CN115309009A - Dual-mode high-resolution interference photoetching device and method - Google Patents

Abstract

The present disclosure provides a dual-mode high-resolution interference lithography apparatus and method, comprising: the front-end light path module sequentially comprises a laser light source, an adjusting mirror group and a prism along a light path, light generated by the laser light source is adjusted through beam splitting of the adjusting mirror group to form at least two beams of coherent light, and the coherent light vertically enters the prism and is converged on the bottom surface of the prism after being totally reflected by the bevel edge of the prism; a back-end film layer module comprising an immersion lithography module or a surface plasmon lithography module; the immersion type photoetching module comprises a matching liquid layer, a substrate layer and a photoetching film layer, and coherent light is emitted through the bottom surface of the prism to form interference in the immersion type photoetching module and expose the photoetching film layer; the surface plasmon lithography module comprises a super lens film layer and a substrate layer, wherein the super lens film layer comprises a photoresist layer and a metal layer, evanescent waves formed by converged coherent light outside the prism bottom surface are coupled with the super lens film layer, and the photoresist layer is exposed. The present disclosure is compatible with both immersion lithography and surface plasmon lithography modes.

Description

Dual-mode high-resolution interference photoetching device and method

Technical Field

The disclosure relates to the technical field of interference lithography, in particular to a dual-mode high-resolution interference lithography device and method.

Background

The interference photoetching technology has the advantages of simple structure, low price, high efficiency, high resolution, large exposure area and the like. By utilizing interference lithography, a fine periodic structure such as a grating, a lattice and the like can be prepared in a large area without using a complex optical system or a lithography mask, so that the method has a wide application prospect in the fields of sensing, solar cells, photonic crystals and the like. However, based on the requirements for miniaturization and high integration of electronic and photoelectric devices, the modern information technology has higher and higher requirements for micro-nano manufacturing and processing precision, and the resolution is necessarily limited by the optical diffraction limit determined by the traditional optical basic theory. For example, laser interference lithography, typically has a maximum resolution of 1/2 to 1/4 wavelength. There is therefore a great need to develop new interferometric lithography techniques that can effectively extend or even break through the diffraction limit.

To realize the preparation of nano-scale patterns (below 100 nm), the wavelength of a light source can be continuously reduced by referring to the traditional projection type photoetching route, so that the diffraction limit resolution of the light source is improved. But the technical difficulty and the cost of the scheme are obviously increased, and the advantages of simple structure and low price are weakened. Besides reducing the wavelength, by using the immersion lithography technology, the exposure equivalent wavelength can be reduced by filling the high-refractive-index immersion liquid between the mask plate and the photoresist, and the method is also an effective method for further improving the limit resolution. However, the current immersion lithography technology can only raise the maximum resolution to about 1/4 wavelength. In addition, immersion lithography also places more stringent requirements on the materials of the photoresist, especially the chemically amplified photoresist, and has certain limitations.

On the other hand, the Surface Plasmon (SP) technology provides a new lithography solution that can break through the diffraction limit. A surface plasmon is a surface electromagnetic wave that exists at the interface of a metal and a medium. Because the wavelength of the light is far smaller than that of the illuminating light, super-resolution lithography can be realized. The interference photoetching technology based on SP has a wider application prospect in the aspect of preparing large-area nano structures, but related photoetching devices reported at present are mostly based on simulation design and have little practical process feasibility.

Disclosure of Invention

Technical problem to be solved

In view of the above problems, the present disclosure provides a dual-mode high-resolution interference lithography apparatus and method, which are used to solve the technical problems that the conventional interference lithography is difficult to implement high-resolution imaging and to be compatible with multiple lithography modes.

(II) technical scheme

One aspect of the present disclosure provides a dual-mode high-resolution interference lithography apparatus, comprising: the front-end light path module sequentially comprises a laser light source, an adjusting mirror group and a prism along a light path, light generated by the laser light source is adjusted through beam splitting of the adjusting mirror group to form at least two beams of coherent light, and the coherent light vertically enters the prism and is converged on the bottom surface of the prism after being totally reflected by a bevel edge of the prism; a back-end film layer module comprising an immersion lithography module or a surface plasmon lithography module; the immersion type photoetching module comprises a matching liquid layer, a substrate layer and a photoetching film layer, and coherent light is emitted through the bottom surface of the prism to form interference in the immersion type photoetching module and expose the photoetching film layer; the surface plasmon lithography module comprises a super lens film layer and a substrate layer, wherein the super lens film layer comprises a photoresist layer and a metal layer, evanescent waves formed by converged coherent light outside the prism bottom surface are coupled with the super lens film layer, and the photoresist layer is exposed.

Further, the immersion lithography module sequentially comprises a first matching liquid layer, a substrate layer, a lithography film layer and a second matching liquid layer along the optical path, wherein the first matching liquid layer is filled in a gap between the prism and the substrate layer; or the immersion type photoetching module sequentially comprises a first matching liquid layer, a photoetching film layer and a substrate layer along the light path, and the first matching liquid layer is filled in a gap between the prism and the photoetching film layer.

