STRAINED CHANNEL FINFET

[0001] The present invention relates generally to transistors and, more particularly, to fin field effect transistors (FinFETs).

[0002] Scaling of device dimensions has been a primary factor driving improvements in integrated circuit performance and reduction in integrated circuit cost. Due to limitations associated with existing gate-oxide thicknesses and source/drain (S/D) junction depths, scaling of existing bulk MOSFET devices below the 0.1 m process generation may be difficult, if not impossible. New device structures and new materials, thus, are likely to be needed to improve FET performance.

[0003] Double-gate MOSFETs represent new devices that are candidates for succeeding existing planar MOSFETs. In double-gate MOSFETs, the use of two gates to control the channel significantly suppresses short-channel effects. A FinFET is a recent double-gate structure that includes a channel formed in a vertical fin. The FinFET is similar to existing planar MOSFET in layout and fabrication. The FinFET also provides a range of channel lengths, CMOS compatibility and large packing density compared to other double-gate structures.

[0004] Consistent with the present invention, a FinFET transistor is provided that uses a vertically formed strained channel layer that is self-aligned to the fin channel. The strained channel layer may include a crystalline material that is lattice constant mismatched with the crystalline material of the fin of the FinFET. The lattice constant mismatch induces tensile strain within the strained channel layer that increases carrier mobility. Increasing the carrier mobility, in turn, increases the drive current of the FinFET transistor, thus, improving FinFET performance.

[0005] Additional advantages and other features of the invention will be set forth in part in the description which follows and, in part, will become apparent to those having ordinary skill in the art upon examination of the following, or may be learned from the practice of the invention. The advantages and features of the invention may be realized and obtained as particularly pointed out in the appended claims.

[0006] According to the present invention, the foregoing and other advantages are achieved in part by a semiconductor structure that includes a fin. The fin includes a first crystalline material and a plurality of surfaces. The structure further includes a layer formed on at least a portion of the plurality of surfaces, the layer including a second crystalline material. The first crystalline material has a different lattice constant than the second crystalline material to induce tensile strain within the layer.

[0007] According to another aspect of the invention, a transistor is provided. The transistor includes a fin that further includes a first crystalline material and first and second end portions. The first crystalline material has a first lattice constant. The transistor further includes source and drain regions formed adjacent the first and second end portions of the fin. The transistor also includes a first layer of second crystalline material formed on at least a portion of the fin. The second crystalline material has a second lattice constant, wherein the first lattice constant is greater than the second lattice constant. The transistor additionally includes a dielectric layer formed on at least a portion of the first layer and a gate electrode formed on at least a portion of the dielectric layer.

[0008] According to a further aspect of the invention, a method of forming a semiconductor device is provided. The method includes forming a fin that includes a first crystalline material and multiple surfaces. The method further includes forming a first layer on at least a portion of the multiple surfaces. The first layer includes a second crystalline material, wherein the first crystalline material is lattice constant mismatched with the second crystalline material to induce tensile strain within the first layer.

[0009] Other advantages and features of the present invention will become readily apparent to those skilled in this art from the following detailed description. The embodiments shown and described provide illustration of the best mode contemplated for carrying out the invention. The invention is capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings are to be regarded as illustrative in nature, and not as restrictive.

[0010] Reference is made to the attached drawings, wherein elements having the same reference number designation may represent like elements throughout.

[0011] FIG. 1 illustrates exemplary layers of a substrate that may be used for forming a fin of a FinFET consistent with the present invention;

[0012] FIG. 2A illustrates an exemplary fin consistent with the invention;

[0013] FIG. 2B illustrates a cross-sectional view of the exemplary fin of FIG. 2A consistent with the invention;

[0014] FIGS. 2C and 2D illustrate exemplary source and drain regions formed adjacent the fin of FIGS. 2A and 2B consistent with the invention;

[0015] FIG. 3A illustrates a cross-sectional view of a strained layer formed on a fin consistent with the invention;

[0016] FIG. 3B illustrates a top view of the strained layer of FIG. 3A formed upon a fin and source and drain regions consistent with the invention;

[0017] FIG. 4A illustrates a cross-sectional view of a gate dielectric and gate electrode formed upon a fin consistent with the invention;

[0018] FIG. 4B illustrates a top view of the gate dielectric and gate electrode of FIG. 4A formed upon a fin consistent with the invention;

[0019] FIG. 5 illustrates a strained insulator underneath the fin of FIGS. 2A and 2B consistent with another embodiment of the present invention; and

[0020] FIG. 6 illustrates damescene source/drain regrowth consistent with another embodiment of the present invention.

[0021] The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

[0022] Consistent with the present invention, an increased mobility channel FinFET is provided. A vertically formed strained channel layer, consistent with the present invention, is self-aligned to the fin channel of the FinFET. The strained channel layer may include a crystalline material that is lattice mismatched with the crystalline material of the fin of the FinFET such that tensile strain is induced within the strained channel layer. The induced tensile strain increases carrier mobility of the strained channel layer, thus, increasing drive current of the FinFET.

[0023] FIG. 1 illustrates a cross-section of a substrate 100 formed in accordance with an exemplary embodiment of the present invention. Substrate 100, consistent with the present invention, may be a silicon on insulator (SOI) structure that includes a fin channel layer 105 formed upon, for example, a buried oxide layer 110. Buried oxide layer 110 may be formed on a silicon layer (not shown). The thickness of fin channel layer 105 may range, for example, from about 500 to about 2000 and the thickness of buried oxide layer 110 may range, for example, from about 1000 to about 3000 .

