Static random access memory device

文档序号:1695852 发布日期:2019-12-10 浏览:32次 中文

阅读说明:本技术 静态随机存取记忆体元件 (Static random access memory device ) 是由 廖忠志 于 2019-02-22 设计创作,主要内容包括:本申请提供一种静态随机存取记忆体元件。在一实施方式中,静态随机存取记忆体元件包含第一传输栅极场效晶体管(FET)和第一上拉场效晶体管,形成于第一N型井区域(N-Well)中的至少一硅锗鳍片之上;第二传输栅极场效晶体管和第二上拉场效晶体管形成于第二N型井区域中的至少一硅锗鳍片之上;第一下拉场效晶体管形成于介于第一和第二N型井区域之间的P型井(P-well)区域中的数个硅鳍片的其中一个之上;以及第二下拉场效晶体管形成于P型井区域中的数个硅鳍片的另一个之上。(The present application provides a static random access memory device. In one embodiment, a static random access memory device includes a first pass gate Field Effect Transistor (FET) and a first pull-up FET formed over at least one silicon germanium fin in a first N-Well region (N-Well); a second pass gate field effect transistor and a second pull-up field effect transistor formed over the at least one silicon germanium fin in the second N-well region; a first pull-down field effect transistor formed over one of the plurality of silicon fins in a P-well (P-well) region between the first and second N-well regions; and a second pull-down field effect transistor formed over another of the plurality of silicon fins in the P-well region.)

1. an SRAM device, comprising:

A P-well region;

a first N-well region and a second N-well region located on opposite sides of the P-well region;

A plurality of silicon fins located in the P-well region;

At least one silicon germanium fin located in the first N-type well region;

At least one silicon germanium fin located in the second N-type well region;

A first pass gate field effect transistor and a first pull-up field effect transistor formed over the at least one silicon germanium fin in the first N-well region;

A second pass gate field effect transistor and a second pull-up field effect transistor formed over the at least one silicon germanium fin in the second N-well region;

a first pull-down field effect transistor formed on one of the plurality of silicon fins in the P-well region; and

a second pull-down field effect transistor formed over another of the plurality of silicon fins in the P-well region,

Wherein channel regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise a first silicon germanium alloy, and source/drain regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise a second silicon germanium alloy, wherein the first silicon germanium alloy is different in composition or impurity doping from the second silicon germanium alloy.

Technical Field

The disclosed embodiments relate to static random access memory devices.

Background

Semiconductor Integrated Circuits (ICs) undergo exponential growth. Technological advances in integrated circuit materials and design have made each generation of integrated circuits smaller and more complex than previous generations of circuits. As integrated circuits evolve, the functional density (the number of interconnected devices in a single wafer area) generally increases as the geometry size (the smallest device (or line) that can be built using a fabrication process) decreases. In this scaling process, benefits are typically provided by increasing production efficiency and reducing associated costs, which also increases the complexity of integrated circuit manufacturing.

For example, in deep sub-micron integrated circuit technology, Static Random Access Memory (SRAM) devices have become a popular memory for high-speed communication, image processing, and system-on-chip (SOC) products, and in microprocessors and system chips, the amount of SRAM devices has increased to meet the performance requirements of each new technology era, although existing SRAM devices have generally met their intended purpose, but they have not been entirely satisfactory in every aspect.

disclosure of Invention

the present disclosure provides a Static Random Access Memory (SRAM) device comprising a P-well region (P-well), a first N-well region (N-well), a second N-well region, a plurality of silicon fins, a silicon germanium fin, another silicon germanium fin, a first pass gate Field Effect Transistor (FET), a first pull-up field effect transistor, a second pass gate field effect transistor, a second pull-up field effect transistor, a first pull-down field effect transistor, and a second pull-down field effect transistor. The first N-well region (N-well) and the second N-well region are located on opposite sides of the P-well region. The plurality of silicon fins are located in the P-type well region. The plurality of silicon fins are located in the P-type well region. The silicon germanium fin is located in the first N-type well region. The other silicon germanium fin is positioned in the second N-type well region. A first transmission gate Field Effect Transistor (FET) and a first pull-up field effect transistor are formed over the silicon germanium fin in a first N-type well region. A second pass gate field effect transistor and a second pull-up field effect transistor formed over the another silicon germanium fin in the second N-well region. A second pass gate field effect transistor and a second pull-up field effect transistor are formed over the another silicon germanium fin in the second N-well region. A first pull-down field effect transistor is formed over one of the plurality of silicon fins in the P-type well region. A second pull-down field effect transistor is formed over another of the plurality of silicon fins in the P-type well region. The channel regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise a first silicon germanium alloy, and the source/drain regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise a second silicon germanium alloy, wherein the first silicon germanium alloy is different in composition or impurity doping from the second silicon germanium alloy.

