How to close ASP.net form from server side

I have an ASP.net application. The server side code is in C#. There is a button on the form. When that button is clicked, then a server side code should be executed and then the page should close.

When I write the code to close the page in .aspx file (by handing OnClick event) then the page closes even before the server side code can run.

I want that the server side code (for the button click handler) should first finish and then the page should close.

How to do that? Is there any way I can write code on server sid (in C#) to close the form?

Code:

---

protected void btnClose_Click(object sender, EventArgs e)
{
    Response.Write("<script language='javascript'>window.open('','_self',''); window.close();</script>");
}

---

this will also suppress the "an application is trying to close this window. Do you want to close it?" message.