Patent Description:
For the technology beyond the <NUM>-nm node CMOS, the use of compressively strained germanium (Ge) as a channel material attracts much interest for the pMOS FinFET. Although Ge material has a higher intrinsic hole mobility than Si, relaxed Ge channel devices do not outperform strained Si channel p-FINFETs. Strained Ge is crucial to boost channel mobility.

Since the <NUM>-nm technology, embedded SiGe source/drain has been used as a stressor in Si pMOS devices. However, with scaling down to sub-<NUM> nodes, much less space will limit the source and drain and this stress technique becomes less efficient.

This resulted in a renewed interest in stress formation in Ge channels by SiGe strain relaxed buffers (SRBs) epitaxially grown on Si. The scheme becomes challenging as downscaling goes together with a reduction in thickness of the shallow trench isolation (STI), which in turn sets a limit on the thickness of the SiGe SRB in the case where the Si in between the STI oxide is recessed and replaced by the SiGe SRB.

When trying to implement compressively strained Ge channels on SiGe strain relaxed buffers, a variety of problems exist for the technology beyond the <NUM>-nm node CMOS.

For instance, fabricating a large relaxation degree (><NUM>%) of strain-relaxed Si<NUM>-xGex (for instance with x><NUM>) is difficult because the thickness of the shallow trench isolation (STI) sets a limit to the thickness of the Si<NUM>-xGex SRB. If the SiGe SRB is not strongly (><NUM>%) or fully relaxed, there is an increased risk for strain relaxation of the strained germanium channel, and for an increased leakage current of the final devices. Moreover, if the SiGe is not sufficiently relaxed, further relaxation might occur during subsequent process steps. This would lead to process unreliability, as there might be a higher wafer to wafer variation and the final degree of relaxation might vary as function of device dimensions.

Also, for future technology nodes, the STI thickness is further reduced, which also reduces the maximal allowable Si<NUM>-xGex thickness. This makes the fabrication of SiGe SRBs extremely challenging. Strain relaxation only happens above a certain critical thickness. For a given layer thickness, the driving force for further relaxation reduces with increasing degree of relaxation. In conventional schemes, a high degree of strain relaxation is achieved by making the semiconductor layer sufficiently thick. Techniques to make relative thin strain relaxed buffers, in general rely on the controlled implementation of material imperfections (defects) to initiate strain relaxation. However, the presence of defects needs to be avoided/minimised as it has a detrimental effect on final device performance.

Moreover, initiation of layer relaxation comes together with the formation of misfit dislocations. On (<NUM>) surfaces, a misfit dislocation network is formed which extends up to <NUM> above the SiGe-SRB/Si-substrate interface which sets a minimum thickness on the SiGe SRB layer to keep the Ge surface channel out of this defective area. If the SiGe has a <NUM> thick defective layer, it limits the minimum thickness of SiGe to keep the Ge channel out of this defective area. Indeed, if a Ge channel layer is grown on such a defective SiGe buffer, the defects can extend to Ge channel layer and thus relax the Ge layer.

Also, due to the formation of facets (e.g. {<NUM>} and/or {<NUM>} facets, but not limited thereto) during the selective epitaxial growth, the Ge content is not uniform in Si<NUM>-xGex (for instance with x><NUM>) SRBs, which results in the non-uniformity of strain distribution in the Ge channel layer. In addition, the top surface of the Si<NUM>-xGex (for instance x><NUM>) SRB may be rounded and not flat, which would also results in an unwanted rounded surface of Ge channel layer.

It is thus very difficult to grow a fully compressively strained Ge channel layer on top of Si<NUM>-xGex SRBs, and there exists a need in industry for such solutions.

It is an aim of the present disclosure to provide a method for manufacturing a transistor device comprising a germanium channel structure on a silicon based substrate, which allows the manufacturing of a fully compressively strained germanium channel structure, having improved channel structure properties, on an underlying layer stack which is limited in thickness.

This aim is achieved according to the disclosure with the method showing the steps of the first independent claim.

In a first aspect of the present disclosure, a method for manufacturing a transistor device comprising a germanium channel material on a silicon based substrate, the method comprising:.

wherein said Si<NUM>-xGex strain relaxed buffer layer comprises a germanium content x which is within the range of <NUM>% to <NUM>%, wherein said strain relaxed buffer layer has a thickness smaller than <NUM>, and wherein said trench has a width smaller than <NUM> and wherein the Germanium based channel layer is fully compressively strained.