Drawings

The present disclosure will be best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the features may be arbitrarily increased or reduced for clarity of discussion. It is emphasized that the drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the disclosure may be equally applicable to other embodiments.

FIG. 1A illustrates a layout of an exemplary SRAM device according to some embodiments of the present disclosure;

FIG. 1B illustrates another exemplary SRAM device layout according to some embodiments of the present disclosure;

FIGS. 2 and 3 illustrate circuit diagrams of exemplary SRAM devices according to some embodiments of the present disclosure;

FIGS. 4A and 4B present perspective schematic views of a Field Effect Transistor (FET) of an exemplary static random access memory device, according to some embodiments of the present disclosure;

FIG. 5A illustrates a layout of power supply lines and signal lines of an exemplary SRAM device according to some embodiments of the present disclosure;

FIG. 5B is a schematic diagram showing metal layers in the layout of FIG. 5A;

FIG. 6 is a flow chart illustrating a method of forming a SRAM device according to one embodiment of the present disclosure.

Detailed Description

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of embodiments of the disclosure. The following disclosure provides many different embodiments or examples for implementing different features of the provided subject matter, and specific examples of components and arrangements are described below to simplify the present disclosure. Of course, the examples are merely exemplary and are not intended to be limiting. For example, in the following description, formation of a first feature over or on a second feature includes embodiments in which the first feature is in direct contact with the second feature, and may also include embodiments in which the first feature is not in direct contact with the second feature. Moreover, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Additionally, spatially relative terms, such as "under," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element (or elements) or feature (or features) as illustrated in the figures. 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 interpreted accordingly.

Further, when a number or series of numbers recites "about," "approximately," and the like, these terms are intended to encompass a reasonable range of numbers, including numbers recited, such as +/-10% of the recited amount or other value understood by one skilled in the art, for example, the term "about 5 nanometers" includes a size range of 4.5 nanometers to 5.5 nanometers.

The present disclosure relates to a static random access memory device including a plurality of field effect transistors, but is not limited thereto. These field effect transistors may be, for example, complementary metal-oxide-semiconductor (CMOS) devices, including P-type metal-oxide-semiconductor (PMOS) field effect transistors and N-type metal-oxide-semiconductor (NMOS) field effect transistors. For example, the field effect transistors may be fin field effect transistors (finfet), nanowire field effect transistors or nanosheet field effect transistors depending on the shape of the channel region of the field effect transistors, and the following disclosure will continue with one or more embodiments of the fin field effect transistors to illustrate the various embodiments disclosed herein. It should be understood that the present application is not limited to one particular type of device, except as by the following claims.

Referring now to FIG. 1A, a layout of an exemplary SRAM device is shown according to some embodiments of the present disclosure. As used herein, an SRAM device refers to a standard SRAM device in an integrated circuit layout. In some embodiments, the SRAM device 100 includes a plurality of field effect transistors within a boundary 108 (depicted in dashed lines). In at least some embodiments as shown in FIG. 1A, the SRAM device 100 may include 6 field effect transistors located in the dashed boundary 108. In some embodiments, the SRAM device 100 is formed on a P-well (P-well) region 101 between a first N-well (N-well) region 102 and a second N-well region 103. P-well region 101, first N-well region 102, and second N-well region 103 are formed on a substrate or wafer. As shown in fig. 1A, the sram device 100 includes fins 111 and 115 in a P-well region 101. Fins 111 and 115 comprise silicon (Si) and may be referred to as silicon fin 111 and silicon fin 115. In some embodiments, fins 111 and 115 are substantially free of germanium. In other words, in those embodiments, no germanium is intentionally introduced into fins 111 and 115. The SRAM device 100 also includes a fin 112 in the first N-well region 102 and another fin 113 in the second N-well region 103. In some embodiments, fins 112 and 113 comprise silicon and germanium or a silicon-germanium alloy and may be referred to as silicon-germanium fin 112 and silicon-germanium fin 113.

In the embodiment shown in FIG. 1A, SRAM device 100 includes a first P-type pass gate field effect transistor ("PG-1"), a first P-type pull-up field effect transistor ("PU-1"), a first N-type pull-down field effect transistor ("PD-1"), a second N-type pull-down field effect transistor ("PD-2"), a second P-type pass gate field effect transistor ("PG-2"), and a second P-type pull-up field effect transistor ("PU-2"). In these embodiments, a first P-type pass gate field effect transistor and a first P-type pull-up field effect transistor are formed over the silicon germanium fin 112 in the first N-type well region and controlled by the gate 122 and the gate 132, respectively. In addition, a first N-type pull-down field effect transistor and a second N-type pull-down field effect transistor are formed on the silicon fin 115 and the silicon fin 111 in the P-well region 101, respectively, and controlled by the gate 132 and the gate 123, respectively. More particularly, a second P-type pull-up fet and a second P-type pass-gate fet are formed over the sige fin 113 in the second N-well region 103 and controlled by the gate 123 and the gate 133, respectively. It is noted that in these embodiments, the first P-type pull-up field transistor and the first N-type pull-down field transistor share the same gate 132, and the second N-type pull-down field transistor and the second P-type pull-up field transistor share the same gate 123. It is also noted that the first P-type transmission gate field effect transistor, the second P-type transmission gate field effect transistor, the first P-type pull-up field effect transistor and the second P-type pull-up field effect transistor are formed on the silicon germanium fin, and have silicon germanium channels.

