WO2015032262A1 - 一种透射式分光光栅及干涉光刻系统 - Google Patents

一种透射式分光光栅及干涉光刻系统 Download PDF

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WO2015032262A1
WO2015032262A1 PCT/CN2014/084170 CN2014084170W WO2015032262A1 WO 2015032262 A1 WO2015032262 A1 WO 2015032262A1 CN 2014084170 W CN2014084170 W CN 2014084170W WO 2015032262 A1 WO2015032262 A1 WO 2015032262A1
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grating
light
transmission
spectroscopic
interference
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PCT/CN2014/084170
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English (en)
French (fr)
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胡进
浦东林
陈林森
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苏州大学张家港工业技术研究院
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Publication of WO2015032262A1 publication Critical patent/WO2015032262A1/zh

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/1086—Beam splitting or combining systems operating by diffraction only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1842—Gratings for image generation
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1866—Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70408—Interferometric lithography; Holographic lithography; Self-imaging lithography, e.g. utilizing the Talbot effect

Definitions

  • the present invention relates to the field of lithography, and more particularly to a spectroscopic grating used in interference lithography and an interferometric lithography system formed using the spectroscopic grating.
  • Interference lithography is an important branch of lithography and has received extensive attention in recent years.
  • the main advantage of interference lithography is that high graphics resolution can be achieved.
  • the minimum line width obtainable by the interference optical system is ⁇ / (4 ⁇ ), which is 1/2 of the ordinary projection imaging optical system.
  • the interference lithography optical path is simple, and the prepared pattern period is accurate and uniform.
  • the light path scheme is a holographic shooting light path.
  • the typical optical path is shown in Figure 1.
  • the laser beam is split into two by a transflective mirror, and then filtered and expanded, respectively.
  • the surface of the workpiece forms an interference of two beams.
  • the main limitations of this optical path scheme are as follows:
  • the optical path is long, bulky, and poorly resistant to interference. At the same time, the optical path requires a higher coherence length of the laser. Generally suitable for use in optical laboratories, not for optical processing equipment.
  • the lithography has a limited surface. Limited by the aperture of the beam expander, the interference lithography area is typically less than 300 mm. If the aperture of the beam expander is to be increased, the manufacturing difficulty and cost are greatly increased.
  • the quality of the edges of the lithographic regions is poor. First, since the light intensity distribution on the beam section is Gaussian, the intensity of the edge of the lithography area is significantly weakened relative to the middle (see Figure 2).
  • the laser beam output through the beam expander is not a strictly parallel beam, but a spherical wave, which causes the fringes in the interference lithography area to be not strictly parallel lines, but in a hyperbolic distribution, especially in the edge regions. (See Figure 3).
  • the optical path scheme 2 is a projection imaging optical path.
  • the optical path scheme has the following characteristics compared to the holographic optical path obvious advantage:
  • Short optical path, small size, strong anti-interference internal force, suitable for optical processing equipment Due to the combination of the imaging optical path, the shape and contour of the exposed area are easily controlled, which facilitates large-area splicing exposure.
  • a plurality of spectroscopic devices can be used in a specific spectroscopic method, and a spectroscopic method based on a diffraction grating is an important representative thereof, which has the following advantages:
  • the optical path structure is simple and reliable, and is easy to combine with the projection imaging optical path.
  • the multi-level light after splitting has good consistency.
  • the core original diffraction grating, small size, easy to prepare.
  • the imaging projection interference optical path based on the diffraction grating splitting plays an important role in interference lithography, and the typical structure of the optical path is as shown in FIG.
  • Diffraction gratings are the core components of such optical path systems.
  • the complex amplitude distribution of the diffraction order of the ideal diffraction grating output is shown in Figure 5: '+ ⁇ and '- ⁇ are equal in intensity and concentrate all the energy in the light field, others The diffraction level energy is zero.
  • the existing diffraction grating cannot achieve the above ideal distribution.
  • the conventional diffraction gratings generally employ several structures which are easy to prepare, and are typically represented by a cosine phase grating and a rectangular phase grating.
  • the former is usually produced by holographic shooting, while the latter is usually produced by laser direct writing and mask exposure.
  • the main shortcomings are:
  • the diffraction efficiency of the currently known sinusoidal phase grating has a maximum diffraction efficiency of about 68.
  • the noise and interference of the light field is large.
  • Level 0 and above are mixed into ⁇ 1 level.
  • the filtering accuracy is difficult to achieve. If the aperture is too small, the filtering is not clean; if the aperture is too much, the ⁇ 1 order light is damaged. Eventually there is distortion in the interference fringes of the exposure Variable and noise, and the quality of the edges is poor.
  • the present invention proposes a transmissive spectroscopic grating and an interference lithography system.
  • this spectroscopic grating and interference lithography system the processed graphics are of higher quality and are easy to achieve large-area precision splicing exposure.
