Agree with 芝達 & WaWaMom. Since your BB is 14months, and can start with him about what's right and what's wrong and 講道理, so you can tell him that screaming is no good and incorrect, and teach him a correct method to catch your attention or tell him the appropriate expression. Then, after a certain period of time, situation will improve.
My son is currently 3year-old, and he used to shout when I talked with others or when he wanted to catch my attention, then when I told him that I'd like him to inform me & count until 10 to draw my attention, and insisted for several weeks, now he will say "mami, I'd like to talk with you" instead of just shouting.