Plasmonic interferometric lithography structure

Abstract

The application discloses an equal plasma interference lithography structure based on a grating second-order diffraction and a hyperbolic multilayer graphene, utilizes surface plasma excited by a second-order diffraction wave of a grating to generate interference, and forms an interference pattern with a half-pitch resolution of 1 / 8 grating period in a photoresist layer. A Fabry-Perot cavity is formed by two sidewalls of a grating groove, the transmittance of the grating to the diffraction wave is enhanced, and the intensity of SPP is improved. The air layer introduced in the structure can effectively improve the reusability of the grating. By utilizing the hyperbolic dispersion characteristics of the hyperbolic multilayer graphene (HMG) and the characteristics that the symmetric mode of the HMG-photoresist layer-HMG waveguide is not sensitive to the thickness of the photoresist layer, a uniform and high-contrast interference pattern can be obtained in the photoresist layer. Compared with a traditional plasma interference lithography structure, the application can obtain an interference pattern with the same half-pitch resolution under the condition of using a larger period grating.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication, and specifically relates to a plasma interference lithography structure. Background Technology

[0002] With the development of science and technology, micro-nano fabrication technology plays an important role in aerospace, biomedicine, and electronic information fields. Among them, interference lithography is an effective method for fabricating nanopatterns, with advantages such as low cost, large area, and no need for precise focusing. However, the resolution of traditional interference lithography is theoretically limited by the optical diffraction limit, making it difficult to break through the half-wavelength order. Currently, a major way to improve resolution is to use light sources with shorter wavelengths, such as deep ultraviolet (DUV), extreme ultraviolet (EUV), and soft X-rays, but expensive laser devices and complex processing procedures raise the application threshold.

[0003] Surface plasmon polariton (SPP) is a light-metal interaction mode: when light irradiates a metal, the light wave resonates with free electrons on the metal surface, thereby exciting electromagnetic oscillations on the metal surface. SPP interference lithography utilizes the interference of two opposing SPP beams at the metal-dielectric interface to produce subwavelength periodic interference patterns. At the same frequency, the wavelength of SPP is shorter than the wavelength of electromagnetic waves in free space, thus it can overcome the diffraction limit and be applied in the field of super-resolution lithography.

[0004] In recent years, SPP (Spectrophotometric Polymerization) interference lithography has gradually become a hot research area of ​​interest for scholars both domestically and internationally. Initially, metal films were introduced into the structure as superlenses or reflectors to improve the resolution of SPP interference lithography. Subsequently, to further improve the resolution, hyperbolic metamaterials composed of metal-dielectric layered structures were introduced between the grating and the photoresist layer, selecting high-k modes to obtain high-resolution interference patterns. However, high-k modes typically have a wide transmission band, resulting in poor contrast and uniformity of the interference pattern. On the other hand, SPP can be excited by higher-order diffraction waves from the grating to improve resolution, but the intensity of higher-order diffraction waves is low, and the uniformity of the resulting interference pattern is sensitive to the thickness of the photoresist layer, thus limiting its widespread application. Summary of the Invention

[0005] To address the problems of insufficient SPP intensity and sensitivity of interference pattern uniformity to photoresist layer thickness in existing SPP lithography using high-order diffraction waves, this invention provides a plasma interference lithography structure based on second-order grating diffraction and hyperbolic multilayer graphene. The SPP excited by the second-order diffraction wave of the grating generates interference, forming an interference pattern with a half-pitch resolution of 1 / 8 of the grating period in the photoresist layer. Simultaneously, a Fabry-Perot cavity is formed by the two sidewalls of the grating trench, enhancing the grating's transmittance to the diffracted waves and increasing the SPP intensity. The air layer introduced into the structure facilitates subsequent pattern transfer and effectively improves the grating's reusability. By utilizing the hyperbolic dispersion characteristics of hyperbolic multilayer graphene (HMG) and the insensitivity of symmetric modes in the HMG-photoresist-HMG waveguide to photoresist layer thickness, a uniform, high-contrast interference pattern insensitive to photoresist layer thickness is obtained in the photoresist layer.

