A deposition process for cobalt thin films

Abstract

The application discloses a deposition process of cobalt film. The process comprises the following steps: placing a substrate in a reaction cavity, wherein the substrate has a plurality of openings defined by sidewalls and bottoms; a deposition step of depositing a cobalt film on the sidewalls and the bottoms of the openings; an etching step of introducing a metal chloride gas into the reaction cavity to open the sidewall necking of the cobalt film; and cyclically performing the deposition step and the etching step for N times, wherein N is a positive integer greater than or equal to 1, until the step coverage of the cobalt film on the sidewalls reaches a process target requirement. The etching reaction between the metal chloride gas and the cobalt film is utilized to solve the hole blocking problem, and the deposition step and the etching step are cyclically performed for multiple times, so that the thickness and the step coverage of the cobalt film formed in the high aspect ratio opening can both reach the process target requirement.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a cobalt thin film deposition process. Background Technology

[0002] As semiconductor device dimensions continue to shrink and integration density continues to increase, the application of high aspect ratio aperture thin film deposition in semiconductor devices is becoming increasingly common. For example, for logic chip manufacturing processes below 14nm technology nodes, it is typically necessary to use CVD processes to deposit Co (cobalt) metal thin films in high aspect ratio apertures.

[0003] However, as Figure 1 As shown, due to the high aspect ratio of the opening 10', existing techniques for depositing cobalt thin films 20' ( Figure 1 The Co source precursor used, such as CCTBA, preferentially adsorbs and reacts at the top of the opening, resulting in an excessively thick Co film deposited at the top of opening 10', causing pore blockage. Figure 1 The presence of Co (C) makes it difficult for the precursor to continuously penetrate into the interior of the opening 10', preventing the formation of a uniform Co film within the opening 10' and ultimately resulting in a low step coverage. To improve the step coverage, the industry has attempted to address the issue of the Co source precursor failing to continuously reach the bottom of the opening by increasing the precursor flow rate, applying radio frequency, and adjusting the radio frequency power, but the improvement has been limited.

[0004] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a cobalt thin film deposition process to overcome the limitations of existing processes in filling high aspect ratio openings, improve step coverage, and meet the manufacturing requirements of increasingly integrated devices.

[0006] To achieve the above objectives, the present invention provides a cobalt thin film deposition process, comprising:

[0007] A substrate is placed in a reaction chamber, the substrate having several openings defined by sidewalls and bottom;

[0008] Deposition step: Deposit a cobalt thin film on the sidewalls and bottom of the opening;

[0009] Etching step: Introduce metal chloride gas into the reaction chamber to open the sidewall necking of the cobalt film;

[0010] The deposition and etching steps are repeated N times until the cobalt film achieves the required step coverage of the sidewall, where N is a positive integer greater than or equal to 1.

[0011] Optionally, the metal chloride gas includes: MoCl5, WCl m At least one of TiCl4, where m is an integer greater than or equal to 2 and less than or equal to 6.

[0012] Optionally, the etching step is followed by a cleaning step: removing chloride ions remaining on the surface of the cobalt film using hydrogen-containing active particles.

[0013] Optionally, the deposition step, etching step, and cleaning step can be performed repeatedly.

[0014] Optionally, the hydrogen-containing active particles are provided by a remote plasma source, in which hydrogen-containing gas and carrier gas are introduced and ionized to form the hydrogen-containing active particles, which are then transported to the reaction chamber.

[0015] Optionally, the reaction chamber is a PECVD reaction chamber, through which hydrogen-containing gas is introduced, plasma is ignited, and the hydrogen-containing active particles are generated in situ.

[0016] Optionally, the hydrogen-containing gas comprises at least one of hydrogen or ammonia.

[0017] Optionally, the deposition process of the cobalt thin film includes chemical vapor deposition.

[0018] Optionally, the cobalt thin film is formed using a chemical vapor deposition process, comprising: introducing a cobalt source precursor, wherein the cobalt source precursor is thermally decomposed in a reaction chamber to form elemental cobalt metal and deposited on the sidewall and bottom of the opening to form the cobalt thin film.

