Multi-wafer quartz crystal film thickness monitoring device and application method thereof

Abstract

The invention belongs to the technical field of thin film preparation, and particularly discloses a multi-wafer quartz crystal film thickness monitoring device and a using method thereof.The device comprises a mechanical driving assembly, a signal control assembly, an environment adaptation assembly and a plurality of quartz crystal wafers, and the signal control assembly is electrically connected with the mechanical driving assembly; the mechanical driving assembly comprises a shell, a stepping motor, a wafer switching turntable and a flexible support, the stepping motor, the wafer switching turntable and the flexible support are arranged in the shell, the quartz crystal wafers uniformly surround the wafer switching turntable through the flexible support, and the stepping motor is located below the wafer switching turntable. And the stepping motor is connected with the wafer switching turntable through a first transmission element. The multi-wafer quartz crystal film thickness monitoring device and the use method thereof are suitable for real-time and high-precision monitoring of the film thickness of a large-area substrate in the film preparation process of physical vapor deposition, chemical vapor deposition and the like.

Description

Technical Field

[0001] This invention relates to the field of thin film preparation technology, and in particular to a multi-crystal quartz crystal film thickness monitoring device and its usage method. Background Technology

[0002] Quartz crystal film thickness monitoring technology is based on the "quartz crystal microbalance principle"—when a thin film is deposited on the surface of a quartz crystal wafer, the wafer's vibration frequency decreases as the film thickness increases; the film thickness can be inferred from the frequency change. In existing technologies, most mainstream monitoring sensors employ single-crystal or dual-crystal designs, which suffer from technical drawbacks such as narrow monitoring range, low monitoring accuracy, and weak anti-interference capabilities. Furthermore, when a single-crystal sensor is in operation, if the film layer on the wafer surface accumulates to a certain thickness (exceeding the linear range of the Sauerbrey equation), the system must be stopped to replace the wafer, leading to production interruptions. This is especially true for vacuum deposition, which requires breaking the vacuum to replace components, with a single interruption lasting over 30 minutes.

[0003] To address the aforementioned issues, there is an urgent need for a quartz crystal film thickness monitoring sensor that can cover a large monitoring area, improve accuracy, and resist interference, in order to meet the needs of high-precision thin film fabrication scenarios (such as semiconductor chips and optical thin films). Summary of the Invention

[0004] The purpose of this invention is to provide a multi-crystal quartz crystal film thickness monitoring device and its usage method, which is suitable for real-time, high-precision monitoring of film thickness on large-area substrates during thin film preparation processes such as physical vapor deposition and chemical vapor deposition.

[0005] To achieve the above objectives, the present invention provides a multi-crystal quartz crystal film thickness monitoring device, comprising a mechanical drive assembly, a signal control assembly, an environmental adaptation assembly, and a plurality of quartz crystal wafers. The signal control assembly is electrically connected to the mechanical drive assembly. The mechanical drive assembly includes a housing and a stepper motor, a wafer switching turntable, and a flexible support disposed within the housing. The quartz crystal wafers are uniformly surrounded on the wafer switching turntable by the flexible support. The stepper motor is located below the wafer switching turntable and is connected to the wafer switching turntable via a first transmission element. The environmental adaptation component includes a metal-sealed probe, which is fixedly connected to the top of the housing. The surface of the metal-sealed probe has an opening, and a splash guard is provided above the opening.

[0006] Preferably, the signal control component includes a control circuit board and a user terminal. The control circuit board integrates a drive unit, an FPGA, a global clock generator, a differential amplifier circuit, and a bandpass filter. The control circuit board is electrically connected to the metal electrodes of the quartz crystal and the stepper motor. The user terminal is electrically connected to the control circuit board.

[0007] Preferably, the drive unit is used to send control signals, provide direct current, and output alternating excitation voltage. The control signals include rotation direction, rotation angle, and speed commands. At the same time, the direct current is converted into alternating current of the stepper motor stator winding to generate a periodic magnetic field, which drives the rotor to rotate precisely. The rotor drives the crystal switching turntable to rotate synchronously through the first transmission element. The alternating excitation voltage is applied to the electrodes of the quartz crystal to generate resonance. The global clock generator provides a unified reference signal for all quartz crystal chips, and combined with the FPGA nanosecond-level synchronization time, enables multi-channel synchronous measurement and calibration. The differential amplifier circuit suppresses common-mode noise and, in conjunction with the bandpass filter, extracts the fundamental frequency signal of the quartz crystal, thereby reducing environmental electromagnetic interference.

[0008] Preferably, the gap between the metal-sealed probe and the housing, and the contact area between the stepper motor and the housing, are filled with damping material.

