Method and apparatus for low-resistance and low-stress tungsten gap filling

Abstract

A method for forming a tungsten gap fill in a structure, including a high aspect ratio structure, includes depositing a tungsten liner in the structure using a physical vapor deposition (PVD) process with high ionization and an argon or krypton ambient gas. The PVD process is performed at a temperature of about 20 degrees Celsius to about 300 degrees Celsius. The method further includes treating the structure with a nitridation process and depositing a bulk fill tungsten in the structure using a chemical vapor deposition (CVD) process to form a seam-inhibited, boron-free tungsten fill. The CVD process is performed at a temperature of about 300 degrees Celsius to about 500 degrees Celsius and a pressure of about 5 Torr to about 300 Torr.

Description

Technical Field

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[0001] Embodiments of the present principle generally relate to the processing of semiconductor substrates.

Background Art

[0002] Tungsten is used as a low-resistance conductor with minimal electromigration in the semiconductor industry. Tungsten can be used to fill holes as contacts for transistors and in the formation of vias between layers of integrated devices. Tungsten can also be used for interconnects in logic and memory devices due to its stability and low resistance. As technology advances, there is a growing demand for even lower resistance and lower stress metal filling solutions. Current technology uses chemical vapor deposition of tungsten, which requires the use of a titanium nitride liner and tungsten atomic layer deposition nucleation followed by tungsten bulk filling. However, current methods are at the limits of technology and cannot provide a metal filling solution that can achieve both lower resistance and lower stress with proper gap filling.

[0003] Therefore, the inventors have provided an improved process that results in tungsten filling with lower stress and lower resistance than current technology.

Summary of the Invention

[0004] Methods and apparatuses are provided herein for reducing the internal stress of tungsten while reducing the resistance of tungsten.

[0005] In some embodiments, methods for forming tungsten gap-filling in a structure may include depositing a tungsten liner within the structure using a physical vapor deposition (PVD) process, depositing a nucleation layer using an atomic layer deposition (ALD) process, treating the structure by a nitriding process, and depositing bulk-filled tungsten within the structure using a chemical vapor deposition (CVD) process configured to form seam-suppressed tungsten filling.

[0006] In some embodiments, the method may further include the nucleation layer thickness being about 10 angstroms to about 60 angstroms, the PVD process being a high-ionization process with an argon or krypton atmosphere gas, the PVD process being carried out at a temperature of about 20 degrees Celsius to about 300 degrees Celsius, the CVD process being carried out at a temperature of about 300 degrees Celsius to about 500 degrees Celsius, the CVD process being carried out at a pressure of about 5 Torre to about 300 Torre, the structure being a high aspect ratio structure of about 8:1 to about 15:1, the nitriding process being carried out by flowing nitrogen at a flow rate of about 1 sccm to about 20 sccm, the nitriding process having a duration of about 2 seconds to about 20 seconds, and / or the tungsten liner thickness being about 40 angstroms to about 60 angstroms.

[0007] In some embodiments, a method for forming tungsten gap packing in a structure may include depositing a tungsten liner within the structure using a physical vapor deposition (PVD) process with a highly ionized and argon or krypton atmosphere gas, wherein the PVD process is carried out at a temperature of about 20°C to about 300°C, treating the structure by a nitriding process, and depositing bulk-filled tungsten within the structure using a chemical vapor deposition (CVD) process to form seam-suppressed tungsten packing, wherein the CVD process is carried out at a temperature of about 300°C to about 500°C and a pressure of about 5 Torr to about 300 Torr.

[0008] In some embodiments, the method may further include performing a rapid thermal process (RTP) on the structure, wherein the RTP is configured to reduce the internal stress of the bulk-filled tungsten and lower the resistance of the bulk-filled tungsten, the RTP is performed at a temperature of about 700°C to about 900°C, the RTP is performed for a period of about 60 seconds or more, the RTP is performed by increasing the temperature at a ramping rate of about 30°C / second to about 100°C / second, the bulk-filled tungsten is boron-free, and / or the structure is a high aspect ratio structure of about 8:1 to about 15:1.

