New contrast enhancement method and its application to positive type electro-deposition resist.

A new contrast enhancement method using the salting out effect has been developed. We have applied this method to the development of a positive type electro-deposition (ED) resist (Sonne EDUV P-100). By designing the resist structure to be suited to the ion strength of its developer, the contrast has been dramatically improved. The dissolution of the unexposed region of this resist is completely inhibited by the salting out effect, while the dissolution of the exposed region and the sensitivity for the UV exposure are being kept high. This resist thus can prevent surface degradation during the development and obtain high durability for the overdevelopment. Otherwise the resist can be removed by dissolution to aqueous alkaline of low ion strength. In the printed circuit board production, very wide process latitude can be obtained for the pattern transfer with this resist.