Transmission-based extreme ultraviolet photolithography

Abstract

A device for transmissive extreme ultraviolet (EUV) photolithography. The device includes a suspended nanomembrane having one or more holes defining a mask pattern. The device further includes a reflective component disposed on the suspended nanomembrane, configured to reflect EUV light directed towards the suspended nanomembrane. The device may be configured to be optically in-line with a wafer. The mask pattern may be configured to accept the EUV light directed towards the suspended nanomembrane such that a pattern based on the mask pattern is applied to the wafer.

Description

TRANSMISSION-BASED EXTREME ULTRAVIOLET PHOTOLITHOGRAPHYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional Application No. 63 / 633,268 filed April 12, 2024, the specification of which is incorporated herein in its entirety by reference.FIELD OF THE INVENTION

[0002] The present invention is directed to the use of suspended nanomembranes to create a transmission-mode EUV lithography system.BACKGROUND OF THE INVENTION

[0003] Mask photolithography is the lithography method used in CMOS foundries due to its high throughput, resolution, overlay accuracy, and low cost due to high production volume. In mask photolithography, a layer of photoresist is applied to the wafer's surface, and the wafer is exposed to ultraviolet (UV) light through a photomask, which contains the desired pattern. The photomask is aligned precisely above the wafer, and the UV light is shone through it. The areas of the photoresist exposed to the light undergo a chemical change, and a pattern is written on the photoresist, which is then transferred to the wafer. This process is done in transmission mode, where collimated light impinges on the photomask and is imaged through a lens on the photoresist. In positive photoresist, the exposed regions become more soluble in the developer solution, while in negative photoresist, the exposed areas become less soluble.

[0004] On the other hand, Extreme Ultraviolet (EUV) photolithography is a complex and costly technology employed in semiconductor manufacturing to pattern extremely fine features on silicon wafers. Unlike traditional photolithography, EUV lithography utilizes light with a much shorter wavelength of approximately 13.5 nanometers, enabling the scaling down of semiconductor devices to smaller dimensions. The nature of EUV light requires the use of reflective optics instead of the transmissive ones used in conventional lithography. This is primarily because materials that are transparent at longer wavelengths, even air, absorb EUV light, making transmissive photomasks impractical.

[0005] To address this, EUV lithography systems employ mirrors coated with multiple layers of materials like molybdenum and silicon, designed to reflect EUV light efficiently. In addition, traditional lenses cannot be used because materials that are transparent atlonger wavelengths are opaque at the EUV wavelength. Instead, the system relies on multilayer mirrors to focus the light. Designing and manufacturing EUV-focusing mirrors with the required precision and reflectivity is a significant challenge. Moreover, aligning the reflective optical components in an EUV lithography system is more difficult than aligning the transmissive optics used in conventional photolithography. The precise alignment of mirrors is crucial to ensure that the EUV light is accurately directed onto the wafer. Any misalignment can lead to significant distortions in the patterned features, affecting the yield and quality of the semiconductor devices. Moreover, the use of reflective optics necessitates a more complex optical path compared to transmissive systems. This results in a larger physical footprint for EUV lithography systems, which can be a challenge in terms of facility space and layout. The size and complexity of the system also contribute to its high cost.BRIEF SUMMARY OF THE INVENTION

[0006] It is an objective of the present invention to provide devices and methods that allow for suspended nanomembranes to create a transmission-mode EUV lithography system, as specified in the independent claims. Embodiments of the invention are given in the dependent claims. Embodiments of the present invention can be freely combined with each other if they are not mutually exclusive.

[0007] The present invention features a device for transmissive extreme ultraviolet photolithography. The device may comprise a suspended nanomembrane comprising one or more holes. The one or more holes may be configured to define a mask pattern. The device may further comprise a reflective component disposed on the suspended nanomembrane, configured to reflect EUV light directed toward the suspended nanomembrane. The device may be configured to be optically in line with a wafer. The mask pattern may be configured to accept the EUV light directed toward the suspended nanomembrane such that a pattern based on the mask pattern is applied to the wafer.

[0008] The present invention features a method for patterning a semiconductor through transmissive extreme ultraviolet photolithography. In some embodiments, the method may comprise providing a wafer and providing a suspended nanomembrane comprising one or more holes defining a mask pattern and a reflective component disposed on the suspended nanomembrane, configured to reflect EUV light. The method may furthercomprise placing the suspended nanomembrane optically in-line with the wafer, directing the EUV light towards the suspended nanomembrane, and applying, by the mask pattern, a pattern based on the mask pattern onto the wafer.