[0009] Preferably, the number of quartz crystal plates is ten.

[0010] Preferably, the splash guard is provided with a plurality of through holes evenly arranged around it.

[0011] Preferably, the circumferential trajectory of the through hole intersects the circumferential trajectory of the quartz crystal sheet on the same vertical plane, and the center position of the opening is located on the same vertical line where the circumferential trajectory of the through hole intersects the circumferential trajectory of the quartz crystal sheet.

[0012] Preferably, the center of the splash guard passes through the metal sealing probe via a second transmission element, and a stepper motor is connected to the through end of the second transmission element.

[0013] Preferably, the quartz crystal wafer is an AT-cut quartz wafer with a temperature coefficient of [missing value]. The chip has a diameter of 0.5 inches and a base frequency of 5-10MHz; Gold or platinum electrodes are sputtered onto the surface of the quartz crystal sheet with a sputtering thickness of 50-100 nm and a surface roughness of less than 0.5 nm. Then, an anti-fouling coating is deposited on the electrode surface. The anti-fouling coating has a trapezoidal structure and is a SiO2 / SiC composite coating with an inner SiO2 content greater than an outer SiC content.

[0014] The present invention also provides a method of using a multi-crystal quartz crystal film thickness monitoring device, comprising the following steps: A temporary protective layer of photoresist or metal foil is deposited on the surface of a quartz crystal wafer, which is then encapsulated in ceramic and sealed by welding. The interior is filled with high-purity nitrogen to prevent oxidation during transportation and storage. The temporary protective layer is removed by plasma etching or chemical dissolution before use. The quartz crystal sheet is connected to the flexible support by a spring or rubber pad, and is encapsulated with Kovar alloy material, which has a thermal expansion coefficient similar to that of quartz. It is assembled with a vacuum coating device as a whole, and under standard conditions, full-range calibration is performed using SiO2 thin films of known thickness to establish frequency-thickness mapping curves and store calibration coefficients. The coating process is initiated by activating the anti-splash plate via a stepper motor to prevent contamination of the quartz crystal. The resonant resistance and dissipation factor of the quartz crystal are monitored in real time. If the resonant resistance exceeds the threshold or the dissipation factor increases significantly, the stepper motor is activated via the drive unit to replace the quartz crystal. At the same time, the frequency of the unloaded quartz crystal is measured periodically to automatically deduct environmental drift errors.

[0015] Therefore, the present invention employs the above-mentioned multi-crystal quartz crystal film thickness monitoring device and its usage method, and the beneficial effects are as follows: This invention employs a quartz crystal film thickness monitoring sensor with 10 monitoring chips. When a monitoring chip fails (i.e., the current monitoring chip reaches saturation), a new monitoring chip switches to the detection position to replace the failed chip, realizing the immediate replacement of the spare chip. This motion mechanism is driven by a motor, which can move the spare chip to the monitoring position within 1-2 seconds without breaking the vacuum or stopping the machine, thus completely solving the problem of "stopping the machine to replace parts".

[0016] This invention provides the automatic operation logic of the sensor through a system integrated into the user's PC. Essentially, it solves the bottlenecks of traditional single-chip sensors in terms of continuity, accuracy, and scene adaptability by combining "multi-chip redundancy design" with "precise mechanical drive + intelligent circuit control". It enables continuous monitoring without interruption, ensuring mass production efficiency, and provides higher monitoring accuracy and stronger stability. Ultimately, it provides a "high-precision, high-stability, and high-efficiency" film thickness monitoring solution for vacuum coating (such as semiconductor, optical thin film, magnetic recording thin film, etc.). Moreover, it has strong scene adaptability and is compatible with multiple types of coating requirements (such as customized chip functions, vacuum and environmental compatibility, etc.).

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of an embodiment of a multi-crystal quartz crystal film thickness monitoring device and its usage method according to the present invention; Figure 2 This is a cross-sectional view of an embodiment of a multi-crystal quartz crystal film thickness monitoring device and its usage method according to the present invention; Figure 3 This is an exploded view of an embodiment of a multi-crystal quartz crystal film thickness monitoring device and its usage method according to the present invention; Figure 4 This is a schematic diagram of the structure of a quartz crystal wafer in an embodiment of a multi-crystal quartz crystal film thickness monitoring device and its usage method according to the present invention.