[0006] The technical solution of the present invention is as follows:

[0007] The photolithography structure is designed from top to bottom as a grating layer, an air layer, a photolithography layer, and a substrate. The grating layer consists of a substrate, a metal grating, a trench, and a bottom dielectric layer. The width of the trench is equal to the period of the metal grating, and the trench and the bottom dielectric layer are made of the same material. The photolithography layer includes a transmission layer, a photoresist layer, and a reflection layer from top to bottom.

[0008] When TM-polarized light is incident perpendicularly on the structure, the SPP excited by the second-order diffraction wave of the grating interferes, forming an interference pattern with a half-pitch resolution of 1 / 8 of the grating period on the photoresist layer.

[0009] Preferably, in the above photolithography structure, the depth of the metal grating is 20–60 nm.

[0010] Preferably, the trench and the bottom dielectric layer are made of silicon dioxide.

[0011] Preferably, the thickness of the bottom dielectric layer is 20nm to 40nm.

[0012] Preferably, in the above photolithography structure, the metal grating material is aluminum.

[0013] Preferably, the materials of the transmission layer and the reflection layer are hyperbolic multilayer graphene materials.

[0014] Preferably, in the above photolithography structure, the thickness of the photoresist layer is 10nm to 85nm.

[0015] Preferably, the thickness of the air layer is 0–10 nm.

[0016] Compared with the prior art, the advantages of the present invention are:

[0017] 1) By using the second-order diffraction wave of the grating to excite the SPP mutual interference, the half-pitch resolution of the resulting interference pattern is further reduced from 1 / 4 of the previous metal grating period to 1 / 8, which reduces the requirement for the grating period and reduces the manufacturing difficulty.

[0018] 2) By utilizing an embedded grating and forming a Fabry-Perot cavity on both sides of the grating trench, the transmittance of the grating to diffracted waves is enhanced, the intensity of SPP at the interface between the grating and the dielectric is increased, the problem of low energy of high-order diffracted waves of the grating is solved, and the high contrast of light intensity in the photoresist layer is ensured.

[0019] 3) The air layer introduced between the grating layer and the photolithography layer makes the subsequent pattern transfer process easier to achieve and can effectively improve the reusability of the grating.

[0020] 4) By utilizing the hyperbolic dispersion characteristics of HMG and the fact that the symmetric modes in the waveguide composed of HMG-photoresist layer-HMG are insensitive to the thickness of the photoresist layer, uniform, high-contrast interference patterns that are insensitive to the thickness of the photoresist layer can be obtained in the photoresist layer. Attached Figure Description

[0021] Figure 1 The diagram shown is a schematic of the plasma interference lithography structure based on second-order grating diffraction and hyperbolic multilayer graphene used in an embodiment of the present invention.

[0022] Figure 2 The diagram shown is a flowchart of the fabrication process of the plasma interference lithography structure of the present invention;

[0023] Figure 3 The figure shown is a diagram of the electric field intensity distribution in the photolithographic structure of the present invention;

[0024] Figure 4 The figure shows the normalized electric field strength along the x-axis at z = 0 nm, 12.5 nm, and 25 nm in the photoresist layer of this invention;

[0025] Figure 5 The figure shows the electric field intensity in the middle of the photoresist layer of the period-reducing photolithography structure based on first-order grating diffraction and plasma interference, which is different from that of the present invention.

[0026] Figure 6 The figure shows the electric field intensity in the middle of the photoresist layer when the grating trench widths are 15 nm and 111 nm, respectively.

[0027] Figure 7 The figure shows the electric field strength at the bottom of the photoresist layer when the photoresist layer thickness is 45nm, 65nm and 85nm. Detailed Implementation

[0028] The technical content of the present invention will be further explained below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of the present invention.

[0029] Please see Figure 1 , Figure 1 This is a schematic diagram of a plasma interference lithography structure based on second-order grating diffraction and hyperbolic multilayer graphene provided by the present invention. From top to bottom, it consists of a grating layer 1, an air layer 2, a lithography layer 3, and a substrate 4. The grating layer 1 comprises a substrate 11, a metal grating 12, a trench 13, and a bottom dielectric layer 14. The lithography layer 3, from top to bottom, includes a transmission layer 31, a photoresist layer 32, and a reflective layer 33. The substrate 11 and substrate 4 are made of SiO2 and Si, respectively; the metal grating 12 is made of Al; the trench 13 and bottom dielectric layer 14 are made of SiO2; and the transmission layer 31 and reflective layer 33 are made of HMG.

