Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-12-09
2004-08-17
Chen, Jack (Department: 2813)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S631000
Reexamination Certificate
active
06777324
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a multi-layer interconnection structure in a semiconductor device and a method for fabricating the same, and more in detail, to the multi-layer interconnection structure including a plurality of interconnects having different interconnect film thicknesses in a single interconnect layer in which a parasitic capacitance and a parasitic resistance can be best established depending on demands on a circuit operation and an interconnect length, and the method for fabricating the same.
(b) Description of the Related Art
With higher integration and miniaturization of a semiconductor device, interconnects for connecting respective regions of a semiconductor element are multi-layer to reduce a surface area required for interconnects in the interconnect design of the semiconductor device because miniaturization of the respective semiconductor elements are more and more requested.
The semiconductor device is configured as a large-scale integrated circuit having a significant number of electronic circuits including semiconductor elements having a variety of functions.
The interconnects of the semiconductor device are composed as a collective member for connecting the respective semiconductor elements. The interconnects include a long-distance interconnect for connecting the semiconductor elements disposed relatively far from each other, a medium-distance interconnect for connecting those disposed in a relatively short distance and a short-distance interconnect for connecting regions in a single semiconductor element.
The interconnects in the semiconductor device have a variety of properties depending on the film thickness and the length thereof.
For example, a delay time with respect to a specified interconnect length was measured, with the film thickness as a parameter, for a CMOS semiconductor having gate widths of 10 &mgr;m and 20 &mgr;m for the N-channel transistor and the P-channel transistor, respectively, an interconnect width of 0.3 &mgr;m and an interconnect interval of 0.3 &mgr;m, that is, an interconnect pitch of 0.6 &mgr;m. The results of the measurements were as shown in FIG.
1
.
If the interconnect length is longer than a critical length, the delay time is longer for the interconnect having a thinner film thickness. Conversely, if the interconnect length is shorter than the critical length, the delay time is basically longer for the interconnect having a thicker film thickness.
Parasitic capacitances (pF/mm) for the interconnect having a thicker film thickness (0.4 &mgr;m thickness) and the interconnect having a thinner film thickness (1.0 &mgr;m thickness) are as shown in Table 1 by employing an index showing the number of adjacent interconnects running parallel to the subject interconnect at the minimum pitch therefrom as a parameter. The parasitic resistance is 158 &OHgr;/mm for the interconnect having a film thickness of 0.4 &mgr;m, and 63 &OHgr;/mm for the interconnect having a film thickness of 1.0 &mgr;m.
TABLE 1
200%
100%
0%
0.4 &mgr;m thickness
0.23
0.18
0.13
1.0 &mgr;m thickness
0.39
0.30
0.18
The above index is defined as follows. If two interconnects extend parallel to the subject interconnect with a minimum pitch at both sides thereof, the index is 200%. If a single interconnect extends parallel to the subject interconnect with the minimum pitch at either side thereof, it is 100%. If no interconnect extends parallel to the subject interconnect, it is 0%.
If the line widths of the interconnects in the semiconductor device are set substantially the same, a relatively large thickness is necessary for a longer-distance interconnect and a relatively small thickness is sufficient for a shorter-distance interconnect.
The interconnect constituting a critical path for the circuit operation is required to be relatively thick, and that not constituting the critical path may be relatively thin. The term “critical path” used herein is the path of an interconnect which determines the speed of operation in a chip.
Optimization of the parasitic capacitance and the parasitic resistance is required depending on the demand on the circuit operation and the interconnect length, otherwise the circuit operation is delayed.
When the short-distance interconnect and the long-distance interconnect are present in a single interconnect layer in a multi-layer structure, the film thicknesses of the two interconnects are substantially the same because they are formed in the same interconnect forming step.
In the step for forming, the optimization of the parasitic capacitance and the parasitic resistance cannot be implemented, thereby delaying the circuit operation.
As an alternative process for the optimization, the layer for the short-distance interconnect and the layer for the long-distance interconnect are separately deposited and the optimization is implemented in the respective layers. In this manner, the parasitic capacitance and the parasitic resistance can be optimized in each of the interconnect layers. However, the number of the steps increases to elevate the manufacturing cost due to the layer increase, and further the interconnection structure becomes larger to be against the miniaturization of the semiconductor device.
JP-A-8(1996)-293551 describes a conventional method for forming a multi-layer interconnection structure in which top layer interconnects has a film thickness different from that of the bottom interconnect.
Referring to
FIGS. 2A
to
2
F, the conventional method for forming the multi-layer interconnection structure described in the publication will be described.
At first, as shown in
FIG. 2A
, bottom interconnects
14
A,
14
B and
14
C having substantially the same film thickness are formed on a dielectric film
12
, and a first interlayer dielectric film
16
is deposited on the bottom interconnects.
The bottom interconnects
14
A and
14
B have small distances and have a small thickness, whereas the bottom interconnect
14
C is required to be thick, which forms a lower layer of a bottom interconnect
26
(
FIG. 2C
) formed as the long-distance interconnect. The thickness of the first interlayer dielectric film
16
is substantially the same as that of the bottom interconnect
26
.
Then, as shown in
FIG. 2B
, the first interlayer dielectric film
16
is etched to form via-holes
18
reaching to the bottom interconnects
14
A and
14
B, and an interconnect trench
20
, on the bottom interconnect
14
C, having the substantially same width as that of the bottom interconnect
14
C.
Further, as shown in
FIG. 2C
, the via-holes
18
and the interconnect trench
20
are filled with the interconnect material the same as that of the bottom interconnects
14
A to
14
C to form via-holes
22
and an upper layer
24
of the bottom interconnect
26
, respectively. The thickness of the bottom interconnect
26
is a sum of those of the bottom interconnect
14
C and the upper layer
24
.
Then, as shown in
FIG. 2D
, a second interlayer dielectric film
28
is deposited on the entire surface of the wafer and etched to form via-holes
30
reaching to the via-holes
22
or the bottom interconnect
26
.
Then, as shown in
FIG. 2E
, an interconnect material is deposited on the entire surface of the wafer by evaporation to fill the via-holes
30
to form via-holes
32
and a top interconnect layer
34
.
Thereafter, as shown in
FIG. 2F
, the top interconnect layer
34
is etched to form top interconnects
36
connected to the bottom interconnects
14
A and
14
B by way of the via-holes
22
, and a top interconnect
38
connected to the bottom interconnect
26
by way of the via-hole
32
, thereby providing a desired multi-layer interconnection structure.
In the above conventional method, the number of the deposition steps of the interconnect material by using an evaporation technique is two, that is, the evaporation for the bottom interconnect
14
and the via-holes
22
/the upper layer of the bottom interconnect
26
, and the number of the photolithographic steps of is three, that is, the patte
Chen Jack
McGinn & Gibb,PLLC
NEC Electronics Corporation
Vesperman William
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