Hide sid in webform confirmation page
No you can not ignore the "sid" from submission confirmation page.

Yes you can create a separate thank you page and redirect to that page.

You can install this modules:

->     rules 

->     webform rules

Now add a rule that redirects the user to your URL after a webform submission.



Using hook_form_alter(), and set the override there.

function mymodule_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'my_form') {
     $form['#submit'][] = 'my_submit_handler';
  }
}

function my_submit_handler(&amp;$form, &amp;$form_state) {
  $form_state['redirect'] = 'home';
}




Refer Redirect Drupal Webform Submissions