Semiconductors are widely used in integrated circuits for electronic devices such as computers and televisions. These integrated circuits typically combine many transistors on a single crystal silicon chip to perform complex functions and store data. The need to integrate more functions and more storage capacity onto a chip has caused the semiconductor industry to search for ways to shrink, or scale, the size of individual transistors and other devices commonly integrated on a chip. However, scaling devices to smaller dimensions can create a multitude of undesirable effects. One of these effects is an increase in the capacitive coupling between conductors in a circuit, since the capacitive coupling is inversely proportional to the distance between the conductors. This coupling may limit the ultimate speed of the device or otherwise inhibit proper device operation, if steps are not taken to reduce the coupling.
The capacitance between conductors is also highly dependent on the insulator, or dielectric, used to separate them. Conventional semiconductor fabrication commonly employs silicon dioxide as a dielectric, which has a dielectric constant of about 3.9. The lowest possible dielectric constant, 1.0, is the dielectric constant of a vacuum. By substituting a partial vacuum for a silicon dioxide dielectric between conductors, capacitive coupling would be reduced by a rough factor of 3.9, as one example.
Others have devised methods for creating partial vacuum dielectrics on semiconductor devices to reduce capacitive coupling. One method in particular (U.S. Pat. No. 4,987,101) comprises depositing a temporary dielectric layer of a material such as poly-para-xylylene between conductors, capping the structure with a layer of oxide, etching holes through the cap layer, selectively removing the temporary dielectric layer, and patching the holes. This method is rather complex and requires a large number of processing steps to create partial vacuum dielectrics. The process may also adversely affect the structural strength and heat transfer capability of the device.