Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal coating
Reexamination Certificate
1999-03-05
2003-04-08
Gorgos, Kathryn (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal coating
Reexamination Certificate
active
06544399
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to new formulations of metal plating solutions designed to provide uniform coatings on substrates and to provide defect free filling of small features, e.g., micron scale features and smaller, formed on substrates with metals.
2. Background of the Related Art
Electrodeposition of metals has recently been identified as a promising deposition technique in the manufacture of integrated circuits and flat panel displays. As a result, much effort is being focused in this area to design hardware and chemistry to achieve high quality films on substrates which are uniform across the area of the substrate and which can fill or conform to very small features.
Typically, the chemistry, i.e., the chemical formulations and conditions., used in conventional plating cells is designed to provide acceptable plating results when used in many different cell designs, on different plated parts and in numerous different applications. Cells which are not specifically designed to provide highly uniform current density (and the deposit thickness distribution) on specific plated parts require high conductivity solutions to be utilized to provide high ‘throwing power’ (also referred to as high Wagner number) so that good coverage is achieved on all surfaces of the plated object. Typically, a supporting electrolyte, such as an acid or a base, or occasionally a conducting salt, is added to the plating solution to provide the high ionic conductivity to the plating solution necessary to achieve high ‘throwing power’. The supporting electrolyte does not participate in the electrode reactions, but is required in order to provide conformal coverage of the plated material over the surface of the object because it reduces the resistivity within the electrolyte, the higher resistivity that otherwise occurs being the cause of the non-uniformity in the current density. Even the addition of a small amount, e.g., 0.2 Molar, of an acid or a base will typically increase the electrolyte conductivity quite significantly (e.g., almost double the conductivity).
However, on objects such as semiconductor substrates that are resistive, e.g., metal seeded wafers, high conductivity of the plating solution negatively affects the uniformity of the deposited film. This is commonly referred to as the terminal effect and is described in a paper by Oscar Lanzi and Uziel Landau, “Terminal Effect at a Resistive Electrode Under Tafel Kinetics”, J. Electrochem. Soc. Vol. 137, No. 4 pp. 1139-1143, April 1990, which is incorporated herein by reference. This effect is due to the fact that the current is fed from contacts along the circumference of the part and must distribute itself across a resistive substrate. If the electrolyte conductivity is high, such as in the case where excess supporting electrolyte is present, it will be preferential for the current to pass into the solution within a narrow region close to the contact points rather than distribute itself evenly across the resistive surface, i.e., it will follow the most conductive path from terminal to solution. As a result, the deposit will be thicker close to the contact points. Therefore, a uniform deposition profile over the surface area of a resistive substrate is difficult to achieve.
Another problem encountered with conventional plating solutions is that the deposition process on small features is controlled by mass transport (diffusion) of the reactants to the feature and by the kinetics of the electrolytic reaction instead of by the magnitude of the electric field as is common on large features. In other words, the replenishment rate at which plating ions are provided to the surface of the object can limit the plating rate, irrespective of voltage. Essentially, if the voltage dictates a plating rate that exceeds the local ion replenishment rate, the replenishment rate dictates the plating rate. Hence, highly conductive electrolyte solutions that provide conventional “throwing power” have little significance in obtaining good coverage and fill within very small features. In order to obtain good quality deposition, one must have high mass-transport rates and low depletion of the reactant concentration near or within the small features. However, in the presence of excess acid or base supporting electrolyte, (even a relatively small excess) the transport rates are diminished by approximately one half (or the concentration depletion is about doubled for the same current density). This will cause a reduction in the quality of the deposit and may lead to fill defects, particularly on small features.
It has been learned that diffusion is of significant importance in conformal plating and filling of small features. Diffusion of the metal ion to be plated is directly related to the concentration of the plated metal ion in the solution. A higher metal ion concentration results in a higher rate of diffusion of the metal into small features and in a higher metal ion concentration within the depletion layer (boundary layer) at the cathode surface, hence faster and better quality deposition may be achieved. In conventional plating applications, the maximum concentration of the metal ion achievable is typically limited by the solubility of its salt. If the supporting electrolyte, e.g., acid, base, or salt, contain a co-ion which provides a limited solubility product with the plated metal ion, the addition of a supporting electrolyte will limit the maximum achievable concentration of the metal ion. This phenomenon is called the common ion effect. For example, in copper plating applications, when it is desired to keep the concentration of copper ions very high, the addition of sulfuric acid will actually diminish the maximum possible concentration of copper ions. The common ion effect essentially requires that in a concentrated copper sulfate electrolyte, as the sulfuric acid (H
2
SO
4
) concentration increases (which gives rise to H
+
cations and HSO
4
−
and SO
4
−
anions), the concentration of the copper (II) cations decreases due to the greater concentration of the other anions. Consequently, conventional plating solutions, which typically contain excess sulfuric acid, are limited in their maximal copper concentration and, hence, their ability to fill small features at high rates and without defects is limited.
Therefore, there is a need for new formulations of metal plating solutions designed particularly to provide good quality plating of small features, e.g., micron scale and smaller features, on substrates and to provide uniform coating and defect-free fill of such small features.
SUMMARY OF THE INVENTION
The present invention provides plating solutions having novel blends of specific additives that enhance defect-free fill of small features. The plating solutions promote uniform metal deposition within the features and can provide highly reflective metal surfaces without polishing. The plating solutions typically contain little or no supporting electrolyte (i.e., which include no acid, low acid, no base, or no conducting salts) and/or high metal ion concentration (e.g., copper). The additives that enhance uniform deposition include a polyether (“carrier”), such as a polyalkylene glycol, wherein the concentration of the carrier ranges from about 0.1 ppm to about 2500 ppm of the plating solution. The additives further include an organic divalent sulfur compound (“accelerator”), wherein the concentration of the accelerator ranges from about 0.05 ppm to about 1000 ppm of the plating solution. The plating solution may further include halide ions at a concentration from about 5 ppm to about 400 ppm. The plating solutions may also contain additives which enhance the plated film quality and performance by serving, inter alia, as brighteners, levelers, surfactants, grain refiners, and stress reducers. An organic nitrogen compound is preferably added to the compositions at a concentration from about 0.01 ppm to about 1000 ppm to improve the filling of vias on a resistive substrate. Most pre
D'Urso John J.
Landau Uziel
Applied Materials Inc.
Gorgos Kathryn
Leader William T.
Thomason, Moser and Patterson LLP
LandOfFree
Electrodeposition chemistry for filling apertures with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrodeposition chemistry for filling apertures with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrodeposition chemistry for filling apertures with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3080138