SEMICONDUCTOR DEVICE HAVING COMPRESSIVELY STRAINED CHANNEL REGION AND METHOD OF MAKING SAME
A semiconductor device and method making it utilize a three-dimensional channel region comprising a core of a first semiconductor material and an epitaxial covering of a second semiconductor material. The first and second semiconductor materials have respectively different lattice constants, thereby to create a strain in the epitaxial covering. The devices are formed by a gate-last process, so that the second semiconductor material is deposited only after the high temperature processes have been performed. Consequently, the lattice strain is not substantially relaxed, and the improved performance benefits of the lattice strained channel region are not compromised.
The invention relates to semiconductor devices and methods of making the same, and more particularly relates to such devices and methods in which a transistor channel region is compressively strained.
2. Description of Related ArtAs the gate length of transistors continues to decrease with successive generations of semiconductor devices, new transistor configurations have been needed to counteract the diminished response that would otherwise occur with shrinking gate lengths. One such design configuration is referred to variously as a FinFET or tri-gate transistor, in which the source, drain and channel region of each transistor is elevated relative to a semiconductor substrate. The elevated portion has the shape of a ridge or fin, and may be formed integrally with the underlying substrate or may be formed on an insulating layer in the case of SOI type devices. The gate wraps around the three projecting sides of the fin, and so the available channel area is increased by the gate contacting not only the top part of the fin but also its side walls.
Previous designs for FinFETs have also utilized a strained lattice configuration, for example by replacing all or part of the silicon fin with a silicon germanium epitaxial layer. The wider lattice constant of SiGe relative to silicon causes a compressive strain to be imparted to the SiGe layer formed epitaxially on silicon, which enhances hole mobility in the channel region and thus enhances pFET drive current relative to an unstrained Si channel. See, Smith et al., “Dual Channel FinFETs as a Single High-k/Metal Gate Solution Beyond 22 nm Node,” 2009 IEDM, pp. 309-312.
However, previous design efforts will likely not meet the demands of future generations of semiconductor devices with respect to minimizing off-current while maximizing on-current and switching speed, especially as gate lengths decrease to 14 nm and below.
SUMMARY OF THE INVENTIONThus, in one aspect, the present invention relates to a semiconductor device, comprising a three-dimensional channel region comprising a core of a first semiconductor material and an epitaxial covering of a second semiconductor material. The first and second semiconductor materials have respectively different lattice constants, thereby to create a strain in the epitaxial covering. A source region is positioned adjacent one end of the three dimensional channel region, and a drain region is positioned adjacent an opposite end of the three dimensional channel region. A gate electrode is superposed on the three dimensional channel region. The second semiconductor material is present only in a region underlying the gate electrode.
In preferred embodiments of the semiconductor device according to the present invention, each of the core and the epitaxial covering projects upwardly relative to an underlying substrate.
In preferred embodiments of the semiconductor device according to the present invention, the core is formed integrally with an underlying substrate of the first semiconductor material.
In preferred embodiments of the semiconductor device according to the present invention, the core is formed on an insulating layer of a semiconductor on insulator (SOI) substrate.
In preferred embodiments of the semiconductor device according to the present invention, each of the three-dimensional channel region, the source region, the drain region and the gate electrode are separated from an underlying substrate by the insulating layer, thereby to form a transistor that is full isolated from the underlying substrate.
In preferred embodiments of the semiconductor device according to the present invention, the second semiconductor material has a larger lattice constant than the first semiconductor material, thereby to create a compressive strain in the epitaxial covering.
In preferred embodiments of the semiconductor device according to the present invention, the first semiconductor material comprises silicon and the second semiconductor material comprises silicon and germanium.
In preferred embodiments of the semiconductor device according to the present invention, the second semiconductor material has a smaller lattice constant than the first semiconductor material, thereby to create a tensile strain in the epitaxial covering.
In preferred embodiments of the semiconductor device according to the present invention, the first semiconductor material comprises silicon and germanium and the second semiconductor material comprises silicon.
