Abstract:
A method for making an integrated circuit includes a) providing a substrate including n-type metal oxide semiconductor field effect transistors (NMOSFETs) and p-type metal oxide semiconductor field effect transistors (PMOSFETs), wherein channel regions of the NMOSFETs and the PMOSFETs include germanium; b) depositing and patterning a mask layer to mask the channel regions of the PMOSFETs and to not mask the channel regions of the NMOSFETs; c) passivating an exposed surface of the substrate; d) removing the mask layer; and e) depositing a metal contact layer on both the NMOSFETs and the PMOSFETs.

Description:
FIELD 
     The present disclosure relates to substrate processing methods, and more particularly to methods for integrating germanium in high performance integrated circuits. 
     BACKGROUND 
     The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     P-channel metal oxide semiconductor field effect transistors (PMOSFETs) and n-channel MOSFETs (NMOSFETs) are used in many high performance integrated circuits. Reducing contact resistance is important for further improving performance. While nickel silicide (NiSi) provides good contact resistance, NiSi includes Si which is a mid-gap work function material (0.65 eV) (similar to cobalt (Co) and titanium (Ti)) and is prone to form pipes of NiSi 2 , which limits performance. 
     A metal insulator silicon (MIS) structure has also been used to reduce contact resistance. However, the insulator (typically titanium dioxide (TiO 2 ) or silicon dioxide (SiO 2 )) does not remain stable during subsequent processing. 
     Another approach for reducing contact resistance uses Ti metal in direct contact with Si. The Ti metal is deposited using physical vapor deposition (PVD) and requires a titanium nitride (TiN) cap deposited using chemical vapor deposition (CVD). As contact dimensions scale, the TiN cap consumes much of the contact fill and has high resistance. Manufacturers have resorted to expensive integration techniques to etch back the high resistance TiN cap and fill the contact and/or metal gate with a lower resistance metal. Both the interface resistance and contact material resistance need to be reduced. 
     In dual silicide integration, providing low contact resistance for NMOSFETs and PMOSFETs involves the use of different materials. Dual silicide integration was actively researched to reduce resistance between the silicide and the silicon. In this integration, a work function of the silicide is tailored to reach the band edge. The candidates are: PMOSFETs&gt;0.8 eV using iridium (Ir), platinum (Pt) or osmium (Os) and NMOSFETs&lt;0.3 eV using erbium (Er), ytterbium (Yb), dysprosium (Dy) or gadolinium (Gd). 
     Other channel materials with higher carrier mobilities have been proposed to replace silicon (Si). For example, germanium (Ge) has higher electron and hole mobilities than Si. Ge is a group IV element (like Si) and is compatible with current manufacturing facilities. 
     Ge PMOSFETs have been demonstrated with good performance. However, Ge NMOSFETs have suffered from poor drive current due to high parasitic resistance. A metal Fermi level at metal/Ge interfaces is pinned close to a Ge valence band, which leads to a large barrier to n-type Ge and a high contact resistance (R s ). R s  needs to be reduced in order to improve Ge NMOSFET performance and realize Ge devices. 
     SUMMARY 
     A method for making an integrated circuit includes a) providing a substrate including n-type metal oxide semiconductor field effect transistors (NMOSFETs) and p-type metal oxide semiconductor field effect transistors (PMOSFETs), wherein channel regions of the NMOSFETs and the PMOSFETs include germanium; b) depositing and patterning a mask layer to mask the channel regions of the PMOSFETs and to not mask the channel regions of the NMOSFETs; c) passivating an exposed surface of the substrate; d) removing the mask layer; and e) depositing a metal contact layer made of a single metal material on both the NMOSFETs and the PMOSFETs. 
     In other features, after d) and before e), depositing an oxide film on the channel regions of the NMOSFETs and the PMOSFETs. Passivating the substrate comprises implanting ions selected from a group consisting of sulfur ions and selenium ions in the channel regions of the NMOSFETs. Passivating the substrate comprises performing a substrate treatment selected from a group consisting of ammonium sulfide ((NH 4 ) 2 S) and thiol-based self-assembled monolayers (SAMs). Passivating the substrate comprises performing a substrate treatment using a liquid selected from a group consisting of dissolved selenium chloride, selenium oxyfluoride and selenium oxychloride. Passivating the substrate comprises exposing the substrate to plasma gas chemistry selected from a group consisting of hydrogen sulfide (H 2 S) and hydrogen selenide (H 2 Se). 
     In other features, the PMOSFETS and the NMOSFETs include FINFETs. The PMOSFETS and the NMOSFETs include gate all around (GAA) transistors. The channel regions include strained germanium. The channel regions include silicon germanium having a germanium concentration greater than or equal to 85%. 
