Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-10-24
2003-11-25
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S329600, C525S327400, C525S437000, C525S444000, C525S443000, C525S511000, C525S518000, C525S519000, C525S540000
Reexamination Certificate
active
06653411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is broadly concerned with anti-reflective compositions and methods of forming the compositions for use as anti-reflective coating (ARC) layers on substrates during integrated circuit manufacturing processes. More particularly, the inventive compositions are formed by polymerizing aminoplasts (e.g., melamine, benzoguanamine) in an acidic environment under elevated temperatures to yield cross-linkable, UV absorbing, fast etching compositions.
2. Description of the Prior Art
A frequent problem encountered by photoresists during the manufacturing of semiconductor devices is that activating radiation is reflected back into the photoresist by the substrate on which it is supported. Such reflectivity tends to cause blurred patterns which degrade the resolution of the photoresist. Degradation of the image in the processed photoresist is particularly problematic when the substrate is non-planar and/or highly reflective. One approach to address this problem is the use of a bottom anti-reflective coating (BARC) applied to the substrate beneath the photoresist layer.
Fill compositions which have high optical density at the typical exposure wavelengths have been used for some time to form these BARC layers. The BARC compositions typically consist of an organic polymer which provides coating properties and a dye for absorbing light. The dye is either blended into the composition or chemically bonded to the polymer. Thermosetting BARC's contain a cross-linking agent in addition to the polymer and dye. Cross-linking must be initiated, and this is typically accomplished by an acid catalyst present in the composition. As a result of all these ingredients which are required to perform specific and different functions, prior art BARC compositions are fairly complex.
U.S. Pat. No. 5,939,510 to Sato et al. discloses a BARC composition which comprises a UV absorber and a cross-linking agent. The UV absorber is a benzophenone compound or an aromatic azomethine compound having at least one unsubstituted or alkyl-substituted amino group on the aryl groups. The cross-linking agent disclosed by Sato et al. is a melamine compound having at least two methylol groups or alkoxymethyl groups bonded to the nitrogen atoms of the molecule.
The Sato et al. composition suffers from two major drawbacks. First, in the two-component composition disclosed, the Sato et al. composition does not include a polymeric material thus resulting in insufficient coverage on the surfaces and edges of the substrate features. Furthermore, the UV absorber disclosed by Sato et al. is physically mixed with the cross-linking agent rather than chemically bonded to some component of the composition. As a result, the UV absorber will often sublime, and in many cases sublime and diffuse into the subsequently applied photoresist layer.
There is a need for a less complex anti-reflective composition which provides high reflection control and increased etch rates while minimizing or avoiding intermixing with photoresist layers.
SUMMARY OF THE INVENTION
The present invention overcomes these problems by broadly providing improved anti-reflective compositions which are formed from a minimal number of components (e.g., two or less) and which exhibit the properties necessary in an effective BARC composition.
In more detail, anti-reflective compositions according to the invention include polymers comprising monomers derived from compounds of Formula I and mixtures thereof.
wherein each X is individually selected from the group consisting of NR
2
(with the nitrogen atom being bonded to the ring structure) and phenyl groups, where each R is individually selected from the group consisting of hydrogen, alkoxyalkyl groups, carboxyl groups, and hydroxymethyl groups. Preferred compounds of Formula I include the following:
When used in reference to Formula I, the phrase “monomers derived from compounds of Formula I” is intended to refer to functional moieties of Formula I. For example, each of the structures of Formula II is derived from compounds of Formula I.
wherein: each X is individually selected from the group consisting of NR
2
(with the nitrogen atom being bonded to the ring structure) and phenyl groups, where each R is individually selected from the group consisting of hydrogen, alkoxyalkyl groups, carboxyl groups, and hydroxymethyl groups; and “M
1
” and “M
2
” represent a molecule (e.g., a chromophore or another monomer derived from the compound of Formula I) bonded to X′ or X″. Thus, “monomers derived from the compounds of Formula I” would include those compounds where any of the constituents (i.e., any of the X groups, and preferably 1-2 of the X groups) is bonded to another molecule.
The polymerized monomers are preferably joined by linkage groups selected from the group consisting of-CH
2
—, —CH
2
—O—CH
2
, and mixtures thereof, with the linkage groups being bonded to nitrogen atoms on the respective monomers. For example, Formula III demonstrates two methoxymethylated melamine moieties joined via a —CH
2
— linkage group and two methoxymethylated melamine moieties joined via a —CH
2
—O—CH
2
— linkage group.
Formula IV illustrates two benzoguanamine moieties joined via CH
2
linkage groups.
Finally, Formula V illustrates two methoxymethylated melamine moieties having a chromophore (2,4-hexadienoic acid) bonded thereto and joined via CH
2
linkage groups.
The inventive compositions are formed by providing a dispersion of the compounds of Formula I in a dispersant (preferably an organic solvent such as ethyl lactate), and adding an acid (such as p-toluenesulfonic acid) to the dispersion either prior to or simultaneous to heating of the dispersion to a temperature of at least about 70° C., and preferably at least about 120° C. The quantity of acid added should be from about 0.001-1 moles per liter of dispersant, and preferably from about 0.01-0.5 moles of acid per liter of dispersant. Furthermore, the heating step should be carried out for at least about 2 hours, and preferably from about 4-6 hours. In applications where only benzoguanamine-based moieties are utilized, the heating step should be carried out for a time period of less than about 7 hours, and preferably from about 5.5-6.5 hours.
Heating the starting compounds under acidic conditions causes the compounds to polymerize by forming the previously described linkage groups. The polymers resulting from the heating step should have an average molecular weight of at least about 1,000 Daltons, preferably at least about 5,000 Daltons, and more preferably at least about 5,000-20,000 Daltons. Furthermore, about 12 hours after the heating step the resulting anti-reflective composition should have a decrease of at least about 20%, preferably at least about 40%, and more preferably from about 40-70% in methoxymethylol (—CH
2
OCH
3
) groups than were present in the starting dispersions of Formula I compounds, with the quantity of methoxymethylol groups being determined by the titration procedure as herein defined.
It will be appreciated that the inventive polymer compositions provide significant advantages over prior art compositions in that the polymerized compositions alone act as conventional anti-reflective coating polymer binders, cross-linking agents, and chromophores, thus greatly simplifying the anti-reflective coating system.
In applications where enhanced light absorbance is desired, a chromophore (e.g., 2,4-hexadienoic acid, 3-hydroxy-2-naphthoic acid) can be mixed with the starting dispersion prior to acid and heat treatment. During subsequent acid treatment, the chromophore will chemically bond to the monomers during polymerization.
The resulting polymerized composition is mixed with a solvent to form an anti-reflective coating composition. Suitable solvents include propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, ethyl lactate, and cyclohexanone. The anti-reflective coating composition is subsequently applied to the surface of a substrate (e.g., silicon waf
Huang Runhui
Puligadda Rama
Acquah Samuel A.
Brewer Science Inc.
Hovey & Williams, LLP
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