JPS6327864B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulated gate field effect transistor or a structure of an insulated gate field effect transistor portion in a semiconductor device.

In order to improve the performance of insulated gate field effect transistors for high frequencies, etc., or to achieve higher performance and higher integration of integrated circuits using insulated gate field effect transistors, miniaturization of insulated gate field effect transistors is required. It's being done.

However, in conventional high-frequency transistors and integrated circuits with a silicon gate structure using polycrystalline silicon as a gate material, signal response or propagation delay due to resistance in gate electrodes and interconnections has reached a level that cannot be ignored. To solve this problem, the use of molybdenum or tungsten as gate materials instead of polycrystalline silicon is being considered (other high-melting point metals such as titanium, zirconium, hafnium, vanadium, niobium, and tantalum are It is not suitable as a gate electrode material because it is easily etched by the hydrofluoric acid used for etching the silicon oxide film, and it easily reacts with the gate oxide film during high-temperature heat treatment.) The specific resistance of a molybdenum or tungsten thin film can easily be as low as about 1×10 ⁻⁵ Ω·cm, which is about 1/100 of the specific resistance of a heavily doped polycrystalline silicon film. In addition, molybdenum and tungsten films formed on silicon dioxide are columnar crystals with axes in the film thickness direction, so they have the excellent feature of small undercuts when forming fine patterns using photoetching methods, etc. There is.

However, when a molybdenum gate or tungsten gate structure is adopted, these metal gates have a small effect as a barrier against the intrusion of alkali ions such as sodium from the outside, or these metal films have a columnar structure. Because it is polycrystalline, some of the ions channel through the gate electrode during ion implantation for source/drain formation, penetrating into the channel region of the transistor, causing fluctuations in characteristics such as the threshold voltage of the transistor. In addition, alkali ions trapped in the grain boundaries may be released into the gate insulating film due to recrystallization during high-temperature heat treatment, and stress may be generated at the interface between the gate electrode and the gate insulating film. There are some undesirable phenomena such as Therefore, the stability and reliability of field effect transistors using metal gate structures such as molybdenum are inferior to those of silicon gate structures, and this has become an obstacle to the practical application of high-melting point metal gate structures.

The present invention provides an insulated gate type field effect transistor using a novel metal gate structure that significantly reduces the problems of conventional silicon gate structure, molybdenum or tungsten gate structure field effect transistors, and semiconductor devices using the field effect transistors. The present invention provides an effect transistor.

In the insulated gate field effect transistor according to the present invention, the gate electrode is constructed using a nitride film of molybdenum or tungsten, or a nitride film of an alloy of both, or a composite film containing a layer of these nitrides. It is characterized by this. Nitrides of molybdenum and tungsten, or nitrides of alloys of both, are usually conductors (here, the term nitride is generally used to refer to non-stoichiometric nitrogen and nitrogen, represented by the chemical formula M _x N _y ). In a broad sense, these compounds are collectively referred to as nitrides. Here, M represents molybdenum, tungsten, or an alloy of both, N represents a nitrogen element, and x and y represent integers. Furthermore, the term nitride layer also refers to nitrides. (This also applies to cases in which nitrides and non-nitrides coexist and form a single layer.) For example, the specific resistance of a thin film of Mo ₂ N, a type of molybdenum nitride, is approximately 2×
It is about 10 ^-4 Ω-cm, which is 10 to 20 times larger than that of a molybdenum thin film, but about one-fifth smaller than that of a polycrystalline silicon film doped with arsenic or phosphorus at a high concentration. Therefore, the Mo ₂ N molybdenum nitride film can be used as it is as a gate electrode structure or internal wiring of an integrated circuit, and the resistance of the gate and internal wiring is 5 minutes lower than that of a conventional polycrystalline silicon gate structure. can be reduced to about 1.

Furthermore, when forming a nitride film M _x N _y of molybdenum, tungsten, or an alloy of both by active sputtering in an atmosphere containing nitrogen gas, the effective degree of nitridation (x and y or, if non-nitrides and nitrides are mixed, their mixture ratio), and therefore the specific resistance,
It is known that it is possible to arbitrarily control the For example, in the formation of a molybdenum nitride film Mo _x N _y , by increasing the ratio of x and y to 2 or more, the above
It is also possible to control the specific resistance to lower it even more than in the case of a molybdenum nitride film such as Mo ₂ N. Regarding the formation of a tungsten nitride film M _x N _y or an alloy nitride film of molybdenum and tungsten, the properties are similar to those of the molybdenum nitride film described above, and the resistivity can be made to be approximately the same value. The same effect as the case where the molybdenum nitride film Mo _x N _y is used for the gate can be obtained.

In addition, molybdenum and tungsten nitride films are
Although it is not attacked by the hydrofluoric acid used for cleaning and etching silicon oxide films, nitride films of other high-melting point metals (titanium, zirconium, hafnium, vanadium, niobium, and tantalum) are easily attacked by hydrofluoric acid, so they are not suitable as gate electrodes. isn't it.

The present invention has the following advantages compared to conventional molybdenum or tungsten gate structures. Nitride M _x N _y of molybdenum, tungsten, or an alloy of both provides a stronger barrier to the diffusion of impurities such as alkali ions than when molybdenum, tungsten, or an alloy of both is used alone. The instability caused by impurities such as alkali ions in the metal gate structure, which had been a problem, is improved, and reliability is improved.

