U.S. patent application number 11/004804 was filed with the patent office on 2005-05-05 for method of electroplating and varying the resistance of a wafer.
Invention is credited to Moore, Scott E..
Application Number | 20050092610 11/004804 |
Document ID | / |
Family ID | 23521167 |
Filed Date | 2005-05-05 |
United States Patent
Application |
20050092610 |
Kind Code |
A1 |
Moore, Scott E. |
May 5, 2005 |
Method of electroplating and varying the resistance of a wafer
Abstract
An electroplating apparatus is provided with a metal target and
a device for supporting a semiconductor wafer (or other workpiece)
in an electroplating solution. The target (anode) may be located
relatively far from the wafer surface (cathode) at the beginning of
the plating process, until a sufficient amount of metal is plated.
When an initial amount of metal is built up on the wafer surface,
the target may be moved closer to the wafer for faster processing.
The movement of the target may be controlled automatically
according to one or more process parameters.
Inventors: |
Moore, Scott E.; (Meridian,
ID) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
2101 L STREET, NW
WASHINGTON
DC
20037
US
|
Family ID: |
23521167 |
Appl. No.: |
11/004804 |
Filed: |
December 7, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11004804 |
Dec 7, 2004 |
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09813164 |
Mar 21, 2001 |
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6830666 |
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09813164 |
Mar 21, 2001 |
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09385381 |
Aug 30, 1999 |
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6217727 |
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Current U.S.
Class: |
205/84 ;
204/228.7 |
Current CPC
Class: |
C25D 7/123 20130101;
C25D 17/001 20130101; C25D 21/12 20130101 |
Class at
Publication: |
205/084 ;
204/228.7 |
International
Class: |
C25B 015/00; C25D
017/00 |
Claims
What is claimed as new and desired to be protected by Letters
Patent of the United States is:
1-50. (canceled)
51. A method of electroplating a wafer, said method comprising:
changing the resistance of said wafer while applying an electric
potential across a first distance; and subsequently, applying an
electric potential to said wafer across a second distance, said
first distance being greater than said second distance.
52. The method of claim 51, wherein the resistance of said wafer is
reduced during said step of changing the resistance of said
wafer.
53. The method of claim 51, further comprising partially forming at
least one layer on said wafer to decrease said resistance of said
wafer.
54. The method of claim 53, wherein the step of decreasing the
resistance of said wafer further comprises moving said wafer from
said first distance to said second distance.
55. A method of controlling the rate at which metal is deposited on
a wafer surface, said method comprising: placing a wafer in an
electroplating solution at a predetermined distance from first and
second electrical contacts; forming a metal layer on at least a
portion of said wafer, wherein said step of forming a metal layer
changes the resistance of the wafer surface; and subsequently,
moving an electrode and/or said wafer in response to the change in
said resistance of the wafer's surface.
56. A method of electroplating a surface of a semiconductor wafer,
said wafer comprising the steps of: using an electrode to
electroplate an initial amount of material on said surface of said
semiconductor wafer such that the variability of the resistance of
said surface relative to a radial position of said wafer is
reduced; and subsequently, changing the distance between said
electrode and said surface of said semiconductor wafer.
57. A method of varying the resistance of a wafer, said method
comprising: placing said wafer in an electroplating solution at a
first distance from a first anode; providing a second anode at a
second distance from said wafer, wherein said first distance is
greater than said second distance.
58. The method of claim 57, further comprising applying a first
electric potential from said first anode to said wafer, wherein
said wafer has a first resistance.
59. The method of claim 58, wherein said step of applying a first
electric potential forms an initial amount of metal on said wafer
at a first deposition rate changing said first resistance of said
wafer to a second resistance.
60. The method of claim 59, wherein subsequently, after said first
resistance of said wafer changes to said second resistance, a
second electric potential is applied to said wafer from said second
anode.
61. The method of claim 60, wherein said step of applying a second
electric potential results in an additional amount of metal formed
on said wafer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a system for electroplating
the surfaces of semiconductor wafers and other workpieces. More
particularly, the present invention relates to an electroplating
apparatus and method that achieves improved performance with
respect to thickness uniformity and rate of metal deposition.
BACKGROUND OF THE INVENTION
[0002] It is known to electroplate the surfaces of semiconductor
wafers. It has been difficult, however, to obtain an electroplated
layer of uniform thickness. It has been especially difficult to
achieve the desired thickness uniformity at a high rate of metal
deposition. Known systems for electroplating semiconductor products
are described in U.S. Pat. No. 5,833,820 (Dubin), U.S. Pat. No.
5,670,034 (Lowery), U.S. Pat. No. 5,472,592 (Lowery), and U.S. Pat.
No. 5,421,987 (Tzanavaras).
