Linerless continuous amorphous metal film

Abstract

Embodiments described herein generally relate to methods of depositing thin films, and more specifically, to depositing metal thin films. The methods herein provide a nucleation free conversion (NFC) method, which involves forming an amorphous silicon layer on a dielectric layer and performing an NFC process, the NFC process being used to convert the amorphous silicon layer into a metal thin film. In some embodiments, the NFC process is performed multiple times until the resulting thin metal film is continuous. Bulk metal is formed on top of the thin metal film.

Description

Background Art Technical Field

[0001] Embodiments described herein relate generally to methods of depositing thin films, and more particularly, to depositing metal thin films.

[0002] Related technical notes

[0003] As circuit integration increases, the need for greater uniformity and process control over layer thickness is also increasing. As a result, various techniques have been developed to deposit layers on substrates in a cost-effective manner while maintaining control over the properties of the layers. Chemical vapor deposition (CVD) is one of the most common deposition processes used to deposit layers on substrates. CVD is a flow-dependent deposition technique that requires precise control of substrate temperature and precursors introduced into the processing chamber in order to produce a desired layer of uniform thickness. As substrate size increases, these requirements become more critical, resulting in more complex requirements for chamber design and gas flow technology to maintain adequate uniformity.

[0004] A variant of CVD that exhibits excellent step coverage is atomic layer deposition (ALD). ALD is based on atomic layer epitaxy and uses chemical adsorption technology to transfer precursor molecules to the substrate surface in a sequential cycle. The cycle exposes the top of the substrate surface to a first precursor, a purge gas, a second precursor, and a purge gas. The first precursor and the second precursor react to form a product compound as a film on the substrate surface. Repeat the cycle to form the layer to a desired thickness. Due to the increasing integration of semiconductor circuits, tungsten has been used to achieve excellent step coverage. As a result, due to the high yield of the process, the deposition of tungsten using CVD technology has been widely used in semiconductor processing. However, there are disadvantages in depositing tungsten by traditional CVD and ALD methods.

[0005] For example, the ALD process deposits tungsten films into vias with high aspect ratios, whereas conventional CVD processes will typically result in similar vias being "pinch-off" and not completely filling features formed in a dielectric layer formed on a substrate. Additionally, ALD tungsten films do not adhere well to silicon or silicon oxide substrate surfaces. Therefore, a titanium nitride barrier / glue layer is used to improve adhesion. However, the titanium nitride barrier / glue layer takes up space in the formed features, and titanium nitride does not conduct electricity well, resulting in very high resistance, which affects the performance of the formed metal contacts. The deposition of the titanium nitride layer can also be time consuming and adds additional complexity to the overall process.

[0006] Therefore, there is a need for improved techniques to deposit tungsten layers without barrier / glue layers and produce bulk metal-containing contacts with low resistance. Summary of the invention

[0007] One or more embodiments described herein are directed to methods for forming thin films.

[0008] In one embodiment, a method for filling a feature formed on a surface of a substrate includes: forming a continuous metal layer on the feature formed on the surface of the substrate, wherein the process of forming the continuous metal layer includes: (a) forming an amorphous silicon layer on the exposed surface of the feature; (b) converting the formed amorphous silicon layer into a metal film, wherein the process of converting the amorphous silicon layer includes exposing the amorphous silicon layer to a metal-containing precursor until substantially all silicon atoms in the amorphous silicon layer are replaced with one or more metal atoms found in the metal-containing precursor; and (c) repeating (a) and (b) at least twice and until a continuous film containing metal atoms is formed on the surface of the feature; and filling the feature formed on the surface of the substrate by forming a bulk metal layer on top of the formed continuous film.

