Patent Application
20080142908
The present invention relates to a method of using the semiconductor material as the gate electrode, and more particularly to a method of using the III-V semiconductor material as the gate electrode.
In the conventional fabrication processes for the MOSFETs, the gate leakage current will be rapidly increased when trying to decrease physical thickness of the SiO2 oxidation layer. Therefore, more and more documents show that the issue of the gate leakage current can be overcome and the gate capacitance can be enhanced by using the gate dielectric layer with a high dielectric constant (high-k dielectric). However, the material of the dielectric layer with a high dielectric constant is harder to be integrated with the conventional poly-crystalline silicon gate electrode. Hence, the method of using the metal as the gate electrode has been proposed. Nevertheless, due to the limitation of the threshold voltage required for the element operation, for a P-channel MOSFET, the work function of its gate electrode needs to be close to the silicon valence band. However, for an N-channel MOSFET, the work function of its gate electrode needs to be close to the silicon conduction band. Due to the above, the metals which can meet the requirement are less. Besides, a single type of metal gate that can be applied to both the P-channel and the N-channel MOSFETs is still under research.
The work function of the III-V semiconductor material can be appropriately close to the silicon valence band or the silicon conduction band. For example, the electron affinity of InAs is 4.9 eV, and after being doped as P+-type, the work function thereof can be adjusted to about 5.2 eV, which can meet the requirement of being close to the silicon valence band. Nevertheless, the electron affinity of GaAs is 4.07 eV, and after being doped as N+-type, the work function thereof can meet the requirement of being close to the silicon conduction band. In addition, the material with a wide band gap, e.g. GaP, may become a single type of gate electrode that can be applied to both the P-channel and the N-channel MOSFETs by doping it as P+-type or N+-type.
A novel field effect transistor and the manufacturing method therefor is disclosed in the Taiwan Patent No. 1234283 by Robert Zhao. The mentioned patent discloses a novel MOSFET using the semiconductor film with a narrow band gap to form the channel region. The material of the semiconductor film with a narrow band gap includes a part of the III-V semiconductor materials, such as InSb, InAs, etc. The mentioned patent proposes that the semiconductor material with a narrow band gap has high channel mobility and saturation velocity, which enables a large driving current for the transistor during low voltage operation.
The present invention proposes using the III-V semiconductor material as the gate electrode. Since the III-V semiconductor has high mobility, the resistance thereof is lower, which is suitable to serve as the gate electrode. Through doping the III-V semiconductor material as P+-type or N+-type and adjusting the doping concentration thereof, the work function thereof can be changed, which meets the requirement of the transistor fabrication processes. Besides, an appropriate threshold voltage can be obtained, thereby enhancing the performance of the field effect transistor.
In order to overcome the drawbacks in the prior art, an improved method of using the III-V semiconductor material as the gate electrode is provided. The particular design in the present invention not only solves the problems described above, but also is easy to be implemented. Thus, the present invention has the utility for the industry.
In accordance with one aspect of the present invention, a method of using the III-V semiconductor material as the gate electrode is provided in order to adjust the threshold voltage. The III-V semiconductor material is formed on the gate dielectric layer. The work function of the III-V semiconductor material can be changed by doping it as P+-type or N+-type and changing the doping concentration thereof arbitrarily. Hence, the threshold voltage thereof can be optimized, thereby enhancing the performance of the filed effect transistor.
In accordance with another aspect of the present invention, a method of using an III-V semiconductor material as a gate electrode is provided. The method includes steps of providing a substrate; forming a gate dielectric layer on the substrate; and forming the III-V semiconductor material on the gate dielectric layer.
Preferably, the substrate is a silicon substrate.
Preferably, the silicon substrate is one of a silicon {100} substrate, a silicon {110} substrate and a silicon {111} substrate.
Preferably, the silicon substrate is doped as one of a P-type substrate and an N-type substrate.
Preferably, the silicon substrate is one of a wafer and a die.
Preferably, a size and a shape of the silicon substrate are changeable.
Preferably, the gate dielectric layer is made of a dielectric layer material with a dielectric constant larger than 3.
Preferably, the dielectric layer material is selected from a group consisting of an SiO2, an Si3N4 and an HfO2.
Preferably, the III-V semiconductor material is formed by one selected from a group consisting of a molecular beam epitaxy, a plasma-enhanced chemical vapor deposition and a chemical vapor deposition.
Preferably, the III-V semiconductor material is one selected from a group consisting of a poly-crystalline material, a single-crystalline material and an amorphous material.
Preferably, the III-V semiconductor material is a compound composed of at least one of an Al, a Ga and an In in Group III of a periodic table and at least one of an N, a P, an As and an Sb in Group V of the periodic table.
Preferably, the compound is one selected from a group consisting of an InAs, an Inp, a GaSb, a GaAs, a Gap, a GaN, an AlxGal-xAs and a GaxInl-xAs.
Preferably, the III-V semiconductor material is doped as one of a P-type material and an N-type material.
Preferably, a doping concentration of the III-V semiconductor material is adjustable.
In accordance with a further aspect of the present invention, a gate electrode is provided. The gate electrode includes an III-V semiconductor material.
Preferably, the III-V semiconductor material is formed by one selected from a group consisting of a molecular beam epitaxy, a plasma-enhanced chemical vapor deposition and a chemical vapor deposition.
Preferably, the III-V semiconductor material is one selected from a group consisting of a poly-crystalline material, a single-crystalline material and an amorphous material.
Preferably, the III-V semiconductor material is a compound composed of at least one of an Al, a Ga and an In in Group III of a periodic table and at least one of an N, a P, an As and an Sb in Group V of the periodic table.
Preferably, the compound is one selected from a group consisting of an InAs, an Inp, a GaSb, a GaAs, a Gap, a GaN, an AlxGal-xAs and a GaxInl-xAs.
Preferably, the III-V semiconductor material is doped as one of a P-type material and an N-type material.
Preferably, a doping concentration of the III-V semiconductor material is adjustable.
The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed descriptions and accompanying drawings, in which:
a)-2(d) are schematic diagrams showing the method of using the III-V semiconductor material as the gate electrode according to a preferred embodiment of the present invention; and
The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for the purposes of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed.
In a metal-oxide-semiconductor capacitor, the flat-band voltage can be modulated by changing the work function of the metal. Therefore, for a MOSFET, the magnitude of the threshold voltage thereof will be affected by the magnitude of the work function of the gate electrode thereof.
A method of using the III-V semiconductor material as the gate electrode is provided in the present invention. Through doping the III-V semiconductor material as P-type or N-type and changing the doping concentration thereof arbitrarily, the work function thereof can be appropriately close to the silicon valence band or the silicon conduction band. In addition, the material with a wide band gap, e.g. GaP, may become a single type of gate electrode that can be applied to both the P-channel and the N-channel MOSFETs by doping it as P-type or N-type.
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After the formation of the P-type heavily-doped (P+) poly-crystalline InAs 23, a gate 24 is defined by photolithography and etching, as shown in
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To sum up, a method of using the III-V semiconductor material as the gate electrode is provided in order to adjust the threshold voltage. The III-V semiconductor material is formed on the gate dielectric layer. The work function of the III-V semiconductor material can be changed by doping it as P-type or N-type and changing the doping concentration thereof arbitrarily. Hence, the threshold voltage thereof can be optimized, thereby enhancing the performance of the filed effect transistor. Therefore, the present invention effectively solves the problems and drawbacks in the prior art, and thus it fits the demand of the industry and is industrially valuable.
While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 095146950 | Dec 2006 | TW | national |
