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Variable work function in MOS capacitors utilizing nitrogen-controlled TiNx gate electrodes
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
2004 (English)In: Microelectronic Engineering, ISSN 0167-9317, Vol. 75, no 4, 389-396 p.Article in journal (Refereed) Published
Abstract [en]

A substantial shift in the work function of TiNx by as much as 0.7 eV is achieved by varying the nitrogen gas flow during the reactive sputter deposition of the metal gate, which indicates tunability for replacing poly-Si in a CMOS process. TiNx MOS capacitors having multiple SiO2 thicknesses have been evaluated and the work function of TiNx can be altered from 4.2 to 4.9 eV depending on the nitrogen content. The values are stable after RTP annealing up to 600 °C in nitrogen gas for 30 s, although annealing at 800 °C changes the work function for the different compositions towards a mid-gap value. No variation in EOT with annealing temperature is observed for the TiNx/SiO2 stacks deposited at high nitrogen gas flow. The change in work function appears not to be correlated to the crystalline orientation of the TiNx. The work function is instead believed to be affected by extrinsic states in the metal/dielectric interface.

Place, publisher, year, edition, pages
2004. Vol. 75, no 4, 389-396 p.
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-94803DOI: 10.1016/j.mee.2004.07.061OAI: oai:DiVA.org:uu-94803DiVA: diva2:168790
Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2013-05-15Bibliographically approved
In thesis
1. Metal Gate Technology for Advanced CMOS Devices
Open this publication in new window or tab >>Metal Gate Technology for Advanced CMOS Devices
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The development and implementation of a metal gate technology (alloy, compound, or silicide) into metal-oxide-semiconductor field effect transistors (MOSFETs) is necessary to extend the life of planar CMOS devices and enable further downscaling. This thesis examines possible metal gate materials for improving the performance of the gate stack and discusses process integration as well as improved electrical and physical measurement methodologies, tested on capacitor structures and transistors.

By using reactive PVD and gradually increasing the N2/Ar flow ratio, it was found that the work function (on SiO2) of the TiNx and ZrNx metal systems could be modulated ~0.7 eV from low near nMOS work functions to high pMOS work functions. After high-temperature anneals corresponding to junction activation, both metals systems reached mid-gap work function values. The mechanisms behind the work function changes are explained with XPS data and discussed in terms of metal gradients and Fermi level pinning due to extrinsic interface states.

A modified scheme for improved Fowler-Nordheim tunnelling is also shown, using degenerately doped silicon substrates. In that case, the work functions of ALD/PVD TaN were accurately determined on both SiO2 and HfO2 and benchmarked against IPE (Internal Photoemission) results. KFM (Kelvin Force Microscopy) was also used to physically measure the work functions of PVD TiN and Mo deposited on SiO2; the results agreed well with C-V and I-V data.

Finally, an appealing combination of novel materials is demonstrated with ALD TiN/Al2O3/HfAlOx/Al2O3/strained-SiGe surface channel pMOS devices. The drive current and transconductance were measured to be 30% higher than the Si reference, clearly demonstrating increased mobility and the absence of polydepletion. Finally, using similarly processed transistors with Al2O3 dielectric instead, low-temperature water vapour annealing was shown to improve the device characteristics by reducing the negative charge within the ALD Al2O3.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 55 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 213
Keyword
Electronics, metal gate, high-k dielectrics, titanium nitride, zirconium nitride, MOSFET, thin film, work function, XPS, Elektronik
Identifiers
urn:nbn:se:uu:diva-7120 (URN)91-554-6640-0 (ISBN)
Public defence
2006-09-29, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30
Opponent
Supervisors
Available from: 2006-09-08 Created: 2006-09-08Bibliographically approved
2. Investigation of Novel Metal Gate and High-κ Dielectric Materials for CMOS Technologies
Open this publication in new window or tab >>Investigation of Novel Metal Gate and High-κ Dielectric Materials for CMOS Technologies
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The demands for faster, smaller, and less expensive electronic equipments are basically the driving forces for improving the speed and increasing the packing density of microelectronic components. Down-scaling of the devices is the principal method to realize these requests. For future CMOS devices, new materials are required in the transistor structure to enable further scaling and improve the transistor performance.

This thesis focuses on novel metal gate and high-κ dielectric materials for future CMOS technologies. Specifically, TiN and ZrN gate electrode materials were studied with respect to work function and thermal stability. High work function, suitable for pMOS transistors, was extracted from both C-V and I-V measurements for PVD and ALD TiN in TiN/SiO2/Si MOS capacitor structures. ZrNx/SiO2/Si MOS capacitors exhibited n-type work function when the low-resistivity ZrNx was deposited at low nitrogen gas flow. Further, variable work function by 0.6 eV was achieved by reactive sputter depositing TiNx or ZrNx at various nitrogen gas flow. Both metal-nitride systems demonstrate a shift in work function after RTP annealing, which is discussed in terms of Fermi level pinning due to extrinsic interface states. Still, the materials are promising in a gate last process as well as show potential as complementary gate electrodes.

The dielectric constant of as-deposited (Ta2O5)1-x(TiO2)x thin films is around 22, whereas that of AlN is about 10. The latter is not dependent on the degree of crystallinity or on the measurement frequency up to 10 GHz. Both dielectrics exhibit characteristics appropriate for integrated capacitors. Finally, utilization of novel materials were demonstrated in strained SiGe surface-channel pMOSFETs with an ALD TiN/Al2O3 gate stack. The transistors were characterized with standard I-V, charge pumping, and low-frequency noise measurements. Correlation between the mobility and the oxide charge was found. Improved transistor performance was achieved by conducting low-temperature water vapor annealing, which reduced the negative charge in the Al2O3.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 71 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1023
Keyword
Electronics, metal gate, high-κ dielectics, titanium nitride, zirconium nitride, MOSFET, thin film, tantalum oxide, aluminum nitride, Elektronik
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-4611 (URN)91-554-6058-5 (ISBN)
Public defence
2004-10-29, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2013-05-15Bibliographically approved

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