Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
1996-11-22
2002-11-26
Brumback, Brenda (Department: 1642)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S032000, C134S033000, C134S022190, C134S023000
Reexamination Certificate
active
06485576
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method for removing unwanted coating material from a semiconductor wafer and more particularly, relates to a method for removing a bead of a coating material of spin-on-glass or photoresist from a wafer flat side by a cleaning solution.
BACKGROUND OF THE INVENTION
Spin-on-glass (SOG) is frequently used for gap fill and planarization of inter-level dielectrics (ILD) in multi-level metalization structures. It is a very suitable material for use in low-cost fabrication of IC circuits. The most commonly used SOG materials are of two basic types; an inorganic type of silicate based SOG and an organic type of siloxane based SOG. The most commonly used SOG materials are silicon oxide based polysiloxanes. These polysiloxanes are featured with radical groups replacing or attaching to oxygen atoms. Based on these two basic structures, the molecular weight the viscosity and the desirable film properties of SOG can be modified and adjusted to suit the requirement of each specific IC fabrication process.
SOG film is typically applied to a pre-deposited oxide surface as a liquid to fill gaps and steps on the substrate. Similar to the application method for photoresist films, a SOG material can be dispensed onto a wafer and spun with a rotational speed which determines the SOG thickness desired. After the film is evenly applied to the surface of the substrate, it is cured at a temperature of approximately 400° C. and then etched back to obtain a smooth surface in preparation for a capping oxide layer on which a second interlevel metal may be patterned. The purpose of the etch-back step is to leave SOG between metal lines but not on top of the metal, while the capping oxide layer is used to seal and protect SOG during further fabrication processes. The siloxane based SOG material is capable of filling 0.15 micron gaps and therefore it can be used in 0.25 micron technology.
When fully cured, silicate SOG has similar properties like those of silicon dioxide. Silicate SOG does not absorb water in significant quantity and is thermally stable. However, one disadvantage of silicate SOG is the large volume shrinkage during curing. As a result, the silicate SOG retains high stress and cracks easily during curing and future handling. The cracking of the SOG layer can cause a serious contamination problem for the fabrication process. The problem can sometimes be avoided by the application of only a thin layer, i.e., 1000~2000 Å of the silicate SOG material. To build up thicker layers for filling gaps, multiple application and curing are required.
In the current SOG coating process, a solvent edge rinse and a solvent backside rinse process are utilized to remove SOG deposited on the wafer edge and on the backside of the wafer. This is shown in FIGS.
1
~
3
. A semiconductor wafer
10
that has a flat side
12
is shown in FIG.
1
. After a SOG coating process, a SOG layer
14
is blanket deposited on the top surface
16
of the wafer. The SOG layer is deposited as a dielectric layer for insulating between metal lines. In order to process the wafer in subsequent fabrication steps, the wafer must be positioned in various reaction chambers for various processes such as etching or deposition. In most of the process chambers, the wafer is positioned on a platform and held down on the edge by a wafer clamp. The function of the wafer clamp is to prevent the wafer from moving during the process where reactant gases or etching gases may be flowing through the reaction chamber. To enable the wafer clamp to function properly, the edge portion of the wafer of approximately 2~4 mm wide must be cleaned and any coating layer removed. The edge area
22
is shown in
FIG. 1
on wafer
10
.
In present wafer fabrication technology, the SOG layer deposited at unintended areas of the wafer can be removed in two different processes. The first process is a solvent edge rinse which is shown in FIG.
2
. In this process, wafer
10
is placed on a platform (not shown) and spun at a predetermined rotational speed along a spin axis
26
. The rotational speed of the wafer can be suitably adjusted for each specific application depending on the thickness of the layer to be removed and the type of chemical solution used. As shown in
FIG. 2
, a chemical solution injector
28
is used to inject chemical solution
32
onto the top edge
34
of the wafer. The chemical solution
38
reflected from the edge
34
of the wafer hits the chamber wall
42
and drain to the bottom of the process chamber. The solvent edge rinse process is effective in removing a limited area, i.e., a width of 2~4 mm, on the top edge of the wafer of unwanted coating materials such as SOG or photoresist. However, as shown in
FIG. 1
, when wafer
10
is spun around its center as a rotational axis, the flat side
12
of the wafer is not touched by the injected solvent
32
each time the wafer rotates. As a result, coating material
18
in the form of a bead remains on wafer
10
.
The second cleaning process is a solvent backside rinse such as that shown in FIG.
3
. The backside
48
of wafer
10
is cleaned in this process. A cleaning solution
52
is injected from a spray nozzle
54
onto the backside
48
of the wafer. The process is also known as a centrifugal spray cleaning process wherein a chemical solution, i.e., normally of a good solvent for the coating layer to be removed, is pressure-fed and injected directly onto a spinning wafer. The process can be effectively used to reduce the volume of fresh chemical consumed and is normally faster than an immersion process. After the injected chemical solution
52
hits the bottom surface
48
of the wafer, the chemical solution
56
reflects from the backside
48
of the wafer and drains into the bottom of the process tank (not shown). During a normal backside rinse process, the sprayed chemical solution
52
is only capable of rinsing on the backside
48
of the wafer and, none of the chemical solution
52
can reach the top surface
16
. The bead
18
at the flat side
12
of the wafer is therefore not affected or cleaned in the backside rinse process.
Consequently, the SOG bead remains on the flat side of the wafer and eventually leads to SOG cracking during subsequent processes when a wafer clamp is pressed down on the SOG bead for mounting the wafer. The particles generated by the cracking of the SOG layer greatly contaminate the surface of the wafer and is detrimental to the yield and the quality of the IC produced.
It is therefore an object of the present invention to provide a method for removing a coating layer from an unintended area on a wafer that does not have the drawbacks or shortcomings of the conventional cleaning methods.
It is another object of the present invention to provide a method for removing a coating layer from wafer flat side to prevent the formation of a bead of the coating material.
It is a further object of the present invention to provide a method for removing a coating layer from an unintended area on the wafer flat side such that the wafer can be processed in subsequent processes without producing particle contaminants.
It is another further object of the present invention to provide a method for removing a spin-on-glass material from a wafer flat side such that a SOG build up at the flat side can be avoided.
It is still another object of the present invention to provide a method for removing a SOG layer from wafer flat side by utilizing existing backside rinse equipment.
It is yet another object of the present invention to provide a method for removing a SOG coating layer from wafer flat side by utilizing a predetermined rotational speed of the wafer such that a cleaning solution can be drawn from the underside of the wafer to the top side of the wafer.
It is still another further object of the present invention to provide a method for removing a coating material from wafer flat side by utilizing a combination of a desirable rotational speed and a desirable solvent mixture such that the solvent can be draw
Huang Kuan-Chi
Lo Chi-Shen
Brumback Brenda
Taiwan SEmiconductor Manufacturing Co., Ltd.
Tung & Associates
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