In some cases, SRAM device 100 includes a bit-line (BL) node 141, a storage node 142, a first core drain voltage (CVdd) node 143, a second CVdd node 144, a storage node bar 145, a bit-line bar (BLB) node 146, a first core source voltage (CVss) node 147, and a second CVss node 148. In addition, some of these nodes, such as word line contacts 104 and 105, are also shown in FIG. 1A. In the present embodiment, a mating plug (plugged contact plug)170 couples the gate 123 to the drain region of the first N-type pull-down fet controlled by the gate 132. In addition, the plug 171 couples the gate 132 to the drain region of the second N-type pull-down fet controlled by the gate 123. In some embodiments, the docking plugs 170 and 171 may be replaced with other types of connection structures.

In some embodiments, as shown in fig. 1A, in the first N-type well region 102, the sige fin 112 extends continuously along the "Y" direction between the upper and lower portions of the boundary 108, while the boundary 108 extends in the "X" direction. Similarly, in the second N-well region 103, the sige fin 113 is continuously extended along the "Y" direction between the upper and lower portions of the boundary 108, and the boundary 108 is extended in the "X" direction. Herein, the references to upper and lower portions are merely for convenience in referring to FIG. 1A and should not be considered as limiting the orientation of the SRAM device 100. In this regard, the sige fins 112 and 113 are continuous in that they are not cut in the "X" direction or are cut or trimmed short at both ends. In contrast, silicon fins 111 and 115 are discontinuous in boundary 108. For example, when one end (lower end in fig. 1A) of the silicon fin 115 reaches the lower portion of the boundary 108, the other end (upper end in fig. 1A) does not reach the upper portion of the boundary 108. Since the sige fins 112 and 113 are strained in several embodiments of the present disclosure, cutting them releases the built-in strain and affects the performance of the first, second, first and second P-type pull-up fets. Silicon fins 111 and 115 are not as sensitive to cutting and trimming as silicon germanium fins 112 and 113 because no lattice strain is intentionally introduced into silicon fins 111 and 115.

FIG. 1B illustrates another layout of an exemplary SRAM device 150 according to some embodiments of the present disclosure. The sram device 150 is similar to the sram device 100 of fig. 1A, except that the pass gate fets (the first and second pass gate fets) and the pull-up fets (the first and second pull-up fets) can be multi-fin fets. In other words, the first P-type transmission gate field effect transistor, the second P-type transmission gate field effect transistor, the first P-type pull-up field effect transistor and the second P-type pull-up field effect transistor may include (or be constructed of) a plurality of parallel fins, but the N-type pull-down field effect transistors (the first and second N-type pull-down field effect transistors) in the sram device 150 of fig. 1B are single-fin field effect transistors. In some embodiments not shown here, the first and second P-type pass gate field effect transistors may include a plurality of fins. By adding more fins, the on-current (Ion) of the PFET is improved, and the speed of the SRAM device 150 is improved.

as shown in FIG. 1B, the SRAM device 150 is defined within a boundary 158, which is depicted by a dashed line. In some embodiments, the SRAM device 150 is formed on a P-well (P-well) region 151 between a first N-well (N-well) region 152 and a second N-well region 153. The P-well region 151, the first N-well region 152, and the second N-well region 153 are formed on a substrate or wafer. As shown in fig. 1B, the sram device 150 includes fins 161 and 165 in the P-well region 151. Fins 161 and 165 comprise silicon and may be referred to as silicon fin 161 and silicon fin 165, respectively. In some embodiments, silicon fins 161 and 165 are substantially free of germanium. In other words, no germanium is intentionally embedded in silicon fins 161 and 165 in those embodiments. The SRAM device 150 also includes two fins 162 present in the first N-well region 152 and two fins 163 present in the second N-well region 153. In some embodiments, fins 162 and 163 comprise silicon and germanium or a silicon-germanium alloy and may be referred to as silicon-germanium fins, such as silicon-germanium fin 162 and silicon-germanium fin 163.

