JPH0479150B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a MOS type semiconductor device with an improved gate electrode.

[Technical Background of the Invention] Recently, metal silicide, which has a relatively low resistance, has been used as a gate electrode instead of polycrystalline silicon for the purpose of increasing the degree of integration and speed of MOS semiconductor devices. A MOS transistor having a gate electrode made of such metal silicide (for example, molybdenum silicide) has conventionally been manufactured by the following method.

First, a field oxide film 3 having a p-type anti-inversion layer 2 around it is formed on a p-type silicon substrate 1 by selective doping with boron and selective oxidation. Subsequently, a gate oxide film 4 is formed by thermal oxidation on the surface of the island-shaped substrate 1 region separated by the field oxide film 3, and then a gate oxide film 4 is formed on the entire surface by sputtering to a thickness of, for example,
A MoSix film 5 of 3000 Å is deposited (as shown in FIG. 1a).

Next, the MoSix film 5 is patterned to form a gate electrode 6 (as shown in FIG. 1b). Continuing,
Using the gate electrode 6 as a mask, n-type impurities such as arsenic are ion-implanted into the substrate 1 through the gate oxide film 4 and activated to form n ⁺ -type source and drain regions 7 and 8 (as shown in FIG. 1c). Continuing,
After depositing a CVD-SiO ₂ film 9 on the entire surface and opening contact holes 10, an Al film was evaporated and patterned to connect the source and drain regions 7 and 8 and the gate electrode 6 through the contact holes 10. A MOS transistor is manufactured by forming Al wirings 11 to 13 (as shown in FIG. 1d).

[Problems with background technology]

However, using MoSix as the gate electrode
MOS transistors had the following problems.
That is, when the composition ratio x of Mo and Si is decreased,
The chemical resistance of MoSix deteriorates, leading to many manufacturing problems. On the other hand, if the composition ratio x of Mo and Si is increased, the specific resistance becomes too large. Therefore, it is desirable to set the composition ratio x in the range of 2<x≦3. In this range, the flat band voltage (V _FB ) of a MOS transistor having a MoSix gate electrode will be as shown by the dotted line in Figure 2. It becomes unstable,
Controllability deteriorates. As a result, a serious problem arises in that the controllability of the threshold voltage of the MOS transistor deteriorates. This phenomenon is also seen in the case of other metal silicides.

[Purpose of the invention]

The present invention aims to provide a MOS type semiconductor device in which the work function of metal silicide forming the gate electrode can be stabilized and the threshold voltage can be stably controlled.

[Summary of the invention]

As a result of various studies on the causes of instability of the flat band voltage (V _FB ) of a MOS structure made of a gate electrode made of MoSix due to fluctuations in the Mo to Si composition ratio x of the gate electrode made of MoSix, the present inventor found that
We found that MoSix separates into MoSi ₂ and Si during the heat treatment process, causing instability in its V _FB . That is, when a MoSix film (x>2) is deposited and then heat treated, the result is as shown in Figure 3.
It is separated into a MoSi ₂ region and a Si region, and the Si region is formed to surround the MoSi ₂ region. Like this MoSi ₂
When separation occurs between the Si region and the Si region, there are many Si regions at the film interface, so the work relationship of the film (gate electrode) is mainly determined by the work and function of the Si region. Therefore, as in the conventional example, the MoSix gate electrode 6
If there is a step of implanting arsenic ions using a mask as shown in FIG. 1c, the Si region shown in FIG. 3 contains a small amount of arsenic, which causes a decrease in the flat band voltage (V _FB ).

Based on the above knowledge, the inventors of the present invention conducted further intensive research and found that by doping acceptor atoms such as boron into the separated Si regions in the MoSix film, the work of the separated Si regions can be improved. By approximating the work function to the work function of MoSi ₂ , the flat band voltage (V _FB ) is stabilized regardless of changes in the composition ratio x of MoSix, as shown by the solid line in Figure 2, and the threshold voltage can be well controlled. This is the discovery of a MOS type semiconductor device.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to manufacturing steps shown in FIGS. 4a to 4d.

() First, a silicon nitride film pattern (none of which is shown) is formed on a p-type silicon substrate 21 with a specific resistance of 5 to 10 Ω·cm via a buffer oxide film.
Boron was ion-implanted into the surface of the substrate 21 using the pattern as a mask, and then heat-treated in a high-temperature oxygen atmosphere to form a field oxide film 22, and at the same time, a p-type anti-inversion layer 23 was formed on the substrate 21 around the field oxide film 22. . Subsequently, after sequentially removing the silicon nitride film pattern and the buffer oxide film, thermal oxidation treatment is performed again to form a gate oxide film 21 with a thickness of, for example, 500 Å on the surface of the island-shaped substrate 21 area separated by the field oxide film 22. was formed. Subsequently, after depositing a MoSi _2.5 film 25 with a thickness of 3000 Å on the entire surface by sputtering,
Boron ions were implanted as acceptor atoms into the entire surface of the MoSi _2.5 film 25 at a dose of 1×10 ¹⁶ /cm ² (as shown in FIG. 4a).

