Perforated anode for uniform deposition of a metal layer

Details Perforated anode for uniform deposition of a metal layer Perforated anode for uniform deposition of a metal layer

2000-03-24

2003-02-18

Phasge, Arun S. (Department: 1741)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S283000

Reexamination Certificate

active

06521102

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to deposition of a metal layer on a substrate. More particularly, the invention relates to anode configurations used in electroplating.
2. Description of the Background Art
Sub-quarter micron, multi-level metallization is an important technology for the next generation of ultra large scale integration (ULSI). Reliable formation of these interconnect features permits increased circuit density, improves acceptance of ULSI, and improves quality of individual processed wafers. As circuit densities increase, the widths of vias, contacts and other features, as well as the width of the dielectric materials between the features, decrease. However, the height of the dielectric layers remains substantially constant. Therefore, the aspect ratio for the features (i.e., their height or depth divided by their width) increases. Many traditional deposition processes, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), presently have difficulty providing uniform filling of features having aspect ratios greater than 4/1, and particularly greater than 10/1. Therefore, a great amount of ongoing effort is directed at the formation of void-free, nanometer-sized features having aspect ratios of 4/1, or higher.
Electroplating, previously limited in integrated circuit design to the fabrication of lines on circuit boards, is now being used to fill vias and contacts for the manufacture of IC interconnects. Metal electroplating, in general, can be achieved by a variety of techniques. One embodiment of an electroplating process involves initially depositing a barrier layer over the feature surfaces of the wafer, depositing a conductive metal seed layer over the barrier layer, and then depositing a conductive metal (such as copper) over the seed layer to fill the structure/feature. Finally, the deposited layers are planarized by, for example, chemical mechanical polishing (CMP), to define a conductive interconnect feature.
In electroplating, depositing of a metallic layer is accomplished by delivering electric power to the seed layer and then exposing the wafer-plating surface to an electrolytic solution containing the metal to be deposited. The subsequently deposited metal layer adheres to the seed layer to provide for uniform growth of the metal layer. A number of obstacles impair consistently reliable electroplating of metal onto wafers having nanometer-sized, high aspect ratio features. These obstacles include non-uniform power distribution and current density across the wafer plating surface to portions of the seed layer.
A system that electroplates a plating surface is depicted in FIG.
1
. The device, known as a fountain plater
10
, electroplates a metal on a surface
15
of a substrate
48
facing, and immersed in, electrolyte solution contained within the fountain plater. The electrolyte solution is filled to the lip
83
of the interior cavity
11
defined within the electrolyte cell
12
. The fountain plater
10
includes an electrolyte cell
12
having a top opening
13
, a removable substrate support
14
positioned above the top opening
13
to support a substrate in the electrolyte solution, and an anode
16
disposed near a bottom portion of the electrolyte cell
12
that is powered from the positive pole of a power supply
42
. The electrolyte cell
12
is typically cylindrically-shaped to conform to the disk-shaped substrate
48
to be positioned therein. Disk-shaped contact ring
20
is configured to secure and support the substrate
48
in position during electroplating, and permits the electrolyte solution contained in the electrolyte cell
12
to contact the plating surface
15
of the substrate
48
while the latter is immersed in the electrolyte solution.
A negative pole of power supply
42
is selectively connected to each of a plurality of contacts
56
(only one is depicted in
FIGS. 1
,
2
, and
4
) which are typically mounted about the periphery of the substrate to provide multiple circuit pathways to the substrate, and thereby limit irregularities of the electrical field applied to the seed layer formed on the plating surface
15
of substrate
48
. Typically, contacts
56
are formed from such conductive material such as tantalum (Ta), titanium (Ti), platinum (Pt), gold (Au), copper (Cu), or silver (Ag). Substrate
48
is positioned within an upper portion
79
of the cylindrical electrolyte cell
12
, such that electrolyte flows along plating surface
15
of substrate
48
during operation of the fountain plater
10
. Therefore, a negative charge applied from negative pole of power supply
42
via contact
56
to a seed layer deposited on plating surface
15
of substrate
48
in effect makes the substrate a cathode. The substrate
48
is electrically coupled to anode
16
by the electrolyte solution. The seed layer (not shown) formed on a cathode plating surface
15
of substrate
48
attracts positive ions carried by the electrolyte solution. The substrate
48
thus may be viewed as a work-piece being selectively electroplated.
A number of obstacles impair consistently reliable electroplating of copper onto substrates having nanometer-sized, high aspect ratio features. These obstacles limit the uniformity of power distribution and current density across the substrate plating surface needed to form a deposited metal layer having a substantially uniform thickness.
Electrolyte solution is supplied to electrolyte cell
12
via electrolyte input port
80
from electrolyte input supply
82
. During normal operation, electrolyte solution overflows from an upper annular lip
83
, formed on top of the electrolyte cell
12
, into annular drain
85
. The annular drain drains into electrolyte output port
86
which discharges to electrolyte output
88
. Electrolyte output
88
is typically connected to the electrolyte input supply
82
via a regeneration element
87
that provides a closed loop for the electrolyte solution contained within the electrolyte cell, such that the electrolyte solution may be recirculated, maintained, and chemically refreshed. The motion associated with the recirculation of the electrolyte also assists in transporting the metallic ions from the anode
16
to the surface
15
of the substrate
48
. In cases where the flow of the electrolyte solution through the anode does not conform to the general horizontal cross-sectional configuration of the electrolyte cell, the resultant electrolyte solution fluid flow through the electrolyte cell
12
can be irregular, non-axial, and even turbulent. Irregular and non-axial flows may produce eddies that lead to disruption of the metal deposition in the boundary layer adjacent to substrate
48
. Such non-axial flow provides uneven distribution of ions across the selected portions of plating surface
15
of substrate
48
. As a result, different regions of the electrolyte solution will have different concentrations of ions, which can lead to variations in plating rate on the substrate when such variation is present in the electrolyte solution that contacts the plating surface. This uneven deposition can result in an uneven depth of electroplated material. It is desired to provide an anode shape so that flow of the electrolyte solution is as uniform across the electrolyte cell
12
as possible. Therefore it is desired that the anode acts as a diffusion nozzle that provides a uniform flow across the cathode-substrate
48
.
The anode
16
shape itself can lead to difficulties in the electroplating process. Irregular shapes of the anode
16
, as well as irregular flows produced by the anode, are undesired. For example, if the anode
16
is located only on the left side of the fountain plater
10
in
FIG. 1
, then the left side of the surface
15
of the substrate will likely be coated more heavily than the right side of the surface
15
. Irregularly shaped anodes
16
also affect the electromagnetic fields generated within the fountain plater
10
, that can result in variation in the electrolyte solution contacting the pl

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