[0009] One of the unique and inventive technical features of the present invention is the implementation of a thin suspended nanomembrane comprising a mask pattern configured to accept EUV light and a reflective component configured to reflect EUV light everywhere except the mask pattern. Without wishing to limit the invention to any theory or mechanism, it is believed that the technical feature of the present invention advantageously provides for efficient transmissive EUV photolithography. None of the presently known prior references or work has the unique, inventive technical feature of the present invention.

[0010] Furthermore, the prior references teach away from the inventive technical features of the present invention. Methods for EUV photolithography thus far have been exclusively based on reflectivity, and transmissive EUV photolithography has not yet been achieved. Standard UV transmissive lithography exists but only implements glass surfaces and not membranes. EUV lithography using membranes exists; for example, one work teaches the use of membranes in vacuum space to generate a metalens. This relies on the fact that the refractive index of a vacuum is higher than that of silicon. However, these systems cannot operate properly at the wavelengths required for EUV photolithography (around 13.5 nm). In fact, there is no benefit to using a vacuum instead of silicon at this wavelength. On the other hand, the present invention implements membranes and reflective components configured to reflect light at all points other than a set of holes defining a pattern for transmissive EUV photolithography. Thus, the prior arts teach away from the inventive technical features of the present invention.

[0011] Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0012] The features and advantages of the present invention will become apparent from a consideration of the following detailed description presented in connection with the accompanying drawings in which:

[0013] FIG. 1 A shows a diagram of a first embodiment of the photolithography device of the present invention comprising a mask pattern.

[0014] FIG. 1 B shows a diagram of a second embodiment of the photolithography device of the present invention comprising a diffractive lens.

[0015] FIG. 1C shows a flow chart diagram of a method for patterning a semiconductor through EUV transmissive photolithography.

[0016] FIG. 2 shows a flow chart diagram of fabricating the photolithography device of the present invention.

[0017] FIG. 3 shows a diagram of the photolithography system of the present invention in use.

[0018] FIG. 4A shows a graph of transmission amplitude through filters having a low index thickness and a high index thickness.

[0019] FIG. 4B shows a graph of transmitted phase through filters having a low index thickness and a high index thickness.

[0020] FIG. 5A shows a diagram of the layout and subwavelength features of the EUV lens of the present invention.

[0021] FIG. 5B shows a graph of the electric field of a lens across an X position and a Z position.DETAILED DESCRIPTION OF THE INVENTION

[0022] Following is a list of elements corresponding to a particular element referred to herein:

[0023] 100 device

[0024] 110 suspended nanomembrane

[0025] 115 diffractive lens

[0026] 120 reflective component

[0027] 200 wafer

[0028] 300 EUV light source

[0029] The term “extreme ultraviolet” is defined herein as electromagnetic radiation inthe part of the electromagnetic spectrum spanning wavelengths shorter than the hydrogen Lyman-alpha line from 121 nm down to the X-ray band of 10 nm.

[0030] The term “suspended nanomembrane” is defined herein as artificial or natural structures with a thickness below 100 nm and a large aspect ratio that may exceed 1.000,000, dispersed through the bulk of a fluid.

[0031] The term “mask pattern” is defined herein as a pattern of transparent areas that allows light to shine through.

[0032] The term “one-dimensional photonic crystal mirror” is defined herein as a dielectric mirror that can produce ultra-high reflectivity at a specified wavelength.

[0033] Referring now to FIGs 1A-1 B, the present invention features a device (100) for transmissive extreme ultraviolet (EUV) photolithography. In some embodiments, the device (100) may comprise a suspended nanomembrane (110) comprising one or more holes. The one or more holes may be configured to define a mask pattern. The device (100) may further comprise a reflective component (120) disposed on the suspended nanomembrane (110), configured to reflect EUV light directed toward the suspended nanomembrane (110). The device (100) may be configured to be optically in line with a wafer (200). The mask pattern may be configured to accept the EUV light directed towards the suspended nanomembrane (110) such that a pattern based on the mask pattern is applied to the wafer (200).

[0034] In some embodiments, the suspended nanomembrane (110) may comprise one or more diffractive lenses (115) disposed in the one or more holes, configured to diffract the EUV light directed towards the suspended nanomembrane (110). In some embodiments, the diffractive lenses (115) may comprise one or more holes patterned on the lenses to diffract light such that interference from the holes constructively interferes at the focal point. In some embodiments, the pattern applied to the wafer (200) may be defined by the EUV light diffracted by the one or more diffractive lenses (115). In some embodiments, the mask pattern may comprise one or more diffractive beam shapers, one or more diffractive beam splitters, one or more diffractive diffusers, or a combination thereof.

