Semiconductor device manufacturing: process – Chemical etching – Combined with coating step
Reexamination Certificate
1999-03-01
2001-07-17
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Chemical etching
Combined with coating step
C438S705000, C438S738000
Reexamination Certificate
active
06261961
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the fabrication of integrated circuits, particularly to the formation of nuclear tracks in a patterned mask layer, and more particularly to the formation of wide tracks (100-200 nm) in nuclear trackable material without causing delamination of the material.
The formation of holes, openings, or passages in dielectric materials has involved directing high-energy charged particles onto the material thereby forming latent nuclear tracks in the dielectric material, followed by etching. The passage of an atomic particle through a dielectric material can result in the creation of a latent nuclear track that extends along a straight line corresponding to the path of the atomic particle. This latent track has a diameter of 5-30 nm with bonding and density different from the non-tracked regions. Various methods for forming tracks in nuclear trackable materials have been developed, as exemplified by U.S. application Ser. No. 08/851,258 filed May 5, 1997, entitled “Vapor Etching of Nuclear Tracks in Dielectric Materials”, and U.S. application Ser. No. 08/847,085 filed May 1, 1997, entitled “Use of a Hard Mask for Formation of Gate Dieclectric Via Nanofilament Field Emission Devices”, each assigned to the same assignee.
Nuclear tracks can be selectively etched in Nuclear trackable materials, such as polycarbonate, exemplified by LEXAN, made by the General Electric Company. In the case of LEXAN, the track is etched with high selectivity, having diameters as small as 30 nm. In order to etch the track wider, on the order of 100-200 nm, which is desirable for field emitter gate structures, the etch becomes nonselective, and the film is eroded away as the track widens. In order to etch the nuclear track wider, an etch is necessary which will not attack the interface between the LEXAN and the gate metal, so as to prevent delamination of the LEXAN film.
Nuclear tracks in LEXAN are conventionally etched using a KOH or NaOH chemistry. These solutions will also readily etch many metal oxides, including Mo-oxide and W-oxide, which form on the surface of metal exposed to air. As a result, the LEXAN-metal interface is etched somewhat selectively, with the result being delamination of the LEXAN film prior to etching to the required diameter.
The present invention provides a solution to widening the tracks in dielectric materials, particularly LEXAN, to >200 nm without delamination of the film. The invention utilizes an adhesion film which allows the track to be sufficiently widened. The adhesion film is composed of a metal having an inert oxide, or a dielectric having a stable surface. The adhesion film is deposited on top of the gate metal layer or film, or if the properties of the gate metal layer are adequate (have an inert oxide) the gate metal will function as to adhesion film to enable the tracks to be etched to the required diameter without delamination problems.
SUMMARY OF THE INVENTION
It is an object of the present invention to enable widening of tracks in nuclear trackable materials without causing delamination of the materials.
A further object of the invention is to provide a method for forming 100-200 nm openings in polycarbonate materials without causing delamination of the materials.
A further object of the invention is to enable selective etching of a nuclear trackable material to widths of >200 nm without an etchant attack of the interface between the material and an adjacent metal layer.
Another object of the invention is to provide a method for selective etching of nuclear trackable material using an adhesion layer composed of a metal having an inert oxide or a dielectric having a stable surface.
Another object of the invention is to utilize an adhesion film intermediate a nuclear trackable material and a gate metal, which allows tracks in the material to be sufficiently widened to >200 nm without delamination of the material at the interface with the gate metal.
Another object of the invention is to enable widening of tracks in nuclear trackable material without delamination of the material, by utilizing an adhesion film intermediate the material and a metal layer or forming the metal layer of a metal having an oxide inert to an etchant used to widen the tracks.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention involves preventing delamination of nuclearly trackable material deposited on a metal during etching to widen tracks in the material. The invention involves a method to enable etching of nuclear tracks in polycarbonate and other nuclear trackable materials without delamination of the materials at the interface with a metal layer.
The invention utilizes an adhesion layer intermediate the metal layer and the nuclear trackable materials, or the use of a metal in the metal layer which has an inert oxide to the etchant being used to widen tracks in the materials. The adhesion layer may be composed of a metal having an inert oxide or a dielectric having a stable surface not effected by the etchant used to widen the tracks in the nuclear trackable material.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated into and form a part of the disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1
is a cross-sectional view of an embodiment utilizing an adhesion layer for widening tracks in nuclear trackable material in accordance with the present invention.
FIG. 2
is a cross-sectional view of another embodiment utilizing a base metal layer which has an oxide inert to the LEXAN etching solution, and with a gate metal deposited after the nanofilament has been deposited in openings in the LEXAN.
FIG. 3
is a cross-sectional view wherein the adhesion layer is deposited on top of the gate metal layer.
FIG. 4
illustrates in cross-section an embodiment wherein an adhesion layer of Cr, for example, is deposited on a layer of Mo, for example, which is deposited on a layer of dielectric material, such as SiO
2
and the adhesion layer functions as a pattern transfer film.
REFERENCES:
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patent: 4559096 (1985-12-01), Friedman et al.
patent: 4713260 (1987-12-01), Roberts et al.
patent: 4732646 (1988-03-01), Elsner et al.
patent: 5356511 (1994-10-01), Hoessel et al.
patent: 5665421 (1997-09-01), Bergeron et al.
patent: 5801477 (1998-09-01), Macaulay
Contolini Robert J.
Morse Jeffrey D.
Carnahan L. E.
Dang Phuc T.
Nelms David
The Regents of the University of California
Thompson Alan H.
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