High resolution lithography method using hydrogen developing reagent

This is a method for forming patterned features. The method comprises: forming a single layer of resist 12 on a substrate 10, the layer 12 having a thickness; patterning the resist by selective exposure to a first energy source 16 to modify the developing properties of portions of the resist, leaving an amount of the thickness unexposed; and developing the resist. This is also a device which comprises: a substrate; a layer of resist over the substrate; and an energy absorbing dye in the resist. Other methods and structures are also disclosed.

FIELD OF THE INVENTION 
This invention generally relates to semiconductor devices and in particular 
for lithography methods. 
BACKGROUND OF THE INVENTION 
The semiconductor industry is constantly striving to achieve higher density 
electronic devices. As the industry has moved into micron, submicron and 
even sub-half-micron sized features to achieve higher densities, the need 
for improved lithography methods to create such minute features has 
increased. 
Among the problems associated with conventional lithography techniques are 
the lack of uniformity of exposure of resist through a thick layer of 
resist and scattered light within the layer of resist due to reflective 
metallized surfaces under the resist. These problems tend to compound the 
loss of resolution problem by creating ill-defined patterns at the onset. 
Standard methods for image development, in the exposed etch resist, fall 
short of the requirements for sub-half-micron feature generation. Wet 
development of the etch resist often produces a positive-grade slope on 
the feature sidewall that degrades the contrast of image transfer into the 
underlying thin film during the dry etch process. This is due to the less 
than infinite etch rate selectivity between the resist and the film 
material. Thus, there is a need for a method for forming high resolution 
submicron and sub-half-micron sized features on a semiconductor device. 
SUMMARY OF THE INVENTION 
This is a method for forming patterned features. The method comprises: 
forming a single layer of resist on a substrate, the layer having a 
thickness; patterning the resist by selective exposure to a first energy 
source to modify the developing properties of portions of the resist, 
leaving an amount of the thickness unexposed; and developing the resist. 
Preferably, the developing is done with a second energy source and a 
developing reagent; the first and second energy sources are both 
ultraviolet light; the resist is acrylic-based; a dye is incorporated into 
the resist to prevent exposure of the amount of the thickness to be left 
unexposed; the developing reagent includes oxygen or hydrogen; the 
patterning step occurs in an oxygen-free environment; a nitrogen purge is 
used to create the oxygen-free environment; and the substrate has multiple 
layers. A diffusion reagent may be diffused into unmodified regions of the 
resist before the developing step. The diffusion reagent may contain 
silicon or may contain titanium. 
This is also a device which comprises: a substrate; a layer of resist over 
the substrate; and an energy absorbing dye in the resist.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Methods to achieve high resolution of a submicron sized feature include 
increasing the numerical aperture of the imaging tool and/or decreasing 
the wavelength of light used to expose the etch resist. In both instances, 
the image depth of field is diminished to less than the dimension of the 
thickness of the etch mask film and the surface topography. Resultantly, 
the projected image transfer from the master reticle is unacceptably 
distorted in various areas of the exposure field. 
Methods to overcome these problems, such as multi-layer resists, have been 
proposed. This involves "sensitizing" the surface layer of the etch mask, 
in some fashion, so the imaging tool only needs to project an accurate 
image onto the surface of the resist. Hence, the depth of field only needs 
to be greater than the characteristic surface topography. However, this 
has not been well-accepted in production environments. Process complexity, 
particle generation and poor critical dimension control and uniformity 
have been cited as shortcomings. 
A surface-imaging technique, that is compatible with an image development 
method, is needed to successfully pattern submicron and sub-half-micron 
features. Surface-imaging is needed to overcome fundamental depth-of-field 
limitations, associated with the optical imaging tool. The surface-imaging 
should preferably not be complex or sensitive to small variations in 
process conditions. A compatible image development technique is needed to 
ensure the exposure image is faithfully transferred to the remainder of 
the resist. In turn, this is preferably done in a manner that creates a 
structure that will faithfully transfer the image into the underlying 
substrate. 
Disclosed is a surface-imaging exposure method in conjunction with a dry 
development method to service submicron and sub-half-micron lithography 
requirements. A layer of resist 12 is deposited on a substrate 10 that is 
to be patterned, shown in FIG. 1. The resist 12 does not need to contain a 
sensitizer, also referred to as a (Photo Active Compound). Referring 
to FIG. 2, a mask 14 may be used to selectively expose the resist 12 to an 
energy source 16, such as a deep UV exposure tool, to crosslink the resist 
12 on selected regions 18 of the resist 12 surface. The crosslinking is 
preferably done in an essentially oxygen-free environment. One method 
which may be used to realize a oxygen-free environment is a nitrogen 
purge. 
A first preferred embodiment is shown in FIG. 3. In this embodiment, after 
crosslinking the resist 12 with the energy source 16, the structure may be 
exposed to a blanket reagent ambient which diffuses into the regions 20, 
in the surface of the resist 12, which were not crosslinked. The 
crosslinked regions 18 serve as diffusion barriers to the reagent. As an 
example, a silicon containing ambient such as HMDS may be used. 
