This disclosure relates to integrated circuit devices, and more specifically, to an advanced method and structure to create multiple gate width patterning in semiconductor devices.
As the dimensions of modern integrated circuitry in semiconductor chips continues to become smaller, conventional lithography is increasingly challenged to make smaller and smaller structures. Sidewall Image Transfer (SIT) patterning for forming a gate structure is frequently used for gate pitches below 64 nm. However, multiple gate width patterning at such small pitches becomes complicated at hard mask assembly. It often requires complicated, multiple mask layers and complex patterning schemes. Further, the prior art process is susceptible to pitch walk for the gate structures without careful process control.
The present disclosure presents an advanced sidewall image transfer process for multiple gate width patterning to alleviate this problem.
According to this disclosure, a method for fabricating a multiple gate width structure for an integrated circuit is described. A fin on a semiconductor substrate with a first hard mask layer is covered by a first and second sacrificial gate each of which includes a second hard mask layer. Spacer layers and a dielectric layer are formed over the first and second sacrificial gate structures. The resulting structure is planarized so that the first and second sacrificial gate structures and the dielectric layer have coplanar top surfaces. The first and second sacrificial gate structures are removed to respectively form first and second trench recesses in the dielectric layer. The trench recesses are filled with a conductor to form permanent gate structures. A first permanent gate structure is formed in the first trench recess has a first length and a second permanent gate structure is formed in the second trench recess has a second length greater than the first length.
The foregoing has outlined some of the more pertinent features of the disclosed subject matter. These features should be construed to be merely illustrative. Many other beneficial results can be attained by applying the disclosed subject matter in a different manner or by modifying the invention as will be described.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings which are not necessarily drawing to scale, and in which:
At a high level, the invention provides a method and resulting structure to practice a Sidewall Image Transfer (SIT) patterning process for forming multi-gate length structures. As compared to a conventional process, the inventive multiple gate length process is performed after a gate stack etch with an extra spacer liner which will be consumed during a replacement metal gate (RMG) gate pull process. According to the invention, sidewall spacers are selectively formed used around some of the set of sacrificial gates. A sacrificial SiGe layer is employed as a protective layer to protect the device layer.
While there have been prior methods to fabricate multi-gate length structure, the present invention has advantages over prior art schemes. Multi-gate length structures, i.e. having at least one nominal length gate length and a second gate length other than the nominal gate length are so-called WIMPY structures. Many of the structure use SIT for patterning. In the prior art, mandrels are formed over the gate material and sidewall material is deposited over the mandrels. The mandrels which will form wimpy gates, i.e., the ones which will be longer, are masked while the mandrels which will form the nominal gates are etched. The critical dimension (CD) control is at the mask open level which causes pitch walk for a WIMPY device unless the mandrel CD is adjusted. Furthermore, the prior art has a complicated mask assembly.
A “substrate” as used herein can comprise any material appropriate for the given purpose (whether now known or developed in the future) and can comprise, for example, Si, SiC, SiGe, SiGeC, Ge alloys, GaAs, InAs, InP, other III-V or II-VI compound semiconductors, or organic semiconductor structures. Insulators can also be used as substrates in embodiments of the invention.
For purposes herein, a “semiconductor” is a material or structure that may include an implanted impurity that allows the material to sometimes be conductive and sometimes be a non-conductive, based on electron and hole carrier concentration. As used herein, “implantation processes” can take any appropriate form (whether now known or developed in the future) and can comprise, for example, ion implantation.
For purposes herein, an “insulator” is a relative term that means a material or structure that allows substantially less (<95%) electrical current to flow than does a “conductor.” The dielectrics (insulators) mentioned herein can, for example, be grown from either a dry oxygen ambient or steam and then patterned. Alternatively, the dielectrics herein may be formed from any of the many candidate high dielectric constant (high-k) materials, including but not limited to hafnium oxide, aluminum oxide, silicon nitride, silicon oxynitride, a gate dielectric stack of SiO2 and Si3N4, and metal oxides like tantalum oxide that have relative dielectric constants above that of SiO2 (above 3.9). The dielectric can be a combination of two or more of these materials. The thickness of dielectrics herein may vary contingent upon the required device performance. The conductors mentioned herein can be formed of any conductive material, such as polycrystalline silicon (polysilicon), amorphous silicon, a combination of amorphous silicon and polysilicon, and polysilicon-germanium, rendered conductive by the presence of a suitable dopant. Alternatively, the conductors herein may be one or more metals, such as tungsten, hafnium, tantalum, molybdenum, titanium, or nickel, or a metal silicide, any alloys of such metals, and may be deposited using physical vapor deposition, chemical vapor deposition, or any other technique known in the art.
