Method of fabricating contact window

Details Method of fabricating contact window Method of fabricating contact window

1998-08-07

2001-09-11

Huff, Mark F. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making electrical device

C430S313000, C430S315000, C216S041000

Reexamination Certificate

active

06287751

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application Ser. No. 87107278, filed May 12, 1998, the full disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a method of fabricating a contact window, and more particularly, to a method of fabricating a contact window with a chamfered top corner by forming an additional gettering layer and a hard mask layer.
2. Description of the Related Art
Due to the higher and higher integration in an integrated circuit, surface areas on a chip available for forming interconnects become more and more limited. To achieve the electrical connection between electrodes or devices on the chips, a technique of multi-level interconnection was developed and is now commonly used. During the fabrication of a multi-level interconnect, an inter-metal dielectric (IMD) layer is formed between two conductive layers to avoid any unwanted connections. To electrically connect the two conductive or metal layers, a contact window is formed to penetrate through the inter-metal dielectric layer. The contact window is then filled with a conductive layer to form contact via or a contact plug. Another conductive layer is further formed and coupled with the contact via or contact plug. Thus, two conductive layers can be electrically connected with each other by means of the contact via or contact plug.
In
FIG. 1A
to
FIG. 1C
, a conventional method of forming a contact window is shown.
In
FIG. 1A
, an inter-metal dielectric layer
14
, for example, a silicon oxide layer formed by chemical vapour deposition (CVD), is formed on a semiconductor substrate which includes a conductive region
12
such as a source/drain region, a gate, or other conductive structures. A photo-resist layer
16
is formed on the dielectric layer
14
with an opening aligned with the conductive region
12
. That is, the opening exposes the dielectric layer
14
right on top of the conductive region
12
.
In
FIG. 1B
using a dry etch, the exposed dielectric layer
14
is removed with the photo-resist layer
16
as a mask. A contact window
18
is formed on the modified dielectric layer
14
a
to expose the conductive region
12
.
In
FIG. 1C
, using sputtering deposition, a glue/barrier layer
20
is formed of, for example, titanium/titanium nitride (Ti/TiN), to enhance the adhesion between a contact via formed subsequently and the contact window
18
.
As shown in
FIG. 1C
, by using this conventional method, a sharp corner
22
is formed on the top edge of the contact window
18
. With the sharp corner
22
, a poor step coverage is obtained for forming the glue/barrier layer
20
. As a consequence, an overhang of the glue/barrier layer
20
is formed at the top corner
22
of the contact window
18
. In the subsequent process of forming a contact via or a contact plug, the overhang causes the formation of a void which causes a poor conductivity. A bad contact is caused between the conductive layer
12
and another conductive layer formed thereafter. Therefore the contact via or contact plug cannot form a good electrical connection between the conductive layer
12
and another conductive layer.
Moreover, during the dry etch process to remove the inter-metal dielectric layer
14
and the deposition process for different layers mentioned above, moisture and alkaline metal ions are existent. The moisture and alkaline metal ions easily penetrate through the dielectric layer
14
. and therefore, the structures or components under the dielectric layer are damaged and degraded by the penetrated moisture or alkaline metal ions. The quality of the integrated circuit is degraded and the lifetime of the integrated circuit is shortened. Furthermore, during the exposure process for defining the contact window
18
, without the formation an anti-reflective layer, an incident light source transmits through the inter-metal dielectric layer
14
and is then reflected by the conductive layer
12
or other metal layers underlying the inter-metal dielectric layer. The reflective light interferes with the incident light source, so that a misalignment is easily caused. Sometimes, the misalignment even causes a blind window. The blind window occurs when photo-resist layer or the inter-metal dielectric layer is not removed completely from the contact window. T he conductive layer within the contact window is thus not exposed at all, and the electrical connection cannot be achieved by the formation of the contact via or contact plug. It is known that the thickness of the dielectric layer is a key factor which affects the critical dimension (CD) in after develop inspection (ADI). If a deviation is introduced due to defocusing or a swing effect of the dielectric layer, an error of critical dimension occurs. In the conventional method, if the photo-resist layer is not thick enough, it is possible that the photo-resist layer is removed while removing the exposed dielectric to form the contact window. Therefore, to be used as a mask layer, the photo-resist layer has to be sufficiently thick to protect the underlying dielectric layer from being etched or removed. However, the thicker the photo-resist layer is, the smaller the tolerance of critical dimension is. Thus, a defocusing phenomenon occurs often.
SUMMARY OF THE INVENTION
It Is an object of the invention to provide a method of fabricating a contact window. By forming an additional gettering layer, the penetration of moisture and alkaline metal ions through the inter-metal dielectric layer are suppressed, so that the underlying structures or components are protected from being degraded.
It is another object of the invention to provide a method of fabricating a contact window without the formation of a blind window. During the exposure process for defining the contact window, an additional hard mask layer blocks an incident light from transmitting through the inter-metal dielectric layer and being reflected by an underlying metal layer. The precision of the exposure process is thus enhanced.
It is yet a further object of the invention to provide a method of fabricating a contact window in which the thickness of the photo-resist layer is reduced, so that the critical dimension (CD) in after develop inspection (ADI) is less affected.
It is a further object of the invention to provide a method of fabricating a contact window with a better step coverage for the subsequent process.
In more detail, before defining the dielectric layer, a gettering layer and a hard mask layer are formed on the dielectric layer in sequence. As a consequence, the penetration of moisture and alkaline metal ions is suppressed by the gettering layer, and a light transmitting through the contact window and reflected by the underlying metal layer is blocked by the hard mask layer. A better step coverage for the subsequent process is obtained by a profile of a chamfering top corner. Therefore, the formation of a blind window is avoided. Furthermore, with the formation of the hard mask layer, the thickness of the photo-resist layer can be reduced. The precision of the subsequent exposure is thus improved.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.


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patent: 3914602 (1990-11-01), None
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