What’s actually happening is that it’s finding the term in the URL. There are two things you can do, and you’ll probably want to do both.
First off, Google sees a period as a word separator, so you’ll want to put “asp.net” in quotation marks so it will know it’s just one term. Secondly, you’ll want to shut off looking in the URL, which can be done by adding "allintext: " to the beginning of your search.
Thus, the full search terms for what you want to do are: allintext: read excel file in “asp.net” C#. I got a good response on the first listing.
EDIT: For more information about Google search operators, try this site.