Patent Publication Number: US-2023140731-A1

Title: Semiconductor device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of U.S. provisional applications serial no. 63/275,938, filed on Nov. 4, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND 
     New semiconductor applications are ever changing our lives, from new smartphones, to healthcare, factory automation and artificial intelligence. Memory working in background plays an important role in enabling these technologies, and has drawn considerable interest along with advances in computing architectures and semiconductor technologies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG.  1 A  and  FIG.  1 B  are schematic sectional and top views of a semiconductor device in accordance with some embodiments of the present disclosure. 
         FIG.  2    is an enlarged sectional view of a portion of a semiconductor device in accordance with some embodiments of the present disclosure. 
         FIG.  3 A  and  FIG.  3 B  are circuit diagrams of a sense amplifier circuit in a semiconductor device according to some embodiments of the present disclosure. 
         FIG.  4 A  to  FIG.  4 E  are cross-sectional views illustrating structures at various stages of manufacturing a transistor at an elevated level over the semiconductor substrate in accordance with some embodiments of the present disclosure. 
         FIG.  5 A  and  FIG.  5 B  are schematic sectional and top views of a semiconductor device in accordance with some other embodiments of the present disclosure. 
         FIG.  6    is a circuit diagram of a memory cell in a semiconductor device according to some embodiments of the present disclosure. 
         FIG.  7    is an enlarged sectional view of a portion of a semiconductor device in accordance with some other embodiments of the present disclosure. 
         FIG.  8 A  is a schematic sectional view of a semiconductor device in accordance with some other embodiments of the present disclosure. 
         FIG.  8 B  is an enlarged sectional view of a portion of the semiconductor device shown in  FIG.  8 A . 
         FIG.  9 A  is a schematic sectional view of a semiconductor device in accordance with some other embodiments of the present disclosure. 
         FIG.  9 B  is an enlarged sectional view of a portion of the semiconductor device shown in  FIG.  9 A . 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components, values, operations, materials, arrangements, or the like, are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Other components, values, operations, materials, arrangements, or the like, are contemplated. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
       FIG.  1 A  and  FIG.  1 B  are schematic sectional and top views of a semiconductor device in accordance with some embodiments of the present disclosure. Referring to  FIG.  1 A , a semiconductor device includes a semiconductor substrate  102 . The semiconductor substrate  102  may be a semiconductor wafer, such as a silicon wafer, or the like. In some embodiments, ground level circuitry  104  are disposed at a ground level LV 1  over the semiconductor substrate  102 . The ground level circuitry  104  may include logic circuits, word line drivers, and the like. The ground level LV 1  described herein may be a front-end-of-line (FEOL) structure of a semiconductor device (semiconductor chip). 
     In some embodiments, a plurality of stacked memory arrays (MA 1 ˜MA 10 ) are disposed at an elevated level over the ground level circuitry  104 . For example, a first memory array MA 1  is disposed at a second level LV 2  over the semiconductor substrate  102  on the ground level circuitry  104 . A second memory array MA 2  is disposed at a third level LV 3  over the semiconductor substrate  102 , above the second level LV 2  and on the ground level circuitry  104 . In a similar way, a plurality of memory arrays including a third memory array MA 3  up till a tenth memory array MA 10  are stacked up in sequence from the fourth level LV 4  till the eleventh level LV 11  over the semiconductor substrate  102 . 
     As illustrated in  FIG.  1 A , each of the memory arrays (MA 1 ˜MA 10 ) includes a plurality of memory cells (MC 1 ˜MC 10 ). For example, the first memory array MA 1  includes a plurality of first memory cells MC 1 , the second memory array MA 2  includes a plurality of second memory cells MC 2 , and the third memory array MA 3  includes a plurality of third memory cells MC 3 , and so forth. In the exemplary embodiment, the memory cells (MC 1 ˜MC 10 ) are for example, dynamic random access memory (DRAM) type memory cells. However, the disclosure is not limited thereto, and other type of memory cells may be applied. 
     In some embodiments, a plurality of sense amplifier units  106  (sense amplifier circuits) is disposed on the semiconductor substrate  102 . For example, each of the sense amplifier units  106  includes an amplifier circuit  106 A and a main circuit  106 B. The amplifying circuit  106 A is disposed aside each of the memory arrays (MA 1 ˜MA 10 ) at the elevated levels (LV 2 ˜LV 11 ) above the ground level circuitry  104 . In some embodiments, the amplifying circuit  106 A may include transistor(s) used for amplifying signals (or voltage) received from the memory arrays (MA 1 ˜MA 10 ) located at the respective levels. Furthermore, the main circuit  106 B is disposed on the semiconductor substrate  102  at the ground level LV 1  aside the ground level circuitry  104 , wherein the main circuit  106 B is electrically coupled to plurality of memory arrays (MA 1 ˜MA 10 ) through the amplifying circuit  106 A. In some embodiments, the main circuit  106 B include transistor(s) used for performing read operation of the signals received from the memory arrays (MA 1 ˜MA 10 ). 
       FIG.  1 B  is a top view of the first memory array MA 1  shown in  FIG.  1 A . As illustrated in  FIG.  1 B , the first memory array MA 1  includes a plurality of first memory cells MC 1  arranged along the first direction X 1  and the second direction X 2 . The second direction X 2  being perpendicular to the first direction X 1 . In some embodiments, those first memory cells MC 1  located in the same row (along the first direction X 1 ) may share the same bit line BLX. For example, the bit line BLX are attached (electrically coupled) to the sense amplifier units  106  (sense amplifier circuits) at the edge of the first memory array MA 1 . In some embodiments, the data (electric charge) stored in a first memory cell MC 1  may affect the voltage on the associated bit line BLX. As an example, when data “ 0 ” is stored in a first memory cell MC 1 , the voltage on the associated bit line BLX may be pulled down from a pre-charge voltage during a read operation. On the other hand, when data “ 1 ” is stored in a first memory cell MC 1 , the voltage on the associated bit line BLX may stay at the pre-charge voltage. In some embodiments, the amplifier circuit  106 A amplifies the voltage difference corresponding to data “ 0 ” and data “ 1 ”, whereby the main circuit  106 B performs readout based on the voltage output by the amplifier circuit  106 A. 
