Gate structure comprising an effective work function tunable work function metal layer and method of making the same

Abstract

The present application belongs to the technical field of semiconductor, and particularly relates to a gate structure containing an effective work function adjustable work function metal layer and a preparation method thereof. The gate structure comprises a semiconductor substrate, a gate dielectric layer, a work function metal layer, and the material of the work function metal layer is TiAlC. The work function metal layer is changed in density so that the effective work function of the metal is regulated to the effective work function required by the target threshold voltage, and other gate layers. In the process of forming the work function metal layer on the gate dielectric layer, the work function metal layer with different densities is obtained through different process conditions, so that the effective work function of the metal is regulated to the effective work function required by the target threshold voltage. The different process conditions include the pretreatment process of the gate dielectric layer and / or the deposition process of the work function metal layer. The present application only needs one layer of work function metal layer to realize the regulation of the threshold voltage, meets the multi-threshold voltage device, avoids the complex process of other work function regulation methods, and reduces the manufacturing cost.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, specifically relating to a gate structure containing a work function metal layer with adjustable effective work function and its preparation method. Background Technology

[0002] The rapid development of integrated circuits has led to continuous scaling down of the size of metal-semiconductor-oxide-semiconductor field-effect transistors (MOSFETs) as the most fundamental components, aiming for higher circuit density. As devices shrink, the gate dielectric layer becomes increasingly thinner, increasing leakage current. The solution is to replace the traditional silicon dioxide gate dielectric layer with a high-k material (a material with a higher dielectric constant compared to silicon oxide), while replacing the polysilicon gate with a metal gate. N-type and P-type field-effect transistors (NMOS) have different threshold voltages, requiring different voltage ranges in circuit design. Currently, adjusting the work function of the gate metal to regulate the device threshold voltage is a common and effective method. Traditional single-material gate metals have low work function regulation efficiency; therefore, one or more work function metal layers are added to the gate, forming a multi-layer stacked structure with diffusion barrier layers. This allows for accurate adjustment of the effective work function of the metal, thus meeting the manufacturing requirements of multi-threshold voltage devices.

[0003] Work function metal layers are currently mostly grown using atomic layer deposition (ALD). Different material compositions, film thicknesses, growth temperatures, and other process parameters all affect the effective work function of the metal. ALD-grown films have a disordered structure, and the structure and density of each atomic layer strongly depend on surface reconstruction characteristics. Furthermore, due to steric hindrance, even if each cycle reaches saturation, the saturation density is still lower than the atomic density of the bulk material's crystal planes. The density of the atomic layers also varies depending on different process conditions.

[0004] The complex processes involved in work function regulation not only significantly increase costs but also limit the choice of gate materials. Finding an effective method to regulate the effective work function of metals is an important issue in high-k dielectric / metal gate engineering. Summary of the Invention

[0005] The purpose of this invention is to provide a gate structure and its fabrication method that includes an effective work function metal layer with adjustable work function, which is simple to process and easy to operate, so as to facilitate the realization of multi-threshold voltage devices.

[0006] The gate structure provided by the present invention includes a work function metal layer with adjustable effective work function, comprising:

[0007] Gate dielectric layer formed on semiconductor substrate;

[0008] An interface layer may exist between the gate dielectric layer and the substrate;

[0009] The work function metal layer above the gate dielectric layer is made of TiAlC. By changing the density of this work function metal layer, the effective work function of the metal can be tuned to meet the effective work function required by the target threshold voltage.

[0010] Other gate layers above the work function metal layer.

[0011] This invention also provides a method for fabricating a gate structure containing a work function metal layer with adjustable effective work function. The method focuses on how, during the formation of the work function metal layer, the density is changed to adjust the effective work function of the metal to meet the requirements of the target threshold voltage. The formation of the remaining parts of the structure employs conventional processes. The specific steps are as follows:

[0012] An interface layer is formed on the semiconductor substrate;

[0013] A gate dielectric layer is formed on the interface layer;

[0014] A work function metal layer is formed on the gate dielectric layer. During the formation process, different density work function metal layers are obtained through different process conditions, so that the effective work function of the metal is regulated to meet the effective work function required by the target threshold voltage.

[0015] Other gate layers are formed above the work function metal layer.

[0016] Specifically, obtaining work function metal layers of different densities through different process conditions includes: pre-treating the surface of the gate dielectric layer material before forming the work function metal layer; and forming the work function metal layer through a process.

[0017] (1) Before the work function metal layer, the surface of the gate dielectric layer material is pretreated; the pretreatment methods include oxygen plasma treatment and 185nm ultraviolet lamp irradiation treatment. Wherein:

[0018] Plasma treatment of a surface includes selectable conditions for controlling one or more of the following: plasma treatment power, plasma treatment time, and plasma gas pressure. For example, plasma power can be from 20W to 100W, plasma treatment time from approximately 1 minute to approximately 10 minutes, and plasma treatment pressure can be 1 torr.

