Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
2001-03-20
2004-04-20
Wilson, Lee D. (Department: 3723)
Abrading
Abrading process
Utilizing fluent abradant
C451S041000, C451S287000, C451S060000, C451S494000
Reexamination Certificate
active
06722949
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a platen/polishing pad assembly for chemical mechanical polishing and a method for using and more particularly, relates to a ventilated platen/polishing pad assembly for chemical mechanical polishing and a method for using such ventilated platen/polishing pad assembly for achieving more uniform polishing.
BACKGROUND OF THE INVENTION
Method and apparatus for polishing thin, flat semiconductor wafers are well-known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semiconductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head rotates and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is “planarized” or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A schematic of a typical CMP apparatus is shown in
FIGS. 1A and 1B
. The apparatus
10
for chemical mechanical polishing consists of a rotating wafer holder
14
that holds the wafer
10
, the appropriate slurry
24
, and a polishing pad
12
which is normally mounted to a rotating table
26
by adhesive means. The polishing pad
12
is applied to the wafer surface
22
at a specific pressure. The chemical mechanical polishing method can be used to provide a planar surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. CMP polishing results from a combination of chemical and mechanical effects. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An altered layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing a metal oxide may be formed and removed repeatedly.
A polishing pad is typically constructed in two layers overlying a platen with the resilient layer as the outer layer of the pad. The layers are typically made of polyurethane and may include a filler for controlling the dimensional stability of the layers. The polishing pad is usually several times the diameter of a wafer and the wafer is kept off-center on the pad to prevent polishing a non-planar surface onto the wafer. The wafer is also rotated to prevent polishing a taper into the wafer. Although the axis of rotation of the wafer and the axis of rotation of the pad are not collinear, the axes must be parallel. It is known in the art that uniformity in wafer polishing is a function of pressure, velocity and the concentration of chemicals. Edge exclusion is caused, in part, by non-uniform pressure on a wafer.
Referring now to
FIG. 1C
, wherein an improved CMP head, sometimes referred to as a Titan® head which differs from conventional CMP heads in two major respects is shown. First, the Titan® head employs a compliant wafer carrier and second, it utilizes a mechanical linkage (not shown) to constrain tilting of the head, thereby maintaining planarity relative to a polishing pad
12
, which in turn allows the head to achieve more uniform flatness of the wafer during polishing. The wafer
10
has one entire face thereof engaged by a flexible membrane
16
, which biases the opposite face of the wafer
10
into face-to-face engagement with the polishing pad
12
. The polishing head and/or pad
12
are moved relative to each other, in a motion to effect polishing of the wafer
10
. The polishing head includes an outer retaining ring
14
surrounding the membrane
16
, which also engages the polishing pad
12
and functions to hold the head in a steady, desired position during the polishing process. As shown in
FIG. 1C
, both the retaining ring
14
and the membrane
16
are urged downwardly toward the polishing pad
12
by a linear force indicated by the numeral
18
which is effected through a pneumatic system.
The mechanism for chemical mechanical polishing of metal is different and more complex than the polishing of silicon oxide. It is generally believed that during the CMP of metal, metal form an oxide layer on the surface which is subsequently removed by the polishing pad by a mechanism similar to that for oxide polishing. For instance, a mechanism that involves hydroxylation, bond formation with slurry and then, bond breaking from wafer. After the metal oxide layer is removed from the metal surface, metal is etched by the chemicals in the slurry solution, while simultaneously the exposed metal forms a new passivation layer through oxidation by the slurry solution. In practice, it is believed that three processes, i.e. the removal of metal oxide, the metal etching and the metal passivation occur simultaneously. A polishing slurry solution for use in metal CMP therefore contains three major components of fine slurry particles, a corrosion or etchant agent and an oxidant. The eventual planarization of the metal surface is achieved by the rigidity and planarity of the polishing pad similar to a process of oxide polishing.
When the metal being polished in the CMP process is copper, the polishing process becomes more complicated due to the characteristics of copper. Since copper is frequently used in multi-level interconnect structures in semiconductor devices, i.e. in damascene or dual damascene structures, a CMP step for forming copper interconnects in the damascene structures with satisfactory polishing uniformity becomes an important link in the entire fabrication process. The copper CMP process produces a fresh copper surface which is susceptible to corrosion caused by a photolytic reaction.
It is therefore an object of the present invention to provide a ventilated platen/polishing pad assembly for use in chemical mechanical polishing of copper conductors on a semiconductor wafer that does not have the drawbacks or shortcomings of the conventional polishing platen.
It is another object of the present invention to provide a ventilated platen/polishing pad assembly for use in chemical mechanical polishing copper conductors on a semiconductor wafer that does not have copper corrosion and polishing non-uniformity problems.
It is a further object of the present invention to provide a ventilated platen/polishing pad assembly for use in chemical mechanical polishing copper conductors on a semiconductor wafer for flowing an oxidizing gas through the ventilated platen/polishing pad assembly such that the oxidizing gas mixes with a slurry solution for polishing the copper surface.
It is another further
Hu Tien-Chen
Twu Jih-Churng
Shanley Daniel
Taiwan Semiconductors Manufacturing Co., Ltd
Tung & Associates
Wilson Lee D.
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