Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
2000-12-27
2003-06-03
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C430S296000, C430S942000
Reexamination Certificate
active
06573014
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to microlithography (projection transfer of a pattern, defined on a reticle or mask, onto a sensitive substrate using an energy beam). Microlithography is a key technique used, for example, in the fabrication of microelectronic devices such as integrated circuits and displays. More specifically, the invention pertains to microlithography performed using a charged particle beam (e.g., electron beam or ion beam) as the energy beam. Even more specifically, the invention pertains to charged-particle-beam (CPB) microlithography performed using a divided (segmented) reticle.
BACKGROUND OF THE INVENTION
Exposure schemes exploited by conventional charged-particle-beam (CPB) microlithographic exposure apparatus can be divided broadly into the following three types: (1) spot-beam exposure systems, (2) variably shaped beam exposure systems, and (3) block (cell) exposure systems. Each of these exposure schemes provides prospects of superior resolution of pattern elements compared to optical microlithography, but exhibit greatly reduced throughput compared to optical micro lithography.
The exposure schemes (1) and (2) perform exposure by tracing a pattern using a charged particle beam having a very small spot diameter (round transverse profile) or a very small rectangular transverse profile. Consequently, throughput obtained with these schemes is very low.
Block exposure was developed to improve throughput over that obtainable using schemes (1) and (2). Block exposure is especially useful for patterns in which a pattern unit (cell) is repeated many times, such as in a pattern containing a large number of identical memory cells. The pattern unit (typically measuring, e.g., 5 &mgr;m×5 &mgr;m on the reticle) covers a larger portion of the overall pattern than is exposed at any one instant by schemes (1) or (2). The pattern unit is transferred onto respective locations on the wafer by individual respective “shots.” I.e., at each respective location on the wafer, the pattern unit is batch-exposed, thereby improving throughput. Unfortunately, this scheme is practical only for a few types of patterns (as noted above, the patterns typically are characterized by having a basic pattern unit or “cell” that is repeated many times in the pattern). However, essentially all such patterns also include non-repeated portions that cannot be formed on the wafer by projecting the cell. Rather, the non-repeated portions typically are exposed using the variable-shaped beam exposure scheme, so throughput is not increased as much as desired.
To improve throughput of CPB microlithography apparatus and methods, considerable research has focused on exposure schemes employing a “divided” or “segmented” reticle. In a divided-reticle scheme, the entire reticle pattern is divided into multiple subfields (each defining a respective portion of the overall pattern) that are exposed individually onto a suitable “sensitive” substrate in an ordered manner (e.g., sequentially). On the reticle, each subfield can have dimensions of, for example, 1 mm×1 mm, which is many times larger than a pattern unit used in the block exposure scheme. Hence, throughput using the divided reticle scheme is correspondingly greater.
Divided-reticle CPB microlithography is described further in connection with
FIGS. 6
,
7
(
a
)-
7
(
b
), and
8
. Turning first to
FIG. 6
, a profile of a typical substrate is shown (in this instance a semiconductor “wafer”). The substrate is rendered “sensitive” by application of a coating of a “resist” that is reactive to exposure by a charged particle beam. Thus, the substrate can be imprinted with a latent image of a pattern defined on the reticle. As shown in the figure, the substrate includes a plurality of “chips” or “dies.” Each chip is divided into a plurality of stripes (without intending to be limiting in any way, the figure shows, by way of example, four stripes a-d). Each stripe is divided into multiple subfields.
After completing exposure of a die, each subfield on the reticle has a counterpart subfield image in the die as formed on the substrate. The subfield images on the substrate typically are smaller than corresponding subfields on the reticle, usually by a factor termed a “demagnification ratio,” such as 1/4 or 1/5, that is determined by the projection lens used to project the pattern from the reticle to the substrate. For example, if the demagnification ratio is 1/4, then a reticle subfield is four times larger than the corresponding image of the subfield on the substrate.
A portion of a divided reticle is shown in FIGS.
7
(
a
)-
7
(
b
), depicting only one representative reticle subfield
100
. FIG.
7
(
a
) provides a plan view of the subfield
100
(with surrounding area), and FIG.
7
(
b
) is an elevational section along the line A—A. For convenience in explanation, the size relationship of the subfield image on the substrate to the corresponding subfield on the reticle is not depicted accurately in the figure. The pattern element defined in the subfield
100
is denoted by the number
101
. The pattern-defining portion
101
typically has a square profile with each side measuring 1 mm, for example. The pattern-defining portion
101
in this example defines a U-shaped pattern element
105
. In this example, the pattern element
105
is defined by a corresponding aperture in a reticle membrane
104
, thereby indicating that the depicted reticle is a “stencil” reticle. Surrounding the subfield
101
is an unpatterned skirt
102
bounded by a strut region
103
. The strut region
103
has a width of 200 &mgr;m, for example. Extending away from each strut region
103
is a respective strut
106
. The strut
106
serves mainly to strengthen and provide rigidity to the reticle. The skirt
102
, having an exemplary width of about 100 &mgr;m, allows a certain positional tolerance for the beam illuminating the subfield
101
. I.e., even if the beam experiences a limited amount of lateral positional displacement, the skirt
102
allows the beam nevertheless to illuminate the entire subfield
101
without impinging on a strut region
103
. As shown in FIG.
7
(
b
), the strut
106
is relatively thick in the Z-dimension. If the beam illuminating the reticle should impinge on a strut region
103
or strut
106
, then significant heating of the reticle would result, which probably would cause undesirable reticle distortion.
It is not necessary that all subfields of a pattern be defined on a single reticle. The subfields alternatively can be distributed among multiple reticles.
Divided-reticle projection-exposure using a charged particle beam generally is performed in a manner as shown in
FIG. 8
, which depicts an exemplary exposure, within a stripe, of a row of subfields. During exposure, the reticle (mounted on a reticle stage) and substrate (mounted on a substrate stage) move synchronously in opposite directions relative to each other. The stage motions can be continuous “scanning” motions at fixed respective velocities that are determined mainly by the demagnification ratio of the projection lens used to project respective images of the subfields onto the substrate. During exposure of individual subfields, unpatterned regions (i.e., skirts
102
and strut regions
103
) are not exposed. Hence, the ratio of substrate-stage velocity to reticle-stage velocity is not exactly equal to the demagnification ratio. I.e., to exclude imaging of skirts and strut regions, the velocity of the substrate stage relative to the reticle stage is slightly slower than would be dictated by the demagnification ratio. As the “illumination beam” illuminates a subfield on the reticle, an image of the illuminated subfield is projected, via a “patterned beam” passing through a projection-optical system, onto a corresponding region on the substrate, thereby “exposing” the substrate with the image. During exposure of successive rows of subfields, the reticle stage and substrate stage move in opposite directions in one dimension (e.g., X-dimension). Meanwhile, the illumin
Kojima Shin-ichi
Yamaguchi Takeshi
Klarquist & Sparkman, LLP
Nikon Corporation
Young Christopher G.
LandOfFree
Charged-particle-beam microlithography methods for exposing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Charged-particle-beam microlithography methods for exposing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charged-particle-beam microlithography methods for exposing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3142024