Method for improving work function material incubation process

Abstract

The application provides a method for improving incubation process of work function material. The method comprises the following steps: providing a semiconductor substrate, a first work function layer is formed on the surface of the semiconductor substrate; performing etching treatment on the first work function layer to remove the surface oxide layer; performing wet cleaning treatment on the first work function layer after the etching treatment to remove etching residues and form a hydroxyl-containing interface on the surface; and depositing a second work function layer on the surface of the first work function layer with the hydroxyl-containing interface. The composite treatment of etching and wet cleaning can effectively eliminate the surface oxide layer and increase the active growth point position, thereby reducing the incubation process time of film deposition, increasing the deposition thickness and improving the device performance.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit manufacturing, and in particular to a method for improving the incubation process of work function materials. Background Technology

[0002] As the feature size of semiconductor devices continues to shrink, work function materials in advanced processes are typically prepared using atomic layer deposition (ALD). However, the ALD process involves a certain incubation process in the early stages of thin film growth, the duration of which depends primarily on the state of the effective growth sites on the substrate surface.

[0003] In existing integrated circuit manufacturing processes, after the deposition of the lower work function material (such as titanium nitride), a natural oxide layer is easily formed on its surface. This significantly reduces the effective growth sites, thereby significantly prolonging the incubation process of the upper work function material (such as titanium aluminum), resulting in increased process time and insufficient deposition thickness in the same amount of time.

[0004] Therefore, how to effectively eliminate the adverse effects of surface oxide layers and increase surface active growth sites, thereby reducing the incubation process of atomic layer deposition, increasing the film deposition thickness, and improving the electrical performance of devices, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects in the prior art where the incubation process of work function materials is too long and the film deposition thickness is insufficient due to the influence of the natural oxide layer on the surface during thin film deposition, which affects the electrical performance of the device. The present invention provides a method to improve the incubation process of work function materials.

[0006] To address the aforementioned technical problems, this invention provides a method for improving the incubation process of work function materials, comprising:

[0007] Step 1: Provide a semiconductor substrate, wherein a first work function layer is formed on the surface of the semiconductor substrate;

[0008] Step 2: Etch the first work function layer to remove the oxide layer on the surface of the first work function layer;

[0009] Step 3: Perform wet cleaning on the first work function layer after etching to remove etching residues and form a hydroxyl-containing interface on the surface of the first work function layer;

[0010] Step 4: Deposit a second work function layer on the surface of the first work function layer having the hydroxyl-containing interface.

[0011] Preferably, in step one, the material of the first work function layer includes a metal nitride.

[0012] Preferably, in step one, the metal nitride includes titanium nitride.

[0013] Preferably, in step two, the etching gas used for the etching process includes a metal halide-containing gas.

[0014] Preferably, in step two, the metal halide-containing gas includes tungsten chloride gas.

[0015] Preferably, in step three, the cleaning solution used for the wet cleaning process includes an alkaline solution.

[0016] Preferably, in step three, the alkaline solution includes ammonia.

[0017] Preferably, in step four, the deposition of the second work function layer is performed using an atomic layer deposition process.

[0018] Preferably, in step four, the material of the second work function layer includes an aluminum-containing metal layer.

[0019] Preferably, in step four, the aluminum-containing metal layer includes a titanium-aluminum layer.

[0020] As described above, the method for improving the incubation process of work function materials of the present invention has the following beneficial effects:

[0021] By employing a composite process combining dry etching and wet cleaning, the inactive oxide layer on the surface of the underlying work function material was effectively removed, and etching residues were thoroughly eliminated, successfully constructing a dense and uniformly distributed hydroxyl-containing interface on the material surface. This hydroxyl-containing interface provides ample chemisorption and reactive sites for subsequent atomic layer deposition, thereby shortening the nucleation delay and incubation time of thin film growth. Within the same process time, this invention not only significantly improves the deposition thickness and continuity of the upper work function film but also optimizes the interlayer interface quality. When applied to semiconductor device manufacturing, it can generate an effective work function offset of approximately 30 millivolts, which is beneficial for achieving lower drive voltages in complementary metal-oxide-semiconductor (CMOS) devices. Attached Figure Description

[0022] Figure 1 The diagram shows a flowchart of the method for incubating materials with improved work function according to the present invention.

[0023] Figure 2 The diagram shown is a cross-sectional view of a semiconductor substrate with a first work function layer formed according to the present invention.

