A resonant cavity structure for fine atomization and a gluing method

Abstract

The present invention relates to the technical field of photoresist coating for wafer-level packaging, specifically a resonant cavity structure and coating method for fine atomization, comprising a resonant cavity, a spherical resonant cavity disposed within the resonant cavity, the diameter of the spherical resonant cavity being an integral multiple of half the wavelength of ultrasonic excitation, an opening for ultrasonic excitation input disposed at the top of the resonant cavity, and an acoustic resonance cavity disposed at the bottom of the resonant cavity; a liquid supply needle is inserted into the acoustic resonance cavity from the resonant cavity. This structure and method can improve the uniformity of photoresist spraying and the quality of the film layer. By utilizing precise acoustic field control, no microchannel is required to provide fluid flow, thus avoiding the potential problem of nozzle blockage. By focusing the acoustic wave in the resonant cavity, the droplets will break up in a very short time, resulting in a small atomized particle size and high concentration, thereby achieving uniform and controllable photoresist film thickness. The film layer has high uniformity and few film defects, is not restricted by the wafer surface morphology, and can achieve conformal coating of complex three-dimensional microstructures.

Description

Technical Field

[0001] The present invention relates to the technical field of photoresist coating for wafer-level packaging, and in particular to a fine atomized resonant cavity structure and a coating method. Background Art

[0002] The rapid development of microelectromechanical systems (MEMS) and three-dimensional integrated circuits (3D-ICs) has brought new challenges to advanced semiconductor processes, particularly nanoscale integrated circuits. Photolithography is a core process in chip manufacturing. To meet the growing demand for smaller and more highly integrated devices, conformal coating must be achieved on surfaces such as trenches, V-grooves, and through-silicon vias (TSVs). The diameter and concentration of atomized droplets directly impact the reliability and yield of integrated circuits.

[0003] Traditional photoresist coating primarily utilizes a spin coating process. The principle is to spread the photoresist onto the wafer surface using the centrifugal force of a rapidly rotating wafer substrate, forming a film. The thickness and uniformity of the spin coating depend on factors such as the viscosity between the photoresist and the substrate, the spin speed, the spin time, and the surface topography. However, 1. Spin coating is generally only suitable for coating a single thin film, making precise control difficult for spray coating applications with specific thickness requirements. 2. For wafer substrates with complex microstructures, the radial flow of the photoresist during spin coating causes the colloid to accumulate in localized areas of the microstructure, making it difficult to precisely control the thickness and uniformity of the photoresist coating. 3. For larger or non-circular wafers, spin coating can be difficult to operate or result in uneven coating, resulting in differences in film thickness between the edge and center of the wafer. 4. During the spin process, excess photoresist is thrown off, resulting in significant waste, especially for thin films.

[0004] The main principle of conventional ultrasonic photoresist atomization spraying technology is to use high-frequency vibration to form photoresist droplets into fine droplets. The driving frequency of this type of atomization technology is usually 100-200kHz, and the atomization scale is 18μm. It is difficult to accurately control the size of the atomized droplets, and the particle size distribution of the atomized droplets is uneven, resulting in inconsistent photoresist film thickness, thereby affecting the exposure effect and the accuracy of pattern transfer. For silicon through-hole structures with large "aspect ratios" (≥5:1), smaller and more uniformly distributed photoresist particles are required to achieve good conformal coverage. In addition, conventional ultrasonic atomization delivers the atomized solution to the atomization surface through microchannels, which can easily cause blockage problems and bring many hidden dangers to atomization spraying.

[0005] As integrated circuit manufacturing processes enter the 10nm stage, their highly integrated microstructures feature uneven surfaces (trenchways, steps, V-grooves, and deep holes). Current ultrasonic atomization spraying technology presents numerous challenges in achieving uniform coating of complex microstructures, hindering further advancements in semiconductor device manufacturing. Consequently, a new fine atomization resonant cavity structure is urgently needed to achieve precise and uniform spraying of photoresist. This invention optimizes a resonant cavity design that produces smaller, more uniform atomized droplets, improving the quality and thickness consistency of photoresist films. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a fine atomization resonant cavity structure and a gluing method. The fine atomization resonant cavity structure and the gluing method can improve the uniformity of photoresist spraying and the quality of the film layer. By utilizing precise acoustic field control, no microchannel is required to provide fluid flow, thereby avoiding the potential problem of nozzle blockage; the sound waves are focused in the resonant cavity, and the droplets will break up in a very short time, resulting in small atomized particle size and high concentration, thereby achieving uniform and controllable photoresist film thickness; the film layer has high uniformity and few film defects, is not restricted by the surface morphology of the wafer, and can achieve conformal coating of complex three-dimensional microstructures.

