Coating apparatus – Projection or spray type – With hood or offtake for waste material
Reexamination Certificate
1999-02-03
2001-04-24
Edwards, Laura (Department: 1734)
Coating apparatus
Projection or spray type
With hood or offtake for waste material
C118SDIG007, C454S238000, C454S239000
Reexamination Certificate
active
06221160
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and an apparatus for controlling the environment in a process chamber and more particularly, relates to a method and an apparatus for controlling the air velocity flown into a spin coating chamber by utilizing a throttle valve control system.
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 desirable material for low-cost fabrication of IC circuits. Commonly used SOG materials may be of two basic types, i.e., an inorganic type silicate based SOG and an organic type siloxane based SOG. One of the typical organic type SOG materials is a silicon oxide based polysiloxane which is featured with radical groups replacing or attaching to oxygen atoms. Based on the two basic structures, the molecular weight, the viscosity and other desirable film properties of SOG can be modified and adjusted to suit the requirement of a 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 at a rotational speed which determines the thickness of the layer. 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 achieve a smooth surface in preparation for a capping oxide layer onto which a second inter-level 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 further 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.
A typical process which utilizes SOG material as an inter-metal dielectric (IMD) insulation is shown in
FIG. 1A. A
semiconductor structure
10
which has metal conductors
12
formed on a pre-processed semi-conducting substrate and an oxide layer
16
deposited on top is shown. The oxide layer may be suitably deposited of a boro-phospho-tetraethoxy-silicate (BPTEOS) material which is used to insulate previously deposited metal layers. The metal conductors
12
are formed by first depositing a metal layer on a diffusion barrier layer (not shown) such as TiN before the deposition of an AlCu material. On top of the metal conductor material, an adhesion promoter layer such as Ti or TiN is then deposited before an oxide cap layer
20
is used to insulate the metal conductors
12
. The oxide cap layer
20
may be deposited of a plasma enhanced oxide (PEOX). On top of the semiconductor structure
10
, a first SOG layer
22
is then deposited to seal the metal conductors
12
therein. Since SOG material has a large volume shrinkage ratio when it is deposited in a liquid form, the deposition step of SOG frequently results in void formations
18
and dips
24
in its top surface
14
. The void formation may also be a serious problem when multi-layered metal structures in which uniform etching profiles are difficult to maintain are used. Voids in an inter-metal dielectric layer not only pose a reliability concern, i.e., for trapping chemicals or contaminents in the void, but also cause breaks in metal lines if a void is etch opened during a subsequent planarization process. This is shown in FIG.
1
B. The open void
26
forms a crack in the SOG layer
22
and may cause a break in the metal lines
12
. The void formation defects are especially serious when SOG layers are deposited into metal spacings of less than 0.5 &mgr;m.
The task of depositing IMD without void formations has been attempted by others in processes that are not 100% conformal. A complicated multi-step process using ion bombardment to round off comers in order to enhance the IMD filling capability has been developed. For instance, when a single deposition process for SOG results in void formation, as shown in
FIG. 2A
wherein void
32
is formed in the IC structure
30
, the voids
32
can be minimized or eliminated by depositing the SOG film in several steps and sputter-etching between the steps. The multi-step process, also known as a “dep-etch-dep” process, alternately deposits and etches the IMD to create a desired profile. As shown in
FIG. 2B
, sputter-etching facets the SOG over vertical metal lines
34
and thus improving the gap-fill in a subsequent deposition step shown in
FIG. 2C
in which a second SOG layer
38
is deposited. The “dep-etch-dep” process, even though results in a substantially void-free SOG layer, requires complicated processing steps which increases the fabrication costs.
Referring now to
FIG. 3
, wherein a conventional set up for a spin coating apparatus
40
in a factory environment is shown. An air processor, or an air conditioner
68
is normally positioned on a lower floor away from the spin coating apparatus
40
to avoid vibration and contamination by the lubricants used in the air conditioner. An air conditioned flow of air
76
is transported to the spin coater
40
through air flow conduit
72
. A damper control valve
80
is normally utilized to control the air flow
76
. An enlarged, cross-sectional view of the spin coater
40
is shown in FIG.
4
. Spin coater
40
is typically used for spin coating a SOG material on a wafer surface. As shown, in the apparatus
40
, a cover
42
, two side wall panels
44
,
46
and a bottom panel
48
forms a sealed chamber containing a cavity
50
therein. The cover
42
also functions as an air duct for connecting to the flow inlet
52
. The flow inlet is normally connected to the air duct through a damper control valve
80
. An air flow
56
enters inlet
52
, through the damper control valve
80
and other internal passageways (not shown) to enter the chamber cavity
50
as air flow
58
. The air flow
56
which is fed into the air duct
42
can be advantageously taken from an air conditioning unit such that the relative humidity and the temperature of the incoming air
56
may be controlled. In the chamber cavity
50
, wafer pedestal
62
is mounted on a rotatable shaft
64
and is rotated by DC motor
66
. After a wafer
70
is positioned on the wafer pedestal
62
and securely mounted by vacuum means (not shown), a liquid dispensing nozzle is lowered to nearly touching the top surface of the wafer
70
at the wafer center. The distance between the nozzle head and the top surface of wafer
70
is between about 0.5 cm and about 3 cm. After wafer
70
is spun at a rotational speed of at least 100 RPM, or preferably at least 500 RPM, a SOG liquid is injected by a dispensing nozzle onto the center of the wafer. The material is spun out to cover the entire surface of the wafer
70
. A drain collecting device
74
, or a drain cup is used to collect excess liquid coating spun off the wafer surface
70
. Excess liquid coating is then carried away by drain pipe
78
. An outlet
82
is used to exhaust the air flow
58
such that the relative humidity in the chamber cavity
50
can be maintained.
In the conventional spin coating apparatus set-up, the air flow rate from an air processor, or an air conditioner is frequently too high to achieve an adequate control of a spin coating process. The only provision in the conventional set-up for correcting the air
Edwards Laura
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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