Patent Application
20200273953
Generally, the present disclosure relates to the manufacture of semiconductor devices, and, more specifically, to various novel methods of forming short-channel and long-channel transistor devices with different heights of work function metal and the resulting integrated circuit (IC) products.
In modern integrated circuits, such as microprocessors, storage devices and the like, a very large number of circuit elements, especially transistors, are provided on a restricted chip area. Transistors come in a variety of shapes and forms, e.g., planar transistors, FinFET transistors, nanowire devices, etc. The transistors are typically either NMOS (NFET) or PMOS (PFET) type devices wherein the “N” and “P” designation is based upon the type of dopants used to create the source/drain regions of the devices.
Some transistor devices are manufactured with relatively shorter gate lengths, e.g., 20 nm or less based upon current-day technology, and such devices may be generally referred to as short-channel devices. Other transistor devices are manufactured with relatively longer gate lengths, e.g., greater than 20 nm (and sometimes much greater) based upon current-day technology, and such devices may be generally referred to as long-channel devices. In general, short-channel devices exhibit faster switching speeds than long-channel devices. Additionally, short-channel devices exhibit larger off-state leakage currents than do long-channel devices. Short-channel devices are typically employed in circuits where high speed performance is necessary, e.g., logic circuits. On the other hand, long-channel devices may be employed in circuits where it is important to reduce power consumption and long-channel devices may also be employed in peripheral circuitry, such as input/output circuitry.
The gate structures for both short-channel devices and long-channel devices may be manufactured using known replacement gate manufacturing techniques. In general, the replacement gate manufacturing technique involves removing a previously formed sacrificial gate structure to define a replacement gate cavity positioned between a sidewall spacer structure that was formed adjacent the sacrificial gate structures. At that point, a plurality of conformal deposition processes are performed to form a plurality of conformal layers of gate materials within the replacement gate cavity. These conformal layers of material typically include a high-k gate insulation layer, a work-function adjusting metal (WFM) layer and one or more additional metal-containing layers. Any unfilled portion of the replacement gate cavity may be eventually filled with a bulk conductive material, such as tungsten. At some point during the process flow, the materials for the replacement gate within the replacement gate cavity will be recessed to make room for a final gate cap structure that will be positioned over the final replacement gate structure. The net result of such replacement gate manufacturing techniques is that the vertical height of the WFM layer along the sidewall spacer structure is typically the same for both short-channel devices and long-channel devices.
In designing IC products, various design or target parameters for the finished IC product are established by the ultimate purchaser of the IC product, and these design parameters are typically established very early in the design process. IC products may also be designed using a library of virtual standard cells that perform basic Boolean operations, such as a NAND gate or a NOR gate. Moreover, these libraries may be based in different categories of transistor devices that have differing operational characteristics. For example, some of the libraries may be based upon cells having transistors that exhibit a low threshold voltage (LVT devices or cells), a regular threshold voltage (RVT devices or cells) or a high threshold voltage (HVT devices or cells). In relative terms, LVT devices operate at faster switching speeds and exhibit greater off-state leakage currents as compared to the HVT devices. The performance of the RVT devices may exhibit speed and leakage current characteristics somewhere between those of the LVT devices and HVT devices. Circuit designers may employ LVT, RVT and HVT devices in any particular application. Typically, the overall product specification may set a targeted ring oscillator frequency for the particular circuit under consideration. At some point during the design process, the circuit was initially designed with LVT library cells (that exhibit the fastest switching speeds and the greatest leakage currents) and this initial LVT-based circuit design exhibits a cycle time that is less than the targeted ring oscillator frequency for the circuit. At that point, the circuit designer may undertake various actions to optimize the performance of the circuit while still meeting all of the target specifications for the product. For example, the circuit designer may try to replace one or more of the LVT cell portions of the initial circuit with HVT cell elements so as to reduce the overall leakage currents from the circuit. If this revised circuit design has a cycle time that is still less than the targeted ring oscillator frequency, the HVT cell element may be substituted for the LVT cell element so as to enhance the performance of the overall circuit in terms of reduced leakage currents. This process is repeated as needed to produce the most optimal design of the circuit in terms of operational speed and reduced leakage currents.
