Diazonaphthoquinone

Diazonaphthoquinone refers to a class of photoactive compounds historically used in positive-tone photoresists, most commonly as diazonaphthoquinone sulfonate esters (DNQ–SO3R) derived from naphthol derivatives. In resist formulations, DNQ sulfonate esters are combined with a phenolic resin such as a novolak to form a chemically amplified system where the DNQ group acts as the light-sensitive component.

Mechanism and function: Upon exposure to ultraviolet light, the diazonaphthoquinone sulfonate undergoes photolytic cleavage to yield a napthoquinone and release the sulfonate leaving group. This chemical change converts the protected (less soluble) phenolic sites on the resin into free phenols, increasing the region’s solubility in alkaline developers. Thus, the exposed areas dissolve away, creating a positive-tone pattern. The efficiency and wavelength sensitivity depend on the DNQ chromophore and the resin, and the system can be integrated into chemically amplified resists to achieve higher sensitivity.

Applications and history: DNQ-based resists were central to early optical lithography and were widely used with novolak resins for i-line (around 365 nm) and deep-UV processes. They helped establish a paradigm for chemically amplified photoresists, although newer chemistries have largely replaced DNQ resists in many applications. DNQ formulations remain a classic example of a positive-resist mechanism.

Synthesis and properties: The active DNQ component is typically prepared as a sulfonate ester of a diazonaphthoquinone, for example a DNQ–tosylate or DNQ–sulfonate. These compounds are photosensitive but can be unstable and require careful handling. In modern contexts, DNQ-based resists are largely of historical and instructional interest, illustrating the principles of light-induced deprotection in positive photoresist technology.