Abstract:
A semiconductor device includes a gate disposed over a substrate; a source region and a drain region on opposing sides of the gate; and a pair of trench contacts over and abutting an interfacial layer portion of at least one of the source region and the drain region; wherein the interfacial layer includes boron in an amount in a range from about 5×10 21  to about 5×10 22  atoms/cm 2 .

Description:
PRIORITY 
     This application is a continuation of and claims priority from U.S. patent application Ser. No. 14/812,399, filed on Jul. 29, 2015, entitled “PURE BORON FOR SILICIDE CONTACT”, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present invention generally relates to metal-oxide-semiconductor field-effect transistors (MOSFET), and more specifically, to source/drain contact structures. 
     The MOSFET is a transistor used for amplifying or switching electronic signals. The MOSFET has a source, a drain, and a metal oxide gate electrode. The metal gate is electrically insulated from the main semiconductor n-channel or p-channel by a thin layer of insulating material, for example, silicon dioxide or glass, which makes the input resistance of the MOSFET relatively high. The gate voltage controls whether the path from drain to source is an open circuit (“off”) or a resistive path (“on”). 
     N-type field effect transistors (NFET) and p-type field effect transistors (PFET) are complementary MOSFETs. The NFET uses electrons as the majority current carriers and is built directly on a p-type substrate with n-doped source and drain junctions (also called epitaxial contacts) and an n-doped gate. The PFET uses holes as the majority current carriers and is built on an n-well with p-doped source and drain junctions (epitaxial contacts) and a p-doped gate. The dopant concentration in the source and drain junctions is an important parameter for optimal transistor function. 
     SUMMARY 
     In one embodiment of the present invention, a semiconductor device includes a gate disposed over a substrate; a source region and a drain region on opposing sides of the gate; and a pair of trench contacts over and abutting an interfacial layer portion of at least one of the source region and the drain region; wherein the interfacial layer includes boron in an amount in a range from about 5×10 21  to about 5×10 22  atoms/cm 2 . 
     In another embodiment, a method of making a semiconductor device includes performing an epitaxial growth process to form epitaxial contacts on opposing sides of a gate positioned over a substrate; removing portions of the epitaxial contacts to form trench contact patterns; depositing a conformal layer including amorphous boron within the trench contact patterns, the conformal layer forming a discrete interfacial layer within the epitaxial contacts, and the discrete interfacial layer including boron in an amount in a range from about 5×10 21  to about 5×10 22  atoms/cm 2 ; removing the conformal layer including amorphous boron; and filling the trench contact patterns with a high-k dielectric material and a conductive metal to form the trench contacts. 
     Yet, in another embodiment, a method of making a semiconductor device includes performing an epitaxial growth process to form epitaxial contacts on opposing sides of a gate positioned over a substrate; removing portions of the epitaxial contacts to form trench contact patterns; performing a deposition process to deposit a conformal layer including substantially pure amorphous boron within the trench contact patterns, the conformal layer forming a discrete interfacial layer within the epitaxial contacts comprising boron in an amount in a range from about 5×10 21  to about 5×10 22  atoms/cm 2 ; removing the conformal layer including amorphous boron; and filling the trench contact patterns with a high-k dielectric material and a conductive metal to form the trench contacts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIGS. 1-7  illustrate an exemplary method of making a PFET source/drain contact according to embodiments the present invention, in which: 
         FIG. 1  is a cross-sectional side view of a semiconductor device with a PFET and a NFET formed over a substrate; 
         FIG. 2  is a cross-sectional side view after performing an etching process to form trench contacts over the source/drain regions; 
         FIG. 3  is a cross-sectional side view after lithographic patterning to block the NFET region; 
         FIG. 4A  is a cross-sectional side view after depositing a conformal layer of amorphous boron; 
         FIG. 4B  is a cross-sectional side view after removing the amorphous boron layer; 
         FIG. 4C  is a cross-sectional side view after removing the lithographic patterning mask; 
         FIG. 5A  is a cross-sectional side view after depositing a liner in the trench contacts; 
         FIG. 5B  is a cross-sectional side view after filling the trench contact with a conductive metal; 
         FIG. 6A  is a cross-sectional side view after depositing an oxide layer over the semiconductor device; 
         FIG. 6B  is a cross-sectional side view after etching to form the gate contact patterns over the gates; and 
         FIG. 7  is a cross-sectional side view after depositing a gate contact liner and conductive gate material. 
     
    
    
     DETAILED DESCRIPTION 
     Although the dopant concentration (e.g., boron (B) concentration) can significantly improve functioning at the PFET source/drain contact, the ability to increase the dopant concentration by ion implantation or other methods (e.g., in-situ based doping) is limited to an upper limit of about 5×10 20  atoms/centimeter 2  (atoms/cm 2 ). 
