1250V and the anode current is 60mA; the voltage of the auxiliary pulse source is 300V and the anode current is 1.2mA.

[0055] In this embodiment, silicon dioxide material is sputtered onto a silicon carbide substrate to achieve a high-reflectivity film with a center wavelength of 1064nm, resulting in a center wavelength reflectivity greater than 99.86%, a transmittance of 0, and an optical film thickness of 300nm.

[0056] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for sputtering deposition of optical thin films based on a dual-pulse source, characterized in that: The pulse source consists of a main source and an auxiliary source. The main pulse source generates high-energy, high-momentum charged particles that bombard the target surface, causing cascade collisions within several atomic layers. Energy exchange occurs between the particles and the target. Once the target atoms gain sufficient energy to overcome their atomic barriers, they leave the target surface. The auxiliary pulse source provides secondary energy to the sputtered target atoms, enabling them to move onto the substrate and form an optical thin film. Simultaneously, the secondary energy from the auxiliary pulse source enhances film adhesion and results in a denser molecular arrangement of the target material on the surface. The secondary energy from the auxiliary pulse source also increases the filling density and refractive index of the optical thin film, reducing water vapor absorption, wavelength drift, and consequently, absorption and scattering effects. The stress σ of the film is controlled by adjusting the substrate curvature radius, as shown in the following formula: In the formula, E represents the Young's modulus of the substrate; d represents the thickness of the optical thin film; v represents the Poisson's ratio of the target material; R p R0 represents the radius of curvature of the substrate after thin film deposition; R0 represents the radius of curvature of the substrate before thin film deposition. According to equations (2), (3), and (4), the optical thickness d of the deposited film is determined by the desired optical properties of the optical thin film: In the formula, R represents the reflectivity of the film layer; δ represents the phase thickness of the film layer; n 0-2 Let λ represent the refractive indices of air, film, and substrate, respectively; λ represent the wavelength; and m represent the number of extreme points.

2. The method for sputtering and depositing optical thin films based on a dual-pulse source as described in claim 1, characterized in that: The thickness of the optical thin film is detected in real time, and the surface of the optical thin film is smoothed by an auxiliary pulse source.

3. An apparatus for implementing the method as described in any one of claims 1 to 2, characterized in that: It mainly consists of a main pulse source (9), an auxiliary pulse source (3), a target stage (6), a deposition stage (11), a light emitting device (4), a film thickness monitor (8), a target material (7), and a substrate (10). The main pulse source (9), the auxiliary pulse source (3), the target stage (6), and the deposition stage (11) are placed in a vacuum chamber (2). The target material (7) is fixed on the target stage (6). The substrate (10) is fixed on the deposition stage (11). The pulse beam emitted by the main pulse source (9) bombards the surface of the target material (7) and sputters the target material atoms. The pulse beam emitted by the auxiliary pulse source (3) helps the target material atoms adhere to the surface of the substrate (10). The light emitting device (4) irradiates the surface of the substrate (10). The film thickness monitor (8) monitors the thickness of the film deposited on the surface of the substrate (10) in real time.

4. The apparatus as described in claim 3, characterized in that: The end face of the target stage (6) is parallel to the end face of the deposition stage (11), and the main pulse source (9) and the target stage (6) are on the same plane. The main pulse source (9) can be flipped so that the emitted pulse beam can bombard the surface of the target stage (6). The auxiliary pulse source (3) and the deposition stage (11) are on the same plane. Similarly, the auxiliary pulse source (3) can be flipped so that the pulse beam emitted by the auxiliary pulse source (3) can provide secondary energy to the target molecules (12) sputtered by the main pulse source (9) to achieve the deposition of the target molecules (12) on the substrate surface to form a film.

5. The apparatus as described in claim 3, characterized in that: The detection principle of the film thickness monitor (8) is to emit light through a light emitting device to irradiate the film layer. After reflection, the light is received by the film thickness monitor to obtain data for analyzing the optical properties of the film layer. The light passes through the beam splitter in the film thickness monitor, which divides the incident light into reflected light and transmitted light. The reflected light passes through a photocell to form a contrasting electrical signal that enters the display. The transmitted light passes through a high-reflection mirror and is focused by a lens to converge the beam onto a monochromator. The monochromator converts the weakened light signal into an electrical signal, which is used as another input signal of the differential amplifier and enters the display. The optical thickness of the film layer is obtained by comparing the two electrical signals.

6. A method for thin film deposition using the apparatus as described in claim 3, characterized in that: Includes the following steps, Step 1: After cleaning the target material (7) and substrate (10) with a lint-free cloth soaked in a mixture of ethanol and ether, place them into the target stage (6) and worktable (11) in the vacuum chamber (2) respectively; before deposition, drive the auxiliary pulse ion source (3) to clean the target material (7) and substrate (10) to remove surface impurities and reduce film stress. Step 2: Start the vacuum pump (1) to evacuate the vacuum chamber (2); achieve different vacuum levels according to the requirements of different optical thin films; Step 3: Drive and turn on the power of the main pulse source (9) to bombard the target material (7); at the same time, turn on the auxiliary source (3) to provide further energy to the sputtered target material molecules so as to achieve deposition on the substrate surface; Step 4: Turn on the film thickness monitor (8); monitor the film thickness in real time until the film meets the optical properties requirements; after the film deposition is completed, the auxiliary pulse source (3) is also used to clean the unstable molecules in the film to ensure the uniformity and stability of the film. Step 5: Inspect the film layer; After the film layer is prepared, the thickness and performance of the prepared film layer need to be tested to ensure that the sputtered deposited optical thin film meets the preset requirements.

7. The thin film deposition method as described in claim 6, characterized in that: The voltage of the main pulse source is 800–1500V, and the anode current is 0.3–0.4mA; The voltage of the auxiliary pulse source is 200–400 eV, and the anode current is 1.1–1.8 mA.

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