In another aspect, the present invention relates to a semiconductor device, comprising a three-dimensional channel region comprising a core of a first semiconductor material and an epitaxial covering of a second semiconductor material. The first and second semiconductor materials have respectively different lattice constants, thereby to create a strain in the epitaxial covering. A source region is positioned adjacent one end of the three dimensional channel region, and a drain region is positioned adjacent an opposite end of the three dimensional channel region. A gate electrode is superposed on the three dimensional channel region. A hollow three-dimensional gate dielectric layer is positioned between the gate electrode and the three-dimensional channel region.
In preferred embodiments of the semiconductor device according to the present invention, each of the core and the epitaxial covering projects upwardly relative to an underlying substrate.
In preferred embodiments of the semiconductor device according to the present invention, the core is formed integrally with an underlying substrate of the first semiconductor material.
In preferred embodiments of the semiconductor device according to the present invention, the core is formed on an insulating layer of a semiconductor on insulator (SOI) substrate.
In preferred embodiments of the semiconductor device according to the present invention, each of the three-dimensional channel region, the source region, the drain region and the gate electrode are separated from an underlying substrate by the insulating layer, thereby to form a transistor that is full isolated from the underlying substrate.
In preferred embodiments of the semiconductor device according to the present invention, the second semiconductor material has a larger lattice constant than the first semiconductor material, thereby to create a compressive strain in the epitaxial covering.
In preferred embodiments of the semiconductor device according to the present invention, the first semiconductor material comprises silicon and the second semiconductor material comprises silicon and germanium.
In preferred embodiments of the semiconductor device according to the present invention, the second semiconductor material has a smaller lattice constant than the first semiconductor material, thereby to create a tensile strain in the epitaxial covering.
In preferred embodiments of the semiconductor device according to the present invention, the first semiconductor material comprises silicon and germanium and the second semiconductor material comprises silicon.
In preferred embodiments of the semiconductor device according to the present invention, the hollow three-dimensional gate dielectric layer extends upwardly from the three-dimensional channel region, between the gate electrode and each of a pair of sidewall spacers.
In preferred embodiments of the semiconductor device according to the present invention, the three-dimensional channel region is repeated as a series of the channel regions, and wherein the gate electrode overlies plural channel regions within the series.
In preferred embodiments of the semiconductor device according to the present invention, the hollow three-dimensional gate dielectric layer extends downwardly between adjacent channel regions within the series.
In yet another aspect, the present invention relates to a method of making a semiconductor device, comprising removing a dummy gate from an intermediate transistor structure comprising a three-dimensional channel region of a first semiconductor material underlying the dummy gate, forming an epitaxial covering of a second semiconductor material on a portion of the three-dimensional channel region exposed by removal of the dummy gate, and forming a gate structure contacting the covering of the second semiconductor material.
In preferred embodiments of the method according to the present invention, the three-dimensional channel region projects upwardly relative to an underlying substrate.
In preferred embodiments of the method according to the present invention, the three-dimensional channel region is formed integrally with an underlying substrate of the first semiconductor material.
In preferred embodiments of the method according to the present invention, the three-dimensional channel region is formed on an insulating layer of a semiconductor on insulator (SOI) substrate.
In preferred embodiments of the method according to the present invention, the method additionally includes forming the three-dimensional channel region on a sacrificial layer of a semiconductor material that can be etched under conditions that do not substantially etch the first semiconductor material, forming the dummy gate on the three-dimensional channel region, removing the sacrificial layer to create a void underlying the three-dimensional channel region, and filling the void with a dielectric material prior to removal of the dummy gate.
In preferred embodiments of the method according to the present invention, each of the three-dimensional channel region, a source region, a drain region and the gate electrode are separated from an underlying substrate by the insulating layer, thereby to form a transistor that is full isolated from the underlying substrate.
In preferred embodiments of the method according to the present invention, the second semiconductor material has a larger lattice constant than the first semiconductor material, thereby to create a compressive strain in the epitaxial covering.
In preferred embodiments of the method according to the present invention, the first semiconductor material comprises silicon and the second semiconductor material comprises silicon and germanium.
In preferred embodiments of the method according to the present invention, the second semiconductor material has a smaller lattice constant than the first semiconductor material, thereby to create a tensile strain in the epitaxial covering.
In preferred embodiments of the method according to the present invention, the first semiconductor material comprises silicon and germanium and wherein the second semiconductor material comprises silicon.