It is a further advantage that the Si<NUM>-xGex SRB grown on a "V"-shape groove has a more uniform Ge content as demonstrated by TEM. This results in a reduced strain variation throughout the SRB layer and a more optimal stress built up in the germanium based/germanium channel layer.

It is a further advantage that formation of the {<NUM>} surface "V"-shape groove results in a better confinement of the {<NUM>} defects in {<NUM>} planes closer to the SiGe/Si-substrate interface. The dense defects/dislocation networks in the V shape region enhance the relaxation degree in SiGe SRB layers.

It is a further advantage that the surface orientations of SiGe SRB and consequently the strained Ge (sGe) fin surface can be very well controlled, by carefully matching the SiGe thickness and the Si recess depth. By surface orientations, both the {<NUM>} top surface as well as the {<NUM>} side walls are meant. In preferred embodiments, the germanium based channel layer comprises more than <NUM>% of germanium or more than <NUM>% of germanium. Preferably, it is a germanium layer. It can be for instance also a SiGeSn layer, wherein preferably the Si and Sn concentration are predetermined such that the SiGeSn layer has the same lattice constant as germanium.

In preferred embodiments, the SRB layer comprises a germanium content x in the range of <NUM>% to <NUM>%, more preferably in the range of <NUM>% to <NUM>%, more preferably in the range of <NUM>% to <NUM>%. The germanium content is preferably smaller than <NUM>%. For higher Ge% levels, there may be an increased risk for leakage currents to occur in the final device.

In preferred embodiments, the Si<NUM>-xGex SRB layer has a thickness larger than <NUM>. The SRB layer thickness preferably lies within the range of <NUM> to <NUM>. For instance, the SRB layer thickness can be smaller than <NUM>.

In preferred embodiments, growing the Si<NUM>-xGex SRB layer in the trenches comprises epitaxially growing the Si<NUM>-xGex SRB layer on the upper surface, for instance on the upper surface of the recessed silicon protrusion.

In preferred embodiments, the method further comprises epitaxially growing a seed layer on the upper surface, and growing the Si<NUM>-xGex SRB layer in the trenches comprises epitaxially growing the Si<NUM>-xGex SRB layer on the seed layer.

This provides the further advantage that the Si<NUM>-xGex SRB layer can be even further relaxed and for an suitable thickness of the Ge seed layer, <NUM>% strain relaxation can be achieved. In addition, the full relaxation of the SiGe SRB has been achieved for thicknesses down to <NUM>, which illustrates that the thickness of the SRB layer can be further reduced. The combined thickness of the seed layer and SRB layer can be smaller than the thickness of a similar SRB layer if it were not combined with the growth of a seed layer.

Preferably, the seed layer is germanium based. In preferred embodiments, the seed layer comprises more than <NUM>% of germanium or more than <NUM>% of germanium. Preferably, it is a germanium layer. It can be for instance also a SiGeSn layer, wherein preferably the Si and Sn concentration are predetermined such that the SiGeSn layer has the same lattice constant as germanium.

The seed layer thickness is preferably comprised within the range of <NUM> to <NUM>, more preferably within the range of <NUM> to <NUM>.

The combined thickness of seed layer and Si<NUM>-xGex SRB layer preferably lies within the range of <NUM> to <NUM>.

In preferred embodiments, the Germanium based channel layer has a thickness of more than <NUM>, or more than <NUM>, or more than <NUM>.

In preferred embodiments, growing a Si<NUM>-xGex SRB layer in the trenches and growing a Germanium based channel layer on the Si<NUM>-Gex SRB layer, and, in case a seed layer is grown, (first) growing the seed layer, is performed in a continuous, uninterrupted process.

In preferred embodiments, the STI thickness is smaller than <NUM>, more preferably smaller than <NUM>, more preferably smaller than <NUM>, more preferably smaller than <NUM>.

In preferred embodiments, the trench has a width smaller than <NUM>, or smaller than <NUM>, or smaller than <NUM> or smaller than <NUM>. In preferred embodiments, the trench width lies in between <NUM> and <NUM>, when manufacturing in the <NUM> and <NUM> nodes as known in the field. It is an advantage of having a narrow trench width that the growth of a Si<NUM>-xGex (e.g. x><NUM>) strain relaxed buffer (SRB) on the "V"-shape groove can result in a flat surface of SiGe buffer layer (SRB) and a flat surface of Ge channel layer.

In preferred embodiments, the trench depth is smaller than <NUM>, more preferably smaller than <NUM>, more preferably smaller than <NUM>.

