Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Thinning of semiconductor substrate
Reexamination Certificate
1999-06-30
2001-02-20
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Thinning of semiconductor substrate
C438S977000
Reexamination Certificate
active
06191008
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method of forming a silicon-on-insulator(SOI) substrate provided with an isolation layer.
2. Description of the Related Art
Due to the fast development in semiconductor device such as high integration and high performance, a semiconductor device using the SOI substrate instead of a silicon substrate made of bulk silicon, has been proposed. The SOI substrate has a stack structure of a base substrate as a means for supporting, a buried oxide layer, and a semiconductor layer in which a device is formed later. The semiconductor device formed on the SOI substrate has advantages such as a complete isolation of adjoining devices by the buried oxide layer and especially a reduced the parasitic capacitance and fast operation.
Conventionally, there have been used methods of forming SOI substrate, such as SIMOX(separation by implanted oxygen) and bonding method.
In the method of forming the SOI substrate according to the SIMOX, a silicon substrate is provided and oxygen ions are then ion-implanted at a predetermined depth from an upper surface of the silicon substrate. Afterward, the silicon substrate is annealed so that the ion-implanted oxygen ions react with silicon of the silicon substrate thereby forming the buried oxide layer to divide the silicon substrate into a base layer and a semiconductor layer. However, the SIMOX method has shortcomings that it is difficult to control thickness of the semiconductor layer in which a device is formed later, and a considerable amount of process time is required.
Referring to the method of forming the SOI substrate according to the bonding method, a base silicon layer as a supporting means is provided and a buried oxide layer is formed on the base silicon layer. Next, a semiconductor silicon layer in which a device is formed later, is bonded on the buried oxide layer, and the semiconductor silicon layer is back-polished according to the CMP process, so as to obtain a semiconductor layer having a desired thickness. According to the bonding method, it is easy to control thickness of the semiconductor layer and the bonding method shortens process time, compared to the SIMOX method. Moreover, since the isolation layer may be provided at the semiconductor layer during the manufacturing process of the SOI substrate, a manufacturing step of forming the isolation layer can be deleted from known semiconductor manufacturing processes.
FIGS. 1A
to
1
D are cross-sectional views showing conventional manufacturing steps of forming the SOI substrate according to a bonding method. Detailed descriptions of the manufacturing method will be discussed with reference to accompanying drawings.
Referring to
FIG. 1A
, a base silicon layer
1
as a means for supporting is provided and a first oxide layer
2
is then formed on the base silicon layer
1
.
Referring to
FIG. 1B
, a semiconductor silicon layer
3
is provided and trenches
4
are then formed in an upper surface of the semiconductor silicon layer
3
according to a known etching process. Herein, the trench
4
has a depth similar to thickness of a semiconductor layer in which a device is formed later. A second oxide layer
5
is formed with a thickness sufficient to fill the trench
4
completely.
Referring to
FIG. 1C
, the base layer
1
and the semiconductor silicon layer
3
is bonded such that the first and second oxide layers
2
,
5
are contacted with each other. Next, the base silicon layer
1
and the bonded semiconductor silicon layer
3
are annealed so that the bonding intensity therebetween is increased.
Referring to
FIG. 1D
, the semiconductor silicon layer
3
is back-polished according to the CMP process using the second oxide layer
5
filled in the trench
4
as a polishing stopper. As a result, an SOI substrate
10
comprising the base silicon layer
1
, the buried oxide layer
7
formed on the base silicon layer
3
, and a semiconductor layer
3
a
having an isolation layer and disposed on the buried oxide layer
7
is obtained.
In general, the property of a semiconductor device being formed in the SOI substrate depends mainly on the uniformity of semiconductor layer. Accordingly, what is most important is to obtain the uniformity of semiconductor layer in case the SOI substrate is formed according to the bonding method.
As described above, however, when the semiconductor silicon layer is polished so as to obtain a semiconductor layer by a thinning process after isolation layers are formed in the semiconductor silicon layer, there is occurred a dishing D at a surface of the semiconductor layer
3
a
as shown in FIG.
1
D. As a result, thickness of the semiconductor layer
3
a
is not uniform owing to the occurrence of dishing D. Therefore, when a device is formed on the above semiconductor layer
3
a
, it is difficult to expect improvements in the device property.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method of forming an SOI substrate capable of improving the uniformity in thickness of the semiconductor layer by preventing from occurring the dishing D on the semiconductor layer.
To accomplish foregoing objects, one embodiment of the present invention provides a method of forming SOI substrate comprising the steps of:
providing a base silicon layer and a semiconductor silicon layer;
forming a buried oxide layer on the base silicon layer;
forming trenches in the semiconductor silicon layer;
boding the base silicon layer and the semiconductor silicon layer so that the buried oxide layer and the trench-formed surface are contacted with each other;
removing a selected thickness of the semiconductor silicon layer to obtain a semiconductor layer having a desired thickness, wherein the trenches formed in the semiconductor silicon layer are exposed by removing the selected thickness of the semiconductor silicon layer and the semiconductor layer is separated into a plurality of regions by the exposed trenches;
forming an etch stop layer only on the semiconductor layer except the trenches;
forming an oxide layer with a thickness sufficient to fill a region between stacked structures comprising the semiconductor layer and the etch stop layer;
etching the oxide layer by means of the etch stop layer, wherein an isolation layer is formed at the region between the stacked structure; and
removing the etch stop layer.
Another embodiment of the present invention further provides a method of forming SOI substrate comprising the steps of:
providing a base silicon layer and a semiconductor silicon layer;
forming a first oxide layer on the base silicon layer;
forming an impurity layer with a first depth within the semiconductor silicon layer;
forming trenches with a second depth in the semiconductor silicon layer, wherein the second depth is deeper than the first depth;
boding the base silicon layer and the semiconductor silicon layer so that the first oxide layer on the base silicon layer and the trench-formed surface are contacted with each other;
removing a selected thickness of the semiconductor silicon layer including an impurity layer formed therein to obtain a semiconductor layer having a desired thickness, wherein the trenches formed in the semiconductor silicon layer are exposed by removing the selected thickness of the semiconductor silicon layer and the semiconductor layer is separated into a plurality of regions by the exposed trenches;
forming an etch stop layer only on the semiconductor layer except the trenches;
forming a second oxide layer with a thickness sufficient to fill a region between stacked structure comprising the semiconductor layer and the etch stop layer;
etching the second oxide layer by means of the etch stop layer, wherein an isolation layer is formed at the region between the stacked structure; and
removing the etch stop layer.
REFERENCES:
patent: 4897703 (1990-01-01), Spratt et al.
patent: 5071792 (1991-12-01), VanVonno et al.
patent: 5137837 (1992-08-01), Chang et al.
paten
Hyundai Electronics Industries Co,. Ltd.
Ladas & Parry
Niebling John F.
Pompey Ron
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