In several embodiments shown in FIG. 1B, the SRAM device 150 includes a first P-type pass gate field effect transistor ("PG-1"), a first P-type pull-up field effect transistor ("PU-1"), a first N-type pull-down field effect transistor ("PD-1"), a second N-type pull-down field effect transistor ("PD-2"), a second P-type pass gate field effect transistor ("PG-2"), and a second P-type pull-up field effect transistor ("PU-2"). In these embodiments, a first P-type pass gate fet and a first P-type pull-up fet are formed over the sige fin 162 in the first N-well region 152 and controlled by the gate 172 and the gate 182, respectively. In addition, a first N-type pull-down field effect transistor and a second N-type pull-down field effect transistor are formed over silicon fin 165 and silicon fin 161, respectively, in P-well region 151 and controlled by gate 182 and gate 173, respectively. Second P-type pull-up fets and second P-type pass-gate fets are formed over sige fin 163 in second N-well region 153 and controlled by gate 173 and gate 183, respectively. It is noted that in these embodiments, the first P-type pull-up field effect transistor and the first N-type pull-down field effect transistor share the same gate 182. The second N-type pull-down field effect transistor and the second P-type pull-up field effect transistor share the same gate 173. It is noted that, since the first P-type transmission gate field effect transistor, the second P-type transmission gate field effect transistor, the first P-type pull-up field effect transistor and the second P-type pull-up field effect transistor are formed on the silicon germanium fin (both shown in fig. 1B), the first P-type transmission gate field effect transistor, the second P-type transmission gate field effect transistor, the first P-type pull-up field effect transistor and the second P-type pull-up field effect transistor have silicon germanium channels.

in some cases, SRAM device 150 includes Bit Line (BL) node 191, storage node 192, first CVdd node 193, second CVdd node 194, storage node bar 195, Bit Line Bar (BLB) node 196, first CVss node 197, and second CVss node 198. In addition, some other nodes, such as word line contacts 154 and 155, are also shown in FIG. 1B. In the embodiment disclosed herein, the docking plug 170 couples the gate 173 to the drain region of the first N-type pull-down fet controlled by the gate 182; in addition, the plug 171 couples the gate 182 to the drain region of the second N-type pull-down fet controlled by the gate 173. In some embodiments, the docking plugs 170 and 171 may be replaced with other types of connection structures.

In some embodiments, as shown in fig. 1B, in the first N-type well region 152, the silicon germanium fin 162 extends continuously along the "Y" direction between the upper and lower portions of the boundary 158, while the boundary 108 extends in the "X" direction. Similarly, in the second N-type well region 153, the silicon germanium fin 163 continuously extends along the "Y" direction between the upper and lower portions of the boundary 158, while the boundary 158 extends in the "X" direction. As described herein, the references to upper and lower portions are merely for convenience in referring to FIG. 1A and should not be taken as limiting the orientation of the SRAM device 150. In this regard, the silicon germanium fins 162 and 163 are continuous in that they are not constrained to be cut in the "X" direction or have one end cut or trimmed short. In contrast, silicon fins 161 and 165 are not continuous within equilateral boundaries 158. For example, when one end (lower end in fig. 1B) of the silicon fin 165 reaches the lower portion of the equal boundary 158, the other end (upper end in fig. 1B) does not reach the upper portion of the equal boundary 158. Since the sige fins 162 and 163 are strained in several embodiments of the present disclosure, cutting them releases the built-in strain and affects the behavior of the first and second P-type pull-up fets and the first and second P-type pass-gate fets. Silicon fins 165 and 161 are not as sensitive to cutting and trimming as silicon germanium fins 112 and 113 because no lattice strain is intentionally introduced into silicon fins 165 and 161.

FIG. 2 is a circuit diagram illustrating an SRAM device 200 according to some embodiments of the present disclosure. In some examples, the SRAM device 200 is shown in the circuit diagram of the SRAM device 100 of FIG. 1A and the circuit diagram of the SRAM device 150 of FIG. 1B. The SRAM device 200 includes a first P-type pass gate field effect transistor 202 ("PG-1"), a second P-type pass gate field effect transistor 204 ("PG-2"), a first P-type pull-up field effect transistor 206 ("PU-1), a second P-type pull-up field effect transistor 208 (" PU-2), a first P-type pull-down field effect transistor 210 ("PD-1), and a second P-type pull-down field effect transistor 212 (" PD-2). The gates of the first and second PFETs 202 and 204 are electrically connected to a Word Line (WL), which determines whether the SRAM device 200 is selected. In the SRAM device 200, memory bits (e.g., latches or flip-flops) are formed in a first PFET 206, a second PFET 208, a first NFET 210, and a second NFET 212 to store one bit of data. The complement of the bit is stored at storage node 214 and storage node 216. the memory cell can write it to SRAM device 200 or read SRAM device 200 through Bit Line (BL) and Bit Line Bar (BLB). In this configuration, the bit lines and bit line bars may carry complementary numbers of bit line signals. SRAM device 200 is charged via positive power supply node CVdd, which has a positive power supply voltage and is also connected to power supply voltage CVss, which may be an electrical ground.

