TW201702756A - Method of operating a microlithographic projection apparatus - Google Patents

Abstract

A method of operating a microlithographic projection apparatus comprises the step of providing a mask (16), an illumination system (12) and a projection objective (20) configured to form an image of an object field (14), which is illuminated on the mask (16) in a mask plane, on an image field positioned on a light sensitive surface (22). Edge placement errors are determined at different field points in the image field. The mask (16) is then illuminated with projection light having an improved field dependency of the angular irradiance distribution. The angular irradiance distribution according to the improved field dependency varies over the object field (14) in such a way that the edge placement errors determined in step (b) are reduced at the different field points.

Description

Method of operating a lithography projection device

The present invention relates generally to the field of lithography, and more particularly to illumination systems for projection exposure apparatus or reticle inspection equipment. The present invention is particularly concerned with correcting edge placement errors (EPE), which represent the difference in ideal and actual feature edge positions in the image plane of the objective lens at the wafer level.

Photolithography (also known as optical lithography or lithography for short) is a technique for making integrated circuits, liquid crystal displays, and other microstructured devices. The lithography process, along with an etch process, is used to pattern features in a thin film stack that has been formed on a substrate, such as a germanium wafer. At each fabrication layer, the wafer is first coated with a photoresist that is a material that is sensitive to radiation, such as deep ultraviolet (DUV) light. Next, the wafer with the photoresist at the top is exposed to the projected light in the projection exposure apparatus. The device projects a mask containing the pattern onto the photoresist such that the photoresist is only exposed at a particular location defined by the reticle pattern. After exposure, the photoresist is developed to produce an image corresponding to the reticle pattern. The etch process then transfers the pattern to the thin film stack on the wafer. Finally, remove the photoresist. This procedure is repeated with different masks to create a multilayer microstructure assembly.

The projection exposure apparatus generally comprises a light source, an illumination system for illuminating the reticle with the projection light generated by the light source, a reticle stage for aligning the reticle, a projection objective lens and a crystal for aligning the wafer coated with the photoresist The circle is aligned with the table. The illumination system illuminates a field on the reticle, which may for example have a moment The shape of a shape or curved slit.

In current projection exposure devices, two different types of devices can be distinguished. In one type, each target portion on the wafer is illuminated by exposing the entire mask pattern to the target portion at a time. This device is often referred to as a wafer stepper. In another type of device (which is commonly referred to as a step-and-scan device or scanner), each substrate is illuminated by progressively scanning the reticle pattern under the projected beam in the scanning direction while simultaneously or in parallel parallel or anti-parallel movement of the substrate. A target part. The ratio of wafer speed to reticle speed is equal to the magnification of the projection objective, which is typically less than 1, such as 1:4.

It should be understood that the term "mask" (or reticle) is broadly interpreted as a patterning device. Commonly used reticlees contain opaque or reflective patterns and may be, for example, binary, alternating phase shifting, attenuating phase shifting or a variety of hybrid reticle types. However, there are also active reticle, such as a reticle that is implemented as a programmable mirror array. In addition, the programmable LCD array can also be used as a active mask.

As the technology for fabricating microstructure devices advances, the requirements for lighting systems continue to increase. Ideally, the illumination system illuminates every point of the illumination field on the reticle with projected light having a well defined spatial and angular irradiance distribution. The term angular radiance distribution describes how the total light energy of a light bundle (which is concentrated toward a particular point in the plane of the reticle) is distributed in various directions of the rays that make up the plexus.

The angular irradiance distribution of the projected light impinging on the reticle is generally suitable for the type of pattern projected onto the photoresist. Generally, the optimal angular irradiance distribution depends on the size, orientation, and pitch of the features contained in the pattern. The angular irradiance distribution most commonly used for projected light is called conventional, toroidal, bipolar, and quadrupole illumination settings. These terms relate to the irradiance distribution in the pupil plane of the illumination system. For example, in a circular illumination setting, only the annular area is illuminated in the pupil plane. Therefore, only a small angular range exists in the angular irradiation range of the projected light, and all the light rays are obliquely irradiated onto the reticle at a similar angle.

Different means are known in the art to modify the angle of the projected light in the plane of the reticle Radiation is distributed to achieve the desired illumination settings. In the simplest case, a stop (diaphragm) containing one or more devices is located in the pupil plane of the illumination system. Since the position in the pupil plane is converted to an angle in a Fourier-related field plane (eg, a reticle plane), the size, shape, and position of the aperture in the pupil plane determine the angular irradiance distribution in the reticle plane. However, any change in lighting settings requires a replacement of the light. This makes it difficult to fine tune the illumination settings as this would require a very large number of apertures with slightly different sizes, shapes or positions. In addition, the use of diaphragms will inevitably lead to light loss and thus reduced equipment throughput.

Accordingly, many common illumination systems include adjustable elements such that illumination of the pupil plane can be continuously changed, at least to a certain extent. Many illumination systems use exchangeable diffractive optical elements to produce the desired spatial irradiance distribution in the pupil plane. If a zoom optics and a pair of axicon elements are provided between the diffractive optical element and the pupil plane, it is possible to adjust this spatial irradiance distribution.

Mirror arrays using illumination pupil planes have recently been proposed. In EP 1 262 836 A1, the mirror array is embodied as a microelectromechanical system (MEMS) comprising more than 1000 micromirrors. Each mirror can be tilted in two different planes that are perpendicular to each other. Thus, the radiation incident on this mirror device can be reflected (substantially) in any desired hemispherical direction. A collecting lens disposed between the mirror array and the pupil plane transfers the angle of reflection generated by the mirror to a position in the pupil plane. This known illumination system makes it possible to illuminate the pupil plane with a plurality of spots, each of which is associated with a particular micromirror and is free to move in the pupil plane by tilting the mirror.

A similar illumination system is disclosed in US 2006/0087634 A1, US 7,061,582 B2, WO 2005/026843 A2 and WO 2010/006687 A1. US 2010/0157269 A1 discloses an illumination system in which an array of micromirrors is directly imaged on a reticle.

As mentioned above, it is generally desirable to illuminate all points on the reticle with the same irradiance and angular irradiance distribution at least after the scan integration. If different irradiances are used to illuminate the dots on the reticle, this usually results in a critical dimension (CD) at the wafer level. Unexpected changes. For example, when there is an irradiance change, the image of the uniform line on the photographic mask on the photographic mask may also have an irradiance change along its length. Because of the fixed exposure threshold of the photoresist, this type of irradiance change translates directly into the width of the structure that should be defined by the image of the line.

If the angular irradiance is unintentionally changed on the illumination field on the reticle, this also has a negative impact on the quality of the image produced on the photographic surface. For example, if the angular irradiation distribution is not perfectly balanced, that is, more light is irradiated from one side to the reticle than from the other side, if the photosensitive surface is not perfectly disposed in the focal plane of the projection objective, the photosensitive The conjugate image point on the surface will be laterally offset.

US 6,404,499 A and US 2006/0244941 A1 propose a mechanical device comprising opaque finger-like aperture elements arranged side by side and aligned in parallel scanning direction for modifying the spatial irradiance distribution in the illumination field (ie, the field dependence of the irradiance). Two relative arrays. Each pair of mutually opposite aperture elements can be displaced in the scanning direction such that the distance between the opposite ends of the aperture elements changes. If the device is arranged in the field plane of the illumination system imaged by the objective lens on the reticle, it is possible to create a slit-shaped illumination field whose width in the scanning direction can vary in the cross-scanning direction. Since the irradiation is integrated during the scanning procedure, the integral irradiation (sometimes referred to as the illumination dose) can be fine-tuned for a plurality of cross-scan locations in the illumination field.

