Dual-gate structure and method of fabricating integrated circuits having dual-gate structures

The present invention relates to methods of forming semiconductor devices and to device structures formed thereby, and more particularly to methods for forming dual-gate semiconductor device structures and to dual-gate semiconductor structures formed thereby.

Integrated circuits that include devices having different gate dielectric thicknesses (hereinafter sometimes referred to as dual-gate structures) are becoming more common as devices operating at different voltage potentials are incorporated into the same integrated circuit designs. For example, operating voltages of input and output transistors in the same circuit design may differ. Generally, high-speed, lower voltage devices utilize thinner gate dielectrics than high voltage devices. The gate dielectric, such as a gate oxide, of lower operating voltage devices, however, cannot withstand the higher voltage of the older technology, higher operating voltage devices. One solution to this problem is to form transistors having thicker gate dielectrics on the same substrate as the low voltage transistors. Fabricating such devices, however, gives rise to manufacturing complexities and challenges, such as the introduction of additional cleaning, growth and/or deposition steps.

One method for forming an integrated circuit device having a dual-gate structure is provided in U.S. Pat. No. 6,261,978 to Chen et al., entitled “Process for Forming Semiconductor Device with Thick and Thin Films” issued Jul. 17, 2001. Chen describes a fabrication process where a first gate oxide layer is grown over a substrate. A resist layer is then patterned to expose portions of the first oxide layer, and portions of the first oxide layer are removed to expose portions of the semiconductor substrate. Subsequently, the resist layer is removed, and the substrate is then cleaned with a solution that does not include fluorine. A second oxide layer is then grown over the cleaned, exposed substrate and the remaining first oxide layer to form two gate dielectric layers having different thicknesses.

While Chen provides one method of fabricating integrated circuit devices having dual-gate dielectrics, there remains a need for a more efficient fabrication process for forming dual-gate dielectric structures that eliminates, for example, the need for additional substrate cleaning steps. Further, as device dimensions continue to decrease, giving rise to leakage current and additional processing difficulties, there remains a need to better utilize high-K dielectric materials in integrated circuit designs utilizing dual-gate dielectric structures, while insuring high film quality for such dielectric structures.

A method of fabricating a dual-gate on a substrate is provided. A first high-K dielectric layer is formed in a first area defined for a first gate structure and in a second area defined for a second gate structure. A second high-K dielectric layer is formed in the first and second areas. The first high-K dielectric layer has a lower etch rate to an etchant relative to said second high-K dielectric layer. The second high-K dielectric layer is etched from the second area to the first high-K dielectric layer with the etchant, and a gate conductive layer is formed in the first and second areas over the second high-K dielectric layer and first high-K dielectric layer, respectively.

An integrated circuit having a dual-gate structure is also provided including a first device having a gate structure including a gate dielectric including a first high-K dielectric layer formed over a substrate and a second high-K dielectric layer formed over the first high-K dielectric layer. The first high-K dielectric layer has a lower etch rate to an etchant relative to the second high-K dielectric layer. The integrated circuit includes a second device having a gate structure including a gate dielectric including the first high-K dielectric layer formed over the substrate.

The above and other features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention that is provided in connection with the accompanying drawings.

The accompanying drawings illustrate preferred embodiments of the invention, as well as other information pertinent to the disclosure, in which:

FIGS. 1–3 are cross-sectional views of portion of a semiconductor substrate illustrating the formation of a dual-gate structure thereon; and

FIG. 4 is an illustration of an integrated circuit device having a plurality of devices including a dual-gate structure.

FIG. 1 is a cross-sectional view of portions of a semiconductor device substrate 10 . The semiconductor substrate 10 may be a monocrystalline semiconductor silicon wafer, a semiconductor-on-insulator wafer, or any other substrate used in forming semiconductor wafers. The semiconductor wafer 10 includes at least a first and second areas, designated generally as 10 A and 10 B, defined for a first and second MOSFET gate structures. In one embodiment, an interfacial layer 12 A, 12 B is formed over the areas 10 A and 10 B such as by growth or chemical reaction. Examples of interfacial layers include SiO, SiON or SiN. Interfacial layer 12 is generally used to avoid drive current degradation sometimes associated with formation of a high-K dielectric layer directly on a silicon substrate. In an alternative embodiment (not shown), no interfacial layer is formed between the gate dielectric and the substrate. Prior to forming the interfacial layer 12 , the substrate surface is preferably cleaned, using any suitable hydrophilic or hydrophobic cleaning process, for example.

After interfacial layer formation, a first high-K dielectric layer 14 A, 14 B is formed in the first and second areas 10 A, 10 B over the interfacial layer 12 . Examples of suitable high-K materials include tantalum oxide (Ta 2 O 5 ), titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), hafnium oxide (HfO 2 ), yttrium oxide (Y 2 O 3 ) and lanthanum oxide (La 2 O 5 ), and their aluminates and silicates. Formation processes may include atomic layer chemical vapor deposition (ALCVD), metal organic CVD (MOCVD) or sputtering. The target physical thickness T 1 for the first high-K dielectric layer should be approximately that of the desired dielectric thickness of the thinner gate dielectric of the dual-gate structure, and preferably, but not necessarily, has a thickness in the range of 1.5–5.0 nm.