SUMMARY OF THE INVENTION
[0003] The present invention relates to an apparatus for
electroplating a semiconductor product. The apparatus includes a
support device for supporting the product in an electroplating
solution, an electrical circuit for applying an electrical
potential across the electroplating solution, and a control device
for reducing the current distance to the product through the
solution after an initial amount of conductive material is
electroplated on the product surface. The semiconductor product may
be, for example, a semiconductor wafer or clip. Integrated circuits
may be formed in the product if desired.
[0004] According to one aspect of the invention, the support device
includes conductive contacts. The contacts may be used to connect
the product to the electrical circuit.
[0005] According to another aspect of the invention, the control
device includes a mechanism for moving a metal target (anode)
toward the electroplated product. In an alternative embodiment of
the invention, the product may be moved toward the anode.
[0006] According to another aspect of the invention, a processor is
used to operate the control device in response to data correlated
to the electroplating process. The input data may be functionally
related or correlated to elapsed electroplating time, the
resistance of the product in the electroplating solution, the
optical characteristics of the product, the surface capacitance of
the product, etc.
[0007] The present invention also relates to a method of
electroplating the surface of a semiconductor wafer. The method
includes the steps of using an electrode to electroplate an initial
amount of conductive material on the wafer surface, then changing
the distance between the electrode and the wafer surface, and then
using the electrode to electroplate an additional amount of
material on the wafer surface. According to a preferred embodiment
of the invention, at the start of the process, while the resistance
of the wafer is significant, thickness uniformity is promoted by
locating the target far from the wafer. Then, when the wafer
resistance is reduced by the initial amount of electrodeposited
metal, higher plating efficiency may be obtained by moving the
target closer to the wafer.
[0008] According to another aspect of the invention, the wafer may
be provided with a refractory seed layer. The seed layer contains
metal and adheres to the semiconductor wafer material. The
resistance of the seed layer is greater than that of the
electrodeposited metal.
[0009] Thus, according to a preferred embodiment of the invention,
a metal target (anode) is located relatively far from the wafer
(cathode) at the beginning of the plating process, until a
sufficient amount of metal is plated on the wafer surface. Once the
metal is built up on the wafer surface, the target is moved closer
to the wafer for faster processing.
[0010] As explained in more detail below, before the metal is built
up on the wafer surface, the high resistance of the seed layer is a
significant factor. The electrical potential near the contacts on
the edges of the wafer is greater than the potential at the center
of the wafer. Consequently, according to the invention, the target
and the wafer are separated from each other to increase the
resistance of the electroplating solution (the bath). A relatively
high bath resistance mutes the significance of the potential
difference in the radial direction of the wafer. Metal built up on
the wafer surface has less resistance than the seed layer, such
that the difference in potential across the surface of the wafer
becomes less significant. Eventually, the target can be moved
closer to the wafer (to reduce the bath resistance and increase the
deposition rate) without impairing plating uniformity.
[0011] These and other features and advantages of the invention
will become apparent from the following detailed description of
preferred embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a cross-sectional view of an electroplating
apparatus constructed in accordance with a preferred embodiment of
the present invention.
[0013] FIG. 2 is another cross-sectional view of the electroplating
apparatus of FIG. 1, showing the apparatus at a subsequent stage of
operation.
[0014] FIG. 3 is a cross-sectional view of an electroplating
apparatus constructed in accordance with another preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0015] Referring now to the drawings, where like reference numerals
designate like elements, there is shown in FIG. 1 an electroplating
apparatus 10 constructed in accordance with a preferred embodiment
of the present invention. The apparatus 10 has a tank 12 containing
electroplating solution 14, a wafer support 16 for supporting a
wafer 18 in the solution 14, and a metal target (anode) 20. The
wafer support 16 may have metal clips 22, 24 for holding the wafer
18 in the desired position. An electrically conductive seed layer
26 may be formed on the wafer surface 28. The seed layer 26 may be
electrically grounded through the clips 22, 24 and suitable wires
30.
[0016] In operation, voltage is applied to the target 20 by a
control device 32. The electrical potential causes current to flow
from the target 20, through the solution 14, through the seed layer
26, and through the clips 22, 24 to the grounding wires 30. The
electroplating process causes a metal layer 34 (FIG. 2) to form on
the seed layer 26. The process may be continued until the metal
layer 34 achieves the desired thickness. The electroplated wafer 18
may then be removed from the tank 12 for further processing.
[0017] The rate at which metal 34 is deposited on the wafer surface
28 is proportional to the combined resistance of the solution 14
and the seed layer 26, as follows:
I=A/(R.sub.1+R.sub.2),
[0018] where I is the metal deposition rate, A is a constant,
R.sub.1 is the resistance of the solution 14, and R.sub.2 is the
resistance of the wafer 18. The solution resistance R.sub.1 depends
on (1) the distance D between the target 20 and the wafer surface
28 and (2) the conductivity of the solution 14. For any particular
point on the wafer surface 28, the wafer resistance R.sub.2 depends
on (1) the distance from that point to the electrical contacts 22,
24 and (2) the conductivity of the wafer 18.
