Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
1999-11-23
2003-09-02
Aulakh, Charanjit S. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C556S113000, C556S117000, C556S112000, C568S412000, C568S579000
Reexamination Certificate
active
06613924
ABSTRACT:
BACKGROUND
Chemical vapor deposition (CVD) processes have been of increasing commercial importance over the past decade. A resurgence of interest in CVD of group II metals is due to efforts to reduce the size of device features as the microelectronics industry moves toward ultra large scale integration (ULSI). Use of group II metals, including silver, in interconnect structures having the submicron geometries required by ULSI is motivated by the lower resistivity of these metals. Chemical vapor deposition processes have an advantage over currently used physical vapor deposition processes such as sputtering and vacuum evaporation in the fabrication of submicron vertical interconnects because conformal layers of metals are more easily produced by CVD.
In chemical vapor deposition of metals, a volatile precursor, usually a complex of a metal with an organic ligand, serves as a source of the metal. The precursor is delivered to the substrate in the vapor phase and decomposed on the surface to release the metal. The precursor must exhibit sufficient thermal stability to prevent premature degradation or contamination of the substrate and at the same time facilitate easy handling. In some cases, the precursor must be depositable at a relatively low temperature in order to preserve the characteristics of the underlying layers previously formed. For example, deposition on a polymer substrate requires processing temperatures below the glass transition temperature of the polymer. Additionally, precursors for use in codeposition processes, where more than one metal is deposited, must have no detrimental effect on the coherent deposition of layers when used in the presence of other precursors.
Precursors for many metals are commercially available, including barium, strontium, and copper. However, there are few reports of organosilver complexes used as metal precursors for CVD, and these complexes have been used solely for the deposition of pure silver films. U.S. Pat. No. 4,948,623 to Beach discloses the use of a cyclopentadienyl-based silver precursor for the deposition of pure silver films. Chi et al,
Organonmetallics
, 1996,2575-2578, discusses the synthesis and CVD of a fluorinated &bgr;-diketonato silver(I) complex, with a silylated alkene as the coordinating ligand. Several Japanese patent applications, including JP 07133285, JP 07188256, and JP 08074055, disclose silver(I) fluorinated &bgr;-diketonato precursors with silylated olefins as coordinating ligands. The formation of silver films by CVD has proved to be difficult in comparison to other metals such as copper. The large atomic nucleus of silver may partly account for this difference. In addition, the large coordination sphere and low oxidation state of silver permits a higher coordination number relative to other metals, facilitating the formation and stability of dimeric compounds, and resulting in low volatility of the dimer. Hard soft acid base theory may also partly explain the poor performance of some silver precursors, which fragment and/or lose coordinating ligands during volatilization.
Thus, there is a lack of silver precursors having an attractive balance of properties for commercial use in CVD processes, either for the deposition of pure silver films or for codeposition of silver with other elements, although silver could be advantageously employed in a variety of applications. As discussed above, silver films could be utilized as low resistance interconnects for ULSI circuits. Layers containing phosphors for use in thin film electroluminescent (TFEL) displays, are commonly formed by a CVD process. Known phosphors are based on metal sulfides, activated by one or more dopants. While phosphors that emit red or yellow light of sufficient brightness are well-developed, there exists a need for blue-emitting phosphors for TFEL displays.
SUMMARY OF THE INVENTION
A class of organosilver complexes has now been discovered that are useful as silver precursors for CVD processes. The silver precursors of the present invention have the structure of formula I:
Ag L
1
L
2
n
(I)
wherein
L
1
is a ligand of formula II;
R
1
and R
2
are independently alkyl, substituted alkyl, aryl, arylalkyl, or fluoroalkyl;
R
3
is lower alkyl;
Z
1
and Z
2
are independently O, N or S;
n is0 or 1;
L
2
is a neutral coordinating ligand chosen from PR
3
, thiophene, pyridine, tetramethylethanediamine, (TMEDA), and tetramethylpropanediamine (TMPDA); and
R is C
3
-C
6
alkyl, aryl or alkylaryl.
In one aspect, the present invention relates to a CVD process for the deposition of silver on a substrate comprising vaporizing a silver precursor of formula I, and decomposing the precursor on a substrate.