[0009] In another embodiment, a method for forming a thin film on a surface of a substrate includes: forming a continuous metal layer on a feature formed on the surface of the substrate, wherein the process of forming the continuous metal layer includes: (a) forming an amorphous silicon layer on the exposed surface of the feature; (b) converting the formed amorphous silicon layer into a metal film, wherein the process of converting the amorphous silicon layer includes exposing the amorphous silicon layer to a metal-containing precursor until substantially all silicon atoms in the amorphous silicon layer are replaced with one or more metal atoms found in the metal-containing precursor; and (c) repeating (a) and (b) at least twice, and until a continuous thin film containing metal atoms is formed on the surface of the feature, and the film is between about 10 angstroms and about 100 angstroms; and filling the feature formed on the surface of the substrate by forming a bulk metal layer on top of the formed continuous film.

[0010] In yet another embodiment, a method for forming a thin film includes: forming a continuous metal layer on a feature formed on a surface of a substrate, wherein the process of forming the continuous metal layer includes: (a) forming an amorphous silicon layer on the exposed surface of the feature, wherein the amorphous silicon layer is between about 10 angstroms and about 40 angstroms; (b) converting the formed amorphous silicon layer into a metal film, wherein the process of converting the amorphous silicon layer includes exposing the amorphous silicon layer to a metal-containing precursor until substantially all silicon atoms in the amorphous silicon layer are replaced with one or more metal atoms found in the metal-containing precursor; and (c) repeating (a) and (b) at least twice, and until a continuous thin film containing metal atoms is formed on the surface of the feature and the film has a thickness between about 10 angstroms and about 100 angstroms; and filling the feature formed on the surface of the substrate by forming a bulk metal layer on top of the formed continuous thin film. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order that the manner in which the above-mentioned features of the present disclosure can be understood in detail, the present disclosure briefly summarized above may be described in more detail by reference to embodiments, some of which are shown in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only typical embodiments of the present disclosure and are therefore not to be considered limiting of its scope, as the present disclosure may admit of other equally effective embodiments.

[0012] FIG1 is a schematic diagram of a membrane stack in the prior art;

[0013] Figure 2 is a method for forming a membrane stack according to at least one embodiment described herein;

[0014] Figure 3A is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0015] Figure 3B is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0016] Figure 3C is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0017] Figure 3D is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0018] Figure 3E is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0019] Figure 3F is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0020] Figure 3G is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0021] Figure 3H is a schematic diagram of a membrane stack according to at least one embodiment described herein;

[0022] Fig. 3I is a schematic diagram of a membrane stack according to at least one embodiment described herein; and

[0023] Figure 3J is a schematic diagram of a membrane stack according to at least one embodiment described herein.

[0024] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. DETAILED DESCRIPTION

[0025] In the following description, many specific details are set forth to provide a more thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that one or more embodiments of the present disclosure may be practiced without one or more of these specific details. In other cases, well-known features are not described to avoid obfuscating one or more embodiments of the present disclosure.

[0026] Embodiments described herein generally relate to methods for depositing thin films, and more specifically, to depositing metal films. The methods herein provide a nucleation free conversion (NFC) method, which involves providing a substrate and forming a dielectric layer on the substrate. An amorphous silicon (α-Si) layer is formed on the dielectric layer. An NFC process is performed, and the NFC process is used to convert the amorphous silicon layer into a thin metal film after performing the NFC process. However, due to the significant volume reduction that occurs during the conversion portion of the NFC process, the resulting thin metal film is generally discontinuous, resulting in isolated metal islands. Therefore, in one or more embodiments described herein, the NFC process may be performed multiple times, wherein the amorphous silicon layer fills the gap left by the previous round of the NFC process, and then the amorphous silicon is converted into a thin metal film. These process steps are performed multiple times until the resulting thin metal film is continuous. When the resulting thin metal film is continuous, a bulk metal is formed on the thin metal film. The method described herein is advantageous because the NFC method is used to make the resistance (R) of the formed metal-containing features (e.g., metal contacts, vias, or trenches) less than that of the conventionally formed metal-containing features. Additionally, the NFC methods described herein also create bulk metals with good material coverage due to the continuous nature of the formed metal films.

