In order to save more data in a limited space of the integrated circuit, the line width is getting smaller and smaller. Currently, the minimum line width is 0.35 .mu.m or 0.25 .mu.m. In the future, the line width may be minimized to 0.18 .mu.m. The smaller the line width, the smaller the space between the metal lines becomes. However, the capacitance between the metals lines will be increased if the space is getting smaller. The large capacitance will decrease the working speed and working efficiency.
The solution of this problem is to develop a new material with a very low dielectric constant. The dielectric material generally used in the case of fabricating the line width of 0.35 .mu.m is SiO.sub.2 and SiOF and the dielectic constant of them is in the range of 3.about.3.7. The polymer/aerogels/air material with a dielectric constant ranged from 1 to 2 is a new dielectric material used in the case of fabricating the line width of 0.25 .mu.m. However, the best dielectric material is air. The dielectric constant of air is almost equal to 1, the minimum dielectric constant. If air is used as the dielectric material, the capacitance between the metal lines can be seriously decreased.
The conventional process for producing a dielectric layer is a spinning spread method as shown in FIG. 1. The present invention provides a method of using air as the inter-metal-dielectric (IMD) material and the semiconductor structure with a dielectric layer can be achieved by this method.