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Fig. 1: One of the COBRA DS screw vacuum pumps at Inficon AG for maintaining the vacuum in an ALD coating process. Source: Busch Vacuum Solutions.

Latest Screw Vacuum Technology Lends Exceptional Reliability to ALD Coating

Inficon AG

At its plant in Balzers, Liechtenstein, Inficon AG produces measuring instruments and sensors for pressure measurement, as well as components for the high-vacuum range. These contain parts that are coated using the ALD process (atomic layer deposition). The vacuum supply for all ALD coating systems is provided exclusively by COBRA DS screw vacuum pumps from Busch. In terms of reliability and service life, Inficon has had the best experience with these vacuum pumps.

About Inficon AG

Inficon has been using the ALD process for coating its components for many years. They have collected a great deal of experience, mainly in the coating of complex 3D components. Inficon began coating components for customers in 2015. OEM customers from the semiconductor industry are the main customers commissioning Inficon to coat their components, which are then used in their coating chambers and come into contact with different gases. The ALD coating of the components, which are mostly made of aluminum, gives them a high corrosion resistance to the process gases used and the gases used to clean the vacuum chambers. However, customers from the vacuum technology sector and other industries also use ALD coating by Inficon.

The ALD coating process

The ALD process is essentially similar to using chemical vapor deposition (CVD). In CVD, two chemical preliminary stages react in the gas phase and are deposited as a product on a substrate. For ALD, this process is divided into different process steps. One advantage of ALD is that the layer thickness is precisely adhered to at all points of a component according to definition. Repeating the coating process allows for several layers to be built up on top of each other. Inficon usually works with layer thicknesses of 250 to 500 nanometers. The coating can consist of aluminum oxide, silicon dioxide and laminates with thicknesses of a few nanometers. In addition to the massive increase in corrosion resistance, an ALD coating has the additional advantage of being extremely dense, pure and of low surface roughness.

The ALD coating process takes place under vacuum. There is a continuous vacuum of 0.1 millibar in the vacuum chamber. The multi-stage vacuum pumps originally supplied with the coating systems had service lives of less than one year and were therefore not convincing. They also required a lot of nitrogen for flushing. Due to their multi-stage design, the gas flow through these vacuum pumps must be diverted several times, which increases the risk of deposits and makes the flushing process more complex. These multi-stage vacuum pumps were also very loud.

Vacuum solution from Busch

When the new clean room with ALD coating systems was commissioned, Project Manager Philip Spring and CTO Urs Wälchli decided against the multi-stage vacuum pump supplied by the system manufacturer and opted for a COBRA DS 2000 G screw vacuum pump from Busch Vacuum Pumps and Systems.
The COBRA screw vacuum pump had a 50 percent lower nitrogen consumption for flushing the vacuum pump and a significantly lower noise level compared to a multi-stage vacuum pump.
This decision was preceded by intensive consultations with Busch's vacuum experts and two one-day workshops for all Inficon employees involved in the project. One workshop took place directly at Inficon in Balzers. Busch then invited to Ateliers Busch S.A. in Chevenez in the Swiss canton of Jura for a second workshop. Those responsible at Inficon were mainly impressed by the 50 percent lower nitrogen consumption for flushing the vacuum pump and the significantly lower noise level of the COBRA screw vacuum pump compared to a multi-stage vacuum pump. In addition, the vacuum experts at Busch guaranteed those responsible at Inficon a service life of twelve months despite the complex process. This is despite the fact that in daily practice, in addition to conveying various process gases, the penetration of abrasive aluminum oxide and other particles, as well as chlorine and fluorine gases, cannot be completely avoided.

After several months of continuous operation of the first COBRA DS, an inspection was carried out. There were no signs of wear or deposits in the vacuum pump, leading Urs Wälchli and Philip Spring to also equip the other ALD coating systems with COBRA DS screw vacuum pumps. Aluminum oxide dust in the exhaust line, however, confirmed the assumption that, despite an upstream particulate filter, it is impossible to prevent dust particles from being conveyed through the vacuum pump. The COBRA DS owes its high particle tolerance to its specially developed screw profile. The one-piece screw rotors have no undercuts, gaps or deflections in the gas flow that would facilitate dust deposits. Thanks to the latest screw vacuum technology, less nitrogen is required as purge gas. Compared to a multi-stage vacuum pump with a purge gas consumption of 96 slm, a COBRA DS with only 50 slm requires almost half the nitrogen. Maintenance of the COBRA DS is limited to checking the oil level in the gear unit and removing the particles conveyed from the exhaust pipe.
Meanwhile, four ALD coating systems at Inficon in Balzers are each equipped with a COBRA DS 2000 G. Several COBRA DS of the same size were also purchased for ALD coating systems in the Inficon production plants in Taiwan and the USA and are now in operation. Since start-up, all vacuum pumps have been running non-stop around the clock. Eighteen months after start-up of the first COBRA DS, CTO Urs Wälchli is highly satisfied:
The one-year service life promised by Busch was significantly exceeded. This shows that we made the right decision from a technical point of view. And the excellent cooperation between our project team and the vacuum experts at Busch was phenomenal. I have never experienced anything like this in my professional life. The vacuum pumps were installed and have been running day and night ever since. We don't even notice them.
Urs Wälchli, CTO, Inficon AG