Other objects, features and advantages of the invention will become more apparent after reading the following detailed description of preferred embodiments of the invention, given with reference to the accompanying drawings, in which:
In
A gate dielectric film 20 is positioned between the gate 22 and sidewall spacers 18, as shown in
The upper part of Si fin 24 is clad with a layer of epitaxial silicon-germanium 26, as is best seen in
The SiGe epitaxial layer is confined to the region beneath the gate electrode 22, by which is meant the region including the gate electrode 22 itself, as well as the surrounding gate dielectric film 20.
In
In
The gate dielectric film 40 is positioned between the gate 42 and sidewall spacers 38, as shown in
The Si fins 44 are clad with a layer of epitaxial silicon-germanium 46, as is best seen in
The SiGe epitaxial layer 46 is again confined to the region beneath the gate electrode 42, by which is meant the region including the gate electrode 42 itself, as well as the surrounding gate dielectric film 40.
In both of the above embodiments, the compressive strain is desirable as it promotes hole mobility in the channel region, as is known. However, in conventional devices utilizing strained channels for increased hole mobility, the lattice strain is substantially relaxed by the high temperature processing that occurs after the strain is created. The devices and methods of the present invention avoid that disadvantage, as will be better understood from the following explanation of preferred manufacturing techniques for the embodiments described above.
As shown in
The process stage shown in
Although this discussion focuses on the manufacture of a device according to
Next, as shown in
The structure illustrated in
Then, as shown in
Next, as shown in
The gate 22 is then formed, as shown in
As discussed above, SiGe intrinsically has larger lattice constant than Si; however, for an epitaxial layer of SiGe, the crystal lattice follows that of the template Si. Therefore, this SiGe layer 26 on Si fin 24 is compressively strained. The hole mobility in a compressively-strained SiGe channel is known to be higher than that in neutral Si. However, in conventional devices, the strain in an SiGe channel is relaxed during high-temperature processes, such that the hole mobility benefit is greatly reduced or lost altogether.
By contrast, in the devices and methods as described above, the high temperature processes (such as isolation dielectric densify anneal and source/drain activation anneal) are done prior to formation of the SiGe epitaxial layer, and thus the favorable compressive strain in the SiGe channel is preserved.
The methods for making devices as described above in connection with
As shown in
In particular, the SiGe layer 33 and Si layer 35 are sequentially grown on the bulk-Si substrate 30 to produce the structure shown in
Next, these voids are refilled with dielectric 48, as shown in
The strained SiGe channel 46 is then formed, as illustrated in
By using fin structures in which both sides of a narrow fin body are covered by the gate electrode, the potential profile in the fin body is well controlled by the gate electrode. Consequently, off-state leakage current can be suppressed compared to a planar device. Still further, in devices according to certain preferred embodiments of the present invention, the fin body has a Si core and a SiGe cladding. As illustrated in
If Ge is diffused into the core region, the compressive strain weakens, and at the same the time band offset between cladding and core gets smaller. This phenomenon results in a loss of off-state leakage suppression. However, in the preferred embodiments of the present invention, the high-temperature processes are performed prior to SiGe channel formation, and thus a relatively abrupt Ge profile is preserved and Ge diffusion into the Si core is minimized.
Furthermore, as illustrated in
By contrast, the silicon on nothing (SON) process provides full-isolation of fin structure from substrate. As shown in
Therefore full-isolation of fin structure and use of strained SiGe channel are not compatible on bulk-Si substrate. However, in preferred embodiments of the present invention, the SiGe channel is formed only after the fins have been fully isolated. Consequently, both high pFET performance by compressively-strained SiGe channel and low-leakage current by fully-isolated fin can be achieved simultaneously on bulk-Si substrate.
While the present invention has been described in connection with various preferred embodiments thereof, it is to be understood that those embodiments are provided merely to illustrate the invention, and should not be used as a pretext to limit the scope of protection conferred by the true scope and spirit of the appended claims.
