JP5861897B2 - Optical system for microlithographic projection exposure apparatus - Google Patents

Description

  This application claims priority to the German patent application DE 10 2013 204 453.4 filed on March 14, 2013. The contents of this application are hereby incorporated by reference.

  The present invention relates to an optical system for a microlithographic projection exposure apparatus.

  Microlithographic projection exposure apparatus are used to produce microstructured components such as, for example, integrated circuits or LCDs. Such a projection exposure apparatus includes an illumination device and a projection lens. In a microlithographic process, an image of a mask (= reticle) illuminated with an illumination device is coated with a photosensitive layer (photoresist) to transfer the mask structure to the photosensitive coating of the substrate, and the image plane of the projection lens. Projection is performed using a projection lens on a substrate (for example, a silicon wafer) disposed on the substrate.

  During operation of the microlithographic projection exposure apparatus, a predetermined illumination setting, i.e. an intensity distribution in the pupil plane of the illumination device, must be set in a target manner. Furthermore, various techniques are known for setting a specific polarization distribution in the illumination pupil in the illumination device in order to optimize the imaging contrast.

  In particular, it is known to set the tangential polarization distribution for high contrast imaging in both the illumination device and the projection lens. “Tangentially polarized light” (or “TE polarized light”) means a polarization distribution in which the orientation of the vibration plane of the electric field intensity vector of each linearly polarized light beam is determined approximately perpendicular to the radius of the circle toward the optical system axis. Then you have to understand. In contrast, “radial polarization” (or “TM polarization”) is the direction in which the oscillation plane orientation of the electric field intensity vector of each linearly polarized light beam is approximately radial with respect to the radius of the circle toward the optical system axis. It must be understood to mean the polarization distribution defined in Accordingly, a pseudo tangential polarization distribution or a pseudo radial polarization distribution should be understood to mean a polarization distribution in which the above criteria are at least approximately satisfied.

  As for the prior art, for example, WO 2005/069081 A2, WO 2005/031467 A2, US 6,191,880 B1, US 2007/0146676 A1, WO 2009/034109 A2, WO 2008/019936 A2, WO 2009/100862 A1 DE 10 2008 009 601 A1, DE 10 2004 011 733 A1, and EP 1 306 665 A2.

WO 2005/069081 A2 WO 2005/031467 A2 US 6,191,880 B1 US 2007/0146676 A1 WO 2009/034109 A2 WO 2008/019936 A2 WO 2009/10082 A1 DE 10 2008 009 601 A1 DE 10 2004 011 733 A1 EP 1 306 665 A2 WO 2005/026843 A2

  It is an object of the present invention to provide an optical system for a microlithographic projection exposure apparatus that makes it possible to generate a desired polarization distribution in the projection exposure apparatus in a relatively simple manner.

  This object is achieved according to the features of independent claim 1.

  An optical system according to the present invention for a microlithographic projection exposure apparatus includes an optical system axis and a polarization-influencing optical array, wherein the polarization-influencing optical array is generated from a uniaxial crystal material and is optical A first polarization-influencing element having a first orientation of the crystal axis and a thickness that varies in the direction of the optical system axis; and disposed downstream of the first polarization-influencing element in the light propagation direction and produced from a uniaxial crystal material And a second polarization influencing element having a second orientation of the optical crystal axis perpendicular to the optical system axis and different from the first orientation and a parallel plane geometry, the polarization influencing optical array comprising: A constant linear input polarization distribution of light incident thereon is converted into an output polarization distribution having a polarization direction that continuously varies across the beam cross section.

