阅读说明：本技术 一种变间距光栅掩模线密度分布可控微调方法 (Variable-pitch grating mask line density distribution controllable fine adjustment method ) 是由 刘颖 林达奎 陈火耀 刘正坤 洪义麟 于 2020-07-03 设计创作，主要内容包括：本发明公开了一种变间距光栅掩模线密度分布可控微调方法,解决常规近场全息方法不能直接复制及微调掩模线密度及其空间分布的问题。通过微调近场全息曝光参数和引入过渡掩模来实现线密度与初始掩模线密度分布相同或呈一定偏移的一系列线密度分布渐变的变间距光栅掩模。本发明可以有效的微调近场全息变间距光栅位相掩模的线密度分布,由此减少了对电子束光刻制作方法的依赖,降低位相掩模的制作成本,在一定程度上灵活快速地获得具有不同线密度分布的掩模,以满足不同场合的不同需求,是一种十分重要的、低成本的变间距光栅的制作方法。本发明对利用近场全息方法调控光栅线密度空间分布,在此基础上提高高精度变间距光栅的制作质量和效率十分重要。(The invention discloses a controllable fine-tuning method for the distribution of the line density of a variable-pitch grating mask, which solves the problem that the line density and the spatial distribution of the mask cannot be directly copied and fine-tuned by the conventional near-field holographic method. A series of variable-pitch grating masks with gradually changed line density distribution, the line density distribution of which is the same as or offset from the line density distribution of the initial mask, are realized by finely adjusting near-field holographic exposure parameters and introducing a transition mask. The invention can effectively fine-tune the line density distribution of the near-field holographic variable-pitch grating phase mask, thereby reducing the dependence on an electron beam lithography manufacturing method, reducing the manufacturing cost of the phase mask, flexibly and quickly obtaining masks with different line density distributions to a certain extent so as to meet different requirements of different occasions, and being an important and low-cost variable-pitch grating manufacturing method. The method is very important for regulating and controlling the linear density spatial distribution of the grating by using a near-field holographic method and improving the manufacturing quality and efficiency of the high-precision variable-pitch grating on the basis.)

1. A method for fine-tuning the line density distribution of a variable-pitch grating mask is characterized in that: the method comprises the following steps:

the method comprises the following steps that (1) a near-field holographic exposure system is established, wherein the holographic exposure system comprises an ultraviolet waveband laser, a pinhole, a collimating lens, a fused quartz phase mask, a grating substrate coated with photoresist and a rotary table, the fused quartz phase mask and the grating substrate are placed on the rotary table, a non-grating pattern surface of the fused quartz phase mask and the grating substrate coated with the photoresist are filled with refractive index matching liquid, light emitted by the ultraviolet waveband laser sequentially passes through the pinhole and the collimating lens to form parallel light, variable-pitch grating patterns on the fused quartz phase mask are irradiated at a certain incident angle theta to generate zero-order diffraction light and negative-order diffraction light, and the zero-order diffraction light and the negative-order diffraction light are mutually interfered on a photoresist layer of the grating substrate to form the variable-pitch photoresist grating patterns;

And (2) exposing by using an initial mask A with the thickness of h _ liq1, wherein the thickness of the refractive index matching fluid is ignored, the distance from the grating pattern surface of the initial mask A to a photoresist layer on a substrate A (the thickness of h _ A is h _ liq1) is h _ liq1, a laser beam firstly irradiates the initial mask A from the side with low linear density at an angle theta, and the negative-order self-collimation angle of the central line density of the variable-pitch grating mask is set as theta_-1The incident angle theta is close to theta_-1Theta and theta_-1The deviation between the two is less than +/-0.5 degrees, interference fringes formed by zero-order and negative first-order diffracted light of the initial mask A are recorded on a photoresist layer of the substrate A, namely, the photoresist layer on the substrate A is exposed, and a variable-pitch photoresist grating mask is obtained after further development;

transferring the interference fringes recorded on the substrate A, namely the mask pattern of the variable-pitch photoresist grating, onto a fused quartz substrate, namely etching a certain groove depth through a reactive ion beam, wherein the groove depth etching parameter is that the contrast ratio of two interference beams (namely the ratio of zero-order diffraction efficiency and negative-order diffraction efficiency of a phase mask) is more than 90% when the near-field holographic exposure is met, removing the residual photoresist, and thus obtaining a transition mask: a mask B;

step (4) exposing the mask B prepared in the step (3) to light by the light path of the step (2), wherein the incident direction is changed to be incident from the high linear density direction at an angle theta in the step (2), and the distance from the grating pattern surface of the mask B to the substrate B (the thickness of the mask B is h _ B-h _ A) is h _ liq 2-h _ liq1, so that the substrate B with the surface of the photoresist recorded with interference fringes is obtained; performing the experiment of the step (3) to obtain a mask C-0 with the linear density distribution consistent with that of the initial mask A;