  • the transmissive spectroscopic grating of the present invention provides the following technical solutions: including a grating trough region on the transmissive surface and a light blocking region on the periphery of the grating trough region, the grating trough region including periodic distribution
  • the grating structure has a trough-shaped transmissive surface and a non-transmissive area, and the trough-shaped transmissive surface forms an oblique angle with the grating base surface.
  • the duty ratio of the groove-shaped transmission surface to the grating structure is 0.6-0.8.
  • the duty ratio of the groove-shaped transmission surface and the grating structure is ⁇ / ( 3 ⁇ ).
  • the non-transmissive region is a deep trench structure having a depth greater than a maximum depth of the trough-shaped transmissive surface.
  • the light blocking region is provided with a light blocking material.
  • the periodically distributed grating structure is a one-dimensional grating or a two-dimensional grating.
  • the light source, the beam splitting device, the projection optics group and the carrier platform are included, and the beam splitting device is the above-mentioned transmissive spectroscopic grating, and the light source emits a light beam having a larger cross section than the grating channel region of the transmissive spectroscopic grating.
  • the light emitted by the light source is incident on a transmissive surface of the transmissive spectroscopic grating, and an incident direction of the light forms an incident angle with the grating base surface, and the incident angle and the oblique angle satisfy the following Relationship:
  • the projection optics group includes at least two groups of lens groups, the lens groups constitute an imaging optical path, the transmissive spectroscopic grating forms an object surface of the imaging optical path, and a workpiece is placed on the loading platform.
  • the surface forms an image plane of the imaging light path.
  • the interference lithography system of the present invention can achieve the enhancement of the ⁇ 1 order diffracted light required for the interference optical path, while sufficiently suppressing the other unwanted levels. Among them, the 0th-order light is completely eliminated, and the higher-order secondary light above the 2nd level is also sufficiently suppressed.
  • the grating structure and the supporting optical path proposed by the invention have higher pollution efficiency, and the highest efficiency is up to 92.3%.
  • the interference pattern obtained by the interference lithography system of the present invention has better uniformity of the interference pattern (streak or lattice), and the obtained light intensity distribution of the exposed light field is closer to the ideal cosine. distributed.
  • the image quality of the edge of the exposed light field obtained by the interference lithography system of the invention is greatly improved, and is particularly suitable for precision splicing exposure to realize large-area lithography.
  • the structure of the interference lithography system of the present invention is simple and reliable, and it is not necessary to provide an aperture for light field filtering.
  • the imaging optical path is used in the optical path, and the contour and shape of the interfering light field are determined by the contour and shape of the diffraction grating itself.
  • the pixelation control of the interference light field pattern can be realized, thereby realizing
  • the processing pattern is not limited to a periodic structure.
  • Figure 1 is a schematic view of a typical interference optical path structure
  • 2 is a schematic view showing the distribution of light intensity in an interference region
  • Figure 3 is a schematic diagram of distortion of typical interference fringes
  • FIG. 4 is a schematic structural view of an existing interference imaging lithography system for projection imaging
  • Figure 5 is a diffraction spectrum of an ideal spectroscopic grating
  • Figure 6 is a diffraction spectrum of an actual prior art spectral grating
  • FIG. 7A is a schematic structural view of a transmissive spectroscopic grating of the present invention.
  • FIG. 7B is a schematic structural view of a projection type spectroscopic grating according to another embodiment of the present invention.
  • FIG. 8 is a schematic structural view of the interference lithography system of the present invention.
  • Figure 9 is a diffraction-level complex amplitude distribution of the transmission type spectroscopic grating of the present invention
  • Figure 10 is an optical micrograph of a single exposure interference pattern obtained with the interference lithography system of the present invention.
  • Fig. 7A is a view showing the structure of a transmission type spectroscopic grating of the present invention.
  • the spectroscopic grating 1 includes a grating trough section 11 on the incident surface 10 and a light blocking section 12 on the periphery of the grating trough section 11.
  • the shape of the grating trough 11 is circular or square. Of course, when the grating trough 11 is designed into other shapes, the use of the spectroscopic grating 1 is not violated.
  • the area of the grating groove type region 11 is not excessively large, and it should be ensured that when the beam expanding light source is irradiated on the beam splitting grating 1, the size of the spot is larger than the area of the grating groove type region 11, so that the incident light is irradiated to the spectroscopic grating 1. After the incident surface 10, the spot portion of the grating slot region 11 is transmitted, and the spot portion of the light blocking region 12 is absorbed or reflected.
  • the present invention passes The distribution of the grating groove region over the entire grating surface acts as a pupil, so that the transmitted spot has good boundary uniformity, and the boundary of each exposure can be automatically aligned without any alignment technique. At the same time, unnecessary useless transmitted light can be reduced to have an unnecessary influence on the interference optical path.
