Fin cut for tight fin pitch by two different sit hard mask materials on fin

Methods that enable fin cut at very tight pitch are provided. After forming a first set of paired sidewall image transfer (SIT) spacers and a second set of paired SIT spacers composed of different materials, portions of the first set of the paired SIT spacers can be selectively removed without adversely affecting the second set of the paired SIT spacers, even portions of both sets of the paired SIT spacers are exposed by the cut mask due to the different etching characteristics of the different materials.

BACKGROUND

The present application relates to semiconductor device fabrication. More particularly, the present application relates to semiconductor fin formation by using two sets of spacers having different etching characteristics in a sidewall image transfer (SIT) process.

As integrated circuits continue to scale downward in size, fin field effect transistors (FinFETs) are becoming increasingly attractive to be used in smaller nodes, e.g., the 22 nm node and beyond. FinFETs can achieve higher drive currents with increasingly smaller dimensions as compared to conventional planar FETs. In order to meet the density targets of advanced nodes, semiconductor fins are typically formed utilizing a sidewall image transfer (SIT) process since the same provides sub-lithographic line widths (i.e., less than 40 nm). In a typical SIT process, spacers are formed on each sidewall of a mandrel structure that is formed on a topmost semiconductor material of a substrate. The mandrel structure is removed and the remaining spacers are used as an etch mask to etch the topmost semiconductor material of the substrate. The spacers are then removed after each semiconductor fin has been formed.

One problem that is associated with forming semiconductor fins at tight pitch is that the process window for cutting of unwanted semiconductor fins is quite narrow. More specifically, the space available between fins at a tight pitch decreases the process window for placement of a fin cut mask edge in between fins. As the pitch of the semiconductor fins decreases, it becomes difficult to remove unwanted semiconductor fins without adversely affecting adjacent device fins due to the process variation and small process margin of lithographic processes. As such, a method is needed that is capable of forming semiconductor fins in which the process window for cutting unwanted semiconductor fins is improved.

SUMMARY

The present application provides methods that enable fin cut at very tight pitch. After forming a first set of paired SIT spacers and a second set of paired SIT spacers composed of different materials, portions of the first set of the paired SIT spacers can be selectively removed without adversely affecting the second set of the paired SIT spacers, even portions of both sets of the paired SIT spacers are exposed by the cut mask due to the different etching characteristics of the different materials.

In one aspect of the present application, a method of forming a semiconductor structure is provided. The method includes first forming a plurality of mandrel structures on a substrate, and then forming first spacers on sidewalls of the plurality of mandrel structures. Next, sacrificial spacers are formed on sidewalls of the first spacers. After forming second spacers on sidewalls of the sacrificial spacers, the plurality of mandrel structures and the sacrificial spacers are removed selective to the first spacers and the second spacers. Next, a cut mask including at least one opening therein is formed over the first spacers, the second spacers and exposed surfaces of the substrate. The at least one opening in the cut mask exposes portions of the first spacers and portions of the second spacers. Next, exposed portions of the first spacers are removed selective to exposed portions of the second spacers.

In another aspect of the present application, a semiconductor structure is provided. The semiconductor structure includes a plurality of semiconductor fins located on a substrate and arranged in pairs. Each pair of the plurality of semiconductor fins has a first pitch. Adjacent semiconductor fins in the plurality of semiconductor fins have a pitch the same as or 3n times the first pitch, and n is an integer greater than 0.

DETAILED DESCRIPTION

Although the following description and drawings of the present application disclose utilizing the methods of the present application for forming semiconductor fins, the present application is not limited to only the formation of semiconductor Fins. Instead, the present application can be used in forming other types of structures.

Referring first toFIG. 1, there is illustrated an exemplary semiconductor structure comprising a plurality of mandrel structures18located on a surface of a substrate10in accordance with an embodiment of the present application.

In one embodiment of the present application and as illustrated in the drawings of the present application, the substrate10is a semiconductor-on-insulator (SOI) substrate that includes, from bottom to top, a handle substrate12, an insulator layer14and a top semiconductor layer16. In some embodiments, the handle substrate12is optional and can be omitted. In another embodiment of the present application, the substrate10can be comprised of a bulk semiconductor substrate. By “bulk semiconductor substrate” it is meant a semiconductor material that is comprised entirely of a semiconductor material. For example, the substrate10shown inFIG. 1would consist entirely of the top semiconductor layer16.