  In principle, the present invention provides three linear retarders (ie, due to linear birefringence, retardation, ie, three polarization effects that result in an optical path difference between two orthogonal or mutually perpendicular polarization states. Based on the consideration that any elliptical retarder can be physically realized using a combination of optical elements) depending on the configuration of the linear retarder. In this case, an “elliptical retarder” is understood as a definition of a polarization-influencing optical element that is generalized as long as the predetermined polarization state rotation provided by such an elliptical retarder can be arbitrarily obtained on the Poincare sphere. The

  The concept of the Poincare sphere underlying this consideration is shown schematically in FIG. In this case, the linear retarder has the effect of rotation on the Poincare sphere in a polarization state around an axis existing in the equatorial plane of the Poincare sphere (for example, around the axis “A” or “B” in FIG. 5). Next, using any combination of three linear retarders each having a predetermined constant birefringence fast axis or optical crystal axis direction, any arbitrary elliptical retarder (any axis on the Poincare sphere, e.g., It can be shown mathematically that a polarization state rotation about axis “D” in FIG. 5 can be provided.

  Starting with the above considerations, the present invention then uses a combination of up to three linear retarders, in particular, to change the polarization direction that is continuous across the light beam cross section (ie, FIG. 5 on the Poincare sphere). This is based on the concept of obtaining the effect of a rotator having a polarization rotation angle that continuously changes in response to rotation of the polarization state about the axis “C”. In this case, firstly, the use of optically active or optically active materials can be omitted, and secondly, with respect to the retarder used, it is naturally available with a uniform optical crystal axis orientation in each case Can rely on simple crystal materials.

ここで、Δφは、位相リターデーション（ラムダが作動波長を表す場合に、直交偏光状態に対する光路差に２π／λを乗じたものからもたらされる）を表し、βは、光学結晶軸の角度を表している。 In principle, a general linear retarder can be described by the Jones matrix J:
J =

Where Δφ represents the phase retardation (derived from the optical path difference for the orthogonal polarization state multiplied by 2π / λ when lambda represents the working wavelength), and β represents the angle of the optical crystal axis. ing.

The rotor Jones matrix J _target obtained by the present invention is generally expressed by the following equation (2).

ここで、Ｊ₁は、β＝０°及び位相リターデーションΔφ₁の場合のリターダーのジョーンズ行列を表し、すなわち、次式で与えられる（４）。

Ｊ₂は、β＝４５°及び位相リターデーションΔφ₂の場合のリターダーのジョーンズ行列を表し、すなわち、次式で与えられる（５）。

Ｊ₃は、β＝０°及び位相リターデーションΔφ₃の場合のリターダーのジョーンズ行列を表し、すなわち、次式で与えられる（６）。

（４）〜（６）から、次式が得られる（７）。

この式は、それぞれの位相リターデーションΔφ₁、Δφ₂、及びΔφ₃に対して以下の解をもたらす（８）。

According to the present invention, the following formulation of three linear retarders each having a predetermined constant direction of the fast axis of birefringence is selected here (3).

Here, J ₁ represents the Jones matrix of the retarder when β = 0 ° and the phase retardation Δφ ₁ , that is, given by the following equation (4).

J ₂ represents the Jones matrix of the retarder when β = 45 ° and the phase retardation Δφ ₂ , that is, given by the following equation (5).

J ₃ represents the Jones matrix of the retarder when β = 0 ° and the phase retardation Δφ ₃ , that is, given by the following equation (6).

From (4) to (6), the following equation is obtained (7).

This equation yields the following solution for each phase retardation Δφ ₁ , Δφ ₂ , and Δφ ₃ (8):

That is, the solution according to (8) is a λ / 4 plate having a 90 ° optical crystal axis orientation (predetermined direction, eg, relative to the y direction of a fixed coordinate system), and 45 ° A linear retarder having an optical crystal axis orientation (predetermined direction, eg, relative to the y direction) and a phase retardation of Δφ ₂ = 2α, and an optical crystal axis orientation of 0 ° (predetermined direction, eg, , With respect to the y-direction) and a further λ / 4 plate. Thus, for the generation of polarization rotation angle α that varies in a location-dependent manner as required by the present invention, this linear retarder with an orientation of the optical crystal axis of 45 ° varies in a location-dependent manner or across the light beam cross section. It also has a phase retardation Δφ ₂ .

  Specifically, the polarization affecting optical array used by the present invention to effectively implement a rotator having a polarization rotation angle that varies across the light beam cross section includes at least two linear retarders, one of which is Still another retarder having a thickness profile that varies in the direction of light propagation or in the direction of the optical system axis and arranged downstream in the direction of light propagation has a parallel plane geometry, and these two linear retarders Each has a different orientation of the optical crystal axis perpendicular to the optical system axis.

