Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of...
Reexamination Certificate
2000-10-31
2002-05-07
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
C438S636000, C438S700000, C043S042090, C043S042090, C257S659000, C257S751000
Reexamination Certificate
active
06383947
ABSTRACT:
TECHNICAL FIELD
The present invention relates to photolithographic techniques used in semiconductor processing, and more particularly, to the use of antireflective coatings (ARCs) in submicron metallization fabrication processes.Further, the present invention relates to the use of anti-reflective coatings which do not chemically react with deep ultraviolet (DUV) photoresists.The present invention also relates to methods for manufacturing integrated circuits and, particularly, to uses and methods for forming and using DUV ARCs.
BACKGROUND OF THE INVENTION
In the construction of integrated circuit devices, one or more conducting layers (e.g., aluminum, copper, titanium, silicon or various alloys thereof) are deposited and subsequently pattern masked, then etched to create ohmic or Schottky contacts and electrical connections between various circuit elements. Conventionally, thin films of conducting materials are formed; and these films are then spin-coated with a photoresist layer. The photoresist layer is exposed to a light pattern and then developed to form a photoresist mask pattern. Selective etching removes portions of the underlying material through the openings in the photoresist pattern. For example, a metallic aluminum conducting layer would be selectively plasma-etched with chlorine-containing gases. The photoresist is then removed leaving a pattern in the conducting layer.
In the art, when the conducting layers are made of reflective materials (e.g., metallic materials), antireflective coatings (ARCs) have been applied to reduce surface reflection. Typical surfaces benefitting from ARCs are layers formed of polysilicon, aluminum, copper, titanium, or other reflective metals and their alloys. ARCs improve photoresist patterning control by reducing standing wave effects or diffuse scattering caused by reflection of radiation offreflective surfaces. These problems are magnified when monochromatic illumination sources are used. Furthermore, as microcircuit density increases, scattering, diffraction, and interference effects become less and less tolerable. As circuit density increases and feature size and line widths decrease below the 0.18-&mgr;m level, such effects become increasingly critical. As line widths approach the 0.20-&mgr;m level, deep ultraviolet (DUV) exposure sources are commonly used to expose photoresists and provide the necessary definition in mask patterns. DUV radiation can be loosely defined as radiation between the wavelengths of 4-400 nanometers (nm). Typical sources of such radiation are, for example, cadmium, xenon, or mercury lamps, and certain types of excimer lasers. DUV sources are used because it is critically important to produce sharply defined mask patterns. To this end, reflected light must be reduced in order to maximize photoresist pattern definition.
Prior to the use of DUV exposure sources and DUV photoresists, a metallization layer (typically formed of aluminum) was coated with an antireflective layer of titanium nitride (TiN) followed by a spin coating of photoresist. This photoresist was then patterned and subsequently etched, then the photoresist was removed. The TiN layer remained in place to help prevent electromigration and serve as a shunt layer permitting continuous current flow, in the event of void formation in the metallization layer. However, due to the increased resolution possible with DUV exposure sources and the need for smaller and smaller feature sizes, the art has moved towards DUV exposure sources and photoresists optimized to take advantage of DUV sources. Unfortunately, TiN ARCs undergo chemical reactions with DUV photoresists and, therefore, are not compatible with the new photoresists. There is a need for new solutions to the old problem of metallization reflectance.
The well understood and commonly used process procedures previously used are not compatible with the use of DUV exposure sources. New photoresists which are sensitive to DUV light have come into use. However, these DUV photoresists present new problems. The new photoresists are chemically-amplified resists, which means that through chemical treatment, a chemically-amplified resist is more sensitive to light than its non-amplified predecessors. Chemically-amplified resists require less exposure time. For example, standard I-line (365 nm) lithographic exposure requires 200 milliJoules (mJ) of activation energy to develop a standard photoresist. In comparison, a typical chemically-amplified resist may only require 10 mJ (at 248 nm). Such typical chemically-amplified resists are manufactured under the trade names of Apex or UV05, both made by Shipley Company of Marlborough, Mass. However, these new photoresists react to nitrogen containing compounds. Consequently, these photoresists react with the previously used TiN or silicon nitride antireflective layers as well as ambient nitrogen in typical reaction chambers.
FIGS. 1A-1C
show the unhappy effect of using DUV photoresists in conjunction with a TiN ARC.
FIG. 1A
is a cross-section view of a portion of an integrated circuit structure identified generally as
10
, having a semiconductor substrate
101
, with a reflective metallization layer
102
, and a TiN ARC
103
, and a DUV photoresist mask pattern
104
. As shown in
FIG. 1B
, the exposed portions of the DUV photoresist
104
T react with the nitrogen containing ambient and also with the nitrogen containing TiN ARC layer
103
in region
104
B. The effects of this exposure to nitrogen degrade the photoresist as shown in
FIG. 1C
, creating the irregularly shaped and undesirable photoresist profiles
104
E.
FIGS. 1D-1E
are plan views of a semiconductor surface which further illustrate some of the problems associated with DUV photoresists and nitrogen-containing ARCs.
FIG. 1D
shows an idealized structure on a semiconductor surface
101
, having microcircuit components (A, B, C, & D) formed thereon. Elements A & B are electrically connected using an idealized metal interconnect
102
AB
. Elements C & D are also electrically connected using an idealized metal interconnect
102
CD
. The sharply defined features of the metal interconnects
102
AB
&
102
CD
are desired. Unfortunately, due to the photoresist degradation disclosed above, interconnect problems arise. For example, as in
FIG. 1E
, the microcircuit components (A, B, C, & D) are electrically connected by the less than ideal interconnects
102
AB
′ &
102
CD
′. A common effect is interconnect shorting, as shown by S, where separate metallization layers contact each other.
Despite this drawback, DUV photolithography has come in to ever more frequent use due to the increased definition possible with DUV lithography. A great need has arisen for ARC materials that are compatible with the newer photoresists.
One solution is to provide a sacrificial layer of oxide (e.g., silicon dioxide (SiO
2
)) over the TiN ARC layer, followed by the application of a DUV photoresist. The sacrificial layer provides a barrier between the TiN ARC and the DUV photoresist. The photoresist is then patterned and fabrication continues as is needed to create the necessary circuit structures. The problem with the oxide sacrificial layer is that it adds an additional process step to each metallization layer. It also requires a separate machine for creating such layers. This drives up cost and increases manufacturing time, in addition to increasing the complexity of the process. Further, by forming an oxide sacrificial layer this process increases the possibility of harmful particle formation during fabrication.
Others have postulated the use of a TiN/Ti ARC bi-layer. The TiN layer is fabricated over the metallization layer, followed by a layer of metallic titanium (Ti) formed over the TiN layer. The top Ti layer prevents a subsequently formed DUV photoresist layer from contacting the TiN layer, thereby preventing the DUV photoresist from reacting with the nitrogen in the TiN layer. Unfortunately, this ARC has the same drawbacks as the sacrificial oxide layer process, namely it is a two step, two chamber pro
Besser Paul R.
Chen Susan H.
Erb Darrell M.
Morales Carmen
Singh Bhanwar
Advanced Micro Devices , Inc.
Elms Richard
Lariviere, Grubman & Payne, LLP
Luu Pho
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