[0019] Optionally, the cobalt source precursor includes: (3,3-dimethyl-1-butyne)hexacarbonyldicobalt.

[0020] Optionally, the opening has a high aspect ratio, greater than 10:1.

[0021] Optionally, prior to depositing the cobalt film, a diffusion barrier layer is further deposited on the sidewalls and bottom of the opening.

[0022] Optionally, the diffusion barrier layer is at least one of a Ta layer and a TaN layer.

[0023] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0024] This invention employs at least one cycle of deposition and etching steps. The etching step involves a metal chloride gas reacting with an excessively thick Co film (typically located at the top of the opening) on ​​the sidewall of the opening. This process opens up the necking of the Co film's sidewall while minimizing the etching rate compared to reaction gases containing carbon, hydrogen, and fluorine. Furthermore, the etching residue is a metal from the metal chloride, with physical properties similar to Co, thus avoiding significant electrical defects and thermal stress cracking. This solves the problem of hole blockage while preventing over-etching that alters the opening morphology. It allows the precursor of the Co film to continuously penetrate into the opening, forming a uniform and well-shaped Co film. This enables the Co film to achieve the desired thickness and step coverage in high aspect ratio opening structures.

[0025] Furthermore, by adding a cleaning step using hydrogen-containing active particles, on the one hand, chloride ions remaining on the surface of the Co film after the etching step can be removed, thus preventing the residual chloride ions from adversely affecting the coating quality and resistance of the Co film. On the other hand, it can also remove C / O impurities that may remain during the precursor decomposition reaction to form the Co film in the deposition step, further improving the coating quality and resistance performance of the Co film, and ultimately helping to improve the performance and reliability of semiconductor devices. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a partial cross-section of the substrate formed during each step of the existing cobalt thin film deposition process.

[0027] Figure 2 This is a cobalt thin film deposition process provided in one embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of a partial cross-section of the substrate formed during each step of the cobalt thin film deposition process according to an embodiment of the present invention.

[0029] Figure 4 This is a cobalt thin film deposition process provided in another embodiment of the present invention.

[0030] Attached Figure Labels

[0031] Substrate 100; openings 10, 10'; cobalt thin film 20, 20'; diffusion barrier layer 30; metal chloride gas 40. Detailed Implementation

[0032] The cobalt thin film deposition process proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, used only to facilitate and clarify the illustration of the embodiments of this invention. Please refer to the drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0033] The “active particles” mentioned in this article refer to plasma formed by dissociation from a radio frequency source, which includes particles such as free radicals, excited-state atoms, ions, or ionic groups.

[0034] The "step coverage" described in this article is an indicator of the degree of fit between the thin film and the substrate surface features (especially steps, trenches, and other three-dimensional structures). It is usually expressed as the ratio of the film thickness at the bottom or sidewall of a feature (such as a trench) to the film thickness at the top. The closer the step coverage is to 100%, the smaller the difference in film thickness between the step (bottom or sidewall) and the flat area, indicating a more uniform film coverage. However, in actual thin film deposition processes, it is difficult to achieve perfect uniform coverage due to various factors.

[0035] As described in the background section, with the continuous improvement of semiconductor device integration, the aspect ratio of the opening structures to be filled in the devices also increases. This can easily lead to excessively thick Co films deposited at the top of the openings, reducing or even closing the opening top size and causing via blockage. Ultimately, this makes it difficult for the film precursor to continuously penetrate into the opening, preventing the formation of a uniformly covering film inside the opening and resulting in a low step coverage rate. Currently, simply adjusting the conditions of the Co film deposition process itself, such as increasing the precursor flow rate, cannot effectively improve the step coverage rate problem of three-dimensional structure filling, especially for opening structures with high aspect ratios.