  In order to obtain the desired output polarization distribution based on the specific configuration of the input polarization distribution of light incident on the polarization-influencing optical array according to the present invention, the parallel plane geometry is also used, as will be described in more detail below. It is also possible to use a third linear retarder having and disposed upstream of the first and second linear retarders with respect to the light propagation direction.

  According to one embodiment, the first polarization influencing element and the second polarization influencing element are arranged directly continuously in the light propagation direction.

  According to one embodiment, the polarization-influencing optical array is arranged upstream of the first polarization-influencing element in the direction of light propagation, is produced from a uniaxial crystal material and has a third optical crystal axis perpendicular to the optical system axis. And a third polarization influencing element having a parallel plane geometry.

  According to one embodiment, the first, second and third polarization affecting elements are arranged directly continuously in the light propagation direction.

  According to one embodiment, the second orientation of the optical crystal axis of the second polarization influencing element and the third orientation of the optical crystal axis of the third polarization influencing element extend perpendicular to each other.

  According to one embodiment, the first orientation of the optical crystal axis of the first polarization affecting element is the second orientation of the optical crystal axis of the second polarization affecting element and the first orientation of the optical crystal axis of the third polarization affecting element. It extends at an angle of 45 ° ± 5 ° in absolute value with respect to 3 orientations.

  According to one embodiment, the first polarization-influencing element has a wedge or wedge cross-sectional geometry.

  According to one embodiment, the first polarization-influencing element has a thickness profile that varies azimuthally with respect to the optical system axis and that is constant radially with respect to the optical system axis.

  According to one embodiment, the second polarization affecting element has a retardation of λ / 4 when the lambda represents the operating wavelength of the optical system.

  According to one embodiment, the third polarization affecting element has a retardation of λ / 4 when the lambda represents the operating wavelength of the optical system.

According to one embodiment, the uniaxial crystalline material is selected from the group comprising magnesium fluoride (MgF ₂ ), sapphire (Al ₂ O ₃ ), and crystalline quartz (SiO ₂ ).

  According to one embodiment, the polarization-influencing optical array converts a constant linear input polarization distribution of light incident on the array at least approximately to a tangential output polarization distribution.

  According to one embodiment, the polarization affecting optical array is placed in the pupil plane of the optical system.

  The invention further relates to a microlithographic projection exposure apparatus and a method for microlithographically generating a microstructured component.

  Further arrangements of the invention can be obtained from the description and the dependent claims.

  The invention will be described in more detail below on the basis of exemplary embodiments shown in the accompanying drawings.

1 is a schematic diagram of a possible configuration of a microlithographic projection exposure apparatus. It is the schematic for demonstrating the structure and function of embodiment of the polarization influence optical arrangement | sequence by this invention. It is the schematic for demonstrating the structure and function of embodiment of the polarization influence optical arrangement | sequence by this invention. It is the schematic for demonstrating the structure and function of embodiment of the polarization influence optical arrangement | sequence by this invention. It is the schematic of the Poincare sphere for explaining the operating system of a different retarder.

  First, a possible configuration of a microlithographic projection exposure apparatus is described below with reference to FIG. 1, which is a simple schematic diagram.

  A microlithographic projection exposure apparatus 100 shown in FIG. 1 includes a light source unit 101, an illumination device 102, a structure-bearing mask 103, a projection lens 104, and a substrate 105 to be exposed. The light source unit 101 can include a light source, eg, an ArF laser for an operating wavelength of 193 nm, and a beam shaping optical unit that generates a parallel light beam. The parallel light beam emitted by the light source unit 101 first enters the diffractive optical element (DOE) 106. The DOE 106 uses the angular emission characteristics defined by the respective diffractive surface structures to generate a desired intensity distribution in the pupil plane PP, such as a dipole or quadrupole distribution. A lens 108 disposed downstream of the DOE 106 in the beam path is designed as a zoom lens that produces a parallel light beam having a variable diameter. The parallel light beam is directed onto the axicon 111 by the deflection mirror 109. The zoom lens 108 is used with the upstream DOE 106 and the axicon 111 to generate different illumination configurations in the pupil plane PP depending on the zoom setting and position of the axicon element.

