For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
a, 1b, 2a and 2b illustrate diagrams to explain one theory behind concepts of the present invention;
a-4g provide cross-sectional views of a present embodiment process; and
Corresponding numerals and symbols in different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale. To more clearly illustrate certain embodiments, a letter indicating variations of the same structure, material, or process step may follow a figure number.
The making and using of preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that may be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The invention will now be described with respect to preferred embodiments in a specific context, namely a method for improving carrier mobility in a CMOS device. Concepts of the invention can also be applied, however, to other electronic devices. As but one example, bipolar transistors (or BiCMOS) can utilize concepts of the present invention.
The theory described herein is provided to aid in understanding. It must be understood, however, the invention is not bound by this theory. Experimental results show that stress remains in recrystallized silicon when topography exists. The explanations provided herein are the inventors' best understanding of why these phenomena occur.
In both
In other embodiments, a compressive stress could benefit a p-channel device and/or a tensile stress could benefit an n-channel device. For example, it is possible that under certain geometries (e.g., edges) the strain could be opposite, i.e., a tensile liner may leave the substrate compressive in parts, e.g., at the edges. (It is also possible that the theory is inaccurate, leading to stresses different than those described herein.) In some embodiments, a biaxial stress will be created, thereby opening up possibilities for both pMOS and nMOS improvements with a tensile stress in the silicon.
b and 2b show a representation of the boundary at the molecular level (and are clearly not to scale relative to
The process illustrated in
Similarly,
In
It should be noted that the stress memorization could also occur in a similar way by the recrystallization of the poly-Si gate in the stressed environment of the stressed liner. Indeed the most likely scenario is that there is a contribution from both the S/D and poly-Si recystallization. Again these are hypotheses and do not bound the scope of the invention. The effect of the SMT has been repeatedly proven in devices.
As a general point, in some cases, a local topography (e.g., near 90 degree edges) is needed to transfer stress from the liner to the silicon during regrowth. The theory is that if you have a flat film, each point in the film has a force pushing from left and right on the silicon, whereas at a 90° edge, there is only force in one direction (the other part is missing). (This is shown in the
The transistor 14 includes a channel region 18 disposed in the semiconductor body 10. This channel 18 is stressed from the adjacent source/drain regions 20 and 22. A gate dielectric 24 overlies the channel region 18 and a gate electrode 26 overlies the gate dielectric 24. A source region 20 and a drain region 22 are disposed in the semiconductor body and spaced from each other by the channel region 18. In one example, the stress memory region 16 is a tensile stress layer and the source region 20 and the drain region 22 are n+regions (and the transistor is therefore an n-channel transistor). In another example, the stress memory region 16 is a compressive stress layer and p+ source and drain regions 20 and 22 form a p-channel transistor.
In other embodiments, other semiconductor devices and elements can be fabricated in the stress memory transfer region 16. For example, if the doped regions 20 and 22 are formed of opposite polarities, the device 14 can be operated as a diode. In another example, the doped regions 20 and 22 can be used as contacts to one plate of a capacitor while the gate electrode 26 is used as another gate of a capacitor. This capacitor could be used, for example, as a decoupling capacitor between supply lines (e.g., VDD and ground) on a semiconductor chip.
a-4g will now be provided to illustrate various embodiments for forming a semiconductor device of the present invention. While certain details may be explained with respect to only one of the embodiments, it is understood that these details can also apply to other ones of the embodiments.
Referring first to
In the first embodiment, isolation trenches 28 are formed in the semiconductor body 10. These trenches 28 can be formed using conventional techniques. For example, a hard mask layer (not shown), such as silicon nitride can be formed over the semiconductor body 10 and patterned to expose the isolation areas. The exposed portions of the semiconductor body 10 can then be etched to the appropriate depth. The trenches 28 define active areas 10a and 10b, in which integrated circuit components can be formed. In this embodiment, the trench regions 28 are filled with an insulating material to form trench isolation regions 36. For example, the trenches can be lined with a first material, e.g., SiN, and filled with a second material 36, e.g., an oxide deposited using a high density plasma process.