In the embodiment illustrated by SRAM device 200 of FIG. 2, the sources of first PFET 206 and second PFET 208 are connected to CVdd. First N-type pull-down fet 210 and second N-type pull-down fet 212 are connected to CVss. The gates of first P-type pull-up field effect transistor 206 and first N-type pull-down field effect transistor 210 are connected to the drains of second P-type pull-up field effect transistor 208 and second N-type pull-down field effect transistor 212 at storage node 214. The gates of second P-type pull-up field effect transistor 208 and second N-type pull-down field effect transistor 212 are connected to the drains of first P-type pull-up field effect transistor 206 and first N-type pull-down field effect transistor 210 at storage node 216. The source/drain regions of the first P-type pass gate field effect transistor 202 are connected to a Bit Line (BL). The source/drain regions of second P-type pass gate field effect transistor 204 are connected to a bitline bar (BLB).

FIG. 3 is a circuit diagram of an SRAM device 300. The SRAM device 300 may be an alternative circuit diagram to the SRAM device 200 of FIG. 2. Specifically, the first current transformer 306 (current transformer-1) in fig. 3 may include the first P-type pull-up fet 206 and the first N-type pull-down fet 210 in fig. 2, and the second current transformer 308 (current transformer-2) may include the second P-type pull-up fet 208 and the second N-type pull-down fet 212 in fig. 2. In some embodiments, each of current transformer-1 and current transformer-2 contains additional transistors. The output of the first current transformer 306 is connected to the inputs of the first P-type pass gate field effect transistor 202 and the second current transformer 308. The output of the second current transformer 308 is connected to the inputs of the second P-type pass gate fet 204 and the first current transformer 306. The first and second current transformers (current transformer-1 and current transformer-2) form a memory bit (e.g., latch or flip-flop).

Fig. 4A and 4B are schematic perspective views of a pfet 400, wherein the pfet 400 can be used as a pull-up fet and a pass-gate fet in any of the sram device 100 in fig. 1A, the sram device 150 in fig. 1B, and the sram device 200 in fig. 2. In some embodiments, PFET 400 is formed over fin 402 of the substrate in N-well region 401. In some embodiments disclosed herein, fin 402 comprises silicon and germanium and may be referred to as a silicon germanium fin 402. Fin 402 may also be referred to as a fin comprising a silicon germanium alloy. In several embodiments illustrated in fig. 4A, isolation regions 403 are formed on opposite sides of the sige fin 402. The isolation regions 403 may serve as a number of Shallow Trench Isolation (STI) regions. In some embodiments, as shown in figure 4A, the silicon germanium fin 402 includes a channel region 405 sandwiched between a drain region 404 and a source region 406. The silicon germanium fin 402 extends continuously between the drain region 404 and the channel region 405 and between the source region 406 and the channel region 405. The pfet 400 thus has a silicon germanium channel region 405. A gate dielectric layer 415 is formed on the top and sides of the channel region 405 of the sige fin 402 and a gate 425 is formed over the gate dielectric layer 415.

In some embodiments shown in fig. 4A and 4B, the source/drain regions 406/404 and the channel region 405 of the pfet are different in composition or impurity doping. In several embodiments illustrated In fig. 4A, the drain region 404 and the source region 406 of the sige fin 402 are implanted with P-type dopants 435, such as boron (B), gallium (Ga), and indium (In). In some embodiments, the drain region 404 and the source region 406 of the sige fin 402 are implanted with boron (B) dopants. In some embodiments shown in fig. 4B, each of the drain 404 and source 406 may include an epitaxial feature 436, although the presence of germanium in the silicon lattice may create strain to increase hole mobility, the nature of the adjacent structure and layers may impose limitations on the germanium concentration in the epitaxial feature 436 and channel region 405. For example, in some embodiments, a silicide (such as titanium silicide or nickel silicide) is formed at the interface between the epitaxial feature 436 and the source/drain contacts, and a lower silicon concentration will prevent silicide formation when the germanium concentration in the epitaxial feature 436 is greater than about 70%, e.g., 75%. Meanwhile, when the germanium concentration in the epitaxial feature 436 is less than about 35%, such as 30%, the epitaxial feature 436 will result in low conductivity. As another example, in some embodiments, a silicon oxide layer is formed at the interface between the channel and the high-K interface layer to mitigate lattice mismatch between the channel and the high-K interface layer (lattice mismatch). When the germanium concentration in channel region 405 is above about 35%, for example 40%, a lower silicon concentration will prevent the formation of silicon oxide on channel region 405. Meanwhile, when the germanium concentration in the channel region is less than about 15%, for example, 10%, the resulting channel region 405 will result in poor performance, such as low on current (Ion). Because of the above example considerations and other considerations, in some embodiments, the epitaxial features 436 comprise a silicon-germanium alloy having a higher germanium concentration than the germanium concentration in the channel region 405. In some examples, the germanium concentration in the epitaxial feature 436 is between about 30% and 75% and the germanium concentration in the channel region 405 is between about 10% and 40%. In some examples, the germanium concentration in the epitaxial feature 436 is between about 35% and 70%, and the germanium concentration in the channel region 405 is between about 15% and 35%. To form the epitaxial features 436, the drain 404 and source 406 of the silicon germanium fin 402 are etched to form a recess, and the epitaxial features 436 are formed in the recess by an epitaxial technique. By having the device include an epitaxial feature 436 with a higher concentration of germanium than the silicon germanium fin, the drain 404 and source 406 have a higher concentration of germanium than the channel region 405. In some embodiments, the drain 404 and source 406 of the PFET are not only doped with P-type dopants, but also include epitaxial features of silicon germanium with a higher concentration of germanium than in the channel region 405. In some embodiments, illustrated by fig. 4B, pfet 400 includes raised source/drain regions 404/406 due to the presence of epitaxial feature 436. Since the epitaxial features 436 are only present in the source/drains 404/406, the height of the source/drain regions 404/406, measured from the top Surface of The Isolation (STI) regions 403, is higher than the height of the silicon germanium channel 405.