In some applications, both short-channel devices and long-channel devices may be initially fabricated such that they exhibit certain characteristics, e.g., threshold voltage, leakage currents, etc., and the characteristic of these initially fabricated transistor devices may make the IC product exhibit operational characteristics that do not meet the target parameters and specification established by the product purchaser. As a result, IC product manufacturers may undertake various activities in an attempt to try to modify or “tune” one or more of the performance characteristics of the initially-manufactured transistors such that the final IC product meets the target specifications set by the purchaser of the final IC product. One of these techniques may involve the implantation of various dopant atoms into the channel region of the short-channel and/or long-channel devices on the product. Unfortunately, while the implanting of such dopant materials may have positive effects with respect to some operational aspects of the transistor device, e.g., increased operational speed, there may also be some detrimental effects to the performance of the transistor devices (and the overall circuity), e.g., greater leakage currents, due to the presence of the performance-modifying implanted dopant materials within the channel region of one or both of the short-channel and long-channel transistor devices.
The present disclosure is directed to various methods of forming short-channel and long-channel transistor devices with different heights of work function metal and the resulting IC products that may solve or reduce one or more of the problems identified above.
The following presents a simplified summary of at least one disclosed embodiment in order to provide a basic understanding of some aspects of the subject matter disclosed herein. This summary is not an exhaustive overview of all of the subject matter disclosed herein. It is not intended to identify key or critical elements of the subject matter disclosed herein or to delineate the scope of any claims directed to any of the subject matter disclosed herein. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later in the application.
Generally, the present disclosure is directed to various novel methods of forming short-channel and long-channel transistor devices with different heights of work function metal and the resulting IC products. One illustrative integrated circuit product disclosed herein includes a short-channel transistor device and a long-channel transistor device formed above a semiconductor substrate, wherein a first gate structure for the short-channel transistor device includes a short-channel WFM layer with a first upper surface that is positioned at a first distance above an upper surface of the semiconductor substrate, and wherein a second gate structure for the long-channel transistor device includes a long-channel WFM layer with a second upper surface that is positioned at a second distance above the upper surface of the semiconductor substrate, wherein the first distance is greater than the second distance.
One illustrative method disclosed herein includes forming first and second sacrificial gate structures, respectively, for a short-channel transistor device and a long-channel transistor device, removing the first and second sacrificial gate structures to form first and second replacement gate cavities, respectively, for the short-channel transistor device and the long-channel transistor device, and forming a conformal work-function adjusting metal layer (conformal WFM layer) in the first and second replacement gate cavities. In this example, the method also includes performing at least one process operation to remove portions of the conformal WFM layer from within the first and second replacement gate cavities to form a short-channel WFM layer for a first final gate structure of the short-channel transistor device and a long-channel WFM layer for a second final gate structure for the long-channel transistor device, wherein a first upper surface of the short-channel WFM layer is positioned at a first distance above an upper surface of the semiconductor substrate and wherein a second upper surface of the long-channel WFM layer is positioned at a second distance above the upper surface of the semiconductor substrate, wherein the first distance is greater than the second distance.
The disclosure may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:
While the subject matter disclosed herein is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Various illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.
The present subject matter will now be described with reference to the attached figures. Various structures, systems and devices are schematically depicted in the drawings for purposes of explanation only and so as to not obscure the present disclosure with details that are well known to those skilled in the art. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present disclosure. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase. As will be readily apparent to those skilled in the art upon a complete reading of the present application, the methods disclosed herein may be employed in manufacturing a variety of different devices, including, but not limited to, logic devices, memory devices, etc., and the devices may be may be either NMOS or PMOS devices.
As will be appreciated by those skilled in the art after a complete reading of the present application, various doped regions, e.g., source/drain regions, halo implant regions, well regions and the like, are not depicted in the attached drawings. Of course, the inventions disclosed herein should not be considered to be limited to the illustrative examples depicted and described herein. The various components and structures of the integrated circuit devices 100 disclosed herein may be formed using a variety of different materials and by performing a variety of known techniques, e.g., a chemical vapor deposition (CVD) process, an atomic layer deposition (ALD) process, a thermal growth process, spin-coating techniques, etc. The thicknesses of these various layers of material may also vary depending upon the particular application. With reference to the attached figures, various illustrative embodiments of the methods and devices disclosed herein will now be described in more detail.
As noted above, in the illustrative examples depicted herein, the short-channel transistor 101S and the long-channel transistor 101L are FinFET devices.
With reference to
Still with reference to
In the examples depicted herein, the integrated circuit product 100 will be formed in and above a semiconductor substrate 102. The substrate 102 may have a variety of configurations, such as a semiconductor-on-insulator (SOI) configuration that includes a base semiconductor layer, a buried insulation layer positioned on the base semiconductor layer and an active semiconductor layer positioned on the buried insulation layer. Alternatively, the substrate 102 may have a simple bulk configuration, like that depicted in the attached drawings. The substrate 102 may be made of silicon or it may be made of semiconductor materials other than silicon. Thus, the terms “substrate” or “semiconductor substrate” should be understood to cover all semiconducting materials and all forms of such materials.
