The window mirror of the etching equipment is an "optical window" for real-time monitoring and process control in the plasma etching environment. It needs to maintain optical transparency and structural integrity under extreme conditions of strong corrosion, high thermal shock, and particle bombardment, and is a key component to ensure etching accuracy.
1、 Core functions and working environment
The window mirror is installed on the side wall or top of the etching chamber and mainly plays three roles:
1. Optical monitoring channel: allows infrared and ultraviolet spectra (190-1100nm) to penetrate, used for real-time analysis of plasma composition (such as CF ₄ decomposition products) and etching progress, with an error rate of<2%;
2. Chamber sealing barrier: maintains airtightness in a vacuum environment of 10 ⁻ Torr and can withstand dielectric stress under radio frequency electric field (13.56MHz);
3. Corrosion protection layer: resistant to plasma erosion such as Cl ₂ and SF ₆, ensuring a transmittance attenuation of<5% after 1000 etching cycles.
2、 Breakthrough in Material Technology and Performance
1. High purity quartz window mirror
Using synthetic quartz with a hydroxyl content<50ppm (SiO ₂ purity>99.99%), the transmittance is ≥ 90% in the ultraviolet band (193nm). A 100nm thick Al ₂ O Ⅲ protective film was deposited by magnetron sputtering, and its corrosion rate in NF Ⅲ plasma decreased from 0.5 μ m/h to 0.05 μ m/h, making it suitable for aluminum interconnect etching process.
2. Sapphire window mirror
The Mohs hardness of single crystal sapphire (Al ₂ O ∝) reaches level 9 and can withstand the bombardment of high-energy ions (such as Ar ⁺). The surface is subjected to chemical mechanical polishing (CMP) to Ra<0.1nm. In deep ultraviolet (DUV) lithography equipment, a flatness of λ/20 (λ=632.8nm) is achieved to avoid optical distortion.
3. Silicon carbide composite window mirror
SiC thin film (thickness 500 μ m) prepared by chemical vapor deposition (CVD) is composite with quartz substrate, with a thermal conductivity of 170 W/(m · K). In high-temperature etching at 150 ℃, the thermal deformation is less than 1 μ m, making it suitable for stacking etching of 3D NAND (>100 layers).
3、 Manufacturing process and precision control
1. Edge stress relief: By annealing treatment after laser cutting (1100 ℃, 2 hours), the edge stress of the window mirror is controlled at<5MPa to avoid thermal shock cracking;
2. Anti reflective coating: using TiO ₂/SiO ₂ multilayer film system (5-7 layers), with a reflectivity of<0.5% in the 193nm band, improving the signal-to-noise ratio of spectral monitoring;
3. Defect detection: Use laser scattering method to detect surface micro scratches (resolution<0.5 μ m), ensuring that the number of defects per square centimeter is less than 1.
4、 Application challenges in advanced manufacturing processes
In EUV etching equipment, the window mirror needs to meet low absorption in the 13.5nm wavelength band (absorption rate<0.1%). Currently, yttrium doped quartz materials are being developed to suppress the formation of color centers through rare earth ion doping. Under 100keV electron bombardment, the transmittance retention rate is increased to over 95%. Domestic enterprises such as Shanghai Xinao Technology have achieved mass production of 8-inch sapphire window mirrors, replacing imported products in SMIC's 14nm etching equipment with a yield rate of over 98%. Jundro Ceramics, as a manufacturer specializing in precision five axis processing of special ceramics and special glass, is committed to providing high-quality material solutions for semiconductor component manufacturing.
