Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1998-11-03
2001-06-05
Utech, Benjamin L. (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S720000, C252S079100
Reexamination Certificate
active
06242358
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 for etching a metal film containing aluminum using a hard mask, and a method for forming an interconnection line for a semiconductor device using the same.
2. Description of the Related Art
An interconnection line is a film material corresponding to the topmost film of a semiconductor device and it electrically connects devices after each device is completed. The main purposes of the interconnection line are either for connecting a PMOS or NMOS transistor to a bit line, or for connecting a cell to another cell. To manufacture a high-speed device, it is preferred that a low-resistivity material is used for an interconnection line. Thus, aluminum (Al), having the lowest resistivity among widely known materials, or its alloys (referred to as a “metal containing Al” hereinafter) are mainly used.
Since Al has excellent conductivity but is structurally weak at high temperatures, a protective film must be formed on the interconnection line formed of a metal containing Al, by a low pressure chemical vapor deposition (LP-CVD) method. Also, if the metal film containing Al is etched, the photoresist must be formed thickly, since the etching selectivity to photoresist is poor. Further, to allow high-speed operation of the semiconductor device, the metal film containing Al must be as thick as 5,000~8,000Å. Thus, in order to etch the metal line containing Al, a highly corrosive etchant must be used, i.e., one having a high etch rate. However, such an etchant is absorbed into the photoresist, causing corrosion in the metal line after etching.
Also, if the photoresist is formed thickly, the throughput is lowered and it is difficult to control the photoresist. Thus, a poor pattern profile is generated due to phenomena produced after the photolithography process, such as residue, notching or slope, and phenomena produced in the metal line after the etching process, such as thinning, bridging or variation in line widths. Particularly, when the semiconductor is highly integrated, the line width of the interconnection line must be reduced. However, it is impossible to reduce the line width of the metal line efficiently using the thick photoresist as in the conventional art.
In forming an interconnection line formed of a metal containing Al, using a photoresist, to avoid diffused reflection from the Al layer there is a widely known method forming the Al line by forming an anti-reflection film on the metal film containing Al by depositing titanium nitride (TiN) or titanium tungsten (TiW), and then forming a photoresist pattern on the anti-reflection film.
The photoresist used in the above-described process is as thick as 18,000~21,000 Å. However, in view of processing characteristics, the etching selectivity of the metal film containing Al to the photoresist does not exceed 3:1. Also, the profile of the photoresist pattern is not vertical, but is inclined to some extent. Further, since the photoresist at the edge of the Al film is much thinner than the other portions, the pattern of the metal film containing Al is thinned, and the margin of the photolithography is reduced.
To solve these problems, there has been proposed a process of injecting a hard material film (oxide group) which can serve as a buffer between the metal film containing Al and the photoresist film. However, this process also needs a photoresist film of 12,000~16,000 Åthick. Also, if the thickness of the metal film containing Al is greater than or equal to 6,000 Å, the process is not effective. Further, during this process, the metal film containing Al is etched when the photoresist exists. Thus, when etching the metal film containing Al, the photoresist must be removed simultaneously in the same machine, to minimize the corrosion caused by a strongly corrosive etchant. However, to this end, since a separate chamber for removing the photoresist must be installed in a chamber for etching the metal film containing Al, it is quite difficult to maintain and operate the facility.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a method of etching a metal film containing Al without pattern corrosion by using a hard mask instead of photoresist.
It is a second objective of the present invention to provide a method of etching an Al containing metal film by which process margins and productivity can be improved.
It is a third objective of the present invention to provide a method for forming a line of a semiconductor device using the Al containing metal film etching method.
Accordingly, to achieve the above objectives of the present invention, first, a metal film containing Al is formed on a semiconductor substrate. A hard mask pattern is formed on the metal film containing Al. Next, the metal film containing Al is etched using an etching gas containing carbon, and using the hard mask pattern as the etching mask.
Preferably, the gas containing carbon is one selected from the group consisting of CF
4
, CHF
3
and CHCI
3
. Also, the gas containing carbon is preferably added at a flow rate of 10~20% of the overall flow rate of the etching gas.
The hard mask pattern may be formed of an oxide film or a nitride film. Also, the step of forming the hard mask pattern comprises the steps of forming a hard mask layer on the metal film containing Al, forming a photoresist pattern on the hard mask layer, patterning the hard mask layer using the photoresist pattern as a mask, and removing the photoresist pattern.
Also, the photoresist pattern is preferably formed to a thickness of 4,000~9,000 Å.
To accomplish another objective of the present invention, a metal layer is formed on a semiconductor substrate. A mask layer for patterning the metal layer is formed on the metal layer. Then, a photoresist pattern is formed on the mask layer. The mask layer is patterned using the photoresist pattern as an etching mask. Then, the photoresist pattern is removed, and the metal layer is patterned using an etching gas containing carbon and using the mask layer as an etching mask.
The gas containing carbon is one selected from the group consisting of CF
4
, CHF
3
and CHCI
3
. Also, the gas containing carbon is added at a flow rate of 10~20% of the overall flow rate of the etching gas.
The mask layer may be formed of an oxide film or a nitride film. Also, the photoresist pattern is preferably formed to a thickness of 4,000~9,000 Å.
Before the step of forming the metal layer, there is further provided the step of forming titanium (Ti) and titanium nitride (TiN) as a barrier layer on the semiconductor substrate to increase adhesion between the metal layer and the semiconductor substrate, and to prevent a metal of the metal layer from diffusing into the semiconductor substrate.
Also, before the step of forming the mask layer, a capping layer may be further formed on the metal layer, to prevent diffused reflection of light from the metal layer during the step of forming the photoresist pattern. The capping layer may be formed of TiN.
The metal layer is preferably formed of Al or an Al alloy.
According to the present invention, corrosion in the metal film pattern containing Al can be prevented by using gas containing carbon when etching the metal line containing Al using the hard mask. Also, the photoresist used in patterning the hard mask may be thin. Further, if the hard mask pattern is formed of a nitride film, then a separate anti-reflective film is not necessary, thereby simplifying the process.
REFERENCES:
patent: 5369053 (1994-11-01), Fang
patent: 5801101 (1998-09-01), Miyoshi
patent: 0924753A2 (1999-06-01), None
Chu Gang-soo
Kim Dong-yun
Jones Volentine, LLC
Samsung Electronics Co,. Ltd.
Umez-Eronini Lynette T.
Utech Benjamin L.
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