Referring to FIG. 4, the resist 12 is preferably anisotropically dry 
developed with high contrast by a gentle, photo-assisted etch process (or 
other "gentle," low-energy etch processes, such as ECR), involving, for 
example, an oxygen-containing source as a reagent and a light source 22 as 
an energy source that is capable of disrupting the surface bonding. The 
diffused regions 20 serve as an etch mask and are minimally affected by 
the energy source/reagent etch. The "dangling bonds" that are generated by 
the disruptive light 24 (or other energy source), react with the 
oxygen-containing reagent (and/or its products), to remove the resist in 
the regions 18 that are crosslinked. The resultant pattern exhibits a 
positive tone. Since such low-energy processing may exhibit excellent etch 
rate selectivity between the crosslinked regions and the uncrosslinked 
regions, acceptable CD (critical dimension) control and uniformity of the 
feature may be achieved and vertical sidewalls, for crisp image transfer 
into the underlying film, may be generated. 
In a second preferred embodiment, the process steps from the first 
preferred embodiment, described above, shown in FIG. 1 and FIG. 2, are 
followed to produce crosslinked regions 18 in the surface or the resist 
12. In this second preferred embodiment, the structure is not exposed to a 
diffusion reagent. Instead, the structure goes directly to the develop 
stage, shown in FIG. 5. The resist 12 is preferably anisotropically dry 
developed with high contrast by a gentle, photo-assisted etch process (or 
other "gentle," low-energy etch processes, such as ECR), involving, for 
example, an oxygen-containing source as a reagent and a light source 22 as 
an energy source that is capable of disrupting the surface bonding. The 
"dangling bonds" that are generated by the disruptive light 24 (or other 
energy source), react with the oxygen-containing reagent (and/or its 
products), to remove the resist in the regions 20 that are not 
crosslinked. The crosslinking serves as an etch mask and the resultant 
pattern in this embodiment is negative tone. Again, since such low-energy 
processing may exhibit excellent etch rate selectivity between the 
crosslinked regions and the uncrosslinked regions, acceptable CD control 
and uniformity of the feature may be achieved and vertical sidewalls, for 
crisp image transfer into the underlying film, may be generated. 
The resists which may be used for the embodiments described above are 
numerous. The choice is limited only by the energy source 22 used and the 
embodiment selected. In the case of the first embodiment the crosslinked 
regions 18 are etched, therefore the resist 12 used serves as a diffusion 
barrier and does not need to be resistant to etching. This allows for very 
low energy sources 22 to be used, dependent on the choice of resist and 
material diffused into the resist. In the second embodiment, the 
crosslinked regions 18 serve as an etch mask and must therefore be more 
resistant to etching. As an example, an acrylic-based resist may be used, 
which when crosslinked becomes very hard and resistant to etching. Dyes 
may be incorporated into the resist to limit the depth of the conversion 
caused by the crosslinking and still avoid depth of field problems even 
with a relatively intense exposure. Preferably the dye is a photon 
absorbing dye. The strength and intensity of the energy source chosen 
directly affects the degree of resistance to etching required in the 
crosslinked regions 18 of the resist 12. 
These embodiments take advantage of surface-imaging by crosslinking the 
surface of the resist 12 in the regions 18 exposed, for example, by a UV 
optical imaging tool. The depth of the crosslinking is not expected to be 
more than several thousand angstroms and could, as an example be in the 
vicinity of 100.ANG.. These embodiments also take advantage of dry 
development, to produce high image contrast vertical sidewalls for good CD 
control and uniformity, and to generate an etch resist feature that will 
accommodate good image transfer into the underlying film. 
This single-layer process does not suffer from the process complexity of 
multi-layered techniques or sensitivity to process variations with reagent 
diffusion profiles, as is the case with prior art surface imaging 
processes. Moreover, it is simpler in process and chemistry than standard 
lithography techniques, since it does not need a sensitizer incorporated 
into the resist. As a result of the high etch rate selectivity, this 
process is not afflicted with poor contrast resulting from poor 
selectivity. 
A preferred embodiment has been described in detail hereinabove. It is to 
be understood that the scope of the invention also comprehends embodiments 
different from those described, yet within the scope of the claims. For 
example, the energy sources used to expose and develop the resist may be 
many things, such as ions, electrons or photons. Similarly, the 
oxygen-containing reagent used in the develop step may be replaced with, 
for example, hydrogen or a hydrogen liberating source such as ammonia. The 
diffused reagent ambient, in the first preferred embodiment, is described 
as a silicon containing ambient but may be other materials such as a 
titanium containing ambient. The crosslinking may be replaced by any 
method that will modify the resist material in a manner such that the 
desired etch and/or diffusion properties are achieved. Words of inclusion 
are to be interpreted as nonexhaustive in considering the scope of the 
invention. 
While this invention has been described with reference to illustrative 
embodiments, this description is not intended to be construed in a 
limiting sense. Various modifications and combinations of the illustrative 
embodiments, as well as other embodiments of the invention, will be 
apparent to persons skilled in the art upon reference to the description. 
It is therefore intended that the appended claims encompass any such 
modifications or embodiments.