Further, the refractive indices of the prism, the matching liquid layer, the substrate layer, and the photolithography film layer are similar or identical to each other, so that coherent light is transmitted and interferes in the immersion lithography module.

Further, the structures and parameters of the matching liquid layer, the substrate layer and the photoetching film layer are obtained by simulation and optimization by using a strict coupled wave analysis method.

Further, the surface plasmon lithography module sequentially comprises a first metal layer, a photoresist layer, a second metal layer and a substrate layer along a light path; the first metal layer is in proximity to or in contact with the bottom surface of the prism.

Further, the structure and parameters of the photoresist layer and the metal layer, and the air gap between the prism and the back end film layer module are obtained by simulation and optimization using a rigorous coupled wave analysis method.

Further, when the rear-end film layer module is the surface plasmon lithography module, a focus detection module is further arranged above the prism and used for detecting the size and distribution of the gap between the bottom surface of the prism and the rear-end film layer module.

Furthermore, the prism is a frustum with symmetrical left and right axes; the prism is a high refractive index material including one of optical glass, quartz glass, sapphire, and metal halide crystal.

Furthermore, the wavelength of the laser light source is 157 nm-436 nm; the adjusting lens group comprises a plurality of facula beam expanding elements, polarization adjusting elements, spatial filtering elements, semi-reflecting and semi-transmitting mirror elements and reflecting mirror elements.

In another aspect, the present disclosure provides a method of dual-mode high-resolution interference lithography, comprising: s1, emitting laser by using a laser light source; utilizing an adjusting mirror group to split and adjust the laser into at least two beams of coherent light which vertically enter a prism; the coherent light is totally reflected on the bevel edge by a prism and then is converged on the bottom surface of the prism; the laser light source, the adjusting mirror group and the prism form a front-end light path module; s2, using an immersion type photoetching module to enable coherent light to form interference after being emitted through the bottom surface of the prism and exposing the photoetching film layer; the immersion lithography module comprises a matching liquid layer, a substrate layer and a lithography film layer; or the surface plasmon lithography module is used for coupling evanescent waves formed by the converged coherent light outside the bottom surface of the prism with the superlens film layer and exposing the photoresist layer; the surface plasmon lithography module comprises a super lens film layer and a substrate layer, wherein the super lens film layer comprises a photoresist layer and a metal layer.

(III) advantageous effects

The double-mode high-resolution interference photoetching device and the double-mode high-resolution interference photoetching method have the advantages that the coherent light beams and the prisms form the front-end light path module, the compatibility of two modes of immersion photoetching and surface plasmon photoetching is realized by designing various photoetching film layers in the rear-end film layer module, the front-end light path module is relatively precise in structure, and the rear-end film layer module is small in size and easy to replace, so that the two modes are flexibly switched and the operation is simple and convenient. Further, by optimizing the design of the multiple film layers in the two modes, the light intensity and the contrast uniformity in the photoresist thickness direction are regulated, so that the contrast optimization and the expansion of the focal depth and the working distance are realized, and the preparation of high-resolution patterns can be realized.

Drawings

FIG. 1 schematically depicts a schematic structural diagram of a dual-mode high-resolution interference lithography apparatus according to an embodiment of the present disclosure;

FIG. 2 schematically illustrates a back end membrane module that is an immersion lithography module according to an embodiment of the disclosure;

FIG. 3 schematically illustrates a structural diagram in which the back end film layer module is a surface plasmon lithography module, according to an embodiment of the disclosure;

FIG. 4 is a schematic diagram illustrating the structure of a laser light source and an adjusting mirror group according to an embodiment of the disclosure;

fig. 5 schematically illustrates a structural diagram of a front-end optical path module according to an embodiment of the present disclosure;

FIG. 6 schematically shows a schematic structural diagram of a prism according to an embodiment of the present disclosure;

FIG. 7 is a diagram schematically illustrating a light intensity distribution simulated by a rigorous coupled wave analysis method according to an embodiment of the disclosure;

FIG. 8 schematically shows a scanning electron microscope image measured in accordance with a first embodiment of the disclosure;

FIG. 9 schematically shows a schematic structural diagram of a prism in accordance with an embodiment of the present disclosure;

FIG. 10 is a diagram schematically illustrating a light intensity distribution simulated by a rigorous coupled wave analysis method according to a second embodiment of the disclosure;

fig. 11 schematically illustrates a scanning electron microscope image measured in accordance with a second embodiment of the disclosure;

FIG. 12 is a diagram schematically illustrating contrast and light intensity distribution simulated by a rigorous coupled wave analysis method according to a third embodiment of the disclosure;

FIG. 13 schematically illustrates a scanning electron microscope image measured in accordance with a third embodiment of the disclosure;

FIG. 14 schematically shows a light intensity distribution simulated by a rigorous coupled-wave analysis method according to a first embodiment of the disclosure;

fig. 15 schematically shows a scanning electron microscope image as measured in comparative example one according to the present disclosure.

Detailed Description

To make the objects, technical solutions and advantages of the present disclosure more apparent, the present disclosure will be described in further detail below with reference to specific embodiments and the accompanying drawings.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.

