Patent Publication Number: US-11031242-B2

Title: Methods for depositing a boron doped silicon germanium film

Description:
FIELD OF INVENTION 
     The present disclosure generally relates to methods for depositing a boron doped silicon germanium (Si 1-x Ge x ) film and semiconductor deposition apparatus configured for depositing a boron doped silicon germanium (Si 1-x Ge x ) film. 
     BACKGROUND OF THE DISCLOSURE 
     High-mobility semiconductors, such as silicon germanium (Si 1-x Ge x ) may be desirable to use in the fabrication of semiconductor devices because of their relatively high electron and/or hole mobility. Devices formed with high-mobility semiconductor materials may theoretically exhibit better performance, faster speeds, reduced power consumption, and have higher breakdown fields compared to similar devices formed with a lower-mobility semiconductor, such as silicon. 
     Monocrystalline silicon germanium (Si 1-x Ge x ) semiconductor materials may be deposited or grown using a variety of techniques. For example, vacuum processes, including molecular beam epitaxy and chemical vapor deposition, may be used to form monocrystalline silicon germanium films. 
     In some semiconductor device applications, the silicon germanium film may be doped with select impurities to obtain a desired electrical conductivity. For example, the silicon germanium film may be doped p-type by the incorporation of boron into the silicon germanium film. In some applications it may be desirable to deposit a silicon germanium film with a controlled doping concentration profile, such as, for example, a controlled or tunable boron dopant concentration profile in a silicon germanium film. Accordingly, methods are desired for forming a silicon germanium film with a controlled doping concentration profile. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with at least one embodiment of the disclosure, a method for depositing a boron doped silicon germanium (Si 1-x Ge x ) film is disclosed. The method may comprise: providing a substrate within a reaction chamber; heating the substrate to a deposition temperature; flowing a silicon precursor, a germanium precursor, and a halide gas into the reaction chamber through a first gas injector; flowing a boron dopant precursor into the reaction chamber through a second gas injector independent from the first gas injectors; contacting the substrate with the silicon precursor, the germanium precursor, the halide gas, and the boron dopant precursor; and depositing the boron doped silicon germanium (Si 1-x Ge x ) film over a surface of the substrate. 
     For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, the advantages of embodiments of the disclosure may be more readily ascertained from the description of certain examples of the embodiments of the disclosure when read in conjunction with the accompanying drawing, in which: 
         FIG. 1  illustrates a process flow diagram illustrating an exemplary deposition method in accordance with embodiments of the disclosure; 
         FIG. 2  illustrates an exemplary semiconductor deposition apparatus that may be utilized to deposit silicon germanium (Si 1-x Ge x ) films according to the embodiments of the disclosure; and 
         FIG. 3  illustrates the boron doping concentration profile for a number of boron doped silicon germanium films deposited according to the embodiments of the disclosure. 
     
    
    
     It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below. 
     As used herein, the term “substrate” may refer to any underlying material or materials that may be used, or upon which, a device, a circuit, or a film may be formed. 
     As used herein, the term “epitaxial layer” may refer to a substantially single crystalline layer upon an underlying substantially single crystalline substrate. 
     As used herein, the term “chemical vapor deposition” may refer to any process wherein a substrate is exposed to one or more volatile precursors, which react and/or decompose on a substrate surface to produce a desired deposition. 
     As used herein, the term “silicon germanium” may refer to a semiconductor material comprising silicon and germanium and may be represented as Si 1-x Ge x  wherein 1≥x≥0. 
     The embodiments of the disclosure may include methods for depositing a boron doped silicon germanium (Si 1-x Ge x ) film and particularly methods for depositing a boron doped silicon germanium film with a controlled boron dopant concentration profile by chemical vapor deposition methods. The embodiments of the disclosure may provide methods for depositing a silicon germanium film which comprises decoupling the uniformity of the germanium incorporation in the silicon germanium film from the uniformity of the boron incorporation in the silicon germanium film, such that the boron concentration in the silicon germanium film may be adjusted independently from the germanium concentration in the silicon germanium film. 
