Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
1999-08-05
2001-02-13
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S270100, C430S325000, C430S330000, C430S327000, C525S326100, C524S555000, C526S312000
Reexamination Certificate
active
06187506
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to novel antireflective coating compositions and their use in forming a thin layer between a reflective substrate and a photosensitive coating. Such compositions are especially useful in the fabrication of semiconductor devices by photolithographic techniques. Furthermore, the novel polymer may be used as an absorbing polymer in photoresist formulations.
Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin coating of film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate any solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.
This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist.
The trend towards the minitiarization of semiconductor devices has led to the use of sophisticated multilevel systems to overcome difficulties associated with such minitiarization. The use of highly absorbing antireflective coatings in photolithography is a simpler approach to diminish the problems that result from back reflection of light from highly reflective substrates. Two deleterious effects of back reflectivity are thin film interference and reflective notching. Thin film interference results in changes in critical linewidth dimensions caused by variations in the total light intensity in the resist film as the thickness of the resist changes. Variations of linewidth are proportional to the swing ratio (S) and therefore must be minimized for better linewidth control. Swing ratio is defined by:
S
=4(
R
1
R
2
)
½
e
−&agr;D
where,
R
1
is the reflectivity at the resist/air or resist/top coat interface,
R
2
is the reflectivity at the resist/substrate interface,
&agr; the resist optical absorption coefficient, and D is the film thickness.
Antireflective coatings function by absorbing the radiation used for exposing the photoresist, that is, reducing R
2
, and thereby reducing the swing ratio. Reflective notching becomes severe as the photoresist is patterned over substrates containing topographical features, which scatter light through the photoresist film, leading to linewidth variations, and in the extreme case, forming regions with complete resist loss.
In the past dyed photoresists have been utilized to solve these reflectivity problems. However, it is generally known that dyed resists only reduce reflectivity from the substrate but do not totally eliminate it. In addition, dyed resists may cause reduction in the lithographic performance of the photoresist, together with possible sublimation of the dye and incompatibility of the dye in resist films. In cases where further reduction or elimination of the swing ratio is required, an antireflective coating is applied to the substrate prior to coating with the photoresist and prior to exposure. The resist is exposed imagewise and developed. The antireflective coating in the exposed area is then etched, typically in an oxygen based plasma, and the resist pattern is thus transferred to the substrate. The etch rate of the antireflective film should be relatively high so that the antireflective film is etched without excessive loss of the resist film during the etch process.
Antireflective coatings containing a dye for absorption of the light and an organic polymer to give coating properties are known. However, the possibility of sublimation and diffusion of the dye into the photoresist layer during the heating process can make these types of antireflective compositions undesirable.
Polymeric organic antireflective coatings are known in the art as described in EP 583,205 and U.S. Par. No. 5,525,457 and incorporated herein by reference. However, these antireflective films are cast from organic solvents, such as cyclohexanone and cyclopentanone. The potential hazards of working with organic solvents, have led to the development of the antireflective coating composition of the instant invention, where the solid components of the antireflective coating are both soluble and spin castable from solvents having lesser toxicity hazards. The preferred solvents that are known in the semiconductor industry to have low toxicity among others are propylene gycol monomethyl etheracetate (PGMEA), propylene gycol monomethylether (PGME), and ethyl lactate.
In another embodiment, by the judicious choice of electrophilic substituents and comonomers, the polymer of the present invention is castable from water. Water based coatings are not only preferred but also provide a distinct advantage in the semiconductor industry due to their ease of handling.
The polymeric coatings disclosed in U.S. Pat. No. 5,652,297 and U.S. Pat. No. 5,652,317 are soluble in the preferred solvents but contain a different pendant chromophore than the present invention. The chromophore disclosed in U.S. Pat. No. 5,733,714 is similar to the present invention but the comonomer in U.S. Pat. No. 5,733,714 contains a crosslinking group. It has now been unexpectedly found that both a homopolymer containing a similar pendant chromophore to the one disclosed in US714, and also a copolymer synthesized from a monomer containing the same pendant chromophore and a comonomer without a crosslinking group, also functions effectively as a bottom coat for the photoresist or as an additive in a photoresist. It has been found that in some instances it is preferable to have a polymer that does not contain a comonomer with a crosslinking group, since this crosslinking group could lead to instability or insolubility of the solution or the coating.
The polymer of the present invention contains a specific dye functionality, and, furthermore, the polymer may be a homopolymer or copolymerized with specific types of monomers that do not contain a crosslinking group. Good coatings are formed with the antireflective coating of the instant invention and, additionally, no intermixing is present between the antireflective coating and the photoresist film. The coating formed from this polymer also has good dry etching properties when used as a bottom coat for a photoresist, which enables a good image transfer from the resist to the substrate and good absorption characteristics to prevent reflective notching and linewidth variations.
SUMMARY
The present invention relates to a novel antireflective coating composition and processes for its use in photolithography. The polymer of the antireflective coating composition comprises at least one unit with a dye and no crosslinking groups. The dye functionality is one that strongly absorbs radiation ranging from about 180 nm (nanometer) to about 450 nm. The antireflective coating composition comprises a solvent and a polymer of the following structure:
where,
R
1
-R
3
are independently H, (C
1
-C
10
) alkyl or (C
1
-C
10
) alkoxy,
R
5
-R
8
do not have a crosslinking group and are independently H, (C
1
-C
10
) alkyl, (C
1
-C
10
) alkoxy, hydroxyalkyl, nitro, halide, cyano, aryl, alkylaryl, alkenyl, dicyanovinyl, SO
2
CF
3
, COOZ, SO
3
Z, COZ, OZ, NZ
2
, SZ, SO
2
Z, NHCOZ, SO
2
NZ
2
, where Z is H or (C
1
-C
10
) alkyl, hydroxy (C
1
-C
10
) alkyl, (C
1
-C
10
)alkylOCOCH
2
COCH
3
, or R
7
and R
8
combine to form a cyclic group,
X
1
is C═O, OCO, CONH, O, aryl, (C
1
-C
10
) alkyl, cyclohexyl, pyridine or pyrollidone,
X
2
is S, S(C
1
-C
10
) alkyl, O, O(C
1
-C
10
) alkyl, NH, N(C
1
-C
10
) alkyl, alkyl, or hydroxyalkyl
Ding Shuji
Durham Dana L.
Gonzalez Eleazer
Khanna Dinesh N.
Shan Jianhui
Chu John S.
Clariant Finance (BVI) Limited
Clarke Yvette M.
Jain Sangya
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