At present, the upgrading of traditional industries has become the country's strategic decision-making, governments at all levels have been introduced, or is about to introduce a variety of funding policies. In this environment, the site will continue to launch a series of vacuum application equipment upgrade program for the user's reference. This paper focuses on the new ways and strategies for the upgrading of magnetron sputtering and cathodic arc coating equipment.
In the vacuum coating equipment, the background vacuum and the rate of deflation is the two most important concepts of quality. The background of the vacuum is intuitive, easy to measure, plus historical reasons, users have been accustomed to it and the quality of the vacuum equivalent. In fact, the background vacuum reflects the idea, the vacuum chamber is the essence of the vacuum quality. In many occasions, the end of the vacuum will mislead the user, resulting in improper use of pumping process, reduce product quality and a series of problems.
It is well known that vacuum coating can be roughly divided into two categories: high vacuum coating (such as evaporation coating) and vacuum coating in the working gas environment (such as magnetron sputtering and cathodic arc coating).
The former, and the bottom of the vacuum coating environment is basically the same, characterized by the base pressure for the vacuum quality is no problem, but this kind of coating equipment, usually a large volume (about a few meters 3), the main pump is widely used in tens of thousands of L/s pumping speed of oil diffusion pump, the main problem is high energy consumption and serious pollution of oil vapor two problems, the corresponding countermeasures will be discussed in another paper.
The latter, coating the base pressure higher than the pressure of tens to hundreds of times, vacuum coated with the base vacuum differ greatly, in the selection of vacuum pump and pumping process, often produce errors and misunderstandings, the focus will be discussed in this article.
Before the discussion, the first clear the following basic issues:
1 the pressure of the vacuum chamber Q is proportional to the amount of S in the vacuum chamber, and is inversely proportional to the actual pumping speed of the vacuum pump working condition, that is, P.
Q/ S P= 1
2 coating stage of active gas pressure (mainly water vapor) is the key to influence the quality of coating, coating equipment is the vacuum quality of the substantive indicators.
3 for the vacuum chamber without carefully baking, often exposed to the atmosphere, the pressure in the bottom of the active gas accounted for more than 90%.
The measured results show that the bottom pressure, pumping gas for half an hour, about 90% of water vapor, pumping 1 hours, about 95% of water vapor, therefore, the coating chamber (including the workpiece) release of the gas can be considered all active gas.
4 essence is to reduce the nature of the coating chamber of the gas rate, the bottom of the fine pumping rate will be brought into the coating phase. It can be a very "puzzling" inference: the effective pumping speed of the vacuum pump 3000L/s, the low smoke to 8 * 10-3 Pa, the vacuum pump drawing quality and the effective pumping speed 1500L/s, the end pumped to 1.6 * 10-2 Pa the same, namely precision pumping stage by vacuum pumping speed the smaller, the base vacuum allows the poor!
The measured results show that: the two kinds of pumps, the same gas rate required to pump the coating chamber to sputter coating, the required time is roughly the same, the latter only increased by 5 minutes. In the reconstruction scheme, the time of the rough pumping phase can be saved 5 minutes, that is, the coating cycle is unchanged.
5 by 1, and the activity of coating gas partial pressure at the bottom of the outgassing rate is proportional to the inverse of the coating and quick pumping stage.
6 for coating stage pumping speed and precision pumping stage the same situations (such as evaporation), by 1 the reactive gas phase coating and partial pressure of drawing the same pressure in the bottom, so the bottom pressure can be used to characterize the quality of vacuum coating equipment.
7 for different occasions in the coating stage, the pressure of the active gas in the coating stage is different from the bottom pressure, that is, the vacuum quality can not be characterized by the background vacuum.
In the 8 stage of magnetron sputtering (usually 0.5Pa), diffusion pump (must be added to the throttle valve) and the pumping speed is only the nominal value of 1/6~1/5, the molecular pump speed for the nominal value of 50~70%, so the coating activity of gas partial pressure were 5~6 times and 1.5~2 times of the bottom pressure. Molecular pump operating under high pressure, but also prone to play a dangerous.
9 inference: the use of coating stage pumping speed large vacuum pump, fine pumping phase of the bottom pressure can be higher, or the pumping speed of the pumping speed can be lower.
Improve. It can be seen that the bottom pressure as a vacuum quality indicator is a big misunderstanding. The reason may be related to the evaporation of coating in the former, magnetron sputtering, and people's habit of thinking.
8 the effective measure to reduce the amount of air in the vacuum chamber is not to increase the pumping speed of the pump, but to extend the pumping time.