Unfortunately these devices are mechanically very complicated and expensive. This is also due to the fact that these devices must be placed in or very close to the field plane, where the blades of the movable field stop are usually arranged in the field plane.

It is more difficult to adjust the angular irradiance distribution in a field dependent manner. This is mainly because the spatial irradiance distribution is only a function of the spatial coordinates x, y, and the angular irradiance distribution is also dependent on the angles α, β.

WO 2012/100791 A1 discloses an illumination system in which a mirror array is used to produce a desired irradiance distribution in the pupil plane of the illumination system. A fly-eye optical integrator having a plurality of light entrance facets is disposed near the pupil plane. The image of the light entrance will be superimposed on the reticle. The area of the spot produced by the mirror array is smaller than the light entrance琢 The total area of the face is at least 5 times smaller. This makes it possible to produce a variable light pattern on the light entrance pupil surface and thus produce different angular irradiance distributions in different parts of the illumination field. For example, an X dipole can be generated in one portion of the illumination field and a Y bipolar illumination setting can be generated in another portion of the illumination field.

WO 2012/028158 A1 discloses an illumination system in which the irradiance distribution on the light entrance pupil surface of the fly-eye optical integrator is modified with the aid of a plurality of regulator units arranged before the optical integrator. Each of the regulator units is variably redistributed to the spatial and/or angular irradiance distribution of the associated light entrance pupil surface associated with one of the light entrance pupil faces and without blocking any light. In this regard, it is possible to illuminate two or more different portions associated with different semiconductor devices on a single die, for example with different illumination settings.

The unpublished patent application PCT/EP2014/003049 discloses a method in which the irradiance distribution on the entrance face of the fly-eye optical integrator is imaged by means of a digital mirror device (DMD). Modified on the entrance. This method is advantageous because it is not necessary to produce a very small spot of light with an analog micromirror array, as is the case with the illumination system disclosed in the aforementioned WO 2012/100791 A1. The field dependence of the angular irradiance distribution is adjusted such that the angular irradiance distribution over the illumination field becomes completely uniform (i.e., field independent).

However, it is also mentioned that it may sometimes be necessary to deliberately introduce field dependence of the angular irradiance distribution. This may be advantageous, for example, if the projection objective or reticle has field dependent properties. In the case of reticle, such field dependent properties are typically the result of features having different orientations or dimensions. The adverse effects of such field dependencies can be successfully reduced by selectively introducing the field dependence of the angular irradiance distribution.

Industries that use lithography projection equipment to produce integrated circuits or other electronic or micromechanical devices are striving for smaller feature sizes, higher output, and higher throughput. One of the key goals is to reduce edge placement error (EPE). The edge position error represents the difference between the position of the actual (or simulated) contour of the structure defined by the lithography on the wafer (or similar support) on the one hand, and the position of the ideal contour on the other hand. The edge position error is a basic quantity that determines other commonly used quantities, such as critical dimensions and overlay errors. The reduction in edge position error will be straight Grounding results in higher yields and/or smaller feature sizes.

Figures 16a, 16b and 16c depict how edge position errors are typically calculated. A target structure ST having an ideal contour is displayed in the upper half of each figure. In the lower half, the rectangle drawn in solid lines indicates the actual structure ST' produced on the wafer in the lithography process.

In the case shown in Fig. 16a, the actual structure ST' is wider than the target structure ST. The edge extending in the longitudinal direction of the structure ST' is shown by the positive edge position error E = d _{m -} d _t , where d _m is the measured distance from the line of symmetry and d _t is the target distance from the line of symmetry.

If the target distance is the same as the measured distance (as shown in Fig. 16b), the edge position error E is zero.

The measuring distance is smaller than the target distance d _m d _t, the edge position error E becomes negative, illustrated in Figure 16c.

It is an object of the present invention to provide a method of operation of a lithographic projection apparatus that makes it possible to reduce edge position errors.

According to the invention, this object is achieved by a method in which a reticle, an illumination system configured to illuminate the reticle, and a projection objective are provided in step (a). The projection objective is configured to form an object field (which is illuminated on a reticle in the reticle plane) on an image field located on a photosensitive surface (eg, a photoresist or a CCD sensor in the case of a reticle inspection apparatus) An image of one.

In the next step (b), the edge position error at different field points in the image field is determined. This can be done by measurement or simulation.

In the last step (c), the reticle is illuminated with projected light having an improved field dependency with an angular irradiance distribution. The angular irradiance distribution based on the improved field dependence varies over the object field such that the edge position error determined in step (b) is reduced.

Although the influence of the angular irradiance distribution on the edge position error is known in the art itself, the field dependence of the edge position error and the field in the illumination field have not been proposed before. The dependent angle irradiance distribution is determined such that the edge position error is reduced in a field dependent manner.

The edge position error determined in step (b) may comprise at least one of the group consisting of a CD change and an overlap change.

When the edge position error is determined in step (b), the reticle can be illuminated by the projected light having an original field dependency of the angular irradiance distribution. Next, the edge position error on the photosensitive surface at different field points in the image field is simulated or measured. In step (c), the field dependence of the original angular irradiance distribution can then be varied to obtain improved field Dependence of the angular irradiance distribution. These steps can be repeated one or several times. This means that the improved field dependence of the angular irradiance distribution becomes the original field dependence of the angular irradiance distribution of the next decision step. In this manner, it is possible to reversibly improve the field dependence of the angular irradiance distribution until the edge position error becomes very small or even reaches a minimum.

When the edge position error is first determined, the original angle irradiance distribution may be constant, that is, there is no field dependency. However, it is also possible to start with an original angle of irradiation distribution that already has field dependence. This raw field dependency can be calculated, for example, based on feature size and orientation on the reticle.

Step (c) may comprise the step of illuminating the reticle with a projected light that not only has an improved field dependence of the angular irradiance distribution but also an improved field dependence of the irradiance. The irradiation varies on the object field such that the edge position error determined in step (b) decreases at different field points. In other words, in a common optimization procedure, the angular irradiance distribution and the field dependence of the irradiation are improved such that the edge position error is reduced.

In this case, step (b) may additionally comprise the step of illuminating the reticle with the projected field dependence of the irradiance, and the step of simulating or measuring the edge position error on the photosensitive surface at different field points. Next, step (c) includes an additional step of changing the original field dependence of the irradiation to obtain improved field dependence of the irradiation.

If the reticle has a portion in which the reticle pattern is uniform (ie, the width, pitch, and orientation of the structure are unchanged), the conventional method is to irradiate the field at an independent angle. A uniform scan of the integrated radiation is used to illuminate the portion.

However, in accordance with the present invention, the angular irradiance distribution can still vary over a region of the object field that coincides with the portion of the reticle having a uniform reticle pattern (at least at a time during step (c)). In other words, the angular irradiance distribution is intentionally varied over the uniform reticle pattern to reduce edge position errors that may be caused by defects in the objective lens.

Of course, if the reticle includes a non-uniform reticle pattern with locally varying characteristics, it is also possible to adjust the improved angular irradiance distribution to suit the locally varying properties of the reticle pattern. The locally varying characteristics of the reticle pattern can include at least one of the group consisting of a structure width, a structure pitch, and a structure orientation.

