C# - ServerTags Don't Work In OnClientClick?

<asp:button runat="server" Text="Save as" OnClick="btnSave_click"
OnClientClick="if(!Check('<% # tb.ClientID %>')) return false; return Object();"
CausesValidation="false"></asp:button>
<asp:TextBox runat="server" ID="tb"></asp:TextBox>

Server tags don't work here. I spend a 1-2 hours to find some way to make this work, but i didn't find anything.

Server tags works in:

<OnClientClick="JSFunc();"
<script type="text/javascript">
function JSFunc()
{
var el = document.getElementById('<% # tb.ClientID %>');
//some actions with el here
}
</script>

or something others with c#.

Is There no way to make server tags working inline? (first example)