[0035] In some embodiments, the reflective component (120) may comprise a onedimensional photonic crystal mirror. In some embodiments, the reflective component (120) may be configured to match the shape of the suspended nanomembrane (110). The reflective component (120) may comprise one or more holes configured to line up with the mask pattern such that an entirety of the mask pattern is exposed by the reflective component (120). In some embodiments, the reflective component (120) may comprise molybdenum, silicon, or a combination thereof. That way, we can have EUV masks or diffractive optical elements by creating apertures through the materials.

[0036] In some embodiments, the pattern applied to the wafer (200) may be identical to the mask pattern. In some embodiments, the suspended nanomembrane (110) may have a thickness of 10 to 500 nm. In some embodiments, the suspended nanomembrane (110) may comprise silicon, derivatives thereof, or a combination thereof.

[0037] Referring now to FIG. 1 C, the present invention features a method for patterning a semiconductor through transmissive extreme ultraviolet (EUV) photolithography. In some embodiments, the method may comprise providing a wafer (200) and providing a suspended nanomembrane (110) comprising one or more holes defining a mask pattern and a reflective component (120) disposed on the suspended nanomembrane (110), configured to reflect EUV light. In some embodiments, the suspended nanomembrane (110) may be configured to reflect EUV light at all points except for the mask pattern. The method may further comprise placing the suspended nanomembrane (110) optically inline with the wafer (200) and directing the EUV light toward the suspended nanomembrane (110). The method may further comprise diffracting, by one or more diffractive lenses (115) disposed optically in-line with the wafer (200) and the suspended nanomembrane (110), the EUV light. The method may further comprise applying, by the mask pattern, a pattern based on the mask pattern and the EUV light diffracted by the one or more diffractive lenses (115) onto the wafer (200).

[0038] In some embodiments, the suspended nanomembrane (110) may comprise one or more diffractive lenses (115) disposed in the one or more holes, configured to diffract the EUV light directed towards the suspended nanomembrane (110). In some embodiments, the pattern applied to the wafer (200) may be defined by the EUV light diffracted by the one or more diffractive lenses (115). In some embodiments, the reflectivecomponent (120) may comprise a one-dimensional photonic crystal mirror. In some embodiments, the pattern applied to the wafer (200) may be identical to the mask pattern. In some embodiments, the suspended nanomembrane (110) may have a thickness of 10 to 500 nm. In some embodiments, the suspended nanomembrane (110) may comprise silicon, derivatives thereof, any nanomembrane, or a combination thereof.

[0039] Referring now to FIG. 3, the present invention features a system for transmissive extreme ultraviolet (EUV) photolithography for applying a pattern to a wafer (200) to generate a semiconductor. In some embodiments, the system may comprise an EUV light source (300) configured to generate EUV light. The system may further comprise a photolithography device (100) optically in-line with the EUV light source (300) and the wafer (200). The device (100) may comprise a suspended nanomembrane (110) comprising one or more holes. The one or more holes may be configured to define a mask pattern. The mask pattern may be configured to accept the EUV light from the EUV light source (300) and apply a pattern based on the mask pattern onto the wafer (200). The device (100) may further comprise a reflective component (120) disposed on the suspended nanomembrane (110), configured to reflect the EUV light directed towards the suspended nanomembrane (110).

[0040] In some embodiments, the suspended nanomembrane (110) may comprise one or more diffractive lenses (115) disposed in the one or more holes, configured to diffract the EUV light directed towards the suspended nanomembrane (110). In some embodiments, the pattern applied to the wafer (200) may be defined by the EUV light diffracted by the one or more diffractive lenses (115). In some embodiments, the reflective component (120) may comprise a one-dimensional photonic crystal mirror, any reflective material, or a combination thereof. In some embodiments, the pattern applied to the wafer (200) may be identical to the mask pattern. In some embodiments, the suspended nanomembrane (110) may comprise silicon, derivatives thereof, or a combination thereof.

[0041] The core idea is to utilize nanomembranes that are on the order of 10s - 100s nm thick suspensions. The membranes can be made of silicon, derivatives thereof, or any other membrane. Moreover, they are produced on a wafer scale. The fact that they are thin allows for patterning with e-beam lithography or focused ion beam milling, where etched portions are holes that allow the transmission of EUV wavelengths. The designcomprises two key components: nanomembrane diffractive optical elements and a transmission lithography mask.

[0042] The nanomembrane diffractive optical elements comprise patterned nanomembranes with holes to create diffractive lenses and other diffractive optical elements. These allow for the transmission and focusing of EUV light through diffraction. The transmission lithography mask utilizes a similar suspended nanomembrane, this mask features patterned holes that selectively transmit EUV light to create the desired exposure pattern on the wafer.