[0024] Figure 3 The diagram shown is a cross-sectional structure after the oxide layer is removed by etching process according to the present invention.

[0025] Figure 4The diagram shows a cross-sectional structure of the hydroxyl-containing interface formed by the wet cleaning process of the present invention.

[0026] Figure 5 The diagram shown is a cross-sectional structure of the second work function layer after deposition according to the present invention.

[0027] Figure 6 The diagram shows a columnar comparison of the effects of different pretreatment methods on the film deposition thickness according to the present invention.

[0028] Figure 7 The diagram shows a test box schematic illustrating the effect of different pretreatment methods of the present invention on the effective work function of semiconductor devices. Detailed Implementation

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] The embodiments provided in this application relate to semiconductor manufacturing processes, and more specifically, to the manufacturing processes of semiconductor devices such as field-effect transistors (FETs) that form metal gate structures with high gate dielectric constants. As semiconductor manufacturing processes continue to shrink towards advanced process nodes, more stringent standards are being imposed on the thickness control of the work function material layer and the electrical performance of the devices. The composite processing technology proposed in this invention is applied to the manufacturing processes of various complementary metal-oxide-semiconductor (CMOS) devices, including but not limited to planar FETs or FETs with three-dimensional spatial structures, helping semiconductor devices meet the performance requirements of different application scenarios.

[0031] Figure 1 A flowchart of a method for improving the incubation process of work function materials provided in this application embodiment. The method for improving the incubation process of work function materials includes:

[0032] Step 1: Provide a semiconductor substrate, on which a first work function layer 101 is formed;

[0033] In some embodiments, in step one, the material of the first work function layer 101 includes a metal nitride.

[0034] In some embodiments, step one includes titanium nitride.

[0035] Please refer to Figure 2In semiconductor manufacturing equipment, a semiconductor substrate is provided, which may include a bulk semiconductor substrate or a silicon-on-insulator (SOI) substrate. An SOI substrate includes an insulating layer beneath a thin semiconductor layer that serves as the active layer of the SOI substrate. The active layer semiconductor and the bulk semiconductor typically comprise the crystalline semiconductor material silicon, but may also include one or more other semiconductor materials, such as germanium, silicon-germanium alloys, compound semiconductors (e.g., GaAs, AlAs, InAs, GaN, AlN, etc.) or alloys thereof (e.g., GaxAl1-xAs, GaxAl1-xN, InxGa1-xAs, etc.), oxide semiconductors (e.g., ZnO, SnO2, TiO2, Ga2O3, etc.), or combinations thereof. The semiconductor material may be doped or undoped. Other substrates that may be used include multilayer substrates, gradient substrates, or mixed-orientation substrates.

[0036] Before forming the first work function layer 101, an isolation structure, such as a shallow trench isolation structure, and an active region structure defining different conductivity types, such as a P-type device region and an N-type device region, are pre-formed on the semiconductor substrate. An interface layer and a high gate dielectric constant material layer are also sequentially stacked on top of the semiconductor substrate. The interface layer contains silicon oxide or silicon oxynitride, and the high gate dielectric constant material layer contains hafnium oxide, zirconium oxide, aluminum oxide, titanium oxide, lanthanum oxide, or silicate mixtures of these materials. The first work function layer 101 is formed on top of the high gate dielectric constant material layer and serves to regulate the threshold voltage of the semiconductor device. Except for titanium nitride, the material of the first work function layer 101 can be replaced with tantalum nitride, tungsten nitride, molybdenum nitride, or other conductive metal compounds with suitable work function characteristics. The process methods for forming the first work function layer 101 encompass thin film deposition techniques such as physical vapor deposition, chemical vapor deposition, or atomic layer deposition. In actual wafer fabrication processes, after the first work function layer 101 is deposited, the wafer is exposed to an oxygen-containing environment during transfer between different process equipment, or is affected by process queuing time. As a result, a natural oxide layer 102, such as a titanium oxide layer, spontaneously forms on the surface of the first work function layer 101. This surface oxide layer 102 is an inactive structure that covers and consumes the original metal active growth sites on the surface of the first work function layer 101, thereby causing subsequent thin film deposition processes to face a longer incubation process time.

[0037] Step 2: Etch the first work function layer 101 to remove the oxide layer 102 on the surface of the first work function layer 101;

[0038] In some embodiments, the etching gas used in step two includes a metal halide-containing gas.

[0039] In some embodiments, in step two, the metal halide-containing gas includes tungsten chloride gas.