It should be noted that, if directional indication is referred to in the embodiment of the present disclosure, the directional indication is only used for explaining a relative positional relationship, a motion situation, and the like between the components in a certain posture, and if the certain posture is changed, the directional indication is changed accordingly.

Embodiments of the present disclosure provide a dual-mode high-resolution interference lithography apparatus, please refer to fig. 1 to 3, including: the front-end light path module sequentially comprises a laser light source 1, an adjusting mirror group 2 and a prism 3 along a light path, light generated by the laser light source 1 is adjusted through beam splitting of the adjusting mirror group 2 to form at least two beams of coherent light, and the coherent light vertically enters the prism 3 and is converged on the bottom surface of the prism 3 after being totally reflected by the bevel edge of the prism 3; a back-end film layer module comprising an immersion lithography module or a surface plasmon lithography module; the immersion lithography module comprises a matching liquid layer 11, a substrate layer 12 and a lithography film layer 13, coherent light is emitted through the bottom surface of the prism 3 and then forms interference in the immersion lithography module, and the lithography film layer 13 is exposed; the surface plasmon lithography module comprises a super lens film layer 21 and a substrate layer 22, the super lens film layer 21 comprises a photoresist layer 211 and a metal layer 212, evanescent waves formed by converged coherent light outside the bottom surface of the prism 3 are coupled with the super lens film layer 21, and the photoresist layer 211 is exposed.

The photoetching device disclosed by the invention takes a high-refractive-index prism 3 as a core optical device, so that at least two fixed coherent light beams (two light beams as shown in figure 1) are totally reflected at the bevel edge of the prism 3 and then converged through the bottom surface of the prism, and enter a rear-end film module to form interference. The period of the interference fringes is determined by the angle of the hypotenuse of the prism 3, the refractive index and the wavelength of the laser source 1. At the emergent surface (bottom surface) of the prism 3, exposure of two modes of immersion type interference and Surface Plasmon (SP) interference can be realized simultaneously by adopting different photoetching film layer schemes.

The back-end film layer module is a plurality of film layer structures, and according to the requirements of two modes of immersion lithography and surface plasmon lithography, the immersion lithography can comprise a matching liquid layer 11, a substrate layer 12 and a lithography film layer 13, and the surface plasmon lithography can comprise a photoresist layer 211, a metal layer 212 and a substrate layer 22. This is disclosed through designing the multiple photoetching rete in the rear end rete module, has realized the compatibility of immersion lithography and surface plasmon lithography two kinds of modes, because the front end light path module structure is relatively accurate, and the rear end rete module is small and be liable to change, therefore the switching between two kinds of modes is nimble and easy and simple to handle.

On the basis of the above embodiment, as shown in fig. 2, the immersion lithography module sequentially includes a first matching liquid layer 111, a substrate layer 12, a lithography film layer 13, and a second matching liquid layer 112 along an optical path, where the first matching liquid layer 111 is filled in a gap between the prism 3 and the substrate layer 12 (a first lithography layer structure, as shown in fig. 2 (a)); or the immersion lithography module, includes a first matching liquid layer 111, a lithography film layer 13, and a substrate layer 12 (a second lithography layer structure, as shown in fig. 2 (b)) in this order along the optical path, and the first matching liquid layer 111 fills the gap between the prism 3 and the lithography film layer 13.

For the immersion lithography mode, the matching liquid needs to be coated on the exit surface of the prism 3, and the refractive index of the first matching liquid layer 111 is required to be as same as that of the prism 3 as possible, so that the light beam enters the lithography layer (the lithography layer includes the substrate layer 12 and the lithography film layer 13) without being totally reflected again on the bottom surface (exit surface) of the prism 3. Wherein the material of the substrate layer 12 is required to be transparent and the refractive index thereof is within a specific range. For the first lithography layer structure, the second matching liquid layer 112 needs to be used to cover the lithography film layer 13; in the second resist layer structure, the resist layer 13 is disposed on the substrate layer 12, and an additional matching liquid layer is not required for covering, but a matching liquid layer (second matching liquid layer 112) may be further provided below the resist layer, if necessary, and the refractive index value thereof is usually adjusted around the refractive index of the resist layer 13.

On the basis of the above embodiment, the refractive indexes of the prism 3, the matching liquid layer 111, the substrate layer 12 and the photoresist layer 13 are similar or identical, so that the interference light is transmitted in the immersion lithography module and forms interference.

For the immersion lithography mode, the beam is transmitted through the back end film layer module. A matching liquid layer is required to be filled between the photoetching layer and the prism 3, so that light beams enter the photoetching layer to expose the photoresist in the photoetching film layer 13. The refractive index of the first matching liquid layer 111 is required to be as identical as possible to the prism 3; in the first photolithography layer structure, the substrate layer 12 is in direct contact with the first matching liquid layer 111, and in order to realize transmission of a light beam through the photolithography layer, it is required that the refractive index of the substrate layer 12 is also close to the first matching liquid layer 111 to avoid occurrence of total reflection. The photoresist layer 13 is a photoresist material sensitive to the wavelength of the light source. The second matching liquid layer 112 directly wets the surface of the photoresist layer 13 to further regulate and optimize the optical field in the photoresist layer. The refractive index parameters of the various film layers (including the matching fluid) in the immersion lithography module are designed in such a way that the light beam is transmitted through the lithography layers, and therefore the refractive indices of the various film layers should be similar or identical.

