MODIFIED FIN CUT AFTER EPITAXIAL GROWTH
A method of forming a gate located above multiple fin regions of a semiconductor device. The method may include removing unwanted fin structures after epitaxially growing junctions.
The present invention relates to semiconductor devices, and particularly to forming source/drain regions and connections on fin field effect transistors.
Field effect transistors (FETs) are commonly employed in electronic circuit applications. FETs may include a source region and a drain region spaced apart by a semiconductor channel region. A gate, including a gate dielectric layer, a work function metal layer, and a metal electrode, may be formed above the channel region. By applying voltage to the gate, the conductivity of the channel region may increase and allow current to flow from the source region to the drain region.
Fin field effect transistors (FinFETs) are an emerging technology which may provide solutions to field effect transistor (FET) scaling problems at, and below, the 22 nm node. FinFET structures may include at least a narrow semiconductor fin gated on at least two sides of each of the semiconductor fin, as well as a source region and a drain region adjacent to the fin on opposite sides of the gate. FinFET structures having n-type source and drain regions may be referred to as nFinFETs, and FinFET structures having p-type source and drain regions may be referred to as pFinFETs.
In some FinFET structures, different materials may be used for the fins of pFinFETs and nFinFETs in order to improve device performance. However, a material that may improve pFinFET performance may reduce nFET performance, and vice versa. For example, while pFinFET performance may be improved by forming fins made of silicon-germanium, nFinFET performance may instead be improved by forming fins made of undoped or carbon-doped silicon and may be degraded by forming fins made of silicon-germanium. Further, pFinFETs and nFinFETs are fabricated on the same substrate.
BRIEF SUMMARYAn embodiment of the invention may include a method of forming a semiconductor structure. The method may include forming fins in a first region, an intermediate region and second region of a substrate. The method may include forming a gate over the at least one fin in the first region of the substrate, the at least one fin in the second region of the substrate and the at least one fin in the intermediate region of the substrate. The method may include forming a first mask above at least the intermediate region of the substrate and the second region of the substrate and epitaxially growing a first junction on the at least one fin located in the first region of the substrate. The method may include removing the first mask, forming a second mask above at least the intermediate region of the substrate and the first region of the substrate and epitaxially growing a second junction on the at least one fin located in the second region of the substrate. The method may include removing the second mask and forming a third mask above the first region of the substrate, the second region of the substrate and the gate. The method may include removing material from the unmasked region and removing the third mask.
Another embodiment of the invention may include a semiconductor structure. The structure may include a first plurality of fins located in a first region of a substrate, where a first junction is located on the first set of fins. The structure may include a second plurality of fins located in a second region of the substrate, where a second junction is located on a second set of fins. The structure may include an intermediate plurality of fins located in an intermediate region of the substrate, where the intermediate region is located between the first and second region. The structure may include a gate running substantially perpendicular to the first plurality of fins, the intermediate plurality of fins, and the third plurality of fins.
Elements of the figures are not necessarily to scale and are not intended to portray specific parameters of the invention. For clarity and ease of illustration, dimensions of elements may be exaggerated. The detailed description should be consulted for accurate dimensions. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements.
DETAILED DESCRIPTIONExemplary embodiments now will be described more fully herein with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments.
For purposes of the description hereinafter, terms such as “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shall relate to the disclosed structures and methods, as oriented in the drawing figures. Terms such as “above”, “overlying”, “atop”, “on top”, “positioned on” or “positioned atop” mean that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements, such as an interface structure may be present between the first element and the second element. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements.
In the interest of not obscuring the presentation of embodiments of the present invention, in the following detailed description, some processing steps or operations that are known in the art may have been combined together for presentation and for illustration purposes and in some instances may have not been described in detail. In other instances, some processing steps or operations that are known in the art may not be described at all. It should be understood that the following description is rather focused on the distinctive features or elements of various embodiments of the present invention.
FinFET structures may be created using sidewall image transfer as a way to create a pattern to transfer the desired fin pattern onto an underlying substrate. Such structures may create a substrate that contains multiple regions, with high variability of aspect ratios between each region. This may result in a non-uniform deposition of material from one region to, as fluids flow more slowly into voids with high aspect ratios, and may create uneven densities between the regions. This may create problems during chemical mechanical planarization (CMP), as less dense regions would be removed much more easily than other regions, leading to an uneven surface. Additionally, the variable density may ultimately impact the performance of the device, due to the differences in the resulting structures across the device. By performing deposition techniques across regions with substantially similar aspect ratios, structures may be created having substantially similar densities across the device.
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The mandrel 110 may be generated using known photolithography and masking techniques. During this step, a mandrel layer may be formed on top of the hardmask layer 106.
