Difference between a cathode ray tube and a magnetron?

[geobob]

Can someone please explain to me the difference between a cathode ray tube and a magnetron? I just started using a magnetron for sputter deposition in a project for a prof, and after reading about it, it seems to be the same. Just wondering, even though it may be a stupid question!

Thanks!

 

[Gokul43201]

A magnetron sputtering setup is nothing like a CRT. And you do not use a megnetron for magnetron sputtering. The term is used because the set-up is similar to a magnetron.

The idea with conventional sputtering is that you slam a bunch of positive ions (usually Ar+, produced by the ionization of Ar gas) into a target (the Ar+ ions are accelerated by the negative potential on the target) and the collision dislodges surface atoms, which fly off and (some of them) get deposited on the substrate. Now a side-effect of the collisions is the production of secondary electrons which shoot out of the target and fly off. . Some of these secondary electrons run into Ar atoms and help ionize them. The more Ar+ ions, the better the sputtering efficiency, so this side-effect is a good thing. But along that reasoning, one might just suggest that you simply increase the Ar pressure if you want more ions, but that is not a good idea. You need very low pressure to have essentially ballistic transport of the sputtered atoms to the substrate, if you want any kind of sputtering uniformity. So, since the secondary electrons are a good thing to have around for as long as possible, a permanent magnet is used (and hence the name 'magnetron sputtering') to make the path of the electrons a spiral (rather than a straight line). By increasing the path length you increase the probability that the electron with ionize an Ar atom, and hence achieve a greater number of ions at the same pressure. Alternatively you can achieve the same sputtering rate as a conventional sputtering arragement at a much lower pressure.