Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/416—Systems
  • G01N27/4161—Systems measuring the voltage and using a constant current supply, e.g. chronopotentiometry

Definitions

• NTRS Technology Roadmap for Semiconductors
• Electroplating is a complex process involving multiple ingredients in the plating bath. - 3 -
• individual solution constituents can be made regularly (such as pH measurement for acid content), and additions made as required.
• addition agents such as brighteners,
• the ability to monitor and control bath composition is a key factor in ensuring uniform and reproducible deposit properties.
• the electronic and morphological properties of the copper films are of principal importance in determining final device performance and reliability.
• the stability of later processes in the Damascene patterning flow depend on repeatable mechanical properties including modulus, ductility, hardness, and
• the throwing power of the electrolyte has a major
• Plating bath analysis for microelectronic applications is strongly driven by the need to limit variability and maintain device yields through maintenance of optimized process parameters.
• One method for controlling such ingredients in an electroplating bath is to make regular additions of particular ingredients based upon empirical rules established by
• voltammetric cycle including a metal plating range and a metal stripping range, for at least two baths of known plating quality and an additional bath whose quality or concentration of - 5 -
• the integrated or peak current utilized during the metal stripping range is correlated with the quality of the bath of known quality.
• the integrated or peak current utilized to strip the metal in the bath of unknown quality is compared to the correlation and its quality evaluated.
• An auxiliary electrode 20 immersed in the plating bath is coupled in series with a function generator and a coulometer to measure the charge from the working electrode 10 during the stripping portion of the cycle.
• the Tench publication pulses the potential, for example at -250 mV for 2 seconds to plate, + 200 mV for a time sufficient to strip, + 1,600 mV to clean for seconds, + 425 mV for 5 seconds to equilibrate, all potentials referenced to a saturated Calomel electrode, after which the cycle is repeated until the - 6 -
• a method for measuring a target constituent of an electroplating solution using an electroanalytical technique is set forth in which the electroplating solution includes one or
• the method comprises a first step in which an electroanalytical measurement cycle of the target constituent is initiated by providing an energy input to a pair of electrodes disposed in the electroplating solution.
• the energy input to the pair of electrodes is provided for at least a predetermined time period corresponding to a time period in which the electroanalytical measurement cycle reaches a steady-state
• an electroanalytical measurement of the energy output of the electroanalytical technique is taken after the electroanalytical measurement cycle has reached the steady-state condition.
• the electroanalytical measurement is then used to determine an amount of the target constituent in the electroplating solution.
• Figure 1 is a diagram of an exemplary analytical cell used to implement an electroanalytical measurement of a an electroplating bath constituents.
• Figures 2 and 3 are graphs illustrating the implementation of a CVS measurement process.
• Figure 4 is a graph illustrating the differences in the electrical response of a new electroplating bath and an old electroplating bath.
• Figure 5 is a graph illustrating an electroanalytical measurement taken in accordance with one embodiment of the present invention.
• Figure 6 is an exemplary calibration graph that may be used to determine the
• Figure 7 is a graph illustrating the effect of different variables on measurements taken during an electroanalytical measurement process.
• Figure 8 is a graph illustrating a normalized curve based on the data of Figure 7 that assists in reducing the effect of the different variables on the measurement data.
• Figure 9 is a schematic block diagram of one embodiment of a dosing system that uses an electroanalytical technique as part of a feedback process to replenish an electroplating bath with a target constituent. - 9 -
• a major category of instrumental analysis suitable for monitoring an electroplating bath is elecfroanalysis.
• the electroanalytical methods use electrically conductive probes,
• Electrodes to make electrical contact with the electroplating solution.
• the electrodes are used in conjunction with electric or electronic devices to which they are attached to measure an electrical parameter of the electroplating solution. The measured parameter is
• Faradaic elecfroanalysis is attractive as an investigative analytical method principally
• Elecfroanalysis further offers the opportunity to study the mechanisms and kinetics of the plating process, and the
• electroanalytical methods are divided into categories according to the electric parameters that are measured.
• the major elecfroanalytical methods include
• Potentiometry measures electric potential (or voltage) while maintaining a constant (normally nearly zero) electric current between the elecfrodes. Amperometry monitors electric current
• Conductometry measures conductance (the ability of a solution to carry an electric current).
• Voltammetry is a technique in which the potential is varied in a regular manner while the current is monitored.
• Polarography is a subtype of voltammetry that utilizes a liquid
• Coulometry is a method that monitors the quantity of electricity (coulombs) that are consumed during an electrochemical reaction involving the analyte.
• Figure 1 shows the schematic wiring diagram for a device useful in practicing the
• the reference electrode 30 may, for example, be a Ag/AgCl double junction or Saturated Calomel Elecfrode (SCE).
