Patent Publication Number: US-2022238387-A1

Title: Gate Profile Control Through Sidewall Protection During Etching

Description:
PRIORITY CLAIM 
     This application is a divisional of U.S. patent application Ser. No. 16/867,158, entitled “Gate Profile Control Through Sidewall Protection During Etching,” filed on May 5, 2020, which application is incorporated herein by reference 
    
    
     BACKGROUND 
     Technological advances in Integrated Circuit (IC) materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generations. In the course of IC evolution, functional density (for example, the number of interconnected devices per chip area) has generally increased while geometry sizes have decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. 
     Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. For example, Fin Field-Effect Transistors (FinFETs) have been introduced to replace planar transistors. The structures of FinFETs and methods of fabricating the FinFETs are being developed. 
     The formation of FinFETs typically includes forming dummy gate stacks, and replacing the dummy gate stacks with replacement gate stacks. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIGS. 1-4, 5A, 5B, 6, 6A, 6B, 6C, 6D, 6E, 7-10, and 11A  are perspective views and/or cross-sectional views of intermediate stages in the formation of Fin Field-Effect Transistors (FinFETs) in accordance with some embodiments. 
         FIGS. 6F, 6G, 6H, and 6I  are cross-sectional views of intermediate stages in the formation of a dummy gate electrode with more than one narrowing sections in accordance with some embodiments of the present disclosure. 
         FIGS. 11B-1, 11B-2, and 11B-3  illustrate the heights of the transition levels of the sidewalls of replacement gates relative to the fin tops in accordance with some embodiments. 
         FIGS. 12-15  are cross-sectional views of intermediate stages in the formation of replacement gates with two transition regions in accordance with some embodiments. 
         FIGS. 16-23  are cross-sectional views of intermediate stages in the formation of replacement gates with the transition regions formed for selected sidewalls of selected replacement gates in accordance with some embodiments. 
         FIG. 24  illustrates a process flow for forming a FinFET in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “underlying,” “below,” “lower,” “overlying,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     A Fin Field-Effect Transistor (FinFET) having a replacement gate with narrower bottom end than the top end and the method of forming the same are provided in accordance with some embodiments. In accordance with some embodiments, the formation of dummy gate stacks is controlled, so that the dummy gate stacks have narrower bottom ends than the respective top ends, and hence the subsequent formation of replacement gates is easier, and the performance of the FinFET is improved. Embodiments discussed herein are to provide examples to enable making or using the subject matter of this disclosure, and a person having ordinary skill in the art will readily understand modifications that can be made while remaining within contemplated scopes of different embodiments. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements. Although method embodiments may be discussed as being performed in a particular order, other method embodiments may be performed in any logical order. 
       FIGS. 1-4, 5A, 5B, 6, 6A, 6B, 6C, 6D, 6E, 7-10, and 11A  are perspective views and/or cross-sectional views of intermediate stages in the formation of Fin Field-Effect Transistors (FinFETs) in accordance with some embodiments of the present disclosure. The corresponding processes are also reflected schematically in the process flow shown in  FIG. 24 . 
     In  FIG. 1 , substrate  20  is provided. The substrate  20  may be a semiconductor substrate, such as a bulk semiconductor substrate, a Semiconductor-On-Insulator (SOI) substrate, or the like, which may be doped (e.g., with a p-type or an n-type dopant) or undoped. The semiconductor substrate  20  may be a part of wafer  10 , such as a silicon wafer. Generally, an SOI substrate is a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a Buried Oxide (BOX) layer, a silicon oxide layer, or the like. The insulator layer is provided on a substrate, typically a silicon or glass substrate. Other substrates such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of semiconductor substrate  20  may include silicon; germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. 
     Further referring to  FIG. 1 , well region  22  is formed in substrate  20 . The respective process is shown as process  202  in the process flow  200  shown in  FIG. 24 . In accordance with some embodiments of the present disclosure, well region  22  is a p-type well region formed through implanting a p-type impurity, which may be boron, indium, or the like, into substrate  20 . In accordance with other embodiments of the present disclosure, well region  22  is an n-type well region formed through implanting an n-type impurity, which may be phosphorus, arsenic, antimony, or the like, into substrate  20 . The resulting well region  22  may extend to the top surface of substrate  20 . The n-type or p-type impurity concentration may be equal to or less than 10 18  cm −3 , such as in the range between about 10 17  cm −3  and about 10 18  cm −3 . 
     Referring to  FIG. 2 , isolation regions  24  are formed to extend from a top surface of substrate  20  into substrate  20 . Isolation regions  24  are alternatively referred to as Shallow Trench Isolation (STI) regions hereinafter. The respective process is shown as process  204  in the process flow  200  shown in  FIG. 24 . The portions of substrate  20  between neighboring STI regions  24  are referred to as semiconductor strips  26 . To form STI regions  24 , pad oxide layer  27  and hard mask layer  29  are formed on semiconductor substrate  20 , and are then patterned. Pad oxide layer  27  may be a thin film formed of silicon oxide. In accordance with some embodiments of the present disclosure, pad oxide layer  27  is formed in a thermal oxidation process, wherein a top surface layer of semiconductor substrate  20  is oxidized. Pad oxide layer  27  acts as an adhesion layer between semiconductor substrate  20  and hard mask layer  29 . Pad oxide layer  27  may also act as an etch stop layer for etching hard mask layer  29 . In accordance with some embodiments of the present disclosure, hard mask layer  29  is formed of silicon nitride, for example, using Low-Pressure Chemical Vapor Deposition (LPCVD). In accordance with other embodiments of the present disclosure, hard mask layer  29  is formed by thermal nitridation of silicon, or Plasma Enhanced Chemical Vapor Deposition (PECVD). A photo resist (not shown) is formed on hard mask layer  29  and is then patterned. Hard mask layer  29  is then patterned using the patterned photo resist as an etching mask to form hard masks  29  as shown in  FIG. 2 . 
