Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-04-14
2002-12-03
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S448000, C428S450000, C427S096400, C427S387000, C438S781000
Reexamination Certificate
active
06489030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the formation of microelectronic devices such as integrated circuit structures. More particularly, the invention relates to microelectronic devices having a cured polycarbosilane barrier layer.
2. Description of the Related Art
The production of microelectronic devices requires multilevel wiring interconnects regions within the devices. In forming such structures, it is conventional to provide a substrate having first level wiring lines, an interlayer dielectric (ILD) and then second level wiring lines. One or more interconnections are typically formed between the first and second level wiring lines. Openings are formed in the dielectric layer which are filled with a metal to form an interconnect. After the two level interconnect structure is formed, it is necessary to provide another interlevel dielectric (ILD) layer to accommodate further processing of the integrated circuit device. The intermetal dielectric layer usually consists of a layer of a dielectric or an oxide such as silicon oxide which is deposited by plasma enhanced chemical vapor deposition or other processes. The introduction of Cu as the interconnect metal has greatly reduced the RC delay and improved speed of integrated circuits. However, the use of Cu as the interconnect metal also introduces many integration challenges. Copper is known to be a fast diffuser through several dielectrics including silicon dioxide. This leads to integration difficulty for copper damascene structures. A dielectric diffusion barrier on top of the copper conductor is therefore needed. When the damascene approach is taken for forming integrated circuits with copper interconnections, the current fabrication method requires a layer of silicon nitride film on top of the copper interconnection to prevent upward copper diffusion into the ILD. Silicon nitride acts as a copper diffusion barrier over the copper interconnects, however its use involves other problems. In particular, it has a high dielectric constant of about 8 and thus degrades speed and performance resulting from increased in-line and inter-level capacitance and causes a larger RC delay. This speed degradation becomes unacceptable for integrated circuits fabricated using 0.18 &mgr;m and more advanced technologies.
According to the invention, these problems are solved by use of a cured polycarbosilane diffusion barrier instead of silicon nitride. Polycarbosilanes are a class of polymer with Si and C as the elements of the polymer backbone. They are inherently less polarizable than silica. Polycarbosilanes contain organic (carbon and hydrogen) or inorganic (hydrogen) groups bonded directly to silicon. These materials are inherently hydrophobic and have low dielectric constants due to their low polarizability and low silanol content. Another advantage of polycarbosilanes is that they are thermally stable. For example, a bridging alkyl group (between Si atoms) is more thermally stable than a pendant alkyl on Si by up to 100° C. Therefore, a low dielectric constant material with good thermal stability can be prepared with polycarbosilanes.
Polycarbosilanes have been used heretofore in the art for the preparation of microelectronic devices. One approach for producing semiconductor devices is known from U.S. Pat. No. 5,602,060 where a polycarbosilane polymer is coated over a semiconductor substrate and then reacted in an oxidizing atmosphere to produce a silicon oxide layer. The present invention does not react polycarbosilanes in an oxidizing atmosphere to convert it to silicon oxide. Rather, the polycarbosilane is cured in an inert or reducing atmosphere to produce a dense, crosslinked polycarbosilane reaction product. As disclosed in Polymerization of C—Si Films on Metal Substrates: Potential Aahesion/diffuision Barrier for Microelectronic, by Li-Chen, et al in Mat. Res. Soc. Symnp. Proc. Vol. 511, 1998. P 297, a monomer (vinyltrichiorosilane or vinyltrimethylsilane) was adsorbed onto substrate surface and then electron beam was used to induce polymerization of the monomer. This led to the formation of film with thickness about 100 Angstroms. However, it is very difficult to form a thick film from this approach. Another problem associated with this approach is that the polymer formed is not thermally stable. For the diffusion barrier or dielectric application, the materials need to be thermally stable up to about 400° C.
The criteria for a good Cu diffusion barrier are a high crosslinking density, i.e. low free volume is necessary, high density, there is no interaction between the barrier and copper, and a high Tg. With a high Tg, the free volume available for copper diffuision is reduced and high film density provides better diffuision barrier characteristics. The polycarbosilanes-derived films of this invention are very dense. The refractive index of the film derived form hydridopolycarbosilane is about 1.54 after cure while refractive index for SiO
2
is 1.46. In general, as refractive index increases film density increases. Also the cured films have a high Tg and high crossinking density and copper is not expected to chemically interact with polycarbosilanes-derived films. Therefore, the cured films prepared from polycarbosilanes have low dielectric constant, high density, high Tg, high crosslinking density, and are a good copper barrier.
SUMMARY OF THE INVENTION
The invention provides a microelectronic device comprising a substrate, and a diffusion barrier layer on a surface of the substrate, which diffusion barrier layer comprises a cured polycarbosilane polymer. Preferably the diffusion barrier layer is a copper diffusion barrier.
The invention also provides a process for producing a microelectronic device which comprises depositing a diffusion barrier layer on a surface of the substrate, which diffusion barrier layer comprises a polycarbosilane polymer, and then curing the polycarbosilane polymer in a substantially inert gas or reducing atmosphere to thereby form a cured polycarbosilane polymer on a surface of the substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
According to the invention, a dielectric layer is deposited onto a substrate. Typical substrates include those suitable to be processed into an integrated circuit or other microelectronic device. Suitable substrates for the present invention non-exclusively include semiconductor materials such as gallium arsenide (GaAs), germanium, silicon, silicon germanium, lithium niobate and compositions containing silicon such as crystalline silicon, polysilicon, amorphous silicon, epitaxial silicon, and silicon dioxide (SiO
2
) and mixtures thereof.
Lines may optionally be on the substrate surface. The lines, when present, are typically formed by well known lithographic techniques and may be composed of a metal, an oxide, a nitride or an oxynitride. Suitable materials for the lines include silica, silicon nitride, titanium nitride, tantalum nitride, aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten, silicon oxynitride, and other types of dielectrics. These lines form the conductors or insulators of an integrated circuit. Such are typically closely separated from one another at distances preferably of from about 20 microns or less, more preferably from about 1 microns or less, and most preferably of from about 0.05 to about 1 microns.
The dielectric may be on and between the lines. The dielectric composition may comprise any of a wide variety of dielectric forming materials which are well known in the art for use in the formation of microelectronic devices. The dielectric layer may nonexclusively include vapor phase deposited silicon oxide, carbon doped silica, particularly vapor phase deposited carbon doped silica, carbon doped silicon oxide, and silicon oxynitride, silicon containing spin-on glasses, i.e. silicon containing polymer such as an alkoxysilane polymer, a silsesquioxane polymer, a siloxane polymer; a poly(arylene ether), a fluorinated poly(arylene ether), other polymeric dielectric materials, na
Drage James S.
Wu Hui-Jung
Dawson Robert
Honeywell International , Inc.
Keehan Christopher
Roberts & Mercanti LLP
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