Step (5), in step (2), the substrate a (thickness h _ a ═ h _ liq1) is subjected to near-field hologram exposure-development using the initial mask a, and unlike step (2), the incident direction is slightly deviated from the low linear density direction by θ_-1The angle of theta is incident, the distance from the grating pattern surface of the initial mask A to the photoresist layer of the substrate A is h _ liq1, and therefore the substrate A with the interference fringes recorded on the surface of the photoresist is obtained; obtaining a variable-pitch photoresist grating mask after developing;

and (6) performing step (3) on the variable-pitch photoresist grating mask obtained in step (5), so as to obtain a transition mask with the thickness h _ a being h _ liq 1: a mask B;

step (7) of exposing the mask B obtained in step (6) to light in the optical path of step (2), the difference from step (2) being that the incident direction is slightly deviated from the high linear density direction by theta_-1Is incident at an angle θ, and the distance h _ liq2 ═ h _ liq1 from the grating pattern surface of the mask B to the substrate B (thickness h _ B ═ h _ a), thereby obtaining a substrate B with interference fringes recorded on the photoresist surface; performing the experiment in the step (3), thus obtaining a mask C-n with a certain offset distributed with the linear density of the initial mask A by finely adjusting the incidence angle theta, wherein n is a non-zero integer number;

step (8), performing near-field holographic exposure-development on the substrate A by adopting the initial mask A in the step (2), wherein the difference from the step (2) is that the thickness h _ A of the substrate A is not equal to h _ liq1, and obtaining a variable-pitch photoresist grating mask after development;

And (9) performing step (3) on the variable-pitch photoresist grating mask obtained in the step (8), so as to obtain a transition mask with the thickness h _ A ≠ h _ liq 1: a mask B;

step (10) of exposing the substrate B (with the thickness h _ B ≠ h _ liq 1) with the mask B with the thickness h _ a ≠ h _ liq1, which is obtained in step (9), to the light path of step (2), wherein the different from the exposure in step (2), the incident direction is changed to be incident from the high linear density direction at an angle θ, and the distance between the grating pattern of the mask B and the photoresist surface of the substrate B is adjusted to h _ liq2 ≠ h _ a ≠ h _ liq1, so as to obtain the substrate B with the interference fringes recorded on the photoresist surface; and (5) performing the experiment in the step (3), so far, obtaining the mask D-n with a certain offset distributed with the linear density of the initial mask A by finely adjusting the substrate thickness of the transition mask B, wherein n is a non-zero integer number.

Technical Field

The invention belongs to the technical field of micro-nano processing of diffraction optical elements, and particularly relates to a controllable fine-tuning method for the density distribution of a variable-pitch grating mask line, which is a variable-pitch grating based on a near-field holographic technology and a controllable fine-tuning method for the density of a phase mask line thereof.

Background

The near-field holographic method is a method for quickly and stably manufacturing diffraction gratings, in particular variable-pitch gratings. The basic principle is as follows: after laser used in near-field holographic exposure passes through a phase mask, the pattern of the phase mask is transferred to a grating substrate coated with photoresist by utilizing the interference between two diffraction orders of the phase mask relative to incident light, and then the pattern of the photoresist grating is transferred to the grating substrate by an etching process. The phase mask used by the near-field holography is a core device of the method, and due to the use of the phase mask, the optical path of the exposure system of the near-field holography is simple, compact and stable. Electron beam lithography provides great flexibility in preparing high linear density grating patterns and in regulating the spatial distribution of grating linear density. Therefore, the use of a high-precision phase mask prepared by an electron beam lithography method in near-field holography is an ideal method for producing high-quality diffraction gratings. On the other hand, as is well known, the electron beam lithography technology has high requirements on environmental stability and long manufacturing period, and is a micro-nano processing method with relatively high cost.

