US20060289299A1

US20060289299A1 - Multi-channel current probe

Info

Publication number: US20060289299A1
Application number: US11/158,976
Authority: US
Inventors: Stephen LeBlanc; Gene Nesmith; James Shirck
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2005-06-22
Filing date: 2005-06-22
Publication date: 2006-12-28

Abstract

A current probe for measuring electrodeposition plating currents. The current monitoring probe includes a conductive layer located on a front face of the current monitoring probe, an insulating layer behind the conductive layer, and a plurality of current sensing circuits located behind the insulating layer. The insulating layer isolates the current sensing circuits from the conductive layer. A plurality of apertures are formed through the conductive layer and the insulating layer, each aperture exposing one of the plurality of current sensing circuits to metal ions incident to the aperture.

Description

FIELD

The present invention relates to a system and method for monitoring and adjusting fields associated with the electrodeposition of a metal onto a surface. More particularly, the present invention relates to a system for monitoring the spatial variation of the current and current density to obtain a desired thickness of electroplated metal.

BACKGROUND

Electrodeposition of a metal onto a surface has many applications. One such application is the deposition of a metal, typically copper, onto a flexible substrate in order to create interconnects on the flexible substrate. Interconnects are essentially low-resistance transmission lines with precisely controlled propagation characteristics. In order to control these propagation characteristics, the thickness of the metal plating must be precisely controlled. Typically, this requires that the electroplated metal be deposited in uniform layers onto the flexible substrate. Uniformity of electrodeposited layers is influenced by the design and adjustment of the plating system, including the current distribution seen by the flexible substrate. If the current distribution is uneven across the flexible substrate, then the plating thickness will also be uneven.
Typical methods of testing and measuring plating uniformity include placing a substrate through the electroplating machine, running the electroplater for an amount of time, removing the substrate from the electroplating machine, and measuring thickness variation using an X-ray fluorescence machine. The plating machine is adjusted based on the results of the X-ray fluorescence machine, and another trial is run until the desired distribution is determined. However, this iterative method of plating and measuring is both costly and time-consuming.