[0007] The technical solutions of the present invention are as follows:

[0008] A resonant cavity structure for fine atomization includes a resonant cavity, a spherical resonant cavity is arranged inside the resonant cavity, the diameter of the spherical resonant cavity is an integer multiple of half the wavelength of ultrasonic excitation, an opening for ultrasonic excitation input is arranged at the top of the resonant cavity, and an acoustic resonance cavity is arranged at the bottom of the resonant cavity; a liquid supply needle is inserted into the acoustic resonance cavity from the resonant cavity.

[0009] The material of the resonant cavity structure is any one of metal, resin, plastic, quartz, glass, acrylic or nylon.

[0010] The excitation source of the ultrasonic excitation is any one of a piezoelectric ultrasonic transducer, a magnetostrictive transducer, an electrostatic transducer or a mechanical ultrasonic transducer.

[0011] The frequency range of ultrasonic excitation can be 0-2 MHz.

[0012] The top opening of the resonant cavity is circular or polygonal.

[0013] A fine atomization glue coating method uses a fine atomization glue coating device, which includes an ultrasonic driving device, an ultrasonic excitation device, an acoustic wave focusing device, a liquid supply device and a motion device;

[0014] The ultrasonic driving device is used to drive the ultrasonic excitation device to generate high-frequency ultrasonic vibration in the longitudinal direction;

[0015] The ultrasonic excitation device includes a transducer, a horn and a tool head;

[0016] The sound wave focusing device includes a spherical resonant cavity and an acoustic resonant cavity, and is used to form a stable standing wave field in the acoustic resonant cavity through the reflection of the sound wave by the spherical resonant cavity;

[0017] The liquid supply device is used to deliver the photoresist droplets to the position of the standing wave node in the acoustic resonant cavity;

[0018] The motion device is used to drive the fine atomization glue coating device to complete the scanning of the entire wafer;

[0019] The use of the fine atomization glue coating device includes the following steps:

[0020] Step 1: Fix the ultrasonic excitation device on the acoustic wave focusing device so that the two are coaxial in the vertical direction, and insert the tool head of the ultrasonic excitation device into the spherical resonant cavity of the acoustic wave focusing device;

[0021] Step 2: Adjust the distance between the tool head and the bottom of the spherical resonant cavity to an integer multiple of the ultrasonic half wavelength;

[0022] Step 3: Fix the needle of the liquid supply device at the position of the standing wave node of the acoustic resonant cavity, and the photoresist solution flows out of the needle to form droplets at the position of the standing wave node;

[0023] Step 4: The ultrasonic driving device drives the ultrasonic excitation device, and the ultrasonic excitation device generates ultrasonic waves that propagate through the tool head into the spherical resonant cavity, forming a stable standing wave in the spherical resonant cavity;

[0024] Step 5: Use a motion device to drive the scanning of the entire wafer in the X and Y axis directions.

[0025] The liquid supply device is provided with a flow control pump for controlling the flow rate of the photoresist.

[0026] The fine atomization gluing method includes the following steps:

[0027] Preparation stage: Fix the acoustic wave focusing device on the motion device, adjust the relative positions of the ultrasonic excitation device, spherical resonant cavity, acoustic resonant cavity and liquid supply needle, inject photoresist into the acoustic resonant cavity, and preset the spraying parameters;

[0028] Atomization stage: The ultrasonic excitation device is activated, generating high-frequency vibrations to produce stable standing waves in the spherical resonant cavity. The acoustic resonant cavity focuses and enhances the acoustic waves, atomizing the photoresist droplets located at the nodes of the standing waves into tiny droplets.