The mandrel layer may include amorphous silicon or any silicon based compound, for example, silicon nitride, silicon oxide, or silicon carbon, or alternatively amorphous carbon. The mandrel layer may preferably include a material that is different enough from the material of the sidewall spacers (described below) and the material of the hardmask layer 106 so that it may be selectively removed. The particular material chosen may partly depend upon the desired pattern to be formed and the materials chosen in subsequent steps discussed below. In one embodiment, the mandrel layer may be formed with a vertical thickness ranging from about 30 nm to about 150 nm. The mandrel layer may then be lithographically patterned to create the mandrel 110. The mandrel 110 may be formed by applying known patterning techniques involving exposing a photo-resist and transferring the exposed pattern of the photo-resist by etching the mandrel layer.
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Next, the substrate 108 may then be etched to a desired depth, form at least one fin body 120. The desired depth may depend on the ultimate function of the semiconductor structure. A directional etching technique such as a reactive-ion-etching technique may be used to etch the substrate 108. In one embodiment, the substrate 108 may be etched with a reactive-ion-etching technique using a chlorine or a bromine based etchant. In the present step, the hardmask layer 106 may function as a mask, and may have a high etch-selectivity relative to the substrate 108. Furthermore, the sidewall spacers 114 and the hardmask layer 106 may be removed in subsequent steps using any suitable removal technique known in the art.
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In a gate-first process, the gate dielectric layer may include any suitable insulating material including, but not limited to: oxides, nitrides, oxynitrides or silicates including metal silicates and nitrided metal silicates. In one embodiment, the gate dielectric may include a high-k oxide such as, for example, silicon oxide (SixOy), hafnium oxide (HfxOy), zirconium oxide (ZrxOy), aluminum oxide (AlxOy), titanium oxide (TixOy), lanthanum oxide (LaxOy), strontium titanium oxide (SrxTiyOz), lanthanum aluminum oxide (LaxAlyOz), and mixtures thereof. The gate dielectric layer may be deposited over the fin 140 using any suitable deposition technique known the art, including, for example, atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), molecular beam deposition (MBD), pulsed laser deposition (PLD), or liquid source misted chemical deposition (LSMCD). The gate electrode may be made of gate conductor materials including, but not limited to, zirconium, tungsten, tantalum, hafnium, titanium, aluminum, ruthenium, metal carbides, metal nitrides, transition metal aluminides, tantalum carbide, titanium carbide, tantalum magnesium carbide, or combinations thereof. The gate electrode may be formed using any suitable metal deposition technique, including, for example, CVD, PVD, and ALD, sputtering, and plating.
In a gate-last process, the gate layer may include a sacrificial gate (not shown) that may be later removed and replaced by a gate dielectric layer and a gate electrode such as those of the gate-first process described above. In an exemplary embodiment, the sacrificial gate may be made of a polysilicon material with a sacrificial dielectric material (e.g., silicon oxide) formed using known deposition techniques known in the art, including, for example, ALD, CVD, PVD, MBD, PLD, LSMCD, sputtering, and plating. Other suitable materials and methods of forming a sacrificial gate are known in the art.
A spacer may be formed on the vertical surfaces of the gate layer and/or the fin. The spacer may be made of any suitable insulating material, such as silicon nitride, silicon oxide, silicon oxynitrides, or a combination thereof, and may have a thickness ranging from 2 nm to approximately 100 nm. In a preferred embodiment, the spacer may be made of silicon nitride and have a thickness ranging from approximately 2 nm to approximately 25 nm. The spacer may be formed by any method known in the art, including depositing a conformal silicon nitride layer over the gate layer, and performing an anisotropic etch to remove the material from the horizontal surfaces of the structure. Further, in various embodiments, the spacer may include one or more layers.
In some embodiments, the hard cap (not shown) may be located above the gate layer. The hard cap may be made of an insulating material, such as, for example, silicon nitride or silicon oxide, capable of protecting the gate layer during subsequent processing steps. In embodiments where the substrate 108 is a bulk substrate, an insulating layer may be deposited around the base of the fin prior to forming the gate layer to insulate the gate layer from the substrate 108. Further, while only a single gate layer is shown, some embodiments may include more than one gate above the fin 140.
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The terms “epitaxial growth and/or deposition” and “epitaxially formed and/or grown” mean the growth of a semiconductor material on a deposition surface of a semiconductor material, in which the semiconductor material being grown may have the same crystalline characteristics as the semiconductor material of the deposition surface. In an epitaxial deposition process, the chemical reactants provided by the source gases are controlled and the system parameters are set so that the depositing atoms arrive at the deposition surface of the semiconductor substrate with sufficient energy to move around on the surface and orient themselves to the crystal arrangement of the atoms of the deposition surface. Therefore, an epitaxial semiconductor material may have the same crystalline characteristics as the deposition surface on which it may be formed. For example, an epitaxial semiconductor material deposited on a {100} crystal surface may take on a {100} orientation. In some embodiments, epitaxial growth and/or deposition processes may be selective to forming on semiconductor surfaces, and may not deposit material on dielectric surfaces, such as silicon dioxide or silicon nitride surfaces.