Claims
1. A semiconductor device, comprising:
- a semiconductor substrate;
- a protrusion part formed on the semiconductor substrate such that the protrusion part extends along a first direction;
- a gate dielectric layer covering the protrusion part;
- a gate electrode formed on the gate dielectric layer such that the gate electrode covers the protrusion part through the gate dielectric layer;
- a source region formed next to a part covered with the gate electrode in the protrusion part; and
- a drain region formed at a position opposed to the source region, the portion covered with the gate electrode sandwiched between the source region and the drain region in the protrusion part,
- wherein the protrusion part comprising:
- a first region composed of a first semiconductor material; and
- a second region formed next to the first region, the second region composed of a second semiconductor material having a lattice constant different from a lattice constant of the first semiconductor material, and
- wherein the second region is formed between the source region and the drain region in a first cross-sectional view through the source region, the drain region and the gate electrode.
2. The semiconductor device according to claim 1,
- wherein the semiconductor substrate is comprised of the first semiconductor material, and
- wherein the first region is formed integrally with the semiconductor substrate.
3. The semiconductor device according to claim 1, wherein the semiconductor substrate is a SOI substrate comprising a substrate, an insulating layer formed on the substrate and a semiconductor layer formed on the insulating layer.
4. The semiconductor device according to claim 3, wherein the source region, the drain region and the gate electrode are electrically separated from the substrate, respectively.
5. The semiconductor device according to claim 1, wherein the lattice constant of the second semiconductor material is greater than the lattice constant of the first semiconductor material.
6. The semiconductor device according to claim 5,
- wherein the first semiconductor material comprises silicon, and
- wherein the first semiconductor material comprises silicon and germanium.
7. The semiconductor device according to claim 1,
- wherein the lattice constant of the second semiconductor material is smaller than the lattice constant of the first semiconductor material.
8. The semiconductor device according to claim 7,
- wherein the first semiconductor material comprises silicon and germanium, and
- wherein the first semiconductor material comprises silicon.
9. The semiconductor device according to claim 1, wherein the gate dielectric layer further covers a side surface of the gate electrode in the first cross-sectional view.
10. The semiconductor device according to claim 1, wherein the second region is epitaxial film.
11. The semiconductor device according to claim 1, wherein the second region covers the first region in a second cross-sectional view perpendicular to the first direction and through the gate electrode.
12. The semiconductor device according to claim 1, wherein the gate electrode extends along a second direction perpendicular to the first direction in plan view.
13. A method of manufacturing a semiconductor device, comprising;
- forming an intermediate transistor; the intermediate transistor comprising; a semiconductor substrate; a core region formed on the semiconductor substrate such that the core region extends along a first direction, the core region comprised of a first semiconductor material; a dummy gate covering the core region; a source region formed next to a part covered with the dummy gate in the core region; and a drain region formed at a position opposed to the source region, the portion covered with the gate electrode sandwiched between the source region and the drain region in the core region,
- removing the dummy gate from the intermediate transistor to expose a part of the core region;
- forming an epitaxial film on a part of the core region, the epitaxial film composed of a second semiconductor material having a lattice constant different from a lattice constant of the first semiconductor material;
- forming a gate dielectric layer so as to cover the core region through the epitaxial film, and
- forming a gate electrode so as to cover the core region through the gate dielectric layer.
14. The method according to claim 13, wherein the core region and the epitaxial film constitute a protrusion part protruding from the semiconductor substrate.
15. The method according to claim 13, wherein a step of the forming the intermediate transistor comprises a step of activating the source region and the drain region by heat treatment.
16. The method according to claim 13,
- wherein the core region is formed on a sacrificial layer, and
- wherein the method further comprising:
- removing the sacrificial layer to make space positioned bellow the core region; and
- burying a dielectric material in the space before the removing the sacrificial layer.
17. The method according to claim 13,
- wherein the first semiconductor material comprises silicon, and
- wherein the first semiconductor material comprises silicon and germanium.
18. The method according to claim 13,
- wherein the first semiconductor material comprises silicon and germanium, and
- wherein the first semiconductor material comprises silicon.
19. The method according to claim 13,
- wherein the epitaxial film covers in a second cross-sectional view perpendicular to the first direction and through the gate electrode.
Type: Application
Filed: Jun 14, 2018
Publication Date: Oct 18, 2018
Inventor: Toshiharu NAGUMO (Tokyo)
Application Number: 16/008,590