Patent Publication Number: US-2013249004-A1

Title: Same-Chip Multicharacteristic Semiconductor Structures

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a divisional application of U.S. patent application Ser. No. 12/861,976 (filed on Aug. 24, 2010), the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The exemplary embodiments of this invention relate generally to semiconductor structures and, more specifically, relate to chips having multiple semiconductor structures. 
     BACKGROUND 
     Fully depleted thin film semiconductor devices, such as extremely thin semiconductor-on-insulator (ETSOI) devices and field effect transistors (FETs) having one or more fin-shaped channels (FinFETs) with an undoped body, for example, are attractive options for the continued scaling of complementary metal-oxide semiconductor (CMOS) technology. 
     System-on-chip applications may require the usage of various devices with different characteristics on the same chip. In bulk technology, device characteristics, such as threshold voltage (V t ), are generally tuned by well/halo doping. However, such a body doping technique is inapplicable for fully depleted undoped body devices. 
     BRIEF SUMMARY 
     In one exemplary embodiment of the invention, a semiconductor structure comprising: a semiconductor-on-insulator substrate comprised of a top semiconductor layer overlying an insulation layer, where the insulation layer overlies a bottom substrate layer; at least one first device at least partially overlying and disposed upon a first portion of the top semiconductor layer, where the first portion of the top semiconductor layer has a first thickness, a first width and a first depth; and at least one second device at least partially overlying and disposed upon a second portion of the top semiconductor layer, where the second portion of the top semiconductor layer has a second thickness, a second width and a second depth, where the first thickness and the second thickness are along a common first axis, where the first width and the second width are along a common second axis, where the first depth and the second depth are along a common third axis, where at least one of the following holds: the first thickness is greater than the second thickness, the first width is greater than the second width and the first depth is greater than the second depth. 
     In another exemplary embodiment of the invention, a method comprising: providing a semiconductor-on-insulator substrate comprised of a top semiconductor layer overlying an insulation layer, where the insulation layer overlies a bottom silicon layer, where the top semiconductor layer has a first thickness, a first width and a first depth, where the top semiconductor layer comprises a first portion and a second portion; removing part of the second portion of the top semiconductor layer to achieve at least one of: a second thickness that is less than the first thickness, a second width that is less than the first width, and a second depth that is less than the first depth, where the removed part of the second portion is less than an entirety of the second portion; forming at least one first device that at least partially overlies and is disposed upon the first portion of the top silicon layer; and forming at least one second device that at least partially overlies and is disposed upon the second portion of the top silicon layer. 
     In a further exemplary embodiment of the invention, a semiconductor structure comprising: a substrate; at least one first transistor at least partially overlying the substrate. where the at least one first transistor comprises a first spacer having a first spacer thickness; and at least one second transistor at least partially overlying the substrate, where the at least one second transistor comprises a second spacer having a second spacer thickness, where the first spacer thickness is greater than the second spacer thickness. 
     In another exemplary embodiment of the invention, a method comprising: providing a substrate; forming at least one first device that at least partially overlies the substrate, where the at least one first device comprises a first transistor with a first spacer having a first spacer thickness; forming at least one second device that at least partially overlies the substrate, where the at least one second device comprises a second transistor with a second spacer having a second spacer thickness; and thinning the second spacer to reduce the second spacer thickness such that the first spacer thickness is greater than the second spacer thickness. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing and other aspects of embodiments of this invention are made more evident in the following Detailed Description, when read in conjunction with the attached Drawing Figures, wherein: 
         FIG. 1  shows one exemplary embodiment of the invention wherein a chip has two FETs with different body thicknesses; 
         FIG. 2  depicts another exemplary embodiment of the invention wherein a chip has two FETs with different spacer thicknesses; 
         FIG. 3  illustrates an exemplary embodiment of the invention (i.e., a chip) that utilizes both body size and spacer thickness to tune the respective devices; 
         FIG. 4  depicts an exemplary embodiment of the invention (i.e., a chip) that includes two FinFETs; 
         FIGS. 5-11  show an exemplary method for producing a chip similar to the one shown in  FIG. 1 ; 
         FIGS. 12-15  show an exemplary method for producing a chip similar to the one shown in  FIG. 2 ; 
         FIG. 16  depicts a flowchart illustrating one non-limiting example of a method for practicing the exemplary embodiments of this invention; 
         FIG. 17  depicts a flowchart illustrating another non-limiting example of a method for practicing the exemplary embodiments of this invention; and 
         FIG. 18  depicts a flowchart illustrating another non-limiting example of a method for practicing the exemplary embodiments of this invention. 
     
    
    
     DETAILED DESCRIPTION 
     Therefore, it is desirable to provide techniques that enable the formation of various devices (e.g., undoped devices, devices having different characteristics) on a same chip. 
     The exemplary embodiments of the invention provide techniques and structures that achieve various semiconductor devices (e.g., thin semiconductor devices) having different device characteristics (e.g., for a plurality of devices) on a same chip. As non-limiting examples, this goal may be achieved by providing devices that have different body thicknesses (e.g., different thicknesses of a silicon layer that underlies the devices) and/or devices that have different spacer thicknesses (e.g., for spacers surrounding the device, for spacers surrounding a gate structure of a FET). 