[0009] In some embodiments, a non-transient computer-readable medium, when executed, stores instructions for executing a method to form tungsten gap-filling in a structure, the method comprising depositing a tungsten liner in the structure using a physical vapor deposition (PVD) process with a highly ionized and argon or krypton atmosphere gas, wherein the PVD process is performed at a temperature of about 20° to about 300°C, processing the structure by a nitriding process, and depositing bulk-filled tungsten in the structure using a chemical vapor deposition (CVD) process to form seam-suppressed tungsten filling, wherein the CVD process is performed at a temperature of about 300° to about 500°C and a pressure of about 5 Torr to about 300 Torr.

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

[0011] Other and further embodiments are disclosed below.

[0012] The embodiments of this disclosure, briefly summarized above and discussed in more detail below, can be understood by referring to the exemplary embodiments of the principle shown in the accompanying drawings. However, the accompanying drawings only show typical embodiments of the principle and should not be considered limiting in scope, as the principle may accept other equally valid embodiments. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of tungsten gap filling in a substrate structure according to several embodiments of this principle. [Figure 2] This diagram illustrates a method for filling gaps in substrates according to several embodiments of this principle. [Figure 3] This is a cross-sectional view of a gap-filled high aspect ratio structure according to several embodiments of this principle. [Figure 4] This figure illustrates a method for filling gaps in a substrate using a nitriding process, according to several embodiments of this principle. [Figure 5] This is a cross-sectional view of a high aspect ratio structure with void-free gap filling, according to several embodiments of this principle. [Figure 6] This diagram illustrates a method for filling gaps in a substrate using an ALD nucleation layer process, based on several embodiments of this principle. [Figure 7] This is a cross-sectional view of a high aspect ratio structure that is gap-filled using an ALD nucleation layer according to several embodiments of this principle. [Modes for carrying out the invention]

[0014] For ease of understanding, where possible, the same reference numerals are used to designate identical elements common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment can be usefully incorporated into other embodiments without further detail.

[0015] This method and apparatus provide low-resistance and low-stress tungsten gap filling. The principle can be used to fill structures such as vias or trenches. The limiting dimension (CD) of the trench or via is in the range of about 5 nm to about 65 nm, and the aspect ratio (AR) can be about 1:1 to about 15:1 (height to width ratio). In some embodiments, the process flow includes physical vapor deposition (PVD) tungsten liner deposition, chemical vapor deposition (CVD) of seam-suppressed (SS) tungsten, and subsequent rapid thermal (RTP) annealing.

[0016] Tungsten is widely used as a metal interconnect in logic and memory devices due to its inherent stability and low resistance. However, with technological advancements, there is a growing need for metal filling solutions with even lower resistance and stress, using reasonable gap filling that can meet requirements such as those for NAND flash memory structures. Conventional CVD tungsten methods (TiN + CVD tungsten) have high tensile stress. The inventors found that while the stress of CVD tungsten can be reduced by changing the deposition conditions (temperature, pressure, and tungsten fluoride (WF6) to hydrogen (H2) gas ratio, etc.), this significantly impacts throughput and gap filling performance. The inventors also found that while the resistance of CVD tungsten can be reduced by changing the deposition conditions (temperature, tungsten atomic layer deposition (ALD) nucleation chemistry, etc.), the resistance response is limited, and performance (primarily throughput) is reduced. The inventors subsequently discovered an integrated method that significantly reduces the stress and resistance of tungsten films along with high throughput. In addition, the tungsten filling is boron-free, which allows for the use of a rapid thermal process without adhesion issues in the integrated approach.

[0017] Figure 1 shows a cross-sectional view 100 of tungsten gap filling in a structure 108 within a substrate 102 according to several embodiments. In conventional tungsten gap filling processes, a titanium nitride layer is first deposited on the substrate surface, followed by an ALD tungsten nucleation layer and CVD tungsten gap filling. In the method and apparatus of this principle, a PVD tungsten liner 104 is first deposited within the structure 108, followed by tungsten bulk filling 106 deposited by a CVD tungsten / SS tungsten process. In some embodiments, an RTP process can be subsequently used to reduce the resistance and stress of the tungsten bulk filling 106. The PVD tungsten liner 104 will have reasonable step coverage within the structure 108. PVD deposition is carried out by a high-ionization process using an atmospheric noble gas such as argon or krypton. The temperature during the PVD deposition process can be approximately room temperature (about 20 degrees Celsius) to about 300 degrees Celsius.

