Asked if the victory at Wembley was down to Arsenal's mental strength, the German international told ITV Sport: "Yeah, I think so because of the second half.
"First half we were a bit timid, couldn't get through enough, but second half I think we hit the post twice and had a couple of good chances so it was a good comeback.
"I think we have great character. A lot of people have questioned that recently but our comeback today, we proved a lot. Now we want to win it."
Arsenal will face either Sheffield United or Hull City in the final, with the pair meeting tomorrow.