[0040] Please refer to Figure 3 To eliminate the adverse effects of oxide layer 102 on subsequent film deposition, the wafer is transferred to a dry etching chamber for etching. Besides tungsten chloride gas, the metal halide-containing gas is replaced with other halogen-containing reaction gases such as molybdenum chloride, tantalum chloride, titanium chloride, or tungsten hexafluoride, depending on the specific process requirements. When introduced into the chamber, the metal halide-containing gas is mixed with inert carrier gases such as argon, helium, and neon, or diluent gases such as nitrogen, to control the partial pressure and flow rate of the reaction gases. Through the introduction of the gas-phase coherent etching process, the reaction gas molecules chemically react with the oxide layer 102 on the surface, breaking the chemical bonds of the surface oxide and generating volatile byproducts, thereby stripping away the oxide layer 102 on the surface of the first work function layer 101, exposing the first work function layer 101. However, when the oxide layer 102 is removed by dry etching alone, intermediate reaction substances containing tungsten or chlorine and byproducts that have not been completely volatilized adhere to the surface of the first work function layer 101 as etching residues. These residues form a new physical barrier layer that occupies the surface space, thus hindering the growth of subsequent materials.

[0041] Step 3: Perform wet cleaning on the first work function layer 101 after etching to remove etching residues and form a hydroxyl-containing interface 103 on the surface of the first work function layer 101.

[0042] In some embodiments, the cleaning solution used in step three for wet cleaning includes an alkaline solution.

[0043] In some embodiments, in step three, the alkaline solution includes ammonia.

[0044] Please refer to Figure 4To remove etching residues introduced by the dry etching process, the etched wafers are transferred to a wet cleaning system for wet cleaning. Wet cleaning is performed on a single-wafer rotary cleaning table or a multi-wafer immersion cleaning tank. The cleaning solution is applied to the surface of the first work function layer 101 by spraying, atomizing, or direct immersion. In addition to ammonia alone, the alkaline solution can be replaced with tetramethylammonium hydroxide aqueous solution, potassium hydroxide solution, or a mixture of ammonia, hydrogen peroxide, and deionized water. During the wet cleaning process, the chemical components in the cleaning solution dissolve and remove metal- or halogen-containing etching residues left from the preceding dry etching steps, which are then carried away by the deionized water. Simultaneously, hydroxide ions in the alkaline cleaning solution react with the exposed surface of the first work function layer 101, causing hydroxylation of the substrate surface. This process converts dangling bonds or oxygen bridges on the surface into stable hydroxyl bonds, generating a uniformly distributed and densely packed hydroxyl-containing interface 103. If the preceding dry etching is omitted and the first work function layer 101 with dense oxide layer 102 is directly wet-cleaned, the alkaline cleaning solution will have little effect on increasing the thickness of the subsequent film growth because the natural oxide layer has strong chemical inertness and blocks the internal metal.

[0045] Step 4: Deposit a second work function layer 104 on the surface of the first work function layer 101 having a hydroxyl-containing interface 103.

[0046] In some embodiments, in step four, the deposition of the second work function layer 104 employs an atomic layer deposition process.

[0047] In some embodiments, in step four, the material of the second work function layer 104 includes an aluminum-containing metal layer.

[0048] In some embodiments, in step four, the aluminum-containing metal layer includes a titanium-aluminum layer.

[0049] Please refer to Figure 5 After cleaning and drying, the wafer enters the deposition chamber for the deposition of the second work function layer 104. Atomic layer deposition (ALD) achieves thin film growth at the atomic layer level by alternately introducing different precursor gases and purging with an inert gas. The second work function layer 104, as a key film for adjusting the device's work function, replaces the aluminum-containing metal layer with tantalum-aluminum, titanium-aluminum carbide, titanium-aluminum nitride, tantalum-aluminum carbide, or other metal alloy layers that can provide a suitable effective work function, in addition to the titanium-aluminum layer. During the initial stage of ALD, i.e., the incubation process, precursor molecules seek suitable surface adsorption sites. The dense hydroxyl-containing interface 103 provides sufficient chemisorption and reactive sites for precursor molecules containing metal elements such as titanium and aluminum, promoting rapid adhesion, ligand exchange reactions, and nucleation of the precursor gas upon contact with the surface of the first work function layer 101, thereby shortening the nucleation delay stage of thin film growth.