     Although  FIG.  1 B  only illustrate a top view of the first memory array MA 1  and its connection with the sense amplifier units  106 , it is noted that the other memory arrays (MA 2 ˜MA 10 ) located at different levels (LV 3 ˜LV 11 ) may have similar configurations and connections. For example, sense amplifier units  106  (amplifying circuit  106 A) may be electrically coupled to the memory arrays (MA 2 ˜MA 10 ) through the respective bit lines BLX for performing amplification and read out functions. 
       FIG.  2    is an enlarged sectional view of a portion of a semiconductor device in accordance with some embodiments of the present disclosure. For example,  FIG.  2    is an enlarged sectional view of a portion of  FIG.  1 A  showing the ground level circuitry  104  at the ground level LV 1 , the first memory cell MC 1  at the second level LV 2 , and the sense amplifier unit  106  extending across the ground level LV 1  and the second level LV 2 . In  FIG.  2   , the detailed components in the first memory cell MC 1  is omitted for ease of illustration, and only one transistor TX of the first memory cell MC 1  is shown. 
     As illustrated in  FIG.  2   , a logic circuit  104 A (part of the ground level circuitry  104 ) is disposed at the ground level LV 1  over the semiconductor substrate  102 , while the first memory cells MC 1  is disposed at the second level LV 2  over the semiconductor substrate  102 . In some embodiments, the logic circuit  104 A includes a plurality of logic transistors  202 . For example, the logic transistors  202  includes a logic active structure  202 A, source/drain terminals  202 B, a gate structure  202 C, a gate dielectric layer  202 D and sidewall spacers  202 E. In some embodiments, the gate structure  202 C is disposed at the ground level LV 1  and cover and intersect with the logic active structures  202 A. The gate dielectric layer  202 D is lying between the gate structure  202 C and the logic active structure  202 A. In certain embodiments, the source/drain terminals  202 B (source/drain regions) are located at opposite sides of the gate structure  202 C and are embedded in the logic active structures  202 A. Furthermore, a height of the source/drain terminals  202 B (source/drain regions) is smaller than a height of the logic active structures  202 A. 
     In some embodiments, source/drain contacts  206 , conductive vias  214  and conductive patterns  218  are formed over the source/drain terminals  202 B for out routing the transistors in the logic circuit  104 A. In some embodiments, the gate structure  202 C, gate dielectric layer  202 D, sidewall spacers  202 E and the source/drain contacts  206  are laterally surrounded by a dielectric layer  210 . Similarly, the conductive vias  214  and the conductive patterns  218  are laterally surrounded by dielectric layers  212 ,  216 . In certain embodiments, isolation structures  204  may be formed at the first level LV 1  on the semiconductor substrate  102  separating the logic active structures  202 A 
     As further illustrated in  FIG.  2   , an interlayer dielectric  220  is disposed on the dielectric layers  212 ,  216  covering the logic circuit  104 A. Furthermore, the first memory cells MC 1  are disposed on the interlayer dielectric  220  over the logic circuit  104 A at the second level LV 2  on the semiconductor substrate  102 . In some embodiments, the first memory cells MC 1  are electrically coupled to the logic circuit  104 A through a plurality of conductive vias  222 . For example, the conductive vias  222  are laterally surrounded by the interlayer dielectric  220 , and electrically connects the first memory cells MC 1  to the logic transistors  202 . 
     In some embodiments, each of the first memory cells MC 1  disposed on the interlayer dielectric  220  includes at least one transistor TX, and may include a storage capacitor (not shown). In some embodiments, the transistor TX includes an active structure TXA, source/drain terminals TXB, a gate structure TXC, a gate dielectric layer TXD and sidewall spacers TXE. In some embodiments, the active structure TXA disposed at the second level LV 2  is a semiconductor pattern (e.g., silicon pattern) laterally surrounded by an insulating layer (not shown). The gate structure TXC covers and intersects with the active structures TXA. The gate dielectric layer TXD is lying between the gate structure TXC and the active structure TXA. In certain embodiments, the source/drain terminals TXB (source/drain regions) are located at opposite sides of the gate structure TXC and are embedded in the active structures TXA. In some embodiments, a height of the active structures TXA located at the second level LV 2  is equal to or smaller than a height of the logic active structures  202 A located at the ground level LV 1 . In certain embodiments, a height of the source/drain terminals TXB is substantially equal to the height of the active structures TXA. 
     Referring to  FIG.  2   , the semiconductor device may further include sense amplifier units  106 , whereby each of the sense amplifier units  106  include an amplifying circuit  106 A disposed on the second level LV 2  and a main circuit  106 B disposed on the ground level LV 1 . In some embodiments, the main circuit  106 B is disposed on the semiconductor substrate  102  at the ground level LV 1  aside the ground level circuitry  104  or aside the logic circuit  104 A. For example, the main circuit  106 B includes a plurality of sense amplifier transistors  302  located aside the logic circuit  104 A. 