Furthermore, since molybdenum, tungsten, and their alloys are extremely easily oxidized, they may be oxidized by trace amounts of oxygen or moisture in the heat treatment atmosphere during high-temperature heat treatment processes such as annealing of ion-implanted layers and thermal diffusion of impurities in the manufacture of field effect transistors. Nitride M _x N _y of molybdenum or tungsten, or an alloy of both, is more resistant to acid than pure molybdenum, tungsten, or an alloy of both, although it has the disadvantage of becoming an insulator and disappearing due to sublimation. It also has superior chemical properties, which alleviates the above-mentioned problems.

Furthermore, thin films formed by vacuum evaporation methods, etc.
Generally, stress is generated between the film and the underlying substrate, and its value and direction (tensile or compressive direction) depend on the conditions for forming the thin film. For example, a high-purity molybdenum thin film with a body-centered cubic lattice structure formed by high-frequency sputtering generates large stress between it and the substrate, resulting in cracks, whereas nitrided molybdenum with a face-centered cubic lattice structure It has been reported that the M _x N _y film exhibits good adhesion to most substrates and has low stress values (RS Nowick
Journal of Vacuum Science and Technology by Nowick et al.
Technology) magazine published in 1974, Vol. 11, No. 4, 675-
Paper published on page 679). Therefore, by selecting an appropriate degree of nitridation, it is possible to achieve an extremely low stress state when used as an insulated gate, and to reduce the yield rate due to substrate deflection caused by stress generated in the semiconductor manufacturing process. Defects such as deterioration of semiconductor characteristics can be significantly reduced compared to conventional methods.

Furthermore, the molybdenum gate or tungsten gate structure has a problem in that the threshold voltage of the transistor varies widely within a wafer, between wafers, and between lots, that is, the controllability of the threshold voltage is poor. This is because when sources and drains are formed by ion implantation using these metal gates as masks, some of the ions pass through these metal gates because these metal films are generally polycrystalline with a columnar structure. This is because it channels and penetrates into the channel region. When a nitride film of molybdenum, tungsten, or an alloy thereof is used, since these nitride films are more amorphous than molybdenum, tungsten, or an alloy film of both, channeling can be prevented and the controllability of the threshold voltage can be improved.

As described above, it has been revealed that the semiconductor device embodying the present invention can significantly reduce the drawbacks of the conventional silicon gate structure, molybdenum gate structure, or tungsten gate structure. Examples will be specifically described using figures.

FIG. 1 is a schematic cross-sectional view of an insulated gate field effect transistor section in which the gate electrode is composed of a single molybdenum nitride Mo _x N _y (x2, y1) layer. 10 is a silicon single crystal substrate, 11 is a gate electrode made of molybdenum nitride, 12 and 13 are
14 shows the heavily doped regions of the source and drain, and 14 shows the silicon dioxide film as the gate insulating film. 15 and 16 are source 1
This is a metal thin film pattern that serves as an ohmic contact to 2 and drain 13 and as internal wiring.

FIG. 2 shows an embodiment in which the gate electrode is composed of a two-layer thin film, and 21a is a molybdenum nitride film Mo _x
N _y and 21b indicate a molybdenum film, respectively.
In this embodiment, the resistance value of the internal wiring of the integrated circuit using the gate electrode and gate electrode configuration is reduced to a fraction of that of the embodiment shown in FIG.

In this example, 0.1 μm Mo ₂ N and 0.2 μm
A two-layer structure of Mo was used, but the layer resistance in this case was about 0.4Ω/□, which is about 1 lower than when using only Mo ₂ N.
We were able to reduce it by an order of magnitude. Also, W ₂ N is used instead of Mo ₂ N.
Good results were also obtained when using a nitride film of Mo and W alloy containing 30%.

In each of the examples, the molybdenum nitride film was formed by reactive sputtering using a molybdenum target in an argon atmosphere containing nitrogen gas, and the molybdenum film was also formed by sputtering. There is no necessity of forming these films by, for example, an electron beam evaporation method. Furthermore, both molybdenum and the molybdenum nitride film were patterned by reactive ion etching using a mixed gas of carbon tetrachloride and oxygen. Tungsten and tungsten nitride films can also be patterned using the same method.

In this example, a structure in which a nitride film of molybdenum, tungsten, or an alloy of both is in contact with a gate insulating film (metal film/metal nitride film/gate insulating film structure) is shown. Taking advantage of the superior oxidation resistance of molybdenum and tungsten, it is also possible to create a structure in which molybdenum, tungsten, or an alloy of both is in contact with the gate insulating film (metal nitride film/metal film/gate insulating film structure).

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic cross-sectional views for explaining the structure of an insulated gate transistor section in which the present invention is implemented. 10... Silicon single crystal substrate, 11... Molybdenum nitride gate electrode, 12... Source heavily doped region, 13... Drain heavily doped region, 14... Silicon dioxide gate insulating film, 1
5... Source electrode, 16... Drain electrode, 21
a...Molybdenum nitride gate electrode layer, 21b...
Molybdenum gate electrode layer.

Claims (1)

[Claims] 1. An insulator characterized in that the gate electrode is constructed using a nitride film of molybdenum, tungsten, or an alloy of both, or a composite film of a nitride film of the metal and the metal film. Gated field effect transistor.