[0029] Spraying stage: The motion device adjusts the movement speed and step distance of the X and Y axes through the host computer to scan the entire wafer to ensure the uniformity of the coating and the consistency of the film thickness;

[0030] Drying stage: After spraying is completed, ultraviolet light is used to quickly cure the photoresist, shortening the drying time and improving production efficiency;

[0031] Maintenance phase: Clean the acoustic wave focusing device and ensure that there is no photoresist residue on the acoustic wave focusing device.

[0032] The beneficial effects of the present invention are:

[0033] 1. The present invention discloses a resonant cavity structure and a gluing method for fine atomization. The resonant cavity structure and the gluing method for fine atomization form a focused standing wave field through the curved surface structure of the resonant cavity, thereby enhancing the focusing of the sound wave energy. Compared with the traditional contact ultrasonic atomization method, smaller particle size and more concentrated particle size distribution can be achieved.

[0034] 2. This invention discloses a fine atomization resonant cavity structure and coating method. By regulating the spraying process parameters, this resonant cavity structure and coating method significantly improve the uniformity of the photoresist film thickness, effectively increasing the yield of the subsequent exposure process. Especially when dealing with MEMS wafers with high aspect ratio structures, smaller droplet size is a prerequisite for conformal coating within TSV holes.

[0035] 3. The present invention discloses a resonant cavity structure and a gluing method for fine atomization. The resonant cavity structure and the gluing method for fine atomization utilize the non-contact propagation characteristics of sound waves and realize the regulation of the sound field by optimizing the resonant cavity structure for fine atomization. The photoresist droplets realize non-contact atomization by absorbing ultrasonic energy. Compared with contact ultrasonic atomization, microchannels are not required to supply liquid to the atomization surface, which effectively avoids the problem of nozzle clogging.

[0036] 4. The present invention discloses a resonant cavity structure for fine atomization and a gluing method. The resonant cavity structure for fine atomization and the gluing method have a simple structural design, are easy to clean and maintain, and reduce the maintenance cost of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] By reading the detailed description of the preferred embodiment below, the solutions and advantages of the present application will become clear to those skilled in the art. The accompanying drawings are only for illustrating the preferred embodiment and are not to be considered as limiting the present invention.

[0038] In the attached figure:

[0039] Figure 1 This is a schematic diagram of a resonant cavity structure for fine atomization according to an embodiment of the present invention;

[0040] Figure 2 The sound field distribution in the acoustic resonant cavity of a fine atomization resonant cavity structure according to an embodiment of the present invention;

[0041] Figure 3 The relationship between the diameter, length and sound pressure of the acoustic resonance cavity of a fine atomization resonance cavity structure according to an embodiment of the present invention;

[0042] Figure 4 The standing wave sound field particle velocity and sound pressure curve of a fine atomization resonant cavity structure according to an embodiment of the present invention;

[0043] The components represented by the reference numerals in the figure are:

[0044] The present invention comprises: 1. a horn, 2. a tool head, 3. a spherical resonant cavity, 4. a liquid supply needle, 5. an acoustic resonant cavity, and 6. a photoresist droplet. DETAILED DESCRIPTION

[0045] The fine atomization glue coating device includes an ultrasonic drive unit, an ultrasonic excitation unit, an acoustic wave focusing unit, a liquid supply unit, and a motion unit. The ultrasonic drive unit primarily comprises a signal generator and a power amplifier. The ultrasonic excitation unit includes a transducer, a horn, and a tool head. The acoustic wave focusing unit includes an acoustic resonator. The liquid supply unit primarily comprises a flow pump, piping, a liquid supply needle, and fluid connectors. The motion unit includes a servo unit, a grating, a lead screw, and a controller.

[0046] like Figure 1 As shown, there is no requirement for the external shape of the acoustic wave focusing device (resonant cavity structure for fine atomization), the internal structure of the cavity is spherical, the spherical diameter is an integer multiple of half the wavelength of the ultrasonic excitation, an opening is left at the top of the resonant cavity structure for fine atomization for ultrasonic excitation input, and the acoustic resonance cavity is arranged at the bottom of the resonant cavity structure for fine atomization.

[0047] The materials of the resonant cavity structure for fine atomization include but are not limited to metal, resin, plastic, quartz, glass, acrylic, nylon and the like.