According to the conventional near-field holography method, the linear density distribution n _ m (x), n _ g (x) and n _ m (x) of the phase mask are not equal to each other according to the near-field holography optical path, the linear density distribution n _ g (x) of the variable-pitch grating to be manufactured and the geometric size optimization design of the phase mask. Therefore, the grating patterns of the phase mask and the preparation grating patterns have a one-to-one correspondence, that is, a certain phase mask only corresponds to a certain specific preparation grating pattern. In other words, the conventional single-pass near-field holography method cannot directly copy the phase mask pattern, and the pattern area length between the phase mask and the production grating (i.e. the length of the variable-pitch grating pattern along the line density variation direction) and the line density distribution thereof are varied. The phase mask is inevitably worn or polluted in the long-term use process, and the preparation of a new fused quartz mask directly by electron beam lithography is high in cost and long in time. Due to the change of the near-field holographic optical path, a new phase mask needs to be manufactured by re-using an electron beam lithography method, so that the time and the economic cost for manufacturing the phase mask are obviously increased; therefore, how to copy or fine-tune the linear density spatial distribution of the variable-pitch grating in a certain range to prepare a new phase mask based on a near-field holographic method is also a work with practical significance for saving the manufacturing cost of the phase mask; the development of a grating pattern linear density regulation and control method based on near-field holography is urgently needed to improve the flexibility and the potential of preparing a grating pattern by a near-field holography method and relieve the pressure of manufacturing a high-quality grating phase mask by an electron beam lithography method.

In order to solve the problem, the invention provides a method for fine tuning the linear density and the spatial distribution thereof based on a near-field holography method, and further develops a controllable fine tuning method for preparing the variable-pitch grating phase mask linear density based on the near-field holography method. Namely, a series of variable-pitch grating masks with gradually changed line density distribution, wherein the line density distribution of the variable-pitch grating masks is the same as or offset from the line density distribution of the initial mask by finely adjusting near-field holographic exposure parameters and introducing a transition mask. The invention is a controllable, stable and fast phase mask making method, which is an important and low-cost making method of the variable-pitch grating.

Disclosure of Invention

The invention provides a method for manufacturing a phase mask with adjustable line density spatial distribution based on a near-field holographic method, namely, a series of variable-pitch grating masks with gradually changed line density distribution, wherein the line density distribution of the variable-pitch grating masks is the same as or offset to a certain extent from the line density distribution of an initial mask by finely adjusting near-field holographic exposure parameters and introducing a transition mask. The method mainly solves the problems that the conventional near-field holographic method can not change the linear density and the spatial distribution of the manufactured grating and the phase mask needs to be manufactured again by an electron beam lithography method after being worn. The invention can improve the flexibility of the pattern making by the near-field holographic method, reduce the cost of making the near-field holographic phase mask and the like. The method has great application potential in the micro-nano manufacturing fields of variable-pitch gratings, periodic submicron structure preparation and the like.

In order to overcome the problems in the prior art, the technical scheme provided by the invention is as follows: a controllable fine-tuning method for the line density distribution of a variable-pitch grating mask comprises the following steps:

the method comprises the following steps that (1) a near-field holographic exposure system is established, wherein the holographic exposure system comprises an ultraviolet waveband laser, a pinhole, a collimating lens, a fused quartz phase mask, a grating substrate coated with photoresist and a rotary table, the fused quartz phase mask and the grating substrate are placed on the rotary table, a non-grating pattern surface of the fused quartz phase mask and the grating substrate coated with the photoresist are filled with refractive index matching liquid, light emitted by the ultraviolet waveband laser sequentially passes through the pinhole and the collimating lens to form parallel light, variable-pitch grating patterns on the fused quartz phase mask are irradiated at a certain incident angle theta to generate zero-order diffraction light and negative-order diffraction light, and the zero-order diffraction light and the negative-order diffraction light are mutually interfered on a photoresist layer of the grating substrate to form the variable-pitch photoresist grating patterns;

and (2) exposing by using an initial mask A with the thickness of h _ liq1, wherein the thickness of the refractive index matching fluid is ignored, the distance from the grating pattern surface of the initial mask A to a photoresist layer on a substrate A (the thickness of h _ A is h _ liq1) is h _ liq1, a laser beam firstly irradiates the initial mask A from the side with low linear density at an angle theta, and the negative-order self-collimation angle of the central line density of the variable-pitch grating mask is set as theta _-1The incident angle theta is close to theta_-1[ theta ] and [ theta ]_-1The deviation between them is less than + -0.5 °]Recording interference fringes formed by zero-order and negative first-order diffracted lights of the initial mask A on a photoresist layer of the substrate A (namely, exposing the photoresist layer on the substrate A), and further developing to obtain a variable-pitch photoresist grating mask;