SUMMARY

In one aspect, the present invention provides a current probe for measuring local electrodeposition plating currents. The current probe comprises a conductive layer located on a front face of the current probe, an insulating layer located adjacent to the conductive layer, and a plurality of current sensing circuits located adjacent to the insulating layer, wherein the insulating layer is located between the conductive layer and the plurality of current sensing circuits. A plurality of apertures are formed through the conductive layer and the insulating layer, wherein each of the plurality of apertures exposes one of the plurality of current sensing circuits.
Another aspect of the present invention provides for an electrodeposition monitoring system. The monitoring system is comprised of a plating cell for holding a metal salt bath, an electrode located in the plating cell, a probe having a plurality of current sensing circuits, wherein each of the plurality of current sensing circuits senses a local electrodeposition plating current, and a computer system connected to the probe that determines an electrodeposition plating thickness based on the local electrodeposition plating currents sensed by the plurality of current sensing circuits.
A further aspect of the present invention provides a method of providing real time analysis of electrodeposition plating currents. The method including placing a multi-channel current probe in a plating cell, generating an electrodeposition plating current, measuring the electrodeposition plating current at a plurality of locations on the multi-channel current probe using a plurality of current sensing circuits and adjusting the distribution of the electrodeposition plating currents based on the measurements taken.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary embodiment of an electrodeposition measurement system.
FIG. 2A is a front view of an exemplary embodiment of a current probe used in the current probe measurement system.
FIG. 2B is a back view of an exemplary embodiment of the current probe.
FIG. 3 is a cross-sectional view of an exemplary embodiment of the current probe.
FIG. 4 is a diagram of an exemplary embodiment of a single channel within the current probe.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of electrodeposition measuring system 10, which includes plating cell 12, plating bath 14 contained within plating cell 12, electrode 16, current probe 18 which includes a plurality of apertures 20 a, 20 b, . . . 20N (“apertures 20”), plastic baffles 22 a and 22 b, data acquisition board 23, and computer system 24.
To measure the spatial distribution of plating currents, current probe 18 is placed in plating cell 12, submerged in plating bath 14. In this exemplary embodiment, plating bath 14 includes copper ions (Cu²⁺). A potential difference is created between electrode 16 (which in this exemplary embodiment, acts as an anode) and current probe 18 (which in this embodiment acts as a cathode). The potential difference causes copper ions (Cu²⁺) located in plating bath 14 to flow toward current probe 18. Copper ions flowing toward current probe 18 eventually come into contact with current probe 18, where the ionic charge is neutralized and the copper ions plate onto the surface of current probe 18. The flow of positive charge to current probe 18 caused by the copper ions results in current being generated at current probe 18. The magnitude of the current, and more specifically of current density, is directly related to the thickness of copper plating deposited on current probe 18. Variations in current density across the area of current probe 18 result in varying plating thickness. By detecting and measuring current magnitude and/or current density at a number of locations along current probe 18, the plating thickness at each location can be determined.
In an exemplary embodiment, current associated with copper ions incident to the plurality of apertures 20 is detected by current sensing circuits, the details of which are described below with respect to FIG. 2B. Currents detected at the plurality of apertures 20 are provided to data acquisition board 23. Data acquisition board 23 measures currents detected at the plurality of apertures 20 by measuring a voltage drop across each current sensing circuit. The measured current value associated with each of the plurality of apertures 20 is converted by the data acquisition board to a digital value, which can be displayed or stored by computer system 24. Knowing the area of each aperture 20 (in one embodiment, each aperture 20 is of equal area) allows either data acquisition board 23 or a processor to calculate current density associated with each aperture 20. In this way, electrodeposition measuring system 10 provides real time data concerning current and/or current density sensed at a number of locations along current probe 18. Based on this data, a user can manipulate the mechanics of plating cell 12 or plating bath 14 to achieve the desired current distribution along current probe 18. In the exemplary embodiment shown, plastic baffles 22 a and 22 b may be manipulated to alter the current distribution. Current distribution can be measured again using current probe 18, and further adjustments can be made.
FIGS. 2A-2B are diagrams of the front and back faces, respectively, of current probe 18. FIG. 2A shows conductive layer 26 located on the front face of current probe 18, along with a plurality of apertures 20 a, 20 b, . . . 20N (“apertures 20”). Conductive layer 26 acts as an electrode (in this example, a cathode) in the electrodeposition process. During testing of electrodeposition current distribution, a potential difference is created between conductive layer 26 and electrode 16 (shown in FIG. 1), causing metal ions to travel toward conductive layer 26. Connector tabs 28 a and 28 b, discussed in more detail below, may be connected to a power supply capable of providing a potential to conductive layer 26. Apertures 20 are small openings in conductive layer 26 that extend through conductive layer 26 (as well as an insulating layer shown in FIG. 3) to one of the plurality of current sensing circuits 32 a, 32 b, . . . 32N. (“current sensing circuits 32”) formed on the back face of current probe 18, as shown in FIG. 2B. Metal ions incident to apertures 20 travel through the apertures and plate onto current sensing circuits 32. The current created at each of the current sensing circuits 32 by incident metal ions allows current probe 18 to determine the magnitude and/or density of current at each of the plurality of apertures 20.
