Work function metal gate device

Abstract

A work function metal gate device includes a gate, a drift region, a source, a drain, and a first insulating structure. The gate is disposed on a substrate, wherein the gate includes a middle protruding stepped work function metal stack structure or a middle recessed stepped work function metal stack structure. The drift region is disposed in the substrate under a portion of the gate. The source is in the substrate, and the drain is in the drift region laterally adjacent to the gate. The first insulating structure is disposed in the drift region between the gate and the drain.

Description

TECHNICAL FIELD

[0001] The present invention relates to a work function metal gate device, and more particularly, to a work function metal gate device having a stepped work function metal. BACKGROUND

[0002] In the current semiconductor industry, polysilicon is widely used in semiconductor devices such as metal-oxide-semiconductor (MOS) transistors as the standard gate fill material. However, as the size of MOS transistors continues to shrink, the conventional polysilicon gate suffers from boron penetration effects that degrade device performance, and the inevitable depletion effect that increases the equivalent gate dielectric thickness and reduces the gate capacitance, thereby degrading device drive capability. Therefore, the semiconductor industry has attempted to replace the conventional polysilicon gate with a new gate fill material, such as a work function metal, to serve as a control electrode for a high-k gate dielectric. SUMMARY

[0003] The present invention provides a work function metal gate device having a gate including a stepped work function metal stack to modulate channel charge density and reduce resistance.

[0004] The present invention provides a work function metal gate device including a gate, a drift region, a source, a drain, and a first insulating structure. The gate is disposed on a substrate, wherein the gate includes a stepped work function metal stack having a protrusion. The drift region is disposed in the substrate beneath a portion of the gate. The source is in the substrate, and the drain is in the drift region laterally adjacent the gate. The first insulating structure is disposed in the drift region between the gate and the drain.

[0005] The present invention provides a work function metal gate device including a gate, a drift region, a source, a drain, and a first insulating structure. The gate is disposed on a substrate, wherein the gate includes a stepped work function metal stack having a recess. The drift region is disposed in the substrate beneath a portion of the gate. The source is in the substrate, and the drain is in the drift region laterally adjacent the gate. The first insulating structure is disposed in the drift region between the gate and the drain.

[0006] The present invention provides a work function metal gate device having a gate disposed on a substrate, wherein the gate includes a stepped work function metal stack having a protrusion or a recess to modulate channel charge density and reduce resistance of the substrate between the source and the drain. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to an embodiment of the present application;

[0008] Figure 2 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to an embodiment of the present application;

[0009] Figure 3 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to an embodiment of the present application;

[0010] Figure 4 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to an embodiment of the present application;

[0011] Figure 5 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to an embodiment of the present application;

[0012] Figure 6 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to another embodiment of the present application;

[0013] Figure 7 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to another embodiment of the present application;

[0014] Figure 8 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to another embodiment of the present application;

[0015] Figure 9 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to another embodiment of the present application;

[0016] Figure 10 A cross-sectional view of a manufacturing process for forming a work function metal gate device according to another embodiment of the present application.

[0017] Main element symbol explanation

[0018] 12: insulating structure

[0019] 14: first insulating structure

[0020] 16: second insulating structure

[0021] 20: gate oxide layer

[0022] 100: work function metal gate device

[0023] 110: substrate

[0024] 112: drift region

[0025] 114: First Drift Zone

[0026] 120: Interlayer dielectric layer

[0027] 122: Spacer wall

[0028] 132: U-shaped high dielectric constant dielectric layer

[0029] 134: U-shaped barrier layer

[0030] 140a: First-order ladder-like work function metal stacked structure

[0031] 142, 142a: First layer of work function metal layer

[0032] 144, 144a: Second work function metal layer

[0033] 150: Second-order ladder-like work function metal stacked structure

[0034] 160: Low resistivity materials

[0035] B1: Underlying work function metal layer

[0036] B2: Top layer work function metal layer

[0037] C1: Stepped work function of the central protrusion in a metallic stacked structure.