[0036] To address this, the present invention adds an etching step to the cobalt thin film deposition step. The etching reaction between the metal chloride gas and the Co thin film at the top of the opening is carried out to open the sidewall necking of the Co thin film, thereby solving the problem of hole blockage. This allows the Co source precursor to continuously enter the opening, ultimately forming a uniformly covered Co thin film inside the opening.

[0037] The following combination Figures 2-4 The embodiments are described in detail below.

[0038] like Figure 2 As shown, one embodiment of the present invention provides a cobalt thin film deposition process, comprising:

[0039] Step 101: Place a substrate 100 in the reaction chamber. The substrate 100 has a plurality of openings 10 defined by sidewalls and bottom. See the structure below. Figure 3 A.

[0040] The reaction chamber is a CVD reaction chamber or a PECVD reaction chamber used for depositing cobalt metal, and the substrate 100 can be a silicon substrate or a compound semiconductor substrate. In semiconductor manufacturing, silicon substrates are often processed with open structures. For example, when used to fabricate integrated circuits, numerous tiny openings, such as contact holes and interconnect holes, are created on the silicon wafer through processes such as photolithography and etching. These openings are mainly used for subsequent metal filling to achieve electrical connections between different device layers.

[0041] In some embodiments, particularly when forming 3D NAND or 3D DRAM devices, the opening 10 has a high aspect ratio, for example, greater than 10:1 or even greater than 20:1. Such high aspect ratio structures present particular challenges when performing metal filling; for example, achieving good step coverage is difficult. The method of the present invention is applicable to cobalt metal filling of opening structures with various aspect ratios.

[0042] Step 102, Deposition step: Deposit a cobalt thin film 20 on the sidewalls and bottom of the opening 10, see structure below. Figure 3 B.

[0043] In this embodiment, before performing step 102, a diffusion barrier layer 30 is deposited on the sidewall and bottom of the opening 10, the structure of which is described in [reference needed]. Figure 3 In step A, the diffusion barrier layer 30 is used to prevent subsequently deposited cobalt metal atoms from diffusing into the surrounding semiconductor material (such as silicon) and causing changes in the electrical properties of the material, thus ensuring the stability of the device's electrical performance. As an example, the diffusion barrier layer 30 is at least one of a Ta layer and a TaN layer.

[0044] The cobalt thin film 20 is further formed using a chemical vapor deposition (CVD) process. Specifically, CCTBA ((3,3-dimethyl-1-butyne)hexacarbonyldicobalt) is used as the cobalt source precursor, and it is transported into the reaction chamber via a carrier gas. The carrier gas can be at least one of helium (He), neon (Ne), argon (Ar), krypton (Kr), etc. The cobalt source precursor transported into the reaction chamber undergoes thermal decomposition under a high-temperature process environment, releasing elemental cobalt metal, which is deposited on the surface of the diffusion barrier layer 30 to form the cobalt thin film 20.

[0045] The reaction process in which CCTBA undergoes thermal decomposition to form elemental cobalt is shown in Equation I below:

[0046] C 12 H 10 O6Co2→C 12-x H 10 O 6-x Co2+(CO) x →Co+CO+C x H y (Equation I, x, y > 0)

[0047] It should be noted that the Co thin film formed by reaction deposition using Formula I may contain residual C / O impurities. The presence of these impurities can adversely affect the performance of the cobalt thin film, such as increasing resistivity and reducing carrier mobility, ultimately affecting the performance of the entire semiconductor device. However, some embodiments of the present invention can solve this problem by removing the ion residue caused by the newly added etching step through a subsequent cleaning step, thereby improving device performance. Specific cleaning steps are detailed below.

[0048] In other embodiments, the cobalt thin film 20 may also be formed using plasma-enhanced chemical vapor deposition (PECVD). Activating the decomposition reaction of the cobalt source precursor with plasma allows the reaction to proceed at a lower temperature.

