Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Involving measuring – analyzing – or testing
Reexamination Certificate
2002-12-20
2004-01-06
Koehler, Robert R. (Department: 1775)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Involving measuring, analyzing, or testing
C205S101000, C205S778500, C205S789000, C436S101000, C436S125000
Reexamination Certificate
active
06673226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is concerned with analysis of halide ions in solutions, and in particular with determination of the chloride concentration in acid copper electroplating baths, as a means of providing control over the deposit properties.
2. Description of the Related Art
Electroplating baths typically contain organic additives whose concentrations must be closely controlled in the low parts per million range in order to attain the desired deposit properties and morphology. One of the key functions of such additives is to level the deposit by suppressing the electrodeposition rate at protruding areas in the substrate surface and/or by accelerating the electrodeposition rate in recessed areas. Accelerated deposition may result from mass-transport-limited depletion of a suppressor additive species that is rapidly consumed in the electrodeposition process, or from accumulation of an accelerating species that is consumed with low efficiency. The most sensitive methods available for detecting leveling additives in plating baths involve electrochemical measurement of the metal electrodeposition rate under controlled hydrodynamic conditions, for which the additive concentration in the vicinity of the electrode surface is well-defined.
Cyclic voltammetric stripping (CVS) analysis [D. Tench and C. Ogden, J. Electrochem. Soc. 125, 194 (1978)] is the most widely used bath additive control method and involves cycling the potential of an inert electrode (e.g., Pt) in the plating bath between fixed potential limits so that metal is alternately plated on and stripped from the electrode surface. Such potential cycling is designed to establish a steady-state condition for the electrode surface so that reproducible results are obtained. Accumulation of organic films or other contaminants on the electrode surface can be avoided by periodically cycling the potential of the electrode in the plating solution without organic additives and, if necessary, polishing the electrode using a fine abrasive. Cyclic pulse voltammetric stripping (CPVS), also called cyclic step voltammetric stripping (CSVS), is a variation of the CVS method that employs discrete changes in potential during the analysis to condition the electrode so as to improve the measurement precision [D. Tench and J. White, J. Electrochem. Soc. 132, 831 (1985)]. A rotating disk electrode configuration is typically employed for both CVS and CPVS analysis to provide controlled hydrodynamic conditions.
For CVS and CPVS analyses, the metal deposition rate may be determined from the current or charge passed during metal electrodeposition but it is usually advantageous to measure the charge associated with anodic stripping of the metal from the electrode. A typical CVS/CPVS rate parameter is the stripping peak area (A
r
) for a predetermined electrode rotation rate. The CVS method was first applied to control copper pyrophosphate baths (U.S. Pat. No. 4,132,605 to Tench and Ogden) but has since been adapted for control of a variety of other plating systems, including the acid copper sulfate baths that are widely used by the electronics industry [e.g., R. Haak, C. Ogden and D. Tench, Plating Surf. Fin. 68(4), 52 (1981) and Plating Surf. Fin. 69(3), 62 (1982)].
Acid copper sulfate baths are employed in the “Damascene” process (e.g., P. C. Andricacos, Electrochem. Soc. Interface, Spring 1999, p.32; U.S. Pat. No. 4,789,648 to Chow et al.; U.S. Pat. No. 5,209,817 to Ahmad et al.) to electrodeposit copper within fine trenches and vias in dielectric material on semiconductor chips. In the Damascene process, as currently practiced, vias and trenches are etched in the chip's dielectric material, which is typically silicon dioxide, although materials with lower dielectric constants are under development. A barrier layer, e.g., titanium nitride (TiN), tantalum nitride (TaN) or tungsten nitride (WN
x
), is deposited on the sidewalls and bottoms of the trenches and vias, typically by reactive sputtering, to prevent Cu migration into the dielectric material and degradation of the device performance. Over the barrier layer, a thin copper seed layer is deposited, typically by sputtering, to provide enhanced conductivity and good adhesion. Copper is then electrodeposited into the trenches and vias. Copper deposited on the outer surface, i.e., outside of the trenches and vias, is removed by chemical mechanical polishing (CMP). A capping or cladding layer (e.g., TiN, TaN or WN
x
) is applied to the exposed copper circuitry to suppress oxidation and migration of the copper. Alternative barrier/capping layers based on electrolessly deposited cobalt and nickel are currently under investigation [e.g., A. Kohn, M. Eizenberg, Y. Shacham-Diamand and Y. Sverdlov, Mater. Sci. Eng. A302, 18 (2001)]. The “Dual Damascene” process involves deposition in both trenches and vias at the same time. In this document, the term “Damascene” also encompasses the “Dual Damascene” process.
Acid copper sulfate electroplating baths require a minimum of two types of organic additives to provide good leveling and satisfactory deposit properties. The “suppressor” additive (also called the “polymer”, “carrier”, or “wetter”, depending on the bath supplier) is typically a polymeric organic species, e.g., high-molecular-weight polyethylene or polypropylene glycol, which adsorbs strongly on the copper cathode surface, in the presence of chloride ion, to form a film that sharply increases the overpotential for copper deposition. The “anti-suppressor” additive (also called the “brightener”, “accelerator” or simply the “additive”, depending on the bath supplier) counters the suppressive effect of the suppressor to provide the accelerated deposition needed for good leveling and bottom up filling of Damascene features. From the prior art literature [e.g., J. D. Reid and A. P. David, Plating Surf. Fin. 74(1), 66 (1987); J. J. Kelly, C. Tian and A. C. West, J. Electrochem. Soc. 146(7), 2540 (1999); and R. D. Mikkola and L. Chen, Proc. IEEE 2000 Int. Interconnect Tech. Conf., p. 117 (2000)], the presence of chloride ion is known to be essential to the functioning of the suppressor and anti-suppressor additives in acid copper baths. In order to avoid overplating ultrafine Damascene trenches and vias, a third additive called the “leveler” (or “booster”, depending on the bath supplier) is used. The leveler is typically an organic compound containing nitrogen or oxygen that also tends to decrease the copper deposition rate. Plating bath suppliers generally provide additives in the form of solutions that may contain additives of more than one type, as well as other organic and inorganic addition agents. The suppressor additive may be comprised of more than one chemical species and generally involves a range of molecular weights.
In order to obtain satisfactory deposits, the concentrations of the organic additives used in acid copper plating baths must be accurately analyzed and controlled. The suppressor, anti-suppressor and leveler concentrations in acid copper sulfate baths can all be determined by CVS analysis methods based on the effects that these additives exert on the copper electrodeposition rate. At the additive concentrations typically employed, the effect of the suppressor in reducing the copper deposition rate is usually much stronger than that of the leveler so that the concentration of the suppressor can be determined by the usual CVS response curve or dilution titration analysis [W. O. Freitag, C. Ogden, D. Tench and J. White, Plating Surf. Fin. 70(10), 55 (1983)]. Likewise, the anti-suppressor concentration can be determined by the linear approximation technique (LAT) or modified linear approximation technique (MLAT) described by R. Gluzman [Proc. 70
th
Am. Electroplaters Soc. Tech. Conf., Sur/Fin, Indianapolis, Ind. (June 1983)]. A method for measuring the leveler concentration in the presence of interference from both the suppressor and anti-suppressor is described in U
Bratin Peter
Kogan Alex
Pavlov Michael
Perpich Michael James
Shalyt Eugene
ECI Technology
Koehler Robert R.
Tench D. Morgan
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