Embodiments of the present disclosure pertain to the field of semiconductor processing and, in particular, to methods of depositing a photoresist material and optimizing post apply bake (PAB) conditions to improve photoresist performance.
2) Description of Related Art
Lithography has been used in the semiconductor industry for decades for creating 2D and 3D patterns in microelectronic devices. The lithography process involves spin-on deposition of a film (photoresist), irradiation of the film with a selected pattern by an energy source (exposure), and removal (etch) of exposed (positive tone) or non-exposed (negative tone) region of the film by dissolving in a solvent. A bake may be carried out to drive off remaining solvent.
The photoresist should be a radiation sensitive material and upon irradiation a chemical transformation occurs in the exposed part of the film which enables a change in solubility between exposed and non-exposed regions. Using this solubility change, either exposed or non-exposed regions of the photoresist is removed (etched). The photoresist is then developed and the pattern can be transferred to the underlying thin film or substrate by etching. After the pattern is transferred, the residual photoresist is removed and repeating this process many times can give 2D and 3D structures to be used in microelectronic devices.
Several properties are important in lithography processes. Such important properties include sensitivity, resolution, lower line-edge roughness (LER), etch resistance, and ability to form thinner layers. When the sensitivity is higher, the energy required to change the solubility of the as-deposited film is lower. This enables higher efficiency in the lithographic process. Resolution and LER determine how narrow features can be achieved by the lithographic process. Higher etch resistant materials are required for pattern transferring to form deep structures. Higher etch resistant materials also enable thinner films. Thinner films increase the efficiency of the lithographic process.
Embodiments disclosed herein include a method of optimizing a post deposition bake of a photoresist layer. In an embodiment, the method comprises depositing the photoresist layer on a substrate, baking the photoresist layer, and measuring properties of the photoresist layer with an optical tool.
Embodiments may also comprise a method of optimizing a post apply bake (PAB) of a photoresist layer. In an embodiment, the method comprises depositing a first photoresist layer on a first substrate, baking the first photoresist layer with a first PAB, measuring a material property of the first photoresist layer during or after the first PAB with an optical tool, depositing a second photoresist layer on a second substrate, baking the second photoresist layer with a second PAB, measuring the material property of the second photoresist layer during or after the second PAB with the optical tool, and selecting the photoresist layer with the material property that provides the most desirable line width roughness, line edge roughness, and/or sensitivity to radiation exposure.
Embodiments may also include a semiconductor processing tool, that comprises a deposition module, where the deposition module is configured to deposit a photoresist layer on a substrate with a dry deposition process, a post apply bake (PAB) module, where the PAB module is configured to bake the photoresist layer, and an optical tool for measuring one or more properties of the photoresist layer during or after the bake.
Methods of optimizing the performance of a post apply bake (PAB) of a photoresist layer using in-situ or ex-situ optical measurement tools are described herein. In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments. It will be apparent to one skilled in the art that embodiments may be practiced without these specific details. In other instances, well-known aspects are not described in detail in order to not unnecessarily obscure embodiments. Furthermore, it is to be understood that the various embodiments shown in the accompanying drawings are illustrative representations and are not necessarily drawn to scale.
To provide context, photoresist systems used in extreme ultraviolet (EUV) lithography suffer from low efficiency. That is, existing photoresist material systems for EUV lithography require high dosages in order to provide the needed solubility switch that allows for developing the photoresist material. Traditionally, carbon based films called organic chemically amplified photoresists (CAR) have been used as a photoresist. However, more recently organic-inorganic hybrid materials (metal-oxo) have been used as a photoresist with extreme ultraviolet (EUV) radiation. Such materials typically include a metal (such as Sn, Hf, Zr), oxygen, and carbon. Transformation from deep UV (DUV) to EUV in the lithographic industry facilitated narrow features with high aspect ratio. Metal-oxo based organic-inorganic hybrid materials have been shown to exhibit lower line edge roughness (LER) and higher resolution which are required for forming narrow features. Also, such films have higher sensitivity and etch resistance properties and can be implemented to fabricate relatively thinner films.
Currently, a metal-oxo photoresist is deposited by spin-on methods which includes wet chemistries. Post bake processes are required to drive off any remaining solvents from the film and to render the film stable. Also, wet methods can generate a lot of wet waste that the industry wants to move away from. Photoresist films deposited by spin-on methods often result in non-uniformity issues. In accordance with embodiments of the present disclosure, addressing one or more of the above issues, processes for vacuum deposition of a metal-oxo positive tone photoresist are described herein.
