Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2001-11-29
2004-06-15
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S492200, C430S005000
Reexamination Certificate
active
06750464
ABSTRACT:
FIELD
This disclosure pertains to microlithography, which involves the transfer of an image of a pattern to the surface of a “sensitized” substrate using an energy beam such as ultraviolet light or a beam of charged particles. Microlithography is a key technology used in the fabrication of microelectronic devices such as integrated circuits, displays, thin-film magnetic-pickup heads, and micromachines. More specifically, the disclosure pertains to alignment marks that are used mainly for aligning and detecting the position of the substrate while performing a microlithographic exposure of the substrate. The disclosure also pertains to alignment-mark patterns, as defined on a reticle, corresponding to such alignment marks.
BACKGROUND
In recent years, the inability of optical microlithography to resolve increasingly finer pattern features has been an obstacle to obtaining currently desired levels of integration and miniaturization of microelectronic devices. Hence, large efforts are ongoing to develop a practical “next-generation” microlithography technology that can achieve satisfactory resolution of substantially finer pattern features than resolvable using optical microlithography.
Microlithography performed using a charged particle beam is a major candidate next-generation microlithography technology. Charged-particle-beam (CPB) microlithography offers prospects of substantially better resolution than optical microlithography for reasons similar to the reasons for which electron microscopy yields better imaging resolution than optical microscopy. An ongoing technical challenge with current CPB microlithography approaches is the attainment of satisfactory throughput.
Another technical challenge with CPB microlithography is a more general problem that arises in any of various efforts to achieve substantially greater imaging resolution (i.e., resolution of smaller pattern linewidths), either by CPB microlithography or other type of microlithography. Namely, the greater the desired imaging resolution, the greater the required accuracy of position detection of, inter alia, the lithographic substrate.
Conventionally, detection of substrate position in a microlithography apparatus is accomplished using an alignment device that detects the respective positions of alignment marks associated with the substrate, e.g., alignment marks defined in or on the surface of the substrate. Exemplary optical-alignment devices include devices based on field image alignment (FIA), which detect alignment marks using a two-dimensional image sensor such as a CCD or the like and perform image processing to obtain position data. The alignment marks for FIA usually are situated on the substrate and are formed by exposing an alignment-mark pattern, defined by a mask or reticle, onto the surface of the substrate.
In view of the fact that many layers are formed on the substrate during fabrication of microelectronic devices on the substrate, alignment marks normally are formed at least in the first layer exposed onto the substrate. Hence, the reticle defining the circuit pattern to be formed in the first layer typically includes an alignment-mark pattern, and both the first-layer circuit pattern and the alignment marks are transferred lithographically from the reticle to the substrate. In addition to the first layer, one or more layers formed subsequent to the first layer also can include respective alignment marks that are transferred to the substrate as required.
Depending upon the type of microelectronic devices being fabricated on the substrate, lithographic pattern exposures can be performed using several types of microlithography apparatus rather than only one type. For example, some layers can be exposed using a CPB microlithography apparatus, and other layers can be exposed using an optical (deep ultraviolet) microlithography apparatus. The reason for this flexibility is that certain layers may have smaller minimum linewidths than other layers, and it is desirable from the standpoint of throughput and other concerns to utilize, for a particular layer, the most efficient lithographic exposure method that also produces the desired linewidth resolution. Hence, it is desirable that the alignment marks formed on the substrate be usable for obtaining high-accuracy position detection by optical means as well as by CPB means.
FIGS.
10
(A)-
10
(B) depict respective examples of alignment marks usable for FIA (which, as noted above, is an optically based alignment-detection method and is used in conventional optical microlithography apparatus). The alignment marks consist of alignment-mark elements (denoted by respective shaded portions in the figures) defined as corresponding through-holes (apertures) in the respective mask. Regarding the alignment mark
10
shown in FIG.
10
(A), certain elements
10
V
are oriented vertically in the figure and other elements
10
H
are oriented horizontally in the figure. The alignment-mark elements
10
V
,
10
H
intersect each other. Regarding the alignment mark
11
shown in FIG.
10
(B), certain alignment-mark elements
11
V
are oriented vertically and other alignment-mark elements
11
H
are oriented horizontally. Respective groups of horizontal elements
11
H
and vertical elements
11
V
are arranged in respective parallel arrays, but do not intersect each other. The exemplary marks shown in FIGS.
10
(A) and
10
(B) provide good two-dimensional detection accuracy using optical alignment detectors and hence are used in many optical microlithography systems.
As noted above, different layers formed on a substrate need not be formed using the same microlithography technology. For example, one layer can be formed using CPB microlithography, and the next layer can be formed using optical microlithography. In the case of the marks shown in FIGS.
10
(A)-
10
(B), if the first layer is to be formed on the substrate using CPB microlithography (wherein the respective pattern as well as the alignment-mark patterns are defined on a stencil reticle), a problem arises with respect to the alignment-mark patterns as defined on the reticle. Specifically, in the case of the alignment mark
10
shown in FIG.
10
(A), the corresponding alignment-mark pattern as defined on the reticle is a “donut” pattern. I.e., the alignment-mark elements
10
V
,
10
H
are defined by respective apertures in the reticle. However, as can be seen, the apertures completely surround “islands”
10
I
in a donut manner, leaving the islands
10
I
without any physical support on the reticle. Complete “donut” elements cannot be defined on a stencil-type reticle. In the case of the alignment mark
11
shown in FIG.
10
(B), defining the corresponding alignment-mark pattern
11
on a stencil reticle poses a high probability of deformation of the alignment-mark elements
11
H
,
11
V
(e.g., warping and/or twisting) due to stress in the reticle.
In view of the foregoing, if exposure of the first layer is to be performed by CPB microlithography using a stencil reticle, then there is an urgent need for alignment marks that are definable in the first layer and that can be detected with good accuracy and precision using an optically based alignment-detection device.
SUMMARY
To address the above and other shortcomings of conventional alignment marks and associated methods, the present invention provides, inter alia, alignment-mark patterns that can be defined on a stencil reticle for transfer using a charged particle beam to a sensitized substrate such as a resist-coated semiconductor wafer. As imprinted on the substrate, the corresponding alignment marks can be used for highly accurate alignments performed using an optically based alignment-detection device (e.g., a detection device based on FIA).
According to a first aspect of the invention, alignment-mark patterns are provided that are defined on a stencil reticle used in charged-particle-beam microlithography. The alignment-mark patterns are configured to be lithographically transferred by a charged particle beam from the stencil reticle to a sensitized substrate
Hirayanagi Noriyuki
Udagawa Jin
Klarquist & Sparkman, LLP
Luu Thanh X.
Nikon Corporation
LandOfFree
Alignment-mark patterns defined on a stencil reticle and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Alignment-mark patterns defined on a stencil reticle and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Alignment-mark patterns defined on a stencil reticle and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3359903