Patent Publication Number: US-2010120235-A1

Title: Methods for forming silicon germanium layers

Description:
FIELD  
     Embodiments of the present invention generally relate to semiconductor processing, and more specifically to methods for depositing silicon germanium (SiGe) layers on substrates. 
     BACKGROUND  
     Silicon germanium (SiGe) layers may be utilized in semiconductor devices in many applications, such as for source/drain regions, source/drain extensions, contact plugs, a base layer of a bipolar device, or the like. Typically, SiGe layers may be epitaxially grown utilizing either dichlorosilane or silane as a silicon-containing precursor along with a germanium precursor. SiGe layers grown with dichlorosilane typically result in layers having a smooth surface, but with undesirably slow deposition rates. Thus, dichlorosilane precursors undesirably limit process throughput. Alternatively, SiGe layers may be grown using silane precursors, which tend to increase the deposition rate. However, such deposited layers typically have an undesirably rough surface. SiGe layers having rough surfaces may result in poor electrical contact with adjacent layers coupled thereto. In addition, the rough surface can result in device breakdown, or poor power consumption in devices utilizing such SiGe layers. 
     Thus, there is a need in the art for a method of depositing a silicon germanium (SiGe) layer on a substrate with a high deposition rate and having a smooth surface and desired properties. 
     SUMMARY 
     Embodiments of methods for depositing silicon germanium (SiGe) layers on a substrate are disclosed herein. In some embodiments, the method includes depositing a silicon germanium seed layer atop the substrate using a first precursor comprising silicon and chlorine; and depositing a silicon germanium bulk layer atop the silicon germanium seed layer using a second precursor comprising silicon and hydrogen. In some embodiments, the first silicon precursor gas may comprise at least one of dichlorosilane (H 2 SiCl 2 ), trichlorosilane (HSiCl 3 ), or silicon tetrachloride (SiCl 4 ). In some embodiments, the second silicon precursor gas may comprise at least one of silane (SiH 4 ), or disilane (Si 2 H 6 ). 
     In some embodiments, a computer readable medium having instructions stored thereon is provided. In some embodiments the instructions, when executed by a processor, cause a semiconductor process tool to perform a method of forming a silicon germanium layer including depositing a silicon germanium seed layer atop the substrate using a first precursor comprising silicon and chlorine; and depositing a silicon germanium bulk layer atop the silicon germanium seed layer using a second precursor comprising silicon and hydrogen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention may be had by reference to the appended drawings and the discussion thereof in further detail, below. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  depicts a flow chart of a method for depositing a silicon germanium layer on a substrate in accordance with some embodiments of the present invention. 
         FIGS. 2A-C  depict a substrate during various stages of the method as referred to in  FIG. 1 . 
         FIG. 3  depicts a schematic side view of a process chamber in accordance with some embodiments of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The above drawings are not to scale and may be simplified for illustrative purposes. 
     DETAILED DESCRIPTION 
     Methods for depositing silicon germanium (SiGe) layers on a substrate are described herein. The methods include depositing the silicon germanium (SiGe) seed layer on the substrate using a first precursor gas and depositing a silicon germanium (SiGe) bulk layer atop the SiGe seed layer using a second precursor gas. The inventive methods advantageously facilitate the deposition of SiGe layers at high deposition rates and having smooth surfaces. The inventive methods further facilitate formation of SiGe layers having desired properties, such as, surface morphology, desired strain, lattice constants, improved device performance, and the like. 
       FIG. 1  illustrates a flow chart of a method  100  for depositing a silicon germanium layer on a substrate. The method  100  may be performed in any suitable process chamber configured for deposition of silicon germanium layers, such as the RP EPI reactor, available from Applied Materials, Inc. of Santa Clara, Calif., or such as the process chamber  300  described below with respect to  FIG. 3 . The method  100  is described below with respect to  FIGS. 2A-C , which illustrate schematic side views of a substrate during various stages of the method as referred to in  FIG. 1 . 
