Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Post imaging radiant energy exposure
Reexamination Certificate
1999-03-01
2001-05-15
Wu, Shean C. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Post imaging radiant energy exposure
C430S313000, C427S526000
Reexamination Certificate
active
06232048
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to photoresists used as a mask for etching purposes, and more particularly to a method of preparing reduced photoresist critical dimensions by forming a hardened top photoresist layer and performing an isotropic etch procedure.
2. Background Art
The process of accurately etching patterns has been the subject of significant development, particularly in the field of semiconductor electronics. The degree of circuit miniaturization, affecting a product's size and operational frequency limits for example, depend on the degree of accuracy of etching. The process of etching a pattern involves the use of a mask to selectively allow an etchant to remove the semiconductor or conductive material, as required to form the desired pattern. Typically, a mask is formed by spin coating a layer of liquid photoresist on the material to be etched. The desired pattern on the photoresist is then exposed to a form of radiation, for example, through use of an optical mask and ultraviolet light. The exposed areas of the photoresist are rendered either soluble or insoluble to a developer, depending on whether the resist is a positive or negative type. The soluble portions are then removed, and the remaining photoresist functions as a mask for selectively allowing an etchant to remove underlying material in areas void of photoresist protection.
A particular problem arises when the creation of resist line widths of small dimensions is required. The minimum resist line width that can be formed in a direct application of photoresist and subsequent etch is often not small enough. For example, the formation of transistor gates of length (actually a line width) less than 0.15 microns is very difficult, requiring expensive UV and/or phase shift methods. A simpler technique that is used is called “gate trimming”, wherein after the lithography (photoresist pattern) is formed on the substrate, the resist is etched down so as to narrow the line widths. This technique has severe limitations, as will be explained in reference to
FIGS. 1A and 1B
.
FIG. 1A
shows a cross section of a photoresist line
10
of width “w” and height “h”. In order to further reduce the width “w” prior to performing an operation on a substrate
12
, a selective isotropic etch procedure is performed on the resist
10
. The result is shown in FIG.
1
B. The width “w” has been reduced to “w
1
” at the cost of losing much of the protective height “h” that is reduced to “h
1
”. Since there are limits to the ratio of “h” to “w” in
FIG. 1A
that can be realized, there is a corresponding limit to the width “w
1
” that can be achieved by etching, before the height “h
1
” is too small to provide adequate protection to the underlying area
14
from subsequent processing steps.
From the above discussion, it is apparent that there is a need for an improved method of preparing narrow photoresist line widths.
DISCLOSURE OF THE INVENTION
Briefly, a preferred embodiment of the present invention includes a method of preparing a narrow photoresist line by first forming a resist pattern on a substrate, having a resist line designed to a width “w” in excess of a desired width “w
1
”. The resist is then bombarded with ionized particles in a direction normal to the planar surface of the resist and substrate. The ionic bombardment causes formation of a hardened, “chemically less reactive” skin on the exposed top surface of the photoresist. The resist is then subjected to an isotropic etch procedure. Due to the hardened top surface of the resist, the side walls erode at a faster rate than the top, causing a narrowing of line widths, while retaining a more substantial photoresist thickness than would occur if the top surface had not been hardened in advance of the etch procedure.
An advantage of the present invention is that it provides a method of constructing narrow width lines of greater thickness.
A further advantage of the present invention is that it provides a method of constructing narrow resist lines without the need for a corresponding narrow resist mask line width.
A still further advantage of the present invention is that it provides a lower cost method of preparing high profile, narrow resist lines.
REFERENCES:
patent: 3997367 (1976-12-01), Yau
patent: 4068018 (1978-01-01), Hashimoto et al.
patent: 4599790 (1986-07-01), Kim et al.
patent: 4670090 (1987-06-01), Sheng et al.
patent: 4731339 (1988-03-01), Ryan et al.
patent: 5332653 (1994-07-01), Cullen et al.
patent: 5538833 (1996-07-01), Ferguson et al.
patent: 5688719 (1997-11-01), Tsai et al.
patent: 5876903 (1999-03-01), Ng et al.
Buynoski Matthew S.
Gupta Subhash
Ng Che-Hoo
Pramanick Shekhan
Singh Bhanwar
Advanced Micro Devices
Jaffer David H.
Pillsbury & Winthrop LLP
Wu Shean C.
LandOfFree
Method for preparing narrow photoresist lines does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for preparing narrow photoresist lines, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for preparing narrow photoresist lines will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2565717