Vacuum chuck is a core component in semiconductor manufacturing that uses negative pressure adsorption to fix wafers. With its characteristics of "no contact stress and strong adaptability", it plays a key role in photolithography, etching, detection and other processes. Unlike the electric field adsorption principle of electrostatic chuck (ESC), vacuum chuck forms adsorption force through physical negative pressure, especially suitable for fixing ultra-thin wafers (<50 μ m) and sensitive devices.
1、 Core working principle and structural design
The vacuum suction cup is based on the Bernoulli principle, which uses a vacuum pump to extract air from the chamber to form negative pressure (usually<10 ⁻ ³ Torr), creating a pressure difference between the wafer and the suction cup surface to achieve adsorption. Typical structures include:
1. Porous adsorption layer: using 99.9% high-purity alumina ceramic (pore size 2-5 μ m) or silicone rubber (Shore hardness 60A), with a porosity of 15-20%, to ensure uniform distribution of airflow;
2. Vacuum channel network: Micro channels with a diameter of 0.1-0.5mm are formed inside the substrate through laser processing, and millisecond level response for adsorption/release is achieved in conjunction with electromagnetic valves;
3. Edge sealing ring: Made of fluororubber (FKM) or perfluoroether rubber (FFKM), it can maintain sealing performance even at high temperatures of 100 ℃, preventing the infiltration of external gases.
2、 Material technology and performance advantages
1. Ceramic based vacuum suction cup
The thermal conductivity of silicon carbide (SiC) ceramic suction cup reaches 170W/(m · K), and the temperature fluctuation of the wafer can be controlled within ± 0.3 ℃ by backside helium cooling (pressure 50Torr) during the etching process. Its surface is polished with diamond to a roughness Ra<0.5 μ m, combined with a 0.1mm thick porous layer, to achieve a uniform adsorption force error of<5% for a 12 inch wafer, avoiding the risk of cracking caused by stress concentration.
2. Flexible vacuum suction cup
The silicone rubber suction cup coated with polytetrafluoroethylene (PTFE) has a Shore hardness adjustable to 40-80A, suitable for curved surface adsorption of 3D integrated chips. In the flip chip soldering process, the suction cup is controlled by partitioned vacuum (64 independent suction units) and can adapt to three-dimensional devices with a height difference of up to 500 μ m, with an suction force of 0.5-1.0 kg/cm ².
3、 Application challenges in advanced manufacturing processes
With the development of semiconductor devices towards three-dimensional integration, vacuum suction cups are facing two major technological breakthroughs:
1. Nano level surface pollution control: In EUV lithography, the suction cup surface needs to be coated with a 50nm thick Al ₂ O3 protective film to control the residual rate of particles (>0.1 μ m) below 0.01 particles/cm ² and avoid photoresist pollution;
2. Optimization of ultra-thin wafer adsorption: For wafers below 20 μ m, a composite structure of "porous ceramic+elastic film" is adopted, and the interface stress is reduced to 0.05 MPa through pressure assisted adsorption (positive pressure 1-2 bar) to prevent wafer warping (<5 μ m).
4、 Technological Innovation and Localization Progress
The VacuChuck series from AMAT in the United States uses molecular pump direct connection technology to shorten the vacuum response time to 50ms, with a market share of over 70% in 3nm etching equipment. The silicon carbide based vacuum suction cup developed by North Huachuang in China has achieved a uniform adsorption force of ± 3% (international level ± 2%), but there is still room for improvement in the machining accuracy of microchannels (international ± 5 μ m vs domestic ± 10 μ m). With the increasing demand for high-temperature resistant suction cups in third-generation semiconductors, silicon nitride ceramic vacuum suction cups with 1500 ℃ thermal shock resistance are becoming a research and development focus, and are expected to achieve mass production by 2025.