[0027] FIG. 1 is a schematic diagram of a film stack 100 in the prior art. The film stack 100 includes a dielectric layer 104 disposed on a substrate 102. Although a bulk metal layer 108 may be disposed on the dielectric layer 104, metals such as tungsten do not easily adhere to the surface of the dielectric layer 104. Therefore, in order to increase the adhesion of the bulk metal layer 108 (such as tungsten (W)) to the surface of the dielectric layer 104, conventional processes use a barrier layer 106 (also referred to as a glue layer) disposed on the dielectric layer 104. The barrier layer 106 is typically a titanium nitride (TiN) film or other similar film. However, the deposition of the barrier layer 106 may be time consuming and add additional complexity to the entire process. In addition, the barrier layer 106 does not conduct electricity well, resulting in very high resistance of the metal contacts containing the bulk metal layer 108 and the barrier layer 106. Therefore, an improved method is needed to deposit thin metals without a barrier layer 106 that will reduce the resistance of the formed metal contacts. The embodiments herein include methods that will meet this need.

[0028] Figure 2 A method 200 for forming a film stack according to at least one embodiment of the present invention is provided. The method 200 is used to create a film stack that can deposit thin metal without a barrier layer, which will ultimately reduce the resistance of the metal in a metal-containing feature (e.g., a metal contact, via, or trench) formed on a surface of a substrate, making the metal-containing feature more conductive and thus improving the RC constant of the device. FIG. 3A to FIG. 3J 2 are schematic diagrams of a film stack 300 that illustrate the structure of the film stack 300 at each block of the method 200 , according to at least some embodiments described herein.

[0029] In block 202, as Figure 3A As shown, a substrate 302 is provided. The substrate 302 may consist essentially of a dielectric or semiconductor material such as silicon, silicon oxide, gallium nitride (GaN), or aluminum oxide. As used in this regard, "consisting essentially of" means that the substrate includes greater than 95%, 98%, 99%, or 99.5% of the material in terms of atomic percentage. Those skilled in the art will recognize that terms such as silicon oxide and aluminum oxide do not convey any specific atomic ratios. These materials may be stoichiometric or non-stoichiometric.

[0030] In block 204, also Figure 3A As shown, a dielectric layer 304 is formed over substrate 302. Dielectric layer 304 may also consist essentially of silicon nitride, silicon oxide, or aluminum oxide.

[0031] In block 206, if Figure 3B As shown, an amorphous silicon layer 306 is formed on the dielectric layer 304. In some embodiments, during the NFC process, the substrate surface is maintained at a temperature between about 250 degrees Celsius and about 500 degrees Celsius. The precursors used in block 206 may include SiH4 and Si2H6 with H2, which may be a thermal process or a plasma enhanced process. In some embodiments, the plasma enhanced process occurs at a radio frequency (RF) power range between about 50W and about 500W. The gas flow in block 206 may be between about 100sccm and about 1000sccm.

[0032] In block 208, the amorphous silicon layer 306 is converted to a thin film comprising a metal. In one embodiment, the conversion process includes forming a metal film by a replacement reaction with the silicon material in the formed amorphous silicon layer. The conversion process includes exposing the silicon layer to a halogen-based metal precursor containing a metal such as tungsten, tantalum, molybdenum, titanium, etc. and a halogen such as F, Cl, Br, and I. The conversion reaction will generally include the following reactions:

[0033] 2WF6+3Si→2W+3SiF4

[0034] In some embodiments, block 208 of the NFC process is performed at a pressure between about 5 Torr and about 20 Torr. In some embodiments, during the NFC process, the substrate surface is maintained at a temperature between about 250 degrees Celsius and about 500 degrees Celsius. The precursor used in block 206 may include tungsten hexafluoride (WF6) with H2 and / or a carrier gas, and the precursor may be plasma enhanced. In some embodiments, the plasma enhanced process occurs at an RF power range between about 50W and about 500W. The gas flow in block 208 may be between about 100sccm and about 1000sccm. The resulting resistivity of the bulk metal layer 310 may be less than or equal to about 20μΩ-cm, such as about 15μΩ-cm.