[0019] Figure Labels 1. Quartz crystal wafer; 2. Housing; 3. Stepper motor; 4. Crystal switching turntable; 5. Flexible support; 6. First transmission element; 7. Metal-sealed probe; 8. Opening; 9. Splash shield; 10. Control circuit board; 11. Through hole; 12. Second transmission element; 13. Electrode; 14. Anti-fouling coating. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0022] Example 1 like Figures 1-4 As shown, a multi-crystal quartz crystal film thickness monitoring device includes a mechanical drive assembly, a signal control assembly, an environmental adaptation assembly, and ten quartz crystal wafers 1. The signal control assembly is electrically connected to the mechanical drive assembly. The signal control assembly includes a control circuit board 10 and a user terminal (not shown in the figure). The control circuit board 10 integrates a drive unit, an FPGA, a global clock generator, a differential amplifier circuit, and a bandpass filter. The control circuit board 10 is electrically connected to the metal electrodes 13 of the quartz crystal wafers 1 and the stepper motor 3. The user terminal is electrically connected to the control circuit board 10.

[0023] The drive unit is used to send control signals, provide DC power, and output alternating excitation voltage. The control signals include rotation direction, rotation angle, and speed commands. In conjunction with ten quartz crystal chips 1, it can output commands such as "rotate clockwise 18°" or "switch a quartz crystal chip 1 to a different position." Simultaneously, energy conversion occurs: DC power is converted into alternating current in the stator windings of the stepper motor 3, generating a periodic magnetic field that drives the rotor to rotate precisely. The rotor, through the first transmission element 6, drives the crystal switching turntable 4 to rotate synchronously, achieving the "positioning" of the designated quartz crystal chip 1 (after positioning, the stepper motor 3 sends a "positioning complete" signal to the drive unit, forming a closed-loop feedback). Specifically, the first transmission element 6 is one of the existing transmission structures such as gears, synchronous belts, or lead screws. The alternating excitation voltage is applied to the electrodes 13 of the quartz crystal chip 1 to generate resonance. Specifically, the piezoelectric effect initiates resonance: the alternating excitation voltage output by the drive unit (e.g., 5MHz / 10MHz, close to the crystal's natural frequency) is applied to the metal electrodes 13 of the quartz crystal chip 1, causing the quartz crystal chip 1 to generate periodic mechanical vibrations due to the piezoelectric effect.

[0024] Synchronization mechanism: Using hardware triggering technology, a global clock generator provides a unified reference signal for all quartz crystal chips 1. Combined with FPGA nanosecond-level synchronization time, multi-channel synchronous measurement and calibration ensure real-time synchronization of frequency data of ten crystal oscillator channels.

[0025] High-precision signal processing and noise suppression: The differential amplifier circuit suppresses common-mode noise, and the bandpass filter is used to extract the fundamental frequency signal of the quartz crystal chip 1, thereby reducing environmental electromagnetic interference.

[0026] Materials and Surface Treatment Technology: Quartz crystal wafer 1 is made of AT-cut quartz wafer with a temperature coefficient of [missing value]. It features a low temperature coefficient, making it suitable for wide-temperature environments. The wafer diameter is 0.5 inches, the fundamental frequency is 5-10MHz, and the thickness control precision reaches the nanometer level. A gold or platinum electrode 13 is sputtered onto the surface of the quartz crystal wafer 1, with a sputtering thickness of 50-100nm and a surface roughness of less than 0.5nm, ensuring high conductivity and film adhesion. Specifically, a uniform electrode 13 is prepared using magnetron sputtering technology to avoid edge effects. Then, an anti-fouling coating 14 is deposited on the surface of the electrode 13. The anti-fouling coating 14 has a trapezoidal structure and employs a SiO2 / SiC composite coating (with a higher SiO2 content in the inner layer near the metal electrode 13 than in the outer SiC layer away from the metal electrode 13), improving resistance to hydrofluoric acid corrosion and high-temperature adhesion, enabling the quartz crystal wafer 1 to withstand temperatures up to 1000°C. It can operate stably in the above environments.

[0027] The mechanical drive assembly includes a housing 2 and a stepper motor 3, a wafer switching turntable 4, and a flexible support 5 disposed within the housing 2. Quartz crystal wafers 1 are evenly arranged around the wafer switching turntable 4 via the flexible support 5. The stepper motor 3 is located below the wafer switching turntable 4 and is connected to the wafer switching turntable 4 via a first transmission element 6. The core function of the stepper motor 3 is to drive the wafer switching turntable 4, solving the "fatigue and contamination bottleneck" of single-crystal monitoring and ensuring efficient scheduling of ten quartz crystal wafers 1. When the currently monitored quartz crystal wafer 1 reaches saturation, the stepper motor 3 can move a spare quartz crystal wafer 1 to the monitoring station within 1-2 seconds.