     In some exemplary embodiments, devices with a thicker body (e.g., a thicker layer of silicon) may have a higher I on  (current when devices are on) and I off  (current when devices are off) for high performance applications. In some exemplary embodiments, devices with a thinner body may have a lower I on  and I off  for low power applications. In some exemplary embodiments, devices with a thinner spacer may have a higher I on  and I off  for high performance applications. In some exemplary embodiments, devices with a thicker spacer may have a lower I on  and I off  for low power applications. 
       FIG. 1  shows one exemplary embodiment of the invention wherein a chip  100  has two 
     FETs  110 ,  120  with different body thicknesses t 1 , t 2 . Both FETs  110 ,  120  are on a semiconductor-on-insulator (SOI) having an insulation layer  102  (e.g., a buried oxide (BOX) layer) overlying a substrate  104  (e.g., silicon, undoped silicon, a bottom silicon layer, a bottom substrate, a bottom substrate layer). The FETs  110 ,  120  are separated by an isolation structure  106  (e.g., a shallow trench isolation (STI), a mesa structure). Each FET  110 ,  120  overlies (e.g., is on, is disposed on, is located on) its own top semiconductor layer  112 ,  122  (e.g., silicon, a top silicon layer, a silicon-containing layer, a top silicon-containing layer, a SOI, a SOI layer, an individual SOI layer) that overlies the BOX  102 . The top semiconductor layer  112  for FET 1   110  (with a thickness t,) is thicker than the top semiconductor layer  122  for FET 2   120  (with a thickness t 2 ). That is, the spacer thickness (t 1 ) for FET  1   110  is greater than the spacer thickness (t 2 ) for FET 2   120  (i.e., t 1 &gt;t 2 ). As non-limiting examples, t 1  may be 10 nm (e.g., approximately, about, substantially) and t 2  may be 5 nm (e.g., approximately, about, substantially). As further non-limiting examples, t 1  may be 8 nm (e.g., approximately, about, substantially) and t 2  may he 5 nm (e.g., approximately, about, substantially). As shown in  FIG. 1  the top semiconductor layer  112 ,  122  for the FETs  110 ,  120  may have source/drain (S/D) regions (e.g., doped portions of the top semiconductor layer that are coupled to the respective FET(s)). 
     In some exemplary embodiments, a raised source/drain (RSD) is used for one or more of the S/D regions. The RSD structure(s) may he particularly useful for contacts and/or for thin SOI devices (e.g., ETSOI). In other exemplary embodiments, more than one device (e.g., a plurality of FETs, at least one FET and at least one other device, at least one capacitor) overlie (e.g., is on, is disposed on, is located on) at least one of the top semiconductor layers  112 ,  122 . In further exemplary embodiments, the FETs  110 ,  120  may comprise one or more FinFETs. In other exemplary embodiments, more than two top semiconductor layers are utilized (e.g., a plurality of separated/individual top semiconductor layer regions/portions having at least two different body thicknesses). In further exemplary embodiments, the top semiconductor layers  112 ,  122  may be coupled to one another (e.g., the isolation structure  106  may be optional, possibly depending on desired characteristics and/or layout of components). 
       FIG. 2  depicts another exemplary embodiment of the invention wherein a chip  200  has two FETs  210 ,  220  with different spacer thicknesses t 3 , t 4 . Both FETs  210 ,  220  are on a semiconductor-on-insulator (SOI) having an insulation layer  202  (e.g., a buried oxide (BOX) layer) overlying a substrate  204  (e.g., silicon, undoped silicon, a bottom silicon layer, a bottom substrate, a bottom substrate layer). The FETs  210 ,  220  are separated by an isolation structure  206  (e.g., a shallow trench isolation (STI), a mesa structure). Each FET  210 ,  220  overlies (e.g., is on, is disposed on, is located on) its own top semiconductor layer  212 ,  222  (e.g., silicon, a top silicon layer, a silicon-containing layer, a top silicon-containing layer, a SOI, a SOI layer, an individual SOI layer) that overlies the BOX  202 . The spacers for FET 1   210  (with a thickness t 3 ) are thicker than the spacers for FET 2   220  (with a thickness t 4 ). That is, the spacer thickness (t 3 ) for FET 1   210  is greater than the spacer thickness (t 4 ) for FET 2   220  (i.e., t 3 &gt;t 4 ). As non-limiting examples, t 3  may be 7.5 nm (e.g., approximately, about, substantially) and t 4  may be 6 nm (e.g., approximately, about, substantially). As shown in  FIG. 1 , the top semiconductor layer  112 ,  122  for the FETs  110 ,  120  may have source,/drain (S/D) regions (e.g., doped portions of the top semiconductor layer that are coupled to the respective FET(s)). In some exemplary embodiments, a raised source/drain (RSD)  214 ,  224  is used for one or more of the S/D regions. The RSD structure(s)  214 ,  224  may be particularly useful for contacts and/or for thin SOI devices (e.g., ETSOI). 