On the basis of the above embodiment, the structures and parameters of the matching liquid layer 11, the substrate layer 12, and the photoresist layer 13 are obtained by simulation and optimization using a rigorous coupled wave analysis method.

Furthermore, the refractive index can be regulated, so that the optical field contrast in the photoresist layer 13 is maximized, and the consistency of the optical field contrast and the peak intensity in the depth direction of the photoresist is the best. Therefore, a strict Coupled Wave Analysis (RCWA) method can be used for simulating and optimizing the refractive index parameters of each film layer, and high-resolution interference lithography in an immersion lithography mode can be realized according to different process requirements.

On the basis of the above embodiment, as shown in fig. 3, the surface plasmon lithography module sequentially includes a first metal layer 2121, a photoresist layer 211, a second metal layer 2122, and a substrate layer 22 along an optical path; first metal layer 2121 is in proximity to or in contact with the bottom surface of prism 3.

For the surface plasmon lithography mode, a metal film layer (including a first metal layer 2121 and a second metal layer 2122) is respectively disposed above and below the photoresist layer 211 in the rear film layer module, the entire rear film layer module is close to or in contact with the exit surface of the prism 3 (i.e., a certain air gap is allowed), and the size of the gap between the bottom surface (exit surface) of the prism 3 and the rear film layer module can be controlled by applying pressure to the bottom of the film layer. The interference light beam is totally reflected in the bottom surface of the prism 3, and generates evanescent waves out of the plane. The super-lens film layer 21 formed by the metal-medium alternation of the back-end film layer module is coupled with evanescent waves, so that the photoresist layer 211 is sensitized.

On the basis of the above embodiment, the structures and parameters of the photoresist layer 211 and the metal layer 212 and the air gap between the prism 3 and the rear film module are obtained by simulation and optimization using a rigorous coupled wave analysis method.

For the surface plasmon lithography mode, the parameter design principle of each film layer in the rear-end film layer module is as follows: the real parts of the dielectric constants of the first metal layer 2121 and the second metal layer 2122 are negative, and the material thickness and the refractive index enable the film structure to meet the SP resonance condition, so that the optical field contrast in the photoresist layer 211 is maximized, and the optical field contrast and the peak intensity in the depth direction in the photoresist layer 211 are the best consistent. Therefore, the RCWA method can be used for simulating and optimizing the refractive index parameters of each film layer, and high-resolution interference lithography in a surface plasmon lithography mode can be realized according to different process requirements. The rigorous coupled wave analysis method is a general method in the field and is not described herein. In addition, because phenomena such as crystal grains, defects, surface oxidation and the like occurring in the preparation process of the metal film layer cannot be fully reflected in the conventional RCWA simulation, the stray light caused by the phenomena needs to be considered for predicting the actual light field. Only when the exposure signal reaches a certain intensity, the signal-to-noise ratio is high enough to realize high-resolution exposure. The inventor proves through experiments that when the peak light intensity of the signal is reduced to 0.1 or below of the sum of the two incident light intensities, the nanometer-level high-resolution imaging cannot be realized.

On the basis of the above embodiment, when the rear end film layer module is a surface plasmon lithography module, a focus detection module 4 is further disposed above the prism 3, and the focus detection module 4 is configured to detect a gap size and a gap distribution between the bottom surface of the prism 3 and the rear end film layer module.

As shown in fig. 1, for the surface plasmon lithography mode, because an air gap exists between the prism 3 and the rear end film layer module, the in-situ focus detection module 4 can be optionally added, and the size and the distribution of the gap between the exit surface of the prism 3 and the rear end film layer module are detected. At this time, the distance between the incident surface of the prism 3 and the first metal layer 2121 should be limited to be within 30mm, so as to avoid that the focal depth of the focus detection lens cannot cover the emergent surface due to the too high prism 3. Meanwhile, enough installation and moving space must be reserved for the focus detection lens by the incident surface of the prism 3; for the optionally-added in-situ focus detection module 4, a focus detection method based on a confocal frequency domain white light interference principle can be adopted to realize the precise detection of the absolute distance between the prism 3 and the rear-end film layer module. The method is based on a multi-wavelength interferometry technology, achieves analysis of air gaps by collecting reflection type interference spectrums through a detection probe, and meets the requirements of absolute distance, high precision and large-range focus detection.

On the basis of the above embodiment, the prism 3 is a frustum of a prism which is symmetrical with respect to the left and right axes; the prism 3 is a high refractive index material including one of optical glass, quartz glass, sapphire, and metal halide crystal.

After the material of the prism 3 is determined (refractive index is determined), the period of the interference fringe is determined by the angle of the hypotenuse of the trapezoid, which is related as follows:

wherein, λ is the laser wavelength, θ is the incident angle of the interference light, and n is the refractive index of the incident layer; incident angle theta and inclined edge angle of trapezoidal prism

The relationship (as shown in FIG. 1) is:

on the basis of the above embodiment, the adjusting lens group 2 includes a plurality of spot beam expanding elements, polarization adjusting elements, spatial filtering elements, half-reflecting and half-transmitting mirror elements, and reflecting mirror elements.