     In some embodiments, each of the sense amplifier transistors  302  includes an active structure  302 A, source/drain terminals  302 B, a gate line  302 C, a gate dielectric layer  302 D and sidewall spacers  302 E. In some embodiments, the gate line  302 C is disposed at the ground level LV 1 , and cover and intersect with the active structures  302 A. The gate dielectric layer  302 D is lying between the gate line  302 C and the active structure  302 A. In certain embodiments, the source/drain terminals  302 B (source/drain regions) are located at opposite sides of the gate line  302 C and are embedded in the active structures  302 A. In some embodiments, a height of the active structures  302 A of the sense amplifier transistors  302  is substantially equal to a height of the logic active structures  202 A of the logic transistors  202  located at the ground level LV 1 . In certain embodiments, a height of the source/drain terminals  302 B is smaller than a height of the active structures  302 A. Furthermore, source/drain contacts  306 , conductive vias  214  and conductive patterns  218  are formed over the source/drain terminals  302 B for out routing the sense amplifier transistors  302 . In some embodiments, the gate line  302 C, gate dielectric layer  302 D, sidewall spacers  302 E and the source/drain contacts  306  are laterally surrounded by the dielectric layer  210 . 
     As further illustrated in  FIG.  2   , the amplifying circuit  106 A is disposed on the interlayer dielectric  220  over the main circuit  106 B at the second level LV 2  on the semiconductor substrate  102 . In some embodiments, the amplifying circuit  106 A is electrically coupled to the main circuit  106 B through the conductive vias  222 . Furthermore, the amplifying circuit  106 A is electrically coupled to the first memory cells MC 1  through conductive vias  244  and bit lines BLX. In other words, the main circuit  106 B may be electrically coupled to the first memory cells MC 1  through the amplifying circuit  106 A. 
     In the exemplary embodiment, the amplifying circuit  106 A includes one sense amplifier transistor  320  disposed on the interlayer dielectric  220 . For example, the sense amplifier transistor  320  includes an active structure  320 A, source/drain terminals  320 B, a gate line  320 C, a gate dielectric layer  320 D and sidewall spacers  320 E. In some embodiments, the gate line  320 C is disposed at the second level LV 2 , and cover and intersect with the active structures  320 A. The gate dielectric layer  320 D is lying between the gate line  320 C and the active structure  320 A. In certain embodiments, the source/drain terminals  320 B (source/drain regions) are located at opposite sides of the gate line  320 C and are embedded in the active structures  320 A. In some embodiments, a height of the active structures  320 A of the sense amplifier transistor  320  is substantially equal to a height of the active structure TXA of the transistors TX of the first memory cells MC 1 . Furthermore, the height of the active structures  320 A of the sense amplifier transistor  320  is equal to or smaller than the height of the active structures  302 A of the sense amplifier transistors  302 , and equal to or smaller than the height of the logic active structure  202 A of the logic transistors  202 . In certain embodiments, a height of the source/drain terminals  320 B is substantially equal to the height of the active structures  320 A. Furthermore, source/drain contacts  322  are formed over the source/drain terminals  320 B for out routing the sense amplifier transistors  320 . For example, the bit lines BLX are electrically coupled to the source/drain terminals  320 B through the conductive vias  244  and the source/drain contacts  322 . 
     In some embodiments, the gate line  320 C, gate dielectric layer  320 D, sidewall spacers  320 E and the source/drain contacts  322  are laterally surrounded by the dielectric layer  240 . Furthermore, the conductive via  244  and the bit lines BLX are laterally surrounded by the dielectric layers  242 ,  246 , while the first memory cell MC 1  are further surrounded by the dielectric layer  248 . In some embodiments, an interlayer dielectric  250  is disposed on the semiconductor substrate  102  and covering the first memory cells MC 1 . For example, the interlayer dielectric  250  separates the first memory cells MC 1  from the second memory cells MC 2  (shown in  FIG.  1 A ) located at the third level LV 3 . 
     In the above embodiments, when the transistors ( 202 ,  302 ) at the ground level LV 1  are planar type field effect transistors (FETs), then their respective active structures may be a doped region in the semiconductor substrate  102 . In some other embodiments where the transistors ( 202 ,  302 ) at the ground level LV 1  are fin type FETs or gate-all-around (GAA) FETs, then their respective active structures may be a semiconductor fin structure or a stack of semiconductor nanosheets/rods formed at a surface of the semiconductor substrate  102 . On the other hand, the transistors (TX,  320 ) at the second level LV 2  may be planar type field effect transistors (FETs), and their respective active structures may be a semiconductor pattern. In some other embodiments where the transistors (TX,  320 ) at the second level LV 2  are fin type FETs or gate-all-around (GAA) FETs, then their respective active structures may be a semiconductor fin structure or a stack of semiconductor nanosheets/rods formed at a surface of the interlayer dielectric  220 . 
     Although the semiconductor device shown in  FIG.  2    only illustrates the ground level LV 1  and the second level LV 2  components, it is noted that a plurality of stacked memory arrays (MA 2 ˜MA 10 ) or stacked memory cells (MC 2 ˜MC 10 ) may be further located above the first memory cells MC 1  at the second level LV 2 . For example, in one embodiment, a plurality of second memory cells MC 2  is further disposed on the interlayer dielectric  250  above the plurality of first memory cells MC 1  (shown in  FIG.  1 A ). Furthermore, a sense amplifier transistor  320  (not shown) may be disposed above the interlayer dielectric  250  aside the second memory cells MC 2  at the third level LV 3  on the semiconductor substrate  102 . For example, the sense amplifier transistor  320  at the third level LV 3  may be part of the amplifying circuit  106 A, and is electrically coupled to the main circuit  106 B located at the ground level LV 1 . 
