Novel gate structure and method of forming the gate dielectric with mini-spacer
A field effect transistor gate structure and a method of fabricating the gate structure with a high-k gate dielectric material and high-k spacer are described. A gate pattern or trench is first etched in a dummy organic or inorganic film deposited over a silicon substrate with source/drain regions. A high-k dielectric material liner is then deposited on all exposed surfaces. Excess poly-silicon gate conductor film is then deposited within and over the trench to provide adequate overburden. Poly-silicon is then planarized with chemical mechanical polishing or etch-back methods such that the high-k material film on top of the dummy film surface is removed during this step. In the final step, the dummy film is disposed off, leaving the final transistor gate structure with high-k gate dielectric and high-k spacer surrounding the gate conductor poly-silicon, with the entire gate structure fabricated to form an FET device on a silicon substrate.
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(1) Field of the Invention
The present invention relates generally to methods of fabricating a gate dielectric and a mini-spacer, and more particularly, to methods of patterning gate structures with high-k gate dielectric films and mini-spacers in the fabrication of semiconductor devices and integrated circuits.
(2) Description of the Prior Art
The current generation ultra large-scale integrated (ULSI) circuits use predominantly field effect transistor (FET) devices, having poly-silicon gate electrode, silicon dioxide gate dielectric, and self-aligned source/drain regions. Typical process of fabricating an FET consists of growing a thin gate silicon dioxide on a silicon substrate and then forming the poly-silicon gate electrode. Source/drain (S/D) regions are then formed adjacent to the gate electrode, which then defines the FET gate length as the distance under the poly-silicon gate between the S/D regions. The gate length and the control of gate length is critical, particularly as channel lengths continue to decrease to achieve high device densities, since short channel effects (SCE) can occur in the device. SCE effects become predominant since band-gap and junction potentials cannot be scaled with channel length, being dependent on the substrate material (i.e. silicon).
Fabrication of the gate electrode structure is critical in achieving optimum performance of the MOSFET (metal-oxide-silicon field effect transistor) device. The gate stack, consisting of the gate electrode and the gate dielectric, essentially determines the operating speed and reliability of the device.
Although silicon dioxide has been the dielectric of choice for many years because of ease of forming the film and patterning it, high-k refractory metal oxides are being increasingly experimented in recent years. The motivation is that high-k gate dielectric films reduce the equivalent gate oxide thickness between the gate metal and the substrate, thereby increasing device performance. If silicon dioxide has to be used in ULSI devices with short channel length, it needs to be quite thin to achieve large capacitance values and formation of nanometer range, high quality oxides without defects is quite difficult if not impossible. Several gate structures with high-k gate dielectric have been proposed in prior art. However, patterning of high-k films, unlike the conventional silicon oxides or nitrided oxides, is difficult for two main reasons: i) plasma etching of these films that do not easily form volatile reaction products requires high self-developed or applied bias voltages will cause device damage of the silicon surface of the transistor and ii) alternatively, non-damaging wet etching processes result in poor dimensional control of the FET channel length and are prone to etch residues that are hard to remove during post-processing steps.
U.S. Pat. No. 5,447,874 describes a method of producing devices with improved gate length control, eliminating contamination induced surface damage, leakage problems without increasing processing steps. A gate opening is anisotropically etched in an oxide layer, creating a reverse gate metal image that has low gate length variability. Dual metal gate is then deposited and the excess gate metal is removed and the top surface of the gate planarized using chemical mechanical polishing. The remaining oxide is then removed. The patent refers to a dual metal gate with a conventional silicon dioxide gate dielectric film.
In U.S. Pat. No. 5,940,698, a device with a high performance gate structure and a fabrication process is described. According to the process disclosed, a gate insulating film is deposited over a substrate, a diffusion barrier layer is then formed over the gate-insulating layer, and a trench is etched in the diffusion barrier layer. In the trench, a metal gate electrode is formed. Although the high-k materials like cobalt niobate, barium strontium nitrate (BST), and tantalum oxide are proposed, the process described is quite complex and it is very likely that etch residues will be left on the silicon substrate when etching the high-k film within the gate trenches and around the gate structure, as previously discussed.
U.S. Pat. No. 5,960,270 describes a process of forming a metal-gate/metal-oxide/semi-conductor MOS transistor with self-aligned source and drain electrodes formed before defining the metal gate. Although high-k metal oxides like TiO2 and Ta2O5 are mentioned as a part of a composite dielectric gate (e.g. grown oxide/deposited high-k material), no specific process is described or taught on how to pattern high-k films without the problems associated with post-etch residues.
U.S. Pat. No. 5,766,998 describes a method of forming reverse self-aligned FETs (field effect transistors) with gate electrode of sub-quarter micrometer dimensions that exceed the lithographic resolution limit with the use of polymer sidewall spacers. The process described includes forming a stack of titanium layer, and N+ doped first poly-silicon layer, and a silicon nitride layer over the device regions. Non-volatile polymer sidewall spacers are then formed on the sidewalls of the first openings. The sidewalls and the photo-resist together act as a mask for selectively etching the said stack down to the substrate and form the second opening to define the FET channel. A gate oxide is grown on the substrate in the channel opening. The gate dielectric film is a conventional silicon dioxide grown by thermal oxidation.