The front-end optical path module adopts a scheme of splitting the same laser light source 1, and achieves an interference condition (as shown in fig. 4) through fine adjustment of light intensity and an optical path, wherein the light source is the laser light source 1, the selection can be carried out according to the resolution requirement of a prepared graph and the selection of the wavelength of a photoresist, the wavelength of the laser light source 1 can be 157 nm-436 nm, and meanwhile, the light spot energy distribution type (Gaussian or flat top) of the light source can be selected according to the illumination field size and the light intensity uniformity requirement required by a photoetching process. According to the requirements of the quality, the area, the uniformity and the like of the interference pattern, the adjusting module 201 is added on the front section of the beam splitting light path, and the properties of the light source are processed, including but not limited to light spot beam expanding, polarization state adjusting and light intensity uniformity improving. The half-reflecting and half-transmitting mirror element 202 corresponding to the wavelength is used for light splitting, the reflectivity of the reflecting mirrors 203, 204 and 205 corresponding to the wavelength can reach 99%, and the optical elements 206 and 207 are used for adjusting the polarization state, the light intensity and the optical path length of the corresponding optical path of the interference light beam formed by the same source.

The method can expand the resolution limit of interference lithography for two modes of immersion lithography and surface plasmon lithography. For immersion lithography mode, the minimum period of the interference fringes is λ/2n, determined by the refractive indices of the prism, matching fluid and the lithographic layer. For the SP photoetching mode, because evanescent waves can keep a high-frequency part of an optical field, and almost no spatial frequency limitation exists theoretically, the highest resolution is mainly limited by the material and the focal depth of a prism.

Conventional prism devices simply contact the photoresist-coated substrate with the prism or apply the photoresist directly to the prism. Although the mode can utilize an excited evanescent field to carry out interference exposure, the problem that the intensity and the contrast of an optical field in a photoetching film layer are not uniformly distributed in a thickness range exists. As the period of the interference fringes is reduced, the problem will cause the depth of focus to be greatly compressed, thereby seriously affecting the lithography effect.

The present disclosure optimizes this problem in both modes: for the immersion lithography mode, the contrast and uniformity in the lithography film layer are optimized by the combined use of a plurality of layers of transparent substrates with different refractive indexes and matching liquid; for the SP photoetching mode, through the design of the metal-medium film layer, an evanescent field formed by the prism forms coupling in the photoresist layer, and the effective expansion of the focal depth and the working distance is realized.

The present disclosure also provides a method of dual-mode high-resolution interference lithography, comprising: s1, emitting laser by using a laser light source 1; utilizing an adjusting mirror group 2 to split and adjust the laser to form at least two beams of coherent light which vertically enter a prism 3; the prism 3 is used for carrying out total reflection on the bevel edge of the coherent light and then converging the coherent light on the bottom surface of the prism 3; the laser light source 1, the adjusting mirror group 2 and the prism 3 form a front end light path module; s2, using an immersion type photoetching module to enable coherent light to form interference after being emitted through the bottom surface of the prism 3 and exposing the photoetching film layer 13; the immersion lithography module comprises a matching liquid layer 11, a substrate layer 12 and a lithography film layer 13; or the surface plasmon lithography module is used for coupling evanescent waves formed by the converged coherent light outside the bottom surface of the prism 3 with the superlens film layer 21 and exposing the photoresist layer 211; the surface plasmon lithography module comprises a super lens film layer 21 and a substrate layer 22, wherein the super lens film layer 21 comprises a photoresist layer 211 and a metal layer 212.

The present disclosure provides a method of dual mode high resolution interference lithography switchable between immersion lithography and SP lithography. The method takes at least two coherent laser beams and a prism 3 as a front-end light path module, and then realizes the compatibility of two modes through various photoetching film layer designs in a rear-end film layer module. For the immersion type photoetching mode, a method of matching double-layer immersion liquid and a substrate is adopted; for the SP lithography mode, this is achieved by a metal-dielectric (photoresist) multi-film scheme; because the front-end optical path module is relatively precise in structure, and the rear-end film layer module is small in size and easy to replace, the two modes are flexibly switched and are easy and convenient to operate. The device and the method can realize the preparation of high-resolution patterns with wavelength far lower than 1/4, and are verified by experiments.

The present disclosure is further illustrated by the following detailed description. The dual-mode high-resolution interference lithography apparatus and method described above are specifically described in the following embodiments. However, the following examples are merely illustrative of the present disclosure, and the scope of the present disclosure is not limited thereto.

As shown in fig. 1, the overall design of the present embodiment is divided into a front-end optical path module and a rear-end film layer module. The front-end optical path module mainly comprises a laser light source 1 for generating two coherent light beams, a regulating mirror group 2 (not specifically shown in the figure) and a trapezoidal prism 3. The double beams vertically enter the prism 3, are totally reflected on the inclined edge and then are converged on the bottom surface of the prism 3. The back end membrane module is a multiple membrane layer structure that may include photoresist, substrate, and other photoresist layers or matching fluid layers as needed for both modes.