[0048] The excitation source for generating ultrasonic excitation includes but is not limited to a piezoelectric ultrasonic transducer, a magnetostrictive transducer, an electrostatic transducer or a mechanical ultrasonic transducer.

[0049] The frequency range of ultrasonic excitation can be 0-2 MHz.

[0050] The opening at the top of the resonant cavity structure for fine atomization includes, but is not limited to, polygons such as circle, triangle, quadrilateral, pentagon, and hexagon.

[0051] The acoustic resonance cavity includes, but is not limited to, a spherical, ellipsoidal, cylindrical, prismatic, and the like.

[0052] A photoresist spraying method for a finely atomized resonant cavity structure comprises the following steps:

[0053] Preparation stage: Fix the fine atomization resonant cavity device on the motion mechanism, adjust the relative positions of the acoustic wave excitation device, resonant cavity structure, acoustic resonant cavity and liquid supply needle, inject photoresist into a specific position in the acoustic resonant cavity, and preset the spraying parameters (such as pressure, substrate temperature, flow rate, spraying speed, step distance, spraying height, photoresist ratio, etc.).

[0054] Atomization stage: Start the ultrasonic excitation device, which generates high-frequency vibrations to produce stable standing waves in the resonant cavity structure of fine atomization. The acoustic resonant cavity focuses and enhances the sound waves, and then atomizes the photoresist droplets located at the standing wave nodes into tiny droplets.

[0055] Spraying stage: The motion device adjusts the movement speed and step distance of the X and Y axes through the host computer to scan the entire wafer to ensure the uniformity of the coating and the consistency of the film thickness.

[0056] Drying stage: After spraying is completed, ultraviolet light is used to quickly cure the photoresist, shortening the drying time and improving production efficiency.

[0057] Maintenance stage: Clean the fine atomization resonant cavity structure and nozzle to ensure that there is no photoresist residue in the fine atomization resonant cavity structure and the acoustic resonant cavity.

[0058] Driven by an ultrasonic drive device, the ultrasonic excitation device generates high-frequency ultrasonic vibrations in the longitudinal direction. The reflection of the sound waves from the spherical resonant cavity creates a stable standing wave field within the acoustic spherical resonant cavity. This patent innovatively incorporates the resonance effect of acoustic waves into non-contact atomization, leveraging the coupling between diffracted waves and waveguide modes within the subwavelength resonator to generate a precisely controlled, highly localized standing wave field. Ultrasonic energy is focused within the acoustic resonant cavity, where kinetic and potential energy are continuously converted between nodes and antinodes. Droplet edges located at the standing nodes generate greater instabilities. Under high ultrasonic energy, droplets are fragmented and atomized in a very short time, resulting in smaller particle size and more concentrated particle size. By optimizing the spraying process (pressure, substrate temperature, flow rate, spray speed, step distance, spray height, photoresist ratio, etc.), the controllability and uniformity of the film thickness are improved, enabling conformal coating of structured wafers.

[0059] The specific implementation steps are as follows:

[0060] Step 1: Fix the ultrasonic excitation device on the spherical resonant cavity, ensuring that the two are coaxial in the vertical direction. The tool head of the ultrasonic excitation device extends into the spherical resonant cavity, and the longitudinal height of the tool head can be adjusted.

[0061] Step 2: Adjust the distance from the tool head to the bottom of the spherical resonant cavity to an integer multiple of the ultrasonic half wavelength.

[0062] Step 3: Fix the liquid supply needle at the position of the standing wave node of the acoustic resonant cavity. The photoresist solution flows out of the needle to form droplets to the position of the standing wave node. The liquid supply needle is connected to an external flow control pump to control the flow rate of the photoresist.

[0063] Step 4: The driver drives the ultrasonic excitation device by adjusting the frequency, phase, waveform, and power of the output signal. The ultrasonic excitation generates ultrasonic waves that propagate through the tool head into the spherical resonant cavity, forming a stable standing wave in the spherical resonant cavity.

[0064] Step 5: Fix the atomization device on the motion device, and use the host computer to adjust the movement speed and step distance of the X and Y axes of the motion device to scan the entire wafer.

[0065] The ultrasonic driving device provides ultrasonic energy input for the ultrasonic excitation device, mainly including a signal generator and a power amplifier, and drives the ultrasonic excitation device by adjusting the frequency, phase, waveform and power of the output signal.