[0038] D: Drain electrode

[0039] E1, E2: End

[0040] M1: Gate

[0041] P1, P2: Photoresist

[0042] R1: Groove

[0043] S: Source

[0044] T1, T2: Sidewall

[0045] g1, g2: gaps Detailed Implementation

[0046] Figures 1-5 This is a cross-sectional schematic diagram illustrating the fabrication process of a forming power function metal gate device according to an embodiment of the present invention. Figure 1As shown, a substrate 110 is provided. The substrate 110 is, for example, a semiconductor substrate such as a silicon substrate, a silicon-containing substrate, a Group III-on-silicon substrate (e.g., GaN-on-silicon), a graphene-on-silicon substrate, or a silicon-on-insulator (SOI) substrate. In this embodiment, a drift region 112 and a first drift region 114 are formed in the substrate 110, for example, by a doping process. Then, an insulating structure 12 is formed in the substrate 110 to electrically isolate the transistors, and a first insulating structure 14 and a second insulating structure 16 are formed in the substrate 110 to electrically isolate the gates, the drains and the sources of the high-voltage transistors. The insulating structure 12, the first insulating structure 14 and the second insulating structure 16 are, for example, shallow trench isolation (STI) structures formed by a shallow trench isolation process, the details of which are well known in the art and will not be described herein. However, the present application is not limited thereto. In this embodiment, the insulating structure 12 and the first insulating structure 14 are located in the drift region 112, and the insulating structure 12 and the second insulating structure 16 are located in the first drift region 114. However, the present application is not limited thereto.

[0047] A gate oxide layer 20 can be selectively formed in the substrate 110 between the first insulating structure 14 and the second insulating structure 16. Then, a metal gate is formed on the gate oxide layer 20, the first insulating structure 14 and the second insulating structure 16.

[0048] In detail, an interlayer dielectric layer 120 is first deposited to cover the substrate 110, wherein the interlayer dielectric layer 120 has a recess R1. The method of forming the interlayer dielectric layer 120 can include the following steps. A sacrificial gate (not shown) is first formed on the gate oxide layer 20, the first insulating structure 14 and the second insulating structure 16, and a drain D is then formed in the drift region 112 between the insulating structure 12 and the first insulating structure 14, and a source S is formed in the first drift region 114 between the insulating structure 12 and the second insulating structure 16. An interlayer dielectric layer (not shown) is then deposited on the substrate 110 around the sides of the sacrificial gate, and the sacrificial gate is removed to form the recess R1 in the interlayer dielectric layer 120. Alternatively, before the interlayer dielectric layer is deposited, a spacer 122 can be selectively formed on the sides of the sacrificial gate, so that after the sacrificial gate is removed, the spacer 122 is formed around the recess R1.

[0049] Thereafter, a U-shaped high dielectric constant dielectric layer 132, a U-shaped barrier layer 134 and a first layer of work function metal layer 142 are formed to conform to the recess Rl. In one embodiment, a high dielectric constant dielectric layer (not shown), a barrier layer (not shown) and a work function metal layer (not shown) are sequentially deposited to conform to the recess Rl, the spacer 122 and the ILD 120, and then the high dielectric constant dielectric layer (not shown), the barrier layer (not shown) and the work function metal layer (not shown) over the recess Rl are removed to form the U-shaped high dielectric constant dielectric layer 132, the U-shaped barrier layer 134 and the first layer of work function metal layer 142 in the recess Rl. The U-shaped high dielectric constant dielectric layer 132 can be selected from the group consisting of hafnium oxide (HfO2), hafnium silicon oxide (HfSiO4), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al2O3), lanthanum oxide (La2O3), tantalum oxide (Ta2O5), yttrium oxide (Y2O3), zirconium oxide (ZrO2), strontium titanate oxide (SrTiO3), zirconium silicon oxide (ZrSiO4), hafnium zirconium oxide (HfZrO4), strontium bismuth tantalate (SrBi2Ta2O9, SBT), lead zirconate titanate (PbZrTiO3, PZT) and barium strontium titanate (BaSrTiO3, BST). The U-shaped barrier layer 134 is, for example, a single layer structure or a composite layer structure of tantalum nitride (TaN), titanium nitride (TiN), but the present application is not limited thereto. x Ti 1-x O3,PZT) and barium strontium titanate (Ba x Sr 1-x TiO3,BST). The U-shaped barrier layer 134 is, for example, a single layer structure or a composite layer structure of tantalum nitride (TaN), titanium nitride (TiN), but the present application is not limited thereto.