In preferred embodiments, the silicon substrate is a (<NUM>) oriented substrate, and the V-shaped groove at an upper surface of the recessed protrusion is defined by {<NUM>} oriented facets.

In preferred embodiments, partially recessing the silicon protrusion in order to provide a trench in between adjacent STI structures, and to provide a V-shaped groove at an upper surface of the recessed protrusion, comprises performing etching the protrusions with a wet-chemical etching solution such as but not limited to a tetramethylammonium hydroxide (TMAH) solution, or any other chemical mixture allowing etching of silicon resulting in preferential {<NUM>} facet formation.

In preferred embodiments, the maximal trench depth is smaller than the STI thickness.

In preferred embodiments, partially recessing the silicon protrusion in order to provide a trench in between adjacent STI structures, and to provide a V-shaped groove at an upper surface of the recessed protrusion, is performed such that the highest points (at a position adjacent to the sidewalls of the trench) of the {<NUM>} oriented facets remains higher than the lower surface of the STI structures.

Indeed, the recess is performed such that undercutting the adjacent STI structures is avoided. The resulting recess does not undercut the adjacent STI structures.

In preferred embodiments, the method further comprises partially recessing the adjacent STI structures after growing the germanium based channel layer in the trenches on the Si<NUM>-xGex SRB layer, preferably directly after. Hereby, preferably, the top and side surfaces of the channel layer become exposed. Then, a gate layer or layer stack can be provided over the exposed top surface and side surfaces of the channel layer.

According to preferred embodiments, the method comprises providing source/drain and gate contact structures on the germanium based channel layer.

In a second aspect not forming part of the claimed invention, a transistor device comprising a germanium based channel structure on a silicon based substrate is disclosed, the transistor device comprising a layer stack embedded in STI dielectric structures which is underlying the germanium channel structure, the layer stack comprising:.

wherein the Si<NUM>-xGex SRB layer comprises a germanium content x which is within the range of <NUM>% to <NUM>% (more preferentially in the range of <NUM>% to <NUM>%, more preferentially in the range of <NUM>% to <NUM>%; preferably equal to or larger than <NUM>%), and wherein the SRB layer has a thickness smaller than <NUM>, for instance smaller than <NUM>.

Preferably, the device further comprises a seed layer, preferably germanium seed layer, in between, preferably directly in between (i.e. there are no other layers in between), the upper surface and the Si<NUM>-xGex SRB layer.

Preferably, the silicon substrate is a (<NUM>) oriented substrate, and the V-shaped groove at an upper surface of the recessed protrusion is defined by {<NUM>} oriented facets.

Preferably, the highest points of the {<NUM>} oriented facets is higher than the lower surface of the STI structures. Thus, preferably, the {<NUM>} oriented facets do not undercut the adjacent STI structures.

Preferably, the SRB layer has a relaxation degree within the range of <NUM>% to <NUM>% and the germanium based channel structure is fully compressively strained with respect to the SRB layer.

Preferably, the degree of relaxation is within the range of <NUM> to <NUM>% in the SiGe SRB layer without Ge seed layer, and within the range of <NUM>% to <NUM>%, e.g. <NUM>%, for the SiGe SRB with seed layer.

Preferably, the transistor device comprises source/drain and gate contact structures provided on the germanium based channel layer.

Features and advantages disclosed for one of the above aspects of the present invention are hereby also implicitly disclosed the other aspects, mutatis mutandis, as the skilled person will recognize.

Certain objects and advantages of various inventive aspects have been described herein above. It is understood that this summary is merely an example and is not intended to limit the scope of the disclosure. The disclosure, both as to organization and method of operation, together with features and advantages thereof, may best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings.

The disclosure will be further elucidated by means of the following description and the appended figures.

The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto but only by the claims. The drawings described are only schematic and are nonlimiting. The dimensions and the relative dimensions do not necessarily correspond to actual reductions to practice of the disclosure.

Furthermore, the various embodiments, although referred to as "preferred" are to be construed as exemplary manners in which the disclosure may be implemented rather than as limiting the scope of the disclosure.

<FIG> illustrate a method for manufacturing a channel of a pMOS transistor device comprising a germanium channel material <NUM> on a silicon based substrate <NUM> according to a preferred embodiment of the present disclosure.