When present, the handle substrate12can include a semiconductor material, a conductive material, and/or a dielectric material. The handle substrate12can provide mechanical support to the insulator layer14, and the top semiconductor layer16of an SOI substrate. The thickness of the handle substrate12can be from 30 microns to 2 mm, although lesser and greater thicknesses can also be employed.

When present, the insulator layer14may be a crystalline, or non-crystalline, oxide or nitride. In one embodiment, the insulator layer14is an oxide such as, for example, silicon oxide. The insulator layer14may be a single continuous layer that spans the entirety of the handle substrate12or it may be discontinuous. When a discontinuous insulator region is present, the insulator region exists as an isolated island that is surrounded by semiconductor material. The thickness of the insulator layer14can be from 50 nm to 5 microns, although lesser and greater thicknesses can also be employed.

The top semiconductor layer16(or the bulk semiconductor substrate) can include a single crystalline semiconductor material or a polycrystalline material. In one embodiment, the top semiconductor layer16(or the bulk semiconductor substrate) can include an elemental semiconductor material such as Si or Ge, a semiconductor material primarily composed of Group IV elements such as a silicon-germanium alloy or a silicon-carbon alloy, a III-V compound semiconductor material, a II-VI compound semiconductor material, or an organic semiconductor material. In one embodiment, the top semiconductor layer16(or the bulk semiconductor substrate) can include a single crystalline elemental semiconductor material, a single crystalline semiconductor material primarily composed of Group IV elements, a single crystalline III-V compound semiconductor material, a single crystalline II-VI compound semiconductor material, or a single crystalline organic semiconductor material. In another embodiment, the top semiconductor layer16(or the bulk semiconductor substrate) can consist essentially of undoped single crystalline silicon or single crystalline silicon doped with p-type dopant atoms or n-type dopant atoms.

The mandrel structures18can include any material (semiconductor, dielectric or conductive) that can be selectively removed from the structure during a subsequently performed etching process. In one embodiment, the mandrel structures18may be composed of amorphous silicon, polysilicon, amorphous or polycrystalline germanium, an amorphous or polycrystalline silicon-germanium alloy material, amorphous carbon, diamond-like carbon, or organosilicate glass. In another embodiment, the mandrel structures18may be composed of a metal such as, for example, Al, W, or Cu.

The mandrel structures18can be formed by first depositing a blanket layer of a mandrel material on the entire topmost surface of substrate10(not shown). The mandrel material layer can be formed, for example, by chemical vapor deposition (CVD) or plasma enhanced chemical vapor deposition (PECVD). The thickness of the mandrel material layer can be from 50 nm to 300 nm, although lesser and greater thicknesses can also be employed. Following deposition of the mandrel material layer, the mandrel material layer can be patterned by lithography and etching. The patterning of the mandrel material layer can be performed, for example, by applying a photoresist layer (not shown) above the mandrel material layer, lithographically patterning the photoresist layer to define a set of areas covered by the patterned photoresist layer, and transferring the pattern in the photoresist layer into the mandrel material layer by an anisotropic etch. The anisotropic etch can be selective to the semiconductor materials of the top semiconductor layer16of the substrate10. The patterned portions of the mandrel material layer constitute the plurality of mandrel structures18.

Each mandrel structure18that is formed may have a rectangular shape in cross-section with a constant width. In one embodiment, the width of each mandrel structure18is from 10 nm to 50 nm, although lesser and greater widths can also be employed. The height of each mandrel structure18that is formed is from 50 nm to 300 nm, although lesser and greater height can also be employed. In the embodiment that is illustrated inFIG. 1, the mandrel structures18are arranged parallel to each other to form an array of periodic patterns that is repeated along a direction perpendicular to an elongated direction (i.e., lengthwise direction) of each mandrel structure18. In one embodiment, the mandrel structures18can have a pitch from 50 nm to 200 nm, although lesser and greater pitch can also be employed. Though the mandrel structures18as shown inFIG. 1have a constant pitch, in some embodiments of the present application, the mandrel structures18may have a non-constant pitch.

Optionally, a pad layer which may be comprised of silicon nitride or a bilayer comprised of a silicon nitride layer and an underlying silicon dioxide layer can be deposited on the top semiconductor layer16before the deposition of the mandrel layer. The pad layer, when present, protects the top semiconductor layer16during the subsequent patterning processes.