[0035] The resulting thin film metal may consist essentially of tungsten. Figure 3C-3H Shown in. Figure 3C 3 is a film stack 300 having an amorphous silicon film 306 initially formed on an exposed surface of a substrate 302 before the conversion step of the process begins. Figure 3C-3H The dielectric layer 304 is not shown in FIG. The amorphous silicon film 306 may be about 20 angstroms thick, or in the range of about 10 angstroms to 40 angstroms thick. If the thickness of the deposited amorphous silicon film 306 is too great, it is possible that not all of the silicon layer will be completely converted (i.e., removed and replaced by a metallic material) in subsequent processing steps.

[0036] Figure 3D 206 and 208 of method 200, which is sometimes referred to herein as an NFC process. However, although the process produces an NFC film 308, the NFC film 308 is discontinuous and, therefore, includes isolated metal islands. The isolated islands are produced because during the NFC process, the conversion process of the amorphous silicon film 306 to the metal-containing NFC film 308 involves a significant volume reduction, resulting in the resulting NFC film 308 being discontinuous, as shown in FIG. Figure 3D As shown. For example, assuming an amorphous silicon film 306 of about 20 angstroms, the volume reduction may result in isolated metal islands of about 10 angstroms in size. The volume reduction and the resulting isolated islands occur particularly in very high aspect ratio structures such as 3D NAND structures. When the bulk metal layer 310 ( Figure 3J ), which in turn creates coverage issues. Therefore, the method 200 creates a resulting continuous NFC film 308 to help prevent this problem.

[0037] To create a continuous NFC film 308, block 210 determines whether the resulting NFC film 308 is discontinuous. If not, the method may proceed to block 212. However, if yes, blocks 206 and 208 of the method 200 will be repeated as many times as necessary to create a continuous NFC film 308. For example, Figure 3D A discontinuous NFC film 308 is depicted as described above. Therefore, block 210 will attempt to repeat blocks 206 and 208 of method 200 for another round (second round) and proceed to Figure 3E The content shown. Figure 3E In the embodiment, another amorphous silicon layer 306 is formed on the discontinuous NFC layer 308. The additional amorphous silicon layer 306 may also be about 20 angstroms, or in the range of about 10 angstroms to 40 angstroms. The amorphous silicon layer 306 may be completely amorphous or have an amorphous phase containing very small grains.

[0038] While not intending to be bound by theory, it is believed that the amorphous structure of the amorphous silicon film 306 enhances the ability of the conversion process performed in block 208 to fully convert the amorphous silicon film 306 to a metal layer relative to a non-amorphous crystalline containing silicon film due to the difference or degree of bonding of silicon atoms in these different crystal structures. Figure 3D-3E The gaps between the isolation islands are shown, and the execution of blocks 206 and 208 of method 200 produces Figure 3F NFC film 308 is shown. The NFC film 308 with the second round of volume reduction as described above can produce a thickness of about 20 angstroms (10 angstroms + 10 angstroms). However, the second round of frames 206 and 208 may create an imperfect film that does not completely cover the gaps formed in the previous round. In this embodiment, in frame 210, it can be found that Figure 3F The NFC film 308 in the embodiment is still discontinuous, and another round (third round) of the method 200 of the frame 206 and the frame 208 is performed to form the Figure 3G The content shown is essential. Figure 3G In, similar to Figure 3E , another amorphous silicon layer 306 is formed on the discontinuous NFC layer 308. In this embodiment, the third round of amorphous silicon layer 306 is filled with Figure 3F-3G Similarly, the amorphous silicon film 306 is uniformly formed in the gap on the dielectric layer 304, thereby producing Figure 3HThe continuous NFC layer 308 shown. The amorphous silicon layer 306 may again be about 20 angstroms, or in the range of about 10 angstroms to about 40 angstroms. However, this is only one embodiment of performing three rounds of the NFC process. In other embodiments, the NFC process will be repeated as many times as needed until the NFC layer 308 becomes a continuous metal film.

[0039] The thickness of the final resulting NFC layer 308 as a continuous metal film may vary depending on, for example, the substrate surface topography and subsequent films to be deposited thereon and subsequent processes to be performed. In some embodiments, the resulting NFC layer 308 has a thickness equal to about 50 angstroms. In other embodiments, the resulting NFC layer 308 has a thickness in the range of about 1 angstrom to about 200 angstroms, or in the range of about 20 angstroms to about 100 angstroms, or in the range of about 40 angstroms to about 100 angstroms.

