Structure and method for FinFET device with asymmetric contact

The present disclosure provides one embodiment of a semiconductor structure. The semiconductor structure includes a fin-type active region extruded from a semiconductor substrate; a gate stack disposed on the fin-type active region; a source/drain feature formed in the fin-type active region and disposed on a side of the gate stack; an elongated contact feature landing on the source/drain feature; and a dielectric material layer disposed on sidewalls of the elongated contact feature and free from ends of the elongated contact feature.

BACKGROUND

Integrated circuits have progressed to advanced technologies with smaller feature sizes, such as 32 nm, 28 nm and 20 nm. In these advanced technologies, the gate pitch (spacing) continuously shrinks and therefore induces contact to gate bridge concern. Furthermore, three dimensional transistors with fin-type active regions are often desired for enhanced device performance. Those three dimensional field effect transistors (FETs) formed on fin-type active regions are also referred to as FinFETs. FinFETs are required narrow fin width for short channel control, which leads to smaller top S/D regions than those of planar FETs. This will further degrade the contact to S/D landing margin.

Along with the scaling down of the device sizes, such as in deep micro technology, the contact size was continuously shrunk for high-density gate pitch requirement. To shrink the contact size without impacting contact resistance, the long contact shape was proposed for 32 nm and beyond technologies. Long contact shape allows tight width dimension on the gate pitch direction but increased length on the gate routing direction to extend both contact area for source/drain and exposure area in the lithography patterning process. Long contact shape can achieve both high gate density and lower contact resistance. However, there are concerns due to the space limitation of line-end side. In line end, the concerns include line-end shortening and line-end to line-end bridging, leading to either contact-to-fin active connection opening (shortening) or contact-to-contact leakage (bridging). To reduce the line end shortening improve, it requires a wider space rule or more aggressive reshaping by optical proximity correction (OPC) on the line end, which will impact the cell size or cause bridging in a given cell pitch. This is getting even worse on future fin-type transistors because fin-type active regions are very narrow.

Therefore, there is a need for a structure and method for fin-type transistors and contact structure to address these concerns for enhanced circuit performance and reliability.

DETAILED DESCRIPTION

FIG. 1is a flowchart100for fabricating a semiconductor structure having fin-type transistors and elongated contact features constructed according to some embodiments.FIGS. 2 through 15are top or sectional views of a semiconductor structure200at various fabrication stages. The semiconductor structure200includes fin-type transistors and elongated contact features with asymmetric design in accordance with some embodiments. The semiconductor structure200and the method100making the same are collectively described below with reference toFIGS. 1 through 15.

Referring toFIG. 2, the method100begins with block102by providing a semiconductor substrate202. The semiconductor substrate202includes silicon. In some other embodiments, the substrate202includes germanium, silicon germanium or other proper semiconductor materials. The substrate202may alternatively be made of some other suitable elementary semiconductor, such as diamond or germanium; a suitable compound semiconductor, such as silicon carbide, indium arsenide, or indium phosphide; or a suitable alloy semiconductor, such as silicon germanium carbide, gallium arsenic phosphide, or gallium indium phosphide.

The semiconductor substrate202also includes various doped regions such as n-well and p-wells. In one embodiment, the semiconductor substrate202includes an epitaxy (or epi) semiconductor layer. In another embodiment, the semiconductor substrate202includes a buried dielectric material layer for isolation formed by a proper technology, such as a technology referred to as separation by implanted oxygen (SIMOX). In some embodiments, the substrate202may be a semiconductor on insulator, such as silicon on insulator (SOI).

Still referring toFIG. 2, the method100proceeds to an operation104by forming shallow trench isolation (STI) features204on the semiconductor substrate202. In some embodiments, the STI features204are formed etching to form trenches, filling the trenches with dielectric material and polishing to remove the excessive dielectric material and planarize the top surface. One or more etching processes are performed on the semiconductor substrate202through openings of soft mask or hard mask, which are formed by lithography patterning and etching. The formation of the STI features204are further described below in accordance with some embodiments.