[0043] In both cases, a reflective surface is deposited on the membrane to reflect EUV light except where a hole is patterned on the membrane, e.g., using focused ion beam milling. The patterns can either represent the photomask pattern or can be designed as a quasicrystal to diffract light in a tailored manner to create an optical element, e.g., a diffractive lens. This approach in creating a nanomembrane lens is different from using a vacuum as a high-index medium compared to the silicon membrane and creating vacuum / air nanoposts that guide light and control its phase to create a metasurface.

[0044] Since both the photomask and the EUV lens can now operate in transmission mode, the same techniques can be utilized for transmissive photolithography. Collimated EUV light, perhaps with another lens, is incident on the EUV transmissive photomask, which is then imaged on the substrate using the EUV transmissive lens.

[0045] Referring now to FIGs 4A-4B, the present invention features a lens that may be fabricated by depositing multiple dielectric films that act as a transmission filter with high transmission and with the desired phase such that an optical element is obtained by spatially varying the thickness of the Fabry-Perot cavity formed by the thin films. FIG. 4A shows the high, near-unity transmittance even using lossy dielectric films due to destructive interference at the technologically relevant wavelength of 13.5 nm. By picking the values where high transmittance and the desired transmitted phase are obtained, optical elements such as high-focusing-efficiency lenses are fabricated on membranes.

[0046] Referring now to FIGs 5A-5B, the present invention features another realization for an EUV lens in a membrane based on creating subwavelength features such that the effective refractive index of the medium is locally modified. Incident light accumulates ina spatially varying relative phase that can be designed to focus light. The electric field of a lens operating at EUV wavelength (50 nm) is shown in FIG. 5B with a focusing efficiency of 35%, exceeding the state-of-the-art transmissive EUV lenses.

[0047] In some embodiments, the wafer (200) may comprise a semiconductor wafer. In some embodiments, the semiconductor wafer may comprise a silicon wafer, a gallium arsenide (GaAs) wafer, a silicon carbide (SiC) wafer, or a combination thereof. In some embodiments, the wafer (200) may comprise a length of 100 to 300 mm. In some embodiments, the wafer (200) may comprise a width of 100 to 300 mm. In some embodiments, the wafer (200) may comprise a thickness of 250 to 800 pm. In some embodiments, the wafer (200) may comprise a circular or rectangular shape.

[0048] In some embodiments, the suspended nanomembrane (110) may have a thickness of 10 to 500 nm. In some embodiments, the suspended nanomembrane (110) may have a length of 1 mm. In some embodiments, the suspended nanomembrane (110) may have a width of 1 mm. In some embodiments, the suspended nanomembrane (110) may have a rectangular shape.

[0049] In some embodiments, the reflective component (120) may have a thickness of 1 micron. In some embodiments, the reflective component (120) may have a length of 1 mm. In some embodiments, the reflective component (120) may have a width of 1 mm. In some embodiments, the reflective component (120) may comprise a rectangular shape.

[0050] In some embodiments, the EUV light source (300) may comprise laser-pulsed tin plasma, discharge-produced plasma using xenon or other high-Z elements, or a combination thereof. In some embodiments, the EUV light source (300) may be positioned 0.5 to 2 meters away from the photolithography device (100).

[0051] In some embodiments, the mask pattern may comprise a circuitry pattern. The circuitry pattern may comprise a one-to-one copy of the intended pattern. In some embodiments, the circuitry pattern may comprise a magnified copy of the intended pattern (e.g., 2X magnification, 5X magnification). In some embodiments, the circuitry pattern may comprise a minimized copy of the intended pattern (e.g., .5 scale, .25 scale).

[0052] In some embodiments, the devices and methods of the present invention may beused for the production of computer chips (e.g., large-scale mass production). In some embodiments, the computer chips may comprise solid-state memory chips, microprocessor chips, graphical processing units (GPUs), computer chips (e.g., GPUs) for use in artificial intelligence and / or machine learning, or a combination thereof.

[0053] Although there has been shown and described the preferred embodiment of the present invention, it will be readily apparent to those skilled in the art that modifications may be made thereto which do not exceed the scope of the appended claims. Therefore, the scope of the invention is only to be limited by the following claims. In some embodiments, the figures presented in this patent application are drawn to scale, including the angles, ratios of dimensions, etc. In some embodiments, the figures are representative only and the claims are not limited by the dimensions of the figures. In some embodiments, descriptions of the inventions described herein using the phrase “comprising” includes embodiments that could be described as “consisting essentially of or “consisting of, and as such the written description requirement for claiming one or more embodiments of the present invention using the phrase “consisting essentially of or “consisting of is met.