transferring the interference fringes recorded on the substrate A, namely the mask pattern of the variable-pitch photoresist grating, onto a fused quartz substrate, namely etching a certain groove depth through a reactive ion beam, wherein the groove depth etching parameter is that the contrast ratio of two interference beams (namely the ratio of zero-order diffraction efficiency and negative-order diffraction efficiency of a phase mask) is more than 90% when the near-field holographic exposure is met, removing the residual photoresist, and thus obtaining a transition mask: a mask B;

step (4) exposing the mask B prepared in the step (3) to light by the light path of the step (2), wherein the incident direction is changed to be incident from the high linear density direction at an angle theta in the step (2), and the distance from the grating pattern surface of the mask B to the substrate B (the thickness of the mask B is h _ B-h _ A) is h _ liq 2-h _ liq1, so that the substrate B with the surface of the photoresist recorded with interference fringes is obtained; performing the experiment of the step (3) to obtain a mask C-0 with the linear density distribution consistent with that of the initial mask A;

Step (5), in step (2), the substrate a (thickness h _ a ═ h _ liq1) is subjected to near-field hologram exposure-development using the initial mask a, and unlike step (2), the incident direction is slightly deviated from the low linear density direction by θ_-1The angle of theta is incident, the distance from the grating pattern surface of the initial mask A to the photoresist layer of the substrate A is h _ liq1, and therefore the substrate A with the interference fringes recorded on the surface of the photoresist is obtained; obtaining a variable-pitch photoresist grating mask after developing;

and (6) performing step (3) on the variable-pitch photoresist grating mask obtained in step (5), so as to obtain a transition mask with the thickness h _ a being h _ liq 1: a mask B;

step (7) of exposing the mask B obtained in step (6) to light in the optical path of step (2), the difference from step (2) being that the incident direction is slightly deviated from the high linear density direction by theta_-1Is incident at an angle θ, and the distance h _ liq2 ═ h _ liq1 from the grating pattern surface of the mask B to the substrate B (thickness h _ B ═ h _ a), thereby obtaining a substrate B with interference fringes recorded on the photoresist surface; performing the experiment in the step (3), thus obtaining a mask C-n with a certain offset distributed with the linear density of the initial mask A by finely adjusting the incidence angle theta, wherein n is a non-zero integer number;

step (8), performing near-field holographic exposure-development on the substrate A by adopting the initial mask A in the step (2), wherein the difference from the step (2) is that the thickness h _ A of the substrate A is not equal to h _ liq1, and obtaining a variable-pitch photoresist grating mask after development;

And (9) performing step (3) on the variable-pitch photoresist grating mask obtained in the step (8), so as to obtain a transition mask with the thickness h _ A ≠ h _ liq 1: a mask B;

step (10) of exposing the substrate B (with the thickness h _ B ≠ h _ liq 1) with the mask B with the thickness h _ a ≠ h _ liq1, which is obtained in step (9), to the light path of step (2), wherein the different from the exposure in step (2), the incident direction is changed to be incident from the high linear density direction at an angle θ, and the distance between the grating pattern of the mask B and the photoresist surface of the substrate B is adjusted to h _ liq2 ≠ h _ a ≠ h _ liq1, so as to obtain the substrate B with the interference fringes recorded on the photoresist surface; and (5) performing the experiment in the step (3), so far, obtaining the mask D-n with a certain offset distributed with the linear density of the initial mask A by finely adjusting the substrate thickness of the transition mask B, wherein n is a non-zero integer number.

Compared with the prior art, the invention has the advantages and positive effects that:

(1) the invention provides a method for effectively regulating and controlling the linear density distribution of a variable-pitch grating phase mask based on a near-field holographic technology, thereby reducing the dependence on an electron beam engraving method, and flexibly and quickly obtaining the phase masks with different linear density distributions to a certain extent so as to meet different requirements of different occasions.

(2) The invention can utilize a near-field holographic method to regulate and control the linear density spatial distribution of the grating and is very important for improving the manufacturing quality and efficiency of the high-precision variable-pitch grating on the basis.