[0066] The ultrasonic excitation device converts alternating electrical signals into acoustic signals within the ultrasonic frequency range, mainly providing ultrasonic energy input for the fine atomization resonant cavity. The ultrasonic excitation device includes but is not limited to a piezoelectric transducer, a magnetostrictive transducer, an electrostatic transducer or a mechanical ultrasonic transducer. In order to improve the acoustic wave transmission efficiency of the piezoelectric ceramic sheet, the transducer is connected to the lower horn by a thread. The structure of the horn can be a stepped, exponential or composite structure. The length of the horn is usually an integer multiple of half the wavelength of the ultrasonic excitation source. The end of the horn is equipped with a metal block as a tool head, and the ultrasonic wave is transmitted to the acoustic wave focusing device through the tool head. The ultrasonic frequency in the present invention can be 0-2MHz.

[0067] The spherical resonant cavity structure uses the radiating end of the ultrasonic excitation device to generate high-frequency vibrations, forming a sound field in the medium, and placing a reflecting end on the sound wave transmission path so that the reflected sound wave is superimposed on the incident sound wave. The distance between the radiating end face and the reflecting end face is adjusted to an integer multiple of half the wavelength of the ultrasonic wave. The incident wave and the reflected wave are repeatedly superimposed in the sound field space to form a high-intensity spherical standing wave sound field. The particle velocity and sound pressure curves of the standing wave sound field are shown as follows: Figure 2 As shown, the droplets placed in the standing wave acoustic field are subjected to the action of the radiated acoustic pressure, thereby achieving non-contact atomization of the photoresist droplets.

[0068] Compared to conventional contact atomization methods, the atomizing nozzle in this invention does not necessarily need to be made of metal. The spherical resonant cavity can be made of, but is not limited to, metal, resin, plastic, quartz, glass, acrylic, and nylon. To create a higher sound pressure gradient within the spherical resonant cavity, the diameter of the spherical resonant cavity is an integer multiple of half the wavelength.

[0069] The acoustic field distribution of the acoustic resonance cavity is as follows: Figure 3 As shown. The acoustic resonant cavity is fixed at the bottom of the spherical resonant cavity, that is, the antinode of the standing wave in the spherical resonant cavity. The material of the acoustic resonant cavity can be metal, resin, plastic, quartz, glass, acrylic, nylon. The shape of the acoustic resonant cavity can be polygonal, spherical, cylindrical, prism, etc. The relationship between the diameter and length of the acoustic resonant cavity and the sound pressure is as follows Figure 4 shown.

[0070] The liquid supply device primarily provides flow for photoresist atomization. The liquid supply device, which can be a flow pump, is connected via a pipeline to a liquid supply needle in the center of the acoustic resonant cavity. The photoresist liquid flows out from the tip of the liquid supply needle, aiming to match the flow rate of the atomized droplets with the ultrasonic energy of the acoustic cavity. It is worth noting that in the present invention, the needle tip thickness serves only as a liquid supply mechanism under a specific acoustic field intensity. As the acoustic field energy input increases, the nozzle diameter can be expanded to increase the liquid supply flow rate.

[0071] The liquid supply needle is fixed at the position of the standing wave node of the acoustic resonant cavity, and the photoresist solution flows out of the needle to form droplets to the position of the standing wave node. The liquid supply needle is connected to an external flow control pump to control the photoresist flow.

[0072] The motion mechanism described above features a fine atomization resonant cavity vertically fixed to the motion mechanism. The motion mechanism controls the speed and splicing width of the motors on the X and Y axes, scanning the wafer in an S-shaped pattern to ensure complete coverage. During this process, the solvent in the photoresist evaporates, leaving a uniform photoresist film.

[0073] Through the above-mentioned specific implementation methods, the fine atomization resonant cavity structure can be effectively utilized to achieve efficient and uniform photoresist spraying, providing reliable technical support for semiconductor manufacturing.