     In other exemplary embodiments, more than one device (e.g., a plurality of FETs, at least one FET and at least one other device, at least one capacitor) overlie (e.g., is on, is disposed on, is located on) at least one of the top semiconductor layers  212 ,  222 . In further exemplary embodiments, the FETs  110 ,  120  may comprise one or more FinFETs. In other exemplary embodiments, more than two top semiconductor layers are utilized (e.g., a plurality of separated/individual top semiconductor layer regions/portions). In further exemplary embodiments, the top semiconductor layers  212 ,  222  may be coupled to one another (e.g., the isolation structure  206  may be optional, possibly depending on desired characteristics and/or layout of components). 
     While discussed above separately, further exemplary embodiments of the invention may involve the usage of both body size and spacer thickness in order to control, affect or modify device characteristics. For example, such usage may enable fine tuning of the individual devices in accordance with various categories, such as: (1) thick-body, thick-spacer devices; (2) thick-body, thin-spacer devices; (3) thin-body, thick-spacer devices; and/or (4) thin-body, thin-spacer devices, as non-limiting examples. The use of at least four categories (e.g., the four identified immediately above) instead of two (e.g., thin-body vs. thick-body or thin-spacer vs. thick-spacer) may provide more options and better selection of suitable and/or desired device characteristics. In other exemplary embodiments, fewer than four of the above-noted categories may be used for a given chip. 
       FIG. 3  illustrates an exemplary embodiment of the invention (i.e., a chip  300 ) that utilizes both body size and spacer thickness to tune the respective devices. In  FIG. 3 , a chip  300  has two FETs  310 ,  320  with different body thicknesses t 1 , t 2  and different spacer thicknesses t 3 , t 4 , respectively. Both FETs  310 ,  320  are on a semiconductor-on-insulator (SOI) having an insulation layer  302  (e.g., a buried oxide (BOX) layer) overlying a substrate  304  (e.g., silicon, undoped silicon, a bottom silicon layer, a bottom substrate, a bottom substrate layer). The FETs  310 ,  320  are separated by an isolation structure  306  (e.g., a shallow trench isolation (STI), a mesa structure). Each FET  310 ,  320  overlies on, is disposed on, is located on) its own top semiconductor layer  312 ,  322  (e.g., silicon, a top silicon layer, a silicon-containing layer, a top silicon-containing layer, a SOI, a SOI layer, an individual SOI layer) that overlies the BOX  302 . The top semiconductor layer  312  for FET 1   310  (with a thickness t 1 ) is thicker than the top semiconductor layer  322  for FET 2   320  (with a thickness t 2 ). That is, the top semiconductor layer thickness (t 1 ) for FET 1   110  is greater than the top semiconductor layer thickness (t 2 ) for FET 2   120  (i.e., t 1 &gt;t 2 ). As non-limiting examples, t 1  may be 8-10 nm (e.g., approximately, about, substantially) and t 2  may be 5 nm (e.g., approximately, about, substantially). 
     The spacers for FET 3   310  (with a thickness t 3 ) are thicker than the spacers for FET 2   320  (with a thickness t 4 ). That is, the spacer thickness (t 3 ) for FET 1   310  is greater than the spacer thickness (t 4 ) for FET 2   320  (i.e., t 3 &gt;t 4 ). As non-limiting examples, t 3  may be 7.5 nm (e.g., approximately, about, substantially) and t 4  may be 6 nm (e.g., approximately, about, substantially). As shown in  FIG. 3 , the top semiconductor layer  312 ,  322  for the FETs  310 ,  320  may have source/drain (S/D) regions (e.g., doped portions of the top semiconductor layer that are coupled to the respective FET(s)). In some exemplary embodiments, a raised source/drain (RSD)  314 ,  324  is used for one or more of the S/D regions. The RSD structure(s)  314 ,  324  may be particularly useful for contacts and/or for thin SOI devices (e.g., ETSOI). 
       FIG. 4  depicts an exemplary embodiment of the invention (i.e., a chip  400 ) that includes two FinFETs (FET 1   410  and FET 2   420 ). Each FinFET  410 ,  420  includes a separate semiconductor layer  412 ,  422  that underlies an insulator  414 ,  424  (e.g., a nitride, a nitride cap). The FinFETs  410 ,  420  include a semiconductor-on-insulator (SOI) (the semiconductor layers  412 ,  422 , also referred to as top semiconductor layers) overlying an insulation layer  402  (e.g., a buried oxide (BOX) layer) that itself overlies a substrate  404  (e.g., silicon, undoped silicon, a bottom silicon layer, a bottom substrate, a bottom substrate layer). Each FinFET  410 ,  420  has a gate  416 ,  426  that enables activation of the respective FET. Note that the semiconductor layers  412 ,  422  of the two FETs  410 ,  420  have different thicknesses (y 1  and y 2 ), for example, with the semiconductor layer  412  of FET 1   410  being thicker than the semiconductor layer  422  of FET 2   420  (y 1 &gt;y 2 ). 
     In further exemplary embodiments, and as shown in  FIG. 4 , in addition or in the alternative to the semiconductor layers  412 ,  422  of the FinFETs  410 ,  420  having different thicknesses (e.g., thickness, height, depth), the semiconductor layers  412 ,  422  may have different widths (x 1  and x 2 ), for example, with the semiconductor layer  412  of FET 1   410  being wider than the semiconductor layer  422  of FET 2   420  (x 1 &gt;x 2 ). 