[0028] The environmental adaptation components include a metal-sealed probe 7, which is fixedly connected to the top of the housing 2. The internal vacuum level reaches 10⁻⁶ Pa to prevent interference from gas molecule adsorption. The surface of the metal-sealed probe 7 has an opening 8, and a splash guard 9 is located above the opening 8. Several through holes 11 are evenly arranged around the splash guard 9. The circumferential trajectory of the through holes 11 intersects the circumferential trajectory of the quartz crystal 1 on the same vertical plane. The center of the opening 8 is located on the same vertical line where the circumferential trajectories of the through holes 11 and the quartz crystal 1 intersect. A second transmission element 12 passes through the metal-sealed probe 7 at the center of the splash guard 9, and a stepper motor 3 is connected to the through end of the second transmission element 12. Damping material, such as silicone, is filled in the gap between the metal-sealed probe 7 and the housing 2, and at the contact points between the stepper motor 3 and the housing 2, to reduce frequency fluctuations caused by vibration or mechanical movement.

[0029] Its usage method is as follows: A temporary protective layer of photoresist or metal foil is deposited on the surface of the quartz crystal wafer 1 to prevent oxidation during transportation and storage. Ceramic encapsulation and welding sealing are employed, with the interior filled with high-purity nitrogen to reduce humidity (<5% RH) and oxygen content, thus delaying the oxidation of electrode 13. Before use, the temporary protective layer is removed by plasma etching or chemical dissolution to ensure that the performance of electrode 13 is not affected.

[0030] The quartz crystal sheet 1 and the flexible support 5 are connected by a spring or rubber pad. The package is made of Kovar alloy material with a thermal expansion coefficient similar to that of quartz to avoid thermal stress cracking caused by temperature changes. The package structure is optimized through finite element simulation to ensure that the interface stress is less than 10MPa.

[0031] Factory calibration: Assembled as a single unit with the vacuum coating apparatus, and calibrated in a standard environment (25°C). At 1 atm, full-range calibration was performed using a SiO2 thin film of known thickness to establish a frequency-thickness mapping curve and store the calibration coefficients.

[0032] Online self-calibration: When the coating process is started, the anti-splash plate 9 is activated by the stepper motor 3 to avoid contamination of the quartz crystal 1. The resonant resistance and dissipation factor of the quartz crystal 1 are monitored in real time. If the resonant resistance exceeds the threshold (e.g., >100Ω in dry state) or the dissipation factor increases significantly, it indicates that there may be contamination or film peeling on the surface of the crystal oscillator, and cleaning or replacement is required. The stepper motor 3 is activated by the drive unit to replace the quartz crystal 1. At the same time, the frequency of the unloaded quartz crystal 1 is measured periodically (e.g., hourly) and environmental drift error is automatically deducted. For example, the temperature compensation model is dynamically updated through a self-learning algorithm to adapt to the aging of the crystal oscillator during long-term use.

[0033] In addition, regular maintenance and cleaning are also included: Electrode 13 Cleaning: Use deionized water, ethanol, or plasma cleaning to remove contaminants (such as dust and metal particles) from the surface of the quartz crystal sheet 1. For example, ultrasonic cleaning (power less than 50W) combined with megasonic technology can be used to ensure effective removal of micron-sized particles.

[0034] Film removal: When the thickness of the film deposited on the surface of the quartz crystal plate 1 exceeds the range, the old film is removed by chemical etching (such as hydrofluoric acid solution) or ion beam etching to restore the initial performance.

[0035] Environmental monitoring and alarms: Temperature and humidity threshold: Set ambient temperature (-20~80) Alarm thresholds for humidity (less than 80% RH) are set, and the coating process is automatically stopped and a maintenance prompt is displayed when the threshold is exceeded.

[0036] Vacuum monitoring: The vacuum level inside the housing 2 is monitored in real time by a vacuum gauge. If it is lower than the set value (e.g., 10-5 Pa), the system triggers emergency venting and power-off protection to prevent damage to the quartz crystal plate 1.

[0037] Therefore, the present invention employs the above-mentioned multi-crystal quartz crystal film thickness monitoring device and its usage method, which is suitable for real-time, high-precision monitoring of film thickness on large-area substrates during thin film preparation processes such as physical vapor deposition and chemical vapor deposition.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A multi-crystal quartz crystal film thickness monitoring device, characterized in that: The device includes a mechanical drive assembly, a signal control assembly, an environmental adaptation assembly, and several quartz crystal wafers. The signal control assembly is electrically connected to the mechanical drive assembly. The mechanical drive assembly includes a housing and a stepper motor, a wafer switching turntable, and a flexible support disposed within the housing. The quartz crystal wafers are uniformly surrounded on the wafer switching turntable by the flexible support. The stepper motor is located below the wafer switching turntable and is connected to the wafer switching turntable through a first transmission element. The environmental adaptation component includes a metal-sealed probe, which is fixedly connected to the top of the housing. The surface of the metal-sealed probe has an opening, and a splash guard is provided above the opening.