[0049] In the deposition step, the step coverage of the deposited cobalt film 20 can be improved by adjusting the flow rate and relative ratio of the cobalt source precursor and carrier gas, or by adjusting the power of the radio frequency source (if an radio frequency source is available). However, as mentioned above, in practical applications, it has been found that even with improvements in the flow rate of the precursor or other process parameters, when depositing a cobalt film in an opening structure with a high aspect ratio, the cobalt source precursor still preferentially reacts at the top of the opening 10 to form a thicker cobalt film, reducing or even closing the top size of the opening 10. This makes it difficult for the cobalt source precursor to continuously enter the opening 10, ultimately resulting in insufficient uniformity and low step coverage of the cobalt film formed within the opening 10. Therefore, this invention solves the problem of hole blockage in the opening 10 by adding the following etching step.

[0050] Step 103, Etching Step: Metal chloride gas 40 is introduced into the reaction chamber to open the sidewall necking of the cobalt thin film 20. (See structure below.) Figure 3 C and D.

[0051] In the etching step, the introduced metal chloride gas 40 will etch the Co film at the top of the opening 10, thereby opening the sidewall necking of the cobalt film 20, avoiding the problem of clogging, and ensuring that the cobalt source precursor can continuously enter the interior of the opening 10 and deposit on the sidewall and bottom surface of the opening 10, thereby achieving complete coverage of the sidewall and bottom of the opening 10 by the cobalt film 20 and improving the step coverage of the cobalt film 20.

[0052] In one embodiment, during the etching step, the chloride active ions in the MCl plasma react with Co to generate Co chloride. The metal M can change its valence state to form a low-valence metal chloride, thereby maintaining the electroneutrality requirement of the system. It is also possible that a small portion of the metal M will be deposited on the etched area.

[0053] In one embodiment, the etching step uses chemical etching rather than plasma etching. Chemical etching refers to the etching process that involves a chemical reaction in a plasma-free environment. It is understood that chloride ions can be generated and supplied to the reaction chamber from a remote plasma source, rather than the plasma being excited within the reaction chamber. The purpose of the etching step is to open the sidewall necking of the cobalt film 20, ensuring that the precursor can continuously pass into the opening 10. Therefore, the etching step only needs to achieve a moderate etching effect on the excessively thick Co film on the sidewall of the opening 10; excessive etching is not required in non-target areas. However, the high-energy ion bombardment during plasma etching, while opening the sidewall necking of the cobalt film 20, inevitably causes significant damage to the material in non-target areas (such as the surface of the substrate 100), leading to a decrease in semiconductor device performance. Therefore, chemical etching is used to achieve a gentler etching process, ensuring successful opening of the sidewall necking of the cobalt film 20 while avoiding unnecessary or excessive damage to the material in non-target areas, thereby improving the performance and quality of the semiconductor device.

[0054] In one embodiment, the etching gas used is a metal chloride gas, including TiCl4 and WCl. m At least one of MoCl5, where m is an integer greater than or equal to 2 and less than or equal to 6. The use of the metal chloride gas not only enhances the controllability of the etching step, but also ensures that the trace amount of metal M (M is the metal in the metal chloride gas) remaining in the cobalt film 20 after the etching reaction does not affect the resistivity of the entire cobalt film 20.

[0055] The study found that compared with other etching gases (such as HCl), metal chloride gases can react with cobalt film 20 at a relatively low etching rate to slowly open the sidewall necking of cobalt film 20. Therefore, the etching is more controllable, which is especially beneficial for the filling and formation of thinner Co films in high aspect ratio openings. This avoids the problem of film uniformity and thickness morphology being difficult to control precisely due to excessively fast etching rates.

[0056] During the etching process, the chloride ions of the metal chloride gas undergo a redox reaction with the cobalt metal to form gaseous cobalt chloride products, which are then extracted from the reaction chamber. This opens the sidewall necking of the cobalt film 20, ensuring that the cobalt source precursor can continuously flow into the opening 10, thereby improving the step coverage of the Co film. Simultaneously, a very small amount of metal M may be deposited in the Co film during this etching process, but the residue of metal M will not significantly affect the resistivity of the final cobalt film 20, thus ensuring the stability of the device's electrical performance.