[0050] Then, a photoresist P1 is formed on the first layer of work function metal layer 142 to pattern the first layer of work function metal layer 142.

[0051] As Figure 2As shown, a first layer work function metal layer 142 is patterned by a photoresist P1 to form a first layer work function metal layer 142a. Then, the photoresist P1 is removed.

[0052] As shown, a second layer work function metal layer 144 is formed to cover the first layer work function metal layer 142a. As shown, the second layer work function metal layer 144 can be deposited to conformally cover the recess R1 first. Then, as shown, a photoresist P2 is formed to cover part of the second layer work function metal layer 144 in the recess R1 to pattern the second layer work function metal layer 144 to form a second layer work function metal layer 144a to cover the first layer work function metal layer 142a. Then, the photoresist P2 is removed. Figures 3-4 Figure 3 As shown, a second layer work function metal layer 144 is formed to cover the first layer work function metal layer 142a. As shown, the second layer work function metal layer 144 can be deposited to conformally cover the recess R1 first. Then, as shown, a photoresist P2 is formed to cover part of the second layer work function metal layer 144 in the recess R1 to pattern the second layer work function metal layer 144 to form a second layer work function metal layer 144a to cover the first layer work function metal layer 142a. Then, the photoresist P2 is removed. Figure 4

[0053] Thus, the present embodiment can form a first stepped work function metal stack structure 140a, wherein the first stepped work function metal stack structure 140a can include a bottom layer work function metal layer B1 and a top layer work function metal layer B2, wherein the two ends E1 / E2 of the bottom layer work function metal layer B1 protrude out of the top layer work function metal layer B2. In the present embodiment, the first stepped work function metal stack structure 140a is formed by depositing the first layer work function metal layer 142a and the second layer work function metal layer 144a respectively, but in other embodiments, the first stepped work function metal stack structure 140a can also be formed by depositing the bottom layer work function metal layer B1 and the top layer work function metal layer B2 respectively, depending on actual conditions.

[0054] As shown, a second layer work function metal layer 144 is formed to cover the first layer work function metal layer 142a. As shown, the second layer work function metal layer 144 can be deposited to conformally cover the recess R1 first. Then, as shown, a photoresist P2 is formed to cover part of the second layer work function metal layer 144 in the recess R1 to pattern the second layer work function metal layer 144 to form a second layer work function metal layer 144a to cover the first layer work function metal layer 142a. Then, the photoresist P2 is removed. Figure 5 As shown, a second stepped work function metal stack structure 150 is deposited to conformally cover the first stepped work function metal stack structure 140a and the substrate 110. The first stepped work function metal stack structure 140a and the second stepped work function metal stack structure 150 are metals that meet the work function requirements of the transistor, which can be a single layer structure or a composite layer structure, such as titanium nitride (TiN), titanium carbide (TiC), tantalum nitride (TaN), tantalum carbide (TaC), tungsten carbide (WC), titanium aluminide (TiAl), or aluminum titanium nitride (TiAlN), etc. In this way, a stepped work function metal stack structure C1 with a middle protrusion is formed, and in a preferred embodiment, the stepped work function metal stack structure C1 with a middle protrusion has a pyramid-shaped stepped cross-sectional structure, but the present application is not limited thereto.​​

[0055] In this embodiment, the first stepped work function metal stack structure 140a and the second stepped work function metal stack structure 150 have different electrical properties. In one embodiment, the first stepped work function metal stack structure 140a has a P-type work function metal (work function between about 4.8 eV and 5.2 eV, such as titanium nitride), and the second stepped work function metal stack structure 150 has an N-type work function metal (work function between about 3.9 eV and 4.3 eV, such as aluminum titanium), but the present application is not limited thereto.