  • the grating trough region 11 includes a stepped grating structure 110 having a gradually increasing depth, and each step of the stepped grating structure has a transmissive step surface 111 and a non-transmissive region 112.
  • the step angle of the stepped grating structure is ⁇ .
  • the step surface of the stepped grating structure may also be a slope as shown in FIG. 7B.
  • a non-transmissive region, the non-transmissive region 112 and The transmission step faces 111 together form a single-order grating structure, and the duty ratio adjustment for the transmission step faces 111 is realized by the non-transmissive regions 112, that is, when the ratio of the transmission step faces 111 to the entire grating structure is large, the non-transmission is required.
  • the area 112 is designed to be smaller, and the duty ratio of the transmission step surface 111 is required to be small, so that the size of the non-transmissive area 112 can be increased. The role played by the above adjustment will be described in detail below.
  • non-transmissive region 112 may be a dark region of light formed by a light-blocking material formed on the surface, and when light is incident on the partial region, transmission cannot be formed.
  • the stepped grating structure 110 may be a one-dimensional grating or a two-dimensional grating.
  • the exposure pattern formed by the interference of the splitting light is a stripe pattern of light and dark.
  • the exposure pattern formed by the interference of the splitting light is a dot pattern of light and dark.
  • the light blocking region 12 is formed of a light blocking material formed on the surface of the spectroscopic grating, and the light blocking material may be a black dye, ink, or a material which does not cause light transmission.
  • FIG. 8 is a schematic structural view of an interference lithography system of the present invention.
  • the interference lithography system includes a light source 20, a beam splitting device 10, a projection optics stack 30, and a carrier platform 40.
  • the beam splitting device 10 is the above-mentioned transmissive spectroscopic grating.
  • the light source 20 preferably uses a laser light source with good coherence performance.
  • the beam emitted by the laser source is obliquely incident on the beam splitting device after being properly collimated and expanded. Transmitted light is formed on the transmission surface of 10.
  • the spot cross-section of the incident beam is required to be larger than the grating trough size of the transmissive spectroscopic grating. In this way, the boundary of the transmitted light is naturally defined by the boundary of the grating groove region, regardless of the alignment problem.
  • the load platform 40 carries a workpiece or an optical system that is movable in two dimensions, X and Y. Large-area lithography can be achieved by controlling the relative movement of the carrier platform and the optical system.
  • the projection optics group 30 includes at least two sets of lenses 31 and 32 which form an imaging optical path.
  • the transmissive surface of the transmissive spectroscopic grating is an object surface, and the surface of the workpiece placed on the loading platform 40 is an image surface.
  • the incident beam is split by the beam splitting device 10, passes through the projection optics 30, and finally forms a double beam interference exposure on the surface of the workpiece placed on the carrier platform 40.
  • the light of the transmission type spectroscopic grating is formed in the equivalent pupil of the projection optical lens group, and the light of the remaining order is formed outside the equivalent pupil. 22 is the equivalent pupil of the projection optics 30, not a separate optical component. Due to the aperture limitation of the projection optics, the light field beyond its effective aperture will be blocked and opaque.
  • the transmissive spectroscopic grating and an interferometric lithography system using the spectroscopic grating are also a part of the creative idea of the present invention, and is not a conventional inference by those skilled in the art, and the specific embodiment of the present invention is only a specific application of the invention.
  • the parallel light of a unit amplitude is illuminated, and incident on the spectroscopic grating 12 at a corner angle, and the complex amplitude distribution of the diffraction order obtained on the spectrum surface is:
  • ⁇ is the wavelength of the incident light
  • f is the focal length of the projection optics 31
  • M is the number of slots of the spectroscopic grating
  • ⁇ is the incident angle of the incident light
  • ⁇ is the step angle of the stepped grating structure
  • d is a single grating structure
  • the groove width is the period
  • a is the width of the groove-shaped transmission surface 111.
  • the first term of the complex amplitude distribution E is the single-slit diffraction factor, which determines the envelope of E, whose outline is the sine function type.
  • the second term of the complex amplitude distribution E is a multi-slit interference factor.
  • the incident angle ⁇ is changed so that each diffraction order can be moved to the left and right with respect to the sine envelope.
  • Changing the duty ratio a/d of the transmission step surface in the entire grating structure can increase or decrease the pitch of each diffraction order relative to the zero point spacing of the sine envelope.
  • the spectroscopic grating designed by the present invention not only the parameters affecting the diffraction splitting of the grating, that is, the step angle of the grating and the angle of the incident light are considered, but also the modulation parameters for the diffraction efficiency in the grating are considered.
  • a non-transmissive region is added to the grating structure such that the transmission step surface occupies an adjustable duty cycle of the entire grating structure. In this way, the energy utilization of the two bundled beams obtained by the spectroscopic grating of the present invention can be maximized, and the resolution of the formed interference pattern is the highest.