In the present example, a hard mask is deposited on the substrate202and is patterned by lithography process. The hard mask layers include a dielectric such as semiconductor oxide, semiconductor nitride, semiconductor oxynitride, and/or semiconductor carbide, and in an exemplary embodiment, the hard mask layer include a silicon oxide film and a silicon nitride film. The hard mask layer may be formed by thermal growth, atomic layer deposition (ALD), chemical vapor deposition (CVD), high density plasma CVD (HDP-CVD), other suitable deposition processes.

A photoresist layer (or resist) used to define the fin structure may be formed on the hard mask layer. An exemplary resist layer includes a photosensitive material that causes the layer to undergo a property change when exposed to light, such as ultraviolet (UV) light, deep UV (DUV) light or extreme UV (EUV) light. This property change can be used to selectively remove exposed or unexposed portions of the resist layer by a developing process referred. This procedure to form a patterned resist layer is also referred to as lithographic patterning.

In one embodiment, the resist layer is patterned to leave the portions of the photoresist material disposed over the semiconductor structure200by the lithography process. After patterning the resist, an etching process is performed on the semiconductor structure200to open the hard mask layer, thereby transferring the pattern from the resist layer to the hard mask layer. The remaining resist layer may be removed after the patterning the hard mask layer. An exemplary lithography process includes spin-on coating a resist layer, soft baking of the resist layer, mask aligning, exposing, post-exposure baking, developing the resist layer, rinsing, and drying (e.g., hard baking). Alternatively, a lithographic process may be implemented, supplemented, or replaced by other methods such as maskless photolithography, electron-beam writing, and ion-beam writing. The etching process to pattern the hard mask layer may include wet etching, dry etching or a combination thereof. The etching process may include multiple etching steps. For example, the silicon oxide film in the hard mask layer may be etched by a diluted hydrofluorine solution and the silicon nitride film in the hard mask layer may be etched by a phosphoric acid solution.

Then etching process may be followed to etch the portions of the substrate102not covered by the patterned hard mask layer. The patterned hard mask layer is used as an etch mask during the etching processes to pattern the substrate202. The etching processes may include any suitable etching technique such as dry etching, wet etching, and/or other etching methods (e.g., reactive ion etching (RIE)). In some embodiments, the etching process includes multiple etching steps with different etching chemistries, designed to etching the substrate to form the trenches with particular trench profile for improved device performance and pattern density. In some examples, the semiconductor material of the substrate may be etched by a dry etching process using a fluorine-based etchant. Particularly, the etching process applied to the substrate is controlled such that the substrate202is partially etched. This may be achieved by controlling etching time or by controlling other etching parameter(s). After the etching processes, the fin structure206with fin active regions is defined on and extended from the substrate102.

One or more dielectric material is filled in the trenches to form the STI feature204. Suitable fill dielectric materials include semiconductor oxides, semiconductor nitrides, semiconductor oxynitrides, fluorinated silica glass (FSG), low-K dielectric materials, and/or combinations thereof. In various exemplary embodiments, the dielectric material is deposited using a HDP-CVD process, a sub-atmospheric CVD (SACVD) process, a high-aspect ratio process (HARP), a flowable CVD (FCVD), and/or a spin-on process.

The deposition of the dielectric material may be followed by a chemical mechanical polishing/planarization (CMP) process to remove the excessive dielectric material and planarize the top surface of the semiconductor structure. The CMP process may use the hard mask layers as a polishing stop layer to prevent polishing the semiconductor layer202. In this case, the CMP process completely removes the hard mask. The hard mask may be removed alternatively by an etching process. Although in further embodiments, some portion of the hard mask layers remain after the CMP process.

Referring toFIGS. 3A and 3B, the method100proceeds to an operation106by forming the fin structure206having multiple fin active regions (or fin features). The operation106includes recessing the STI features204such that the fin active regions206are extruded above from the STI features204. The recessing process employs one or more etching steps (such as dry etch, wet etch or a combination thereof) to selectively etch back the STI features204. For example, a wet etching process using hydrofluoric acid may be used to etch when the STI features204are silicon oxide.FIG. 3Bis a top view of the semiconductor structure200. Exemplary fin active regions206are spaced from each in a first direction (X direction). The fin active regions206have elongated shape and oriented along a second direction (Y direction), which is orthogonal with the X direction.

Various doping processes may be applied to the semiconductor regions to form various doped wells, such as n-wells and p-wells at the present stage or before the operation106. Various doped wells may be formed in the semiconductor substrate by respective ion implantations.

