Escape a backslash in Scala [duplicate]

Question

I have two different strings I would like to filter out/set to none:

val str1 = Option("n/a")
val str2 = Option("N\/A")

I tried to achieve this with the following regex, by escaping the backslash character once and then matching it zero or 1 time with '?' character:

val notAvailablePattern = "[Nn]\\?/[Aa]".r

However this returns:

str1.filterNot(_.matches(notAvailablePattern.toString))
str2.filterNot(_.matches(notAvailablePattern.toString))    

Some(n/a) Some(N/A)

But this works for some reason, but I don't understand why?

val notAvailablePattern = "[Nn]\\\\?/[Aa]".r

None None

As far as I can see I'm double escaping the backslash character? While there is only one in my string.