Gate dielectric 24 is deposited over exposed portions of the semiconductor body 10. In one embodiment, the gate dielectric 24 comprises an oxide (e.g., SiO2), a nitride (e.g., Si3N4), or combination of oxide and nitride (e.g., SiON, oxide-nitride-oxide sequence). In other embodiments, a high-k dielectric material having a dielectric constant of about 5.0 or greater is used as the gate dielectric 24. Suitable high-k materials include HfO2, HfSiOX, Al2O3, ZrO2, ZrSiOX, Ta2O5, La2O3, nitrides thereof, HfAlOx, HfAlOxN1-x-y, ZrAlOx, ZrAlOxNy, SiAlOx, SiAlOxN1-x-y, HfSiAlOx, HfSiAlONy, ZrSiAlOx, ZrSiAlOxNy, combinations thereof, or combinations thereof with SiO2, as examples. Alternatively, the gate dielectric 24 can comprise other high-k insulating materials or other dielectric materials. As implied above, the gate dielectric 24 may comprise a single layer of material, or alternatively, the gate dielectric 24 may comprise two or more layers.
The gate dielectric 24 may be deposited by chemical vapor deposition (CVD), atomic layer deposition (ALD), metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD), or jet vapor deposition (JVD), as examples. In other embodiments, the gate dielectric 24 may be deposited using other suitable deposition techniques. The gate dielectric 24 preferably comprises a thickness of about 10 Å to about 60 Å in one embodiment, although alternatively, the gate dielectric 24 may comprise other dimensions.
In the illustrated embodiment, the same dielectric layer is used to form the gate dielectric 24 for both the p-channel and n-channel transistors. This feature is not required, however. In an alternate embodiment, the p-channel transistors and the n-channel transistor each have different gate dielectrics.
The gate electrode 26 is formed over the gate dielectric 24. The gate electrode 26 preferably comprises a semiconductor material, such as polysilicon or amorphous silicon, although alternatively, other semiconductor materials may be used for the gate electrode 26. In other embodiments, the gate electrode 26 may comprise TiN, HfN, TaN, W, Al, Ru, RuTa, TaSiN, NiSix, CoSix, TiSix, Ir, Y, Pt, Ti, PtTi, Pd, Re, Rh, borides, phosphides, or antimonides of Ti, Hf, Zr, TiAlN, Mo, MoN, ZrSiN, ZrN, HfN, HfSiN, WN, Ni, Pr, VN, TiW, a partially silicided gate material, a fully silicided gate material (FUSI), other metals, and/or combinations thereof, as examples. In one embodiment, the gate electrode 26 comprises a doped polysilicon layer underlying a silicide layer (e.g., titanium silicide, nickel silicide, tantalum silicide, cobalt silicide, platinum silicide).
If the gate electrode 26 comprises FUSI, for example, polysilicon may be deposited over the gate dielectric 24, and a metal such as nickel can deposited over the polysilicon. Other metals may alternatively be used. The substrate 10 can then be heated to about 600 or 700° C. to form a single layer of nickel silicide. The gate electrode 26 can comprise a plurality of stacked gate materials, such as a metal underlayer with a polysilicon cap layer disposed over the metal underlayer. A gate electrode 26 between about 500 to 2000 Å thick may be deposited using CVD, PVD, ALD, or other deposition techniques.
The p-channel transistors and the n-channel transistor preferably include gate electrodes 26 formed from the same layers. If the gate electrodes include a semiconductor, the semiconductor can be doped differently for the p-channel transistors and the n-channel transistors. In other embodiments, the different types of transistors can include gates of different materials and/or thicknesses.
The gate layer (and optionally the gate dielectric layer) are patterned and etched using known photolithography techniques to create the gate electrodes 26 of the proper pattern. After formation of the gate electrodes, lightly doped source/drain regions (not shown) can be implanted using the gate electrode 26 as a mask. Other implants (e.g., pocket implants, halo implants or double diffused regions) can also be performed as desired.
Spacers 38, which are formed from an insulating material such as an oxide and/or a nitride, can be formed on the sidewalls of the gate electrode 26. The spacers 38 are typically formed by the deposition of a conformal layer followed by an anisotropic etch. The process can be repeated for multiple layers, as desired.
b illustrates the formation of a resist layer 30 over one of the active regions 10b. Accordingly, active region 10a is left exposed. The resist layer 30 can be any standard positive or negative tone photoresist, as an example.