     The method  100  generally begins at  102 , where a substrate  200  is provided. The substrate  200  refers to any substrate or material surface upon which a film processing is performed. In some embodiments, the substrate  200  may comprise silicon, crystalline silicon (e.g., Si&lt;100&gt; or Si&lt;111&gt;), strained silicon, silicon germanium, doped or undoped polysilicon, doped or undoped silicon wafers, patterned or non-patterned wafers, silicon on insulator (SOI), doped silicon, or the like. In some embodiments, the substrate  200  may have various dimensions, such as 200 or 300 mm diameter wafers, as well as rectangular or square panels. In some embodiments, the substrate  200  comprises silicon. The substrate  200  may be patterned and/or may contain multiple materials layers. For example, in some embodiments, the patterning may comprise a patterned photomask or the like. 
     At  104 , a silicon germanium seed layer  202  is deposited atop the substrate  200  (see  FIG. 2B ). The silicon germanium seed layer  202  may be utilized to, for example, cover defects in the surface of the substrate  200  and provide a smooth surface from which to grow a bulk SiGe layer. Specifically, the substrate  200  may comprise defects or contaminants arising, for example, from patterning processes, manufacturing and/or handling of the substrate, or the like. 
     In some embodiments, where a patterned substrate is used, the SiGe seed layer  202  may be deposited on an exposed portion of the substrate surface. In some embodiments, the SiGe seed layer  202  is deposited at a first deposition rate between about 25 to about 150 Angstroms/minute. The seed layer  202  may be deposited to any suitable thickness, for example, sufficient to cover any defects or to provide a smooth surface for subsequent deposition of a bulk SiGe layer (as described below). In some embodiments, the seed layer  202  is deposited to a thickness of up to about 100 Angstroms. The concentration of germanium in the SiGe seed layer  202  may be between about 10 to about 35 percent. 
     The silicon germanium seed layer  202  is deposited atop the substrate  200  using a first process gas mixture including a first silicon precursor gas and a germanium precursor gas. The first silicon precursor may be utilized for depositing the silicon element of the silicon germanium SiGe seed layer  202 . The first silicon precursor may comprise silicon, chlorine, and hydrogen. In some embodiments, the first silicon precursor includes at least one of dichlorosilane (H 2 SiCl 2 ), trichlorosilane (HSiCl 3 ), silicon tetrachloride (SiCl 4 ), or the like. In some embodiments, the first silicon precursor comprises dichlorosilane (H 2 SiCl 2 ). The first silicon precursor may be combined with a germanium precursor for depositing the silicon germanium (SiGe) seed layer  202 . The germanium precursor may include at least one of germane (GeH 4 ), germanium tetrachloride (GeCl 4 ), silicon tetrachloride (SiCl 4 ), or the like. In some embodiments, the germanium precursor comprises germane (GeH 4 ). In some embodiments, the silicon germanium seed layer  202  is deposited at a pressure of about 5 to about 15 Torr. In some embodiments, the silicon germanium seed layer  202  is deposited at a temperature of about 700 to about 750 degrees Celsius. 
     The first silicon precursor and the germanium precursor may be flowed simultaneously in a first process gas mixture, and utilized to form the SiGe seed layer  202  atop the substrate  200 . In some embodiments, the first process gas mixture may further include a dilutant/carrier gas. The dilutant/carrier gas may include at least one of hydrogen (H 2 ), nitrogen (N 2 ), helium (He), argon (Ar), or the like. In some embodiments, the dilutant/carrier gas comprises hydrogen (H 2 ). The first process gas mixture may further include an etch gas to be a selective process. The etch gas may include at least one of hydrogen chloride (HCl), chlorine (Cl 2 ), or the like. In some embodiments, the inert gas comprises hydrogen chloride (HCl), 
     In some embodiments, the first process gas mixture for the deposition of the silicon germanium seed layer  202  may be supplied at a total gas flow from about 10000 to about 35000 sccm, or at about 25000 sccm. The first process gas mixture may utilize a range of compositions. In some embodiments, the first process gas mixture may comprise between about 0.1 to about 1 percent of the first silicon precursor (e.g., a first silicon precursor flow of between about 25 to about 250 sccm). In some embodiments, the first process gas mixture may comprise between about 0.004 to about 0.02 percent of the germanium precursor (e.g., a germanium precursor gas flow of between about 1 to about 5 sccm). In some embodiments, the first process gas mixture may comprise between about 0.1 to about 1 percent of the etch gas (e.g., an etch gas flow of between about 25 to about 250 sccm). In some embodiments, the first process gas mixture may comprise between about 98 to about 99.9 percent of the dilutant/carrier gas. For example, in one specific embodiment, a first silicon precursor comprising dichlorosilane (H 2 SiCl 2 ) may be provided at a rate of about 100 sccm, a germanium precursor comprising germane (GeH 4 ) may be provided at a rate of about 3 sccm, an etch gas comprising hydrogen chloride may be provided at a rate of about 100 sccm, and a dilutant/carrier gas comprising hydrogen (H 2 ) may be provided at a rate of about 25000 sccm. 