[0040] Fig. 3I The film stack 300 is shown when the NFC process is complete. Thus, the amorphous silicon layer 306 is completely converted into a metal-containing NFC layer 308. Here, the NFC layer 308 is a continuous thin metal film, the NFC layer 308 does not contain silicon or at least does not contain a large amount of silicon, and the NFC layer 308 is formed on the dielectric layer 304. In block 212, a bulk metal layer 310 is formed on the NFC layer 308, such as Figure 3J As shown. Since the barrier layer 106 in FIG. 1 is eliminated, the contact containing the bulk metal layer 310 in this embodiment has a lower resistance. Therefore, the metal contact containing the formed bulk metal layer 310 is more conductive. In addition, because in these embodiments, the bulk metal layer 310 is formed on the continuous NFC layer 308, the bulk film has a greatly improved coverage of the substrate surface. Therefore, compared with when the bulk metal layer 310 is deposited on the discontinuous NFC layer 308, the coverage problem is reduced.

[0041] The quality of the amorphous silicon film 306 can be determined based on the hydrogen content of the film, as measured by Rutherford Backscattering Spectrometry (RBS) in combination with Hydrogen Forward Scattering Spectrometry (HFS). In some embodiments, the hydrogen content of the amorphous silicon layer 306 is less than or equal to 6 atomic percent, less than or equal to 5 atomic percent, less than or equal to 4 atomic percent, less than or equal to 3 atomic percent, less than or equal to 2 atomic percent, less than or equal to 1 atomic percent, or less than or equal to 0.5 atomic percent. According to some embodiments, the amorphous silicon layer 306 is capped to a thin metal layer (such as tungsten) at low temperature to provide a film with less fluorine penetration to reduce film peeling. In some embodiments, amorphous silicon layer 306 is exposed to the first metal precursor at a temperature of less than or equal to about 450 degrees Celsius, less than or equal to about 425 degrees Celsius, less than or equal to about 400 degrees Celsius, less than or equal to about 375 degrees Celsius, or less than or equal to about 350 degrees Celsius. In some embodiments, amorphous silicon layer 306 is exposed to the first metal precursor at a temperature in a range of about 250 degrees Celsius to about 450 degrees Celsius, or in a range of about 275 degrees Celsius to about 425 degrees Celsius, or in a range of about 300 degrees Celsius to about 400 degrees Celsius.

[0042] The relatively low fluorine permeation of some embodiments provides better film adhesion and lower resistivity for the resulting NFC layer 308. In some embodiments, the fluorine concentration of the resulting NFC layer 308 is less than or equal to about 1×10 21 Atom / cm 3 , less than or equal to about 7.5×10 20 Atom / cm 3 , or less than or equal to about 5×10 20 Atom / cm 3 , or less than or equal to about 2.5×10 20 Atom / cm 3 , or less than or equal to about 1×10 20 Atom / cm 3 In some embodiments, the resistivity of the resulting NFC layer 308 having a thickness of about 20 nm is less than or equal to about 20 μΩ-cm, less than or equal to about 19 μΩ-cm, less than or equal to about 18 μΩ-cm, less than or equal to about 17 μΩ-cm, less than or equal to 16 μΩ-cm, or less than or equal to about 15 μΩ-cm.

[0043] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof and the scope of the disclosure is determined by the claims that follow.

Claims

1. A method of filling a feature formed on a surface of a substrate, comprising: Forming a continuous metal layer on the features formed on the surface of the substrate, wherein the process of forming the continuous metal layer comprises: (a) forming an amorphous silicon layer on an exposed surface of the feature; (b) converting the formed amorphous silicon layer into a metal film, the metal film being discontinuous, wherein the process of converting the amorphous silicon layer comprises exposing the amorphous silicon layer to a metal-containing precursor until substantially all silicon atoms in the amorphous silicon layer are replaced with one or more metal atoms found in the metal-containing precursor, wherein the metal-containing precursor comprises tungsten, tantalum, molybdenum or titanium; as well as (c) repeating (a) and (b) at least twice until a continuous film comprising the metal atoms is formed on the surface of the feature and the continuous film is between 1 angstrom and 200 angstroms, and wherein the process is performed at a pressure between 5 Torr and 20 Torr; as well as A bulk metal layer is formed over the formed continuous thin film.

