INTEGRATED CIRCUIT HAVING HETEROSTRUCTURE FINFET WITH TUNABLE DEVICE PARAMETERS AND METHOD TO FABRICATE SAME
A field effect transistor (FET) device has a fin disposed over a substrate. The fin has opposing ends defining a source and a drain and intermediate the source and the drain a channel underlying a gate. The fin is formed as a heterostructure having at least one first layer of material and at least one second layer of material that is adjacent to the first layer of material. A thickness of at least one of the first layer of material and the second layer of material is selected to obtain a particular effective device width W. Methods to fabricate the FET device are also described.
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The exemplary embodiments of this invention relate generally to semiconductor devices and fabrication techniques and, more specifically, relate to the fabrication of semiconductor transistor devices, such as those used in random access memory (RAM) such as static RAM (SRAM), logic circuitry and input/output (I/O) circuitry.
BACKGROUNDOne feature of a heterojunction is that the bandgaps of two adjacent semiconductors are typically different. As a result the energy of the carriers (electrons or holes) that exists at at least one of the band edges must change as the carriers pass through the heterojunction. In most cases the discontinuities exist in both the conduction band and the valence band. In conventional nomenclature, sometimes used with superlattices, if the extrema of both the conduction and valence bands lie in the same layers, the superlattice is referred to as Type I, whereas if the band extrema are found in different layers the superlattice is referred to as Type H.
The FinFET is becoming a main architecture for CMOS technology due to its excellent scalability. However FinFET circuit design is challenging due at least to the discrete values that are available for W (the effective device width). For example, if the fin height is 30 nm and W is equal to two times the height (H) of the fin or 60 nm, and if a circuit designer desires a value of W equal to 90 nm, the circuit designer should either use one fin with W equal to 60 nm or two fins with a total W equal to 120 nm. Moreover the effective device width for various chip blocks such as SRAM and logic are typically similar. It can be appreciated that constraints can be placed on the circuit designer.
SUMMARYIn accordance with a first non-limiting aspect of this invention there is a provided a field effect transistor (FET) device that comprises a fin disposed over a substrate. The fin has opposing ends defining a source and a drain and intermediate the source and the drain a channel underlying a gate. The fin is comprised of a heterostructure comprised of at least one first layer of material and at least one second layer of material that is adjacent to the first layer of material. A thickness of at least one of the first layer of material and the second layer of material is selected to obtain a particular effective device width W.
In accordance with a further non-limiting aspect of this invention there is a provided a method that comprises providing a substrate and forming a fin disposed over the substrate. The fin is formed to have opposing ends defining a source and a drain and intermediate the source and the drain a channel underlying a gate. The fin is formed to comprise a hetero structure comprised of at least one first layer of material and at least one second layer of material that is adjacent to the first layer of material. A thickness of at least one of the first layer of material and the second layer of material is selected to obtain a particular effective device width W.
The challenges facing a circuit designed were outlined above. As a result a ‘tunable’ FinFET design is preferred. As an example, for a typical SRAM stronger nFETs are required than pFETs. Assuming as a non-limiting case the material choice has similar electron and hole mobilities, the nFETs and pFETs in the logic block can be symmetric (note that this invention is not limited to materials with similar mobilities, since for materials with different mobilities the layer thicknesses can be adjusted accordingly). It is typically desirable for lithography and other process steps that the height of the fins are similar for the different circuitry blocks, e.g., about 30 nm.
As a result, and in accordance with embodiments of this invention, a heterostructure is composed of 2N layers, where N is at least equal to 1. In one non-limiting example the heterostructure contains 10 nm strained SiGe (s-SiGe)/20 nm strained Si (s-Si) for the SRAM block and 15 nm s-SiGe/15 nm s-Si for the logic block, while the total fin height for both the SRAM and logic remains constant, e.g., about 30 nm.
Within a single block, such as SRAM, the pull-up transistor may have a smaller width, and thus a stack of 20 nm s-SiGe/10 nm s-Si can be used.
By way of introduction
The heterostructure 10 is composed in this non-limiting example of four layers comprised of two different materials labeled A and B that alternate one with the other. The two materials exhibit a conduction band (Ec) and a valence band (Ev) where holes ‘fall down’ in material B while electrons ‘fall down’ in material A. For example, and for the system shown in
As non-limiting examples material A can be composed of Si, strained Si or a group III-V material, and material B can be composed of silicon germanium (SiGe), Ge or a group III-V material. The layers A and B have ‘tunable’ thicknesses as described below.