In U.S. Pat. No. 6,033,963, a method is described to form a metal gate for a CMOS device, using a replacement gate process. According to the process, a dummy gate oxide and a poly-silicon gate electrode layer are formed and patterned to form a a dummy gate. Lightly doped source and drain regions are formed using dummy gate as implant mask. After forming sidewall spacers, source and drain regions are formed and annealed Tungsten layer is then selectively deposited on the exposed silicon surfaces. Blanket dielectric layer is then deposited and planarized, stopping on the tungsten layer. The tungsten overlying the dummy gate are removed, thereby forming a gate opening. A gate oxide layer and a metal gate electrode layer are then deposited in the gate opening and planarized, stopping on the blanket oxide layer. The structure uses a conventional oxide as the gate dielectric.
SUMMARY OF THE INVENTIONAccordingly, it is a primary object of the invention to describe a simple method to form a gate structure with high-k dielectric gate and mini-spacer surrounding the gate.
Another object of the invention is to describe a gate structure with high-k gate dielectric and high-k mini-spacer as an integral part of the device.
It is yet another object of the invention to describe a damage-free and residue-free process for forming a high-k gate dielectric and simultaneously form high-k mini-spacer as part of the gate forming process.
Yet another object of the invention is to describe a process for forming high-k gate dielectric and mini spacer structure, using a disposable dummy trench structure.
A further object of the invention is to provide an FET device with a gate structure having a high-k gate dielectric with improved control of gate length and an integral mini-spacer.
In accordance with these objectives, a method is described to fabricate a gate structure with high-k dielectric material, a mini-spacer of the same high-k material, and improved gate length. The high-k gate film is patterned damage-free and without leaving any process residues. A trench pattern is formed in a disposable dummy film that is deposited over a silicon substrate. A high-k dielectric film liner is then deposited within said trench pattern. The trench, with high-k film as the liner, is then filled with poly-silicon gate conductor. The structure is then planarized preferably using chemical mechanical polishing method or other etch-back processes, such that said high-k film on the planar surfaces of the dummy film is also removed during the planarizing step, thereby leaving the high-k film liner only inside the trenches. The dummy film around the gate is then removed to leave a structure with mini-spacer of high-k material surrounding the gate. Because the process uses a deposition method to form the high-k gate structure within a dummy trench, the gate length is much more precisely defined as compared to methods using etching process to pattern high-k gate.
BRIEF DESCRIPTION OF THE DRAWINGSThe objects, advantages, and details of fabricating a semiconductor device according to this invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings.
The process described in the present invention provides a simplified method to fabricate a gate structure in an FET semiconductor device with a high-k gate dielectric and a mini-spacer, without producing any device damage or leaving any process residues. Although in the present invention a dummy trench is etched in nitride or organic BARC film, any material that can be easily patterned using conventional wet or plasma etching process can be used.
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The advantages of the aforementioned invention are:
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- a) A gate structure is formed with high-k gate dielectric and high-k mini spacer, both formed simultaneously without the use of additional steps.
- b) A non-etching process is used for forming the high-k gate dielectric pattern and the mini-spacers, thereby not producing any etch residues.
- c) High-k gate structure is patterned without any etch damage since plasma etching, which is inherently prone to producing device damage, is not directly used to etch the high-k film. Only the dummy film patterning uses the plasma etching process.
- d) High-k gate pattern is formed by a deposition process and not by plasma etching.
While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the concept, spirit, and the scope of the invention.
Claims
1-9. (canceled)
10. An FET gate structure comprising
- high-k gate dielectric on a substrate,
- gate conductor on said dielectric, and
- high-k spacer surrounding said gate conductor and gate dielectric.
11. An FET gate structure according to claim 10, wherein said gate dielectric is selected from the group comprising ZrxOy, HfxOy, TaxOy, TixOy, AlxOy, HfxSiyOz, and ZrxSiyOz.
12. A gate structure according to claim 10, wherein said gate conductor is selected from the group comprising silicon-based gate material and metal-based gate material.
13. A gate structure according to claim 12, wherein said silicon-based gate material is selected from the group comprising single crystal silicon, poly silicon, doped silicon, doped poly-silicon, amorphous silicon, and silicon-germanium.
14. A gate structure according to claim 12, wherein said metal-based gate material is selected from the group comprising tungsten, tungsten nitride, aluminum, TixNy, TaxNy, copper, WSix, and CoSix.
15. An FET device comprising
- a silicon substrate;
- source and drain regions on said silicon substrate;
- transistor gate structure having a gate conductor and a high-k gate dielectric disposed between said gate conductor and said substrate; and
- high-k spacers surrounding said gate conductor and high-k gate dielectric.
16. An FET device according to claim 15, wherein the said gate dielectric film is selected from the group comprising ZrxOy, HfxOy, TaxOy, TixOy, AlxOy, HfxSiyOz, and ZrxSiyOz.
17. An FET device according to claim 15, wherein said gate conductor is selected from the group comprising silicon-based gate material and metal-based gate material.
18. An FET device according to claim 17, wherein said silicon-based gate material is selected from the group comprising single crystal silicon, poly silicon, doped silicon, doped poly-silicon, amorphous silicon, and silicon-germanium.
19. An FET device according to claim 17, wherein said metal-based gate material is selected from the group comprising tungsten, tungsten nitride, aluminium, TixNy, TaxNy, copper, WSix, and CoSix.
Type: Application
Filed: Feb 1, 2005
Publication Date: Jun 16, 2005
Applicant: Taiwan Semiconductor Manufacturing Company, Ltd. (Hsin-Chu)
Inventors: Yuan-Hung Chiu (Hsin-Chu), Ming-Huan Tsai (Hsin-Chu), Fang-Cheng Chen (Hsin-Chu), Hun-Jan Tao (Hsin-Chu)
Application Number: 11/048,205