Automation client for Microsoft Excel by using C#.
its a very basic requirement in Client side automation for Microsoft Application like
Excel / Word / OutLook / Powerpoint and all.
To Automate Excel application using C# have a look on this Article
Known Issues with Automation
Because the CLR uses a garbage collector for memory management, and because your RCW is itself a managed object, the lifetime of your Automation object is not guaranteed to end.you can get the actual help from here
317109 : Office Application Does Not Quit After Automation from Visual Studio .NET Client