       FIG.  3 A  is a circuit diagram of an amplifying circuit  106 A in a sense amplifier unit  106 , according to some embodiments of the present disclosure.  FIG.  3 B  is a circuit diagram of a main circuit  106 B coupled to the amplifying circuit  106 A, according to some embodiments of the present disclosure. 
     Referring to  FIG.  3 A , in some embodiments, the amplifying circuit  106 A is realized by a single sense amplifier transistor  320 , which may be an N-type field effect transistor. One of the source/drain terminals of the sense amplifier transistor  320  is coupled to a bit line BLX, and functioned as an input of the amplifying circuit  106 A. The other source/drain terminal of the sense amplifier transistor  320  may be functioned as an output terminal SEN of the amplifying circuit  106 A, and is coupled to the main circuit  106 B in the same sense amplifier unit  106 . During a read operation, a gate voltage V BLS  is provided to a gate terminal of the sense amplifier transistor  320 , and may be controlled to ensure that the sense amplifier transistor  320  is operated in a subthreshold region. Accordingly, small difference between bit line voltages corresponding to data “ 0 ” and data “ 1 ” can result in significant changes of the on-current I BLS  of the sense amplifier transistor  320 . Therefore, the output terminal SEN can be charged/discharged to differentiable voltage levels. 
     Referring to  FIG.  3 A  and  FIG.  3 B , the output terminal SEN of the amplifying circuit  106 A may be coupled to an input terminal of the main circuit  106 B. The voltage level at the terminal SEN may influence switching of a sense amplifier transistor  302  (referred as a transistor  302 - 1  hereinafter) with a gate terminal coupled to the terminal SEN. A source/drain terminal of the transistor  302 - 1  may be coupled to a voltage V DDL  through another sense amplifier transistor  302  (referred as a transistor  302 - 2  hereinafter), while the other source/drain terminal of the transistor  302 - 1  may be coupled to a latch circuit LC. During a read operation, the transistor  302 - 2  is turned on, and switching of the transistor  302 - 1  is dependent on the voltage level of the terminal SEN. When the transistor  302 - 1  is turned on, the voltage V DDL  can be provided to the latch circuit LC through the transistors  302 - 1 ,  302 - 2 , and one of the complementary nodes DL, DLD of the latch circuit LC as an output terminal of the main circuit  106 B (e.g., the node DL) may be charged. On the other hand, when the transistor  302 - 1  is kept in an off state, such node of the latch circuit LC (e.g., the node DL) may not be charged by the voltage V DDL . Therefore, a voltage level at the output terminal of the main circuit  106 B (e.g., the node DL) is controlled by the transistor  302 - 1 , and switching of the transistor  302 - 1  is dependent on the voltage level at the terminal SEN, which reflects the data stored in the associated memory cell. In other words, the data stored in a memory cell can be initially amplified by the amplifying circuit  106 A, and further amplified and output by the main circuit  106 B. 
       FIG.  4 A  to  FIG.  4 E  are cross-sectional views illustrating structures at various stages of manufacturing a transistor at an elevated level over the semiconductor substrate in accordance with some embodiments of the present disclosure. For example, a method of forming the sense amplifier transistor  320  located at the second level LV 2  over the semiconductor substrate  102  will be described. 
     Referring to  FIG.  4 A , a semiconductor pattern SP 1  may be formed on the interlayer dielectric  220 . In some embodiments, a method for forming the semiconductor pattern SP 1  includes globally depositing a semiconductor layer, and patterning the semiconductor layer to form the semiconductor pattern SP 1  by a lithography process and an etching process. The semiconductor pattern SP 1  is formed of a semiconductor material. For instance, the semiconductor material is amorphous silicon. 
     Referring to  FIG.  4 B , another interlayer dielectric  224  may be formed to laterally surround the semiconductor pattern SP 1 . In some embodiments, a method for forming the interlayer dielectric  224  includes forming a dielectric layer globally covering the semiconductor pattern SP 1  and the underlying interlayer dielectric  220 , and performing a planarization process to remove portions of the dielectric layer above the semiconductor pattern SP 1 . Remained portions of the dielectric layer form the interlayer dielectric  224 . As examples, the planarization process may include a polishing process, an etching process or a combination thereof. 
     Referring to  FIG.  4 C , an annealing process is performed on the semiconductor pattern SP 1 , such that the semiconductor pattern SP 1  turns into the active structures  320 A for the sense amplifier transistor  320  described above. In those embodiments where the semiconductor pattern SP 1  is formed of amorphous silicon, the amorphous silicon may be crystallized to form polycrystalline silicon or crystalline silicon during the annealing process. Accordingly, in these embodiments, the formed active structures  320 A include polycrystalline silicon or crystalline silicon. In some embodiments, the annealing process is a laser annealing process or thermal annealing process, and a process temperature of the annealing process may be about 400° C. As a result of such annealing process, a field effect mobility and/or other characteristics of the transistors can be significantly improved. 
     Referring to  FIG.  4 D , a gate line  320 C, a gate dielectric layer  320 D and sidewall spacers  320 E are respectively formed. For example, similar to that described in  FIG.  3   , the gate line  320 C is disposed over the active structure  320 A; the gate dielectric layer  320 D is lying between the gate line  320 C and the active structure  320 A; and the sidewalls spacers  320 E are covering the gate line  320 C and the gate dielectric layer  320 E. 