In a specific embodiment, the angular irradiance distribution based on improved field dependence is non-telecentric, at least at certain field points. At least one of the reticle and the photosensitive surface is displaced along the optical axis of the projection objective prior to step (c). This results in a lateral offset of the image position. In this way, the edge position error, in particular the overlap error, can be reduced in a field-dependent manner.

If the reticle is continuously moved during step (c) during the scan cycle, the angular irradiance distribution may change during the scan cycle. Then, the angular irradiance distribution depends not only on the field coordinates but also on time.

An illumination system capable of generating a field dependent angle irradiance distribution and field dependent irradiance preferably includes an optical integrator configured to generate a plurality of auxiliary light sources located in a pupil plane of the illumination system. The optical integrator includes a plurality of light entrance pupil faces, each associated with one of the auxiliary light sources. The image of the pupil of the light entrance is at least substantially superimposed on the plane of the reticle. A spatial light modulator is provided having a light exit surface and configured to transmit or reflect the projected light in a spatially resolved manner. An objective lens images the light exit surface of the spatial light modulator on the light entrance pupil of the optical integrator. In step (c), the spatial light modulator is controlled to obtain a modified angular irradiance distribution in the reticle plane.

The illumination system further includes an adjustment aperture forming unit that directs the projected light to the spatial light modulator. The pupil forming unit itself may comprise a first reflective or transmitted beam deflecting element The first beam deflects the array. Each beam deflecting element is configured to illuminate a spot on the illumination spatial light modulator at a position that can be varied by varying the angle of deflection produced by the beam deflecting element.

The spatial light modulator can include a second beam deflecting array of second reflected or transmitted beam deflecting elements. Each of the second beam deflecting elements can be in an "on" state (where it directs the illumination light toward the optical integrator) and in an "off" state (where it directs the illumination light elsewhere). For example, the second beam deflection array can be implemented as a digital mirror device (DMD).

The subject of the invention is also an illumination system for a lithographic projection apparatus comprising an optical integrator configured to generate a plurality of auxiliary light sources in a pupil plane of the illumination system. The optical integrator includes a plurality of light entrance pupil faces, each associated with one of the auxiliary light sources. The spatial light modulator has a light exit surface and is configured to transmit or reflect the illuminated projected light in a spatially resolved manner. The pupil forming unit is configured to direct the projected light on the spatial light modulator. An objective lens images the light exit surface of the spatial light modulator onto the light entrance pupil surface of the optical integrator. The control unit is configured to control the pupil forming unit and the spatial light modulator such that the reticle is illuminated by the projected light of the improved field dependence of the angular irradiance distribution. The angular irradiance distribution based on the improved field dependence varies across the object field to reduce the edge position error that varies over the image field.

The subject of the invention is also a lithographic projection apparatus comprising a reticle, an illumination system configured to illuminate the reticle, and a configuration to form an object field on the image field on the photosensitive surface (which is in the reticle plane) A projection objective of the image that is illuminated on the reticle. Providing means for illuminating a reticle with a projected light having an improved field dependence of an angular irradiance distribution, wherein the angular irradiance distribution based on the improved field dependence varies over the object field such that edge position errors are varied over the image field reduce.

【definition】

The term "light" as used herein refers to any electromagnetic radiation, particularly visible light, UV, DUV, VUV, and EUV light, as well as X-rays.

The term "light ray" as used herein refers to light whose propagation path can be described by a straight line.

The term "light bundle" as used herein refers to a plurality of light rays having a common source in the field plane.

The term "light beam" as used herein refers to all light passing through a particular lens or another optical element.

The term "location" as used herein refers to the position of a reference point of a subject in three dimensions. This position is usually indicated by a set of three Cartesian coordinates. The orientation and position thus fully describe the arrangement of a subject in three dimensions.

The term "surface" as used herein refers to any plane or curved surface in three-dimensional space. The surface may be part of the body or may be completely separated from it, as is the case with field planes or pupil planes.

The term "field plane" as used herein refers to a reticle plane or any other plane that is optically conjugate with the reticle plane.

The term "light plane" is a plane in which a Fourier relationship is established (at least approximately) to a plane. Generally, edge rays passing through different points in the plane of the mask intersect in a pupil plane, and the main rays intersect the optical axis. Usually in the prior art, if it is not actually a plane in the mathematical sense, but is slightly curved, the term "a pupil plane" is still used, which is strictly referred to as a pupil surface.

The term "uniform" as used herein refers to a property that does not depend on location.

As used herein, the term "optical raster element" means any optical element, such as a lens, 稜鏡 or diffractive optical element, which is co-located with other identical or similar optical grating elements such that each optical grating element is associated In one of a plurality of adjacent optical channels.

The term "optical integrator" as used herein refers to the addition of the product NA. a is an optical system, wherein NA is a numerical aperture of illumination and field area.

As used herein, the term "concentrator" means an optical element or an optical system that establishes (at least approximately) a Fourier relationship between two planes (e.g., a field plane and a pupil plane).

The term "conjugate plane" as used herein refers to a plane in which an imaging relationship is established. More information on the concept of conjugate planes is described in an article by E. Delano entitled "First-order Design and y," The Diagram", Applied Optics, 1963, Vol. 2, No. 12, pp. 1251-1256.

The term "field dependence" as used herein refers to any functional dependency of a physical quantity from a position in a plane.

The term "angular irradiation distribution" as used herein means how the irradiation of a beam varies depending on the angle of the light ray constituting the beam. The angular irradiance distribution can generally be described by a function I _a (α, β) , where α and β are angular coordinates describing the direction of the light ray. If the angular irradiance distribution has a dependence such that it varies at different field points, then I _a will also be a function of the field coordinates, ie I _a = I _a (α, β, x, y) . The field dependence of the angular irradiance distribution can be described by a set of expansion coefficients a _{ij of} I _a (α, β, x, y) with respect to Taylor (or other suitable) expansion of x , y .

The term "irradiation" as used herein refers to the total exposure that can be measured at a particular field. Irradiation can be inferred from the angular irradiance distribution by integrating all angles α , β. Irradiation usually also has a field dependence such that I _s = I _s (x, y) , where x and y are the angular coordinates of the field point. The field dependence of the irradiation is also referred to as the spatial irradiance distribution. In a scanner type projection device, the light dose at a field point is obtained by integrating the irradiation over time.