     Next, the patterned hard masks  29  are used as an etching mask to etch pad oxide layer  27  and substrate  20 , followed by filling the resulting trenches in substrate  20  with a dielectric material(s). A planarization process such as a Chemical Mechanical Polish (CMP) process or a mechanical grinding process is performed to remove excessing portions of the dielectric materials, and the remaining portions of the dielectric material(s) are STI regions  24 . STI regions  24  may include a liner dielectric (not shown), which may be a thermal oxide formed through a thermal oxidation of a surface layer of substrate  20 . The liner dielectric may also be a deposited silicon oxide layer, silicon nitride layer, or the like formed using, for example, Atomic Layer Deposition (ALD), High-Density Plasma Chemical Vapor Deposition (HDPCVD), or Chemical Vapor Deposition (CVD). STI regions  24  may also include a dielectric material over the liner oxide, wherein the dielectric material may be formed using Flowable Chemical Vapor Deposition (FCVD), spin-on coating, or the like. The dielectric material over the liner dielectric may include silicon oxide in accordance with some embodiments. 
     The top surfaces of hard masks  29  and the top surfaces of STI regions  24  may be substantially level with each other. Semiconductor strips  26  are between neighboring STI regions  24 . In accordance with some embodiments of the present disclosure, semiconductor strips  26  are parts of the original substrate  20 , and hence the material of semiconductor strips  26  is the same as that of substrate  20 . In accordance with alternative embodiments of the present disclosure, semiconductor strips  26  are replacement strips formed by etching the portions of substrate  20  between STI regions  24  to form recesses, and performing an epitaxy to regrow another semiconductor material in the recesses. Accordingly, semiconductor strips  26  are formed of a semiconductor material different from that of substrate  20 . In accordance with some embodiments, semiconductor strips  26  are formed of silicon germanium, silicon carbon, or a III-V compound semiconductor material. 
     Referring to  FIG. 3 , STI regions  24  are recessed. The top portions of semiconductor strips  26  thus protrude higher than the top surfaces  24 A of the remaining portions of STI regions  24  to form protruding fins  26 ′. The respective process is shown as process  206  in the process flow  200  shown in  FIG. 24 . The etching may be performed using a dry etching process, wherein HF 3  and NH 3 , for example, are used as the etching gases. During the etching process, plasma may be generated. Argon may also be included. In accordance with alternative embodiments of the present disclosure, the recessing of STI regions  24  is performed using a wet etching process. The etching chemical may include HF, for example. 
     In above-illustrated embodiments, the fins may be patterned by any suitable method. For example, the fins may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Generally, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in one embodiment, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-aligned process. The sacrificial layer is then removed, and the remaining spacers, or mandrels, may then be used to pattern the fins. 
       FIG. 4  illustrates the formation of dummy gate stack  34  in accordance with some embodiments, with the dummy gate stack  34  including dummy gate dielectric layer  28 , dummy gate electrode layer  30 , and hard mask  32 . The respective process is shown as process  208  in the process flow  200  shown in  FIG. 24 . Dummy gate dielectric layer  28  is formed on the sidewalls and the top surfaces of protruding fins  26 ′. In accordance with some embodiments of the present disclosure, dummy gate dielectric layer  28  is formed using a conformal deposition process, which may include Atomic Layer Deposition (ALD), Chemical Vapor Deposition (CVD), or the like. The material of dummy gate dielectric layer  28  may include silicon oxide, silicon nitride, silicon carbo-nitride, or the like. In accordance with alternative embodiments, the formation of dummy gate dielectric layer  28  includes oxidizing (for example, using a thermal oxidation process) the surface portions of protruding fins  26 ′. The resulting dummy gate dielectric layer  28  includes an oxide formed on the exposed surfaces of protruding fins  26 ′, but not on the top surfaces of STI regions  24 . The formation of dummy gate dielectric layer  28  may or may not include a deposition process. Dashed lines are used to show that some portions of dummy gate dielectric layer  28  on the top of STI regions  24  may or may not be formed, depending on the formation process. 
     Dummy gate electrode layer  30  is deposited on dummy gate dielectric layer  28 . Dummy gate electrode layer  30  may be formed of or comprise polysilicon or amorphous silicon, and other materials may also be used. The formation process may include a deposition process followed by a planarization process. Hard mask layer  32  is then deposited on dummy gate electrode layer  30 . Hard mask layer  32  may be formed of or comprise silicon nitride, silicon oxide, silicon oxy-carbo-nitride, or multi-layers thereof. 
     Next, referring to  FIG. 5A , hard mask layer  32  is patterned, for example, etched by using a patterned photo resist (not shown) as an etching mask, hence forming hard masks  32 ′. The respective process is shown as process  210  in the process flow  200  shown in  FIG. 24 .  FIG. 5B  illustrates the reference vertical cross-section  5 B- 5 B as shown in  FIG. 5A . In  FIGS. 5A, 5B  and subsequent figures, the level of the top surface  26 T of protruding fins  26 ′ is illustrated. Also, dummy gate dielectric layer  28  is formed of or includes a dielectric material, which may be (or may not be) the same material as that of STI regions  24 . Accordingly, dummy gate dielectric layer  28  is shown in  FIG. 5B , but may not be illustrated separately in subsequent figures. Accordingly, the top surface portion of the illustrated STI region  24  in subsequent figures may be considered as being the dummy gate dielectric layer  28 . 
     In subsequent processes, dummy gate electrode layer  30  and possibly dummy gate dielectric layer  28  are patterned, with hard mask  32 ′ being used as an etching mask. The dummy gate electrodes  30 ′ are thus formed, as shown in  FIG. 6 . Dummy gate stacks  34 ′ may have lower portions (also referred to as narrowing portions) narrower and more tapered than the upper portions, and the details of dummy gate electrodes  30 ′ are shown in  FIG. 6E . 