  • the laser has a wavelength of 405 nm and a laser power of 200 mW. After the laser beam is filtered and expanded, it is projected onto the transmission surface of the transmission spectroscopic grating.
  • the material of the spectroscopic grating is silicon.
  • the parameters are as follows: the period is 10um, the step angle of the transmission step surface (like the blaze angle) is 13 degrees, and the duty ratio is 0.75.
  • the optimum incident angle is about 27.4 degrees, and the incident angle can be fine-tuned in the actual optical path so that the energy of the '+ ⁇ and '- ⁇ levels are symmetric.
  • the flight exposure mode can be used, that is, the laser is used for short pulse exposure and the platform is continuously moving.
  • the relative displacement speed between the platform and the exposure head can be controlled to splicing each single exposure pattern. Since the single exposure pattern of the present invention has a good boundary quality, boundary distortion does not occur and Better resolution, so after the splicing is completed, it has better integrity and precision than the existing interference lithography.
  • FIG. 10 is a single exposure interference pattern obtained by the interference lithography system of the present invention. As can be seen from the figure, at the edge of the pattern, almost the complete boundary topography is maintained, and all The interference lattice is also clearly visible, and the effect is far better than the current interference lithography pattern.
  • the present invention provides a transmissive spectroscopic grating and an interference lithography system capable of achieving maximum modulation of ⁇ 1 order light, so that the transmitted split beam has the highest energy utilization rate.
  • the interference pattern obtained by the transmissive spectroscopic grating has good boundary quality, and the precise splicing pattern can be completed, so that the large-format interference lithography technology is significantly improved.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

Abstract