Referring now toFIG. 2, there is illustrated the exemplary semiconductor structure ofFIG. 2after forming a first spacer material layer20L. The first spacer material layer20L may be conformally deposited over mandrel structures18and exposed surfaces of substrate10by a conformal deposition process, such as, for example, CVD. The thickness of the first spacer material layer20L may vary depending upon the desired width of final semiconductor fins structures to be formed in the top semiconductor layer16of structure10, and can be from 5 nm to 15 nm, although lesser and greater thicknesses can also be employed.

The first spacer material layer20L may include any dielectric material that has a different etching characteristics comparing to the material of the mandrel structures18in embodiments in which the mandrel structures18comprise a dielectric material, so that the mandrel structures18can be selectively removed with respect to the first spacer subsequently formed.

In one embodiment of the present application, the first spacer material layer20L may include a nitride such as silicon nitride or an oxide such as silicon dioxide.

In another embodiment of the present application, the dielectric material that is used in providing the first spacer material layer20L may be a dielectric material having a dielectric constant of less than silicon dioxide (such dielectric materials may be referred to herein as low k). Examples of dielectric materials having a low dielectric constant include, but are not limited to, silsesquioxanes, C-doped oxides (i.e., organic silicates) that include atoms of Si, C, O and H, and thermosetting polyarylene ethers. The term “polyarylene” is used throughout the present application to denote aryl moieties or inertly substituted aryl moieties which are linked together by bonds, fused rings, or inert linking groups such as, for example, oxygen, sulfur, sulfone, sulfoxide, carbonyl and the like.

In yet another embodiment of the present application, the dielectric material that is used in providing the first spacer material layer20L may be a dielectric material having a dielectric constant that is equal to or even greater than that of silicon dioxide (such dielectric materials may be referred to herein as high k). Examples of high k dielectric materials include, for example, a dielectric metal oxide such as, for example, HfO2, ZrO2, La2O3, Al2O3, TiO2, SrTiO3, LaAlO3, Y2O3, HfOxNy, ZrOxNy, La2OxNy, Al2OxNy, TiOxNy, SrTiOxNy, LaAlOxNy, Y2OxNy, SiON, SiNx, a silicate thereof, and an alloy thereof. Each value of x is independently from 0.5 to 3 and each value of y is independently from 0 to 2.

Referring now toFIG. 3, there is illustrated the exemplary semiconductor structure ofFIG. 2after removing horizontal portions of the first spacer material layer20L to provide first spacers20. Each first spacer20comprises a remaining portion of the first spacer material layer20L on each sidewall of the mandrel structures18. The removal of the horizontal portions of the first spacer material layer20L can be achieved utilizing an anisotropic etch, such as, for example, reactive ion etch (RIE).

After removal of the horizontal portions of the first spacer material layer20L, a topmost surface of each mandrel structure18is exposed and is coplanar with a topmost surface of each first spacer20. A width of each first spacer, as measured at its base, can be from 5 nm to 10 nm, although lesser and greater thicknesses can also be employed.

Referring now toFIG. 4, there is illustrated the exemplary semiconductor structure ofFIG. 3after forming a sacrificial spacer22on each sidewall of the first spacers20. The sacrificial spacers22that are employed in the present application may comprise a sacrificial spacer material that can be selectively removed with respect to materials of the first spacers20and the second spacer to be subsequently formed. The sacrificial spacer material can be the same or different from the material used for the mandrel structures18. In one embodiment, the sacrificial spacers22include amorphous carbon.

The sacrificial spacers22can be formed by conformally depositing a sacrificial spacer material over the mandrel structures18, the first spacers20and exposed surfaces of substrate10utilizing a conformal deposition process such as, for example, CVD, PECVD, or ALD. After depositing the sacrificial spacer material to provide a sacrificial spacer material layer (not shown), the sacrificial spacer material layer is anisotropically etched to remove horizontal portions of the sacrificial spacer layer. After removal of the horizontal portions of the sacrificial spacer material layer, the topmost surface of each mandrel structure18and each first spacer20is exposed and is coplanar with a topmost surface of each sacrificial spacer22. The remaining vertical portions of the sacrificial spacer layer present on sidewalls of the first spacer20constitute the sacrificial spacers22. A width of each sacrificial spacer22that is formed can be from 10 nm to 50 nm, although lesser and greater thicknesses can also be employed. In one embodiment and as shown inFIG. 4, each sacrificial spacer22has a width substantially the same as that of each mandrel structure18. The term “substantially the same” as used herein in connection with the widths denotes that the width variations are within 10%. In another embodiment of the present application, each sacrificial spacer22may have a width different from that of each mandrel structure18.