     In further exemplary embodiments, in addition or in the alternative to the semiconductor layers  412 ,  422  of the FinFETs  410 ,  420  having different thicknesses (y 1  and y 2 ) and/or different widths (x 1  and x 2 ), the semiconductor layers  412 ,  422  may have different depths (z 1  and z 2 ), for example, with the semiconductor layer  412  of FET 1   410  being deeper than the semiconductor layer  422  of FET 2   420  (z 1 &gt;z 2 ). As may be appreciated, the different thicknesses, widths and/or depths enable the formation of semiconductor devices (e.g., FinFETs) having different device characteristics on a same chip. 
     As an example, to achieve different widths of the fins, one can start by forming both fins with a same width using any suitable known techniques in the art (e.g., sidewall image transfer). Subsequently, a mask is used to cover one fin (e.g., the wider one) and expose the other fin (e.g., the narrower one). The exposed fin is then thinned, for example, by etching. For example, if the fin is silicon one can use an aqueous solution containing ammonia to etch the silicon. Alternatively, in other exemplary embodiments an oxidation is performed to convert a portion of the fin into oxide. Subsequently, an oxide etch process (e.g., by hydrofluoric acid) is performed to etch the oxide and remove it (e.g., substantially). 
       FIGS. 5-11  show an exemplary method for producing a chip similar to the one shown in  FIG. 1 . As shown in  FIG. 5 , begin with a SOI substrate comprising a top semiconductor layer, such as a top Si layer  506  (e.g., SOI), overlying an insulation layer  502  (e.g., BOX) that itself overlies a substrate  504 . The thickness of the top Si layer  506  should be t 1 , the thicker of the two desired body thicknesses (e.g., about 10 nm). In  FIG. 6 , a pad layer  518  is deposited. The pad layer  518  comprises a pad oxide  508  and a pad nitride  510 . In  FIG. 7 , a resist layer  512  is used as a pattern to remove the pad layer  518  from a second region of the chip (i.e., a second device region). The first region (i.e., the first device region) is the portion of the chip in  FIG. 7  that is still covered by the pad layer  518 . By removing the pad layer  518  from the second region, the top Si layer  506  is exposed only for this portion of the chip. 
     In  FIG. 8 , the resist  512  is stripped and oxidization is used to consume part (e.g., about 5 nm) of the exposed top Si layer  506 , resulting in the formation of oxide  514  at the second device region. In  FIG. 9 , the pad layer  518  and oxide  514  are removed. The resulting structure is a chip having two SOI regions: a first region  532  having a thickness of t 1  (e.g., about 10 nm) and a second region  542  having a thickness of t 2  (e.g., about 5 nm). As is apparent from  FIG. 9 , t 1 &gt;t 2 . Note that reference numbers  532  and  542  in  FIGS. 9-11 , while labeled in  FIG. 9  as “first portion” and “second portion” respectively, directly correspond to the top Si layer (e.g., the SOI) for the respective device regions. In  FIG. 10 , an isolation structure  516  (e.g., mesa, STI) is formed. In addition, gates and spacers are formed for the two devices, forming a first FET (FET 1 )  530  and a second FET (FET 2 )  540 . In  FIG. 11 , sources/drains (S/Ds) are formed in the respective top Si layers  532 ,  542 . In addition, RSD structures  534 ,  544  are formed for the FETs  530 ,  540 . The RSD can be in-situ doped or undoped. The S/D extensions are formed, for example, by driving dopant from in-situ doped RSD structures or by implantation followed by anneal. 
     The difference in body thickness (t 1  and t 2 ) between FET 1   530  and FET 2   540  result in different device characteristics. 
       FIGS. 12-15  show an exemplary method for producing a chip similar to the one shown in  FIG. 2 . As shown in  FIG. 12 , begin with a SOI substrate comprising a top Si layer (e.g., SOI) overlying an insulation layer  602  (e.g., BOX) that itself overlies a substrate  604 . The top Si layer is divided into two regions: a first region (a first device region)  612  and a second region (a second device region)  622 . The two regions are separated by an isolation structure (e.g., a STI  606 ). A first FET (FET 1 )  610  is formed on the first region  612  while a second FET (FET 2 )  620  is formed on the second region  622 . Note that both of the FETs have a gate structure with spacers that have a same thickness t 3 . 
     In  FIG. 13 , a mask  608  is applied in order to mask the FET 1   610  and leave the FET 2   620  exposed. The spacer of the exposed FET 2   620  is thinned to a smaller thickness of t 4  (i.e., t 3 &gt;t 4 ). As a non-limiting example, the spacer of FET 2   620  may be thinned by using an etch. As a further non-limiting example, 300:1 diluted HF acid may be used to etch the spacer very precisely. In  FIG. 14 , the mask  608  is removed and RSD structures  614 ,  624  are formed for the FETs  530 ,  540 . The RSD can be in-situ doped or undoped. In  FIG. 15 , the S/D extensions  616 ,  626  are formed, for example, by driving dopant from in-situ doped RSD structures or by implantation followed by anneal. The difference in spacer thickness (t 3  and t 4 ) between FET 1   610  and FET 2   620  result in different extension dopant profiles and, therefore, different device characteristics. 