       FIGS. 6A, 6B, 6C, 6D, and 6E  illustrate the intermediate stages in the patterning of dummy gate electrode layer  30  in accordance with some embodiments. Referring to  FIG. 6A , a first etching process  36 , which is anisotropic etching process, is performed using hard masks  32 ′ as an etching mask. In accordance with some embodiments, the process gas includes both of an etching gas and a byproduct-generating gas. The etching gas may include Cl 2 , HBr, CF 4 , CHF 3 , CH 2 F 2 , CH 3 F, C 4 F 6 , or combinations thereof. The byproduct-generating gas may include nitrogen (N 2 ), oxygen (O 2 ), SO 2 , CO 2 , CO, or combinations thereof. Other gases such as Ar, He, Ne, or the like, may also be added into the process gas. In accordance with some embodiments of the present disclosure, the etching process is performed with a source power in a range between about 10 watts and about 3,000 watts. The bias power is higher than about 200 watts, and may be in the range between about 10 watts and about 3,000 watts. The pressure of the process gas may be in the range between about 1 mTorr and about 800 mTorr. The flow rate of the process gas may be in the range between about 1 sccm and about 5,000 sccm. 
     In the etching process  36 , the surface layer of the formed dummy gate electrodes  30 ′ reacts with the byproduct-generating gas to form byproduct layer  38 , which includes portions on the sidewalls of the newly formed portions of dummy gate electrodes  30 ′. The respective process is shown as process  212  in the process flow  200  shown in  FIG. 24 . Byproduct layer  38  may (or may not, as shown in  FIG. 6F ) be formed on the surfaces of hard masks  32 ′, depending on the composition of hard masks  32 ′. The byproduct layer  38  may include Si w O x N y C z , SiBr a Cl b O c , or the like, depending on the process gas. In order to generate byproduct layer  38 , and to make byproduct layer  38  to be thick enough as an etching mask in the subsequent process, more byproduct-generating gas is introduced. For example, the ratio of the flow rate of the byproduct-generating gas to the flow rate of the etching gas may be higher than about 40, and may be in the range between about 1 and about 1,000. With the proceeding of the etching process  36 , the byproduct layer  38  extends down, as shown by  FIG. 6B . The thickness T 1  of byproduct layer  38  may be in the range between about 2 Å and about 300 Å. In etching process  36 , plasma is turned on. The temperature of the respective wafer may be in the range between about 0° C. and about 150° C. 
     In accordance with some embodiments, after the etching process  36 , the etching gas is stopped, and the byproduct-generating gas is conducted to increase the thickness of byproduct layer  38 . The respective byproduct-generating gas may include N 2 , O 2 , SO 2 , CO 2 , CO, SiCl 4 , or the like, or combinations thereof. In this process, plasma may be turned on. The respective process is referred to as a byproduct-thickening process. In accordance with some embodiments, the byproduct-thickening process is performed in-situ with (in the same process chamber as) the etching process  36  (and the subsequently performed etching process  40  ( FIG. 6C )), and there is no vacuum break between these processes. In accordance with alternative embodiments, the byproduct-thickening process is performed ex-situ with processes  36  and  40 , with vacuum break therebetween. The ex-situ byproduct-thickening process may be performed using N 2 , O 2 , SO 2 , CO 2 , CO, or the like, or combinations thereof as process gases. 
     In accordance with alternative embodiments, the byproduct-thickening process is performed using a chemical solution, which may include ozone and/or CO 2  dissolved in de-ionized water, with wafer  10  being dipped in the chemical solution for the byproduct layer  38  to form. 
     In accordance with yet alternative embodiments, in etching process  36 , the process gas includes the etching gas, and is free from the byproduct-generating gas. Accordingly, in etching process  36 , no byproduct layer is generated. The byproduct layer  38  is generated by a byproduct-thickening process, which may include the in-situ, ex-situ, or the wet process as aforementioned. In accordance with some embodiments, in the in-situ, ex-situ, or the wet process, byproduct layer  38  is also formed on the exposed horizontal surface of the un-etched portion of dummy gate electrode layer  30 , similar to the protection layer  38 ′ as shown in  FIG. 6G . In accordance with other embodiments, in some in-situ or ex-situ processes, byproduct layer  38  is formed (or thickened) on the sidewalls, but not on the horizontal surface of the un-etched portion of dummy gate electrode layer  30 . 
     Referring to  FIG. 6C , after the first etching process  36  is performed, a second anisotropic etching process  40  is performed to further etch dummy gate electrode layer  30 , until dummy gate electrode layer  30  is etched-through to generate dummy gate electrode  30 ′. The respective process is shown as process  214  in the process flow  200  shown in  FIG. 24 . In etching process  40 , plasma is turned on. Dummy gate dielectric layer  28  may then be patterned, or may not be patterned at this time. The second etching process  40  is performed using an etching gas, which may include Cl 2 , HBr, CF 4 , CHF 3 , CH 2 F 2 , CH 3 F, C 4 F 6 , or combinations thereof. In accordance with some embodiments, the process gas is free from any byproduct-generating gas, which may include N 2 , O 2 , SO 2 , CO 2 , CO, or the like. In accordance with alternative embodiments, the process gas includes one or more of the byproduct-generating gas. The flow rate of the byproduct-generating gas, however, is reduced compared to the etching process  36 . If the flow rates of the byproduct-generating gas in etching processes  36  and  40  are denoted as being BPFR 36  and BPFR 40 , respectively, the ratio BPFR 40 /BPFR 36  may be smaller than about 0.2 or 0.1, and may be in the range between about 0 and about 0.2 or 0.1. On the other hand, the flow rates of the etching gases in etching processes  36  and  40  may be equal to each other, or may be different from each other. Accordingly, substantially no new byproduct layer is generated in etching process  40 , or although there is byproduct layer  38  generated by etching process  40 , the thickness T 2  of the newly generated byproduct layer  38  is smaller than thickness T 1 . For example, in  FIG. 6C , dashed lines are used to illustrate the byproduct layer  38  generated in etching process  40 , which byproduct layer  38  has thickness T 2 . In accordance with some embodiments, ratio T 2 /T 1  is smaller than about 0.2 or 0.1, and may be in the range between 0 and about 0.2 or 0.1. 
