Process for photoresist rework to avoid sodium incorporation

Details Process for photoresist rework to avoid sodium incorporation Process for photoresist rework to avoid sodium incorporation

1999-09-21

2001-04-17

Le, Hoa Van (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Removal of imaged layers

C430S260000, C438S711000

Reexamination Certificate

active

06218085

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the semiconductor arts. It finds particular application in the control of sodium incorporation during photoresist rework of semiconductor devices, and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to control of sodium incorporation in other applications.
BACKGROUND OF THE INVENTION
Semiconductor integrated circuits typically comprise layers of stacked interconnected metal layers with dielectric materials between them to form a device, such as a transistor. Typically, a plurality of such layers are laid down on a substrate of silicon, or the like. The layers forming the device, including gates, etc., are then covered with a barrier layer, a metal layer, and finally a layer of titanium nitride, which serves as an anti-reflective coating. A pattern of photoresist material is deposited on the titanium nitride layer for providing electrical contacts with the transistor, or other device. Lithographic techniques are used to pattern the photoresist using a photo-sensitive mask.
In the event that the photoresist pattern is unsatisfactory, for example, improperly shaped, the photoresist may be reworked, i.e., removed and a fresh photoresist layer deposited.
Current photoresist rework processes use a solvent/and or an oxygen-containing plasma to remove the photoresist before starting the lithographic sequence again. Typically, the wafer on which the photoresist is deposited is subjected to an oxygen plasma at a temperature of about 250 °C. to strip the photoresist. After, the stripping process, the surface is cleaned with a rework solvent to remove photoresist residues. Commonly used solvents include H
2
SO
4
/H
2
O
2
or solutions commonly known in the trade as EKC-265 (a solution comprising hydroxyl amine, 2-(2-aminoethoxy)ethanol, cathecol, and an alkaline buffer), and ACT-CMI (a solution of dimethylacetamide and diethanolamine).
The high temperatures and oxygen gas used to strip the photoresist tends to cause oxidation of the titanium nitride layer. The TiN reacts with oxygen radicals to form an oxynitride of the general formula TiO
X
N
Y
. The oxidation changes the conductivity of the TiN layer and it becomes more susceptible to contamination by mobile ions during the solvent cleaning step. Mobile ions, such as Na
+
, K
+
Cl
−
, fluoride species, or other ionic inorganic compounds, tend to become incorporated into the solvent over time. If they become absorbed by the titanium nitride layer, the contaminants may travel through the various layers and cause electrical device defects and degradation in the overall performance and yield of the device.
The present invention provides a new and improved method of photoresist rework, which overcomes the above referenced problems, and others.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method for removing a photoresist layer from a substrate is provided. The method includes providing a substrate having an oxidizable layer and a photoresist layer. The layers are located directly or indirectly on a surface of the substrate. The method further includes exposing the substrate to a plasma containing hydrogen and oxygen in an amount effective to substantially strip the photoresist layer.
In accordance with another aspect of the present invention, a method for removing a photoresist layer from a substrate is provided. The method includes providing a substrate having an oxidizable anti-reflective coating and a photoresist layer. The layer and coating are located directly or indirectly on a surface of the substrate. The method further includes exposing the substrate to a plasma containing hydrogen and oxygen in an amount effective to substantially strip the photoresist layer. Further, the method includes exposing the substrate to a plasma formed from a reducing gas that reverses any oxidation of the oxidizable layer which has occurred in the plasma containing hydrogen and oxygen.
One advantage of the present invention is that it reduces contamination of a semiconductor device by mobile ions during photoresist rework.
Another advantage of the present invention is that it enables a relatively rapid photoresist strip without unduly oxidizing the titanium nitride layer.
Another advantage of the present invention is that it prevents degradation of device electrical performance.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.


REFERENCES:
patent: 4414606 (1983-11-01), Cynkar et al.
patent: 4778739 (1988-10-01), Protschka
patent: 5849639 (1998-12-01), Molloy et al.
patent: 6033990 (2000-03-01), Kishimoto et al.
patent: 6114259 (2000-09-01), Sukharev et al.

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