Patent Publication Number: US-10319811-B2

Title: Semiconductor device including fin having condensed channel region

Description:
DOMESTIC PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 14/809,688, filed Jul. 27, 2015, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present invention relates to semiconductor devices, and more specifically, to fin-type field effect transistor (finFET) devices. 
     Recent semiconductor fabrication methods have been developed to replace pure silicon (Si) fins with silicon germanium (SiGe) fins, especially in p-type finFET devices. Forming the fins from SiGe reduces the threshold voltage (Vt) of the semiconductor device, thereby increasing the drive current that flows through the channel. Further, SiGe material provides higher carrier mobility than Si. Accordingly, SiGe fins may have improve hole mobility performance with respect to Si fins. Conventional methods use an ion implantation process that drives Ge ions into the fin to form a SiGe fin. However, these conventional ion implantation methods may damage the fin and reduce overall performance of the finFET device. 
     SUMMARY 
     According to a non-limiting embodiment, a finFET semiconductor device includes at least one semiconductor fin on an upper surface of a substrate. The semiconductor fin includes a channel region interposed between opposing source/drain regions. A gate stack is on the upper surface of the substrate and wraps around sidewalls and an upper surface of only the channel region. The channel region further includes a condensed portion formed of a first semiconductor material and a second semiconductor material. Unlike the channel region, the source/drain regions are formed of the first semiconductor material while excluding the second semiconductor material. 
     According to another non-limiting embodiment, a method of fabricating a finFET device comprises forming, on an upper surface of a semiconductor substrate, at least one semiconductor fin comprising a first semiconductor material. The at least one semiconductor fin has a channel region interposed between opposing source/drain regions. The method further includes forming a flowable insulator layer on the source/drain regions, and forming a dummy gate stack on the channel region. The method further includes selectively removing the dummy gate stack with respect to the flowable insulator layer to expose the channel region. The method further includes performing a condensation process to selectively transform the exposed channel region into a second semiconductor material different from the first semiconductor material so as to increase carrier mobility conductivity of the channel region, while maintaining the first semiconductor material of the source/drain regions. 
     Additional features are realized through the techniques of the present invention. Other embodiments are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the features, refer to the description and to the drawings. 
    
    
     
       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 features are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1A  illustrates an intermediate semiconductor device in a first orientation including a plurality of semiconductor fins including source/drain regions covered by a flowable insulator material and a channel region covered by a dummy gate stack according to a non-limiting embodiment; 
         FIG. 1B  illustrates the semiconductor device according to a second orientation; 
         FIG. 2A  illustrates the semiconductor device of  FIGS. 1A-1B  in the first orientation following removal of the dummy gate stack to expose the channel regions of the fins; 
         FIG. 2B  illustrates the semiconductor device of  FIG. 2A  in the second orientation; 
         FIG. 3A  illustrates the semiconductor device of  FIGS. 2A-2B  in the first orientation after growing a condenser layer on the sidewalls and an upper surface of the channel regions; 
         FIG. 3B  illustrates the semiconductor device of  FIG. 3A  in the second orientation; 
         FIG. 4A  illustrates the semiconductor device of  FIGS. 3A-3B  in the first orientation undergoing a condensation processes so as to drive a donor material into the channel regions and oxidize the condenser layer; 
         FIG. 4B  illustrates the semiconductor device of  FIG. 4A  in the second orientation; 
         FIG. 5A  illustrates the semiconductor device of  FIGS. 4A-4B  in the first orientation after selectively removing the oxidized condenser layer from the condensed channel regions of the fins; 
         FIG. 5B  illustrates the semiconductor device of  FIG. 5A  in the second orientation; 
         FIG. 6A  illustrates the semiconductor device of  FIGS. 5A-5B  in the first orientation after forming a planarized metal gate structure that wraps around the condensed channel region of the fins; and 
         FIG. 6B  illustrates the semiconductor device of  FIG. 6A  in the second orientation. 