The final gate structures 108 for the transistors 101S, 101L disclosed herein will be manufactured using one illustrative embodiment of a replacement gate (or “gate-last”) manufacturing technique. Accordingly, still referencing
Similarly, with reference to
In one illustrative and non-limiting process flow, each of the sacrificial structures 104 comprises a sacrificial gate insulation layer (e.g., silicon dioxide—not separately shown) and a sacrificial gate electrode material (e.g., polysilicon or amorphous silicon—not separately shown). A sacrificial gate cap 110 (e.g., silicon nitride) is positioned above each of the sacrificial gate structures 104. In one illustrative process flow, the sacrificial gate structures 104 (with the gate cap 110 there above) are initially formed as continuous line-type structures that extend across substantially the entire substrate 102, i.e., across both active regions and isolation regions located between active regions. The long continuous line-type sacrificial gate structures 104/gate cap 110 structures may be formed by depositing the materials for the sacrificial gate structures 104 as well as a layer of material for the sacrificial gate caps 110 across the entire substrate 102, forming a patterned gate etch mask (not shown) above the deposited layer of the material for the sacrificial gate caps 110, and performing one or more etching processes through the patterned gate etch mask to remove the exposed portions of sacrificial gate cap material and, thereafter, the exposed portions of the sacrificial gate materials.
Next, still referencing
Various process operations are typically performed with the sacrificial gate structures 104, gate caps 110 and spacer structures 112 in position, e.g., source/drain implantation processes, the formation of epi semiconductor material 120 in the source/drain regions of the transistors 101S, 101L, etc. Then, a conformal contact etch stop layer (not shown, e.g., silicon nitride) may be formed on the product 100 and above the regions of epi semiconductor material 120. At that point, one or more layers of insulating material 113 (e.g., silicon dioxide) was formed across the product 100 so as to over-fill the open spaces between the spacer structures 112. Thereafter, a CMP and/or etch-back process was performed to planarize the upper surface of the layer of insulating material 113 with the upper surface of the sacrificial gate caps 110. In one illustrative example, the sacrificial gate caps 110 may be comprised of silicon nitride, the spacer structures 112 may be comprised of silicon nitride, SiNC, etc. and the insulating material 113 may be silicon dioxide.
As noted above, the final gate structures 108 for the transistor devices 101S, 101L disclosed herein will be manufactured using one illustrative embodiment of a replacement gate (or “gate-last”) manufacturing technique. Accordingly,
In one illustrative example, the gate insulation layer 117 may be comprised of a high-k insulating material (a material having a dielectric constant greater than 10), such as hafnium oxide, etc. The conformal WFM layer 119 may also be comprised of a variety of different materials depending upon whether the transistors 101S, 101L are NFET transistors or PFET transistors. In the illustrative example where the transistors 101S, 101L are NFET transistors, the conformal WFM layer 119 may be comprised of a variety of different materials including, but not limited to, TiAlC, TiN, TiN (with a relatively high amount of N-type dopant), TaN, etc. In the illustrative example where the transistors 101S, 101L are PFET transistors, the conformal WFM layer 119 may be comprised of a variety of different materials including, but not limited to, TaN, TiN, TiON, TiAlC, etc. As noted above, the thickness of the conformal WFM layer 119 may vary depending upon the particular application, e.g., 0.5-6 nm. Additionally, in some applications, two or more conformal WFM layers 119 may be formed within each of the replacement gate cavities 115.
Similarly, the metal-containing layer 121 may also be comprised of a variety of different materials depending upon whether the transistors 101S, 101L are NFET transistors or PFET transistors. In the illustrative example where the transistors 101S, 101L are PFET transistors, the metal-containing layer 121 may be comprised of a variety of different materials including, but not limited to, TiN, W, etc. In the illustrative example where the transistors 101S, 101L are NFET transistors, the metal-containing layer 121 may be comprised of a variety of different materials including, but not limited to, TiN, W, etc. As noted above, the thickness of the metal-containing layer 121 may vary depending upon the particular application, e.g., 1-8 nm.