() Next, the boron-doped MoSi _2.5 film 25 was patterned by photoetching to form a gate electrode 26 (as shown in FIG. 4b). Next, the gate electrode 26 and the field oxide film 2
2 as a mask, the gate oxide film 24 is coated with an n-type impurity, such as arsenic, at a dose of 5×10 ¹⁵ /cm ^{2 .}
After implanting ions into the surface of the substrate 21 through the
Activate for 10 minutes in an oxygen atmosphere at 1000 °C to n ⁺
Type source and drain regions 27 and 28 were formed (as shown in FIG. 4c). In this case, gate electrode 2
In order to make the arsenic concentration in the oxide film 6 lower than the boron concentration, the amount of arsenic ions implanted was set to be lower than the amount of ions implanted into the boron described above. Note that if arsenic ions are implanted while the resist pattern used in patterning the gate electrode 26 is directly formed on the gate electrode 26, the dose of arsenic can be freely set regardless of the dose of boron.

() Next, the entire surface is coated with a CVD film with a thickness of, for example, 8000 Å.
After depositing the SiO ₂ film 29 and selectively removing the SiO ₂ film 29 corresponding to the source and drain regions 27, 28 and part of the gate electrode 26 using photoetching technology to open contact holes 30, An N-channel MOS transistor was manufactured by depositing an Al film on the entire surface and patterning it to form Al wirings 31 to 33 connected to the source and drain regions 27 and 28 and the gate electrode 26 via contact holes 30. (Illustrated in Figure 4d).

Therefore, since the MOS transistor of the present invention has the gate electrode 26 made of MoSi _2.5 doped with boron, the gate electrode 26 is separated.
The flat band voltage of the Si region is close to that of MoSi ₂ and has a stable flat band voltage. As a result, the controllability of the threshold voltage is improved, and stable operation according to the designed value is possible.

Furthermore, since the gate electrode 26 is made of MoSi _2.5 ,
It becomes possible to reduce gate resistance and, in turn, achieve high-speed operation.

Furthermore, by performing boron ion implantation after depositing the MoSi _2.5 film 25 as in the manufacturing method described above,
Stress in the MoSi _2.5 film 25 can be alleviated.

In the above embodiment, MoSix having a composition ratio x of 2.5 was used, but if the composition ratio x is larger than 2, the same effect can be achieved.

Further, as the material for the gate electrode, other than MoSix, metal silicides such as TaSix, WSix, PtSix, TiSix (where x is larger than 2 in all cases) may be used.

Furthermore, although boron was used as the acceptor atom in the above embodiment, the acceptor atom is not limited to this, and gallium, indium, etc. may also be used.

The MOS type semiconductor device according to the present invention is not limited to an n-channel MOS transistor, but also a p-channel MOS transistor.
It can be similarly applied to MOS transistors, CMOS, etc.

〔Effect of the invention〕

As described in detail above, according to the present invention, by stabilizing the work function of the metal silicide forming the gate electrode, a MOS type semiconductor device with stable threshold voltage control and capable of high performance and high speed operation is achieved. It is possible to provide

[Brief explanation of the drawing]

Figures 1a to d are cross-sectional views showing the manufacturing process of a conventional n-channel MOS transistor, and Figure 2 is a cross-sectional view showing the manufacturing process of a conventional n-channel MOS transistor.
The relationship between the variation of x of the gate electrode made of MoSix and the flat band voltage of the MOS structure, and the variation of x of the gate electrode made of boron-doped MoSix.
A diagram showing the relationship between the flat band voltage of the MOS structure, and Figure 3 shows the relationship between the flat band voltage of the MoSix film after heat treatment.
An explanatory diagram showing a separated state of _two MoSi regions and a Si region, FIGS. 4a to 4d are one embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a manufacturing process for obtaining a channel MOS transistor. 21... p-type silicon substrate, 22... field oxide film, 24... gate oxide film, 26... gate electrode made of boron-doped MoSi _2.5 , 27...
n ⁺ type source region, 28...n ⁺ type drain region,
31-33...Al wiring.

Claims (1)

[Claims] 1. A MOS type represented by MSix (where M is a metal and x is a number larger than 2) and is characterized by having a gate electrode made of a metal silicide containing an acceptor atom. Semiconductor equipment. 2 Metal silicides include MoSix, TaSix, TiSix,
WSix and PtSix (however, x is a number larger than 2)
2. The MOS type semiconductor device according to claim 1, wherein the MOS type semiconductor device is selected from the following. 3. The MOS semiconductor device according to claim 1, wherein the acceptor atom is one or a mixture of two or more selected from boron, indium, and gallium. 4. The MOS semiconductor device according to claim 1, wherein the metal silicide constituting the gate electrode contains acceptor atoms and donor atoms, and the concentration of the acceptor atoms is higher than that of the donor atoms. .