     A method for making an integrated circuit includes a) providing a substrate including n-type metal oxide semiconductor field effect transistors (NMOSFETs) and p-type metal oxide semiconductor field effect transistors (PMOSFETs), wherein channel regions of the NMOSFETs and the PMOSFETs are made of germanium; b) depositing a metal contact layer made of a single metal material over the channel regions of both the NMOSFETs and the PMOSFETs; c) depositing and patterning a mask layer on the metal contact layer to mask the channel regions of the PMOSFETs and to not mask the channel regions of the NMOSFETs; and d) passivating the channel regions of the NMOSFETs and not passivating the channel regions of the PMOSFETs. 
     In other features, the method includes removing the mask layer. After a) and before b), depositing an oxide film on the channel regions of the NMOSFETs and the PMOSFETs. Passivating the channel regions of the NMOSFETs comprises implanting ions selected from a group consisting of sulfur ions and selenium ions in the channel regions of the NMOSFETs through the metal layer. The PMOSFETS and the NMOSFETs include FINFETs. The PMOSFETS and the NMOSFETs include gate all around (GAA) transistors. 
     In other features, the channel regions include strained germanium. The channel regions include silicon germanium having a germanium concentration greater than or equal to 85%. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description, the claims and the drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a graph illustrating metal Fermi levels for dual silicide integration; 
         FIG. 2  is a graph illustrating electron barrier height as a function of metal work function; 
         FIG. 3  is a graph illustrating ideal Schottky limits and Fermi level pinning; 
         FIG. 4A  is a side cross-sectional view of an example of a substrate including a silicon layer and a mask film layer according to the present disclosure; 
         FIG. 4B  is a side cross-sectional view of an example of the substrate after etching of trenches and deposition of film to form shallow trench isolation (STI) regions according to the present disclosure; 
         FIG. 4C  is a side cross-sectional view of an example of the substrate after silicon is etched between the STI regions to create trenches according to the present disclosure; 
         FIG. 4D  is a side cross-sectional view of an example of the substrate after a first film is deposited in a lower portion of the trenches between the STI regions according to the present disclosure; 
         FIG. 4E  is a side cross-sectional view of an example of the substrate after a second film is deposited in an upper portion of the trenches between STI regions according to the present disclosure; 
         FIG. 4F  is a side cross-sectional view of an example of the substrate after the STI regions are etched back to expose the second film according to the present disclosure; 
         FIG. 4G  is a side cross-sectional view of an example of the substrate after a mask film layer is deposited over the second film associated with PMOSFETs according to the present disclosure; 
         FIG. 4H  is a side cross-sectional view of an example of the substrate during passivation of the second film associated with the NMOSFETs according to the present disclosure; 
         FIG. 4I  is a side cross-sectional view of an example of the substrate after the mask film layer is removed and a metal layer is deposited according to the present disclosure; 
         FIG. 5  is a flowchart illustrating steps of an example of a method for making the substrate of  FIGS. 4A-4I  according to the present disclosure; 
         FIG. 6A  is a side cross sectional view of an example of the substrate of  FIG. 4F  after a metal layer is deposited thereon according to the present disclosure; 
         FIG. 6B  is a side cross sectional view of an example of the substrate of  FIG. 6A  including a mask formed on the metal layer over the PMOSFETs and passivation of channels of the NMOSFETs through the metal layer according to the present disclosure; 
         FIG. 7  is a flowchart illustrating steps of an example of a method for making the substrate of  FIGS. 6A-6B  according to the present disclosure; and 
         FIGS. 8-10  are perspective views of an example of a gate-all-around transistor according to the present disclosure. 
     
    
    
     In the drawings, reference numbers may be reused to identify similar and/or identical elements. 
     DETAILED DESCRIPTION 
     As was described above, dual silicides can be realized on Si. The work function (Fermi Level) of the silicide is pinned by the contact material and tailored to reach the band edge. The candidates are: PMOSFET&gt;0.8 eV=Ir, Pt, Os and NMOSFET&lt;0.3 eV=Er, Yb, Dy, Gd. As shown in  FIG. 1 , this works well for Si as described by T. Nishimura, K. Kita, and A. Toriumi in Applied Physics Letter, 91, 123123 (2007). However, in the case of substrates using Ge, all metals contacting Ge fall within a narrow range within the band gap due to Fermi-level pinning. 
     Referring now to  FIG. 2 , electron barrier height is not modulated significantly by changing the metal work function and remains about 0.58 eV for Ge as described by A. Dimoulas, P. Tsipas, and A. Sotiropoulos in Applied Physics Letter 89, 252110 (2006). 