Referring toFIGS. 4A, 4B and 4C, the method100proceeds to an operation108by forming various gate stacks208on the fin active regions206.FIG. 4Bis a top view;FIG. 4Ais a sectional view along the dashed line AA′; andFIG. 4Cis a sectional view along the dashed line BB′ of the semiconductor structure200. In the present embodiment, the gate stacks208include exemplary gate stacks208a,208b,208cand208d, as illustrated inFIG. 4B. The gate stacks208have elongated shapes and are oriented in the first direction (X direction). Each of the gate stacks208is disposed over multiple fin active regions206. Particularly, one gate stack208(such as gate stack208aor208d) is disposed on ends of the fin active regions206so that this gate stack is partially landing on the fin active region206and partially landing on the STI feature204along the Y direction. Those edges are configured as dummy structures to reduce edge effect and improve overall device performance.

The gate stacks208each include a gate dielectric layer and a gate electrode. The gate dielectric layer includes a dielectric material, such as silicon oxide and the gate electrode includes a conductive material, such as polysilicon. The formation of the gate stacks208includes depositing the gate materials (including polysilicon in the present example); and patterning the gate materials by a lithographic process and etching. A gate hard mask layer may be formed on the gate material layer and is used as an etch mask during the formation of the gate stacks. The gate hard mask layer may include any suitable material, such as a silicon oxide, a silicon nitride, a silicon carbide, a silicon oxynitride, other suitable materials, and/or combinations thereof. In one embodiment, the gate hard mask includes multiple films, such as silicon oxide and silicon nitride. In some embodiments, the patterning process to form the gate stacks includes forming a patterned resist layer by lithography process; etching the hard mask layer using the patterned resist layer as an etch mask; and etching the gate materials to form the gate stacks208using the patterned hard mask layer as an etch mask.

One or more gate sidewall features (or gate spacers)210are formed on the sidewalls of the gate stacks208. The gate spacers210may be used to offset the subsequently formed source/drain features and may be used for designing or modifying the source/drain structure profile. The gate spacers210may include any suitable dielectric material, such as a semiconductor oxide, a semiconductor nitride, a semiconductor carbide, a semiconductor oxynitride, other suitable dielectric materials, and/or combinations thereof. The gate spacers210may have multiple films, such as two films (a silicon oxide film and a silicon nitride film) or three films ((a silicon oxide film; a silicon nitride film; and a silicon oxide film). The formation of the gate spacers210includes deposition and anisotropic etching, such as dry etching.

The gate stacks208are configured in the fin active regions for various field effect transistors (FETs), therefore also referred to as FinFETs. In some examples, the field effect transistors include n-type transistors and p-type transistors. In other examples, those field effect transistors are configured to form one or more static random access memory (SRAM) cells. Each SRAM cell includes two cross-coupled inverters configured for data storage. Furthermore, the gate stacks are configured to increase the pattern density uniformity and enhance the fabrication quality. For example, as noted above, the gate stacks208includes edge gate stacks208aand208beach being extended from the fin active region206to the STI feature204along the Y direction and lands on both the STI feature and the fin active region.

Referring toFIG. 5, the method100proceeds to an operation110by forming various source and drain features212to respective FinFETs. The source and drain features212may include both light doped drain (LDD) features and heavily doped source and drain (S/D). For example, each field effect transistor includes source and drain features formed on the respective fin active region and interposed by the gate stack208. A channel is formed in the fin active region in a portion that is underlying the gate stack and spans between the source and drain features.

The raised source/drain features may be formed by selective epitaxy growth for strain effect with enhanced carrier mobility and device performance. The gate stacks208and gate spacer210constrain the source/drain features212to the source/drain regions. In some embodiments, the source/drain features212are formed by one or more epitaxy or epitaxial (epi) processes, whereby Si features, SiGe features, SiC features, and/or other suitable features are grown in a crystalline state on the fin active regions206. Alternatively, an etching process is applied to recess the source/drain regions before the epitaxy growgth. Suitable epitaxy processes include CVD deposition techniques (e.g., vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD), molecular beam epitaxy, and/or other suitable processes. The epitaxy process may use gaseous and/or liquid precursors, which interact with the composition of the fin structure206.

