Method for forming tungsten gap fill on a substrate

Abstract

A method for forming tungsten interstitial fillers in structures including high aspect ratio structures includes depositing tungsten pads in the structure using physical vapor deposition (PVD) with a highly ionized ambient gas of argon or krypton. The PVD process is performed at a temperature of approximately 20°C to approximately 300°C. The method further includes treating the structure with nitriding and using chemical vapor deposition (CVD) to fill the tungsten mass deposit into the structure to form a joint-suppressing boron-free tungsten filler. The CVD process is performed at a temperature of approximately 300°C to approximately 500°C and a pressure of approximately 5 Torr to approximately 300 Torr.

Description

Technical Field

[0001] The embodiments of this principle generally pertain to the processing of semiconductor substrates. Prior Technology

[0002] Tungsten is used in the semiconductor industry as a low-resistivity conductor with minimal electromigration. Tungsten can be used to fill voids for transistor contacts and to form through-holes between layers in integrated circuits. Due to its stability and low resistivity, tungsten is also used for internal connections in logic and memory components. With technological advancements, there is a growing demand for metal-filled solutions with even lower resistivity and lower stress. Current technology uses chemical vapor deposition of tungsten, requiring the use of titanium nitride pads and tungsten atomic layer deposition nucleation followed by bulk tungsten filling. However, current methods are not the limit of technology and cannot provide a metal-filled solution with both lower resistivity and reasonable gap filling at low stress.

[0003] Therefore, the inventors have provided a strengthening process to produce tungsten-filled materials with low stress and even lower resistivity than current technologies. Summary of the Invention

[0004] Methods and apparatus for reducing internal stress and resistivity of tungsten are provided herein.

[0005] In some embodiments, a method for forming a tungsten interstitial fill in a structure may include depositing a tungsten pad in the structure using a physical vapor deposition (PVD) process; depositing a nucleation layer using an atomic layer deposition (ALD) process; treating the structure with a nitriding process; and depositing a bulk tungsten filler into the structure using a chemical vapor deposition (CVD) process, configured to form a tungsten filler with seam suppression.

[0006] In some embodiments, the method may further include the following: the nucleation layer having a thickness of approximately 10 angstroms to approximately 60 angstroms; the PVD treatment being a highly ionized treatment with an ambient gas of argon or krypton; the PVD treatment being carried out at a temperature of approximately 20 degrees Celsius to approximately 300 degrees Celsius; the CVD treatment being carried out at a temperature of approximately 300 degrees Celsius to approximately 500 degrees Celsius; the CVD treatment being carried out at a pressure of approximately 5 Torr to approximately 300 Torr; the structure being a high aspect ratio structure of approximately 8:1 to approximately 15:1; the nitriding treatment comprising flowing nitrogen at a rate of approximately 1 sccm to approximately 20 sccm; the nitriding treatment having a period of approximately 2 seconds to approximately 20 seconds; and / or the tungsten pad having a thickness of approximately 40 angstroms to approximately 60 angstroms.

[0007] In some embodiments, a method for forming a tungsten interstitial fill on a structure may include depositing a tungsten liner in the structure using a physical vapor deposition (PVD) process with a highly ionized ambient gas of argon or krypton, wherein the PVD process is performed at a temperature of approximately 20°C to approximately 300°C; treating the structure with a nitriding process; and depositing a bulk tungsten filler into the structure using a chemical vapor deposition (CVD) process to form a seam-suppressing tungsten filler, wherein the CVD process is performed at a temperature of approximately 300°C to approximately 500°C and a pressure of approximately 5 Torr to approximately 300 Torr.

[0008] In some embodiments, the method may further include performing a rapid heat treatment (RTP) on the structure, wherein the RTP is configured to reduce the internal stress of the bulk tungsten filler and reduce the resistivity of the bulk tungsten filler; wherein the RTP is performed at a temperature of approximately 700°C to approximately 900°C; wherein the RTP is performed for a period of approximately 60 seconds or longer; wherein the RTP is performed by increasing the temperature at a slope of approximately 30°C to approximately 100°C per second; wherein the bulk tungsten filler is boron-free; and / or wherein the structure is a high aspect ratio structure of approximately 8:1 to approximately 15:1.

