Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-03-19
2004-08-24
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S610000, C438S672000, C438S770000
Reexamination Certificate
active
06780765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to microelectronic trenched feature formation and more particularly to the formation of an interconnect from metal nanocrystal seeds.
BACKGROUND OF THE INVENTION
An integrated circuit requires conductive interconnects between semiconducting domains in order to communicate signals therebetween. In order to create ever faster microprocessors, smaller dimension interconnects of higher conductivity materials is an ongoing goal.
As microelectronic efficiencies have increased, interconnects have decreased in dimensional size and efforts have been made to increase the electrical conductivity of interconnect features. There is an ongoing need for ever smaller interconnects.
The rapid miniaturization of interconnects is occurring simultaneously with the transition from Al to Cu metallization for sub-0.25 &mgr;m ICs. The transition from Al to Cu has led to a change in the way interconnects are formed. While Al has been deposited as a blanket layer which is then patterned by reactive ion etching, Cu interconnects are formed by evaporative deposition into preformed (damascene) trenches and vias followed by chemical mechanical polishing (CMP).
As the interconnect width decreases and the aspect ratio increases, conventional vacuum deposition techniques approach the theoretical resolution threshold. Deep, narrow trenches and vias preferentially collect material at the damascene feature edges, leading to void formation. Electrochemical deposition (ECD) is currently the most widely used technique to fill trenches and vias with copper. However, ECD requires a seed layer. Chemical vapor depositions (CVD) and physical vapor depositions (PVD) are well-established Cu seed layer formation techniques.
Nonetheless, CVD and PVD do not inherently fill etched features preferentially over any other portion of substrate having nucleation sites. The preferential seeding of trenches with metal on which CVD or PVD deposited material can grow would yield selective deposition and lower the temperature of heating of the IC substrate during CVD or PVD to assure crystalline growth that degrades fine architecture structures on the substrate. Thus, the semiconductor industry is in need of an interconnect formation process capable of achieving higher resolution at lower temperature and ideally, at a lower cost.
The mesoscopic size regime between atoms and bulk materials is characterized by unusual properties. Mesoscopic systems exhibit collective atomic behavior, but not to a sufficient extent so as to preclude quantized effects. Many of the unusual thermodynamic and spectroscopic anomalies associated with mesoscopic systems are attributable to surface effects. Studies have shown surface energies that are 10 to 400% greater for nanocrystals than for bulk Au and Pt (C. Solliard and M. Flueli, Surf. Sci. 156, (1985), pp. 487-494) and Al (J. Wolterdorf, A. S. Nepijko and E. Pippel, Sur. Sci. 106, (1981), pp. 64-72). In the bulk, surface atoms represent such a small percentage of the total that surface effects are largely inconsequential. Surfaces generally possess modified atomic coordination numbers, geometries and diminished lattice energies relative to the bulk. The result of these modifications is that physical, spectroscopic, and thermodynamic properties, which are constant in the bulk, become size dependent variables in nanocrystals. Since a nanocrystal is a small portion of a bulk material lattice, nanocrystals are exploited in the present invention as seeds to produce thin film IC structures at low temperature.
Metallic nanocrystals have been shown to reduce melting temperatures compared with the bulk. (Ph. Buffat and J-P. Borel, Phys. Rev. A, 13, (1976), pp. 2287-2298. 2287-2298; C. J. Coombes, J. Phys., 2, (1972), pp. 441-449; J. Eckert, J. C. Holzer, C. C. Ahn, Z. Fu and W. L. Johnson, Nanostruct. Matls., 2, (1993). 407-413; C. R. M. Wronski, Brit. J. Appl. Phys. 18, (1967), pp. 1731-1737 and M. Wautelet, J. Phys. D, 24, (1991), 343-346). The depression in melting and annealing temperature is evident throughout the nanocrystal size regime, with the most dramatic effects observed in nanocrystals having a diameter from 2 to 6 nm. Melting studies on a range of nanocrystals have established that the melting temperature is size dependent in the nanometer size regime and is approximately proportional to the inverse particle radius regardless of the material identity. The size dependent melting temperature of metallic nanocrystals has included studies of Au, Pb and In, Al and Sn. (Au: Ph. Buffat and J-P. Borel, Phys. Rev. A, 13, (1976), 2287-2298. 2287-2298; Pb and In: C. J. Coombes, J. Phys., 2, (1972), 441-449; Al: J. Eckert, J. C. Holzer, C. C. Ahn, Z. Fu and W. L. Johnson, Nanostruct. Matls, 2, (1993), 407-413; and Sn: C. R. M. Wronski, Brit. J. Appl. Phys. 18, (1967), 1731-1737). The reduction in melting temperature as a function of nanocrystal size can be enormous. For example, 2 nm Au nanocrystals melt at about 300° C., as compared to 1065° C. for bulk gold. (M. Wautelet, J. Phys. D, 24, (1991), 343-346).
SUMMARY OF THE INVENTION
A method for producing a polycrystalline structure includes applying a metal in the form of nanocrystal seeds to a wafer having a trench or via cut therein. The nanocrystal seeds have a diameter between 2 and 40 nanometers. Thereafter, a substance is deposited onto the nanocrystalline seeds to form a polycrystalline structure. The presence of a nanocrystal seed functions herein as a nucleation site for crystal growth. A method for producing a microelectronic interconnect includes applying a solution comprising soluble copper nanocrystal seeds to a wafer having a trench or via cut therein have a diameter between 2 and 20 nanometers. Thereafter, copper is deposited onto the copper nanocrystal seeds to form a continuous polycrystalline copper interconnect within said trench or via.
A microelectronic structure is detailed including electrically isolated nanocrystalline domains. The domains are formed to an existing trench or via within a wafer substrate.
A method for healing a void in the film includes contacting a solution of nanocrystals dissolved in a solvent to the film and allowing the solvent to evaporate isolating the nanocrystals in the void. Thereafter, the nanocrystals are heated to fill the void with contiguous material derived from the nanocrystals wherein the void has irregular dimensions.
DETAILED DESCRIPTION OF THE INVENTION
A method is detailed herein which uses a metal nanocrystal as a CVD or PVD seed to create interconnects or electrochemical deposition seed layers therefor by conventional processes. While the present invention is not limited to a particular metal, or metallic cation-containing compound such as an oxide, nitride, phosphide, or intermetallic, it is particularly well suited for the efficient formation of copper interconnects at temperatures below 400° Celsius and even below 300° Celsius. A silicon wafer that has been patterned by lithography and etched to form a series of trenches and/or vias is the substrate for the instant invention the exposed surface of which also contains SiO
2
. It is appreciated that an intermediate wetting layer is optionally applied to the substrate to promote interconnect wetting thereof and to prevent interdiffusion during subsequent IC processing.
A semiconductor processing method is provided for growing a polycrystalline metal film by preferably chemical vapor deposition (CVD) from a suitable precursor gas or gases on a substrate which has been coated with metal nanocrystal seeds, of the semiconductor material. The structure of the nanocrystal seeds serves as a template for the structure of the final polycrystalline film. The density of the seeds and the thickness of the grown polycrystalline film determine the grain size of the polycrystalline film at the surface of said film with more seeds, leading to small grain size. CVD onto the seeds to produce the polycrystalline film avoids the recrystallization step generally necessary for the formation of a polycrystalline film,
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Picardat Kevin M.
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