     
    
    
     DETAILED DESCRIPTION 
     The transistor gain of semiconductor devices such as finFET devices, for example, is proportional to the mobility of the majority carrier traveling through the channel region. The current carrying capability, and therefore the performance of a finFET device is proportional to the mobility of the majority carrier in the channel. Traditional finFET devices include one or more semiconductor fins formed of silicon (Si). However, studies of semiconductor materials have shown that silicon germanium (SiGe) provides increased hole mobility, which are the majority carriers in a P-channel field effect transistor (i.e., PFET devices). Various non-limiting embodiments of the invention provide a finFET device including one or more fins having a SiGe condensed channel region. In this manner, hole mobility through the channel region of the fin is improved so as to enhance the overall performance of the finFET device. 
     With reference now to  FIGS. 1A-1B , a semiconductor structure  100  which serves as a starting point for fabricating a finFET device in accordance with an exemplary embodiment is shown. The semiconductor structure  100  includes a semiconductor substrate  102  extending along a first axis (e.g., X-axis) to define a length, a second axis (e.g., Y axis) to define a width, and a third axis (Z-axis) to define a height. The substrate  102  is formed as a semiconductor-on-insulator (SOI) substrate, for example, including a buried insulator layer  104  ( FIG. 1B ) formed on an upper surface of a bulk substrate layer  106 . The buried insulator layer  104  is formed of, for example, silicon dioxide (SiO 2 ) and the bulk substrate layer  106  is formed, for example, of silicon (Si). The buried insulator layer  104  has a vertical thickness (e.g., height) ranging from, for example, approximately 0.5 nanometers to approximately 200 nm. An active semiconductor layer (not shown) formed atop the buried insulator layer  104  is patterned to form one or more semiconductor fins  108 , as further illustrated in  FIG. 1B . According to a non-limiting embodiment, the semiconductor fins  108  are initially formed of silicon (Si). Various fin fabrications can be used to form the semiconductor fins  108  such as, for example, a sidewall image transfer (SIT) process. The semiconductor fins  108  extend along the X-axis to define a fin length, the Y-axis to define a fin width, and the Z-axis to define a fin height. The fin width ranges from approximately 3 nm to approximately 10 nm, the fin length ranges from approximately 50 nm to approximately 2000 nm, and the fin height ranges from ranges from approximately 20 nm to approximately 60 nm. 
     As further illustrated in  FIGS. 1A-1B , the semiconductor fins  108  are covered by one or more dummy gate stacks  110  and a flowable insulator layer  112  ( FIG. 1A ). The dummy gate stacks  110  are formed on an upper surface of the buried insulator layer  104  and wrap around the channel region  114  of the semiconductor fins  108 . According to at least one embodiment, the dummy gate stacks  110  are formed, for example, of an amorphous or polysilicon material. The dummy gate stacks  110  extend along the Y-axis to define a gate width, the X-axis to define a gate length, and the Z-axis to define a gate height. The gate width ranges from approximately 50 nm to approximately 2000 nm, the gate length ranges from approximately 15 nm to approximately 500 nm, and the gate height ranges from approximately 50 nm to approximately 150 nm. Although not illustrated, the dummy gate stack  110  may further include a gate oxide layer (not shown). The gate oxide layer is interposed between the dummy gate stack  110  and the fin  108 . The gate oxide layer may be formed as a dummy gate oxide layer, with the intention of being replaced by a high-k gate oxide layer or metal gate layer as understood by one of ordinary skill in the art. In addition, gate spacers  116  are formed on sidewalls of each dummy gate stack  110 . In this manner, the gate spacers  116  are interposed between the dummy gate stacks  110  and the flowable insulator layer  112 . The gate spacers  116  are formed from, for example, silicon nitride (SiN). 