       FIG. 6C  illustrates several embodiments, wherein several possible positions of the bottom end  38 BE of byproduct layer  38  are illustrated. The level of the top surfaces  26 T of protruding fins  26 ′ is also shown. In various embodiments, the bottom end  38 BE may be higher than, level with, or lower than, the top surfaces  26 T of protruding fins  26 ′. For example, the bottom end  38 BE of byproduct layer  38  may be higher than fin top surface  26 T by height difference D 1 , which may be in the range between 0 nm and about 50 nm. The bottom end  38 BE of byproduct layer  38  may be lower than fin top surface  26 T by height difference D 2 , which may be in the range between 0 nm and about 100 nm. 
     Referring to  FIG. 6D , after the formation of dummy gate electrode  30 ′, etching process  42  is performed, which process is also referred to as a reshaping process of the dummy gate electrode  30 ′. The respective process is shown as process  216  in the process flow  200  shown in  FIG. 24 . In accordance with some embodiments, the etching process  42  is performed using a process gas that can etch dummy gate electrode  30 ′, which process gas may be selected from Cl 2 , HBr, CF 4 , CHF 3 , CH 2 F 2 , CH 3 F, C 4 F 6 , or combinations. The process gas may be free from the byproduct-generating gases such as N 2 , O 2 , SO 2 , CO 2 , CO, or the like, or may include a small amount of byproduct-generating gas to tune the etching process. Accordingly, no byproduct layer is further generated. The etching process  42  may be performed using a source power in a range between about 10 watts and about 3,000 watts. The pressure of the process gas may be in the range between about 1 mTorr and about 800 mTorr. The flow rate of the process gas may be in the range between about 1 sccm and about 5,000 sccm. The bias power is reduced compared to what are used in processes  36  and  40 , so that the etching process  42 , besides the anisotropic effect, also has some isotropic effect. The bias power may smaller than about 40 percent, and may be between about 5 percent and about 80 percent of the bias power used in etching processes  36  and  40 . In accordance with some embodiments, the bias power used in etching process  42  may be lower than about 100 watts, and may be in the range between about 10 watts and about 3,000 watts. 
     As a result of the etching process  42 , dummy gate electrode  30 ′ is reshaped, and the resulting structure is shown in  FIG. 6D  in accordance with some embodiments. Dummy gate stack  34 ′ is thus formed, which may include the patterned dummy gate dielectric  28 ′ ( FIG. 7 ) when it is patterned, or not include dummy gate dielectric  28 ′ if it is not patterned. In the etching process  42 , byproduct layer  38  partially protects the lower portion  30 A′ of dummy gate electrode  30 ′, which lower portion is lower than the bottom ends  38 BE of byproduct layer  38 . Accordingly, byproduct layer  38  is alternatively referred to as a protection layer. Since etching process  42  also has isotropic effect, there is also lateral etching on the lower portion  30 A′ of dummy gate electrode  30 ′. The upper parts of the lower portion  30 A′ are protected more, and the lateral etching is less significant. The lower parts of the lower portion  30 A′ are protected less, and the lateral etching is more significant. As a result, the lower portion  30 A′ is tapered. Throughout the description, lower portion  30 A′ is also referred to as a narrowing portion. 
     In accordance with some embodiments, lower portion  30 A′ has slanted and straight sidewalls. The top width W 2  is greater than bottom width W 3 . In accordance with some embodiment, the difference (W 2 −W 3 ) is greater than about 3 Å. The height H 1  of the lower portion  30 A′ may be greater than about 300 Å. The tilt angle θ 1  of the sidewalls of the lower portion  30 A′ is smaller than 90 degrees, and may be smaller than about 88 degrees, or in the range between about 80 degrees and about 88 degrees. 
     Upper portion  30 B′ (having a top width W 1 ) has sidewalls that may be straight, and are more vertical than lower portion  30 A′, with the tilt angle θ 2  being greater than 01. In accordance with some embodiments, the tilt angle θ 2  is equal to or smaller than 90 degrees. The difference (θ 2 −θ 1 ) is greater than about 2 degrees, about 5 degrees, or about 10 degrees, and may be in the range between about 1 degree and about 30 degrees. Height H 2  of the upper portion  30 B′ may be greater than about 40 nm, and may be in the range between about 10 nm and about 200 nm. 
     After the etching process  42 , the byproduct layer  38  is removed, for example, in an etching process. The respective process is shown as process  218  in the process flow  200  shown in  FIG. 24 . The resulting structure is shown in  FIG. 6E . Next, as shown in  FIG. 7 , gate spacers  46  are formed on the sidewalls of dummy gate stacks  34 ′. The respective process is shown as process  220  in the process flow  200  shown in  FIG. 24 . In accordance with some embodiments of the present disclosure, gate spacers  46  are formed of a dielectric material(s) such as silicon nitride, silicon carbo-nitride, or the like, and may have a single-layer structure or a multi-layer structure including a plurality of dielectric layers. 
     An etching process is then performed. The portions of protruding fins  26 ′ that are not covered by dummy gate stacks  34 ′ and gate spacers  46  are etched, resulting in the structure shown in  FIG. 8 . The respective process is shown as process  222  in the process flow  200  shown in  FIG. 24 . The etching process may be anisotropic, and hence the portions of protruding fins  26 ′ directly underlying dummy gate stacks  34 ′ and gate spacers  46  are protected, and are not etched. The top surfaces of the recessed semiconductor strips  26  may be lower than the top surfaces  24 A of STI regions  24  in accordance with some embodiments. Recesses  50  are accordingly formed. Recesses  50  include some portions located on the opposite sides of dummy gate stacks  34 ′, and some portions between remaining portions of protruding fins  26 ′. 
