Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Involving measuring – analyzing – or testing
Reexamination Certificate
2001-03-09
2002-10-01
Nguyen, Nam (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Involving measuring, analyzing, or testing
C204S228600, C204S229200, C204S232000, C204S237000, C205S101000
Reexamination Certificate
active
06458262
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to silicon wafer electroplating and quantitative analysis of electroplating bath components. More specifically, it relates to analysis of electroplating bath constituents during integrated circuit fabrication. Even more specifically, the invention pertains to a particular monitoring and feedback system used for analysis and control of electroplating bath formulations and plating hardware.
BACKGROUND OF THE INVENTION
Improved integrated circuit fabrication processes continue to necessitate more complex and demanding control of process parameters to ensure wafer uniformity and quality. Electroplating is a good example. Electroplating for integrated circuit fabrication is typically performed in a series of plating steps, with each having a particular hardware configuration and specific plating bath formulation. Often bath formulations include metal salts, acids, and organic additives. More than ever, it is critical to monitor plating bath electrolyte constituents and maintain bath formulations within a specific range of parameters to ensure the desired outcome and quality of a particular plating process.
Conventional methods of assaying bath constituents commonly employ cyclic voltammetric stripping (CVS) or other forms of Faradaic electroanalysis, which have limitations in specificity and sensitivity. For example, voltammetric analyses suffer from lack of detection capability for compounds and ions that are not electrochemically active over the range of potentials used. Additionally, voltammetric analyses are sensitivity-limited by matrix effects (convoluted electrochemical interactions due to the response of breakdown products).
High-pressure liquid chromatography (HPLC) has been proposed as a method to monitor plating bath constituents by Taylor et al. “Electroplating Bath Control for Copper Interconnects,”
Solid State Technology
, vol. 4, issue Nov. 11, 1998. In this article, the authors describe using HPLC to separate electrolyte species. Although HPLC techniques have improved dramatically over the past decade, this type of analysis has limitations with regard to plating bath composition. While organic additives such as accelerators, suppressors, and levelers are well suited for chromatographic separation, some important primary bath species, ions, metal salts, and acids are not. Analysis of purified bath components via chromatography can provide valuable information about organic plating bath electrolyte components, but only provides a partial picture of the plating environment.
Another problem associated with conventional plating bath analysis is time, or more specifically turnaround. Although analysis techniques have improved to include shorter analysis time frames, the time necessary for conventional analyses as compared to the time frame of possible change in a plating bath composition can be inadequate. Presently, concentrations of most chemicals in plating baths are measured by removing a sample from the bath and performing an analysis in a remote lab. Although these “off-line” measurements made in a separate lab are cost effective and reliable, the turnaround is often unacceptable for monitoring and controlling production equipment. Under such conditions, data regarding composition change obtained from plating bath analysis is rendered useless because the data may no longer reflect the actual bath formulation. This can be particularly problematic when such data is used to adjust bath component stoichiometries, i.e. the stoichiometry imbalance noted in the analysis can be compounded by addition of bath components based on inaccurate data.
An improved approach toward monitoring electrolyte composition is “on-line” monitoring; that is, using a system that is integral to plating production hardware and is continually supplied with electrolyte sample for time efficient regular feedback to the plating system. Existing on-line monitoring systems for plating baths rely on titration of bath samples or cyclic voltammetry.
An example of an “on-line” analyzer that uses cyclic voltammetry is the QUALI-LINE AC-1000, from ECI Technology of East Rutherford, N.J. This system has a relatively small footprint, but voltammetric methods suffer the drawbacks as described above. A more elegant approach is utilized by Technic, of Providence, R.I. with their RTA (real time analyzer) system. The RTA uses a probe that is immersed directly into a plating bath electrolyte. Although this system is very simple, and a good monitoring tool, the data obtained from cyclic voltammetry methods is not as accurate or reliable as desired for modem production plating environments.
Systems utilizing “on-line” titration methods also have drawbacks. First, each titration requires one or more chemical reactants that are used only once with the sample being analyzed. These chemicals must be replenished. Second, detection of an endpoint for a titration usually requires an electrode that must be frequently calibrated. Third, such systems have large footprints, due to the syringe assemblies and reservoirs supplying the assemblies. Finally, titrations produce waste, which results in disposal issues.
Another alternative for on-line monitoring is ion chromatography. Besides having large waste streams, this method uses relatively expensive equipment and is of questionable reliability.
What is needed therefore is improved technology for on-line analysis and control of electroplating bath formulations during electroplating and electroplating processes during integrated circuit fabrication.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus for analysis and monitoring of electrolyte bath composition. Based on analysis results, the invention controls electrolyte bath composition and plating hardware. Thus, the invention provides control of electroplating processes based on plating bath composition data. The invention accomplishes this by incorporating accurate bath component analysis data into a feedback control mechanism for electroplating. Bath electrolyte is treated and analyzed in a flow-through system in order to identify plating bath component concentrations and based on the results, the plating bath formulation and plating process are controlled.
One aspect of the invention pertains to methods for monitoring and controlling an electroplating process. These methods may be characterized by the following sequence: (a) obtaining a sample of electrolyte, comprising an acid, a metal salt, and one or more organic components, from the electroplating process; (b) removing an organic fraction of the sample of electrolyte to give a substantially organic-free electrolyte sample; (c) determining the density of the substantially organic-free electrolyte sample; (d) determining at least one of the conductivity and the light absorption of the substantially organic-free electrolyte sample; (e) comparing at least one of the conductivity and the light absorption measurement of the substantially organic-free electrolyte sample with the density in order to determine a concentration value for each of the metal salt and the acid; and (f) adjusting conditions of the electroplating process in response to a comparison of the concentration value for each of the metal salt and the acid, with an associated target value. Methods of the invention can monitor plating bath chemistries “on-line,” that is, during the plating process in real time.
In these methods, the sample of electrolyte is obtained directly from a plating cell of the electroplating process, from a separate sampling vessel of the electroplating process, or from a central plating chemistry vessel.
Methods of the invention find particular use in the context of copper electroplating in a damascene scenario. In damascene copper electroplating, typically copper sulfate, sulfuric acid systems are used. Organic agents are often added to impart leveling, suppressing, or accelerating elements to the plating environment. As well, other inorganic additives may be added such as chloride ion, in the form of hydrochloric
Beyer Weaver & Thomas LLP
Leader William T.
Nguyen Nam
Novellus Systems Inc.
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