一种透射式分光光栅及干涉光刻系统，该透射式分光光栅（1）包括位于入射面（10）的光栅槽形区（11）和位于该光栅槽形区（11）外围的阻光区（12），所述光栅槽形区（11）包括阶梯状光栅结构（110），该阶梯状光栅结构（110）具有透射阶梯面（111）和非透射区（112）。该透射式分光光栅（1）能够实现对±1级光的最大调制，使得透射出去的分束光具有最高的能量利用率，通过该透射式分光光栅的获得的干涉图形，具有良好的边界质量，能够完成进行精密的拼接图形，使得大幅面干涉光刻技术得到显著的提升。

Description

一种透射式分光光栅及干涉光刻系统
本申请要求于 2013 年 09 月 03 日提交中国专利局、 申请号为 201310395325.X,发明名称为"一种透射式分光光栅及干涉光刻系统"的中国专 利申请的优先权， 其全部内容通过引用结合在本申请中。
技术领域
本发明涉及光刻技术领域，特别是一种干涉光刻技术中用到的分光光栅以 及利用该分光光栅形成的干涉光刻系统。
背景技术
干涉光刻技术是光刻技术中的重要分支， 近年来受到了广泛的重视。干涉 光刻的主要优势在于可以获得很高的图形分辨率。在光学系统的波长 λ和数值 孔径 ΝΑ—定的情况下， 干涉光学系统可获得的最小线宽为 λ /(4ΝΑ)， 是普通 投影成像光学系统的 1/2。 此外， 干涉光刻光路简单， 制备的图形周期准确， 均匀性好。
干涉光刻有两类典型的光路方案。 光路方案一是全息拍摄光路。 （参考： 博士论文 Toward Nano-accuracy in Scan Beam Interference Lithography P24-26 ) 典型光路如图 1所示， 激光束被半透半反分光镜一分为二， 然后各自经过滤波 和扩束， 最后在工件表面形成两光束的干涉。该光路方案的主要局限有以下几 点：
第一， 光路长， 体积大， 耐干扰能力差。 同时， 光路对激光的相干长度要 求较高。 一般适用于光学实验室内， 不适用于光学加工设备中。 第二， 光刻幅 面有限。 受扩束镜的孔径的限制， 干涉光刻区域一般小于 300mm。 如果要增 加扩束镜的孔径， 则制造难度和成本大幅增加。 第三， 光刻区域的边缘的图形 质量较差。 首先， 由于光束截面上的光强分布成高斯分布， 导致光刻区域边缘 的光强相对中部明显减弱 （请参见图 2 )。 其次， 经过扩束镜输出的激光束也 不是严格的平行光束， 而是一个球面波， 由此导致干涉光刻区域的条纹不是严 格的平行直线， 而是呈双曲线分布， 在边缘区域尤其明显 （请参见图 3 )。
由于上述第 3点。其曝光区域不易于实现精密拼接曝光，从而限制了该方 案用于大幅面光刻。
光路方案二是投影成像光路。 该光路方案， 相比全息拍摄光路， 具有以下 明显优势：
光路短、 体积小巧、 抗干扰内力强， 适用于光学加工设备中。 由于结合了 成像光路， 其曝光区域的形状和轮廓易于控制， 有利于实现大面积拼接曝光。
在具体的分光方法上可釆用多种分光器件，其中基于衍射光栅的分光方法 是其中的重要代表， 它具有如下优点：
一、 对照明光源的相干性要求低。
二、 光路结构简单可靠， 并且易于与投影成像光路相结合。
三、 分束后的多级光具有良好的一致性。
四、 核心原件衍射光栅， 体积小巧， 易于制备。
由于上述优点，基于衍射光栅分光的成像投影干涉光路在干涉光刻中占有 重要地位， 其光路典型结构如图 4所示。
衍射光栅是此类光路系统中核心元件。 为了实现理想的双光束干涉， 理想 的衍射光栅输出的衍射级的复振幅分布如图 5所示： '+Γ 级和 '-Γ 级的强 度相等， 并且集中了光场中的全部能量， 其它的衍射级能量为零。
实际上，现有的衍射光栅无法达到上述理想分布。现有的衍射光栅的一般 釆用几种易于制备的结构， 其典型代表为余弦位相光栅和矩形位相光栅。前者 通常一般釆用全息拍摄的方法制作，而后者通常釆用激光直写和掩模曝光等方 法制作。
基于这两种衍射光栅所获得的衍射级复振幅分布，与理想分布仍然有较大 的差距。 即使对其结构参数， 包括周期、 槽深和占空比等加以调控和优化， 仍 然只能获得有限的改善。 其典型输出衍射级分布如图 6所示。
其主要不足表现为：
第一： ± 1级衍射效率有待提高。 第二： 对无用的衍射级（ 0级和 2级以 上级次）无法实现充分抑制。
对于第一点，目前已知的正弦位相光栅的士 1级的衍射效率最大值约为 68
% ; 矩形位相光栅， 在占空比为 1/2， 并且位相调制度为 π时， 可以获得最大 士 1级衍射效率约 81 %。 但是仍然有待进一步提高。
对于第二点， 光场的噪声和干扰较大。 0级和 2以上级次混入 ± 1级中。 即使釆用光阑滤波， 其滤波准确性难以实现。 如果光阑遮挡过少， 导致过滤不 干净； 如果光阑遮挡过多， 损伤 ± 1级光。 最终使得曝光的干涉条纹中存在畸 变和噪声， 而且边缘的图形质量欠佳。
由于上述第 2点。其曝光区域不易于实现精密拼接曝光，从而限制了该方 案用于大幅面光刻。
发明内容
有鉴于此， 本发明提出了一种透射式分光光栅和干涉光刻系统。釆用该分 光光栅和干涉光刻系统，加工的图形质量更高， 并且易于实现大面积精密拼接 曝光。
