Robben netted from 12 yards in the 27th minute to help Bayern back in the game after conceding two early goals. Although the Bavarians lost the match 2-1, the attacker's goal eventually proved vital as the German giants reached the final after a series of spot kicks.
However, Robben opted not to take a spot kick in the decisive penalty-series as he felt a second attempt from 12 yards is always more difficult, especially against his former team-mate.
"Casillas and I know each other as we've played together for two years. And it's more difficult to take a second spot kick. That's why I didn't take another one."
The Dutchman also took a dig at Franz Beckenbauer after the German legend was critical of him after the winger recently missed from the spot in the Bundesliga title decider against Borussia Dortmund.
"I'd like to hear what mister Beckenbauer has to say now. Whether I've already spoken with him? No, and I don't really feel the need to do so either at the moment," Robben said to NOS.
"It was not the first time that I stood face-to-face with [Iker] Casillas at an important moment. My shot was powerful and accurate enough, though."
Bayern lock horns with Chelsea at the Allianz Arena on May 19 in the final of the Champions League.
