Method of manufacturing shallow trench isolation

Details Method of manufacturing shallow trench isolation Method of manufacturing shallow trench isolation

1998-11-12

2001-06-26

Utech, Benjamin L. (Department: 1765)

Semiconductor device manufacturing: process

Chemical etching

Combined with the removal of material by nonchemical means

C438S693000, C438S694000

Reexamination Certificate

active

06251783

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to method of manufacturing shallow trench isolation (STI). More particularly, the present invention relates to a method of manufacturing shallow trench isolation that includes the use of a chemical-mechanical polishing (CMP) operation.
2. Description of Related Art
Chemical-mechanical polishing (CMP) is a method for providing global planarization during the fabrication of very large scale integration (VLSI) circuits or the higher-density ultra large scale integration (ULSI) circuits. Since CMP is the only method capable of providing the necessary planarization when the feature size is small, most manufacturers are now pooling research efforts to investigate methods of improving this technique.
As size of semiconductor devices continues to shrink, for example, to a line width of between 0.18 &mgr;m to 0.25 &mgr;m or even smaller (deep sub-half micron range), the performance of a CMP operation, especially in the planarization of an oxide layer above a shallow trench, is becoming increasingly important. However, in order to prevent the dishing of a polished oxide layer above a wide trench opening, a manufacturing method that utilizes a reverse tone mask followed by an etching back operation is deployed. The addition of a reverse tone mask and an etching back operation is capable of improving CMP uniformity.
In a conventional shallow trench isolation manufacturing operation, size of active regions varies tremendously. Therefore, the shallow trenches formed between those active regions may have various sizes.
FIGS. 1A through 1D
are schematic, cross-sectional views showing the progression of steps in a manufacturing process for fabricating a conventional shallow trench isolation structure by forming a reverse tone mask followed by a chemical-mechanical polishing operation.
First, as shown in
FIG. 1A
, a shallow trench
101
and active regions
102
a
/
102
b
are formed in a substrate
100
using photolithographic and etching processes. Since the sizes of active region
102
a
and active region
102
b
are different, the size of each shallow trench
110
will be different as well. Furthermore, a silicon nitride layer
104
is also formed over the active regions
102
a
/
102
b
. Thereafter, a layer of oxide is deposited to fill completely the shallow trenches
101
and cover the entire substrate
100
, thereby forming an oxide layer
106
. The oxide layer
106
can be formed using, for example, atmospheric pressure chemical vapor deposition (APCVD). Due to the presence of shallow trenches in the substrate
100
, the upper surface of the oxide layer
106
has an undulating profile.
Next, as shown in
FIG. 1B
, a photoresist layer is formed over the oxide layer
106
. Then, the photoresist layer is developed and etched using photolithographic method to form a reverse tone mask
108
. This reverse tone mask
108
covers the shallow trenches
101
with an opening
110
exposing a portion of the substrate in the active region
102
a
, which occupies a larger surface area. In fact, the opening
110
forms a complementary region of the active region
102
a.
Thereafter, as shown in
FIG. 1C
, the exposed oxide layer
106
above the active region
102
a
is etched using the reverse tone mask
108
as an etching mask. Consequently, a large portion of the oxide layer
106
above the active region
102
a
is removed resulting in the appearance of small bumps on the upper surface of the oxide layer
106
near the edge of the opening
110
. Subsequently, the reverse tone mask
108
is removed.
Next, as shown in
FIG. 1D
, a chemical-mechanical polishing operation is carried out to remove a portion of the oxide layer
106
that lies above the shallow trenches
101
(
FIG. 1B
) using the silicon nitride layer
104
as a polishing stop layer. Eventually, the upper surface of the oxide layer
106
a
is level with the top surface of the silicon nitride layer
104
.
One of the advantages of using a reverse tone mask to form shallow trench isolation structures includes the reduction of polishing time. Consequently, both productivity and window of tolerance in producing the isolation structures are increased. Furthermore, the reduction of polishing time can reduce the degree of over-polishing of the silicon nitride layer. Hence, dishing of the oxide layer resulting from chemical-mechanical polishing is minimized.
Nevertheless, the utilization of a reverse tone mask introduces one more processing step in the fabrication of shallow trench isolation structures. Therefore, production cost and degree of complexity are affected. Moreover, due consideration must be paid regarding the proper alignment of the reverse tone mask. If the reverse tone mask is not properly aligned, the opening within the mask exposes a portion of the oxide layer within the shallow trench. Therefore, when the oxide layer is subsequently etched, a portion of the oxide within the shallow trench is etched away, and grooves are formed. These grooves may intensify any kink effect within a wafer chip so that current may leak out from the grooves and result in a short-circuit. Hence, the yield of the silicon chip may be lowered.
In light of the foregoing, there is an urgent need to combat the problems caused by the use of a reverse tone mask in chemical-mechanical polishing so that the yield rate of devices can increase despite a reduction in line width.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method of manufacturing shallow trench isolation structures that utilizes a photoresist cap layer together with an etching back operation to replace the conventional processing method of using a reverse tone mask. This method of manufacturing shallow trench isolation structures has the advantage of using a reverse tone mask but without the disadvantage of mask alignment problems because no extra mask is formed. Therefore, the method is capable of lowering production cost and reducing the complexity of processing.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of manufacturing shallow trench isolation structures. The method includes the steps of first depositing insulating material into the trench of a substrate to form an insulation layer. The substrate has a plurality of active regions each occupying a different area and having a different size, and each active region is covered on top by a silicon nitride layer. Thereafter, a photoresist layer is deposited over the insulation layer. Next, a portion of the photoresist layer is etched back to expose a portion of the oxide layer so that the remaining photoresist material forms a cap layer over the recessed areas of the insulation layer. Subsequently, using the photoresist cap layer as a mask, the insulation layer is etched to remove a portion of the exposed oxide layer, thereby forming trenches within the oxide layer. After that, the photoresist cap layer is removed. Finally, a chemical-mechanical polishing operation is carried out to polish the insulation layer until the silicon nitride layer is exposed.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.


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patent: 5482894 (1996-01-01), Havermann
patent: 5691215 (1997-11-01), Dai et al.
patent: 5851899 (1998-12-01), Weigand
patent: 5981355 (1999-11-01), Lee

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