Using different gate dielectrics with NMOS and PMOS transistors of a complementary metal oxide semiconductor integrated circuit
Complementary metal oxide semiconductor integrated circuits may be formed with NMOS and PMOS transistors having different gate dielectrics. The different gate dielectrics may be formed, for example, by a replacement process. The gate dielectrics may differ in material, thickness, or formation techniques, as a few examples.
This application is a continuation of U.S. patent application Ser. No. 10/881,055, filed on Jun. 30, 2004.
BACKGROUNDThis invention relates generally to semiconductor technology, semiconductor processing, and the formation of complementary metal oxide semiconductor integrated circuits.
Complementary metal oxide semiconductor integrated circuits include NMOS transistors and PMOS transistors. Generally, these transistors may be made by forming a gate dielectric and then forming NMOS and PMOS gate structures on top of that dielectric. The gate electrode structures may be made of polysilicon, silicide, or metal.
A dummy gate electrode, such as a polysilicon gate electrode, may also be formed over a gate dielectric. Then the dummy gate electrode may be removed and replaced with a metal gate electrode. In such a process, different metal gate electrodes may be utilized for the NMOS and PMOS transistors, but a common dielectric is utilized.
Thus, there is a need for complementary metal oxide semiconductor fabrication techniques.
BRIEF DESCRIPTION OF THE DRAWINGS
Complementary metal oxide semiconductor (CMOS) integrated circuits may be fabricated with NMOS and PMOS transistors having different gate dielectrics. The dielectrics may be different in terms of the materials used, their thicknesses, or the techniques used to form the gate dielectrics, to mention a few examples. As a result, the gate dielectric can be tailored to the particular type of transistor, be it an NMOS or PMOS transistor, as the case may be.
Referring to
Referring to
For example, in accordance with one embodiment of the present invention, the material 16 may be an N-doped polysilicon, while the material 18 is a P-doped polysilicon. An etchant such as tetramethylammonium hydroxide (TMAH) or NH40H, together with sonication, may be utilized to selectively etch one of the materials 16 or 18, while not significantly etching the other material. Depending on the choice of wet etchant utilized to etch the material 16 or 18, one of the dummy gate materials 16 and 18 can be etched while the other one is substantially unetched. Then the other or remaining gate material 16 or 18 may be removed.
Referring to
For example, the NMOS transistor may use a larger conduction band offset material, such as silicon dioxide, and the PMOS transistor may use a material with a higher dielectric constant, such as hafnium dioxide, which also happens to have good band offset for holes. Higher dielectric constants may be greater than ten in one embodiment. As another example, a thicker material may be utilized for the NMOS than the PMOS transistors in some cases. For example, hafnium dioxide leaks electrons more than holes, so a thicker hafnium dioxide layer may be utilized on the NMOS transistors and a thinner hafnium dioxide layer may be utilized on the PMOS transistors. For example, in one embodiment, the hafnium dioxide gate dielectric may be 30 Angstroms for the NMOS transistors and 15 Angstroms for the gate dielectric for PMOS transistors.
As still another example, the deposition techniques may be different for the two gate dielectrics. For example, materials for the NMOS transistor, such as silicon dioxide, may be deposited using diffusion techniques, while atomic layer deposition, sputtering, or metal organic chemical vapor deposition (MOCVD) may be utilized to deposit high dielectric constant materials such as hafnium dioxide.
One gate dielectric may be a high-k material (having a dielectric constant greater than 10) and the other may be a low-k material (having a dielectric constant less than 10). Alternatively, both dielectrics may be high-k or both may be low-k dielectrics.
The appropriate gate electrode material 24 may then be deposited over the gate dielectric 22 in the opening 20 created by the removal of the material 16.
Referring to
Referring to
Then, as shown in
In some embodiments of the present invention, it may be desirable to ensure that the material 18 is selectively etchable relative to the material 24. For example, selective etching may be based on the fact that the materials 18 and 24 are of a different material type.
Referring to
In some embodiments, a single gate dielectric material may not provide the highest performance for both NMOS and PMOS structures. This may be due, for example, to poor band offset with conduction or valence bonds, incompatibility to the gate electrode material, incompatibility with gate electrode processing or thickness requirements. By selecting the better candidate dielectric film for each structure, and depositing the best film with the optimal thickness, higher performance complementary metal oxide semiconductor devices may be created in some embodiments. By using better gate dielectric material of optimal thickness for each electrode stack, higher performance structures may be created that may exhibit higher mobility, higher saturation current, or better threshold voltage in some embodiments.
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
Claims
1. an integrated circuit comprising:
- a substrate; and
- an NMOS transistor and a PMOS transistor, said NMOS and PMOS transistors formed on said substrate, said NMOS transistor and said PMOS transistor forming a complementary metal oxide semiconductor structure, said NMOS transistor and said PMOS transistor having different gate dielectrics, one of said transistors having a gate dielectric with a dielectric constant greater than 10 and the other of said transistors having a gate dielectric with a dielectric constant of less than 10.
2. The circuit of claim 1 wherein said dielectrics have different dielectric thicknesses.
3. The circuit of claim 1 wherein said dielectrics are formed of different dielectric materials.
4. The circuit of claim 1 wherein said dielectrics are formed by different techniques.
5. The circuit of claim 1 wherein said dielectrics are covered by metal gate electrodes.
6. The circuit of claim 1 wherein said NMOS transistor has a gate dielectric with a larger conduction band offset.
7. The circuit of claim 1 wherein said PMOS transistor has a gate dielectric with a higher dielectric constant.
8. The circuit of claim 1 wherein the gate dielectric of said NMOS transistor is thicker than the gate dielectric of said PMOS transistor.
Type: Application
Filed: May 5, 2006
Publication Date: Sep 28, 2006
Inventors: Matthew Metz (Hillsboro, OR), Suman Datta (Beaverton, OR), Jack Kavalieros (Portland, OR), Mark Doczy (Beaverton, OR), Justin Brask (Portland, OR), Robert Chau (Beaverton, OR)
Application Number: 11/418,577
International Classification: H01L 29/94 (20060101); H01L 29/76 (20060101);