10‧‧‧Projection exposure equipment

11‧‧‧Light source

12‧‧‧Lighting system

14‧‧‧Lighting field

16‧‧‧Photomask

18‧‧‧ pattern

18’‧‧‧Reduced image

19‧‧‧Characteristics

20‧‧‧Projection objective

22‧‧‧Photosensitive layer

24‧‧‧Substrate

26a‧‧‧Exporting light

26b‧‧‧Exporting light

26c‧‧‧Exporting light

27‧‧‧ pole

27a‧‧‧ pole

27b‧‧‧ pole

27b’‧‧‧ center pole

27c‧‧‧ pole

32‧‧‧beam expansion unit

34‧‧‧ Beam

36‧‧‧Light forming unit

38‧‧‧First Mirror Array

40‧‧‧Mirror

42‧‧‧ Beam

44‧‧‧ Beam

46‧‧‧稜鏡

48a‧‧‧Flat surface

48b‧‧‧planar surface

49‧‧‧Exit surface

50‧‧‧ concentrator

52‧‧‧Digital Space Light Regulator

54‧‧‧second mirror array

56‧‧‧micromirrors

56’‧‧‧ images

56d‧‧‧micromirrors

56d’‧‧‧ Dark spots

57‧‧‧Mirror plane

58‧‧‧First objective

60‧‧‧ optical integrator

62‧‧‧ absorber

64‧‧‧稜鏡

65‧‧‧ entrance surface

66a‧‧‧Flat surface

66b‧‧‧planar surface

68‧‧‧ Surface

70‧‧‧First array

72‧‧‧second array

74‧‧‧Optical grating components

75‧‧‧Light entrance screen

76‧‧‧Light plane

78‧‧‧Second concentrator

80‧‧ ‧ field light plane

82‧‧‧ adjustable field light

84‧‧‧Raster field plane

86‧‧‧Second objective

88‧‧‧mask plane

90‧‧‧Control unit

92‧‧‧System Controller

94‧‧ points

95 ‧ ‧ point overlap

101‧‧‧Microlens

102‧‧‧Microlens

106‧‧‧Auxiliary light source

110‧‧‧Object area

110’‧‧‧Image area

120‧‧‧The telecentric light

120’‧‧‧ Non-telecentric light

122‧‧‧Image plane

124‧‧‧Image points

124’‧‧‧Image points

126‧‧‧ parallel plane

128‧‧‧Image points

128’‧‧‧ image points

181a‧‧‧First pattern area

181b‧‧‧First pattern area

181c‧‧‧First pattern area

182a‧‧‧second pattern area

182b‧‧‧second pattern area

182c‧‧‧second pattern area

A1‧‧‧ arrow

A2‧‧‧ arrow

C‧‧‧Magnification profile

C’‧‧‧Amplified section

F‧‧‧Common focus

F1‧‧ Focus

F2‧‧ Focus

F3‧‧‧ focus

L1‧‧ lens

L1a‧‧‧ light cluster

L1b‧‧‧ light cluster

L2‧‧ lens

L2a‧‧‧ light cluster

L2b‧‧‧ light cluster

L3‧‧ lens

L3a‧‧‧ light cluster

L3b‧‧‧ light cluster

L4‧‧ lens

L5‧‧ lens

L6‧‧ lens

OA‧‧‧ optical axis

ST‧‧‧target structure

ST’‧‧‧ actual structure

The various features and advantages of the present invention will be more readily understood from the following detailed description of the accompanying drawings in which: FIG. 1 is a schematic perspective view of a projection exposure apparatus in accordance with an embodiment of the present invention; Figure 2 is an enlarged perspective view of the reticle projected by the projection exposure apparatus shown in Figure 1, which depicts a local variation of the angular irradiance distribution on the reticle; Figure 3 is a longitudinal section of an illumination system, which is shown in Figure 1. Figure 4 is a perspective view of a first mirror array included in the illumination system of Figure 3; Figure 5 is a perspective view of a second mirror array included in the illumination system of Figure 3; Figure 6 is a perspective view of the optical integrator included in the illumination system of Figure 3; Figure 7 is a schematic longitudinal section of the first and second mirror arrays shown in Figures 4 and 5; Figure 8 is Figure 5 A perspective view on the second mirror array, but with bipolar illumination; Figure 9 is a perspective view of the optical integrator shown in Figure 6, but with bipolar illumination; Figure 10 is a schematic longitudinal section of one portion of the illumination system , wherein only one array of mirrors, a concentrator, and an array of optical grating elements are shown; FIGS. 11a and 11b are top views of the second mirror array and optical integrator shown in FIG. 3; and FIG. 12 is depicted in the optical integrator The irradiance distribution on the entrance surface of the light entrance; Figure 13 shows the light entrance shown in Figure 12. A graph of the scanned integrated irradiance distribution along the X direction produced by the face; FIG. 14 depicts another irradiance distribution on the light entrance pupil surface of the optical integrator; FIG. 15 is a view showing the light entrance face shown in FIG. A graph of the resulting scanned integrated irradiance distribution along the X direction; Figures 16a through 16c depict the definition of the edge position error; and Figures 17a and 17b depict how the edge position error can be corrected by generating a telecentric error and shifting the mask or wafer ; Figure 18 is an enlarged perspective view of a reticle similar to that of Figure 2, depicting how the illuminating different reticle patterns are illuminated at different angles; and Figure 19 is a flow chart depicting important method steps.

I. General construction of projection exposure equipment

1 is a greatly simplified perspective view of a projection exposure apparatus 10 in accordance with the present invention. Apparatus 10 includes a light source 11 that can be implemented, for example, as a quasi-molecular laser. The light source 11 in this embodiment produces projected light having a central wavelength of 193 nm. Other wavelengths are conceivable, such as 157 nm or 248 nm.

Apparatus 10 further includes an illumination system 12 that adjusts the projected light provided by source 11 in a manner that will be explained in more detail below. Projected light is emitted from illumination system 12 and illuminates illumination field 14 on reticle 16. The reticle 16 comprises a pattern 18 formed by a plurality of small features 19, indicated schematically by thin lines in FIG. In this particular embodiment, the illumination field 14 has a rectangular shape. However, other shapes of illumination fields 14, such as ring segments, are also contemplated.

Projection objective 20 includes lenses L1 through L6 and images 18 within illumination field 14 onto a photosensitive layer 22 (eg, a photoresist) supported by substrate 24. The substrate 24 formed of the wafer is disposed on a wafer stage (not shown) such that the top surface of the photosensitive layer 22 is accurately positioned in the image plane of the projection objective 20. The reticle 16 is positioned within the object plane of the projection objective 20 by a reticle stage (not shown). Since the projection objective 20 has a magnification β and |β|<1, the reduced image 18' of the pattern 18 in the illumination field 14 is projected onto the photosensitive layer 22.

During projection, the reticle 16 and the substrate 24 move in a scanning direction corresponding to the Y direction shown in FIG. The illumination field 14 is then scanned over the reticle 16 such that a larger patterned area than the illumination field 14 can be continuously imaged. The ratio between the speed of the substrate 24 and the reticle 16 is equal to the magnification β of the projection objective 20. If the projection objective 20 does not reverse the image (β>0), the reticle 16 and the substrate 24 move in the same direction, which is indicated by arrows A1 and A2 in FIG. However, the invention can also be applied to a stepper tool, The reticle 16 and the substrate 24 do not move during the projection of the reticle.

II. Field-related angular irradiation distribution

2 is an enlarged perspective view of a reticle 16 including another example pattern 18. For the sake of simplicity, it is assumed that the pattern 18 is uniform, i.e., contains only the same features 19 that extend in the Y direction and are equally spaced apart. It is further assumed that the feature 19 extending in the Y direction is optimally imaged on the photosensitive layer 22 having the X dipole illumination setting.

In Fig. 2, an exit pupil 26a associated with a light bundle is illustrated by a circle. At the first time during the scan cycle, the light clusters are concentrated toward a field point located at a particular X position of the illumination field 14. In the exit pupil 26a, the two poles 27a spaced apart in the X direction represent the direction in which the projected light propagates toward this field point. It is assumed that the light energy concentrated in each pole 27a is equal. Therefore, the projected light irradiated from the +X direction has the same energy as the projected light irradiated from the -X direction. Since the feature 19 is assumed to be evenly distributed over the pattern 18, this X bipolar illumination setting should be produced at each point on the reticle 16.