When patterning any material herein, the material to be patterned can be grown or deposited in any known manner and a patterning layer (such as an organic photoresist aka “resist”) can be formed over the material. The patterning layer (resist) can be exposed to some form of light radiation (e.g., patterned exposure, laser exposure) provided in a light exposure pattern, and then the resist is developed using a chemical agent. This process changes the characteristic of the portion of the resist that was exposed to the light. Then one portion of the resist can be rinsed off, leaving the other portion of the resist to protect the material to be patterned. A material removal process is then performed (e.g., plasma etching) to remove the unprotected portions of the material to be patterned. The resist is subsequently removed to leave the underlying material patterned according to the light exposure pattern.
For purposes herein, “sidewall structures” are structures that are well-known to those ordinarily skilled in the art and are generally formed by depositing or growing a conformal insulating layer (such as any of the insulators mentioned above) and then performing a directional etching process (anisotropic) that etches material from horizontal surfaces at a greater rate than its removes material from vertical surfaces, thereby leaving insulating material along the vertical sidewalls of structures. This material left on the vertical sidewalls is referred to as a sidewall structure. The sidewall structures can be used as masking structures for further semiconducting processing steps.
Embodiments will be explained below with reference to the accompanying drawings. The various layers in the structures below are deposited and removed using well known processes. Examples of processes that can be used to perform the steps of the invention, but should not be viewed as limiting.
When both pFETs and nFETs are formed, mask steps are used to limit the epitaxial growth to the appropriate fin regions. For example, if a pFET epitaxial region was first grown on the fin, the nFET region is covered with a mask to prevent epitaxial growth, e.g., a thin SiN cap. After the pFET epitaxial growth, the pFET region is blocked and the mask covering the nFET regions is opened, then the nFET epitaxial growth process is performed. In embodiments of the invention SiGe with boron is used for epitaxial growth of the pFET regions and SiP with carbon is used for the nFET regions. In alternative embodiments, the process order can change to grow the nFET epitaxial regions first and then grow the pFET epitaxial regions. Other sources can be used to create different epitaxial layers in different embodiments of the invention.
Processing of additional layers of the integrated circuit device proceeds after the steps illustrated in the disclosure. For example, a set of conductive lines could be created using an embodiment of the invention in subsequent steps if required for completion of the integrated circuit.
The resulting structure can be included within integrated circuit chips, which can be distributed by the fabricator in wafer form (that is, as a single wafer that has multiple chips), as a bare die, or in a packaged form. In any case, the chip is then integrated with other chips, discrete circuit elements, and/or other signal processing devices as part of either (a) an intermediate product, such as a motherboard, or (b) an end product. The end product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products having a display, a keyboard or other input device, and a central processor.
While only one or a limited number of features are illustrated in the drawings, those ordinarily skilled in the art would understand that many different types of features could be simultaneously formed with the embodiment herein and the drawings are intended to show simultaneous formation of multiple different types of features. However, the drawings have been simplified to only show a limited number of features for clarity and to allow the reader to more easily recognize the different features illustrated. This is not intended to limit the invention because, as would be understood by those ordinarily skilled in the art, the invention is applicable to structures that include many of each type of feature shown in the drawings.
While the above describes a particular order of operations performed by certain embodiments of the invention, it should be understood that such order is exemplary, as alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, or the like. References in the specification to a given embodiment indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic.
In addition, terms such as “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”, “over”, “overlying”, “parallel”, “perpendicular”, etc., used herein are understood to be relative locations as they are oriented and illustrated in the drawings (unless otherwise indicated). Terms such as “touching”, “on”, “in direct contact”, “abutting”, “directly adjacent to”, etc., mean that at least one element physically contacts another element (without other elements separating the described elements).
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.
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