Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
2000-08-07
2002-05-14
Cintins, Ivars (Department: 1724)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S003000
Reexamination Certificate
active
06386212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to methods for performing a wet clean of a composite surface, i.e., a surface having at least two materials exposed, where the composite surface is situated on a semiconductor wafer. The methods are particularly useful during the manufacture of a semiconductor device for a post chemical mechanical polishing clean of a surface having an exposed interface of silica and nitride, silica and low &kgr; dielectric, or nitride and low &kgr; dielectric, where &kgr; (lower kappa) is intended to represent the dielectric constant.
2. The Relevant Technology
Wet clean processes used in semiconductor manufacturing are typically applied to surfaces of uniform composition. While the contamination to be removed may of course have a different composition, the surface to be cleaned is itself generally of uniform composition, i.e., all silica, all silicon, all silicon nitride, etc. In certain instances, however, it has become desirable to perform wet cleaning on a composite surface, a surface having at least two different materials exposed, such as at least two of silica, silicon, nitride, low &kgr; dielectric, and other materials used in the formation of semiconductor devices. For example, where chemical mechanical polishing is used to planarize a layer of silica stopping on nitride, both silica and nitride are exposed on the resulting planarized surface. Such composite surfaces are not well cleaned by standard wet cleans. Particulate contamination is especially difficult to remove from composite surfaces with standard wet cleans. Thus, an improved method for wet cleaning composite surfaces is needed.
SUMMARY AND OBJECTS OF THE INVENTION
An object of the present invention is to provide a method for wet cleaning a composite surface.
Another object of the present invention is to provide a method for performing a post chemical mechanical polishing clean of a composite surface.
Yet another object of the present invention is to provide a method for performing a post chemical mechanical polishing wet clean of a composite surface including silica and silicon nitride.
Still a further object of the present invention is to provide a method for performing a wet clean of a composite surface including at least two exposed materials with differing isoelectric points.
Still a further object of the present invention is to provide a method for performing a wet clean of a composite surface, which method substantially reduces particulate contamination.
In accordance with the present invention, a composite surface is cleaned by an HF dip or scrub, followed immediately by a rinse or dip in a low pH surfactant. The dip may also be aided by ultrasonic waves. Preferred low pH surfactants include organic carboxylic acids, currently most preferably citric acid, but additionally pentadecanoic acid or other similar long chain acids. The low pH of the low pH surfactant significantly prevents the formation of a charge differential between portions of the composite surface having different materials exposed, which charge differential would otherwise potentially cause any particles present to remain on one or another portion of the composite surface. The surfactant properties of the selected low pH surfactant help to remove any particles from the surface.
Next follows a dip or scrub in ammonium hydroxide, followed immediately by a dip or scrub in a high pH surfactant. The dip may also be aided by ultrasonic waves. Preferred high pH surfactants include any compounds having a structure including a hydrophobic organic structure with at least one ammonium hydroxide group, currently most preferably tetramethylammoniumhydroxide (TMAH). Following the rinse in the high pH surfactant is a rinse in deionized water. The high pH of the high pH surfactant significantly prevents the formation of a charge differential between portions of the composite surface having different materials exposed, which charge differential would otherwise potentially cause any particles still present to remain on one or another portion of the composite surface. The surfactant properties of the selected high pH surfactant help to remove any particles from the surface. The deionized water rinse then removes the high pH surfactant from the surface, leaving a very clean, low particulate surface on all portions of the composite surface.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.
REFERENCES:
patent: 3597667 (1971-08-01), Horn
patent: 4817652 (1989-04-01), Liu et al.
patent: 5259888 (1993-11-01), McCoy
patent: 5944906 (1999-08-01), Robinson
patent: 6098639 (2000-08-01), Robinson
Cintins Ivars
Workman & Nydegger & Seeley
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