     It is noted that in some exemplary embodiments, the exact coverage of the mask  608  in  FIG. 13  is not critical as long as the spacer in the second FET, FET 2   620 , is exposed and thinned. Whether or not other elements of the device (e.g., BOX  602  exposed via the STI  606 , gate cap of FET 2   620 ) are etched during the spacer etch depends on the materials of these components, the material of the exposed spacer and the etchant used. For example, if the BOX were silicon oxide, the exposed spacer and the gate cap were silicon nitride, and the etchant were hot phosphoric acid (which etches silicon nitride selective to silicon oxide), then no BOX would be etched away. Regardless, in some exemplary embodiments the spacer etch is considered mild since one may be etching only a small portion of the spacer. In such a case, the loss of BOX or gate cap during the spacer etch may be insignificant compared with the original thickness of the BOX and/or gate cap. 
     As described herein, it should be clear that the difference in body thickness and/or spacer thickness between the devices in question is outside (e.g., greater than) the range of normal tolerances. As a non-limiting example, and assuming that the normal tolerance is on the order of 5% or less, the difference in body thickness and/or spacer thickness may be greater than a 5% difference. In some exemplary embodiments, the different in body thickness and/or spacer thickness may be greater than or equal to 20-35%. As such, the difference in body thickness and/or spacer thickness will not, for example, be an incidental characteristic that occurs through normal usage of the materials in question nor as a result of normal process variations (e.g., in the formation of the semiconductor structure/device). As is apparent from  FIGS. 5-15  and the accompanying description thereof, the difference in body thickness and/or spacer thickness is a purposeful characteristic that is designed to result in specific, different device characteristics. 
     One of ordinary skill in the art will appreciate the various techniques available to form the above-described structures. 
     In some exemplary embodiments, one or more of the RSD structures are formed using epitaxial deposition. In some exemplary embodiments of the invention the epitaxially deposited material matches the composition of the surface of the body. For example, if the body is essentially Si, the epitaxially deposited material may be essentially/primarily Si. As a further example, if there is a Ge content at the surface, the epitaxially deposited material may match that Ge content. In an alternative exemplary embodiment of the invention, the composition of the epitaxially deposited material is different from the composition of the surface of the body. For example, if the body is essentially/primarily Si, the epitaxially deposited material may be SiGe or Si:C. During the epitaxy process, the epi layer can be in-situ doped with one or more dopants such as phosphorus, arsenic, boron, and/or indium, as non-limiting examples. Alternatively, the epi layer can be ex-situ doped by performing a doping process after the epitaxy process. The doping techniques may include, but are not limited to: ion implantation, gas phase doping, plasma doping, plasma immersion ion implantation, cluster doping, infusion doping, liquid phase doping, and solid phase doping 
     One or multiple cleaning processes may be performed before the epitaxy process to remove oxygen or other undesired material from the surface of the exposed semiconductor material in order to improve the epitaxy quality. The cleaning processes may include, but are not limited to: etching in a solution containing hydrofluoric acid and plasma etching with fluorine-containing species. As non-limiting examples, such fluorine-containing species include: ammonia (NH3), nitrogen trifluoride (NF3), ammonia fluoride (NH4F), ammonium hydrogen fluoride (NH4F.HF), and ammonium hexafluorosilicate ((NH4)2SiF6). In addition or in the alternative, a hydrogen prebake process may be performed after the above cleaning process and before the actual start of the epitaxy. For example, the semiconductor substrate may be heated at a temperature ranging from 700° C. to 950° C. in a hydrogen containing environment (e.g., for 10 to 200 seconds). This can be performed in the epitaxy chamber right before the epitaxy process to further clean the (exposed) semiconductor surface. 
     Below are further descriptions of various non-limiting, exemplary embodiments of the invention. The below-described exemplary embodiments are numbered separately for clarity purposes. This numbering should not be construed as entirely separating the various exemplary embodiments since aspects of one or more exemplary embodiments may be practiced in conjunction with one or more other aspects or exemplary embodiments. 
     (1) In one exemplary embodiment, a semiconductor structure comprising: a semiconductor-on-insulator substrate comprised of a top semiconductor layer overlying an insulation layer, where the insulation layer overlies a bottom substrate layer; at least one first device at least partially overlying and disposed upon a first portion of the top semiconductor layer, where the first portion of the top semiconductor layer has a first body thickness; and at least one second device at least partially overlying and disposed upon a second portion of the top semiconductor layer, where the second portion of the top semiconductor layer has a second body thickness, where the first body thickness is greater than the second body thickness. 
     A semiconductor structure as above, where the at least one first device comprises at least one first transistor and the at least one second device comprises at least one second transistor. A semiconductor structure as in any above, where the at least one first transistor comprises a first spacer having a first spacer thickness, where the at least one second transistor comprises a second spacer having a second spacer thickness, where the first spacer thickness is greater than the second spacer thickness. A semiconductor structure as in any above, further comprising at least one raised source/drain structure coupled to at least one of the at least one first device and the at least one second device. A semiconductor structure as in any above, where the first portion is separated from the second portion by an isolation structure. A semiconductor structure as in any above, where the semiconductor-on-insulator substrate comprises a thin semiconductor-on-insulator or an extremely thin silicon-on-insulator. A semiconductor structure as in any above, where a difference in thickness between the first body thickness and the second body thickness is outside a range of normal tolerance. A semiconductor structure as in any above, further comprising one or more aspects of the exemplary embodiments of the invention as described herein. 