Claims

1. A resonant cavity structure for fine atomization, characterized in that: The invention comprises a resonant cavity, wherein a spherical resonant cavity (3) is arranged inside the resonant cavity, the diameter of the spherical resonant cavity (3) is an integer multiple of half the wavelength of the ultrasonic excitation, an opening for ultrasonic excitation input is arranged at the top end of the resonant cavity, and an acoustic resonance resonant cavity (5) is arranged at the bottom end of the resonant cavity; a liquid supply needle (4) is inserted from the resonant cavity into the acoustic resonance resonant cavity (5).

2. The resonant cavity structure for fine atomization according to claim 1, characterized in that: The resonant cavity structure is made of any one of metal, resin, plastic, quartz, glass, acrylic or nylon.

3. The resonant cavity structure for fine atomization according to claim 1, characterized in that: The excitation source of the ultrasonic excitation is any one of a piezoelectric ultrasonic transducer, a magnetostrictive transducer, an electrostatic transducer or a mechanical ultrasonic transducer.

4. The resonant cavity structure for fine atomization according to claim 3, characterized in that: The frequency range of the ultrasonic excitation may be 0-2 MHz.

5. The resonant cavity structure for fine atomization according to claim 1, characterized in that: The top opening of the resonant cavity is circular or polygonal.

6. A fine atomization gluing method, characterized in that: Using a fine atomization glue coating device, the fine atomization glue coating device includes an ultrasonic driving device, an ultrasonic excitation device, an acoustic wave focusing device, a liquid supply device and a motion device; The ultrasonic driving device is used to drive the ultrasonic excitation device to generate high-frequency ultrasonic vibration in the longitudinal direction; The ultrasonic excitation device includes a transducer, a horn (1) and a tool head (2); The acoustic wave focusing device comprises a spherical resonant cavity (3) and an acoustic resonant cavity (5), and is used for forming a stable standing wave field in the acoustic resonant cavity (5) through the reflection of the acoustic wave by the spherical resonant cavity (3); The liquid supply device is used to deliver the photoresist droplet (6) to the position of the standing wave node in the acoustic resonance cavity (5); The motion device is used to drive the fine atomization glue coating device to complete the scanning of the entire wafer; The use of the fine atomization glue coating device comprises the following steps: Step 1: Fix the ultrasonic excitation device on the acoustic wave focusing device so that the two are coaxial in the vertical direction, and the tool head (2) of the ultrasonic excitation device extends into the spherical resonant cavity (3) of the acoustic wave focusing device; Step 2: Adjust the distance between the tool head (2) and the bottom of the spherical resonant cavity (3) to an integer multiple of the ultrasonic half wavelength; Step 3: Fix the needle of the liquid supply device at the position of the standing wave node of the acoustic resonance cavity (5), and the photoresist solution flows out of the needle to form droplets at the position of the standing wave node; Step 4: The ultrasonic driving device drives the ultrasonic excitation device, and the ultrasonic excitation device generates ultrasonic waves that propagate through the tool head (2) to the spherical resonant cavity (3), forming a stable standing wave in the spherical resonant cavity (3); Step 5: Use a motion device to drive the scanning of the entire wafer in the X and Y axis directions.

7. A fine atomization gluing method according to claim 6, characterized in that: The liquid supply device is provided with a flow control pump for controlling the flow rate of the photoresist.

8. A fine atomization gluing method according to claim 6, characterized in that: The following steps are involved: Preparation stage: fix the acoustic wave focusing device on the motion device, adjust the relative positions of the ultrasonic excitation device, the spherical resonant cavity (3), the acoustic resonant cavity (5) and the liquid supply needle (4), inject the photoresist into the acoustic resonant cavity (5), and preset the spraying parameters; Atomization stage: the ultrasonic excitation device is activated, and the ultrasonic excitation device generates high-frequency vibration to generate a stable standing wave in the spherical resonant cavity (3). The acoustic resonant cavity (5) focuses and enhances the acoustic wave, and then atomizes the photoresist droplets (6) located at the nodes of the standing wave into tiny droplets; Spraying stage: The motion device adjusts the movement speed and step distance of the X and Y axes through the host computer to scan the entire wafer to ensure the uniformity of the coating and the consistency of the film thickness; Drying stage: After spraying is completed, ultraviolet light is used to quickly cure the photoresist, shortening the drying time and improving production efficiency; Maintenance phase: Clean the acoustic wave focusing device and ensure that there is no photoresist residue on the acoustic wave focusing device.

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