Referring to FIG. 2 , a second high-K dielectric layer 16 ( 16 A, 16 B) is shown formed over the first high-K dielectric layer 14 . The physical thickness T 2 for the combined dielectric structure including the first high-K dielectric layer 14 and second high-K dielectric layer 16 should be that of the target physical thickness for the thicker gate dielectric of the dual-gate structure. The second high-K dielectric layer 16 preferably, but not necessarily, has a thickness of less than 10 nm.

In an exemplary method of forming a dual-gate structure and integrated circuit device having a dual-gate structure, the first high-K dielectric layer 14 has a lower etch rate to an etchant relative to the etch rate to the same etchant of the second high-K dielectric layer 16 . Put another way, in the presence of the same etchant solution or environment, the second high-K layer 16 etches faster than the first high-K layer 14 . This can be accomplished through material selection and/or by processing the first high-K dielectric layer 14 to have a lower etch rate. The first high-K layer 14 may be, for example, a metal oxide and the second high-K layer 16 may be a metal silicate, which has a higher etch rate than the metal oxide to the selected etchant.

As mentioned, in lieu of or in addition to material selection, the first high-K dielectric layer 14 may be processed to reduce its etch rate to an etchant before formation of the second high-K dielectric layer 16 thereover. One exemplary processing method for high-K materials that has been shown to reduce the etch rate of the high-K material is a thermal anneal step. It is believed that the anneal step increases the density of the annealed layer, but the applicants do not wish to be limited by any particular theory. This is a particularly effective method when it is desired to use the same material for both the first and second high-K layers. After formation of the first high-K dielectric layer 14 in FIG. 1 and before the formation of the second high-K dielectric layer 16 thereover, as shown, in FIG. 2 , the first high-K dielectric layer is annealed in a N 2 , NH 3 , O 2 , NO or N 2 O environment at, for example, 500° C. to 1000° C. for between 30 seconds to 1 hour. According to J. Chambers, ECS Sep., Effect of Composition and Post-Deposition Annealing on the Etch Rate of Hafnium and Zirconium Silicates in Dilute HF, the etch rate of a dielectric materials decreases as the silicon content of the dielectric materials decreases and anneal steps are added. This is indicated by the following chart showing the etch rate of various dielectrics in a dilute HF solution.

Thermal PVD Oxide (non- Hf- PVD Hf- high-K) PVD PVD Silicate Silicate material HfO 2 HfO 2 (50:50) (50:50) Thermal No anneal No anneal 1000° C. for No 1000° C. for treat- step step 30 minutes anneal 30 minutes ment (N 2 anneal) step (N 2 anneal) Etch 23 Å/min 33 Å/min <0.1 Å/min 85 2 Å/min Rate Å/min

The above chart shows, inter alia, that for a physical vapor deposited (PVD) hafnium oxide layer, the etch rate decreases from 33 Å/min to less than 0.1 Å/min after a 30 minute nitrogen anneal process at 1000° C. Similar results are seen with hafnium silicate. Although the etch rate of the annealed Hafnium silicate is higher than that of annealed hafnium oxide, it is still significantly lower than non-processed Hafnium Silicate.

Similar results were also reported for Hafnium Oxide deposited on a substrate by atomic layer chemical vapor deposition (ALCVD) and etched using H 2 SO 4 at 150° C. for 30 minutes, both in and out of the presence of HF, as reported by the semiconductor research consortium International SEMATECH (ISMT).

Dielectric HF Initial Final Delta Etch Rate Layer present? Thick. Thick. Thick. (Å/min) ALCVD No 218.9 34.1 −184.8 6.2 HfO 2 (no- anneal step) ALCVD 500 ppm 240.7 26.5 −214.2 7.1 HfO 2 (no- anneal step) ALCVD No 219.8 215.3 −4.5 0.2 HfO 2 (anneal - 120 min. @ 560° C.) ALCVD 500 ppm 220.4 216.2 −4.2 0.1 HfO 2 (anneal - 120 min. @ 560° C.) Thermal No 3037.9 3035.0 −2.9 0.1 Oxide Thermal 500 ppm 3061.9 2964.9 −97.0 3.2 Oxide

As can be seen from the table, the etch rate of the hafnium oxide dielectric layer decreases significantly with the addition of the anneal step.