     In some embodiments, the gate line  320 C is formed of polycrystalline silicon. In these embodiments, a method for forming the gate structure may include sequentially forming a dielectric layer and a polycrystalline silicon layer on the active structure  320 A, and patterning the dielectric layer and the polycrystalline silicon layer to form the gate dielectric layer  320 D the gate line  320 C respectively. Subsequently, the sidewall spacer  320 E may be formed on sidewalls of the gate line  320 C and the gate dielectric layer  320 D by a deposition process and an etching back process. In alternative embodiments where the gate line  320 C is formed of a metallic material, a replacement gate process may be used for forming the gate structure. Further, although not shown, a pair of lightly doped regions may be optionally formed in the active structure  320 A at opposite sides of the gate line  320 C before formation of the sidewall spacers  320 E. 
     Referring to  FIG.  4 E , source/drain terminals  320 B are formed in the active structures  320 A at opposite sides of the gate line  320 C. In those embodiments where the source/drain terminals  320 B are doped regions in the active structure  320 A, a method for forming the source/drain terminals  320 B may include an ion implantation process and an annealing process. In alternative embodiments, a method for forming the source/drain terminals  320 B includes forming openings in the active structure  320 A, and filling the source/drain terminals  320 B into these openings by, for example, an epitaxial process. 
     Up to here, the sense amplifier transistor  320  located at the second level LV 2  of the semiconductor substrate  102  are formed. As compared with transistors ( 302 ,  202 ) formed using active structures on the semiconductor substrate  102  (or active structures being part of the semiconductor wafer), the transistors in the second level LV 2  uses the active structures formed from a deposited semiconductor layer. Although, the transistors located at the second level LV 2  is used as an example for description, it is noted that the transistors located at the elevated levels (e.g. third level LX 3 , fourth level LX 3  etc.) in the back-end-of-line (BEOL) process may be formed in a similar manner. In other words, the process described in  FIG.  4 A  to  FIG.  4 E  is a BEOL compatible process. 
       FIG.  5 A  and  FIG.  5 B  are schematic sectional and top views of a semiconductor device in accordance with some other embodiments of the present disclosure. The semiconductor device illustrated in  FIG.  5 A  and  FIG.  5 B  is similar to the semiconductor device illustrated in  FIG.  1 A  and  FIG.  1 B . Therefore, the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. 
     In the previous embodiment, the amplifying circuit  106 A is located at elevated levels (e.g. second level LV 2  or above), while the main circuit  106 B is located at the ground level LV 1 . However, the disclosure is not limited thereto. As illustrated in  FIG.  5 A  and  FIG.  5 B , in some embodiments, the entire sense amplifier units  106  are located at the elevated levels. In addition, the amplification and readout functions are integrated as one circuit in each of the sense amplifier units  106 . As an example, each memory array (MA 1 ˜MA 10 ) is electrically coupled to the sense amplifier units  106  located at the same level. As shown in  FIG.  5 B , illustrating the memory array MA 1  at the second level LV 2 , the first memory cells MC 1  located in the same row may be electrically coupled to the sense amplifier unit  106  at the same level using two complementary bit lines BL 1 , BL 2 . 
     In the exemplary embodiment, the bit lines BL 1 , BL 2  are attached (electrically coupled) to the sense amplifier units  106  (sense amplifier circuits) at the edge of the first memory array MA 1 . In some embodiments, the sense amplifier unit  106  is configured to compare voltages on the associated bit lines BL 1 , BL 2 , and output a signal indicating the data stored in a selected first memory cell MC 1  during a read operation. In such embodiment, the memory cells (MC 1 ˜MC 10 ) in the memory arrays (MA 1 ˜MA 10 ) are for example, static random access memory (SRAM) type memory cells. 
       FIG.  6    is a circuit diagram of a memory cell in a semiconductor device according to some embodiments of the present disclosure. The circuit diagram may correspond to each of the memory cells (MC 1 ˜MC 10 ) located in the memory arrays (MA 1 ˜MA 10 ) shown in  FIG.  5 A  and  FIG.  5 B . In some embodiments, the memory cells (MC 1 ˜MC 10 ) are SRAM memory cells including the transistors TX (including T 1 ˜T 6 ). 
     As illustrated in  FIG.  6   , each of the memory cells (MC 1 ˜MC 10 ) includes a latch circuit LX 1 . The latch circuit LX 1  is configured to retain stored data without being periodically refreshed. In some embodiments, the latch circuit LX 1  includes two inverters. A first inverter may include a pull up transistor T 1  and a pull down transistor T 2 . The pull up transistor T 1  may be a P-type field effect transistor (PFET), while the pull down transistor T 2  may be an N-type field effect transistor (NFET). The pull up transistor T 1  and the pull down transistor T 2  share a common source/drain terminal, and such common source/drain terminal may be referred as a storage node SN 1  of the memory cell (MC 1 ˜MC 10 ). In addition, the other source/drain terminal of the pull up transistor T 1  is coupled to a working voltage V DD . On the other hand, the other source/drain terminal of the pull down transistor T 2  is coupled to a reference voltage V SS , such as a ground voltage. Furthermore, gate terminals of the pull up transistor T 1  and the pull down transistor T 2  are connected with each other. A node N 1  coupled to the gate terminals of the pull up transistor T 1  and the pull down transistor T 2  may be an input terminal of the first inverter, and the storage node SN 1  may be an output terminal of the first inverter. 
     Similarly, a second inverter in the latch circuit LX 1  may include a pull up transistor T 3  and a pull down transistor T 4 . The pull up transistor T 3  may be a PFET, while the pull down transistor T 4  may be an NFET. The pull up transistor T 3  and the pull down transistor T 4  share a common source/drain terminal, which may be referred as a storage node SN 2  of the memory cell (MC 1 ˜MC 10 ). The other source/drain terminal of the pull up transistor T 3  is coupled to the working voltage V DD , while the other source/drain terminal of the pull down transistor T 4  is coupled to the reference voltage V SS  In addition, gate terminals of the pull up transistor T 3  and the pull down transistor T 4  are connected with each other. A node N 2  coupled to the gate terminals of the pull up transistor T 3  and the pull down transistor T 4  may be an input terminal of the second inverter, while the storage node SN 2  may be an output terminal of the second inverter. 
