The passive form of 쓰다 is 쓰이다, whose contraction is 씌다. 씌 also appears in 씌우다, which is the causative form of 쓰다.
The 표준 발음법 states that ㅢ following a consonant is pronounced as [ㅣ]. That means 씌 is pronounced as [씨]. But I'm still unsure because the 외래어 표기법 states that both [si] and [ɕi] are to be transcribed to 시.
Is the ㅆ in 씌 palatalized or not? Or in other words, is ㅆ in 씌 [s͈] or [ɕ͈]?