[0019] The surface is treated by irradiation with a 185nm ultraviolet lamp, including one or more selectable conditions such as treatment time and treatment temperature. For example, the treatment time is from 1 minute to about 10 minutes, and the treatment temperature is from 10°C to 30°C;

[0020] (2) The process of forming the functional metal layer is to use atomic layer deposition process, and the material is TiAlC (metallic titanium aluminum carbon); the deposition temperature is controlled to be 300℃ to 450℃.

[0021] This invention provides a gate structure comprising a single-layer work function metal layer. By using different process conditions, work function metal layers of different densities are obtained, effectively adjusting the effective work function of the metal, facilitating threshold voltage adjustment, and enabling the realization of multi-threshold voltage devices. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the process of forming work function metal layers of different densities in this invention.

[0023] Figure 2-4 A flowchart illustrating an embodiment of the present invention is shown.

[0024] Figure 5 A schematic diagram showing the results of an embodiment of the present invention is presented. Detailed Implementation

[0025] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings; however, it should be understood that these descriptions of the disclosed embodiments are merely exemplary. The present invention may be implemented in many different forms and should not be construed as limiting the invention. Furthermore, in the following description, details of well-known features and techniques are omitted to avoid unnecessarily obscuring the presented embodiments.

[0026] The accompanying drawings show structural schematic diagrams of embodiments of the present invention. These drawings are not to scale, and some details may be enlarged or omitted for clarity. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary. In practice, there may be deviations due to manufacturing or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0027] The gate structure in this invention can be formed on planar devices, three-dimensional devices, or gate-around devices. Planar devices form the gate dielectric layer and gate on a semiconductor substrate. Three-dimensional devices, such as fin field-effect transistors (FinFETs), form the gate dielectric layer and gate on fins. Gate-around devices, such as nanowire transistors, form the gate dielectric layer and gate on nanowires.

[0028] The inventors discovered a close relationship between the Fermi level and work function of the work function metal titanium-aluminum-carbon and the film density. The effective work function of the metal can be controlled by adjusting the density of the work function metal layer, thereby enabling multi-threshold devices. Therefore, a method for adjusting the effective work function of a metal by controlling its material density is proposed. Specifically, the material density of the work function metal layer is adjusted by controlling the process conditions during atomic layer deposition, such as the growth temperature; the material density of the work function metal layer is also adjusted by pre-treating the gate dielectric material and its surface; thus, the effective work function of the work function metal can be effectively controlled.

[0029] The method proposed in this invention based on density-controlled effective work function of metals, referencing... Figure 1 As shown, the process includes: depositing a gate dielectric layer on a semiconductor substrate; controlling the density of the work function metal layer on the gate dielectric through process conditions to obtain the target effective work function of the metal; and depositing other gate layers on the metal work function layer.

[0030] The method for fabricating a gate structure comprising metal layers with different work functions, as proposed in this invention, includes the following specific steps:

[0031] First, refer to Figure 2 As shown, a substrate 100 is provided. The substrate can be a suitable substrate of various forms, such as bulk semiconductor materials like Si substrates, Ge substrates, etc., or compound substrates such as GaAs, SiC, InP, InGaAs, GaN, etc., or layered structures such as silicon-on-insulator (SOI), etc. However, it should be noted that this disclosure is not limited thereto.

[0032] Next, a dummy gate dielectric layer 101 and a dummy gate layer 102 are deposited sequentially. The dummy gate dielectric layer material can be an oxide such as silicon dioxide, and the dummy gate layer material can be polysilicon.

[0033] Then, a pseudo-gate stack structure is formed by photolithography to serve as a mask for ion implantation.

[0034] Subsequently, a nitride layer is deposited, and a sidewall structure 103 is formed by selective etching such as reactive ion etching. The sidewall is used as a mask for source / drain implantation, and the implanted ions are activated by annealing to form the source / drain region.

[0035] Then, an interlayer dielectric layer 104 is applied, which may include materials such as silicon dioxide, borosilicate glass, phosphosilicate glass, and silicon nitride. The layer is then planarized, such as by chemical mechanical polishing, until the dummy gate stack structure is exposed.

[0036] Next, remove the dummy gate stack structure.

[0037] Specifically, selective etching techniques such as wet etching are used to remove the dummy gate stack structure, forming openings, such as... Figure 3As shown.

[0038] Next, a real grid stack is formed within the opening.

[0039] Optionally, an interface layer (not shown) may exist between the gate dielectric and the substrate. This interface layer is typically formed by rapid oxidation of the substrate surface to improve interface characteristics. Then, the gate dielectric layer 105 and the work function metal layer 106 are deposited sequentially, as follows: Figure 4 As shown, the gate dielectric layer material can be a high-k material such as hafnium-based oxide, hafnium dioxide, hafnium zirconium oxide, etc., and the work function metal layer material includes titanium aluminum carbon, titanium nitride, etc. In this example, the gate dielectric layer material is hafnium dioxide with a thickness of about 1-2 nm, and the work function metal layer material is titanium aluminum carbon with a thickness of about 1-5 nm.