     Next, epitaxy regions (source/drain regions)  54  are formed by selectively growing (through epitaxy) a semiconductor material in recesses  50 , resulting in the structure in  FIG. 9 . The respective process is shown as process  224  in the process flow  200  shown in  FIG. 24 . Depending on whether the resulting FinFET is a p-type FinFET or an n-type FinFET, a p-type or an n-type impurity may be in-situ doped with the proceeding of the epitaxy. For example, when the resulting FinFET is a p-type FinFET, silicon germanium boron (SiGeB), silicon boron (SiB), or the like may be grown. Conversely, when the resulting FinFET is an n-type FinFET, silicon phosphorous (SiP), silicon carbon phosphorous (SiCP), or the like may be grown. In accordance with alternative embodiments of the present disclosure, epitaxy regions  54  comprise III-V compound semiconductors such as GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlAs, AlP, GaP, combinations thereof, or multi-layers thereof. After recesses  50  are filled with epitaxy regions  54 , the further epitaxial growth of epitaxy regions  54  causes epitaxy regions  54  to expand horizontally, and facets may be formed. The further growth of epitaxy regions  54  may also cause neighboring epitaxy regions  54  to merge with each other. Voids (air gaps)  56  may be generated. 
     After the epitaxy process, epitaxy regions  54  may be further implanted with a p-type or an n-type impurity to form source and drain regions, which are also denoted using reference numeral  54 . In accordance with alternative embodiments of the present disclosure, the implantation step is skipped when epitaxy regions  54  are in-situ doped with the p-type or n-type impurity during the epitaxy. 
       FIG. 10  illustrates a perspective view of the structure after the formation of Contact Etch Stop Layer (CESL)  58  and Inter-Layer Dielectric (ILD)  60 . The respective process is shown as process  226  in the process flow  200  shown in  FIG. 24 . CESL  58  may be formed of silicon oxide, silicon nitride, silicon carbo-nitride, or the like, and may be formed using CVD, ALD, or the like. ILD  60  may include a dielectric material formed using, for example, FCVD, spin-on coating, CVD, or another deposition method. ILD  60  may be formed of an oxygen-containing dielectric material, which may be a silicon-oxide based material such as Tetra Ethyl Ortho Silicate (TEOS) oxide, Phospho-Silicate Glass (PSG), Boro-Silicate Glass (BSG), Boron-Doped Phospho-Silicate Glass (BPSG), or the like. A planarization process such as a CMP process or a mechanical grinding process may be performed to level the top surfaces of ILD  60 , dummy gate stacks  34 ′, and gate spacers  46  with each other. 
     Dummy gate stacks  34 ′ are then removed. The portions of dummy gate dielectric layer on protruding fins  26 ′ are also removed to expose protruding fins  26 ′. Replacement gate stacks  66  and self-aligned hard masks  80  are formed in the resulting trenches. The resulting structure is shown in  FIG. 11A . The respective process is shown as process  228  in the process flow  200  shown in  FIG. 24 . Gate stack  66  includes gate dielectric  62  and gate electrode  64 . Gate dielectric  62  may include an Interfacial Layer (IL) (not shown) and a high-k dielectric layer. The IL is formed on the exposed surfaces of protruding fins  26 ′, and may include an oxide layer such as a silicon oxide layer, which is formed through the thermal oxidation of protruding fins  26 ′, a chemical oxidation process, or a deposition process. The high-k dielectric layer includes a high-k dielectric material such as hafnium oxide, lanthanum oxide, aluminum oxide, zirconium oxide, or the like. 
     Referring further to  FIG. 11A , gate electrode  64  is formed on gate dielectric  62 . Gate electrode  64  may include stacked layers, which may include a diffusion barrier layer (a capping layer), and one or more work-function layer over the diffusion barrier layer. The diffusion barrier layer may be formed of titanium nitride, which may (or may not) be doped with silicon, titanium silicon nitride, or the like. The work-function layer determines the work-function of the gate electrode, and includes at least one layer, or a plurality of layers formed of different materials. Gate electrode  64  may also include a metal-filling region, which may be formed of or comprise cobalt, tungsten, alloys thereof, or other metals or metal alloys. 
     Next, a planarization process such as a Chemical Mechanical Polish (CMP) process or a mechanical grinding process is performed, so that the top surface of gate stack  66  is coplanar with the top surface of ILD  60 . In a subsequent process, gate stack  66  is etched back, resulting in a recess formed between opposite gate spacers  46 . Next, hard masks  80  are formed over replacement gate stacks  66 . In accordance with some embodiments of the present disclosure, the formation of hard masks  80  includes a deposition process to form a blanket dielectric material, and a planarization process to remove the excess dielectric material over gate spacers  46  and ILD  60 . Hard masks  80  may be formed of silicon nitride, for example, or other like dielectric materials. FinFET  81  is thus formed. 
       FIGS. 11B-1, 11B-2, and 11B-3  illustrate the cross-sectional views of replacement gate stacks  66  in accordance with some embodiments, wherein the cross-sectional views are obtained from the reference cross-section  11 B- 11 B in  FIG. 11A . The positions of the top surfaces  26 T and the bottom ends  26 B of protruding fins  26 ′ are also marked, and protruding fins  26 ′ will extend between the top surfaces  26 T and the bottom ends  26 B, although protruding fins  26 ′ are not shown since they are in a different plane than the illustrated plane. Lower portions  66 A′ of replacement gate stacks  66  replace, and hence have the same profile as, the lower portions  30 A′ of dummy gate electrodes  30 ′ in  FIG. 6D . As a result, the lower portions  30 A′ are tapered. Throughout the description, lower portions  66 A′ are also referred to as narrowing portions. Upper portions  66 B′ of replacement gate stacks  66  replace, and hence have the same profile as, the upper portions  30 B′ of dummy gate electrodes  30 ′ in  FIG. 6D . Accordingly, the tilt angles θ 1  and θ 2  are the same as discussed referring to  FIG. 6D , and the details are not repeated herein. Also, the sidewall profiles of replacement gate stacks  66  will follow the sidewall profiles of dummy gate electrodes  30 ′ in  FIG. 6D . 
