Hi andrea93,
Whenever a new file is started a temporary file is created. The temporary file most of the time appears when there is an issue with a previously saved version of the file. Power failure, system crash or a human failure causes that file to be present. You might have noticed sometimes when you open Excel it asks which copy needs to be Recovered.
Are you making sure the Excel instance, either opened through BP or otherwise, is properly handled/closed.
See to it that you are not abruptly ending any Excel instance without properly running till the end ofthe process although it sometimes does get closed when clicked on the Reset button but it is preferable not to run the process halfway that opens Excel instances.