[0040] In this invention, the work function metal layer 106 is formed by atomic layer deposition. The density of this work function metal layer changes the effective work function of the metal, thus serving as a material layer for controlling the effective work function. In this example, the density of the work function metal layer can be controlled by changing the process temperature during atomic layer deposition.

[0041] In this embodiment, the work function metal layer 106 is made of titanium aluminum carbon (TIA). The precursors in the atomic layer deposition process are titanium tetrachloride and trimethylaluminum. Titanium tetrachloride serves as the Ti source, and trimethylaluminum as the Al source. The carrier gas is high-purity nitrogen, with a pulse introduction time of 0.2 s. The gas pulse introduction sequence is titanium tetrachloride, nitrogen, trimethylaluminum, and then nitrogen. The reaction chamber pressure ranges from 1 torr to 10 torr. Depending on the choice of precursor, the TiAlC layer deposition process temperature ranges from 300°C to 450°C. Four process temperatures were selected: 300°C, 325°C, 350°C, and 375°C, resulting in a work function metal layer with gradually increasing density. The effective work function of the metal is calculated using a flat-band voltage measurement method. The results in this example are as follows: Figure 5 As shown, the effective work function of a metal can be controlled by density regulation.

[0042] Furthermore, the present invention proposes a density-controlled metal effective work function method. Different processing methods during the growth of the work function metal layer can include different pretreatments of the gate dielectric layer 105 surface to obtain work function metal layers 106 with different densities, thereby achieving control over the metal's effective work function. In atomic layer deposition, the growth of a single atomic layer is closely related to the material surface reconstruction characteristics. By changing the surface reconstruction characteristics of the gate dielectric layer 105, work function metal layers 106 with different densities can be obtained, thus achieving control over the metal's effective work function. In another example, after depositing the gate dielectric layer 105, it can be treated with oxygen plasma in an oxygen atmosphere. The plasma power is 20W to 100W, the plasma treatment time is approximately 1 minute to approximately 10 minutes, and the plasma treatment pressure is 1 torr. After treatment, a higher density work function metal layer can be obtained. Alternatively, a 185nm ultraviolet lamp can be used to pre-treat the surface of the gate dielectric layer. The treatment atmosphere is air, the treatment pressure is atmospheric pressure, the treatment time is about 1 minute to about 10 minutes, and the treatment temperature is 10°C to 30°C. This can also yield a higher density work function metal layer.

[0043] It should be noted that the above description uses the back-gate process as an example. However, this disclosure is not limited to this and can also be applied to the front-gate process. In addition, the above description does not provide a detailed description of the processing and parameters of the back-gate process itself, and those skilled in the art can design various suitable parameters and processing methods.

[0044] Next, the other gates 107 are deposited. These other gates may typically include one or more layers such as a gate dielectric protection layer and a diffusion barrier layer, and the materials may include metals such as titanium nitride, copper, and tungsten.

[0045] The embodiments of this disclosure have been described above, but these embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Those skilled in the art should understand that various changes in form and detail can be made without departing from the scope defined by the claims of the present invention.

Claims

1. A method for fabricating a gate structure comprising a metal layer with an effective work function adjustable work function, characterized in that, The specific steps are as follows: An interface layer is formed on the semiconductor substrate; A gate dielectric layer is formed on the interface layer; A work function metal layer is formed on the gate dielectric layer. During the formation process, different density work function metal layers are obtained through different process conditions, so that the effective work function of the metal is regulated to meet the effective work function required by the target threshold voltage. Other gate layers are formed above the work function metal layer; The process of obtaining work function metal layers of different densities through different process conditions specifically includes: pre-treating the surface of the gate dielectric layer material before forming the work function metal layer; wherein: Before the work function metal layer, the surface of the gate dielectric layer material is pretreated; the pretreatment methods include oxygen plasma treatment or 185nm ultraviolet lamp irradiation treatment; wherein: Plasma-treated surfaces include one or more selectable conditions for controlling plasma treatment power, plasma treatment time, and plasma gas pressure. Surface irradiation with 185nm ultraviolet lamp, including one or more selectable conditions for controlling processing time and processing temperature; The process for forming the functional metal layer is atomic layer deposition, using TiAlC as the material; the deposition temperature is controlled between 300℃ and 450℃. When treating a surface with plasma, the plasma power is controlled to be 20W to 100W, the plasma treatment time is 1 minute to 10 minutes, and the plasma treatment pressure is 1 torr.

2. The preparation method according to claim 1, characterized in that, When the surface is irradiated with a 185nm ultraviolet lamp, the treatment time is controlled to be 1 to 10 minutes and the treatment temperature is controlled to be 10℃ to 30℃.

3. The gate structure comprising an effective work function adjustable work function metal layer obtained by the preparation method described in claim 1 or 2, characterized in that, include: Gate dielectric layer formed on semiconductor substrate; An interface layer exists between the gate dielectric layer and the substrate; The work function metal layer above the gate dielectric layer is made of TiAlC. By changing the density of the work function metal layer, the effective work function of the metal can be tuned to meet the requirements of the target threshold voltage. Other gate layers above the work function metal layer.

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