     (2) In a further exemplary embodiment, and as shown in  FIG. 16 , a method comprising: providing a semiconductor-on-insulator substrate comprised of a top semiconductor layer overlying an insulation layer, where the insulation layer overlies a bottom silicon layer, where the top semiconductor layer has a first thickness and comprises a first portion and a second portion ( 701 ); removing part of the second portion of the top semiconductor layer to achieve a second thickness that is less than the first thickness, where the removed part of the second portion is less than an entirety of the second portion ( 702 );forming at least one first device that at least partially overlies and is disposed upon the first portion of the top silicon layer ( 703 ); and forming at least one second device that at least partially overlies and is disposed upon the second portion of the top silicon layer ( 704 ). 
     A method as above, where the at least one first device comprises at least one first transistor and the at least one second device comprises at least one second transistor. A method as in any above, where the at least one first transistor comprises a first spacer having a first spacer thickness, where the at least one second transistor comprises a second spacer having a second spacer thickness, the method further comprising: thinning the second spacer to reduce the second spacer thickness such that the first spacer thickness is greater than the second spacer thickness. A method as in any above, further comprising: forming at least one raised source/drain structure coupled to at least one of the at least one first device and the at least one second device. A method as in any above, further comprising: forming at least one isolation structure that separates the first portion from the second portion. A method as in any above, where the semiconductor-on-insulator substrate comprises a thin semiconductor-on-insulator or an extremely thin silicon-on-insulator. A method as in any above, where a difference in thickness between the first body thickness and the second body thickness is outside a range of normal tolerance. A method as in any above, further comprising one or more aspects of the exemplary embodiments of the invention as described herein. 
     A semiconductor structure formed in accordance with any of the above methods (i.e., one or more of the above-described methods). 
     (3) In another exemplary embodiment, a semiconductor structure comprising: a substrate; at least one first transistor at least partially overlying the substrate, where the at least one first transistor comprises a first spacer having a first spacer thickness; and at least one second transistor at least partially overlying the substrate, where the at least one second transistor comprises a second spacer having a second spacer thickness, where the first spacer thickness is greater than the second spacer thickness. 
     A semiconductor structure as above, where the at least one first transistor comprises at least one first field effect transistor and the at least one second transistor comprises at least one second field effect transistor. A semiconductor structure as in any above, further comprising at least one raised source/drain structure coupled to at least one of the at least one first transistor and the at least one second transistor. A semiconductor structure as in any above, further comprising at least one first raised source/drain structure coupled to the at least one first transistor and at least one second raised source/drain structure coupled to the at least one second transistor, where the at least one first raised source/drain structure has a first length and the at least one second raised source/drain structure has a second length, where the first length is less than the second length. A semiconductor structure as in any above, where the at least one first transistor is separated from the at least one second transistor by an isolation structure. A semiconductor structure as in any above, where the substrate comprises a semiconductor-on-insulator substrate, a thin semiconductor-on-insulator substrate or an extremely thin semiconductor-on-insulator substrate. A semiconductor structure as in any above, where a difference in thickness between the first spacer thickness and the second spacer thickness is outside a range of normal tolerance. A semiconductor structure as in any above, further comprising one or more aspects of the exemplary embodiments of the invention as described herein. 
     (4) In another exemplary embodiment, and as shown in  FIG. 17 , a method comprising: providing a substrate ( 801 ); forming at least one first device that at least partially overlies the substrate, where the at least one first device comprises a first transistor with a first spacer having a first spacer thickness ( 802 ); forming at least one second device that at least partially overlies the substrate, where the at least one second device comprises a second transistor with a second spacer having a second spacer thickness ( 803 ); and thinning the second spacer to reduce the second spacer thickness such that the first spacer thickness is greater than the second spacer thickness ( 804 ). 
     A method as above, where the at least one first device comprises at least one first field effect transistor and the at least one second device comprises at least one second field effect transistor. A method as in any above, further comprising: forming at least one raised source/drain structure coupled to at least one of the at least one first device and the at least one second device. A method as in any above, further comprising: forming at least one first raised source/drain structure coupled to the at least one first transistor; and forming at least one second raised source/drain structure coupled to the at least one second transistor, where the at least one first raised source/drain structure has a first length and the at least one second raised source/drain structure has a second length, where the first length is less than the second length. A method as in any above, further comprising: forming at least one isolation structure that separates the at least one first device from the at least one second device. A method as in any above, where the substrate comprises a semiconductor-on-insulator substrate, a thin semiconductor-on-insulator substrate or an extremely thin semiconductor-on-insulator substrate. A method as in any above, where a difference in thickness between the first spacer thickness and the second spacer thickness is outside a range of normal tolerance. A method as in any above, where thinning comprises using an etch. A method as in any above, where thinning comprises using a HF etch. A method as in any above, further comprising one or more aspects of the exemplary embodiments of the invention as described herein. 
     A semiconductor structure formed in accordance with any of the above methods (i.e., one or more of the above-described methods). 