Referring now toFIG. 5, there is illustrated the exemplary semiconductor structure ofFIG. 4after forming a second spacer24on each exposed sidewall surface of the sacrificial spacers22. The second spacer24that is employed in the present application may comprise a dielectric material that is different from the materials of the first spacer20and sacrificial spacer22, so that first spacer20and the sacrificial spacer22can be selectively removed with respect to the second spacer24. In one embodiment and when the first spacer20is composes of silicon nitride and the sacrificial spacer22is composed of amorphous carbon, the second spacer24may be composed of a high k dielectric material, such as, for example, HfO2.

The second spacer24can be formed by conformally depositing a second spacer material over the mandrel structures18, the first spacer20, the sacrificial spacer22and exposed surfaces of substrate10utilizing a conformal deposition process such as, for example, CVD, PECVD, or ALD to provide a second spacer material layer (not shown). As shown inFIG. 5, the thickness of the second spacer material layer is controlled such that the second spacer material layer does not entirely fill the spaces between adjacent sacrificial spacers22. The thickness of the second spacer material layer that is formed can be from 5 to 10 nm, although lesser and greater thicknesses can also be employed.

Subsequently, horizontal portions of the second spacer material layer are removed utilizing an anisotropic etch forming the second spacers24on sidewalls of the sacrificial spacers22. After removal of the horizontal portions of the second spacer material layer, the topmost surface of each mandrel structure18, each first spacer20and each sacrificial spacer22is exposed and is coplanar with a topmost surface of each second spacer24.

The width of each second spacer24, as measured from its base, can be from 5 nm to 10 nm, although lesser and greater thicknesses can also be employed. In one embodiment and as shown inFIG. 5, each second spacer24has a width substantially the same as that of each first spacer20. In another embodiment of the present application, each second spacer24may have a width different from that of each first spacer20. In one embodiment, a uniform space26can be formed between each adjacent second spacers24. In one embodiment, each space26has a width that is defined by the distance between each adjacent second spacers24the same as that of each mandrel structure18and each sacrificial spacer22.

Referring now toFIG. 6, there is illustrated the exemplary semiconductor structure ofFIG. 5after removing the mandrel structures18and the sacrificial spacers22from the structure. At least one etching process, either a wet etching or a dry etching, can be performed to remove each mandrel structure18and each sacrificial spacer22selective to each first spacer20and each second spacer24. The at least one etching process can be an anisotropic or an isotropic etch. Removal of the mandrel structures18and the sacrificial spacers22provides a plurality of first spacers20and a plurality of second spacers24which are arranged in a way such that every adjacent pairs of the first spacers20are separated from each other by a pair of second spacers24, and vice versa. In one embodiment and as shown inFIG. 6, each first spacer20has a width substantially the same as that of each second spacer24, although they may be different from each other. Also shown inFIG. 6, the spacing between each adjacent first spacers20, second spacers24and first and second spacers are substantially the same, although they may be different from each other.

Referring now toFIG. 7, there is illustrated the exemplary semiconductor structure ofFIG. 6after forming a first cut mask28over the first spacers20and second spacers24. In one embodiment, the first cut mask28can be a photoresist layer that is lithographically patterned to form an opening that exposes unwanted pairs of first spacers20. The opening also exposes second spacers24adjacent to or between the unwanted pairs of first spacers20.

Referring now toFIG. 8, there is illustrated the exemplary semiconductor structure ofFIG. 7after removing the unwanted pairs of first spacers20that are not covered by the first cut mask28. Physically exposed unwanted pairs of first spacers20may be removed by an anisotropic etch. The chemistry of the anisotropic etch is selected such that the material of the first spacers20is etched during the anisotropic etch, while the material of the second spacers24is not etched. A vacancy20X is thus provided at a location from which each first spacer20is removed. Because the first and the second spacers20,24of the present application are composed of two different materials possessing different etching characteristics, the etching process used to remove unwanted first spacers20will not adversely affect or cut the exposed second spacers24. The second spacers24are left intact after the etching process. The cut mask overlay requirements are thus relaxed. This would allow fin cut at a very tight pitch.