[0009] In some embodiments, a non-transitory computer-readable medium having instructions stored thereon, when executed, causes to perform a method for forming a tungsten interstitial filler in a structure. This method may include depositing a tungsten liner in the structure using a physical vapor deposition (PVD) process with a highly ionized ambient gas of argon or krypton, wherein the PVD process is performed at a temperature of approximately 20°C to approximately 300°C; treating the structure with a nitriding treatment; and using a chemical vapor deposition (CVD) process to deposit a bulk tungsten filler into the structure to form a seam-suppressing tungsten filler, wherein the CVD process is performed at a temperature of approximately 300°C to approximately 500°C and a pressure of approximately 5 Torr to approximately 300 Torr.

[0010] In some embodiments, the method may further include depositing a nucleation layer using an atomic layer deposition (ALD) process prior to treating the structure with the nitriding treatment; and / or performing a rapid thermal treatment (RTP) on the structure, wherein the RTP is configured to reduce the internal stress of the bulk tungsten-filled material and reduce the resistivity of the bulk tungsten-filled material.

[0011] Other and further embodiments are disclosed below. Simple Explanation of the Diagram

[0012] The embodiments of the principle briefly summarized above and discussed in more detail below can be understood by referring to the illustrated embodiments of the principle depicted in the accompanying drawings. However, the accompanying drawings only illustrate general embodiments of the principle and should therefore not be considered as limiting the scope, as other embodiments with equivalent effects are permissible with respect to the principle.

[0013] Figure 1 depicts a cross-sectional view of tungsten gap filling in a structure on a substrate, according to certain embodiments of this principle.

[0014] Figure 2 illustrates a method for filling gaps on a substrate according to certain embodiments of this principle.

[0015] Figure 3 depicts a cross-sectional view of a high aspect ratio structure with gap filling, according to certain embodiments of this principle.

[0016] Figure 4 illustrates a method for filling gaps on a substrate using nitriding, according to certain embodiments of this principle.

[0017] Figure 5 depicts a cross-sectional view of a high aspect ratio structure with gap filling and no voids, according to certain embodiments of this principle.

[0018] Figure 6 illustrates, according to certain embodiments of this principle, a method for filling gaps on a substrate using an ALD nucleation layer.

[0019] Figure 7 depicts a cross-sectional view of a high aspect ratio structure with gap filling using an ALD nucleation layer, according to certain embodiments of this principle.

[0020] To facilitate understanding, the same element symbols have been used as much as possible to represent the same elements in the common symbols. The symbols are not drawn to scale and have been simplified for clarity. Elements and features of one embodiment may be beneficially incorporated into other embodiments without further explanation. Implementation

[0021] The method and apparatus provide tungsten interstitial filling with low resistivity and low stress. This principle can be used to fill structures such as vias or channels and the like. The critical dimension (CD) of the channel or via can range from about 5 nm to about 65 nm, having an aspect ratio (AR) (height to width ratio) of about 1:1 to about 15:1. In some embodiments, the process flow includes physical vapor deposition (PVD) of tungsten pads, chemical vapor deposition (CVD) of seam-suppressed (SS) tungsten, followed by rapid thermal annealing (RTP).

[0022] Due to its unique stability and low resistivity, tungsten is widely used as a metal interconnect in logic and memory components. However, along with its technological advantages, there is an increasing need for metal filling solutions with reasonable gap filling, even with lower resistivity and lower stress, to meet requirements such as those for NAND flash memory structures and the like. Conventional CVD tungsten methods (TiN + CVD tungsten) exhibit high tensile stress. The inventors have found that the stress of CVD tungsten can be reduced by changing deposition conditions (temperature, pressure, and the ratio of tungsten fluoride (WF6) to hydrogen (H2), etc.), but this has a significant impact on yield and gap filling performance. The inventors have also found that the resistivity of CVD tungsten can be reduced by changing deposition conditions (temperature, tungsten atomic layer deposition (ALD) nucleation chemistry, etc.), but this has a limited resistivity response and reduced performance (mainly yield). The inventors subsequently discovered an integrated method that significantly reduces the stress and resistivity of the tungsten film, resulting in high yield. Furthermore, the tungsten filler is boron-free, allowing for rapid heat treatment in the integrated method without adhesion problems.