[0056] Then, a low resistivity material 160 is formed to fill the recess Rl, thereby forming a (metal) gate Ml, wherein the low resistivity material 160 can be composed of aluminum, tungsten, titanium aluminum alloy (TiAl), or cobalt tungsten phosphide (CoWP), etc.

[0057] As mentioned above, the present embodiment forms a work function metal gate device 100, wherein the work function metal gate device 100 includes the gate Ml disposed on the substrate 110, and the gate Ml includes the stepped work function metal stack structure C1 with a middle protrusion. The stepped work function metal stack structure C1 with a middle protrusion can include the bottom work function metal layer B1 and the top work function metal layer B2.

[0058] The drift region 112 is disposed in the substrate 110 under part of the gate Ml, and the first insulating structure 14 is disposed in the drift region 112 between the gate Ml and the drain D. The first drift region 114 is disposed in the substrate 110 under part of the gate Ml, and the second insulating structure 16 is disposed in the first drift region 114 between the gate Ml and the source S. Thus, the present application can adjust the channel charge density (especially the channel charge density near the drain D), and reduce the resistance of the drift region 112. In a preferred embodiment, the first stepped work function metal stack structure 140a vertically overlaps a portion of the first insulating structure 14, or a sidewall Tl of the first stepped work function metal stack structure 140a is flush with a sidewall T2 of the first insulating structure 14. In a more preferred embodiment, the bottom work function metal layer B1 vertically covers a gap g1 between the first insulating structure 14 and the second insulating structure 16, and the top work function metal layer B2 vertically overlaps a gap g2 between the drift region 112 and the first drift region 114.

[0059] The above describes the work function metal gate device of the present application with the stepped work function metal stack structure with a middle protrusion. The following describes another embodiment of the present application, which has a work function metal gate device with a stepped work function metal stack structure with a middle recess.

[0060] Figures 6-10This is a cross-sectional schematic diagram illustrating the fabrication process of a functional metal gate device according to another embodiment of the present invention. Figure 6 As shown, a substrate 110 is provided. The substrate 110 is, for example, a silicon substrate, a silicon-containing substrate, a group III-V silicon-coated substrate (e.g., GaN-on-silicon), a graphene-on-silicon substrate, or a silicon-on-insulator (SOI) substrate, etc., semiconductor substrates. In this embodiment, a drift region 112 and a first drift region 114 are formed in the substrate 110, for example, using a doping fabrication process. Next, an insulating structure 12 can be formed in the substrate 110 to electrically insulate each transistor, and a first insulating structure 14 and a second insulating structure 16 can be formed in the substrate 110 to serve as the gate, drain, and source of the high-voltage transistors. The insulating structure 12, the first insulating structure 14, and the second insulating structure 16 are, for example, shallow trench isolation (STI) structures, formed using a shallow trench isolation fabrication process. Detailed formation methods are well known in the art and will not be described in detail here, but the present invention is not limited thereto. In this embodiment, the insulating structure 12 and the first insulating structure 14 are located in the drift region 112, while the insulating structure 12 and the second insulating structure 16 are located in the first drift region 114, but the present invention is not limited thereto.