     At  106 , a silicon germanium bulk layer  204  is deposited atop the silicon germanium seed layer  202  (see  FIG. 2C ). The SiGe seed layer  202  may advantageously provide a smooth surface, thus facilitating uniform growth of a SiGe bulk layer having a smooth surface. The bulk layer  204  may be deposited at a second deposition rate between about 150 to 300 Angstroms/minute. In some embodiments, the second deposition rate of the SiGe bulk layer  204  is greater than the first deposition rate of the SiGe seed layer  202 . The bulk layer  204  may be deposited to a thickness of between about 200 to about 1000 Angstroms. The concentration of germanium in the SiGe bulk layer  204  may be between about 10 to about 35 percent. In some embodiments, the concentration of germanium in the SiGe bulk layer  204  is the same as the concentration of germanium in the SiGe seed layer  202 . 
     The silicon germanium bulk layer  204  is deposited atop the silicon germanium seed layer  202  using a second process gas mixture including a second silicon precursor gas and a germanium precursor gas at a pressure of about 5 to about 15 Torr and a temperature of about 700 to about 750 degrees Celsius. The second silicon precursor may be utilized for depositing the silicon element of the silicon germanium SiGe bulk layer  204 . The second silicon precursor may comprise silicon and hydrogen. In some embodiments, the second silicon precursor may include at least one of silane (SiH 4 ), disilane (Si 2 H 6 ), or the like. In some embodiments, the second silicon precursor comprises silane (SiH 4 ). The second silicon precursor may be combined with a germanium precursor for depositing the silicon germanium (SiGe) bulk layer  204 . The germanium precursor may be any of the germanium precursors discussed above with respect to depositing the silicon germanium seed layer  202 . In some embodiments, the germanium precursor comprises germane (GeH 4 ). 
     The second silicon precursor and the germanium precursor may be flowed simultaneously in a second process gas mixture, and utilized to form the SiGe bulk layer  204  atop the seed layer  202 . The second process gas mixture may further comprises a dilutant/carrier gas and an etch gas. The dilutant/carrier gas may include any of the dilutant/carrier gases discussed above with respect to depositing the silicon germanium seed layer  202 . In some embodiments, the dilutant/carrier gas comprises hydrogen (H 2 ). The etch gas may include any of the etch gases discussed above with respect to depositing the silicon germanium seed layer  202 . In some embodiments, the etch gas comprises hydrogen chloride (HCl). 
     In some embodiments, the second process gas mixture for the deposition of the silicon germanium bulk layer  204  may be supplied at a total gas flow from about 9000 to about 35000 sccm, or at about 10000 sccm. The second process gas mixture may have a range of compositions. In some embodiments, the second process gas mixture may comprise between about 0.2 percent to about 1 percent of the second silicon precursor (e.g., a second silicon precursor flow of between about 20 to about 100 sccm). In some embodiments, the second process gas mixture may comprise between about 0.01 to about 0.05 percent of the germanium precursor (e.g., a germanium precursor flow of between about 1 to about 5 sccm). In some embodiments, the first process gas mixture may comprise between about 0.2 to about 2 percent of the etch gas (e.g., an etch gas flow of between about 20 to about 200 sccm). In some embodiments, the second process gas mixture may comprise between about 97 to about 99.9 percent of a dilutant/carrier gas. For example, in one specific embodiment, a second silicon precursor comprising silane (SiH 4 ) may be provided at a rate of about 50 sccm, a germanium precursor comprising germane (GeH 4 ) may be provided at a rate of about 3 sccm, an etch gas comprising hydrogen chloride may be provided at a rate of about 100 sccm, and a dilutant/carrier gas comprising hydrogen (H 2 ) may be provided at a rate of about 10000 sccm. 