       FIG. 11B-1  illustrates the embodiments in which the joining level  82  of the lower portions  66 A′ and the corresponding upper portions  66 B′ is higher than the top surface  26 T of protruding fin  26 ′.  FIG. 11B-2  illustrates the embodiments in which the joining level  82  is level with the top surface  26 T of protruding fin  26 ′.  FIG. 11B-3  illustrates the embodiments in which the joining level  82  is lower than the top surface  26 T of protruding fin  26 ′. The adjustment of joining level  82  may include adjusting when to transit from process  36  ( FIG. 6B ) to process  40  ( FIG. 6C ), adjusting the pressure, power, gas flow, and etching time of etching processes  36  and  40 . For example, increasing pressure and power of the etching process may help to form a thick-enough byproduct layer on the sidewalls of the lower portion of dummy gate electrode  30 ′, and hence may help to achieve the embodiments in  FIG. 11B-3 . It is also appreciated that since the high-k dielectric layer of gate dielectric  62  may be conformal, the above-discussed tilt angles of gate stacks  66  may also be equal to the tilt angles of the sidewalls of the corresponding portions of gate electrodes  64 . 
     In accordance with some embodiments, two immediate neighboring replacement gate stacks  66  may have their joining levels  82  to be different from each other. For example, one of the two immediate neighboring replacement gate stacks  66  may adopt the one of embodiments as shown in one of  FIGS. 11B-1, 11B-2, and 11B-3 , while the other one of the two immediate neighboring replacement gate stacks  66  may adopt a different one of embodiments as shown in one of  FIGS. 11B-1, 11B-2, and 11B-3 . 
       FIGS. 6F, 6G, 6H, and 6I  illustrate the formation of dummy gate stacks  34 ′ in accordance with alternative embodiments. Unless specified otherwise, the materials and the formation processes of the components in these embodiments (and the embodiments in  FIGS. 12-23 ) are essentially the same as the like components, which are denoted by like reference numerals in the preceding embodiments shown in  FIGS. 1-4, 5A, 5B, 6, 6A, 6B, 6C, 6D, and 6E . The details regarding the formation process and the materials of the components shown in  FIGS. 6F, 6G, 6H, and 6I  and  FIGS. 12-23  may thus be found in the discussion of the preceding embodiments. 
     The initial processes are the same as shown in  FIGS. 1-4, 5A, and 5B . Next, referring to  FIG. 6F , etching process  40  (also denoted as  40 A) is performed. The process details are the same as what have been discussed referring to the etching process  40  in  FIG. 6C . Accordingly, dummy gate electrode layer  30  is etched, and no byproduct layer is formed. Referring to  FIG. 6G , protection layer  38 ′ is deposited, for example, using ALD, CVD, PEALD, PECVD, or the like. The material of protection layer  38 ′ may include SiN, SiON, SiCON, SiC, SiOC, SiO 2 , or the like. The thickness of protection layer  38 ′ may be in the range between about 2 Å and about 300 Å. Next, referring to  FIG. 6H , another etching process  40  (denoted as  40 B) is performed, which is performed using essentially the same process conditions as discussed referring to  FIG. 6C . Dummy gate electrode layer  30  is thus etched-through to form dummy gate electrode  30 ′. 
       FIG. 6I  illustrates etching process  42 , which is used to reshape the profile of dummy gate electrode  30 ′. The process details may be found referring to  FIG. 6D , and is not repeated herein. The profile of dummy gate electrode  30 ′ may also be found referring to the discussion of  FIG. 6D . Protection layer  38 ′ is then removed through etching. The remaining processes for forming the FinFET  81  are shown in  FIGS. 7-11A, 11B-1, 11B-2, and 11B-3 . 
     The dummy gate electrodes  30 ′ as shown in  FIGS. 6D and 6I  have one narrowing (lower portion) portion  30 A′ and one transition region, at which the underlying portion starts to narrow down. In accordance with alternative embodiments, dummy gate electrodes may have more than one (such as two, three, four, or more) narrowing portions.  FIGS. 12 through 15  illustrate the process for forming a dummy gate electrode  34 ′ with two narrowing portions, with the sidewalls of the lower portions tilted more than the respective upper portions. The process may start from the structure shown in  FIG. 6D , and the respective structure is reproduced as  FIG. 12 . The formation of the structure shown in  FIG. 12  accordingly may include the first etching process  36  ( FIGS. 6A and 6B ), the second etching process  40  ( FIG. 6C ), and the third etching process  42  ( FIG. 6D ). 
     Next, referring to  FIG. 13 , another etching process  36  (denoted as  36 B) is performed. The details of etching process  36  may be found referring to  FIGS. 6A and 6B , and the process gas includes the etching gas and the byproduct-generating gas. The lower portion  30 A′ is actually not etched since the etching is anisotropic. In the meantime, byproduct layer  38  extends downwardly onto the slanted sidewalls of dummy gate electrode  30 ′. In accordance with some embodiments, the position of the bottom ends of byproduct layer  38  is determined by adjusting the respective process. For example, the pressure of the process gas is adjusted not to be too high, and not to be too low. If the pressure is too high, the byproduct layer  38  extends down too much, and may even be formed as a conformal layer on the entire surface of dummy gate electrode  30 ′. If the pressure is too low, the byproduct layer  38  cannot extend down for the desirable distance. In accordance with some embodiments, the pressure is in the range between about 1 mTorr and about 800 mTorr. Similarly, a too-high source power may result in the byproduct layer  38  to extend down too much, and a too-low source power may result in the byproduct layer  38  not to extend down enough. In accordance with some embodiments, the source power is in the range between about 10 watts and about 3,000 watts. The bias power is lower than that are used in both etching processes  36  and  40  in order to have both anisotropic and isotropic effect in the etching process. In accordance with some embodiments, the bias power is in the range between about 10 watts and about 3,000 watts. Furthermore, N 2  is more active than O 2 , and more N 2  may result in byproduct layer  38  to extend more. In accordance with some embodiments, the etching process as shown in  FIG. 13  has a higher (for example, more than 50 percent) flow rate of N 2 , and/or a lower (for example, lower than 50 percent) flow rate of O 2  than the etching process  36  in  FIGS. 6A and 6B . 