[0061] A gate oxide layer 20 can be formed first in the substrate 110 between the first insulating structure 14 and the second insulating structure 16. Then, a metal gate is formed on the gate oxide layer 20, the first insulating structure 14, and the second insulating structure 16. Specifically, an interlayer dielectric layer 120 can be deposited first to cover the substrate 110, wherein the interlayer dielectric layer 120 has a groove R2. The method of forming the interlayer dielectric layer 120 may include the following steps: First, a sacrificial gate (not shown) is formed on the gate oxide layer 20, the first insulating structure 14, and the second insulating structure 16; then, a drain D is formed in the drift region 112 between the insulating structure 12 and the first insulating structure 14, and a source S is formed in the first drift region 114 between the insulating structure 12 and the second insulating structure 16. An interlayer dielectric layer (not shown) is deposited all the way on the substrate 110 on the side of the sacrificial gate, and then the sacrificial gate is removed to form a groove R2 in the interlayer dielectric layer 120. In addition, before depositing another inter-dielectric layer, spacer walls 122 can be selectively formed on the side of the sacrificial gate. In this way, after the sacrificial gate is removed, spacer walls 122 can be formed around the groove R2.

[0062] Thereafter, a U-shaped high dielectric constant dielectric layer 132, a U-shaped barrier layer 134, and a first layer of work function metal layer 142 are formed to conform to the recess R2. In one embodiment, a high dielectric constant dielectric layer (not shown), a barrier layer (not shown), and a work function metal layer (not shown) are sequentially deposited to conform to the recess R2, the spacer 122, and the ILD 120, and then the high dielectric constant dielectric layer (not shown), the barrier layer (not shown), and the work function metal layer (not shown) over the recess R2 are removed to form the U-shaped high dielectric constant dielectric layer 132, the U-shaped barrier layer 134, and the first layer of work function metal layer 142 in the recess R2. The U-shaped high dielectric constant dielectric layer 132 can be selected from the group consisting of hafnium oxide (HfO2), hafnium silicon oxide (HfSiO4), hafnium silicon oxynitride (HfSiON), aluminum oxide (Al2O3), lanthanum oxide (La2O3), tantalum oxide (Ta2O5), yttrium oxide (Y2O3), zirconium oxide (ZrO2), strontium titanate oxide (SrTiO3), zirconium silicon oxide (ZrSiO4), hafnium zirconium oxide (HfZrO4), strontium bismuth tantalate (SrBi2Ta2O9, SBT), lead zirconate titanate (PbZrTiO3, PZT), and barium strontium titanate (BaSrTiO3, BST). The U-shaped barrier layer 134 is, for example, a single layer structure or a composite layer structure of tantalum nitride (TaN), titanium nitride (TiN), etc., but the present application is not limited thereto. x Ti 1-x O3,PZT) and barium strontium titanate (Ba x Sr 1-x TiO3,BST), but the present application is not limited thereto.

[0063] Then, a photoresist P3 is formed on the first layer of work function metal layer 142 to pattern the first layer of work function metal layer 142.

[0064] As Figure 7As shown, a first work function metal layer 142 is patterned with photoresist P3 to form a first work function metal layer 142b, exposing part of the barrier layer 134. Subsequently, the photoresist P3 is removed.

[0065] like Figures 8-9 As shown, a second work function metal layer 244a is formed to cover the first work function metal layer 142b. Figure 8 As shown, a second work function metal layer 244 can be deposited first to conform to and cover the groove R2. Then, as... Figure 9 As shown, a second work function metal layer 244 is formed by covering a portion of the groove R2 with a photoresist P4, thereby patterning the second work function metal layer 244, and forming a second work function metal layer 244a covering the first work function metal layer 142b. Subsequently, the photoresist P4 is removed.

[0066] In this way, this embodiment can form a first-step work function metal stack structure 240, wherein the first-step work function metal stack structure 240 may include a bottom work function metal layer B11 and a top work function metal layer B22. The bottom work function metal layer B11 has a first groove r1 and the top work function metal layer B22 has a second groove r2, wherein the second groove r2 perpendicularly overlaps the first groove r1. In a preferred embodiment, the first groove r1 and the second groove r2 share a centerline to form a symmetrical work function metal structure.

[0067] In this embodiment, a first step-like work function metal stack structure 240 is formed by depositing a first work function metal layer 142b and a second work function metal layer 244a respectively. However, in other embodiments, a first step-like work function metal stack structure 240 can also be formed by depositing a bottom work function metal layer B11 and a top work function metal layer B22 respectively, depending on the actual situation.

