Creating a temporary file in PHP with a specific name and extension

Question

I'm trying to create an attachment that gets sent via email with PHP and PHPMailer. I'm not having trouble doing that, but I specifically need to create a file with a .ics extension. I basically want the following to happen:

1. Create a temporary file with a specific name, ie. My Date.ics
2. Write a string to that file.
3. Attach the file and send the email.
4. Close the file and delete it (via unlinking it).

Unfortunately, I can't get past step 1. Just doing:

$tmpfname = tempnam(sys_get_temp_dir(), 'My Date.ics');
echo $tmpfname;

Gives me my file name followed by six random characters. For example the above might say something like this:

/tmp/My Date.icsnn8B34

I've also gone into /tmp/ and the files aren't actually being deleted after they are unlinked via unlink($tmpfname);

How can I just get a temporary file with a specific extension?