Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
2001-06-22
2002-09-24
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S671000, C438S717000, C438S950000, C438S952000
Reexamination Certificate
active
06455439
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a mask suitable for use in forming a container in a substrate, and more specifically to a mask having a fine geometry, rectangular opening that may be utilized to etch a substrate and define an opening or hole therein having an outline corresponding to the rectangular opening of the mask. Additionally, the present invention relates to a container-cell capacitor for a dynamic random access memory (DRAM).
An exemplary prior art dynamic random access memory (DRAM) device comprises an array of container-cell capacitors that are formed in a substrate. In the current application, the. term “substrate” or “semiconductor substrate” will be understood to mean any construction comprising semiconductor material, including but not limited to bulk semiconductive materials such as a semiconductor wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). Further, the term “substrate” also refers to any supporting structure including, but not limited to, the semiconductive substrates described above.
One known container structure for the container-cell capacitors of a memory array, comprises a container having cylindrical or “bath-tub” shape. In a known method of fabricating a container in a substrate, with reference to
FIGS. 1-3
, a single layer of photoresist
12
is coated over layer
10
of, for example, borophosphosilicate glass (BPSG). Light
14
, such as ultraviolet light, irradiates a select region
16
of photoresist
12
as determined by an exposure plate or reticle (not shown). Advancing to
FIG. 2
, photoresist
12
is developed to form opening
18
. Opening
18
exposes surface
20
of layer
10
. With this mask
12
, layer
10
can be etched (e.g., by a reactive plasma etch) to form container
19
within layer
10
, see FIG.
3
. As used herein, the term “container” shall be inclusive of similar structural descriptors such as void, pocket, hole, contact opening, via and the like. A radius of curvature r
1
of the container corresponds to the radius of curvature of opening
18
of mask
12
. To form a capacitor, container
19
is lined with first conductive material, dielectric, and second conductive material layers respectively.
In order to minimize costs, manufactures of DRAM's strive to reduce the dimensions of the container-cell capacitors and increase the density of such cells within the array. Accordingly, some have developed a container-cell capacitor having a primarily rectangular cross-section for providing increased capacitance without sacrificing cell density. Referencing
FIGS. 4A and 4B
, such exemplary prior art container
19
comprises a cross-section of rectangular outline
23
offering an increase in the area of the container walls. This increased area, in-turn, increases electrode area and capacitance value of the container-cell over that which might otherwise be provided by an equivalent width cylindrical container
18
.
In a prior art method of forming a mask with a rectangular aperture, referencing
FIGS. 5A and 5B
, insulating material
10
, e.g., BPSG, is layered over a silicon wafer of a supporting substrate
21
. Etch resistant material
96
is layered over insulating material
10
. Etch resistant material
96
is capable of resisting an etchant that is used during subsequent etching of insulating material
10
, and may comprise, e.g., nitride of about 1,000 angstroms thickness. Photoresist (not shown) is layered over the top of etch resistant material
96
and patterned to define lateral apertures therein. The lateral apertures of the photoresist are used to define lateral openings
100
into etch resistant material
96
. After forming lateral openings
100
in etch resistant material
96
, the first photoresist is removed.
Continuing with this particular, exemplary, prior art method, additional photoresist
94
is applied over the patterned etch resistant material
96
. This new photoresist is patterned to define longitudinal openings
106
that overlap lateral openings
100
, thereby defining rectangular openings
18
(
FIG. 5B
) at overlapping regions. Thereafter, select regions of substrate
21
are processed or etched in accordance with the openings to define containers
19
. In this exemplary prior art method of forming a rectangular opening for a mask, the second photoresist is layered over the substrate and processed only after the first, lower photoresist has been fully processed. In other words, the lower photoresist is processed first, and only then is the upper layer of photoresist coated thereover and processed.
After forming this mask opening, the substrate is etched in accordance with the rectangular opening of the patterned photoresist and lower mask material, so as to provide a container within the substrate having primarily a rectangular cross-section corresponding to the rectangular opening of the mask.
In the above, exemplary, prior art method of forming a mask with a rectangular aperture, the upper photoresist is applied to the substrate only after the lower mask material has already been processed to define the lateral opening therein. In other words, the exemplary prior art sequence of steps comprises, in general, processing the first mask material, applying photoresist over the first mask material, followed by processing the photoresist. With this sequence of steps, the substrate is moved from, firstly, an etch or development station associated with processing the first mask material; to, secondly, a photoresist coat station for applying the photoresist over the processed mask material; and then back to, thirdly, an etch or resist development station to define the longitudinal openings in the photoresist. Recognizing a need in the manufacture of semiconductors to reduce handling and travel of wafers during semiconductor production flows, so as to reduce the time and costs associated with such wafer transport, the present invention proposes a new mask and method of manufacture thereof that can provide for effective and efficient semiconductor production flows.
Accordingly, the present invention provides a new mask and method of manufacture thereof, for use in forming a container for a container-cell capacitor having a rectangular cross-section, which mask and method of manufacture are capable of overcoming some of the above limitations. Furthermore, an array of containers are formed in a substrate by etching a substrate in accordance with fine geometry openings of such mask, providing for an efficient process flow.
SUMMARY OF THE INVENTION
In accordance with a first embodiment of the present invention, a method of forming a mask comprises layering radiation blocking material over a layer of first radiation sensitive material, such as photoresist. The radiation blocking material is patterned to provide a first opening therein that uncovers a portion of the layer of radiation sensitive material. Next, the layered structure is irradiated in accordance with an exposure pattern that overlaps a portion of the first opening, thereby irradiating a region of the lower radiation sensitive material. The radiation sensitive material is then developed to remove the irradiated region thereof and form an opening for the mask.
In a accordance with one aspect of this embodiment, a second layer of radiation sensitive material, e.g., photoresist, is layered over the layer of radiation blocking material and patterned to provide a longitudinal opening therein and uncover a corresponding region of the radiation blocking material. A visible portion of the radiation blocking material is removed using the patterned, second layer of radiation sensitive material as a mask, thereby forming the first opening in the radiation blocking material.
Preferably, the second layer of radiation sensitive material is provided a longitudinal opening, and the lower layer of radiation sensitive material is irradiated using a lateral exposure strip that overlaps the longitudinal opening.
In accordan
Elms Richard
Howrey Simon Arnold & White , LLP
Pyonin Adam J.
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