The present invention relates to capacitors, and more particularly to High-κ MIM Capacitors.
Metal-Insulator-Metal (MIM) capacitors are widely used for analog module, RF and DRAM functions in ICs. Higher relative permittivity (or higher dielectric coefficient κ) dielectrics have been used for MIM capacitors to reach higher capacitance density (ε0κ/tD) with low leakage current. However, the conduction band offset (ΔEC) of metal-oxides generally decreases rapidly with increasing κ value. The small ΔEC of SrTiO3 (STO) has significant impact to degrade analog capacitor reliability and leakage current. Besides, the physical thickness of the high-κ insulator should be scaled down to fit the minimum feature size that limits the use of very high κ material. Therefore, using new higher-κ dielectric materials may not be a feasible option.
Therefore the applicant attempts to deal with the above situation encountered in the prior art.
In view of the prior art, in the present invention, we propose an alternative method to enhance permittivity through the laser annealing technique (conventionally used in ultra-shallow junction formation) which initiates a microstructural polycrystalline tetragonal-phase change in the dielectric (preferably ZrO2) thereby the κ value is enhanced. The new process sequence helps enhancing the capacitance density, for example, from 38 to 52 fF/μm2 with low leakage and good 10-year reliability.
In accordance with the first aspect of the present invention, a method for forming a capacitor device is provided. The method includes steps of: providing a substrate; forming a first metal layer on the substrate; forming a dielectric on the first metal layer; applying a laser-annealing to the dielectric; and forming a second metal layer on the dielectric.
Preferably, the substrate is an SiO2/Si substrate.
Preferably, the first metal layer is a bottom electrode of the capacitor device, is one selected from a group consisting of TaN, TiN, Al, Ni, Ir Pt, Ru and RuO2 and is deposited and patterned on the substrate.
Preferably, the first metal layer has a first surface, and the step of forming a first metal layer on the substrate further comprises a step of treating the first surface by NH3+ plasma.
Preferably, the dielectric is one selected from a group consisting of ZrO2, Al2O3, HfO2, TiO2, La2O3, LaAlO and SrTiO3.
Preferably, the step of forming a dielectric on the first metal layer further comprises a step of depositing the dielectric by an Atomic Layer Deposition (ALD).
Preferably, the method further includes a step, before forming a dielectric on the first metal layer, of applying an O2 post-deposition annealing (PDA) to the dielectric.
Preferably, the second metal layer on the dielectric is a top electrode of the capacitor device and is a high work-function metal.
Preferably, the second metal layer on the dielectric is a top electrode of the capacitor device and is one selected from a group consisting of Ni, TiN, Pt, Ir, Ru and RuO2.
In accordance with the second aspect of the present invention, a capacitor device is provided. The capacitor device includes: a dielectric having a tetragonal phase.
Preferably, the dielectric is processed by a laser annealing.
Preferably, the capacitor device further includes: a substrate; a first metal layer formed on the substrate and forming thereon the dielectric; and a second metal layer formed on the dielectric.
Preferably, the substrate is an SiO2/Si substrate.
Preferably, the first metal layer is a bottom electrode of the capacitor device, is one selected from a group consisting of TaN, TiN, Al, Ni, Ir and Pt, Ru, RuO2 and is deposited and patterned on the substrate.
Preferably, the first metal layer has a first surface treated by NH3+ plasma.
Preferably, the second metal layer on the dielectric is a top electrode of the capacitor device and is a high work-function metal.
Preferably, the second metal layer on the dielectric is a top electrode of the capacitor device and is one selected from a group consisting of Ni, TiN, Pt, Ir, Ru, RuO2.
Preferably, the dielectric is one selected from a group consisting of ZrO2, Al2O3, HfO2, TiO2, La2O3, LaAlO and SrTiO3.
Preferably, the dielectric is deposited by an Atomic Layer Deposition (ALD).
In accordance with the third aspect of the present invention, a method for forming a capacitor device with a dielectric is provided. The method includes a step of: processing the dielectric to have a tetragonal phase.
The foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the drawings, wherein:
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.
Please refer to
Then the surface was treated by NH3+ (S30) to prevent capacitance-equivalent-thickness (CET) degradation by forming interfacial TiON during post-deposition anneal (PDA). After that, 8 nm ZrO2 was formed by Atomic Layer Deposition (ALD) and an O2 PDA at 400° C. was used to improve the dielectric quality (S40˜S60). Then laser, preferably continuous wave (CW) laser such as Ar+ laser at 157 nm˜514.5 nm wavelength or pulsed excimer laser such as KrF and ArF laser, was applied under various annealing conditions (S70). Finally, the high work-function and low-cost Ni of 50 nm was deposited and patterned to form the top electrode (S80˜S90).
The capacitor size is 100-μm×100-μm. The crystallinity of the second electrode/dielectric/first electrode, preferably Ni/ZrO2/TiN, structure was examined using the X-ray diffraction (XRD) tool. The MIM device was characterized by C-V and J-V measurements.
It is important to notice that the surface nitridation is necessary to reach high capacitance density after laser annealing. The capacitance density will decrease without the surface nitridation treatment due to the oxidation of bottom electrode.
To understand the performance improvements, we have examined the devices by XRD. The anneal improves the ZrO2 crystallinity of higher-κ tetragonal-phase by showing stronger XRD peaks, compared with the reference TiN, as shown in
We used the TEM to study the laser annealing effect.
An important reliability criterion in the industry is the expected degradation of device performance for a 10-year target lifespan.
We have fabricated high-κ Ni/ZrO2/TiN metal-insulator-metal (MIM) capacitors with a very high 52 fF/μm2 capacitance density, a low leakage current of 1.6×10−7 A/cm2 and good 10-year reliability with a small ΔC/C of 1.7% at 2 V. From x-ray diffraction measurements, laser annealing can improve the permittivity of ZrO2 due to tetragonal-phase formation which in turn helps enhance capacitance density and reliability. Such excellent device integrity is attributed to the combination of enhanced ZrO2 tetragonal-phase by laser annealing, high work-function Ni electrode and good bottom-interface treatment.
In the present application, high performance Ni/ZrO2/TiN device is realized with higher capacitance density, low leakage current, good analog capacitor reliability, low cost electrodes, smaller CET and physical oxide thickness using laser annealing. This provides an alternative technology to attain higher κ dielectric for future generation devices without continuously changing to new materials.
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.