• SCE Saturated Calomel Elecfrode
• electrode 10 may be one of several types, including the dropping mercury elecfrode (DME), hanging mercury drop elecfrode (HMDE), mercury thin film electrodes (MTFE), or an inert elecfrode which may be either stationary or of a rotating disc electrode
• DME dropping mercury elecfrode
• HMDE hanging mercury drop elecfrode
• MTFE mercury thin film electrodes
• inert elecfrode which may be either stationary or of a rotating disc electrode
• RDE-type working electrodes with Pt, Pd, Ir, or Rh surfaces are most often employed in
• Figure 1 illustrates use of an RDE-type elecfrode in which relative motion between the working elecfrode 10 and the bath is established by a motor (5) that rotates the working electrode 10. Electrical contact to the working electrode 10 is made by,
• a computer (6) is used to control an electronic potentiostat (7) which controls the energy input between the working electrode 10 and the reference electrode 30.
• instrumentation such as a Pine Instruments potentiostat under IBM computer confrol may be used.
• the energy input sequences may be applied to the working electrode 10.
• the output of the device can also be plotted on an X-Y
• energy input and energy output in the following description of the methods will refer to confrol of the potential (energy input) while monitoring current density (energy output), or control of current density (energy input) while monitoring potential (energy
• CPVS Cyclic Pulsed Voltammetric Stripping
• a metal film is alternately reduced on the working electrode 10 surface and subsequently stripped by anodic dissolution.
• the potentiostat cycle is defined so that the current can be integrated over time during the stripping period, allowing quantification of the electric charge in coulombs
• the charge is directly related to the molar quantity of metal stripped (and therefore to the amount initially deposited) by Faraday's laws.
• the stripping charge is monitored rather than the charge
• the stripping charge is less sensitive to changing elecfrode surface state and less influenced by factors such as charging and impurity currents.
• the current/voltage/time relationship during analysis is extremely sensitive to variations in electroplating bath composition and, not incidentally, measurement conditions such as temperature. If sufficient care is taken in methods development and measurement
• Electrode 20 is swept at a constant rate between user-defined limits.
• the voltage sweep may be repeated several times per analysis cycle, with the working elecfrode 10 alternating between film deposition and stripping, until a repeatable current vs. voltage response is obtained.
• the plot showing current as the dependent variable over the traversed potential range is termed a voltammogram, and provides a kind of 'fingerprint' of the electrochemical response of the elecfroplating bath.
• An example of a voltammogram for an acid copper electrolyte of specific composition is shown as Figure 2, with the regions associated with
• the area of the current peak associated with stripping is proportional to the stripping charge and, therefore, to variation in the electrolyte composition.
• CPVS differs in that the potential between working electrode 10 and auxiliary elecfrode 20 is not swept over a range at a constant rate, but rather stepped between discrete values while the pulse width at each voltage is either held to fixed times (e.g., during
• V c ⁇ ea n a high anodic potential (V c ⁇ ea n ) for a few seconds, followed by a few seconds at V e q U iii b eration •
• Metal is deposited on the elecfrode surface during a cathodic pulse V p ⁇ ate then anodically dissolved at V str j P until all the metal is removed (i.e., stripping current is extinguished).
• CVS interprets this as plating bath suppression because the CVS technique never reaches steady-state - 15 -
• the normally used scan rate is 100 mV/sec giving a total metal deposition
• Figure 4 is a plot of a used and new bath with approximately the same amount of suppressor in each. Note that at a time of 5 seconds, the current exhibited by the used bath is much less than that of the new bath. This difference is mistakenly measured by the CVS method as extra suppressor.
• inventive analysis techniques set forth herein modify existing techniques so that the analytical measurements are taken as the particular technique achieves or approaches a steady-state condition.
• inventive analysis techniques include, but are not
• Suppressor analysis using chronoamperometry can be performed using a series of basic steps, some of which are optional, including:
• a preferred manner of executing the chronoamperometry includes the following 17 -
• the potentials listed are relative to a Ag-AgCl electrode.
• FIG. 5 An example CA analysis is shown in Figure 5 where the measured parameter is current at a user specified time.
• the current is measured at about 60 seconds.
• the calibration curve mentioned in step 1 above comprises a series of CA plots of
• the optional next step is to mathematically calculate the rate of suppression by taking the 1 st derivative of the data shown in Figure 7. This calculated data is shown in Figure 8 and - 18 -
• the final step is to relate the data taken and/or take data in such a way so that the amount of suppressor in the bath can be calculated.
• concentration tifration refers to a method that
• Step 2 Perform a CA measurement using the electroplating bath removed in Step 1, ensuring that the measurement is taken during the CA process as it approaches or reaches a steady-state (e.g., by using the preferred process steps set forth above);
• additive i.e., suppressant
• Exemplary Method I is advantageous in that it is a very simple process to implement.