2. The multi-crystal quartz crystal film thickness monitoring device according to claim 1, characterized in that: The signal control component includes a control circuit board and a user terminal. The control circuit board integrates a drive unit, an FPGA, a global clock generator, a differential amplifier circuit, and a bandpass filter. The control circuit board is electrically connected to the metal electrodes of the quartz crystal and the stepper motor. The user terminal is electrically connected to the control circuit board.

3. The multi-crystal quartz crystal film thickness monitoring device according to claim 2, characterized in that: The drive unit is used to send control signals, provide DC power, and output alternating excitation voltage. The control signals include rotation direction, rotation angle, and speed commands. At the same time, the DC power is converted into alternating current of the stepper motor stator winding to generate a periodic magnetic field, which drives the rotor to rotate precisely. The rotor drives the crystal switching turntable to rotate synchronously through the first transmission element. The alternating excitation voltage is applied to the electrodes of the quartz crystal sheet to generate resonance. The global clock generator provides a unified reference signal for all quartz crystal chips, and combined with the FPGA nanosecond-level synchronization time, enables multi-channel synchronous measurement and calibration. The differential amplifier circuit suppresses common-mode noise and, in conjunction with the bandpass filter, extracts the fundamental frequency signal of the quartz crystal, thereby reducing environmental electromagnetic interference.

4. The multi-crystal quartz crystal film thickness monitoring device according to claim 1, characterized in that: The gap between the metal-sealed probe and the housing, and the contact area between the stepper motor and the housing, are filled with damping material.

5. The multi-crystal quartz crystal film thickness monitoring device according to claim 1, characterized in that: The number of quartz crystal plates is ten.

6. The multi-crystal quartz crystal film thickness monitoring device according to claim 1, characterized in that: The splash guard is provided with several through holes evenly arranged around it.

7. The multi-crystal quartz crystal film thickness monitoring device according to claim 6, characterized in that: The orbital path of the through hole intersects the orbital path of the quartz crystal sheet on the same vertical plane, and the center of the opening is located on the same vertical line where the orbital path of the through hole intersects the orbital path of the quartz crystal sheet.

8. The multi-crystal quartz crystal film thickness monitoring device according to claim 1, characterized in that: The splash guard passes through the metal sealing probe via a second transmission element at its center, and a stepper motor is connected to the through end of the second transmission element.

9. The multi-crystal quartz crystal film thickness monitoring device according to claim 1, characterized in that: The quartz crystal wafer is made using AT-cut quartz wafers with a temperature coefficient of [missing value]. The chip has a diameter of 0.5 inches and a base frequency of 5-10MHz; Gold or platinum electrodes are sputtered onto the surface of the quartz crystal sheet with a sputtering thickness of 50-100 nm and a surface roughness of less than 0.5 nm. Then, an anti-fouling coating is deposited on the electrode surface. The anti-fouling coating has a trapezoidal structure and is a SiO2 / SiC composite coating with an inner SiO2 content greater than an outer SiC content.

10. A method of using the multi-crystal quartz crystal film thickness monitoring device as described in any one of claims 1-9, characterized in that, Includes the following steps: A temporary protective layer of photoresist or metal foil is deposited on the surface of a quartz crystal wafer, which is then encapsulated in ceramic and sealed by welding. The interior is filled with high-purity nitrogen to prevent oxidation during transportation and storage. The temporary protective layer is removed by plasma etching or chemical dissolution before use. The quartz crystal sheet is connected to the flexible support by a spring or rubber pad, and is encapsulated with Kovar alloy material, which has a thermal expansion coefficient similar to that of quartz. It is assembled with a vacuum coating device as a whole, and under standard conditions, full-range calibration is performed using SiO2 thin films of known thickness to establish frequency-thickness mapping curves and store calibration coefficients. The coating process is initiated by activating the anti-splash plate via a stepper motor to prevent contamination of the quartz crystal. The resonant resistance and dissipation factor of the quartz crystal are monitored in real time. If the resonant resistance exceeds the threshold or the dissipation factor increases significantly, the stepper motor is activated via the drive unit to replace the quartz crystal. At the same time, the frequency of the unloaded quartz crystal is measured periodically to automatically deduct environmental drift errors.

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