[0050] Combination Figure 6 , Figure 6 This study presents comparative test results showing the effect of different pretreatment methods on the thickness of the second work function layer 104 containing the titanium-aluminum layer within the same deposition time. (Benchmark reference process) Figure 6 The layer marked BSL did not undergo preceding dry etching and wet cleaning. If only the first work function layer 101 is wet cleaned ( Figure 6 The thickness variation is small (marked as WET), indicating that wet cleaning alone is insufficient to overcome the barrier of the dense oxide layer 102 and does not significantly contribute to the increase in thickness. If only the first work function layer 101 is subjected to dry etching (…), Figure 6 The thickness of the deposited layer (marked as WE) further decreased, demonstrating that the etching residue left by the simple dry etching severely hindered the growth of the second work function layer 104. In contrast, the combined dry etching and wet cleaning process provided in this application embodiment (…) Figure 6 The thickness of the deposited layer (labeled WE & WET) is increased. Therefore, the composite treatment method combining dry etching to remove the oxide layer 102 with wet cleaning to achieve surface hydroxylation breaks the limitations of a single process. Compared with the reference process without composite treatment, this invention can increase the thickness of the second work function layer 104 within the same process time. The increased thickness not only improves the continuity and step coverage of the film, but the optimized interface quality is also directly reflected in the electrical performance of the final device.

[0051] Combination Figure 7 , Figure 7 The results of the effective work function comparison obtained through electrical testing of metal-oxide-semiconductor capacitors are presented. After testing, the benchmark reference process ( Figure 7 The baseline level of effective work function corresponding to (marked as BSL) is relatively high. Only dry etching was used ( Figure 7 While the WE-only method can slightly reduce the effective work function, the performance improvement is extremely limited due to the constraints of thin film growth and poor interface quality. When a composite process of dry etching combined with wet cleaning is introduced... Figure 7When the process is labeled as WE+Wet strip, for example, by setting the etching time and adjusting process parameters such as the flow rate of the dry etching gas and the chamber pressure within a certain range, the effective work function of the fabricated semiconductor device shows a significant decreasing trend. Test data shows that the effective work function of the semiconductor device fabricated using this composite process is approximately 30 millivolts lower than that of the reference process. This robust reduction in effective work function helps complementary metal-oxide-semiconductor (CMOS) devices achieve lower drive voltages and better leakage current control, meeting the requirements of design-for-manufacturability (CPM) techniques in advanced processes. After completing the deposition of the second work function layer 104, the semiconductor manufacturing process further includes depositing a main conductive metal layer such as a tungsten layer, an aluminum layer, or other low-resistivity metal material, and performing a chemical mechanical polishing (CMP) process to complete the fabrication of the metal gate structure.

[0052] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0053] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for improving the incubation process of work function materials, characterized in that, At least including: Step 1: Provide a semiconductor substrate, wherein a first work function layer is formed on the surface of the semiconductor substrate; Step 2: Etch the first work function layer to remove the oxide layer on the surface of the first work function layer; Step 3: Perform wet cleaning on the first work function layer after etching to remove etching residues and form a hydroxyl-containing interface on the surface of the first work function layer; Step 4: Deposit a second work function layer on the surface of the first work function layer having the hydroxyl-containing interface.

2. The method for improving the incubation process of work function materials according to claim 1, characterized in that: In step one, the material of the first work function layer includes a metal nitride.

3. The method for improving the incubation process of work function materials according to claim 2, characterized in that: In step one, the metal nitride includes titanium nitride.

4. The method for improving the incubation process of work function materials according to claim 1, characterized in that: In step two, the etching gas used for the etching process includes a metal halide-containing gas.

5. The method for improving the incubation process of work function materials according to claim 4, characterized in that: In step two, the metal halide-containing gas includes tungsten chloride gas.

6. The method for improving the incubation process of work function materials according to claim 1, characterized in that: In step three, the cleaning solution used for the wet cleaning process includes an alkaline solution.

7. The method for improving the incubation process of work function materials according to claim 6, characterized in that: In step three, the alkaline solution includes ammonia.

8. The method for improving the incubation process of work function materials according to claim 1, characterized in that: In step four, the second work function layer is deposited using an atomic layer deposition process.

9. The method for improving the incubation process of work function materials according to claim 1, characterized in that: In step four, the material of the second work function layer includes an aluminum-containing metal layer.

10. The method for improving the incubation process of work function materials according to claim 9, characterized in that: In step four, the aluminum-containing metal layer includes a titanium-aluminum layer.

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