In accordance with one illustrative process flow,
Continuing with this illustrative process flow,
Next, with the patterned etch mask 125 in position, one or more etching processes were performed to remove portions of the conformal layers 117, 119 and 121 on the short-channel transistor 101S that are positioned or located vertically at, near or above the first recessed upper surface 123A of the sacrificial layer of material 123. In the depicted example, the upper surfaces of the conformal layers 117, 119 and 121 are all simplistically depicted as being approximately level with the first recessed upper surface 123A. In a real-world device, the recessing of the conformal layers 117, 119 and 121 may not be so uniform. Importantly, at the conclusion of these process operations, a portion of the original conformal WFM layer 119 becomes the short-channel WFM layer 119X for the short-channel transistor 101S. The short-channel WFM layer 119X has an upper surface 119A that may be positioned at or near the level of the first recessed upper surface 123A of the sacrificial layer of material 123.
Continuing with this illustrative process flow,
Continuing with this illustrative process flow,
Continuing with this illustrative process flow,
With continuing reference to
Additionally, in one illustrative embodiment, the overall vertical height 133 of the short-channel WFM layer 119X (e.g., the height of the portion of the short-channel WFM layer 119X that contacts the spacer structure 112) may be about 10-25 nm. Similarly, the overall vertical height 135 of the long-channel WFM layer 119Y (e.g., the height of the portion of the long-channel WFM layer 119Y that contacts the spacer structure 112) may be as much as about 10 nm or it may only be about equal to the thickness of the horizontally oriented portions of the long-channel WFM layer 119Y, e.g., the upstanding leg portions of the long-channel WFM layer 119Y may essentially be removed during the processing disclosed above. Stated another way, the vertical height 135 may be the greater of the approximate thickness of the long-channel WFM layer 119Y or 10 nm. However, in some applications, the overall height 135 of the long-channel WFM layer 119Y may be equal to the combined thickness of the long-channel WFM layer 119Y and the thickness of the metal-containing layer 121. Additionally, in one illustrative embodiment, the difference between the overall vertical heights 133, 135 may be about 5-20 nm.
Of course, as will be appreciated by those skilled in the art after a complete reading of the present application, the illustrative process flow described above, i.e., the initial recessing of the sacrificial material layer 123 on both of the transistor devices 101S, 101L, followed by a further recessing of the sacrificial material layer 123 on the long-channel transistor 101L, etc. is but one manner of achieving the desired difference in height between the short-channel WFM layer 119X and the long-channel WFM layer 119Y. In the example depicted herein, the short-channel WFM layer 119X on the short-channel transistor 101S was etched first so as to establish the overall vertical height 133 and, thereafter, the long-channel WFM layer 119Y on the long-channel transistor device 101L was etched to establish the overall vertical height 135. In other process flows, perhaps less efficient and perhaps requiring the formation of additional layers of material (such as an additional layer of sacrificial material 123), the order of etching the original conformal WFM layer 119 to form the short-channel WFM layer 119X and the long-channel WFM layer 119Y may be reversed.
As will be appreciated by those skilled in the art after a complete reading of the present application, the novel method and products disclosed herein may be beneficial to both device manufacturers and the purchasers of IC products as it relates to the manufacture of a final IC product such that it meets or exceeds the originally established product performance specification. In one illustrative example, the formation of the short-channel device 101S and the long-channel device 101L with, respectively, a short-channel WFM layer 119X and a long-channel WFM layer 119Y, may be part of a process flow that effectively provides one means for a product designer to modify the parameters of one or more of the transistors within a given IC product. For example, the formation of the relatively shorter long-channel WFM layer 119Y in the long-channel transistor 101L and the formation of the relatively taller short-channel WFM layer 109X in the short-channel transistor 101S may provide the device designers with a tool to effectively cause a relatively large differential in threshold voltage levels between the short-channel device 101S and the long-channel device 101L. More specifically, with respect to NFET devices, for example, the formation of the taller short-channel WFM layer 109X and the shorter long-channel WFM layer 119Y may cause the threshold voltage of the long-channel device 101L (channel length of at least 60 nm) to be about 60 mV greater than the threshold voltage of the short-channel device 101S. At that point, the threshold voltage characters may be performed (by, for example, a Boolean change to a lithography mask) to effectively change the long-channel device 101L (with the shorter long-channel WFM layer 119Y) from a regular threshold voltage (RVT) device to a low threshold voltage (LVT) device.
The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. For example, the process steps set forth above may be performed in a different order. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Note that the use of terms, such as “first,” “second,” “third” or “fourth” to describe various processes or structures in this specification and in the attached claims is only used as a shorthand reference to such steps/structures and does not necessarily imply that such steps/structures are performed/formed in that ordered sequence. Of course, depending upon the exact claim language, an ordered sequence of such processes may or may not be required. Accordingly, the protection sought herein is as set forth in the claims below.