[0018] Conventional CVD tungsten gap filling into titanium nitride layers consists of tungsten ALD nucleation using tungsten fluoride and diborane (B2H6) / silane (SiH4) precursors, and tungsten CVD bulk filling deposition using WF6 / H2 as a precursor. In the method and apparatus of this principle, tungsten CVD bulk filling is deposited directly at a temperature of approximately 300°C to 500°C and a pressure of approximately 5 Torr to 300 Torr, without a tungsten ALD nucleation layer. By eliminating the use of boron in the process, it becomes possible to improve the resistance and stress levels of tungsten using the RTP process without causing the adhesion problems with tungsten exacerbated by boron. The annealing temperature can be in the range of approximately 700°C to 900°C. The annealing duration can be approximately 60 seconds or more. The annealing atmosphere gas can be hydrogen or argon, etc. In some embodiments, the temperature ramping rate can be in the range of approximately 30 degrees Celsius / second to approximately 100 degrees Celsius / second or more.

[0019] Figure 2 shows a method 200 for filling gaps in a substrate according to several embodiments. Figure 3 shows a cross-sectional view 300 of a structure 304 within a substrate 302 that has been filled according to method 200. In block 202, a tungsten liner 306 is deposited on the structure 304 using a PVD process. As previously mentioned, the PVD process is carried out by high ionization using a noble gas such as argon or krypton. The PVD process temperature can be approximately room temperature (about 20 degrees Celsius) to about 300 degrees Celsius. The thickness of the tungsten liner 306 can be in the range of about 40 angstroms to about 200 angstroms, depending on the CD variation. In block 204, bulk-filled tungsten 308 is deposited on the structure 304 using a CVD process with a WF6 precursor along with hydrogen gas, and the structure 304 is filled with boron-free tungsten. The CVD process can be carried out at temperatures of approximately 300 to 500 degrees Celsius and pressures of approximately 5 Torrell to 300 Torrell.

[0020] In an optional block 206, the RTP process can be performed on the structure 304 to reduce the internal stress of the bulk-filled tungsten 308 and also reduce its resistance. The bulk-filled tungsten 308 is deposited without the use of boron, thus avoiding the problems associated with the RTP process of boron-implanted tungsten. As described above, the annealing temperature can be in the range of approximately 700°C to approximately 900°C. The annealing duration can be approximately 60 seconds or more. The annealing atmosphere gas can be hydrogen or argon, etc. In some embodiments, the temperature ramping rate can be in the range of approximately 30°C / second to approximately 100°C / second or more. Method 200 works well for structures with an aspect ratio of less than 8:1. The inventors found that when the aspect ratio is too high (e.g., 8:1 to 15:1), voids 310 may appear in the bulk-filled tungsten 308 due to the formation of overhangs 312 during PVD tungsten deposition and due to the conformal nature of the bulk-filled tungsten 308. To overcome the formation of voids within the structure 304, the inventors discovered an alternative method that can be used for higher aspect ratios, as illustrated in Figures 4 and 6.

[0021] Figure 4 shows a method 400 for filling voids in a substrate 302 using a nitriding process, according to several embodiments. Figure 5 shows a cross-sectional view 500 of a structure 304 that has been void-filled according to method 400. In block 402, a tungsten liner 306 is deposited on the structure 304 using a PVD process. The thickness of the tungsten liner 306 depends on the CD variation and can range from about 40 angstroms to about 200 angstroms. The tungsten liner 306 functions as a nucleating layer for subsequent bulk filling. The PVD process is carried out by high ionization using a noble gas such as argon or krypton. The PVD process temperature can be from approximately room temperature (about 20 degrees Celsius) to about 300 degrees Celsius. In block 404, the structure 304 is treated with a nitriding process to form tungsten nitride 506. In the nitriding process, nitrogen radicals form tungsten nitride only on or near the top surface 510 of the structure 304. Due to the tungsten nitride, subsequent CVD tungsten deposition undergoes incubation delay on the top surface 510, but the CVD tungsten deposition grows vertically upward from the bottom 512 inside the structure 304. The nitriding process results in bottom-up or hyperconformal deposition behavior of the CVD tungsten deposition, reducing void formation inside the structure 304. In some embodiments, the nitriding process involves flowing nitrogen at a flow rate of about 1 sccm to about 20 sccm and a duration of about 2 seconds to about 20 seconds. Local or remote plasma sources may be used.

