Coating processes – Electrical product produced – Integrated circuit – printed circuit – or circuit board
Reexamination Certificate
2000-12-12
2003-01-14
Yoon, Tae H. (Department: 1714)
Coating processes
Electrical product produced
Integrated circuit, printed circuit, or circuit board
C427S385500, C430S271100, C430S302000
Reexamination Certificate
active
06506441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to novolac polymer planarization films for microelectronic devices, such as integrated circuits, and more specifically to planarization films with high temperature stability.
2. Description of the Related Art
Novolac polymers have been used extensively in the manufacture of integrated circuits and other semiconductor and microelectronic devices. In particular, photoresists used for microlithographic patterning of semiconductor structures often contain anovolac component along with a photosensitive agent. See, for example, U.S. Pat. No. 5,601,961 to Nakayama et al.
In addition, novolac polymers are also components of planarizing films used in the fabrication of microelectronic devices to provide a relatively flat surface. See, for example, U.S. Pat. No. 5,276,126 and references therein. As the characteristic feature size on such devices becomes smaller, planarizing films are increasingly important in the device fabrication process. Low weight average molecular weight novolac polymers, i.e. those ranging between about 200 and about 2300 atomic mass units (amu) have been found to be useful in forming planarizing films because they tend to flow more readily than polymers having higher molecular weights.
In a typical process of forming a planarization film, a solution containing a novolac polymer is formulated with a surfactant. The surfactant-containing polymer solution is applied to a substrate by conventional spinning techniques. The polymer solution-coated substrate is heated to evaporate any residual solvent present in the film material and to reduce the viscosity of the film. The reduced viscosity causes the material to flow and enhances leveling of the film on the substrate. One difficulty in using these novolac polymer formulations to form planarizing films is that fuming may be observed on heating. Thermally volatilized material is detrimental in that it may form particles that can lead to defects in the manufactured devices and may clog vacuum lines.
It would be desirable to provide a process of forming a planarizing film from a novolac polymer material that retains the excellent planarization of previous materials but does not fume or smoke on heating.
SUMMARY OF THE INVENTION
In accordance with this invention, a process of forming a planarizing film on a substrate is provided, the process including first applying to the surface of the substrate a solution including a novolac resin having a weight average molecular weight between about 1000 and 3000 amu and wherein the novolac resin is fractionated to remove the molecules with molecular weight below about 350 amu and a surfactant selected from a group consisting of a non-fluorinated hydrocarbon, a fluorinated hydrocarbon and combinations thereof. The process additionally includes heating the solution-covered substrate to form a planarized film.
According to another aspect of the present invention, a substrate having a planarized film applied thereon is provided, the film comprising a novolac resin having a molecular weight between about 1000 and 3000 amu and wherein the novolac resin is fractionated to remove the molecules with molecular weight below about 350 amu and a surfactant selected from the group consisting of a non-fluorinated hydrocarbon, a fluorinated hydrocarbon and combinations thereof.
In yet another embodiment of the invention, there is provided a composition for use in the formation of planarizing films on substrates, the composition comprising the fractionated novolac resin as described above, a surfactant selected from the group consisting of a non-fluorinated hydrocarbon, a fluorinated hydrocarbon and combinations thereof, and an optional organic solvent. The novolac resins used in the composition according to the present invention are fractionated by extraction techniques such as column extraction, liquid-liquid extraction, or supercritical fluid extraction to remove the fraction with molecular weight below about 350 amu.
Using the composition according to the present invention in forming planarizing films, no fuming or smoking is observed during the process of heating a coated substrate.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process of forming a planarizing film according to this invention uses a composition including a novolac resin that has been fractionated to remove low molecular weight components and a surfactant. Novolac polymers and surfactants that can be used in this invention are described in detail in U.S. application Ser. No. 08/271,291, entitled “Novolac Polymer Planarization Films for Microelectronic Structures”, (denoted the '291 application), now U.S. Pat. No. 5,595,547 which is commonly assigned with the present application and is incorporated herein by reference.
As described above, novolac polymers with low molecular weights are especially useful in forming planarizing films because they tend to flow more readily than polymers having higher molecular weights. Polymer molecular weight, as used here, refers to weight average molecular weight, as determined, for example, by gel permeation chromatography, calibrated against polystyrene. According to the present invention, it has been determined that the lowest molecular weight fraction, that is those novolac molecules with molecular weight less than about 350 amu are thermally volatilized when the formulation containing novolac polymers is heated in forming planarizing films. Thus removal of the lowest molecular weight fraction overcomes the problem of fuming or smoking on heating a coated substrate.
Novolac polymers are commercially available or may be derived from reacting phenols or derivatives therefrom, such as ortho-, meta- and para cresol, with formaldehyde or with other aldehyde compounds. The lowest molecular weight fraction can be substantially removed by extraction techniques such as toluene extraction, column extraction, liquid-liquid extraction, and supercritical fluid extraction.
In the toluene extraction process, solid novolac resin is combined with toluene and heated to between approximately 75 and 80° C. The toluene is decanted and a second lot of toluene is added; the mixture is heated; and the toluene is decanted. The remaining solid is a novolac polymer with the lowest molecular weight fraction reduced. An alternative extraction process, column extraction, is performed on a mixture of polymer resin ground to a fine powder and dry silica gel, installed in a glass column. The mixture in the column is eluted with a first solvent mixture, for example, an ethyl acetate and hexane mixture, until a large volume of elution solvent is obtained, capturing the low molecular weight components. The column is then eluted with a second solvent, for example, methanol, from which the novolac polymer with the lowest molecular weight fraction removed is recovered.
In the liquid-liquid extraction process, the novolac polymer is combined with two solvents with different polarity, for example, ethyl acetate and hexane, and mixed with a sonicator. The contents separate into two phases; the polymer with the lowest molecular weight fraction removed is recovered from the bottom layer. A supercritical fluid extraction technique can also be used. In this process, flows of a polar solvent, such as ethyl acetate, ethanol, or methanol, and CO
2
are passed over a novolac polymer sample in an extractor vessel, heated to temperatures in the range between about 60 and 65° C. and pressurized to about 200 to 300 bar. The remaining novolac polymer in the vessel is depleted of the low molecular weight component.
As reported in detail in the appended examples, extraction using the above techniques results in a novolac polymer with increased molecular weight and narrowed polydispersity. Polydispersity is defined as the ratio of the weight average molecular weight to the number average molecular weight. For example, extraction of the phenolic novolac denoted SD-333A, provided by Borden Chemical, Inc. increases the molecular weight from about 900 to between a
Hacker Nigel
Krajewski Todd
Spear Richard
Fish Robert D.
Honeywell International , Inc.
Rutan & Tucker LLP
Thompson Sandra P.
Yoon Tae H.
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