     Prior methods for depositing a boron doped silicon germanium (Si 1-x Ge x ) film by chemical vapor deposition methods may utilize a first gas injector to flow a silicon precursor, a germanium precursor, and a boron dopant precursor into a reaction chamber wherein the precursors contact a heated substrate upon which deposition occurs. In some prior chemical vapor deposition methods, the boron doped silicon germanium (Si 1-x Ge x ) film may be deposited by selective deposition methods and in such methods a second gas injector, independent from the first gas injector, may be utilized to introduce an etchant gas into the reaction chamber to enable a selective deposition process. In the described prior chemical vapor deposition methods for depositing a boron doped silicon germanium (Si 1-x Ge x ) film, both the germanium precursor and the boron dopant precursor may be introduced into the reaction chamber using a common gas injector for both precursors. Since the germanium precursor and the boron dopant precursor may be introduced into the reaction chamber utilizing a common gas injector, any modification to the germanium precursor flow will have a resulting effect on the boron dopant incorporation in the silicon germanium film, thereby eliminating independent control over the boron concentration and the germanium concentration in the silicon germanium (Si 1-x Ge x ) film. In some prior CVD methods, the silicon precursor and the halide gas may be introduced into the reaction chamber through a second gas injector, while the boron dopant precursor and germanium dopant precursor may be introduced into the reaction chamber through a first gas injector. 
     Therefore, the embodiments of the current disclosure may comprise methods for depositing a boron doped silicon germanium (Si 1-x Ge x ) film which allows independent control of the germanium concentration and the boron concentration within the silicon germanium film. The embodiments may include decoupling the flow of the germanium precursor from the flow of the boron dopant precursor by introducing the germanium precursor into the reaction chamber through a first gas injector and introducing the boron dopant precursor into the reaction chamber through a second gas injector independent from the first gas injector. The embodiments of the disclosure may also allow for tuning of the boron concentration profile in the boron doped silicon germanium film to enable regulation of the boron concentration profile for substrate with various surface areas. For example, a substrate including high aspect ratio features may incorporate the boron dopant differently to a planar substrate and the embodiments of the disclosure may allow for tunability of the boron dopant concentration in the deposited silicon germanium film to compensate for differences in substrate surface area. 
     The embodiments of the disclosure therefore comprise methods for depositing a boron doped silicon germanium (Si 1-x Ge x ) film. The deposition methods may comprise: providing a substrate within a reaction chamber; heating the substrate to a deposition temperature; flowing a silicon precursor, a germanium precursor, and a halide gas into the reaction chamber through a first gas injectors; flowing a boron dopant precursor into the reaction chamber through a second gas injector independent from the first gas injector; contacting the substrate with the silicon precursor, the germanium precursor, the halide gas, and the boron dopant precursor; and depositing the boron doped silicon germanium (Si 1-x Ge x ) film over a surface of the substrate. 
     The methods of the disclosure may be understood with reference to  FIG. 1  which illustrates an exemplary process flow demonstrating a non-limiting method for depositing a boron doped silicon germanium (Si 1-x Ge x ) film. The method  100  of depositing a boron doped silicon germanium film may commence by means of a process block  110 , which comprises providing a substrate into a reaction chamber and heating the substrate to a deposition temperature. 
     In some embodiments of the disclosure, the substrate may comprise a planar substrate or a patterned substrate. Patterned substrates may comprise substrates that may include semiconductor device structures formed into or onto a surface of the substrate; for example, the patterned substrates may comprise partially fabricated semiconductor device structures such as transistors and memory elements. A patterned substrate may comprise a non-planar surface which may comprise one or more fin structures extending up from the main surface of the substrate and/or one or more indentations extending into the surface of the substrate. The substrate may contain monocrystalline surfaces and/or one or more secondary surfaces that may comprise a non-monocrystalline surface, such as a polycrystalline surface and an amorphous surface. Monocrystalline surfaces may comprise, for example, one or more of: silicon (Si), silicon germanium (SiGe), germanium tin (GeSn), or germanium (Ge). Polycrystalline or amorphous surfaces may include dielectric materials, such as oxides, oxynitrides, or nitrides, including for example, silicon oxides and silicon nitrides. 
     As a non-limiting example, the reaction chamber may comprise a reaction chamber of a chemical vapor deposition system. However, it is also contemplated that other reaction chambers (such as, for example, atomic layer deposition reaction chambers) and alternative chemical vapor deposition systems may also be utilized to perform the embodiments of the present disclosure. 
     With continued reference to  FIG. 1 , the process block  110  of exemplary method  100  may continue by heating the substrate to a desired deposition temperature within a reaction chamber. In some embodiments of the disclosure, the method  100  may comprise heating the substrate to a temperature of less than approximately 700° C., or to a temperature of less than approximately 650° C., or to a temperature of less than approximately 600° C., or to a temperature of less than approximately 550° C., or to a temperature of less than approximately 500° C., or to a temperature of less than approximately 450° C., or even to a temperature of less than approximately 400° C. For example, in some embodiments of the disclosure, heating the substrate to a deposition temperature may comprise heating the substrate to a temperature between approximately 400° C. and approximately 700° C. 
