How can I prevent oracle to create minidumps?
Minidump files

The "minidump files" appear to be a Windows OS thing.

https://support.microsoft.com/en-us/help/307973/how-to-configure-system-failure-and-recovery-options-in-windows

But, if you disable them, you will just be hiding the fact that there is a problem.

I would prefer to hunt down the reason why they are being created and fix that problem.

The first thing to do is check which version you are running. For example, version 11.2.0.1 is known to be buggy.  If that is the case, your first step should be upgrading your database.

After that, I would look at the Oracle Alert logs and go from there.

note:  ORA-600/7554 usually means "Call Oracle Support".