The embodiment provides a device and a method for realizing high-resolution interference lithography below 1/4 wavelength by a method with relatively simple structure and relatively low cost. The embodiment uses a relatively traditional design scheme for the front-end light path module, and can also use other prism interference lithography designs, such as four-beam laser interference to form a dot pattern in a regular quadrangular prism.

The immersion lithography mode has the advantages of simple film preparation, high optical field uniformity and good repeatability, but has certain limitation on the selection of the substrate and the matching fluid (the substrate requires a transparent material, and the substrate and the matching fluid need to have a specific refractive index according to the resolution requirement). Furthermore, the use of photoresists that are partially sensitive to surface environments is also limited due to the need for direct contact between the photoresist layer and the matching liquid layer.

The SP photoetching mode has the advantages that the resolution ratio is hardly influenced by the refractive index of the photoetching film layer, the matching fluid is not required to be introduced, and the substrate is not particularly limited. However, the photoetching film layer is relatively complex, relatively accurate thickness and roughness control is needed, the light intensity is greatly influenced by an air gap, and the dose fluctuates under the condition of no focus detection module, so that the repeatability is influenced.

Therefore, the present embodiment realizes compatibility and simple switching between two modes in a modular form, and a suitable mode can be selected according to actual requirements. And in any mode, the exposure effect can be optimized through the optimized design of the film layer.

In this embodiment, a Rigorous Coupled Wave Analysis (RCWA) method is used to optimally design the optical field in the photoresist. Wherein the immersion lithography mode requires the design of the multilayer structure of the matching fluid and the transparent substrate material and the design of the parameters (mainly refractive index); the SP lithography mode requires the design of the thickness of the metal and photoresist layers, the refractive index and the air gap between the prism and the refractive index. Through the design of multiple film layers, the light intensity and the contrast in two modes are regulated and controlled, so that the contrast optimization and the expansion of the focal depth and the working distance are realized.

According to the above scheme, 3 specific examples and 1 comparative example are provided below.

The first embodiment is as follows: 120nm periodic immersion interference lithography

According to the above requirements, in the first embodiment, a set of dual-beam interference optical system is designed, the laser light source 1 selects a single longitudinal mode ultraviolet continuous laser with a wavelength of 360nm, the maximum power is 50mW, the light spot is a gaussian light beam with a diameter of 1mm, and the system is matched with an optical beam expanding module 51 (including a beam expanding lens module with double, five and ten times beam expanding magnification), an ultraviolet spectroscope 52 (with a beam splitting ratio of 50: 50), a light intensity fine-tuning module 53 (i.e., an adjusting lens 2) and a plurality of ultraviolet reflectors 54, and the optical path difference is controlled within the coherence length of the light source through the light path design, and enters the prism 3 (as shown in fig. 5) on the premise of ensuring coherence.

The prism 3 is a trapezoidal prism with an incident angle of 56.7 degrees, the material is sapphire, the corresponding refractive index under the exposure wavelength is 1.794, and the angle and the refractive index correspond to interference fringes with a period of 120 nm. The prism specific parameters are shown in fig. 6.

In the rear film layer module behind the prism exit surface, as shown in fig. 2 (a), a matching liquid having a refractive index equal to that of sapphire is used as the first matching liquid layer 111, and the refractive index is 1.79; the substrate layer 12 is a sapphire substrate having a thickness of 0.5 mm; the photoresist layer 13 is an I-line photoresist with a thickness of 50nm, and the measured value of the dielectric constant of the photoresist is as follows: n =1.58, k =0.018; the second matching liquid layer 112 has a refractive index of 1.69 and is directly coated on the surface of the photoresist layer 13. The interference photoetching film layer structure is geometrically modeled according to a numerical electromagnetic simulation algorithm program RCWA, then the refractive index of the structure is set, and when two 360nm wavelength plane wave beams enter at a symmetrical angle, interference fringes can be obtained on the photoetching film layer 13. As shown in fig. 7, the photoresist depth range can achieve completely uniform light intensity distribution (the peak light intensity deviation between 5-35 nm depth is only 0.07%) under the current parameters, and the contrast can be as high as more than 0.82, thereby meeting the requirement of high-quality lithography imaging.

After exposing the photoresist for 3 seconds according to the parameters of the apparatus, the sapphire substrate was removed from the prism 3, and the matching solution was rinsed with deionized water for 30 seconds. Drying the substrate by nitrogen, then baking the substrate on a constant temperature hot plate at 100 ℃ for 60 seconds, and then carrying out conventional development and fixation to obtain the grating pattern with the period of 120 nm.

The actual measurement scanning electron microscope image is shown in fig. 8. The visible target photoresist pattern has good resolution and clear line edge, which shows that the light field contrast is high, and the light intensity uniformity in the photoresist thickness direction obtains the expected optimization effect.

