Accelerated H2O desorption and surface cleaning
Easy removal of organic molecules
In many industrial sectors, e.g. the medical devices sector, the automotive industry, the semiconductor industry, or with the drying of coatings, the surface properties of a component play a crucial role in its applicability. In interfacial engineering the functionalisation and coating of surfaces in vacuum conditions is nowadays at the state of the art and cannot be neglected.
During every evacuation procedure the slow desorption of water films on the surface of the chamber represents a problem. The rate of desorption slows after a few hours of evacuation to a constant. Absorbed water molecules can only be pumped out while in gaseous form. To actively free the water molecules from the surface requires an input of energy to the system sufficient to break the molecular bonds (condensation energy).
Up until now it was normal practise to accelerate the desorption by heating to a temperature of 250°C. The heating procedure provides approximately 1 meV of energy and significantly accelerates the procedure. However, conventional thermal heating can still require several hours or days to achieve a sufficient level of cleaning.
Cold heating of the Vacuum Chamber using VUV
High energy “cold” UV-radiation in the Vacuum-UV (VUV) at 185nm (approximately 6.7 eV), which corresponds to the resonant frequency of H2O, is used to quickly dissolve the molecular bonds on the substrate, after which the free gaseous molecules can be extracted. This process is highly efficient, due to the extremely high photon yield of the sources composed of a special synthetic quartz glass.
Furthermore, it has been demonstrated that the hard UV radiation also dissociates other impurities, such as for example hydrocarbons and other organic compounds, and as such the procedure is suitable for substrate cleaning. If the high power radiation source is used in a normal air or oxygen atmosphere, instead of in vacuum, the dissociation of the oxygen produces ozone.
This side effect can be advantageously used to oxidise the so called fingerprints and residues of cleaning agents, which are otherwise difficult to locate and remove.
Installation and Operation
Due to the advantageous design of the VUV-DTS System the pressure tightness of the system increases with lower levels of pressure. To compensate for the change in position of the cladding tube due to a change in pressure, the headpiece is equipped with calibrated pressure springs, which compensate for changes in length and maintain a constant pressure tightness in the system. The VUV-DTS is mounted using a CF40 flange on the vacuum chamber.
The inerting of the region between the lamp tube of the radiation source and the inner wall of the cladding tube with nitrogen, prevents the undesired formation of ozone in this area, which would otherwise absorb the short wavelength radiation at 185nm.
The quartz glass tube is made of high-purity synthetic quartz and is designed to be particularly thick-walled in order to reduce to a minimum the risk of breakage through any violent damage of the radiation source within the vacuum chamber, and to ensure the vacuum is maintained. Due to the form-fitting design of the head no UV radiation leaves the VUV-DTS head part. The head part is easily removed without much effort. The internal grounding of the system ensures it meets all requirements for the use of high-power radiation sources, which operate with a voltage greater than the Safety Extra Low Voltage (SELV).
The UV-Radiation Source
For use in very small vacuum chambers or machinery, we offer designs, in which „Compact“ sources from natural quartz are used. To ensure optimal desorption and cleaning efficiency, this design should only be used in small systems and low volume laboratory equipment, spanning short distances.
For professional applications the high power-low pressure modules are available, which are equipped with a special high-performance „High Power“ source composed of synthetic quartz glass and boasting the highest efficiency includung long-life technology.
Disadvantages of the heating method
- High energy requirements (cost)
- Substantial time requirement
- High equipment costs, e.g. metal gaskets for flanges, expensive heating jackets, etc.
- All components must be designed to be temperature resistant
Advantages of the VUV-DTS lamps
- Low power consumption and excellent efficiency
- Fast and efficient desorption of water molecules
- Additional dissociation of other contaminants, such as for example hydrocarbons
- Removal of „fingerprints“ by ozonation in an air / oxygen atmosphere possible for cleaning purposes
- Low operating and capital costs
- Lamp life of up to 10,000 hours (HP versions only)
- Suitable for full vacuum
|Description||Lamp type||Nominal Immersion depth||Nominal Lamp power||Art. No. (230V, 50-60 Hz)||Art. No. (115V, 50-60 Hz)|
|VUV-DTS CF40/200-5W||Compact||200 mm [7.87“]||5 Watt||#53211||#53209|
|VUV-DTS CF40/280-10W||Compact||280 mm [11.00“]||10 Watt||#53214||#53208|
|VUV-DTS CF40/280-40W||High Power||280 mm [11.00“]||40 Watt||#53213||#53212|