However, if the X bipolar illumination setting is maintained throughout the scan cycle and over the entire length of the illumination field 14, the result may be that the structure created on the substrate 24 after the exposure and subsequent edge steps is not as expected. position. More particularly, the edges of the structure may be displaced in the X direction in the manner previously explained with reference to Figures 16a and 16c. In other words, although the same feature 19 is illuminated with the same irradiation and the same angular irradiation, edge position errors may still occur. Edge position errors typically have a detrimental effect on the critical dimension (CD) budget and can cause serious coverage problems.

There are many reasons for this type of edge position error. For example, certain proximity effects (e.g., scattered light associated with feature 19) may cause features 19 located around reticle 16 to be imaged differently from features 19 at their center. Other causes of edge position error include lens heating effects in the projection objective 20. For example, the optical elements in the projection objective 20 located near the field plane are illuminated in a non-rotating manner. Since (although) a small portion of the projected light is absorbed by each optical element, this can result in a non-rotationally symmetric heat distribution of these optical elements and thus a non-rotationally symmetric deformation. If the position of the optical element is close to the field plane (but not in the field plane), then this shape Variations can result in field-related aberrations, such as distortion.

In accordance with one of the various aspects of the present invention, the present invention is directed to eliminating or at least reducing edge position errors that occur for these and similar reasons. Surprisingly, it has been demonstrated that edge position errors caused by a large number of different effects can be substantially reduced by slightly varying the angular irradiance distribution (and irradiation, preferably) in a field dependent manner. Basically, it may even be that each point on the reticle 16 is illuminated by a different combination of irradiance and angular irradiance distribution. If the pattern 18 is not uniform as shown in Figure 2 but varies across the reticle 16, this correction requirement is generally more intense. However, even with a uniform pattern 19 as shown in FIG. 2 or having a uniform pattern portion, field dependent edge position errors are often found and at least partial correction is required.

In Figure 2, the different illumination conditions at different field points are represented by the other two exit pupils 26b, 26c that are produced at different X positions and at different times during the scan cycle. In the exit pupil 26b, the light energy concentrated on each pole 27b remains the same. However, the cone of light associated with pole 27b is inclined compared to the cone of light associated with the exit pupil 26a.

In the exit pupil 26c, the pole 27c is located at the same position as the pole 27a. Therefore, the direction in which the projected light is irradiated at each field point is the same. However, the poles 27c are not balanced, that is, the light energies concentrated on the poles 27c are not identical to each other. Therefore, the projected light irradiated from the +X direction has a lower energy than the projected light irradiated from the -X direction.

Both exit pupils 26b, 26c cause telecentric errors. This means that the energy centerline of the light cone does not illuminate the reticle 16 vertically, but is inclined. Using a method that will be explained in more detail below, this can be used to affect the edge position at the substrate level, along with axial displacement of the reticle 16 and/or substrate 24.

The field dependence of the angular irradiance distribution may not only follow the X direction but also the Y direction within the illumination field 14. Then, when a point on the reticle 16 passes through the illumination field 14 during the scan cycle, it will illuminate through different angles. If field dependence in the Y direction (ie, the scanning direction) occurs, the total effect for a particular field point obtained by integrating the different angles of the irradiation distribution over time must be taken into account.

Many other field dependent changes in angular irradiance distribution may be necessary to reduce edge position errors. For example, it is highly probable that the exit pupil associated with certain field points will be distorted, blurred, or may have a desired non-uniform irradiance distribution.

As mentioned above, it may also be desirable to not only change the angular irradiance variation on the illumination field 14, but also the irradiance obtained by integrating the angular irradiance distribution for all possible angles. The next two sections III and IV will explain in more detail how the desired changes in the irradiation and angular irradiance distribution can be accomplished by the illumination system 12.

III. General construction of the lighting system

3 is a longitudinal section through the illumination system 12 shown in FIG. For the sake of simplicity, the diagram of Figure 3 has been simplified and not to scale. This means in particular that only one or very few optical elements are used to represent different optical units. In fact, these units can contain significantly more lenses and other optical components.

In the particular embodiment shown, the projected light emitted by source 11 enters a beam expanding unit 32 which outputs a beam 34 that has been expanded and nearly collimated. To this end, the beam expanding unit 32 may comprise a number of lenses or may for example be implemented as a mirror configuration.

Next, the projected beam 34 enters a pupil forming unit 36 for producing a variable spatial irradiance distribution in a subsequent plane. To this end, the pupil forming unit 36 comprises a first mirror array 38 of very small mirrors 40 which are individually tiltable about the two vertical axes by means of an actuator. 4 is a perspective view of the first mirror array 38 illustrating how the two parallel beams 42, 44 are reflected in different directions depending on the angle of inclination of the mirror 40 illuminated by the beams 42, 44. In FIGS. 3 and 4, the first mirror array 38 includes only 6x6 mirrors 40; in practice, the first mirror array 38 can include hundreds or even thousands of mirrors 40.

The aperture forming unit 36 further includes a prism 46 having a first planar surface 48a and a second planar surface 48b, both of which are inclined relative to an optical axis OA of the illumination system 12. On these inclined surfaces 48a, 48b, the illumination light is reflected by internal total reflection. The first surface 48a reflects the illumination light toward the mirror 40 of the first mirror array 38, and the second surface The light reflected from the mirror 40 is directed toward the exit surface 49 of the crucible 46. As such, with the mirror 40 that individually tilts the first mirror array 38, the angular irradiance distribution of the light emanating from the exit surface 49 can be varied. More details regarding the pupil forming unit 36 are known from US 2009/0116093 A1.

By means of the first concentrator 50, the angular irradiance distribution produced by the pupil forming unit 36 can be converted into a spatial irradiance distribution. The concentrator 50 (which may be omitted in other embodiments) directs the illumination light toward a digital spatial light modulator 52 that is configured to reflect the illumination light in a spatially resolved manner. To this end, the digital spatial light modulator 52 includes a second mirror array 54 of micro-mirrors 56 disposed in a mirror plane 57, and can be viewed in the enlarged cross-section C of FIG. 3 and the enlarged cross-section C' of FIG. clear. However, compared to the mirror 40 of the first mirror array 38, each micromirror 56 of the second mirror array 54 has only two stable operating states, that is, the illumination light is directed toward the optical integral through the first objective lens 58. The "on" state of the device 60 and the "off" state directing the illumination light toward a light absorbing surface 62.

The second mirror array 54 can be implemented as a digital mirror device (DMD), which is commonly used, for example, for beamers. Such devices can contain up to millions of micromirrors that can be switched thousands of times per second between two operational states.

Similar to the pupil forming unit 36, the spatial light modulator 52 further includes a bore 64 having an inlet surface 65 disposed perpendicular to the optical axis OA and a first planar surface 66a and a second planar surface 66b. Both are tilted relative to the optical axis OA of the illumination system 12. On these inclined surfaces 66a, 66b, the illumination light is reflected by internal total reflection. The first surface 66a reflects the illumination light toward the micromirror 56 of the second mirror array 54, and the second surface 66b directs the light reflected from the micromirror 56 toward a surface 68 of the crucible 64.

If all of the micromirrors 56 of the second mirror array 54 are in their "on" state, the second mirror array 54 essentially has the effect of a planar beam folding mirror. However, if one or more of the micromirrors 56 are switched to their "off" state, the spatial irradiance distribution of the light emanating from the mirror plane 57 will change. This can be done in a way that is explained in further detail below Field dependent modification of the angular light distribution is produced on the cover 16.

