Patent Document

RELATED APPLICATION 
     This application is a divisional application of U.S. patent application Ser. No. 13/184,537 filed Jul. 16, 2011, entitled “THREE DIMENSIONAL FET DEVICES HAVING DIFFERENT DEVICE WIDTHS”, now U.S. Pat. No. 8,742,508, the disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     The exemplary embodiments relate to three dimensional semiconductor structures and, more particularly, to three dimensional semiconductor structures having different device widths. 
     Non-planar, three-dimensional device structures may be used as a replacement for planar devices, which have limitations on scalability. In particular, fin-type field effect transistors (FinFETs) are low-power, high speed non-planar devices that can be more densely packed on a substrate than traditional planar transistors. In addition, FinFETs also offer superior short channel control. 
     BRIEF SUMMARY 
     The various advantages and purposes of the exemplary embodiments as described above and hereafter are achieved by providing, according to a first aspect of the exemplary embodiments, a method of manufacturing a three dimensional FET device structure. The method includes providing a substrate having a semiconductor layer on an insulator layer; forming a plurality of three dimensional fins in the semiconductor layer; applying a masking material to a first fin while exposing a second fin; applying a hydrogen atmosphere to the substrate and exposed second fin for a first predetermined time at a first predetermined temperature and pressure, the hydrogen atmosphere causing the exposed second fin to reflow and change shape; removing the masking material from the first fin; and forming a gate to wrap around each of the first and second fins. The first and second fins are formed having a device width being defined as the circumference of the three dimensional fin in contact with its gate and the first fin having a first device width and a second fin having a second device width with the first device width being different than the second device width. 
     According to a second aspect of the exemplary embodiments, there is provided a method of manufacturing a three dimensional FET device structure. The method includes providing a substrate having a semiconductor layer on an insulator layer; forming a plurality of three dimensional fins in the semiconductor layer; applying a masking material to a first plurality of fins while exposing a second plurality of fins; applying a hydrogen atmosphere to the substrate and exposed second plurality of fins for a first predetermined time at a first predetermined temperature and pressure, the hydrogen atmosphere causing the exposed second plurality of fins to reflow and change shape while the masked first plurality of fins do not change shape; removing the masking material from the first plurality of fins; and forming a gate to wrap around each of the fins of the first and second plurality of fins, the gate having a longitudinal dimension which is perpendicular to a longitudinal dimension of each of the first and second plurality of fins. The first and second plurality of fins are formed having a device width being defined as the circumference of the three dimensional fin in contact with its gate and the first plurality of fins having a first device width and a second plurality of fins having a second device width with the first device width being different than the second device width. 
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     The features of the exemplary embodiments believed to be novel and the elements characteristic of the exemplary embodiments are set forth with particularity in the appended claims. The Figures are for illustration purposes only and are not drawn to scale. The exemplary embodiments, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
       FIGS. 1 to 6  illustrate a process of forming a first exemplary embodiment where: 
       FIG. 1  illustrates a starting structure of at least two vertical fins formed on a semiconductor substrate; 
       FIG. 2  illustrates covering a first fin with a hard mask while exposing a second fin to a hydrogen bake; 
       FIG. 3  illustrates the first and second fins after the hydrogen bake; 
       FIG. 4  illustrates the first and second fins after gates have been formed; 
       FIG. 5  illustrates the first and second fins after spacers have been formed on the gates; and 
       FIG. 6  is a cross-sectional view of  FIG. 5 . 
       FIGS. 7 to 11  illustrate a process of forming a second exemplary embodiment where: 
       FIG. 7  illustrates a starting structure of at least two vertical fins formed on a semiconductor substrate; 
       FIG. 8  illustrates covering a first fin with a hard mask while exposing a second fin to a first hydrogen bake; 
       FIG. 9  illustrates covering the second fin with a hard mask while exposing the first fin to a second hydrogen bake; 
       FIG. 10  illustrates the first and second fins after the first and second hydrogen bakes; and 
       FIG. 11  illustrates the first and second fins after gates have been formed. 
    
    
     DETAILED DESCRIPTION 
     Fully depleted metal oxide semiconductor field effect transistors (MOSFETs), such as FinFETs or trigates, exhibit superior short channel control. However, the three dimensional (3D) structure of these devices creates several fabrication challenges. 
     Integrated circuits that include 3D devices such as FinFETs may be fabricated on a bulk semiconductor substrate or, more commonly, on a semiconductor on insulator (SOI) substrate that includes an active SOI layer of a semiconductor, such as silicon, a semiconductor substrate, and a buried insulator layer that separates and electrically isolates the semiconductor substrate from the SOI layer. Each 3D device includes a narrow vertical fin body of semiconductor material with vertically-projecting sidewalls. A gate contact or electrode may intersect a channel region of the fin body and may be isolated electrically from the fin body by a thin gate dielectric layer. Flanking the central channel region at opposite ends of the fin body are heavily-doped source/drain regions. 
     One particular problem of 3D structures is the quantization of the device width. The device width may be defined as the circumference of the fin in contact with the gate dielectric. 