[0030] Example:

[0031] The depth, period, and width of the metal grating 12 and the trench 13 are d1 = 50 nm, P, and P, respectively. x =222nm and w=111nm, the thickness of the bottom dielectric layer 14 is d m =25nm, the HMG thickness of the transmission layer 31 and the reflection layer 33 is d2=35nm, the thickness of the photoresist layer 32 is d3=25nm, and at a wavelength of 193nm, the relative permittivity of Al, SiO2, photoresist and Si are -4.84+0.5i, 2.44, 2.89 and -6.94+4.91i, respectively.

[0032] SPP can be excited by a grating under the following conditions:

[0033]

[0034] Where k sp Let m denote the wave vector of SPP, m denote the diffraction order of the grating, and P x This indicates the grating period.

[0035] like Figure 2 As shown, the fabrication method of the plasma interference lithography structure is as follows:

[0036] Raster layer 1:

[0037] (S1) A 50 nm thick aluminum film is deposited on the surface of substrate 11 by physical sputtering, and a 30 nm thick photoresist layer is spin-coated on it; a large-area immersion laser interference lithography system is used to fabricate the above photoresist layer into a one-dimensional grating with a grating period of 222 nm and a duty cycle of 0.5.

[0038] (S2) The grating pattern obtained in step (S1) is transferred to the aluminum film in step (S1) by ion beam etching (IBE) to obtain an aluminum grating with a period of 222nm and a duty cycle of 0.5.

[0039] (S3) Growing or filling the gaps of the aluminum grating obtained in step (S2) with silicon dioxide of the same thickness as the metal grating 12 as trenches 13;

[0040] (S4) A 25 nm thick silicon dioxide layer is deposited on the surface of the metal grating 12 and the trench 13 as a bottom dielectric layer 14;

[0041] (S5) Physically deposit aluminum spacers with a height of 5 nm on both sides of the bottom of grating layer 1;

[0042] Photolithography layer 3 and substrate 4:

[0043] (S6) Hyperbolic multilayer graphene is grown on substrates such as copper by CVD;

[0044] (S7) A photoresist layer is prepared on the top of hyperbolic multilayer graphene by spin coating;

[0045] (S8) Transfer hyperbolic multilayer graphene and photoresist layer onto substrate 4;

[0046] (S9) Hyperbolic multilayer graphene, the same as in step (S6), is grown on a substrate such as copper by CVD, and the hyperbolic multilayer graphene is transferred to the top of the photoresist layer in step (S7).

[0047] Air layer 2:

[0048] (S10) The grating layer 1 and the substrate 4 are clamped and controlled by a mechanical clamping device, and the grating layer 1 is covered on the photolithography layer 3. Due to the presence of spacers, a 5nm air layer 2 is formed.

[0049] Figure 3 The diagram shows the electric field intensity distribution in the simulated photolithographic structure. The HMG (High-Magnetic Resonance Magnet) plays a role in the transmission and shaping of electromagnetic waves. Because its transmission spectrum exhibits narrow-band transmission, supporting only modes with a wave vector near 1.7k0, it can filter out incident waves and other diffracted waves. Only SPP (Self-Propagated Point) excited by second-order diffracted waves can be transmitted. The transmitted electromagnetic waves, after leaving the HMG, transform from evanescent waves into propagating waves, thus enhancing their propagation capability in the z-direction. Alternating bright and dark field intensity variations can be observed in photoresist layer 32, representing the SPP interference pattern excited by the second-order diffracted wave of the grating, with a half-pitch resolution of 29 nm.

[0050] Figure 4The figure shows the normalized electric field intensity along the x-axis at z = 0 nm, 12.5 nm, and 25 nm in photoresist layer 32. It can be seen that the period remains consistent at these three locations. The contrast of the interference pattern is defined as (|E max | 2 -|E min | 2 ) / (E max | 2 +|E min | 2 ), where E max and E min These represent the maximum and minimum values ​​of the normalized electric field strength along the x-axis, respectively. The contrast ratios at the three locations are 0.70, 0.67, and 0.79, respectively.