The source/drain features212may be in-situ doped during the epitaxy process by introducing doping species including: p-type dopants, such as boron or BF2; n-type dopants, such as phosphorus or arsenic; and/or other suitable dopants including combinations thereof. If the source/drain features212are not in-situ doped, an implantation process (i.e., a junction implant process) is performed to introduce the corresponding dopant into the source/drain features212. In an exemplary embodiment, the source/drain features212in an nFET include SiC or Si doped with phosphorous, while those in a pFET include Ge or SiGe doped with boron. In some other embodiments, the raised source/drain features212include more than one semiconductor material layers. For example, a silicon germanium layer is epitatially grown on the substrate within the source/drain regions and a silicon layer is epitaxially grown on the silicon germanium layer. One or more annealing processes may be performed thereafter to activate the source/drain features110. Suitable annealing processes include rapid thermal annealing (RTA), laser annealing processes, other suitable annealing technique or a combination thereof.

Referring toFIG. 6, the method proceeds to an operation112, in which an inter-level dielectric material (ILD) layer220is formed on the substrate to cover the source/drain features212in the source/drain regions. The ILD220surround the gate stacks208and the gate spacers210allowing the gate stacks208to be removed and a replacement gate to be formed in the resulting cavity (also referred to as gate trench). Accordingly, in such embodiments, the gate stacks208are removed after forming the ILD layer220. The ILD layer220may also be part of an electrical interconnect structure that electrically interconnects various devices of the semiconductor structure200. In such embodiments, the ILD layer220acts as an insulator that supports and isolates the conductive traces. The ILD layer220may include any suitable dielectric material, such as a semiconductor oxide, a semiconductor nitride, a semiconductor oxynitride, other suitable dielectric materials, or combinations thereof. In some embodiments, the formation of the ILD layer220includes deposition and CMP to provide a planarized top surface.

Referring toFIG. 7, the method proceeds to an operation114for gate replacement. The gate stacks208are replaced by gate stacks230with high k dielectric and metal, therefore also referred to as high-k metal gates. As illustrated inFIG. 7, the fin-type active region spans from one end238A to another end238B along the Y direction. The gate replacement process may include etching, deposition and polishing. In the present example for illustration, exemplary gate stacks208a,208b,208cand208dare removed, resulting in gate trenches. In some embodiments, the gate stacks208are removed by an etching process, such as a wet etch, to selectively remove the gate stacks208. The etching process may include multiple etching steps to remove the dummy gate if more materials present. Then the gate materials, such as high k dielectric material and metal, are deposited in the gate trenches to form the gate stacks230, such as exemplary gate stacks230a,230b,230cand230d. A CMP is further implemented to polish and remove the excessive gate materials from the semiconductor structure200. The structure and the formation of the gate stacks230are further described below with a reference toFIGS. 8A and 8B.FIGS. 8A and 8Billustrate sectional views of an exemplary gate stack230in accordance with various embodiments.

The gate stack230(such as230b) is formed on the substrate202overlying the channel region of the fin active region206. The gate stack230includes a gate dielectric feature232and a gate electrode234disposed on the gate dielectric feature232. In the present embodiment, the gate dielectric feature232includes high-k dielectric material and the gate electrode234includes metal or metal alloy. In some examples, the gate dielectric layer and the gate electrode each may include a number of sub-layers. The high-k dielectric material may include metal oxide, metal nitride, such as LaO, AlO, ZrO, TiO, Ta2O5, Y2O3, SrTiO3(STO), BaTiO3(BTO), BaZrO, HfZrO, HfLaO, HfSiO, LaSiO, AlSiO, HfTaO, HfTiO, (Ba,Sr)TiO3(BST), Al2O3, Si3N4, oxynitrides (SiON), or other suitable dielectric materials. The gate electrode may include Ti, Ag, Al, TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, Al, WN, Cu, W, or any suitable materials. In some embodiments, different metal materials are used for nFET and pFET devices with respective work functions. The gate stack230is formed in the gate trench by a proper procedure, such as a procedure that includes deposition and CMP. Although it is understood that the gate stack230may be any suitable gate structure.