     The flowable insulator layer  112  is formed atop the buried insulator layer  104  and covers the source/drain (S/D) regions  118  of the semiconductor fins  108 . The flowable insulator layer  112  is formed, for example, of SiO 2 . The flowable insulator layer  112  has a vertical thickness (e.g., height) ranging from approximately 50 nm to approximately 150 nm. Although not illustrated, it should be appreciated that an epitaxially grown semiconductor layer formed of Si, for example, may be grown from sidewalls and upper surfaces of the S/D regions  118  of the semiconductor fins  108  prior to forming the flowable insulator layer  112 . The epitaxially grown semiconductor layer is configured to merge the S/D regions  118  of each semiconductor fin  108  as understood by one of ordinary skill in the art. 
     Turning to  FIGS. 2A-2B , the semiconductor device  100  is illustrated following removal of the dummy gate stack  110 . Removal of the dummy gate stack  110  exposes the channel portion  114  of the semiconductor fins  108  and the underlying buried insulator layer  104 . The dummy gate stack  110  may be removed (i.e., pulled) using various etching processes such as, an ammonium hydroxide etching process, for example, which is implemented in well-known replacement metal gate fabrication processes. Since source/drain regions  118  are covered by the gate spacers  116  and flowable insulator layer  112 , no additional masking layers are necessary to remove the dummy gate stack  110 . 
     Referring now to  FIGS. 3A-3B , a condenser layer  120  is epitaxially deposited on sidewalls and an upper surface of the channel region  114 . According to an embodiment, the condenser layer  120  is formed using an epitaxial deposition process to ensure sufficient contact between the condenser and the surfaces of the fins  108 . The epitaxial growth process is selective to semiconductor materials such as, for example, silicon (Si). In this manner, the condenser layer  120  grows readily on the exposed semiconductor (e.g., Si) material of the channel region  114 , while avoiding growth on the exposed buried insulator layer  104 . According to a non-limiting embodiment, the condenser layer has a thickness ranging from approximately 1 nm to approximately 5 nm. 
     The condenser layer  120  may include a donor material (not shown in  FIGS. 3A-3B ) which, when driven into the semiconductor material of fins  108 , increases carrier mobility through the channel regions  114  without increasing or substantially increasing the dimensions of the fins  108 . According to a non-limiting embodiment, the donor material includes germanium (Ge) whereby a SiGe condenser layer  120  is epitaxially grown on the sidewalls and upper surface of the channel region  114 . The concentration of Ge donor material included in the condenser layer  120  ranges, for example, from approximately 50 to approximately 90. Since source/drain regions  118  are covered by the gate spacers  116  and flowable insulator layer  112 , no additional masking layers are necessary to protect the source/drain regions  118  when epitaxially growing the condenser layer  120  on the channel regions  114  of the fins  108 . 
     Turning to  FIGS. 4A-4B , a condensation process is performed to drive or push donor material from the condenser layer  120  into the channel region  114  of the fins  108 . According to a non-limiting embodiment, the condensation process includes exposing the channel region  114  to ions capable of condensing the channel region  114  into a second semiconductor material different from the initial semiconductor layer of the fins (e.g., Si). For example, the exposed channel region  114  is exposed to oxygen (O 2 ) ions, for example, at a temperature of approximately 600 degrees Celsius for a time period of approximately 15 minutes. In this manner, the condenser layer  120  is oxidized and the released donor material  122  is driven into the channel region  114  so as to condense the channel region  114 , i.e., chemically transform the first semiconductor material into the second semiconductor material. 
