How to call codebehind LinkButton click event from JavaScript in ASP.Net

<script type="text/javascript">
         function KeyPress(e) {
             var evtobj = window.event ? event : e
             //Do action on Alt + A
             if (evtobj.keyCode == 65 && evtobj.altKey) {
                 alert("alt + A Pressed");//Msg Display Properly
                 //document.getElementById('<%= btnSaveBill %>').click()//i want to call btnSaveBill Onclick Event
                 //document.getElementById('ctl00_Content1_btnSaveBill').click();
             }
             //Do action on SHIFT + DELEETE
             if (evtobj.keyCode == 46 && evtobj.shiftKey) {
                 alert("Shift + Delete Pressed");
             }

         }
         document.onkeydown = KeyPress;
    </script>

<div class="col-md-3 col-lg-3">
     <asp:LinkButton ID="btnSaveBill" runat="server" CssClass="form-control  btn btn-success btn-block" OnClick="btnSaveBill_Click"><span class="glyphicon glyphicon-save"></span>&nbsp;Save Bill</asp:LinkButton>
</div>

protected void btnSaveBill_Click(object sender, EventArgs e)
{
    SaveBill();
    lblPopMsg.Text = "Bill Saved !!!";
    mpeMessageAlert.Show();
    GenerateBillNumber();
}