The gate dielectric feature232may further includes an interfacial layer sandwiched between the high-k dielectric material layer and the fin active region. The interfacial layer may include silicon oxide, silicon nitride, silicon oxynitride, and/or other suitable material. The interfacial layer is deposited by a suitable method, such as ALD, CVD, ozone oxidation, etc. The high-k dielectric layer is deposited on the interfacial layer (if the interfacial layer presents) by a suitable technique, such as ALD, CVD, metal-organic CVD (MOCVD), PVD, thermal oxidation, combinations thereof, and/or other suitable techniques. In some embodiments, the gate dielectric feature232is formed on the fin active region206at the operation108that forms the gate stack208. In this case, the gate dielectric feature232is shaped as illustrated inFIG. 8A. In some other embodiments, the gate dielectric feature232is formed in the high-k last process, in which the gate dielectric feature232is deposited in the gate trench at the operation118. In the case, the gate dielectric feature232is U-shaped, as illustrated inFIG. 8B.

The gate electrode234may include multiple conductive materials. In some embodiments, the gate electrode234includes a capping layer234-1, a blocking layer234-2, a work function metal layer234-3, another blocking layer234-4and a filling metal layer234-5. In furtherance of the embodiments, the capping layer234-1includes titanium nitride, tantalum nitride, or other suitable material, formed by a proper deposition technique such as ALD. The blocking layer234-2includes titanium nitride, tantalum nitride, or other suitable material, formed by a proper deposition technique such as ALD. In some examples, the block layers may not present or only one of them presents in the gate electrode.

The work functional metal layer234-3includes a conductive layer of metal or metal alloy with proper work function such that the corresponding FET is enhanced for its device performance. The work function (WF) metal layer1606is different for a pFET and a nFET, respectively referred to as an n-type WF metal and a p-type WF metal. The choice of the WF metal depends on the FET to be formed on the active region. For example, the semiconductor structure200includes a first active region for an nFET and another active region for a pFET, and accordingly, the n-type WF metal and the p-type WF metal are respectively formed in the corresponding gate stacks. Particularly, an n-type WF metal is a metal having a first work function such that the threshold voltage of the associated nFET is reduced. The n-type WF metal is close to the silicon conduction band energy (Ec) or lower work function, presenting easier electron escape. For example, the n-type WF metal has a work function of about 4.2 eV or less. A p-type WF metal is a metal having a second work function such that the threshold voltage of the associated pFET is reduced. The p-type WF metal is close to the silicon valence band energy (Ev) or higher work function, presenting strong electron bonding energy to the nuclei. For example, the p-type work function metal has a WF of about 5.2 eV or higher. In some embodiments, the n-type WF metal includes tantalum (Ta). In other embodiments, the n-type WF metal includes titanium aluminum (TiAl), titanium aluminum nitride (TiAlN), or combinations thereof. In other embodiments, the n-metal include Ta, TiAl, TiAlN, tungsten nitride (WN), or combinations thereof. The n-type WF metal may include various metal-based films as a stack for optimized device performance and processing compatibility. In some embodiments, the p-type WF metal includes titanium nitride (TiN) or tantalum nitride (TaN). In other embodiments, the p-metal include TiN, TaN, tungsten nitride (WN), titanium aluminum (TiAl), or combinations thereof. The p-type WF metal may include various metal-based films as a stack for optimized device performance and processing compatibility. The work function metal is deposited by a suitable technique, such as PVD.

The blocking layer234-4includes titanium nitride, tantalum nitride, or other suitable material, formed by a proper deposition technique such as ALD. In various embodiments, the filling metal layer234-5includes aluminum, tungsten or other suitable metal. The filling metal layer234-5is deposited by a suitable technique, such as PVD or plating.

Referring back toFIG. 7, the method100may also include an operation to form a hard mask236on top of the gate stacks230to protect the gate stacks230from loss during subsequent processing. The formation of the hard mask236includes recessing the gate stacks230by selective etching; deposition (such as CVD); and CMP according to the present example. The hard mask may include a suitable material different from the dielectric material of the ILD layers to achieve etching selectivity during the etching process to form contact openings. In some embodiments, the hard mask236includes silicon nitride. For examples, the hard mask236of silicon nitride (SiN) is formed by CVD using chemicals including Hexachlorodisilane (HCD or Si2Cl6), Dichlorosilane (DCS or SiH2Cl2), Bis(TertiaryButylAmino) Silane (BTBAS or C8H22N2Si) and Disilane (DS or Si2H6).