     (5) In another exemplary embodiment, a semiconductor structure comprising: a semiconductor-on-insulator substrate comprised of a top semiconductor layer overlying an insulation layer, where the insulation layer overlies a bottom substrate layer; at least one first device at least partially overlying and disposed upon a first portion of the top semiconductor layer, where the first portion of the top semiconductor layer has a first thickness, a first width and a first depth; and at least one second device at least partially overlying and disposed upon a second portion of the top semiconductor layer, where the second portion of the top semiconductor layer has a second thickness, a second width and a second depth, where the first thickness and the second thickness are along a common first axis, where the first width and the second width are along a common second axis, where the first depth and the second depth are along a common third axis, where at least one of the following holds: the first thickness is greater than the second thickness, the first width is greater than the second width and the first depth is greater than the second depth 
     A semiconductor structure as above, where the at least one first device comprises at least one first transistor and the at least one second device comprises at least one second transistor. A semiconductor structure as in any above, where the at least one first transistor comprises a first spacer having a first spacer thickness, where the at least one second transistor comprises a second spacer having a second spacer thickness, where the first spacer thickness is greater than the second spacer thickness. A semiconductor structure as in any above, further comprising at least one raised source/drain structure coupled to at least one of the at least one first device and the at least one second device. A semiconductor structure as in any above, where the first portion is separated from the second portion by an isolation structure. A semiconductor structure as in any above, where the semiconductor-on-insulator substrate comprises a thin semiconductor-on-insulator or an extremely thin silicon-on-insulator. A semiconductor structure as in any above, where a difference between at least one of the first thickness and the second thickness, the first width and the second width, and the first depth and second depth is outside a range of normal tolerance. 
     A semiconductor structure as in any above, further comprising one or more aspects of the exemplary embodiments of the invention as described herein. 
     (6) In another exemplary embodiment, and as shown in  FIG. 18 , a method comprising: providing a semiconductor-on-insulator substrate comprised of a top semiconductor layer overlying an insulation layer, where the insulation layer overlies a bottom silicon layer, where the top semiconductor layer has a first thickness, a first width and a first depth, where the top semiconductor layer comprises a first portion and a second portion ( 901 ); removing part of the second portion of the top semiconductor layer to achieve at least one of: a second thickness that is less than the first thickness, a second width that is less than the first width, and a second depth that is less than the first depth, where the removed part of the second portion is less than an entirety of the second portion ( 902 ); forming at least one first device that at least partially overlies and is disposed upon the first portion of the top silicon layer ( 903 ); and forming at least one second device that at least partially overlies and is disposed upon the second portion of the top silicon layer ( 904 ). 
     A method as above, where the at least one first device comprises at least one first transistor and the at least one second device comprises at least one second transistor. A method as in any above, where the at least one first transistor comprises a first spacer having a first spacer thickness, where the at least one second transistor comprises a second spacer having a second spacer thickness, the method further comprising: thinning the second spacer to reduce the second spacer thickness such that the first spacer thickness is greater than the second spacer thickness. A method as in any above, further comprising: forming at least one raised source/drain structure coupled to at least one of the at least one first device and the at least one second device. A method as in any above, further comprising: forming at least one isolation structure that separates the first portion from the second portion. A method as in any above, where the semiconductor-on-insulator substrate comprises a thin semiconductor-on-insulator or an extremely thin silicon-on-insulator. A method as in any above, where a difference between at least one of the first thickness and the second thickness, the first width and the second width, and the first depth and second depth is outside a range of normal tolerance. 
     A method as in any above, where forming the at least one first device and forming the at least one second device are performed after removing the part of the second portion of the top semiconductor layer. A method as in any above, where forming the at least one first device and forming the at least one second device are performed before removing the part of the second portion of the top semiconductor layer. A method as in any above, where the at least one first device comprises a first fin field effect transistor and the at least one second device comprises a second fin field effect transistor. A method as in any above, where removing the part of the second portion of the top semiconductor layer comprises performing an etch. A method as in any above, where removing the part of the second portion of the top semiconductor layer comprises performing an etch on the at least one second device. A method as in any above, further comprising one or more aspects of the exemplary embodiments of the invention as described herein. 
     A semiconductor structure formed in accordance with any of e above methods (i.e., one or more of the above-described methods). 
     The blocks shown in  FIGS. 16 ,  17  and  18  further may be considered to correspond to one or more functions and/or operations that are performed by one or more components, circuits, chips, apparatus, processors, computer programs and/or function blocks. Any and/or all of the above may be implemented in any practicable solution or arrangement that enables operation in accordance with the exemplary embodiments of the invention as described herein. 
     In addition, the arrangement of the blocks depicted in  FIGS. 16 ,  17  and  18  should be considered merely exemplary and non-limiting. It should be appreciated that the blocks shown in  FIGS. 16 ,  17  and  18  may correspond to one or more functions and/or operations that may be performed in any order (e.g., any suitable, practicable and/or feasible order) and/or concurrently (e.g., as suitable, practicable and/or feasible) so as to implement one or more of the exemplary embodiments of the invention. In addition, one or more additional functions, operations and/or steps may be utilized in conjunction with those shown in  FIGS. 16 ,  17  and  18  so as to implement one or more further exemplary embodiments of the invention. 