     In addition to controlling the temperature of the substrate, the pressure within the reaction chamber may also be regulated. For example, in some embodiments of the disclosure, the pressure within the reaction chamber may be less than 200 Torr, or less than 100 Torr, or less than 50 Torr, or less than 25 Torr, or even less than 10 Torr. In some embodiments, the pressure in the reaction chamber may be between 10 Torr and 100 Torr. 
     The exemplary deposition method  100  of  FIG. 1  may continue by means of a process block  120  comprising, flowing a silicon precursor, a germanium precursor, and a halide gas into the reaction chamber through a first gas injector. In some embodiments of the disclosure, a process block  130  may be performed concurrently with the process block  120 , wherein the process block  130  further comprises, flowing a boron dopant precursor into the reaction chamber through a second gas injector independent from the first gas injector. In some embodiments, the first gas injector and the second gas injector may both comprise multi-port injectors (MPIs) including a plurality of individual port injectors for providing a gas mixture into the reaction chamber. 
     In more detail,  FIG. 2  illustrates an exemplary semiconductor deposition apparatus  200  that may be utilized to deposit silicon germanium (Si 1-x Ge x ) films according to the embodiments of the disclosure. In some embodiments, the exemplary semiconductor deposition apparatus  200  may comprise a chemical vapor deposition apparatus. 
     The exemplary semiconductor deposition apparatus  200  may comprise a reaction chamber  202 , a substrate  204  upon which deposition is performed, a first gas injector  206 A, and a second gas injector  206 B independent from the first gas injector  206 A. In some embodiments, the first gas injector  206 A and the second gas injector  206 B may comprise multi-port injectors (MPIs). For example, the first gas injector  206 A may comprise a first MPI and may comprise a plurality of individual injection ports, such as exemplary individual injection port  208 A. In addition, the second gas injector  206 B may comprise a second MPI and may comprise a plurality of individual injections ports, such as exemplary individual injection port  208 B. The individual injection ports may comprise a BMW series metering valve manufactured by Swagelok® and a brushless DC motor manufactured by HanBay Inc., for example. In addition, individual injection ports may be controlled by mass flow controllers (MFCs) manufactured by Horiba or MKS instruments, for example. In some embodiments, the first MPI  206 A and the second MPI  206 B may be disposed in a close spatial relationship or separated spatially. The first MPI  206 A and the second MPI  206 B are not limited to five individual injections ports (as illustrated in  FIG. 2 ) and may have more or less than five individual injections ports depending on the application. For example, the number of individual injection ports per MPI may range from 1 to 15, or from 3 to 10, or from 5 to 8, depending on the application. It should be noted that other geometries and arrangements of the individual ports of the first MPI  206 A and the second MPI  206 B are possible other than those illustrated in  FIG. 2 . 
     In some embodiments of the disclosure, the first gas injector  206 A may flow a silicon precursor, a germanium precursor, and a halide gas into the reaction. For example, the silicon precursor may comprise a hydrogenated silicon precursor selected from the group comprising: silane (SiH 4 ), disilane (Si 2 H 6 ), trisilane (Si 3 H 8 ), or tetrasilane (Si 4 H 10 ). Alternatively, the silicon precursor may comprise a chlorinated silicon precursor selected from the group comprising: monochlorosilane (MCS), dichlorosilane (DCS), trichlorosilane (TCS), hexachlorodisilane (HCDS), octachlorotrisilane (OCTS), or silicon tetrachloride (STC). In some embodiments, the germanium precursor may comprise at least one of germane (GeH 4 ), digermane (Ge 2 H 6 ), trigermane (Ge 3 H 8 ), or germylsilane (GeH 6 Si). In addition, the halide gas may comprise at least one of chlorine (Cl 2 ), or hydrochloric acid (HCl). 
     In some embodiments of the disclosure, the second gas injector  206 B may flow a boron dopant precursor into the reaction chamber. In some embodiments, the second gas injector  206 B may flow a single gas consisting of the boron dopant precursor. In some embodiments, the second gas injector  206 B may flow a gas mixture consisting of carrier gas (e.g., N 2 , Ar, H 2  and He) and the boron dopant precursor. In some embodiments, the boron dopant precursor comprises at least one of diborane (B 2 H 6 ), or boron trichloride (BCl 3 ), boron trifluoride (BF 3 ), deuterium-Diborane (B 2 D 6 ). 