[0057] Step 104: Repeat the deposition and etching steps N times until the cobalt film 20 achieves the target step coverage of the sidewall, where N is a positive integer greater than or equal to 1. (See structure below.) Figure 3 E.

[0058] This invention does not impose a specific limit on the number of cycles. In extreme cases, only one deposition and etching step is required for the formed cobalt film 20 to meet the set process target requirements: the thickness of the cobalt film 20 formed within the opening 10 reaches the required thickness (i.e., the set thickness) and the required step coverage (i.e., the set step coverage). If, during the cycle, either the thickness or the step coverage of the formed cobalt film 20 fails to meet the process target requirements after testing, at least one of the deposition and etching steps needs to be performed again until the thickness and step coverage meet the target requirements. Furthermore, this invention allows the number of deposition and etching steps to be the same during the cycle, and also allows the number of deposition steps to be one more than the number of etching steps; this invention does not impose any restrictions on this.

[0059] Different processes have different requirements for step coverage and cobalt film 20 thickness, and this invention does not impose specific limitations. As an example, the step coverage can be 80%, or it could be 85%, 90%, 95%, or 99%, etc., which can be achieved through multiple cycles of deposition and etching steps in the method of this invention. The set thickness of the cobalt film 20 can be in the nanometer range, for example, less than 3 nm; in other embodiments, the cobalt film 20 can also fill the opening 10.

[0060] This embodiment of the method, based on the cobalt thin film deposition step, introduces a metal chloride gas to perform an etching step, allowing the Co source precursor to continuously penetrate into the opening, ultimately forming a Co thin film with the required step coverage and thickness. However, after etching with metal chloride gas, some chloride ions inevitably remain on the surface of the Co thin film. These residual chloride ions affect the resistivity, corrosion resistance, and other properties of the Co thin film, thereby reducing the performance stability of the semiconductor device. To solve this problem and improve the performance and quality of the device, one embodiment of the present invention provides another cobalt thin film deposition process, such as... Figure 4 As shown, it includes:

[0061] Step 201: Place a substrate in the reaction chamber, the substrate having several openings defined by the sidewalls and the bottom.

[0062] Step 202, Deposition step: Deposit a cobalt film on the sidewalls and bottom of the opening.

[0063] Step 203, Etching step: Introduce metal chloride gas into the reaction chamber to open the sidewall necking of the cobalt film.

[0064] Step 204, Cleaning step: Remove chloride ions remaining on the surface of the cobalt film by using hydrogen-containing active particles.

[0065] Step 205: Repeat the deposition step, etching step, and cleaning step N times until the cobalt film achieves the required step coverage of the sidewall, where N is a positive integer greater than or equal to 1.

[0066] In this embodiment, the specific operation steps and reaction principles of steps 201-203 are the same as those of steps 101-103 mentioned above, and will not be repeated here.

[0067] In step 204, if the reaction chamber is a CVD reaction chamber, the hydrogen-containing active particles are generated by ionizing hydrogen-containing gas using a remote plasma source (RPS), and further introduced onto the surface of the cobalt film via a carrier gas to remove residual chloride ions. The hydrogen-containing gas includes at least one of hydrogen or ammonia, and the carrier gas can be at least one of helium (He), neon (Ne), argon (Ar), krypton (Kr), etc. If the reaction chamber is equipped with a radio frequency source, such as a PECVD reaction chamber, hydrogen-containing gas can be introduced into the reaction chamber to ignite the plasma and generate the hydrogen-containing active particles in situ.

[0068] It is understandable that the cleaning step has a shorter processing time and lower applied power than the etching step in order to avoid affecting the morphology of the cobalt film.

