Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2002-01-16
2004-09-14
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S394000, C430S396000, C430S397000, C430S330000, C430S005000, C347S020000, C347S071000
Reexamination Certificate
active
06790598
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to methods of patterning resists. This invention also separately relates to structures including the patterned resists.
2. Description of Related Art
Photolithography is used to form patterns in resists applied on substrates. Typically, radiation, typically light, is passed through a patterned mask to transfer the pattern of the mask into the resist. After development, the pattern exists in the resist.
Organic-based resists or photoresist include blends of polymeric and other organic and inorganic materials. The two broad classifications of resists are negative and positive working resists, which produce negative and positive images, respectively. In negative working resists, regions that are exposed to radiation, typically light, are polymerized and, consequently, more insoluble to a developer. Thus, the regions that are not exposed to light are more soluble to the developer and can be preferentially removed relative to the exposed regions during development. In contrast to negative resists, when regions of positive resists are exposed to light, they are chemically altered to exhibit a higher degree of solubility, so they can be preferentially removed relative to the non-exposed regions during development.
Photoresists have been used as structural layers in micro-mechanical devices, as described, for example, in S. Hagen et al., “Photosensitive Polyimide: Lithography in the Thick-Film Regime,”
Proceedings
11
th
International Conference Photopolymers Principles, Processes, and Materials
, Society of Plastics Engineers, Inc., Oct. 6-8, 1997; incorporated herein by reference in its entirety.
Resist layers have been formed in ink jet print heads. Ink jet print heads include flow channels for flowing ink and nozzles for discharging ink droplets onto recording media to form images. Ink jet print heads include an energy source that applies energy to the ink to cause the ink droplets to be discharged out of the nozzles and onto the recording medium. Resist layers have been formed as permanent structural layers that define flow channels in ink jet print heads. See, for example, U.S. Pat. No. 6,294,317 to Calistri-Yeh et al.
Openings, or “features,” can be formed in resists with various configurations. The openings can be generally round, rectangular or have other like shapes. The openings can also be relatively narrow and long. In such latter types of openings, the openings are defined by the side walls and bottom walls. The sidewalls can have different angular orientations relative to the upper major (planar) surface of the photoresist layers. For example, the sidewalls can be substantially perpendicular to the major surface to form substantially rectangular openings, known as lines or trenches. The sidewalls can alternatively be tapered relative to the major face. Lines and trenches can be either deep or shallow.
Another type of opening or feature formed in resists is an island. Islands are discrete upstanding structures that are generally parallel to each other. Islands have generally elongated shapes. Vias and other through openings can also be formed in resists.
The openings formed in resists can be characterized by their aspect ratio. The definition of the aspect ratio depends on the amount of taper of the sidewalls that define the opening.
FIGS. 1 and 2
show two different opening configurations that have aspect ratios defined by respectively different relationships.
FIG. 1
shows a photoresist layer
10
having an upper surface
12
and an opening
14
formed in the surface. The opening
14
has a height h and a width w. The height can be less than or equal to the thickness of the resist layer
10
. The side walls
16
defining the opening
14
are perpendicular to the upper surface
12
. For the opening
14
having such perpendicular side walls
16
, the aspect ratio “A” can be defined as the ratio of the height “h” of the opening
14
to the width “w” of the opening
14
, i.e. A=h/w. Thus, according to this definition, the aspect ratio “A” of an opening can be increased by increasing the height “h” at a constant width “w”. It is common for the aspect ratio to be described according to this relationship.
FIG. 2
shows a negative resist layer
20
formed on a substrate
22
. A mask
24
is positioned above the resist layer
20
. The mask
24
includes openings
25
having a width “b” and separated from each other by a distance “a”. The resist layer
20
includes an upper surface
28
, a lower surface
30
, and an opening
32
extending vertically between the upper surface
28
and the lower surface
30
and being aligned with the opening “b” in the mask
24
. The opening
32
is defined by side walls
34
, which are tapered relative to the upper surface
28
, such that the width of the opening
32
varies from a width b′ at the upper surface
28
to a width b″ at the lower surface
30
. The resist layer
20
has a width a′ at the upper surface
28
, and a width a″ at the lower surface
30
. For the opening
32
having such tapered side walls
34
, the average aspect ratio “A” of the opening
32
can be defined as follows: A=2h/(b′+b″). Likewise, the average aspect ratio of the wall between the openings can be defined as A=2h(a′+a″).
SUMMARY OF THE INVENTION
Methods that have been used to pattern resists, such as photoresists, have not been satisfactory. Namely, these methods have not produced satisfactory opening patterns including fine features with relatively higher aspect ratios in certain selected areas of the resist, and grossly patterned areas, with only little or even no detail, in other selected areas of the same resist layer.
Namely, in known methods of forming opening patterns in resists, a lesser amount of exposure to patterning radiation occurs in areas of resists where finer patterns are to be formed, due to proximity effects by the overlying mask. Areas of negative working resists at which finer patterned details are needed receive less exposure than more open areas and, consequently, remain more soluble, so that increased removal occurs during development of the resist. In contrast, more grossly patterned areas on the same resist, for example, areas having little or no detail, receive a greater amount of light exposure than the finer features, so that the exposed more grossly patterned areas become less soluble. Consequently, there is minimal removal of the more grossly patterned areas during development.
FIG. 3
schematically illustrates the relationship between the resist film thickness (resist film thickness=thickness of the resist film remaining after development/resist film thickness before exposure) versus the exposure dose or energy. As shown, the film thickness remaining after development versus the exposure dose increases rapidly at low exposure doses, and flattens out at high exposure doses. Lower exposure doses can be used to form higher aspect ratio features as compared to higher exposure doses. When exposure doses are high, even though fine areas of the resist receive relatively less exposure than coarse features using conventional mask patterns, the final resist film thickness after development is relatively uniform. However, when low exposure doses are used, to achieve resolution of finer features (i.e., features having relatively higher aspect ratios), the thickness of the resist remaining is on the steep slope portion of the curve. The differences in the exposure dose between resist regions including finer features and regions including coarser features, produces significant differences in surface topography in resists. In known patterning methods, significant post-patterning processing has been required to obtain a sufficiently flat surface under these conditions.
For example, as described above, resists have been used to form permanent structural layers that define ink flow channels and the like in ink jet print heads. Problems have occurred in methods of patterning resists that ha
Atkinson Diane
Burke Cathie J.
Calistri-Yeh Mildred
Chacko-Davis Daborah
McPherson John A.
Oliff & Berridg,e PLC
Xerox Corporation
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