More particularly, embodiments disclosed herein include methods for optimizing the performance of photoresist films. The optimization relies on optical inspection of the film during and/or after the post apply bake (PAB). Material properties, such as, but not limited to, refractive index, dielectric constant, thickness, reflectance, and/or extinction coefficient can be used as a guide in order to select the optimal PAB conditions. Optical tools, such as reflectometry, ellipsometry, and other optical techniques can be used to predict and optimize the best temperature and duration that allows the photoresist film to rearrange and optimize its sensitivity to exposure of the patterning radiation. Additionally, correlations between optical properties and line width roughness and line edge roughness can also be used to further optimize the photoresist film. In a specific embodiment, the photoresist films may include metal-oxo photoresist systems, such as those described above. In other embodiments, the photoresist films may be any type of CAR material system.
In some embodiments, the optical inspection is implemented by an in-situ optical tool. An in-situ optical tool is integrated with the tool that is implementing the PAB process. In one embodiment, the PAB process is implemented in the same tool used to deposit the photoresist, For example, a resistive heater in the chuck may be used in order to bake the photoresist. An optical tool may be provided opposite from the chuck in order to measure one or more optical properties and/or thickness of the photoresist. Such an embodiment is particularly beneficial because the substrate (e.g., wafer or the like) does not need to be transferred between tools.
Additionally, embodiments disclosed herein allow for the optimization of the photoresist layer without the need to expose and develop the photoresist layer. The exposure and developing process is a particularly time intensive and costly process. In order to form the contrast curves typical of photoresist analysis, many substrates with photoresist layers need to be formed, exposed, and developed. Such a process is expensive. In embodiments disclosed herein, the optical properties and/or thickness of the photoresist layer can be used to identify trends that point towards more optimal PAB processes. Accordingly, the cost and duration of the photoresist layer optimization is significantly reduced.
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In an embodiment, the process 280 may continue with operation 282, which comprises performing a PAB on the photoresist layer. The PAB process may include exposing the photoresist layer to an elevated temperature. For example, the temperature may be between 15° C. and 300° C. In a particular embodiment, the temperature may be between 50° C. and 250° C. In an embodiment, the duration of the PAB may be between thirty seconds and five minutes. The elevated temperature may be provided by any heating architecture. In some embodiments the chuck on which the substrate is supported may include a resistive heating element or the like. In other embodiments, one or more lamps may be used in order to heat the photoresist layer.
In an embodiment, the process 280 may continue with operation 283, which comprises measuring properties of the photoresist layer with an optical tool. In an embodiment, the optical tool may include single lamp reflectometry, dual lamp reflectometry, ellipsometry, or ultraviolet-visible spectrophotometry. In an embodiment, the properties may include one or more of a refractive index, a dielectric constant, a thickness, a reflectance, and/or an extinction coefficient. The different material properties may be correlated to properties of the photoresist layer, such as sensitivity to exposure radiation, line edge roughness, and line width roughness. That is, the measured material properties may not have a one-to-one relationship with sensitivity, line edge roughness, and line width roughness, but can be used in order to determine trends of the photoresist layer.
In an embodiment, operation 283 is implemented at the same time as the PAB. That is, changes to the photoresist layer can be determined in real time. Such an embodiment helps with determining the optimal duration of the PAB process. In an embodiment, operation 283 may be implemented after the PAB. Operation 283 may be implemented with an optical tool that is in-situ with the tool that executes that PAB. In other embodiments, operation 283 may be implemented with an optical tool that is ex-situ with the tool that executes the PAB.
In the particular embodiment described with process 280, a single substrate and photoresist layer are measured. However, it is to be appreciated that embodiments may include measuring the material properties of multiple photoresist layers on different substrates. For example, a first photoresist layer may be provided on a first substrate, and the first photoresist layer may be baked with a first PAB. Thereafter, a second photoresist layer may be provided on a second substrate, and the second photoresist layer may be baked with a second PAB. The second PAB may be different than the first PAB. The difference may include a different baking temperature and/or baking duration. As such, data can be obtained from a plurality of different PAB conditions in order to find the optimal PAB conditions.