Referring to FIG. 3 , a resist layer (not shown) is then patterned to expose portions of the second high-K dielectric layer in area 10 B defined for the thinner gate structure, and the second high-K dielectric layer 16 is then etched from second area 10 B in order to form the gate dielectric of the thin gate structure of the dual gate structure. The second high-K dielectric layer 16 is preferably etched completely from the area 10 B utilizing the first dielectric layer 14 B, which has a lower etch rate to the selected etchant compared with the second high K dielectric layer 16 B (due to material selection and/or processing), as an etch stop layer. The etch process may be, for example, a wet-chemical etch using HF, H 2 SO 4 , H 3 PO 4 or HNO 3 , or any other etch process appropriate for high-K materials.

In one embodiment of the present method, the second high-K dielectric layer 16 A and 14 B are optionally annealed after the aforementioned etch process, which removes second high-K dielectric layer 16 B from area 10 B. This post-annealing step could further improve the film quality of the second high-K dielectric layer 16 A and also remove some etching damage on the first high-K layer 14 B.

After forming the gate dielectric layers of the first and second gate structures in areas 10 A and 10 B, processing can continue to form the devices of the integrated circuit that include the aforementioned gate dielectric structures, i.e., combined dielectric layers 14 A and 16 A for the first device and dielectric later 14 B for the second device. Typical post-gate dielectric formation processing steps are set forth in U.S. Pat. No. 6,261,978 to Chen et al, the entirety of which is hereby incorporated herein by reference, but are briefly outlined hereafter in connection with FIG. 4 .

Gate electrodes 18 A, 18 B and source/drain regions 20 A, 20 B are formed. In one embodiment, a conductive material, such as poly-silicon or silicon germanium, is formed over the first and second gate dielectric structures 10 A and 10 B. The conductive material is patterned and etched to form gate electrodes. Appropriate masking layers and implants are used to dope the gates and their respective source/drain regions. N-type dopants are used in P-well regions to form n-channel transistors, and p-type dopants are used in N-well regions to form p-channel transistors.

In one exemplary processing method, silicide regions 22 A, 22 B are formed over exposed surfaces of the source/drain regions 20 and the gate electrodes 18 of the devices after forming doped source/drain regions and doping the gate electrodes. The silicide material can include refractory metals such as titanium, cobalt, molybdenum, or the like. Silicide formation may be accomplished by a self aligning process.

Following the formation of the transistors, an interleval dielectric (ILD) layer 24 ( 24 A, 24 B) and interconnects 26 are generally formed. The ILD layer typically includes one or more films that include an oxide, a nitride, a low dielectric constant (low-K) material or the like. The interconnects 26 generally include two portions. The via portions are relatively narrow and make contact to the silicide regions 22 . It should be noted that for illustrative purposes only one interconnect 26 is shown, but other interconnects can certainly be formed to connect to other silicide regions 22 . The trench portions are wider and allow connections to be made between via portions. Trenches, therefore, primarily form horizontal connections within ILD layers, whereas vias primarily form vertical connections between overlying conductive layers. The interconnects can include conductive materials such as aluminum, copper, or the like. Dopants or alloying elements can be added to the interconnects to improve electromigration resistance or other electrical or reliability properties. Typically, adhesion/barrier layers are formed within the interconnect opening before forming the conductive material within the interconnect opening.

Following the formation of the interconnects 26 , a passivation layer 28 A, 28 B is formed over the semiconductor device. In addition, other ILD layers and interconnect levels can be formed as needed to forma a substantially completed integrated circuit device and ultimately an integrated circuit chip.

As mentioned above, annealing the first high-K dielectric layer 14 after formation thereof lowers the etch rate of the layer such that the first high-K dielectric layer 14 can be used as an etch stop layer, particularly when it is desired to use the same high-K dielectric material for layer 14 and layer 16 . The annealing step also provides the benefit of improving the quality of the thicker high-K dielectric structure—the combined first high-K dielectric layer 14 A and second high-K dielectric layer 16 A of the device of area 10 A. This phenomena has been illustrated through experiments on Hafnium Oxide/Poly-Si capacitors, wherein a double high-K dielectric layer deposition process with an intermediate anneal step resulted in suppression of leakage density of the formed capacitor device, as again reported by the semiconductor research consortium International SEMATECH (ISMT).

Further, by utilizing the etch selectivity of the high-K dielectric layers in the method described above, the method avoids the need to re-clean the substrate and re-form the interfacial layer 12 during the dual-gate formation process, as may be expected from a more conventional dual-gate formation process, such as that described in Chen. Further, the anneal process may be accomplished in-situ by using cluster high-K deposition tools, such as are available from ASM International under the trademark POLYGON. The method thereby provides a cleaner and more robust approach to forming dual-gate structures and specifically dual-gate structures having different dielectric thicknesses.

In one embodiment of the present method and dual-gate structure, at least one of the dielectric layers 14 , 16 is not a high-K dielectric layer, as long as the first dielectric layer 14 has a lower etch rate to an etchant relative to the second dielectric layer 16 . For example, the first dielectric layer 14 may be a high-K dielectric layer and the second layer 16 may be, for example, SiO 2 , SiON or SiN.

Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly to include other variants and embodiments of the invention that may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.