Above the sram devices (e.g., sram device 100 and sram device 150), a plurality of metallization layers or metal wire layers are formed above the first and second P-type pull-up fets, the first and second P-type transmission gate fets, and the first and second N-type pull-down fets to provide connections therebetween. Referring now to FIG. 5A, therein is shown a layout 500 of power supply lines and signal lines for an exemplary SRAM device, such as the SRAM device 100 of FIG. 1A or the SRAM device 150 of FIG. 1B. Here, the layout 500 of the power supply lines and the signal lines may be referred to as a metal line layout 500. In the embodiment illustrated by fig. 5A, the metal wiring layout 500 includes metal lines disposed in three metal layers: a first metal layer M1, a second metal layer M2 disposed over the first metal layer M1, and a third metal layer M3 disposed over the second metal layer M2. The first metal layer M1 includes at least metal lines 501, 502, and 503. Metal line 501 is connected to a bitline bar (BLB) node via 531. Metal line 502 is connected to CVss via vias 533 and 543, respectively. Metal line 503 is connected to the Bit Line (BL) node through via 532. The second metal layer M2 includes at least metal lines 511, 512, and 513. The metal line 511 connects the gates of the first and second P-type gate transfer gate field effect transistors through a word-line contact structure (word-line contact). Metal lines 512 and 513 are CVdd landing pads and are connected to the CVdd node. The third metal layer M3 includes at least metal lines 521 and 522. Metal line 521 is connected to the CVdd node through CVdd landing pad 512 and may be considered a first CVdd conductor. Metal line 522 is connected to the CVdd node via CVdd landing pad 513 and may be considered a second CVdd conductor.

FIG. 5B is a schematic diagram illustrating the metal layers M1, M2 and M3 shown in FIG. 5A. As shown in fig. 5A, the first metal layer M1 at least includes the metal lines 501, 502, and 503; the second metal layer M2 includes at least the metal lines 511, 512, and 513; and the third metal layer M3 includes at least the metal lines 521 and 522. The first metal layer M1 has a first thickness T1, the second metal layer has a second thickness T2 and the third metal layer has a third thickness T3. In some embodiments, the second thickness T2 is greater than the first thickness T1 and the third thickness T3. In those embodiments, the thicker second metal layer may have a lower resistance value, and thus may reduce power consumption and voltage drop along the length of the second metal layer.

FIG. 6 is a flow chart illustrating a method 600 of forming an SRAM device (such as the SRAM device 100 of FIG. 1A and the SRAM device 150 of FIG. 1B). The method 600 is an example only and is not intended to limit the present disclosure to limitations not expressly recited in the claims. Additional operations may be provided before, during, and after the method 600, and some of the operations described above may be replaced, eliminated, or moved from additional embodiments of the method 600. The operation of method 600 will be described below in conjunction with fig. 1A, 1B, 4A, 4B, 5A, and 5B.

At operation 602 of the method 600, a work piece is received. In some embodiments, a work-piece may include a substrate having a P-well region sandwiched between a first N-well region and a second N-well region. An exemplary layout of the P-well region and the first and second N-well regions is shown in fig. 1A and 1B. At operation 604 of the method 600, at least one silicon germanium fin is formed in each of the first and second N-well regions, and a plurality of silicon fins are formed in the P-well regions. The silicon germanium fin is a fin of a first silicon germanium alloy comprising silicon (Si) and germanium (Ge). The first silicon-germanium alloy includes a first germanium concentration. Fig. 4A and 4B illustrate a silicon germanium fin (silicon germanium fin 402) in an N-type well region. In some embodiments, the formation of silicon germanium and silicon fins is performed by a plurality of epitaxial processes followed by a plurality of other suitable processes. At operation 606 of the method 600, a first N-type pull-down field effect transistor is formed over one of the silicon fins in the P-well and a second N-type pull-down field effect transistor is formed over the other silicon fin. At operation 608 of the method 600, a first P-type pass gate field effect transistor and a first P-type pull-up field effect transistor are formed over the at least one silicon germanium fin in the first N-well region, and a second P-type pass gate field effect transistor and a second P-type pull-up field effect transistor are formed over the at least one silicon germanium fin in the second N-well region.