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As noted above, existing processes for optimizing a PAB for a photoresist material is complex and expensive. An example of such a process is shown in
Thereafter, the wafer 501 is removed from the coating track tool 551 and inserted into an exposure tool 552. The exposure tool may be a DUV or EUV exposure tool. The exposure tool 552 may use a mask in order to selectively expose regions of the photoresist layer.
In an embodiment, the exposed wafer 501 is then moved to a develop tool 553 where the photoresist layer is developed. The process of exposing the photoresist layer and developing the photoresist layer is significantly time and cost intensive. Particularly, the exposure tool 552 is an expensive tool and generally has a low throughput.
After the photoresist layer is developed, the wafer may be provided into a metrology tool 554 in order to analyze the developed photoresist layer. In some embodiments, a contrast curve is used in order to determine the optimal PAB conditions of the photoresist layer. The contrast curve requires the exposure and development of a plurality of wafers. As such, the cost and time necessary to develop the contrast curve is high.
Accordingly, embodiments disclosed herein include an in-situ metrology tool so that the wafer dies not need to be passed between various tools. Additionally, the photoresist layer does not need to be exposed and patterned in some embodiments, As such, the cost and throughput of the photoresist layer optimization is improved.
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In an embodiment, the tool 555 may further comprise an in-situ metrology tool. The metrology tool may include an optical metrology tool such as, single lamp reflectometry, dual lamp reflectometry, ellipsometry, or ultraviolet-visible spectrophotometry. The metrology tool may provide thickness measurements and/or optical properties of the photoresist layer. For example, graphs similar to those shown in
Particularly, it is noted that the photoresist layer does not need to be developed in order to perform the metrology. In some embodiments, the photoresist layer may not be exposed either. This improves throughput and allows for more PAB conditions to be analyzed. As such, optimal photoresist PAB conditions can be obtained at a lower cost and within a reduced period of time. Additionally, since the tool 555 is self-contained, there is no need to transfer the wafer 501 between different tools, as is the case in the embodiment shown in
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In an embodiment, an optical metrology tool 670 is provided through the lid 640. The optical metrology tool 670 may include one or more of a single lamp reflectometry tool, a dual lamp reflectometry tool, an ellipsometry tool, or an ultraviolet-visible spectrophotometry tool. While shown as passing through the lid 640, it is to be appreciated that the optical metrology tool 670 may be provided through any component of the processing tool 600 that allows for measurements of the photoresist layer on the wafer 601. For example, light 671 may be directed to the wafer 601 and reflected back to the optical metrology tool 670. Particularly, it is to be appreciated that the optical metrology tool 670 is provided as an in-situ tool. Therefore, the wafer 601 does not need to be transported to another chamber in order to execute the metrology necessary in order to optimize PAB conditions.
In an embodiment, a displaceable column for supporting a wafer 601 is provided in the chamber 605. In an embodiment, the wafer 601 may be any substrate on which a photoresist material is deposited. For example, the wafer 601 may be a 300 mm wafer or a 450 mm wafer, though other wafer diameters may also be used. Additionally, the wafer 601 may be replaced with a substrate that has a non-circular shape in some embodiments. The displaceable column may include a pillar 614 that extends out of the chamber 605. The pillar 614 may have a port to provide electrical and fluidic paths to various components of the column from outside the chamber 605.
In an embodiment, the column may include a baseplate 610. The baseplate 610 may be grounded. The baseplate 610 may include fluidic channels to allow for the flow of an inert gas to provide an edge purge flow. In an embodiment, an insulating layer 615 is disposed over the baseplate 610. The insulating layer 615 may be any suitable dielectric material. For example, the insulating layer 615 may be a ceramic plate or the like. In an embodiment, a pedestal 630 is disposed over the insulating layer 615. The pedestal 630 may include a single material or the pedestal 630 may be formed from different materials. In an embodiment, the pedestal 630 may utilize any suitable chucking system to secure the wafer 601. For example, the pedestal 630 may be a vacuum chuck or a monopolar chuck. In embodiments where a plasma is not generated in the chamber 605, the pedestal 630 may utilize a bipolar chucking architecture.