     The exemplary embodiments provide a structure and method of tuning the shape of the fin of the 3D device so that 3D device structures are produced having different device widths. Device characteristics are improved by shaping of the fins. 
     Referring to the drawings in more detail, a first exemplary embodiment will be discussed. Particularly referring to  FIG. 1 , there is shown a 3D device structure  10  in an early stage of formation. The 3D device structure  10  includes a substrate  12  which may be a bulk semiconductor substrate, such as silicon, silicon germanium, germanium, III-V compound, or II-VI compound semiconductor, or may be an SOI substrate as shown in  FIG. 1 . The SOI substrate  12  includes a bottom semiconductor layer  14  and a buried insulator layer  16 . The buried insulator layer  16  is typically an oxide so the buried insulator layer  16  may be called a buried oxide layer or simply a BOX layer. Hereafter, layer  16  will be referred to as the BOX layer  16 . 
     On top of BOX layer  16  is usually an SOI layer but in  FIG. 1 , the SOI layer has been conventionally patterned to form first fin  18  and second fin  20 . It should be understood that there will usually be a plurality of such first and second fins  18 ,  20  but only two such fins are shown for clarity. 
     First and second fins  18 ,  20  are conventionally formed from an SOI substrate. 
     The SOI substrate  12  may be fabricated by any suitable conventional technique, such as a wafer bonding technique or a separation by implantation of oxygen (SIMOX) technique, familiar to a person having ordinary skill in the art. The thickness of the SOI layer determines the vertical height of the first and second fins  18 ,  20 . The SOI layer may have a thickness that varies from about 10 nm to about 50 nm. 
     A pad layer may be formed on the SOI layer of the SOI substrate  12 . The pad layer may be composed of a nitride formed utilizing a conventional deposition process such as chemical vapor deposition (CVD) or plasma-assisted CVD. The material constituting the pad layer may be selected such that the pad layer functions as a hardmask. The material forming the pad layer must also etch selectively to the material constituting the SOI layer. 
     Thereafter, the pad layer may be patterned by a conventional lithography and dry etching process. The pattern in the patterned pad layer is then transferred into the SOI layer by an etching process using the patterned pad layer as an etch mask. The etching process removes the material of the SOI layer selective to the material of the BOX layer  16 . The pad layer may then be removed. The result is the first and second fins  18 ,  20  on BOX layer  16  and semiconductor substrate  12  shown in  FIG. 1 . 
     Referring now to  FIG. 2 , a hard mask layer  22 , such as a nitride, is conventionally deposited and patterned to cover the first fin  18  (now shown in phantom) but leave the second fin  20  exposed. Thereafter, the substrate may be subjected to a hydrogen bake to reflow the exposed second fin  20 , resulting in the second fin  20  having the rounded profile shown in  FIG. 2 . 
     Deuterium (D or  2 H) is an isotope of hydrogen (H). Deuterium is often referred to as heavy hydrogen. The hydrogen bake of the exemplary embodiments may be performed with hydrogen gas (H 2 ) composed of hydrogen (H) with a mass number of about 1, with deuterium gas ( 2 H 2 ) composed of deuterium ( 2 H) with a mass number of about 2 or combinations of hydrogen gas and deuterium gas. It should be understood that whenever a hydrogen bake is mentioned, the hydrogen utilized may be hydrogen, deuterium or combinations of hydrogen and deuterium. 
     The hydrogen bake may be performed in a hydrogen environment at 800 to 1000° C. with a pressure of 50-100 Torr for 20 to 60 seconds. The hydrogen bake lowers the surface energy of the second fin  20  so that the second fin  20  changes shape from a rectangular fin to a rounded fin. 
     The conditions of the hydrogen bake may be varied to change the shape and material of the vertical fin in a controlled way so that shapes other than the semicircular second fin  20  may be obtained. 
     After the hydrogen bake, the hard mask layer  22  may be conventionally stripped to result in the structure shown in  FIG. 3 . First fin  18  may retain its original shape while second fin  20  has a modified shape. 
     The device widths may be determined for each of the first fin  18  and second fin  20 . First fin  18  has a height H and a width W so that its device width is (2×H+W) which is the circumference of the first fin  18  that will be contact with the gate dielectric that is applied in a subsequent process. The device width of second fin  20  may be determined by the equation (Pi×r) which is the circumference of the second fin  20  that will be in contact with the gate dielectric that is applied in a subsequent process. 
     Referring now to  FIG. 4 , gates  24 ,  26  are then formed for each of the first fin  18  and second fin  20 . The gates  24 ,  26  may include a gate dielectric  28 ,  30 , a gate conductor  32 ,  34  and a gate hardmask  36 ,  38 . The gate dielectric  28 ,  30  for the first and second fins  18 ,  20 , respectively, may include a high-k gate dielectric or any other gate dielectric material. The gate conductor  32 ,  34  for the first and second fins  18 ,  20 , respectively, may include a metal gate or any other suitable gate material. The gate hard mask  36 ,  38  for the first and second fins  18 ,  20 , respectively, may include a nitride or any other gate hardmask. The gate dielectric  28 ,  30 , gate conductor  32 ,  34  and gate hardmask  36 ,  38  may be formed by conventional deposition and patterning of gate dielectric, gate conductor and gate hardmask materials as is known to a person skilled in the art. The gate dielectric  28  and gate conductor  32  for gate  24  may be the same or different than the gate dielectric  30  and gate conductor  34  for gate  26  as required by the design of the 3D device structure  10 . 