[0068] like Figure 10As shown, a second stepped work function metal stack structure 250 is deposited conformally covering the first stepped work function metal stack structure 240 and the substrate 110. The first stepped work function metal stack structure 240 and the second stepped work function metal stack structure 250 are metals that satisfy the work function requirement of the transistor, which can be a single layer structure or a composite layer structure, such as titanium nitride (TiN), titanium carbide (TiC), tantalum nitride (TaN), tantalum carbide (TaC), tungsten carbide (WC), titanium aluminide (TiAl), or aluminum titanium nitride (TiAlN), etc. In this way, a concave stepped work function metal stack structure C2 is formed, and in a preferred embodiment, the concave stepped work function metal stack structure C2 has a disc-shaped stepped cross-sectional structure, but the present application is not limited thereto.

[0069] In this embodiment, the first stepped work function metal stack structure 240 and the second stepped work function metal stack structure 250 have different electrical properties. In an embodiment, the first stepped work function metal stack structure 240 has a P-type work function metal (work function approximately between 4.8 eV and 5.2 eV, such as titanium nitride), and the second stepped work function metal stack structure 250 has an N-type work function metal (work function approximately between 3.9 eV and 4.3 eV, such as titanium aluminide).

[0070] Then, a low-resistivity material 260 is formed to fill the recess R2, thereby forming a (metal) gate electrode M2, wherein the low-resistivity material 260 can be composed of a low-resistivity material such as aluminum, tungsten, titanium aluminide (TiAl), or cobalt tungsten phosphide (CoWP).

[0071] As shown, a second stepped work function metal stack structure 250 is deposited conformally covering the first stepped work function metal stack structure 240 and the substrate 110. The first stepped work function metal stack structure 240 and the second stepped work function metal stack structure 250 are metals that satisfy the work function requirement of the transistor, which can be a single layer structure or a composite layer structure, such as titanium nitride (TiN), titanium carbide (TiC), tantalum nitride (TaN), tantalum carbide (TaC), tungsten carbide (WC), titanium aluminide (TiAl), or aluminum titanium nitride (TiAlN), etc. In this way, a concave stepped work function metal stack structure C2 is formed, and in a preferred embodiment, the concave stepped work function metal stack structure C2 has a disc-shaped stepped cross-sectional structure, but the present application is not limited thereto.

[0072] The drift region 112 is disposed in the substrate 110 under part of the gate M2, and the first insulating structure 14 is disposed in the drift region 112 between the gate M1 and the drain D. The first drift region 114 is disposed in the substrate 110 under part of the gate M1, and the second insulating structure 16 is disposed in the first drift region 114 between the gate M1 and the source S. Thus, the present application can adjust the channel charge density between the source S and the drain D, especially near the drain D, and reduce the resistance of the drift region 112. In a preferred embodiment, the second recess r2 of the top work function metal layer B22 vertically covers a gap g3 between the first insulating structure 14 and the second insulating structure 16. In a further preferred embodiment, the first recess r1 of the bottom work function metal layer B11 vertically overlaps a gap g4 between the drift region 112 and the first drift region 114.

[0073] In summary, the present application proposes a work function metal gate device, which sets a gate on a substrate, and the gate can include a protruding stepped work function metal stack structure or a concave stepped work function metal stack structure to adjust the channel charge density and reduce the resistance of the substrate between the source and the drain. The protruding stepped work function metal stack structure preferably has a pyramid-shaped stepped cross-sectional structure. The concave stepped work function metal stack structure preferably has a disc-shaped stepped cross-sectional structure.

[0074] Further, a drain is located in a drift region on the side of a gate, and a source is located in a first drift region on the side of the gate. A first insulating structure is disposed in the drift region between the gate and the drain, and a second insulating structure is disposed in the first drift region between the gate and the source. By adjusting the positions of the metal layers in the stepped work function metal stack structure vertically corresponding to the drift region and the insulating structure, the channel charge density can be locally adjusted, and the resistance of the local substrate or drift region can be changed.