The pedestal 630 may include a plurality of cooling channels 631. The cooling channels 631 may be connected to a fluid input and a fluid output (not shown) that pass through the pillar 614. In an embodiment, the cooling channels 631 allow for the temperature of the wafer 601 to be controlled during operation of the processing tool 600. For example, the cooling channels 631 may allow for the temperature of the wafer 601 to be controlled to between approximately −40° C. and approximately 200° C. In an embodiment, the pedestal 630 may also comprise a resistive heating element (not shown). The resistive heating element may be used in order to set a PAB baking temperature for the wafer 601. In a particular embodiment, the PAB baking temperature may be provided between approximately 15° C. and 250° C. The resistive heating element allows for the wafer 601 and the photoresist layer to be heated to a particular temperature for a desired duration. The optical metrology tool 670 may measure optical and/or thickness properties of the photoresist layer on the wafer 601. The optical metrology may be implemented during the PAB process or after the PAB process. In an embodiment, the pedestal 630 connects to the ground through filtering circuitry 645, which enables DC and/or RF biasing of the pedestal with respect to the ground.
In an embodiment, an edge ring 620 surrounds a perimeter of the insulating layer 615 and the pedestal 630. The edge ring 620 may be a dielectric material, such as a ceramic. In an embodiment, the edge ring 620 is supported by the base plate 610. The edge ring 620 may support a shadow ring 635. The shadow ring 635 has an interior diameter that is smaller than a diameter of the wafer 601. As such, the shadow ring 635 blocks the photoresist from being deposited onto a portion of the outer edge of the wafer 601. A gap is provided between the shadow ring 635 and the wafer 601. The gap prevents the shadow ring 635 from contacting the wafer 601, and provides an outlet for the edge purge flow. In an embodiment, a dual channel showerhead can be used for a positive tone photoresist fabrication process.
While the shadow ring 635 provides some protection of the top surface and edge of the wafer 601, processing gasses may flow/diffuse down along a path between the edge ring 620 and the wafer 601. As such, embodiments disclosed herein may include a fluidic path between the edge ring 620 and the pedestal 630 to enable an edge purge flow. Providing an inert gas in the fluidic path increases the local pressure in the fluidic path and prevents processing gasses from reaching the edge of the wafer 601. Therefore, deposition of the photoresist is prevented along the edge of the wafer 601.
The exemplary computer system 700 includes a processor 702, a main memory 704 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 706 (e.g., flash memory, static random access memory (SRAM), MRAM, etc.), and a secondary memory 718 (e.g., a data storage device), which communicate with each other via a bus 730.
Processor 702 represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processor 702 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processor 702 may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processor 702 is configured to execute the processing logic 726 for performing the operations described herein.
The computer system 700 may further include a network interface device 708. The computer system 700 also may include a video display unit 710 (e.g., a liquid crystal display (LCD), a light emitting diode display (LED), or a cathode ray tube (CRT)), an alphanumeric input device 712 (e.g., a keyboard), a cursor control device 714 (e.g., a mouse), and a signal generation device 716 (e.g., a speaker).
The secondary memory 718 may include a machine-accessible storage medium (or more specifically a computer-readable storage medium) 732 on which is stored one or more sets of instructions (e.g., software 722) embodying any one or more of the methodologies or functions described herein. The software 722 may also reside, completely or at least partially, within the main memory 704 and/or within the processor 702 during execution thereof by the computer system 700, the main memory 704 and the processor 702 also constituting machine-readable storage media. The software 722 may further be transmitted or received over a network 720 via the network interface device 708.
While the machine-accessible storage medium 732 is shown in an exemplary embodiment to be a single medium, the term “machine-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable storage medium” shall also be taken to include any medium that is capable of storing or encoding a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. The term “machine-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media.
In accordance with an embodiment of the present disclosure, a machine-accessible storage medium has instructions stored thereon which cause a data processing system to perform a method of forming a positive tone photoresist layer over a substrate in a vacuum chamber. The method includes providing a metal precursor vapor into the vacuum chamber. The method also includes providing an oxidant vapor into the vacuum chamber. A reaction between the metal precursor vapor and the oxidant vapor results in the formation of a positive tone photoresist layer on a surface of the substrate.
Thus, methods for forming a positive tone photoresist using dry processes have been disclosed.
This application claims the benefit of U.S. Provisional Application No. 63/388,205, filed on Jul. 11, 2022, the entire contents of which are hereby incorporated by reference herein.
Number | Date | Country | |
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63388205 | Jul 2022 | US |