     The node N 1  as the input terminal of the first inverter is coupled to the storage node SN 2  as the output terminal of the second inverter, and the node N 2  as the input terminal of the second inverter is coupled to the storage node SN 1  as the output terminal of the first inverter. In other words, the first and second inverters of the latch circuit LX 1  are cross-coupled. As a result, the storage nodes SN 1 , SN 2  are ensured to store complementary logic data. For instance, when a logic data “ 0 ” is stored at the storage node SN 1 , the P-type pull up transistor T 3  may be turned on as its gate terminal is coupled to the storage node SN 1 , and the storage node SN 2  as a source/drain terminal of the pull up transistor T 3  is pulled up by the working voltage V DD  coupled to the other source/drain terminal of the pull up transistor T 3 . Therefore, a logic data “ 1 ” complementary to the logic data “ 0 ” is stored at the storage node SN 2 . 
     On the other hand, the N-type pull down transistor T 4  is kept in an off state as its gate terminal is also coupled to the storage node SN 1  holding at the logic data “ 0 ”, thus the storage node SN 2  as a source/drain terminal of the pull down transistor T 4  would not be pulled down by the reference voltage V SS  coupled to the other source/drain terminal of the pull down transistor T 4 . In addition, the N-type pull down transistor T 2  is turned on as its gate terminal is coupled to the storage node SN 2  holding at the logic data “ 1 ”, and the storage node SN 1  as a source/drain terminal of the pull down transistor T 2  is kept discharged by the reference voltage V ss  coupled to the other source/drain terminal of the pull down transistor T 2 . In addition, the P-type pull up transistor T 1  is kept in an off state as its gate terminal is also coupled to the storage node SN 2  holding at the logic data “ 1 ”, thus the storage node SN 1  as a source/drain terminal of the pull up transistor T 1  would not be pulled up by the working voltage V DD  coupled to the other source/drain terminal of the pull up transistor T 1 . Therefore, the logic data “ 0 ” can be retained at the storage node SN 1 . 
     Moreover, the memory cell (MC 1 ˜MC 10 ) may further include an access transistor T 5 . A gate terminal of the access transistor T 5  is connected to a word line WL. In addition, a source/drain terminal of the access transistor T 5  is coupled to the storage node SN 1 , while the other source/drain terminal of the access transistor T 5  is connected to a bit line BL 1 . When the access transistor T 5  is turned on, the bit line BL 1  can charge/discharge the storage node SN 1 , or vice versa. Accordingly, logic data can be programmed to the storage node SN 1 , or read out from the storage node SN 1 . On the other hand, when the access transistor T 5  is in an off state, the storage node SN 1  is decoupled from the bit line BL 1 , and logic data cannot be written to or read out from the storage node SN 1 . In other words, the access transistor T 5  may control access of the storage node SN 1 . 
     Similarly, access of the storage node SN 2  is controlled by an access transistor T 6 . The word line WL for controlling switching of the access transistor T 5  may also connect to a gate terminal of the access transistor T 6 . In this way, the access transistors T 5 , T 6  may be switched simultaneously. In addition, a source/drain terminal of the access transistor T 6  is coupled to the storage node SN 2 , while the other source/drain terminal of the access transistor T 5  is connected to a bit line BL 2 . When the access transistor T 6  is turned on, the bit line BL 2  can charge/discharge the storage node SN 2 , or vice versa. Accordingly, logic data can be programmed to the storage node SN 2 , or read out from the storage node SN 2 . On the other hand, when the access transistor T 6  is in an off state, the storage node SN 2  is decoupled from the bit line BL 2 , and logic data cannot be written to or read out from the storage node SN 2 . During a write operation, the bit lines BL 1 , BL 2  may receive complementary logic data, in order to overwrite the logic data previously stored at the storage nodes SN 1 , SN 2 . In addition, during a read operation using the sense amplifier unit  106 , both of the bit lines BL 1 , BL 2  are pre-charged, and one of them is slightly pulled down by the corresponding storage node. By comparing voltage difference of the bit lines BL 1 , BL 2 , the logic data stored at the storage nodes SN 1 , SN 2  can be read out using the sense amplifier unit  106 . 
       FIG.  7    is an enlarged sectional view of a portion of a semiconductor device in accordance with some other embodiments of the present disclosure. For example,  FIG.  7    is an enlarged sectional view of a portion of  FIG.  5 A  showing the ground level circuitry  104  at the ground level LV 1 , the first memory cell MC 1  and the sense amplifier unit  106  at the second level LV 2 . The semiconductor device illustrated in  FIG.  7    is similar to the semiconductor device illustrated in  FIG.  2   . Therefore, the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. 
     As illustrated in the embodiment of  FIG.  7   , the logic circuit  104 A (part of the ground level circuitry  104 ) is disposed at the ground level LV 1  over the semiconductor substrate  102 , while the first memory cells MC 1  and the sense amplifier unit  106  are disposed at the second level LV 2  over the semiconductor substrate  102 . For example, the first memory cells MC 1  and the sense amplifier unit  106  are located at the second level LV 2  and overlapped with the transistors  202  of the logic circuit  104 A. In some embodiments, the sense amplifier unit  106  includes sense amplifier transistors  303 ,  321  for performing amplification and read out. The sense amplifier transistors  303 ,  321  are structurally similar to the sense amplifier transistors  302 ,  320  described in  FIG.  2   , thus its details will not be repeated herein. For example, the sense amplifier transistors  303 ,  321  respectively includes active structures  303 A,  321 A, source/drain terminals  303 B,  321 B, gate lines  303 C,  321 C, gate dielectric layers  303 D,  321 D and sidewall spacers  303 E,  321 E. 