     Upon completion of the deposition of the SiGe bulk layer  204 , the method  100  generally ends and further processing may performed, as desired. For example, the SiGe bulk layer  204  may be etched or further planarized as necessary. In device applications, for example, when the SiGe layer is used as a source/drain region of a transistor device, contacts may be adhered to the smooth surface of the SiGe bulk layer  204 . Such contacts may include, for example, a metal silicide layer. 
     The inventive methods disclosed herein may be performed in any suitable semiconductor process chamber adapted for performing epitaxial silicon deposition processes, such as the RP EPI reactor, available from Applied Materials, Inc. of Santa Clara, Calif. An exemplary process chamber is described below with respect to  FIG. 3 , which depicts a schematic, cross-sectional view of a semiconductor substrate process chamber  300  suitable for performing portions of the present invention. The process chamber  300  may be adapted for performing epitaxial silicon deposition processes and illustratively comprises a chamber body  310 , support systems  330 , and a controller  340 . 
     The chamber body  310  generally includes an upper portion  302 , a lower portion  304 , and an enclosure  320 . The upper portion  302  is disposed on the lower portion  304  and includes a lid  306 , a clamp ring  308 , a liner  316 , a baseplate  312 , one or more upper lamps  336  and one or more lower lamps  352 , and an upper pyrometer  356 . In some embodiments, the lid  306  has a dome-like form factor, however, lids having other form factors (e.g., flat or reverse curve lids) are also contemplated. The lower portion  304  is coupled to a process gas intake port  314  and an exhaust port  318  and comprises a baseplate assembly  321 , a lower dome  332 , a substrate support  324 , a pre-heat ring  322 , a substrate lift assembly  360 , a substrate support assembly  364 , one or more upper lamps  338  and one or more lower lamps  354 , and a lower pyrometer  358 . Although the term “ring” is used to describe certain components of the process chamber  300 , such as the pre-heat ring  322 , it is contemplated that the shape of these components need not be circular and may include any shape, including but not limited to, rectangles, polygons, ovals, and the like. 
     During processing, the substrate  200  is disposed on the substrate support  324 . The lamps  336 ,  338 ,  352 , and  354  are sources of infrared (IR) radiation (i.e., heat) and, in operation, generate a pre-determined temperature distribution across the substrate  200 . The lid  306 , the clamp ring  308 , and the lower dome  332  are formed from quartz; however, other IR-transparent and process compatible materials may also be used to form these components. 
     The substrate support assembly  364  generally includes a support bracket  334  having a plurality of support pins  366  coupled to the substrate support  324 . The substrate lift assembly  360  comprises a substrate lift shaft  326  and a plurality of lift pin modules  361  selectively resting on respective pads  327  of the substrate lift shaft  326 . In one embodiment, a lift pin module  361  comprises an optional upper portion of the lift pin  328  is movably disposed through a first opening  362  in the substrate support  324 . In operation, the substrate lift shaft  326  is moved to engage the lift pins  328 . When engaged, the lift pins  328  may raise the substrate  200  above the substrate support  324  or lower the substrate  325  onto the substrate support  324 . 
     The support systems  330  include components used to execute and monitor pre-determined processes (e.g., growing epitaxial silicon films) in the process chamber  300 . Such components generally include various sub-systems. (e.g., gas panel(s), gas distribution conduits, vacuum and exhaust sub-systems, and the like) and devices (e.g., power supplies, process control instruments, and the like) of the process chamber  300 . These components are well known to those skilled in the art and are omitted from the drawings for clarity. 
     The controller  340  generally comprises a Central Processing Unit (CPU)  342 , a memory  344 , and support circuits  346  and is coupled to and controls the process chamber  300  and support systems  330 , directly (as shown in  FIG. 3 ) or, alternatively, via computers (or controllers) associated with the process chamber and/or the support systems. 
     Thus, methods for depositing a silicon germanium layer on a substrate have been provided herein. The inventive methods advantageously facilitate the deposition of a SiGe layer at a high rate and having a smooth surface. The inventive methods further facilitate deposition of a SiGe layer having desired properties such as, for example, constant germanium concentrations throughout the film, improved balance of surface morphology and deposition rates, and the like. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.