     In some embodiments of the disclosure, the p-type dopant precursor, i.e., the boron dopant precursor, may be replaced by an alternative p-type dopant precursor. For example, the p-type dopant precursor may comprise a gallium (Ga) containing dopant precursor or an aluminum (Al) containing dopant precursor, such as, for example, a borohydride (e.g., (Ga(BH 4 ) 3 ) or (Al(BH 4 ) 3 )), a halide, or an organohalide. 
     The exemplary deposition methods  100  ( FIG. 1 ) may continue by means of a process block  140 , which comprises contacting the substrate with silicon precursor, the germanium precursor, the halide gas, and the boron dopant precursor. In some embodiments, contacting the substrate with the silicon precursor, the germanium precursor, the halide precursor, and the boron dopant precursor may occur concurrently; in other words, the silicon precursor, the germanium precursor, the halide gas, and the boron dopant precursor are co-flowed into the reaction chamber and interact with the heated substrate as a gas mixture comprising the silicon precursor, the germanium precursor, the halide gas, and the boron dopant precursor. In some embodiments, exposing the substrate to the silicon precursor, the germanium precursor, the halide gas, and the boron dopant precursor may comprise sequentially introducing the precursors into the reaction chamber, in other words, the precursors are separately and sequentially introduced into the reaction chamber and contact the substrate. 
     In some embodiments, contacting the substrate with the silicon precursor comprises flowing the silicon precursor into the reaction chamber through the first gas injector at a flow rate of less than 500 sccm, or less than 250 sccm, or even less than 50 sccm. For example, the silicon precursor may flow into the reaction chamber at a silicon precursor flow rate between approximately 1 sccm and approximately 500 sccm. 
     In some embodiments, contacting the substrate with the germanium precursor comprises flowing the germanium precursor into the reaction chamber through the first gas injector at a flow rate of less than 1000 sccm, or less than 300 sccm, or even less than 10 sccm. For example, the germanium precursor may flow into the reaction chamber at a germanium precursor flow rate between approximately 1 sccm and approximately 1000 sccm. In some embodiments, the gallium precursor may be provided in diluted form and the diluted form may comprise approximately 1.5% germanium precursor, such as, GeH 4 , for example. 
     In some embodiments, contacting the substrate with the halide gas comprises flowing the halide gas into the reaction chamber through the first gas injector at a flow rate of less than 500 sccm, or less than 250 sccm, or even less than 100 sccm. For example, the halide gas may flow into the reaction chamber at a halide gas flow rate between approximately 1 sccm and approximately 500 sccm. 
     In some embodiments, contacting the substrate with the boron dopant precursor comprises flowing the boron dopant precursor into the reaction chamber through the second gas injector at a flow rate of less than 500 sccm, or less than 250 sccm, or even less than 50 sccm. For example, the boron dopant precursor may flow into the reaction chamber at a boron dopant precursor flow rate between approximately 1 sccm and approximately 500 sccm. In some embodiments, the boron precursor may be provided in diluted form and the diluted form may comprise approximately 1% boron dopant precursor, such as, diborane, for example. 
     The exemplary deposition method  100  may continue by means of a process block  150 , comprising depositing a boron doped silicon germanium (Si 1-x Ge x ) film over a surface of the substrate. In some embodiments, the addition of the halide gas to the gas mixture introduced into the reaction chamber may enable the selective deposition of a boron doped silicon germanium (Si 1-x Ge x ) film over select regions of the surface of the substrate. For example, the methods of the disclosure may be utilized to selectively deposit boron doped silicon germanium source and drain regions over a semiconductor device structure, such as a FinFET structure or a planar FET structure. 
     In some embodiments, the deposited boron doped silicon germanium (Si 1-x Ge x ) film may have a boron concentration of greater than 1×10 20 /cm 3 , or greater than 5×10 20 /cm 3 , or even greater than 3×10 21 /cm 3 . For example, the deposited boron doped silicon germanium films of the current disclosure may have a boron concentration between approximately 1×10 20 /cm 3  and approximately 3×10 21 /cm 3 . In addition, the deposited boron doped silicon germanium (Si 1-x Ge x ) film may have a germanium content (x) greater than 0.2, or greater than 0.3, or greater than 0.4, or greater than 0.5, or greater than 0.6, or even greater than 0.7. In some embodiments, the deposited boron doped silicon germanium (Si 1-x Ge x ) film may have a germanium content (x) between approximately 0.2 and approximately 0.7, or even between approximately 0.3 and approximately 0.5. In some embodiments, the germanium content within the deposition silicon germanium film may not be constant but may be varied such that germanium content may have a graded composition within the deposited silicon germanium film. 
