Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal coating
Reexamination Certificate
2001-12-05
2003-05-13
Wong, Edna (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal coating
C205S297000, C205S291000, C205S210000
Reexamination Certificate
active
06562222
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a copper electroplating solution for forming copper wiring on a semiconductor wafer, and more specifically to a copper electroplating solution, a pretreatment liquid for copper electroplating, and a method of copper electroplating suitable for filling fine via holes or trenches formed on a semiconductor wafer without producing defects such as voids or seams.
BACKGROUND OF THE INVENTION
In processing semiconductor wafers, aluminum has chiefly been used as a wiring material; however, as the density of wirings integration increases, copper, which has higher electric conductivity, has substituted aluminum to prevent increase in the delay time of signals.
For the formation of copper wirings, the Damascene method is used, in which after forming a wiring pattern on a silicon wafer, a barrier layer and a seed layer are formed using a CVD method or a sputtering method, then the wiring pattern is filled using electroplating, and excessively deposited copper is removed using CMP (chemical-mechanical polishing).
In order to form a copper wiring on the semiconductor wafer, as described above, it is required to fill via holes or trenches. In recent times, however, since the wiring patterns have become finer, the coverage of the copper seed layers in via holes or trenches formed using sputtering or the like have become poor, and the portions where the copper films is extremely thin are often produced.
Although an electroplating solution based on an aqueous solution containing copper sulfate acidified with sulfuric acid has generally been used for the above-described copper electroplating, the use of such an electroplating solution acidified with sulfuric acid has caused a phenomenon of easy dissolution of copper seed layers by the sulfuric acid contained in the electroplating solution.
Therefore, there have been problems that copper is not deposited, and defects such as voids and seams occur inevitably on the area lacking the seed layer due to this dissolution.
Heretofore, copper electroplating solutions and methods of electroplating, which enable the filling without copper seed layer dissolution, have not existed, and the method for solving the problems has been sought.
OBJECTS OF THE INVENTION
The object of the present invention is to develop a copper electroplating solution and a method of electroplating for filling fine via holes or trenches of a wiring (LSI) pattern formed on a semiconductor wafer. This is accomplished by adding a copper dissolution inhibiting component in the electroplating solution or by pretreatment using a solution that contains a copper dissolution inhibiting component to inhibit the dissolution of the cooper seed layer of poor coverage and to prevent producing defects such as voids or seams.
SUMMARY OF THE INVENTION
In view of the above-described problems, the present invention provides a copper electroplating solution containing an azole or silane coupling agent, such as, 1 to 10000 mg/L, or 10 to 5000 mg/L, of the azole or silane coupling agent. The copper electroplating solution can be a copper sulfate electroplating solution containing copper sulfate, sulfuric acid, chlorine, and additives as major components. The present invention also provides a pretreatment solution for copper electroplating containing an azole or silane coupling agent, such as, 1 to 10000 mg/L, or 10 to 5000 mg/L, of the azole or silane coupling agent.
The present invention also provides a method of copper electroplating including immersion in a copper sulfate electroplating solution containing the azole or silane coupling agent and, as major components, copper sulfate, sulfuric acid, chlorine, and additives for 1 to 60 seconds, or for 3 to 10 seconds. The copper electroplating solution contains 1 to 10000 mg/L, or 10 to 5000 mg/L, of the azole or silane coupling agent. The electroplating can also be carried out using a copper sulfate electroplating solution containing copper sulfate, sulfuric acid, chlorine, and additives as major components after the step of immersion in an aqueous solution containing an azole or silane coupling agent, for instance, for 1 to 60 seconds, or for 3 to 10 seconds. The aqueous solution can contain 1 to 10000 mg/L, or 10 to 5000 mg/L, of the azole or silane coupling agent.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A via hole or a trench for filling copper wiring is formed on the surface of a semiconductor (such as silicon) wafer, and is covered with a barrier metal selected from a group consisting of titanium (Ti), tantalum (Ta), tungsten (W), the nitrides thereof, and the like, of a thickness of about 0.01 to 0.1 &mgr;m, for preventing the diffusion of copper (Cu) into silicon (Si) on the surface by a covering method such as vapor deposition sputtering and CVD method or the like.
On the barrier metal layer is deposited a thin copper layer (seed layer) using a covering method such as vapor deposition, sputtering, and CVD, similarly to the above.
Since the above-described barrier metal has generally a high electric resistance, and in subsequent copper electroplating to be covered, difference in current densities between the vicinity of the contact provided in the circumferential portion of the wafer and the central portion becomes large, copper, which has a low electric resistance, is previously applied (thin coating).
The thickness of the copper layer is 0.01 to 0.1 &mgr;m. However, the thickness of the copper layer may be determined optionally in semiconductor processing, and is not limited to the above-described range.
In general, the copper wiring (LSI etc.) is formed by using a process, in which after forming a wiring pattern on a silicon wafer using the Damascene method, a barrier layer and a seed layer (a thin copper layer) are formed using a CVD method or a sputtering method, then the wiring pattern is filled using electroplating, and excessively deposited copper is removed using CMP (chemical-mechanical polishing).
The present invention uses a copper electroplating solution containing an azole or silane coupling agent, in place of conventional copper electroplating methods for filling.
The addition of an azole or silane coupling agent to the copper electroplating solution is a significant feature of the present invention, and effectively inhibits the dissolution of the seed layer formed by sputtering.
As a result, the problems of the occurrence of defects such as voids and seams in conventional copper electroplating methods for filling can be solved at a stroke.
The azole added to the above-described electroplating solution is the general term for heterocyclic compounds with five atoms having two or more different atoms, among which at least one is a nitrogen atom.
The representative example of the azoles include imidazole, thiazole, 1,2,3-triazole, 1,2,3-thiazole, 1,2,3,4-tetrazole, 1,2,3,4-thiatriazole, bendazole, benzimidazole, 1,2,3-benzotriazole, and 5-methyl-1-H-benzotriazole.
These azoles have an excellent effect in that they form a complex compound with copper by the lone election pair of nitrogen atoms to form a durable film on the surface of copper, which inhibits dissolution by an acid.
Also, the silane coupling agent is an organo-silicic compound (silane) having the action to chemically bond an organic material with an inorganic material (coupling), and has an organic functional group (X) having affinity (or reactivity) with the organic material and a hydrolyzing group (OR) having affinity (or reactivity) with the inorganic material. The chemical structure thereof is represented by a general formula, XSi(OR)
3
.
The representative example of the silane coupling agents includes imidazole silane as indicated by the following general formulas (1), (2), and (3).
(where R
1
denotes a hydrogen atom, a vinyl group, or an alkyl group having 1 to 5 carbon atoms; R
2
denotes a hydrogen atom, or an alkyl group having 1 to 20 carbon atoms; each of R
3
and R
4
denotes an alkyl group having 1 to 3 carbon atoms; and n denotes an integer from 1 to 3.); aminosilanes (e.g., &ggr;-aminoprop
Sekiguchi Jyunnosuke
Yamaguchi Syunichiro
Howson and Howson
Nikko Materials Company Limited
Wong Edna
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