The current drive of a MOSFET is directly proportional to its effective width, W, and thus the effective width, W, can be used by a circuit designed to achieve desired device operational characteristics.
More generally, for an n-type FET case device current is proportional to W=2×N×(t1A+t2A, . . . +tNA), where N is the number of first layers of material and where t1A is a thickness of one of the first layers of material, where t2A is a thickness of another one of the first layers of material, and where tNA is a thickness of the Nth first layer of material. For a p-type FET case device current is proportional to W=2×N×(t1B+t2B, . . . +tNB), where N is the number of second layers of material, where t1B is a thickness of one of the second layers of material, where t2B is a thickness of another one of the second layers of material, and where tNB is a thickness of the Nth second layer of material. In general N can be equal to one or more than one.
The aforementioned example for device widths of n-type FETs and p-type FETs is valid for a type II band alignment. While such a band alignment is preferred, this invention is not limited for use with only the type II band alignment. If for a given band (either conduction or valence band), the bands of material A and B align, where no quantum well forms, the above definitions change. For example if a quantum well forms only in the valence band and the conduction band is perfectly aligned, a similar W can be calculated for the p-type FET while for n-type FET, W=2×total fin height.
During fabrication, and in one non-limiting fabrication embodiment, the wafer from which the die 20 is eventually cut could be selectively masked to first epitaxially deposit multiple layers in one region, e.g., the SRAM region 22, the multiple layers A and B with thicknesses t1A and t2A and the layers B having thicknesses t1B and t2B, followed by mask stripping and remasking to epitaxially deposit multiple layers in a second region, e.g., the logic region 24, the multiple layers A and B with thicknesses t3A and t4A and the layers B having thicknesses t3B and t4B, followed by mask stripping and remasking to epitaxially deposit multiple layers in a third region, e.g., the I/O region 26, the multiple layers A and B with thicknesses t5A and t6A and the layers B having thicknesses t5B and t6B. Described below are other more preferred fabrication embodiments.
The following description provides two exemplary embodiments of this invention, specifically a SOI embodiment and a bulk (Si) embodiment.
In the SOI embodiment of
In the bulk embodiment of
A non-limiting example of process steps for the SOI embodiment of
In
The epitaxy process used for the step in
At this point the intermediate structure formed thus far is further processed to remove the hardmask 48 and to define the heterostructure fins 10A, 10B, 10C from the layers 40, 46 and 50 as shown in
A non-limiting example of process steps for the bulk embodiment of
At this point the intermediate structure formed thus far is further processed to remove the hardmask 64, to recess the STI 62 down to the level of the layer 34 of strain-relaxed Si1-yGey, to form the HMs 30 and to define the heterostructure fins 10A, 10B, 10C from the layers 40, 40A, 46, 46A to result in the structure shown in
Further in this regard,
It is to be understood that the exemplary embodiments discussed above with reference to
In accordance with the various exemplary embodiments of this invention described above the band structure of the constituent materials need not be altered, instead heterostructures are provided in which, by selecting materials, electrons fall in one layer and holes in the other layer. As a result a high mobility material can be used for each charge carrier separately in conjunction with adjusting the height (thickness) of each material in such as manner as to obtain a desired effective width for a particular type of circuit design. Different thicknesses of materials for nFET, pFET, logic, SRAM, etc., FinFETS are achieved by epitaxial layer deposition.
In accordance with the various exemplary embodiments of this invention described above a FinFET structure is provided with different materials for electron and hole mobility enhancement, where bands are aligned in a such a manner that only one semiconductor type confines only one type of charge carrier. With tunable parameters such as mobility and thickness of the layers for nFET, pFET, logic, SRAM and I/O types of devices a freedom of design is provided to the circuit designer, as opposed to conventional practice of simply varying the number of fins for a single channel FinFET, particularly in those cases where a maximum fin height is constrained across the die based on topological and other considerations.