[0023] Figure 1 depicts a cross-sectional view 100 of tungsten interstitial filling in structure 108 of substrate 102 according to certain embodiments. In conventional tungsten interstitial filling processes, a tungsten nitride layer is first deposited on the surface of the substrate, followed by an ALD tungsten nucleation layer and CVD tungsten interstitial filling. In the method and apparatus of this principle, a PVD tungsten pad 104 is first deposited in structure 108, and then a tungsten bulk fill 106 is deposited by CVD tungsten / SS tungsten processing. In some embodiments, an RTP treatment is subsequently used to reduce the resistivity and stress of the tungsten bulk fill 106. The PVD tungsten pad 104 will have a reasonable stepped coverage in structure 108. PVD deposition is performed using an ambient rare gas such as argon or krypton and the like with high ionization. The temperature during the PVD deposition process can range from approximately room temperature (~20 degrees Celsius) to approximately 300 degrees Celsius.

[0024] Conventional CVD interstitial deposition on a titanium nitride layer consists of tungsten ALD nucleation using tungsten fluoride and diborane (B₂H₆) / silane (SiH₄) precursors, followed by tungsten CVD bulk filling deposition using WF₆ / H₂ as a precursor. In this method and apparatus, the direct deposition of the tungsten CVD bulk filler does not have a tungsten ALD nucleation layer, but is performed at temperatures of approximately 300°C to approximately 500°C and pressures of approximately 5 Torr to approximately 300 Torr. Eliminating the use of boron in the process allows for the use of RTP treatment to enhance the resistivity and stress level in the tungsten without causing boron-induced adhesion problems. Annealing temperatures can range from approximately 700°C to approximately 900°C. Annealing periods can be approximately 60 seconds or longer. The annealing atmosphere gas can be hydrogen or argon and the like. In some embodiments, the temperature slope can range from approximately 30°C per second to approximately 100°C per second or more.

[0025] Figure 2 illustrates a method 200 for filling gaps on a substrate, according to certain embodiments. Figure 3 depicts a cross-sectional view 300 of structure 304 in a substrate 302 gap-filled according to method 200. In block 202, a tungsten pad 306 is deposited on structure 304 using a PVD process. As previously described, the PVD process is performed using a rare gas, such as argon or krypton and the like, with high ionization. The PVD process temperature can range from approximately room temperature (~20°C) to approximately 300°C. The thickness of the tungsten pad 306 depends on the CD variation and can range from approximately 40 angstroms to approximately 200 angstroms. In block 204, bulk tungsten 308 is deposited on structure 304 using a CVD process with a WF 6 precursor along with hydrogen, filling structure 304 with boron-free tungsten. The CVD process can be carried out at temperatures from approximately 300°C to approximately 500°C and at pressures from approximately 5 Torr to approximately 300 Torr.

[0026] In optional block 206, an RTP treatment can be performed on structure 304 to reduce the internal stress of the bulk tungsten filler 308 and also reduce the resistivity of the bulk tungsten filler 308. This avoids the problems associated with RTP treatment of boron-injected tungsten without the use of boron for depositing the bulk tungsten filler 308. As described above, the annealing temperature can be in the range of approximately 700°C to approximately 900°C. The annealing period can be approximately 60 seconds or longer. The annealing atmosphere gas can be hydrogen or argon and the like. In some embodiments, the temperature slope can be in the range of approximately 30°C per second to approximately 100°C per second or more. Method 200 works well for structures with an aspect ratio of less than 8:1. The inventors have found that if the aspect ratio is too high (e.g., 8:1 to 15:1), voids 310 can appear in the bulk tungsten filler 308, due to the formation of overhangs 312 during PVD tungsten deposition and due to the conformal nature of the bulk tungsten filler 308. To address the formation of voids in structure 304, the inventors have discovered alternative methods, as described in Figures 4 and 6, that can be used for higher aspect ratios.

[0027] Figure 4, according to some embodiments, illustrates a method 400 for filling gaps on substrate 302 using a nitriding treatment. Figure 5 depicts a cross-sectional view 500 of a void-free structure 304 filled with gaps according to method 400. In block 402, a tungsten pad 306 is deposited on structure 304 using a PVD treatment. The thickness of the tungsten pad 306 depends on the CD variation and can range from approximately 40 angstroms to approximately 200 angstroms. The tungsten pad 306 serves as a nucleation layer for subsequent bulk filling. The PVD treatment is performed using a rare gas, such as argon or krypton and the like, with high ionization. The PVD treatment temperature can range from approximately room temperature (~20 degrees Celsius) to approximately 300 degrees Celsius. In block 404, structure 304 is treated with a nitriding treatment to form tungsten nitride 506. During the nitriding treatment, nitrogen radicals form tungsten nitride only on or near the top surface 510 of structure 304. Tungsten nitride causes a growth delay in subsequent CVD tungsten deposition on the top surface 510, but the CVD tungsten deposition will have normal growth from the bottom 512 and upwards from the inside of structure 304. The nitriding treatment results in bottom-up or super-conformal deposition behavior of the CVD tungsten deposition to reduce void formation on the inside of structure 304. In some embodiments, the nitriding treatment includes flowing nitrogen at a rate of approximately 1 sccm to approximately 20 sccm for a period of approximately 2 seconds to approximately 20 seconds. Local or remote plasma sources can be used.