Next, method 600 branches into operation 610 and operation 612. In some embodiments, method 600 may perform one of operations 610 and 612, respectively. In some other embodiments, method 600 may perform operations 610 and 612 simultaneously or sequentially. In operation 610, the source/drain regions of the first and second P-type pass gate field effect transistors and the source/drain regions of the first and second P-type pull-up field effect transistors are doped with P-type dopants, such as boron, gallium, and indium. In some embodiments, the P-type dopant is boron. An embodiment of operation 610 is illustrated in fig. 4A. At operation 612, an epitaxial feature is formed over the source/drain regions of the first and second P-type transmission gate field effect transistors and the first and second P-type pull-up field effect transistors to become part of the source/drain regions. In some embodiments, the epitaxial features are formed from a second silicon-germanium alloy of silicon (Si) and germanium (Ge). The second silicon-germanium alloy includes a second germanium concentration that is greater than the first germanium concentration. Thus, the P-type pass gate field effect transistor and pull-up field effect transistor formed using method 600 include a channel region having a first germanium concentration and an epitaxial feature (in the source/drain regions) having a second germanium concentration. As mentioned above, the selection of the first and second germanium concentration ranges is based on a number of considerations, which for the sake of brevity will not be repeated here. An embodiment of operation 612 is illustrated in FIG. 4B. In some examples, operations 610 and 612 may be performed sequentially, followed by a P-type impurity doping process, such as a boron implant, as epitaxial features are formed. In some other cases, operations 610 and 612 may be performed simultaneously when the epitaxial features are doped in-situ as they are formed epitaxially. At operation 614, metal layers (such as the first, second, and third metal layers described in conjunction with fig. 5A and 5B) are formed to interconnect the first and second P-type transmission gate field effect transistors, the first and second P-type pull-up field effect transistors, and the first and second N-type pull-down field effect transistors.

Based on the above discussion, it can be seen that the present disclosure provides advantages over conventional SRAM devices. However, it is to be understood that other embodiments may provide additional advantages, not all of which need be disclosed herein, and that no particular advantage is required for all embodiments. One advantage is a continuous silicon germanium fin for a P-type field effect transistor in an sram device that reduces undesirable relaxation of built-in strain in the silicon germanium fin. This adverse strain relief may lead to a degradation of the performance of the PFET. The source/drain regions of the pfet in the disclosed sram device are different from the sige channel region in impurity doping and germanium concentration when the two source/drain regions and channel region are formed in the sige fin. According to various embodiments disclosed herein, Ion (on-current) performance may be improved and advantageous speed gain may be provided by doping the source/drain regions with a P-type dopant, such as boron, or by forming epitaxial features on the source/drain regions of a P-type field effect transistor. In these embodiments, the epitaxial features have a higher germanium concentration than the germanium concentration in the silicon germanium fin and the silicon germanium channel.

In one exemplary aspect, the present disclosure is directed to a Static Random Access Memory (SRAM) device. The device comprises a P-well (P-well) region, a first N-well (N-well) region, a second N-well region on both sides of the P-well region, a silicon fin in the P-well region, at least one silicon germanium fin in the first N-well region, at least one silicon germanium fin in the second N-well region, a first transmission gate Field Effect Transistor (FET) and a first pull-up field effect transistor formed over the at least one silicon germanium fin in the first N-well region, a second transmission gate field effect transistor and a second pull-up field effect transistor formed over the at least one silicon germanium fin in the second N-well region, a first pull-down field effect transistor formed over one of the silicon fins in the P-well region, and a second pull-down field effect transistor formed over the other of the silicon fins in the P-well region. The channel regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise a first silicon germanium alloy, and the source/drain regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise a second silicon germanium alloy. The first silicon germanium alloy is different in composition or impurity doping from the second silicon germanium alloy.

In one embodiment of the device, the source/drain regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors include P-type dopants, and the channel regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors are substantially free of P-type dopants.

in another embodiment of the device, the source/drain regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise epitaxial features. The channel regions of the first and second pass gate field effect transistors and the first and second pull-up field effect transistors comprise a first germanium concentration; and the epitaxial features include a second germanium concentration greater than the first germanium concentration. In one embodiment, the first germanium concentration is between about 10% and about 40%. In another embodiment, the second germanium concentration is between about 30% and about 75%.

In another embodiment of the apparatus, the SRAM device further comprises: a first metal layer including Bit Lines (BL) and Bit Line Bars (BLB) of the SRAM device, a second metal layer on the first metal layer, the second metal layer including Word Lines (WL) coupled to gates of the first and second pass gate FETs, and a third metal layer on the second metal layer, the third metal layer including power supply (Vdd) conductors electrically connecting source regions of the first and second pull-up FETs. The second metal layer includes a thickness that is greater than the thickness of the first metal layer and the thickness of the third metal layer.

