As much as it is important to take a backup of data files, the same is true for the control file, the SPFILE, and the archived redo logs as well. A database won't halt for a lost SPFILE but losing its control file or one or more archived redo logs may prove fatal.
To take a backup of an SPFILE, you can use the command
BACKUP with the option SPFILE. If you have made some significant parameter changes, this is highly recommended. If the database hasn't been shut down, you can even create the SPFILE from the instance using the statement
CREATE SPFILE FROM MEMORY. But if the database has already crashed and you have lost the SPFILE (and the text parameter file) with no backup ...