As already mentioned above, the light emitted from the crucible 64 passes through the first objective lens 58 and is illuminated on the optical integrator 60. Because the light passing through the first objective lens 58 is nearly collimated, the first objective lens 58 can have a very low numerical aperture (e.g., 0.01 or even lower), and thus can be achieved with a very small spherical lens. The first objective lens 58 images the mirror plane 57 of the spatial light modulator 52 onto the optical integrator 60.

In the particular embodiment shown, optical integrator 60 includes a first array 70 and a second array 72 of optical grating elements 74. Figure 6 is a perspective view of two arrays 70, 72, each of which includes a parallel array of cylindrical lenses extending along the X and Y directions on each side of the support plate. The volume at the intersection of the two cylindrical lenses forms an optical grating element 74. Thus, each optical grating element 74 can be a microlens having a cylindrical curved surface. The use of a cylindrical lens is particularly advantageous in those cases where the refractive index of the optical grating element 74 should be different along the X and Y directions. If, as is often the case, if the square irradiance distribution on the optical integrator 60 should be converted to a slit-shaped illumination field 14, a different index of refraction must be present. The surface of the optical grating element 74 that is directed toward the spatial light modulator 52 will hereinafter be referred to as the light entrance pupil face 75.

The optical grating elements 74 of the first and second arrays 70, 72 are respectively arranged one behind the other such that an optical grating element 74 of the first array 70 is associated with an optical grating element 74 of the second array 72 in a one-to-one manner. The two optical grating elements 74 associated with each other are aligned along a common axis and define an optical channel. Within optical integrator 60, a beam propagating within an optical channel does not intersect or overlap with a beam propagating within other optical channels. Thus, the optical channels associated with the optical grating elements 74 are optically isolated from one another.

In this particular embodiment, the pupil plane 76 of the illumination system 12 is located after the second array 72; however, it can also be disposed before the second array 72. The second concentrating mirror 78 establishes a Fourier relationship between the pupil plane 76 and the field stop plane 80, and an adjustable field stop 82 can be disposed in the field stop plane 80.

The field stop plane 80 is optically conjugate with a grating field plane 84, wherein the grating field is flat Face 84 is located within or near the light entrance pupil face 75 of optical integrator 60. This means that each of the light entrance pupil faces 75 in the grating field plane 84 is imaged by the associated optical grating element 74 of the second array 72 and the second concentrating mirror 78 onto the entire field stop plane 80. Images of the irradiance distribution on the light entrance pupil face 75 in all optical channels are superimposed in the field stop plane 80, which results in very uniform illumination of the reticle 16. Another way to describe the uniform illumination of the reticle 16 is based on the irradiance distribution produced by each optical channel within the pupil plane 76. This irradiance distribution is often referred to as an auxiliary source. All of the auxiliary light sources collectively illuminate the field stop plane 80 using projected light from different directions. If the auxiliary source is "dark", then no light illuminates the reticle 16 from the (small) direction range associated with this particular source. Thus, with the simple opening and closing of the auxiliary light source formed in the pupil plane 76, it is possible to set the desired angular light distribution on the reticle 16. This can be achieved by using the help of the pupil forming unit 36 to vary the irradiance distribution on the optical integrator 60.

Field stop plane 80 is imaged by second objective lens 86 on retset plane 88, with reticle 16 being configured with the aid of a reticle stage (not shown). The adjustable field stop 82 is also imaged on the reticle plane 88 and defines at least the short lateral sides of the illumination field 14 that extend in the scan direction Y.

Both the aperture forming unit 36 and the spatial light modulator 52 are coupled to a control unit 90, which is then coupled to an integral system controller 92 (which is illustrated herein as a personal computer). The control unit 90 is configured to control the mirror 40 of the pupil forming unit 36 and the spatial light modulator 52 in a manner that the angular irradiance distribution in the reticle plane 88 varies within the illumination field 14 during the scanning cycle in a desired manner. Micromirror 56. The function and control of the lighting system will be described below.

IV. Function and control of the lighting system 1. Photoforming

FIG. 7 graphically illustrates how the pupil forming unit 36 produces an irradiance distribution on the micromirror 56 of the spatial light modulator 52. For the sake of simplicity, 稜鏡46, 64 are not shown.

Each mirror 40 of the first mirror array 38 is configured to illuminate the mirror plane 57 of the spatial light modulator 52 at a position that is variable by varying the deflection angle produced by the individual mirrors 40. Up to 94. Therefore, by tilting the mirror 40 around its tilting axis, point 94 It is free to move on the mirror plane 57. As such, it is possible to produce a wide variety of different irradiance distributions on the mirror plane 57. Points 94 may also overlap partially or completely, as shown at 95. A graded irradiance distribution can then also be produced.

FIG. 8 is a perspective view of the second mirror array 54 included in the spatial light modulator 52, similar to FIG. It is assumed here that the pupil forming unit 36 has produced an irradiance distribution on the second mirror array 54 composed of two square poles 27, each of which extends exactly on the 6x6 micromirrors 56. The poles 27 are arranged in a point symmetrical manner along the X direction.

The objective lens 58 forms an image of this irradiance distribution on the light entrance pupil face 75 of the optical integrator 60, as shown in FIG. It is assumed herein that all of the micromirrors 56 are in the "on" state such that the irradiance distribution formed on the second mirror array 54 is identically reproduced on the light entrance pupil face 75 of the optical integrator 60 (except for the objective lens 58). The magnification caused by the possible scaling). The regular grid displayed on the light entrance pupil 75 represents the image of the boundary of the micromirror 56, but this image does not appear outside of the pole 27 and is shown in Figure 9 for illustrative purposes only.

Field dependence

Because the light entrance pupil face 75 is located in the grating field plane 84, the irradiance distribution on the light entrance pupil face 75 is imaged onto the field stop plane 80 through the optical grating elements 74 of the second array 72 and the second concentrating mirror 78.

Reference will now be made to Fig. 10, which is an enlarged view and not cut out from Fig. 3. Only two pairs of optical grating elements 74, second concentrating mirrors 78 and intermediate field stop plane 80 of optical integrator 60 are shown schematically herein.

The two optical grating elements 74 associated with a single optical channel will hereinafter be referred to as a first microlens 101 and a second microlens 102. The microlenses 101, 102 are sometimes referred to as field and pupil honeycomb lenses. Each pair of microlenses 101, 102 associated with a particular optical channel produces an auxiliary source 106 in the pupil plane 76. In the upper half of Fig. 10, it is assumed that the convergent light bundles L1a, L2a, and L3a indicated by solid lines, broken lines, and broken lines, respectively, are irradiated to different points of the light entrance pupil face 75 of the first microlens 101. After passing through the two microlenses 101, 102 and the condensing mirror 78, each light The bundles L1a, L2a, and L3a converge to the focal points F1, F2, and F3, respectively. As is clear from the upper half of Fig. 10, the point at which the light ray illuminates the light entrance pupil face 75 is optically conjugate with the point at which the light rays pass through the field stop plane 80 (or any other conjugate field plane).