     According to at least one embodiment, if the condenser layer  120  is formed of SiGe, and the fins  108  are formed of Si, then Ge donor material  122  is released from the condenser layer  120  and driven into the channel region  114  during the condensation process. As a result, the composition of the fins  108  is altered as the donor material  122  is diffused into the first semiconductor material (e.g., Si) of the exposed channel region  114 . In this manner the fin channel regions  114  are condensed, i.e., chemically transformed, into a condensed channel region  124  such as, for example, a SiGe channel region  124 . According to a non-limiting embodiment, the concentration of Ge contained in the condensed channel region  124  is greater than 50% of the Si contained in the condensed channel region. Condensing the channel regions of the fins may also induce a strain in the fins. In the case where the channel region  124  is formed of SiGe, for example, the condensation process may induce a compressive strain in the SiGe. The S/D regions  118  are not condensed and remain comprising their initial semiconductor material (e.g., Si) since they are covered by the flowable insulator layer  112 . In the case where the channel regions  124  are formed from SiGe, for example, maintaining the S/D regions  118  as Si achieves a bandgap offset between Si and SiGe, thereby increasing carrier velocity which increases current and overall device performance. Following the oxidation process, the condenser layer  120  in chemically transformed into an oxidized layer  126  as further illustrated in  FIGS. 4A-4B . If the condenser layer  120  is formed of SiGe, then the resulting oxidized layer  126  is formed, for example, of SiO 2 . 
     Referring now to  FIGS. 5A-5B , the semiconductor device  100  is illustrated following removal of the oxidized layer (previously identified as numeral  126 ) from the surfaces of the condensed channel region  124 . According to a non-limiting embodiment, a reactive ion etching (RIE) process selective to the gate spacer material (e.g., SiN) and the condensed fin material (SiGe) is performed to selectively remove the oxidized layer. The flowable insulator layer  112  is formed with a thickness so as to serve as a buffer when removing the oxidized layer. Accordingly, a portion of the flowable insulator layer  112  is permitted to be etched while still adequately protecting the S/D regions  118 . According to a non-limiting embodiment, the thickness of oxidized layer  126  is limited to around 10 nm, for example. In this manner, S/D channel shorting between the buried insulator layer  104  and the S/D regions  118  may be prevented even if a portion of the buried insulator layer  104  is recessed when etching away the oxidized layers  126  from the fins  108 . 
     Turning now to  FIGS. 6A-6B , the semiconductor device  100  is illustrated after depositing a metal gate structure  128  between the gate spacers  116  and atop the buried insulator layer  104 . The metal gate structure  128  wraps around the sidewalls and the upper surface of the condensed channel region  124  so as to serve as a gate electrode as understood by one of ordinary skill in the art. The metal gate structure  128  can be formed of various metal gate materials including, but not limited to, tungsten (W). 
     Although not illustrated, it should be appreciated that the metal gate structure  128  may include one or more work function metal layers including, but not limited to, a titanium nitride (TiN) liner and a tantalum nitride (TaN) liner, formed on sidewalls of the metal gate structure  128  as understood by one of ordinary skill in the art. As mentioned earlier, a gate dielectric layer (e.g., a high-k gate dielectric layer) may be disposed atop the buried insulator layer  104 . In this case, it should be appreciated that the metal gate structure  128  includes the metal gate material, the gate dielectric layer, and the work function metals. It should also be appreciated that a chemical-mechanical planarization (CMP) process may be performed after depositing the metal gate structure  128 . In this manner, the upper surface of the metal gate structure  128  is formed flush with the upper surface of the gate sidewalls  106  as further illustrated in  FIGS. 6A-6B . 
     Accordingly, at least one embodiment described above provides a finFET device including one or more semiconductor fins having a SiGe condensed channel region. In this manner, hole mobility through the channel region of the fins is improved compared to conventional finFET devices. For example, the hole mobility through the channel region may be approximately 3 times higher compared to conventional semiconductor fins having channel regions formed solely of silicon, e.g., Si&lt;100&gt; or Si&lt;110&gt;. In this manner, a finFET device according to at least one embodiment of the invention provides a finFET device having improved overall device performance compared to conventional finFET devices. 
     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. 
     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 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 inventive teachings 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 operations described therein without departing from the spirit of the invention. For instance, the operations may be performed in a differing order or operations may be added, deleted or modified. All of these variations are considered a part of the claimed invention. 
     While various embodiments have been described, it will be understood that those skilled in the art, both now and in the future, may make various modifications which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.