     In the exemplary embodiment, the sense amplifier transistors  303 ,  321  are located at the second level LV 2 , wherein heights of the active structures  303 A,  321 A of the sense amplifier transistors  303 ,  321  are equal to or smaller than a height of the logic active structures  202 A located at the ground level LV 1 . Furthermore, the heights of the active structures  303 A,  321 A of the sense amplifier transistors  303 ,  321  are substantially equal to the height of the active structures TXA of the first memory cells MC 1  located at the second level LV 2 . In certain embodiments, the first memory cells MC 1  further include bit lines BL 1 , BL 2  (only BL 1  is shown) that are electrically coupled to source/drain regions  303 B,  321 B of the sense amplifier transistors  303 ,  321  through the conductive vias  244 . 
       FIG.  8 A  is a schematic sectional view of a semiconductor device in accordance with some other embodiments of the present disclosure. The semiconductor device illustrated in  FIG.  8 A  is similar to the semiconductor device illustrated in  FIG.  1 A  and  FIG.  1 B . Therefore, the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. 
     As illustrated in  FIG.  8 A , in some embodiments, a plurality of sense amplifier units  106  is disposed at the first level LV 1  and the second level LV 2  on the semiconductor substrate  102 . For example, the main circuit  106 B is disposed at the first level LV 1  on the semiconductor substrate  102  aside the ground level circuitry  104  (not shown). Furthermore, the amplifier circuit  106 A is disposed above the main circuit  106 B, and located at the second level LV 2  on the semiconductor substrate  102 . For example, the main circuit  106 B is electrically coupled to the stacked memory arrays (MA 1 ˜MA 10 ) through the amplifier circuit  106 A. The memory cells (MC 1 ˜MC 10 ) are for example, flash type memory cells. 
     In the exemplary embodiment, the stacked memory arrays (MA 1 ˜MA 10 ) are disposed at an elevated level over the ground level circuitry  104  (not shown). For example, a first memory array MA 1  is disposed at a third level LV 3  over the semiconductor substrate  102  over the ground level circuitry  104  and on the sense amplifier units  106 . A second memory array MA 2  is disposed at a fourth level LV 4  over the semiconductor substrate  102 , above the third level LV 3  and over the ground level circuitry  104 . In a similar way, a plurality of memory arrays including a third memory array MA 3  up till a tenth memory array MA 10  are stacked up in sequence from the fifth level LV 5  till the twelfth level LV 12  over the semiconductor substrate  102 . 
     In some embodiments, the semiconductor device further includes a plurality of through vias  402  electrically coupling bit lines BLX (not shown) of the plurality of stacked memory arrays (MA 1 ˜MA 10 ) to the amplifying circuit  106 A of each sense amplifier units  106 . For example, the through vias  402  extends from the twelfth level LV 12  to the second level LV 2  and are electrically connecting the bit lines BLX of the memory cells (MC 1 ˜MC 10 ) located in the same vertical column to the amplifying circuit  106 A located at the second level LV 2 . 
       FIG.  8 B  is an enlarged sectional view of a portion of the semiconductor device shown in  FIG.  8 A . As illustrated in  FIG.  8 B , the main circuits  106 B are disposed at the first level LV 1  on the semiconductor substrate  102  aside the ground level circuitry  104  (not shown). For example, each of the main circuits  106 B includes a plurality of sense amplifier transistors  302  for performing readout operation. Furthermore, the amplifier circuits  106 A are disposed above the main circuit  106 B, and located at the second level LV 2  on the semiconductor substrate  102 . For example, each of the amplifier circuits  106 A includes a sense amplifier transistor  320  that is electrically coupled to the sense amplifier transistors  302 . In certain embodiments, the source/drain terminals  320 B of the sense amplifier transistor  320  at the second level LV 2  is electrically coupled to the source/drain terminals  302 B of the sense amplifier transistor  302  at the first level LV 1  through the conductive vias  214 ,  222 , conductive patterns  218  and source/drain contacts  306 . 
     As further illustrated in  FIG.  8 B , the first memory cells MC 1  are located at the third level LV 3  above the amplifier circuits  106 A, while the second memory cells MC 2  are located at the fourth level LV 4  above the first memory cells MC 1 . The first memory cells MC 1  and the second memory cells MC 2  may be surrounded by interlayer dielectrics ILDX. In some embodiments, an interlayer dielectric (not shown) is located in between the first memory cells MC 1  and the second memory cells MC 2 . In some embodiments, the first memory cells MC 1  and the second memory cells MC 2  are overlapped with the sense amplifier units  106  (sense amplifier circuits), and are overlapped with the ground level circuitry  104  (such as the logic circuit  104 A). In some embodiments, the through vias  402  extends through the first memory cells MC 1  and the second memory cells MC 2 , and electrically connect the bit lines BLX of the memory cells (MC 1 , MC 2 ) to the sense amplifier transistor  320 . 
       FIG.  9 A  is a schematic sectional view of a semiconductor device in accordance with some other embodiments of the present disclosure. The semiconductor device illustrated in  FIG.  9 A  is similar to the semiconductor device illustrated in  FIG.  8 A . Therefore, the same reference numerals are used to refer to the same or liked parts, and its detailed description will be omitted herein. 
