$($a$)$ In a photolithographic process, either a positive or negative photoresist is used to transfer micro$-$ and nanoscale patterns onto a silicon wafer.

$($i$)$ List the three essential components of a photoresist and briefly explain their roles.

$($ii$)$ Describe the major advantages and disadvantages of a positive photoresist as compared to a negative photoresist.

$($iii$)$ During exposure to a UV source, briefly describe the photochemical reaction that occurs in a positive photoresist and name the type of developer that is used.

$(9$ Marks$)$