     Referring now to  FIG. 3 , if the N-type Ge can be passivated while the P-type Ge is unpassivated, then a single metal material can create two work functions (see circled region in  FIG. 3 ). A Thathachary et al., Applied Physics Letter 96, 152108. This would create two barrier heights: one for N and one for P, while using a single contact metal. In some examples, the contact metal includes aluminum (Al), zirconium (Zr), tungsten (W) or tantalum (Ta), although other materials can be used. The N-type Ge can be passivated using sulfur (S) or selenium (Se) as will be described further below. 
     While the present disclosure will be described in the context of an STI-first integration approach in  FIGS. 4A-7  below, an STI-last approach may also be used. Referring now to  FIGS. 4A-4I , an example integration of germanides in high performance integrated circuits according to the present disclosure is shown. In  FIG. 4A , a substrate  40  including a silicon layer  50  is shown. A mask film layer  52  is deposited and patterned to mask selected portions of the silicon layer  50 . In  FIG. 4B , the substrate  40  is shown after etching trenches  54  in the silicon layer  50 . Film is deposited in the trenches  54  to create shallow trench isolation (STI) regions  56 . For example, the film may include oxide such as silicon dioxide (SiO 2 ), although other materials may be used. 
     In  FIG. 4C , the substrate  40  is shown after the silicon layer  50  is etched between the STI regions  56  to create trenches  60 . In  FIG. 4D , the substrate  40  is shown after a first film  62  is deposited in a lower portion of the trenches  60 . In some examples, the first film  62  includes relaxed silicon germanium (Si 1-x Ge x ) film. An upper portion of the trenches  60  is not filled by the first film  62 . 
     In  FIG. 4E , the substrate  40  is shown after a second film  64  is deposited in an upper portion of the trenches  60 . In some examples, the second film  64  includes strained germanium (Ge) film. In other examples, the second film includes SiGe with Ge concentrations greater than or equal to 85%. In  FIG. 4F , the substrate  40  is shown after the STI regions  56  are etched back to expose the second film  64 . 
     In  FIG. 4G , the substrate  40  is shown after a mask film layer  70  is deposited and patterned over the second film  64  associated with PMOSFETs but not NMOSFETs. While the example in  FIG. 4G  shows two PMOSFETs  72  arranged adjacent to two NMOSFETs  74 , other arrangements can be used. The mask film layer  70  is selected to protect the second film  64  of the PMOSFETs during subsequent selective passivation described below. 
     In  FIG. 4H , the substrate  40  is shown during passivation  75  of the second film  64  associated with the NMOSFETs. In some examples, the passivation treatment includes using sulfur ion implantation, treatment using thiol-based self-assembled monolayers (SAMs), treatment using ammonium sulfide (NH 4 ) 2 S, or treatment using hydrogen sulfide (H 2 S) plasma. In some examples, treatment using hydrogen sulfide (H 2 S) plasma is performed using remote plasma or inductively coupled plasma (ICP). When using thiol-based SAMs, a carbon film may remain on the surface. The carbon film may be removed using plasma or handled during metal deposition. Some metals may absorb carbon without issue. 
     In some examples, passivation treatment includes using sulfur ion implantation according to a process described in “Plasma Implant Update”, SemiCon San Francisco (July 2015), which is hereby incorporated by reference in its entirety. In other examples, the passivation may be performed using hydrogen selenide (H 2 Se) plasma, Se ion implantation or exposure to Se-based salts such as Se 2 Cl 2  (dissolved for liquid phase passivation), selenium oxyfluorides, and selenium oxychlorides. In some examples, treatment using H 2 Se plasma is performed using remote plasma or inductively coupled plasma (ICP). 
     In some examples, sulfurization treatment using (NH 4 ) 2 S includes treating the substrate to 40% aqueous ammonium sulfide (NH 4 ) 2 S solution at a predetermined temperature for a predetermined period. In some examples, the predetermined temperature is between 20° C. and 95° C. In other examples, the predetermined temperature is between 60° C. to 80° C. (e.g. 70° C.). For example only, the predetermined period may be 4 to 6 minutes (e.g. 5 minutes). After the predetermined period, the substrate is rinsed. For example only, the substrate may be rinsed using deionized (DI) water or isopropyl alcohol (IPA). After rinsing, the substrate may be blow dry. In some examples, the substrate is blown dry using molecular nitrogen (N 2 ). For further details, see A Thathachary et al., Applied Physics Letter 96, 152108 (2010), which is hereby incorporated by reference in its entirety. 