  According to FIG. 1, a polarization-influencing optical array 200 is placed in the pupil plane PP, in which a possible embodiment is described below with reference to FIG. 2 and beyond.

  The illumination device 102 further includes a light mixing system 112 disposed in the region of the pupil plane PP downstream of the axicon 111 (in FIG. 1, just downstream of the axicon 111), which provides, for example, light mixing. Suitable micro-optical element arrays can be included. The light mixing system 112 and, where appropriate, further optical components (only a single lens element 110 is shown) are followed by a reticle masking system (REMA) 113, which is reticulated by the REMA lens 114. An image is formed on 103, thereby delimiting an illumination area on reticle 103. The reticle 103 is imaged on the photosensitive substrate 105 using the projection lens 104. In the illustrated embodiment, an immersion liquid 116 having a refractive index different from air is placed between the last optical element 115 of the projection lens 104 and the photosensitive substrate 105.

  In yet another embodiment, the lighting device 102 includes a plurality of independently adjustable mirror elements known from, for example, WO 2005/026843 A2, to generate different lighting configurations. Can be included.

  Hereafter, a possible embodiment of the polarization-influencing optical array 200 placed in the pupil plane PP shown in FIG. 1 will be described in terms of construction and function with reference to FIG. 2 and the following.

  Referring to FIG. 2, the polarization-influencing optical array 200 is a wedge-shaped polarization-influencing optical element 220 (hereinafter referred to as a wedge-shaped optical element 220) having a thickness that changes in the light propagation direction (corresponding to the z direction of the illustrated coordinate system) in the first embodiment. (Also referred to as “first polarization influencing element”) between the two parallel plane polarization influencing optical elements 210 and 230, the latter immediately following the (first) wedge-shaped polarization influencing optical element 220 with respect to the light propagation direction. Arranged upstream and downstream respectively.

Polarization influencing elements 210, 220, and 230 are uniaxial crystalline materials that have sufficient transmission in each case at their respective operating wavelengths, eg, magnesium fluoride (MgF ₂ ), sapphire (with an exemplary operating wavelength of about 193 nm). Al ₂ O ₃ ) or crystalline quartz (SiO ₂ ). In these materials, the difference between the extraordinary refractive index n _e and ordinary index n _o, respectively _{n e -n o (SiO 2)} ≒ + 0.013, n e -n o (Al 2 O 3) ≒ - _{0.011, n e -n o (MgF} 2) is a ≒ + 0.014.

  In certain exemplary embodiments, in the polarization affecting elements 210 and 230, the retardation (constant across the light beam cross section due to the parallel plane configuration of these elements) is λ / 4 in each case. Here, lambda represents the operating wavelength of the optical system. In the polarization-influencing optical elements 210, 220, and 230 of FIG. 2, the direction of the optical crystal axis is encoded with a double-headed arrow that indicates in each case, and in certain exemplary embodiments, this direction is the coordinate shown. With respect to the system, element 210 extends parallel to the y direction, element 230 extends parallel to the x direction, and element 220 extends at an angle of 45 ° with respect to the x and y directions.

  FIG. 2 also shows the polarization rotation angle α that is obtained in a generally location-dependent manner by the polarization-influencing optical array 200, which in certain exemplary embodiments is the light along the y direction. It varies between 0 ° and 90 ° across the beam cross-section, and is particularly provided by the wedge cross-sectional configuration of the polarization affecting element 220.

  Generation of polarization states that change in a location-dependent manner or continuously across the light beam cross-section achieved by the polarization-influencing optical array 200 described above can be achieved, for example, with the desired distribution in the illumination device using an appropriate distribution of these polarization states. It can be used to generate illumination settings (eg, using a mirror array that includes a plurality of independently adjustable mirror elements). In yet another application, it can provide at least partial compensation for undesirable disturbances in the polarization state present in the illumination device or projection lens.

