Servicenow - How to generate custom excel file from script

Question

I'm trying to generate a xls custom file through script and attach it to a record.

It works fine when I use csv extension but when I change into xls or xlsx the file will be corrupted once I downloaded it from attachment.

Is there any way to achieve this through script?

EDIT: This is my sample script when I attach the file to a record:

`

var grRec = new GlideRecord("table"); 
grRec.addQuery("sys_id", sys_id); 
grRec.query(); 
if (grRec.next()) { 
var grAttachment = new GlideSysAttachment(); 
grAttachment.write(grRec, "test.xls", 'application/xls', xlsData); 
}

`