     In  FIG. 4I , the substrate  40  is shown after the mask film layer  70  is removed and a metal layer  76  is deposited over the second film  64  associated with the PMOSFETs  72  and NMOSFETs  74  and the STI regions  56 . In some examples, a thin oxide film  77  may be deposited before the metal layer  76 . In some examples, the oxide film  77  includes SiO 2 , although other film materials can be used. The metal layer  76  may be patterned during subsequent steps. 
     Referring now to  FIG. 5 , a method  100  for making the substrate of  FIGS. 4A-4I  is shown. At  104 , a mask layer is deposited and patterned on the substrate. Trenches are etched in a silicon layer in areas that are not masked. At  108 , the mask layer is removed and STI film is deposited in the trenches. At  110 , the silicon layer is etched to create trenches between the STI regions. At  112 , a first film is deposited in a lower portion of the trenches. For example only, the first film may include relaxed silicon germanium (Si 1-x Ge x ), although other types of film may be used. 
     At  116 , a second film (such as strained germanium or SiGe having a Ge concentration greater than or equal to 85%) is deposited in an upper portion of the trenches. At  118 , the STI film is etched back to expose the strained germanium or SiGe. At  122 , the second film portions associated with PMOSFETs is masked. The portions of the second film associated with NMOSFETs remain unmasked. At  124 , the second film associated with the NMOSFETs is passivated. At  126 , the mask layer is stripped. In some examples, a thin oxide film layer (such as SiO 2 ) is deposited at  128 . At  130 , a metal layer is deposited and patterned. In some examples, the metal includes aluminum (Al), zirconium (Zr), tungsten (W) or tantalum (Ta), although other materials can be used. 
     Referring now to  FIG. 6A-6B , passivation of the second film above the NMOSFETs may be performed in another manner. In  FIG. 6A , the substrate  40  of  FIG. 4F  is shown after a metal layer  82  is deposited thereon and before the second film associated with the NMOSFETs is passivated. In some examples, the metal layer  82  includes aluminum (Al), zirconium (Zr), tungsten (W) or tantalum (Ta), although other materials can be used. In  FIG. 3B , a mask layer  84  is deposited and patterned on the metal layer  82  over the PMOSFETs but not the NMOSFETs. Passivation  75  of the second film of the NMOSFETs is performed through the metal layer  82 . 
     In some examples, passivation through the metal layer  82  is performed via ion implantation at a sufficiently high enough energy to pass through the metal layer  82 . The energy that is used will depend on the thickness of the metal layer  82 . In some examples, annealing is performed after the ion implantation to drive the S or Se ions through the metal layer  82 . In some examples, the annealing is performed at a temperature less than or equal to 600° C. 
     Referring now to  FIG. 7 , a method  148  for making the substrate of  FIGS. 6A-6B  is shown. After step  118  from  FIG. 5 , the method continues at  150  and a metal layer is deposited on the substrate. In some examples, the metal includes aluminum (Al), zirconium (Zr), tungsten (W) or tantalum (Ta), although other materials can be used. At  154 , a mask layer is patterned and deposited on the substrate to block passivation of the second film associated with PMOSFETs but not NMOSFETs. At  158 , the second film associated with the NMOSFETs is passivated through the metal layer. At  160 , the mask is stripped. 
     Referring now to  FIGS. 8-10 , a similar technique may be used for gate-all-around (GAA) transistors  210 . In  FIGS. 8-9 , the GAA transistors  210  include source and drain regions  214  and  220 , respectively. Gate regions  224  are formed around channel regions  230  between the source region  214  and the drain region  220 . The channel regions  230  may be formed using germanium (Ge) nanowires or SiGe nanowires (with a Ge concentration greater than or equal to 85%). Some of the transistors may be PMOSFETs  240  and some of the transistors may be NMOSFETs  242 . In  FIG. 10 , the channel regions  230  are surrounded by an oxide layer  232  and the gate regions  224 . 
     Prior to depositing a metal gate layer corresponding to the gate regions  224 , the Ge or SiGe nanowires in the channel regions  230  corresponding to NMOSFET transistors  242  are passivated as described above. The channel regions  230  corresponding to PMOSFETs  240  are masked before deposition of the metal gate layer in a manner similar to  FIGS. 4A-5 . In some examples, the metal gate layer includes aluminum (Al), zirconium (Zr), tungsten (W) or tantalum (Ta), although other materials can be used. Alternately, the masking may be performed after deposition of the metal gate layer in a manner similar to  FIGS. 6A-7 . 
     The foregoing description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure. 
     Spatial and functional relationships between elements (for example, between modules, circuit elements, semiconductor layers, etc.) are described using various terms, including “connected,” “engaged,” “coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and “disposed.” Unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship can be a direct relationship where no other intervening elements are present between the first and second elements, but can also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.”