In
Referring now to
The source drain ion implantation step also amorphizes the silicon and makes it sensitive to deformation using a stress inducing liner. In the preferred embodiment of the invention, the resist 30 is removed and a spike RTA step, typically at 900° C., is applied to the silicon to facilitate regrowth of crystals in the heavily doped source and drain regions of the p-channel transistor. The spike RTA step usually takes less than one second and is performed by increasing the temperature to its target, then immediately ramping down the temperature once it has reached the target. The annealing step can successfully occur, however, in temperatures ranging from about 550° C. to about 1000° C. The temperature of this intermediate RTA step is kept as low as possible to reduce dopant diffusion.
Referring to
As shown in
f depicts the structure after the amorphous layer is recrystallized to form stress memory region 16 as at least an upper portion of the source-drain regions 54/56. Since the active area 10a was recrystallized before the stress layer was applied, the crystalline structure of this region should not be substantially affected by the stress liner and subsequent RTA step. (e.g., the elasticity of the silicon crystal will allow the region to regain shape after liner removal). The subsequent RTA step, typically at 1050° C., is applied to the silicon to facilitate regrowth of crystals in the heavily doped source and drain regions of the n-channel transistor, as well as to activate the dopants. The RTA step is usually performed for between about 0-10 seconds. The annealing step can successfully occur, however, in temperatures greater than 1000° C.
In some embodiments, it has been found to be desirable to use a low temperature anneal for a compressive stressed semiconductor and a high temperature anneal for a tensile stressed semiconductor. (The theory is that H out-diffuses to give a lower Si—H/Si—N bond ratio as mentioned above.) For example, the low temperature recrystallization anneal can be performed at a temperature less than about 700° C., for example at between about 500° C. and about 600° C. The high temperature anneal can be performed at a temperature greater than about 1000° C., for example at between about 1100° C. and 1200° C. This intermediate RTA can also be used to neutralize stress in the other device, e.g. n-channel device instead of p-channel device.
Referring now to
This concept of selectively stressing devices when applying a blanket stress liner can be used in alternative device architectures such as FinFETs or multi-gated devices. One example is shown in
Referring first to
To form the structure of
Embodiments of the present invention can be utilized in conjunction with other stress-inducing techniques. For example, it is known to form the contact etch stop layer (CESL) 60 as a stress-inducing layer. Any stress induced by this layer can be additive to the stress already discussed above. As one example, co-pending application Ser. No. ______ (Attorney Docket No. 2006 P 50407) filed concurrently herewith, which is incorporated herein by reference, teaches an example of a stress-inducing layer 60. The techniques for forming this layer that are taught in that application can be applied here.
Another example of a stress-inducing technique is taught in co-pending application Ser. No. ______ (Attorney Docket No. 2006 P 50537) filed concurrently herewith, which is incorporated herein by reference. In this application, stress is induced directly into the gate 20 prior to formation of spacers 38. The process taught in this co-pending application can be utilized in conjunction with the techniques taught herein.
Yet another example of a stress inducing technique is taught in co-pending application Ser. No. 11/354,616, which was filed on Feb. 16, 2006 and is incorporated herein by reference. In this application, stress is induced in the active areas 10a and 10b prior to formation of the gate electrodes. Once again, the process taught in this co-pending application can be utilized with the techniques taught herein. In fact, any of the techniques from these applications can be combined as desired.
It will also be readily understood by those skilled in the art that materials and methods may be varied while remaining within the scope of the present invention. It is also appreciated that the present invention provides many applicable inventive concepts other than the specific contexts used to illustrate preferred embodiments. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
This application claims the benefit of U.S. Provisional Application No. 60/841,601 (Attorney Docket No. 2006 P 50407P), filed on Aug. 31, 2006, entitled “Strained Semiconductor Device and Method of Making Same”, which application is hereby incorporated herein by reference. This application relates to the following co-pending and commonly assigned patent applications: Ser. No. ______ (Attorney Docket No. 2006 P 50407), filed Sep. 15, 2006; and Ser. No. ______ (Attorney Docket No. 2006 P 50537), filed Sep. 15, 2006, which applications are hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60841601 | Aug 2006 | US |