Drawings

FIG. 1 is a schematic diagram of a near-field holographic optical path with a refractive index matching liquid phase connection (exposure mode I) between a fused silica phase mask and a grating substrate;

FIG. 2 is a flow chart of a technical route for fabricating a fused silica phase mask [ abbreviated as mask in the figure ] by a near-field holography method in an exposure mode I, wherein FIG. 2(a) is a schematic diagram of a near-field holography (exposure-development) on a substrate A (with a thickness of h _ liq1) by using an initial fused silica phase mask A (with a thickness of h _ liq1) to fabricate a variable pitch photoresist grating mask of a transitional fused silica phase mask B; FIG. 2(B) is a schematic illustration of a variable pitch photoresist grating mask pattern of a transition mask B transferred onto a substrate A by reactive ion beam etching; FIG. 2(C) is a schematic diagram of a near field holography (exposure-development) of a photoresist grating mask for making a fused silica phase mask C on a substrate B using a transition mask B; FIG. 2(d) is a phase mask made by the variable pitch photoresist grating mask of mask C after the pattern transfer process of FIG. 2 (b): and (5) masking C.

Fig. 3 is a graph showing the difference between (a) the spatial distribution of the linear density and (B) the distribution of the linear density of the initial mask a and the transition mask B used in the exposure method I.

FIG. 4 is a C-1, C-2, C-0, C-3, C-4 linear density distribution curve of the mask prepared in exposure mode I, wherein the incidence angles are 34.5 °, 35 °, 35.5 °, 36 °, 36.5 °, respectively, and FIG. 4(a) is a C-0, C-1, C-2, C-3, C-4 linear density distribution curve; FIG. 4(b) is a graph of the difference between the linear density distributions of C-0, C-1, C-2, C-3, C-4 and the initial mask A;

FIG. 5 is a D-0, D-1, D-2, D-3, and D-4 linear density distribution curve of the mask prepared by trimming the thickness of the transition mask B to 5mm, 5.5mm, 6mm, 6.5mm, and 7mm, respectively, in the exposure mode I, wherein FIG. 5(a) is a D-0, D-1, D-2, D-3, and D-4 linear density distribution curve; FIG. 5(b) is a graph of the difference between the line density distributions of D-0, D-1, D-2, D-3, D-4 and the original mask A.

FIG. 6 is a schematic diagram of a near-field holographic optical path with an air gap (exposure mode II) between the fused silica phase mask and the grating substrate;

fig. 7 is a flow chart of a technical route for fabricating a fused silica phase mask [ abbreviated as mask in the figure ] by a near-field holography method in an exposure mode II, wherein fig. 7(a) is a schematic diagram of near-field holography (exposure-development) on a substrate a by using an initial fused silica phase mask a to fabricate a near-field holography (exposure-development) of a photoresist grating mask of a transition phase mask B, wherein a distance between a grating pattern surface of the initial mask a and a photoresist surface of the substrate a is h _ air 1; FIG. 7(B) is a schematic illustration of a variable pitch photoresist grating mask pattern of a transition mask B transferred onto a substrate A by reactive ion beam etching; FIG. 7(C) is a schematic diagram of a near field holography (exposure-development) of a variable pitch photoresist grating mask for making a fused silica phase mask C on a substrate B using a transition mask B; fig. 7(d) is a phase mask fabricated by the photoresist grating mask of mask C after the pattern transfer process of fig. 7 (b): and (5) masking C.

Fig. 8 is a graph showing the difference between (a) the spatial distribution of the linear density and (B) the distribution of the linear density of the initial mask a and the transition mask B used in the exposure method II.

FIG. 9 is a C-1, C-2, C-0, C-3, C-4 linear density distribution curve of the mask prepared in exposure type II with incidence angles of 34.5 °, 35 °, 35.5 °, 36 °, 36.5 °, respectively, wherein FIG. 9(a) is a C-0, C-1, C-2, C-3, C-4 linear density distribution curve; FIG. 9(b) is a graph of the difference between the linear density distributions of C-0, C-1, C-2, C-3, C-4 and the initial mask A;

FIG. 10 is a graph showing the linear density distribution curves of the masks D-1, D-2, D-0, D-3, and D-4 obtained when the thicknesses of the transition mask B are 2mm, 2.5mm, 3mm, 3.5mm, and 4mm, respectively, in the exposure pattern II, wherein FIG. 10(a) is a graph showing the linear density distribution curves of D-0, D-1, D-2, D-3, and D-4; FIG. 10(b) is a graph of the difference between the line density distributions of D-0, D-1, D-2, D-3, D-4 and the original mask A.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

The invention discloses a variable-pitch grating mask line density distribution controllable fine adjustment method, which specifically comprises the following steps: