Method of fabricating self-aligned contacts

Details Method of fabricating self-aligned contacts Method of fabricating self-aligned contacts

2000-09-28

2002-11-26

Kunemund, Robert (Department: 1765)

Etching a substrate: processes

Forming or treating electrical conductor article

C216S018000, C216S041000, C216S079000, C438S720000, C438S723000, C438S724000, C438S947000, C438S597000

Reexamination Certificate

active

06485654

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of fabricating a DRAM. More particularly, the invention relates to a method of fabricating self-aligned contacts between conductor lines.
2. Description of the Prior Art
A process of producing the DRAM main purpose of self-alignment is that the isolation effect for the isolating layer being not reduced due to subsequent etching steps.
FIGS. 1A
to
1
B show cross-sectional views of a process for producing a non self-aligned contact.
Referring to
FIG. 1A
, a process for producing a non self-aligned contact includes forming conductor lines
102
on a substrate
100
, depositing a dielectric layer
104
having a flat upper surface on the substrate
100
and conductor line
102
; then defining a contact hole
106
into the dielectric layer
104
between two conductor lines
102
by etching so as to expose and connect the substrate
100
.
Next, referring to
FIG. 1B
, an isolating spacer
108
is formed on the sidewall of the contact holes
106
. Finally, a conductive material is deposited to form a conductive plug
110
.
With increasing integrity, the distance between the conductor lines is shortened. In the above mentioned process for producing contacts, it may result in exposure of the conductor lines to the contact hole because of non self-alignment when a dielectric layer is etched to form contact holes.
Two processes for producing a self-aligned contact to improve the disadvantages caused from the above method are known in the art. One of them is showed in
FIGS. 2A-2C
, the other in
FIGS. 2A
,
2
D-
2
F.
Referring to
FIG. 2A
, a general process for producing a self-aligned contact includes forming conductor lines
202
on a substrate
200
, depositing a cap layer
204
on the leads
202
, then forming an isolating layer
206
on the substrate
200
and cap layer
204
.
Next, referring to
FIG. 2B
, etching is carried out so as to allow the cap layer
204
to be exposed, and an isolating spacer
206
a
is formed on both sidewalls of the conductor line
202
.
Finally, referring to
FIG. 2C
, a dielectric layer
208
with a flat upper surface is deposited on the substrate
200
and cap layer
204
. A contact hole which will be connected with the substrate
200
is defined between two conductor lines
202
and formed by etching part of the dielectric layer
208
. Finally, a conductive material is deposited in the contact hole to form a conductive plug
212
.
With the process for producing a contact, a part of the cap layer and spacer will be etched off to be thinner. It will result in the poor isolation characteristics between conductor lines and plugs.
Referring to
FIG. 2A
, another process for producing self-aligned contact is disclosed. Conductor lines
202
are patterned on a substrate
202
. A cap layer
204
is deposited on the leads
202
. Then, an isolating layer
206
is deposited on the cap layer
204
and substrate
200
.
Referring to
FIG. 2E
, a contact hole
210
which will be connected with the substrate
200
is defined between two conductor lines
202
and formed by etching a part of the dielectric layer
208
.
Referring to
FIG. 2F
, a conductive material is deposited in the contact hole to form a conductive plug
212
.
When the dielectric layer was etched by this method, the isolating layer in the bottom of the contact hole will be etched together with the dielectric layer. The bottom of contact hole will have residues if existing non-complete etching on bottom isolating layer. It will result in increased resistance of the contact between the contact hole and the substrate.
SUMMARY OF THE INVENTION
The invention thus provides a process for producing a self-aligned contact, which improves the disadvantages of the prior art, such as poor isolating characteristics between contact holes and conductor lines and non complete etching on the bottom area between the contact hole and substrate.
The process according to the present invention comprises the steps of forming conductor lines on a substrate, forming an etching stop layer on the conductor lines by depositing, then forming a sacrificed oxide layer, after the structure of the conductor lines is defined, forming a spacer on each side of the structure, removing the sacrificed oxide layer, allowing the spacer to protrude in the form of horn. Next, a dielectric layer having a flat upper surface is deposited on the substrate and the conductor lines, a contact hole being formed between the structure of the conductor lines so as to connect the substrate, and a conductive material then being filled in the contact hole and back-etched to form a plug.
The main advantage of the present invention is that: with the structure of spacer, a stack structure of a conductor line layer, an etching stop layer and a sacrificed oxide layer, the spacer subsequently formed is pulled up, then protruding in the form of horn by removing the sacrificed oxide layer.
Because the etchant with higher etching selectivity for the dielectric layer to silicon nitride is used during forming the contact hole by removing part of the dielectric layer, the tip of the horn-shaped silicon nitride spacer is etched less. It can avoid the spacer at the top outside the structure of conductor lines to be etched off to cause the problem of poor isolating characteristics and exposure of conductor lines.
Additionally, according to the present invention, the spacer is very important during forming the contact hole by removing the dielectric layer. It can, improve the isolation between the conductor lines and the conductive plug. Furthermore, the problem of non-complete etching of the dielectric layer in the bottom of the contact can be also improved.
Another advantage of the present invention is to improve the process window. Because the spacer can not be etched readily during forming the contact hole by etching the dielectric layer, the limit to the time of etching has a broader range, achieving an improvable process window.
There is lower contact resistance between the contact hole and the substrate, because the contact area between the contact hole and substrate is etched more completely.


REFERENCES:
patent: 5496750 (1996-03-01), Moslehi
patent: 5966600 (1999-10-01), Hong
patent: 6093627 (2000-07-01), Sung
patent: 6274425 (2001-08-01), Park
patent: 6274441 (2001-08-01), Mandelman et al.
Wolf et al, “Silicon Processing For The VLSI ERA” vol. 1, 1986, pp. 168-169.

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