Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-02-05
2001-04-10
Kunemund, Robert (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S710000, C438S720000
Reexamination Certificate
active
06214739
ABSTRACT:
BACKGROUND OF INVENTION
1) Field of the Invention
This invention relates generally to fabrication of semiconductor devices and more particularly to a process for etching metal with an in-situ plasma cleaning step.
2) Description of the Prior Art
In semiconductor fabrication, circuit elements or devices are typically connected by patterned metal layers. Metal gates are also increasingly formed from patterned metal layers. The patterned metal layers are typically formed by photolithography and etching. During etching polymers form on the metal sidewalls. The photoresist mask and polymer formations on the metal sidewalls are difficult to remove. When the metal etching source gasses include both CHF
3
and N
2
polymers form easily on the chamber walls as well as the metal sidewalls. Typically multiple wet etching cycles are required to adequately remove the polymers.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering: U.S. patents:
U.S. Pat. No. 5,759,916 (Hsu et al.) discloses a method for forming a void free TiN anti-reflective coating on aluminum containing, conductor layer and patterning using a conventional etching process.
U.S. Pat. No. 5,767,015 (Tabara) discloses a W-plug etch back using SF
6
and N
2
and switching to a chlorinated gas before exposing the Al alloy layer to prevent AlF
3
formation which makes photoresist removal difficult.
U.S. Pat. No. 5,599,742 (Kadomura) discloses a method of coating Al sidewalls with a sulpher nitride to prevent corrosion.
U.S. Pat. No. 5,540,812 (Kadomura) discloses a method of etching an Al layer using a Cl or Br compound followed by an etch using a compound containing S and F to deposit S on Al sidewalls.
U.S. Pat. No. 5,451,293 (Tabara) discloses a method of ashing using O
2
, an H and O containing gas, and a F containing gas to remove resist after etching.
U.S. Pat. No. 5,378,653 (Yanagida) discloses a method of forming an Al-based pattern using a post-etch processing step using CF
4
and O
2
to remove a sidewall protection film.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for metal etching that requires fewer cycles of wet stripping to remove sidewall polymer formation.
It is another object of the present invention to reduce the cycle time for the metal etch stage of manufacturing a semiconductor device.
It is another object of the present invention to reduce chemical consumption during the metal etch stage of manufacturing a semiconductor device.
It is yet another object of the present invention to extend the periodic maintenance schedule for the etch chamber by reducing particle contamination.
To accomplish the above objectives, the present invention provides a method of etching a metal layer on a semiconductor device using an in situ plasma cleaning step following the metal etch. The process begins by forming a metal layer over a semiconductor substrate. A photoresist mask is formed over the metal layer using photolithography. The metal layer is dry etched in a plasma etching chamber to form metal structures with sidewalls. The dry etch causes a reaction which forms polymer formations on the sidewalls of the metal structures. In the key step, the the photoresist mask is partially removed and the polymer formations are softened and partially removed in an in-situ plasma cleaning step using O
2
and SF
6
as source gasses. Polymer formations are also removed from the chamber walls in the in-situ cleaning step. Next, the substrate is removed from the plasma etching chamber and the remaining portion of the photoresist mask is removed. Finally, the remaining portion of the hard polymer formations are removed in a single wet etch cycle.
The present invention provides considerable improvement over the prior art. In conventional metal etching, it is typical to perform two or more cycles of wet stripping. The present invention allows the polymer formations to be removed by a single wet stripping cycle. The elimination of multiple wet strip cycles reduces chemical usage and reduces cycle time. An additional benefit of the present invention is that the in-situ plasma etch removes polymers that have formed on the walls of the etching chamber, thereby extending the periodic maintenance cycle of the etching chamber. Together these benefits provide a more economical process for metal etching.
The present invention achieves these benefits in the context of known process technology. However, a further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings. Additional objects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 5277750 (1994-01-01), Frank
patent: 5378653 (1995-01-01), Yanagida
patent: 5451293 (1995-09-01), Tabara
patent: 5540812 (1996-07-01), Kadomura
patent: 5599742 (1997-02-01), Kadomura
patent: 5647953 (1997-07-01), Williams et al.
patent: 5756400 (1998-05-01), Ye et al.
patent: 5759916 (1998-06-01), Hsu et al.
patent: 5767015 (1998-06-01), Tabara
patent: 5851302 (1998-12-01), Solis
Chen Pei-Hung
Huang Cheng-Hao
Tang Wen-Hsiang
Ackerman Stephen B.
Kunemund Robert
Perez-Ramos Vanessa
Saile George O.
Stoffel William J.
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