This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2009-004241 filed on Jan. 13, 2009, the entire contents of which are incorporated herein by reference.
The embodiments discussed herein are related to a manufacture method for a semiconductor device whose gate insulating film contains Hf and O.
In order to thin an equivalent oxide film thickness (EOT) of a gate insulating film, hafnium-based oxide is used, a dielectric constant of which is higher than that of silicon oxide. Further, a metal gate electrode is adopted in place of conventional polysilicon in order to prevent a gate electrode from being depleted and to lower a gate resistance.
High speed calculation MOSFETs used in a super computer and the like require a low threshold voltage. For example, threshold voltages of high speed calculation pMOSFET and nMOSFET are set to about −100 to −200 meV and about 100 to 200 meV, respectively. An apparent work function of the gate electrode moves near to 4.5 eV (approximately the center of a silicon forbidden band), if hafnium-based oxide is used as a gate insulating film, and TiN, TaN, Ta or the like is, for example, used as a metal gate electrode, and high temperature thermal treatment is performed. Therefore, an absolute value of a flat band voltage becomes small so that it becomes difficult to obtain a low threshold voltage. It is known that it becomes possible to make small an absolute value of a threshold voltage if an alumina (Al2O3) film is disposed on a hafnium-based oxide film used as a gate insulating film of pMOSFET, and heating and diffusion are conducted.
[Patent Document 1] Japanese Laid-open Patent Publication 2007-67266
[Non-Patent Document 1] H. Arimura et al., “Structural Optimization of HfTiSiO High-k Gate Dielectrics by Utilizing In-Situ PVD-based Fabrication Method”, Fifth International Symposium on Control of Semiconductor Interfaces (ISCSI-V), Nov. 12 to 14, 2007
A dielectric constant of alumina is lower than that of hafnium-based oxide. Therefore, as the alumina film is stacked on a gate insulating film made of hafnium-based oxide, it becomes difficult to thin an equivalent oxide film thickness. Al diffusion lowers a mobility of holes in the channel.
Accordingly, it is an object in one aspect of the embodiment to provide a manufacture method for a semiconductor device, including:
forming an insulating film containing Hf and O over a semiconductor substrate;
forming a cap film containing oxygen and titanium as constituent elements over the insulating film;
thermally treating the insulating film and the cap film in a nitrogen gas or noble gas to diffuse titanium in the cap film into the insulating film to form a gate insulating film; and
forming a gate electrode film over the gate insulating film.
It is an object in another aspect of the embodiment to provide a manufacture method for a semiconductor device, including:
forming an insulating film containing Hf and O over a semiconductor substrate;
forming a cap film of titanium over the insulating film;
thermally treating the insulating film and the cap film in an atmosphere containing oxygen gas and ammonia gas to diffuse titanium in the cap film into the insulating film to form a gate insulating film; and
forming a gate electrode film over the gate insulating film.
The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.
With reference to the accompanying drawings, the first and second embodiments will be described.
With reference to
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After the silicon oxide film is formed, plasma nitridation may be performed to form the first gate insulating film of silicon oxynitride.
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The thermal treatment may be performed in an atmosphere of noble gas such as Ar, instead of nitrogen gas. Ammonia gas may be added to the thermal treatment atmosphere. In this case, an ammonia gas partial pressure ratio is set to, for example, 0.1% to 1%.
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A polysilicon film 20 is formed on the metal gate electrode film 19 using CVD or the like.
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A mobility of the sample b in which Al2O3 is used as the cap film 17 is lower than that of the sample c in which the cap film 17 is not formed. A mobility of the sample a in which TiO2 is used as the cap film 17 is higher than that of the sample c. By using TiO2 as the cap film 17, it is possible to prevent deterioration of a mobility which would occur when Al2O3 is used as the cap film 17.
A relative dielectric constant of TiO2 is about 50 to 60 which is larger than a relative dielectric constant of Al2O3 which is about 12. A dielectric constant of HfTiO is higher than that of HfAlO. Therefore, as TiO2 is used as the cap film 17, it is possible to thin the equivalent oxide film thickness of the second gate insulating film 18 compared to the case of Al2O3.
In the first embodiment, an atmosphere during thermal treatment illustrated in
If ammonia is added to the atmosphere of thermal treatment illustrated in
The insulating film 16 illustrated in
With reference to
The processes until forming the insulating film 16 illustrated in
As illustrated in
Ammonia gas may be added to the thermal treatment atmosphere in such a condition that a ratio of a partial pressure of ammonia gas to total pressure is, for example, 0.1% to 1%.
As illustrated in
The processes after the second gate insulating film 18 is formed are common to the processes of the first embodiment illustrated in
Also in the second embodiment, the second gate insulating film 18 of HfTiO is formed. It is therefore possible to make small an absolute value of a threshold voltage of pMOSFET, as in the case of the first embodiment.
In the second embodiment, titanium is used as the cap film 17A, and the cap film 17A does not contain oxygen. O2 is added to the atmosphere gas during thermal treatment illustrated in
As ammonia gas is added to a thermal treatment atmosphere, the second gate insulating film 18 contains nitrogen so that it is possible to increase a dielectric constant of the second gate insulating film 18 as in the case of the first embodiment.
All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.
Number | Date | Country | Kind |
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2009-004241 | Jan 2009 | JP | national |