       FIG. 14  illustrates another etching process  42  (denoted as  42 C). The process condition may be essentially the same as in  FIG. 6D . Alternatively, the bias power may be further reduced than used in the process  42  shown in  FIG. 6D . As a result, the portions of dummy gate electrode  30 ′ underlying the bottom end  38 BE of byproduct layer  38  are etched, and the sidewalls become further tilted (and may be straight). The lower portion  30 A′ thus includes portions  30 A 1 ′ and  30 A 2 ′, which have tilt angles θ 3  and θ 1 , respectively. Tilt angle θ 3  is smaller than tilt angle θ 1 , which is further smaller than tilt angle θ 2 . In accordance with some embodiments, angle difference (θ 2 −θ 1 ) and the angle difference (θ 1 −θ 3 ) are greater than about 2 degrees, 5 degrees, or 10 degrees, and may be in the range between about 1 degrees and about 30 degrees. 
       FIG. 15  illustrates replacement gate stacks  66 , which replace the dummy gate stacks  34 ′ in  FIG. 14 . The resulting replacement gate stacks  66  have the same profile as dummy gate stack  34 ′, and have the tilt angles θ 1 , θ 2 , and θ 3  as discussed referring to  FIG. 14 . The possible levels of top surface  26 T of the protruding fins  26 ′ are also illustrated. 
       FIGS. 16 through 23  illustrate the process for selectively reshaping dummy gate stacks  34 ′ in accordance with some embodiments. Again, the details of the processes and the materials of these embodiments may be found from the like processes and materials as discussed in preceding embodiments. Referring to  FIG. 16 , STI region  24  is formed extending into substrate  20 . Dummy gate dielectric layer  28 , dummy gate electrode layer  30 , and hard masks  32 ′ are formed. The formation processes are essentially the same as shown in  FIGS. 1-4, 5A, and 5B , and are not repeated herein. Again, since the cross-sectional view in  FIG. 16  is obtained crossing STI region  24 , and both gate dielectric layer  28  and STI region  24  are dielectrics, gate dielectric layer  28  is not shown separately in subsequent figures. 
       FIG. 17  illustrates the etching process  36 , whose details may be found referring to  FIGS. 6A and 6B . Byproduct layer  38  is thus formed. Next, referring to  FIG. 18 , etching process  40  is performed to etch-through dummy gate electrode layer  30  and to form dummy gate electrode  30 ′. The details of etching processes  36  and  40  may be found from the preceding embodiments. There is no byproduct layer newly formed by etching process  40 , or the byproduct layer, if formed, is thin, similar to what is shown in  FIG. 6C . Again, the bottom ends of byproduct layer  38  may be higher than, level with, or lower than, the top surface  26 T (the possible levels are illustrated) of protruding fins  26 ′. 
       FIG. 19  illustrates the formation of etching mask  84 , which may be photo resist in accordance with some embodiments. Etching mask  84  protects some of the dummy gate electrodes  30 ′ partially or entirely, and leaves some other dummy gate electrodes  30 ′ uncovered. Next, referring to  FIG. 20 , etching process  42  is performed. The details of etching process  42  may be found from the preceding embodiments. The sidewalls of the dummy gate electrodes  30 ′ exposed to the etching gas are reshaped. The profiles of the reshaped sidewalls may be essentially the same as the reshaped sidewalls as shown in  FIG. 6D , and the details may be found referring to the discussion of  FIG. 6D . The other sidewalls of the dummy gate electrodes  30 ′ protected by etching mask  84  are not reshaped. Furthermore, an example is also shown with the right sidewall of the right-most dummy gate electrode  30 ′ not reshaped since the distance of the sidewall is close to the etching mask enough, so that the etching gas cannot reach the sidewall. Throughout the description, the reshaped (and hence more slanted) sidewalls are denoted as  30 SL (with SL meaning “slanted”), and the non-reshaped (and hence straighter) sidewalls are denoted as  30 ST (with ST meaning “straighter”). Also, letter “A,” “B,” “C,” “D,” or the like are added for identifying individual sidewalls. The profiles of dummy gate electrodes  30 ′ are discussed referring to  FIGS. 22 and 23 . 
     Next, etching mask  84  is removed, and the resulting structure is shown in  FIG. 21 . Byproduct layer  38  is then removed, and the resulting structure is shown in  FIG. 22 . The remaining processes for forming FinFETs, which are similar to the FinFET  81 , are shown in  FIGS. 7-10, 11A, 11B-1, 11B-2, and 11B-3 . The corresponding replacement gate stacks  66 , which replace dummy gate stacks  34 ′, are shown in  FIG. 23 . 
       FIGS. 22 and 23  illustrate the profiles such as the slanted edges and the tilt angles θ 1  and θ 2  of dummy gate electrodes  30 ′ and replacement gate stacks  66 . Some of the sidewalls of dummy gate electrodes  30 ′ and replacement gate stacks  66  have more tilted lower portions than the respective upper portions. For example, lower sidewall portions  30 SLA,  30 SLB,  30 SLC, and  30 SLD are more tilted than the respective upper portions of the respective sidewalls. On the other hand, some other lower dummy portions  30 STA,  30 STB,  30 STC, and  30 STD and their corresponding upper portions form continuous straight sidewalls. Furthermore, a dummy gate electrode  30 ′ (and the corresponding replacement gate electrode), such as the second dummy gate electrode  30 ′ counting from the right side of  FIG. 22  may have one slanted lower sidewall, while the opposing sidewall is straight and less tilted. Some dummy gate electrode  30 ′ may have sidewalls with both lower portions being more slanted than the upper portions, and some other dummy gate electrode  30 ′ may have sidewalls with both lower portions having the same tilt angles as the corresponding upper portions. 
     Furthermore, the embodiments in  FIG. 15  may also be applied to the embodiments in  FIGS. 16 through 23 , so that each of the slanted sidewalls  30 SLA,  30 SLB,  30 SLC, and  30 SLD may have more than one, such as between about 2 and about 10, straight and slanted portions, with each of the lower portions being straight and increasingly more slanted than the respective upper portions. 
