Plasma RIE polymer removal

A method for removal of post reactive ion etch by-product from a semiconductor wafer surface or microelectronic composite structure comprising: supplying a reducing gas plasma incorporating a forming gas mixture selected from the group consisting of a mixture of N 2 /H 2 or a mixture of NH 3 /H 2 into a vacuum chamber in which a semiconductor wafer surface or a microelectronic composite structure is supported to form a post-RIE polymer material by-product on the composite structure without significant removal of an organic, low K material which has also been exposed to the reducing gas plasma; and removing the post-RIE polymer material by-product with a wet clean.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing and other objects and advantages of the invention will be better understood by resort to the following detailed description of the preferred embodiments of the invention. In previous processes for post RIE plasma clean solutions, the use of oxidizing chemistries are well known; however, these chemistries cannot be utilized with organic low K dielectrics due to the fact that there is extremely poor selectivity of the polymer strip/clean to the low K dielectric material. On the other hand, when previous approaches to removing RIE fluoropolymer used no post RIE clean, this led to high contact resistance and reliability failures. Or, when wet chemical only clean was utilized to remove RIE fluoropolymer on wafer surfaces deposited during the RIE process, this caused severe contamination of the wet chemical bath due to delamination of the fluoropolymer on the wafer surface. In the context of the invention, with the current trend towards the use of hard mask (silicon dioxide and silicon nitride layers), the use of the reducing gas plasma chemistry following the RIE process enables removal of the post-RIE polymer to be achieved efficiently without significant removal of an organic, low dielectric constant material which is exposed to the gas plasma. In this connection, reference is made to FIG. 1 which depicts a wafer surface comprising metal 10 on which there is an organic low k dielectric material 11 , a silicon nitride layer 12 and a silicon dioxide layer 13 , the latter two of which may constitute hard masks. Following post reactive ion etching, a fluoropolymer layer 14 remains and is in need of removal prior to completion of the process for forming the semiconductor wafer or chip. After the exposure and development of the photo-resist, and the use of RIE to define the metal line, the post RIE fluoropolymer 14 of the composite chip is subjected to a reducing gas plasma that incorporates a forming gas mixture of N 2 /H 2 to completely remove the post-reactive ion etch fluoropolymer by-product from the wafer surface prior to the use of a wet chemical clean. The removal of the post-reactive ion etch fluoropolymer by-product is accomplished without significant removal (<200 &angst;) of the organic, low dielectric constant material 11 , which has also been exposed to the gas plasma of the forming gas mixture of N 2 /H 2 . In a further embodiment of the invention process, the reducing gas plasma incorporates a forming gas mixture of NH 3 /H 2 to completely remove the post-reactive ion etch fluoropolymer by-product from the wafer surface prior to a wet chemical clean. Significantly, this removal is also achieved without significant removal (<200 &angst;) of the organic, low dielectric constant material which has also been exposed to the gas plasma. In the present invention, use of the particular reducing gas plasma incorporating a forming gas mixture of N 2 /H 2 or NH 3 /H 2 is important to have a good process as a post-clean, since removing the fluoropolymer prevents enhancement of corrosion of the metal line; however, the reducing gas plasma incorporating the forming gas mixture of the invention, unlike existing post RIE plasma clean solutions is very selective with respect to removal of the fluoropolymer while only removing an insignificant amount of the organic low k dielectric. Accordingly, the prior art process of not being able to use any post RIE clean (on the basis that it would led to high contact resistance and reliability failures) or the prior art use of a wet chemical clean only that would cause severe contamination of the wet chemical bath from delamination of the fluoropolymer on the wafer surface (deposited during the RIE process) are avoided. While the invention process of utilizing a reducing gas plasma incorporating either a forming gas mixture of N 2 /H 2 or NH 3 /H 2 to completely remove post reactive ion etch polymer by-product from a wafer surface, the invention is equally as useful for particularly removing post reactive ion etch polymer by-product from Via structures prior to a wet chemical clean.