Is there any perfect vocal removal software? Then what is the technique behind that? What are all the methods that already exist in the field?

Sorry I'm not a specialist

Its hard to say sometimes we could remove vocals completely sometimes not. Its hard to do it , because anything associated with that given vocals for example instruments could be ruined or even became asynchronous. Lets take for instance , the stereo recording. You can adjust the singer's voice , the instrument's sound or even add sounds that were not before. Also, the Mp3 vocals , you cannot remove unless you reduces its level from great quality to good quality. 

I believe its hard to say there is and there isn't, because of the low quality that would be gained from such processing.

There are several , ways that we could choose from , and regarding which is best it depends on the type of processing to be done.

1- Removing background noise

2- low frequencies

3- Compressing dynamics  

and the list goes on...