PowerPoint process is not quit, after end PowerPoint application!?

Greeting experts,

I have a VB.NET Office AddIn and I create a Powerpoint application:

        Dim PPAnw As Microsoft.Office.Interop.PowerPoint.Application
        PPAnw = CreateObject("PowerPoint.Application")
        PPAnw.Visible = Microsoft.Office.Core.MsoTriState.msoTrue

        .......And then I create many shapes in the Slide.

The program in the AddIn is finish and the Powerpoint is open. The user can edit the Slide, store and close PowerPoint.

If the user close Powerpoint, the powerpoint process in the task manager is not cancled.

Only I close my AddIn, then the Powerpoint process is also cleared.

How can I cleard the powerpoint process, after that the user manually closed the PP application?

Regards

  Michael