Ultrasonic Spraying Photoresist Coating Technology

Ultrasonic Spraying Photoresist Coating Technology: A Revolutionary Solution for High-Precision Coatings in Microelectronics Manufacturing

In the microelectronics manufacturing industry, the quality of the photoresist coating on the substrate surface is a core factor determining the final performance and production yield of devices. This impact is particularly significant for devices with complex microstructures. Traditional spraying processes have consistently struggled to overcome technical challenges in this stage, such as insufficient coating uniformity, severe material loss, and poor coverage of complex morphologies. The advent of ultrasonic spraying photoresist technology provides an efficient and feasible solution to the high-precision coating requirements of MEMS (Micro-Electro-Mechanical Systems) wafers and various irregularly shaped substrates, successfully breaking through the technical barriers of traditional processes.

The outstanding advantages of ultrasonic spraying technology stem from its unique atomization mechanism. This technology utilizes high-frequency ultrasonic vibrations (20kHz-100kHz) acting on the photoresist solution, atomizing the liquid into highly uniform microdroplets without high-pressure impact. The droplet diameter can be precisely controlled within the range of 5μm-50μm. Compared to traditional pressure spraying, this atomization process is gentler, fundamentally avoiding defects such as droplet splashing and coating edge buildup caused by high-pressure spraying. Simultaneously, the atomized droplets possess excellent dispersibility and flowability, and under the guidance of precise airflow, they can spread evenly on the substrate surface. Even when facing micro-grooves, micro-protrusions, or irregular curved surfaces, it can achieve complete, all-around coverage without dead angles, greatly optimizing the coating uniformity of substrates with complex morphologies.

The surface of MEMS wafers typically integrates a massive number of micron- and nanon-scale microstructures, such as trenches and cavities for microsensors and microactuators. Traditional spraying processes, when coating such wafers, are prone to problems such as thinner coatings at the bottom of trenches and excessively thicker coatings at the top of protrusions. This leads to reduced pattern transfer accuracy in subsequent photolithography processes, directly affecting the normal function of the device. Ultrasonic spraying technology, with its finely atomized droplets and precise spray control, can leverage the microstructural characteristics of MEMS wafers. By adjusting the spraying distance (typically controlled between 5cm and 20cm), ultrasonic vibration frequency, and airflow velocity, photoresist droplets can precisely fill the gaps in the microstructure while ensuring the smoothness of the surface coating. Taking the coating of MEMS wafers with microtrench depths of 1μm-5μm as an example, this technology can control the coating thickness deviation inside and outside the trenches to within ±5%, a figure far superior to the ±15% deviation level of traditional processes, laying a solid technological foundation for the high-precision manufacturing of MEMS devices.

Besides MEMS wafers, ultrasonic spraying photoresist technology can also be adapted to substrates of various materials and morphologies, such as ceramics, flexible metals, and glass. Taking flexible metal substrates as an example, their surfaces often exhibit slight wrinkles or bends. Traditional spraying processes are prone to coating breakage and uneven thickness due to substrate morphology variations. Ultrasonic spraying, however, utilizes atomized droplets with excellent adhesion and ductility, adapting to the surface morphology of flexible substrates. Even on substrates with bending angles not exceeding 30°, it maintains coating thickness stability. For substrates with high surface roughness, such as ceramic substrates, this technology, by optimizing atomization parameters, allows photoresist droplets to fully fill the micropores on the substrate surface, forming a continuous, pinhole-free, dense coating, effectively enhancing its insulation and corrosion resistance.

In the field of coating large-size substrates, ultrasonic spraying technology also demonstrates significant advantages, particularly in achieving high-precision coating of 2μm-thick photoresist on 300mm wafers. As the mainstream large-size substrate in semiconductor manufacturing, 300mm wafers have extremely stringent standards for coating uniformity—the coating thickness deviation across the entire wafer must be controlled within ±0.1μm. Exceeding this range will cause differences in the photolithographic pattern between the wafer edges and the center, reducing device consistency. Ultrasonic spraying technology employs a multi-nozzle collaborative operation mode, coupled with a high-precision motion platform with a positioning accuracy of ±1μm, enabling precise, zoned spraying of the 300mm wafer surface. In the preparation of 2μm ultrathin coatings, this technology eliminates pinhole defects caused by excessively thin coatings in traditional processes by precisely controlling the deposition rate of the atomized droplets (adjustable within the range of 0.1μm/s-1μm/s). Simultaneously, it significantly increases material utilization from 30%-40% in traditional spraying to over 70%, effectively reducing manufacturing costs.

Furthermore, ultrasonic photoresist spraying technology also possesses excellent process compatibility and flexible adaptability. For photoresists of varying viscosities, stable atomization can be achieved by adjusting the ultrasonic vibration frequency and liquid supply rate. Furthermore, this technology can seamlessly integrate with automated production lines, enabling real-time monitoring systems to detect coating thickness and uniformity online and dynamically adjust parameters, further improving production efficiency and product yield. In the current industry trend of rapid miniaturization and high integration of microelectronic devices, ultrasonic photoresist spraying technology, with its core advantages in adapting to complex morphologies, precise coating of large sizes, and efficient utilization of raw materials, is gradually becoming a key technology in MEMS manufacturing and coating processes for various substrates, providing strong technical support for the high-quality and sustainable development of the microelectronics industry.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

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