     As illustrated in  FIG.  9 A , in some embodiments, a plurality of sense amplifier units  106  is disposed at the second level LV 2  on the semiconductor substrate  102 , in between the stacked memory arrays (MA 1 ˜MA 10 ) and the ground level circuitry  104 . For example, the ground level circuitry  104  is disposed at the ground level LV 1  on the semiconductor substrate  102 , while all the sense amplifier units  106  are disposed on the second level LV 2  above the ground level circuitry  104 . In the exemplary embodiment, the memory cells (MC 1 ˜MC 10 ) are for example, SRAM type memory cells. 
     Similar to the embodiment of  FIG.  8 A , the semiconductor device shown in  FIG.  9 A  further includes a plurality of through vias  402  electrically coupling bit lines BL 1 , BL 2  (not shown) of the plurality of stacked memory arrays (MA 1 ˜MA 10 ) to each sense amplifier units  106  located at the second level LV 2 . For example, the through vias  402  extends from the twelfth level LV 12  to the second level LV 2  and are electrically connecting the bit lines BL 1 , BL 2  of the memory cells (MC 1 ˜MC 10 ) located in the same vertical column to the sense amplifier units  106  located at the second level LV 2 . Further, as similar to the sense amplifier units  106  as described with reference to  FIG.  5 A  and  FIG.  5 B , amplification and readout functions are integrated in each of the sense amplifier units  106 . 
       FIG.  9 B  is an enlarged sectional view of a portion of the semiconductor device shown in  FIG.  9 A . As illustrated in  FIG.  9 B , the ground level circuitry  104  including logic circuits  104 A are disposed at the first level LV 1  on the semiconductor substrate  102 . For example, the logic circuits  104 A includes a plurality of logic transistors  202  disposed on the semiconductor substrate. In some embodiments, the sense amplifier units  106  includes a plurality of sense amplifier transistors  303 ,  321  (similar to that described in  FIG.  7   ) located at the second level LV 2  on the semiconductor substrate  102 . For example, the sense amplifier transistors  303 ,  321  may be overlapped with the logic circuits  104 A and electrically coupled to the logic transistors  202 . 
     As further illustrated in  FIG.  9 B , the first memory cells MC 1  are located at the third level LV 3  above the sense amplifier units  106 , while the second memory cells MC 2  are located at the fourth level LV 4  above the first memory cells MC 1 . For example, the first memory cells MC 1  and the second memory cells MC 2  are overlapped with the sense amplifier units  106  (sense amplifier circuits), and are overlapped with the ground level circuitry  104  (such as the logic circuit  104 A). In some embodiments, the through vias  402  extends through the first memory cells MC 1  and the second memory cells MC 2 , and electrically connect the bit lines BL 1 , BL 2  of the memory cells (MC 1 , MC 2 ) to the sense amplifier transistor  321 . Alternatively, the through vias  402  extends through the first memory cells MC 1  and the second memory cells MC 2 , and electrically connect the bit lines BL 1 , BL 2  of the memory cells (MC 1 , MC 2 ) to the sense amplifier transistor  303 . 
     In the above embodiments, the semiconductor device includes a plurality of sense amplifier units disposed on the semiconductor substrate and electrically coupled to the plurality of stacked memory arrays. At least a portion of each of the sense amplifier units is disposed at the elevated level over the ground level circuitry. As such, by arranging the circuits of the sense amplifier units along with the memory cells at different horizontal levels with the ground level circuitry, connection between the memory cells and the sense amplifier units can be significantly shortened. Therefore, latency of signal traveling between the memory cells and the sense amplifier units can be effectively reduced, and operation speed of the memory cells can be improved. Furthermore, the sense amplifier unit and the memory cells occupy minimal area in the front-end-of-line (FEOL) structure, thus the chip area and costs of the semiconductor device can be reduced to a minimum. As such, a semiconductor device having high speed performance with area shrinkage may be achieved. 
     In accordance with some embodiments of the present disclosure, a semiconductor device includes a semiconductor substrate, ground level circuitry, a plurality of stacked memory arrays and a plurality of sense amplifier units. The ground level circuitry is disposed on the semiconductor substrate. The stacked memory arrays are disposed at an elevated level over the ground level circuitry. The sense amplifier units are disposed on the semiconductor substrate and electrically coupled to the stacked memory arrays, wherein at least a portion of each of the sense amplifier units is disposed at the elevated level over the ground level circuitry. 
     In accordance with some other embodiments of the present disclosure, a semiconductor device includes a logic circuit, a plurality of first memory cells and a sense amplifier transistor. The logic circuit includes logic active structures and gate structures. The logic active structures are disposed at a ground level on a semiconductor substrate. The gate structures are disposed at the ground level, wherein the gate structures cover and intersect with the logic active structures. The first memory cells are disposed on the logic circuit at a second level on the semiconductor substrate. The sense amplifier transistors are disposed over the logic circuit at the second level on the semiconductor substrate and electrically coupled to the plurality of first memory cells. The sense amplifier transistor includes a first active structure and a first gate line. The first active structure is disposed at the second level on the semiconductor substrate. The first gate line is disposed at the second level on the semiconductor substrate, wherein the first gate line covers and intersects with the first active structure. 
     In accordance with yet another embodiment of the present disclosure, a semiconductor device includes a plurality of first memory cells, an interlayer dielectric, a plurality of second memory cells, a first sense amplifier transistor and a second sense amplifier transistor. The first memory cells are disposed on a semiconductor substrate. The interlayer dielectric is disposed on the semiconductor substrate covering the first memory cells. The second memory cells are disposed on the interlayer dielectric above the first memory cells. The first sense amplifier transistor is disposed on the semiconductor substrate aside the first memory cells below the interlayer dielectric. The second sense amplifier transistor is disposed on the interlayer dielectric aside the plurality of second memory cells. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.