为了实现上述目的， 本发明的透射式分光光栅提供的技术方案如下： 包括位于透射面的光栅槽形区和位于该光栅槽形区外围的阻光区，所述光 栅槽形区包括周期性分布的光栅结构， 该光栅结构具有槽形透射面和非透射 区， 所述槽形透射面与光栅基面之间形成一斜角。
优选的， 所述槽形透射面与所述光栅结构的占空比为 0.6-0.8。
优选的， 所述槽形透射面与所述光栅结构的占空比为 π/(3^)。
优选的， 所述非透射区为深沟结构， 其深度大于所述槽形透射面的最大深 度。
优选的， 所述阻光区上设有阻光材料。
优选的， 所述周期性分布的光栅结构为一维光栅或二维光栅。
进一步的， 本发明提供的一种干涉光刻系统的技术方案如下：
包括光源、 分束器件、投影光学镜组和载物平台， 所述分束器件为上述的 透射式分光光栅，所述光源发射的光线截面大于所述透射式分光光栅的光栅槽 形区尺寸。
优选的， 所述光源发射的光线入射到所述透射式分光光栅的透射面上， 该 光线的入射方向与所述光栅基面形成入射角，所述入射角与所述斜角之间满足 如下的关系：
[sin ( Θ )— Sin ( θ— 2 γ )]d/入 = N + 1/2， 其中， Θ为入射角， γ为斜角， N为自然数。
优选的， 所述投影光学镜组包括至少两组透镜组， 该些透镜组组成成像光 路，所述透射式分光光栅形成该成像光路的物面，所述载物平台上放置一工件， 该工件表面形成该成像光路的像面。 与现有技术相比， 本发明的技术方案具有如下的技术优势：
第一、 本发明的干涉光刻系统可实现对干涉光路所需的 ± 1级衍射光的增 强， 而对其它无用的^ ^射级次充分抑制。 其中， 0级光被完全消除， 而 2级以 上的高级次光也被充分的抑制。相比已有的基于余弦位相光栅或者矩形位相光 栅的分光干涉光学加工系统和方法， 本发明所提出的光栅结构和配套光路， 士 1级 4汙射效率更高， 最高可达 92.3 %。
第二、相比已有的干涉光刻系统， 本发明的干涉光刻系统获得的干涉图案 (条纹或者点阵）的均匀性更佳， 获得的曝光光场的光强分布更加接近理想的 余弦分布。
第三、 本发明的干涉光刻系统获得的曝光光场边缘的图形质量大幅提升， 特别适用于精密拼接曝光以实现大面积光刻。
第四、本发明的干涉光刻系统的结构简单可靠， 无需设置光阑进行光场滤 波。 光路中釆用成像光路， 干涉光场的轮廓和形状由衍射光栅自身的轮廓和形 状决定，通过对衍射光栅多个槽面的取舍控制， 可以实现干涉光场图案的像素 化控制， 因而可实现的加工图形并不局限于周期状结构。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施 例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地， 下面描述 中的附图仅仅是本申请中记载的一些实施例， 对于本领域普通技术人员来讲， 在不付出创造性劳动的前提下， 还可以根据这些附图获得其他的附图。
图 1是典型的干涉光路结构示意图；
图 2是干涉区域光强的分布示意图；
图 3是典型干涉条纹的畸变示意图；
图 4是现有的投影成像的干涉光刻系统结构示意图；
图 5是理想分光光栅的衍射光谱；
图 6是实际的现有分光光栅的衍射光谱；
图 7A是本发明的透射式分光光栅的结构示意图；
图 7B是本发明另一种实施方式的投射式分光光栅的结构示意图； 图 8是本发明干涉光刻系统的结构示意图；
图 9是本发明的透射式分光光栅的衍射级复振幅分布； 图 10为釆用本发明的干涉光刻系统获得的单次曝光干涉图案的光学显微 镜图。
具体实施方式
正如背景技术中所述，现有的干涉光刻工艺中，使用衍射光栅作为分光器 件时， 由于衍射光栅存在衍射效率低和无用衍射级无法充分抑制的缺陷，使得 曝光时的干涉图像存在条纹不清晰和边缘畸变的问题。
因此本发明的目的在于提出一种应用在干涉光刻工艺中的透射式分光光 栅和使用该分光光栅的干涉光刻技术，该透射式分光光栅能够在提高衍射光栅 士 1级衍射效率的同时， 抑制其它级次的衍射光能量， 尤其是 0级光和 ± 2级 光的效率， 使得该光栅的 ± 1级衍射效率能够达到 92%以上， 明显优于现有的 分光光栅的衍射效率。
下面， 将对本发明的技术方案做详细描述。
请参见图 7A， 图 7A是本发明的透射式分光光栅的结构。 如图所示， 该 分光光栅 1包括位于入射面 10的光栅槽形区 11和位于该光栅槽形区 11外围 的阻光区 12。 一般来说， 光栅槽形区 11的形状为圓形或正方形， 当然将该光 栅槽型区 11设计成其它形状时， 也不违背该分光光栅 1的使用。 光栅槽型区 11 的面积不宜过大， 应保证扩束光源照射在该分光光栅 1上时， 光斑的尺寸 大于该光栅槽型区 11的面积， 这样一来， 入射光线照射到分光光栅 1的入射 面 10之后， 在光栅槽型区 11的光斑部分被透射， 而位于阻光区 12的光斑部 分则被吸收或反射，相对于普通的表面全尺光栅结构的衍射光栅而言， 本发明 通过限定光栅槽区域在整个光栅表面的分布大小，起到一个光阑的作用，使得 被透射的光斑具有很好的边界一致性，无需任何对准技术即可实现每次曝光的 边界自动对准。 同时又可以减少无用的透射光对干涉光路造成不必要的影响。
