Selective deposition of thin films by substrate argon ion bombardment

Abstract

As an alternative to normal patterning in sub-micron integrated circuit technology, selective processes have gained in interest. One fairly well known process is the thermally activated decomposition of WF 6 to deposit selectively a thin tungsten film onto silicon areas of patterned wafers. Some problems with the thermal decomposition technique are the need for a specific metal carrying gas and an elevated process temperature. In a series of articles we have presented a completely new process for selective deposition, using high bias sputtering in an argon atmosphere. If the substrate bias is increased to the point where the net deposition rate becomes almost zero, substrate-dependent effects such as different sputtering yields (because of the difference in binding energy to different substrate atoms) and sticking coefficients for different surfaces come into action. On a patterned silicon wafer, it is thus possible to deposit material on silicon areas but not on the oxide (or vice versa), without the use of any photoresist masking. To make the mathematical model describing this selective process more comprehensible, we have developed a graphical method using a nomogram, that simplifies the prediction of selectivity between various materials. To further point out the possibilities of this selective method, results from ion beam selective deposition of platinum onto patterned silicon wafers are also presented.