The lower half of Fig. 10 describes the case where the collimated light bundles L1b, L2b, and L3b are irradiated on different regions of the light entrance pupil face 75 of the first microlens 101. This is a more practical situation because the light impinging on the optical integrator 60 is typically substantially collimated. The light bundles L1b, L2b, and L3b are focused on a common focus F located in the second microlens 102 and then passed through (at this time again collimated) the field stop plane 80. Again, it can be seen that due to the optical conjugation, the regions illuminated by the beams L1b, L2b and L3b on the light entrance pupil face 75 correspond to the regions illuminated in the field stop plane 80. Of course, if the microlenses 101, 102 have refractive indices in both the X and Y directions, these considerations are applied to the X and Y directions, respectively.

Thus, each point on the light entrance pupil face 75 directly corresponds to a conjugate point in the intermediate field stop plane 80 (and thus in the illumination field 14 on the reticle 16). If it is possible to selectively influence the irradiation at a point on the light entrance pupil surface 75, it may thus affect the irradiation of a light ray from the optical axis OA depending on the light entrance pupil surface 75 relative to the illumination system. The direction of the position is illuminated to the conjugate point in the illumination field 14. The greater the distance between the light entrance pupil face 75 and the optical axis OA, the greater the angle at which the light ray illuminates the spot on the reticle 16.

3. Modify the irradiation on the surface of the light entrance

Within the illumination system 12, a spatial light modulator 52 is used to modify the illumination at various points on the light entrance pupil face 75. As can be seen in Figure 9, each pole 27 extends over a plurality of small areas that are images of the micro-mirror 56. If a micromirror enters the "off" state, the conjugate region on the light entrance pupil face 75 will not be illuminated, so that no projected light will be illuminated from the (small) direction range associated with the particular light entrance pupil face 75. To a conjugated area on the mask.

This will be explained in more detail with reference to Figures 11a and 11b, which are a top view of the micromirror 56 of the spatial light modulator 52 and a top view of the light entrance pupil 75 of the optical integrator 60, respectively.

The thick dashed line on the second mirror array 54 divides its mirror plane 57 into complex A plurality of object regions 110, each of which contains 3x3 micromirrors 56. The objective lens 58 forms an image of each object region 110 on the optical integrator 60. This image will hereinafter be referred to as image area 110'. Each image area 110' completely coincides with the light entrance pupil surface 75, that is, the image area 110' has the same shape, size, and orientation as the light entrance pupil surface 75, and is completely superposed on the light entrance pupil surface 75. Since each object region 110 includes 3x3 micromirrors 56, the image region 110' also includes 3x3 images 56' of the micromirrors 56.

In Fig. 11a, there are eight object regions 110 that are completely illuminated by the pupil forming unit 36 with projected light. These eight object regions 110 form two poles 27. It can be seen that in some object regions 110, one, two or more micromirrors 56d, which are represented as black squares, have been controlled by the control unit 90 such that they are in an "off" state in which the projected light is not directed toward The objective lens 58 is directed toward the absorber 62. By switching the micromirrors between the "on" and "off" states, it is possible to variably prevent the projection light from being incident on the corresponding area within the image area 110' on the light entrance pupil face 75, as shown in FIG. 11b. Show. These areas are hereinafter referred to as dark spots 56d'.

As explained above with reference to Figure 10, the irradiance distribution on the light entrance pupil face 75 is imaged on the field stop plane 80. If a light entrance pupil surface 75 includes one or more dark spots 56d', as illustrated in the upper half of FIG. 12, the irradiance distribution produced by the associated optical channel in the reticle plane 88 will also be at a particular X position. Has a dark spot. If a point on the reticle passes through the illumination field 14, the total scan integral exposure will therefore depend on the X position of that point in the illumination field 14, as shown in the graph of FIG. The points in the middle of the illumination field 14 will be irradiated with the highest scan integration because they do not pass dark spots, and the points on the longitudinal ends of the illumination field 14 will receive the total radiation that is reduced to varying degrees. Therefore, by selectively changing one or more micromirrors 56 of the spatial light modulator 52 from the "on" state to the "off" state, the field dependence and space of the angular light distribution on the reticle 16 can be modified. Irradiation distribution.

It has been assumed in the foregoing that each object region 110 imaged on one of the light entrance pupil faces 75 contains only 3x3 micromirrors 56. Therefore, the resolution of the field dependence that can be used to modify the angular light distribution along the cross-scanning direction X is relatively coarse. This resolution can be improved if the number of micromirrors 56 in each object region 110 is increased.

14 shows a top view of one of the light entrance pupils 75 of a particular embodiment including 20x20 micromirrors 56 for each object region 110. A more complex scan integrated irradiance distribution along the X direction can then be achieved on the reticle 16, as shown in the graph shown in FIG.

V. Reduction of edge position error 1.CD uniformity

In a first step, an attempt is made to improve CD uniformity by carefully defining the illumination in the illumination field 14 along the cross-scan direction X. Since this method is well known in its own field, it will not be described in more detail here. Next, the micromirror 56 is controlled to obtain the target field dependence of the illumination in the illumination field 14. Since the influence of the projection objective 20 on the field dependence of the irradiation at the wafer level cannot be easily predicted, it may be necessary to repeat this procedure several times. After several iterations, the field dependent change of the CD usually reaches a minimum.

After determining the target field dependence of the irradiation, it is necessary to determine the target field dependence of the angular irradiance distribution.

Since it is known how various defects in illumination settings affect the critical dimension of the wafer level, it is in turn possible to determine which modifications of the original field dependence of the angular irradiance distribution are needed to reduce the critical dimension pattern and field dependent variation. Usually only the small field dependence of the angular irradiance distribution is required to reduce the change in critical dimension, as it usually happens.

Next, the micromirror 56 is controlled to produce a target field dependence of the angular irradiance distribution in the illumination field 14. Since the setting of each micromirror between the "on" and "off" states generally affects not only the field dependence of the angular irradiance distribution but also the field dependence of the irradiance, irradiation and angle can be achieved in a single program. Optimization of the field dependence of the irradiance distribution.

Experiments have shown that if not only the irradiation but also the angular irradiance distribution is optimized differently at different field locations, the critical dimension change can be reduced by almost 2 times for dense line spacing.

2. Overlap control

If the field dependent overlap error should be corrected, a similar method as described above can be used.

In the first step, field-measurement at the wafer level or analog overlay error Sex. As explained above with reference to Figure 2, the asymmetry in the angular irradiance distribution results in a telecentric error. In this case, the energy center of the projected light is obliquely illuminated on the image point. This can be used to laterally shift the image point by axially displacing the wafer surface from its ideal position in the image plane.

This is illustrated in Figures 17a and 17b. In the upper half of Fig. 17a, the telecentric cluster 120 is shown schematically through the image plane 122 of the projection objective 20. In the middle portion of Figure 17b, it can be seen that image point 124 has its smallest diameter in image plane 122. In the parallel plane 126 that is axially displaced relative to the image plane 122, the diameter of the image point 128 is larger, but the X and Y coordinates are not affected by this displacement (refer to the lower half of Figure 17a).

Figure 17b shows the same image for the case of non-telecentric clusters 120'. It can be seen that this does not affect the size and position of the image spot 124' in the image plane 122. However, in the parallel plane 126, the image point 128' is not only large but laterally displaced in the X direction.

By carefully introducing the asymmetry into the angular irradiance distribution and slightly shifting the wafer along the optical axis, it is possible to produce a field-dependent lateral shift of the image that can be used to correct the field dependence of the edge position error. Since any defocusing configuration of the wafer is achieved by a reduction in image contrast, the correction of the field-dependent edge position error and the trade-off between contrasts are required.

