Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-08-09
2003-10-21
Rachuba, M. (Department: 3724)
Abrading
Abrading process
Glass or stone abrading
C451S054000, C451S060000
Reexamination Certificate
active
06634930
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and apparatus for chemical mechanical polishing and more particularly, relates to a method and apparatus for preventing metal corrosion on an electronic substrate during a chemical mechanical polishing process when the process is temporarily halted due to tool alarm by removing slurry solution from the substrate surface.
BACKGROUND OF THE INVENTION
Method and apparatus for polishing thin, flat semi-conductor 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 walfer 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.
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 when contacted by a variety of chemicals, including those contained in a slurry solution.
The corrosion of a metal layer on a wafer surface is more severe when the metal layer is formed of copper. Since in other metals such as tungsten and aluminum, a thin layer of metal oxide will be formed to stop further oxidation of fresh metal under the oxide layer. The formation of copper oxide does not stop the further oxidation of fresh copper under copper oxide. As a result, when the fresh copper surface is in contact with a CMP slurry solution for any significant length of time, i.e., more than three minutes, deep pitted areas of, copper oxide are formed. The depth of the copper oxide areas formed is so large such that any repair attempted on the wafer surface would not be effective to save the wafer from being scrapped. It therefore presents a serious problem in chemical mechanical polishing a copper layer on a wafer surface when the wafer surface may be subjected to a stationary contact with a slurry solution for any extended length of time, such as in a tool alarm situation wherein the polishing apparatus is shut down temporarily for correcting mechanical or other problems.
It is therefore an object of the present invention to provide a method for chemical mechanical polishing copper that does not have the drawbacks or shortcomings of the conventional copper CMP process.
It is another object of the present invention to provide a method for chemical mechanical polishing copper on a semiconductor device that does not have copper corrosion problem.
It is a further object of the present invention to provide a method for chemical mechanical polishing copper on a semiconductor device that does not have copper corrosion problem even when the process is temporarily halted due to a tool alarm situation.
It is another further object of the present invention to provide a method for prevent meal corrosion on a wafer during a chemical mechanical polish process by spraying a cleaning solvent toward the wafer surface removing slurry solution when the polishing process is stopped.
It is still another object of the present inventio
Chen Ying-Ho
Chiou Wen-Chih
Jang Syun-Ming
Shih Tsu
Yang Chia-Ming
Rachuba M.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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