Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
1998-08-22
2001-01-09
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S313000
Reexamination Certificate
active
06171764
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to methods for reducing the intensity of reflected rays experienced during the exposure process in semiconductor manufacturing. More particularly, the invention relates to methods of utilizing a dielectric anti-reflective coating (DARC) layer to effectively control the intensity of reflected rays encountered during the photolithography process.
2. Background of the Invention
During the exposure process in photolithography, rays that penetrate the photo mask will be transmitted through the surface of the underlying layer and will be reflected by the substrate. These reflected rays will then expose portions of the photoresist that were supposed to be blocked by the mask during the initial exposure. In other words, the reflected rays will result in unwanted exposure in portions of the photoresist causing chemical reactions in the photoresist and the subsequent removal of the photoresist when developed (unwanted photoresist removal will occur for positive photoresist, and vice versa for negative photoresist). The resulting pattern distortion during the exposure process, due to the reflected rays, is referred to as the reflected ray effect.
With the continual shrinkage of line width in semiconductor processing, the proportion of pattern distortion in relation to the overall line width is increasing and will severely effect yield and reliability, causing unwanted shorts and a deterioration in CD (critical dimension) control. To overcome this problem, anti-reflective layer, such as the TiN (titanium nitride) in metal layers, is commonly used to control the intensity of reflected rays.
In more sophisticated technology, it is common practice to use a DARC layer to reduce the amount of reflected rays from non-metalic layers. Due to its ability to absorb rays and to produce a phase shift in the reflected rays, the DARC layer is extensively used in 0.25 &mgr;m technology to inhibit the effects of non-metal layer reflection in the photolithography process.
Referring to
FIG. 1
, the utilization of a DARC layer in the photolithography process is illustrated. It includes a substrate
10
, an underlying layer
11
that do not have physical contact with the photoresist, but need to be patterned, and a hard mask layer
12
namely SiO
2
that serves as an indirect photo mask. In the situation in which the photoresist cannot have physical contact with the underlying layer, and in which the underlying layer needs to be defined, a SiO
2
layer would first be deposited as the hard mask
12
. The pattern on the photoresist will first be transferred onto the hard mask and the defined hard mask will then be used as an indirect mask to define the underlying layer
11
.
Above the hard mask layer
12
are a DARC layer
13
and a photoresist
14
. During exposure, the DUV ray
20
enters from the top. Its first reflected ray
21
is the reflection from the DARC layer
13
; the second reflected ray
22
is the reflection from the substrate
10
, which has already undergone the absorption and the phases shifting when penetrating the DARC layer
13
. Hence, when the second reflected ray
22
penetrates the DARC layer
13
and combines with the first reflected ray
21
, the phase shifting cancellation occurs between both reflected rays
21
and
22
, thereby reducing the intensity of reflected rays.
Theoretically, when a ray penetrates a multi-layer structure, it will produce a reflected ray and a transmitted ray at each interface as shown in FIG.
1
. Hence, in theory, there would be a third reflected ray
23
and a fourth reflected ray
24
besides the reflected rays
21
and
22
. However, since the DUV ray can easily penetrate the various layers shown in
FIG. 1
, the third reflected ray and the fourth reflected ray
24
can be combined with the second reflected ray
22
.
Nonetheless, the method of suppressing reflected rays during the photolithography process as mentioned above has the following problems:
1) If the hard mask film thickness is non-uniform, it will produce non-uniform reflections. It is not possible to suppress this kind of non-uniform reflections by traditional methods.
2) The DUV active photoresist on the DARC layer will undergo chemical reaction when it has the physical contact with the DARC layer producing a thin amino group (NH
2
) film. This will result in the footing effect with the subsequent patterning of the photoresist.
3) During the formation of the DARC layer, the subsequent rapid thermal processing associated with the plasma enhanced chemical vapor deposition (PECVD) process will cause the hard mask layer to undergo physical change as a result of ionic and thermal stress, affecting the etching process of the hard mask that follows.
4) With the DARC layer being on top of the hard mask, the pattern definition process requires the removal of the DARC and hard mask layers. During the etching process of the hard mask layer, the sidewall is easily etched away, forming a bowing profile.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method of suppressing reflected rays in the photolithography process in order to avoid the problems associated with the unwanted reflection.
The anti-reflection process of the present invention involves the formation of an underlying layer to be patterned on a wafer substrate, followed by the deposition of a DARC layer, a hard mask layer, and photoresist. The exposure is then performed to transfer the pattern. The difference between this invention and other known methods rests in that the DARC layer lies beneath the hard mask layer, and not vice versa.
In addition, it is also possible to deposit a DARC layer both above and beneath the hard mask layer, forming a “sandwich” structure. The process involves the formation of an underlying layer on the substrate, followed by the deposition of a DARC layer, a hard mask layer, and a 2
nd
DARC layer. Finally, the photoresist is coated and the pattern is defined through the exposure.
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The description is made with reference to the accompanying drawings.
REFERENCES:
patent: 5472829 (1995-12-01), Ogawa
patent: 5600165 (1997-02-01), Tsukamoto et al.
patent: 5741626 (1998-04-01), Jain et al.
patent: 5858870 (1999-01-01), Zheng et al.
patent: 5963841 (1999-10-01), Karlsson et al.
Ku Chia-Lin
Yen Wen-Ping
Liauh W. Wayne
Rosasco S.
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