First stop backing up the SQL data files. Unless you are shutting down the SQL Server first, you aren’t doing anything that is usable.
Use the BACKUP DATABASE command to backup the database to disk, then move that backup off to tape. If you need point in time recovery then put the database into full recovery mode, and schedule log backups via the BACKUP LOG command to run through out the day. The log should be backed up how ever often you need to in order to meet your recovery requirements. In other words, if you can only afford to loose 10 minutes of data, then you need to backup the log every 10 minutes.
Make sure that the backups are written to a disk other than the one that the SQL Server data files are on.
Shadow copies aren’t supported with SQL Server as SQL Server never releases the locks on the files.