Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-11-27
2002-11-19
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S485000, C219S411000, C118S724000, C118S050100, C392S416000
Reexamination Certificate
active
06483081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to heat treatment of semiconductor wafers, and more specifically to vertical furnaces used in thermal curing of semiconductor wafers during fabrication.
2. Description of the Related Art
Semiconductor devices are formed from silicon wafers containing various circuitry defining the semiconductor device. During the formation of the circuitry on and in the silicon wafer, the wafers are processed through a plurality of fabrication operations to form, define, and refine the layers that make up the multi-layered structure. As is known, some layers are formed over wafers in the form of thin films that must be cured in order to carry out thermolytic reactions and/or remove solvents.
Vertical furnaces have been used in curing processes of semiconductor manufacture for many years. Typically, a vertical furnace is used in batch processing wherein 25 or more wafers at a time are inserted into a vertical furnace tube for heat treatment. Such heat treatment includes the curing of low k dielectric films applied to a surface of a semiconductor wafer. As an alternative to the batch processing of vertical or horizontal furnace tubes, semiconductor wafers are processed individually in curing modules.
FIG. 1A
shows a typical prior art single wafer curing module
10
. The curing module
10
includes a heating plate
12
and a cooling chamber
20
. A semiconductor wafer
11
is positioned within a chamber
14
of the curing module
10
through a door
24
attached to an arm
24
a
. Once the wafer
11
is within the chamber
14
, the door
24
seals the curing environment within. The semiconductor wafer
11
is positioned on lift pins
22
in the curing module
10
as shown. During a heating process, the wafer
11
is lowered onto heating plate standoffs
21
which are integral to the heating plate
12
.
After the wafer
11
is heated, the wafer
11
must be cooled to prevent oxidation of the organic components of the film on the surface of the wafer
11
when the wafer is removed from the chamber
14
and once again exposed to the ambient atmosphere. The wafer
11
is cooled by first raising the wafer
11
on the lift pins
22
from the heating plate
12
towards a diffusion plate
18
. The diffusion plate serves as a shower head to dispense the cooling medium of the cure module
10
. The wafer
11
is typically cooled with water (H
2
O)-cooled nitrogen gas (N
2
) flowing through the cooling chamber
20
and dispersed by the diffusion plate
18
and over the wafer
11
. Once the wafer
11
is cooled to an appropriate temperature at which the film will not oxidize, the wafer
11
is removed from the curing module
10
through door
24
.
Common problems with the curing module
10
processing technique include thermal discontinuities on the surface of the wafer
11
resulting from the lift pins
22
. Further, the curing module
10
is generally inefficient in performing both the heating and cooling operations of the curing process. By way of example, while the wafer
11
is being heated, heat rises from the heating plate
12
to the diffusion plate
18
which increases the surface temperature of the diffusion plate
18
. The increased temperature of the diffusion plate
18
raises the temperature of the cooled nitrogen gas as it exits through the diffusion plate
18
. The higher temperature of the nitrogen gas increases the cooling time of the wafer
11
, thereby decreasing the overall efficiency of the curing process. Additionally, the cure module is a single-wafer process, consuming precious time and resources in the wafer fabrication process.
FIG. 1B
shows a typical prior art vertical furnace unit
50
. The vertical furnace unit commonly includes a heating element
52
which can surround or define the furnace cavity or furnace tube
54
. Wafers
11
are staged in a cassette or boat
58
designed specifically for use in a vertical furnace unit
50
. The boat
50
can be designed to hold a plurality of wafers
11
ranging from 25 to more than a hundred. The primary advantage of the vertical furnace unit for wafer curing is batch wafer processing.
In the illustrated vertical furnace unit
50
, the wafer boat
58
is positioned on a pedestal
56
that lifts and withdraws the wafers
11
into and from the furnace tube
54
. The pedestal
56
is commonly configured to provide a means for dispersing N
2
while the wafers
11
are disposed within the furnace tube
54
. Such dispersion can occur through the pedestal itself acting as a diffusion plate, or by way of providing plumbing or ducting to flow N
2
around the wafers
11
and/or within the furnace tube
54
.
One common alternative to the pedestal
56
is a wafer boat
58
that is on a gear-driven track configured to move the boat
58
into and out of the furnace tube
54
. As an alternative to the vertical orientation of the vertical furnace unit
50
, the unit can be configured to be oriented horizontally. In such an orientation, corresponding similar components as those described perform essentially the same functions as described to cure wafers.
There are numerous disadvantages to typical prior art vertical or horizontal furnace units. As true batch processors, vertical or horizontal furnace units that are configured to cure 25 or more wafers at a time are ill suited for single wafer processing such as used in cluster arrangements of spin coat tracks and the like. Further, the furnace tube can result in non-uniform curing of the surface of a wafer as the applied heat in the tube structure results in the periphery of the wafers heating faster and to a greater degree than the center of the wafers. Additionally, in situations in which the desired cure time is short (e.g., less than 15 minutes), the single point of entry into the furnace tube results in a first in/last out wafer curing process. The difference in time at the desired temperature causes a significant difference in the degree of cure experienced by the first wafer and the last wafer in a batch of wafers. In the case of low k dielectric films, the needed cure time can be as short as 3-5 minutes, and the prior art vertical or horizontal furnace units don't provide the necessary high speed and continuous processing.
In view of the foregoing, there is a need for a cure furnace which is configured to efficiently and uniformly cure semiconductor wafers. The cure furnace should be efficient in low k dielectric applications in which high speed and continuous processing is required, and should be configured to integrate batch and single-wafer processing environments. The cure furnace should therefore be configured to avoid the problems of the prior art.
SUMMARY OF THE INVENTION
Broadly speaking, the present invention fills these needs by providing an in-line cure furnace configured to thermally cure films on semiconductor substrates while achieving high through-put, rapid processing, and precisely controlled thermal profiles. The present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several embodiments of the present invention are described below.
In one embodiment, an in-line cure furnace is disclosed. The in-line cure furnace includes a vertical furnace tube configured to thermally process a substrate, a hot plate configured to pre-heat the substrate for thermally processing in the vertical furnace tube, and a passageway connecting the hot plate to the vertical furnace tube. The in-line cure furnace further includes a cooling chamber and a passageway connecting the vertical furnace tube to the cooling chamber through which the substrate is transitioned from the vertical furnace tube to the cooling chamber.
In another embodiment, a method for thermally curing a substrate is disclosed. The method includes providing a substrate having a film requiring thermal curing and pre-heating the substrate on a hot plate. The substrate is then transitioned from the hot plate to a cassette disposed within a vertical furnace tube. The casse
Fuqua Shawntina
Martine & Penilla LLP
Novellus Systems Inc.
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