Referring toFIG. 9, the method100proceeds to an operation116by forming another ILD layer240similar to the ILD layer220in terms of composition and formation. For example, the formation of the ILD layer240may include deposition and CMP.

Referring toFIGS. 10A and 10B, the method100proceeds to an operation118by patterning the ILD layer240to form continuous openings242by lithography patterning and etching. A hard mask may be used to pattern the ILD layer240. The etching process etches through the ILD layers240and220until the source/drain features212are exposed.FIG. 10Ais a top view, in portion (only show the ILD layer240and the contact openings242).FIG. 10Bis a sectional view along the dashed line AA′.

Referring toFIGS. 11A and 11B, the method100proceeds to an operation120by forming a high-k dielectric material layer246on sidewalls of the continuous contact openings242by deposition such that the high-k dielectric material layer is formed on the sidewalls. In some embodiments, the high k-dielectric material is different from that of the gate stacks230. For examples, the high k-dielectric material layer246includes silicon nitride or other nitride-based dielectric material. In other examples, the high k-dielectric material layer246includes metal oxide dielectric material, such as Hf oxide, Ta oxide, Ti oxide, Zr oxide, Al oxide or a combination thereof. The high k-dielectric material layer246has a thickness ranging between 5 and 30 angstroms in some examples.FIG. 11Ais a top view, in portion (only show the ILD layer240; the high k-dielectric material layer246; and the openings242).FIG. 11Bis a sectional view along the dashed line AA′.

Referring toFIG. 12, the method100proceeds to an operation122by depositing a dielectric material layer248to fill in the continuous contact openings242. Instead of filling a conductive material to the contact openings242to form contact features, the dielectric material layer248is filled in the contact openings. The dielectric material layer248may have a composition different from those dielectric materials of the ILD layers. For example, the dielectric material layer248includes silicon oxide formed by flowable CVD (FCVD).

Referring toFIGS. 13A and 13B, the method100proceeds to an operation124by patterning the dielectric material layer248to define contact openings250, which will be filled to form contact features. The contact openings250are different from the openings242. The openings242are defined by the patterned ILD layer240while the contact openings250are collectively defined by the patterned ILD layer240, the patterned dielectric material layer248and the high-k dielectric material layer246.FIG. 13Ais a top view, in portion (only show the ILD layer240; the high k-dielectric material layer246; the dielectric material layer248and the contact openings250).FIG. 13Bis a sectional view along the dashed line AA′. In the operation124, the dielectric material layer248is patterned by lithography process and etching. In some example, a patterned mask is formed on the dielectric material layer248by lithography process and etching, in which the etching process selectively removes the dielectric material layer248so that the source/drain features212are exposed.

FIG. 13Cis a top view of the semiconductor structure200constructed according to other embodiments.FIG. 13Cis similar toFIG. 13Abut it zooms out to include large area of the semiconductor structure200so for better illustrating both the original openings242and the contact openings250. The openings242is defined in the ILD layer240and spans to continuous long openings while the contact openings250are defined collectively by the high-k dielectric material layer246and the dielectric material layer248. Especially, the high-k dielectric material layer246only on sidewalls of the openings250along the X direction but not on the end sidewalls along the Y direction. Furthermore, thus formed contact openings250have elongated shape extending through one or more FinFETs, as illustrated inFIG. 13C. As the high-k dielectric material layer246is absent from the ends of the contact openings250, the contact features to be formed in the openings250will have more contact areas for reduced contact resistance and enlarged margin for improved process windows. Therefore, it enlarges the landing margin between slot contacts to FinFET source/drain regions.

Referring toFIG. 14, the method100proceeds to an operation126by etching back the high-k dielectric material layer246such that the source/drain features212are exposed within the openings. During the etching-back process, the top surface of the high-k dielectric material layer246is also recessed as well.