FIG. 2B is a diagram of the back face of current probe 18, including a plurality of current sensing circuits 32 a, 32 b, . . . 32N, deposited on an insulating layer 34. A current measuring device 35 (in one embodiment, current measuring device 35 is included within data acquisition board 23 (FIG. 1)) connects to probe 18 by way of connector tabs 28 a and 28 b. In this embodiment, there are eight current sensing circuits, each providing a channel of data to current measuring device 35. Each current sensing circuit 32 intersects with one of the plurality of apertures 20 shown in FIG. 2A and is extended to the edge of connector tabs 28 a and 28 b. Current measuring device 35 is connected between connector tabs 28 a and 28 b, which closes the circuit between points A and B for each current sensing circuit 32 and allows current measuring device 35 to measure current by determining a voltage drop between points A and B.
Insulating layer 34 isolates current sensing circuits 32 from conductive layer 26 located on the front face of current probe 18. Therefore, apertures 20 are formed through conductive layer 26 as well as insulating layer 34 to expose a conductive portion of current sensing circuit 32 to incoming metal ions. In order for the sensing circuits 32 to sample representative plating currents on electrode 26, current sensing circuits 32 are held at nearly the same cathodic potential as electrode 26. Current generated in each of the current sensing circuits 32 by incoming metal ions is provided to current measuring device 35.
The conductive lines (having a thickness and depth) making up each current sensing circuit 32 are formed by pattern plating copper onto insulating layer 34. As shown in FIG. 2B, the conductive line length of each current sensing circuit 32 varies depending on the distance to connector tabs 28 a and 28 b. This varying length of each current sensing circuit 32 can result in varying overall resistance values of each current sensing circuit 32. For example, the conductive line length of current sensing circuit 32 a is shorter than the conductive line length of current sensing circuit 32 b, which results in current sensing circuit 32 a having a lower overall resistance than current sensing circuit 32 b. Varying overall resistances of each current sensing circuit 32 must be taken into account when current measuring device 35 measures the voltage drop between points A and B.
In one exemplary embodiment, the conductive line of each of the number of current sensing circuits 32 is designed such that each current sensing circuit 32 is of equal resistance. By varying the thickness and/or width of the conductive lines making up each current sensing circuit 32, the overall resistance of each current sensing circuit 32 can be made equal. Configuring current sensing circuits 32 to have equal overall resistance allows for easier measuring and comparison of currents by current measuring device 35. For instance, if currents associated with each current sensing circuit 32 are determined by measuring a voltage drop between points A and B, then the measured voltages can be directly compared without having to employ external resistors to take into account the differences in resistance of current sensing circuits 32.
FIG. 3 is a cross sectional view taken along dashed line 37 in FIG. 2B, illustrating the locations of conductive layer 26, insulating layer 34, current sensing circuit 32 a, and epoxy layer 36 within a portion of current probe 18. The resistance of current sensing circuit 32 a is made sufficiently small so that conductive layer 26 and current sensing circuit 32 a are at nearly the same cathodic potential. Aperture 20 a is formed through conductive layer 26 and insulating layer 34 to expose current sensing circuit 32 a to incident or incoming metal ions (e.g., Cu²⁺). Insulating layer 34 separates conductive layer 26 from current sensing circuit 32 a. Epoxy layer 36 prevents current incident to the back face of current probe 18 from affecting current sensing circuit 32 a. During the measuring process, metal ions will plate onto current sensing circuit 32 a. However, this does not have any significant effect on the overall resistance of current sensing circuit 32 a, and therefore does not affect current magnitude or density measurements. Therefore, a single current probe 18 can be used a number of times to measure current magnitude and/or density distribution despite some amount of metal plating being deposited on each of the number of current sensing circuits 32, provided metal plating deposited on current sensing circuit 32 a does not extend up to conductive layer 26, resulting in a short circuit condition.
FIG. 4 is a schematic diagram of current sensing circuit 32 a located on current probe 18. Current sensing circuit 32 a includes current sensing area 40 a and conductive line 42 a and 42 b, which provides sensed currents to current measuring device 35 connected between connecting tabs 28 a and 28 b. It should be noted that each current sensing circuit 32 a-32N will include similar current sensing area and conductive line connecting the current sensing area to connector tabs 28 a and 28 b. Aperture 20 a is formed through conductive layer 26 (shown in FIG. 3) and insulating layer 34 (shown in FIG. 3) to expose a portion of current sensing area 40 a to incident currents. It is important that the area exposed by aperture 20 a be entirely within current sensing area 40 a. If a portion of aperture 20 a exposes an area outside of current sensing area 40 a, any current incident to this outside area will not generate current within current sensing circuit 32 a. Knowing the amount of current sensing area 40 a exposed by aperture 20 a allows current density to be determined along with the magnitude of the current measured. If each of the plurality of current sensing circuits 32 employed have an equal amount of current sensing area exposed, then current densities of each can be compared without the need for additional compensation or calculations.
A multi-channel current probe has been described. Although the current probe described with reference to FIGS. 1-4 is a current probe with eight apertures and corresponding current sensing circuits located in vertical fashion, it should be understood that any number of apertures and corresponding current sensing circuits may be employed and may be located in any pattern order to gather information relevant to a particular application.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims

1. A current probe for measuring electrodeposition plating currents, the current probe comprising:

a conductive layer located on a front face of the current probe;

an insulating layer located adjacent to the conductive layer;

a plurality of current sensing circuits located adjacent to the insulating layer, wherein the insulating layer is located between the conductive layer and the plurality of current sensing circuits; and

a plurality of apertures formed through the conductive layer and the insulating layer, wherein each of the plurality of apertures exposes one of the plurality of current sensing circuits.

2. The current probe of claim 1, wherein the plurality of current sensing circuits have equal overall resistance.

3. The current probe of claim 1, wherein each of the plurality of current sensing circuits includes:

a current sensing area, a portion of which is exposed by one of the plurality of apertures formed through the conductive layer and the insulating layer; and

a conductive line connecting the current sensing area to a current or voltage measuring device.

4. The current probe of claim 3, wherein each of the plurality of apertures exposes an equal amount of the current sensing area.

5. The current probe of claim 1, including an epoxy layer formed adjacent to the plurality of current sensing circuits opposite the insulating layer, the epoxy layer located on a back face of the current probe.

6. The current probe of claim 1, wherein the conductive layer consists of copper.

7. The current probe of claim 1, wherein the insulation layer consists of polyimide.

8. The current probe of claim 3, wherein the conductive line and the current sensing area of each of the plurality of current sensing circuits consists of copper.

9. An electrodeposition measuring system, comprising:

a plating cell for holding a metal salt bath;

an electrode located in the plating cell;

a current probe having a plurality of current sensing circuits, wherein each of the plurality of current sensing circuits senses a local electrodeposition plating current; and

a computer system connected to the current probe that determines an electrodeposition plating thickness based on the local electrodeposition plating currents sensed by the plurality of current sensing circuits.

10. The electrodeposition measuring system of claim 9, including:

a plurality of plastic baffles that are adjustable to alter the electrodeposition plating currents.

11. The electrodeposition measuring system of claim 9, wherein the computer system further comprises:

a data acquisition board operatively connected to the current probe that converts electrodeposition plating currents sensed by the plurality of current sensing circuits to a plurality of digital values;

a computer operatively connected to the data acquisition board that receives the plurality of digital values provided by the data acquisition board; and

a monitor operatively connected to the computer for displaying the plurality of digital values provided to the computer.

12. The electrodeposition measuring system of claim 9, wherein the current probe further comprises:

a conductive layer located on a front face of the current probe;

a insulating layer formed adjacent to the conductive layer; and

a plurality of apertures formed through the conductive layer and the insulating layer, wherein each of the plurality of apertures exposes one of the plurality of current sensing circuits to local electrodeposition plating currents generated between the electrode and the current probe.

13. The electrodeposition measuring system of claim 12, wherein each of the plurality of current sensing circuits include:

a current sensing region, wherein a portion of the current sensing region is exposed to electrodeposition plating currents by one of the plurality of apertures formed through the conductive layer and the insulating layer; and

a conductive line connecting the current sensing region to a current measuring device, wherein local electrodeposition plating currents incident to the portion of the current sensing region exposed by one of the plurality of apertures is sensed by the current sensing region and provided by way of the conductive line to the current measuring device.

14. The electrodeposition measuring system of claim 13, wherein each of the plurality of apertures exposes an equal amount of the current sensing regions of the plurality of current sensing circuits, wherein the amount of the current sensing region exposed and the current measured by each of the plurality of current sensing circuits allows local electrodeposition plating current density to be determined at each of the plurality of apertures.

15. The electrodeposition measuring system of claim 12, wherein the current probe further comprises:

an epoxy layer formed adjacent to the plurality of current sensing circuits, the epoxy layer located on a back face of the current monitoring probe, wherein the epoxy layer prevents electrodeposition plating currents incident to the back face of the probe from affecting the current sensing circuits.

16. A method of providing real time analysis of electrodeposition plating currents, the method comprising:

A. placing a multi-channel current probe in a plating cell;

B. generating an electrodeposition plating current;

C. measuring the electrodeposition plating current at a plurality of locations on the multi-channel current probe using a plurality of current sensing circuits; and

D. adjusting the distribution of the electrodeposition plating current based on the measurements taken.

17. The method of claim 16, wherein steps C and D are repeated until the distribution of the electrodeposition plating currents reaches a threshold level of uniformity.

18. The method of claim 16, wherein measuring the electrodeposition plating current includes determining electrodeposition plating current density based on the electrodeposition plating current measured and a surface area of a current sensing region exposed to the electrodeposition plating currents.

19. The method of claim 16, wherein adjusting the distribution of the electrodeposition plating current based on the measurements taken includes adjusting a plurality of plastic baffles.

20. The method of claim 16, wherein measuring the electrodeposition plating current includes:

sensing the electrodeposition plating currents at a plurality of current sensing regions;

providing the sensed electrodeposition plating currents to a data acquisition board via a plurality of conductive lines; and

converting the sensed electrodeposition plating currents provided to the data acquisition board to a plurality of digital values representative of the electrodeposition plating currents sensed at the plurality of current sensing regions.