[0028] In block 406, bulk tungsten 508 is deposited on structure 304 using a CVD process to form seam-suppressing tungsten. The CVD process is performed using a WF 6 precursor with hydrogen to form boron-free tungsten. The CVD process can be carried out at temperatures ranging from approximately 300°C to approximately 500°C and pressures ranging from approximately 5 Torr to approximately 300 Torr. In optional block 408, an RTP process can be performed on structure 304 to reduce internal stresses in the bulk tungsten 508 and also to reduce its resistivity. This deposits the bulk tungsten 508 without using boron and avoids the problems associated with RTP processes for boron-injected tungsten. The annealing temperature can range from approximately 700°C to approximately 900°C. The annealing period can be approximately 60 seconds or longer. The annealing atmosphere gas can be hydrogen or argon and similar gases. In some embodiments, the temperature slope may be in the range of approximately 30 degrees Celsius per second to approximately 100 degrees Celsius per second or more.

[0029] Figure 6 illustrates, according to certain embodiments, a method for filling gaps on substrate 302 using an ALD nucleation layer treatment. Figure 7 depicts a cross-sectional view 700 of a structure 304 gap-filled using an ALD nucleation layer according to method 600. In block 602, a tungsten pad 306 is deposited on structure 304 using a PVD treatment. The thickness of the tungsten pad 306 depends on the CD variation and can range from approximately 40 angstroms to approximately 200 angstroms. The PVD treatment is performed using a rare gas such as argon or krypton and the like with high ionization. The PVD treatment temperature can range from approximately room temperature (~20°C) to approximately 300°C. In block 604, a thin tungsten nucleation layer 702 is formed on structure 304 using an ALD treatment. The thickness of the thin tungsten nucleation layer 702 can range from approximately 10 angstroms to approximately 60 angstroms. The tungsten nucleation layer is applied prior to nitriding treatment to aid in delayed growth on the top surface 710. The internal stress level of the subsequently deposited bulk tungsten-filled tungsten will remain the same, but the resistivity of the subsequently deposited bulk tungsten-filled tungsten can increase by about 10% compared to the treatment without ALD treatment.

[0030] In block 606, structure 304 is treated with nitriding to form a tungsten nitride layer 706. During nitriding, nitrogen radicals form tungsten nitride only on or near the top surface 710 of structure 304. The tungsten nitride layer 706 causes a growth delay in subsequent CVD tungsten deposition on the top surface 710, but CVD tungsten deposition will have normal growth from the bottom 712 and upwards on the inside of structure 304. Nitriding results in bottom-up or super-conformal deposition behavior of CVD tungsten deposition to reduce void formation on the inside of structure 304. In some embodiments, nitriding includes flowing nitrogen at a rate of approximately 1 sccm to approximately 20 sccm for a period of approximately 2 seconds to approximately 20 seconds. Local or remote plasma sources can be used. In block 608, bulk-filled tungsten 708 is deposited on structure 304 using CVD treatment to form seam-suppressed tungsten. The CVD treatment is performed using a WF 6 precursor with hydrogen. CVD processing can be carried out at temperatures ranging from approximately 300 degrees Celsius to approximately 500 degrees Celsius, and at pressures ranging from approximately 5 Torr to approximately 300 Torr.