Referring toFIGS. 15A and 15B, the method100proceeds to an operation128by forming contact features260in the contact openings250. The formation of the contact features260includes deposition of conductive material and CMP according to some examples. The deposition may be implemented through proper technique, such as physical vapor deposition (PVD), plating, CVD or other suitable method. The openings250are filled with one or more conductive material, such as Ti, TiN, TaN, Co, W, Al, Cu, or combination. As noted above, thus formed contact features260has elongated shape with length to width ratio greater than 2 for reduced contact resistance and improved process window. Especially, the elongated contact feature260is asymmetric along its width direction and its length direction. As illustrated inFIG. 15B, the elongated contact feature260includes two long edges262laterally contacting the high-k dielectric material layer246and two short edges (also referred to as ends)264laterally contacting the dielectric material layer248. In other words, the sidewalls of the two ends264are free of the high-k dielectric material layer246.

In some embodiments, prior to the filling in the conductive material in the openings250, silicide may be formed on the source/drain features212to further reduce the contact resistance. The silicide includes silicon and metal, such as titanium silicide, tantalum silicide, nickel silicide or cobalt silicide. The silicide may be formed by a process referred to as self-aligned silicide (or salicide). The process includes metal deposition, annealing to react the metal with silicon, and etching to remove unreacted metal.

Other fabrication steps may be implemented before, during and after the operations of the method. For example, various metal lines and vias in the interconnect structure are further formed on the semiconductor structure to electrically connect various FinFETs and other devices into a functional circuit by proper technique, such as dual damascene process. In various patterning processes above in the method100, each patterning procedure may be implemented through double patterning or multiple patterning.

The present disclosure provides a contact structure and a method making the same in accordance with various embodiments. Thus formed contact features have elongated shape and asymmetric structure along its length direction and width direction. The high-k dielectric material layer is disposed on length sidewalls of the contact features but absent from two ends. The elongated contact features will have more contact areas for reduced contact resistance and enlarged margin for improved process windows. Therefore, it enlarges the landing margin between slot contacts to FinFET source/drain regions. This allows the designer to push the line-end space rule and therefore increases the line end landing areas of contacts to fin active regions. The disclosed structure can be used in various applications where FinFETs are incorporated for enhanced performance. For example, the FinFETs with multi-fin devices can be used to form static random access memory (SRAM) cells. In other examples, the disclosed structure can be incorporated in various integrated circuits, such as logic circuit, dynamic random access memory (DRAM), flash memory, or imaging sensor.

Thus, the present disclosure provides a semiconductor structure in accordance with some embodiments. The semiconductor structure includes a fin-type active region extruded from a semiconductor substrate; a gate stack disposed on the fin-type active region; a source/drain feature formed in the fin-type active region and disposed on a side of the gate stack; an elongated contact feature landing on the source/drain feature; and a dielectric material layer disposed on sidewalls of the elongated contact feature and free from ends of the elongated contact feature. The sidewalls of the elongated contact feature are parallel with the gate stack

The present disclosure provides a semiconductor structure in accordance with some other embodiments. The semiconductor structure includes a first fin-type active region extruded from a semiconductor substrate and spanning from a first end to a second end along a first direction; a second fin-type active region extruded from the semiconductor substrate and spanning from a third end to a fourth end along the first direction; a first gate stack and a second gate stack each disposed on the first and second fin-type active regions, wherein the first and second gate stacks space away in the first direction and extend along a second direction that is orthogonal to the first direction; a first source/drain feature formed in the first fin-type active region and interposed between the first and second gate stacks; a second source/drain feature formed in the second fin-type active region and interposed between the first and second gate stacks; an elongated contact feature extending along the second direction and landing on the first and second source/drain features; and a dielectric material layer disposed on sidewalls of the elongated contact feature and is free from two ends of the elongated contact feature. The sidewalls of the elongated contact feature extend along the second direction.

The present disclosure provides a method forming an integrated circuit structure in accordance with some embodiments. The method includes forming a shallow trench isolation (STI) structure in a semiconductor substrate of a first semiconductor material, thereby defining a plurality of fin-type active regions separated from each other by the STI structure; forming gate stacks on the fin-type active regions; forming an inter-layer dielectric (ILD) layer filling in gaps between the gate stacks; patterning the ILD layer to form a trench between adjacent two of the gate stacks; depositing a first dielectric material layer that is conformal in the trench; filling the trench with a second dielectric material layer; patterning the second dielectric material layer to form a contact opening; and filling a conductive material in the contact opening to form a contact feature.