Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-05-04
2001-01-09
Wu, Shean C. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06171732
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method of manufacturing and an application of a dual alignment photomask. More particularly, the present invention relates to a method of manufacturing a dual alignment photomask and a method of forming a dual damascene structure using only one dual alignment photomask.
2. Description of Related Art
Conventionally, two photolithographic operations using two different photomasks have to be conducted to form a dual damascene structure. One photomask is used for forming the metal trench lines, while the other photomask is used for forming the metal vias.
FIGS. 1A through 1F
are schematic, cross-sectional views showing the progression of steps in producing a conventional dual damascene structure. First, as shown in
FIG. 1A
, a semiconductor substrate (not shown in the figure) is provided. The semiconductor substrate has a first inter-metal dielectric layer
12
, a silicon nitride (SiN) layer
14
and a second inter-metal dielectric layer
16
formed on top. The silicon nitride layer
14
serves an etching stop layer that prevents the over-etching of material during the metal trench line etching operation.
Next, as shown in
FIG. 1B
, a photoresist layer
18
is formed over the second inter-metal dielectric layer
16
using a special photomask (not shown). Then, the second inter-metal dielectric layer
16
is etched to form metal trench lines
20
and
22
(shown as a U-shaped cut in the cross-sectional diagram). Thereafter, the photoresist layer
18
is removed forming a structure as shown in FIG.
1
C.
As shown in
FIG. 1D
, another photoresist layer
24
is formed over the second inter-metal dielectric layer
16
again using another special photomask (not shown). Then, a portion of the silicon nitride layer
14
and the first inter-metal dielectric layer
12
are etched to form a via
26
within the metal trench line region
20
. Subsequently, metal is deposited, filling the via
26
and the metal trench lines
20
and
22
, to form a metallic layer
28
as shown in FIG.
1
E. Finally, excess metal above the second inter-metal dielectric layer
16
is removed using, for example, a chemical-mechanical polishing (CMP) method. The remaining portions of metallic layer
28
a
have a planar upper surface as shown in FIG.
1
F.
In the aforementioned operation, the dual damascene structure requires two etching operations using two different photomasks. This not only increases the production cost, but also increases incidence of mask misalignment. Any mask misalignment contributes to processing errors that may ultimately lower the reliability of devices.
Furthermore, although using the silicon nitride layer as an etching stop layer is able to prevent over-etching, the deposition of a silicon nitride layer on top of an inter-metal dielectric layer can lead to additional film compression stresses. Together with film tensile stresses produced by the silicon dioxide of the inter-metal dielectric layer, these stresses are capable of producing cracks or discontinuity along the sidewalls of the vias. In addition, the silicon nitride layer can affect the ultimate width of the via after an etching operation, and hence may lead to variation and instability of device resistance.
In light of the foregoing, there is a need to reduce the number of mask-making operations as well as to improve the processing steps needed to carry out for forming the dual damascene structure.
SUMMARY OF THE INVENTION
Accordingly, the purpose of the present invention is to provide a method of forming a dual alignment photomask and illustrate how the same photomask can be used to form metal trench lines and metal vias of a dual damascene structure. Hence, severe discrepancies due to mask misalignment can be prevented and cost of production can be decreased. Moreover, the silicon nitride layer is no longer needed, and therefore, possible formation of cracks or discontinuities along the sidewalls of the vias can be avoided.
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 forming a dual alignment photomask. The method includes the steps of depositing a blocking layer over a glass plate, and then patterning the light-blocking aye Next, a switchable mask layer is deposited over the light-blocking layer and the glass plate, and then the switchable mask layer is patterned. Finally, a protective layer is formed over the switchable mask layer, the light-blocking layer and the glass plate.
According to this invention, the light-blocking layer can be a chromium layer. The switchable mask layer can be a liquid crystal layer whose degree of transparency depends on temperature (for example, switching at about 29.9° C.). As soon as the surrounding temperature exceeds the phase-switching temperature, the liquid crystal blocks incoming light. On the other hand, if the surrounding temperature falls below the phase-switching temperature, the liquid crystal permits incoming light to pass through. Furthermore, the optimal light-passing state of liquid crystal material can be enhanced by a magnetic or an electric field.
This invention also provides a method of using the dual alignment photomask to fabricate a dual damascene structure. The method includes the steps of forming a photoresist layer over an inter-metal dielectric layer, and then aligning the dual alignment photomask on top of a photoresist layer. Then, the photoresist layer is exposed to light with the surrounding temperature above the phase-switching temperature of the liquid crystal material. Next, the photoresist layer is developed to form a via in the photoresist layer. Thereafter, the surrounding temperature is lowered to a temperature below the phase-switching temperature of the liquid crystal material and then exposing the photoresist layer through the photomask again. Hence, a trench is formed in the photoresist layer. After that, the inter-metal dielectric layer is etched to form a trench/via structure or a trench structure in the inter-metal dielectric layer using the patterned photoresist layer as an etching mask. Finally, metal is deposited into the via/trench structure and trench structure of the inter-metal dielectric layer.
An alternative method of using the dual alignment photomask to form a dual damascene structure is to expose the photoresist layer through the photomask at a temperature below the phase-switching temperature so that trenches are formed after development. Next, the photoresist layer is exposed to light through the same photomask at a temperature above the phase-switching temperature, and then the photoresist layer is developed to form a via within the trench line region. Finally, the same operations needed to form a complete damascene structure are performed.
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.
REFERENCES:
patent: 5666176 (1997-09-01), Kwrematsu et al.
patent: 5872042 (1999-02-01), Hsu et al.
patent: 5904563 (1999-05-01), Yu
Chen Chih-Rong
Huang Wen-Yuan
Martine Penilla & Kim LLP
United Microelectronics Corp.
Wu Shean C.
LandOfFree
Method of manufacturing and application of dual alignment... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of manufacturing and application of dual alignment..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing and application of dual alignment... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2480991