     That is, the exemplary embodiments of the invention shown in  FIGS. 16 ,  17  and  18  may be utilized, implemented or practiced in conjunction with one or more further aspects in any combination (e.g., any combination that is suitable, practicable and/or feasible) and are not limited only to the steps, blocks, operations and/or functions shown in  FIGS. 16 ,  17  and  18 . 
     The exemplary methods and techniques described herein may be used in the fabrication of integrated circuit chips. The resulting integrated circuit chips can be distributed by the fabricator in raw wafer form (i.e., as a single wafer that has multiple unpackaged chips), as a bare die, or in a packaged form. In the latter case, the chip is mounted in a single chip package (e.g., a plastic carrier, with leads that are affixed to a motherboard or other higher level carrier) or in a multichip package (e.g., a ceramic carrier that has either or both surface interconnections or buried interconnections). 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 numerous components, such as a display, a keyboard or other input device and/or a central processor, as non-limiting examples. 
     The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting of the exemplary embodiments 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. 
     Unless described otherwise herein, “depositing” may include any now known or later developed techniques appropriate for the material to be deposited, including, but not limited to: chemical vapor deposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), semi-atmosphere CVD (SACVD), high density plasma CVD (HDPCVD), rapid thermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reaction processing CVD (LRPCVD), metalorganic CVD (MOCVD), sputtering deposition, ion beam deposition, electron beam deposition, laser assisted deposition, thermal oxidation, thermal nitridation, spin-on methods, physical vapor deposition (PVD), atomic level deposition (ALD), chemical oxidation, molecular beam epitaxy (MBE), plating or evaporation. Any references to “poly,” “polysilicon” or “poly Si” should be understood to refer to polycrystalline silicon. 
     While described herein in relation to a layer of BOX, the exemplary embodiments are not limited thereto and may be used in conjunction any suitable layer of insulating material. Furthermore, while described herein in relation to one or more transistors, the exemplary embodiments are not limited thereto and may be used in conjunction any suitable electronic device or structure. 
     While described above at least partly in relation to a top semiconductor layer that comprises silicon, the exemplary embodiments of the invention are not limited thereto, and may be utilized in conjunction with any suitable semiconductor material. For example, besides Si, the top semiconductor layer (i.e., the semiconductor layer overlying the insulator) may comprise one or more of: germanium, silicon germanium, silicon carbide, and those consisting essentially of III-V compound semiconductors having a composition defined by the formula A1X1GaX2InX3AsY1PY2NY3SbY4, where X1, X2. X3, Y1, Y2, Y3, and Y4 represent relative proportions, each greater than or equal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relative mole quantity). Other suitable semiconductor materials include II-VI compound semiconductors having a composition ZnA1CdA2SeB1TeB2, where A1, A2, B1, and B2 are relative proportions each greater than or equal to zero and A1+A2+B1+B2=1 (1 being a total mole quantity). In further exemplary embodiments, the semiconductor layer may also comprise an organic semiconductor or a layered semiconductor. A portion or the entirety of the semiconductor layer may comprise amorphous, polycrystalline or monocrystalline material. In other exemplary embodiments, the top semiconductor layer may be doped, undoped or contain doped regions and undoped regions therein. In further exemplary embodiments, the top semiconductor layer may contain regions with strain and/or regions without strain, or contain regions of tensile strain and/or compressive strain. 
     While described above primarily in relation to semiconductor-on-insulator (SOI) structures and ETSOI structures in particular, the exemplary embodiments of the invention are not limited thereto, and may be utilized in conjunction with any suitable substrate. Similarly, while described above primarily in relation to transistors and FETs in particular, the exemplary embodiments of the invention are not limited thereto, and may be utilized in conjunction with any suitable semiconductor device(s) whose characteristics may be modified, changed, affected or tuned in accordance with the exemplary embodiments of the invention. 
     One of ordinary skill in the art will appreciate the various methods, techniques, components and/or materials available to form the various structures and perform the various steps described herein. Any suitable method, technique, component and/or material may be utilized in conjunction with the described structures and methods in order to perform and/or realize the exemplary embodiments of the invention as described herein. 
     Any use of the terms “connected,” “coupled” or variants thereof should be interpreted to indicate any such connection or coupling, direct or indirect, between the identified elements. As a non-limiting example, one or more intermediate elements may be present between the “coupled” elements. The connection or coupling between the identified elements may be, as non-limiting examples, physical, electrical, magnetic, logical or any suitable combination thereof in accordance with the described exemplary embodiments. 
     As non-limiting examples, the connection or coupling may comprise one or more printed electrical connections, wires, cables, mediums or any suitable combination thereof. 
     Generally, various exemplary embodiments of the invention can be implemented in different mediums, such as software, hardware, logic, special purpose circuits or any combination thereof. As a non-limiting example, some aspects may be implemented in software which may be run on a computing device, while other aspects may be implemented in hardware. 
     The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the best method and apparatus presently contemplated by the inventors for carrying out the invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications will still fall within the scope of the teachings of the exemplary embodiments of the invention. 
     Furthermore, some of the features of the preferred embodiments of this invention could be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles of the invention, and not in limitation thereof.