Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
1998-12-10
2001-03-20
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S021000, C134S028000, C134S033000
Reexamination Certificate
active
06203625
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the cleaning of a semiconductor wafer and more specifically the cleaning of a semiconductor wafer exhibiting, after plasma etching, traces of a residual polymer especially containing aluminum.
2. Discussion of the Related Art
The manufacturing of integrated circuits from silicon wafers requires many steps of etching and implantation of various materials according to some predetermined patterns. A specific step consists of creating, on a silicon oxide surface, patterns formed of aluminum. Silicon oxide is conventionally boron and phosphorus-doped (BPSG). During this step, a uniform aluminum layer is deposited over the entire surface of the silicon oxide, then this aluminum layer is covered with a uniform resist layer on which are formed, by a conventional photolithographic etching method, the patterns that are desired to be reproduced on the aluminum.
The wafer is then submitted to a plasma etching which will etch the aluminum anisotropically in a direction substantially perpendicular to the wafer surface and form the desired patterns in the aluminum. This plasma etching operation consists of digging vertical holes of various cross-sections in the aluminum. At the end of the etching, it can be seen that a thin film especially formed of a polymer including aluminum, boron, chlorine, and carbon, has been deposited on the substantially vertical walls of the hole.
This conductive film is a source of defects and it is desired to eliminate it.
A conventional method to remove the polymer film consists of cleaning the surface of the silicon wafer with a specific solvent, available under denomination EKC.265. This solution has several disadvantages. A cleaning operation using this solvent is relatively long, which represents a significant cost. The solvent used is highly inflammable, and its handling is delicate and costly. Further, the solvent used is likely to harm the environment. It has to be recycled with great precautions, which is long and costly. It is thus desired to avoid using this solvent.
Another cleaning method consists of submitting the wafer to a corrosive atmosphere composed of hydrofluoric acid in gas form and of water vapor for a given time, then rinsing the wafer with water. A disadvantage of this method is that the corrosive atmosphere used to remove the polymer strongly etches the silicon oxide layer located under the aluminum. As a result, the height between the upper surface of the aluminum layer and the upper surface of the oxide layer increases, and the oxide layer may be pierced. Even in the absence of such a piercing, the above-mentioned height increase corresponds to a step height increase for the following layers to be formed, which can create difficulties in following manufacturing steps, for example, during the planarization of a subsequently deposited dielectric layer.
SUMMARY OF THE INVENTION
The present invention provides a method enabling, in an economic, rapid, and reliable manner, removal of the residual polymer film.
The present invention also provides a method of cleaning the residual polymer which does not use any solvent.
The present invention provides a method of cleaning a semiconductor wafer covered with silicon oxide, topped with an aluminum layer in which patterns are formed by plasma etching of the aluminum, this etching causing the formation of a polymer containing, in particular, aluminum and carbon on the substantially vertical walls of the patterns, including rotating the wafer in its plane around its axis, in an enclosure under a controlled atmosphere, at ambient temperature, including the following steps:
rotating the wafer at a speed between 500 and 2000 rpm in an enclosure filled with nitrogen;
sprinkling the wafer with water, substantially at the center of the wafer;
introducing hydrofluoric acid during a determined cleaning time, while maintaining the sprinkling; and
rinsing the wafer by continuing the sprinkling to remove any trace of hydrofluoric acid from the wafer, at the end of the cleaning time.
According to an embodiment of the present invention, the hydrofluoric acid is introduced in the enclosure under a pressure close to the atmospheric pressure at a flow rate substantially equal to 20 cm
3
per minute.
According to an embodiment of the present invention, the cleaning duration is comprised between 10 and 100 seconds.
According to an embodiment of the present invention, the water is a deionized water and the water is supplied at a rate of approximately 430 cm
3
per minute.
According to an embodiment of the present invention, the temperature of the enclosure is substantially 30° C.
According to an embodiment of the present invention, the silicon oxide is boron and phosphorus doped and forms a borophosphosilicate.
The foregoing objects, features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with
FIG. 1
, which shows an example of a device enabling to implement the present invention.
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French Search Report from French Patent Application 97 16041, filed Dec. 12, 1997.
Derie Michel
Severac Didier
Galanthay Theodore E.
Gulakowski Randy
Morris James H.
STMicroelectronics S.A.
Wolf Greenfield & Sacks P.C.
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