Method of manufacturing a transistor in a semiconductor device

Details Method of manufacturing a transistor in a semiconductor device Method of manufacturing a transistor in a semiconductor device

2001-06-25

2003-03-25

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

Insulated gate formation

C438S584000, C438S585000

Reexamination Certificate

active

06537901

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to a method of manufacturing a transistor in a semiconductor device. More particularly, the invention relates to a method of manufacturing a transistor in a semiconductor device capable of lowering the threshold voltage by implementing a surface channel CMOS device both in the NMOS region and the PMOS region, in such a way that a Ta film or a TaNx film is formed at a low temperature or a first TaNx film in which the composition(x) of nitrogen is 0.45~0.55 is formed, on a gate insulating film in a NMOS region, so that the work function becomes 4.0~4.4 eV, and a Ta film or a TaNx film is formed at a high temperature or a second TaNx film in which the composition(x) of nitrogen is 0.6~1.4 is formed, on a gate insulating film in a PMOS region, so that the work function becomes 4.8~5.2 eV.
2. Description of the Prior Art
In semiconductor devices, a silicon oxide film (SiO
2
) is mainly used as a gate insulating film in DRAMs and logic devices. As the design rule is reduced, there is a trend that the thickness of the silicon oxide film is reduced below 25~30 Å, which is a tunneling limit.
In case of below 0.1 &mgr;m DRAM, it is expected that the thickness of the gate insulating film will be about 30~35 Å. In case of logic devices, on the other hand, it is expected that the thickness of the gate dielectric film will be about 13~15 Å. When the gate electrode is formed of polysilicon, however, as the thickness of the gate insulating film increased electrically by means of a depletion phenomenon of polysilicon is about 3~8 Å, there is a significant obstacle in reducing the thickness (T
eff
) of the effective gate insulating film with about 15~30 Å. Therefore, as one solution to overcome this, a study has recently been made in which a high dielectric constant material is used as a gate insulating film. Meanwhile, there is a study in which the gate electrode is formed of a metal instead of polysilicon in order to minimize the depletion phenomenon of polysilicon.
Also, a lot of studies has recently been made in which the gate electrode is formed of a metal since it can prevent the problem of boron penetration, which is generated when the gate electrode is formed of polysilicon and a junction region is formed using a p-type impurity, for example, boron.
In order to form the gate electrode with a metal, there has been a lot of studies on TiN or WN. However, as they has the work function of 4.75~4.85 eV, the work function is formed near the valence band in the mid-gap work function. It could be said that the work function is an adequate level in case of a surface channel PMOS. In case of NMOS, however, if the channel doping is 2~5×10
17
/cm
3
the threshold voltage is almost 0.8~1.2 V. In other words, in this case, it could not meet the threshold voltage target of 0.3~0.6 V, that is required in high-performance devices having low voltage or low power characteristic. Therefore, in order to obtain a low threshold voltage of about 0.3~0.6 V both in a NMOS and a PMOS, it is preferred that a dual metal electrode having the work function of about 4.0~4.4 eV in case of NMOS and a dual metal electrode having the work function of about 4.8~5.2 eV in case of PMOS are used.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of manufacturing a transistor in a semiconductor device capable of solving the above problem, by forming a metal gate electrode that has a low work function in a NMOS region but has a high work function in a PMOS region.
Another object of the present invention is to provide a method of manufacturing a transistor in a semiconductor device by which a metal gate electrode having a dual work function is formed by using the fact that the work function of a Ta film or a TaNx film is changed depending on the deposition temperature.
Still another object of the present invention is to provide a method of manufacturing a transistor in a semiconductor device by which a metal gate electrode having a dual work function is formed by using the fact that the work function of a TaNx film is changed depending on the composition of nitrogen.
In order to accomplish the above object, a method of manufacturing a transistor in a semiconductor device according to a first embodiment of the present invention is characterized in that it comprises the steps of injecting each of first impurity and second impurities into given regions of a semiconductor substrate to define a first region and a second region; forming a gate insulating film on the semiconductor substrate in which the first region and the second region are defined; forming a first Ta film having a first work function on the first region; forming a second Ta film having a second work function on the second region; forming a metal layer on the entire structure including the first and second Ta films; patterning the metal layer, the first and second Ta films, and the gate insulating film to form gate electrodes in the first and second regions, respectively; and forming a first junction region by injecting a first impurity into the semiconductor substrate in the first region and forming a second junction region by injecting a second impurity into the semiconductor substrate in the second region.
Also, a method of manufacturing a transistor in a semiconductor device according to a second embodiment of the present invention is characterized in that it comprises the steps of injecting each of first impurity and second impurities into given regions of a semiconductor substrate to define a first region and a second region; forming a gate insulating film on the semiconductor substrate in which the first region and the second region are defined; forming a first Ta film having a first nitrogen composition on the first region so that the first Ta film have a first work function; forming a second Ta film having a second nitrogen composition on the second region so that the second Ta film have a second work function; forming a metal layer on the entire structure including the first and second TaNx films; patterning the metal layer, the first and second TaNx films, and the gate insulating film to form gate electrodes in the first and second regions, respectively; and forming a first junction region by injecting a first impurity into the semiconductor substrate in the first region and forming a second junction region by injecting a second impurity into the semiconductor substrate in the second region.


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