Example two: 104nm periodic immersion interference lithography

The prism 3 in the first embodiment is replaced by a trapezoidal prism with an incident angle of 72.06 °, the material is sapphire, the corresponding refractive index under the exposure wavelength is 1.794, and the angle and the refractive index correspond to the interference fringe with a period of 104 nm. The prism specific parameters are shown in fig. 9.

In the rear film layer module behind the prism exit surface, as shown in fig. 2 (a), a matching liquid having a refractive index equal to that of sapphire is used as the first matching liquid layer 111, and the refractive index is 1.79; the substrate layer 12 is a sapphire substrate having a thickness of 0.5 mm; the photoresist layer 13 is an I-line photoresist with a thickness of 50nm, and the dielectric constant of the photoresist is measured as follows: n =1.58, k =0.018; the second matching liquid layer 112 is directly coated on the surface of the photoresist layer 13, as is the first matching liquid layer 111. As shown in FIG. 10, according to RCWA simulation, uniform light intensity distribution (the peak light intensity deviation between 5-35 nm depth is less than 5%) can be realized in the photoresist depth range under the parameter, and the contrast can be as high as more than 0.94, thereby meeting the requirement of high-quality lithography imaging.

After exposing the photoresist for 3 seconds according to the parameters of the apparatus, the sapphire substrate was removed from the prism 3, and the matching solution was rinsed with deionized water for 30 seconds. Drying the substrate by nitrogen, then baking the substrate on a constant temperature hot plate at 100 ℃ for 60 seconds, and then carrying out conventional development and fixation to obtain the grating pattern with the period of 104 nm.

The actual measurement scanning electron microscope image is shown in fig. 11. The visible target photoresist pattern has good resolution and clear line edge, which shows that the light field contrast is high, and the light intensity uniformity in the photoresist thickness direction obtains the expected optimization effect.

Example three: 104nm periodic SP interference lithography

Following the light source and prism combination of example two, the back end film layer module below the prism exit surface was replaced with a surface plasmon lithography module, i.e. "first metal layer 2121-photoresist layer 211-second metal layer 2122-substrate layer 22". The first metal layer 2121 is a silver film with the thickness of 15nm, the photoresist layer 211 is an I-line photoresist with the thickness of 30nm, the second metal layer 2122 is a silver film with the thickness of 50nm, and the substrate layer 22 is a silicon substrate with a polished single surface and the thickness is 0.5mm. After the substrate of the rear film layer is contacted with the prism 3, the size of the air gap between the substrate and the prism is adjusted by applying pressure to the bottom. In the third embodiment, the average air gap measured by the added in-situ focus detection module 4 is 36nm. As shown in fig. 12, according to RCWA simulation, uniform light intensity distribution with contrast as high as 0.9 can be achieved within the photoresist depth range under the parameter. At 36nm air gap, the internal light intensity of the photoresist exceeds 0.3 of the sum of the two incident light intensities. Within the air gap variation range, only the light intensity value is changed, and the light field uniformity and the contrast in the photoresist are kept unchanged.

And exposing the photoresist for 5 seconds according to the parameters of the device, taking down the substrate, tearing off the first metal layer 2121 (silver film layer) at the top by using an adhesive tape, baking the silver film layer on a constant-temperature hot plate at 100 ℃ for 60 seconds, and then carrying out conventional development and fixation to obtain the grating pattern with the period of 104 nm.

The actual measurement scanning electron microscope image is shown in fig. 13. The visible target photoresist pattern has good resolution and clear line edge, which shows that the light field contrast is high, and the light intensity uniformity in the photoresist thickness direction obtains the expected optimization effect.

Comparative example one: 104nm periodic immersion interference

Following the light source and prism combination of example two, and the back end film module, the second matching liquid layer 112 was replaced with a matching liquid having a refractive index of 1.46, and the remaining process parameters were kept constant. As shown in fig. 14, according to the RCWA simulation, the photoresist center contrast at this parameter will drop to around 0.5, which is not in accordance with the optimized design and does not meet the high quality lithography imaging requirements.

And cleaning the matching solution according to the process conditions in the second embodiment, and performing post-baking and developing on the photoresist to obtain a 104nm periodic grating pattern.

The actual measurement scanning electron microscope image is shown in fig. 15. It can be seen that in the second comparative example, the quality of the grating pattern is significantly degraded, and the edge roughness and the pattern uniformity are also significantly reduced, which is consistent with the simulation result.

Comparative example two: 104nm periodic SP interference lithography

The air gap value was adjusted to 80nm, following the light source, prism, and back end film layer module combination of example three. As shown in fig. 12, according to RCWA simulation, although the photoresist can maintain uniform light intensity distribution and high contrast theoretically under this parameter, its internal light intensity is attenuated to 0.1 below the sum of the two incident light intensities. Considering the influence of the flatness of the actual film layer and stray light, it is expected that it is difficult to form an image with high resolution under such conditions.

Comparing the light intensity under the parameter with the light intensity in the third embodiment, exposing the photoresist for 20, 40 and 60 seconds according to the light intensity ratio, and observing no photoetching pattern in a scanning electron microscope.