[0022] In block 406, bulk-fill tungsten 508 is deposited on structure 304 using a CVD process to form seam-suppression tungsten. The CVD process uses a WF6 precursor with hydrogen gas to form boron-free tungsten. The CVD process can be performed at a temperature of about 300 degrees Celsius to about 500 degrees Celsius and a pressure of about 5 Torr to about 300 Torr. In optional block 408, an RTP process can be performed on structure 304 to reduce the internal stress of bulk-fill tungsten 508 and also reduce the resistance of bulk-fill tungsten 508. Bulk-fill tungsten 508 is deposited without using boron, avoiding problems associated with the RTP process of boron-implanted tungsten. The annealing temperature can range from about 700 degrees Celsius to about 900 degrees Celsius. The annealing duration can be 60 seconds or more. The annealing ambient gas can be hydrogen or argon, etc. In some embodiments, the temperature ramp rate can range from about 30 degrees Celsius per second to about 100 degrees Celsius per second or more.

[0023] Figure 6 shows a method for filling gaps in a substrate 302 using an ALD nucleation layer process according to several embodiments. Figure 7 shows a cross-sectional view 700 of a structure 304 that has been filled using an ALD nucleation layer according to method 600. In block 602, a tungsten liner 306 is deposited on the structure 304 using a PVD process. The thickness of the tungsten liner 306 can range from about 40 angstroms to about 200 angstroms, depending on the CD variation. The PVD process is carried out by high ionization using a noble gas such as argon or krypton. The PVD process temperature can range from approximately room temperature (about 20 degrees Celsius) to about 300 degrees Celsius. In block 604, a thin tungsten nucleation layer 702 is formed on the structure 304 using an ALD process. The thickness of the thin tungsten nucleation layer 702 can range from about 10 angstroms to about 60 angstroms. The tungsten nucleation layer is applied prior to the nitride formation treatment to enhance the incubation delay of the upper surface 710. The internal stress level of the subsequently deposited bulk-filled tungsten remains the same, but the resistance of the subsequently deposited bulk-filled tungsten can increase by approximately 10% compared to the process without the ALD process.

[0024] In block 606, the structure 304 is processed in a nitridation process to form a tungsten nitride layer 706. In the nitridation process, nitrogen radicals form tungsten nitride only on or near the upper surface 710 of the structure 304. Due to the tungsten nitride layer 706, subsequent CVD tungsten deposition has an incubation delay at the upper surface 710, but the CVD tungsten deposition will grow vertically upward inside the structure 304 from the bottom 712. The nitridation process results in bottom-up or superconformal deposition behavior of CVD tungsten deposition, reducing void formation inside the structure 304. In some embodiments, the nitridation process includes flowing nitrogen at a flow rate of about 1 sccm to about 20 sccm and a duration of about 2 seconds to about 20 seconds. A local or remote plasma source may be used. In block 608, bulk fill tungsten 708 is deposited on the structure 304 using a CVD process to form seam suppression tungsten. The CVD process uses a WF6 precursor together with hydrogen gas. The CVD process can be carried out at a temperature of about 300 degrees Celsius to about 500 degrees Celsius and a pressure of about 5 torr to about 300 torr.

[0025] Even without incorporating the RTP process in some embodiments of the method described above, the internal stress (measured in MPa units) of the tungsten bulk filling was reduced by approximately 10% (for film thicknesses exceeding 2000 angstroms) to over 50% (for film thicknesses of 500 angstroms or less) compared to conventional processes, with the greatest reduction observed in thinner films. Simultaneously, the resistance of the tungsten bulk filling was reduced by approximately 30% to over 40% compared to conventional processes. Additional RTP processes in some embodiments of the method described above further reduced internal stress and thus the resistance of the tungsten bulk filling compared to conventional processes using heat treatment. The RTP process reduced the internal stress of the tungsten bulk filling by approximately 45% to over 55% for all thicknesses compared to conventional processes. The RTP process also reduced the resistance of the tungsten bulk filling by approximately 35% to over 45% compared to conventional processes. Furthermore, the method of this principle does not have the problem of adhesion degradation after the annealing process, as is found in conventional processes using boron derivatives.