     Referring now to  FIG. 5 , spacers  40 ,  42  have been conventionally formed on gates  24 ,  26  by deposition of a spacer material, such as a nitride, followed by a dry etching process. Sources  44 ,  46  and drains  48  (the drain for first fin  18  is hidden by gate  24 ) may be formed, for example, by doping. The spacers  40 ,  42 , sources  44 ,  46  and drains  48  for each of the structures in the 3D device structure  10  may be the same or different as required by the design of the 3D device structure  10 . 
     A cross section of the 3D device structure shown in  FIG. 5  is taken in the plane indicated by arrows  6 - 6  and shown in  FIG. 6 . Shown is a 3D device structure  10  including a first 3D device  50  (such as a FinFET or Trigate device) and a second 3D device  52  (such as a FinFET or Trigate device). The first 3D device  50  has a first device width and the second 3D device  52  has a second device width such that the first device width is different from the second device width. The difference in device width is more than that obtained just through manufacturing tolerances. In an exemplary embodiment, the first device width and the second device width should differ by at least 20%. 
     Referring now to  FIG. 7 , a second exemplary embodiment of the 3D device structure  110  will be discussed. The starting structure shown in  FIG. 7  is the same starting structure shown in  FIG. 1 . The 3D device structure  110  includes a substrate  112  which may be a bulk semiconductor substrate, such as silicon, or may be an SOI substrate as shown in  FIG. 7 . The SOI substrate  112  includes a bottom semiconductor layer  114  and a BOX layer  116 . 
     As discussed above with respect to  FIG. 1 , the SOI layer has been conventionally patterned to form first fin  118  and second fin  120 . It should be understood that there will usually be a plurality of such first and second fins  118 , 120  but only two such fins are shown for clarity. 
     Referring now to  FIG. 8 , a hard mask layer  122 , such as a nitride, is conventionally deposited and patterned to cover the first fin  118  (now shown in phantom) but leave the second fin  120  exposed. Thereafter, the substrate may be subjected to a hydrogen bake to reflow the exposed second fin  120 , resulting in the second fin  120  having the rounded profile shown in  FIG. 8 . 
     The hydrogen bake may be performed in a hydrogen environment at 800 to 1000° C. with a pressure of 50-100 Torr for 20 to 60 seconds. 
     The conditions of the hydrogen bake may be varied to change the shape of the vertical fin in a controlled way so that shapes other than the semicircular second fin  120  may be obtained. 
     After the hydrogen bake, the hard mask layer  122  may be conventionally stripped. First fin  118  may retain its original shape after the hydrogen bake while second fin  120  has a modified shape. 
     In this second exemplary embodiment, there may be two different hydrogen bakes so as result in two different types of fins. 
     Referring now to  FIG. 9 , another hard mask  124 , such as a nitride, is conventionally deposited and patterned to cover the second fin  120  (now shown in phantom) but leave the first fin  118  exposed. Thereafter, the substrate may be subjected to the second hydrogen bake to reflow the exposed second fin  118 , resulting in the first fin  118  having the rounded profile to form part of an oval (i.e., semioval) as shown in  FIG. 9 . Note that the configuration of first fin  118  may be different than the configuration of second fin  120 . 
     The first hydrogen bake may be performed at 950° C. with a pressure of 80 Torr for 60 seconds while the second hydrogen bake may be performed at 850° C. with a pressure of 80 Torr for 60 seconds. 
     After the second hydrogen bake, the hard mask layer  124  may be conventionally stripped to result in the structure shown in  FIG. 10 . As a result of the two hydrogen bakes, the shapes of first fin  118  and second fin  120  have been modified but in different ways so that fins of two different device widths have been obtained. 
     Subsequent processing may then take place to form the gate dielectric, gate conductor, gate hard mask, spacers, sources and drains as discussed with respect to the first exemplary embodiment. 
     Shown in  FIG. 11  is a 3D device structure  110  including a first 3D device  128  (such as a FinFET or Trigate device) and a second 3D device  130  (such as a FinFET or Trigate device). The first 3D device  128  has a first device width and the second 3D device  130  has a second device width such that the first device width is different from the second device width. The difference in device width is more than that obtained just through manufacturing tolerances. In an exemplary embodiment, the first device width and the second device width should differ by at least 20%. 
     While the exemplary embodiments have been discussed with fins of two device widths, it should be understood that contemplated within the scope of the exemplary embodiments are 3D device structures with fins of three or more device widths. 
     Further, once the 3D device structures have been formed as described, further conventional processing known to those skilled in the art may take place such as forming contacts, depositing an interlevel dielectric, back end of the line wiring layers, etc. 
     It will be apparent to those skilled in the art having regard to this disclosure that other modifications of the exemplary embodiments beyond those embodiments specifically described here may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.

Technology Category: 5