Why is Molybdenum Gasket for Coating High-Temp Sealing?
The pain points of the working conditions of the vacuum coating industry: why are there strict requirements for gaskets?
Magnetron sputtering and electron beam evaporation are the core processes of semiconductor wafer coating, optical lens coating, and photovoltaic glass coating. There are three core pain points in their production conditions, and conventional gaskets cannot adapt at all. This is also the industry's special requirements for sealing components. Reasons for requirements:
High vacuum requirements: The process needs to maintain an ultra-high vacuum environment of 10 ³ ~ 10 ₹ Pa. If the gasket has problems with deflation and vacuum leakage, it will cause defects such as pinholes, pits, and decreased adhesion in the coating layer.
High temperature working condition: During the coating process, the target heating and substrate baking temperature can reach 300-800 °C, and some high-end electron beam evaporation processes even exceed 1000 °C. The gasket needs to maintain a stable size at high temperatures, without deformation or softening.
Medium corrosion resistance: Metal vapors such as aluminum, titanium, chromium, and silicon will be produced during coating. At the same time, accompanied by ion bombardment, the gasket must avoid alloying reactions with the coated metal, and cannot be oxidized by ion bombardment to produce impurity particles.
Conventional gaskets (rubber gaskets have a high temperature resistance of < 200 °C, stainless steel gaskets have a large high temperature thermal expansion coefficient, and copper gaskets are easily soaked by coated metal) cannot meet the above requirements at the same time, and the material characteristics of molybdenum just match the working conditions of vacuum coating. Become the best choice for sealing components in this industry.
What are the core technical characteristics of molybdenum gaskets adapting to high-temperature vacuum seals in the vacuum coating industry?
three dimensions
Molybdenum gaskets can accurately solve the pain points of vacuum coating conditions. The core stems from the refractory metal nature of molybdenum, as well as material and processing optimization according to industry needs. Its high-temperature vacuum sealing adaptability is mainly reflected in three dimensions:
Low thermal expansion at high temperature and high dimensional stability to avoid sealing surface failure
The melting point of molybdenum is as high as 2610 °C, there is no softening, no plastic deformation in the coating working condition below 800 °C, and the thermal expansion coefficient is low (5.8 × 10 ± →/°C, 20 ~ 500 °C), which is consistent with the core cavity of vacuum coating equipment The thermal expansion coefficient of body materials (304/316 stainless steel, titanium alloy) is highly matched.
Compared with the core competing stainless steel gaskets, the thermal expansion coefficient of stainless steel is about 17 × 10 °C/°C. Under high temperature, the thermal expansion deformation difference between the cavity and the gasket is large, which will lead to gaps on the sealing surface and cause vacuum leakage; The molybdenum gasket and the cavity expand and contract synchronously, which can always maintain the tight fit of the sealing surface, and avoid the sealing failure caused by thermal deformation from the root.
Low bleeding performance under high purity to ensure an ultra-high vacuum environment
Vacuum coating has extremely high requirements on the bleeding rate of the gasket. If there are pores and impurities inside the gasket, gases such as H ₂ O, CO ₂, and N ₂ will be released at high temperature, destroying the vacuum.
The molybdenum purity of molybdenum gaskets for vacuum coating in the industry must be ≥ 99. 95%, and that of high-end electron beam evaporation coating must be ≥ 99. 99%; The internal porosity of high-purity molybdenum is < 0.01%, and after vacuum annealing treatment (vacuum degree is above 10 ˚ Pa, temperature is 1000 ~ 1200 ℃), the oil, water and internal residual gas adsorbed during the processing process can be removed, so that the molybdenum gasket The total outgassing rate under high temperature vacuum is < 1 × 10 ˚ Pa m ³/s, which fully meets the process requirements of 10 ˚ Pa ultra-high vacuum.
Anti-coating medium, anti-ion bombardment, and avoiding introducing impurities
Molybdenum has excellent chemical stability. In a vacuum and high-temperature environment, it will not alloy with mainstream coating metals such as aluminum, titanium, and chromium, nor will it be soaked by coating metal vapor. At the same time, molybdenum has a strong anti-ion bombardment ability. Under the ion impact of magnetron sputtering, there will be no oxidation debris or shedding particles on the surface, which avoids product defects caused by impurities entering the coating layer.
Conventional stainless steel gaskets are prone to producing oxide particles such as Cr ₂ O ˚, Fe ˚ O ˚ under ion bombardment, which is one of the main causes of pinholes and pits in coating products.
What practical application value can molybdenum gaskets bring to the vacuum coating industry?
Compared with conventional gaskets, molybdenum gaskets can bring significant improvements in production efficiency and product quality in the vacuum coating production line. The core value is reflected in the cost reduction, efficiency increase, and quality improvement of actual production:
Lifting equipment utilization rate: the service life of molybdenum gaskets under working conditions below 800 °C is 5-8 times that of stainless steel gaskets, and 3-5 times that of copper gaskets, which reduces the number of shutdowns and pad changes caused by seal failure. Conventional coating. The production line can reduce the monthly shutdown maintenance time from 8-10h to 1-2h.
Improve the yield rate of coating products: the characteristics of low outgassing and no impurity shedding can reduce the non-good rate of pinholes and pits of coating products by more than 80%, especially suitable for high-end coating fields such as semiconductors and optical lenses.
Reduce comprehensive cost: Although the unit price of molybdenum gaskets is 3 to 5 times higher than that of stainless steel and copper gaskets, the cost savings brought about by the ultra-long service life and improved yield rate are much higher than the initial procurement cost. The cost of consumables can be reduced by about 40%.
How to optimize the application pain points of molybdenum gaskets in the vacuum coating industry?
At present, in the application of molybdenum gaskets in the vacuum coating industry, there is a small pain point of insufficient oxidation resistance at high temperatures above 800 °C. Molybdenum is easy to oxidize to form MoO ㎡ (volatile, will pollute the vacuum cavity) under high temperature air/low vacuum. In response to this problem, the optimization direction in the industry has formed a clear solution, and the core revolves around molybdenum-based composite gaskets:
Surface composite modification: a layer of thin tantalum sheet is composite on the surface of the molybdenum gasket (tantalum has better high-temperature oxidation resistance and chemical stability), which not only retains the low thermal expansion characteristics of molybdenum, but also improves high-temperature oxidation resistance.
Molybdenum alloy gaskets: Mo-Ti-Zr alloy gaskets are used to improve the high-temperature oxidation resistance and strength of the material itself through alloying optimization, and are suitable for ultra-high temperature coating processes above 1000 °C;
Vacuum protection treatment: The molybdenum gasket is treated by vacuum ion plating, and a dense ceramic protective film is formed on the surface to isolate the oxidation reaction at high temperature without affecting the fit of the sealing surface.
NAME
Ava