     Accordingly, embodiments of the present invention provide a PFET source/drain contact with a high boron concentration in silicon (Si) or silicon germanium (SiGe), up to about 3×10 22  atoms/cm 2 . Further, the boron mixes with the Si or SiGe with to provide high activity in the contact because a high boron concentration provides decreased resistance. A method of making the PFET source/drain contact with a high boron concentration (e.g., 1×10 19  to about 1×10 21  atoms/cm 2 ) is now described in detail with accompanying figures. It is noted that like reference numerals refer to like elements across different embodiments. 
     The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus. 
     As used herein, the articles “a” and “an” preceding an element or component are intended to be nonrestrictive regarding the number of instances (i.e. occurrences) of the element or component. Therefore, “a” or “an” should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular. 
     As used herein, the terms “invention” or “present invention” are non-limiting terms and not intended to refer to any single aspect of the particular invention but encompass all possible aspects as described in the specification and the claims. 
     As used herein, the term “about” modifying the quantity of an ingredient, component, or reactant of the invention employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or solutions. Furthermore, variation can occur from inadvertent error in measuring procedures, differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods, and the like. In one aspect, the term “about” means within 10% of the reported numerical value. In another aspect, the term “about” means within 5% of the reported numerical value. Yet, in another aspect, the term “about” means within 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value. 
     Turning now to the Figures,  FIGS. 1-7  illustrate an exemplary method of making a PFET source/drain contact according to embodiments of present invention.  FIG. 1  is a cross-sectional side view of a semiconductor device with a NFET  150  and a PFET  151  formed over a common substrate  101 . Non-limiting examples of suitable substrate materials include silicon, silicon dioxide, aluminum oxide, sapphire, germanium, gallium arsenide (GaAs), an alloy of silicon and germanium, indium phosphide (InP), or any combination thereof. Other examples of suitable substrates  101  include silicon-on-insulator (SOI) substrates with buried oxide (BOX) layers. The thickness of the substrate  101  is not intended to be limited. In one aspect, the thickness of the substrate  101  is in a range from about 2 mm to about 6 mm for bulk semiconductor substrates. In another aspect, the thickness of the substrate  101  is in a range from about 25 nm to about 50 nm for the silicon layer in SOI substrates 
     To form the epitaxial contacts forming the source regions  120  and  122  and the drain region  121  and  123 , lithography and etching are performed. Lithography can include depositing a photoresist (not shown) onto the substrate  101  and developing the exposed photoresist with a resist developer to provide a patterned photoresist. The epitaxial contacts are formed by performing an epitaxial growth process to deposit a doped material (e.g., silicon). The type of dopant used depends on whether the MOSFET is the NFET  150  or the PFET  151 . Non-limiting examples of suitable dopants for the NFET  150  include n-type dopants (e.g., Group V elements such as phosphorus). Non-limiting examples of suitable dopants for the PFET  151  include p-type dopants (e.g., Group III such as boron). Generally, the concentration of dopant in the epitaxial contacts is in a range from about 1×10 19  to about 1×10 21  atoms/cm 2 . 
     The thickness of the epitaxial contacts forming the source regions  120  and  122  and the drain regions  121  and  123  is not intended to be limited. In one aspect, the thickness of the epitaxial contacts is in a range from about 5 nm to about 60 nm. In another aspect, the thickness of the epitaxial contacts is in a range from about 5 nm to about 10 nm. 
     The gates  110  and  112  are formed by lithographic patterning and etching. Initially, a “dummy gate” is formed by filling the gate region with a suitable removable gate material, for example, amorphous silicon (polysilicon). The removable gate material is subsequently removed, and the gates  110  and  112  are filled with a conductive gate material. A high-k dielectric liner can be deposited before filling with the conductive gate material. 
     The high-k dielectric material can be a dielectric material having a dielectric constant greater than 4.0, 7.0, or 10.0. Non-limiting examples of suitable materials for the high-k dielectric material include oxides, nitrides, oxynitrides, silicates (e.g., metal silicates), aluminates, titanates, nitrides, or any combination thereof. Other non-limiting examples of suitable high-k dielectric materials include HfO 2 , ZrO 2 , Al 2 O 3 , TiO 2 , La 2 O 3 , SrTiO 3 , LaAlO 3 , Y 2 O 3 , a pervoskite oxide, or any combination thereof. The high-k dielectric material layer may be formed by known deposition processes, for example, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), evaporation, physical vapor deposition (PVD), chemical solution deposition, or other like processes. The thickness of the high-k dielectric material may vary depending on the deposition process as well as the composition and number of high-k dielectric materials used. The high-k dielectric material layer may have a thickness in a range from about 0.5 to about 20 nm. 