所述光栅槽形区 11 包括深度逐渐递增的阶梯状光栅结构 110， 该阶梯状 光栅结构的每一阶梯上具有透射阶梯面 111和非透射区 112。 所述阶梯状光栅 结构的阶梯角为丫。在另一种实施方式， 该阶梯状光栅结构的阶梯面也可以是 斜面， 如图 7B所示。 当入射光线入射到该光栅结构上时， 在透射阶梯面 111 上的部分被透射， 而在非透射区 112上的部分则被吸收。 透射阶梯面 111与普 通的闪耀光栅原理相似，起到衍射分光的作用。与普通衍射分光光栅不同的是， 本发明的分光光栅， 在光栅结构中， 加入了非透射的区域， 该非透射区 112和 透射阶梯面 111共同形成了单阶的光栅结构，利用非透射区 112实现对于透射 阶梯面 111的占空比调控， 即当需要透射阶梯面 111 占整个光栅结构的比例大 时， 则将非透射区 112设计的小些， 而需要将透射阶梯面 111所占的占空比小 时， 则可以加大非透射区 112的尺寸。 对于上述调节所起到的作用， 将在下文 中做详细描述。
进一步地，该非透射区 112可以是由制作在表面的阻光材料形成的光线暗 区， 当光线入射到该部分区域时， 无法形成透射。
进一步地， 该阶梯状的光栅结构 110可以为一维光栅或二维光栅。对于一 维光栅， 经过分束光线干涉之后形成的曝光图形为明暗相间的条纹状图形。对 而二维光栅， 经过分束光线干涉后形成的曝光图形则为明暗相间的点阵图形。
所述阻光区 12由制作在分光光栅表面的阻光材料形成， 该阻光材料可以 为黑色染料、 墨水、 或其不能引起光透射的材料。
请参见图 8， 图 8是本发明的干涉光刻系统的结构示意图。 如图所示， 该 干涉光刻系统包括光源 20、 分束器件 10、 投影光学镜组 30和载物平台 40。 分束器件 10即为上述的透射式分光光栅，光源 20最好釆用相干性能好的激光 光源， 该激光光源发出的光束， 经过适当的准直和扩束光路后， 斜入射到分束 器件 10的透射面上形成透射光。 通常， 要求该入射光束的光斑截面大小要大 于透射式分光光栅的光栅槽形区尺寸。这样一来就能使得透射光的边界被光栅 槽形区的边界自然限定， 不用考虑对准的问题。
所述载物平台 40托载加工工件或光学系统， 该载物平台 40在 X、 Y两个 维度上可动。通过控制载物平台与光学系统的相对移动， 可实现大面积的光刻 加工。
所述投影光学镜组 30包含至少两组透镜 31和 32， 该两组透镜 31和 32 形成成像光路。 其中的透射式分光光栅的透射面为物面， 载物平台 40上放置 的工件表面为像面。 入射光束经过分束器件 10分光后， 再经过投影光学镜组 30， 最终在置于载物平台 40上的加工工件表面形成双光束干涉曝光。
进一步地， 透射式分光光栅的士 1级光形成在所述投影光学镜组的等效光 阑内， 其余级次的光形成在该等效光阑外。 图中 22是投影光学镜组 30的等效 光阑， 并非独立的光学元件。 由于投影光学镜组的孔径限制， 超出其有效孔径 的光场将被遮挡而无法透过。 为了更好地理解本发明的创造性以及技术效果，下面将对上述透射式分光 光栅以及利用该分光光栅组成的干涉光刻系统的物理原理做具体分析。需要指 出的是， 下述的理论分析部分也是本发明创作思想的一部分， 而非本领域技术 人员的常规推断， 本发明的具体实施部分仅是该发明创作的一种具体应用。
根据信息光学理论， 以单位振幅的平行光照明， 以 Θ角入射到所述分光光 栅 12上， 在频谱面上获得的衍射级复振幅分布为：
1
， ―
Figure imgf000009_0001
其中 λ为入射光的波长， f 为投影光学镜组 31的焦距， M为分光光栅的 槽数， Θ为入射光的入射角， γ为阶梯状光栅结构的阶梯角， d为单个光栅结 构的槽宽即周期， a为槽形透射面 111的所占宽度。
复振幅分布 E的第一项为单缝衍射因子， 它决定了 E的包络， 其轮廓为 sine函数类型。
复振幅分布 E的第二项为多缝干涉因子。
申请人在对该表达式进行数学分析时， 得出以下结论：
1、 在光源波长 λ和光栅参数（阶梯角 γ和槽宽 d )—定的情况下， 改变 入射角 Θ， 可以使得各衍射级次相对 sine包络的左右移动。
根据本结论， 特别地， 当入射角 Θ满足下式时：
sin ( 9 ) - Sin ( 9 - 2 y )]d/ X = Ν + 1/2， ^整数。 可以使得某两个衍射级次位于 sine包络的主峰中，并呈对称分布。 由此可 以获得对 0级光的完全消除， 同时 ± 1级光集中了光场的绝大部分能量。
2、 改变透射阶梯面在整个光栅结构中的占空比 a/d， 可以实现各衍射级次 的间距相对 sine包络的零点间距的增大或减小。
根据本结论， 选取合适的占空比 a/d， 可以实现 ± 2级以上的高级次位于 sine包络的零点的附近，从而被充分抑制。通常，将该占空比 a/d选取在 0.6-0.8 之间时， 可以得到一个较高的衍射效率。 最优的当占空比 a/d= 3^ 时， 可得 士 1级的衍射效率的最大值 92.3%， 在图 9中给出了对应的各个级次复振幅分 布。 如图所示， 通过设置恰当的占空比 a/d和入射角， 该分光光栅的衍射光谱 中， 零级光被消除， 士 2级以上的光被抑制在 sine包络的零点间距附近从而其 所占的振幅能量最小， 而此时 ± 1级的衍射效率的最大， 接近理想的衍射光栅 输出效率。
