Noble high-k device

The present invention relates generally to semiconductor fabrication and more specifically to formation of devices incorporating high-k dielectric gate oxide layers.

High-k dielectric materials have been investigated to replace conventional gate oxide layers due to excellent current-leakage reduction seen when using the high-k dielectric materials at the same equivalent-oxide-thickness (EOT). However, high-k dielectric materials also suffer poor mobility and high threshold voltage issues in the electric performance of devices.

U.S. Pat. No. 6,310,367 B1 to Yagishita et al. describes a strained Si and high-k gate dielectric Tx process wherein the concentration of Ge in the channel layer of the NMOSFET is lower that the concentration of Ge in the channel layer of the PMOSFET. The gate electrodes of the NMOSFET and the PMOSFET are made of metallic materials.

U.S. Pat. No. 5,357,119 to Wang et al. describes an SiGe and gate oxide process.

U.S. Pat. No. 6,353,249 B1 to Boyd et al. describes an SiGe substrate and high-k gate dielectric.

U.S. Pat. No. 6,271,094 B1 to Chooi et al. and U.S. Pat. No. 6,335,238 B1 to Hanttangady et al. are related SiGe substrate and high-k dielectric Tx patents.

U.S. Pat. No. 6,287,903 B1 to Okuno et al. describes a structure and method for a large-permittivity dielectric using a germanium layer.

Accordingly, it is an object of one or more embodiments of the present invention to provide improved substrate/high-k dielectric gate oxide material structures and methods of forming same.

Other objects will appear hereinafter.

It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a structure having a strained substrate formed thereover is provided. The strained substrate comprising at least an uppermost strained-Si epi layer. At least one dielectric gate oxide portion over the strained substrate. The at least one dielectric gate oxide portion having a dielectric constant of greater than about 4.0. The at least one dielectric gate oxide portion being comprised of HfO 2 , HfSiO 4 , N-doped hafnium silicate (N-doped HfSiO x ), ZrO 2 or ZrSiO x . A device over each of the at least one dielectric gate oxide portion to complete the least one high-k device. The invention also includes a method of forming the at least one high-k device.

The present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:

FIG. 1 schematically illustrate a preferred embodiment of the present invention employing a first preferred embodiment strained-Si substrate.

FIG. 2 schematically illustrates a second preferred embodiment of the strained-Si substrate of the present invention.

FIG. 3 schematically illustrates a third preferred embodiment of the strained-Si substrate of the present invention.

FIG. 4 schematically illustrates a fourth preferred embodiment of the strained-Si substrate of the present invention.

FIG. 5 schematically illustrates a fifth preferred embodiment of the strained-Si substrate of the present invention.

For the purposes of this invention, all strained-Si epi layers/substrates have a dislocation density of strained-Si epi of less than about 1E6/cm 2 and a high-k dielectric material has a dielectric constant (k) of greater than about 4.0.

Strained-Si Epi Layer 12 — FIG. 1 (First Embodiment)

As shown in FIG. 1 , the preferred structure of the present embodiment includes a semiconductor structure 10 having a strained substrate 12 formed thereover to a thickness of preferably from about 3000 to 100,000 Å and more preferably from about 4000 to 50,000 Å.

In the first embodiment, strained substrate 12 is comprised of entirely of strained-silicon epitaxial (strained-Si epi). As noted above, strained-Si epi substrate 12 has a dislocation density of strained-Si epi of less than about 1E6/cm 2 .

Structure 10 is preferably a silicon substrate or a germanium substrate, is more preferably a silicon substrate and is understood to possibly include a semiconductor wafer or substrate.

Structure 10 may include: one or more NMOS areas 14 within which one or more NMOSFETs 18 (N-type metal-oxide semiconductor field effect transistors) are formed; and may include one or more PMOS areas 16 within which one or more PMOSFETs 28 (P-type metal-oxide semiconductor field effect transistors) are formed. It is noted that a single, unitary strained-Si epi substrate layer 12 is formed under the NMOSFET's 18 and PMOSFET's 28 as this allows for enhanced mobility for both NMOS and PMOS devices 18 , 28 and allows for a simpler process in forming the underlying strained substrate layer 12 .