     Non-limiting examples of suitable conductive gate metals include aluminum (Al), platinum (Pt), silver (Au), tungsten (W), titanium (Ti), or any combination thereof. The conductive metal may be deposited by a known deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, and sputtering. 
     The thickness of the gates  110  and  112  is not intended to be limited. In one aspect, the thickness of the gates  110  and  112  is in a range from about 20 nm to about 75 nm. In another aspect, the thickness of the gates  110  and  112  is in a range from about 20 nm to about 50 nm. 
     A blanket oxide layer  130  is deposited onto both NFET  150  and PFET  151  regions over the substrate  101 . Non-limiting examples of suitable materials for the oxide layer  130  include flowable oxides (e.g., liquid solutions of hydrogen silsesquioxane in a carrier solvent) and silicon dioxide. The thickness of the oxide layer  130  is not intended to be limited. In one aspect, the thickness of the oxide layer  130  is in a range from about 50 nm to about 150 nm. In another aspect, the thickness of the oxide layer  130  is in a range from about 60 nm to about 115 nm. 
     An optional silicon nitride (SiN) layer  140  is deposited onto the oxide layer  130 . The thickness of the SiN layer  140  is not intended to be limited. In one aspect, the thickness of the SiN layer  140  is in a range from about 5 nm to about 20 nm. In another aspect, the thickness of the SiN layer  140  is in a range from about 10 nm to about 15 nm. 
       FIG. 2  is a cross-sectional side view after performing an etching process to form trench contacts  201  over the source regions  120  and  122  and drain regions  121  and  123 . The etching process may be a dry etching process, for example, reactive ion etching (ME). The etching process is performed through the SiN layer  140 , the oxide layer  130 , and a portion of the epitaxial contacts of the source regions  120  and  122  and drain regions  121  and  123 . The etching process removes a portion of and stops within a region of the epitaxial contacts to form a recess. The open trench contacts  201  form a trench contact pattern. The trench contact patterns have side walls (y) and a base (x) that protrude into the epitaxial contacts of the source region  122  and the drain region  123 . 
       FIG. 3  is a cross-sectional side view after lithographic patterning to block the NFET  150  region. A hard mask layer  301  is deposited over the NFET  150  portion of the substrate  110 . The hard mask layer  301  may include, for example, amorphous carbon (a-C), silicon nitride (SiN), or silicon dioxide (SiO 2 ). The hard mask layer  301  fills the open regions of the trench contacts  201 . 
       FIG. 4A  is a cross-sectional side view after depositing a conformal layer of amorphous boron. The amorphous boron layer  401  is formed by using a deposition process (e.g., CVP or ALD) to deposit a conformal layer of amorphous boron within the trench contacts  201  over the PFET  151 . The amorphous boron layer  401  includes substantially pure boron. In one embodiment, the amorphous boron layer  401  includes 100 atomic % (at. %) boron. In another embodiment, the amorphous boron layer  401  includes at least 99 at. % boron. Yet, in another embodiment, the amorphous boron layer  401  includes at least 98 at. % boron. 
     Deposition of the amorphous boron layer  401  may be performed by Chemical Vapor Deposition (CVD). The conditions of the CVD process may be tailored to the particular semiconductor device. The CVD process may be performed at atmospheric pressure (i.e., about 760 Torr), or reduced pressures, for example 60 Torr or 36 Torr. In one exemplary embodiment, the deposition is performed at processing temperatures ranging from about 500° C. to about 800° C. Diborane (B 2 H 6 ) is injected into the reactor chamber as the dopant gas at a flow rate of, for example, 490 standard cubic centimeters per minute (sccm). Hydrogen gas (H 2 ) may be used as the carrier gas and for dilution of the doping source. 
     The hard mask layer  301  protects the trench contacts  201  over the NFET  150  region. The amorphous boron layer  401  lines the trench contacts  201  of the PFET  151  and forms an interfacial layer  410  including a high boron concentration in the epitaxial contacts of the source region  122  and drain region  123 . The interfacial layer  410  naturally forms in the source region  122  and drain region  123  upon disposing amorphous boron layer  401  within the trench contacts  201 . 
     In one aspect, the interfacial layer  410  has a thickness in a range from about 0.5 nm to about 2 nm. In another aspect, the interfacial layer  410  has a thickness in a range from about 1 nm to about 1.5 nm. Yet, in another aspect, the interfacial layer  410  has a thickness about or in any range from about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1., 1.2, 1.3, 1.4, and 1.5 nm. 