In another aspect, the present invention relates to a phosphor layer of a thin film electroluminescent device comprising a silver activator dopant. Preferably, the phosphor layer additionally comprises strontium sulfide and a copper coactivator dopant. The present invention also relates to a thin film electroluminescent display panel comprising a silver-doped phosphor, or a phosphor that comprises a silver activator dopant.
In yet another aspect, the present invention relates to a CVD process for the preparation of a phosphor layer of a thin film electroluminescent device comprising vaporizing at least one volatile non-silver metal precursor and a silver precursor of formula III,
Ag L
1
L
3
n
(III)
wherein
L
1
is a ligand of formula II;
R
1
and R
2
are independently alkyl, substituted alkyl, aryl, arylalkyl, or fluoroalkyl;
R
3
is lower alkyl;
Z
1
and Z
2
are independently O, N or S;
n is 0 or 1;
L
3
is a neutral coordinating ligand chosen from PR
3
, thiophene, pyridine, tetramethylethanediamine (TMEDA), tetramethylpropanediamine (TMPDA), vinyltriethylsilane (VTES), vinyltriethoxysilane (VTEXS) and 1,5 cyclooctadiene (COD); and
R is C
2
-C
6
alkyl, aryl or alkylaryl
and decomposing at least one volatile non-silver metal precursor and the silver precursor on the substrate. A preferred non-silver metal is strontium; more preferably strontium and copper are the non-silver metals. The precursors are preferably vaporized under an atmosphere of a reactive gas, and more preferably under an atmosphere of hydrogen sulfide. In this case, hydrogen sulfide serves as a source of sulfur. Preferred &bgr;-diketonate ligands (L
1
) of Formula III are: 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate (hfac), acetylacetonate (acac), 2,2,6,6-tetramethyl-3,5-heptanedionate (tmhd), 1,1,1-trifluoro-2,4-pentanedionate (tfac), 2,2,7-trimethyl-3,5-octanedionate (tmod), 1,1,1-trifluoro-5,5-dimethyl-2,4-pentanedionate (tfh) and 1,1,1,2,2,3,3,7,7,8,8,9,9,9-tetradecafluoro-4,6-nonanedionate (tdf). For L
3
, preferred neutral coordinating ligands are triphenylphosphine, tributylphosphine, triethylphosphine, pyridine, tetramethylethanediamine (TMEDA) tetramethylpropanediamine (TMPDA), vinyltriethylsilane (VTES), vinyltriethoxysilane (VTEXS) and 1,5 cyclooctadiene (COD). Preferred silver precursors are: Ag(acac)(PPh
3
), Ag(hfac)(C
5
H
5
N), Ag(hfac)(PBu
3
), Ag(hfac)(PPh
3
), Ag(hfac)(TMEDA), Ag(hfac)(TMPDA), Ag(tmhd)(PBu
3
), Ag(tmhd)(PPh
3
), Ag(tmod)(PPh
3
), Ag(tmod)(PEt
3
), Ag(tmod)(PBu
3
), Ag(hfac)(COD), Ag(tfac)(VTES), Ag(tfh)(VTES) and Ag(hfac)(VTEXS).
DETAILED DESCRIPTION OF THE INVENTION
Volatile silver precursors for use in chemical vapor deposition processes according to the present invention comprise three elements: a silver ion, Ag
+
, an organic &bgr;-diketonate ligand, and a neutral coordinating ligand. The silver precursors have the structure of formula I:
Ag L
1
L
2
n
(I)
wherein
L
1
is a ligand of formula II;
R
1
and R
2
are independently alkyl, substituted alkyl, aryl, arylalkyl, or fluoroalkyl;
R
3
is lower alkyl;
Z
1
and Z
2
are independently O, N or S;
n is 0 or 1;
L
2
is a neutral coordinating ligand chosen from PR
3
, thiophene, pyridine, tetramethylethanediamine, (TMEDA), and tetramethylpropanediamine (TMPDA); and
R is C
3
-C
6
alkyl, aryl or alkylaryl.
For L
1
, preferred &bgr;-diketonate ligands of Formul
Banger Kulbinder K.
Ngo Silvana C.
Welch John T.
Aulakh Charanjit S.
Gioeni, Esq. Mary Louise
Heslin Rothenberg Farley & & Mesiti P.C.
Research Foundation of State of New York
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