[0054] The reference numbers recited in the below claims are solely for ease of examination of this patent application, and are exemplary, and are not intended in any way to limit the scope of the claims to the particular features having the corresponding reference numbers in the drawings.

Claims

WHAT IS CLAIMED IS:

1. A device (100) for transmissive extreme ultraviolet (EUV) photolithography comprising: a. a suspended nanomembrane (110) comprising one or more holes, wherein the one or more holes are configured to define a mask pattern; and b. a reflective component (120) disposed on the suspended nanomembrane (110), configured to reflect EUV light directed towards the suspended nanomembrane (110); wherein the device (100) is configured to be optically in-line with a wafer (200); wherein the mask pattern is configured to accept the EUV light directed towards the suspended nanomembrane (110) such that a pattern based on the mask pattern is applied to the wafer (200).

2. The device (100) of claim 1 , wherein the suspended nanomembrane (110) further comprises one or more diffractive lenses (115) disposed in the one or more holes, configured to diffract the EUV light directed towards the suspended nanomembrane (110).

3. The device (100) of claim 2, wherein the pattern applied to the wafer (200) is defined by the EUV light diffracted by the one or more diffractive lenses (115).

4. The device (100) of claim 1 , wherein the reflective component (120) comprises a one-dimensional photonic crystal mirror, any reflective material, or a combination thereof.

5. The device (100) of claim 1 , wherein the pattern applied to the wafer (200) is identical to the mask pattern.

6. The device (100) of claim 1 , wherein the pattern applied to the wafer (200) is proportional to the mask pattern.

7. The device (100) of claim 1 , wherein the suspended nanomembrane (110) has a thickness of about 10 to 500 nm.

8. The device (100) of claim 1 , wherein the suspended nanomembrane (110) comprises silicon, derivatives thereof, any nanomembrane, or a combination thereof.

9. A method for patterning a semiconductor through transmissive extreme ultraviolet(EUV) photolithography comprising: a. providing a wafer (200); b. providing a suspended nanomembrane (110) comprising one or more holes defining a mask pattern, and a reflective component (120) disposed on the suspended nanomembrane (110), wherein the suspended nanomembrane (110) is configured to reflect EUV light at all points except for the mask pattern; c. placing the suspended nanomembrane (110) optically in-line with the wafer (200); d. directing the EUV light towards the suspended nanomembrane (110); and e. applying, by the mask pattern, a pattern based on the mask pattern onto the wafer (200).

10. The method of claim 9, wherein the suspended nanomembrane (110) comprises one or more diffractive lenses (115) disposed in the one or more holes, configured to diffract the EUV light directed towards the suspended nanomembrane (110).11 .The method of claim 10, wherein the pattern applied to the wafer (200) is defined by the EUV light diffracted by the one or more diffractive lenses (115).

12. The method of claim 9, wherein the reflective component (120) comprises a onedimensional photonic crystal mirror, any reflective material, or a combination thereof.

13. The method of claim 9, wherein the pattern applied to the wafer (200) is identical to the mask pattern.

14. The method of claim 9, wherein the suspended nanomembrane (110) has a thickness of 10 to 500 nm.

15. The method of claim 9, wherein the suspended nanomembrane (110) comprises silicon, derivatives thereof, any nanomembrane, or a combination thereof.

16. A system for transmissive extreme ultraviolet (EUV) photolithography for applying a pattern to a wafer (200) to generate a semiconductor, the system comprising: a. an EUV light source (300) configured to generate EUV light; and b. a photolithography device (100) optically in-line with the EUV light source (300) and the wafer (200), comprising: i. a suspended nanomembrane (110) comprising one or more holes, wherein the one or more holes are configured to define a maskpattern, wherein the mask pattern is configured to accept the EUV light from the EUV light source (300) and apply a pattern based on the mask pattern onto the wafer (200); andII. a reflective component (120) disposed on the suspended nanomembrane (110), configured to reflect the EUV light directed towards the suspended nanomembrane (110).

17. The system of claim 16, wherein the suspended nanomembrane (110) comprises one or more diffractive lenses (115) disposed in the one or more holes, configured to diffract the EUV light directed towards the suspended nanomembrane (110).

18. The system of claim 17, wherein the pattern applied to the wafer (200) is defined by the EUV light diffracted by the one or more diffractive lenses (115).

19. The system of claim 16, wherein the reflective component (120) comprises a onedimensional photonic crystal mirror, any reflective material, or a combination thereof.

20. The system of claim 16, wherein the suspended nanomembrane (110) comprises silicon, derivatives thereof, any nanomembrane, or a combination thereof.

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