  Hereinafter, with reference to FIGS. 3 and 4, the configuration and function of a polarization-influencing optical array 300 according to still another embodiment of the present invention will be described below.

  The polarization affecting optical array 300 functions to convert the constant linear input polarization distribution 305 to at least approximately a tangential output polarization distribution 335, as shown in FIG. In contrast to the polarization influencing optical array 200 described in FIG. 2, in the case of the polarization influencing optical array 300, the central polarization influencing optical element 320 is not implemented in a wedge cross-section manner and is shown in FIGS. 4a and 4b. As such, it has a thickness profile that varies in the azimuthal direction with respect to the optical system axis (ie, the z direction) and that is constant in the radial direction with respect to the optical system axis. In the embodiment schematically illustrated in FIG. 4a, the polarization-influencing optical element 320 has a constant thickness along a radius R that is perpendicular to the element axis EA and forms an angle θ with the reference axis RA. Therefore, in this embodiment, the thickness profile depends only on the azimuth angle θ. A central hole 321 is placed in the center of the polarization-influencing optical element 320.

  FIG. 4a shows an exemplary thickness profile in a perspective view, and FIG. 4b shows a graph in which the thickness d is plotted as a function of the azimuth angle θ for this thickness profile. In an exemplary embodiment, the thickness profile has a jump at θ = 180 °, and the thickness difference in this jump corresponds to a retardation of lambda (or an integer multiple of lambda). Further, the polarization-influencing optical element 320 in this exemplary embodiment is composed of two subelements or has a segment configuration. However, the present invention is not limited to these. In yet another embodiment, a configuration that includes more (eg, four) segments, or otherwise a non-segment or integral configuration, and a continuous thickness profile throughout (ie, no jump in thickness profile) You can also choose.

  Polarization-influencing optical elements 310 and 330, respectively disposed upstream and downstream of element 320 with respect to the direction of light propagation, are parallel plane geometry and a constant retardation of λ / 4, as in the exemplary embodiment described in FIG. It is comprised using.

Similar to the exemplary embodiment described in FIG. 2, at an exemplary operating wavelength of about 193 nm, polarization influencing elements 310, 320, and 330 are, for example, magnesium fluoride (MgF ₂ ), sapphire (Al ₂ O ₃ ) or crystalline quartz (SiO ₂ ). In this case, the maximum height difference of the polarization-influencing optical element 320 that must be present in the thickness profile of the element 320 to provide retardation in the range of -λ / 2 to + λ / 2 is in the region of about 15 μm. .

  In the embodiments described above with reference to FIGS. 2 and 3, arrays 200 and 300, each formed from three polarization-influencing optical elements, were used, but the present invention is not limited thereto. Based on the configuration of the input polarization distribution of light incident on the polarization-influencing optical array according to the present invention rather than three polarization-influencing optical elements, two polarization-influencing optical elements (described above) are used to generate the desired output polarization distribution. It should be pointed out that the elements 220, 230 and 320, 330) in the exemplary embodiment may suffice. This is because, for example, when the input polarization distribution of light incident on each polarization-effecting optical array is constant linear (eg, having a polarization direction extending in the y direction), the optical crystal axis is also oriented in the y direction, for example. Because the λ / 4 plate (corresponding to element 210 in FIG. 2 and element 310 in FIG. 3) has no effect on the input polarization distribution (in the example mentioned, the light is It is incident on each element 210 and 310 in a unique state).

  Although the invention has been described with reference to particular embodiments, many variations and alternative embodiments, for example, by combining and / or exchanging features of individual embodiments will be apparent to those skilled in the art. Accordingly, such modifications and alternative embodiments are included by the present invention and the scope of the present disclosure is limited only by the scope of the appended claims and their equivalents. Needless to say to those skilled in the art.