[0075] The above description is only the preferred embodiments of the present application, and any equivalent changes and modifications made according to the claims of the present application should be included in the scope of the present application.

Claims

1. A work function metal gate device, characterized in that, Include: A gate is disposed on a substrate, wherein the gate comprises a centrally protruding stepped work function metal stack structure; A drift region is disposed in the substrate below a portion of the gate; The source is located in the substrate, and the drain is located in the drift region on the side of the gate; as well as A first insulating structure is disposed in the drift region between the gate and the drain. The stepped work function metal stacking structure of the central protrusion has a pyramid-shaped stepped cross-section structure.

2. The work function metal gate device of claim 1, wherein the protruding stepped work function metal stack structure comprises a first stepped work function metal stack structure and a second stepped work function metal stack structure, wherein the second stepped work function metal stack structure conformally covers the first stepped work function metal stack structure and the substrate.

3. The work function metal gate device as claimed in claim 2, wherein the first step-shaped work function metal stack structure and the second step-shaped work function metal stack structure have different electrical properties.

4. The work function metal gate device of claim 2, wherein the first step-like work function metal stack structure includes a bottom work function metal layer and a top work function metal layer, wherein the two ends of the bottom work function metal layer protrude from the top work function metal layer in an extension direction parallel to the substrate.

5. The work function metal gate device as claimed in claim 4, further comprising: A second insulating structure is disposed in the substrate between the gate and the source; and A gate oxide layer is located in the substrate between the first insulating structure and the second insulating structure.

6. The work function metal gate device of claim 5, wherein the underlying work function metal layer vertically covers the gap between the first insulating structure and the second insulating structure.

7. The work function metal gate device of claim 5, further comprising: Another drift region is disposed in the substrate below a portion of the gate, and the drain and the second insulating structure are located in the other drift region, wherein the top work function metal layer vertically overlaps the other drift region and the gap between the drift regions.

8. The work function metal gate device of claim 2, wherein the first stepped work function metal stack structure vertically overlaps a portion of the first insulating structure.

9. The work function metal gate device of claim 2, wherein the sidewall of the first stepped work function metal stack structure is flush with the sidewall of the first insulating structure.

10. A work function metal gate device, comprising: A gate is disposed on a substrate, wherein the gate comprises a recessed stepped work function metal stack structure; A drift region is disposed in the substrate below a portion of the gate; The source is located in the substrate, and the drain is located in the drift region on the side of the gate; as well as A first insulating structure is disposed in the drift region between the gate and the drain. The concave stepped work function metal stacked structure has a disk-shaped stepped cross-sectional structure.

11. The work function metal gate device of claim 10, wherein the recessed stepped work function metal stack structure includes a first stepped work function metal stack structure and a second stepped work function metal stack structure, wherein the second stepped work function metal stack structure conforms to and covers the first stepped work function metal stack structure.

12. The work function metal gate device of claim 11, wherein the first step-type work function metal stack structure and the second step-type work function metal stack structure have different electrical properties.

13. The work function metal gate device of claim 11, wherein the first stepped work function metal stack structure includes a bottom work function metal layer having a first groove and a top work function metal layer having a second groove.

14. The work function metal gate device of claim 13, wherein the second groove vertically overlaps the first groove.

15. The work function metal gate device of claim 14, wherein the first recess and the second recess share a common centerline.

16. The work function metal gate device of claim 15, further comprising: A second insulating structure is disposed in the substrate between the gate and the source; and A gate oxide layer is located in the substrate between the first insulating structure and the second insulating structure.

17. The work function metal gate device of claim 16, wherein the second groove of the top work function metal layer vertically covers the gap between the first insulating structure and the second insulating structure.

18. The work function metal gate device of claim 16, further comprising: Another drift region is disposed in the substrate below a portion of the gate, and the source and the second insulating structure are located in the other drift region, wherein the first groove of the bottom work function metal layer vertically overlaps the other drift region and the gap between the drift regions.

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