     In one aspect, the interfacial layer  410  has a boron concentration in a range from about 5×10 21  to about 5×10 22  atoms/cm 2 . In another aspect, the interfacial layer  410  has a boron concentration in a range from about 1×10 22  to about 3×10 22  atoms/cm 2 . 
       FIG. 4B  is a cross-sectional side view after removing the amorphous boron layer  401 . The amorphous boron layer  401  may be removed using any suitable process. Although the amorphous boron layer  401  is stripped, the interfacial layer  410  remains over the source region  122  and the drain region  123 . In one non-limiting example, a boiling solution of concentrated nitric acid (HNO 3 ) is used to remove the amorphous boron layer  401 . The temperature of the HNO 3  can be, for example, 110° Celsius (° C.). The concentration of the HNO 3  can be, for example, between about 50 and about 85%. In another non-limiting example, an aqua regia process can be used to remove the amorphous boron layer  401 . An aqua regia process involves using a nitro-hydrochloric acid (HCl) to etch away the amorphous boron layer  401 . The nitro-HCl mixture is formed by mixing concentrated nitric acid and hydrochloric acid in a volume ratio of, for example, 1:3. 
       FIG. 4C  is a cross-sectional side view after removing the hard mask layer  301  over the NFET  150  region. The hard mask layer  301  can be removed by a wet cleaning process using, for example, HF or HCl and dry etching. Suitable dry etching processes include ME, plasma etching, ion beam etching, laser ablation, or any combination thereof. 
       FIG. 5A  is a cross-sectional side view after depositing a liner  501  in the trench contacts  201 . To form the liner  501 , a high-k dielectric material is deposited into the trench contacts. The high-k dielectric material can be a dielectric material having a dielectric constant greater than 4.0, 7.0, or 10.0. Non-limiting examples of suitable materials for the high-k dielectric material include oxides, nitrides, oxynitrides, silicates (e.g., metal silicates), aluminates, titanates, nitrides, or any combination thereof. Other non-limiting examples of suitable high-k dielectric materials include HfO 2 , ZrO 2 , Al 2 O 3 , TiO 2 , La 2 O 3 , SrTiO 3 , LaAlO 3 , Y 2 O 3 , a pervoskite oxide, or any combination thereof. The high-k dielectric material layer may be formed by known deposition processes, for example, CVD, PECVD, ALD, evaporation, PVD, chemical solution deposition, or other like processes. The thickness of the high-k dielectric material may vary depending on the deposition process as well as the composition and number of high-k dielectric materials used. 
     In one embodiment, the liner  501  includes a bilayer of Ti and TiN. The TiN is deposited over the layer of Ti to form the Ti/TiN liner. The thickness of the liner  501  can generally vary and is not intended to be limited. In one aspect, the thickness of the liner  501  is in a range from about 3 nm to about 10 nm. In another aspect, the thickness of the liner  501  is in a range from about 4 nm to about 9 nm. 
       FIG. 5B  is a cross-sectional side view after filling the trench contacts  201  with a conductive metal  501 . Non-limiting examples of suitable conductive metals include tungsten, aluminum, platinum, gold, or any combination thereof. A planarization process, for example chemical mechanical planarization (CMP), is performed over the conductive metal  501 . The conductive metal may be deposited by a known deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, and sputtering. 
       FIG. 6A  is a cross-sectional side view after depositing a blanket oxide layer  601  over the NFET  150  and PFET  151  regions of the semiconductor device. The oxide layer  601  can include, for example, tetraethyl-ortho-silicate (TEOS) or silicon dioxide. 
       FIG. 6B  is a cross-sectional side view after etching to form the gate contact patterns  610  over the gates  110  and  112 . In one non-limiting example, a RIE process is performed to form the gate contact patterns  610 . 
       FIG. 7  is a cross-sectional side view after depositing a gate contact liner  701  and conductive gate material  702  into the gate contact patterns  610 . The gate contact liner  701  can include, for example, a high-k dielectric material as described above for liner  501  (see  FIG. 5A ). The conductive gate material  702  can be any of the conductive metal materials described above for the trench contacts  201  (see  FIG. 5B ). A planarization process, for example, a CMP process, is performed over the conductive gate material  702 . 
     The above described embodiments of semiconductor devices and methods of making such devices provide various advantages. The methods provide a PFET source/drain contact with a high boron concentration in Si or SiGe, up to about 3-5×10 22  atoms/cm 2 . After depositing a layer of amorphous boron over the source and drain a contact, the boron mixes with the Si or SiGe with to provide high activity in the contact. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting 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, element components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 
     The flow diagrams depicted herein are just one example. There may be many variations to this diagram or the steps (or operations) described therein without departing from the spirit of the invention. For instance, the steps may be performed in a differing order or steps may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.