A colloid fluid that is obtained by dispersing ultra-fine particles of metals such as gold having particle diameter of 100 nm or less in a fluid such as water or an organic solvent is applied on an electronic circuit board on which fine grooves or holes in μm or sub-μm size are made in advance. The colloid solution is automatically absorbed in the grooves or holes due to the capillary effect (capillary phenomenon). Thereafter, the colloid solution is dried up to condense the ultra-fine metal particles into the holes. Next, by heating the board under the temperature ranging from 50℃ up to 400℃ to be sintered, ultra-fine metal particles in the grooves or holes are fused together to be electrically bonded for integration. After the above-stated processes, the metal wiring is formed so that it is embedded in the grooves or holes of the board.
Conventional mainstream methods for forming wiring are of the dry method, such as metallization, sputter deposition and CVD method. In recent years, wet methods such as electrolytic plating and electroless plating methods are used. However, the dry methods have the problem of higher manufacturing equipment costs. In addition, both of the dry and the wet methods have problems of instability that, for embedding of wiring metal in grooves or holes that have smaller openings compared to depth, air bubbles form in the wiring, and metals may not be fully embedded in the grooves or holes. The instability constitutes an important problem in miniaturization of wiring through higher integration technologies of ultra LSI and other devices.
Our study solves such problems inherent in conventional methods at the time, and we achieved formation of wiring in a hole having the aspect ratio of 3 (depth: 2.1μm; width: 0.7μm) without causing any corrosion on wiring by using a gold-water colloid solution having particle diameter of 8 nm.