[0026] Embodiments based on this principle can be implemented in hardware, firmware, software, or any combination thereof. Embodiments can also be implemented as instructions stored using one or more computer-readable media that can be read and executed by one or more processors. The 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, the computer-readable media may include any suitable form of volatile or non-volatile memory. In some embodiments, the computer-readable media may include non-temporary computer-readable media.

[0027] The foregoing describes embodiments of the principle, but other and further embodiments of the principle can be devised without departing from the basic scope of the principle.

Claims

1. A method for forming tungsten gap fillers in a structure, (a) Depositing tungsten directly onto the surface of the structure and forming a tungsten liner within the structure using a physical vapor deposition (PVD) process with high ionization and an argon or krypton atmosphere, wherein the PVD process is carried out at a temperature of approximately 20 to 300 degrees Celsius, and the tungsten liner is a liner layer and nucleation layer of bulk tungsten deposited by a chemical vapor deposition (CVD) process, (b) The tungsten liner is subjected to a nitriding process to form a tungsten nitride layer on or near the upper surface of the tungsten liner of the structure, wherein the nitriding process includes flowing nitrogen at a flow rate of about 1 sccm to about 20 sccm. (c) Depositing bulk-filled tungsten into the structure on the tungsten liner using a chemical vapor deposition (CVD) process to form a seam-suppressed tungsten filling, wherein the CVD process is carried out at a temperature of approximately 300 to 500 degrees Celsius and a pressure of approximately 5 Torre to 300 Torre. The method involves performing a rapid thermal process (RTP) on the structure, wherein the RTP is configured to reduce the internal stress of the bulk-filled tungsten and lower the resistance of the bulk-filled tungsten. A method that includes these in this order.

2. The method according to claim 1, wherein the RTP is performed at a temperature of approximately 700 degrees Celsius to approximately 900 degrees Celsius.

3. The method according to claim 1, wherein the RTP is performed for a period of about 60 seconds or more.

4. The method according to claim 1, wherein the RTP is performed by increasing the temperature at a ramping rate of approximately 30 degrees Celsius / second to approximately 100 degrees Celsius / second.

5. The method according to claim 1, wherein the bulk-filled tungsten is boron-free.

6. The method according to claim 1, wherein the structure is a high aspect ratio structure of about 8:1 to about 15:

1.

7. A non-temporary computer-readable medium that, when executed, stores instructions causing a method to perform a method for forming tungsten gap fillers in a structure, wherein the method (a) Depositing tungsten directly onto the surface of the structure and forming a tungsten liner within the structure using a physical vapor deposition (PVD) process with high ionization and an argon or krypton atmosphere, wherein the PVD process is carried out at a temperature of approximately 20 to 300 degrees Celsius, and the tungsten liner is a liner layer and nucleation layer of bulk tungsten deposited by a chemical vapor deposition (CVD) process, (b) The tungsten liner is subjected to a nitriding process to form a tungsten nitride layer on or near the upper surface of the tungsten liner of the structure, wherein the nitriding process includes flowing nitrogen at a flow rate of about 1 sccm to about 20 sccm. (c) Depositing bulk-filled tungsten into the structure on the tungsten liner using a chemical vapor deposition (CVD) process to form a seam-suppressed tungsten filling, wherein the CVD process is carried out at a temperature of approximately 300 to 500 degrees Celsius and a pressure of approximately 5 Torre to 300 Torre. The method involves performing a rapid thermal process (RTP) on the structure, wherein the RTP is configured to reduce the internal stress of the bulk-filled tungsten and lower the resistance of the bulk-filled tungsten. A non-temporary computer-readable medium containing these elements in this order.

8. The method described above, Prior to processing the structure with the nitriding process, a nucleation layer is deposited using an atomic layer deposition (ALD) process. The non-temporary computer-readable medium according to claim 7, further comprising:

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