The method starts by providing a shallow trench isolation (STI) substrate, which is known to the skilled person. A STI substrate can be manufactured for instance by providing a silicon wafer or substrate <NUM>, and patterning silicon protrusions <NUM> into the substrate <NUM>, followed by embedding the silicon protrusions <NUM> in so called shallow trench isolation structures <NUM> , typically comprising a dielectric material as for instance SiO<NUM>. The sidewalls of the silicon protrusions <NUM> are preferably perpendicular to a front surface of the silicon wafer <NUM>, but may form a small angle with respect to the normal thereto, in such a way that the remaining Si protrusions are slightly narrower at the top compared to the bottom.

wherein the Si<NUM>-xGex SRB layer <NUM> comprises a germanium content x being in the range of <NUM>% to <NUM>% (more preferably in the range of <NUM>% to <NUM>%, more preferably in the range of <NUM>% to <NUM>%), and wherein the SRB layer <NUM> has a thickness smaller than <NUM> (preferably smaller than <NUM>).

The step of partially recessing the silicon protrusion in order to provide a trench in between adjacent STI structures, and to provide a V-shaped groove at an upper surface of the recessed protrusion, is preferably performed such that the highest points (at a position adjacent to the sidewalls of the trench) of the {<NUM>} oriented facets remains higher than the lower surface of the STI structures. Indeed, the recess is preferably performed such that undercutting the adjacent STI structures is avoided (such that T10>T).

A fully strained Ge channel FINFET device was produced by a process including the above method, by using a wet-chemical treatment (e.g. applying a tetramethylammonium hydroxide (TMAH) solution, or any other wet etch process which can form a V-shaped groove) for the recessing of the Si recess <NUM>. The process comprised:.

As seen in <FIG>, the TMAH recess created the {<NUM>} facet planes on (<NUM>) Si substrate STI regions which is denoted as "V"-shape grooves. With diluted HF (<NUM>%) pre-cleaning for <NUM> and a <NUM> pre-bake in the CVD growth chamber, <NUM>-nm thick Si<NUM>-xGex (x=<NUM>) SRBs were grown selectively in the ~<NUM> wide trenches <NUM> and a <NUM>-<NUM> thick Ge channel layer <NUM> was grown continuously, i.e. without growth interruption, on top of the Si<NUM>-xGex (x=<NUM>) SRBs <NUM>. XRD {<NUM>} Reciprocal Space Mapping (RSM) demonstrates that the <NUM>-thick Si<NUM>-xGex is <NUM>% relaxed with a Ge content of <NUM>% and the Ge layer is fully compressively strained with respect to the Si<NUM>Ge<NUM> SRB, as seen in <FIG>.

In particular, the formation of facets, e.g. mainly {<NUM>} and {<NUM>} facets, but not only, on top of SiGe SRB has been largely suppressed. As a consequence, the Ge channel growth can end up with a flat surface, if all dimensions are suitable scaled. Most importantly, Ge content of <NUM>% in SiGe SRB is uniform as demonstrated in the HAADF-STEM image of <FIG>. Finally, a flat smooth surface of the fully strained Ge channel layer was obtained.

To demonstrate the advantage of "V"-shape groove, the structural material properties were compared with the standard approach which consists of Ge and SiGe growth on the "flat" Si (<NUM>) plane in the trenches, where the Si recess is done in-situ using suitable HCl vapor etching. It was found that the SiGe SRB layers have a pronounced facet issue which gives rise to a "triangular" shape on the top of SiGe SRBs. As a consequence, SiGe SRB layers exhibit a variation of Ge content as demonstrated from HAADF-STEM (<FIG>, dotted line). This is a consequence of the formation of {<NUM>} facets since Ge incorporation in {<NUM>} SiGe is higher than in (<NUM>) oriented. Most importantly, such SiGe SRB layers grown on the "flat" {<NUM>} surface are typically less (e.g. only about <NUM>%) relaxed.

<FIG> illustrates the different nature of facet growth between embodiments of the present disclosure (b) and embodiments of the above mentioned the standard approach (a). The growth in the trenches from bottom to top provides facets which are systematically becoming larger in case (a). To the contrary, in case (b), these facets become smaller and end up in a flat surface. In <FIG>, as an example, only one kind of orientation facets is shown. This is not a limitation, and also other orientation facets or a mixture of different orientation facets may be formed.

This comparison clearly demonstrates that the "V"-shape groove method has at least the following advantages:.

By taking advantage of the larger relaxation degree (within the range of <NUM>% to <NUM>%) of SiGe SRBs, the fully strained Ge channel layer has been grown.

In summary, the method described above can be used to fabricate fully compressively strained Ge FINFET on thin (<NUM> to about <NUM>) <NUM>%-<NUM>% relaxed Si<NUM>-xGex (e.g. x=<NUM>) SRBs, for instance for the application of Ge pMOS at the nodes of <NUM> and below.

