Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-06-08
2001-11-20
Fourson, George (Department: 2823)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S788000
Reexamination Certificate
active
06319843
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to improved photolithographic methods. In particular, the present invention relates to treating nitride surfaces to prevent poisoning of acid catalyzed photoresists.
BACKGROUND ART
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required.
The requirement of small features (and close spacing between adjacent features) requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, X-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the photomask, for a particular pattern. The lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive of the subject pattern. Exposure of the coating through the photomask causes a chemical transformation in the exposed areas of the coating thereby making the image area either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Projection lithography is a powerful and essential tool for microelectronics processing. Attempts made to improve lithography include advances made in developing new photoresists. For example, so-called deep UV (ultra-violet) photoresists take advantage of improved resolution associated with the relatively short wavelength of light used to expose the deep UV photoresists prior to development. However, some deep UV photoresists are made of acid catalyzed or chemically amplified photoresist materials. This is a concern because problems occur in many instances when using an acid catalyzed photoresist material over a nitride layer.
In particular, acid catalyzed photoresist materials are deleteriously affected or poisoned by nitride layers. Although not completely understood, it is believed that nitrogen atoms from the nitride layer poison a thin portion of the acid catalyzed photoresist material adjacent the nitride layer. More particularly, it is believed that nitrogen atoms at the interface of the nitride layer and the acid catalyzed photoresist act as a Lewis base neutralizing the photogenerated acid preventing chemical change (acid catalysis) within the photoresist following exposure to actinic radiation. Thus, the acid catalyzed photoresist is contaminated as a thin desensitized layer is formed within the photoresist (adjacent the nitride layer) that prevents or deforms subsequent pattern formation of the photoresist.
Referring to
FIG. 1
, the profile of a poorly developed acid catalyzed photoresist
12
is illustrated. The poorly developed photoresist
12
is formed over a silicon nitride layer
10
. This particular poorly developed photoresist
12
exhibits footing, wherein a portion
14
of the developed photoresist is deformed, presumably due to desensitization or acid quenching from the top surface of the silicon nitride layer
10
. It is noted that even poorly developed photoresist
12
is difficult to obtain on the top surface of the silicon nitride layer
10
, as in many instances development is impossible.
Procedures that increase resolution, improved critical dimension control, and provide small conductive features are desired. These procedures include those that enable the use of high resolution acid catalyzed photoresist materials.
SUMMARY OF THE INVENTION
The present invention provides methods of using acid catalyzed photoresist materials. The present invention also provides methods of treating nitride surfaces to prevent poisoning of acid catalyzed photoresists. As a result, the present invention effectively addresses the concerns raised by the trend towards the miniaturization of semiconductor devices by facilitating the use of high resolution acid catalyzed photoresists.
In one embodiment, the present invention relates to a method of minimizing or preventing contamination of an acid catalyzed photoresist when using the acid catalyzed photoresist over a nitride containing film, involving contacting the nitride containing film with an oxidizing plasma comprising from about 1% to about 90% by volume of an oxygen containing gas and from about 10% to about 99% by volume of a forming gas prior to deposition of the acid catalyzed photoresist over the nitride containing film.
In another embodiment, the present invention relates to a method of processing a semiconductor substrate having a nitride containing film over at least a portion thereof, involving the steps of providing the semiconductor substrate having the nitride containing film over at least a portion thereof; contacting the nitride containing film with an oxidizing plasma comprising an oxygen containing gas and a forming gas; and depositing an acid catalyzed photoresist over at least a portion of the nitride containing film.
In yet another embodiment, the present invention relates to a method of forming a crisp, well defined developed photoresist pattern over a nitride containing film using an acid catalyzed photoresist, involving the steps of providing the nitride containing film; contacting the nitride containing film with an oxidizing plasma comprising from about 5% to about 70% by volume of an oxygen containing gas and from about 30% to about 95% by volume of a forming gas comprising hydrogen and nitrogen; depositing the acid catalyzed photoresist over at least a portion of the nitride containing film; irradiating the acid catalyzed photoresist with actinic radiation; and developing the irradiated acid catalyzed photoresist thereby providing the crisp, well defined developed photoresist pattern.
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Advanced Micro Devices
Estrada Michelle
Fourson George
Renner , Otto, Boisselle & Sklar, LLP
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