NMOSFET 18 and PMOSFET 28 each include respective high-k dielectric gate oxide portions 20 , 30 that each have a thickness of preferably from about 10 to 200 Å and more preferably from about 10 to 100 Å. The respective high-k dielectric gate oxide portions 20 , 30 each are preferably comprised of HfO 2 , HfSiO 4 , N-doped hafnium, HfSiO x , ZrO 2 , ZrSiO x or N-doped zirconium silicate (N-doped ZrSiO x ) and more preferably HfO 2 and HfSiO 4 . It is noted that respective high-k dielectric gate oxide portions 20 , 30 are not formed of Ta 2 O 5 , TiO 2 or Al 2 O 3 as they have been found to have poor mobility, difficult process control and poor thermal stability. As noted above, high-k dielectric gate oxide portions 20 , 30 have a dielectric constant (k) of greater than about 4.0.

Respective high-k dielectric gate oxide portions 20 , 30 may be formed by depositing a layer of high-k dielectric gate oxide and then patterning it.

The high-k dielectric gate oxide portions 20 , 30 have respective gate electrode portions 22 , 32 having a thickness of preferably from about 500 to 2000 Å and more preferably from about 700 to 1500 Å and being preferably formed of polysilicon (poly Si), TaN, WSi x or tungsten (W) and more preferably polysilicon (poly Si) which is compatible with the current technology. It is noted that gate electrode portions 22 , 32 are not metal gates, for example not TiN metal gates which, although having a lower work function, is hard to control even when employing dummy gates and has difficult integration issues.

Respective sidewall spacers 24 , 34 are formed over NMOS and PMOS gate electrode portions 22 , 32 to a maximum thickness of preferably from about 200 to 800 Å and more preferably from about 250 to 600.

Respective source/drains 26 , 36 are also formed adjacent NMOS and PMOS gate electrode portions 22 , 32 within strained-Si epi substrate 12 to a maximum depth of preferably from about 300 to 1500 Å and more preferably from about 400 to 1200 Å.

As shown in FIG. 1 , an isolation structure 40 may be formed within strained-Si epi substrate 12 /structure 10 between NMOS/PMOS devices 18 , 28 to electrically isolate them from each other for example. Isolation structure 40 may be a shallow trench isolation (STI) structure, for example.

It is noted that only NMOS devices 18 , only PMOS devices 28 or other devices or a combination thereof may be formed over structure 10 and strained-Si epi substrate 12 .

Strained-Si Epi Layer 54 /Relaxed Si 1-x Ge x Layer 52 /Graded Si 1-y Ge y Layer Substrate 12 — FIG. 2 (Second Embodiment)

As shown in FIG. 2 and in the second embodiment, strained substrate 12 is comprised of an upper strained-Si epi layer 54 over a relaxed Si 1-x Ge x layer 52 (where x is greater than 0 and less than about 0.50) which is in turn over a graded Si 1-y Ge y layer 50 (where y is 0 or about 0 proximate the interface between graded Si 1-y Ge y layer 50 which is in turn over a seed layer 41 and structure 10 and gradually increases (therefore graded) to about X at the interface between graded Si 1-y Ge y layer 50 and relaxed Si 1-x Ge x layer 52 ).

Upper strained-Si epi layer 54 has a thickness of preferably from about 100 to 500 Å, more preferably from about 150 to 400 Å and most preferably from about 200 to 300 Å. Relaxed Si 1-x Ge x layer 52 has a thickness of preferably from about 1000 to 50,000 Å. Graded Si 1-y Ge y layer 50 has a thickness of preferably from about 2000 to 50,000 Å. Seed layer 41 has a thickness of preferably from about 10 to 200 nm.

As noted above, strained-Si epi layer 54 has a dislocation density of strained-Si epi of less than about 1E6/cm 2 .

Strained-Si Epi Layer 62 /SiO 2 Layer 60 (SOI Layer 12 )— FIG. 3 (Third Embodiment)

As shown in FIG. 3 and in the third embodiment, strained substrate 12 is comprised of an upper strained-Si epi layer 62 over a Si 1-x Ge x layer 61 which in turn is over a silicon oxide (SiO 2 ) layer 60 thus forming a silicon-on-insulator (SOI). Upper strained-Si epi layer 62 is bonded to SiO 2 layer 60 .