In one embodiment and as shown inFIG. 8, when a width of each first spacer20is the same as that of each second spacer24and a spacing between each adjacent first spacers20is the same as that between each adjacent second spacers24and that between each adjacent first and second spacers20,24, after removing a pair of first spacers20that are located between adjacent pairs of second spacers24, in the exposed region, the distance between center points of one second spacer24in one pair of second spacers24and an adjacent second spacer24in an adjacent pair of second spacers24(i.e., pitch P3) is three times the distance between center points of each pair of first spacers20(i.e., pitch P1) or the distance between center points of each pair of each pair of second spacers24(i.e., pitch P2).

Subsequently, the first cut mask28is removed selective to the first and the second spacers20,24. In one embodiment and when the first cut mask28is a patterned photoresist layer, the first cut mask28can be removed by ashing.

Unwanted pairs of the second spacers24can also be removed by performing the processing steps described above with respect to the first spacers20. Referring now toFIG. 9, there is illustrated the exemplary semiconductor structure ofFIG. 8after forming a second cut mask30over the first spacers20and second spacers24. In one embodiment, the second cut mask30can be a photoresist layer that is lithographically patterned to form an opening that exposes an unwanted pair of second spacers24. The opening also exposes first spacers20adjacent to the unwanted pair of second spacers24.

Referring now toFIG. 10, there is illustrated the exemplary semiconductor structure ofFIG. 9after removing the unwanted pair of second spacers24that are not covered by the second cut mask30. Physically exposed unwanted pair of second spacers24may be removed by an anisotropic etch. The chemistry of the anisotropic etch is selected such that the material of the second spacers24is etched during the anisotropic etch, while the material of the first spacers20is not etched. A vacancy24X is thus provided at a location from which each second spacer24is removed.

In one embodiment and as shownFIG. 10, after one pair of second spacers24is removed, the distance between center points of one first spacer20in one pair of the first spacers20and an adjacent second spacer24in an adjacent pair of second spacer (i.e., pitch P3) is six times the first pitch.

Subsequently, the second cut mask30is removed selective to the first and the second spacers20,24. In one embodiment and when the second cut mask28is a patterned photoresist layer, the second patterned mask layer28can be removed by ashing.

Referring now toFIG. 11, there is illustrated the exemplary semiconductor structure ofFIG. 10after patterning the substrate10using remaining first spacers20and second spacers24as an etch mask. The patterning of the substrate10can be performed by utilizing an anisotropic etching process. In one embodiment of the present application and as is illustrated inFIG. 11, the patterning of the substrate10includes patterning of the topmost semiconductor layer16to provide a plurality of first semiconductor fins32having a width that is the same as the width of each first spacer20and a plurality of second semiconductor fin34having a width that is the same as the width of each second spacer24. Each first semiconductor fin32and each second semiconductor fin34comprises a remaining portion of the topmost semiconductor layer16.

As used herein, a “semiconductor fin” refers to a semiconductor structure including a portion having a shape of a rectangular parallelepiped. The direction along which a semiconductor fin laterally extends the most is herein referred to as a “lengthwise direction” of the semiconductor fin. The height of each first semiconductor fin32and each second semiconductor fin34can be in a range from 5 nm to 300 nm, although lesser and greater heights can also be employed. The width of each first semiconductor fin32and each second semiconductor fin can be in a range from 5 nm to 50 nm, although lesser and greater widths can also be employed. The width of each first semiconductor fin32can be the same or different than the width of each second semiconductor fin34. Multiple first semiconductor fins32and multiple second semiconductor fins34may be arranged such that each semiconductor fin has the same lengthwise direction, and is laterally spaced from each other along a horizontal direction that is perpendicular to the lengthwise direction. In this case, the horizontal direction that is perpendicular to the common lengthwise direction is referred to as a “widthwise direction.” Each semiconductor fin (32,34) includes a pair of parallel sidewalls along the lengthwise direction and a pair of parallel sidewalls along the widthwise direction and at each end segment of the semiconductor fin (32,34).

Referring now toFIG. 12, there is illustrated the first exemplary semiconductor structure ofFIG. 11after removing the remaining first spacers20and second spacers24. The remaining first and second spacers20,24can be removed utilizing at least one etch which can be an anisotropic or an isotropic etch. Alternatively, the remaining pairs of the first and the second spacer20,24can also be removed by a chemical mechanical planarization (CMP) process. The removal of the remaining first and second spacers20,24exposes topmost surfaces of the first semiconductor fins32and the second semiconductor fins34.

At this point of the present application, a functional gate structure utilizing a gate first or a gate last process can be performed to provide FinFET structures. It is noted that while the above describes a method of forming semiconductor fins from a semiconductor substrate, the method of the present application can be applied to pattern any other type substrate.