VI.EUV

In the foregoing, the invention has been described with reference to a projection exposure apparatus 10 that uses VUV to project light. However, it is also possible to use the concepts presented above in an EUV projection device.

WO 2009/100856 A1 describes an EUV illumination system which enables the generation of the desired field dependence of the irradiation and angular irradiance distribution. Also in this case, the small mirrors need to be individually controlled to achieve the desired field dependence.

VII. Multi-device grain

Figure 18 is a schematic illustration of a reticle 16 that can be used to create different integrated circuits or other devices on a single die, similar to Figure 2. For this purpose, the reticle 16 includes three first pattern regions 181a, 181b, 181c and three second pattern regions 182a, 182b, 182c along the scanning direction. Y is configured one after the other. In the simplified embodiment shown, the first and second pattern regions differ from each other in the density of the line features 19 extending in the Y direction.

It is assumed here that the first pattern regions 181a, 181b, 181c are illuminated with projection light having an angular irradiation distribution corresponding to the bipolar setting. The aperture 26a thus comprises two poles 27a which are spaced apart in the cross-scanning direction X.

The second pattern regions 182a, 182b, 182c are illuminated with projected light having an angular irradiance distribution corresponding to a combination of bipolar settings and conventional settings. Therefore, the exit pupil 26b associated with the cluster of light irradiated on the second pattern region includes not only the two poles 27b but also the center pole 27b'. The illumination settings associated with the exit pupil 26b are thus fully incorporated into the illumination settings associated with the exit pupil 26a.

Micromirrors 56 of illumination system 12 can be controlled to produce exit pupils 26a, 26b at various fields in illumination field 14. The control scheme also corrects the field dependent edge position error by slightly changing the exit pupils 26a, 26b in the two halves of the illumination field 14 during the scan cycle. This complicated work is possible because the micromirrors 56 can be controlled very quickly and reliably, even for a large number of micromirrors 56.

In other embodiments, the illumination settings are not abruptly changed, but are continuously converted such that immediate illumination settings are generated at the intermediate field point.

VIII. Important method steps

The important method steps of the present invention will now be summarized with reference to the flow chart shown in FIG.

In a first step S1, a reticle, an illumination system and a projection objective are provided. The projection objective is configured to form an image of an object field (which is illuminated on a reticle in the reticle plane) on an image field located on a photosensitive surface.

In a second step S2, an edge position error at different field points in the image field is determined.

In a third step S3, improved field dependence with angular irradiance distribution The projected light illuminates the reticle such that the edge position error determined in step S2 is reduced.

14‧‧‧Lighting field

16‧‧‧Photomask

18‧‧‧ pattern

19‧‧‧Characteristics

26a‧‧‧Exporting light

26b‧‧‧Exporting light

27a‧‧‧ pole

27b‧‧‧ pole

27b’‧‧‧ center pole

181a‧‧‧First pattern area

181b‧‧‧First pattern area

181c‧‧‧First pattern area

182a‧‧‧second pattern area

182b‧‧‧second pattern area

182c‧‧‧second pattern area

Claims (11)

A method for operating a lithography projection apparatus, comprising the steps of: (a) providing - a reticle, - an illumination system configured to illuminate the reticle, and - configured to be located on a photosensitive surface a projection objective that forms an image of an object field on an image field, wherein the object field is illuminated on the reticle in a reticle plane; (b) determining a plurality of different field points in the image field Edge position error; and (c) illuminating the reticle with projected light that improves field dependence with one of the angular irradiance distributions, wherein the angular irradiance distribution varies over the object field based on the improved field dependence, such that The edge position errors at the different field points determined by step (b) will decrease. The method of claim 1, wherein the step (b) comprises the steps of: - illuminating the reticle with projection light having an original field dependence of the angular irradiance distribution; and - simulating or measuring The edge position errors at the different field points on the photosensitive surface; wherein step (c) includes the step of varying the original field dependence of the angular irradiance distribution to obtain the improved field dependence of the angular irradiance distribution. A method according to any one of the preceding claims, wherein the step (c) comprises the step of illuminating the reticle with projected light having an improved field dependence of the irradiance, wherein the irradiance is on the object field The variation causes the edge position errors determined in step (b) to decrease at the different field points. The method of claim 3, wherein the step (b) comprises the following steps: - illuminating the reticle with projection light having an original field dependence of the irradiance; and - simulating or measuring the edge position errors at the different field points on the photosensitive surface; wherein step (c) comprises changing the The original field dependence of the irradiation to obtain the improved field dependence of the irradiation. The method of any of the preceding claims, wherein the reticle has a portion comprising a uniform reticle pattern, and wherein the angular irradiance distribution is based on the improved field dependence of the angular irradiance distribution A time during the step (c) varies over an area in which the object field coincides with the portion. The method of any of the preceding claims, wherein the reticle comprises a non-uniform reticle pattern having locally varying characteristics, and wherein the modified angular irradiance distribution is adapted to the local variation of the reticle pattern characteristic. The method of any of the preceding claims, wherein the angular irradiance distribution is non-telecentric at least at certain field points based on the improved field dependence, and wherein at least the reticle and the photosensitive surface are One is displaced along the optical axis of one of the projection objectives before step (c). The method of any of the preceding claims, wherein the illumination system provided in step (a) comprises: - an optical integrator configured to generate a pupil plane in the illumination system a plurality of auxiliary light sources, wherein the optical integrator comprises a plurality of light entrance pupil faces, each of the light entrance pupil faces being associated with one of the auxiliary light sources, and wherein the plurality of images of the light entrance faces At least substantially superimposed on the reticle plane, a spatial light modulator having a light exit surface and configured to transmit or reflect the projected light in a spatially resolved manner, an objective lens imaging the light exit surface of the spatial light modulator to the optical integrator The light entrance faces, wherein in step (c), the spatial light modulator is controlled such that the improved angular irradiance distribution is obtained in the reticle plane. An illumination system for a lithography projection apparatus, comprising: (a) a pupil plane, (b) an optical integrator configured to generate a plurality of auxiliary sources in the pupil plane, wherein the optical integrator Included in the plurality of light entrance pupil faces, each of the light entrance pupil faces associated with one of the auxiliary light sources, (c) a spatial light modulator having a light exit surface and configured to be transmitted in a spatial resolution manner or Reflecting the projected light, (d) a pupil forming unit configured to direct the projected light to the spatial light modulator, (e) an objective lens that images the light exit surface of the spatial light modulator to The optical inlets of the optical integrator, (f) a control unit configured to control the pupil forming unit and the spatial light modulator such that the mask is improved by one of the angular irradiation distributions Field dependent projection illumination, wherein the angular irradiance distribution varies over the object field based on the improved field dependence such that a plurality of edge position errors that vary over the image field decrease. The lighting system of claim 9, wherein the control unit is configured to control the aperture forming unit and the spatial light adjuster to achieve any one of claims 2-8 The method described. A lithography projection apparatus comprising: (a) a reticle, (b) an illumination system configured to illuminate the reticle, and (c) a projection objective configured to form an image of an object field in position On an image field on a photosensitive surface, wherein the object field is illuminated on the reticle in a reticle plane, (d) for projecting light with improved field dependence of one of the angular irradiance distributions A device for illuminating the reticle, wherein the angular irradiance distribution varies over the object field based on the improved field dependence such that a plurality of edge position errors that vary over the image field decrease.