Integrated circuit dies can be fabricated with various devices such as a field-effect transistors, bipolar transistors, metal-oxide-semiconductor transistors, diodes, resistors, capacitors, inductors, etc., that also have FinFETS that are formed using the methods as described herein. An integrated circuit in accordance with the present invention can be employed in applications, hardware, and/or electronic systems. Suitable hardware and systems in which such integrated circuits can be incorporated include, but are not limited to, personal computers, communication networks, electronic commerce systems, portable communications devices (e.g., phones), solid-state media storage devices, functional circuitry, etc. Systems and hardware incorporating such integrated circuits are considered part of this invention. Given the teachings of the invention provided herein, one of ordinary skill in the art will be able to contemplate other implementations and applications of the techniques of the invention.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form 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 invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
As such, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. As but some examples, the use of other similar or equivalent semiconductor fabrication processes, including deposition processes, etching processes may be used by those skilled in the art. Further, the exemplary embodiments are not intended to be limited to only those materials, layer thicknesses and the like that were specifically disclosed above. Any and all such and similar modifications of the teachings of this invention will still fall within the scope of this invention.
Claims
1. A semiconductor structure, comprising:
- a plurality of devices disposed over a substrate, the plurality of devices being comprised of at least two field effect transistors (FETs) comprising an n-type FET (nFET) device and a p-type FET (pFET) device;
- where the nFET and the pFET each have the same channel material stacks each comprised of a heterostructure, the heterostructure being comprised of at least one first layer of semiconductor material (A) having a thickness (tA) and at least one second layer of semiconductor material (B) having a thickness (tB), where the second layer of semiconductor material is adjacent to the first layer of semiconductor material and is different from the first layer of semiconductor material;
- where for the nFET device current flow is proportional to tA and for the pFET device current flow is proportional to tB, and where an effective device width (W) of the nFET device is a function of tA and the effective device width of the pFET device is a function of tB.
2. The semiconductor structure of claim 1, where for the n-type FET device current is proportional to W=2×N×(t1A+t2A,... +tNA), where N is the number of first layers of semiconductor material and where t1A is a thickness of one of the first layers of semiconductor material, where t2A is a thickness of another one of the first layers of semiconductor material, and where tNA is a thickness of the Nth first layer of semiconductor material.
3. The semiconductor structure of claim 1, where for the p-type FET device current is proportional to W=2×N×(t1B+t2B,... +tNB), where N is the number of second layers of semiconductor material, where t1B is a thickness of one of the second layers of semiconductor material, where t2B is a thickness of another one of the second layers of semiconductor material, and where tNB is a thickness of the Nth second layer of semiconductor material.
4. The semiconductor structure of claim 1, where the first layer of semiconductor material is comprised of strained Si and where the second layer of semiconductor material is comprised of strained-Si1-xGex.
5. The semiconductor structure of claim 4, where the substrate is comprised of a bulk Si substrate, and where said first layer of strained Si overlies a layer comprised of strain-relaxed Si1-yGey disposed between said first layer and a surface of said bulk Si substrate.
6. The semiconductor structure of claim 4, where the substrate is comprised of a strained Si directly on insulator (SSDOI) substrate that provides said first layer of strained Si.
7. The semiconductor structure of claim 1, where the nFET channel material stack is contained within a first Fin structure and the pFET channel material stack is contained within a second Fin structure, and where a total thickness of the nFET channel material stack is approximately equal to a total thickness of the nFET channel material stack, and where the effective width of the nFET device is different than the effective device width of the pFET device.
8. The semiconductor structure of claim PE 7, where the plurality of devices are used in a memory circuit, where another plurality of devices are used in a logic circuit, and where still another plurality of devices are used in an input/output (I/O) circuit, and where all of the plurality of devices are disposed over the same substrate.
9. The semiconductor structure of claim 1, where said substrate comprises a layer of dielectric material and where said first layer is disposed on the layer of dielectric material.
10. A method to fabricate a field effect transistor (FET) device comprising:
- providing a substrate; and
- forming over the substrate a plurality of devices comprised of at least two field effect transistors (FETs) comprising an n-type FET (nFET) device and a p-type FET (pFET) device, where the nFET and the pFET are formed to each have the same channel material stacks each comprised of a hetero structure, the heterostructure being comprised of at least one first layer of semiconductor material (A) having a thickness (tA) and at least one second layer of semiconductor material (B) having a thickness (tB), where the second layer of semiconductor material is adjacent to the first layer of semiconductor material and is different from the first layer of semiconductor material; where for the nFET device current flow is proportional to tA and for the pFET device current flow is proportional to tB, and where an effective device width (W) of the nFET device is a function of tA and the effective device width of the pFET device is a function of tB.
11. The method of claim 10, where for the n-type FET device current is proportional to W=2×N×(t1A+t2A,... +tNA), where N is the number of first layers of semiconductor material and where t1A is a thickness of one of the first layers of semiconductor material, where t2A is a thickness of another one of the first layers of semiconductor material, and where tNA is a thickness of the Nth first layer of semiconductor material.
