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
1998-10-23
2002-03-26
Hamilton, Cynthia (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
C430S286100, C430S176000, C430S197000, C430S192000, C526S262000, C526S281000, C526S279000, C526S284000
Reexamination Certificate
active
06361926
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polymers of benzocyclobutene monomers having acid functionality and their use in microelectronics applications.
BACKGROUND OF THE INVENTION
In certain applications in the microelectronics industry, such as interlayer insulators for integrated circuits, interposers, flat panel displays, and multichip modules, bumping redistribution, passivation/stress buffers, and thin film build-up layers on printed circuit boards, having a pattern of a dielectric material is useful or even necessary. Methods of forming this pattern include dry etching, wet etching, screen printing, ink jet printing, and use of dielectric materials which are themselves photoimageable.
In dry etching, a mask, composed of a material which is resistant to the etching process (frequently an O
2
plasma), is applied over the dielectric material. A plasma or laser is used to remove portions of the dielectric material which are not protected by the mask. The mask is then removed, leaving a patterned dielectric layer. See for example, Photosensitive Polyimides; Technomic Publishing Company, Inc.; 1995, pp. 254-55.
Similarly, a mask, typically a photoresist, is used in wet etching. The photoresist is applied over the dielectric material and image-wise exposed to activating radiation. The photoresist and the dielectric material are then removed in a corresponding image-wise manner during a developing step (typically with a aqueous base). The remaining photoresist material is subsequently removed, leaving an image-wise distribution of the dielectric material. For examples of this process see e.g. Photosensitive Polyimides; Technomic Publishing Company, Inc.; 1995, pp. 248-253. When the dielectric or dielectric precursor is itself photosensitive, some costs and complexities of the etching methods are avoided. Specifically, there is no need for a mask material and no need to coat, image, and remove the mask material. See for example, Photosensitive Polyimides; Technomic Publishing Company, Inc.; 1995, pp. 258-260. In negative photosensitive systems, the portion of the dielectric material or its precursor which is not exposed to activating radiation is removed during development. In positive systems, the portion of the dielectric material or its precursor which is exposed to activating radiation is removed during development. In other words, positive systems use a dark field mask rather than a light field mask. Positive systems generally have the additional benefit of being less susceptible to contamination than solvent developed negative systems.
Polymers of cyclobutarenes (also referred to herein as benzocyclobutenes) are known to be useful as insulating layers in electrical devices, protective films for semiconductor elements, as passivation films and as photoresists. Negative photosensitive cyclobutarene compositions, developable with a solvent have been developed. See for example, Cyclotene™ Series 4000 available from The Dow Chemical Company;
Negative Tone Photodefinable Benzocyclobutene Formulations For Thin Film MicroElectronic Applications
, Proceedings of 10
th
International Conference on Photopolymers, October-November 1994; and WO 96/31805.
However, a cyclobutarene based composition developable in an aqueous base would be highly desirable. Such a composition would be highly useful in both photosensitive methods and wet etch methods for forming a patterned dielectric.
SUMMARY OF THE INVENTION
The Inventors have developed a cyclobutarene based polymer system having acid functionality. The materials, upon further cure, have excellent qualities of toughness, adhesion, dielectric constant, and low stress. The preferred system is soluble in an aqueous base and can be used to generate patterned films with excellent resolution without the need to handle organic developer solvents.
Thus, according to a first embodiment, the invention is a curable cyclobutarene based polymer comprising acid functional pendant groups. “Curable polymer” as used herein includes polymers that can be further cured or crosslinked as well as oligomers that can be further reacted to form higher molecular weight polymeric materials. Preferably, the acid functional groups are present at equivalent weights of about 200 to about 330 g/mole of acid functionality, more preferably about 220 to about 300 g/mole of acid functionality, and most preferaly about 230 to about 270 g/mole of acid functionality. For the preferred monomer (a) 1,3-bis(2-bicyclo[4.2.0]octa 1,3,5-trien-3-yl ethenyl)-1,1,3,3 tetramethylsiloxane (referred to herein as DVS-bisBCB) and BCB-acrylic acid as made in Example 1, an equivalent weight of less than about 290 g/mole of acid functionality provides solubility in alkaline aqueous solutions. If the amount of acid groups is too low, the material will be insufficiently soluble in aqueous base. If the amount of acid groups becomes too high, water retention by the polymer may become a problem in certain uses or applications of the material.
Preferably, the polymer is the partially polymerized product of monomers comprising
(a) a cyclobutarene monomer having the formula:
wherein
B
1
is an n-valent organic linking group, preferably comprising ethylenic unsaturation,
Ar
1
is a polyvalent aromatic or heteroaromatic group and the carbon atoms of the cyclobutane ring are bonded to adjacent carbon atoms on the same aromatic ring of Ar
1
;
m is an integer of 1 or more;
n is an integer of 1 or more; and
R
1
is a monovalent group;
and (b) a cyclobutarene monomer having a pendant group with acid functionality. Additional monomers, such as acrylate ester functional cyclobutarenes, may also be used. In fact, in effect, a terpolymer can be formed using certain acrylate ester functional cyclobutarene monomers (b′), such as a t-butyl acrylate ester, instead of the acid functional cyclobutarene. Under normal polymerization conditions the t-butyl groups are at least partially eliminated to generate carboxylic acid groups. Alternatively, the acrylate ester functional cyclobutarenes can be at least partially hydrolyzed by conventional methods (Organic Chemsitry, Morrison and Boyd, Allyn and Bacon, N.Y., 1975, 3rd Ed, pp. 675-681) to generate carboxylic acid groups.
According to a second embodiment the invention is a photosensitive composition comprising a curable cyclobutarene based polymer comprising acid functional pendant groups and a photoactive composition which functions as a dissolution inhibitor. Photosensitive as used in this application means that a latent, developable image or an immediately discernible image is formed if the material is exposed to activating wavelengths of radiation.
According to a third embodiment the invention is the use of a curable cyclobutarene based polymer comprising acid functional pendant groups in a wet etch process.
According to a fourth embodiment the invention is the use of a curable cyclobutarene based polymer comprising acid functional pendant groups as an aqueous developable, positive photoresist.
As used herein the term “group” means the structure as shown or recited with or without reasonable substitution so long as that substitution does not effect the function of the group. In contrast, the term “moiety” means the structure shown with no substitution.
DETAILED DESCRIPTION OF THE INVENTION
The cyclobutarene monomer (a) has the formula
wherein
B
1
is an n-valent organic linking group, preferably comprising ethylenic unsaturation, or B
1
is absent. Suitable single valent B
1
groups preferably have the formula —CR
8
═CR
9
Z, wherein R
8
and R
9
are independently selected from hydrogen, alkyl groups of 1 to 6, most preferably 1 to 3 carbon atoms, and aryl groups, and Z is selected from hydrogen, alkyl groups of 1 to 6 carbon atoms, aryl groups, —CO
2
R
7
wherein R
7
is an alkyl group, preferably of up to 6 carbon atoms, an aryl group, an aralkyl group, or an alkaryl group. Most preferably Z is —CO
2
R
7
wherein R
7
is an alkyl group, preferably of up to 6 carbon atoms, an aryl group, an aralkyl group, or an alkaryl
DeCaire Richard P.
DeVries Robert A.
Dibbs Mitchell G.
McGee Robert L.
Radler Michael J.
Hamilton Cynthia
The Dow Chemical Company
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