     In accordance with some embodiments, distances S 1  between some fins are smaller than distances S 2 . For example, ratio S 2 /S 1  is greater than about 2.0. The dummy gate electrodes  30 ′ having distances S 1  are referred to as being in a pattern-dense region, and the dummy gate electrodes  30 ′ having distances S 2  are referred to as being in a pattern-iso region. The sidewall profiles of dummy gates and replacement gates may be affected by whether the respective FinFETs are in pattern-dense or pattern-iso regions, which sidewall profile may not be desirable. In accordance with some embodiments of the present disclosure, by forming etching mask  84  in selected regions, the sidewall profile of dummy gate electrodes  30 ′ is controllable, and are not determined by whether the respective dummy gate electrodes  30 ′ are in pattern-dense or pattern-iso regions, and may be adjusted individually through etching mask  84 . 
     The embodiments as shown in  FIG. 23  may be used for satisfying both of the performance requirement and the reliability requirement. For example, for the dummy gate electrodes with narrowing lower portions, the respective transistors have better performance. The dummy gate electrodes of these transistors, however, are prone to collapsing. The FinFETs whose dummy gate electrodes are straight, on the other hand, are less prone to collapsing, but the performance of the resulting FinFETs may be not as good as those FinFETs with narrowing lower portions. By adopting the embodiments as shown in  FIGS. 16-23 , the performance-demanding FinFETs may adopt slanted sidewalls, while other FinFETs may adopt straight sidewalls to have better yield. 
     The embodiments of the present disclosure have some advantageous features. By etching dummy gate electrodes to have tapered lower portions, the performance of the resulting FinFETs is improved, and the saturation current is increased. By selectively forming slanted sidewalls for selected dummy gate electrodes, the requirement of improving performance and reliability is balanced. 
     In accordance with some embodiments of the present disclosure, a method includes depositing a dummy gate dielectric layer over a semiconductor region; depositing a dummy gate electrode layer over the dummy gate dielectric layer; performing a first etching process, wherein an upper portion of the dummy gate electrode layer is etched to form an upper portion of a dummy gate electrode; forming a protection layer on sidewalls of the upper portion of the dummy gate electrode; performing a second etching process, wherein a lower portion of the dummy gate electrode layer is etched to form a lower portion of the dummy gate electrode; performing a third etching process to etch the lower portion of the dummy gate electrode using the protection layer as an etching mask, wherein the dummy gate electrode is tapered by the third etching process; removing the protection layer; and replacing the dummy gate electrode with a replacement gate electrode. In an embodiment, the protection layer is formed simultaneously when the first etching process is performed. In an embodiment, the first etching process is performed using a process gas comprising an etching gas and a byproduct-generating gas. In an embodiment, the method further comprises, after the second etching process and before the third etching process, forming an additional etching mask to cover an additional dummy gate electrode; and after the third etching process, removing the additional etching mask. In an embodiment, the protection layer is a byproduct layer generated by the first etching process, and the protection layer comprises silicon and oxygen atoms. In an embodiment, the byproduct layer further comprises bromine and chlorine. In an embodiment, the first etching process and the second etching process are anisotropic, and the third etching process has both of an anisotropic effect and an isotropic effect. In an embodiment, the first etching process and the second etching process are preformed using first bias powers, and the third etching process is performed using a second bias power lower than the first bias powers. In an embodiment, the removing the protection layer is achieved through etching. 
     In accordance with some embodiments of the present disclosure, a structure includes a protruding semiconductor fin; a first gate stack on the protruding semiconductor fin, wherein the first gate stack comprises a first sidewall comprising a first lower straight portion having a first tilt angle; and a first upper straight portion having a second tilt angle greater than the first tilt angle; and a first gate spacer contacting both of the first lower straight portion and the first upper straight portion of the first gate stack. In an embodiment, the first gate stack further comprises a second sidewall opposing the first sidewall, and wherein the second sidewall comprises a second lower straight portion having the first tilt angle; and a second upper straight portion having the second tilt angle. In an embodiment, the first gate stack further comprises a second sidewall opposing the first sidewall, and wherein substantially an entirety of the second sidewall is straight. In an embodiment, the structure further includes a second gate stack comprising a third sidewall, and wherein substantially an entirety of the third sidewall is straight. In an embodiment, the first sidewall of the first gate stack further comprises a bottom straight portion lower than, and joined to, the first lower straight portion, wherein the bottom straight portion has a third tilt angle smaller than the first tilt angle. In an embodiment, a difference between the second tilt angle and the first tilt angle is greater than about 5 degrees. 
     In accordance with some embodiments of the present disclosure, a structure includes a semiconductor fin; a gate dielectric on the semiconductor fin; a gate electrode over the gate dielectric, wherein the gate electrode comprises an upper portion having a first sidewall; and a lower portion underlying and joined to the upper portion, wherein the lower portion has a second sidewall joined to the first sidewall, and wherein the first sidewall is more up straight than the second sidewall, and there is an abrupt change in tilting angles of the first sidewall and the second sidewall; and a gate spacer contacting the first sidewall and the second sidewall. In an embodiment, the gate electrode further comprises a bottom portion underlying and joined to the lower portion, wherein the bottom portion has a third sidewall joined to the second sidewall, and wherein the third sidewall is more tilted than the second sidewall, and there is an abrupt change in tilting angles of the second sidewall and the third sidewall. In an embodiment, the upper portion further comprises a third sidewall opposing the first sidewall, and the lower portion further comprises a fourth sidewall opposing the second sidewall, and wherein there is an abrupt change in tilting angles of the third sidewall and the fourth sidewall. In an embodiment, the upper portion further comprises a third sidewall opposing the first sidewall, and the lower portion further comprises a fourth sidewall opposing the second sidewall, and wherein the third sidewall and the fourth sidewall are parts of a same continuous and straight sidewall. In an embodiment, the gate electrode comprises metal, and the gate dielectric comprises a high-k dielectric material. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.