Strained-Si epi layer 62 has a thickness of preferably from about 100 to 500 Å, more preferably from about 150 to 400 Å and most preferably from about 200 to 300 Å. Si 1-x Ge x layer 61 has a thickness of preferably from about 700 to 1200 Å. SiO 2 layer 60 has a thickness of preferably from about 800 to 2000 Å.

As noted above, strained-Si epi layer 62 has a dislocation density of strained-Si epi of less than about 1E6/cm 2 .

Strained-Si Epi Layer 78 /Upper Relaxed Si 1-x Ge x Layer 76 /Graded Si 1-y Ge y Layer 74 /Thin Epi Layer 72 /Lower Relaxed Si 1-z Ge z Layer 70 — FIG. 4 (Fourth Embodiment)

As shown in FIG. 4 and in the fourth embodiment, strained substrate 12 is comprised of an upper strained-Si epi layer 78 over an upper relaxed Si 1-x Ge x layer 76 (where x is greater than 0 and less than about 0.50 which is in turn over a graded Si 1-y Ge y layer 74 (where y is about z proximate the interface between graded Si 1-y Ge y layer 74 and epi layer 72 and gradually increases (therefore graded) to about x at the interface between graded Si 1-y Ge y layer 74 and upper relaxed Si 1-x Ge x layer 77 ) which is in turn over a thin epi silicon layer 72 which is in turn over a lower relaxed Si 1-z Ge z layer 70 (where z is greater than 0 and less than about y where x≧y≧z.

Upper strained-Si epi layer 78 has a thickness of preferably from about 100 to 500 Å, more preferably from about 150 to 400 Å and most preferably from about 200 to 300 Å. Upper relaxed Si 1-x Ge x layer 76 has a thickness of preferably from about 1000 to 50,000 Å and more preferably from about 2000 to 40,000 Å. Graded Si 1-y Ge y layer 74 has a thickness of preferably from about 200 to 50,000 Å and more preferably from about 500 to 25,000 Å. Thin epi silicon layer 72 has a thickness of preferably from about 20 to 500 Å and more preferably from about 50 to 200 Å. Lower relaxed Si 1-z Ge z layer 70 has a thickness of preferably from about 200 to 50,000 Å and more preferably from about 500 to 25,000 Å.

As noted above, strained-Si epi layer 78 has a dislocation density of strained-Si epi of less than about 1E6/cm 2 .

Upper Strained-Si epi layer 88 /Relaxed-Si 1-x Ge x Layer 86 /Constant Si 1-y Ge y Layer 84 /Si Epi Layer 82 /Constant Si 1-z Ge z Layer 80 — FIG. 5 (Fifth Embodiment)

As shown in FIG. 5 and in the fifth embodiment, strained substrate 12 is comprised of an upper strained-Si epi layer 88 over an upper relaxed epi Si 1-x Ge x layer 86 (where x may be constant or graded) over constant (i.e. non-graded with a constant Ge concentration Si 1-y Ge y layer 84 which is in turn over Si epi layer 82 which is in turn over constant Si 1-z Ge z layer 80 (i.e. non-graded with a constant Ge concentration); where x≧y≧z.

Upper strained-epi Si layer 88 has a thickness of preferably from about 20 to 500 Å and more preferably from about 50 to 300 Å. Upper relaxed Si 1-x Ge x layer 86 (constant or graded) has a thickness of preferably from about 200 to 30,000 Å and more preferably from about 300 to 5000 Å. Constant Si 1-y Ge y layer 84 has a thickness of preferably from about 200 to 20,000 Å and more preferably from about 300 to 5000 Å. Si Epi Layer 82 has a thickness of preferably from about 20 to 500 Å and more preferably from about 50 to 300 Å. Constant Si 1-z Ge z layer 80 has a thickness of preferably from about 200 to 20,000 Å and more preferably from about 300 to 5000 Å.

Layers 80 , 82 , 84 , 88 are strained layers.

NMOSFET(s) 18 , PMOSFET(s) 28 and other devices formed over the high-k dielectric gate oxide portions 20 , 30 /strained substrate 12 may also be referred to as high-k devices as they incorporate high-k dielectric gate oxide portions.

Advantages of the Present Invention

The advantages of one or more embodiments of the present invention include:

1. higher mobility of high-k devices is achieved; and 3. reduced threshold voltage of high-k devices is achieved.

While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.