[0069] The cleaning step added in this embodiment, by providing hydrogen-containing active particles, can not only remove chloride ions remaining on the surface of the cobalt film after the etching step, but also remove C / O impurities remaining in the deposition step, significantly reducing the impurity content of the cobalt film and avoiding adverse effects of residual impurities on the corrosion resistance and electrical properties of the film, thereby improving the performance and reliability of the device.

[0070] In summary, this invention performs deposition and etching steps in at least one cycle. During the etching step, a metal chloride gas reacts with an excessively thick Co film (typically located at the top of the opening) on ​​the sidewall of the opening, opening up the necking of the Co film sidewall. Compared to reaction gases containing carbon, hydrogen, and fluorine, this method minimizes the etching rate. Furthermore, the etching residue is a metal from the metal chloride, with physical properties similar to Co, avoiding significant conductivity defects and thermal stress cracking. This solves the problem of via blockage while preventing over-etching that alters the opening morphology, allowing the Co film precursor to continuously penetrate the opening and form a uniform and straight Co film. The thickness and step coverage of the Co film formed in the high aspect ratio opening structure meet the process target requirements. In addition, a cleaning step is added to remove impurities from the Co film, preventing residual impurities from adversely affecting film performance, ultimately improving the performance and reliability of semiconductor devices.

[0071] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A cobalt thin film deposition process, characterized in that, Include: A substrate is placed in a reaction chamber, the substrate having several openings defined by sidewalls and bottom; Deposition step: Deposit a cobalt thin film on the sidewalls and bottom of the opening; Etching step: Introduce metal chloride gas into the reaction chamber to open the sidewall necking of the cobalt film; The deposition and etching steps are repeated N times until the cobalt film achieves the required step coverage of the sidewall, where N is a positive integer greater than or equal to 1.

2. The cobalt thin film deposition process as described in claim 1, characterized in that, The metal chloride gas includes: MoCl5, WCl m At least one of TiCl4, where m is an integer greater than or equal to 2 and less than or equal to 6.

3. The cobalt thin film deposition process as described in claim 1, characterized in that, The etching step is followed by a cleaning step: removing residual chloride ions on the surface of the cobalt film using hydrogen-containing active particles.

4. The cobalt thin film deposition process as described in claim 3, characterized in that, The deposition, etching, and cleaning steps are repeated multiple times.

5. The cobalt thin film deposition process as described in claim 3, characterized in that, The hydrogen-containing active particles are provided by a remote plasma source. Hydrogen-containing gas and carrier gas are introduced into the remote plasma source, and after ionization to form the hydrogen-containing active particles, they are transported to the reaction chamber.

6. The cobalt thin film deposition process as described in claim 3, characterized in that, The reaction chamber is a PECVD reaction chamber, through which hydrogen-containing gas is introduced, plasma is ignited, and the hydrogen-containing active particles are generated in situ.

7. The cobalt thin film deposition process as described in claim 5 or 6, characterized in that, The hydrogen-containing gas includes at least one of hydrogen or ammonia.

8. The cobalt thin film deposition process as described in claim 1, characterized in that, The deposition process of the cobalt thin film includes chemical vapor deposition.

9. The cobalt thin film deposition process as described in claim 8, characterized in that, The cobalt thin film is formed using a chemical vapor deposition process, including: A cobalt source precursor is introduced, which thermally decomposes in the reaction chamber to form elemental cobalt metal, which is deposited on the sidewalls and bottom of the opening to form the cobalt film.

10. The cobalt thin film deposition process as described in claim 9, characterized in that, The cobalt source precursor includes: (3,3-dimethyl-1-butynedi)hexacarbonyldicobalt.

11. The cobalt thin film deposition process as described in claim 1, characterized in that, The opening has a high aspect ratio, greater than 10:

1.

12. The cobalt thin film deposition process as described in claim 1, characterized in that, Prior to depositing the cobalt film, a diffusion barrier layer is also deposited on the sidewalls and bottom of the opening.

13. The cobalt thin film deposition process as described in claim 12, characterized in that, The diffusion barrier layer is at least one of a Ta layer and a TaN layer.

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