In another embodiment of the device, the device comprises a first boundary and a second boundary parallel to the first boundary. At least one silicon germanium fin in the first N-type well region continuous between the first boundary and the second boundary; and at least one silicon germanium fin in the second N-type well region is continuous between the first boundary and the second boundary.

In another exemplary aspect, the present disclosure is directed to a Static Random Access Memory (SRAM) device. The device comprises a first P-type pull-up Field Effect Transistor (FET) and a first N-type pull-down field effect transistor, wherein the first P-type pull-up field effect transistor and the first N-type pull-down field effect transistor form a first current transformer; a second P-type pull-up field effect transistor and a second N-type pull-down field effect transistor, the second P-type pull-up field effect transistor and the second N-type pull-down field effect transistor forming a second current transformer; the first P-type transmission grid field effect transistor is coupled with the output of the first converter and the input of the second converter; and a second P-type pass gate field effect transistor coupled to the output of the second current transformer and the input of the first current transformer. Each of the first and second P-type pass gate field effect transistors and the first and second P-type pull-up field effect transistors includes a fin having a silicon germanium channel region and two silicon germanium source/drain regions sandwiched between the silicon germanium channel regions. The silicon germanium channel region comprises a first germanium concentration and the silicon germanium source/drain regions comprise a second germanium concentration that is greater than the first germanium concentration.

In one embodiment of the device, the first germanium concentration is between about 15% and about 35%. In another embodiment of the device, the second germanium concentration is between about 35% and about 70%. In yet another embodiment of the device, the silicon germanium source/drain regions include P-type dopants and the silicon germanium channel region is substantially free of P-type dopants. In one embodiment, the P-type dopant is boron.

In yet another embodiment of the device, each of the first and second N-type pull-down field effect transistors includes another fin having a silicon channel region, and two silicon source/drain regions sandwiched between the silicon channel region.

In another embodiment of the apparatus, the SRAM device further comprises a first metal layer comprising Bit Lines (BL) and Bit Line Bars (BLB) of the SRAM device, a second metal layer on the first metal layer, the second metal layer comprising Word Lines (WL) coupled to gates of the first and second PFETs, and a third metal layer on the second metal layer, the third metal layer comprising a power supply (Vdd) conductor electrically connecting source regions of the first and second PFETs. The second metal layer includes a thickness that is greater than the thickness of the first metal layer and the thickness of the third metal layer.

In yet another exemplary method, the disclosure relates to a Static Random Access Memory (SRAM) device. The device comprises a PFET including a gate, a second PFET including a gate, a first PFET including a source region, a second PFET including a source region, the memory device includes a first N-type pull-down field effect transistor, a second N-type pull-down field effect transistor, a first metal layer including Bit Lines (BL) and Bit Line Bars (BLB) of the SRAM device, a second metal layer on the first metal layer, the second metal layer including Word Lines (WL) coupled to gates of the first and second P-type transmission gate field effect transistors, and a third metal layer on the second metal layer, the third metal layer including a power supply (Vdd) conductor electrically connected to source regions of the first and second P-type pull-up field effect transistors, the second metal layer including a thickness greater than a thickness of the first metal layer and a thickness of the second metal layer.

In one embodiment of the device, the first P-type transmission gate field effect transistor and the first P-type pull-up field effect transistor are formed on at least one silicon germanium fin in a first N-well (N-well) region of the sram cell. A second P-type transmission grid field effect transistor and a second P-type pull-up field effect transistor are formed on the at least one silicon germanium fin in the second N-type well region of the static random access memory device. The first and second N-type pull-down field effect transistors are formed on the silicon fin in the P-type well region of the SRAM device, respectively. The P-well region is disposed between the first N-well region and the second N-well region.

in another embodiment of the device, the source/drain regions of the first and second P-type transmission gate field effect transistors and the first and second P-type pull-up field effect transistors comprise epitaxial features. The channel regions of the first and second P-type transmission gate field effect transistors and the channel regions of the first and second P-type pull-up field effect transistors comprise a first germanium concentration. The epitaxial feature includes a second germanium concentration greater than the first germanium concentration. In one embodiment, the first germanium concentration is between about 10% to about 40%; the second germanium concentration is between about 30% and about 75%.

In yet another embodiment of the device, the source/drain regions of the first and second P-type pass gate field effect transistors and the first and second P-type pull-up field effect transistors include P-type dopants, and the channel regions of the first and second P-type pull-up field effect transistors and the first and second P-type pull-up field effect transistors are substantially free of P-type dopants. In one embodiment, the P-type dopant is boron.

the foregoing outlines features of several embodiments or examples 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. For example, by implementing the bit line conductors and the word line conductors with different thicknesses, one may implement different resistances through the conductors, however, other techniques may be utilized to change the resistance of the metal conductors.

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