基于上述原理，在本发明设计的分光光栅中， 不仅考虑光栅对于衍射分光 的影响参数， 即光栅的阶梯角和入射光角度等参数，也考虑了该光栅中对于衍 射效率的调制参数， 即在光栅结构中加入了非透射的区域，使得透射阶梯面占 整个光栅结构的占空比可调。 这样一来， 可以使得由本发明的分光光栅得到的 两束分束光的能量利用率最大、 且形成的干涉图形的分辨率最高。 涉光刻的方法。
1、 釆用半导体激光器作为光源， 激光波长为 405nm， 激光功率 200mw， 激光束经滤波和扩束准直后， 投射到透射式分光光栅的透射面上。
2、投影光学镜组 30釆用微缩投影光路，微缩倍数根据镜头倍率从 5倍到 100倍可选。 典型的情况下， 釆用 20倍镜头， 其数值孔径 NA=0.45。
3、分光光栅的材料为硅，参数如下：周期 10um，透射阶梯面的阶梯角（类 似闪耀角） 13度， 占空比为 0.75。 最佳入射角度约为 27.4度， 在实际光路中 可以微调入射角， 以使得 '+Γ 级和 '-Γ 级的能量对称相等。
4、 具体加工时， 可以釆用飞行曝光方式， 即激光器做短脉冲曝光， 平台 连续运动。将加工工件表面放置在载物平台的加工区域， 可以获得极高的加工 效率和定位精度。 飞行曝光时， 可以控制平台和曝光头之间的相对位移速度， 将每次的单幅曝光图形进行拼接，由于本发明的单次曝光图形具有很好的边界 质量， 即不会发生边界畸变和较好的分辨率， 所以拼接完成后， 相对现有的干 涉光刻图形， 就有更好的完整性和精密性。
请参见图 10， 图 10为釆用本发明的干涉光刻系统获得的单次曝光的干涉 图案， 从该图中可以看出， 在图形边缘处， 几乎保持着完整的边界形貌， 并且 所有的干涉点阵也清晰可见， 效果远远好于目前的干涉光刻图案。
综上所述， 本发明提出了一种透射式分光光栅和干涉光刻系统， 该透射式 分光光栅能够实现对 ± 1级光的最大调制， 使得透射出去的分束光具有最高的 能量利用率，通过该透射式分光光栅的获得的干涉图形，具有良好的边界质量， 能够完成进行精密的拼接图形， 使得大幅面干涉光刻技术得到显著的提升。 对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本 发明。 对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见 的， 本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下， 在 其它实施例中实现。 因此， 本发明将不会被限制于本文所示的实施例， 而是要 符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims

权 利 要 求
1、 一种透射式分光光栅， 其特征在于： 包括位于入射面的光栅槽形区和 位于该光栅槽形区外围的阻光区，所述光栅槽形区包括深度逐渐递增的阶梯状 光栅结构， 该阶梯状光栅结构具有透射阶梯面和非透射区。
2、 如权利要求 1所述的透射式分光光栅， 其特征在于： 所述槽形透射面 与所述光栅结构的占空比为 0.6-0.8。
3、 如权利要求 1所述的透射式分光光栅， 其特征在于： 所述槽形透射面 与所述光栅结构的占空比为 π/(3^)。
4、 如权利要求 1所述的透射式分光光栅， 其特征在于： 所述非透射区由 制作在表面的阻光材料形成的光线暗区。
5、 如权利要求 1所述的透射式分光光栅， 其特征在于： 所述阻光区上设 有阻光材料。
6、 如权利要求 1所述的透射式分光光栅， 其特征在于： 所述阶梯状光栅 结构为一维光栅或二维光栅。
7、 一种干涉光刻系统， 包括光源、 分束器件、 投影光学镜组和载物平台， 其特征在于： 所述分束器件为权利要求 1至 6所述的透射式分光光栅， 所述光 源发射的光线截面大于所述透射式分光光栅的光栅槽形区尺寸。
8、 如权利要求 7所述的干涉光刻系统， 其特征在于： 所述光源发射的光 线入射到所述透射式分光光栅的透射面上，该光线的入射方向与所述光栅基面 形成入射角， 所述入射角与所述斜角之间满足如下的关系：
sin ( Θ ) - Sin ( θ _ 2 γ )]d/入 = N + 1/2， 其中， Θ为入射角， γ为斜角， N为自然数。
9、 如权利要求 7所述的干涉光刻系统， 其特征在于： 所述投影光学镜组 包括至少两组透镜组， 该些透镜组组成成像光路， 所述透射式分光光栅形成该 成像光路的物面， 所述载物平台上放置一工件， 该工件表面形成该成像光路的 像面。
PCT/CN2014/084170 2013-09-03 2014-08-12 一种透射式分光光栅及干涉光刻系统 WO2015032262A1 (zh)

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