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The terms “epitaxial growth and/or deposition” and “epitaxially formed and/or grown” mean the growth of a semiconductor material on a deposition surface of a semiconductor material, in which the semiconductor material being grown may have the same crystalline characteristics as the semiconductor material of the deposition surface. In an epitaxial deposition process, the chemical reactants provided by the source gases are controlled and the system parameters are set so that the depositing atoms arrive at the deposition surface of the semiconductor substrate with sufficient energy to move around on the surface and orient themselves to the crystal arrangement of the atoms of the deposition surface. Therefore, an epitaxial semiconductor material may have the same crystalline characteristics as the deposition surface on which it may be formed. For example, an epitaxial semiconductor material deposited on a {100} crystal surface may take on a {100} orientation. In some embodiments, epitaxial growth and/or deposition processes may be selective to forming on semiconductor surfaces, and may not deposit material on dielectric surfaces, such as silicon dioxide or silicon nitride surfaces.
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Following etching and removal of the mask, a structure remains with a first set of fins 142 is located in a first region 210 and a second set of fins 143 in a second region 220. The first set of fins 142 has a first junction material 310 covering the fins 140 in the source/drain region located on both sides of the gate 155. The second set of fins 143 has a second junction material 320 covering the fins 140 in the source/drain region located on both sides of the gate 155. Located between the first set of fins 142 and the second set of fins 143, is a set of remnant fins 144, containing at least one fin remnant 145. The fin remnant 145 is the portion of the fin 140 left over following etching, and is not used to form any semiconductor structures. In some embodiments, the fin remnant 145 is only present under a gate 155, in the gate region. In other embodiments, the fin remnant 145 may not extend the same length as the first set of fins 142 and the second set of fins 143, but still may contain a portion of the fin in the source/drain region. The gate 155, formed from the gate structure 150, spans the first set of fins 142 to the second set of fins 143, crossing over the remnant fins 144. Additionally, by forming the gate structure 150, prior to removal of fins from unwanted areas, the resulting gate 155 may have a substantially uniform density due to the deposition of material across areas having substantially similar aspect ratios.
The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable other of ordinary skill in the art to understand the embodiments disclosed herein. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated but fall within the scope of the appended claims.
Claims
1. A semiconductor structure comprising:
- a first plurality of fins located in a first region of a substrate, wherein a first junction is located on a first set of fins in the first plurality of fins;
- a second plurality of fins located in a second region of the substrate, wherein a second junction is located on a second set of fins in the second plurality of fins;
- an intermediate plurality of fins located in an intermediate region of the substrate, wherein the intermediate region is located between the first region and the second region, wherein the length of the intermediate plurality of fins is substantially shorter than a length of the first plurality of fins; and
- a gate running substantially perpendicular to the first plurality of fins, the intermediate plurality of fins, and the second plurality of fins.
2. The structure of claim 1, wherein the first junction comprises a semiconductor material.
3. The structure of claim 2, wherein the semiconductor material comprises silicon, silicon-germanium or silicon-carbon.
4. The structure of claim 1, wherein the second junction material comprises a semiconductor material.
5. The structure of claim 4, wherein the semiconductor material comprises silicon, silicon-germanium or silicon-carbon.
6. The structure of claim 1, wherein the substrate is a semiconductor on insulator substrate.
7. The structure of claim 1, wherein the fin pitch amongst the fins is substantially uniform.
8. The structure of claim 1, wherein the intermediate plurality of fins is only located beneath the gate.
9. The structure of claim 1, wherein the gate has a substantially uniform density.
10. A semiconductor structure comprising:
- a first plurality of fins located in a first region of a substrate, wherein a first junction is located on a first set of fins in the first plurality of fins;
- a second plurality of fins located in a second region of the substrate, wherein a second junction is located on a second set of fins in the second plurality of fins;
- an intermediate plurality of fins located in an intermediate region of the substrate, wherein the intermediate region is located between the first region and the second region, wherein the length of the intermediate plurality of fins is substantially shorter than a length of the first plurality of fins; and
- a gate running substantially perpendicular to the first plurality of fins, the intermediate plurality of fins, and the second plurality of fins,
- wherein the fin pitch amongst the fins is substantially uniform, and
- wherein the gate has a substantially uniform density.
11. The structure of claim 10, wherein the first junction comprises a semiconductor material.
12. The structure of claim 11, wherein the semiconductor material comprises silicon, silicon-germanium or silicon-carbon.
13. The structure of claim 10, wherein the second junction material comprises a semiconductor material.
14. The structure of claim 13, wherein the semiconductor material comprises silicon, silicon-germanium or silicon-carbon.
15. The structure of claim 10, wherein the substrate is a semiconductor on insulator substrate.
Type: Application
Filed: Aug 26, 2015
Publication Date: Jun 16, 2016
Inventors: Sivananda K. Kanakasabapathy (Niskayuna, NY), Fee Li Lie (Albany, NY), Soon-Cheon Seo (Glenmont, NY), Raghavasimhan Sreenivasan (Schenectady, NY)
Application Number: 14/836,264