[0031] In some embodiments of the methods described above, even without incorporating RTP treatment, the internal stress (measured in MPa) of the tungsten bulk filler is reduced by approximately 10% (for a film thickness of approximately 2000 Å) to approximately 50% (for a film thickness of 500 Å or less) or more over conventional treatment, with the greatest reduction for thinner films. Simultaneously, the resistivity of the tungsten bulk filler is reduced by approximately 30% to approximately 40% or more over conventional treatment. In some embodiments of the methods described above, the additional RTP treatment further reduces internal stress and further lowers the resistivity of the tungsten bulk filler compared to conventional treatment with heat treatment. RTP treatment reduces the internal stress of the tungsten bulk filler by approximately 45% to approximately 55% or more for all thicknesses compared to conventional treatment. RTP treatment reduces the resistivity of the tungsten bulk filler by approximately 35% to approximately 45% compared to conventional treatment. Furthermore, the method of this principle does not have degraded adhesion problems after annealing treatment using boron derivatives, as in conventional treatment.

[0032] Embodiments based on this principle may be implemented in hardware, firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored using one or more computer-readable media, which may be read and executed by one or more processors. Computer-readable media may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing platform or a "virtual machine" running on one or more computing platforms). For example, computer-readable media may include any suitable form of volatile and non-volatile memory. In some embodiments, computer-readable media may include non-transitory computer-readable media.

[0033] Although the above embodiments are oriented towards this principle, other and further embodiments of this principle may be derived without departing from its basic scope.

[0034] 100: View 102:Substrate 104: Tungsten gasket 106: Block Fill 108: Structure 200: Method 202: Square 204: Square 206: Square 300: View 302:Substrate 304: Structure 306: Tungsten gasket 308: Bulk-filled tungsten 310: Void 312: Overhang 400: Method 402: Square 404: Square 406: Square 408: Square 500: View 506: Tungsten nitride 508: Bulk-filled tungsten 510: Top surface 600: Method 602: Square 604: Square 606: Square 608: Square 700: View 702: Floor 706: Tungsten nitride layer 708: Bulk-filled tungsten 710: Top surface 712: Bottom

[0035] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A method for forming a tungsten interstitial fill in a structure, comprising the following steps in sequence: (a) depositing a tungsten pad in the structure using a physical vapor deposition (PVD) process, wherein the tungsten pad has a thickness of approximately 40 angstroms to approximately 60 angstroms; (b) depositing a nucleation layer on the tungsten pad using an atomic layer deposition (ALD) process; (c) treating the structure with a nitriding process to form a tungsten nitridation layer on the nucleation layer, wherein the nitriding process includes flowing nitrogen at a rate of approximately 1 sccm to approximately 20 sccm; and (d) after the nitriding process, depositing a bulk tungsten filler into the structure using a chemical vapor deposition (CVD) process, the CVD process being configured to form a seam-suppressing tungsten filler, wherein the CVD process is performed at a pressure of approximately 5 Torr to approximately 300 Torr.

2. The method as described in claim 1, wherein the nucleation layer has a thickness of approximately 10 angstroms to approximately 60 angstroms.

3. The method as described in claim 1, wherein the PVD process is a highly ionized process with an ambient gas of argon or krypton.

4. The method as described in claim 1, wherein the PVD process is performed at a temperature of approximately 20 degrees Celsius to approximately 300 degrees Celsius.

5. The method as described in claim 1, wherein the CVD process is performed at a temperature of approximately 300 degrees Celsius to approximately 500 degrees Celsius.

6. The method as described in claim 1, wherein the structure is a high aspect ratio structure of approximately 8:1 to approximately 15:

1.

7. The method as described in claim 1, wherein the nitriding treatment has a period of approximately 2 seconds to approximately 20 seconds.

8. The method as claimed in claim 1, wherein the PVD process is performed at a temperature of approximately 20 degrees Celsius to approximately 300 degrees Celsius; and wherein the CVD process is performed at a temperature of approximately 300 degrees Celsius to approximately 500 degrees Celsius.

9. The method as described in claim 1 further comprises the step of: performing a rapid heat treatment (RTP) on the structure, wherein the RTP is configured to reduce the internal stress of the bulk tungsten filling and reduce the resistivity of the bulk tungsten filling.

10. The method as described in claim 9, wherein the RTP is carried out at a temperature of approximately 700 degrees Celsius to approximately 900 degrees Celsius.

11. The method as described in claim 9, wherein the RTP is performed for a period of approximately 60 seconds or longer.

12. The method as described in claim 9, wherein the RTP is carried out by increasing a temperature at a slope of approximately 30 degrees Celsius per second to approximately 100 degrees Celsius per second.

13. The method as described in claim 1, wherein the bulk material is filled with tungsten that is boron-free.

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