• a disadvantage of this approach is the fact that it requires a predetermined calibration curve. - 20 -
• the second exemplary method involves concentration tifration using the unknown
• Step 2 Perform a CA measurement using the electroplating bath removed in Step 1, ensuring that the measurement is taken during the C A process as it approaches or reaches a steady-state (e.g., by using the preferred process steps set forth above);
• the measurement is taken during the CA process as it approaches or reaches a steady-state (e.g., by using the preferred process steps set forth above);
• the third exemplary method involves concentration tifration using the diluted
• the measurement is taken during the CA process as it approaches or reaches a
• Step 5 Perform a CA measurement using the solution formed in Step 4, ensuring that the measurement is taken during the CA process as it approaches or reaches a
• Steps 4 and 5 as necessary to generate a slope, or to otherwise gather enough data to answer a logic criteria (e.g., is the concentration below the "knee"); - 22 -
• Exemplary Method III exhibits an increased accuracy over Exemplary Method II by diluting the electroplating bath sample to the more accurate end of the calibration curve
• the fourth exemplary method involves concentration tifration using Virgin Make-Up (VMS) as the diluent and the unknown bath as the titrant.
• VMS Virgin Make-Up
• Step 3 Perform a CA measurement using the solution formed in Step 2, ensuring that the measurement is taken during the CA process as it approaches or reaches a
• Step 5 Perform a CA measurement using the solution formed in Step 4, ensuring that the measurement is taken during the CA process as it approaches or reaches a
• the fifth exemplary method involves concentration tifration using using linear slope analysis. To this end, the following process steps may be implemented:
• the measurement is taken during the CA process as it approaches or reaches a
• the measurement is taken during the C A process as it approaches or reaches a steady-state (e.g., by using the preferred process steps set forth above);
• Step 7 Perform a CA measurement using the solution formed in Step 6, ensuring that the measurement is taken during the CA process as it approaches or reaches a steady-state (e.g., by using the preferred process steps set forth above);
• the sixth exemplary method involves dilution tifration and comprises performing a CA test on the unknown bath, dividing the unknown bath by diluting it with Virgin Make-Up
• VMS Video Solution
• the measurement is taken during the CA process as it approaches or reaches a steady-state (e.g., by using the preferred process steps set forth above); - 25 -
• Step 4 Perform a CA measurement using the solution formed in Step 3, ensuring that the measurement is taken during the CA process as it approaches or reaches a
• Exemplary Method VI is advantageous in that it is relatively easy to implement.
• the method can be repeated until the sensitive range of the calibration curve is reached thereby providing for a wide range of measurement sensitivity and resolution.
• Such systems may be suitable for certain - 26 -
• both the plating bath constituents may be obtained using a dosing system that employs measurement feedback to ascertain the proper quantity of a bath
• dosing system shown generally at 100, includes a cenfral processor 105 that is used to confrol the operations necessary to perform the following functions: 1) extract a sample of the electroplating bath that is to be analyzed; 2) execute an elecfroanalytical technique on the electroplating bath sample; 3) calculate the amount of the electroplating bath constituent present in the sample based on the results of the electroanalytical technique; and 4) use the resulting calculation to automatically confrol the supply of an amount of the constituent to replenish the elecfroplating bath, raising the constituent concenfration to a predetermined level.
• the central processor 105 is connected to
• a bath sample extraction unit 110 is connected for control by the cenfral processor 105.
• the bath is connected for control by the cenfral processor 105.
• sample extraction unit 110 is connected to receive electroplating solution along line 120 from the principal elecfroplating bath 115 in response to control signals/commands received from the cenfral processor 105 along communication link 125. In response to such confrol
• the bath sample extraction unit 110 provides the bath sample to either an elecfroanalysis unit 130 or to an optional tifration system 135.
• Both the elecfroanalysis unit 130 and the optional tifration system 135 are under the - 27 -
• the central processor 105 coordinates the activities of
• the electroanalytical technique can be any of the known techniques, or can be any of the known techniques.
• the central processor 105 that acquires the requisite data based on the electroanalytical technique to directly calculate or otherwise determine in a relative manner the concentration of the plating bath constituent. Based on this calculation/determination, the
• central processor 105 directs one or more constituent dosing supply units 140 to provide the necessary amount of the constituent (or amount of solution containing the constituent) to the elecfroplating bath 115, thus completing the feedback control process.
• Dosing system 100 is merely provided as an illustrative, yet novel manner in which to implement one

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• 1999
  • 1999-05-03 KR KR1019997012635A patent/KR20010014440A/ko not_active Application Discontinuation
  • 1999-05-03 EP EP99921622A patent/EP0993606A1/en not_active Withdrawn
  • 1999-05-03 WO PCT/US1999/009659 patent/WO1999057549A1/en not_active Application Discontinuation
  • 1999-05-03 JP JP55571099A patent/JP2002506531A/ja active Pending
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