Microelectronic circuits, as encountered with, for example, wiring boards for plasma displays, wiring boards for liquid-crystal displays, large-scale integrated circuits, thin transistors, semiconductor packages, and so forth, are typically produced through a process known as photolithography that involves the formation of a resist pattern. In photolithography, a conductor pattern is formed on a substrate, for example, as follows. A photosensitive layer disposed on the substrate is first exposed to light, for example, ultraviolet radiation, through a mask film bearing a prescribed pattern. A resist pattern is then formed by development with a developing solution in which the exposed regions and unexposed regions have different solubilities. Then a conductor pattern is formed on the substrate, for example, by a plating step or an etching step, using this resist pattern as a mask.
The development of technology that enables even higher densities for the wiring of electronic circuits is being actively pursued in particular in the surface mounting technology sector, for example, in connection with printed wiring boards, semiconductor packages, and so forth. There is demand in this sector that the conductor pattern constituting the wiring be formed on the scale of 10 μm or less. The photosensitive resin composition used in photolithography must therefore provide resolution on the scale of 10 μm or less.
Ever higher sensitivities are also being required of the photosensitive resin composition. Escalating wiring densities have a tendency to bring out the problem of a voltage drop due to the resistance of the power lines. An effective response to this problem is to thicken the conductor layer that forms the wiring to at least about 10 μm by increasing the film thickness of the resist pattern. Additional increases in sensitivity are then required of the photosensitive resin in order to be able to form the thicker resist patterns at high productivities.
On the other hand, the procedure known as direct imaging exposure, in which the resist pattern is directly imaged without the use of a mask pattern, is receiving attention within the sphere of methods for forming resist patterns. Direct imaging exposure is believed to have the capacity to form resist patterns at high resolutions and high productivities. Moreover, the application of a long-life, high-output gallium nitride-type blue laser light source, i.e., laser light emission at a wavelength of 405 nm, as a practical light source has become more and more possible in recent years. The use of such short wavelength laser light in direct imaging exposure is expected to make possible the formation of high density resist patterns that have heretofore been difficult to produce. A method that applies the Digital Light Processing (DLP) system championed by Texas Instruments has been proposed by Ball Semiconductor Inc., and the practical application of photoexposure devices that use this method has already begun.
Moreover, there have already been a few disclosures with regard to photosensitive resin compositions intended for the formation of resist patterns by direct imaging exposure using a laser, such as the blue laser cited above, as the active light (for example, refer to Japanese Patent Application Laid-open Nos. 2002-296764 and 2004-45596).