In conclusion, the dual-mode high-resolution interference photoetching device and method disclosed by the invention can be compatible with high-resolution interference photoetching in two modes of immersion photoetching and SP photoetching according to different process requirements; and the method which has relatively simple structure and relatively low cost is utilized to realize the high-resolution interference lithography with the wavelength below 1/4, and the problems of small focal depth, nonuniform distribution of the intensity and contrast of the optical field in the lithography film layer in the thickness range and the like of the traditional prism (evanescent field) interference lithography are solved.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims (10)

1. A dual-mode high-resolution interference lithography apparatus, comprising:

the front-end light path module sequentially comprises a laser light source (1), an adjusting mirror group (2) and a prism (3) along a light path, light generated by the laser light source (1) is adjusted through beam splitting of the adjusting mirror group (2) to form at least two beams of coherent light, and the coherent light vertically enters the prism (3) and is converged on the bottom surface of the prism (3) after being totally reflected by a bevel edge of the prism (3);

a back-end film layer module comprising an immersion lithography module or a surface plasmon lithography module;

the immersion lithography module comprises a matching liquid layer (11), a substrate layer (12) and a lithography film layer (13), wherein coherent light is emitted through the bottom surface of the prism (3) and then forms interference in the immersion lithography module and exposes the lithography film layer (13);

the surface plasmon lithography module comprises a super lens film layer (21) and a substrate layer (22), the super lens film layer (21) comprises a photoresist layer (211) and a metal layer (212), and the converged coherent light is coupled with the super lens film layer (21) through evanescent waves formed outside the bottom surface of the prism (3) and exposes the photoresist layer (211).

2. A dual-mode high-resolution interferometric lithography device according to claim 1, characterized in that the immersion lithography module comprises, in order along the optical path, a first matching liquid layer (111), a substrate layer (12), a lithography film layer (13), a second matching liquid layer (112), the first matching liquid layer (111) filling the gap between the prism (3) and the substrate layer (12); or

The immersion type photoetching module sequentially comprises a first matching liquid layer (111), a photoetching film layer (13) and a substrate layer (12) along an optical path, wherein the first matching liquid layer (111) is filled in a gap between the prism (3) and the photoetching film layer (13).

3. A dual-mode high-resolution interference lithography device according to claim 1, wherein the refractive indices of the prism (3), the matching liquid layer (11), the substrate layer (12), and the lithography film layer (13) are similar or identical so that the coherent light is transmitted and interferes in the immersion lithography module.

4. A dual-mode high-resolution interference lithography device according to claim 1, characterized in that the structures and parameters of the matching liquid layer (11), the substrate layer (12), and the lithography film layer (13) are simulated and optimized using rigorous coupled-wave analysis methods.

5. A dual-mode high-resolution interference lithography device according to claim 1, wherein the surface plasmon lithography module comprises, in order along the optical path, a first metal layer (2121), a photoresist layer (211), a second metal layer (2122), a substrate layer (22); the first metal layer (2121) is in proximity to or in contact with the bottom surface of the prism (3).

6. A dual-mode high resolution interference lithography apparatus according to claim 1, wherein the structure and parameters of the photoresist layer (211), the metal layer (212) and the air gap between the prism (3) and the back end film module are simulated and optimized using a rigorous coupled wave analysis method.

7. A dual-mode high-resolution interference lithography device according to claim 1, wherein when the rear film layer module is a surface plasmon lithography module, a focus detection module (4) is further disposed above the prism (3), and the focus detection module (4) is configured to detect a gap size and a gap distribution between the bottom surface of the prism (3) and the rear film layer module.

8. A dual-mode high-resolution interference lithography device according to claim 1, characterized in that the prism (3) is a truncated pyramid with left-right axial symmetry; the prism (3) is made of a high-refractive-index material and comprises one of optical glass, quartz glass, sapphire and metal halide crystals.

9. A dual-mode high-resolution interference lithography device according to claim 1, characterized in that the wavelength of the laser light source (1) is comprised between 157nm and 436nm; the adjusting lens group (2) comprises a plurality of spot beam expanding elements, polarization adjusting elements, spatial filtering elements, semi-reflecting and semi-transmitting mirror elements and reflecting mirror elements.

10. A method of dual-mode high-resolution interference lithography, comprising:

s1, emitting laser by using a laser light source (1); utilizing an adjusting mirror group (2) to split and adjust the laser into at least two beams of coherent light which vertically enter a prism (3); the coherent light is totally reflected on the hypotenuse of the coherent light by a prism (3) and then is converged on the bottom surface of the prism (3); the laser light source (1), the adjusting mirror group (2) and the prism (3) form a front-end light path module;

s2, enabling the coherent light to form interference after being emitted through the bottom surface of the prism (3) by using an immersion type photoetching module, and exposing a photoetching film layer (13); the immersion lithography module comprises a matching liquid layer (11), a substrate layer (12) and the lithography film layer (13); or

Coupling evanescent waves formed by the converged coherent light outside the bottom surface of the prism (3) with an ultra-lens film layer (21) by using a surface plasmon lithography module, and exposing the photoresist layer (211); the surface plasmon lithography module comprises the super lens film layer (21) and a substrate layer (22), wherein the super lens film layer (21) comprises the photoresist layer (211) and a metal layer (212).

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