Semiconductor device manufacturing: process – Making passive device – Stacked capacitor
Reexamination Certificate
1999-11-19
2001-05-08
Tsai, H Jey (Department: 2812)
Semiconductor device manufacturing: process
Making passive device
Stacked capacitor
C438S964000
Reexamination Certificate
active
06228740
ABSTRACT:
BACKGROUND OF THE INVENTION
2. The Field of the Invention
The present invention relates to the fabrication of integrated circuits. More particularly, the present invention relates to an anti-reflective enhancement for integrated circuit fabrication. In particular, the present invention relates to an anti-reflective enhancement for reducing critical dimension loss during mask patterning.
3. The Relevant Technology
In the microelectronics industry, a substrate refers to one or more semiconductor layers or structures which includes active or operable portions of semiconductor devices. In the context of this document, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including but not limited to bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term substrate refers to any supporting structure including but not limited to the semiconductive substrates described above.
In the microelectronics industry, the process of miniaturization entails shrinking the size of individual semiconductor devices and crowding more semiconductor devices within a given unit area. With miniaturization, problems arise with proper electrical isolation between components. When miniaturization demands the shrinking of individual devices, isolation structures must also be shrunk. Attempts to isolate components from each other in the prior art are limited to photolithographic limits of about 0.25 microns. One way to form structures that electrically isolate conductive materials on a semiconductor substrate from each other is to use photolithography in patterning dielectrics layers upon the semiconductor substrate.
To form an isolation trench on a semiconductor substrate by photolithography, a photoresist mask through which the isolation trench is etched generally utilizes a beam of light, such as ultraviolet (UV) light and deep UV (DUV) light, to transfer a pattern through an imaging lens from a photolithographic template to a photoresist coating which has been applied to the structural layer being patterned. The pattern of the piotolithographic templat includes opaque and transparent regions with selected shapes that match corresponding openings and intact portions intended to be formed into the photoresist coating. The photolithographic template is conventionally designed by computer assisted drafting and is of a much larger size than the semiconductor wafer on which the photoresist coating is located. Light is directed through the photolithographic template and is focused on the photoresist coating in a manner that reduces the pattern of the photolithographic template to the size of the photolithographic coating and that develops the portions of the photoresist coating that are unmasked and are intended to remain. The undeveloped portions are thereafter easily removed. Other photolithographic techniques for formation of isolation trenches are also possible.
The resolution with which a pattern can be transferred the photoresist coating from the photolithographic template is currently limited in commercial applications to widths of about 0.25 microns. In turn, the dimensions of the openings and intact regions of the photoresist mask, and consequently the dimensions of the shaped structures that are formed with the use of the photoresist mask, are correspondingly limited. Photolithographic resolution limits are thus a barrier to further miniaturization of integrated circuits. Accordingly, a need exists for an improved method of forming isolation trenches that have a size that is reduced from what can be formed with conventional photolithography.
During photolithography, reflected light that occurs during exposure of a mask tends to blur the desired image because the reflected light escapes beyond exposed regions on the photoresist. The blurring problem is caused by reflected light affecting areas of the photoresist that are outside the design pattern.
FIG. 1
illustrates the problem of blurring caused by reflected light that occurs during exposure of a photoresist. A semiconductor structure
10
may be, for example, an isolated active area
8
X that was designed to have a width D, but due to blurring caused by reflectivity of patterning light from structures beneath the photorcsist, isolated active area
8
X has an actual width A. The variance between design width D and actual width A is illustrated as the distance 2(B/2) or B. By way of example, isolated active area
8
X was designed to have a width D of 10 in arbitrary units, but due to blurring caused from reflectivity, the actual width A is nine in arbitrary units. It can be seen that a ten percent variance between design and actual width has occurred.
As miniaturization technology continues, a blurring variance of B as illustrated in
FIG. 1
will increase relative to an ever-decreasing design width D. Thus, as also illustrated in
FIG. 1
, an isolated active area
8
Z that may have a design width D′ of, for example two and one-half in arbitrary units, variance B will have the effect of causing a 40 percent error. A variance B may leave insufficient space upon isolated active area
8
Z to form desired contacts or structures. It can be seen from the demonstration illustrated in
FIG. 1
, that the need to eliminate or substantially reduce blurring must keep pace with miniaturization.
Prior art methods for avoiding reflected light and its photoresist blurring problems include using layers such as titanium nitride or organic materials that reduce the reflected light in order to better control resolution of the photoresist.
Another hindrance to photolithographic limitations are conventional antireflective coating (ARC) schemes. As the ever-increasing pressure to miniaturize bears upon the microelectronics industry, the conventional antireflective enhancements such as a titanium nitride layer, organic layers, or other layers known in the art are proving inadequate at resolutions below about 0.25 microns.
One problem at a dimension below about 0.25 microns is that of fouling caused by titanium nitride or organic materials. Fouling is defined as a tendency for a selected antireflective layer to resist staying within preferred boundaries. Resistance to staying within preferred boundaries tends to cause photolithographic techniques to be compromised.
When the ARC is a polymer film, it is applied directly to the semiconductor structure to a thickness of about 0.5 microns and photoresist is deposited on top of the ARC. The ARC then has the function of absorbing most of the radiation used during exposure of the resist that penetrates the resist material. Both standing wave effects and destructive scattering from typographical features are suppressed with use of the ARC. A disadvantage of a polymer film ARC is that the process is increased in complexity and dimensional control may be lost. A polymer film ARC requires application by spin coating of the ARC material and pre-baking of same before applying the photoresist material. A problem of removing the ARC exists following an etch. For example, during anisotropic etching, portions of a photoresist are mobilized and form a liner within a recess that is being etched that further assists in achieving the anisotropic etch. Due to the anisotropic etch, however, the photoresist that was mobilized may have mingled with other elements that cause it to resist removal by conventional stripping techniques. This resistance to stripping requires stripping solutions that have a chemical intensity that may detrimentally effect the structure that was achieved during the anisotropic etch. Thus, using a substance that is intended to aid anti-reflectivity the benefit thereof mitigated by the requirement of a more chemically intensive stripping solution treatment.
Another method of attempting to avoid reflected light is to use a metallic mask. Metallic materials, however, can cause contamination of th
Gonzalez Fernando
Niroomand Ardavan
Micro)n Technology, Inc.
Tsai H Jey
Workman & Nydegger & Seeley
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