12. The method of claim 10, where for the p-type FET device current is proportional to W=2×N×(t1B×t2B,... +tNB), where N is the number of second layers of semiconductor material, where t1B is a thickness of one of the second layers of semiconductor material, where t2B is a thickness of another one of the second layers of semiconductor material, and where tNB is a thickness of the Nth second layer of semiconductor material.
13. The method of claim 10, where the first layer of semiconductor material is comprised of strained Si and where the second layer of semiconductor material is comprised of strained-Si1-xGex.
14. The method of claim 13, where the substrate is provided to be comprised of a bulk Si substrate, and where said first layer of strained Si overlies a layer comprised of strain-relaxed Si1-yGey disposed between said first layer of strained Si and a surface of said bulk Si substrate.
15. The method of claim 13, where the substrate is comprised of a strained Si directly on insulator (SSDOI) substrate that provides said first layer of strained Si.
16. The method of claim 10, where the nFET channel material stack is contained within a first fin and the pFET channel material stack is contained within a second fin, and where a total thickness of the nFET channel material stack is approximately equal to a total thickness of the nFET channel material stack, and where the effective width of the nFET device is different than the effective device width of the pFET device and is selected to obtain the particular effective device width W depending on a type of FET device in which the fin is incorporated, where one type of FET device is used in a memory circuit, where another type of FET device is used in a logic circuit, and where a third type of FET device is used in an input/output (I/O) circuit.
17. A method to fabricate a field effect transistor (FET) device comprising:
- providing a substrate; and
- forming a fin disposed over the substrate, the fin having opposing ends defining a source and a drain and intermediate the source and the drain a channel underlying a gate, the fin being formed to comprise a hetero structure comprised of at least one first layer of material and at least one second layer of material that is adjacent to the first layer of material, where a thickness of at least one of the first layer of material and the second layer of material is selected to obtain a particular effective device width W;
- where the substrate is provided to be comprised of a bulk Si substrate, where said first layer of material is disposed on a layer of strain-relaxed material that is disposed over a surface of the substrate, and where the method further comprises:
- forming a first fin and a second fin each comprising part of the strain-relaxed material layer, the first layer of material and the second layer of material;
- embedding the first fin and the second fin in a layer of dielectric material;
- removing the first layer of material and the second layer of material from the second fin to form an opening in the layer of dielectric material that exposes an underlying portion of the strain-relaxed material layer; and
- depositing a new first layer of material and a new second layer of material into the opening, where a thickness of at least one of the new first layer of material and the new second layer of material differs from a thickness of the first layer of material and the second layer of material of the first fin.
18. The method of claim 17, where the first layer of material is comprised of strained Si, where the second layer of material is comprised of strained-Si1-xGex, and where the layer of strain-relaxed material is comprised of Si1-yGey.
19. The method of claim 10, where the substrate is comprised of a silicon-on-insulator (SOI) substrate having a silicon layer overlying a buried oxide layer, where the first layer of semiconductor material comprises the silicon layer, and where the method further comprises:
- applying a mask to a first portion of the first layer of semiconductor material;
- thinning an unmasked second portion of the first layer of semiconductor material;
- depositing the second layer of semiconductor material over the thinned second portion of the first layer of semiconductor material;
- masking the deposited second layer of semiconductor material over the thinned second portion of the first layer of semiconductor material;
- removing the mask from the first portion of the first layer of semiconductor material and depositing the second layer of semiconductor material over the first portion of the first layer of semiconductor material; and
- forming a first fin and a second fin having approximately equal thicknesses, where the first fin comprises the first portion of the first layer of semiconductor material and the overlying second layer of semiconductor material, and where the second fin comprises the thinned second portion of the first layer of semiconductor material and the overlying second layer of semiconductor material.
20. The method of claim 19, where the first layer of semiconductor material is comprised of strained Si and where the second layer of semiconductor material is comprised of strained-Si1-xGex.
Type: Application
Filed: Mar 17, 2014
Publication Date: Sep 17, 2015
Applicant: International Business Machines Corporation (Armonk, NY)
Inventors: Kangguo Cheng (Schenectady, NY), Bruce B. Doris (Slingerlands, NY), Pouya Hashemi (White Plains, NY), Ali Khakifirooz (Mountain View, CA), Alexander Reznicek (Troy, NY)
Application Number: 14/215,123