[0024] Fin channel layer 105 may include a crystalline material with a lattice constant larger than the lattice constant of a crystalline material selected for a strained channel layer (described with respect to FIGS. 3A and 3B below). If, for example, silicon is selected for the strained channel layer, fin channel layer 105 may include a crystalline material with a lattice constant large than the lattice constant of silicon. Fin channel layer 105 may include, for example, Si_xGe_(1-x) with x approximately equal to 0.7. Other values of x may be appropriately selected. One skilled in the art will recognize that crystalline materials other than Si_xGe_(1-x) may be used such that the material's lattice constant is larger than the lattice constant of the crystalline material selected for the strained channel layer. In some embodiments, substrate 100 may be formed by wafer bonding epitaxial Si_xGe_(1-x) to an oxide/Si substrate wafer. One skilled in the art will recognize, however, that other existing techniques may be used for forming substrate 100.

[0025] As shown in FIGS. 2A and 2B, after forming substrate 100, a vertical fin 205 may be formed from fin channel layer 105. Fin 205 may be formed, for example, with a width (w) in a range of 10-15 nm. Fin 205 may be formed from fin channel layer 105 using any existing process, including, but not limited to, existing photolithographic and etching processes.

[0026] Subsequent to formation of fin 205, source 210 and drain 215 regions may be formed adjacent the respective ends of fin 205, as shown in FIGS. 2C and 2D. Source 210 and drain 215 regions may be formed by, for example, deposition of a layer of crystalline material over fin 205. The source 210 and drain 215 regions may be formed from the layer of crystalline material using, for example, existing photolithographic and etching processes. One skilled in the art will recognize, however, that other existing techniques may be used for forming source 210 and drain 215 regions. Source 210 and drain 215 regions may include a crystalline material such as, for example, Si_xGe_(1-x), with x approximately equal to 0.7.

[0027] After formation of source 210 and drain 215 regions, a strained layer 305 may be formed on fin 205, source 210 and drain 215, as shown in FIGS. 3A and 3B. Strained layer 305 may be formed on fin 205, source 210 and drain 215 using any appropriate existing process. In some exemplary embodiments, for example, strained layer 305 may be formed on fin 205, source 210 and drain 215 using a selective epitaxial deposition process. Strained layer 305 may include a crystalline material whose lattice constant is smaller that the lattice constant of the crystalline material used for fin 205. With a lattice mismatch between fin 205 and strained layer 305 tensile strain is produced in strained layer 305. Strained layer 305 may be formed, for example, with a thickness t that is approximately {fraction (1/2)} to of the fin 205 width w. For example, the thickness t of strained layer 305 may be 5 nm. Strained layer 305 may include, but is not limited to, silicon. One skilled in the art will recognize that other crystalline materials with lattice constants less than the crystalline material used to form fin 205 may, alternatively, be used.

[0028] After formation of strained layer 305, a gate dielectric 405 and gate electrode 410 may be formed on the portion of fin 205 not covered by source 210 and drain 215, as shown in FIGS. 4A and 4B. The gate dielectric 405 may include a thin layer of dielectric material, such as SiO, SiO₂, SiN, SiON, HFO₂, ZrO₂, Al₂O₃, HFSiO(x)ZnS, MgF₂, or other dielectric materials. Gate electrode 410 may be formed upon gate dielectric 405 and may include, for example, a layer of polysilicon. Gate dielectric 405 and gate electrode 410 may be formed on fin 205 using any existing processes, such as, for example, existing deposition and patterning processes. Formation of gate dielectric 405 and gate electrode 410 upon fin 205, thus, produces a FET sidewall vertical channel that includes a thin strained layer 305 at both vertical surfaces of fin 205. Strained layer 305 provides improved carrier mobility through the induction of tensile strain in strained layer 305 caused by the lattice mismatch between strained layer 305 and fin 205. This carrier mobility enhancement can increase the drive current of a FinFET transistor created using the semiconductor structure shown in FIGS. 4A and 4B.

[0029] FIG. 5 illustrates an exemplary strained insulator 505 that may, consistent with another embodiment of the present invention, be formed beneath a fin of a FinFET, such as fin 205 shown in FIGS. 2A and 2B. Fin 205 may be formed upon the insulating material of strained insulator 505 such that the crystalline material of fin 205 and strained insulator 505 are lattice mismatched. A lattice mismatch between fin 205 and strained insulator 505 produces tensile strain in fin 205 that, in turn, improves carrier mobility of the FinFET. One skilled in the art will recognize that any appropriate insulating material, with a lattice constant that is mismatched with the crystalline material of fin 205, may be used as strained insulator 505.

[0030] FIG. 6 illustrates exemplary damascene source/drain regrowth consistent with another embodiment of the present invention. After forming an active area 600 and fin 605 upon a substrate, tetraethylorthosilicate (TEOS) may be deposited upon fin 605 and active area 600 and then polished. A mask (mask 1) 610 may then be used to open a gate area 615. Fin 605 may be thinned down and a gate 620 may be formed by depositing and polishing polysilicon in gate area 615. A second mask (mask 2) 625 may be used to open a source and drain area 630. A nitride layer of active area 600, within the opened source and drain area 630, may be etched to expose a region of the source and drain area 630. From the exposed region, silicon can be selectively re-grown to produce a source 635 and a drain 640.

[0031] In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, the present invention can be practiced without resorting to the details specifically set forth herein. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the thrust of the present invention. In practicing the present invention, conventional photolithographic and etching techniques may be employed, and hence, the details of such techniques have not been set forth herein in detail.

[0032] Only the preferred embodiments of the invention and a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the invention is capable of use in various other combinations and environments and is capable of modifications within the scope of the inventive concept as expressed herein.