2. The method of claim 1, wherein the substrate temperature during the process is maintained at a temperature between 250 degrees Celsius and 500 degrees Celsius.

3. The method of claim 1, wherein the process occurs at an RF power range between 50 W and 500 W. The method according to claim 1 , wherein the metal thin film is made of tungsten.

5. The method of claim 1, wherein the substrate is made of a material consisting essentially of silicon nitride, silicon oxide, or aluminum oxide.

6. The method of claim 1, wherein the bulk metal has a resistivity less than or equal to 20 μΩ-cm.

7. A method for forming a thin film on a surface of a substrate, comprising: forming a continuous metal layer on the features formed on the surface of the substrate, wherein the process of forming the continuous metal layer comprises: (a) forming an amorphous silicon layer on an exposed surface of the feature; (b) converting the formed amorphous silicon layer into a metal film, the metal film being discontinuous, wherein the process of converting the amorphous silicon layer comprises exposing the amorphous silicon layer to a metal-containing precursor until substantially all silicon atoms in the amorphous silicon layer are replaced with one or more metal atoms found in the metal-containing precursor, wherein the metal-containing precursor comprises tungsten, tantalum, molybdenum or titanium; as well as (c) repeating (a) and (b) at least twice until a continuous film containing the metal atoms is formed on the surface of the feature and the continuous film is between 10 angstroms and 100 angstroms; as well as The features formed on the surface of the substrate are filled by forming a bulk metal layer over the formed continuous film.

8. The method of claim 7, wherein the process is performed at a pressure between 5 Torr and 20 Torr.

9. The method of claim 7, wherein the substrate temperature during the process is maintained at a temperature between 250 degrees Celsius and 500 degrees Celsius.

10. The method of claim 7, wherein the process occurs at an RF power range between 50 W and 500 W.

11. The method of claim 7, wherein the metal thin film is made of tungsten.

12. The method of claim 7, wherein the substrate is made of a material consisting essentially of silicon nitride, silicon oxide, or aluminum oxide.

13. The method of claim 7, wherein the bulk metal has a resistivity less than or equal to 20 μΩ-cm.

14. A method for forming a thin film, comprising: A continuous metal layer is formed on the features formed on the surface of the substrate, wherein the process of forming the continuous metal layer comprises: (a) forming an amorphous silicon layer on the exposed surface of the feature, wherein the amorphous silicon layer is between 10 angstroms and 40 angstroms; (b) converting the formed amorphous silicon layer into a metal film, the metal film being discontinuous, wherein the process of converting the amorphous silicon layer comprises exposing the amorphous silicon layer to a metal-containing precursor until substantially all silicon atoms in the amorphous silicon layer are replaced with one or more metal atoms found in the metal-containing precursor, wherein the metal-containing precursor comprises tungsten; and (c) repeating (a) and (b) at least twice until a continuous film containing the metal atoms is formed on the surface of the feature and the continuous film has a thickness between 10 angstroms and 100 angstroms; and The features formed on the surface of the substrate are filled by forming a bulk metal layer over the formed continuous film.

15. The method of claim 14, wherein the process is performed at a pressure between 5 Torr and 20 Torr.

16. The method of claim 14, wherein the substrate temperature during the process is maintained at a temperature between 250 degrees Celsius and 500 degrees Celsius.

17. The method of claim 14, wherein the process occurs at an RF power range between 50 W and 500 W.

18. The method of claim 14, wherein the metal thin film is made of tungsten.

19. The method of claim 14, wherein the bulk metal has a resistivity less than or equal to 20 μΩ-cm.

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