制作复杂形状镜片：极端紫外线光刻照明系统中的飞点镜制造工艺

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"Fabrication of a complex-shaped mirror for an extreme ultraviolet lithography (EUVL) illumination system" 本文探讨了用于极紫外光刻（EUVL）照明系统的复杂形状镜片，特别是飞眼镜的设计与制造工艺。飞眼镜是一种具有众多球面截面凹镜元素的复合反射镜，其每个元素的顶部呈弧形。研究的重点在于一种制造方法，即先独立制作每个弧形元素，然后将它们并排组装成完整的镜片。首先，文章中提到了采用因瓦合金（Invar）材料并结合电镀镍工艺来制作这些弧形元素。因瓦合金因其低的热膨胀系数而常用于精密光学部件，确保在温度变化时保持稳定的尺寸。电镀镍则可以提供良好的反射表面，并提高镜片的耐腐蚀性。在制造过程中，所得到的反射表面的峰值到谷值（PV）精度达到了0.31毫米，这意味着整个表面的高度差控制在一个非常小的范围内，这对于高精度的EUVL系统至关重要。此外，这些表面在1103x140毫米和131毫米区域内的均方根（RMS）粗糙度分别为约0.23纳米和0.35纳米，表明表面极其平滑，这有助于减少光的散射，提高光刻过程的分辨率。镜片的表面斜率精度也是衡量其质量的重要指标。文章指出，这些表面相对于底部表面的斜率精度在y方向为2166弧秒，在x方向为43弧秒。弧秒是一个极小的角度单位，用于描述微小的倾斜，这些数值证明了镜片的几何形状控制得极其精确，对于EUV光的聚焦和成像至关重要。尽管这些镜片元素具有特殊的形状，但通过精细的工艺流程，研究人员成功地制造出了具有高精度和光滑表面的飞眼镜元素。这些元素将被用于EUVL系统，以实现更先进的半导体制造技术，提高集成电路的集成度和性能。该研究对极紫外光刻技术的发展和光学制造工艺的进步具有重要意义。

Fabrication of a complex-shaped mirror for an

extreme ultraviolet lithography illumination

system

Hideo Takino

Teruki Kobayashi

Norio Shibata

Masaaki Kuki

Akinori Itoh

Hideki Komatsuda

Nikon Corporation

1-10-1 Asamizodai Sagamihara

Kanagawa 228-0828, Japan

E-mail: takino@nikongw.nikon.co.jp

Abstract. We propose and discuss several fabrication processes for a

complex-shaped mirror, which is a ﬂy-eye mirror, used in an extreme

ultraviolet lithography (EUVL) illumination system. The mirror has a com-

plex reﬂective surface consisting of many concave mirror elements that

are sections of a sphere; the top of each element is arc shaped. In the

present study, we focus on one process in which all elements are fabri-

cated individually and then arranged side-by-side to form the mirror.

Thus, as the ﬁrst step in this process, we fabricate the arc-shaped ele-

ments made of invar with electroless nickel plating. The resultant reﬂec-

tive surfaces have a peak-to-valley (PV) surface accuracy of 0.31

␮

The surfaces have the rms roughnesses of about 0.23 and 0.35 nm in

areas of 110⫻ 140

␮

m and 1⫻ 1

␮

m, respectively. The slope accuracies

of the surfaces relative to the bottom surfaces are ⫺166 and 43 arc-sec

in the

and

directions, respectively. Thus, the mirror elements for the

ﬂy-eye mirror can be fabricated very accurately with smooth surfaces,

although the mirror elements have a special shape compared to that of

general optics.

2003 Society of Photo-Optical Instrumentation Engineers.

[DOI: 10.1117/1.1591797]

Subject terms: extreme ultraviolet lithography; illumination; ﬂy eye; mirror; inte-

grator; fabrication; optics; metal.

Paper 020539 received Dec. 11, 2002; revised manuscript received Feb. 21,

2003; accepted for publication Feb. 24, 2003. This paper is a revision of a paper

presented at the SPIE conference on Emerging Lithographic Technologies V,

February 2001, Santa Clara, CA. The paper presented there appears

(unrefereed) in SPIE Proceedings Vol. 4343.

1 Introduction

Reduction-projection exposure systems are widely used in

lithography processes for very large scale integration

共VLSI兲 manufacturing. In such a system, electronic circuit

patterns on a mask are illuminated and are reduced through

a projection lens, such that the reduced patterns are pro-

jected onto a silicon wafer. To further minimize the width

of the lines of the circuit patterns, an extreme ultraviolet

lithography 共EUVL兲 system, in which exposure is carried

out using an extreme ultraviolet wavelength of about 13

nm, has attracted attention and has been investigated glo-

bally.

In an EUVL system, the illumination system must

project light from a source onto the arc ﬁeld of a mask

efﬁciently. The illumination system must also have both

irradiance uniformity and spatial coherence

␴

uniformity

across the arc ﬁeld. In recent years, several types of illumi-

nation systems for EUVL have been proposed.

1–6

One such

system, proposed by Komatsuda, includes two types of ﬂy-

eye mirrors used as key optics: an arc-shaped ﬂy-eye mirror

and a rectangular ﬂy-eye mirror.

Both the arc-shaped and the rectangular ﬂy-eye mirrors

have a complex reﬂective surface consisting of many con-

cave mirror elements; the top of each element is arc shaped

for the former and rectangular for the latter. Owing to this

complexity, these mirrors are difﬁcult to fabricate. To our

knowledge, a mirror with such a complex reﬂective surface

has not yet been realized.

We propose and discuss several fabrication processes for

ﬂy-eye mirrors. In particular, we focus on one process in

which all elements are fabricated individually and then ar-

ranged side by side to form the mirror. Here, the arc-shaped

Fig. 1 EUVL optical system using the illuminator with ﬂy-eye mir-

rors. Light source: laser, lens, nozzle for emitting gas jet, and EUV

light source. Collector mirror group: ellipsoidal and concave mirrors.

Fly-eye mirror group: arc-shaped and rectangular ﬂy-eye mirrors.

Condenser mirror group: aspheric and plane mirrors.

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