Avoid Memory Issues while storing millions of rows in C# DataTable

Hi,

I have a windows application that processes around 500k documents in a directory, while storing some information in a two local DataTables, which will be used later in the application.
This works fine for small input, something like 100k documents. But, the application is eating up all the memory when each DataTable has to store more than million rows.

So, kindly let me know if there is any better structure than datatable in .NET, that will be able to store huge data with rows and columns.
Any help, ideas, suggestions in this regard will be greatly appreciated.

Thanks,
Jayanthi