DESCRIPTION OF SYMBOLS 100 Microlithography projection exposure apparatus 101 Light source unit 103 Structure support mask 104 Projection lens 200 Polarization influence optical arrangement

Claims (16)

An optical system for a microlithographic projection exposure apparatus,
An optical system axis (OA);
A polarization-influencing optical array;
Including
The polarization affecting optical array (200, 300) is
A first polarization effect produced from a uniaxial crystal material and having a first orientation of an optical crystal axis perpendicular to the optical system axis (OA) and a thickness varying in the direction of the optical system axis (OA) Elements (220, 320);
The first orientation is located downstream of the first polarization influencing element (220, 320) in the direction of light propagation, is produced from a uniaxial crystal material, and is perpendicular to the optical system axis (OA) and A second polarization-influencing element (230, 330) having a different second orientation of the optical crystal axis and a parallel plane geometry;
Including
The polarization-influencing optical array (200, 300) converts a constant linear input polarization distribution of light incident on the array (200, 300) into an output polarization distribution having a polarization direction that continuously varies across the light beam cross section. ,
An optical system characterized by that.   The first polarization influencing element (220, 320) and the second polarization influencing element (230, 330) are arranged directly and continuously in the light propagation direction. Optical system.   The polarization affecting optical array (200, 300) further includes a third polarization affecting element (210, 310), the third polarization affecting element (220) in the light propagation direction. , 320), is produced from a uniaxial crystal material and has a third orientation of the optical crystal axis and a parallel plane geometry perpendicular to the optical system axis (OA). The optical system according to claim 1 or 2.   The optical system according to claim 3, wherein the first, second, and third polarization affecting elements are arranged directly and continuously in the light propagation direction.   The second orientation of the optical crystal axis of the second polarization affecting element (230, 330) and the third orientation of the optical crystal axis of the third polarization affecting element (210, 310) are mutually different. The optical system according to any one of claims 1 to 4, wherein the optical system extends vertically.   The first orientation of the optical crystal axis of the first polarization influencing element (220, 320) is relative to the second orientation of the optical crystal axis of the second polarization influencing element (230, 330). And extending at an angle of 45 ° ± 5 ° in absolute value relative to the third orientation of the optical crystal axis of the third polarization influencing element (210, 310). 6. The optical system according to any one of items 5.   The optical system according to any one of claims 1 to 6, wherein the first polarization affecting element (220) has a wedge cross-sectional geometry.   The first polarization affecting element (320) has a thickness profile that varies in an azimuth direction with respect to the optical system axis (OA) and is constant in a radial direction with respect to the optical system axis (OA). The optical system according to any one of claims 1 to 6, wherein:   The second polarization influencing element (230, 330) has a retardation of lambda / 4 when the lambda represents the operating wavelength of the optical system. The optical system described in 1.   10. The third polarization-influencing element (210, 310) according to any one of claims 3 to 9, wherein the third polarization-influencing element (210, 310) has a retardation of lambda / 4 when the lambda represents the operating wavelength of the optical system. The optical system described in 1. 11. The uniaxial crystalline material is selected from the group comprising magnesium fluoride (MgF ₂ ), sapphire (Al ₂ O ₃ ), and crystalline quartz (SiO ₂ ). The optical system according to any one of the above.   12. The polarization-influenced optical arrangement (300) converts at least approximately a constant linear input polarization distribution of light incident on the arrangement into a tangential output polarization distribution. The optical system according to any one of the above.   The optical system according to any one of claims 1 to 12, wherein the polarization-influenced optical arrangement (200, 300) is arranged on a pupil plane of the optical system.   14. The optical system according to claim 1, wherein the optical system is an illumination device (102) of a microlithographic projection exposure apparatus (100). A lighting device (102) embodied according to any one of claims 1 to 14;
A projection lens (104);
A microlithographic projection exposure apparatus (100) comprising: A method for microlithographically generating a microstructured component, comprising:
Providing a substrate (105) to which a layer composed of photosensitive material is at least partially applied;
Providing a mask (103) having a structure to be imaged;
Providing a microlithographic projection exposure apparatus (100) according to claim 15,
Projecting at least a portion of the mask (103) onto a certain area of the layer using the projection exposure apparatus;
A method comprising the steps of:

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