[0051] Figure 5 The diagram shows the electric field intensity in the middle of the photoresist layer 32 of the period-reducing photolithography structure based on first-order grating diffraction and plasma interference, as described in this invention. It is evident that even when the method described in this invention uses a second-order diffraction wave, the normalized electric field intensity of the interference fringes is still higher than that obtained by traditional first-order grating diffraction.

[0052] Figure 6 The figure shows the electric field intensity at the center of the photoresist layer 32 when the widths of the grating trench 13 are 15 nm and 111 nm. When w = nλ sp When (n is an integer, λ) sp (Where the SPP wavelength is) with wavelength λ sp The diffracted waves can resonate in the Fabry-Perot cavity formed by the two sidewalls of the trench 13. Fabry-Perot resonance enhances the transmittance of the grating to these diffracted waves, thereby increasing the electric field intensity of the excited SPP at the interface between the grating and the dielectric. Although the interference pattern intensity corresponding to w = 111 nm is higher, the contrast and uniformity of the interference pattern are greatly reduced. There are two main factors contributing to this phenomenon: a mismatch exists in the transmission of electromagnetic waves from free space to the grating, and the metal loss is relatively large. The buried metal grating 12 is a grating structure in which the metal grating 12 is buried in a dielectric. In this structure, the incident light energy can be relatively easily coupled into the dielectric, such as the SiO2 trench 13, thus facilitating electromagnetic wave transmission and significantly enhancing electromagnetic wave transmission capability. By adjusting the thickness of the bottom dielectric layer 14, the contrast of the interference fringes is improved.

[0053] Figure 7 The figure shows the electric field intensity at the bottom of photoresist layer 32 when the thicknesses are 45nm, 65nm, and 85nm, with contrast ratios of 0.97, 0.73, and 0.7, respectively. It can be seen that the interference pattern in the photoresist layer 32 of this structure is insensitive to the photoresist thickness.

[0054] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A plasma interference lithography structure, characterized in that: The photolithography structure consists of a grating layer (1), an air layer (2), a photolithography layer (3), and a substrate (4) from top to bottom. The grating layer (1) is composed of a substrate (11), a metal grating (12), a trench (13) and a bottom dielectric layer (14) from top to bottom; the width of the trench (13) is 1 / 2 of the period of the metal grating (12); The trench (13) and the bottom dielectric layer (14) are made of the same material; The photolithography layer (3) includes, from top to bottom, a transmission layer (31), a photoresist layer (32), and a reflective layer (33); the materials of the transmission layer (31) and the reflective layer (33) are hyperbolic multilayer graphene. When TM polarized light is incident perpendicularly on the photolithography structure, an interference pattern with a half-pitch resolution of 1 / 8 of the grating period can be formed in the photoresist layer (32).

2. The plasma interference lithography structure according to claim 1, characterized in that: The trench (13) and the bottom dielectric layer (14) are made of silicon dioxide.

3. The plasma interference lithography structure according to claim 1, characterized in that, The depth of the metal grating (12) is 20~60nm.

4. The plasma interference lithography structure according to claim 3, characterized in that, The metal grating (12) has a depth of 50 nm.

5. The plasma interference lithography structure according to claim 1, characterized in that, The material of the metal grating (12) is aluminum.

6. The plasma interference lithography structure according to claim 1, characterized in that, The thickness of the bottom dielectric layer (14) is 20nm~40nm.

7. The plasma interference lithography structure according to claim 6, characterized in that, The thickness of the bottom dielectric layer (14) is 25 nm.

8. The plasma interference lithography structure according to claim 1, characterized in that, The thickness of the photoresist layer (32) is 10nm~85nm.

9. The plasma interference lithography structure according to claim 1, characterized in that, The thickness of the air layer (2) is no greater than 10 nm.

10. The plasma interference lithography structure according to claim 1, characterized in that, The thickness of the transmission layer (31) and the reflection layer (33) is 35 nm.

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