According to preferred embodiments, a seed layer <NUM> can be epitaxially grown on the recessed silicon protrusion <NUM>', and the SRB layer <NUM> can be epitaxially grown on the seed layer <NUM>. These embodiments allow a further reduction of the SRB thickness, more specifically they allow the use of a smaller combined thickness of seed layer and SRB layer (T5+T3) when compared to a required thickness for a single SRB layer (T5). The resulting device of such a process is illustrated in <FIG>. <FIG> shows XRD {<NUM>} RSM images of the about <NUM> thick Ge on top of an about <NUM> thick Si<NUM>-xGex (x=<NUM>) grown with an about <NUM> thick Ge seed layer in between the Si substrate and the SiGe SRB, showing <NUM>% strain relaxation in the Si<NUM>Ge<NUM> SRB and fully uniaxial strained Ge channel layer in the direction along the FIN (Ge seed layer is too thin to detect by XRD). This shows that the relaxation is relatively increased when a seed layer is added.

Devices manufactured by the above methods are illustrated in relation with <FIG> (without seed layer <NUM>) and <FIG> (with seed layer <NUM>). These devices may be intermediate devices, and may for instance result from recessing the STI structures <NUM> up until a level equal or below the lower level of the channel layer <NUM> (or the upper level of the SRB layer <NUM>).

<FIG> illustrates a transistor device not forming part of the claimed invention, and comprising a germanium based channel structure <NUM> on a silicon based substrate <NUM>, the transistor device comprising a layer stack embedded in STI dielectric structures <NUM> which is underlying the germanium channel structure <NUM>, the layer stack comprising:.

wherein the Si<NUM>-xGex SRB layer comprises a germanium content x being in the range of <NUM>% to <NUM>% (more preferably in the range of <NUM>% to <NUM>%, more preferably in the range of <NUM>% to <NUM>%), and wherein the SRB layer <NUM> has a thickness smaller than <NUM>, for instance smaller than <NUM>.

<FIG> illustrates another preferred example, in which the layer stack further comprises a seed layer <NUM>, preferably a germanium seed layer <NUM>, in between, preferably directly in between (i.e. there are no other layers in between), the upper surface of the recessed protrusion <NUM>' and the Si<NUM>-xGex SRB layer <NUM>.

Preferably, the sidewalls and upper surface of the channel layer <NUM> can be provided/covered with a gate layer or layer stack, as well as source/drain contacts (not depicted).

In both preferred examples, the silicon substrate <NUM> is a (<NUM>) oriented substrate, and the V-shaped groove at an upper surface of the recessed protrusion <NUM>' is defined by {<NUM>} oriented facets.

In both preferred examples, the highest points of the {<NUM>} oriented facets is preferably higher than the lower surface of the STI structures. Thus, preferably, the {<NUM>} oriented facets do not undercut the adjacent STI structures <NUM>.

In preferred examples, the SRB layer <NUM> has a relaxation degree of in between <NUM>% to <NUM>% and the germanium based channel structure <NUM> is fully compressively strained with respect to the SRB layer <NUM>.

The foregoing description details certain embodiments of the disclosure. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the disclosure may be practiced in many ways.

Claim 1:
Method for manufacturing a transistor device comprising a germanium channel material on a silicon based substrate (<NUM>), the method comprising:
a. providing a shallow trench isolation (STI) substrate (<NUM>,<NUM>,<NUM>) comprising a silicon protrusion (<NUM>) embedded in STI dielectric structures (<NUM>);
b. partially recessing said silicon protrusion (<NUM>) in order to provide a trench (<NUM>) in between adjacent STI structures (<NUM>), and to provide a V-shaped groove at an upper surface of said recessed protrusion (<NUM>');
c. growing a Si<NUM>-xGex strain relaxed buffer layer (<NUM>) in said trenches (<NUM>);
d. growing a Germanium based channel layer (<NUM>) in the trenches (<NUM>) on said Si<NUM>-xGex strain relaxed buffer layer (<NUM>) thereby not overgrowing the STI structures (<NUM>) which define the trenches (<NUM>);
wherein said Si<NUM>-xGex strain relaxed buffer layer (<NUM>) comprises a germanium content x which is within the range of <NUM>% to <NUM>%, wherein said strain relaxed buffer layer (<NUM>) has a thickness (T3) smaller than <NUM>, and wherein said trench (<NUM>) has a width smaller than <NUM> and wherein the Germanium based channel layer (<NUM>) is fully compressively strained.