[0019] At the start of the electroplating process (that is, before
any metal 34 is formed on the seed layer 26), the wafer resistance
R.sub.2 is a significant factor with respect to the deposition rate
I. The resistance of the seed layer 26 may be substantial.
Consequently, at the start of the process, the value of R.sub.2 may
vary substantially as a function of radial position on the wafer
18. That is, the value of R.sub.2 would tend to increase as
distance increases from the clips 22, 24. To mute the significance
of the wafer resistance R.sub.2 and to thereby improve the
thickness uniformity of the initially deposited metal 34, the
target 20 initially may be located relatively far from the wafer 18
(FIG. 1). As the conductive metal 34 is formed on the seed layer
26, the wafer resistance R.sub.2 becomes much less significant
relative to the solution resistance R.sub.1. After the initial
amount of metal 34 is formed on the wafer 18, the target may be
moved closer to the wafer 18 to reduce the solution resistance
R.sub.1 and to increase the deposition rate I.
[0020] The target 20 may be moved by a suitable mechanism 36
controlled by the control device 32. In an alternative embodiment
of the invention, shown in FIG. 3, the wafer 18 may be moved closer
to the target 20. In another alternative embodiment, (not shown)
more than one anode may be employed--one relatively far away from
the wafer 18 to form the initial amount of metal on the wafer 18
and the other located relatively close to the wafer 18 to form the
rest of the metal layer 34 at a relatively high deposition
rate.
[0021] The control device 32 (FIG. 2) may be operated by a suitable
microprocessor 38 or the like. Signals 40 may be input to the
processor 38 representative of elapsed electroplating time, the
measured resistance of the wafer 18, the optical characteristics
(e.g. reflectivity) of the wafer 18, and/or the surface capacitance
of the wafer 18. The input signals 40 may be generated by a
suitable input device 42, such as a clock or a suitable measuring
device. The resistance of the wafer 18 may be determined by
measuring the voltage between the contacts 22, 24. The bulk
resistance of the wafer 18 also may be determined off-line, for
example, by a four-point probe device (not shown).
[0022] The processor 38 may have a look-up table and/or an
algorithm that correlates elapsed electroplating time to metal
thickness and/or deposition rate for known solutions 14 and target
positions. Feedback signals 46 representative of the position of
the target 20 (and/or the distance D between the target 20 and the
wafer 18) may be provided to the processor 38 by the controller 32.
The processor 38 may be programmed to send operating signals 44 to
the controller 32 to automatically move the target 20 closer to the
wafer 18 when a predetermined amount of metal 34 is formed on the
seed layer 26.
[0023] The motion of the target 20 toward the wafer 18 may be
continuous or gradual, and, the motion may be programmed to
optimize plating efficiency while achieving the desired uniformity.
In an alternative embodiment of the invention, the target 2Q may be
moved in a stepwise fashion toward the wafer 18 at a predetermined
time in the process or when a predetermined amount of metal 34 is
determined to have been formed on the wafer 18.
[0024] In a preferred embodiment of the invention, the target 20
may be located about five centimeters from the wafer surface 28 in
the start position (FIG. 1), and about one to two centimeters in
the high efficiency plating position (FIG. 2). The present
invention should not be limited, however, to the preferred
embodiments described and illustrated in detail herein.
[0025] The solution 14 may be arranged to deposit copper, platinum,
gold or another suitable material on the wafer 18. The seed layer
26 may be formed by a known chemical vapor deposition (CVD)
process. The seed layer 26 may be, for example, a refractory and
metal composite material that adheres to the wafer surface 28. The
metal component of the seed layer 26 may be the same as or
different than the plated metal material 34.
[0026] If desired, the tank 12 may be provided with a cascade
structure (not shown) to ensure that fresh solution 14 is made
available to the wafer (cathode) 18. Other suitable means, such as
a diffuser or baffle plate, for agitating and flowing the solution
14 against the wafer 18 may be employed, if desired. Although the
tank 12 is shown with only one support device 16, the invention may
be employed with more than one support device 16 per tank 12. If
desired, a number of wafers 18 may be electroplated in the same
solution 14 simultaneously. Suitable electrodes 20, 22, 24 may be
provided for each wafer 18.
[0027] The above descriptions and drawings are only illustrative of
preferred embodiments which achieve the features and advantages of
the present invention, and it is not intended that the present
invention be limited thereto. Any modification of the present
invention which comes within the spirit and scope of the following
claims is considered part of the present invention.
* * * * *