How to send subscribable report in xls format as an attachment in mail?

Hi,

I have created a process which sends an email with report as an attachment. While configuring mail, I have kept the format "mail template, report in attachment" and provided report in report parameter set. But here it is sending an email with report as an attachment in PDF format. I want to send this report in XLS format in email. How can this be achieved? Please guide. Thank you