     In some embodiments, depositing the boron doped silicon germanium (Si 1-x Ge x ) film may comprise depositing the boron doped silicon germanium film to a thickness greater than 20 Angstroms, or greater than 40 Angstroms, or greater than 60 Angstroms, or greater than 80 Angstroms, or greater than 100 Angstroms, or greater than 250 Angstroms, or even greater than 500 Angstroms. In some embodiments, the boron doped silicon germanium film may be deposited to a thickness less than 20 Angstroms, or less 10 Angstroms, or even less than 5 Angstroms. In some embodiments, the boron doped silicon germanium film may be deposited to a thickness between approximately 20 Angstroms and approximately 300 Angstroms. 
     In some embodiments, depositing the boron doped silicon germanium (Si 1-x Ge x ) film may further comprise depositing a doped silicon germanium film with an electrical resistivity of less than 0.8 mΩ·cm, or less than 0.6 mΩ·cm, or less than 0.4 mΩ·cm, or even less than 0.2 mΩ·cm. In some embodiments, the deposited doped silicon germanium film has an electrical resistivity between approximately 0.2 mΩ·cm and approximately 0.8 mΩ·cm. 
     The embodiments of the current disclosure may allow for the modification of the boron dopant concentration profile across the substrate. In some embodiments, the boron dopant concentration profile in the silicon germanium film deposited on a substrate may be modified whilst maintaining a desired germanium concentration profile in the silicon germanium film, such that the boron dopant concentration profile and the germanium concentration profile may be independently controlled in the deposited silicon germanium film. 
     In more detail,  FIG. 3  comprises a graph  300  which illustrates the boron concentration in three exemplary boron doped silicon germanium films denoted as films  304 ,  306 , and  308 , the three exemplary films being deposited according to the embodiments of the current disclosure. Graph  300  also illustrates the variation achieved between the boron concentration at the edge of the substrate (edge boron concentration “EBC”) and the boron concentration at the center of the substrate (center boron concentration “CBC”) for the three exemplary boron doped silicon germanium films deposited according to the embodiments of the disclosure. 
     In addition, the variation in the boron concentration in the exemplary silicon germanium films may be expressed by EBC/CBC and the value for EBC/CBC is plotted in the graph labelled  302  for the three exemplary silicon germanium films deposited according to the embodiments of the disclosure. 
     In more detail, the data labelled as  304  was obtained from a boron doped silicon germanium film deposited by a baseline process wherein the EBC and CBC are somewhat matched, resulting in an EBC/CBC value close to 1. As a non-limiting example, in a baseline process the MPI may comprise multiple individual injection ports which are opened to the same value. In some embodiments, the methods of the disclosure may deposit a boron doped silicon germanium film wherein EBC and CBC are substantially matched and therefore EBC/CBC equals 1. 
     However, the data labelled  306  was obtained from a boron doped silicon germanium film deposited according to the embodiments of the disclosure wherein the CBC is significantly greater than the EBC thereby resulting in an EBC/CBC value of less than 1. In addition, the data labelled  308  was obtained from a boron doped silicon germanium film deposited according to the embodiments of the disclosure wherein the CBC is significantly lower than the EBC thereby resulting in an EBC/CBC value of greater than 1. In some embodiments, the EBC/CBC value and hence the doping profile of the boron doped silicon germanium may be altered by controlling of the flow rate of the precursors through the individual injection ports comprising the MPIs. As a non-limiting example, an EBC/CBC value of less than 1 may be achieved by increasing the flow of precursor at the center regions of the MPI compared with the flow from edge regions of the MPI. 
     The embodiments of the disclosure which utilize separate, independent gas injectors for the germanium precursor and the boron dopant precursor allow for a wide modification in the boron concentration profile in the deposited silicon. For example, in some embodiments the EBC/CBC value may have a minimum value of approximately 0.3 and may have a maximum value of approximately 3. In some embodiments, the EBC/CBC value may range between approximately 0.3 and approximately 3 while maintaining a substantially constant germanium content in the boron doped silicon germanium film. 
     The example embodiments of the disclosure described above do not limit the scope of the invention, since these embodiments are merely examples of the embodiments of the invention, which is defined by the appended claims and their legal equivalents. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternative useful combination of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims.